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2005-07-19 | Resistance profile measurements on a symmetric electrical pulse induced resistance change device | We report the first direct measurements of the micro scale resistance profile
between the terminals of a two terminal symmetric thin film Pr0.7Ca0.3MnO3
electrical pulse induced resistance change device composed of a Pr0.7Ca0.3MnO3
active layer. The symmetric device is one in which the electrode shape, size,
composition, and deposition processing are identical. We show that under
certain limitations of pulse switching voltage, such a symmetric electrical
pulse induced resistance change device can exhibit either no net device
resistance switching at room temperature, or bipolar switching with the
resistance hysteresis curve exhibiting a "table leg" structure. The resistance
measurements are made using surface scanning Kelvin probe microscopy, which
allows for the measurement of the profile of resistance from one electrode,
across the Pr0.7Ca0.3MnO3 material and into the second electrode, both before
resistance switching and after switching. The results show that resistance
switching in the symmetric device occurs primarily in the interface region
within about 1 to 3 micron of the electrical contact surface. Resistance
switching is also observed in the bulk Pr0.7Ca0.3MnO3 material although at a
lower level. Symmetry considerations for a two terminal symmetric device that
can switch resistance are discussed, and the data reported here is consistent
with the symmetric model previously developed. | 0507432v2 |
2019-07-03 | Suppression of the antiferromagnetic metallic state in the pressurized MnBi2Te4 single crystal | MnBi2Te4 has attracted tremendous research interest recently as the first
intrinsic antiferromagnetic (AF) topological insulator. It undergoes a
long-range AF order at TN = 24 K accompanied with a cusp-like anomaly in the
metallic resistivity. Here, we studied the effect of hydrostatic pressure on
its electrical transport properties up to 12.5 GPa by using a cubic anvil cell
apparatus. We find that TN determined from the resistivity anomaly first
increases slightly with pressure and then decreases until vanished completely
at ~7 GPa. Intriguingly, its resistivity rho(T) is enhanced gradually by
pressure, and evolves from metallic to activated behavior as the AF order is
suppressed. From the Hall resistivity measurements, we confirm that the n-type
carriers dominate the transport properties and the carrier density is raised by
pressure. In addition, the critical magnetic field Hc1 ~3.3 T at 0 GPa for the
spin-flop transition to the canted AF state is found to increase to ~ 5 T and
7.5 T at 1 and 3 GPa. High-pressure XRD evidenced no structural transition up
to 12.8 GPa. Based on the Hall resistivity results and first-principles
calculations, we proposed that the intralayer direct AF interactions are
strengthened by pressure and the competition between AF and FM interactions not
only prevents long-range magnetic order but also promotes charge carrier
localizations through enhance magnetic fluctuations at high pressures. | 1907.01760v1 |
2020-09-02 | Understanding modes of negative differential resistance in amorphous and polycrystalline vanadium oxides | Metal-oxide-metal devices based on amorphous VOx are shown to exhibit one of
two distinct negative differential resistance (NDR) characteristics depending
on the maximum current employed for electroforming. For low compliance currents
they exhibit a smooth S-type characteristic and have a temperature-dependent
device resistance characterised by an activation energy of 0.25 eV, consistent
with conduction in polycrystalline VO2, while for high-compliance currents they
exhibit an abrupt snap-back characteristic and a resistance characterised by an
activation energy of 0.025 eV, consistent with conduction in oxygen deficient
VOx. In both cases, the temperature dependence of the switching voltage implies
that the conductivity change is due to the insulator-metal transition in VO2.
From this analysis it is concluded that electroforming at low currents creates
a conductive filament comprised largely of polycrystalline VO2, while
electroforming at high currents creates a composite structure comprised of VO2
and a conductive halo of oxygen deficient VOx. The effect of electroforming on
the NDR mode is then explained with reference to a lumped element model of
filamentary conduction that includes the effect of a parallel resistance
created by the halo. These results provide new insight into the NDR response of
vanadium-oxide-based devices and a basis for designing devices with specific
characteristics. | 2009.00810v1 |
2022-03-31 | Atomic-scale origin of the low grain-boundary resistance in perovskite solid electrolytes | Oxide solid electrolytes (OSEs) have the potential to achieve improved safety
and energy density for lithium-ion batteries, but their high grain-boundary
(GB) resistance is a general bottleneck. In the most well studied perovskite
OSE, Li3xLa2/3-xTiO3 (LLTO), the ionic conductivity of GBs is about three
orders of magnitude lower than that of the bulk. In contrast, the related
Li0.375Sr0.4375Ta0.75Zr0.25O3 (LSTZ0.75) perovskite exhibits low GB resistance
for reasons yet unknown. Here, we used aberration-corrected scanning
transmission electron microscopy and spectroscopy, along with an active
learning moment tensor potential, to reveal the atomic scale structure and
composition of LSTZ0.75 GBs. Vibrational electron energy loss spectroscopy is
applied for the first time to characterize the otherwise unmeasurable Li
distribution in GBs of LSTZ0.75. We found that Li depletion, which is a major
reason for the low GB ionic conductivity of LLTO, is absent for the GBs of
LSTZ0.75. Instead, the low GB resistivity of LSTZ0.75 is attributed to the
formation of a unique defective cubic perovskite interfacial structure that
contained abundant vacancies. Our study provides insights into the atomic scale
mechanisms of low GB resistivity and sheds light on possible paths for
designing OSEs with high total ionic conductivity. | 2204.00091v1 |
2008-03-29 | Superconductivity at 52 K in iron-based F-doped layered quaternary compound Pr[O1-xFx]FeAs | Since the discovery of copper oxide superconductor in 1986 [1], extensive
efforts have been devoted to the search of new high-Tc superconducting
materials, especially high-Tc systems other than cuprates. The recently
discovered quaternary superconductor La[O1-xFx]FeAs with the superconducting
critical transition Tc of 26 K [2], which has a much simple layered structure
compared with cuprates, has attracted quick enthusiasm and is going to become a
new high-Tc system [3-6]. Here we report the discovery of bulk
superconductivity in the praseodymium-arsenide oxides Pr[O1-xFx]FeAs with an
onset drop of resistivity as high as 52 K, and the unambiguous zero-resistivity
and Meissner transition at low temperature, which will place these quaternary
compounds to another high-Tc superconducting system explicitly. | 0803.4283v1 |
2017-01-14 | Systematic comprehension the metal phase of Pr0.7(CaxSr1-x)0.3MnO3 via temperature and magnetic induction | Temperature, magnetic induction and substitution dependent resistivity are a
crucial factor in determining the physical properties of magneto-resistive
materials. The first objective of this work was to find out an applicable
method of using temperature to predict the resistivity of
Pr0.7(CaxSr1-x)0.3MnO3 in the metal phase within the transition area. Based on
non-linear curve fitting, a typical numerical method is used to quantitatively
analyze the temperature-dependent resistivity within temperatures lower than
the metal-insulator transition temperature (Tp). The simulations agree very
well with the observed curves (resistivity versus temperature). The second
objective of this work is to search for the applicable method to link
magneto-resistivity to magnetic induction, calculation on the principle of
non-linear curve fitting, four typical numerical methods are highlighted
because the magnetic induction-dependent magneto-resistivity are quantitatively
analyzed by these methods. The observed effects of magnetic induction on the
shift of temperature-resistive curve should be more essential in physics and
are quantitatively discussed in magneto-resistive materials. Lastly, the
influences of Ca substitution on magneto-resistivity are detected. | 1701.04688v1 |
1999-04-23 | Shot noise in ferromagnetic single electron tunneling devices | Frequency dependent current noise in ferromagnetic double junctions with
Coulomb blockade is studied theoretically in the limit of sequential tunneling.
Two different relaxation processes are found in the correlations between spin
polarized tunneling currents; low frequency spin fluctuations and high
frequency charge fluctuations. Spin accumulation in strongly asymmetric
junctions is shown to lead to a negative differential resistance. We also show
that large spin noise activated in the range of negative differential
resistance gives rise to a significant enhancement of the current noise. | 9904341v1 |
2001-02-28 | Pressure dependence of Tc in the MgB2 superconductor as probed by resistivity measurements | High-pressure resistivity experiments were performed on the recently
discovered superconductor, MgB2. Tc decreases quasi-linearly with applied
pressure to 1.4 GPa at a rate of -2.0(1) K/GPa, which is somewhat larger than
that derived from recently-reported ac susceptibility measurements. The
reduction of Tc is consistent with the BCS picture, in a similar way to the
C60-based superconductors. Taking into account the pressure dependence of the
unit cell volume, V, the volume coefficient of Tc, d(lnTc)/dV is significantly
large. | 0102511v1 |
2003-03-11 | Microscopic origin of collective exponentially small resistance states | The formation of "zero" (exponentially small) resistance states (ESRS) in
high mobility two-dimensional electron systems (2DES) in a static magnetic
field B and subjected to strong microwave (MW) radiation has attracted great
theoretical interest. These states appear to be associated with a new kind of
energy gap $\Delta$. Here I show that the energy gap $\Delta$ is explained by a
microscopic quantum model that involves the Prime Number Theorem, hitherto
reserved for only mathematical contexts. | 0303184v2 |
2003-11-03 | Inverted current-driven switching in Fe(Cr)/Cr/Fe(Cr) nanopillars | From both theory and experiment, scattering of minority electrons is expected
to be weaker than scattering of majority electrons in both dilute Fe(Cr) alloys
and at Fe(Cr)/Cr interfaces. We show that Fe(Cr)/Cr/Fe(Cr) trilayer nanopillars
display a normal magnetoresistance--i.e., largest resistance at low magnetic
fields and smallest at high fields, but an inverted current-driven
switching--i.e., positive current flowing from the fixed to the reversing layer
switches the trilayer from higher to lower resistance, and negative current
switches it from lower to higher. | 0311047v1 |
2004-04-06 | Superconductivity in diamond | We report the discovery of superconductivity in boron-doped diamond
synthesized at high pressure (8-9 GPa) and temperature (2,500-2,800 K).
Electrical resistivity, magnetic susceptibility, specific heat, and
field-dependent resistance measurements show that boron-doped diamond is a
bulk, type-II superconductor below the superconducting transition temperature
Tc=4 K; superconductivity survives in a magnetic field up to Hc2(0)=3.5 T. The
discovery of superconductivity in diamond-structured carbon suggests that Si
and Ge, which also form in the diamond structure, may similarly exhibit
superconductivity under the appropriate conditions. | 0404156v1 |
2007-03-21 | Electronic Properties of the Semiconductor RuIn$_3$ | Temperature dependent measurements of the resistivity on RuIn$_3$ single
crystals show a semiconducting behaviour, in contrast to previously published
results. In the high temperature range the semiconducting gap was measured to
be $0.4-0.5$eV. We observe an anisotropy of the resistivity along [110] and
[001] orientations of the tetragonal single crystals. At low temperatures two
activation energies of impurities were estimated to 1meV and 10meV. The
temperature dependence of the specific heat and the band structure calculations
provide also a semiconducting behaviour of RuIn$_3$. | 0703563v1 |
2002-06-13 | Potential of RPCs for tracking | We have demonstrated that small gap (0.1 to 0.4 mm) RPCs made of low
resistivity materials (less than 1E8 Ohm.cm) can operate at counting rates of
up to 1E5 Hz/mm2 with position resolutions better than 50 micrometer. Results
of preliminary tests allow us to suggest a possible application of this new
type of RPC for tracking. | 0206039v1 |
2008-03-31 | Percolation Model Explaining Both Unipolar Memory and Threshold Resistance Switchings in NiO Film | We observed two types of unipolar resistance switching (RS) in NiO film:
memory RS at low temperature and threshold RS at high temperature. We explain
these phenomena using a bond percolation model that describes the forming and
rupturing of conducting filaments. Assuming Joule heating and thermal
dissipation processes in the bonds, we explain how both RS types could occur
and be controlled by temperature. We show that these unipolar RS are closely
related and can be explained by a simple unified percolation picture. | 0803.4258v1 |
2009-08-21 | Measuring Charge Transport in an Amorphous Semiconductor Using Charge Sensing | We measure charge transport in hydrogenated amorphous silicon (a-Si:H) using
a nanometer scale silicon MOSFET as a charge sensor. This charge detection
technique makes possible the measurement of extremely large resistances. At
high temperatures, where the a-Si:H resistance is not too large, the charge
detection measurement agrees with a direct measurement of current. The device
geometry allows us to probe both the field effect and dispersive transport in
the a-Si:H using charge sensing and to extract the density of states near the
Fermi energy. | 0908.3181v2 |
2010-04-22 | Small gap semiconducting organic charge-transfer interfaces | We investigated transport properties of organic heterointerfaces formed by
single-crystals of two organic donor-acceptor molecules,
tetramethyltetraselenafulvalene (TMTSF) and 7,7,8,8-tetracyanoquinodimethane
(TCNQ). Whereas the individual crystals have un-measurably high resistance, the
interface exhibits a resistivity of few tens of MegaOhm with a temperature
dependence characteristic of a small gap semiconductor. We analyze the
transport properties based on a simple band-diagram that naturally accounts for
our observations in terms of charge transfer between two crystals. Together
with the recently discovered tetrathiafulvalene (TTF)-TCNQ interfaces, these
results indicate that single-crystal organic heterostructures create new
electronic systems with properties relevant to both fundamental and applied
fields. | 1004.3927v1 |
2011-05-26 | Coulomb Drag and High Resistivity Behavior in Double Layer Graphene | We show that Coulomb drag in ultra-clean graphene double layers can be used
for controlling the on/off ratio for current flow by tunning the external gate
voltage. Hence, although graphene remains semi-metallic, the double layer
graphene system can be tuned from conductive to a highly resistive state. We
show that our results explain previous data of Coulomb drag in double layer
graphene samples in disordered SiO2 substrates. | 1105.5399v2 |
2013-09-04 | Low temperature magnetic transitions of single crystal HoBi | We present resistivity, specific heat and magnetization measurements in high
quality single crystals of HoBi, with a residual resistivity ratio of 126. We
find, from the temperature and field dependence of the magnetization, an
antiferromagnetic transition at 5.7 K, which evolves, under magnetic fields,
into a series of up to five metamagnetic phases. | 1309.1113v1 |
2018-02-25 | Field-effect-driven half-metallic multilayer graphene | Rhombohedral stacked multilayer graphene displays the occurrence of a
magnetic surface state at low temperatures. Recent angular resolved
photoemission experiments demonstrate the robustness of the magnetic state in
long sequences of ABC graphene. Here, by using first-principles calculations,
we show that field-effect doping of these graphene multilayers induces a
perfect half-metallic behaviour with 100% of spin current polarization already
at dopings attainable in conventional field effect transistors with solid state
dielectrics. Our work demonstrates the realisability of a new kind of
spintronic devices where the transition between the low resistance and the high
resistance state is driven only by electric fields. | 1802.09028v1 |
2020-06-04 | Materials & Properties: Thermal & Electrical Characteristics | This lecture gives an introduction to the basic physics of the electrical
conductivity of metals, its temperature dependence and its limiting factors. We
will then introduce the concept of surface resistance, of high relevance in
accelerators for its link with beam impedance and for RF applications,
including notions related to the anomalous skin effect. The surface resistance
will help establishing a link to heat exchanges between bodies by radiation,
and to the concept of emissivity. Thermal conductivity will then be introduced,
discussing both its electron and phonon exchange components, and the relevant
limiting factors. | 2006.02842v1 |
2020-09-10 | Solid-state Li-ion batteries operating at room temperature using new borohydride argyrodite electrolytes | Using a new class of (BH4)- substituted argyrodite Li6PS5Z0.83(BH4)0.17, (Z =
Cl, I) solid electrolyte, Li-metal solid-state batteries operating at room
temperature have been developed. The cells were made by combining the modified
argyrodite with an In-Li anode and two types of cathode: an oxide, LixMO2 (M =
1/3Ni, 1/3Mn, 1/3Co; so called NMC) and a titanium disulfide, TiS2. The
performance of the cells was evaluated through galvanostatic cycling and
Alternating Current AC electrochemical impedance measurements. Reversible
capacities were observed for both cathodes for at least tens of cycles.
However, the high-voltage oxide cathode cell shows lower reversible capacity
and larger fading upon cycling than the sulfide one. The AC impedance
measurements revealed an increasing interfacial resistance at the cathode side
for the oxide cathode inducing the capacity fading. This resistance was
attributed to the intrinsic poor conductivity of NMC and interfacial reactions
between the oxide material and the argyrodite electrolyte. On the contrary, the
low interfacial resistance of the TiS2 cell during cycling evidences a better
chemical compatibility between this active material and substituted
argyrodites, allowing full cycling of the cathode material, 240 mAhg-1, for at
least 35 cycles with a coulombic efficiency above 97%. | 2009.04779v1 |
2000-04-08 | Electrical Conductivity in Magnesium-Doped Al_2 O_3 Crystal at Moderate Temperatures | AC and DC electrical measurements between 273 and 800 K were used to
characterize the electrical conductivity of Al_2 O_3:Mg single crystals
containing [Mg]^{0} center. At low fields contacts are blocking. At high
fields, electrical current flows steadily through the sample and the I-V
characteristic corresponds to a directly biased barrier whit a series
resistance (bulk resistance). AC measurements yield values for the junction
capacitance as well as for the sample resistance, and provide perfectly
reproducible conductivity values. The conductivity varies linearly whit the
[Mg]^{0} concentration and a thermal activation energy of 0.68 eV was obtained,
which agrees very well with the activation energy previously reported for
motion of free holes. | 0004123v1 |
2001-07-13 | Superconductivity in the Correlated Pyrochlore Cd_2Re_2O_7 | We report the observation of superconductivity in high-quality
Cd$_2$Re$_2$O$_7$ single crystals with room-temperature pyrochlore structure.
Resistivity and ac susceptibility measurements establish an onset transition
temperature T$_c^{onset}$ = 1.47 K with transition width $\Delta$T$_c$ = 0.25
K. In applied magnetic field, the resistive transition shows a type-II
character, with an approximately linear temperature-dependence of the upper
critical field H$_{c2}$. The bulk nature of the superconductivity is confirmed
by the specific heat jump with $\Delta$C = 37.9 mJ/mol-K. Using the $\gamma$
value extracted from normal-state specific heat data, we obtain
$\Delta$C/$\gamma$T$_c$ = 1.29, close to the weak coupling BCS value. In the
normal state, a negative Hall coefficient below 100 K suggests electron-like
conduction in this material. The resistivity exhibits a quadratic T-dependence
between 2 and 60 K, i.e., $\rho =\rho_0$+AT$^2$, indicative of Fermi-liquid
behavior. The values of the Kadowaki-Woods ratio A/$\gamma^2$ and the Wilson
ratio are comparable to that for strongly correlated materials. | 0107309v3 |
2002-03-12 | Magnetoresistances observed by decomposition of the magnetic moment in La1-xCaxMnO3 films | A ferromagnetic phase, characterized by electron carriers and a high
temperature colossal magnetoresistance (HTCMR) dependent on the magnetic
moment, and a semiconducting phase, characterized by hole carriers and a low
temperature CMR (LTCMR), are observed in La$_{1-x}$Ca$_{x}$MnO$_3$ thin films
by the van der Pauw method. The LTCMR is much more sensitive to the magnetic
field than the HTCMR. In the ferromagnetic phase for films with anisotropic
moments in two dimensions, a remnant resistivity of the order of 10$^{-8}
\~{\Omega}m$ is observed up to 100 K and increases exponentially with both a
temperature up to $T_c$ and a magnetic field above one Tesla (a positive
magnetoresistivity). We found that the ferromagnetic phase below $T_c$ is in a
polaronic state with a polaronic mobile conduction, and the carrier density
dips near $T_c$. For resistances measured by the four-probe method with line
electrodes, low temperature information of the HTCMR is not revealed. The van
der Pauw method is more effective for the resistance measurement of a magnetic
material than the four-probe method. | 0203245v2 |
2004-01-20 | A New Approach to the Josephson Effect | We introduce a new approach to the Josephson effect in SIS tunnel junctions.
The Josephson coupling energy is calculated from the overlap of real space
Cooper pair wavefunctions in two superconductors through an insulating barrier.
It is shown that the Josephson tunneling is limited by the size of the Cooper
pair and its shrinking during the tunneling. Therefore, the Josephson coupling
energy and the critical current become extremely small in high $T_{c}$
superconductors, including $MgB_{2}$. This shrinking also causes the observed
DC supercurrent in low $T_{c}$ superconductors, such as Pb and Sn, to fall off
much faster than $1/R_{n}$ for tunneling resistance $R_{n}$ above several ohms.
Consequently there is a material-dependent threshold resistance, above which
the supercurrent decreases much faster with increasing resistance. The
impurity-induced shrinking is also shown to limit the critical current.
Furthermore, the (weak) temperature dependence of the Cooper pair size is found
to contribute to the temperature dependence of the DC supercurrent. | 0401374v2 |
2008-05-12 | Influence of sintering temperature on resistivity, magnetoresistance and thermopower of La0.67Ca0.33MnO3 | A systematic investigation of La0.67Ca0.33MnO3 manganites has been
undertaken, mainly to understand the influence of varying crystallite size
(nanometer range) on electrical resistivity, magnetic susceptibility and
thermoelectric power. The materials were prepared by the sol-gel method of
sintering at four different temperatures between 800 and 1100 degrees C. The
samples were characterized by X-ray diffraction and data were analyzed using
Rietveld refinement. The metal-insulator transition temperatures (TP) are found
to increase with increasing sintering temperatures, while the magnetic
transition temperatures (TC) decrease. The electrical resistivity and
thermoelectric power data at low temperatures (T < TP) have been analyzed by
considering various scattering phenomena, while the high temperature (T > TP)
data were analyzed with Mott's small polaron hopping conduction mechanisms.
PACS Codes: 73.50.Lw, 75.47.Gk, 75.47.Lx | 0805.1663v1 |
2008-09-12 | Two insulating phases in compressed Pr1-xCaxMnO3 thin films | The temperature dependent resistivity of two Pr1-xCaxMnO3 (x=0.5 and 0.4)
thin films grown on LaAlO3 has been studied as a function of hydrostatic
pressure (up to 2.5 GPa) and magnetic field (up to 9T). Both samples show a
monotonic decrease in the resistivity with an increase in pressure,
corresponding to a change of -35% at 2.5 GPa. No pressure induced
metal-to-insulator transition was observed in the temperature-dependent
resistivity. The non-trivial interaction between high pressure and magnetic
field reveals that the effect of pressure cannot be simply rescaled to that of
a specific field, as has been reported for the corresponding bulk material. We
propose an interpretation of the data based on phase separation, where two
different insulating phases coexist: the charge ordered phase, which is
sensitive to both magnetic field and pressure, and a second insulating phase
that can be tuned by magnetic field. Such a result demonstrates that phase
separation can be manipulated in thin films by independent application of
magnetic field and/or external pressure. | 0809.2184v1 |
2008-10-28 | Electrical properties of boron-doped MWNTs synthesized by hot-filament chemical vapor deposition | We have synthesized a large amount of boron-doped multiwalled carbon
nanotubes (MWNTs) by hot-filament chemical vapor deposition. The synthesis was
carried out in a flask using a methanol solution of boric acid as a source
material. The scanning electron microscopy, transmission electron microscopy,
and micro-Raman spectroscopy were performed to evaluate the structural
properties of the obtained MWNTs. In order to evaluate the electrical
properties, temperature dependence of resistivity was measured in an individual
MWNTs with four metal electrodes. The Ramman shifts suggest carrier injection
into the boron-doped MWNTs, but the resistivity of the MWNTs was high and
increased strongly with decreasing temperature. Defects induced by the plasma
may cause this enhanced resistivity. | 0810.4971v1 |
2011-06-15 | An Analytical Approach for Memristive Nanoarchitectures | As conventional memory technologies are challenged by their technological
physical limits, emerging technologies driven by novel materials are becoming
an attractive option for future memory architectures. Among these technologies,
Resistive Memories (ReRAM) created new possibilities because of their
nano-features and unique $I$-$V$ characteristics. One particular problem that
limits the maximum array size is interference from neighboring cells due to
sneak-path currents. A possible device level solution to address this issue is
to implement a memory array using complementary resistive switches (CRS).
Although the storage mechanism for a CRS is fundamentally different from what
has been reported for memristors (low and high resistances), a CRS is simply
formed by two series bipolar memristors with opposing polarities. In this paper
our intention is to introduce modeling principles that have been previously
verified through measurements and extend the simulation principles based on
memristors to CRS devices and hence provide an analytical approach to the
design of a CRS array. The presented approach creates the necessary design
methodology platform that will assist designers in implementation of CRS
devices in future systems. | 1106.2927v2 |
2013-02-05 | Graphene-Ferroelectric Hybrid Structure for Flexible Transparent Electrodes | Graphene has exceptional optical, mechanical and electrical properties,
making it an emerging material for novel optoelectronics, photonics and for
flexible transparent electrode applications. However, the relatively high sheet
resistance of graphene is a major constrain for many of these applications.
Here we propose a new approach to achieve low sheet resistance in large-scale
CVD monolayer graphene using non-volatile ferroelectric polymer gating. In this
hybrid structure, large-scale graphene is heavily doped up to 3{\times}1013
cm-2 by non-volatile ferroelectric dipoles, yielding a low sheet resistance of
120 {\Omega}{\Box} at ambient conditions. The graphene-ferroelectric
transparent conductors (GFeTCs) exhibit more than 95% transmittance from the
visible to the near infrared range owing to the highly transparent nature of
the ferroelectric polymer. Together with its excellent mechanical flexibility,
chemical inertness and the simple fabrication process of ferroelectric
polymers, the proposed GFeTCs represent a new route towards large-scale
graphene based transparent electrodes and optoelectronics. | 1302.0993v1 |
2013-03-11 | Crystals, magnetic and electronic properties of a new ThCr2Si2-type BaMn2Bi2 and K-doped compositions | This is a report on the new 122 ternary transition-metal pnictide of
BaMn2Bi2, which is crystallized from bismuth flux. BaMn2Bi2 adopts
ThCr2Si2-type structure (I4/mmm) with a = 4.4902(3) {\AA} and c = 14.687(1)
{\AA}; it is antiferromagnetic with anisotropic magnetic susceptibility and
semiconducting with a band gap of Eg = 6 meV. Heat capacity result confirms the
insulating ground state in BaMn2Bi2 with the electronic residual Sommerfeld
coefficient of {\gamma} ~ 0. The high temperature magnetization results show
that magnetic ordering temperature is TN ~ 400 K. Hole-doping in BaMn2Bi2 via
potassium in Ba1-xKxMn2Bi2 results in metallic behavior for x = 0.10(1),
0.32(1) and 0.36(1). With K-doping, more magnetically anisotropic behavior is
observed. Although there is a downturn in electrical resistivity and low-field
magnetization data below 4 K in > 30%-doped crystals, there is no sign of zero
resistance or diamagnetism. This manuscript is a report on new materials of
BaMn2Bi2 and Ba1-xKxMn2Bi2 (0 < x < 0.4). Results from powder X-ray
diffraction, anisotropic temperature- and field-dependent magnetization,
temperature-and field-dependent electrical resistivity, and heat capacity are
presented. | 1303.2695v2 |
2015-02-09 | Surface-state-dominated transport in crystals of the topological crystalline insulator In-doped Pb$_{1-x}$Sn$_x$Te | Three-dimensional topological insulators and topological crystalline
insulators represent new quantum states of matter, which are predicted to have
insulating bulk states and spin-momentum-locked gapless surface states.
Experimentally, it has proven difficult to achieve the high bulk resistivity
that would allow surface states to dominate the transport properties over a
substantial temperature range. Here we report a series of indium-doped
Pb$_{1-x}$Sn$_x$Te compounds that manifest huge bulk resistivities together
with strong evidence of topological surface states, based on
thickness-dependent transport studies and magnetoresistance measurements. For
these bulk-insulating materials, the surface states determine the resistivity
for temperatures approaching 30 K. | 1502.02696v1 |
2016-04-20 | Magnetoresistance and Shubnikov-de Hass oscillation in YSb | YSb crystals are grown and the transport properties under magnetic field are
measured. The resistivity exhibits metallic behavior under zero magnetic field
and the low temperature resistivity shows a clear upturn once a moderate
magnetic field is applied. The upturn is greatly enhanced by increasing
magnetic field, finally resulting in a metal-to-insulator-like transition. With
temperature further decreased, a resistivity plateau emerges after the
insulator-like regime. At low temperature (2.5 K) and high field (14 T), the
transverse magnetoresistance (MR) is quite large (3.47 $\times 10^4\%$ ). In
addition, Shubnikov-de Haas (SdH) oscillation has also been observed in YSb.
Periodic behavior of the oscillation amplitude reveals the related information
about Fermi surface and two major oscillation frequencies can be obtained from
the FFT spectra of the oscillations. The trivial Berry phase extracted from SdH
oscillation, band structure revealed by angle-resolved photoemission
spectroscopy (ARPES) and first-principles calculations demonstrate that YSb is
a topologically trivial material. | 1604.05912v2 |
2016-04-06 | Structural characterization of APPJ treated Bismaleimide coatings and heat treated Titania-BMI | Bismaleimide (BMI) are thermosetting polymers mainly used in aerospace
applications having properties of dimensional stability, low shrinkage,
chemical resistance, fire resistance, good mechanical properties and high
resistance against various solvents, acids, and water. BMI is commercially
available as Homide 250. BMI coating has also been used for the corrosion
protection. Metallization (AL) of BMI using vacuum evaporation was done which
serves the purpose of prevention of space charge accumulation in aircraft
bodies. Addition of inorganic materials like metal oxides can influence the
properties of the polymer as an inorganic-organic composite. The
organic-ionorganic composites have wide applications in electronics, optics,
chemistry and medicine. Titanium dioxide (TiO2, Titania) has a wide range of
applications starting from photocatalysis, dye-sensitized solar cells to
optical coatings and electronics. A BMI-TiO2 composite was prepared by chemical
route. Atmospheric Plasma Jet (APPJ) using Helium gas was also treated on BMI.
XRD and FTIR studies of the composite system prepared at different temperatures
showed its crystalline and structural configuration. | 1604.07297v1 |
2016-06-27 | Structural and electrical properties of Sn substituted double sintering derived Ni-Zn ferrite | The Sn substituted Ni-Zn ferrites were synthesized by the standard double
sintering technique using nano powders of nickel oxide (NiO), zinc oxide (ZnO),
iron oxide (Fe2O3) and tin oxide (SnO2). The structural and electrical
properties have been investigated by the X-ray diffraction, scanning electron
microscopy, DC resistivity and dielectric measurements. Extra intermediate
phase has been detected along with the inverse cubic spinel phase of Ni-Zn
ferrite. Enhancement of grain size is observed in Sn substituted Ni-Zn
ferrites. DC resistivity as a function of temperature has been investigated by
two probe method. The DC resistivity was found to decrease whereas the
dielectric constants increase with increasing Sn content in Ni-Zn ferrites. The
dielectric constant of the as prepared samples is high enough to use these
materials in miniaturized memory devices based capacitive components or energy
storage principles. | 1606.08118v1 |
2017-02-18 | Scaling limits of graphene nanoelectrodes | Graphene is an ideal material for fabricating atomically thin nanometre
spaced electrodes. Recently, carbon-based nanoelectrodes have been employed to
create single-molecule transistors and phase change memory devices. In spite of
the significant recent interest in their use in a range of nanoscale devices
from phase change memories to molecular electronics, the operating and scaling
limits of these electrodes are completely unknown. In this paper, we report on
our observations of consistent voltage driven resistance switching in sub-5 nm
graphene nanogaps. We find that we are able to reversibly cycle between a low
and a high resistance state using feedback-controlled voltage ramps.We
attribute this unexplained switching in the gap to the formation and breakdown
of carbon filaments.By increasing the gap, we find that such intrinsic
resistance switching of graphene nanogaps imposes a scaling limit of 10 nm
(approx.) on the gap-size for devices with operating voltages of 1 to 2 volts. | 1702.05668v1 |
2019-09-23 | Nanoscale ballistic diodes made of polar materials for amplification and generation of radiation in 10 THz-range | We investigate ultra-high frequency electrical properties of nanoscale
$n^+$-$i$-$n^+$ diodes made of polar semiconductors. The calculations show that
the coupling between optical vibrations of the lattice and the ballistic
electrons strongly modifies and enhances the time-of-flight effects giving rise
to narrow resonances of the diode impedance in the reststrahlen frequency
range. Particularly, negative dynamic resistance is induced in close proximity
to the optical phonon frequency. The resonant effects in the dynamic resistance
of nanoscale GaAs and InP diodes are studied in detail. The obtained magnitudes
of the negative dynamic resistance effect indicate that the nanoscale diodes
are capable of generating electromagnetic radiation in far-infrared spectral
range under electric pumping. | 1909.10185v1 |
2019-12-20 | Electron-phonon interaction and zero-field charge carrier transport in the nodal-line semimetal ZrSiS | We study electron-phonon interaction and related transport properties of
nodal-line semimetal ZrSiS using first-principles calculations. We find that
ZrSiS is characterized by a weak electron-phonon coupling on the order of 0.1,
which is almost energy independent. The main contribution to the
electron-phonon coupling originates from long-wavelength optical phonons,
causing no significant renormalization of the electron spectral function. At
the charge neutrality point, we find that electrons and holes provide a
comparable contribution to the scattering rate. The phonon-limited resistivity
calculated within the Boltzmann transport theory is found to be strongly
direction-dependent with the ratio between out-of-plane and in-plane directions
being $\rho_{zz}/\rho_{xx}\sim 7.5$, mainly determined by the anisotropy of
carrier velocities. We estimate zero-field resistivity to be
$\rho_{xx}\approx12$ $\mu\Omega$ cm at 300 K, which is in good agreement with
experimental data. Relatively small resistivity in ZrSiS can be attributed to a
combination of weak electron-phonon coupling and high carrier velocities. | 1912.09832v2 |
2015-04-06 | Gate-tunable Memristive Phenonmena Mediated by Grain Boundaries in Single Layer MoS2 | Continued progress in high speed computing depends on breakthroughs in both
materials synthesis and device architectures. The performance of logic and
memory can be enhanced significantly by introducing a memristor, a two terminal
device with internal resistance that depends on the history of the external
bias voltage. State of the art memristors, based on metal insulator metal (MIM)
structures with insulating oxides, such as TiO2, are limited by a lack of
control over the filament formation and external control of the switching
voltage. Here, we report a class of memristors based on grain boundaries (GBs)
in single-layer MoS2 devices. Specifically, the resistance of GBs emerging from
contacts can be easily and repeatedly modulated, with switching ratios up to
1000 and a dynamic negative differential resistance (NDR). Furthermore, the
atomically thin nature of MoS2 enables tuning of the set voltage by a third
gate terminal in a field-effect geometry, which provides new functionality that
is not observed in other known memristive devices. | 1504.01416v1 |
2020-12-09 | Potassium-Doped Para-Terphenyl: Structure, Electrical Transport Properties and Possible Signatures of a Superconducting Transition | Preliminary evidence for the occurrence of high-Tc superconductivity in
alkali-doped organic materials, such as potassium-doped p-terphenyl (KPT), were
recently obtained by magnetic susceptibility measurements and by the opening of
a large superconducting gap as measured by ARPES and STM techniques. In this
work, KPT samples have been synthesized by a chemical method and characterized
by low-temperature Raman scattering and resistivity measurements. Here, we
report the occurrence of a resistivity drop of more than 4 orders of magnitude
at low temperatures in KPT samples in the form of compressed powder. This fact
was interpreted as a possible sign of a broad superconducting transition taking
place below 90 K in granular KPT. The granular nature of the KPT system appears
to be also related to the 20 K broadening of the resistivity drop around the
critical temperature. | 2012.04899v1 |
2020-12-23 | Direct observation of the electrically triggered Insulator-Metal transition in V3O5 far below the transition temperature | Resistive switching is one of the key phenomena for applications such as
nonvolatile memories or neuromorphic computing. V3O5, a compound of the
vanadium oxide Magn\'eli series, is one of the rare materials to exhibit an
insulator-metal transition (IMT) above room temperature (Tc ~ 415 K). Here we
demonstrate both static dc resistive switching (RS) and fast oscillatory
spiking regimes in V3O5 devices at room temperature (120 K below the phase
transition temperature) by applying an electric field. We use operando optical
imaging to track a reflectivity change during the RS and find that a
percolating high temperature metallic phase filament is formed. This
demonstrates that the electrically induced RS triggers the phase transition.
Furthermore, we optically capture the spiking oscillations that we link to the
negative differential resistance regime and find the filament forms and
dissolves via a periodic spatio-temporal instability that we describe by
numerical simulations. | 2012.13009v1 |
2021-02-10 | Current-limiting amplifier for high speed measurement of resistive switching data | Resistive switching devices, important for emerging memory and neuromorphic
applications, face significant challenges related to control of delicate
filamentary states in the oxide material. As a device switches, its rapid
conductivity change is involved in a positive feedback process that would lead
to runaway destruction of the cell without current, voltage, or energy
limitation. Typically, cells are directly patterned on MOS transistors to limit
the current, but this approach is very restrictive as the necessary integration
limits the materials available as well as the fabrication cycle time. In this
article we propose an external circuit to cycle resistive memory cells,
capturing the full transfer curves while driving the cells in such a way to
suppress runaway transitions. Using this circuit, we demonstrate the
acquisition of $10^5$ I-V loops per second without the use of on-wafer current
limiting transistors. This setup brings voltage sweeping measurements to a
relevant timescale for applications, and enables many new experimental
possibilities for device evaluation in a statistical context. | 2102.05770v1 |
2021-04-13 | Negative Differential Resistance in Carbon-Based Nanostructures | Nonlinear electrical properties, such as negative differential resistance
(NDR), are essential in numerous electrical circuits, including memristors.
Several physical origins have been proposed to lead to the NDR phenomena in
semiconductor devices in the last more than half a century. Here, we report NDR
behavior formation in randomly oriented graphene-like nanostructures up to 37 K
and high on-current density up to 10^5 A/cm^2. Our modeling of the
current-voltage characteristics, including the self-heating effects, suggests
that strong temperature dependence of the low-bias resistance is responsible
for the nonlinear electrical behavior. Our findings open opportunities for the
practical realization of the on-demand NDR behavior in nanostructures of 2D and
3D material-based devices via heat management in the conducting films and the
underlying substrates. | 2104.06337v2 |
2021-05-17 | Enhancement of the superconductivity and quantum metallic state in the thin film of superconducting Kagome metal KV$_3$Sb$_5$ | Recently V-based Kagome metal attracted intense attention due to the
emergence of superconductivity in the low temperature. Here we report the
fabrication and physical investigations of the high quality single-crystalline
thin films of the Kagome metal KV$_3$Sb$_5$. For the sample with the thickness
of about 15 nm, the temperature dependent resistance reveals a
Berezinskii-Kosterlitz-Thouless (BKT) type behavior, indicating the presence of
two-dimensional superconductivity. Compared with the bulk sample, the onset
transition temperature $T^{onset}_{c}$ and the out-of-plane upper critical
field $H_{c2}$ are enhanced by 15\% and more than 10 times respectively.
Moreover, the zero-resistance state is destroyed by a magnetic field as low as
50 Oe. Meanwhile, the temperature-independent resistance is observed in a wide
field region, which is the hallmark of quantum metallic state. Our results
provide evidences for the existence of unconventional superconductivity in this
material. | 2105.07732v1 |
2021-06-28 | Superconductivity in an extreme strange metal | Some of the highest-transition-temperature superconductors across various
materials classes exhibit linear-in-temperature `strange metal' or `Planckian'
electrical resistivities in their normal state. It is thus believed by many
that this behavior holds the key to unlock the secrets of high-temperature
superconductivity. However, these materials typically display complex phase
diagrams governed by various competing energy scales, making an unambiguous
identification of the physics at play difficult. Here we use electrical
resistivity measurements into the micro-Kelvin regime to discover
superconductivity condensing out of an extreme strange metal state -- with
linear resistivity over 3.5 orders of magnitude in temperature. We propose that
the Cooper pairing is mediated by the modes associated with a recently
evidenced dynamical charge localization-delocalization transition, a mechanism
that may well be pertinent also in other strange metal superconductors. | 2106.14849v2 |
2022-01-28 | Factors that control stability, variability, and reliability issues of endurance cycle in ReRAM devices: a phase field study | The morphological evolution of the conducting filament (CF) predominantly
controls the electric response of the resistive random access memory (ReRAM)
devices. However, the parameters -- in terms of the material and the processing
-- which control the growth of such CF are plenty. Extending the phase field
technique for ReRAM systems presented by Roy and Cha [J. Appl. Phys. 128,
205102 (2020)], we could successfully model the complete SET (low resistance
state) and RESET (high resistance state) sates due to the application of
sweeping voltage. The key parameters that influence the stability of the
multi-cycle \emph{I-V} response or the endurance behavior are identified. The
computational findings of the presented model ReRAM system are practical in
correlating the multi-parametric influence with the stability, variability, and
reliability of the endurance cycle that affect the device performance and also
lead to the device failure. We believe that our computational approach of
connecting the morphological changes of the CF with the electrical response,
has the potential to further understand and optimize the performance of the
ReRAM devices. | 2201.12304v2 |
2022-07-03 | An Atomistic Modelling Framework for Valence Change Memory Cells | We present a framework dedicated to modelling the resistive switching
operation of Valence Change Memory (VCM) cells. The method combines an
atomistic description of the device structure, a Kinetic Monte Carlo (KMC)
model for the creation and diffusion of oxygen vacancies in the central oxide
under an external field, and an ab-initio quantum transport method to calculate
electrical current and conductance. As such, it reproduces a realistically
stochastic device operation and its impact on the resulting conductance. We
demonstrate this framework by simulating a switching cycle for a
TiN/HfO$_2$/TiN VCM cell, and see a clear current hysteresis between high/low
resistance states, with a conductance ratio of one order of magnitude.
Additionally, we observe that the changes in conductance originate from the
creation and recombination of vacancies near the active electrode, effectively
modulating a tunnelling gap for the current. This framework can be used to
further investigate the mechanisms behind resistive switching at an atomistic
scale and optimize VCM material stacks and geometries. | 2207.01095v1 |
2023-06-16 | Piezo-resistive pressure sensor based on CVD-grown ZnO nanowires on Polyethylene Tetrathalate substrate | Recent developments in the domain of electronic materials and devices have
attracted the interest of researchers toward flexible and printable electronic
components like organic transistors, printable electrodes and sensors. Zinc
Oxide (ZnO) nanowires (NWs) possess a number of excellent properties like high
mobility, large exciton binding energy and the direct-band gap in addition to
large piezoelectric coefficients. Here, we report on flexible piezo-resistive
sensor based on Indium tin oxide (ITO)-coated Polyethylene tetrathalate (PET)
substrate. The device shows sensitivity in terms of change in resistance from
100 {\Omega} to 2.4 K{\Omega} at an applied potential of 5V upon bending from
flat to 95 degrees. The 1-D nanowire flexible device in its flat state shows
saturated output current. We observed ten folds enhanced variation as compared
to previous reports. Improved sensitivity was observed in our experiments due
to fewer defects in CVD-grown NWs as compared to others where hydrothermally
grown nanowires were used. The methodology of device fabrication reported here
requires less time and enables efficient devices for the realization of
flexible and wearable technology. | 2307.13805v1 |
2023-10-22 | Microstructure evolution and characteristics of laser-clad lightweight refractory NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr high-entropy alloy | Lightweight refractory high-entropy alloy coatings (RHEAcs) of
NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr (where $x=$ 1, 1.3, 1.5, and 2) were
fabricated on the surface of 316L stainless steel using laser cladding (LC)
technology. A comprehensive study was conducted to elucidate the effect of Nb
content on the microstructure, microhardness and wear resistance of
NbxMo$_{0.5}$Ti$_{1.5}$Ta$_{0.2}$Cr RHEAcs before and after annealing at 900
for 10 h. The results show that the grains are gradually refined with the
increase of Nb content. The coating consists mainly of a body-centered cubic
(BCC) solid solution, C15-Laves phase, and a small amount of hexagonal
close-packed (HCP) solid solution containing Ti. The microhardness of RHEAcs is
significantly higher compared to the base material. Notably, at Nb1.3, due to
the influence of lattice dislocations, the microhardness reaches a peak of
1066.5 HV, which is about 7.11 times higher than that of the base material. On
the contrary, at Nb$_2$, the microhardness is at its lowest point, averaging
709.31 HV, but 4.72 times that of the base material. After annealing, an
increase in microhardness is observed at all Nb concentrations, up to 31.2% at
Nb$_2$. Before annealing, the wear resistance of RHEAcs was slightly better
than that of 316L stainless steel at different Nb contents. However, after
annealing, the coefficient of friction (COF) and wear rate of the coatings are
lower than those of annealed 316L stainless steel, highlighting their excellent
wear resistance. It is noteworthy that the loss of wear properties after
annealing at Nb1 is at a minimum, obtaining the most balanced wear resistance
before and after annealing. The enhanced wear resistance after annealing can be
attributed to the presence of ultra-fine grain oxide friction layers, mainly
composed of TiO2 and Ta2O5 . The main mode of wear is oxidative wear, with a
small amount of wear from abrasive wear. | 2310.14223v1 |
2019-08-16 | Scaling Analysis of Anomalous Hall Resistivity in the Co$_{2}$TiAl Heusler Alloy | A comprehensive magnetotransport study including resistivity ($\rho_{xx}$) at
various fields, isothermal magnetoresistance and Hall resistivity ($\rho_{xy}$)
has been carried out at different temperatures on the Co$_{2}$TiAl Heusler
alloy. Co$_{2}$TiAl alloy shows a paramagnetic (PM) to ferromagnetic (FM)
transition below the curie temperature (T$_{C}$) $\sim$ 125 K. In the FM
region, resistivity and magnetoresistance reveals a spin flip electron-magnon
scattering and the Hall resistivity unveils the anomalous Hall resistivity
($\rho_{xy}^{AH}$). Scaling of anomalous Hall resistivity with resistivity
establishes the extrinsic scattering process responsible for the anomalous hall
resistivity; however Skew scattering is the dominant mechanism compared to the
side-jump contribution. A one to one correspondence between magnetoresistance
and side-jump contribution to anomalous Hall resistivity verifies the
electron-magnon scattering being the source of side-jump contribution to the
anomalous hall resistivity. | 1908.05974v1 |
2009-08-20 | Magnetism, Superconductivity and Stoichiometry in Single Crystals of Fe1+y(Te1-xSx)z | We report synthesis of high quality Fe1+y(Te1-xSx)z single crystals and a
comprehensive study of structural, magnetic and transport properties. There is
high sensitivity to material stoichiometry which includes vacancies on the
Te(S) site. Our results reveal competition and coexistence of magnetic order
and percolative superconductivity for x >= 0.03, while zero resistivity is
acheived for x >= 0.1. | 0908.3011v1 |
2020-11-20 | Phonons, electrons and thermal transport in Planckian high T$_c$ materials | The room temperature thermal diffusivity of high T$_c$ materials is dominated
by phonons. This allows the scattering of phonons by electrons to be discerned.
We argue that the measured strength of this scattering suggests a converse
Planckian scattering of electrons by phonons across the room temperature phase
diagram of these materials. Consistent with this conclusion, the temperature
derivative of the resistivity of strongly overdoped cuprates is noted to show a
kink at a little below 200 K that we argue should be understood as the onset of
a high temperature Planckian $T$-linear scattering of electrons by classical
phonons. This kink continuously disappears towards optimal doping, even while
strong scattering of phonons by electrons remains visible in the thermal
diffusivity, sharpening the long-standing puzzle of the lack of a feature in
the $T$-linear resistivity at optimal doping associated to onset of phonon
scattering. | 2011.10466v2 |
2017-08-10 | Zero resistance from one atmosphere to the pressure of earth's outer core in a superconducting high entropy alloy | We report the observation of extraordinarily robust zero-resistance
superconductivity in the pressurized (TaNb)0.67(HfZrTi)0.33 high entropy alloy
- a new kind of material with a body-centered cubic crystal structure made from
five randomly distributed transition metal elements. The transition to
superconductivity (TC) increases from an initial temperature of 7.7 K at
ambient pressure to 10 K at ~ 60 GPa, and then slowly decreases to 9 K by 190.6
GPa, a pressure that falls within that of the outer core of the earth. We infer
that the continuous existence of the zero-resistance superconductivity from one
atmosphere up to such a high pressure requires a special combination of
electronic and mechanical characteristics. This high entropy alloy
superconductor thus may have a bright future for applications under extreme
conditions, and also poses a challenge for understanding the underlying quantum
physics. | 1708.03146v2 |
2020-05-16 | Electric-field induced strange metal states and possible high-temperature superconductivity in hydrogenated graphitic fibers | In this work, we have studied the effects from increasing the strength of the
applied electric field on the charge transport of hydrogenated graphitic
fibers. Resistivity measurements were carried out for direct currents in the nA
- mA range and for temperatures from 1.9 K to 300 K. The high-temperature
non-ohmic voltage-current dependence is well described by the nonlinear random
resistor network model applied to systems that are disordered at all scales.
The temperature-dependent resistivity shows linear, step-like transitions from
insulating to metallic states as well as plateau features. As more current is
being sourced, the fiber becomes more conductive and thus the current density
goes up. The most interesting features is observed in high electric fields. As
the fiber is cooled, the resistivity first decreases linearly with the
temperature and then enters a plateau region at a temperature T ? 260 ? 280 K
that is field-independent. These observations on a system made out of carbon,
hydrogen, nitrogen, and oxygen atoms suggest possible electric-field induced
superconductivity with a high critical temperature that was predicted from
studying the role of chirality on the origin of life [1]. | 2005.07885v1 |
2021-09-28 | Development of high-rate capable and ultra-low mass Resistive Plate Chamber with Diamond-Like Carbon | A new type of resistive plate chamber (RPC) is under development using
thin-film resistive electrodes based on diamond-like carbon (DLC). Planned to
be put on the path of high-intensity low-momentum muon beam of the MEG II
experiment, this detector is required to be high-rate capable and ultra-low
mass. Using a prototype detector with 2 cm $\times$ 2 cm size and 0.1 % $X_0$
material budget, performance studies were conducted for MIP detection
efficiency, timing resolution and high rate capability in low-momentum muon
beam. In this paper, the measured performance is presented including the result
with low-momentum muon beam at rate up to 1 $\mathrm{MHz/cm^2}$. Based on the
result, the expected performance of the full-scale detector in the MEG~II
experiment is also discussed. | 2109.13525v1 |
2014-02-06 | High-performance ferroelectric memory based on fully patterned tunnel junctions | In tunnel junctions with ferroelectric barriers, switching the polarization
direction modifies the electrostatic potential profile and the associated
average tunnel barrier height. This results in strong changes of the tunnel
transmission and associated resistance. The information readout in
ferroelectric tunnel junctions (FTJs) is thus resistive and non-destructive,
which is an advantage compared to the case of conventional ferroelectric
memories (FeRAMs). Initially, endurance limitation (i.e. fatigue) was the main
factor hampering the industrialization of FeRAMs. Systematic investigations of
switching dynamics for various ferroelectric and electrode materials have
resolved this issue, with endurance now reaching $10^{14}$ cycles. Here we
investigate data retention and endurance in fully patterned submicron
Co/BiFeO$_3$/Ca$_{0.96}$Ce$_{0.04}$MnO$_3$ FTJs. We report good reproducibility
with high resistance contrasts and extend the maximum reported endurance of
FTJs by three orders of magnitude ($4\times10^6$ cycles). Our results indicate
that here fatigue is not limited by a decrease of the polarization or an
increase of the leakage but rather by domain wall pinning. We propose
directions to access extreme and intermediate resistance states more reliably
and further strengthen the potential of FTJs for non-volatile memory
applications. | 1402.1289v1 |
2021-07-02 | Topological surface conduction in Kondo insulator YbB$_{12}$ | Kondo insulators have recently aroused great interest because they are
promising materials that host a topological insulator state caused by the
strong electron interactions. Moreover, recent observations of the quantum
oscillations in the insulating state of Kondo insulators have come as a great
surprise. Here, to investigate the surface electronic state of a prototype
Kondo insulator YbB$_{12}$, we measured transport properties of single crystals
and microstructures. In all samples, the temperature dependence of the
electrical resistivity is insulating at high temperatures and the resistivity
exhibits a plateau at low temperatures. The magnitude of the plateau value
decreases with reducing sample thickness, which is quantitatively consistent
with the surface electronic conduction in the bulk insulating YbB$_{12}$.
Moreover, the magnetoresistance of the microstructures exhibits a
weak-antilocalization effect at low field. These results are consistent with
the presence of topologically protected surface state, suggesting that
YbB$_{12}$ is a candidate material of the topological Kondo insulator. The high
field resistivity measurements up to $\mu_0H$ = 50 T of the microstructures
provide supporting evidence that the quantum oscillations of the resistivity in
YbB$_{12}$ occurs in the insulating bulk. | 2107.00912v2 |
2021-07-22 | Quantum oscillations in 2D insulators induced by graphite gates | We demonstrate a mechanism for magnetoresistance oscillations in insulating
states of two-dimensional (2D) materials arising from the interaction of the 2D
layer and proximal graphite gates. We study a series of devices based on
different two-dimensional systems, including mono- and bilayer Td-WTe2,
angle-aligned MoTe2/WSe2 heterobilayers and Bernal-stacked bilayer graphene,
which all share a similar graphite-gated geometry. We find that the resistivity
of the 2D system generically shows quantum oscillations as a function of
magnetic field corresponding to a high-density Fermi surface when they are
tuned near an insulating state, in contravention of na\"ive band theory.
Simultaneous measurement of the resistivity of the graphite gates show that
these oscillations are precisely correlated with quantum oscillations in the
resistivity of the graphite gates themselves. Further supporting this
connection, the oscillations are quenched when the graphite gate is replaced by
TaSe2, a high-density metal that does not show quantum oscillations. The
observed phenomenon arises from the oscillatory behavior of graphite density of
states, which modulates the device capacitance and, as a consequence, the
carrier density in the sample layer even when a constant electrochemical
potential is maintained between the sample and the gate electrode. Oscillations
are most pronounced near insulating states where the resistivity is strongly
density dependent. Our study suggests a unified mechanism for quantum
oscillations in graphite-gated 2D insulators based on sample-gate coupling. | 2107.10430v2 |
2014-11-10 | Low carrier concentration crystals of the topological insulator Bi$_{2-x}$Sb$_{x}$Te$_{3-y}$Se$_{y}$: a magnetotransport study | In 3D topological insulators achieving a genuine bulk-insulating state is an
important research topic. Recently, the material system
(Bi,Sb)$_{2}$(Te,Se)$_{3}$ (BSTS) has been proposed as a topological insulator
with high resistivity and a low carrier concentration (Ren \textit{et al.}
\cite{Ren2011}). Here we present a study to further refine the bulk-insulating
properties of BSTS. We have synthesized Bi$_{2-x}$Sb${_x}$Te$_{3-y}$Se$_{y}$
single crystals with compositions around $x = 0.5$ and $y = 1.3$. Resistance
and Hall effect measurements show high resistivity and record low bulk carrier
density for the composition Bi$_{1.46}$Sb$_{0.54}$Te$_{1.7}$Se$_{1.3}$. The
analysis of the resistance measured for crystals with different thicknesses
within a parallel resistor model shows that the surface contribution to the
electrical transport amounts to 97% when the sample thickness is reduced to $1
\mu$m. The magnetoconductance of exfoliated BSTS nanoflakes shows 2D weak
antilocalization with $\alpha \simeq -1$ as expected for transport dominated by
topological surface states. | 1411.2479v2 |
2022-05-20 | Resistivity and Thermal Conductivity of an Organic Insulator beta'-EtMe3Sb[Pd(dmit)2]2 | A finite residual linear term in the thermal conductivity at zero temperature
in insulating magnets indicates the presence of gapless excitations of
itinerant quasiparticles, which has been observed in some candidate materials
of quantum spin liquids (QSLs). In the organic triangular insulator
beta'-EtMe3Sb[Pd(dmit)2]2, a QSL candidate material, the low-temperature
thermal conductivity depends on the cooling process and the finite residual
term is observed only in samples with large thermal conductivity. Moreover, the
cooling rate dependence is largely sample dependent. Here we find that, while
the low-temperature thermal conductivity significantly depends on the cooling
rate, the high-temperature resistivity is almost perfectly independent of the
cooling rate. These results indicate that in the samples with the finite
residual term, the mean free path of the quasiparticles that carry the heat at
low temperatures is governed by disorders, whose characteristic length scale of
the distribution is much longer than the electron mean free path that
determines the high-temperature resistivity. This explains why recent X-ray
diffraction and nuclear magnetic resonance measurements show no cooling rate
dependence. Naturally, these measurements are unsuitable for detecting
disorders of the length scale relevant for the thermal conductivity, just as
they cannot determine the residual resistivity of metals. Present results
indicate that very careful experiments are needed when discussing itinerant
spin excitations in beta'-EtMe3Sb[Pd(dmit)2]2. | 2205.10039v1 |
2022-09-17 | Superfunctional high-entropy alloys and ceramics by severe plastic deformation | High-entropy alloys and ceramics containing at least five principal elements
have recently received high attention for various mechanical and functional
applications. The application of severe plastic deformation (SPD), particularly
the high-pressure torsion (HPT) method, combined with the CALPHAD and
first-principles calculations resulted in the development of numerous
superfunctional high-entropy materials with superior properties compared to the
normal functions of engineering materials. This article reviews the recent
advances in the application of SPD to developing superfunctional high-entropy
materials. These superfunctional properties include (i) ultrahigh hardness
levels comparable to the hardness of ceramics in high-entropy alloys, (ii) high
yield strength and good hydrogen embrittlement resistance in high-entropy
alloys; (iii) high strength, low elastic modulus, and high biocompatibility in
high-entropy alloys, (iv) fast and reversible hydrogen storage in high-entropy
hydrides, (v) photovoltaic performance and photocurrent generation on
high-entropy semiconductors, (vi) photocatalytic oxygen and hydrogen production
from water splitting on high-entropy oxides and oxynitrides, and (vii) CO2
photoreduction on high-entropy ceramics. These findings introduce SPD as not
only a processing tool to improve the properties of existing high-entropy
materials but also as a synthesis tool to produce novel high-entropy materials
with superior properties compared with conventional engineering materials. | 2209.08291v3 |
2016-06-10 | Short channel effects in graphene-based field effect transistors targeting radio-frequency applications | Channel length scaling in graphene field effect transistors (GFETs) is key in
the pursuit of higher performance in radio frequency electronics for both rigid
and flexible substrates. Although two-dimensional (2D) materials provide a
superior immunity to Short Channel Effects (SCEs) than bulk materials, they
could dominate in scaled GFETs. In this work, we have developed a model that
calculates electron and hole transport along the graphene channel in a
drift-diffusion basis, while considering the 2D electrostatics. Our model
obtains the self-consistent solution of the 2D Poisson's equation coupled to
the current continuity equation, the latter embedding an appropriate model for
drift velocity saturation. We have studied the role played by the
electrostatics and the velocity saturation in GFETs with short channel lengths
L. Severe scaling results in a high degradation of GFET output conductance. The
extrinsic cutoff frequency follows a 1/L^n scaling trend, where the index n
fulfills n < 2. The case n = 2 corresponds to long-channel GFETs with low
source/drain series resistance, that is, devices where the channel resistance
is controlling the drain current. For high series resistance, n decreases down
to n= 1, and it degrades to values of n < 1 because of the SCEs, especially at
high drain bias. The model predicts high maximum oscillation frequencies above
1 THz for channel lengths below 100 nm, but, in order to obtain these
frequencies, it is very important to minimize the gate series resistance. The
model shows very good agreement with experimental current voltage curves
obtained from short channel GFETs and also reproduces negative differential
resistance, which is due to a reduction of diffusion current. | 1606.03264v2 |
2007-01-29 | Long-term Correlations and 1/f^alpha Noise in the Steady States of Multi-Species Resistor Networks | We introduce a multi-species network model which describes the resistance
fluctuations of a resistor in a non-equilibrium stationary state. More
precisely, a thin resistor characterized by a 1/f^alpha resistance noise is
described as a two-dimensional network made by different species of elementary
resistors. The resistor species are distinguished by their resistances and by
their energies associated with thermally activated processes of breaking and
recovery. Depending on the external conditions, stationary states of the
network can arise as a result of the competition between these processes. The
properties of the network are studied as a function of the temperature by Monte
Carlo simulations carried out in the temperature range 300 \div 800 K. At low
temperatures, the resistance fluctuations display long-term correlations
expressed by a power-law behavior of the auto-correlation function and by a
value approx 1 of the alpha-exponent of the spectral density. On the contrary,
at high temperatures the resistance fluctuations exhibit a finite and
progressively smaller correlation time associated with a non-exponential decay
of correlations and with a value of the alpha-exponent smaller than one. This
temperature dependence of the alpha coefficient reproduces qualitatively well
the experimental findings. | 0701712v1 |
2008-06-26 | Different resistivity response to spin density wave and superconductivity at 20 K in $Ca_{1-x}Na_xFe_2As_2$ | We report that intrinsic transport and magnetic properties, and their
anisotropy from high quality single crystal $CaFe_2As_2$. The resistivity
anisotropy ($\rho_c/\rho_{ab}$) is $\sim 50 $, and less than 150 of
$BaFe_2As_2$, which arises from the strong coupling along c-axis due to an
apparent contraction of about 0.13 nm compared to $BaFe_2As_2$. Temperature
independent anisotropy indicates that the transport in ab plane and along
c-axis direction shares the same scattering mechanism. In sharp contrast to the
case of parent compounds $ROFeAs$ (R=rare earth) and $MFe_2As_2$ (M=Ba and Sr),
spin-density-wave (SDW) ordering (or structural transition) leads to a steep
increase of resistivity in $CaFe_2As_2$. Such different resistivity response to
SDW ordering is helpful to understand the role played by SDW ordering in
Fe-based high-$T_c$ superconductors. The susceptibility behavior is very
similar to that observed in single crystal $BaFe_2As_2$. A linear temperature
dependent susceptibility occurs above SDW transition of about 165 K. Partial
substitution of Na for Ca suppresses the SWD ordering (anomaly in resistivity)
and induces occurrence of superconductivity at $\sim 20$ K. | 0806.4279v1 |
2014-02-25 | Measurement of junction conductance and proximity effect at superconductor/semiconductor junctions | The superconducting proximity effect has played an important role in recent
work searching for Majorana modes in thin semiconductor devices. Using
transport measurements to quantify the changes in the semiconductor caused by
the proximity effect provides a measure of dynamical processes such as
screening and scattering. However, in a two terminal measurement the resistance
due to the interface conductance is in series with resistance of transport in
the semiconductor. Both of these change, and it is impossible to separate them
without more information. We have devised a new three terminal device that
provides two resistance measurements that are sufficient to extract both the
junction conductance and the two dimensional sheet resistance under the
superconducting contact. We have compared junctions between Nb and InAs and Nb
and 30% InGaAs all grown before being removed from the ultra high vacuum
molecular beam epitaxy growth system. The most transparent junctions are to
InAs, where the transmission coefficient per Landauer mode is greater than 0.6.
Contacts made with ex-situ deposition are substantially more opaque. We find
that for the most transparent junctions, the largest fractional change as the
temperature is lowered is to the resistance of the semiconductor. | 1402.6055v1 |
2018-08-14 | Impurities and Defects in Mott Systems | Disorder has intriguing consequences for correlated electronic materials,
which include several families of high-temperature superconductors and
resistive switching systems. We address the question of why strongly correlated
d-wave superconductors, such as the cuprates, prove to be surprisingly robust
against the introduction of non-magnetic impurities. We show that, very
generally, both the pair-breaking and the normal state transport scattering
rates are significantly suppressed by strong correlations effects arising in
the proximity to a Mott insulating state. We also show that the
correlation-renormalized scattering amplitude is generically enhanced in the
forward direction, an effect which was previously often ascribed to the
specific scattering by charged impurities outside the copper-oxide planes. We
provide the theoretical insights for resistive switching systems and show how
impurities and underlying correlations can play significant roles in practical
devices. We report the striking result of a connection between the resistive
switching and shock wave formation, a classic topic of non-linear dynamics. We
argue that the profile of oxygen vacancies that migrate during the commutation
forms a shock wave that propagates through a highly resistive region of the
device. We validate the scenario by means of model simulations and experiments
in a manganese-oxide based memristor device and we extend our theory to the
case of binary oxides. The shock wave scenario brings unprecedented physical
insight and enables to rationalize the process of oxygen-vacancy-driven
resistive change with direct implications for a key technological aspect- the
commutation speed. | 1808.04767v1 |
2023-01-10 | Microstructuring YbRh2Si2 for resistance and noise measurements down to ultra-low temperatures | The discovery of superconductivity in the quantum critical Kondo-lattice
system YbRh2Si2 at an extremely low temperature of 2 mK has inspired efforts to
perform high-resolution electrical resistivity measurements down to this
temperature range in highly conductive materials. Here we show that control
over the sample geometry by microstructuring using focused-ion-beam (FIB)
techniques allows to reach ultra-low temperatures and increase signal-to-noise
ratios (SNR) tenfold, without adverse effects to sample quality. In five
experiments we show four-terminal sensing resistance and magnetoresistance
measurements which exhibit sharp phase transitions at the N\'eel temperature,
and Shubnikov-de-Haas (SdH) oscillations between 13 T and 18 T where we
identified a new SdH frequency of 0.39 kT. The increased SNR allowed resistance
fluctuation (noise) spectroscopy that would not be possible for bulk crystals,
and confirmed intrinsic 1/f-type fluctuations. Under controlled strain, two
thin microstructured samples exhibited a large increase of T_N from 67 mK up to
188 mK while still showing clear signatures of the phase transition and SdH
oscillations. SQUID-based thermal noise spectroscopy measurements in a nuclear
demagnetisation refrigerator down to 0.95 mK, show a sharp superconducting
transition at T_c = 1.2 mK. These experiments demonstrate microstructuring as a
powerful tool to investigate the resistance and the noise spectrum of highly
conductive correlated metals over wide temperature ranges. | 2301.03928v1 |
2024-05-06 | Bayesian optimization for stable properties amid processing fluctuations in sputter deposition | We introduce a Bayesian optimization approach to guide the sputter deposition
of molybdenum thin films, aiming to achieve desired residual stress and sheet
resistance while minimizing susceptibility to stochastic fluctuations during
deposition. Thin films are pivotal in numerous technologies, including
semiconductors and optical devices, where their properties are critical.
Sputter deposition parameters, such as deposition power, vacuum chamber
pressure, and working distance, influence physical properties like residual
stress and resistance. Excessive stress and high resistance can impair device
performance, necessitating the selection of optimal process parameters.
Furthermore, these parameters should ensure the consistency and reliability of
thin film properties, assisting in the reproducibility of the devices. However,
exploring the multidimensional design space for process optimization is
expensive. Bayesian optimization is ideal for optimizing inputs/parameters of
general black-box functions without reliance on gradient information. We
utilize Bayesian optimization to optimize deposition power and pressure using a
custom-built objective function incorporating observed stress and resistance
data. Additionally, we integrate prior knowledge of stress variation with
pressure into the objective function to prioritize films least affected by
stochastic variations. Our findings demonstrate that Bayesian optimization
effectively explores the design space and identifies optimal parameter
combinations meeting desired stress and resistance specifications. | 2405.03092v1 |
2023-04-06 | Performance Analysis of DNA Crossbar Arrays for High-Density Memory Storage Applications | Deoxyribonucleic acid (DNA) has emerged as a promising building block for
next-generation ultra-high density storage devices. Although DNA has high
durability and extremely high density in nature, its potential as the basis of
storage devices is currently hindered by limitations such as expensive and
complex fabrication processes and time-consuming read-write operations. In this
article, we propose the use of a DNA crossbar array architecture for an
electrically readable Read-Only Memory (DNA-ROM). While information can be
written error-free to a DNA-ROM array using appropriate sequence encoding, its
read accuracy can be affected by several factors such as array size,
interconnect resistance, and Fermi energy deviations from HOMO levels of DNA
strands employed in the crossbar. We study the impact of array size and
interconnect resistance on the bit error rate of a DNA-ROM array through
extensive Monte Carlo simulations. We have also analyzed the performance of our
proposed DNA crossbar array for an image storage application, as a function of
array size and interconnect resistance. While we expect that future advances in
bioengineering and materials science will address some of the fabrication
challenges associated with DNA crossbar arrays, we believe that the
comprehensive body of results we present in this paper establishes the
technical viability of DNA crossbar arrays as low-power, high-density storage
devices. Finally, our analysis of array performance vis-a-vis interconnect
resistance should provide valuable insights into aspects of the fabrication
process such as the proper choice of interconnects necessary for ensuring high
read accuracies. | 2304.14269v1 |
2023-11-09 | Signature of superconductivity in pressurized La$_4$Ni$_3$O$_{10}$ | The discovery of high-temperature superconductivity near 80 K in bilayer
nickelate La$_3$Ni$_2$O$_7$ under high pressures has renewed the exploration of
superconducting nickelate in bulk materials. The extension of superconductivity
in other nickelates in a broader family is also essential. Here, we report the
experimental observation of superconducting signature in trilayer nickelate
La$_4$Ni$_3$O$_{10}$ under high pressures. By using a modified sol-gel method
and post-annealing treatment under high oxygen pressure, we successfully
obtained polycrystalline La$_4$Ni$_3$O$_{10}$ samples with different transport
behaviors at ambient pressure. Then we performed high-pressure electrical
resistance measurements on these samples in a diamond-anvil-cell (DAC)
apparatus. Surprisingly, the signature of possible superconducting transition
with a maximum transition temperature ($T_\text{c}$) of about 20 K under high
pressures is observed, as evidenced by a clear drop of resistance and the
suppression of resistance drops under magnetic fields. Although the resistance
drop is sample-dependent and relatively small, it appears in all of our
measured samples. We argue that the observed superconducting signal is most
likely to originate from the main phase of La$_4$Ni$_3$O$_{10}$. Our findings
will motivate the exploration of superconductivity in a broader family of
nickelates and shed light on the understanding of the underlying mechanisms of
high-$T_\text{c}$ superconductivity in nickelates. | 2311.05453v1 |
2024-04-29 | Thermoelectric transport properties of the quasi-one-dimensional dimer-Mott insulator $β'$-(BEDT-TTF)$_2$ICl$_2$ | Low-dimensional materials, in which the electronic and transport properties
are drastically modified in comparison to those of three-dimensional bulk
materials, yield a key class of thermoelectric materials with high conversion
efficiency. Among such materials, the organic compounds may serve peculiar
properties owing to their unique molecular-based low-dimensional structures
with highly anisotropic molecular orbitals. Here we present the thermoelectric
transport properties of the quasi-one-dimensional dimer-Mott insulator
$\beta'$-(BEDT-TTF)$_2$ICl$_2$, where BEDT-TTF stands for
bis(ethylenedithio)-tetrathiafulvalene. We find that the thermopower exhibits
typical activation-type temperature variation expected for insulators but its
absolute value is anomalously large compared to the expected value from the
activation-type temperature dependence of the electrical resistivity.
Successively, the Jonker-plot analysis, in which the thermopower is usually
scaled by the logarithm of the resistivity, shows an unusual relation among
such transport quantities. We discuss a role of the low dimensionality for the
enhanced thermopower along with recent observations of such a large thermopower
in several low-dimensional materials. | 2404.19137v1 |
2021-12-28 | Review of Transition-Metal Diboride Thin Films | We review the thin film growth, chemistry, and physical properties of Group
4-6 transition-metal diboride (TMB2) thin films with AlB2-type crystal
structure (Strukturbericht designation C32). Industrial applications are
growing rapidly as TMB2 begin competing with conventional refractory ceramics
like carbides and nitrides, including pseudo-binaries such as Ti1-xAlxN. The
TMB2 crystal structure comprises graphite-like honeycombed atomic sheets of B
interleaved by hexagonal close-packed TM layers. From the C32 crystal structure
stems unique properties including high melting point, hardness, and corrosion
resistance, yet limited oxidation resistance, combined with high electrical
conductivity. We correlate the underlying chemical bonding, orbital overlap,
and electronic structure to the mechanical properties, resistivity, and
high-temperature properties unique to this class of materials. The review
highlights the importance of avoiding contamination elements (like oxygen) and
boron segregation on both the target and substrate sides during sputter
deposition, for better-defined properties, regardless of the boride system
investigated. This is a consequence of the strong tendency for B to segregate
to TMB2 grain boundaries for boron-rich compositions of the growth flux. It is
judged that sputter deposition of TMB2 films is at a tipping point towards a
multitude of applications for TMB2 not solely as bulk materials, but also as
protective coatings and electrically conducting high-temperature stable thin
films. | 2112.14099v1 |
2016-06-10 | On the search for the chiral anomaly in Weyl semimetals: The negative longitudinal magnetoresistance | Recently, the existence of massless chiral (Weyl) fermions has been
postulated in a class of semi-metals with a non-trivial energy dispersion.These
materials are now commonly dubbed Weyl semi-metals (WSM).One predicted property
of Weyl fermions is the chiral or Adler-Bell-Jackiw anomaly, a chirality
imbalance in the presence of parallel magnetic and electric fields. In WSM, it
is expected to induce a negative longitudinal magnetoresistance (NMR), the
chiral magnetic effect.Here, we present experimental evidence that the
observation of the chiral magnetic effect can be hindered by an effect called
"current jetting". This effect also leads to a strong apparent NMR, but it is
characterized by a highly non-uniform current distribution inside the sample.
It appears in materials possessing a large field-induced anisotropy of the
resistivity tensor, such as almost compensated high-mobility semimetals due to
the orbital effect.In case of a non-homogeneous current injection, the
potential distribution is strongly distorted in the sample.As a consequence, an
experimentally measured potential difference is not proportional to the
intrinsic resistance.Our results on the MR of the WSM candidate materials NbP,
NbAs, TaAs, TaP exhibit distinct signatures of an inhomogeneous current
distribution, such as a field-induced "zero resistance' and a strong dependence
of the `measured resistance" on the position, shape, and type of the voltage
and current contacts on the sample. A misalignment between the current and the
magnetic-field directions can even induce a "negative resistance".
Finite-element simulations of the potential distribution inside the sample,
using typical resistance anisotropies, are in good agreement with the
experimental findings. Our study demonstrates that great care must be taken
before interpreting measurements of a NMR as evidence for the chiral anomaly in
putative Weyl semimetals. | 1606.03389v1 |
2011-10-07 | Overlapping-gate architecture for silicon Hall bar MOSFET devices in the low electron density and high magnetic field regime | A common issue in low temperature measurements of enhancement-mode
metal-oxide-semiconductor (MOS) field-effect transistors (FETs) in the low
electron density regime is the high contact resistance dominating the device
impedance. In that case a voltage bias applied across the source and drain
contact of a Hall bar MOSFET will mostly fall across the contacts (and not
across the channel) and therefore magneto-transport measurements become
challenging. However, from a physical point of view, the study of MOSFET
nanostructures in the low electron density regime is very interesting (impurity
limited mobility [1], carrier interactions [2,3] and spin-dependent transport
[4]) and it is therefore important to come up with solutions [5,6] that work
around the problem of a high contact resistance in such devices (c.f. Fig. 1
(a)). | 1110.1418v1 |
2013-04-01 | Novel Bismaleimide Resin/Silsesquioxane and Titania Nanocomposites by the Sol-Gel Process: the Preparation, Morphology, Thermal and Thermo-mechanical Properties | Bismaleimide(BMI) resin/silsesquioxane or titania nanocomposites were
synthesized from bismaleimide resin and SiO3/2 or TiO2 via the sol-gel process
of N-{\gamma}-triethoxylsilylpropyl-maleamic acid (TESPMA) or
tetrabutyltitanate (Ti(OnBu)4, TBT), respectively, in the presence of the
AP-BMI prepolymers. These nanocomposite materials were characterized by FT-IR,
FE-SEM, TGA and DMA. It was found that the nano-scale SiO3/2 or TiO2 particles
were formed in the AP-BMI resin matrix and the average original particle size
of the dispersed phase in the nanocomposites was less than 100nm, but the
particle aggregates with bigger size existed. Obvious improvements of Tg and
the heat resistance of the AP-BMI resin were achieved by introduction of the
nano-sized SiO3/2 inorganic phase, and the modulus at high temperatures was
improved too. The incorporation of nano-scale TiO2 particles into the AP-BMI
resin improved the Tg of the polymer, but lowered the thermal resistance of the
material, and improved the modulus of the material at lower temperatures, but
lowered the modulus at higher temperatures. | 1304.0288v1 |
2016-04-19 | Observation of spin Seebeck contribution to the transverse thermopower in Ni-Pt and MnBi-Au bulk nanocomposites | Transverse thermoelectric devices produce electric fields perpendicular to an
incident heat flux. Classically, this process is driven by the Nernst effect in
bulk solids, wherein a magnetic field generates a Lorentz force on thermally
excited electrons. The spin Seebeck effect (SSE) also produces
magnetization-dependent transverse electric fields. SSE is traditionally
observed in thin metallic films deposited on electrically insulating
ferromagnets, but the films' high resistance limits thermoelectric conversion
efficiency. Combining Nernst and SSE in bulk materials would enable devices
with simultaneously large transverse thermopower and low electrical resistance.
Here we demonstrate experimentally this is possible in composites of conducting
ferromagnets (Ni or MnBi) containing metallic nanoparticles with strong
spin-orbit interactions (Pt or Au). These materials display positive shifts in
transverse thermopower attributable to inverse spin Hall electric fields in the
nanoparticles. This more than doubles the power output of the Ni-Pt materials,
establishing proof-of-principle that SSE persists in bulk nanocomposites. | 1604.05626v3 |
2016-01-18 | Large magnetoresistance in LaBi: origin of field-induced resistivity upturn and plateau in compensated semimetals | The discovery of non-magnetic extreme magnetoresistance (XMR) materials has
induced great interests because the XMR phenomenon challenges our understanding
of how a magnetic field can alter electron transport in semimetals. Among XMR
materials, the LaSb shows XMR and field-induced exotic behaviors but it seems
to lack the essentials for these properties. Here, we study the
magnetotransport properties and electronic structure of LaBi, isostructural to
LaSb. LaBi exhibits large MR as in LaSb, which can be ascribed to the nearly
compensated electron and hole with rather high mobilities. More importantly,
our analysis suggests that the XMR as well as field-induced resistivity upturn
and plateau observed in LaSb and LaBi can be well explained by the two-band
model with the compensation situation. We present the critical conditions
leading to these field-induced properties. It will contribute to understanding
the XMR phenomenon and explore novel XMR materials. | 1601.04618v2 |
2003-03-14 | Microwave performance of high-density bulk MgB2 | We have performed microwave measurements on superconducting
hot-isostatically- pressed (HIPed) bulk MgB2 using a parallel-plate resonator
technique. The high density and strength of the HIPed material allowed
preparation of samples with mirror-like surfaces for microwave measurements.
The microwave surface resistance decreased by about 40% at 20 K when the
root-mean-square surface roughness was reduced from 220 nm to 110 nm through
surface-polishing and ion-milling. The surface resistance was independent of
surface microwave magnetic field at least up to 4 Oe and below 30 K. We
attribute this behavior, and the overall low surface resistance (~0.8 mOhms at
10 GHz and 20 K), to the high density of our samples and the absence of weak
links between grains. | 0303283v1 |
2006-02-23 | Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition | We investigate ultrathin superconducting TiN films, which are very close to
the localization threshold. Perpendicular magnetic field drives the films from
the superconducting to an insulating state, with very high resistance. Further
increase of the magnetic field leads to an exponential decay of the resistance
towards a finite value. In the limit of low temperatures, the saturation value
can be very accurately extrapolated to the universal quantum resistance h/e^2.
Our analysis suggests that at high magnetic fields a new ground state, distinct
from the normal metallic state occurring above the superconducting transition
temperature, is formed. A comparison with other studies on different materials
indicates that the quantum metallic phase following the magnetic-field-induced
insulating phase is a generic property of systems close to the disorder-driven
superconductor-insulator transition. | 0602557v2 |
2013-09-18 | Pressure-Induced Superconductivity in Mineral Calaverite AuTe2 | The pressure dependences of resistivity and ac susceptibility have been
measured in the mineral calaverite AuTe$_2$. Resistivity clearly shows a
first-order phase transition into a high-pressure phase, consistent with the
results of a previous structural analysis. We found zero resistivity and a
diamagnetic shielding signal at low temperatures in the high-pressure phase,
which clearly indicates the appearance of superconductivity. Our experimental
results suggest that bulk superconductivity appears only in the high-pressure
phase. For AuTe$_2$, the highest superconducting transition temperature under
pressure is $T_{\rm c}$ = 2.3 K at 2.34 GPa; it was $T_{\rm c}$ = 4.0 K for
Pt-doped (Au$_{0.65}$Pt$_{0.35}$)Te$_2$. The difference in $T_{\rm c}$ between
the two systems is discussed on the basis of the results obtained using the
band calculations and McMillan's formula. | 1309.4827v2 |
2018-03-07 | Saturation and negative temperature coefficient of electrical resistivity in liquid iron-sulfur alloys at high densities from first principles calculations | We report results on electronic transport properties of liquid Fe-S alloys at
conditions of planetary cores, computed by first-principle techniques in the
Kubo-Greenwood formalism. We describe a combined effect of resistivity
saturation due to temperature, compression, and chemistry by comparing the
electron mean free path from the Drude response of optical conductivity to the
mean interatomic distance. At high compression and high sulfur concentration
the Ioffe-Regel condition is satisfied, and the temperature coefficient of
resistivity changes sign from positive to negative. We show that this happens
due to a decrease of the $d$-density of states at the Fermi level in response
to thermal broadening. | 1803.02649v1 |
2018-10-03 | On the temperature scaling behaviour of the linear magnetoresistance observed in high-temperature superconductors | An analytical model invoking variations in the charge-carrier density is used
to generate magnetoresistance curves that are almost indistinguishable from
those produced by sophisticated numerical models. This demonstrates that,
though disorder is pivotal in causing linear magnetoresistance, the form of the
magnetoresistance thus generated is insensitive to details of the disorder.
Taken in conjunction with the temperature ($T$) dependence of the zero-field
resistivity, realistic levels of disorder are shown to be sufficient to explain
the linear magnetoresistance and field-$T$ resistance scaling observed in
high-temperature pnictide and cuprate superconductors. Hence, though the
$T$-linear zero-field resistance is a definite signature of the "strange metal"
state of high-temperature superconductors, their linear magnetoresistance and
its scaling is unlikely to be so. | 1810.01998v3 |
2020-04-17 | High-pressure characterization of multifunctional CrVO4 | The structural stability and physical properties of CrVO4 under compression
were studied by X-ray diffraction, Raman spectroscopy, optical absorption,
resistivity measurements, and ab initio calculations up to 10 GPa.
High-pressure X-ray diffraction and Raman measurements show that CrVO4
undergoes a phase transition from the ambient pressure orthorhombic CrVO4-type
structure (Cmcm space group, phase III) to the high-pressure monoclinic CrVO4-V
phase, which is isomorphic to the wolframite structure. Such a phase transition
(CrVO4-type - wolframite), driven by pressure, also was previously observed in
indium vanadate. The crystal structure of both phases and the pressure
dependence in unit-cell parameters, Raman-active modes, resistivity, and
electronic band gap, is reported. Vanadium atoms are sixth-fold coordinated in
the wolframite phase, which is related to the collapse in the volume at the
phase transition. Besides, we also observed drastic changes in the phonon
spectrum, a drop of the band-gap, and a sharp decrease of resistivity. All the
observed phenomena are explained with the help of first-principles
calculations. | 2004.08072v1 |
2020-08-28 | High-Bandwidth, Variable-Resistance Differential Noise Thermometry | We develop Johnson noise thermometry applicable to mesoscopic devices with
variable source impedance with high bandwidth for fast data acquisition. By
implementing differential noise measurement and two-stage impedance matching,
we demonstrate noise measurement in the frequency range 120-250 MHz with a wide
sample resistance range 30 {\Omega}-100 k{\Omega} tuned by gate voltages and
temperature. We employ high-frequency, single-ended low noise amplifiers
maintained at a constant cryogenic temperature in order to maintain the desired
low noise temperature. We achieve thermometer calibration with temperature
precision up to 650 mK on a 10 K background with 30 s of averaging. Using this
differential noise thermometry technique, we measure thermal conductivity on a
bilayer graphene sample spanning the metallic and semiconducting regimes in a
wide resistance range, and we compare it to the electrical conductivity. | 2008.12739v1 |
2014-09-19 | Fluorine doping: A feasible solution to enhancing the conductivity of high-resistance wide bandgap Mg0.51Zn0.49O active components | N-type doping of high-resistance wide bandgap semiconductors, wurtzite
high-Mg-content MgxZn1-xO for instance, has always been a fundamental
application-motivated research issue. Herein, we report a solution to enhancing
the conductivity of high-resistance Mg0.51Zn0.49O active components, which has
been reliably achieved by fluorine doping via radio-frequency plasma assisted
molecular beam epitaxial growth. Fluorine dopants were demonstrated to be
effective donors in Mg0.51Zn0.49O single crystal film having a solar-blind 4.43
eV bandgap, with an average concentration of 1.0E19 F/cm3.The dramatically
increased carrier concentration (2.85E17 cm-3 vs ~1014 cm-3) and decreased
resistivity (129 ohm.cm vs ~10E6 ohm cm) indicate that the electrical
properties of semi-insulating Mg0.51Zn0.49O film can be delicately regulated by
F doping. Interestingly, two donor levels (17 meV and 74 meV) associated with F
were revealed by temperature-dependent Hall measurements. A Schottky type
metal-semiconductor-metal ultraviolet photodetector manifests a remarkably
enhanced photocurrent, two orders of magnitude higher than that of the undoped
counterpart. The responsivity is greatly enhanced from 0.34 mA/W to 52 mA/W
under 10 V bias. The detectivity increases from 1.89E9 cm Hz1/2/W to 3.58eE10
cm Hz1/2/W under 10 V bias at room temperature.These results exhibit F doping
serves as a promising pathway for improving the performance of high-Mg-content
MgxZn1-xO-based devices. | 1409.5657v2 |
2021-11-03 | Resistive switching in HfO2-x/La0.67Sr0.33MnO3 heterostructure: An intriguing case of low H-field susceptibility of an E-field controlled active interface | High-performance non-volatile resistive random access memories (ReRAM) and
their small stimuli control are of immense interest for high-speed computation
and big-data processing in the emergent Internet of Things (IOT) arena. Here,
we examine the resistive switching (RS) behavior in growth controlled
HfO2/La0.67Sr0.33MnO3 heterostructures and their tunability under low magnetic
field. It is demonstrated that oxygen-deficient HfO2 films show bipolar
switching with high on/off ratio, stable retention, as well as good endurance
owing to the orthorhombic-rich phase constitution and charge
(de)-trapping-enabled Schottky-type conduction. Most importantly, we have
demonstrated that, the RS can be tuned by a very low externally applied
magnetic field (0-30 mT). Remarkably, application of a magnetic field of 30 mT
causes the RS to be fully quenched and frozen in the high resistance state
(HRS) even after the removal of magnetic field. However, the quenched state
could be resurrected by applying higher bias voltage than the one for initial
switching. This is argued to be a consequence of the electronically and
ionically active nature of the HfO2-x/LSMO interface on both sides, and its
susceptibility to the electric and low magnetic field effects. This result
could pave the way for new designs of interface engineered high-performance
oxitronic ReRAM devices. | 2111.02476v1 |
2002-09-26 | Kapitza resistance at the liquid solid interface | Using equilibrium and nonequilibrium molecular dynamics simulations, we
determine the Kapitza resistance (or thermal contact resistance) at a model
liquid solid interface. The Kapitza resistance (or the associated Kapitza
length) can reach appreciable values when the liquid does not wet the solid.
The analogy with the hydrodynamic slip length is discussed. | 0209607v1 |
2008-02-06 | On the calculation of Schottky contact resistivity | This numerical study examines the importance of self-consistently accounting
for transport and electrostatics in the calculaiton of semiconductor/metal
Schottky contact resistivity. It is shown that ignoring such self-consistency
results in significant under-estimation of the contact resistivity. An explicit
numerical method has also been proposed to efficiently improve contact
resistivity calculations. | 0802.0729v1 |
2016-12-17 | Upper critical field, pressure-dependent superconductivity and electronic anisotropy of Sm$_4$Fe$_2$As$_2$Te$_{1-x}$O$_{4-y}$F$y$ | We present a detailed study of the electrical transport properties of a
recently discovered iron-based superconductor:
Sm$_4$Fe$_2$As$_2$Te$_{0.72}$O$_{2.8}$F$_{1.2}$. We followed the temperature
dependence of the upper critical field by resistivity measurement of single
crystals in magnetic fields up to 16 T, oriented along the two main
crystallographic directions. This material exhibits a zero-temperature upper
critical field of 90 T and 65 T parallel and perpendicular to the Fe$_2$As$_2$
planes, respectively. An unprecedented superconducting magnetic anisotropy
$\gamma_H=H_{c2}^{ab}/H_{c2}^c \sim 14$ is observed near Tc, and it decreases
at lower temperatures as expected in multiband superconductors. Direct
measurement of the electronic anisotropy was performed on microfabricated
samples, showing a value of $\rho_c/\rho_{ab}(300K) \sim 5$ that raises up to
19 near Tc. Finally, we have studied the pressure and temperature dependence of
the in-plane resistivity. The critical temperature decreases linearly upon
application of hydrostatic pressure (up to 2 GPa) similarly to overdoped
cuprate superconductors. The resistivity shows saturation at high temperatures,
suggesting that the material approaches the Mott-Ioffe-Regel limit for metallic
conduction. Indeed, we have successfully modelled the resistivity in the normal
state with a parallel resistor model that is widely accepted for this state.
All the measured quantities suggest strong pressure dependence of the density
of states. | 1612.05792v1 |
2019-07-28 | Field-dependent nonlinear surface resistance and its optimization by surface nano-structuring in superconductors | We propose a theory of nonlinear surface resistance of a dirty superconductor
in a strong radio-frequency (RF) field, taking into account magnetic and
nonmagnetic impurities, finite quasiparticle lifetimes, and a thin
proximity-coupled normal layer characteristic of the oxide surface of many
materials. The Usadel equations were solved to obtain the quasiparticle density
of states (DOS) and the low-frequency surface resistance $R_s$ as functions of
the RF field amplitude $H_0$. It is shown that the interplay of the broadening
of the DOS peaks and a decrease of a quasiparticle gap caused by the RF
currents produces a minimum in $R_s(H_0)$ and an extended rise of the quality
factor $Q(H_0)$ with the RF field. Paramagnetic impurities shift the minimum in
$R_s(H_0)$ to lower fields and can reduce $R_s(H_0)$ in a wide range of $H_0$.
Subgap states in the DOS can give rise to a residual surface resistance while
reducing $R_s$ at higher temperatures. A proximity-coupled normal layer at the
surface can shift the minimum in $R_s(H_0)$ to either low and high fields and
can reduce $R_s$ below that of an ideal surface. The theory shows that the
behavior of $R_s(H_0)$ changes as the temperature and the RF frequency are
increased, and the field dependence of $Q(H_0)$ can be very sensitive to the
materials processing. Our results suggest that the nonlinear RF losses can be
minimized by tuning pairbreaking effects at the surface using impurity
management or surface nanostructuring. | 1907.12040v1 |
2019-08-08 | Substrate induced nanoscale resistance variation in epitaxial graphene | Graphene, the first true two-dimensional material still reveals the most
remarkable transport properties among the growing class of two-dimensional
materials. Although many studies have investigated fundamental scattering
processes, the surprisingly large variation in the experimentally determined
resistances associated with a localized defect is still an open issue. Here, we
quantitatively investigate the local transport properties of graphene prepared
by polymer assisted sublimation growth (PASG) using scanning tunneling
potentiometry. PASG graphene is characterized by a spatially homogeneous
current density, which allows to analyze variations in the local
electrochemical potential with high precision. We utilize this possibility by
examining the local sheet resistance finding a significant variation of up to
270% at low temperatures. We identify a correlation of the sheet resistance
with the stacking sequence of the 6H-SiC substrate as well as with the distance
between the graphene sheet and the substrate. Our results experimentally
quantify the strong impact of the graphene-substrate interaction on the local
transport properties of graphene. | 1908.02956v2 |
2021-01-16 | Optical Tuning of Resistance Switching in Polycrystalline Gallium Phosphide Thin Films | The nanoscale resistive switching characteristics of gallium phosphide (GaP)
thin films directly grown on Si are investigated as a function of incident
light. Firstly, as-grown GaP films show a high RON/ROFF (~10^4), shown to arise
from the formation of conductive channels along the grain boundaries. It is
proposed that point defects (most likely Ga interstitials) and structural
disorder at the grain boundaries provide the ideal environment to enable the
filamentary switching process. Next, we explored if such defects can give rise
to mid-gap states, and if so could they be activated by photonic excitation.
Both first-principles calculations as well as UV-vis and photoluminescence
spectroscopy strongly point to the possibility of mid-gap electronic states in
the polycrystalline GaP film. Photoconductive atomic force microscopy (phAFM),
a scanning probe technique, is used to image photocurrents generated as a
function of incident photon energy (ranging from sub band-gap to above
band-gap) on the GaP film surface. We observe photocurrents even for incident
photon energies lower than the band-gap, consistent with the presence of
mid-gap electronic states. Moreover the photocurrent magnitude is found to be
directly proportional to the incident photon energy with a concomitant decrease
in the filament resistance. This demonstrates GaP directly integrated on Si can
be a promising photonic resistive switching materials system. | 2101.06538v1 |
2020-11-03 | Switchable domains in point contacts based on transition metal tellurides | We report resistive switching in voltage biased point contacts (PCs) based on
series of van der Waals transition metals tellurides (TMTs) such as MeTe2
(Me=Mo, W) and TaMeTe4 (Me= Ru, Rh, Ir). The switching occurs between a low
resistive "metallic-type" state, which is the ground state, and a high
resistive "semiconducting-type" state by applying certain bias voltage (<1V),
while reverse switching takes place by applying voltage of opposite polarity.
The origin of the effect can be formation of domain in PC core by applying a
bias voltage, when a strong electric field (about 10kV/cm) modifies the crystal
structure and controls its polarization. In addition to the discovery of the
switching effect in PCs, we also suggest a simple method of material testing
before functionalizing them, which offers a great advantage in finding suitable
novel substances. The new functionality of studied TMTs arising from switchable
domains in submicron hetero-structures that are promising, e.g., for
non-volatile resistive random access memory (RRAM) engineering. | 2011.01569v2 |
2020-11-30 | Above-room-temperature giant thermal conductivity switching in spintronic multilayer | Thermal switching provides an effective way for active heat flow control,
which has recently attracted increasing attention in terms of nanoscale thermal
management technologies. In magnetic and spintronic materials, the thermal
conductivity depends on the magnetization configuration: this is the
magneto-thermal resistance effect. Here we show that an epitaxial
Cu/Co$_{50}$Fe$_{50}$ multilayer film exhibits giant magnetic-field-induced
modulation of the cross-plane thermal conductivity. The magneto-thermal
resistance ratio for the Cu/Co$_{50}$Fe$_{50}$ multilayer reaches 150% at room
temperature, which is much larger than the previous record high. Although the
ratio decreases with increasing the temperature, the giant magneto-thermal
resistance effect of ~100% still appears up to 400 K. The magnetic field
dependence of the thermal conductivity of the Cu/Co$_{50}$Fe$_{50}$ multilayer
was observed to be about twice greater than that of the cross-plane electrical
conductivity. The observation of the giant magneto-thermal resistance effect
clarifies a potential of spintronic multilayers as thermal switching devices. | 2011.14558v1 |
2022-03-01 | Cu-doping effects on the ferromagnetic semimetal CeAuGe | We present a study of Cu-substitution effects in 4f-Ce intermetallic compound
CeAu1-xCuxGe, with potentially unusual electronic states, in the whole
concentration range (x = 0.0 - 1.0). The parent CeAuGe compound, crystallizing
in a non-centrosymmetric hexagonal structure, is a ferromagnetic semimetal with
Curie temperature 10 K. Cu-doping on Au-site of CeAuGe, CeAu1-xCuxGe, changes
the crystal structure from the non-centrosymmetric (P63mc) to centrosymmetric
(P63/mmc) space group at the concentration x ~ 0.5, where the c-lattice
constant has a maximum value. Magnetic susceptibility and electrical
resistivity measurements reveal that all Cu-doped compounds undergo magnetic
phase transition near 10 K, with the maximum transition temperature of 12 K for
x = 0.5. The neutron powder diffraction experiments show the ferromagnetic
ordering of Ce3+ magnetic moments with a value of ~ 1.2 Bohr magneton at 1.8 K,
oriented perpendicular to the hexagonal c-axis. By using symmetry analysis, we
have found the solutions for the magnetic structure in the ferromagnetic
Shubnikov space groups Cmc'21' and P21'/m' for x < 0.5 and x >= 0.5,
respectively. Electrical resistivity exhibits a metallic temperature behaviour
in all compounds. The resistivity has a local minimum in the paramagnetic state
due to Kondo effects at high doping x = 0.8 and 1.0. At the small Cu-doping
level, x = 0.2, the resistivity shows a broad feature at the ferromagnetic
transition temperature and an additional transition-like peculiarity at 2.5 K
in the ferromagnetic state. | 2203.00335v1 |
2022-06-13 | The two-dimensional metallic triangular lattice antiferromagnet CeCd3P3 | Single crystals of $R$Cd$_{3}$P$_{3}$ ($R$ = La and Ce) have been
investigated by magnetization, electrical resistivity, Hall coefficient, and
specific heat. Magnetization measurements of CeCd$_{3}$P$_{3}$ demonstrate
clear quasi-2D magnetic behavior. Electrical resistivity and Hall coefficient
measurements suggest that $R$Cd$_{3}$P$_{3}$ compounds are low carrier density
metallic systems, in strong contrast to an earlier study of polycrystalline
material. Specific heat and electrical resistivity measurements of
CeCd$_{3}$P$_{3}$ reveal a high temperature (structural) phase transition at
$T_{s} = 127$~K and antiferromagnetic ordering below $T_{N} = 0.41$~K. Upon
applying magnetic field in the easy-plane ($H {\parallel} ab$) the magnetic
ordering temperature increases to 0.43~K at $H \sim 15$~kOe, demonstrating
partial lifting of the magnetic frustration. The large electronic specific heat
persists in an unusually wide range of temperature above $T_{N}$, due to the
frustrated spins. The observation of conventional metallic behavior in the
electrical resistivity suggests that the $f$-electrons in CeCd$_{3}$P$_{3}$
undergo negligible hybridization with the conduction electrons. Thus,
CeCd$_{3}$P$_{3}$ may be a model system for exploring the complex interplay
between magnetic frustration and RKKY physics on a low carrier density Ce
triangular lattice. | 2206.06366v1 |
2023-01-13 | Image-Force Barrier Lowering of Schottky Barriers in Two-Dimensional Materials as a Function of Metal Contact Angle | Two-dimensional (2D) semiconductors are a promising solution for the
miniaturization of electronic devices and for the exploration of novel physics.
However, practical applications and demonstrations of physical phenomena are
hindered by high Schottky barriers at the contacts to 2D semiconductors. While
the process of image-force barrier lowering (IFBL) can considerably decrease
the Schottky barrier, IFBL is not fully understood for the majority of
prevalent contact geometries. We introduce a novel technique to determine the
IFBL potential energy with application spanning far beyond that of any existing
method. We do so by solving Poisson's equation with the boundary conditions of
two metal surfaces separated by an angle Omega. We then prove that our result
can also be obtained with the method of images provided a non-Euclidean,
cone-manifold space is used. The resulting IFBL is used to calculate the
expected contact resistance of the most prevalent geometric contacts. Finally,
we investigate contact resistance and show how the stronger IFBL counteracts
the effect of larger depletion width with increasing contact angle. We find
that top contacts experience lower contact resistance than edge contacts.
Remarkably, our results identify tunable parameters for reducing Schottky
barriers and likewise contact resistance to edge-contacted 2D materials,
enhancing potential applications. | 2301.05373v2 |
2023-12-07 | Demonstration of high-impedance superconducting NbRe Dayem bridges | Here we demonstrate superconducting Dayem-bridge weak-links made of different
stoichiometric compositions of NbRe. Our devices possess a relatively high
critical temperature, normal-state resistance, and kinetic inductance. In
particular, the high kinetic inductance makes this material a good alternative
to more conventional niobium-based superconductors (e.g., NbN or NbTiN) for the
realization of superinductors and high-quality factor resonators, whereas the
high normal-state resistance yields a large output voltage in superconducting
switches and logic elements realized upon this compound. Moreover, out-of-plane
critical magnetic fields exceeding 2 T ensure that possible applications
requiring high magnetic fields can also be envisaged. Altogether, these
features make this material appealing for a number of applications in the
framework of quantum technologies. | 2312.04331v2 |
2019-01-11 | A Piezoelectric, Strain-Controlled Antiferromagnetic Memory Insensitive to Magnetic Fields | Spintronic devices based on antiferromagnetic (AFM) materials hold the
promise of fast switching speeds and robustness against magnetic fields.
Different device concepts have been predicted and experimentally demonstrated,
such as low-temperature AFM tunnel junctions that operate as spin-valves, or
room-temperature AFM memory, for which either thermal heating in combination
with magnetic fields, or N\'eel spin-orbit torque is used for the information
writing process. On the other hand, piezoelectric materials were employed to
control magnetism by electric fields in multiferroic heterostructures, which
suppresses Joule heating caused by switching currents and may enable low
energy-consuming electronic devices. Here, we combine the two material classes
to explore changes of the resistance of the high-N\'eel-temperature
antiferromagnet MnPt induced by piezoelectric strain. We find two non-volatile
resistance states at room temperature and zero electric field, which are stable
in magnetic fields up to 60 T. Furthermore, the strain-induced resistance
switching process is insensitive to magnetic fields. Integration in a tunnel
junction can further amplify the electroresistance. The tunneling anisotropic
magnetoresistance reaches ~11.2% at room temperature. Overall, we demonstrate a
piezoelectric, strain-controlled AFM memory which is fully operational in
strong magnetic fields and has potential for low-energy and high-density memory
applications. | 1901.03551v1 |
2020-07-09 | Frequency domain measurements of thermal properties using 3omega-Scanning Thermal Microscope in a vacuum environment | Material thermal properties characterization at nanoscales remains a
challenge even if progresses were done in developing specific characterization
techniques like the Scanning Thermal Microscopy (SThM). In the present work, we
propose a detailed procedure based on the combined use of a SThM probe
characterization and its Finite Element Modeling (FEM) to recover in-operando
3omega measurements achieved under high vacuum. This approach is based on a
two-step methodology: (i) a fine description of the probe s electrical and
frequency behaviors in out of contact mode to determine intrinsic parameters of
the SThM tip, (b) a minimization of the free parameter of our model, i.e. the
contact thermal resistance, by comparing 3omega measurements to our simulations
of the probe operating in contact mode. Such an approach allows us to
accurately measure thermal interface resistances of the probe as a function of
the strength applied between the tip and the surface for three different
materials (silicon, silica and gold). In addition, FEM modeling provides
insights about the 3omega-SThM technique sensitivity, as a function of probe /
sample interface resistance to measure material thermal conductivity, paving
the way to quantitative SThM measurements. | 2007.04632v1 |