publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2003-10-23 | Correlation between the Extraordinary Hall Effect and Resistivity | We study the contribution of different types of scattering sources to the
extraordinary Hall effect. Scattering by magnetic nano-particles embedded in
normal-metal matrix, insulating impurities in magnetic matrix, surface
scattering and temperature dependent scattering are experimentally tested. Our
new data, as well as previously published results on a variety of materials,
are fairly interpreted by a simple modification of the skew scattering model. | 0310551v1 |
2003-12-29 | La0.95Sr0.05CoO3: An efficient room-temperature thermoelectric oxide | We present measurements of electrical resistivity, thermal conductivity and
thermopower of polycrystalline Sr-doped LaCoO3 with composition
La0.95Sr0.05CoO3. Our data show that the investigated compound exhibits a very
respectable room temperature thermoelectric figure of merit value of 0.18. Our
results not only show that oxides are promising candidates for thermoelectric
cooling applications, but also point towards the need for careful theoretical
calculations that will serve as a guide in producing the next generation of
thermoelectric materials. | 0312670v1 |
2004-01-06 | Superstructure, sodium ordering and antiferromagnetism in NaxCoO2 (0.75<x<1.0) | Transmission-electron-microscopy investigation reveals the presence of a
superstructure with a doubled period of 2d110 in the NaxCoO2 materials for x
ranging from 0.75 to 1.0. Systematic analyses suggest that this superstructure
in general appears just below a phase transition which could yield an anomalous
kink in resistivity. We herein interpret this superstructure in terms of sodium
ordering occurring at low temperatures. Measurements of magnetic susceptibility
for all NaxCoO2 (0.75<x<1.0) materials show an antiferromagetic state with Neel
temperature TN~4K. | 0401052v1 |
2004-09-15 | Drying model for porous material based on the dynamics of the evaporation front | A receding-front model for drying of porous material is proposed that
explains their drying-rate curves based on the dynamics of the evaporation
front. The falling-rate regime is attributed to the slowing down of the front's
propagation inside the medium due to the resistance offered by the disorder
generated by porosity. The model is solved numerically and the resulting
drying-rate curve is obtained for the falling-rate period. The curve shows a
linear behavior at early times in conformance with experiment. | 0409384v1 |
2004-10-20 | Spin-polarized transport through carbon nanotubes | Carbon nanotubes (CNT) belong to the most promising new materials which can
in the near future revolutionize the conventional electronics. When sandwiched
between ferromagnetic electrodes, the CNT behaves like a spacer in conventional
spin-valves, leading quite often to a considerable giant magneto-resistance
effect (GMR). This paper is devoted to reviewing some topics related to
electron correlations in CNT. The main attention however is directed to the
following effects essential for electron transport through nanotubes: (i)
nanotube/electrode coupling and (ii) inter-tube interactions.It is shown that
these effects may account for some recent experimental reports on GMR,
including those on negative (inverse) GMR. | 0410507v1 |
2005-11-25 | Decoupled magnetic and electrical switching in manganite trilayer | We report magnetic and electrical transport studies of an epitaxially grown
trilayer thin film structure comprising La0.59Ca0.41MnO3 sandwiched between
La0.67Ca0.33MnO3 electrodes. Since La0.59Ca0.41MnO3 lies at the edge of the
thin film ferromagnetic metallic phase field, phase separation effects are
expected. These effects can explain the observed magnetic isotropy of the
middle layer. By contrast, the electrode material is magnetically uniaxial.
Easy axis magnetic field sweeps of the trilayer produce two sharp magnetic
transitions, but only one sharp transition in current-in-plane resistance
measurements. | 0511632v1 |
2005-12-08 | Charge order in photosensitive Bi0.4Ca0.6MnO3 films | We report structural and electronic characterization of the charge order
phase in Bi0.4Ca0.6MnO3 films, in which photoinduced resistivity changes have
been observed at temperatures approaching room temperature. In all films,
lattice distortions associated with the charge order are observed, and both the
wavevectors and displacements of the distortions are in the plane of the film.
Films under compressive and tensile strain are observed to have different
resonant x-ray scattering characteristics-- a result that may shed light on the
mechanism responsible for the photosensitivity exhibited by this material. | 0512179v1 |
2006-03-21 | Effect of rolling on dissipation in fault gouge | Sliding and rolling are two outstanding deformation modes in granular media.
The first one induces frictional dissipation whereas the latter one involves
deformation with negligible resistance. Using numerical simulations on
two-dimensional shear cells, we investigate the effect of the grain rotation on
the energy dissipation and the strength of granular materials under quasistatic
shear deformation. Rolling and sliding are quantified in terms of the so-called
Cosserat rotations. The observed spontaneous formation of vorticity cells and
clusters of rotating bearings may provide an explanation for the long standing
heat flow paradox of earthquake dynamics. | 0603542v1 |
2006-06-20 | Resonant Tunneling Magneto Resistance in Coupled Quantum Wells | A three barrier resonant tunneling structure in which the two quantum wells
are formed by a dilute magnetic semiconductor material (ZnMnSe) with a giant
Zeeman splitting of the conduction band is theoretically investigated.
Self-consistent numerical simulations of the structure predict giant
magnetocurrent in the resonant bias regime as well as significant current spin
polarization for a considerable range of applied biases. | 0606531v2 |
2006-08-07 | Structure and Function of Window Glass and Pyrex | Window glass is a ternary mixture, while pyrex (after window glass, the most
common form of commercial glass) is a quaternary. Building on our previous
success in deriving the composition of window glass (sodium calcium silicate)
without adjustable parameters, and borrowing from known reconstructed
crystalline surfaces, we model pyrex as silica clusters with a specific ternary
interface. Our global model explains the thermal expansivity contours of
ternary sodium borosilicates, and it is consistent with the optimized
resistance of pyrex to mechanical and thermal shocks. It suggests new
directions for studying the nanoscopic structure of these remarkable materials. | 0608157v2 |
2006-08-28 | A Novel Pyrochlore Ruthenate: Ca2Ru2O7 | Single crystals of a novel ruthenate, Ca2Ru2O7, were obtained. An X-ray
diffraction study on a single crystal revealed that this material crystallizes
in a pyrochlore structure with a lattice parameter, a = 10.197 Angstroms. The
magnetic susceptibility above 30 K is the summation of a Curie-Weiss
contribution and a constant term independent of temperature. The effective
moment per Ru atom is only 0.36 Bohr magnetons, one order of magnitude smaller
than that expected from a localized spin model with S=3/2 for Ru5+. Below 23 K,
the localized spins freeze in a spin-glass state. The resistivity at room
temperature is 2E-3 Ohm cm, comparable to that in metallic, highly correlated
oxides.} | 0608593v1 |
2006-08-30 | Electromagnetic shielding with polypyrrole-coated fabrics | Several shielding applications, to protect human health and electronic
devices against dangerous effects of electromagnetic radiation, require
solutions that fabrics can suitably fulfill. Here, we will investigate the
electromagnetic interference shielding effectiveness of polypyrrole-coated
polyester textiles, in the frequency range 100-1000 MHz. Insertion losses for
several conductive fabrics with different surface resistivity ranging from 40
Ohm till the very low value of 3 Ohm were evaluated with a dual-tem cell.
Correlations between the shielding effectiveness and the conductivity of
composites are also discussed. | 0608664v1 |
2007-03-19 | Understanding the Branly effect | At the end of the nineteenth century \'{E}douard Branly discovered that the
electrical resistance of a granular metallic conductor could drop by several
orders of magnitude when excited by the electromagnetic field emitted by an
electrical spark. Despite the fact that this effect has been used to detect
radio waves in the early times of wireless telegraphy and more recently studied
in the field of granular materials, no satisfactory explanation of the physical
origin of the effect has been given yet. In this contribution we propose to
relate the Branly effect to the induced tunnelling effect first described by
Fran\c{c}ois Bardou and Dominique Boos\'{e}. | 0703495v1 |
2007-04-09 | Electron Transport in Nanogranular Ferromagnets | We study electronic transport properties of ferromagnetic nanoparticle arrays
and nanodomain materials near the Curie temperature in the limit of weak
coupling between the grains. We calculate the conductivity in the Ohmic and
non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at
the transition temperature. The results are applicable for many emerging
materials, including artificially self-assembled nanoparticle arrays and a
certain class of manganites, where localization effects within the clusters can
be neglected. | 0704.1167v2 |
2007-07-06 | Thermal rectification and negative differential thermal resistance in lattices with mass gradient | We study thermal properties of one dimensional(1D) harmonic and anharmonic
lattices with mass gradient. It is found that the temperature gradient can be
built up in the 1D harmonic lattice with mass gradient due to the existence of
gradons. The heat flow is asymmetric in the anharmonic lattices with mass
gradient. Moreover, in a certain temperature region the {\it negative
differential thermal resistance} is observed. Possible applications in
constructing thermal rectifier and thermal transistor by using the graded
material are discussed. | 0707.0977v1 |
2008-03-28 | On the electronic structure of the charge-ordered phase in epitaxial and polycrystalline La1-xCaxMnO3 (x = 0.55, 0.67) perovskite manganites | In this work the charge transport properties of charge ordered (CO)
La1-xCaxMnO3 (LCMO) (x= 0.55, 0.67) epitaxial thin films and polycrystals are
discussed following the recent controversy of localised electron states vs.
weakly or de- localised charge density wave (CDW) states in CO manganites. The
transport properties were investigated by current vs. voltage, direct current
resistivity vs. temperature, local activation energy vs. temperature,
magnetoresistance and admittance spectroscopy measurements, which all indicated
a localised electronic structure in the single CO phase. Delocalised charge
anomalies observed previously may be restricted to phase separated materials. | 0803.4157v1 |
2008-11-02 | Deposition of Diamond-like Carbon films using Dense Plasma Focus | Diamond Like Carbon (DLC) films were deposited on quartz substrates using
Dense Plasma Focus (DPF) method. The formation of ${\rm sp^3}$ bonds as is it's
content in the film strongly depends on the substrate and it seems quartz is
not a suitable substrate. However, we report here the formation of DLC films on
quartz substrates that were maintained at elevated temperatures and show the
content of carbon atoms with ${\rm sp^3}$ bonds in the film is directly
proportional to the substrate's temperature. Not only does this give good
control of film fabrication, but also shows how to take advantage of DLC film's
anti-wear, scratch resistant properties on material surfaces that require
protection. | 0811.0162v1 |
2009-05-03 | Magnetic state electrical readout of Mn12 molecules | We demonstrate that the different magnetic states of a Mn12 molecule can be
distinguished in a two-probe transport experiment from a complete knowledge of
the current-voltage curve. Our results, obtained with state-of-the-art
non-equilibrium transport methods combined with density functional theory,
demonstrate that spin configuration-specific negative differential resistances
(NDRs) appear in the I-V curves. These originate from the interplay between
electron localization and the re-hybridization of the molecular levels in an
external electric field and allow the detection of the molecule's spin-state. | 0905.0281v1 |
2010-04-10 | Extremely Low Drift in Amorphous Phase Change Nanowire Materials | Time-dependent drift of resistance and threshold voltage in phase change
memory (PCM) devices is of concern as it leads to data loss. Electrical drift
in amorphous chalcogenides has been argued to be either due to electronic or
stress relaxation mechanisms. Here we show that drift in amorphized Ge2Sb2Te5
nanowires with exposed surfaces is extremely low in comparison to thin-film
devices. However, drift in stressed nanowires embedded under dielectric films
is comparable to thin-films. Our results shows that drift in PCM is due to
stress relaxation and will help in understanding and controlling drift in PCM
devices. | 1004.1695v1 |
2010-06-30 | Control of the structural and magnetic properties of perovskite oxide ultrathin films through the substrate symmetry effect | Perovskite transition-metal oxides are networks of corner-sharing octahedra
whose tilts and distortions are known to affect their electronic and magnetic
properties. We report calculations on a model interfacial structure to avoid
chemical influences and show that the symmetry mismatch imposes an interfacial
layer with distortion modes that do not exist in either bulk material, creating
new interface properties driven by symmetry alone. Depending on the resistance
of the octahedra to deformation, the interface layer can be as small as one
unit cell or extend deep into the thin film. | 1006.5758v1 |
2011-05-25 | Non-Gaussian resistance noise in the ferromagnetic insulating state of a hole doped manganite | We report the observation of a large 1/f noise in the ferromagnetic
insulating state (FMI) of a hole doped manganite single crystal of
La0.80Ca0.20MnO3 which manifests hopping conductivity in presence of a Coulomb
gap. The temperature dependent noise magnitude shows a deep within the FMI
state, there is a sharp freeze out of the noise magnitude with temperature on
cooling. As the material enters the FMI state, the noise becomes non-Gaussian
as seen through probability density function and second spectra. It is proposed
to arise from charge fluctuations in a correlated glassy phase of the polaronic
carriers which develop in these systems as reported in recent simulation
studies. | 1105.5079v1 |
2013-12-03 | Doped Polyaniline: A Possible Anode for Organic Electronics | Polymer based printable organic thin film transistor (OTFT) is a viable low
cost alternative to amorphous silicon based thin film transistors and possesses
light-weight and flexibility advantage. In this paper, we report on the hole
injecting properties of doped PANI in OLED devices using it as an anode. From
these results we conclude that hole doped PANI layers can be used as a low
contact resistance source and drain electrode material for polymer OTFTs. | 1312.0737v1 |
2013-12-28 | Understanding Branly's effect through Induced Tunnelling | At the end of the nineteenth century \'Edouard Branly discovered that the
electrical resistance of a granular metallic conductor could drop by several
orders of magnitude when excited by the electromagnetic field emitted by a
distant electrical spark [ ]. Despite the fact that this effect was used to
detect radio waves in the early days of wireless telegraphy and more recently,
studied in the field of granular materials, no satisfactory explanation of the
physical origin of the effect has been proposed. In this contribution, we
relate the Branly effect to the induced tunnelling effect first described by
Fran\c{c}ois Bardou and Dominique Boos\'e [ ]. | 1312.7464v2 |
2014-05-08 | Inverse spin Hall effect in a closed loop circuit | We present measurements of inverse spin Hall effects (ISHEs) in which the
conversion of a spin current into a charge current via the ISHE is detected not
as a voltage in a standard open circuit but directly as the charge current
generated in a closed loop. The method is applied to the ISHEs of Bi-doped Cu
and Pt. The derived expression of ISHE for the loop structure can relate the
charge current flowing into the loop to the spin Hall angle of the SHE material
and the resistance of the loop. | 1405.2100v2 |
2014-09-23 | Negative differential resistance: another banana? | Just like the artefact found in ferroelectric hysteresis loops, the nearly
identical NDR effect shown in Sr3Co2Fe24O41, TiO2, Al2O3, glass and even banana
skins is confirmed to be a kind of water behavior. The combination of water
induced tunneling effect, water decomposition and absorption plays a crucial
role in the NDR effect. The results and mechanism demonstrated here illustrate
that much attention should be paid to the chemical environment when studying
electrical properties of materials / devices. | 1409.6438v1 |
2015-01-13 | The Electronic and Magnetic Properties of Magnetoresistant Nd1-xSrxMnAsO Oxyarsenides | The oxypnictides Nd1-xSrxMnAsO have been successfully synthesised with x up
to 0.1. A synchrotron X-ray diffraction study demonstrates that there is no
change in crystal symmetry upon doping with Sr. An expansion of the inter-layer
distance between Nd-O-Nd and As-Mn-As blocks is observed with increasing x.
Results from variable temperature neutron diffraction and resistivity
measurements show that the local moment antiferromagnetic order of the Mn spins
is preserved as the [MnAs]- layers are hole doped and the materials are driven
metallic for x > 0.05. A sizeable positive magnetoresistance is observed at low
temperature which demonstrates that multiple MR mechanisms are possible in
LnMnAsO oxypnictides. | 1501.02996v1 |
2015-03-02 | Functional Materials for Information and Energy Technology: Insights by Photoelectron Spectroscopy | The evolution of both information and energy technology is intimately
connected to complex condensed matter systems, the properties of which are
determined by electronic and chemical interactions and processes on a broad
range of length and time scales. Dedicated photoelectron spectroscopy and
spectromicroscopy experiments can provide important insights. We discuss some
recent methodological developments with application to relevant questions in
spintronics, and towards in-operando studies of resistive switching and
electrochemical processes. | 1503.00464v2 |
2015-03-29 | Cooperative Multiscale Aging in a Ferromagnet/Antiferromagnet Bilayer | We utilize anisotropic magnetoresistance to study temporal evolution of the
magnetization state in epitaxial Ni$_{80}$Fe$_{20}$/Fe$_{50}$Mn$_{50}$
ferromagnet/antiferromagnet bilayers. The resistance exhibits power-law
evolution over a wide range of temperatures and magnetic fields, indicating
that aging is characterized by a wide range of activation time scales. We show
that aging is a cooperative process, i.e. the magnetic system is not a
superposition of weakly interacting subsystems characterized by simple
Arrhenius activation. The observed effects are reminiscent of avalanches in
granular materials, providing a conceptual link to a broad class of critical
phenomena in other complex condensed matter systems. | 1503.08380v1 |
2015-11-17 | On melting of boron phosphide under pressure | Melting of cubic boron phosphide, BP has been studied at pressures to 9 GPa
using synchrotron X-ray diffraction and electrical resistivity measurements. It
has been found that above 2.6 GPa BP melts congruently, and the melting curve
exhibits negative slope -60(7) K/GPa, which is indicative of a higher density
of the melt as compared to the solid phase. | 1511.05995v1 |
2015-11-30 | Electronic Origins of Large Thermoelectric Power Factor of LaOBiS2-xSex | We examined the electrical transport properties of densified LaOBiS2-xSex,
which constitutes a new family of thermoelectric materials. The power factor
increased with increasing concentration of Se, i.e., Se substitution led to an
enhanced electrical conductivity, without suppression of the Seebeck
coefficient. Hall measurements indicated that the low electrical resistivity
resulted from increases in the carrier mobility, and the decrease in carrier
concentration led to large absolute values of the Seebeck coefficient of the
system. | 1511.09133v1 |
2016-04-04 | Two-dimensional Dirac fermions in YbMnBi2 antiferromagnet | We report two-dimensional quantum transport and Dirac fermions in YbMnBi2
single crystals. YbMnBi2 is a layered material with anisotropic conductivity
and magnetic order below 290 K. Magnetotransport properties, nonzero Berry
phase and small cyclotron mass indicate the presence of quasi two dimensional
Dirac fermions. Quantum oscillations in Hall resistivity suggest the presence
of both electron and hole parts of the Fermi surface whereas the Berry phase
suggests spin-orbit coupling. | 1604.01009v1 |
2016-08-17 | Field effect in stacked van der Waals heterostructures: Stacking sequence matters | Stacked van der Waals (vdW) heterostructures where semi-conducting
two-dimensional (2D) materials are contacted by overlayed graphene electrodes
enable atomically-thin, flexible electronics. We use first-principles quantum
transport simulations of graphene-contacted MoS2 devices to show how the
transistor effect critically depends on the stacking configuration relative to
the gate electrode. We can trace this behavior to the stacking-dependent
response of the contact region to the capacitive electric field induced by the
gate. The contact resistance is a central parameter and our observation
establish an important design rule for devices based on 2D atomic crystals. | 1608.05023v1 |
2017-06-30 | Structural and dielectric characterization of Sm2MgMnO6 | The polycrystalline Sm2MgMnO6 (SMMO) was synthesized at 1173K by means of
sol-gel technique. Rietveld refine-ment of X-ray diffraction (XRD) pattern
confirmed the formation of a single phase monoclinic structure with space group
P21/n. The band gap achieved from UV-vis spectra shows the semiconducting
nature of the material. To observe the effect of grains and grain-boundaries in
the conduction process and dielectric relaxation measurements are carried out
on SMMO sample at different frequencies between 313 K and 673 K. An electrical
equivalent circuit consisting of the resistance and constant phase element is
used to clarify the impedance data. | 1706.10038v1 |
2017-10-08 | Hall effect spintronics for gas detection | We present the concept of magnetic gas detection by the Extraordinary Hall
effect (EHE). The technique is compatible with the existing conductometric gas
detection technologies and allows simultaneous measurement of two independent
parameters: resistivity and magnetization affected by the target gas.
Feasibility of the approach is demonstrated by detecting low concentration
hydrogen using thin CoPd films as the sensor material. The Hall effect
sensitivity of the optimized samples exceeds 240% per 104 ppm at hydrogen
concentrations below 0.5% in the hydrogen/nitrogen atmosphere, which is more
than two orders of magnitude higher than the sensitivity of the conductance
detection. | 1710.03700v1 |
2017-10-12 | Martensitic relief observation by atomic force microscopy in yttria stabilized zirconia | The tetragonal to monoclinic (t-m) phase transformation of zirconia has been
the object of extensive investigations of the last twenty years, and is now
recognised as being of martensitic nature. However, martensitic transformation
has only been observed by transmission electron microscopy or indirect methods.
Though the benefit on the fracture toughness and crack resistance was the main
interest, the transformation is now considered for its consequences on the
degradation of the material. The use of AFM reported here allowed the
observation of the first stages of martensite relief growth and of new
martensitic features. | 1710.04442v1 |
2017-10-25 | Ordered C vacancies in titanium carbides: a correlation between crystal structure and the effects on oxidation behavior at elevated temperature | It has been widely accepted that the introduction of titanium carbides into
titanium-based alloys can significantly enhance the oxidation resistance due to
their superior physicochemical stability at elevated temperatures. The present
study reported for the first time that the ordered C vacancies within titanium
carbides could lead to an uncommon phenomenon particularly at the very initial
stage of oxidation. The intrinsic micro-to-macro oxidation mechanisms were
systematically clarified with the aids of transmission electron microscope and
ab-initio molecular dynamics simulation. | 1710.09311v1 |
2017-12-28 | Theoretical calculation of transport properties of oxide material using narrow band model | We report about the results of theoretical calculations of temperature
dependence of resistivity ($\rho$) and Seebeck coefficient ($S$) for
thermoelectric (TE) and superconductivity (SC) phases by arithmetic equations
based on narrow band model with oxygen deficient structure, as the functions of
band-filling degree ($F$), and band width ratio of electron and spin states
($W$\sigma/$W$D). The phase diagrams of TE and SC states, and boundary were
imaged to the properties of $\rho$ and $S$ as a function of $F$ and
$W$\sigma/$W$D. | 1712.09840v1 |
2018-01-12 | Tunable elastic Parity-Time symmetric structure based on the shunted piezoelectric materials | We theoretically and numerically report on tunable elastic Parity-Time (PT)
symmetric structure based on shunted piezoelectric units. We show that the
elastic loss and gain can be archived in piezoelectric materials when they are
shunted by external circuits containing positive and negative resistances. We
present and discuss, as an example, the strongly dependent relationship between
the exceptional points of a three-layered system and the impedance of their
external shunted circuit. The achieved results evidence the PT symmetric
structures based on this proposed concept can actively be tuned without any
change of their geometric configurations. | 1801.04114v1 |
2018-02-12 | Crack initiation in viscoelastic materials | In viscoelastic materials, individually short-lived bonds collectively result
in a mechanical resistance which is long-lived but finite, as ultimately cracks
appear. Here we provide a microscopic mechanism by which cracks emerge from the
nonlinear local bond dynamics. This mechanism is different from crack
initiation in solids, which is governed by a competition between elastic and
adhesion energy. We provide and numerically verify analytical equations for the
dependence of the critical crack length on the bond kinetics and applied
stress. | 1802.04017v1 |
2017-01-27 | Delicate competing electronic states in ultrathin manganite films | The coupling between the electrical transport properties of La2/3Sr1/3MnO3
(LSMO) thin films and structural phase transitions of SrTiO3 (STO) substrates
at Ts = 105 K has been investigated. We found that the electrical resistivity
of LSMO films exhibit a cusp at Ts, which is greatly amplified by tuning films
to the verge of metallic and insulating phases, i.e., to the boundary of two
delicate competing electronic states. Our results demonstrate that small
amounts of strain can tip the subtle balance of competing interactions and tune
the electronic properties in correlated electron materials. | 1701.07933v1 |
2019-07-03 | Precision measurements of the AC field dependence of the superconducting transition in strontium titanate | Strontium titanate has resurfaced as a material prompting vigorous debate
about the origin of its superconductivity in the extremely low carrier
concentration regime. Here, we used simultaneous AC susceptibility and
transport methods to explore the superconducting phase transition region in
this material. We determined that strontium titanate is extremely sensitive to
even small AC fields, which also influence the resistive transition; we suggest
that extreme vortex sizes and mobilities contribute to this large effect. Our
findings will be of importance for accurately determining transition
temperature, informing the debate about the pairing mechanism in strontium
titanate, for which even millikelvin errors may be critical. | 1907.01733v1 |
2020-04-14 | Compaction Self-Assembly of Ultralow-Binder-Content Thermoplastic Composites Based on Lunar Soil Simulant | In a recent study, we developed ultralow-binder-content (UBC) structural
materials based on lunar soil simulant and thermoset binders. In the current
research, we investigated thermoplastic binders. Compared to thermosets,
advanced thermoplastics could be more UV resistant, more durable, more robust,
and recyclable. Our main technology is the compaction self-assembly (CSA). By
using only ~4 wt% polyetherketoneketone (PEKK) binder, the thermoplastic-binder
UBC composite was stronger than typical steel-reinforced concrete. The CSA
operation was separate from the curing process. This study may provide an
important in-situ resource utilization method for large-scale construction on
Moon. | 2004.06273v1 |
2017-05-01 | On melting of boron subnitride B13N2 under pressure | Melting of rhombohedral boron subnitride B13N2 has been studied in situ at
pressures to 8 GPa using synchrotron X-ray diffraction and electrical
resistivity measurements. It has been found that above 2.6 GPa B13N2 melts
incongruently, and the melting curve exhibits positive slope of 31(3) K/GPa
that points to a lower density of the melt as compared to the solid phase. | 1705.03753v1 |
2019-03-25 | Optical Hoovering on Plasmonic Rinks | Excitation of surface waves on conducting materials provides a near
resistance-free interface capable of a material glissade either by plasmon
forces or optical beam tractors. Analogous to an ice hockey rink, as proof of
principle plasmon assisted optical traction, or hoovering, of water drops on a
gold surface is demonstrated. Variability in thresholds and movement is
observed and can be explained by the presence of significant roughness,
measured by SEM. The demonstration opens a path to directly integrate various
optical and plasmonic glissade technologies. Ways of improving transport and
potential applications spanning configurable microfluidics, antennas,
diagnostics,sensing and active devices are discussed. | 1903.10106v1 |
2021-04-23 | Microwave response in a topological superconducting quantum interference device | Photon detection at microwave frequency is of great interest due to its
application in quantum computation information science and technology. Herein
are results from studying microwave response in a topological superconducting
quantum interference device (SQUID) realized in Dirac semimetal Cd3As2. The
temperature dependence and microwave power dependence of the SQUID junction
resistance are studied, from which we obtain an effective temperature at each
microwave power level. It is observed the effective temperature increases with
the microwave power. This observation of microwave response may pave the way
for single photon detection at the microwave frequency in topological quantum
materials. | 2104.11841v1 |
2021-04-29 | Thickness Dependence of Magneto-transport Properties in Tungsten Ditelluride | We investigate the electronic structure of tungsten ditelluride (WTe$_2$)
flakes with different thicknesses in magneto-transport studies. The
temperature-dependent resistance and magnetoresistance (MR) measurements both
confirm the breaking of carrier balance induced by thickness reduction, which
suppresses the `turn-on' behavior and large positive MR. The Shubnikov-de-Haas
oscillation studies further confirm the thickness-dependent change of
electronic structure of WTe$_2$ and reveal a possible temperature-sensitive
electronic structure change. Finally, we report the thickness-dependent
anisotropy of Fermi surface, which reveals that multi-layer WTe$_2$ is an
electronic 3D material and the anisotropy decreases as thickness decreases. | 2104.14464v1 |
2022-03-04 | Impedance spectroscopy: Impedance spectroscopy of nanomaterials | Solid state impedance spectroscopy enables the various contributions to the
resistive and capacitive properties of electronically inhomogeneous condensed
matter to be deconvoluted and characterized separately. The different
contributions arise from electronically distinct areas in the sample, which can
in an ideal case be represented each by one standard RC element. In the
following, the basic principles of impedance spectroscopy, different types of
experimental setups and several examples of experimental impedance data sets
from nanostructured materials are reviewed and discussed. The data analysis and
equivalent circuit modelling processes which are relevant for the application
of this technique to nanomaterials are emphasized. The different dimensions and
structure of nanomaterials as compared to macroscopic bulk samples leads to
quite different and sometimes more complex data that require detailed analysis
and advanced equivalent circuit models. | 2203.02387v1 |
1998-12-08 | Anomalous Low Temperature States in CeNi2Ge2 | Ambient pressure studies on high purity single crystals of the stoichiometric
4f-electron metal CeNi2Ge2 reveal anomalous low temperature forms of the
resistivity which challenge our understanding of the metallic state.
Comparisons are made with the isostructural and isoelectronic compound CePd2Si2
near the border of magnetism at high pressure, and possible reasons for this
novel non-Fermi liquid form of the resistivity are discussed. Phase diagrams of
further anomalies are presented, which involve a loss of resistance at low
temperature in some samples of CeNi2Ge2 and unexpected high pressure phases. | 9812133v1 |
2003-03-20 | Electrical resistivity and magnetization measurements on the heavy fermion superconductor PrOs4Sb12 | The filled skutterudite compound PrOs4Sb12, the first example of a Pr-based
heavy fermion superconductor, displays superconductivity with $T_c\sim 1.85$ K
and has an effective mass $m^* \sim$ {50 $m_e$}, where $m_e$ is the free
electron mass. For magnetic fields above 4.5 T, sharp features in the normal
state electrical resistivity, magnetization, specific heat, and thermal
expansion data suggest the occurrence of a phase transition at high fields.
This high field ordered phase in the normal state may originate from a
combination of crystalline electric field enhanced Zeeman splitting and
quadrupolar ordering. We present an investigation of the electrical resistivity
and magnetization of PrOs4Sb12 as a function of temperature between {350 mK}
and {3.5 K} and magnetic field up to {18 T}. The data reveal a detailed phase
boundary of the high field ordered phase as well as the lower critical field
$H_{c1}$ and the onset field of the peak effect in the superconducting state of
PrOs4Sb12. | 0303405v1 |
2004-04-12 | Universality of the Mott-Ioffe-Regel limit in metals | The absence of resistivity saturation in many strongly correlated metals,
including the high-temperature superconductors, is critically examined from the
viewpoint of optical conductivity measurements. Coherent quasiparticle
conductivity, in the form of a Drude peak centred at zero frequency, is found
to disappear as the mean free path (at $\omega$ = 0) becomes comparable to the
interatomic spacing. This basic loss of coherence at the so-called
Mott-Ioffe-Regel (MIR) limit suggests that the universality of the MIR
criterion is preserved even in the presence of strong electron correlations. We
argue that the shedding of spectral weight at low frequencies, induced by
strong correlation effects, is the primary origin of the extended positive
slope of the resistivity to high temperatures observed in all so-called "bad
metals". Moreover, in common with those metals which exhibit resistivity
saturation at high temperatures, the scattering rate itself, as extracted from
optical spectra, saturates at a value consistent with the MIR limit. We
consider possible implications that this ceiling in the scattering rate may
have for our understanding of transport within a wide variety of bad metals and
suggest a better method for analysing their optical response. | 0404263v1 |
2005-02-21 | High pressure effects on the superconductivity of beta-pyrochlore oxides AOs2O6 | High pressure effects on the superconducting transitions of beta-pyrochlore
superconductors AOs2O6 (A = Cs, Rb, K) are studied by measuring resistivity
under high pressures up to 10 GPa. The superconducting transition temperature
Tc first increases with increasing pressure in all the compounds and then
exhibits a broad maximum at 7.6 K (6 GPa), 8.2 K (2 GPa) and 10 K (0.6 GPa) for
A = Cs, Rb and K, respectviely. Finally, the superconductivity is suppressed
completely at a critical pressure near 7 GPa and 6 GPa for A = Rb and K and
probably above 10 GPa for A = Cs. Characteristic changes in the coefficinet A
of the T2 term in resistivity and residual resistivity are observed, both of
which are synchronized with the corresponding change in Tc. It is suggested
that electron correlations and certain quantum fluctuations play important
roles in the occurrence or suppression of superconductivity in the
beta-pyrochlore oxides. | 0502490v1 |
2003-07-30 | Position Sensing from Charge Dispersion in Micro-Pattern Gas Detectors with a Resistive Anode | Micro-pattern gas detectors, such as the Gas Electron Multiplier (GEM) and
the Micromegas need narrow high density anode readout elements to achieve good
spatial resolution. A high-density anode readout would require an unmanageable
number of electronics channels for certain potential micro-detector
applications such as the Time Projection Chamber. We describe below a new
technique to achieve good spatial resolution without increasing the electronics
channel count in a modified micro-detector outfitted with a high surface
resistivity anode readout structure. The concept and preliminary measurements
of spatial resolution from charge dispersion in a modified GEM detector with a
resistive anode are described below. | 0307152v2 |
2008-09-30 | High Pressure studies of the magnetic phase transition in MnSi: revisited | New measurements of AC magnetic susceptibility and DC resistivity of a high
quality single crystal MnSi were carried out at high pressure making use of
helium as a pressure medium. The form of the AC magnetic susceptibility curves
at the magnetic phase transition suddenly changes upon helium solidification.
This implies strong sensitivity of magnetic properties of MnSi to non
hydrostatic stresses and suggests that the early claims on the existence of a
tricritical point at the phase transition line are probably a result of
misinterpretation of the experimental data. At the same time resistivity
behavior at the phase transition does not show such a significant influence of
helium solidification. The sharp peak at the temperature derivative of
resistivity, signifying the first order nature of the phase transition in MnSi
successfully survived helium crystallization and continued the same way to the
highest pressure. | 0809.5117v1 |
2014-05-21 | Waveguide-mode interference lithography technique for high contrast subwavelength structures in the visible region | We explore possibilities of waveguide-mode interference lithography (WMIL)
technique for high contrast subwavelength structures in the visible region.
Selecting an appropriate waveguide-mode, we demonstrate high contrast resist
mask patterns for the first time. TM1 mode in the waveguide is shown to be
useful for providing a three-dimensional structure whose cross section is
checkerboard pattern. Applying our WMIL technique, we demonstrate 1D, 2D and 3D
subwavelength resist patterns that are widely used for the fabrication of
metamteterials in the visible region. In addition to the resist patterns, we
demonstrate a resonance at 1.9 eV for a split tube structure experimentally. | 1405.5395v1 |
2015-10-28 | Effect of ambient on the resistance fluctuations of graphene | In this letter we present the results of systematic experimental
investigations of the effect of different chemical environments on the low
frequency resistance fluctuations of single layer graphene field effect
transistors (SLG-FET). The shape of the power spectral density of noise was
found to be determined by the energetics of the adsorption-desorption of
molecules from the graphene surface making it the dominant source of noise in
these devices. We also demonstrate a method of quantitatively determining the
adsorption energies of chemicals on graphene surface based on noise
measurements. We find that the magnitude of noise is extremely sensitive to the
nature and amount of the chemical species present. We propose that a chemical
sensor based on the measurement of low frequency resistance fluctuations of
single layer graphene field effect transistor devices will have extremely high
sensitivity, very high specificity, high fidelity and fast response times. | 1510.08198v1 |
2016-07-09 | In-beam evaluation of a medium-size Resistive-Plate WELL gaseous particle detector | In-beam evaluation of a fully-equipped medium-size 30$\times$30 cm$^2$
Resistive Plate WELL (RPWELL) detector is presented. It consists here of a
single element gas-avalanche multiplier with Semitron ESD225 resistive plate, 1
cm$^2$ readout pads and APV25/SRS electronics. Similarly to previous results
with small detector prototypes, stable operation at high detection efficiency
(>98%) and low average pad multiplicity (~1.2) were recorded with 150 GeV muon
and high-rate pion beams, in Ne/(5%CH$_4$), Ar/(5%CH$_4$) and Ar/(7%CO$_2$).
This is an important step towards the realization of robust detectors suitable
for applications requiring large-area coverage; among them Digital Hadron
Calorimetry. | 1607.02587v2 |
2017-12-26 | Microwave-induced zero-resistance states in a high-mobility two-subband electron system | In this study we used selectively-doped GaAs/AlAs heterostructure to
fabricate a high-mobility two-subband electronic system with substantially
different concentration of electrons in subbands. We observe microwave
photoresistance at high numbers of magneto-intersubband oscillations (MISO).
The system under study demonstrates microwave-induced resistance oscillations
(MIRO) and MISO interference. MIRO in the studied two-subband system appear in
lower magnetic fields comparing to MISO. This is an indication of some unknown
mechanism that exists in the two-subband system and is responsible for MISO
amplitude damping in low magnetic fields, while it does not affect the MIRO
amplitude. Zero resistance states (ZRS) appear in the system under study under
microwave irradiation in the narrow range of magnetic fields near the MISO
maximum. | 1712.09244v1 |
2020-04-11 | Characterisation of an RPC prototype with moderate resistivity plates using tetrafluoroethane ($C_2H_2F_4$) | Keeping in mind the requirements of high rate capable, cost effective, large
area detectors to be used in future high energy physics experiments,
commercially available bakelite plates having moderate bulk resistivity are
used to build an RPC module. The chamber is tested with cosmic rays in the
avalanche mode using 100\% Tetrafluoroethane ($C_2H_2F_4$). Standard NIM
electronics are used for this study. The efficiency, noise rate and time
resolution are measured. The detailed method of measurement and the first test
results are presented. | 2004.05469v2 |
2019-08-29 | Onset of phase diffusion in high kinetic inductance granular aluminum micro-SQUIDs | Superconducting granular aluminum is attracting increasing interest due to
its high kinetic inductance and low dissipation, favoring its use in kinetic
inductance particle detectors, superconducting resonators or quantum bits. We
perform switching current measurements on DC-SQUIDs, obtained by introducing
two identical geometric constrictions in granular aluminum rings of various
normal-state resistivities in the range from $\rho_\mathrm{n} =
250\,\mu\Omega\mathrm{cm}$ to $5550\,\mu\Omega\mathrm{cm}$. The relative high
kinetic inductance of the SQUID loop, in the range of tens of nH, leads to a
suppression of the modulation in the measured switching current versus magnetic
flux, accompanied by a distortion towards a triangular shape. We observe a
change in the temperature dependence of the switching current histograms with
increasing normal-state film resistivity. This behavior suggests the onset of a
diffusive motion of the superconducting phase across the constrictions in the
two-dimensional washboard potential of the SQUIDs, which could be caused by a
change of the local electromagnetic environment of films with increasing
normal-state resistivities. | 1908.11067v1 |
2019-12-18 | Multiplex stimulated Raman scattering imaging cytometry reveals cancer metabolic signatures in a spatially, temporally, and spectrally resolved manner | In situ measurement of cellular metabolites is still a challenge in biology.
Conventional methods, such as mass spectrometry or fluorescence microscopy,
would either destruct the sample or introduce strong perturbations to the
functions of target molecules. Here, we present multiplex stimulated Raman
scattering (SRS) imaging cytometry as a label-free single-cell analysis
platform with chemical specifity, and high-throughput capabilities. Cellular
compartments such as lipid droplets, endoplasmic reticulum, and nuclei are
seperated from the cytoplasm. Based on these chemical segmentations, 260
features from both morphology and molecular composition were generated and
analyzed for each cell. Using SRS imaging cytometry, we studied the metabolic
responses of human pancreatic cancer cells under stress by starvation and
chemotherapy drug treatments. We unveiled lipid-facilitated protrusion as a
metabolic marker for stress-resistant cancer cells through statistical analysis
of thousands of cells. Our findings also demonstrate the potential of targeting
lipid metabolism for selective treatment of starvation-resistant and
chemotherapy-resistant cancers. These results highlight our SRS imaging
cytometry as a powerful label-free tool for biological discoveries with a
high-throughput, high-content capacity. | 1912.08340v1 |
2020-05-31 | Towards a two-dimensional readout of the improved CMS Resistive Plate Chamber with a new front-end electronics | As part of the Compact Muon Solenoid experiment Phase-II upgrade program, new
Resistive Plate Chambers will be installed in the forward region. High
background conditions are expected in this region during the high-luminosity
phase of the Large Hadron Collider, therefore an improved RPC design has been
proposed with a new front-end electronics to sustain a higher rate capability
and better time resolution. A new technology is used in the front-end
electronics resulting in very low achievable thresholds of the order of several
fC. Crucial in the design of the improved RPC is the capability of a
two-dimensional readout in order to improve the spatial resolution, mainly
motivated by trigger requirements. In this work, the first performance results
towards this two-dimensional readout are presented, based on data taken on a
real-size prototype chamber with two embedded orthogonal readout strips.
Furthermore, dedicated studies of the muon cluster size as a function of the
graphite resistivity are discussed. | 2006.00576v1 |
2020-06-24 | Microwave response of interacting oxide two-dimensional electron systems | We present an experimental study on microwave illuminated high mobility
MgZnO/ZnO based two-dimensional electron systems with different electron
densities and, hence, varying Coulomb interaction strength. The photoresponse
of the low-temperature dc resistance in perpendicular magnetic field is
examined in low and high density samples over a broad range of illumination
frequencies. In low density samples a response due to cyclotron resonance (CR)
absorption dominates, while high density samples exhibit pronounced
microwave-induced resistance oscillations (MIRO). Microwave transmission
experiments serve as a complementary means of detecting the CR over the entire
range of electron densities and as a reference for the band mass unrenormalized
by interactions. Both CR and MIRO-associated features in the resistance permit
extraction of the effective mass of electrons but yield two distinct values.
The conventional cyclotron mass representing center-of-mass dynamics exhibits
no change with density and coincides with the band electron mass of bulk ZnO,
while MIRO mass reveals a systematic increase with lowering electron density
consistent with renormalization expected in interacting Fermi liquids. | 2006.13627v1 |
2020-10-15 | Extreme High-Field Superconductivity in Thin Re Films | We report the high-field superconducting properties of thin, disordered Re
films via magneto-transport and tunneling density of states measurements. Films
with thicknesses in the range of 9 nm to 3 nm had normal state sheet
resistances of $\sim$0.2 k$\Omega$ to $\sim$1 k$\Omega$ and corresponding
transition temperatures in the range of 6 K to 3 K. Tunneling spectra were
consistent with those of a moderate coupling BCS superconductor.
Notwithstanding these unremarkable superconducting properties, the films
exhibited an extraordinarily high upper critical field. We estimate their
zero-temperature $H_{c2}$ to be more than twice the Pauli limit. Indeed, in 6
nm samples the estimated reduced critical field $H_{c2}/T_c\sim$ 5.6 T/K is
among the highest reported for any elemental superconductor. Although the sheet
resistances of the films were well below the quantum resistance $R_Q=h/4e^2$,
their $H_{c2}$'s approached the theoretical upper limit of a strongly
disordered superconductor for which $k_F\ell\sim1$. | 2010.07674v2 |
2021-09-29 | High-performance Ba1-xKxFe2As2 superconducting joints for persistent current operation | Superconducting joints are one of the key technologies to make Ba1-xKxFe2As2
(Ba-122) superconducting wires or tapes for high-field applications. Herein,
superconducting joints were fabricated by a simple cold-pressing method, and
the joint resistance of the iron-based superconducting joint was estimated for
the first time. The superconducting properties, microstructures, and elements
distribution in the joint regions were investigated. At 4.2 K and 10 T, a
transport critical current Ic of 105 A for the joint was obtained, and the
critical current ratio (CCR= Ic-joint/Ic-tape) of the joint was 94.6%. On the
other hand, the joint show very low joint resistance of 2.7x10^-13 ohm in
self-field at 4.2 K. Among iron-based superconductors (IBS), this work is the
first to successfully realize a superconducting joint with such high CCR and
low joint resistance. This work shows great potential to apply Ba-122 in a
range of practical applications, where superconducting joints are essential. | 2109.14300v1 |
2022-09-01 | Directed flow in relativistic resistive magneto-hydrodynamic expansion for symmetric and asymmetric collision systems | We construct a dynamical model for high-energy heavy-ion collision based on
the relativistic resistive magneto-hydrodynamic framework. Using our newly
developed (3+1)-dimensional relativistic resistive magneto-hydrodynamics code,
we investigate magneto-hydrodynamic expansion in symmetric and asymmetric
collision systems as a first application to high-energy heavy-ion collisions.
As a realistic initial condition for electromagnetic fields, we consider the
solutions of the Maxwell equations with the source term of point charged
particles moving in the direction of the beam axis, including finite constant
electrical conductivity of the medium. We evaluate the directed flow in the
symmetric and asymmetric collisions at RHIC energy. We find a significant
effect of finite electrical conductivity on the directed flow in the asymmetric
collision system. We confirm that a certain amount of energy transfer by
dissipation associated with Ohmic conduction occurs in the asymmetric collision
system because of asymmetry of the electric field produced by two different
colliding nuclei. Because this energy transfer makes the pressure gradient of
the medium flatter, the growth of directed flow decreases. | 2209.00323v1 |
2023-02-21 | A novel fast response and radiation-resistant scintillator detector for beam loss monitor | At high luminosity areas, beam loss monitor with fast response and high
radiation resistance is crucial for accelerator operation. In this article, we
report the design and test results of a fast response and radiation-resistant
scintillator detector as the beam loss monitor for high luminosity colliders,
especially at low energy regions such as RFQ. The detector consists of a 2 cm*2
cm 0.5 cm LYSO crystal readout by a 6 mm*6 mm Silicon photomultiplier. Test
results from various radioactive sources show that the detector has good
sensitivity to photons from tens of keV to several MeV with good linearity and
energy resolution (23% for 60 keV {\gamma}-ray). For the field test, two such
detectors are installed outside of the vacuum chamber shell of an 800 MeV
electron storage ring. The details of the test and results are introduced. | 2302.14662v1 |
2023-11-28 | Transport properties of a half-filled Chern band at the electron and composite fermion phases | We consider a half-filled Chern band and its transport properties in two
phases that it may form, the electronic Fermi liquid and the composite-fermion
Fermi liquid. For weak disorder, we show that the Hall resistivity for the
former phase is very small, while for the latter it is close to $2h/e^2$,
independent of the distribution of the Berry curvature in the band. At rising
temperature and high frequency, we expect the Hall resistivity of the
electronic phase to rise, and that of the composite-fermion phase to deviate
from $2h/e^2$. At high frequency, sign changes are expected as well.
Considering high-frequency transport, we show that the composite fermion phase
carries a gapped plasmon mode which does not originate from long ranged Coulomb
interaction, and we show how this mode, together with the reflection of
electro-magnetic waves off the Chern band, allow for a measurement of the
composite-fermion Drude weight and Berry curvature. Finally, we consider a
scenario of a mixed-phase transition between the two phases, for example as a
function of displacement-field, and show that such transition involves an
enhancement of the longitudinal resistivity, as observed experimentally. | 2311.16761v1 |
2024-05-17 | Possible spin-polarized Cooper pairing in high temperature FeSe superconductor | Superconductivity and long-range ferromagnetism hardly coexist in a uniform
manner. The counter-example has been observed, in uranium-based superconductors
for instance, with a coexisting temperature limited to about 1 K. Here, we
report the coexistence of high temperature superconductivity and itinerant
ferromagnetism in lithium intercalated FeSe flakes. In superconducting samples
with transition temperature around 40 K, we observe the anomalous Hall effect
with a hysteresis loop in transverse resistivity and a butterfly-like pattern
of magneto-resistance. Intriguingly, such ferromagnetism persists down to a
temperature at which the zero-field resistance fully vanishes. Furthermore, the
superconductivity is enhanced under an in-plane magnetic field, suggestive of
the participation of spin-polarized Cooper pairs. The surprising finding
underscores a uniform coexistence of the two antagonistic phenomena on a
record-high energy scale. | 2405.10482v1 |
2006-05-24 | Tuning of magnetic and electronic states by control of oxygen content in lanthanum strontium cobaltites | We report on the magnetic, resistive, and structural studies of perovskite
La$_{1/3}$Sr$_{2/3}$CoO$_{3-\delta}$. By using the relation of synthesis
temperature and oxygen partial pressure to oxygen stoichiometry obtained from
thermogravimetric analysis, we have synthesized a series of samples with
precisely controlled $\delta=0.00-0.49$. These samples show three structural
phases at $\delta=0.00-0.15$, $\approx0.25$, $\approx0.5$, and two-phase
behavior for other oxygen contents. The stoichiometric material with
$\delta=0.00$ is a cubic ferromagnetic metal with the Curie temperature $T_{\rm
C}=274$ K. The increase of $\delta$ to 0.15 is followed by a linear decrease of
$T_{\rm C}$ to $\approx$ 160 K and a metal-insulator transition near the
boundary of the cubic structure range. Further increase of $\delta$ results in
formation of a tetragonal $2a_p\times 2a_p \times 4a_p$ phase for
$\delta\approx 0.25$ and a brownmillerite phase for $\delta\approx0.5$. At low
temperatures, these are weak ferromagnetic insulators (canted antiferromagnets)
with magnetic transitions at $T_{\rm m}\approx230$ and 120 K, respectively. At
higher temperatures, the $2a_p\times 2a_p \times 4a_p$ phase is $G$-type
antiferromagnetic between 230 K and $\approx$360 K. Low temperature magnetic
properties of this system for $\delta<1/3$ can be described in terms of a
mixture of Co$^{3+}$ ions in the low-spin state and Co$^{4+}$ ions in the
intermediate-spin state and a possible spin transition of Co$^{3+}$ to the
intermediate-spin state above $T_{\rm C}$. For $\delta>1/3$, there appears to
be a combination of Co$^{2+}$ and Co$^{3+}$ ions, both in the high-spin state
with dominating antiferromagnetic interactions. | 0605611v1 |
2008-06-23 | Phase transitions in LaFeAsO: structural, magnetic, elastic, and transport properties, heat capacity and Mossbauer spectra | We present results from a detailed experimental investigation of LaFeAsO, the
parent material in the series of "FeAs" based oxypnictide superconductors. Upon
cooling this material undergoes a tetragonal-orthorhombic crystallographic
phase transition at ~160 K followed closely by an antiferromagnetic ordering
near 145 K. Analysis of these phase transitions using temperature dependent
powder X-ray and neutron diffraction measurements is presented. A magnetic
moment of ~0.35 Bohr magnetons per iron is derived from Mossbauer spectra in
the low temperature phase. Evidence of the structural transition is observed at
temperatures well above the structural transition (up to near 200 K) in the
diffraction data as well as the polycrystalline elastic moduli probed by
resonant ultrasound spectroscopy measurements. The effects of the two phase
transitions on the transport properties (resistivity, thermal conductivity,
Seebeck coefficient, Hall coefficient), heat capacity, and magnetization of
LaFeAsO are also reported, including a dramatic increase in the magnitude of
the Hall coefficient below 160 K. The results suggest that the structural
distortion leads to a localization of carriers on Fe, producing small local
magnetic moments which subsequently order antiferromagnetically upon further
cooling. Evidence of strong electron-phonon interactions in the
high-temperature tetragonal phase is also observed. | 0806.3878v2 |
2011-03-07 | Reversibly tuning the insulating and superconducting state in KxFe2-ySe2 crystals by post-annealing | Since the discovery of superconductivity at 26 K in oxy-pnictide
LaFeAsO1-xFx, enormous interests have been stimulated in the field of condensed
matter physics and material sciences. Among the many kind of structures in the
iron pnictide superconductors, FeSe with the PbO structure has received special
attention since there is not poisonous pnictogen element in chemical
composition and its structure is the simplest one. However, the superconducting
transition temperature (Tc) in iron chalcogenide compounds is not enhanced as
high as other iron pnictide superconductors under ambient pressure until the
superconductivity at above 30 K in potassium intercalated iron selenide
KxFe2-ySe2 was discovered. The insulating and the superconducting state are
both observed in KxFe2-ySe2 with different stoichiometries and some groups have
tuned the system from insulating to superconducting state by varying the ratio
of starting materials[10, 11]. The recent data from neutron scattering suggest
that the superconductivity may be built upon an ordered state of Fe vacancies
as well as the antiferromagnetic state with a very strong ordered magnetic
moment 3.4 B. Here we show that the superconductivity can actually be tuned on
a single sample directly from an insulating state by post-annealing and fast
quenching. Upon waiting for some days at room temperatures, the
superconductivity will disappear and the resistivity exhibits an insulating
behavior again. The spatial distribution of the compositions of the as-grown
sample and the post-annealed-quenched one was analyzed by the Energy Dispersive
X-ray Spectrum (EDXS) and found to be very close to each other. Therefore it is
tempting to conclude that the superconductivity is achieved when the
Fe-vacancies are in a random (disordered) state. Once they arrange in an
ordered state by relaxation or slow cooling, the system turns out to be an
insulator. | 1103.1347v1 |
2014-09-16 | Hydrogen Diffusion and Stabilization in Single-crystal VO2 Micro/nanobeams by Direct Atomic Hydrogenation | We report measurements of the diffusion of atomic hydrogen in single
crystalline VO2 micro/nanobeams by direct exposure to atomic hydrogen, without
catalyst. The atomic hydrogen is generated by a hot filament, and the doping
process takes place at moderate temperature (373 K). Undoped VO2 has a
metal-to-insulator phase transition at ~340 K between a high-temperature,
rutile, metallic phase and a low-temperature, monoclinic, insulating phase with
a resistance exhibiting a semiconductor-like temperature dependence. Atomic
hydrogenation results in stabilization of the metallic phase of VO2
micro/nanobeams down to 2 K, the lowest point we could reach in our measurement
setup. Based on observing the movement of the hydrogen diffusion front in
single crystalline VO2 beams, we estimate the diffusion constant for hydrogen
along the c-axis of the rutile phase to be 6.7 x 10^{-10} cm^2/s at
approximately 373 K, exceeding the value in isostructural TiO2 by ~ 38x.
Moreover, we find that the diffusion constant along the c-axis of the rutile
phase exceeds that along the equivalent a-axis of the monoclinic phase by at
least three orders of magnitude. This remarkable change in kinetics must
originate from the distortion of the "channels" when the unit cell doubles
along this direction upon cooling into the monoclinic structure. Ab initio
calculation results are in good agreement with the experimental trends in the
relative kinetics of the two phases. This raises the possibility of a
switchable membrane for hydrogen transport. | 1409.4661v1 |
2012-01-04 | Synthesis and physical properties of the new potassium iron selenide superconductor K0.80Fe1.76Se2 | In this article we review our studies of the K0.80Fe1.76Se2 superconductor,
with an attempt to elucidate the crystal growth details and basic physical
properties over a wide range of temperatures and applied magnetic field,
including anisotropic magnetic and electrical transport properties,
thermodynamic, London penetration depth, magneto-optical imaging and Mossbauer
measurements. We find that: (i) Single crystals of similar stoichiometry can be
grown both by furnace-cooled and decanted methods; (ii) Single crystalline
K0.80Fe1.76Se2 shows moderate anisotropy in both magnetic susceptibility and
electrical resistivity and a small modulation of stoichiometry of the crystal,
which gives rise to broadened transitions; (iii) The upper critical field,
Hc2(T) is ~ 55 T at 2 K for H||c, manifesting a temperature dependent
anisotropy that peaks near 3.6 at 27 K and drops to 2.5 by 18 K; (iv) Mossbauer
measurements reveal that the iron sublattice in K0.80Fe1.76Se2 clearly exhibits
magnetic order, probably of the first order, from well below Tc to its Neel
temperature of Tn = 532 +/- 2 K. It is very important to note that, although,
at first glance there is an apparent dilemma posed by these data: high Tc
superconductivity in a near insulating, large ordered moment material, analysis
indicates that the sample may well consist of two phases with the minority
superconducting phase (that does not exhibit magnetic order) being finely
distributed, but connected with in an antiferromagnetic, poorly conducting,
matrix, essentially making a superconducting aerogel. | 1201.0953v2 |
2019-04-24 | Role of Oxygen Adsorption in Nanocrystalline ZnO Interfacial Layers for Polymer-Fullerene Bulk Heterojunction Solar Cells | Colloidal zinc oxide (ZnO) nanoparticles are frequently used in the field of
organic photovoltaics for the realization of solution-producible,
electron-selective interfacial layers. Despite of the widespread use, there is
a lack of detailed investigations regarding the impact of structural properties
of the particles on the device performance. In this work, ZnO nanoparticles
with varying surface-area-to-volume ratio were synthesized and implemented into
polymer-fullerene bulk heterojunction solar cells with a gas-permeable top
electrode. By comparing the electrical characteristics before and after
encapsulation, it was found that the internal surface area of the ZnO layer
plays a crucial role under conditions where oxygen can penetrate the solar
cells. The adsorption of oxygen species at the nanoparticle surface causes band
bending and electron depletion next to the surface. Both effects result in the
formation of a barrier for electron injection and extraction at the ZnO/bulk
heterojunction interface and were more pronounced in case of small ZnO
nanocrystals (high surface-area-to-volume ratio). Different transport-related
phenomena in the presence of oxygen are discussed in detail, i.e., Ohmic
losses, expressed in terms of series resistance, as well as the occurrence of
space-charge-limited currents, related to charge accumulation in the
polymer-fullerene blend. Since absorption of UV light can cause desorption of
adsorbed oxygen species, the electrical properties depend also on the
illumination conditions. With the help of systematic investigations of the
current versus voltage characteristics of solar cells under different air
exposure and illumination conditions as well as studies of the
photoconductivity of pure ZnO nanoparticle layers, we gain detailed insight
into the role of the ZnO nanoparticle surface for the functionality of the
organic solar cells. | 1904.10916v1 |
2020-10-12 | Landau Quantization and Highly Mobile Fermions in an Insulator | In strongly correlated materials, quasiparticle excitations can carry
fractional quantum numbers. An intriguing possibility is the formation of
fractionalized, charge-neutral fermions, e.g., spinons and fermionic excitons,
that result in neutral Fermi surfaces and Landau quantization in an insulator.
While previous experiments in quantum spin liquids, topological Kondo
insulators, and quantum Hall systems have hinted at charge-neutral Fermi
surfaces, evidence for their existence remains far from conclusive. Here we
report experimental observation of Landau quantization in a two dimensional
(2D) insulator, i.e., monolayer tungsten ditelluride (WTe$_{2}$), a large gap
topological insulator. Using a detection scheme that avoids edge contributions,
we uncover strikingly large quantum oscillations in the monolayer insulator's
magnetoresistance, with an onset field as small as ~ 0.5 tesla. Despite the
huge resistance, the oscillation profile, which exhibits many periods, mimics
the Shubnikov-de Haas oscillations in metals. Remarkably, at ultralow
temperatures the observed oscillations evolve into discrete peaks near 1.6
tesla, above which the Landau quantized regime is fully developed. Such a low
onset field of quantization is comparable to high-mobility conventional
two-dimensional electron gases. Our experiments call for further investigation
of the highly unusual ground state of the WTe$_{2}$ monolayer. This includes
the influence of device components and the possible existence of mobile
fermions and charge-neutral Fermi surfaces inside its insulating gap. | 2010.05383v2 |
2021-07-29 | Shearing Mechanisms of Co-Precipitates in IN718 | The Ni-base superalloy 718 is the most widely used material for
turbomachinery in the aerospace industry and land-based turbines. Although the
relationship between processing and the resulting properties is well known, an
understanding of the specific deformation mechanisms activated across its
application temperature range is required to create more mechanistically
accurate property models. Direct atomic-scale imaging observations with high
angle annular dark-field scanning transmission electron microscopy,
complemented by phase-field modeling informed by generalized stacking fault
surface calculations using density functional theory, were employed to
understand the shear process of ${\gamma}''$ and ${\gamma}'/{\gamma}''$
co-precipitates after 1 \% macroscopic strain at lower temperature (ambient and
$427 {\deg}C$). Experimentally, intrinsic stacking faults were observed in the
${\gamma}''$, whereas the ${\gamma}'$ was found to exhibit anti-phase
boundaries or superlattice intrinsic stacking faults. Additionally, the
atomically flat ${\gamma}'/{\gamma}''$ interfaces in the co-precipitates were
found to exhibit offsets after shearing, which can be used as tracers for the
deformation events. Phase-field modeling shows that the developing
fault-structure is dependent on the direction of the Burgers vector of the $a/2
\langle110\rangle$ matrix dislocation (or dislocation group) due to the lower
crystal symmetry of the ${\gamma''}$ phase. The interplay between ${\gamma}'$
and ${\gamma}''$ phases results in unique deformation pathways of the
co-precipitate and increases the shear resistance. Consistent with the
experimental observations, the simulation results indicate that complex
shearing mechanisms are active in the low-temperature deformation regime and
that multiple $a/2 \langle110\rangle$ dislocations of non-parallel Burgers
vectors may be active on the same slip plane. | 2107.13840v1 |
2021-08-24 | In Situ Photothermal Response of Single Gold Nanoparticles Through Hyperspectral Imaging AntiStokes Thermometry | Several fields of applications require a reliable characterization of the
photothermal response and heat dissipation of nanoscopic systems, which remains
a challenging task both for modeling and experimental measurements. Here, we
present a new implementation of anti-Stokes thermometry that enables the in
situ photothermal characterization of individual nanoparticles (NPs) from a
single hyperspectral photoluminescence confocal image. The method is
label-free, applicable to any NP with detectable anti-Stokes emission, and does
not require any prior information about the NP itself or the surrounding media.
With it, we first studied the photothermal response of spherical gold NPs of
different sizes on glass substrates, immersed in water, and found that heat
dissipation is mainly dominated by the water for NPs larger than 50 nm. Then,
the role of the substrate was studied by comparing the photothermal response of
80 nm gold NPs on glass with sapphire and graphene, two materials with high
thermal conductivity. For a given irradiance level, the NPs reach temperatures
18% lower on sapphire and 24% higher on graphene than on bare glass. The fact
that the presence of a highly conductive material such as graphene leads to a
poorer thermal dissipation demonstrates that interfacial thermal resistances
play a very significant role in nanoscopic systems, and emphasize the need for
in situ experimental thermometry techniques. The developed method will allow
addressing several open questions about the role of temperature in
plasmon-assisted applications, especially ones where NPs of arbitrary shapes
are present in complex matrixes and environments. | 2108.10954v1 |
2022-01-10 | Superior enhancement in thermal conductivity of epoxy/graphene nanocomposites through use of dimethylformamide (DMF) relative to acetone as solvent | In this work, we demonstrate that use of dimethylformamide (DMF) as a solvent
leads to better dispersion of graphene nanoplatelets in epoxy matrix compared
to acetone solvent, in turn leading to higher thermal conductivity
epoxy-graphene nanocomposites. While role of solvents in enabling superior
mechanical properties has been addressed before, outlined study is the first to
address the effect of solvents on thermal conductivity enhancement and provides
novel pathways for achieving high thermal conductivity polymer composite
materials. Uniform dispersion of graphene nanoparticles into epoxy can improve
thermal contact with polymer leading to superior interface thermal conductance
between polymer matrix and graphene. Organic solvents are typically employed to
achieve efficient dispersion of graphene into the epoxy matrix. In this study,
we compare the effect of two organic solvents, dimethylformamide (DMF) and
acetone, in terms of their efficiency in dispersing graphene into the epoxy
matrix and their effect on enhancing thermal conductivity of the composite. We
find that polymer-graphene composites made with DMF solvent show 44% higher
thermal conductivity compared to those made using acetone at 7 weight% filler
composition. Laser scanning confocal microscopy (LSCM) imaging reveals that
graphene-epoxy composites, prepared using DMF as solvent, exhibit more uniform
dispersion of graphene-nanoplatelets compared to the case of acetone with
acetone-based samples exhibiting up to 211% larger graphene agglomerations.
Comparison with effective medium theory reveals an almost 35% lower interface
thermal resistance between graphene and epoxy for DMF relative to acetone
prepared composite. These results provide fundamentally new avenues to achieve
higher thermal conductivity graphene-epoxy composites, of key importance for a
wide range of thermal management technologies. | 2201.03527v2 |
2022-04-15 | Universal Non-Polar Switching in Carbon-doped Transition Metal Oxides (TMOs) and Post TMOs | Transition metal oxides (TMOs) and post-TMOs (PTMOs), when doped with Carbon,
show non-volatile current-voltage (I-V) characteristics, which are both
universal and repeatable. We have shown spectroscopic evidence of the
introduction of carbon-based impurity states inside the existing larger bandgap
effectively creating a smaller bandgap which we suggest could enable Mott-like
correlation effect. Our findings indicate new insights for yet to be understood
unipolar and nonpolar resistive switching in the TMOs and PTMOs. We have shown
that device switching is not thermal-energy dependent and have developed an
electronic-dominated switching model that allows for the extreme temperature
operation (from 1.5 K to 423 K) and state retention up to 673 K for a 1-hour
bake. Importantly, we have optimized the technology in an industrial process
and demonstrated integrated 1-transistor/1-resistor (1T1R) arrays up to 1 kbit
with 47 nm devices on 300 mm wafers for advanced node CMOS-compatible
correlated electron RAM (CeRAM). These devices are shown to operate with 2 ns
write pulses and retain the memory states up to 200 C for 24 hours. The
collection of attributes shown, including scalability to state-of-the-art
dimensions, non-volatile operation to extreme low and high temperatures, fast
write, and reduced stochasticity as compared to filamentary memories such as
ReRAMs show the potential for a highly capable two-terminal back-end-of-line
non-volatile memory. | 2204.07656v1 |
2022-07-18 | Room temperature spin-orbit torque efficiency in sputtered low-temperature superconductor delta-TaN | In the course of searching for promising topological materials for
applications in future topological electronics, we evaluated spin-orbit torques
(SOTs) in high-quality sputtered ${\delta}-$TaN/Co20Fe60B20 devices through
spin-torque ferromagnetic resonance ST-FMR and spin pumping measurements. From
the ST-FMR characterization we observed a significant linewidth modulation in
the magnetic Co20Fe60B20 layer attributed to the charge-to-spin conversion
generated from the ${\delta}-$TaN layer. Remarkably, the spin-torque efficiency
determined from ST-FMR and spin pumping measurements is as large as ${\Theta}
=$ 0.034 and 0.031, respectively. These values are over two times larger than
for ${\alpha}-$Ta, but almost five times lower than for ${\beta}-$Ta, which can
be attributed to the low room temperature electrical resistivity $\sim
74{\mu}{\Omega}$ cm in ${\delta}-$TaN. A large spin diffusion length of at
least $\sim8$ nm is estimated, which is comparable to the spin diffusion length
in pure Ta. Comprehensive experimental analysis, together with density
functional theory calculations, indicates that the origin of the pronounced SOT
effect in ${\delta}-$TaN can be mostly related to a significant contribution
from the Berry curvature associated with the presence of a topically nontrivial
electronic band structure in the vicinity of the Fermi level (EF). Through
additional detailed theoretical analysis, we also found that an isostructural
allotrope of the superconducting ${\delta}-$TaN phase, the simple hexagonal
structure, ${\theta}-$TaN, has larger Berry curvature, and that, together with
expected reasonable charge conductivity, it can also be a promising candidate
for exploring a generation of spin-orbit torque magnetic random access memory
as cheap, temperature stable, and highly efficient spin current sources. | 2207.08872v2 |
2023-03-30 | Observation of non-superconducting phase changes in LuH$_{2\pm\text{x}}$N$_y$ | The recent report of near-ambient superconductivity in nitrogen doped
lutetium hydride has triggered a worldwide fanaticism and raised major
questions about the latest claims. An intriguing phenomenon of color changes in
pressurized samples from blue to pink to red was observed and correlated with
the claimed superconducting transition, but the origin and underlying physics
of these color changes have yet to be elucidated. Here we report synthesis and
characterization of high-purity nitrogen doped lutetium hydride
LuH$_{2\pm\text{x}}$N$_y$ with the same structure and composition as in the
main phase of near-ambient superconductor1. We find a new purple phase of
LuH$_{2\pm\text{x}}$N$_y$ between blue and pink phase, and reveal that the
sample color changes likely stem from pressure-driven redistribution of
nitrogen and its interaction with the LuH$_2$ framework. No superconducting
transition is found in all blue, purple, pink and red phases at temperatures
1.8-300 K and pressures 0-30 GPa. Instead, we identify a notable
temperature-induced resistance anomaly of structural and/or electronic origin
in LuH$_{2\pm\text{x}}$N$_y$, which is most pronounced in the pink phase and
may have been erroneously interpreted as a sign of superconducting transition.
This work establishes key benchmarks for nitrogen doped lutetium hydrides,
allowing an in-depth understanding of the novel pressure-induced phase changes. | 2303.17587v2 |
2023-10-02 | Resistless EUV lithography: photon-induced oxide patterning on silicon | In this work, we show the feasibility of extreme ultraviolet (EUV) patterning
on an HF-treated Si(100) surface in the absence of a photoresist. EUV
lithography is the leading lithography technique in semiconductor manufacturing
due to its high resolution and throughput, but future progress in resolution
can be hampered because of the inherent limitations of the resists. We show
that EUV photons can induce surface reactions on a partially H-terminated Si
surface and assist the growth of an oxide layer, which serves as an etch mask.
This mechanism is different from the H-desorption in scanning tunneling
microscopy-based lithography. We achieve SiO2/Si gratings with 75 nm half-pitch
and 31 nm height, demonstrating the efficacy of the method and the feasibility
of patterning with EUV lithography without the use of a photoresist. Further
development of the resistless EUV lithography method can be a viable approach
to nm-scale lithography by overcoming the inherent resolution and roughness
limitations of photoresist materials. | 2310.01268v1 |
2023-10-31 | Signature of Topological Semimetal in Harmonic-honeycomb ReO3 | Transition-metal honeycomb compounds are capturing scientific attention due
to their distinctive electronic configurations, underscored by the
triangular-lattice spin-orbit coupling and competition between multiple
interactions, paving the way for potential manifestations of phenomena such as
Dirac semimetal, superconductivity, and quantum spin liquid states. These
compounds can undergo discernible pressure-induced alterations in their
crystallographic and electronic paradigms, as exemplified by our high-pressure
(HP) synthesis and exploration of the honeycomb polymorph of ReO3 (P6322). This
HP-P6322 polymorph bears a phase transition from P6322 to P63/mmc upon cooling
around Tp = 250 K, as evidenced by the evolution of temperature-dependent
magnetization (M-T curves), cell dimension, and conductivity initiated by an
inherent bifurcation of the oxygen position in the ab plane. Insightful
analysis of its band structure positions suggests this HP-P6322 polymorph being
a plausible candidate for Dirac semimetal properties. This phase transition
evokes anomalies in the temperature-dependent variation of paramagnetism
(non-linearity) and a crossover from semiconductor to temperature-independent
metal, showing a temperature independent conductivity behavior below ~200 K.
Under increasing external pressure, both the Tp and resistance of this
HP-polymorph is slightly magnetic-field dependent and undergo a "V"-style
evolution (decreasing and then increasing) before becoming pressure independent
up to 20.2 GPa. Theoretical calculations pinpoint this anionic disorder as a
probable catalyst for the decrement in the conductive efficiency and muted
temperature-dependent conductivity response. | 2310.20341v2 |
2024-01-13 | Reliable operation of Cr$_2$O$_3$:Mg/ $β$-Ga$_2$O$_3$ p-n heterojunction diodes at 600$^\circ$C | $\beta$-Ga$_2$O$_3$-based semiconductor heterojunctions have recently
demonstrated improved performance at high voltages and elevated temperatures
and are thus promising for applications in power electronic devices and
harsh-environment sensors. However, the long-term reliability of these
ultra-wide band gap (UWBG) semiconductor devices remains barely addressed and
may be strongly influenced by chemical reactions at the p-n heterojunction
interface. Here, we experimentally demonstrate operation and evaluate the
reliability of Cr$_2$O$_3$:Mg/ $\beta$-Ga$_2$O$_3$ p-n heterojunction diodes at
during extended operation at 600$^\circ$C, as well as after 30 repeated cycles
between 25-550$^\circ$C. The calculated pO2-temperature phase stability diagram
of the Ga-Cr-O material system predicts that Ga$_2$O$_3$ and Cr$_2$O$_3$ should
remain thermodynamically stable in contact with each other over a wide range of
oxygen pressures and operating temperatures. The fabricated Cr$_2$O$_3$:Mg /
$\beta$-Ga$_2$O$_3$ p-n heterojunction diodes show room-temperature on/off
ratios >10$^4$ at $\pm$5V and a breakdown voltage (V$_{Br}$) of -390V. The
leakage current increases with increasing temperature up to 600$^\circ$C, which
is attributed to Poole-Frenkel emission with a trap barrier height of 0.19 eV.
Over the course of a 140-hour thermal soak at 600$^\circ$C, both the device
turn-on voltage and on-state resistance increase from 1.08V and 5.34
m$\Omega$-cm$^2$ to 1.59V and 7.1 m$\Omega$-cm$^2$ respectively. This increase
is attributed to the accumulation of Mg and MgO at the Cr$_2$O$_3$/Ga$_2$O$_3$
interface as observed from TOF-SIMS analysis. These findings inform future
design strategies of UWBG semiconductor devices for harsh environment operation
and underscore the need for further reliability assessments for
$\beta$-Ga$_2$O$_3$ based devices. | 2401.07166v1 |
2024-02-09 | BaMn$_2$P$_2$: Highest magnetic ordering temperature 122-pnictide compound | We report the growth of high-quality single crystals of ThCr$_2$Si$_2$-type
tetragonal BaMn$_2$P$_2$ and investigation of its structural, electrical
transport, thermal and magnetic properties. Our results of basal plane
electrical resistivity and heat capacity measurements show that the compound
has an insulating ground state with a small band gap. Anisotropic
susceptibility $\chi_{ab,c}(T)$ data infer a collinear local-moment N\'eel-type
antiferromagnetic (AFM) ground state below the ordering temperature $T_{\rm N}
= 795(15)$~K, which is highest among all the ThCr$_2$Si$_2$- and
CaAl$_2$Si$_2$-type 122-pnictide compounds reported so far suggesting that the
strength of magnetic exchange interactions is strongest in this material. The
magnetic transition temperatures of BaMn$_2$$Pn_{2}$ ($Pn$ = P, As, Sb, Bi)
compounds exhibit a monotonic decrease with the increase of tetragonal unit
cell parameters $a$ and $c$, suggesting a strong dependence of the strength of
the decisive magnetic exchange interactions on the separation between the
localized spins residing on the Mn-ions. The observed monotonic increase of
both $\chi_{ab}$ and $\chi_{c}$ for $T > T_{\rm N}$ suggests that short-range
dynamic quasi-two dimensional AFM correlations persist above the $T_{\rm N}$ up
to the highest temperature of the measurements. The large $T_{\rm N}$ of
BaMn$_2$P$_2$ demands for systematic hole-doping studies on this material as
similar investigations on related BaMn$_2$As$_{2}$ with $T_{\rm N} = 618$~K
have led to the discovery of an outstanding ground state where AFM of localized
Mn-spins and itinerant half-metallic ferromagnetism with $T_{\rm c} \approx
100$~K originating from the doped holes coexist together. | 2402.06432v1 |
2016-07-07 | Temperature dependence of the electrical resistivity and the anisotropic magnetoresistance (AMR) of electrodeposited Ni Co alloys | The electrical resistivity and the anisotropic magnetoresistance (AMR) was
investigated for Ni Co alloys at and below room temperature. The Ni Co alloy
layers having a thickness of about 2 um were prepared by electrodeposition on
Si wafers with evaporated Cr and Cu underlayers. The alloy composition was
varied in the whole concentration range by varying the ratio of Ni sulfate and
Co sulfate in the electrolyte. The Ni Co alloy deposits were investigated first
in the as deposited state on the substrates and then, by mechanically stripping
them from the substrates, as self supporting layers both without and after
annealing. According to an X ray diffraction study, a strongly textured face
centered cubic (fcc) structure was formed in the as deposited state with an
average grain size of about 10 nm. Upon annealing, the crystal structure was
retained whereas the grain size increased by a factor of 3 to 5, depending on
alloy composition. The zero field resistivity decreased strongly by annealing
due to the increased grain size. The annealing hardly changed the AMR below 50
at.% Co but strongly decreased it above this concentration. The composition
dependence of the resistivity and the AMR of the annealed Ni Co alloy deposits
was in good quantitative agreement with the available literature data both at
13 K and at room temperature. Both transport parameters were found to exhibit a
pronounced maximum in the composition range between 20 and 30 at.% Co and the
data of the Ni Co alloys fit well to the limiting values of the pure component
metals (fcc Ni and fcc Co). The only theoretical calculation reported formerly
on fcc Ni Co alloys yielded at T=0K a resistivity value smaller by a factor of
5 and an AMR value larger by a factor of about 2 than the corresponding low
temperature experimental data, although the theoretical results properly
reproduced the composition dependence of both quantities. | 1607.01960v1 |
2012-06-07 | Resistive and magnetoresistive properties of CrO2 pressed powders with different types of inter-granular dielectric layers | Resistive, magnetoresistive and magnetic properties of four kinds of pressed
CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been
investigated. The particles in powders constituted of rounded particles
(diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm
and average length of 302 nm. All of the particles had a surface dielectric
shell of varying thickness and different types (such as oxyhydroxide -CrOOH or
chromium oxide Cr2O3). For all the samples at low temperatures we found
non-metallic temperature dependence of resistivity and giant negative
magnetoresistance (MR). The maximum value of MR at low temperatures (T \approx
5 K) is \approx 37% in relatively small fields (0.5 T). At higher temperatures
there was a rapid decrease of MR (up to \approx 1% / T at T \approx 200 K). The
main objective of this work was studying the influence of properties and
thickness of the intergranular dielectric layers, as well as CrO2 particle
shape, on the magnitude of the tunneling resistance and MR of the pressed
powder. The new results obtained in this study include: (1) detection at low
temperatures in powders with needle-like particles a new type of MR hysteresis,
and nonmonotonic MR behaviour with increasing magnetic field (absolute value of
the MR at first grows rather rapidly with the field, and then begins
diminishing markedly, forming a maximum), and (2) detection of non-monotonic
temperature dependence, where - a field in which the resistance in a magnetic
field has a maximum, as well as finding discrepancies in values of and
coercivity fields, (3) detection of the anisotropy of MR, depending on the
relative orientation of the transport current and the magnetic field, (4) a new
method of synthesis, to regulate the thickness of dielectric coating. | 1206.1533v1 |
2021-07-23 | Modeling the dynamical behavior of memristive {NiTi} alloy at constant stress for time-varying electric current input signals | The dynamical electric behavior of a NiTi smart alloy thin filament when
driven by time varying current pulses is studied by a structure-based
phenomenological model that includes rate-based effects. The simulation model
relates the alloy's electrical resistivity to the relative proportions of the
three main structural phases namely Martensite, Austenite and R-phase,
experimentally known to exist in NiTi alloy lattice structure. The relative
proportions of the phases depend on temperature and applied stress. Temperature
varies due to the self-heating of the filament by the Joule effect when a
current pulse passes and also due to convective/radiative interchange with the
ambient. The temperature variation with time causes structural phase
transitions, which result in abrupt changes in the sample resistivity as the
proportions of each lattice phase vary. The model is described by a system of
four 1st-order nonlinear differential-algebraic equations yielding the temporal
evolution of resistivity and output voltage across the filament for any given
time-varying input current pulse. The model corresponds to a 4th-order extended
memristor, described by four state variables, which are the proportions of each
of the three NiTi lattice phases and temperature. Simulations are
experimentally verified by comparing to measurements obtained for samples
self-heated by triangular current input waveforms as well as for passively
samples with no current input. Numerical results reproduce very well
measurements of resistance vs. temperature at equilibrium as well as the full
dynamics of experimentally observed I-V characteristic curves and resistance
vs. driving current for time-varying current input waveforms of a wide range of
frequencies (0.01-10~Hz). | 2107.11060v1 |
2024-05-06 | Speckle pattern analysis of PVK:rGO composite based memristor device | The memristors are expected to be fundamental devices for neuromorphic
systems and switching applications. For example, the device made of a
sandwiched layer of poly(N-vinylcarbazole) and reduced graphene composite
between asymmetric electrodes (ITO/PVK:rGO/Al) exhibits bistable resistive
switching behavior. Depending on the resistance state of the (ON-state or
OFF-state) at a constant applied voltage, it may show two different
resistivities. The performance of the memristor can be optimized by controlling
the doping amount of graphene oxide in the PVK polymer. To assess the
performance of the device, when it switches between ON and OFF states, optical
characterization approaches are highly promising due to their non-destructive
and remote nature. Here, we characterize the memristor device by the use of
speckle pattern (SP) analysis. The speckle pattern is the interference of
multiple light waves with random relative phases, which is generated via
different mechanisms such as scattering from diffusive materials. Therefore,
SPs can be used to investigate such samples as they include a huge amount of
information to be statistically elaborated. The experimental paradigm includes
\textit{in situ} acquisition of SPs of the PVK:rGO in different states followed
by statistical post-processing toward examining its conduction mechanism. The
variations in these statistical parameters are attributed to the resistance
state of the PVK:rGO samples under the applied voltage with regard to the
physical switching mechanism of the device. The resistance/conduction state, in
turn, depends on the activity and properties of PVK:rGO memristors as well as
the additional non-uniformities induced through the variations of density of
carriers. The present optical methodology can be potentially served as a
bench-top device for characterization purposes of similar devices while they
are operating. | 2405.03369v1 |
2017-10-09 | Superconductivity in the Nb-Ru-Ge $σ$-Phase | We show that the previously unreported ternary $\sigma$-phase material
Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is a superconductor with a critical temperature
of 2.2 K. Temperature-dependent magnetic susceptibility, resistance, and
specific heat measurements were used to characterize the superconducting
transition. The Sommerfeld constant $\gamma$ for
Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ is 91 mJ mol-f.u.$^{-1}$K$^{-2}$ and the
specific heat anomaly at the superconducting transition,
$\Delta$C/$\gamma$T$_c$, is approximately 1.38. The zero-temperature upper
critical field ($\mu_0$H$_{c2}$(0)) was estimated to be 2 T by resistance data.
Field-dependent magnetization data analysis estimated $\mu_0$H$_{c1}$(0) to be
5.5 mT. Thus, the characterization shows Nb$_{20.4}$Ru$_{5.7}$Ge$_{3.9}$ to be
a type II BCS superconductor. This material appears to be the first reported
ternary phase in the Nb-Ru-Ge system, and the fact that there are no previously
reported binary Nb-Ru, Nb-Ge, or Ru-Ge $\sigma$-phases shows that all three
elements are necessary to stabilize the material. A $\sigma$-phase in the
Ta-Ru-Ge system was synthesized but did not display superconductivity above 1.7
K, which suggests that electron count cannot govern the superconductivity
observed. Preliminary characterization of a possible superconducting
$\sigma$-phase in the Nb-Ru-Ga system is also reported. | 1710.03347v1 |
2022-02-28 | Colloquium: Quantum anomalous Hall effect | The quantum Hall (QH) effect, quantized Hall resistance combined with zero
longitudinal resistance, is the characteristic experimental fingerprint of
Chern insulators - topologically non-trivial states of two-dimensional matter
with broken time-reversal symmetry. In Chern insulators, non-trivial bulk band
topology is expressed by chiral states that carry current along sample edges
without dissipation. The quantum anomalous Hall (QAH) effect refers to QH
effects that occur in the absence of external magnetic fields due to
spontaneously broken time-reversal symmetry. The QAH effect has now been
realized in four different classes of two-dimensional materials: (i) thin films
of magnetically (Cr- and/or V-) doped topological insulators in the (Bi,Sb)2Te3
family, (ii) thin films of the intrinsic magnetic topological insulator
MnBi2Te4, (iii) moir\'e materials formed from graphene, and (iv ) moir\'e
materials formed from transition metal dichalcogenides. In this Article, we
review the physical mechanisms responsible for each class of QAH insulator,
highlighting both differences and commonalities, and comment on potential
applications of the QAH effect. | 2202.13902v4 |
2018-08-12 | Low Temperature Specific Heat of Doped SrTiO$_3$: Doping Dependence of the Effective Mass and Kadowaki-Woods Scaling Violation | We report wide-doping-range ($8 \times 10^{17}$ to $4 \times 10^{20}$
cm$^{-3}$ Hall electron density) low temperature specific heat measurements on
single crystal SrTiO$_3$:Nb, correlated with electronic transport data and
tight-binding modeling. Lattice dynamic contributions to specific heat are
shown to be well understood, albeit with unusual sensitivity to doping, likely
related to the behavior of soft modes. Electronic contributions to specific
heat provide effective masses that increase substantially, from $1.8$ to $4.8
m_e$, across the two SrTiO$_3$ Lifshitz transitions. It is shown that this
behavior can be quantitatively reconciled with quantum oscillation data and
calculated band structure, establishing a remarkably doping-independent mass
enhancement factor of $2.0$. Most importantly, with the doping-dependent $T^2$
resistivity prefactor and Sommerfeld coefficient known, Kadowaki-Woods scaling
has been tested over the entire doping range probed. Despite classic Fermi
liquid behavior in electronic specific heat, standard Kadowaki-Woods scaling is
dramatically violated, highlighting the need for new theoretical descriptions
of $T^2$ resistivity in SrTiO$_3$. | 1808.03909v2 |
2015-06-07 | Temperature dependent three-dimensional anisotropy of the magnetoresistance in WTe$_2$ | Extremely large magnetoresistance (XMR) was recently discovered in WTe$_2$,
triggering extensive research on this material regarding the XMR origin. Since
WTe$_2$ is a layered compound with metal layers sandwiched between adjacent
insulating chalcogenide layers, this material has been considered to be
electronically two-dimensional (2D). Here we report two new findings on
WTe$_2$: (1) WTe$_2$ is electronically 3D with a mass anisotropy as low as $2$,
as revealed by the 3D scaling behavior of the resistance
$R(H,\theta)=R(\varepsilon_\theta H)$ with $\varepsilon_\theta =(\cos^2 \theta
+ \gamma^{-2}\sin^2 \theta)^{1/2}$, $\theta$ being the magnetic field angle
with respect to c-axis of the crystal and $\gamma$ being the mass anisotropy;
(2) the mass anisotropy $\gamma$ varies with temperature and follows the
magnetoresistance behavior of the Fermi liquid state. Our results not only
provide a general scaling approach for the anisotropic magnetoresistance but
also are crucial for correctly understanding the electronic properties of
WTe$_2$, including the origin of the remarkable 'turn-on' behavior in the
resistance versus temperature curve, which has been widely observed in many
materials and assumed to be a metal-insulator transition. | 1506.02214v2 |
2019-10-09 | Preferential out-of-plane conduction and quasi-one-dimensional electronic states in layered 1T-TaS2 | Layered transition metal dichalcogenides (TMDs) are commonly classified as
quasi-two-dimensional materials, meaning that their electronic structure
closely resembles that of an individual layer, which results in resistivity
anisotropies reaching thousands. Here, we show that this rule does not hold for
1T-TaS2 - a compound with the richest phase diagram among TMDs. While the onset
of charge density wave order makes the in-plane conduction non-metallic, we
reveal that the out-of-plane charge transport is metallic and the resistivity
anisotropy is close to one. We support our findings with ab-initio calculations
predicting a pronounced quasi-one-dimensional character of the electronic
structure. Consequently, we interpret the highly debated metal-insulator
transition in 1T-TaS2 as a quasi-one-dimensional instability, contrary to the
long-standing Mott localisation picture. In a broader context, these findings
are relevant for the newly born field of van der Waals heterostructures, where
tuning interlayer interactions (e.g. by twist, strain, intercalation, etc.)
leads to new emergent phenomena. | 1910.03817v2 |
2019-10-23 | Complex Transport and Magnetism in Inhomogeneous Mixed Valence Ce$_3$Ir$_4$Ge$_{13}$ | We report the discovery of Ce$_3$Ir$_4$Ge$_{13}$, a new Remeika phase
compound with a complex array of structural, electronic, and magnetic
properties. Our single crystal x-ray diffraction measurements show that
Ce$_3$Ir$_4$Ge$_{13}$ forms in the tetragonally distorted $I4_1/amd$ space
group. The electrical resistivity is almost temperature independent over three
decades in temperature, from 0.4 K to 400 K, while the Hall coefficient
measurements are consistent with a low-carrier semimetal. Magnetic
susceptibility measurements reveal an effective moment of
$\mu^{\text{exp}}_{\text{eff}} = 1.87 \mu_B$/Ce, suggesting that this material
has a mixture of magnetic Ce$^{3+}$ and non-magnetic Ce$^{4+}$. Upon cooling,
Ce$_3$Ir$_4$Ge$_{13}$ first enters a short range magnetically ordered state
below $T_{\text{SRO}}=10$ K, marked by a deviation from Curie-Weiss behavior in
susceptibility and a broad field-independent heat capacity anomaly. At lower
temperatures, we observe a second, sharper peak in the heat capacity at $T^* =
1.7$ K, concurrent with a splitting of the field-cooled and zero-field-cooled
susceptibilities. A small resistivity drop at $T^*$ suggests a loss of spin
disorder scattering consistent with a magnetic ordering or spin freezing
transition. Ce$_3$Ir$_4$Ge$_{13}$ is therefore a rare example of an
inhomogeneous mixed valence compound with a complex array of thermodynamic and
transport properties. | 1910.10764v1 |
2020-05-01 | Characterisation of Cryogenic Material Properties of 3D-Printed Superconducting Niobium using a 3D Lumped Element Microwave Cavity | We present an experimental characterisation of the electrical properties of
3D-printed Niobium. The study was performed by inserting a 3D-printed Nb post
inside an Aluminium cylindrical cavity, forming a 3D lumped element re-entrant
microwave cavity resonator. The resonator was cooled to temperatures below the
critical temperature of Niobium (9.25K) and then Aluminium (1.2K), while
measuring the quality factors of the electromagnetic resonances. This was then
compared with finite element analysis of the cavity and a measurement of the
same cavity with an Aluminium post of similar dimensions and frequency, to
extract the surface resistance of the Niobium post. The 3D-printed Niobium
exhibited a transition to the superconducting state at a similar temperature to
the regular Niobium, as well as a surface resistance of $3.1\times10^{-4}$
$\Omega$. This value was comparable to many samples of traditionally machined
Niobium previously studied without specialised surface treatment. Furthermore,
this study demonstrates a simple new method for characterizing the material
properties of a relatively small and geometrically simple sample of
superconductor, which could be easily applied to other materials, particularly
3D-printed materials. Further research and development in additive
manufacturing may see the application of 3D-printed Niobium in not only
superconducting cavity designs, but in the innovative technology of the future. | 2005.00271v1 |
2021-09-30 | Spin-flip-driven giant magneto-transport in A-type antiferromagnet NaCrTe2 | For anisotropic magneto-resistance (AMR) effect, its value synergistically
depends on the magnitudes of magneto-resistance (MR) and magneto-crystalline
anisotropy energy (MAE) simultaneously. In a magnetic material, the concurrence
of gigantic AMR and MR signals is rather difficult due to weak spin-lattice
coupling and small MAE. Here we report the considerable magneto-transport
effect in layered A-type antiferromagnetic (AFM) NaCrTe2 by realigning the spin
configurations. By applying H, the antiparallel spins of adjacent layers are
flipped to ferromagnetic (FM) coupling either Ising-type along c-axis or
XY-type within ab-plane. Theoretical calculations reveal that the energy
bandgap narrows from 0.39 eV to 0.11 eV, accompanying a transition from
semiconductor (high-R state) and half-semiconductor (low-R state),
respectively. Thus, gigantic negative MR ratio of -90% is obtained at 10 K.
More importantly, the decrement of R along H//c is far quicker than that of
H//ab because the MAE of Ising-FM state is 1017 {\mu}eV/Cr3+ lower than that of
XY-FM. The distinct trends result in the AMR ratio of 732% at 10 K, which is
the record value to our best knowledge. These findings unravel the intrinsic
origin of magneto in NaCrTe2 and will stimulate us to exploring the H-sensitive
transport property in more AFM materials. | 2109.14923v1 |
2021-11-12 | Recrystallization and Interdiffusion Processes in Laser-Annealed Strain-Relaxed Metastable Ge$_{0.89}$Sn0$_{.11}$ | The prospect of GeSn semiconductors for silicon-integrated infrared
optoelectronics brings new challenges related to the metastability of this
class of materials. As a matter of fact, maintaining a reduced thermal budget
throughout all processing steps of GeSn devices is essential to avoid possible
material degradation. This constraint is exacerbated by the need for higher Sn
contents along with an enhanced strain relaxation to achieve efficient
mid-infrared devices. Herein, as a low thermal budget solution for post-epitaxy
processing, we elucidate the effects of laser thermal annealing (LTA) on
strain-relaxed Ge$_{0.89}$Sn0$_{.11}$ layers and Ni-Ge$_{0.89}$Sn0$_{.11}$
contacts. Key diffusion and recrystallization processes are proposed and
discussed in the light of systematic microstructural studies. LTA treatment at
a fluence of 0.40 J/cm2 results in a 200-300 nm-thick layer where Sn atoms
segregate toward the surface and in the formation of Sn-rich columnar
structures in the LTA-affected region. These structures are reminiscent to
those observed in the dislocation-assisted pipe-diffusion mechanism, while the
buried GeSn layers remain intact. Moreover, by tailoring the LTA fluence, the
contact resistance can be reduced without triggering phase separation across
the whole GeSn multi-layer stacking. Indeed, a one order of magnitude decrease
in the Ni-based specific contact resistance was obtained at the highest LTA
fluence, thus confirming the potential of this method for the functionalization
of direct bandgap GeSn materials. | 2111.06788v1 |
2022-04-18 | Material properties of a low contraction and resistivity silicon-aluminum composite for cryogenic detectors | We report on the cryogenic properties of a low-contraction silicon-aluminum
composite, namely Japan Fine Ceramics SA001, to use as a packaging structure
for cryogenic silicon devices. SA001 is a silicon--aluminum composite material
(75% silicon by volume) and has a low thermal expansion coefficient ($\sim$1/3
that of aluminum). The superconducting transition temperature of SA001 is
measured to be 1.18 K, which is in agreement with that of pure aluminum, and is
thus available as a superconducting magnetic shield material. The residual
resistivity of SA001 is 0.065 $\mathrm{\mu \Omega m}$, which is considerably
lower than an equivalent silicon--aluminum composite material. The measured
thermal contraction of SA001 immersed in liquid nitrogen is
$\frac{L_{293\mathrm{K}}-L_{77\mathrm{K}}}{L_{293\mathrm{K}}}=0.12$%, which is
consistent with the expected rate obtained from the volume-weighted mean of the
contractions of silicon and aluminum. The machinability of SA001 is also
confirmed with a demonstrated fabrication of a conical feedhorn array, with a
wall thickness of 100 $\mathrm{\mu m}$. These properties are suitable for
packaging applications for large-format superconducting detector devices. | 2204.08111v2 |
2022-06-07 | Phase-field modelling and analysis of rate-dependent fracture phenomena at finite deformation | Fracture of materials with rate-dependent mechanical behaviour, e.g.
polymers, is a highly complex process. For an adequate modelling, the coupling
between rate-dependent stiffness, dissipative mechanisms present in the bulk
material and crack driving force has to be accounted for in an appropriate
manner. In addition, the fracture toughness, i.e. the resistance against crack
propagation, can depend on rate of deformation. In this contribution, an
energetic phase-field model of rate-dependent fracture at finite deformation is
presented. For the deformation of the bulk material, a formulation of finite
viscoelasticity is adopted with strain energy densities of Ogden type assumed.
The unified formulation allows to study different expressions for the fracture
driving force. Furthermore, a possibly rate-dependent toughness is
incorporated. The model is calibrated using experimental results from the
literature for an elastomer and predictions are qualitatively and
quantitatively validated against experimental data. Predictive capabilities of
the model are studied for monotonic loads as well as creep fracture.
Symmetrical and asymmetrical crack patterns are discussed and the influence of
a dissipative fracture driving force contribution is analysed. It is shown
that, different from ductile fracture of metals, such a driving force is not
required for an adequate simulation of experimentally observable crack paths
and is not favourable for the description of failure in viscoelastic rubbery
polymers. Furthermore, the influence of a rate-dependent toughness is discussed
by means of a numerical study. From a phenomenological point of view, it is
demonstrated that rate-dependency of resistance against crack propagation can
be an essential ingredient for the model when specific effects such as
rate-dependent brittle-to-ductile transitions shall be described. | 2206.03460v1 |
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