publicationDate stringlengths 10 10 | title stringlengths 17 233 | abstract stringlengths 20 3.22k | id stringlengths 9 12 |
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2007-09-12 | Reducing the Possibility of Subjective Error in the Determination of the Structure-Function-Based Effective Thermal Conductivity of Boards | The thermal response function given to a unit-step dissipation accurately
characterizes the thermal system. Instead of the thermal response function the
so-called structure function describing three-dimensional as the equivalent
model of one-dimensional heat-spreading, created from the thermal response
function with the help of complex mathematical procedures, is often used. Using
the structure function the partial thermal capacity and partial heat resistance
of certain elements of the thermal system can be identified. If the geometrical
measurements of a thermal system of simple geometry and homogeneous material
(such as a homogeneous rod or board, etc.) are known, the coefficient of
thermal conductivity of the material in question can be determined from two
points of the structure function at 2-5 per cent of accuracy. In this paper a
method is presented which applies a wide range/section instead of two points of
the cumulative structure function to determine the thermal coefficient, thus
reducing the subjective error deriving from the selection of the two points.
The above method is presented and illustrated in simulated as well as measured
thermal transient responses. | 0709.1863v1 |
2008-01-22 | Phase coherent transport in (Ga,Mn)As | Quantum interference effects and resulting quantum corrections of the
conductivity have been intensively studied in disordered conductors over the
last decades. The knowledge of phase coherence lengths and underlying dephasing
mechanisms are crucial to understand quantum corrections to the resistivity in
the different material systems. Due to the internal magnetic field and the
associated breaking of time-reversal symmetry quantum interference effects in
ferromagnetic materials have been scarcely explored. Below we describe the
investigation of phase coherent transport phenomena in the newly discovered
ferromagnetic semiconductor (Ga,Mn)As. We explore universal conductance
fluctuations in mesoscopic (Ga,Mn)As wires and rings, the Aharonov-Bohm effect
in nanoscale rings and weak localization in arrays of wires, made of the
ferromagnetic semiconductor material. The experiments allow to probe the phase
coherence length L_phi and the spin flip length L_SO as well as the temperature
dependence of dephasing. | 0801.3363v1 |
2008-08-03 | Use of a nanoindentation fatigue test to characterize the ductile-brittle transition | When considering grinding of minerals, scaling effect induces competition
between plastic deformation and fracture in brittle solids. The competition can
be sketched by a critical size of the material, which characterizes the
ductile-brittle transition. A first approach using Vickers indentation gives a
good approximation of the critical size through an extrapolation from the
macroscopic to the microscopic scales. Nanoindentation tests confirm this
experimental value. According to the grain size compared to the indent size, it
can reasonably be said that the mode of damage is deformation-induced
intragranular microfracture. This technique also enables to perform cyclic
indentations to examine calcite fatigue resistance. Repeated loadings with a
nanoindenter on CaCO3 polycrystalline samples produce cumulative mechanical
damage. It is also shown that the transition between ductile and brittle
behaviour depends on the number of indentation cycles. The ductile domain can
be reduced when the material is exposed to a fatigue process. | 0808.0329v1 |
2008-10-02 | Metallic conduction at organic charge-transfer interfaces | The electronic properties of interfaces between two different solids can
differ strikingly from those of the constituent materials. For instance,
metallic conductivity, and even superconductivity, have been recently
discovered at interfaces formed by insulating transition metal oxides. Here we
investigate interfaces between crystals of conjugated organic molecules, which
are large gap undoped semiconductors, i.e. essentially insulators. We find that
highly conducting interfaces can be realized with resistivity ranging from 1 to
30 kOhm square, and that, for the best samples, the temperature dependence of
the conductivity is metallic. The observed electrical conduction originates
from a large transfer of charge between the two crystals that takes place at
the interface, on a molecular scale. As the interface assembly process is
simple and can be applied to crystals of virtually any conjugated molecule, the
conducting interfaces described here represent the first examples of a new
class of electronic systems. | 0810.0361v1 |
2009-11-13 | Internal relaxation time in immersed particulate materials | We study the dynamics of the solid to liquid transition for a model material
made of elastic particles immersed in a viscous fluid. The interaction between
particle surfaces includes their viscous lubrication, a sharp repulsion when
they get closer than a tuned steric length and their elastic deflection induced
by those two forces. We use Soft Dynamics to simulate the dynamics of this
material when it experiences a step increase in the shear stress and a constant
normal stress. We observe a long creep phase before a substantial flow
eventually establishes. We find that the typical creep time relies on an
internal relaxation process, namely the separation of two particles driven by
the applied stress and resisted by the viscous friction. This mechanism should
be relevant for granular pastes, living cells, emulsions and wet foams. | 0911.2531v1 |
2010-02-18 | The influence of Ga$^+$-irradiation on the transport properties of mesoscopic conducting thin films | We studied the influence of 30keV Ga$^+$-ions -- commonly used in focused ion
beam (FIB) devices -- on the transport properties of thin crystalline graphite
flake, La$_{0.7}$Ca$_{0.3}$MnO$_3$ and Co thin films. The changes of the
electrical resistance were measured in-situ during irradiation and also the
temperature and magnetic field dependence before and after irradiation. Our
results show that the transport properties of these materials strongly change
at Ga$^+$ fluences much below those used for patterning and ion beam induced
deposition (IBID), limiting seriously the use of FIB when the intrinsic
properties of the materials of interest are of importance. We present a method
that can be used to protect the sample as well as to produce selectively
irradiation-induced changes. | 1002.3565v1 |
2010-09-24 | Photoemission induced gating of topological insulator | The recently discovered topological insulators exhibit topologically
protected metallic surface states which are interesting from the fundamental
point of view and could be useful for various applications if an appropriate
electronic gating can be realized. Our photoemission study of Cu intercalated
Bi2Se3 shows that the surface states occupancy in this material can be tuned by
changing the photon energy and understood as a photoemission induced gating
effect. Our finding provides an effective tool to investigate the new physics
coming from the topological surface states and suggests the intercalation as a
recipe for synthesis of the material suitable for electronic applications. | 1009.4855v2 |
2011-08-23 | Single-Crystal and Powder Neutron Diffraction Study of FeXMn1-XS Solid Solutions | FeXMn1-XS (0 <x< 0.3) synthesized on the basis of {\alpha}-MnS are the novel
Mott-type substances with the rock salt structure. Neutron diffraction study
shows that the shift of the Neel temperature of these materials from 150 (x =
0) to 200 K (x = 0.29) under the action of chemical pressure (x) is accompanied
by a decrease in the cubic NaCl lattice parameters. The structural transition
with a change in crystal symmetry and a decrease in resistance before the
magnetic transition at x = 0.25 is found. Therefore, FeXMn1-XS are interesting
materials for both fundamental study of the interrelation between the magnetic,
electrical, and structural properties in systems with the strong electron
correlations of a MnO-type and application. | 1108.4537v2 |
2012-02-11 | Temperature dependence of the conductivity of graphene on boron nitride | The substrate material of monolayer graphene influences the charge carrier
mobility by various mechanisms. At room temperature, the scattering of
conduction electrons by phonon modes localized at the substrate surface can
severely limit the charge carrier mobility. We here show that for substrates
made of the piezoelectric hexagonal boron nitride (hBN), in comparison to the
widely used SiO$_2$, this mechanism of remote phonon scattering is --at room
temperature-- weaker by almost an order of magnitude, and causes a resistivity
of approximately 3\,$\Omega$. This makes hBN an excellent candidate material
for future graphene based electronic devices operating at room temperature. | 1202.2440v2 |
2012-10-15 | Theory of Charge Order and Heavy-Electron Formation in the Mixed-Valence Compound KNi$_2$Se$_2$ | The material KNi$_2$Se$_2$ has recently been shown to possess a number of
striking physical properties, many of which are apparently related to the mixed
valency of this system, in which there is on average one quasi-localized
electron per every two Ni sites. Remarkably, the material exhibits a charge
density wave (CDW) phase that disappears upon cooling, giving way to a
low-temperature coherent phase characterized by an enhanced electron mass,
reduced resistivity, and an enlarged unit cell free of structural distortion.
Starting from an extended periodic Anderson model and using the slave-boson
formulation, we develop a model for this system and study its properties within
mean-field theory. We find a reentrant first-order transition from a CDW phase,
in which the localized moments form singlet dimers, to a heavy Fermi liquid
phase as temperature is lowered. The magnetic susceptibility is Pauli-like in
both the high- and low-temperature regions, illustrating the lack of a
single-ion Kondo regime such as that usually found in heavy-fermion materials. | 1210.4041v3 |
2012-10-24 | Magnetic phase diagram of CePt3B1-xSix | We present a study of the main bulk properties (susceptibility,
magnetization, resistivity and specific heat) of CePt_3B_(1-x)Si-x, an alloying
system that crystallizes in a noncentrosymmetric lattice, and derive the
magnetic phase diagram. The materials at the end point of the alloying series
have previously been studied, with CePt_3B established as a material with two
different magnetic phases at low temperatures (antiferromagnetic below T_N =
7.8 K, weakly ferromagnetic below T_C ~ 5 K), while CePt3Si is a heavy fermion
superconductor (T_c = 0.75 K) coexisting with antiferromagnetism (T_N = 2.2 K).
From our experiments we conclude that the magnetic phase diagram is divided
into two regions. In the region of low Si content (up to x ~ 0.7) the material
properties resemble those of CePt3B. Upon increasing the Si concentration
further the magnetic ground state continuously transforms into that of CePt3Si.
In essence, we argue that CePt_3B can be understood as a low pressure variant
of CePt3Si. | 1210.6489v3 |
2013-04-26 | Preparation and characterization of Bismaleimide resin/titania nanocomposites via sol-gel process | Bismaleimide (BMI) resin/ titania nanocomposites were synthesized from
allylated-phenolic modified bismaleimide resin and TiO2 via the sol-gel process
of tetrabutyltitanate (Ti(OnBu)4, TBT). These nanocomposite materials were
characterized by FT-IR, XRD, FE-SEM, TGA and DMA. It was found that the
nano-scale TiO2 particles were formed in the AP-BMI resin matrix, and the
average primary particle size of the dispersed phase in the nanocomposites was
less than 100nm, but the particle aggregates with bigger size existed. Obvious
improvements of glass transition temperature and heat resistance properties of
the AP-BMI resins were achieved by the introduction of nano-sized TiO2
inorganic phase, and the modulus of the material was also improved. | 1304.7082v1 |
2013-10-05 | Engineered spin-valve type magnetoresistance in Fe$_3$O$_4$-CoFe$_2$O$_4$ core-shell nanoparticles | Naturally occurring spin-valve-type magnetoresistance (SVMR), recently
observed in Sr2FeMoO6 samples, suggests the possibility of decoupling the
maximal resistance from the coercivity of the sample. Here we present the
evidence that SVMR can be engineered in specifically designed and fabricated
core-shell nanoparticle systems, realized here in terms of soft magnetic Fe3O4
as the core and hard magnetic insulator CoFe2O4 as the shell materials. We show
that this provides a magnetically switchable tunnel barrier that controls the
magnetoresistance of the system, instead of the magnetic properties of the
magnetic grain material, Fe3O4, and thus establishing the feasibility of
engineered SVMR structures. | 1310.1469v1 |
2013-10-23 | A simple method to characterize the electrical and mechanical properties of micro-fibers | A procedure to characterize the electrical and mechanical properties of
micro-fibers is presented here. As the required equipment can be found in many
teaching laboratories, it can be carried out by physics and
mechanical/electrical engineering students. The electrical resistivity, mass
density and Young's modulus of carbon micro-fibers have been determined using
this procedure, obtaining values in very good agreement with the reference
values. The Young's modulus has been obtained by measuring the resonance
frequency of carbon fiber based cantilevers. In this way, one can avoid common
approaches based on tensile or bending tests which are difficult to implement
for microscale materials. Despite the simplicity of the experiments proposed
here, they can be used to trigger in the students interest on the electrical
and mechanical properties of microscale materials. | 1310.6134v1 |
2014-07-31 | Quantum Criticality Based on Large Ising Spins: YbCo$_2$Ge$_4$ with New 1-2-4 Structure Type | We present a new type of quantum critical material YbCo$_2$Ge$_4$, having the
largest quantum-critical pseudospin size ever. The YbCo$_2$Ge$_4$-type
structure is new, forms in the orthorhombic $Cmcm$ system, and is related to
the well-known ThCr$_2$Si$_2$ structure. Heavy rare earth (Tm,Yb,Lu, or Y)
members are also possible to be grown. YbCo$_2$Ge$_4$ possesses the Ising-type
ground-state doublet, namely the simplest ones of uniaxially up or down, $|\pm
\sim 7/2\rangle$. It is clearly manifested through comprehensive resistivity,
magnetization, specific heat, and NQR/NMR experiments. Large pseudospin state
usually tends to order in simple magnetisms, or hard to be screened by Kondo
effect. Therefore, the discovery of the quantum criticality of the fluctuating
large spins opens a new door to new-material search and theoretical studies. | 1407.8274v1 |
2014-09-19 | Analysis of the internal heat losses in a thermoelectric generator | A 3D thermoelectric numerical model is used to investigate different internal
heat loss mechanisms for a thermoelectric generator with bismuth telluride p-
and n-legs. The model considers all thermoelectric effects, temperature
dependent material parameters and simultaneous convective, conductive and
radiative heat losses, including surface to surface radiation. For radiative
heat losses it is shown that for the temperatures considered here, surface to
ambient radiation is a good approximation of the heat loss. For conductive heat
transfer the module efficiency is shown to be comparable to the case of
radiative losses. Finally, heat losses due to internal natural convection in
the module is shown to be negligible for the millimetre sized modules
considered here. The combined case of radiative and conductive heat transfer
resulted in the lowest efficiency. The optimized load resistance is found to
decrease for increased heat loss. The leg dimensions are varied for all heat
losses cases and it is shown that the ideal way to construct a TEG module with
minimal heat losses and maximum efficiency is to either use a good insulating
material between the legs or evacuate the module completely, and use small and
wide legs closely spaced. | 1409.6743v1 |
2015-01-17 | Superconductivity in the orthorhombic phase of thermoelectric CsPbxBi4-xTe6 with 0.3=<x=<1.0 | Experimental measurements clearly reveal the presence of bulk
superconductivity in the CsPbxBi4-xTe6 (0.3=<x=<1.0) materials, i.e. the first
member of the thermoelectric series of Cs[PbmBi3Te5+m], these materials have
the layered orthorhombic structure containing infinite anionic [PbBi3Te6]-
slabs separated with Cs+ cations. Temperature dependences of electrical
resistivity, magnetic susceptibility, and specific heat have consistently
demonstrated that the superconducting transition in CsPb0.3Bi3.7Te6 occurs at
Tc=3.1K, with a superconducting volume fraction close to 100% at 1.8 K.
Structural study using aberration-corrected STEM/TEM reveals a rich variety of
microstructural phenomena in correlation with the Pb-ordering and chemical
inhomogeneity. The superconducting material CsPb0.3Bi3.7Te6 with the highest Tc
shows a clear ordered structure with a modulation wave vector of q=a*/2+
c*/1.35 on the a-c plane. Our study evidently demonstrates that
superconductivity deriving upon doping of narrow-gap semiconductor is a viable
approach for exploration of novel superconductors. | 1501.04184v1 |
2015-01-22 | DFT+U simulation of the Ti${}_4$O${}_7$-TiO${}_2$ interface | The formation of conducting channels of Ti${}_4$O${}_7$ inside
TiO${}_2$-based memristors is believed to be the origin for the change in
electric resistivity of these devices. While the properties of the bulk
materials are reasonably known, the interface between them has not been studied
up to now mostly due to their different crystalline structures. In this work we
present a way to match the interfaces between TiO${}_2$ and Ti${}_4$O${}_7$ and
subsequently the band offset between these materials is obtained from density
functional theory based calculations. The results show that while the valence
band is located at the Ti${}_4$O${}_7$, the conduction band is found at the
TiO${}_2$ structure, resulting into a type II interface. In this case, the
Ti${}_4$O${}_7$ would act as a donor to the TiO${}_2$ matrix. | 1501.05564v1 |
2015-02-09 | A theory of finite deformation magneto-viscoelasticity | This paper deals with the mathematical modelling of large strain
magneto-viscoelastic deformations. Energy dissipation is assumed to occur both
due to the mechanical viscoelastic effects as well as the resistance offered by
the material to magnetisation. Existence of internal damping mechanisms in the
body is considered by decomposing the deformation gradient and the magnetic
induction into `elastic' and `viscous' parts. Constitutive laws for material
behaviour and evolution equations for the non-equilibrium fields are derived
that agree with the laws of thermodynamics. To illustrate the theory the
problems of stress relaxation, magnetic field relaxation, time dependent
magnetic induction and strain are formulated and solved for a specific form of
the constitutive law. The results, that show the effect of several modelling
parameters on the deformation and magnetisation process, are illustrated
graphically. | 1502.02482v1 |
2015-08-06 | Odd-parity magnetoresistance in pyrochlore iridate thin films with broken time-reversal symmetry | A new class of materials termed topological insulators have been intensively
investigated due to their unique Dirac surface state carrying dissipationless
edge spin currents. Recently, it has been theoretically proposed that the three
dimensional analogue of this type of band structure, the Weyl Semimetal phase,
is materialized in pyrochlore oxides with strong spin-orbit coupling,
accompanied by all-in-all-out spin ordering. Here, we report on the fabrication
and magnetotransport of Eu2Ir2O7 single crystalline thin films. We reveal that
one of the two degenerate all-in-all-out domain structures, which are connected
by time-reversal operation, can be selectively formed by the polarity of the
cooling magnetic field. Once formed, the domain is robust against an oppositely
polarised magnetic field, as evidenced by an unusual odd field dependent term
in the magnetoresistance and an anomalous term in the Hall resistance. Our
findings pave the way for exploring the predicted novel quantum transport
phenomenon at the surfaces/interfaces or magnetic domain walls of pyrochlore
iridates. | 1508.01318v1 |
2015-09-04 | Hall effect in the extremely large magnetoresistance semimetal WTe$_2$ | We systematically measured the Hall effect in the extremely large
magnetoresistance semimetal WTe$_2$. By carefully fitting the Hall resistivity
to a two-band model, the temperature dependencies of the carrier density and
mobility for both electron- and hole-type carriers were determined. We observed
a sudden increase of the hole density below $\sim$160~K, which is likely
associated with the temperature-induced Lifshitz transition reported by a
previous photoemission study. In addition, a more pronounced reduction in
electron density occurs below 50~K, giving rise to comparable electron and hole
densities at low temperature. Our observations indicate a possible electronic
structure change below 50~K, which might be the direct driving force of the
electron-hole ``compensation'' and the extremely large magnetoresistance as
well. Numerical simulations imply that this material is unlikely to be a
perfectly compensated system. | 1509.01463v2 |
2015-11-19 | `Ferroelectric' Metals Reexamined: Fundamental Mechanisms and Design Considerations for New Materials | The recent observation of a ferroelectric-like structural transition in
metallic LiOsO$_3$ has generated a flurry of interest in the properties of
polar metals. Such materials are thought to be rare because free electrons
screen out the long-range electrostatic forces that favor a polar structure
with a dipole moment in every unit cell. In this work, we question whether
long-range electrostatic forces are always the most important ingredient in
driving polar distortions. We use crystal chemical models, in combination with
first-principles Density Functional Theory calculations, to explore the
mechanisms of inversion-symmetry breaking in LiOsO$_3$ and both insulating and
electron-doped ATiO$_3$ perovskites, A = Ba, Sr, Ca. Although electrostatic
forces do play a significant role in driving the polar instability of BaTiO$_3$
(which is suppressed under electron doping), the polar phases of CaTiO$_3$ and
LiOsO$_3$ emerge through a mechanism driven by local bonding preferences and
this mechanism is `resistant' to the presence of charge carriers. Hence, our
results suggest that there is no fundamental incompatibility between
metallicity and polar distortions. We use the insights gained from our
calculations to suggest design principles for new polar metals and promising
avenues for further research. | 1511.06187v2 |
2016-01-12 | Superconductivity in Tl_{0.6}Bi_{2}Te_{3} Derived from a Topological Insulator | Bulk superconductivity has been discovered in Tl_{0.6}Bi_{2}Te_{3}, which is
derived from the topological insulator Bi2Te3. The superconducting volume
fraction of up to 95% (determined from specific heat) with Tc of 2.28 K was
observed. The carriers are p-type with the density of ~1.8 x 10^{20} cm^{-3}.
Resistive transitions under magnetic fields point to an unconventional
temperature dependence of the upper critical field B_{c2}. The crystal
structure appears to be unchanged from Bi2Te3 with a shorter c-lattice
parameter, which, together with the Rietveld analysis, suggests that Tl ions
are incorporated but not intercalated. This material is an interesting
candidate of a topological superconductor which may be realized by the strong
spin-orbit coupling inherent to topological insulators. | 1601.02877v1 |
2016-05-06 | Intrinsic Negative Poisson's Ratio for Single-Layer Graphene | Negative Poisson's ratio (NPR) materials have drawn significant interest
because the enhanced toughness, shear resistance and vibration absorption that
typically are seen in auxetic materials may enable a range of novel
applications. In this work, we report that single-layer graphene exhibits an
intrinsic NPR, which is robust and independent of its size and temperature. The
NPR arises due to the interplay between two intrinsic deformation pathways (one
with positive Poisson's ratio, the other with NPR), which correspond to the
bond stretching and angle bending interactions in graphene. We propose an
energy-based deformation pathway criteria, which predicts that the pathway with
NPR has lower energy and thus becomes the dominant deformation mode when
graphene is stretched by a strain above 6%, resulting in the NPR phenomenon. | 1605.01827v2 |
2016-03-24 | Isotoxal star-shaped polygonal voids and rigid inclusions in nonuniform antiplane shear fields. Part II: Singularities, annihilation and invisibility | Notch stress intensity factors and stress intensity factors are obtained
analytically for isotoxal star-shaped polygonal voids and rigid inclusions (and
also for the corresponding limit cases of star-shaped cracks and stiffeners),
when loaded through remote inhomogeneous (self-equilibrated, polynomial)
antiplane shear stress in an infinite linear elastic matrix. Usually these
solutions show stress singularities at the inclusion corners. It is shown that
an infinite set of geometries and loading conditions exist for which not only
the singularity is absent, but the stress vanishes ('annihilates') at the
corners. Thus the material, which even without the inclusion corners would have
a finite stress, remains unstressed at these points in spite of the applied
remote load. Moreover, similar conditions are determined in which a star-shaped
crack or stiffener leaves the ambient stress completely unperturbed, thus
reaching a condition of 'quasi-static invisibility'. Stress annihilation and
invisibility define optimal loading modes for the overall strength of a
composite and are useful for designing ultra-resistant materials. | 1605.04942v1 |
2016-10-30 | Characteristics of Interlayer Tunneling Field Effect Transistors Computed by a "DFT-Bardeen" Method | Theoretical predictions are made for the current-voltage characteristics of
two-dimensional heterojunction interlayer tunneling field-effect transistors
(Thin-TFETs), focusing on the magnitude of the current that is achievable in
such devices. A theory based on the Bardeen tunneling method is employed, using
wavefunctions from first-principles density-functional theory. This method
permits convenient incorporation of differing materials into the source and
drain electrodes, i.e. with different crystal structures, lattice constants,
and/or band structures. Large variations in the tunnel currents are found,
depending on the particular two-dimensional materials used for the source and
drain electrodes. Tunneling between states derived from the center
(Gamma-point) of the Brillouin zone (BZ) is found, in general, to lead to
larger current than for zone-edge (e.g. K-point) states. Differences, as large
as an order of magnitude, between the present results and various prior
predictions are discussed. Predicted values for the tunneling currents,
including subthreshold swing, are compared with benchmark values for low-power
digital applications. Contact resistance is considered and its effect on the
tunneling currents is demonstrated. | 1610.09695v1 |
2016-10-31 | Signature of Hanle Precession in Trilayer MoS2: Theory and Experiment | Valley-spin coupling in transition-metal dichalcogenides (TMDs) can result in
unusual spin transport behaviors under an external magnetic field. Nonlocal
resistance measured from 2D materials such as TMDs via electrical Hanle
experiments are predicted to exhibit nontrivial features, compared with results
from conventional materials due to the presence of intervalley scattering as
well as a strong internal spin-orbit field. Here, for the first time, we report
the all-electrical injection and non-local detection of spin polarized carriers
in trilayer MoS_2 films. We calculate the Hanle curves theoretically when the
separation between spin injector and detector is much larger than spin
diffusion length, \lamda_s. The experimentally observed curve matches the
theoretically-predicted Hanle shape under the regime of slow intervalley
scattering. The estimated spin life-time was found to be around 110 ps at 30 K. | 1611.00059v1 |
2016-11-23 | Electron interactions, spin-orbit coupling, intersite correlations in pyrochlore iridates | We perform combined density functional and dynamical mean-field calculations
to study the pyrochlore iridates Lu$_2$Ir$_2$O$_7$, Y$_2$Ir$_2$O$_7$ and
Eu$_2$Ir$_2$O$_7$. Both single-site and cluster dynamical mean-field
calculations are performed and spin-orbit coupling is included. Paramagnetic
metallic phases, antiferromagnetic metallic phases with tilted Weyl cones and
antiferromagnetic insulating phases are found. The magnetic phases display
all-in/all-out magnetic ordering, consistent with previous studies. Unusually
for electronically three dimensional materials, the single-site dynamical
mean-field approximation fails to reproduce qualitative material trends,
predicting in particular that the paramagnetic phase properties of
Y$_2$Ir$_2$O$_7$ and Eu$_2$Ir$_2$O$_7$ are almost identical, although in
experiments the Y compound has a much higher resistance than the Eu compound.
This qualitative failure is attributed to the importance of intersite magnetic
correlations in the physics of these materials. | 1611.07997v2 |
2017-02-27 | Quantum critical scaling and fluctuations in Kondo lattice materials | We propose a new phenomenological framework for three classes of Kondo
lattice materials that incorporates the interplay between the fluctuations
associated with the antiferromagnetic quantum critical point and those produced
by the hybridization quantum critical point that marks the end of local moment
behavior. We show that these fluctuations give rise to two distinct regions of
quantum critical scaling: hybridization fluctuations are responsible for the
logarithmic scaling in the density of states of the heavy electron Kondo liquid
that emerges below the coherence temperature T*; while the unconventional power
law scaling in the resistivity that emerges at lower temperatures below T_QC
may reflect the combined effects of hybridization and antiferromagnetic quantum
critical fluctuations. Our framework is supported by experimental measurements
on CeCoIn5, CeRhIn5 and other heavy electron materials. | 1702.08132v2 |
2017-06-30 | Two-Dimensional h-BN and MoS2 as Diffusion Barriers for Ultra-Scaled Copper Interconnects | Copper interconnects in modern integrated circuits require ultra-thin
barriers to prevent intermixing of Cu with surrounding dielectric materials.
Conventional barriers rely on metals like TaN, however their finite thickness
reduces the cross-sectional area and significantly increases the resistivity of
nanoscale interconnects. In this study, a new class of two-dimensional (2D) Cu
diffusion barriers, hexagonal boron nitride (h-BN) and molybdenum disulfide
(MoS2), is demonstrated for the first time. Using time-dependent dielectric
breakdown measurements and scanning transmission electron microscopy coupled
with energy dispersive X-ray spectroscopy and electron energy loss
spectroscopy, these 2D materials are shown to be promising barrier solutions
for ultra-scaled interconnect technology. The predicted lifetime of devices
with directly deposited 2D barriers can achieve three orders of magnitude
improvement compared to control devices without barriers. | 1706.10178v1 |
2017-08-31 | Nonmonotonic dependence of polymer glass mechanical response on chain bending stiffness | We investigate the mechanical properties of amorphous polymers by means of
coarse-grained simulations and nonaffine lattice dynamics theory. A small
increase of polymer chain bending stiffness leads first to softening of the
material, while hardening happens only upon further strengthening of the
backbones. This nonmonotonic variation of the storage modulus $G'$ with bending
stiffness is caused by a competition between additional resistance to
deformation offered by stiffer backbones and decreased density of the material
due to a necessary decrease in monomer-monomer coordination. This
counter-intuitive finding suggests that the strength of polymer glasses may in
some circumstances be enhanced by softening the bending of constituent chains. | 1709.00024v2 |
2017-12-31 | Geometry Effects on Switching Currents in Superconducting Ultra Thin Films | Vortex dynamics is strongly connected with the mechanisms responsible for the
photon detection of superconducting devices. Indeed, the local suppression of
superconductivity by photon absorption may trigger vortex nucleation and motion
effects, which can make the superconducting state unstable. In addition,
scaling down the thickness of the superconducting films and/or the width of the
bridge geometry can strongly influence the transport properties of
superconducting films, e.g. affecting its critical current as well as its
switching current into the normal state. Understanding such instability can
boost the performances of those superconducting devices based on nanowire
geometries. We present an experimental study on the resistive switching in NbN
and NbTiN ultra-thin films with a thickness of few nanometers. Despite both
films were patterned with the same microbridge geometry, the two
superconducting materials show different behaviors at very low applied magnetic
fields. A comparison with other low temperature superconducting materials
outlines the influence of geometry effects on the superconducting transport
properties of these materials particularly useful for devices applications. | 1801.00306v1 |
2018-02-22 | Shear strength of wet granular materials: macroscopic cohesion and effective stress | Rheometric measurements on assemblies of wet polystyrene bead assemblies, in
steady uniform quasistatic shear flow, for varying liquid content within the
small saturation (pendular) range of isolated liquid bridges, are supplemented
with a systematic study by discrete numerical simulations. Numerical results
and experimental ones agree quantitatively is the intergranular friction
coefficient is set to 0.09, suitable for the dry material. Shear resistance and
solid fraction are recorded as functions of the reduced pressure p, comparing
normal stress to capillary bridge tensile strength. The Mohr-Coulomb relation
with p-independent cohesion c applies for p above 2. The assumption that
contact force contributions to stress act as effective stresses predicts shear
strength quite well throughout the numerically investigated range of
parameters.. A generalized Mohr-Coulomb cohesion c is defined, which relates to
the dry material internal friction, coordination numbers and capillary force
network anisotropy. The Rumpf formula approximation, ignoring capillary shear
stress is correct for the larger saturation range within the pendular regime,
but fails to describe its decrease for small liquid contents. | 1802.08172v1 |
2018-09-12 | Elastoresistive and Elastocaloric Anomalies at Magnetic and Electronic-Nematic Critical Points | Using Ba(Fe$_{0.975}$Co$_{0.025}$)$_2$As$_{2}$ as an exemplar material
exhibiting second order electronic-nematic and antiferromagnetic transitions,
we present measurements that reveal anomalies in the elastoresistance
$\left(\frac{\partial \rho_{ij}}{\partial\varepsilon_{kl}}\right)$ and
elastocaloric effect $\left(\frac{\partial T}{\partial\varepsilon_{kl}}\right)$
at both phase transitions. Both effects are understood to arise from the effect
of strain on the transition temperatures; in the region close to the phase
transitions this leads to (1) similarity between the strain and temperature
derivatives of the resistivity and (2) similarity between the elastocaloric
effect and the singular part of the specific heat. These mechanisms for
elastoresistance and elastocaloric effect should be anticipated for any
material in which mechanical deformation changes the transition temperature.
Furthermore, these measurements provide evidence that the Fisher-Langer
relation $\rho^{(c)} \propto U^{(c)}$ between the scattering from critical
degrees of freedom and their energy-density, respectively, holds near each of
the Ne\'{e}l and electronic nematic transitions in the material studied. | 1809.04582v1 |
2018-09-17 | Electric-Field Control of Magnetic Order: From FeRh to Topological Antiferromagnetic Spintronics | Using an electric field instead of an electric current (or a magnetic field)
to tailor the electronic properties of magnetic materials is promising for
realizing ultralow energy-consuming memory devices because of the suppression
of Joule heating, especially when the devices are scaled to the nanoscale. In
the review, we summarize recent results on the giant magnetization and
resistivity modulation in a metamagnetic intermetallic alloy - FeRh, which is
achieved by electric-field-controlled magnetic phase transitions in
multiferroic heterostructures. Furthermore, the approach is extended to
topological antiferromagnetic spintronics, which is currently receiving
attention in the magnetic society, and the antiferromagnetic order parameter
has been able to switch back and forth by a small electric field. In the end,
we envision the possibility of manipulating exotic physical phenomena in the
emerging topological antiferromagnetic spintronics field via the electric-field
approach. | 1809.06011v1 |
2017-03-02 | Morphology and properties evolution upon ring-opening polymerization during extrusion of cyclic butylene terephthalate and graphene-related-materials into thermally conductive nanocomposites | In this work, the study of thermal conductivity before and after in-situ
ring-opening polymerization of cyclic butylene terephthalate into poly
(butylene terephthalate) in presence of graphene-related materials (GRM) is
addressed, to gain insight in the modification of nanocomposites morphology
upon polymerization. Five types of GRM were used: one type of graphite
nanoplatelets, two different grades of reduced graphene oxide (rGO) and the
same rGO grades after thermal annealing for 1 hour at 1700{\deg}C under vacuum
to reduce their defectiveness. Polymerization of CBT into pCBT, morphology and
nanoparticle organization were investigated by means of differential scanning
calorimetry, electron microscopy and rheology. Electrical and thermal
properties were investigated by means of volumetric resistivity and bulk
thermal conductivity measurement. In particular, the reduction of nanoflake
aspect ratio during ring-opening polymerization was found to have a detrimental
effect on both electrical and thermal conductivities in nanocomposites. | 1703.00805v2 |
2015-05-18 | Unique opportunity to harness polarization in GaN to override the conventional power electronics figure-of-merits | Owing to the large breakdown electric field, wide bandgap semiconductors such
as SiC, GaN, Ga2O3 and diamond based power devices are the focus for next
generation power switching applications. The unipolar trade-off relationship
between the area specific-on resistance and breakdown voltage is often employed
to compare the performance limitation among various materials. The GaN material
system has a unique advantage due to its prominent spontaneous and
piezoelectric polarization effects in GaN, AlN, InN, AlxInyGaN alloys and
flexibility in inserting appropriate heterojunctions thus dramatically broaden
the device design space. | 1505.04651v1 |
2015-05-21 | Impedance Matching of Atomic Thermal Interfaces Using Primitive Block Decomposition | We explore the physics of thermal impedance matching at the interface between
two dissimilar materials by controlling the properties of a single atomic mass
or bond. The maximum thermal current is transmitted between the materials when
we are able to decompose the entire heterostructure solely in terms of
primitive building blocks of the individual materials. Using this approach, we
show that the minimum interfacial thermal resistance arises when the
interfacial atomic mass is the arithmetic mean, while the interfacial spring
constant is the harmonic mean of its neighbors. The contact induced broadening
matrix for the local vibronic spectrum, obtained from the self-energy matrices,
generalizes the concept of acoustic impedance to the nonlinear phonon
dispersion or the short-wavelength (atomic) limit. | 1505.05564v1 |
2017-11-06 | On the relation between plasticity, friction, and geometry | Plasticity refers to thermodynamically irreversible deformation associated
with a change of configuration of materials. Friction is a phenomenological law
that describes the forces resisting sliding between two solids or across an
embedded dislocation. These two types of constitutive behaviors explain the
deformation of a wide range of engineered and natural materials. Yet, they are
typically described with distinct physical laws that cloud their inherent
connexion. Here, I introduce a multiplicative form of kinematic friction that
closely resembles the power-law flow of viscoplastic materials and that
regularizes the constitutive behavior at vanishing velocity, with important
implications for rupture dynamics. Using a tensor-valued state variable that
describes the degree of localization, I describe a constitutive framework
compatible with viscoplastic theories that captures the continuum between
distributed and localized deformation and for which the frictional response
emerges when the deformed region collapses from three to two dimensions. | 1711.01954v2 |
2018-10-12 | Non-volatile ferroelectric memory effect in ultrathin α-In2Se3 | Recent experiments on layered {\alpha}-In2Se3 have confirmed its
room-temperature ferroelectricity under ambient condition. This observation
renders {\alpha}-In2Se3 an excellent platform for developing two-dimensional
(2D) layered-material based electronics with nonvolatile functionality. In this
letter, we demonstrate non-volatile memory effect in a hybrid 2D ferroelectric
field effect transistor (FeFET) made of ultrathin {\alpha}-In2Se3 and graphene.
The resistance of graphene channel in the FeFET is tunable and retentive due to
the electrostatic doping, which stems from the electric polarization of the
ferroelectric {\alpha}-In2Se3. The electronic logic bit can be represented and
stored with different orientations of electric dipoles in the top-gate
ferroelectric. The 2D FeFET can be randomly re-written over more than $10^5$
cycles without losing the non-volatility. Our approach demonstrates a protype
of re-writable non-volatile memory with ferroelectricity in van de Waals 2D
materials. | 1810.05328v1 |
2018-10-17 | From plastic flow to brittle fracture: role of microscopic friction in amorphous solids | Plasticity in soft amorphous materials typically involves collective
deformation patterns that emerge upon intense shearing. The microscopic basis
of amorphous plasticity has been commonly established through the notion of
"Eshelby"-type events, localized abrupt rearrangements that induce flow in the
surrounding material via non-local elastic-type interactions. This universal
mechanism in flowing disordered solids has been proposed despite their
diversity in terms of scales, microscopic constituents, or interactions.
However, we argue that the presence of frictional interactions in granular
solids alters the dynamics of flow by nucleating micro shear cracks that
continually coalesce to build up system-spanning fracture-like formations on
approach to failure. The plastic-to-brittle failure transition is uniquely
controlled by the degree of frictional resistance which is in essence similar
to the role of heterogeneities that separate the abrupt and smooth yielding
regimes in glassy structures. | 1810.07418v1 |
2018-10-17 | Modeling Heterogeneous Melting in Phase Change Memory Devices | We present thermodynamic crystallization and melting models and calculate
phase change velocities in $Ge_2 Sb_2 Te_5$ based on kinetic and thermodynamic
parameters. The calculated phase change velocities are strong functions of
grain size, with smaller grains beginning to melt at lower temperatures. Phase
change velocities are continuous functions of temperature which determine
crystallization and melting rates. Hence, set and reset times as well as power
and peak current requirements for switching are strong functions of grain size.
Grain boundary amorphization can lead to a sufficient increase in cell
resistance for small-grain phase change materials even if the whole active
region does not completely amorphize. Isolated grains left in the amorphous
regions, the quenched-in nuclei, facilitate templated crystal growth and
significantly reduce set times for phase change memory cells. We demonstrate
the significance of heterogeneous melting through 2-D electrothermal
simulations coupled with a dynamic materials phase change model. Our results
show reset and set times on the order of ~1 ns for 30 nm wide confined
nanocrystalline (7.5 nm - 25 nm radius crystals) phase change memory cells. | 1810.07764v1 |
2018-11-08 | Magnetically-driven orbital-selective insulator-metal transition in double perovskite oxides | Interaction-driven metal-insulator transitions or Mott transitions
are widely observed in condensed-matter systems. In multi-orbital
systems, many-body physics is richer in which an orbital-selective
metal-insulator transition is an intriguing and unique
phenomenon. Here we use first-principles calculations to show that a
magnetic transition (from paramagnetic to long-range magnetically
ordered) can simultaneously induce an orbital-selective
insulator-metal transition in rock-salt ordered double perovskite
oxides $A_2BB'$O$_6$ where $B$ is a non-magnetic ion (Y$^{3+}$ and
Sc$^{3+}$) and $B'$ a
magnetic ion with a $d^3$ electronic configuration (Ru$^{5+}$ and
Os$^{5+}$). The orbital selectivity originates from
geometrical frustration of a face-centered-cubic lattice on which
the magnetic ions $B'$ reside. Including realistic structural
distortions and spin-orbit interaction do
not affect the transition. The predicted orbital-selective transition
naturally explains the anomaly observed in the electric resistivity
of Sr$_2$YRuO$_6$. Implications of other available experimental data
are also discussed. Our work shows that by exploiting
geometrical frustration on non-bipartite lattices, novel
electronic/magnetic/orbital-coupled phase transitions can occur in
correlated materials that are in the vicinity of metal-insulator phase
boundary. | 1811.03465v1 |
2018-11-08 | Giant anomalous Nernst effect in the magnetic Weyl semimetal Co3Sn2S2 | In ferromagnetic solids, even in absence of magnetic field, a transverse
voltage can be generated by a longitudinal temperature gradient. This
thermoelectric counterpart of the Anomalous Hall effect (AHE) is dubbed the
Anomalous Nernst effect (ANE). Expected to scale with spontaneous
magnetization, both these effects arise because of the Berry curvature at the
Fermi energy. Here, we report the observation of a giant ANE in a
newly-discovered magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$ crystal. Hall
resistivity and Nernst signal both show sharp jumps at a threshold field and
exhibit a clear hysteresis loop below the ferromagnetic transition temperature.
The ANE signal peaks a maximum value of about 5 miuV/K which is comparable to
the largest seen in any magnetic material. Moreover, the anomalous transverse
thermoelectric conductivity becomes as large as about 10 A/K.m at 70 K, the
largest in known semimetals. The observed ANE signal is much larger than what
is expected according to the magnetization. | 1811.03485v2 |
2018-11-23 | Extremely large magnetoresistance induced by hidden three-dimensional Dirac bands in nonmagnetic semimetal InBi | Extremely large positive magnetoresistance (XMR) was found in a nonmagnetic
semimetal InBi. Using several single crystals with different residual
resistivity ratios (RRRs), we revealed that the XMR strongly depended on the
RRR (sample quality). Assuming that there were no changes in effective mass m*
and carrier concentrations in these single crystals, this dependence was
explained by a semiclassical two-carrier model. First-principle calculations
including the spin-orbit interactions (SOI) unveiled that InBi had a
compensated carrier balance and SOI-induced "hidden" three-dimensional (3D)
Dirac bands at the M and R points. Because the small m* and the large carrier
mobilities will be realized, these hidden 3D Dirac bands should play an
important role for the XMR in InBi. We suggest that this feature can be
employed as a novel strategy for the creation of XMR semimetals. | 1811.09383v2 |
2019-02-07 | In situ control of diamagnetism by electric current in Ca$_3$(Ru$_{1-x}$Ti$_x$)$_2$O$_7$ | Non-equilibrium steady state (NESS) conditions induced by DC current can
alter the physical properties of strongly correlated electron systems (SCES).
In this regard, it was recently shown that DC current can trigger novel
electronic states, such as current-induced diamagnetism, which cannot be
realized in equilibrium conditions. However, reversible control of diamagnetism
has not been achieved yet. Here, we demonstrate reversible in situ control
between a Mott insulating state and a diamagnetic semimetal-like state by DC
current in the Ti-substituted bilayer ruthenate
Ca$_3$(Ru$_{1-x}$Ti$_x$)$_2$O$_7$ ($x=0.5$%). By performing simultaneous
magnetic and resistive measurements, we map out the temperature vs
current-density phase diagram in the NESS of this material. The present results
open up the possibility of creating novel electronic states in a variety of
SCES under DC current. | 1902.02515v1 |
2019-05-15 | Unconventional Hall Effect induced by Berry Curvature | Berry phase and Berry curvature play a key role in the development of
topology in physics and do contribute to the transport properties in solid
state systems. In this paper, we report the finding of novel nonzero Hall
effect in topological material ZrTe5 flakes when in-plane magnetic field is
parallel and perpendicular to the current. Surprisingly, both symmetric and
antisymmetric components with respect to magnetic field are detected in the
in-plane Hall resistivity. Further theoretical analysis suggests that the
magnetotransport properties originate from the anomalous velocity induced by
Berry curvature in a tilted Weyl semimetal. Our work not only enriches the Hall
family but also provides new insights into the Berry phase effect in
topological materials. | 1905.06040v2 |
2020-02-13 | Guest-Tunable Dielectric Sensing Using a Single Crystal of HKUST-1 | There is rising interest on low-k dielectric materials based on porous
metal-organic frameworks (MOFs) for improved electrical insulation in
microelectronics. Herein, we demonstrate the concept of MOF dielectric sensor
built from a single crystal of HKUST-1. We study guest encapsulation effects of
polar and non-polar molecules, by monitoring the transient dielectric response
and AC conductivity of the crystal exposed to different vapors (water, I2,
methanol, ethanol). The dielectric properties were measured along the <100>
crystal direction in the frequency range of 100 Hz to 2 MHz. The dielectric
data show the efficacy of MOF dielectric sensor for discriminating the guest
analytes. The time-dependent transient response reveals dynamics of the
molecular inclusion and exclusion processes in the nanoscale pores. Since
dielectric response is ubiquitous to all MOF materials (unlike DC conductivity
and fluorescence), our results demonstrate the potential of dielectric MOF
sensors compared to resistive sensors and luminescence-based approaches. | 2002.05705v1 |
2020-04-08 | Nonreciprocal thermal transport in a multiferroic helimagnet | Breaking of spatial inversion symmetry (SIS) induces unique phenomena in
condensed matter. Besides the classic examples such as natural optical activity
and piezoelectricity, the spin-orbit interaction further enriches the effect of
SIS breaking, as exemplified by the Rashba effect. In particular, by combining
this symmetry with magnetic fields or another type of time-reversal symmetry
(TRS) breaking, noncentrosymmetric materials can be made to exhibit
nonreciprocal responses, which are responses that differ for rightward and
leftward stimuli. For example, resistivity becomes directionally dependent;
that is to say, rectification appears in noncentrosymmetric materials in a
magnetic field. However, the effect of SIS breaking on thermal transport
remains to be elucidated. Here we show nonreciprocal thermal transport in the
multiferroic helimagnet TbMnO3. The longitudinal thermal conductivity depends
on whether the thermal current is parallel or antiparallel to the vector
product of the electric polarization and magnetization. This phenomenon is
thermal rectification that is controllable with external fields in a uniform
crystal. This discovery may pave the way to thermal diodes with controllability
and scalability. | 2004.03801v1 |
2012-01-13 | Ferroelectric PbTiO$_{3}$/SrRuO$_{3}$ superlattices with broken inversion symmetry | We have fabricated PbTiO$_{3}$/SrRuO$_{3}$ superlattices with ultra-thin
SrRuO$_{3}$ layers. Due to the superlattice geometry, the samples show a large
anisotropy in their electrical resistivity, which can be controlled by changing
the thickness of the PbTiO$_{3}$ layers. Therefore, along the ferroelectric
direction, SrRuO$_{3}$ layers can act as dielectric, rather than metallic,
elements. We show that, by reducing the concentration of PbTiO$_{3}$, an
increasingly important effect of polarization asymmetry due to compositional
inversion symmetry breaking occurs. The results are significant as they
represent a new class of ferroelectric superlattices, with a rich and complex
phase diagram. By expanding our set of materials we are able to introduce new
behaviors that can only occur when one of the materials is not a perovskite
titanate. Here, compositional inversion symmetry breaking in bi-color
superlattices, due to the combined variation of A and B site ions within the
superlattice, is demonstrated using a combination of experimental measurements
and first principles density functional theory. | 1201.2893v2 |
2012-01-31 | Effect of starting materials on the superconducting properties of SmFeAsO1-xFx tapes | SmFeAsO1-xFx tapes were prepared using three kinds of starting materials. It
shows that the starting materials have an obvious effect on the impurity phases
in final superconducting tapes. Compared with the other samples, the samples
fabricated by SmAs, FeO, Fe2As, and SmF3 have the smallest arsenide impurity
phase and voids. As a result, these samples possess much denser structure and
better grain connectivity. Moreover, among the three kinds of samples
fabricated in this work, this kind of sample has the highest zero-resistivity
temperature ~40 K and largest critical current density ~4600 A/cm^2 in
self-field at 4.2 K. This is the highest Jc values reported so far for
SmFeAsO1-xFx wires and tapes. | 1201.6522v1 |
2014-01-05 | Phase-coexistence and glass-like behavior in magnetic and dielectric solids with long range order | Phase-coexistence in the manganese-oxide compounds or manganites with
colossal magneto-resistance (CMR) has been generally considered to be an
inhomogeneous ground state. An alternative explanation of phase-coexistence as
the manifestation of a disorder-broadened first order magnetic phase transition
being interrupted by the glasslike arrest of kinetics is now gradually gaining
ground. This kinetic arrest of a first order phase transitions, between two
states with long-range magnetic order, has actually been observed in various
other classes of magnetic materials in addition to the CMR manganites. The
underlying common features of this kinetic arrest of a first order phase
transition are discussed in terms of the phenomenology of glasses. The possible
manifestations of such glass-like arrested states across disorder-influenced
first order phase transitions in dielectric solids and in multiferroic
materials, are also discussed. | 1401.0891v2 |
2017-04-04 | Mechanics of disordered auxetic metamaterials | Auxetic materials are of great engineering interest not only because of their
fascinating negative Poisson's ratio, but also due to their increased toughness
and indentation resistance. These materials are typically synthesized polyester
foams with a very heterogeneous structure, but the role of disorder in auxetic
behavior is not fully understood. Here, we provide a systematic theoretical and
experimental investigation in to the effect of disorder on the mechanical
properties of a paradigmatic auxetic lattice with a re-entrant hexagonal
geometry. We show that disorder has a marginal effect on the Poisson's ratio
unless the lattice topology is altered, and in all cases examined the disorder
preserves the auxetic characteristics. Depending on the direction of loading
applied to these disordered auxetic lattices, either brittle or ductile failure
is observed. It is found that brittle failure is associated with a
disorder-dependent tensile strength, whereas in ductile failure disorder does
not affect strength. Our work thus provides general guidelines to optimize
elasticity and strength of disordered auxetic metamaterials. | 1704.00943v3 |
2017-05-31 | Tuning of Magnetic and Electrical Properties in Complex oxide Thin Films Deposited By Pulsed Laser Deposition | Lanthanum manganite, LaMnO (LMO) is the parent compound for a class of hole
doped(e.g. La1-xCaxMnO3, La1-xSrxMnO3) and electron doped (e.g. . La1-xCexMnO3,
La1-xSnxMnO3) perovskite complex oxide materials. Strong correlation between
the spin,lattice, charge and orbital degrees of freedom is a hallmark of these
class of materials (popularly known as manganites). Competition and interplay
of these degrees of freedom lead to a wide range of interesting electronic
behavior including half-metallicity, colossal magneto-resistivity, etc.
Although a lot of experimental research has been carried out on the hole doped
and the electron doped counterparts, the parent system LMO remains less
investigated. This could be attributed to the difficulty in making
stoichiometric LMO (whether in bulk polycrystalline, single crystals or thin
films). There exists phenomenon like double-exchange (DE) and
anti-ferromagnetic super-exchange (SE) interactions which leads to
ferromagnetism in LMO thin films. This project work is aimed at the fabrication
and characterization of thin films of stoichiometric LMO and their structural,
magnetic and electrical studies. | 1705.11003v1 |
2017-07-04 | Time-temperature superposition in grain and grain boundary response regime of A2HoRuO6 (A = Ba, Sr, Ca) double perovskite ceramics: A Conductivity Spectroscopic Analysis | The pursuit for an appropriate universal scaling factor to satisfy the
time-temperature superposition principle for grain and grain boundary responses
has been explored in the ac conductivity domain for polycrystalline double
perovskite oxides A2HoRuO6 (AHR; A = Ba, Sr, Ca). The samples show different
structural phases ranging from cubic to monoclinic with decreasing ionic radii.
The degree of distortion in the materials is correlated to the strength of
bonding through the bond valence sum (BVS). The conductivity spectra for all
the samples obey the power law behaviour. The contribution of different
microstructural features to the conduction process is established. Thermal
variation of dc resistivity points towards a gradual crossover from nearest
neighbour to variable range hopping. The activation energies obtained from dc
conductivity, hopping frequency and relaxation frequency show close correlation
between the conduction and relaxation mechanisms. The scaled conductivity
curves for AHR showed the presence of two different conduction processes with
dissimilar activation energies in the grain boundary and grain response
regimes. It is thus concluded that a single scaling parameter is insufficient
to satisfy the time temperature superposition principle universally when two
different thermally activated regions are present simultaneously in the
materials. | 1707.00881v1 |
2017-07-18 | Insulator to Metal Transition in WO$_3$ Induced by Electrolyte Gating | Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an
alkali metal) are well known for their interesting optical and electrical
characteristics. We have modified the transport properties of thin WO$_3$ films
by electrolyte gating using both ionic liquids and polymer electrolytes. We are
able to tune the resistivity of the gated film by more than five orders of
magnitude, and a clear insulator-to-metal transition is observed. To clarify
the doping mechanism, we have performed a series of incisive operando
experiments, ruling out both a purely electronic effect (charge accumulation
near the interface) and oxygen-related mechanisms. We propose instead that
hydrogen intercalation is responsible for doping WO$_3$ into a highly
conductive ground state and provide evidence that it can be described as a
dense polaronic gas. | 1707.05748v1 |
2019-04-02 | Solid Propellants | Solid propellants are energetic materials used to launch and propel rockets
and missiles. Although their history dates to the use of black powder more than
two millennia ago, greater performance demands and the need for "insensitive
munitions" that are resistant to accidental ignition have driven much research
and development over the past half-century. The focus of this review is the
material aspects of propellants, rather than their performance, with an
emphasis on the polymers that serve as binders for oxidizer particles and as
fuel for composite propellants. The prevalent modern binders are discussed
along with a discussion of the limitations of state-of-the-art modeling of
composite motors. | 1904.01510v1 |
2019-04-08 | Superhydrophobic frictions | Contrasting with its sluggish behavior on standard solids, water is extremely
mobile on superhydrophobic materials, as shown for instance by the continuous
acceleration of drops on tilted water-repellent leaves. For much longer
substrates, however, drops reach a terminal velocity that results from a
balance between weight and friction, allowing us to question the nature of this
friction. We report that the relationship between force and terminal velocity
is non-linear. This is interpreted by showing that classical sources of
friction are minimized, so that the aerodynamical resistance to motion becomes
dominant, which eventually explains the matchless mobility of water. Our
results are finally extended to viscous liquids, also known to be unusually
quick on these materials. | 1904.03913v1 |
2019-04-23 | Hydrated lithium intercalation into the Kitaev spin liquid candidate material $α-$RuCl$_3$ | We study on transport and magnetic properties of hydrated and
lithium-intercalated $\alpha$-RuCl$_3$, Li$_x$RuCl$_3 \cdot y$H$_2$O, for
investigating the effect on mobile-carrier doping into candidate materials for
a realization of a Kitaev model. From thermogravitometoric and one-dimensional
electron map analyses, we find two crystal structures of this system, that is,
mono-layer hydrated Li$_x$RuCl$_3 \cdot y$H$_2$O~$(x\approx0.56, y\approx1.3)$
and bi-layer hydrated Li$_x$RuCl$_3 \cdot y$H$_2$O~$(x\approx0.56,
y\approx3.9)$. The temperature dependence of the electrical resistivity shows a
temperature hysteresis at 200-270 K, which is considered to relate with a
formation of a charge order. The antiferromagnetic order at 7-13 K in pristine
$\alpha$-RuCl$_3$~ is successfully suppressed down to 2 K in bi-layer hydrated
Li$_x$RuCl$_3 \cdot y$H$_2$O, which is sensitive to not only an electronic
state of Ru but also an interlayer distance between Ru-Cl planes. | 1904.10231v2 |
2019-12-03 | Large Resistance Change on Magnetic Tunnel Junction based Molecular Spintronics Devices | Molecular bridges covalently bonded to two ferromagnetic electrodes can
transform ferromagnetic materials and produce intriguing spin transport
characteristics. This paper discusses the impact of molecule induced strong
coupling on spin transport. To study the molecular coupling effect
organometallic molecular complex (OMC) was bridged between two ferromagnetic
electrodes of a magnetic tunnel junction (Ta/Co/NiFe/AlOx/NiFe/Ta) along the
exposed side edges. OMCs induced strong iter-ferromagnetic electrode coupling
to yield drastic changes in transport properties of the magnetic tunnel
junction testbed at the room temperature. These OMCs also transformed the
magnetic properties of magnetic tunnel junctions. SQUID and ferromagnetic
resonance studies provided insightful data to explain transport studies on the
magnetic tunnel junction based molecular spintronics devices. | 1912.01305v1 |
2021-01-04 | Unraveling the optical contrast in Sb2Te and AgInSbTe phase-change materials | Chalcogenide phase-change materials (PCMs) show a significant contrast in
optical reflectivity and electrical resistivity upon crystallization from the
amorphous phase and are leading candidates for non-volatile photonic and
electronic applications. In addition to the flagship Ge2Sb2Te5 phase-change
alloy, doped Sb2Te alloys, in particular AgInSbTe used in rewritable optical
discs, have been widely investigated for decades, and nevertheless the
theoretical insights on the optical properties of this important family of PCMs
are scarce. Here, we carry out thorough ab initio simulations to gain an
atomistic understanding of the optical properties of Sb2Te and AgInSbTe. We
show that the large optical contrast between the amorphous and crystalline
phase stems from the change in bond type in the parent compound Sb2Te. Ag and
In impurities serve mostly the purpose of stabilization of the amorphous phase,
and have marginal impact on the large variation in the dielectric function upon
the phase transitions. | 2101.00789v2 |
2011-04-05 | Viscoelastic Fracture of Biological Composites | Soft constituent materials endow biological composites, such as bone, dentin
and nacre, with viscoelastic properties that may play an important role in
their remarkable fracture resistance. In this paper we calculate the scaling
properties of the quasi-static energy release rate and the viscoelastic
contribution to the fracture energy of various biological composites, using
both perturbative and non-perturbative approaches. We consider coarse-grained
descriptions of three types of anisotropic structures: (i) Liquid-crystal-like
composites (ii) Stratified composites (iii) Staggered composites, for different
crack orientations. In addition, we briefly discuss the implications of
anisotropy for fracture criteria. Our analysis highlights the dominant
lengthscales and scaling properties of viscoelastic fracture of biological
composites. It may be useful for evaluating crack velocity toughening effects
and structure-dissipation relations in these materials. | 1104.0814v1 |
2012-03-12 | Circuital model for the Maxwell Fish Eye perfect drain | Perfect drain for the Maxwell Fish Eye (MFE) is a non-magnetic dissipative
region placed in the focal point to absorb all the incident radiation without
reflection or scattering. The perfect drain was recently designed as a material
with complex electrical permittivity that depends on frequency. However, this
material is only a theoretical material, so it can not be used in practical
devices. Recently, the perfect drain has been claimed as necessary to achieve
super-resolution [Leonhard 2009, New J. Phys. 11 093040], which has increased
the interest for practical perfect drains suitable for manufacturing. Here, we
analyze the super-resolution properties of a device equivalent to the MFE,
known as Spherical Geodesic Waveguide (SGW), loaded with the perfect drain. In
the SGW the source and drain are implemented with coaxial probes. The perfect
drain is realized using a circuit (made of a resistance and a capacitor)
connected to the drain coaxial probes. Super-resolution analysis for this
device is done in Comsol Multiphysics. The results of simulations predict the
super-resolution up to wavelength/3000 and optimum power transmission from the
source to the drain. | 1203.2424v1 |
2015-06-22 | Fracture Toughness of Silicate Glasses: Insights from Molecular Dynamics Simulations | Understanding, predicting and eventually improving the resistance to fracture
of silicate materials is of primary importance to design new glasses that would
be tougher, while retaining their transparency. However, the atomic mechanism
of the fracture in amorphous silicate materials is still a topic of debate. In
particular, there is some controversy about the existence of ductility at the
nano-scale during the crack propagation. Here, we present simulations of the
fracture of three archetypical silicate glasses using molecular dynamics. We
show that the methodology that is used provide realistic values of fracture
energy and toughness. In addition, the simulations clearly suggest that
silicate glasses can show different degrees of ductility, depending on their
composition. | 1506.06441v1 |
2015-06-26 | Conduction through subsurface cracks in bulk topological insulators | Topological insulators (TIs) have the singular distinction of being
electronic insulators while harboring metallic, conductive surfaces. In
ordinary materials, defects such as cracks and deformations are barriers to
electrical conduction, intuitively making the material more electrically
resistive. Peculiarly, 3D TIs should become better conductors when they are
cracked because the cracks themselves, which act as conductive topological
surfaces, provide additional paths for the electrical current. Significantly,
for a TI material, any surface or extended defect harbors such conduction. In
this letter, we demonstrate that small subsurface cracks formed within the
predicted 3D TI samarium hexaboride (SmB$_{6}$) via systematic scratching or
sanding results in such an increase in the electrical conduction. SmB$_{6}$ is
in a unique position among TIs to exhibit this effect because its
single-crystals are thick enough to harbor cracks, and because it remarkably
does not appear to suffer from conduction through bulk impurities. Our results
not only strengthen the building case for SmB$_{6}$'s topological nature, but
are relevant to all TIs with cracks, including TI films with grain boundaries. | 1506.08233v1 |
2018-12-14 | VI3 - a new layered ferromagnetic semiconductor | Two-dimensional (2D) materials are promising candidates for next-generation
electronic devices. In this regime, insulating 2D ferromagnets, which remain
rare, are of special importance due to their potential for enabling new device
architectures. Here we report the discovery of ferromagnetism in a layered van
der Waals semiconductor, VI3, which is based on honeycomb vanadium layers
separated by an iodine-iodine van der Waals gap. It has a BiI3-type structure
(R-3, No.148) at room temperature, and our experimental evidence suggests that
it may undergo a subtle structural phase transition at 78 K. VI3 becomes
ferromagnetic at 49 K, below which magneto-optical Kerr effect imaging clearly
shows ferromagnetic domains, which can be manipulated by the applied external
magnetic field. The optical band gap determined by reflectance measurements is
0.6 eV, and the material is highly resistive. | 1812.05982v1 |
2019-01-06 | Low-Frequency Noise Spectroscopy of Charge-Density-Wave Phase Transitions in Vertical Quasi-2D Devices | We report results regarding the electron transport in vertical quasi-2D
layered 1T-TaS2 charge-density-wave devices. The low-frequency noise
spectroscopy was used as a tool to study changes in the cross-plane electrical
characteristics of the quasi-2D material below room temperature. The noise
spectral density revealed strong peaks - changing by more than an
order-of-magnitude - at the temperatures closely matching the electrical
resistance steps. Some of the noise peaks appeared below the temperature of the
commensurate to nearly-commensurate charge-density-wave transition, possibly
indicating the presence of the debated "hidden" phase transitions. These
results confirm the potential of the noise spectroscopy for investigations of
electron transport and phase transitions in novel materials. | 1901.01475v1 |
2019-06-12 | Simulation and experimental studies of induction hardening behavior of a new medium-carbon, low-alloy wear resistance steel | Flux2D commercial software together with a Gleeble thermomechanical simulator
has been employed to numerically and physically simulate the material
properties profile of an induction hardened slurry transportation pipe made of
a recently developed 0.4 wt.% C, Nb-microalloyed steel. After calculating the
thermal history of a 400 mm diameter, 10 mm thick pipe at various positions
through the thickness, different heating and cooling paths were physically
simulated using the Gleeble machine to predict the through-thickness material
microstructure and hardness profiles. The results showed that by coupling a
phase transformation model considering the effect of heating rate on the
austenite transformation temperatures which allows calculations for arbitrary
cooling paths with calculated induction heating and quenching thermal cycles,
it has been possible to design induction hardening parameters for a slurry
transport pipe material. | 1906.05007v1 |
2019-06-15 | Nonlinear planar Hall effect | An intriguing property of three-dimensional (3D) topological insulator (TI)
is the existence of surface states with spin-momentum locking, which offers a
new frontier of exploration in spintronics. Here, we report the observation of
a new type of Hall effect in a 3D TI Bi2Se3 film. The Hall resistance scales
linearly with both the applied electric and magnetic fields and exhibits a
{\pi}/2 angle offset with respect to its longitudinal counterpart, in contrast
to the usual angle offset of {\pi}/4 between the linear planar Hall effect and
the anisotropic magnetoresistance. This novel nonlinear planar Hall effect
originates from the conversion of a nonlinear transverse spin current to a
charge current due to the concerted actions of spin-momentum locking and time
reversal symmetry breaking, which also exists in a wide class of
non-centrosymmetric materials with a large span of magnitude. It provides a new
way to characterize and utilize the nonlinear spin-to-charge conversion in a
variety of topological quantum materials. | 1906.06462v1 |
2019-06-15 | Effect of tungsten on vacancy behaviors in Ta-W alloys from first-principles | Alloying elements play an important role in the design of plasma facing
materials with good comprehensive properties. Based on first-principles
calculations, the stability of alloying element W and its interaction with
vacancy defects in Ta-W alloys are studied. The results show that W tends to
distribute dispersedly in Ta lattice, and is not likely to form precipitation
even with the coexistence of vacancy. The aggregation behaviors of W and
vacancy can be affected by their concentration competition. The increase of W
atoms has a negative effect on the vacancy clustering, as well as delays the
vacancy nucleation process, which is favorable to the recovery of point
defects. Our results are in consistent with the defect evolution observed in
irradiation experiments in Ta-W alloys. Our calculations suggest that Ta is a
potential repairing element that can be doped into Ta-based materials to
improve their radiation resistance. | 1906.06610v1 |
2019-06-24 | Electrical and magnetic properties of thin films of the spin-filter material CrVTiAl | The spin-filter material CrVTiAl is a promising candidate for producing
highly spin-polarized currents at room temperature in a nonmagnetic
architecture. Thin films of compensated-ferrimagnetic CrVTiAl have been grown
and their electrical and magnetic properties have been studied. The resistivity
shows two-channel semiconducting behavior with one disordered gapless channel
and a gapped channel with activation energy $\Delta E$=~0.1~-~0.2~eV.
Magnetoresistance measurements to B~=~35~T provide values for the mobilities of
the gapless channel, leading to an order of magnitude difference in the carrier
effective masses, which are in reasonable accord with our
density-functional-theory based results. The density of states and electronic
band structure is computed for permutations of the four sublattices arranged
differently along the (111) body diagonal, yielding metallic (Cr-V-Al-Ti),
spin-gapless (Cr-V-Ti-Al) and spin-filtering (Cr-Ti-V-Al) phases. Robustness of
the spin-gapless phase to substitutional disorder is also considered. | 1906.10222v1 |
2019-11-25 | Fracturing of polycrystalline MoS$_2$ nanofilms | The possibility of tailoring the critical strain of 2D materials will be
crucial for the fabrication of flexible devices. In this paper, the fracture in
polycrystalline MoS2 films with two different grain orientations is studied at
the micro- and nanoscale using electron microscopy. The critical uniaxial
strain is determined to be approximately 5% and independent of the sample
morphology. However, electron beam irradiation is found to enhance the
interaction between the MoS2 and the PDMS substrates, leading to an increased
critical strain that can exceed 10%. This enhancement of strain resistance was
used to fabricate a mechanically robust array of lines 1 mm in length. Finally,
nanoscale crack propagation studied by transmission electron microscopy showed
that cracks propagate along the grain boundaries as well as through the grains,
preferentially along van der Waals bonding. These results provide insight
regarding the fracture of polycrystalline 2D materials and a new method to
tailor the critical strain and nanofabrication of ultra-thin MoS2 devices using
well-developed tools, which will be of great interest to the flexible
electronics industry. | 1911.10769v1 |
2019-11-27 | Large topological Hall effect in a geometrically frustrated kagome magnet Fe$_3$Sn$_2$ | We report on the observation of a large topological Hall effect (THE) over a
wide temperature region in a geometrically frustrated Fe3Sn2 magnet with a
kagome-bilayer structure. We found that the magnitude of the THE resistivity
increases with temperature and reaches -0.875 {\mu}{\Omega}.cm at 380 K.
Moreover, the critical magnetic fields with the change of THE are consistent
with the magnetic structure transformation, which indicates that the real-space
fictitious magnetic field is proportional to the formation of magnetic
skyrmions in Fe3Sn2. The results strongly suggest that the large THE originates
from the topological magnetic spin textures and may open up further research
opportunities in exploring emergent phenomena in kagome materials. | 1911.12214v1 |
2020-01-21 | Huge linear magnetoresistance due to open orbits in $γ$-PtBi$_2$ | Some single-crystalline materials present an electrical resistivity which
decreases between room temperature and low temperatures at zero magnetic field
as in a good metal and switches to a nearly semiconductinglike behavior at low
temperatures with the application of a magnetic field. Often, this is
accompanied by a huge and nonsaturating linear magnetoresistance which remains
difficult to explain. Here we present a systematic study of the
magnetoresistance in single-crystal $\gamma$-PtBi$_2$. We observe that the
angle between the magnetic field and the crystalline $c$ axis fundamentally
changes the magnetoresistance, going from a saturating to a nonsaturating
magnetic field dependence. In between, there is one specific angle where the
magnetoresistance is perfectly linear with the magnetic field. We show that the
linear dependence of the nonsaturating magnetoresistance is due to the
formation of open orbits in the Fermi surface of $\gamma$-PtBi$_2$. | 2001.07674v2 |
2020-01-22 | Chemical segregation in Ge2Sb2Te5 thin films during in-situ heating | Germanium antimony telluride has been the most used and studied phase-change
material for electronic memory due to its suitable crystallization temperature,
amorphous to crystalline resistance contrast, and stability of the amorphous
phase. In this work, the segregation of Ge in a Ge2Sb2Te5 film of 30 nm
thickness during heating inside the transmission electron microscope was
observed and characterized. The Ge2Sb2Te5 film was deposited using sputtering
on a Protochips Fusion holder and left uncapped in atmosphere for about four
months. Oxygen incorporated within the film played a significant role in the
chemical segregation observed which resulted in amorphous Ge-O grain boundaries
and Sb and Te rich crystalline domains. Such composition changes can occur when
the phase-change material interfaces insulating oxide layers in an integrated
device and would significantly impact its electrical and thermal properties. | 2001.08100v1 |
2020-05-10 | Determination of the magnetocaloric effect from thermophysical parameters and their relationships near magnetic phase transition in doped manganites | We present the results of a comparative analysis of the magnetocaloric effect
(MCE) in Pr0.7Sr0.2Ca0.1MnO3, through direct and indirect measurements, using
experimentally measured magnetization, specific heat, magnetostriction,
resistivity, thermal diffusivity and thermal conductivity parameters. We have
demonstrated that the change in each parameter in response to a magnetic field
near the ferromagnetic-paramagnetic phase transition temperature of the
material correlates with the change in magnetic entropy. These findings allow
us to interrelate these parameters and provide an alternative, effective
approach for accessing the usefulness of magnetocaloric materials. | 2005.04569v1 |
2020-07-05 | Deep Learning based Dimple Segmentation for Quantitative Fractography | In this work, we try to address the challenging problem of dimple detection
and segmentation in Titanium alloys using machine learning methods, especially
neural networks. The images i.e. fractographs are obtained using a Scanning
Election Microscope (SEM). To determine the cause of fracture in metals we
address the problem of segmentation of dimples in fractographs i.e. the
fracture surface of metals using supervised machine learning methods.
Determining the cause of fracture would help us in material property,
mechanical property prediction and development of new fracture-resistant
materials. This method would also help in correlating the topography of the
fracture surface with the mechanical properties of the material. Our proposed
novel model achieves the best performance as compared to other previous
approaches. To the best of our knowledge, this is one the first work in
fractography using fully convolutional neural networks with self-attention for
supervised learning of dimple fractography, though it can be easily extended to
account for brittle characteristics as well. | 2007.02267v3 |
2020-07-10 | Canted Spin Texture and Quantum Spin Hall Effect in WTe2 | We report an unconventional quantum spin Hall phase in the monolayer
T$_\text{d}$-WTe$_2$, which exhibits hitherto unknown features in other
topological materials. The low-symmetry of the structure induces a canted spin
texture in the $yz$ plane, which dictates the spin polarization of
topologically protected boundary states. Additionally, the spin Hall
conductivity gets quantized ($2e^2/h$) with a spin quantization axis parallel
to the canting direction.
These findings are based on large-scale quantum simulations of the spin Hall
conductivity tensor and nonlocal resistances in multi-probe geometries using a
realistic tight-binding model elaborated from first-principle methods.
The observation of this canted quantum spin Hall effect, related to the
formation of topological edge states with nontrivial spin polarization, demands
for specific experimental design and suggests interesting alternatives for
manipulating spin information in topological materials. | 2007.05626v1 |
2020-07-14 | Tuning Conductivity and Spin Dynamics in Few-Layer Graphene via In Situ Potassium Exposure | Chemical modification, such as intercalation or doping of novel materials is
of great importance for exploratory material science and applications in
various fields of physics and chemistry. In the present work, we report the
systematic intercalation of chemically exfoliated few-layer graphene with
potassium while monitoring the sample resistance using microwave conductivity.
We find that the conductivity of the samples increases by about an order of
magnitude upon potassium exposure. The increased of number of charge carriers
deduced from the ESR intensity also reflects this increment. The doped phases
exhibit two asymmetric Dysonian lines in ESR, a usual sign of the presence of
mobile charge carriers. The width of the broader component increases with the
doping steps, however, the narrow components seem to have a constant line
width. | 2007.07057v1 |
2020-07-31 | Quantum breakdown of superconductivity in low-dimensional materials | In order to understand the emergence of superconductivity it is useful to
study and identify the various pathways leading to the destruction of
superconductivity. One way is to use the increase in Coulomb-repulsion due to
the increase in disorder, which overpowers the attractive interaction
responsible for Cooper-pair formation. A second pathway, applicable to
uniformly disordered materials, is the competition between superconductivity
and Anderson localization, which leads to electronic granularity in which phase
and amplitude fluctuations of the superconducting order parameter play a role.
Finally, a third pathway is an array of superconducting islands coupled by some
form of proximity-effect, due to Andreev-reflections, and which leads from a
superconducting state to a state with finite resistivity, which appears like a
metallic groundstate. This review summarizes recent progress in understanding
of these different pathways, including experiments in low dimensional materials
and application in superconducting quantum devices. | 2007.15870v1 |
2020-08-06 | Creep in reactive colloidal gels: a nanomechanical study of cement hydrates | From soft polymeric gels to hardened cement paste, amorphous solids under
constant load exhibit a pronounced time-dependent deformation called creep. The
microscopic mechanism of such a phenomenon is poorly understood in amorphous
materials and constitutes an even greater challenge in densely packed and
chemically reactive granular systems. Both features are prominently present in
hydrating cement pastes composed of calcium silicate hydrate (C-S-H)
nanoparticles, whose packing density increases as a function of time, while
cement hydration is taking place. Performing nano-indentation tests and
porosity measurements on a large collection of samples at various stages of
hydration, we show that the creep response of hydrating cement paste is mainly
controlled by the inter-particle distance and results from slippage between
(C-S-H) nanoparticles. Our findings provide a unique insight into the
microscopic mechanism underpinning the creep response in aging granular
materials, thus paving the way for the design of concrete with improved creep
resistance. | 2008.02617v3 |
2020-12-04 | Epitaxial stabilization of SrCu$_3$O$_4$ with infinite Cu$_{3/2}$O$_2$ layers | We report the epitaxial thin film synthesis of SrCu$_3$O$_4$ with infinitely
stacked Cu$_3$O$_4$ layers composed of edge-sharing CuO$_4$ square-planes,
using molecular beam epitaxy. Experimental and theoretical characterizations
showed that this material is a metastable phase that can exist by applying
tensile biaxial strain from the (001)-SrTiO$_3$ substrate. SrCu$_3$O$_4$ shows
an insulating electrical resistivity in accordance with the Cu$^{2+}$ valence
state revealed X-ray photoelectron spectroscopy. First-principles calculations
also indicated that the unoccupied $d_{3z^2-r^2}$ band becomes substantially
stabilized owing to the absence of apical anions, in contrast to
$A_2$Cu$_3$O$_4$Cl$_2$ ($A = $Sr, Ba) with an $A_2$Cl$_2$ block layer and
therefore a trans-CuO$_4$Cl$_2$ octahedron. These results suggest that
SrCu$_3$O$_4$ is a suitable parent material for electron-doped
superconductivity based on the Cu$_3$O$_4$ plane. | 2012.02433v1 |
2021-03-02 | Bioinspired approaches to toughen calcium phosphate-based ceramics for bone repair | To respond to the increasing need for bone repair strategies, various types
of biomaterials have been developed. Among those, calcium phosphate ceramics
(CPCs) are promising since they possess a chemical composition similar to that
of bones. To be suitable for implants, CPCs need to fulfill a number of
biological and mechanical requirements. Fatigue resistance and toughness are
two key mechanical properties that are still challenging to obtain in CPCs.
This paper thus reviews and discusses current progress in the processing of
CPCs with bioinspired microstructures for load-bearing applications. First,
methods to obtain CPCs with bioinspired structure at individual lengthscales,
namely nano-, micro-, and macroscale are discussed. Then, approaches to attain
synergetic contribution of all lengthscales through a complex and biomimetic
hierarchical structure are reviewed. The processing methods and their design
capabilities are presented and the mechanical properties of the materials they
can produce are analysed. Their limitations and challenges are finally
discussed to suggest new directions for the fabrication of biomimetic bone
implants with satisfactory properties. The paper could help biomedical
researchers, materials scientists and engineers to join forces to create the
next generation of bone implants. | 2103.01443v1 |
2021-04-14 | Combining AFM imaging and elementally resolved spectro-electrochemistry for understanding stability and quality of passive films formed on Alloy 600 | Understanding elemental corrosion currents and visualizing corroding
topographies provide a detailed insight into corrosion mechanisms at the
nano-scale. Here, we develop a strategy to understand the elemental
composition, corrosion resistivity and local stability of passive materials.
Specifically, we utilize a pulse voltammetry approach in a novel
electrochemical AFM cell and complement this data by real-time dissolution
currents based on spectro-electrochemical online analysis in an ICP-MS flow
cell. We study the oxide properties and their protective behaviour, when formed
under different applied potentials using alloy 600 as model sample. Both AFM
and ICP-MS data show that passive films formed on alloy 600 at around +0.3 to
+0.4~V in neutral 1 mM NaCl solution are most stable during anodic corrosion at
+1.0~V, while AFM further demonstrates that local dissolution occurs,
indicating locally varying defect levels in the passive film. In combination of
both techniques, our approach provide real-time elementally resolved and
localized information of passive film quality under corrosive conditions, and
it may prove useful for other corroding materials. | 2104.07100v1 |
2021-06-11 | Measurement of onset of structural relaxation in melt-quenched phase change materials | Chalcogenide phase change materials enable non-volatile, low-latency
storage-class memory. They are also being explored for new forms of computing
such as neuromorphic and in-memory computing. A key challenge, however, is the
temporal drift in the electrical resistance of the amorphous states that encode
data. Drift, caused by the spontaneous structural relaxation of the newly
recreated melt-quenched amorphous phase, has consistently been observed to have
a logarithmic dependence in time. Here, we show that this observation is valid
only in a certain observable timescale. Using threshold-switching voltage as
the measured variable, based on temperature-dependent and short timescale
electrical characterization, we experimentally measure the onset of drift. This
additional feature of the structural relaxation dynamics serves as a new
benchmark to appraise the different classical models to explain drift. | 2106.06270v1 |
2021-08-08 | Strong-coupling superconductivity of SrIr2 and SrRh2: Phonon engineering of metallic Ir and Rh | Experimental and theoretical studies on superconductivity in SrIr$_2$ and
SrRh$_2$ Laves phases are presented. The measured resistivity, heat capacity,
and magnetic susceptibility confirm the superconductivity of these compounds
with $T_c$ = 6.07 K and 5.41 K, respectively. Electronic structure calculations
show that the Fermi surface is mostly contributed by 5$d$ (4$d$) electrons of
Ir (Rh), with Sr atoms playing the role of electron donors. The effect of the
spin-orbit coupling is analyzed and found to be important in both materials.
Lattice dynamics and electron-phonon coupling (EPC) are studied and the strong
electron-phonon interaction is found, contributed mostly by the low-frequency
Ir and Rh vibrations. The enhancement of EPC when compared to weakly-coupled
metallic Ir and Rh is explained by the strong modifications in the propagation
of phonons in the network of Ir (Rh) tetrahedrons, which are the building
blocks of the Laves phase, and originate from the metallic fcc structures of
elemental iridium and rhodium. | 2108.03692v1 |
2021-08-06 | Manipulating thermal fields with inhomogeneous heat spreaders | We design a class of spatially inhomogeneous heat spreaders in the context of
steady-state thermal conduction leading to spatially uniform thermal fields
across a large convective surface. Each spreader has a funnel-shaped design,
either in the form of a trapezoidal prism or truncated cone, and is forced by a
thermal source at its base. We employ transformation-based techniques, commonly
used to study metamaterials, to determine the require thermal conductivity for
the spreaders. The obtained materials, although strongly anisotropic and
inhomogeneous, can be accurately approximated by assembling isotropic,
homogeneous layers, rendering them realisable. An alternative approach is then
considered for the conical and trapezoidal spreaders by dividing them into two
or three isotropic, homogeneous components respectively. We refer to these
simple configurations as neutral layers. All designs are validated numerically
both with and without the effects of thermal contact resistance between
interfaces. Such novel designs pave the way for future materials that can
manipulate and control the flow of heat, helping to solve traditional heat
transfer problems such as controlling the temperature of an object and energy
harvesting. | 2108.04881v2 |
2021-08-20 | Peak in the superconducting transition temperature of the nonmagnetic topological line-nodal material CaSb$_2$ under pressure | Investigating the pressure dependence of the superconducting (SC) transition
temperature $T_{\rm c}$ is crucial for understanding the SC mechanism. Herein,
we report on the pressure dependence of $T_{\rm c}$ in the nonmagnetic
topological line-nodal material CaSb$_2$, based on measurements of electric
resistance and alternating current magnetic susceptibility. $T_{\rm c}$
initially increases with increasing pressure and peaks at $\sim$ 3.1~GPa. With
a further increase in pressure, $T_{\rm c}$ decreases and finally becomes
undetectable at 5.9~GPa. Because no signs of phase transition or Lifshitz
transition are observed in the normal state, the peculiar peak structure of
$T_{\rm c}$ suggests that CaSb$_2$ has an unconventional SC character. | 2108.08992v1 |
2021-09-09 | Bias factor of dislocation loops in quasicrystalline materials | Vacancy swelling of quasicrystals under irradiation is considered. In
quasicrystals, the evolution of dislocations is accompanied by the formation of
phasons which are localized topological defects of the vacancy and interstitial
types. At moderate temperatures the diffusivity of phasons is low which leads
to the formation of ring-or disk-shaped phason trails inside dislocation loops.
To find the capture efficiency of point defects by a dislocation loop with the
complementary ring of phasons the steady-state drift-diffusional problem is
solved in the toroidal geometry by the successive overrelaxation method. It is
shown that phasons significantly reduce the bias of dislocations towards
absorption of interstitial atoms. For this reason, quasicrystalline materials
are predicted to exhibit increased resistance to vacancy swelling. | 2109.04136v2 |
2021-09-20 | Coexistence of superconductivity and weak anti-localization at KTaO3 (111) interfaces | The intersection of two-dimensional superconductivity and topologically
nontrivial states hosts a wide range of quantum phenomena, including Majorana
fermions. Coexistence of topologically nontrivial states and superconductivity
in a single material, however, remains elusive. Here, we report on the
observation of two-dimensional superconductivity and weak anti-localization at
the TiOx/KTaO3(111) interfaces. A remnant, saturating resistance persists below
the transition temperature as superconducting puddles fail to reach phase
coherence. Signatures of weak anti-localization are observed below the
superconducting transition, suggesting the coexistence of superconductivity and
weak anti-localization. The superconducting interfaces show roughly one order
of magnitude larger weak anti-localization correction, compared to
non-superconducting interfaces, alluding to a relatively large coherence length
in these interfaces. | 2109.09786v1 |
2021-09-23 | Plastic deformation of the CaMg$_{2}$ C14-Laves phase from 50-250$^\circ$C | Intermetallic phases can significantly improve the creep resistance of
magnesium alloys, extending their use to higher temperatures. However, little
is known about the deformation behaviour of these phases at application
temperatures, which are commonly below their macroscopic
brittle-to-ductile-transition temperature. In this study, we therefore
investigate the activation of different slip systems of the CaMg$_2$ phase and
the occurrence of serrated yielding in the temperature range from 50$^\circ$C
to 250$^\circ$C. A decreasing amount of serrated flow with increasing
temperature suggests that solute atoms govern the flow behaviour when the
CaMg$_{2}$ phase is off-stoichiometric. | 2109.11367v1 |
2021-11-08 | Microstructure and the Boson-peak in thermally-treated In_{x}O films | We report on the correlation between the boson-peak and structural changes
associated with thermally-treating amorphous indium-oxide films. In this
process, the resistance of a given sample may decrease by a considerable margin
while its amorphous structure is preserved. In the present study, we focus on
the changes that result from the heat-treatment by employing
electron-microscopy, X-ray, and Raman spectroscopy. These techniques were used
on films with different stoichiometry and thus different carrier-concentration.
The main effect of heat-treatment is material densification, which presumably
results from elimination of micro-voids. The densified system presents better
wavefunction-overlap and more efficient connectivity for the current flow.
X-ray, and electron-beam diffraction experiments indicate that the heat-treated
samples show significantly less spatial heterogeneity with only a moderate
change of the radial-distribution function metrics. These results are
consistent with the changes that occur in the boson-peak characteristics due to
annealing as observed in their Raman spectra. | 2111.04277v1 |
2021-11-11 | NbReSi: A Noncentrosymetric Superconductor with Large Upper Critical Field | We report the discovery of superconductivity in noncentrosymmetric NbReSi,
which crystallizes in a hexagonal ZrNiAl-type crystal structure with space
group $P\bar{6}2m$ (No.~189). Bulk superconductivity, with $T_c$ = 6.5 K was
characterized via electrical-resistivity, magnetization, and heat-capacity
measurements. The low-temperature electronic specific heat suggests a fully
gapped superconducting state in NbReSi, while a large upper critical field of
$\mu_0H_\mathrm{c2}(0)$ $\sim$ 12.6 T is obtained, which is comparable to the
weak-coupling Pauli limit. The electronic band-structure calculations show that
the density of states at the Fermi level are dominated by Re and Nb
$d$-orbitals, with a sizeable band splitting induced by the antisymmetric
spin-orbit coupling. NbReSi represents another candidate material for revealing
the puzzle of time-reversal symmetry breaking observed in some Re-based
superconductors and its relation to the lack of inversion symmetry. | 2111.06010v1 |
2021-11-14 | Superconductivity in noncentrosymmetric NbReSi investigated by muon spin rotation and relaxation | Noncentrosymmetric materials are promising paradigm to explore unconventional
superconductivity. In particular, several Re containing noncentrosymmetric
materials have attracted considerable attention due to a superconducting state
with a broken time reversal symmetry. A comprehensive study on the
superconducting ground state of NbReSi was investigated using magnetization,
resistivity, and muon spin rotation/relaxation measurements. Zero field muon
spectroscopy results showed the absence of any spontaneous magnetic field below
the superconducting transition temperature, T$ _{c} $ = 6.29 K, indicating the
preserved time-reversal symmetry. Transverse field muon spin rotation
measurements confirms a s-wave nature of the sample with $\Delta(0)/k_{B}T_{c}
$ = 1.726. This study urges further investigation on more noncentrosymmetric
materials to elucidate the selective appearance of unconventional nature and
unveil its dependence on antisymmetric spin-orbit coupling strength. | 2111.07247v1 |
2021-12-26 | Tuning Ferroelectrics to Antiferroelectrics in Multiferroic LaxSr1-xFe12O19 Ceramics | The combination of antiferroelectricity (AFE) and ferromagnetism (FM) in one
structure would allow the development of new type of multiferroic candidates,
which be applicable not only in magnetoelectric memories but also in novel
energy storage devices. Here we propose a novel type of multiferroic candidate
LaxSr1-xFe12O19, whose room temperature state could betuned from ferroelectrics
(FE) to antiferroelectrics by changing x from 0 to 0.5. The emphasis of this
paper will be focused on the La0.5Sr0.5Fe12O19 system, in which full AFE and FM
coexist. The pure antiferroelectric behavior in La0.5Sr0.5Fe12O19 ceramics is
demonstrated by double polarization-electric field (P-E) hysteresis loops,
which are fully separated by a linear antiferroelectric AFE component with zero
net polarization. The material of La0.2Sr0.7Fe12O19 with the intermediate
composition exhibits a hybrid ferroelectric/antiferroelectric state. The
recoverable energy density of the antiferroelectric La0.5Sr0.5Fe12O19 phase
reaches 14.3 J/cm3. This material demonstrates strong magnetoelectric coupling
and giant magnetoresistance (GMR) effect. A 1.1T magnetic field generates
electronic polarization up to 0.95uC/cm2, reduce the resistance by 117%,
enhances dielectric constants by 540% and right shifts the maximum dielectric
loss peak by 208 kHz. The combined functional responses provide an opportunity
to develop novel multifunctional electric and energy storage devices. | 2112.13307v1 |
2022-01-03 | Aerogel from sustainably grown bacterial cellulose pellicle as thermally insulative film for building envelope | Improving building energy performance requires the development of new highly
insulative materials. An affordable retrofitting solution comprising a thin
film could improve the resistance to heat flow in both residential and
commercial buildings and reduce overall energy consumption. Here we propose
cellulose aerogel films formed from pellicles produced by the bacteria
Gluconacetobacter hansenii as insulation materials. We studied the impact of
density and nanostructure on the aerogels' thermal properties. Thermal
conductivity as low as 13 mW/(K*m) was measured for native pellicle-based
aerogels dried as-is with minimal post-treatment. The use of waste from the
beer brewing industry as a solution to grow the pellicle maintained the
cellulose yield obtained with standard Hestrin-Schramm medium, making our
product more affordable and sustainable. In the future, our work can be
extended through further diversification of the sources of substrate among food
wastes, facilitating larger potential production and applications. | 2201.00449v1 |
2022-03-13 | Electronic and topological properties of the van der Waals layered superconductor PtTe | We report the crystal growth and structural and electronic properties of
superconducting, van der Waals layered PtTe. Easily cleavable crystals with a
plate-like morphology consistent with the layered structure were grown from a
platinum rich flux. A consistent determination of $T_c = 0.57$ K is made from
the onset of diamagnetism, the zero of resistivity, and the midpoint of the
heat capacity jump. The observed behavior is consistent with type-II
superconductivity, with upper critical field at $T=0$ estimated using the
Werthamer-Helfand-Hohenberg theory to be 143 and 65 Oe for fields out of and in
the plane, respectively. The heat capacity discontinuity is close to the weak
coupling BCS value. Density functional theory calculations and analysis of the
electronic structure finds that PtTe is a topological semimetal with numerous
surface states, but suggests the superconducting state itself may be
topologically trivial. Angle resolved photoemission spectroscopy reveals a
normal-state Fermi surface in remarkable agreement with theory, and confirms
the overall topological nature of the material by experimental identification
of the surface bands. Together, these findings identify PtTe as an interesting
example of a cleavable, topological, and superconducting material. | 2203.06655v1 |
2022-04-28 | Vacancy formation energies and migration barriers in multi-principal element alloys | Multi-principal element alloys (MPEAs) continue to garner interest as
structural and plasma-facing materials due to their structure stability and
increased resistance to radiation damage. Despite sensitivity of mechanical
behavior to irradiation and point-defect formation, there has been scant
attention on understanding vacancy stability and diffusion in refractory-based
MPEAs. Using density-functional theory, we examine vacancy stability and
diffusion barriers in body-centered cubic (Mo0.95W0.05)0.85Ta0.10(TiZr)0.05.
The results in this MPEA show strong dependence on environment, originating
from local lattice distortion associated with charge-transfer between
neighboring atoms that vary with different chemical environments. We find a
correlation between degree of lattice distortion and migration barrier: (Ti,
Zr) with less distortion have lower barriers, while (Mo, W) with larger
distortion have higher barriers, depending up local environments. Under
irradiation, our findings suggest that (Ti, Zr) are significantly more likely
to diffuse than (Mo, W) while Ta shows intermediate effect. As such, material
degradation caused by vacancy diffusion can be controlled by tuning composition
of alloying elements to enhance creep strength at extreme operating
temperatures and harsh conditions. | 2204.13616v1 |
2022-08-01 | Boundary scattering in micro-size crystal of topological Kondo insulator SmB$_6$ | We have studied the effects of phonon-boundary scattering on the thermal
transport in topological Kondo insulator, SmB$_6$. The studies have been
performed by using the $3\omega$ method in the temperature range 300K - 3K. We
show that the observed thermal conductivity of micro-size SmB$_6$ is of the
order of magnitude smaller than for a bulk single-crystal. Using the Callaway
model we analyzed the low-temperature lattice thermal conductivity of the micro
crystal and show that phonon scattering by sample boundaries plays a major role
in the thermal resistance in this topological material. In addition, we show
that the temperature dependence of the lattice thermal conductivity shows a
double peak structure that suggests complex phonon-phonon or phonon-defects
interactions in SmB$_6$. These findings provide guidance for the understanding
of the thermal transport of advanced materials and devices at a micro-scale. | 2208.01145v1 |
2022-08-09 | Pressure-Independent Through-Plane Electrical Conductivity Measurements of Highly Filled Conductive Polymer Composites | Highly filled conductive polymer composites (CPCs) are widely used in
applications such as bipolar plate materials for polymer electrolyte membrane
fuel cells and redox flow batteries, electromagnetic interference shielding and
sensors due to their useful electrical properties. A common method for
determining through-plane electrical conductivities $\left(\sigma_{\rm tp}
\right)$ of such highly filled CPCs applies a conductive carbon paper between
electrodes and sample with application of external pressure to improve
electrical contact. We show the pressure-dependence of the measured
$\sigma_{\rm tp}$ can be eliminated by using a liquid metal such as the
gallium-indium eutectic alloy (EGaIn) as contact material. Results indicate
that EGaIn reduces contact resistances and cause three to five times larger
$\sigma_{\rm tp}$ compared to measurements with carbon paper contacts and
pressures up to 20 bar. | 2208.04643v1 |
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