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Condensed Matter

New submissions

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New submissions for Thu, 22 Aug 19

[1]  arXiv:1908.07513 [pdf]
Title: Hetero-bilayers of 2D-materials as a platform for excitonic superfluidity
Comments: 5 figure
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Gases (cond-mat.quant-gas); Computational Physics (physics.comp-ph)

Excitonic condensate has been a phase long-sought within bulk indirect-gap semiconductors, quantum wells, and 2D material layers, all tried as carrying media. Here we propose intrinsically stable 2D semiconductor heterostructures with doubly-indirect overlapping bands as optimal material platforms for realizing excitonic condensation. After screening a list of exfoliable 2D materials, we identify several pairs as candidate heterostructures where spontaneous excitonic condensation mediated by purely electronic interaction should occur. Unlike other single-layered systems, where excitonic condensation may be hampered by the Peierls instability, these hetero-bilayers retain stable phonon spectra while offering near-optimal carrier density. Different parts of the electron-hole phase diagram, including BEC-BCS crossover, can be accessed through in-plane strain, external electric field, or changing interlayer distance, with exciting applications in superfluid transport, Josephson-like tunneling, and dissipationless charge counterflow.

[2]  arXiv:1908.07515 [pdf]
Title: Direct and inverse spin Hall effect: Lorentz force and Zeeman energy
Comments: 3 pages main body, 3 figures, 1 page supplementary information
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

It is shown that magnetic forces as the Lorentz force, exerted on electric currents, and the force {\mu}Div(B), exerted on electron spins at rest, account for both the transverse spin imbalance typical of spin Hall effect and the transverse charge imbalance associated with pure spin currents (inverse spin Hall effect). Considering that for stationary currents the laboratory reference frame and those for which the spin up and spin down carriers are at rest are inertial systems, one can easily find the forces exerted by the lattice on both spin sub-bands, as well as the force between sub-bands.

[3]  arXiv:1908.07530 [pdf, other]
Title: Prethermal Phases of Non-equilibrium Matter in Long-range Interacting Systems
Comments: 18 pages + 12 pages appendices
Subjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

We prove the existence of non-equilibrium phases of matter in the prethermal regime of periodically-driven, long-range interacting systems, with power-law exponent $\alpha > d$, where $d$ is the dimensionality of the system. In this context, we predict the existence of a disorder-free, prethermal discrete time crystal in one dimension -- a phase strictly forbidden in the absence of long-range interactions. Finally, using a combination of analytic and numerical methods, we highlight key experimentally observable differences between such a prethermal time crystal and its many-body localized counterpart.

[4]  arXiv:1908.07545 [pdf, other]
Title: Isometric Tensor Network representation of string-net liquids
Comments: 20 pages, 22 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

Recently, a class of tensor networks called isometric tensor network states (isoTNS) was proposed which generalizes the canonical form of matrix product states to tensor networks in higher dimensions. While this ansatz allows for efficient numerical computations, it remained unclear which phases admit an isoTNS representation. In this work, we show that two-dimensional string-net liquids, which represent a wide variety of topological phases including discrete gauge theories, admit an exact isoTNS representation. We further show that the isometric form can be preserved after applying a finite depth local quantum circuit. Taken together, these results show that long-range entanglement by itself is not an obstruction to isoTNS representation and suggest that all two-dimensional gapped phases with gappable edges admit an isoTNS representation.

[5]  arXiv:1908.07548 [pdf]
Title: Ta, Ti and Hf effects on Nb$_3$Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation
Comments: 9 pages, 10 figures
Subjects: Superconductivity (cond-mat.supr-con); Materials Science (cond-mat.mtrl-sci)

The increasing demand for improving the high-field (16-22 T) performance of Nb$_3$Sn conductors requires a better understanding of the properties of modern wires much closer to irreversibility field, H$_{Irr}$. In this study we investigated the impact of Ta, Ti and Hf doping on the high-field pinning properties, the upper critical field, H$_{c2}$, and H$_{Irr}$. We found that the pinning force curves of commercial Ti and Ta doped wires at different temperatures do not scale and that the Kramer extrapolation, typically used by magnet designers to estimate high-field critical current density and magnet operational margins from lower field data, is not reliable and significantly overestimates the actual H$_{Irr}$. In contrast, new laboratory scale conductors made with Nb-Ta-Hf alloy have improved high-field J$_c$ performance and, despite contributions by both grain boundary and point defect pinning mechanisms, have more predictable high-field behavior. Using Extended X-ray Absorption Fine Structure spectroscopy, EXAFS, we found that for the commercial Ta and Ti doped conductors, the Ta site occupancy in the A15 structure gradually changes with the heat treatment temperature whereas Ti is always located on the Nb site with clear consequences for H$_{c2}$. This work reveals the still limited understanding of what determines H$_{c2}$, H$_{Irr}$ and the high-field J$_c$ performance of Nb$_3$Sn and the complexity of optimizing these conductors so that they can reach their full potential for high-field applications.

[6]  arXiv:1908.07575 [pdf, other]
Title: Sparse sampling approach to efficient ab initio calculations at finite temperature
Comments: 13 pages, 8 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Computational Physics (physics.comp-ph)

Efficient ab initio calculations of correlated materials at finite temperature require compact representations of the Green's functions both in imaginary time and Matsubara frequency. In this paper, we introduce a general procedure which generates sparse sampling points in time and frequency from compact orthogonal basis representations, such as Chebyshev polynomials and intermediate representation (IR) basis functions. These sampling points accurately resolve the information contained in the Green's function, and efficient transforms between different representations are formulated with minimal loss of information. As a demonstration, we apply the sparse sampling scheme to diagrammatic $GW$ and GF2 calculations of a hydrogen chain, of noble gas atoms and of a silicon crystal.

[7]  arXiv:1908.07579 [pdf, other]
Title: Multiple Andreev reflections and Shapiro steps in a Ge-Si nanowire Josephson junction
Journal-ref: Phys. Rev. Materials 3, 084803 (2019)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We present a Josephson junction based on a Ge-Si core-shell nanowire with transparent superconducting Al contacts, a building block which could be of considerable interest for investigating Majorana bound states, superconducting qubits and Andreev (spin) qubits. We demonstrate the dc Josephson effect in the form of a finite supercurrent through the junction, and establish the ac Josephson effect by showing up to 23 Shapiro steps. We observe multiple Andreev reflections up to the sixth order, indicating that charges can scatter elastically many times inside our junction, and that our interfaces between superconductor and semiconductor are transparent and have low disorder.

[8]  arXiv:1908.07580 [pdf, ps, other]
Title: Magic high-order harmonics from a quasi-one-dimensional hexagonal solid
Comments: 16 pages, Four figures, 2 Tables
Journal-ref: Physical Review B, Volume 99, 094313 (2019)
Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)

High-order harmonic generation (HHG) from atoms is a coherent light source that opens up attosecond physics, but it is the application of HHG to solids that brings much of excitement for the last decade. Here we report a completely new kind of harmonics in a quasi-one-dimensional and hexagonal barium titanium sulfide: Under circularly polarized laser excitation, harmonics are generated only at first, fifth, seventh and eleventh orders. These magic harmonics appear only with circularly polarized light, not with linearly polarized light. Neither cubic nor tetragonal cells have magic harmonics even with circularly polarized light. Through a careful group-theory analysis, we find that two subgroups of symmetry operations unique to the hexagonal symmetry cancel out third and ninth harmonics. This feature presents a rare opportunity to develop HHG into a crystal-structure characterization tool for phase transitions between hexagonal and nonhexagonal structures.

[9]  arXiv:1908.07594 [pdf, other]
Title: Chaotic wave packet spreading in two-dimensional disordered nonlinear lattices
Comments: 15 pages, 5 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Chaotic Dynamics (nlin.CD); Computational Physics (physics.comp-ph)

We reveal the generic characteristics of wave packet delocalization in two-dimensional nonlinear disordered lattices by performing extensive numerical simulations in two basic disordered models: the Klein-Gordon system and the discrete nonlinear Schr\"{o}dinger equation. We find that in both models (a) the wave packet's second moment asymptotically evolves as $t^{a_m}$ with $a_m \approx 1/5$ ($1/3$) for the weak (strong) chaos dynamical regime, in agreement with previous theoretical predictions~\cite{F10}, (b) chaos persists, but its strength decreases in time $t$ since the finite time maximum Lyapunov exponent $\Lambda$ decays as $\Lambda \propto t^{\alpha_{\Lambda}}$, with $\alpha_{\Lambda} \approx -0.37$ ($-0.46$) for the weak (strong) chaos case, and (c) the deviation vector distributions show the wandering of localized chaotic seeds in the lattice's excited part, which induces the wave packet's thermalization. We also propose a dimension-independent scaling between the wave packet's spreading and chaoticity, which allows the prediction of the obtained $\alpha_{\Lambda}$ values.

[10]  arXiv:1908.07601 [pdf, ps, other]
Title: Novel Fracton Phases from Gauge Theories
Comments: 13 pages, 12 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)

We introduce new models of fracton order based on $\mathbb{Z}_2$ lattice gauge theories in $d=2$ and $d=3$ spatial dimensions. In the $3d$ models, the ground state degeneracy grows exponentially with the square of the linear size of the system at the same time as it exhibits a dependence on the topology of the underlying manifold. Also, there are completely mobile gauge charges living along with immobile fractons. Until now most fracton models were obtained from a process of gauging subsystem symmetries of some generalized Abelian lattice gauge theories, and our method shows that fracton phases are also present in more usual lattice gauge theories. We also show how to construct fracton models from lattice gauge theories with arbitrary, possibly non-Abelian finite gauge groups and as examples, we study fracton models obtained from choosing $\mathbb{Z}_3$ and $S_3$ as gauge groups.

[11]  arXiv:1908.07606 [pdf, ps, other]
Title: Vortex Shear Banding Transitions in Superconductors with Inhomogeneous Pinning Arrays
Comments: 14 pages, 11 figures
Subjects: Superconductivity (cond-mat.supr-con); Soft Condensed Matter (cond-mat.soft)

We numerically examine the flow of superconducting vortices in samples containing square pinning arrays in which a band of pins is removed. When a drive is applied at an angle with respect to the band orientation, we find that the vortex depinning initiates in the pin-free channel. The moving vortices form a series of quasi-one-dimensional shear bands that begin flowing in the bulk of the pin-free channel, and the motion gradually approaches the edge of the pinned region. The consecutive depinning of each shear band appears as a series of jumps in the velocity-force curves and as sharp steps in the spatial velocity profiles. When a constant drive is applied parallel to the pin-free channel along with a gradually increasing perpendicular drive, the net vortex velocity decreases in a series of steps that correspond to the immobilization of bands of vortices, and in some cases the flow can drop to zero, creating a field effect transistor phenomenon. These results should also be relevant to other types of systems that exhibit depinning in the presence of inhomogeneous pinning.

[12]  arXiv:1908.07609 [pdf]
Title: Persistent, rewritable frequency tuning of a nanoelectromechanical resonator using photoinduced doping
Comments: 19 pages, 4 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)

Tuning the frequency of a resonant element is of vital importance in both the macroscopic world, such as when tuning a musical instrument, as well as at the nanoscale. In particular, precisely controlling the resonance frequency of isolated nanoelectromechanical resonators (NEMS) has enabled innovations such as tunable mechanical filtering and mixing as well as commercial technologies such as robust timing oscillators. Much like their electronic device counterparts, the potential of NEMS grows when they are built up into large-scale arrays. Such arrays have enabled neutral-particle mass spectroscopy and have been proposed for ultralow-power alternatives to traditional analog electronics as well as nanomechanical information technologies like memory, logic, and computing. A fundamental challenge to these applications is to precisely tune the vibrational frequency and coupling of all resonators in the array, since traditional tuning methods, like patterned electrostatic gating or dielectric tuning, become intractable when devices are densely packed. Here, we demonstrate a persistent, rewritable, scalable, and high-speed frequency tuning method for graphene-based NEMS. Our method uses a focused laser and two shared electrical contacts to photodope individual resonators by simultaneously applying optical and electrostatic fields. After the fields are removed, the trapped charge created by this process persists and applies a local electrostatic tension to the resonators, tuning their frequencies. By providing a facile means to locally address the strain of a NEMS resonator, this approach lays the groundwork for fully programmable large-scale NEMS lattices and networks.

[13]  arXiv:1908.07612 [pdf, other]
Title: Accessing temperature waves: a dispersion relation perspective
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

In order to account for non-Fourier heat transport, occurring on short time and length scales, the often-praised Dual-Phase-Lag (DPL) model was conceived, introducing a causality relation between the onset of heat flux and the temperature gradient. The most prominent aspect of the first-order DPL model is the prediction of wave-like temperature propagation, the detection of which still remains elusive. Among the challenges to make further progress is the capability to disentangle the intertwining of the parameters affecting wave-like behaviour. This work contributes to the quest, providing a straightforward, easy-to-adopt, analytical mean to inspect the optimal conditions to observe temperature wave oscillations. The complex-valued dispersion relation for the temperature scalar field is investigated for the case of a localised temperature pulse in space, and for the case of a forced temperature oscillation in time. A modal quality factor is introduced showing that, for the case of the temperature gradient preceding the heat flux, the material acts as a bandpass filter for the temperature wave. The bandpass filter characteristics are accessed in terms of the relevant delay times entering the DPL model. The optimal region in parameters space is discussed in a variety of systems, covering nine and twelve decades in space and time-scale respectively. The here presented approach is of interest for the design of nanoscale thermal devices operating on ultra-fast and ultra-short time scales, a scenario here addressed for the case of quantum materials and graphite.

[14]  arXiv:1908.07628 [pdf, other]
Title: A linear-scaling algorithm for rapid computation of inelastic transitions in the presence of multiple electron scattering
Comments: 10 pages, 5 figures, 2 tables
Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)

Strong multiple scattering of the probe in scanning transmission electron microscopy (STEM) means image simulations are usually required for quantitative interpretation and analysis of elemental maps produced by electron energy-loss spectroscopy (EELS). These simulations require a full quantum-mechanical treatment of multiple scattering of the electron beam, both before and after a core-level inelastic transition. Current algorithms scale quadratically and can take up to a week to calculate on desktop machines even for simple crystal unit cells and do not scale well to the nano-scale heterogeneous systems that are often of interest to materials science researchers. We introduce an algorithm with linear scaling that typically results in an order of magnitude reduction in compute time for these calculations without introducing additional error and discuss approximations that further improve computational scaling for larger scale objects with modest penalties in calculation error. We demonstrate these speed-ups by calculating the atomic resolution STEM-EELS map using the L-edge transition of Fe, for of a nanoparticle 80 \AA\ in diameter in 16 hours, a calculation that would have taken at least 80 days using a conventional multislice approach.

[15]  arXiv:1908.07629 [pdf, other]
Title: Spin-polarized currents in corrugated graphene nanoribbons
Comments: 9 pages, 9 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We investigate the production of spin-polarized currents in corrugated graphene nanoribbons. We model the corrugation as multiple regions with Rashba spin-orbit interactions. Concave and convex curvatures are modeled as Rashba regions with opposite signs. Numerical examples for different separated Rashba-zone geometries calculated within the tight-binding approximation are provided. Remarkably, the spin-polarized current in a system with several Rashba areas can be enhanced with respect to the case with a single Rashba part of the same total area. The enhancement is larger for configurations with multiple regions with the same Rashba sign. Additionally, we relate the appearance of the spin-polarized currents to novel symmetry relations between the spin-dependent conductances. These symmetries turn out to be a combination of different symmetry operations in real and spin spaces, as those occurring in non-planar systems like carbon nanotubes. Our results show that two-dimensional devices with Rashba spin-orbit interaction can be used as excellent spintronic devices in an all-electrical or mechanical setup.

[16]  arXiv:1908.07648 [pdf]
Title: Hot exciton transport in WSe2 monolayers
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph); Optics (physics.optics)

We experimentally demonstrate hot exciton transport in h-BN encapsulated WSe2 monolayers via spatially and temporally resolved photoluminescence measurements at room temperature. We show that the nonlinear evolution of the mean squared displacement of the non-resonantly excited hot exciton gas is primarily due to the relaxation of its excess kinetic energy and is characterized by a density-dependent fast expansion that converges to a slower, constant rate expansion. We also observe saturation of the hot exciton gas' expansion rate at high excitation densities due to the balance between Auger-assisted hot exciton generation and the phonon-assisted hot exciton relaxation processes.

[17]  arXiv:1908.07649 [pdf, other]
Title: Nematic state in CeAuSb$_{2}$
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

At ambient pressure and zero field, tetragonal CeAuSb$_{2}$ hosts stripe antiferromagnetic order at $T_{N} = 6.3$ K. Here we first show via bulk thermodynamic probes and x-ray diffraction measurements that this magnetic order is connected with a structural phase transition to a superstructure which likely breaks $C_{4}$ symmetry, thus signaling nematic order. The temperature-field-pressure phase diagram of CeAuSb$_{2}$ subsequently reveals the emergence of additional ordered states under applied pressure at a multicritical point. Our phenomenological model supports the presence of a vestigial nematic phase in CeAuSb$_{2}$ akin to iron-based high-temperature superconductors; however, superconductivity, if present, remains to be discovered.

[18]  arXiv:1908.07652 [pdf, ps, other]
Title: Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance
Comments: 8 pages, 6 figures
Journal-ref: Phys. Rev. B 100, 064413 (2019)
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures T_C ~ 85 and 23 K, respectively. UTeS and USeS crystallize in the same orthorhombic TiNiSi-type crystal structure as those of uranium ferromagnetic superconductors URhGe and UCoGe. We determine the critical exponents, beta for the spontaneous magnetization M_s, gamma for the magnetic susceptibility chi, and delta for the magnetization isotherm at T_C with several methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising model with short-range magnetic exchange interactions. Similar sets of the critical exponents have been reported for the uranium ferromagnetic superconductors UGe_2 and URhGe, and uranium intermetallic ferromagnets URhSi, UIr and U(Co_0.98Os_0.02)Al. The universality class of the ferromagnetic transitions in UTeS and USeS may belong to the same one for the uranium compounds. The novel critical phenomenon associated with the ferromagnetic transition is observed not only in the uranium intermetallic ferromagnets with the itinerant 5f electrons but also in the low carrier concentration systems UTeS and USeS with the localized 5f electrons. The large negative magnetoresistance in UTeS and USeS, and the superconductivity in UGe_2 and URhGe share the similarity of their closeness to the ferromagnetism characterized by the novel critical exponents.

[19]  arXiv:1908.07671 [pdf, other]
Title: Magnetic-field Induced Quantum Phases in Tensor Network Study of Kitaev Magnets
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

Recent discovery of the half-quantized thermal Hall conductivity in $\alpha$-RuCl$_3$, a candidate material for the Kitaev spin liquid, suggests the presence of a highly-entangled quantum state in external magnetic fields. This field-induced phase appears between the low-field zig-zag magnetic order and the high-field polarized state. Motivated by this experiment, we study possible field-induced quantum phases in theoretical models of the Kitaev magnets, using the two-dimensional tensor network approach or infinite tensor product states (iTPS). More specifically, we map out the magnetic-field phase diagram of the $K$-$\Gamma$-$\Gamma'$ model, where $K$ is the ferromagnetic Kitaev interaction and $\Gamma$, $\Gamma'$ are additional bond-dependent anisotropic interactions between spin-1/2 moments. We find various novel quantum ground states in addition to the chiral Kitaev spin liquid occupying a small area in the phase diagram. They form a band of emergent quantum phases in an intermediate window of external magnetic fields, somewhat reminiscent of the experiment. We discuss the implications of these results in view of the experiment and previous theoretical studies.

[20]  arXiv:1908.07692 [pdf, ps, other]
Title: Majorana zero modes by engineering topological kink states in two dimensional electron gas
Comments: 6 page, 4 figures, Supplementary include
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Majorana zero modes (MZMs)--bearing potential applications for topological quantum computing--are verified in quasi-one-dimensional (1D) Fermion systems, including semiconductor nanowires, magnetic atomic chains, planar Josephson junctions. However, the existence of multi-bands in these systems makes the MZMs fragile to the influence of disorder. Moreover, in practical perspective, the proximity induced superconductivity may be difficult and restricted for 1D systems. Here, we propose a flexible route to realize MZMs through 1D topological kink states by engineering a 2D electron gas with antidot lattices, in which both the aforementioned issues can be avoided owing to the robustness of kink states and the intrinsically attainable superconductivity in high-dimensional systems. The MZMs are verified to be quite robust against disorders and the bending of kink states, and can be conveniently tuned by varying the Rashba spin-orbit coupling strength. Our proposal provides an experimental feasible platform for MZMs with systematic manipulability and assembleability based on the present techniques in 2D electron gas system.

[21]  arXiv:1908.07702 [pdf, other]
Title: Effects of staggered Dzyaloshinskii-Moriya interactions in a quasi-two-dimensional Shastry-Sutherland model
Comments: 7 pages, 6 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

Frustrated quantum spin systems exhibit exotic physics induced by external magnetic field with anisotropic interactions. Here, we study the effect of non-uniform Dzyaloshinskii-Moriya (DM) interactions on a quasi-$2$D Shastry-Sutherland lattice using a matrix product states (MPS) algorithm. We first recover the magnetization plateau structure present in this geometry and then we show that both interdimer and intradimer DM interactions significantly modify the plateaux. The non-number-conserving intradimer interaction smoothen the shape of the magnetization curve, while the number-conserving interdimer interaction induces different small plateaux which are signatures of the finite size of the system. Interestingly, the interdimer DM interaction induces chirality in the system. We thus characterize these chiral phases with particular emphasis to their robustness against intradimer DM interactions.

[22]  arXiv:1908.07710 [pdf]
Title: Two-dimensional Ferromagnetic van der Waals CrX3 (X=Cl, Br, I) Monolayers with Enhanced Anisotropy and Curie Temperature
Comments: 4 figures and 11 pages
Subjects: Materials Science (cond-mat.mtrl-sci)

Among the recently widely studied van der Waals layered magnets CrX3 (X=Cl, Br, I), CrCl3 monolayer (ML) is particularly puzzling as it is solely shown by experiments to have an in-plane magnetic easy axis and, furthermore, all of previous first-principles calculation results contradict this. Through systematical first-principles calculations,we unveil that its in-plane shape anisotropy that dominates over its weak perpendicular magnetocrystalline anisotropy is responsible for the in-plane magnetic easy axis of CrCl3 ML. To tune the in-plane ferromagnetism of CrCl3 ML into the desirable perpendicular one, we propose substituting Cr with isovalent tungsten (W). We find that CrWCl6 has a strong perpendicular magnetic anisotropy and a high Curie temperature up to 76 K. Our work not only gives insight into understanding the two-dimensional ferromagnetism of van der Waals MLs but also sheds new light on engineering their performances for nanodevices.

[23]  arXiv:1908.07714 [pdf, other]
Title: Effective transport properties of conformal Voronoi-bounded columns via recurrent boundary element expansions
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Computational Physics (physics.comp-ph)

Effective transport properties of heterogeneous structures are predicted by geometric microstructural parameters, but these can be difficult to calculate. Here, a boundary element code with a recurrent series method accurately and efficiently determines the high order parameters of polygonal and conformal prisms in regular two-dimensional lattices and Voronoi tessellations (VT). This reveals that proximity to simpler estimates is associated with: centroidal VT (cf random VT), compactness, and VT structures (cf similarly compact semi-regular lattices). An error in previously reported values for triangular lattices is noted.

[24]  arXiv:1908.07728 [pdf, other]
Title: Ordering phenomena of spin trimers accompanied by large geometrical Hall effect
Comments: 15 pages, 12 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Materials Science (cond-mat.mtrl-sci)

The wavefuntion of conduction electrons moving in the background of a non-coplanar spin structure can gain a quantal phase - Berry phase - as if the electrons were moving in a strong fictitious magnetic field. Such an emergent magnetic field effect is approximately proportional to the solid angle subtended by the spin moments on three neighbouring spin sites, termed the scalar spin chirality. The entire spin chirality of the crystal, unless macroscopically canceled, causes the geometrical Hall effect of real-space Berry-phase origin, whereas the intrinsic anomalous Hall effect (AHE) in a conventional metallic ferromagnet is of the momentum-space Berry-phase origin induced by relativistic spin-orbit coupling (SOC). Here, we report the ordering phenomena of the spin-trimer scalar spin chirality and the consequent large geometrical Hall effect in the breathing kagom\'e lattice compound Dy$_3$Ru$_4$Al$_{12}$, where the Dy$^{3+}$ moments form non-coplanar spin trimers with local spin chirality. Using neutron diffraction, we show that the local spin chirality of the spin trimers as well as its ferroic/antiferroic orders can be switched by an external magnetic field, accompanying large changes in the geometrical Hall effect. Our finding reveals that systems composed of tunable spin trimers can be a fertile field to explore large emergent electromagnetic responses arising from real-space topological magnetic orders.

[25]  arXiv:1908.07730 [pdf]
Title: Pure spin current in a robust pigment-red film
Comments: 15 pages, 4 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

We report the spin current properties in a pigment-red (perylene-3,4,9,10-tetracarboxylic dianhydride: PTCDA) film prepared by thermal evaporation. In a palladium(Pd)/PTCDA/Ni80Fe20 tri-layer sample, a pure spin-current is generated in the PTCDA layer by the spin-pumping of the Ni80Fe20. The spin current is absorbed into the Pd layer, converted into a charge current with the inverse spin-Hall effect in Pd, and detected as an electromotive force. This is clear evidence for the pure spin current in a PTCDA film, and it is confirmed that a PTCDA film is useful not only as a robust protection layer material but also as a spintronic material.

[26]  arXiv:1908.07735 [pdf, other]
Title: Negative excitonic diffusion in transition metal dichalcogenides
Comments: 6 pages, 5 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

While exciton relaxation in transition metal dichalcogenides (TMDs) has been intensively studied, spatial exciton propagation has received only little attention - in spite of being a key process for optoelectronics and having already shown interesting unconventional behaviours (e.g. spatial halos). Here, we study the spatiotemporal dynamics in TMDs and track the way of optically excited excitons in time, momentum, and space. In particular, we investigate the temperature-dependent exciton diffusion including the remarkable exciton landscape constituted by bright and dark states. Based on a fully quantum mechanical approach, we show at low temperatures an unexpected negative transient diffusion. This phenomenon can be traced back to the existence of dark exciton states in TMDs and is a result of an interplay between spatial exciton diffusion and intervalley exciton-phonon scattering.

[27]  arXiv:1908.07739 [pdf, other]
Title: One- and three-dimensional quantum phase transitions and anisotropy in Rb$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

Single crystal samples of the frustrated quasi one-dimensional quantum magnet Rb$_{2}$Cu$_{2}$Mo$_{3}$O$_{12}$ are investigated by magnetic, thermodynamic and electron spin resonance (ESR) measurements. Quantum phase transitions between the gapped, magnetically ordered and fully saturated phases are observed. Surprisingly, the former has a distinctive three-dimensional character, while the latter is dominated by one-dimensional quantum spin fluctuations. The entire $H$-$T$ phase diagram is mapped out and found to be substantially anisotropic. In particular, the lower critical fields differ by over 50\% depending on the direction of applied field, while the upper ones are almost isotropic, as is the magnetization above saturation. The ESR spectra are strongly dependent on field orientation and point to a helical structure with a rigidly defined spin rotation plane.

[28]  arXiv:1908.07764 [pdf, other]
Title: Diffusion-influenced reaction rates in the presence of pair interactions
Subjects: Soft Condensed Matter (cond-mat.soft)

The kinetics of bimolecular reactions in solution depends, among other factors, on intermolecular forces such as steric repulsion or electrostatic interaction. Microscopically, a pair of molecules first has to meet by diffusion before the reaction can take place. In this work, we establish an extension of Doi's volume reaction model to molecules interacting via pair potentials, which is a key ingredient for interacting-particle-based reaction-diffusion (iPRD) simulations. As a central result, we relate model parameters and macroscopic reaction rate constants in this situation. We solve the corresponding reaction-diffusion equation in the steady state and derive semi-analytical expressions for the reaction rate constant and the local concentration profiles. Our results apply to the full spectrum from well-mixed to diffusion--limited kinetics. For limiting cases, we give explicit formulas, and we provide a computationally inexpensive numerical scheme for the general case, including the intermediate, diffusion-influenced regime. The obtained rate constants decompose uniquely into encounter and formation rates, and we discuss the effect of the potential on both subprocesses, exemplified for a soft harmonic repulsion and a Lennard-Jones potential. The analysis is complemented by extensive stochastic iPRD simulations, and we find excellent agreement with the theoretical predictions.

[29]  arXiv:1908.07768 [pdf, other]
Title: Non-affinity and fluid-coupled viscoelastic plateau for immersed fiber networks
Comments: 5 pages, 5 figures. Supplementary information provided in submission ("suppInf.pdf")
Subjects: Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)

We employ a matrix-based solver for the linear rheology of fluid-immersed disordered spring networks to reveal four distinct dynamic response regimes. One regime - completely absent in the known vacuum response - exhibits coupled fluid flow and network deformation, with both components responding non-affinely. This regime contains an additional plateau (peak) in the frequency-dependent storage (loss) modulus - features which vanish without full hydrodynamic interactions. The mechanical response of immersed networks such as biopolymers and hydrogels is thus richer than previously established, and offers additional modalities for design and control through fluid interactions.

[30]  arXiv:1908.07770 [pdf, other]
Title: Ensemble inequivalence in the Blume-Emery-Griffiths model near a fourth order critical point
Comments: 9 pages, 10 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech)

The canonical phase diagram of the Blume-Emery-Griffiths (BEG) model with infinite-range interactions is known to exhibit a fourth order critical point at some negative value of the bi-quadratic interaction $K<0$. Here we study the microcanonical phase diagram of this model for $K<0$, extending previous studies which were restricted to positive $K$. A fourth order critical point is found to exist at coupling parameters which are different from those of the canonical ensemble. The microcanonical phase diagram of the model close to the fourth order critical point is studied in detail revealing some distinct features from the canonical counterpart.

[31]  arXiv:1908.07771 [pdf, other]
Title: Collective oscillations of a two-component Fermi gas on the repulsive branch
Comments: 8 pages, 8 figures
Subjects: Quantum Gases (cond-mat.quant-gas)

We calculate frequencies of collective oscillations of two-component Fermi gas that is kept on the repulsive branch of its energy spectrum. Not only is a paramagnetic phase explored, but also a ferromagnetically separated one. Both in-, and out-of-phase perturbations are investigated, showing contributions from various gas excitations. Additionally, we compare results coming from both time-dependent Hartree-Fock and density-functional approaches.

[32]  arXiv:1908.07804 [pdf, other]
Title: Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi
Comments: 9 pages, 8 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

We report a combined theoretical and experimental investigation of half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi. Room temperature XRD analysis reveals that the alloy crystallizes in L21 disorder instead of pristine Y-type structure due to 50% swap disorder between the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal a net magnetization of 4 $\mu_B$ with Curie temperature of ~780 K. Resistivity measurement reveals the presence of localization effect below 35 K while above 100 K, a linear dependence is observed. Resistivity behavior indicates the absence of single magnon scattering, which indirectly supports the half-metallic nature. The majority spin band near the Fermi level clearly indicates the overlap of flat eg bands with sharply varying conduction bands that are responsible for the localization. In-depth analysis of the projected atomic d-orbital character of band structure reveals unusual bonding, giving rise to the flat eg bands purely arising out of Ru ions. Co-Ru swap disorder calculations indicate the robustness of half-metallic nature, even when the structure changes from Y-type to L21-type, with no major change in the net magnetization of the system. Thus, robust half-metallic nature, stable structure, and high Curie temperature make this alloy quite a promising candidate to be used as a source of highly spin-polarized currents in spintronic applications.

[33]  arXiv:1908.07843 [pdf]
Title: Microstructure and Elastic Constants of Transition Metal Dichalcogenide Monolayers from Friction and Shear Force Microscopy
Journal-ref: Advanced Materials 30 1803748 (2018)
Subjects: Materials Science (cond-mat.mtrl-sci)

Optical and electrical properties of two-dimensional transition metal dichalcogenides (TMDCs) grown by chemical vapor deposition (CVD) are strongly determined by their microstructure. Consequently, the visualization of spatial structural variations is of paramount importance for future applications. Here we demonstrate how grain boundaries, crystal orientation, and strain fields can unambiguously be identified with combined lateral force microscopy (LFM) and transverse shear microscopy (TSM) for CVD-grown tungsten disulfide (WS2) monolayers, on length scales that are relevant for optoelectronic applications. Further, angle-dependent TSM measurements enable us to acquire the fourth-order elastic constants of monolayer WS2 experimentally. Our results facilitate high-throughput and nondestructive microstructure visualization of monolayer TMDCs, insights into their elastic properties, thus providing an accessible tool to support the development of advanced optoelectronic devices based on such two-dimensional semiconductors.

[34]  arXiv:1908.07848 [pdf, other]
Title: Phase-separated symmetry-breaking vortex-lattice in a binary Bose-Einstein condensate
Authors: S. K. Adhikari
Comments: arXiv admin note: text overlap with arXiv:1811.06816
Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS)

We study spontaneous-symmetry-breaking circularly-asymmetric phase separation of vortex lattices in a rapidly rotating harmonically-trapped quasi-two-dimensional (quasi-2D) binary Bose-Einstein condensate (BEC) with repulsive inter- and intra-species interactions. The phase separated vortex lattices of the components appear in different regions of space with no overlap between the vortices of the two components, which will permit an efficient experimental observation of such vortices and accurate study of the effect of atomic interaction on such vortex lattice. Such phase separation takes place when the intra-species interaction energies of the two components are equal or nearly equal with relatively strong inter-species repulsion. When the intra-species energies are equal, the two phase-separated vortex lattices have identical semicircular shapes with one being the parity conjugate of the other. When the intra-species energies are nearly equal, the phase separation is also complete but the vortex lattices have different shapes. We demonstrate our claim with a numerical solution of the mean-field Gross-Pitaevskii equation for a rapidly rotating quasi-2D binary BEC.

[35]  arXiv:1908.07853 [pdf, other]
Title: Multimode probing of superfluid $\mathbf{^4He}$ by tuning forks
Comments: 4 pages, 3 figures
Subjects: Other Condensed Matter (cond-mat.other); Quantum Gases (cond-mat.quant-gas)

Flexural mode vibrations of miniature piezoelectric tuning forks (TF) are known to be highly sensitive to superfluid excitations and quantum turbulence in $\mathrm{^3He}$ and $\mathrm{^4He}$ quantum fluids, as well as to the elastic properties of solid $\mathrm{^4He}$, complementing studies by large scale torsional resonators. Here we explore the sensitivity of a TF, capable of simultaneously operating in both the flexural and torsional modes, to excitations in the normal and superfluid $\mathrm{^4He}$. The torsional mode is predominantly sensitive to shear forces at the sensor - fluid interface and much less sensitive to changes in the density of the surrounding fluid when compared to the flexural mode. Although we did not reach the critical velocity for quantum turbulence onset in the torsional mode, due to its order of magnitude higher frequency and increased acoustic damping, the torsional mode was directly sensitive to fluid excitations, linked to quantum turbulence created by the flexural mode. The combination of two dissimilar modes in a single TF sensor can provide a means to study the details of elementary excitations in quantum liquids, and at interfaces between solids and quantum fluid.

[36]  arXiv:1908.07868 [pdf, other]
Title: Tunable room-temperature spin galvanic and spin Hall effects in van der Waals heterostructures
Comments: 13 pages, 4 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)

Spin-orbit coupling stands as a powerful tool to interconvert charge and spin currents and to manipulate the magnetization of magnetic materials through the spin torque phenomena. However, despite the diversity of existing bulk materials and the recent advent of interfacial and low-dimensional effects, control of the interconvertion at room-temperature remains elusive. Here, we unequivocally demonstrate strongly enhanced room-temperature spin-to-charge (StC) conversion in graphene driven by the proximity of a semiconducting transition metal dichalcogenide(WS2). By performing spin precession experiments in properly designed Hall bars, we separate the contributions of the spin Hall and the spin galvanic effects. Remarkably, their corresponding conversion effiencies can be tailored by electrostatic gating in magnitude and sign, peaking nearby the charge neutrality point with a magnitude that is comparable to the largest efficiencies reported to date. Such an unprecedented electric-field tunability provides a new building block for spin generation free from magnetic materials and for ultra-compact magnetic memory technologies.

[37]  arXiv:1908.07881 [pdf, other]
Title: Apollonian Packing in Polydisperse Emulsions
Comments: 5 pages, 4 figures
Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci); Chemical Physics (physics.chem-ph)

We have discovered the existence of polydisperse High Internal-Phase-Ratio Emulsions (HIPE) in which the internal-phase droplets, present at 95% volume fraction, remain spherical and organize themselves in the available space according to Apollonian packing rules. These polydisperse HIPE are formed during emulsification of surfactant-poor compositions of oil-surfactant-water two-phase systems. Their droplet size-distributions evolve spontaneously towards power laws with the Apollonian exponent. Small-Angle X-Ray Scattering performed on aged HIPEs demonstrated that the droplet packing structure coincided with that of a numerically simulated Random Apollonian Packing. We argue that these peculiar, space-filling assemblies are a result of coalescence and fragmentation processes obeying simple geometrical rules of conserving total volume and total interface area.

[38]  arXiv:1908.07900 [pdf]
Title: Fatigue-resistant high-performance elastocaloric materials via additive manufacturing
Comments: 38 pages, 3 figures, 8 supplementary figures, 1 supplementary table
Subjects: Materials Science (cond-mat.mtrl-sci)

Elastocaloric cooling, which exploits the latent heat released and absorbed as stress-induced phase transformations are reversibly cycled in shape memory alloys, has recently emerged as a frontrunner in non-vapor-compression cooling technologies. The intrinsically high thermodynamic efficiency of elastocaloric materials is limited only by work hysteresis. Here, we report on creating high-performance low-hysteresis elastocaloric cooling materials via additive manufacturing of Titanium-Nickel (Ti-Ni) alloys. Contrary to established knowledge of the physical metallurgy of Ti-Ni alloys, intermetallic phases are found to be beneficial to elastocaloric performances when they are combined with the binary Ti-Ni compound in nanocomposite configurations. The resulting microstructure gives rise to quasi-linear stress-strain behaviors with extremely small hysteresis, leading to enhancement in the materials efficiency by a factor of five. Furthermore, despite being composed of more than 50% intermetallic phases, the reversible, repeatable elastocaloric performance of this material is shown to be stable over one million cycles. This result opens the door for direct implementation of additive manufacturing to elastocaloric cooling systems where versatile design strategy enables both topology optimization of heat exchangers as well as unique microstructural control of metallic refrigerants.

[39]  arXiv:1908.07907 [pdf, other]
Title: Nonreciprocity and Unidirectional Invisibility in Cavity Magnonics
Comments: 6 pages, 4 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We reveal the cooperative effect of coherent and dissipative magnon-photon couplings in an open cavity magnonic system, which leads to nonreciprocity with a considerably large isolation ratio and flexible controllability. Furthermore, we discover unidirectional invisibility for microwave propagation, which appears at the zero-damping condition for hybrid magnon-photon modes. A simple model is developed to capture the generic physics of the interference between coherent and dissipative couplings, which accurately reproduces the observations over a broad range of parameters. This general scheme could inspire methods to achieve nonreciprocity in other systems.

[40]  arXiv:1908.07923 [pdf, ps, other]
Title: Suppression of ferromagnetic spin fluctuations in the filled skutterudite superconductor SrOs4As12 revealed by 75As NMR-NQR measurements
Comments: 8 pages, 5 figures, accepted for publication in Phys. Rev. B. arXiv admin note: substantial text overlap with arXiv:1810.08302
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

Motivated by the recent observation of ferromagnetic spin correlations in the filled skutterudite SrFe$_4$As$_{12}$ [Ding et al., Phys. Rev. B 98, 155149 (2018)], we have carried out $^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements to investigate the role of magnetic fluctuations in a newly discovered isostructural superconductor SrOs$_4$As$_{12}$ with a superconducting transition temperature of $T_{\rm c}$ $\sim$ 4.8 K. Knight shift $K$ determined by the NQR spectrum under a small magnetic field ($\le$ 0.5 T) is nearly independent of temperature, consistent with the temperature dependence of the magnetic susceptibility. The nuclear spin-lattice relaxation rate divided by temperature, 1/$T_1T$, is nearly independent of temperature above $\sim$ 50 K and increases slightly with decreasing temperature below the temperature. The temperature dependence is reasonably explained by a simple model where a flat band structure with a small ledge near the Fermi energy is assumed. By comparing the present NMR data with those in SrFe$_4$As$_{12}$, we found that the values of $|K|$ and $1/T_1T$ in SrOs$_4$As$_{12}$ are smaller than those in SrFe$_4$As$_{12}$, indicating no obvious ferromagnetic spin correlations in SrOs$_4$As$_{12}$. From the temperature dependence of 1/$T_1$ in the superconducting state, an $s$-wave superconductivity is realized.

[41]  arXiv:1908.07939 [pdf, ps, other]
Title: Steady state cyclic behaviour of a half-plane contact in partial slip subject to varying normal load, moment, shear load, and moderate differential bulk tension
Comments: 13 pages, 6 figues
Subjects: Soft Condensed Matter (cond-mat.soft)

A new solution for a general half-plane contact in the steady state is presented. The contacting bodies are subject to a set of constant loads - normal force, shear force and bulk tension parallel with the interface - together with an oscillatory set of the same quantities. Partial slip conditions are expected to ensue for a range of these quantities. In addition, the line of action of the normal load component does not necessarily need to pass the centre-line of the contact, thereby introducing a moment and asymmetry in the contact extent. This advancement enables a mapping to be formalised between the normal and tangential problem. An exact and easy to apply recipe is defined.

[42]  arXiv:1908.07945 [pdf, ps, other]
Title: Inertial migration of neutrally-buoyant particles in superhydrophobic channels
Comments: 10 pages, 10 figures
Subjects: Soft Condensed Matter (cond-mat.soft); Fluid Dynamics (physics.flu-dyn)

At finite Reynolds numbers particles migrate across flow streamlines to their equilibrium positions in microchannels. Such a migration is attributed to an inertial lift force, and it is well-known that the equilibrium location of neutrally-buoyant particles is determined only by their size and the channel Reynolds number. Here we demonstrate that the decoration of a bottom wall of the channel by superhydrophobic grooves provides additional possibilities for manipulation of neutrally-buoyant particles. It is shown that the effective anisotropic hydrodynamic slip of such a bottom wall can be readily used to alter the equilibrium positions of particles and to generate their motion transverse to the pressure gradient. These results may guide the design of novel inertial microfluidic devices for efficient sorting of neutrally-buoyant microparticles by their size.

[43]  arXiv:1908.07950 [pdf, other]
Title: On the multifractal dimensions and statistical properties of critical ensembles characterized by the three classical Wigner-Dyson symmetry classes
Comments: 9 pages, 4 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mathematical Physics (math-ph)

We introduce a power-law banded random matrix model for the third of the three classical Wigner-Dyson ensembles, i.e., the symplectic ensemble. A detailed analysis of the statistical properties of its eigenvectors and eigenvalues, at criticality, is presented. This ensemble is relevant for time-reversal symmetric systems with strong spin-orbit interaction. For the sake of completeness, we also review the statistical properties of eigenvectors and eigenvalues of the power-law random banded matrix model for the corresponding systems in the presence and absence of time reversal invariance, previously considered in the literature. Our results show a good agreement with heuristic relations for the eigenstate and eigenenergy statistics at criticality, proposed in previous studies. With this, we provide a full picture of the power-law random banded matrix model corresponding to the three classical Wigner-Dyson ensembles.

[44]  arXiv:1908.07953 [pdf, other]
Title: Quasiclassical circuit-theory of contiguous disordered multiband superconductors
Comments: 14 pages, 8 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

We consider a general problem of a Josephson contact between two multiband superconductors with coexisting superconducting and magnetic phases. As a particular example, we use the quasiclassical theory of superconductivity to study the properties of a Josephson contact between two disordered $s^{\pm}$-wave superconductors allowing for the coexistence between superconductivity and spin-density-wave orders. The intra- and inter-band scattering effects of disorder are treated within the self-consistent Born approximation. We calculate the spatial profile of the corresponding order parameters on both sides of the interface assuming that the interface has finite reflection coefficient and use our results to evaluate the local density of states at the interface as well as critical supercurrent through the junction as a function of phase or applied voltage. Our methods are particularly well suited for describing spatially inhomogeneous states of iron-based superconductors where controlled structural disorder can be created by an electron irradiation. We reveal the connection between our theory and the circuit-theory of Andreev reflection and extend it to superconducting junctions of arbitrary nature. Lastly, we outline directions for further developments in the context of proximity circuits of correlated electron systems.

[45]  arXiv:1908.07969 [pdf, other]
Title: Magnetic signatures of domain walls in $s+is$ and $s+id$ superconductors: observability and what that can tell us about the superconducting order parameter
Comments: 8 pages, 5 figures
Subjects: Superconductivity (cond-mat.supr-con)

One of the defining features of spontaneously broken time reversal symmetry (BTRS) is the existence of domain walls, the detection of which would be strong evidence for such systems. There is keen interest in BTRS currently, in part due to recent muon spin rotation experiments, which have pointed towards $\textrm{Ba}_{1-x}\textrm{K}_x\textrm{Fe}_2\textrm{As}_2$ exhibiting spontaneously broken time reversal symmetry. A key question however is how to differentiate between the different theoretical models which describe such a state. Two particularly popular choices of model are $s+is$ and $s+id$ superconducting states. In this paper we obtain solutions for domain walls in $s+is$ and $s+id$ systems, including the effects of anisotropies, showing that in general they exhibit strong spontaneous magnetic fields that extend along the entire length of the domain wall. We will demonstrate the qualitative difference between the magnetic signatures of $s+is$ and $s+id$ domain walls and propose a procedure, that one could use to extract the superconducting pairing symmetry from the magnetic field response of domain walls.

[46]  arXiv:1908.07982 [pdf, other]
Title: Nonaffine lattice dynamics with the Ewald method reveals strongly nonaffine elasticity of α-quartz
Subjects: Materials Science (cond-mat.mtrl-sci)

A lattice dynamical formalism based on nonaffine response theory is derived for non-centrosymmetric crystals, accounting for long-range interatomic interactions using the Ewald method. The framework takes equilibrated static configurations as input to compute the elastic constants in excellent agreement with both experimental data and calculations under strain. Besides this methodological improvement, which enables faster evaluation of elastic constants without the need of explicitly simulating the deformation process, the framework provides insights into the nonaffine contribution to the elastic constants of {\alpha}-quartz. It turns out that, due to the non-centrosymmetric lattice structure, the nonaffine (softening) correction to the elastic constants is very large, such that the overall elastic constants are at least 3-4 times smaller than the affine Born-Huang estimat

[47]  arXiv:1908.07995 [pdf]
Title: On the Magnetism of C14 Nb(Fe89.4Al10.6)2 Laves Phase Intermetallic Compound
Comments: 12 Pages, 4 Figures, 18 References
Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)

C14 Nb(Fe89.4Al10.6)2 Laves phase intermetallic compound was investigated by DC magnetization (M) measurements performed in the temperature (T) interval of 20 to 175 K,under an applied magnetic field (H) ranging between 50 and 1250 Oe. Magnetization curves were recorded in the field-cooled (FC) and in the zero-field-cooled (ZFC) modes. They clearly showed an irreversible character that vanished at H=1250 Oe. Both magnetization curves exhibited well-defined peaks around T_N =72.3 K whose positions were H-independent, so they were identified as the compound's N\'eel temperature. The existence of irreversibility which decreases with H testify to a re-entrant character of magnetism in the studied compound. An increase of both MFC and MZFC observed below TN likely indicates a mixed i.e. ferromagnetic and antiferromagnetic ground magnetic state of the studied system.

[48]  arXiv:1908.08002 [pdf, other]
Title: Virtual clusters model on branching random graphs for confined fluid thermodynamics in heterogeneous solid geometry
Comments: 24 pages, 7 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)

Fluid properties near rough surfaces are crucial in both a description of fundamental surface phenomena and modern industrial material design implementations. One of the most powerful approach to model real rough materials is based on the surface representation in terms of random geometry. Understanding the influence of random solid geometry on the low temperature fluid thermodynamics is a cutting edge problem. Therefor this work extends recent studies bypassing high temperature expansion and small heterogeneity scale. We introduce random branching trees whose topology reflects the hierarchical properties of random solid geometry. This mathematical representation allows to obtain averaged free energy using novel statistical model of virtual clusters interacting through random ultrametric pairwise potentials. Excellent agreement with direct Monte Carlo calculations is obtained. Moreover, we find that this model leads to interesting features of fluid-solid interactions that have not been discussed in the literature. Our results demonstrate that at low temperature a significant impact to fluid-solid interface energy is induced by hierarchical structure of random geometry. Due to the interdisciplinary nature of the study, our approach can be generalized and applied to a wide range of quenched disorder systems on random graphs. Cooperative phenomena in biological populations and social networks seem most attractive.

[49]  arXiv:1908.08008 [pdf, other]
Title: Small polarons and the Janus nature of $\text{TiO}_\text{2}(110)$
Subjects: Materials Science (cond-mat.mtrl-sci); Computational Physics (physics.comp-ph)

Polarons are ubiquitous in many semiconductors and have been linked with conductivity and optical response of materials for photovoltaics and heterogeneous catalysis, yet how surface polarons influence adsorption remains unclear. Here, by modelling the surface of rutile titania using density functional theory, we reveal the effect of small surface polarons on water adsorption, dissociation, and hydrogen bonding. On the one hand the presence of such polarons significantly suppresses dissociation of water molecules that are bonded directly to polaronic sites. On the other hand, polarons facilitate water dissociation at certain non-polaronic sites. Furthermore, polarons strengthen hydrogen bonds, which in turn affects water dissociation in hydrogen bonded overlayer structures. This study reveals that polarons at the rutile surface have complex, multi-faceted, effects on water adsorption, dissociation and hydrogen bonding, highlighting the importance of polarons on water structure and dynamics on such surfaces. We expect that many of the physical properties of surface polarons identified here will apply more generally to surfaces and interfaces that can host small polarons, beyond titania.

Cross-lists for Thu, 22 Aug 19

[50]  arXiv:1908.07540 (cross-list from hep-th) [pdf, other]
Title: The negativity contour: a quasi-local measure of entanglement for mixed states
Comments: 19 pages, 6 figures
Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

In this paper, we study the entanglement structure of mixed states in quantum many-body systems using the $\textit{negativity contour}$, a local measure of entanglement that determines which real-space degrees of freedom in a subregion are contributing to the logarithmic negativity and with what magnitude. We construct an explicit contour function for Gaussian states using the fermionic partial-transpose. We generalize this contour function to generic many-body systems using a natural combination of derivatives of the logarithmic negativity. Though the latter negativity contour function is not strictly positive for all quantum systems, it is simple to compute and produces reasonable and interesting results. In particular, it rigorously satisfies the positivity condition for all holographic states and those obeying the quasi-particle picture. We apply this formalism to quantum field theories with a Fermi surface, contrasting the entanglement structure of Fermi liquids and holographic (hyperscale violating) non-Fermi liquids. The analysis of non-Fermi liquids show anomalous temperature dependence of the negativity depending on the dynamical critical exponent. We further compute the negativity contour following a quantum quench and discuss how this may clarify certain aspects of thermalization.

[51]  arXiv:1908.07570 (cross-list from q-bio.SC) [pdf, other]
Title: How kinesin waits for ATP affects the nucleotide and load dependence of the stepping kinetics
Subjects: Subcellular Processes (q-bio.SC); Soft Condensed Matter (cond-mat.soft); Biological Physics (physics.bio-ph)

Dimeric molecular motors walk on polar tracks by binding and hydrolyzing one ATP per step. Despite tremendous progress, the waiting state for ATP binding in the well-studied kinesin that walks on microtubule (MT), remains controversial. One experiment suggests that in the waiting state both heads are bound to the MT, while the other shows that ATP binds to the leading head after the partner head detaches. To discriminate between these two scenarios, we developed a theory to calculate accurately several experimentally measurable quantities as a function of ATP concentration and resistive force.
In particular, we predict that measurement of the randomness parameter could discriminate between the two scenarios for the waiting state of kinesin, thereby resolving this standing controversy.

[52]  arXiv:1908.07583 (cross-list from math-ph) [pdf, other]
Title: Entropy in Themodynamics: from Foliation to Categorization
Comments: 19 pages, 1 figure, a survey paper by no means an original research;
Subjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)

We overview the notion of entropy in thermodynamics. We start from the smooth case using differential forms on the manifold, which is the natural language for thermodynamics. Then the axiomatic definition of entropy as ordering on set that is induced by adiabatic processes will be outlined. Finally, the viewpoint of category theory is provided, which reinterprets the ordering structure as a category of pre-ordered sets.

[53]  arXiv:1908.07588 (cross-list from physics.optics) [pdf]
Title: Improving indistinguishability of single photons from colloidal quantum dots using nanocavities
Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

Colloidal quantum dots have garnered active research interest as quantum emitters due to their robust synthesis process and straightforward integration with nanophotonic platforms. However, obtaining indistinguishable photons from the colloidal quantum dots at room temperature is fundamentally challenging because they suffer from an extremely large dephasing rate. Here we propose an experimentally feasible method of obtaining indistinguishable single photons from an incoherently pumped solution-processed colloidal quantum dot coupled to a system of nanocavities. We show that by coupling a colloidal quantum dot to a pair of silicon nitride cavities, we can obtain comparable performance of a single photon source from colloidal quantum dots as other leading quantum emitters like defect centers and self-assembled quantum dots.

[54]  arXiv:1908.07595 (cross-list from math-ph) [pdf, other]
Title: Connection probabilities in the double-dimer model -- the case of two connectivity patterns
Subjects: Mathematical Physics (math-ph); Statistical Mechanics (cond-mat.stat-mech)

We apply the Grassmannian representation of the dimer model, an equivalent approach to Kasteleyn's solution to the close-packed dimer problem, to calculate the connection probabilities for the double-dimer model with wired/free/wired/free boundary conditions, on a rectangular subdomain of the square lattice with four marked boundary points at the corners. Using some series identities related to Schwarz-Christoffel transformations, we show that the continuum of the result is consistent with the corresponding one in the upper half-plane (previously obtained by Kenyon-Wilson), which is in turn identical to the connection probabilities for 4SLE$_4$ emanating from the boundary, or equivalently, to a conditioned version of CLE$_4$ with wired/free/wired/free boundary conditions in the context of conformal loop ensembles.

[55]  arXiv:1908.07598 (cross-list from physics.optics) [pdf, other]
Title: Unitary Light-2D matter Interaction and Universal Absorption in a Monolayer $\mbox{WS}_2$ Van der Waals Heterostructure Cavity
Subjects: Optics (physics.optics); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

A direct bandgap and large exciton binding energies provide an optical response dominated by excitons in monolayer transition-metal-dichalcogenides (TMDs). While various approaches have been applied to light-exciton interaction in TMDs, the achieved strength have been far below unity, and a complete picture of its underlying physical mechanisms and fundamental limits has not been provided. Here, we introduce a TMD-based Van der Waals heterostructure cavity that provides unitary excitonic absorption, and excitonic complexes emission that are observed at ultra-low excitation powers. Our results are in full agreement with a quantum theoretical framework introduced to describe the light-exciton-cavity interaction. We find that the subtle interplay between the radiative, non-radiative and dephasing decay rates plays a crucial role, and unveil a universal absorption law for excitons in 2D-systems. This enhanced light-exciton interaction paves the way to new possibilities for 2D semiconductors-based optoelectronic devices and allows more fundamental studies on phase-transitions of excitonic complexes.

[56]  arXiv:1908.07637 (cross-list from quant-ph) [pdf, other]
Title: Universal gates for protected superconducting qubits using optimal control
Comments: 12 pages, 6 figures
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We employ quantum optimal control theory to realize quantum gates for two protected superconducting circuits: the heavy-fluxonium qubit and the 0-$\pi$ qubit. Utilizing automatic differentiation facilitates the simultaneous inclusion of multiple optimization targets, allowing one to obtain high-fidelity gates with realistic pulse shapes. For both qubits, disjoint support of low-lying wave functions prevents direct population transfer between the computational-basis states. Instead, optimal control favors dynamics involving higher-lying levels, effectively lifting the protection for a fraction of the gate duration. For the 0-$\pi$ qubit, offset-charge dependence of matrix elements among higher levels poses an additional challenge for gate protocols. To mitigate this issue, we randomize the offset charge during the optimization process, steering the system towards pulse shapes insensitive to charge variations. Closed-system fidelities obtained are 99% or higher, and show slight reductions in open-system simulations.

[57]  arXiv:1908.07661 (cross-list from physics.app-ph) [pdf]
Title: Designing Anisotropic Microstructures with Spectral Density Function
Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)

Materials' microstructure strongly influences its performance and is thus a critical aspect in design of functional materials. Previous efforts on microstructure mediated design mostly assume isotropy, which is not ideal when material performance is dependent on an underlying transport phenomenon. In this article, we propose an anisotropic microstructure design strategy that leverages Spectral Density Function (SDF) for rapid reconstruction of high resolution, two phase, isotropic or anisotropic microstructures in 2D and 3D. We demonstrate that SDF microstructure representation provides an intuitive method for quantifying anisotropy through a dimensionless scalar variable termed anisotropy index. The computational efficiency and low dimensional microstructure representation enabled by our method is demonstrated through an active layer design case study for Bulk Heterojunction Organic Photovoltaic Cells (OPVCs). Results indicate that optimized design, exhibiting strong anisotropy, outperforms isotropic active layer designs. Further, we show that Cross-sectional Scanning Tunneling Microscopy and Spectroscopy (XSTM/S) is as an effective tool for characterization of anisotropic microstructures.

[58]  arXiv:1908.07685 (cross-list from physics.app-ph) [pdf, other]
Title: Characterising Quantum Devices at Scale with Custom Cryo-CMOS
Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We make use of a custom-designed cryo-CMOS multiplexer (MUX) to enable multiple quantum devices to be characterized in a single cool-down of a dilution refrigerator. Combined with a packaging approach that integrates cryo-CMOS chips and a hot-swappable, parallel device test platform, we describe how this setup takes a standard wiring configuration as input and expands the capability for batch-characterization of quantum devices at milli-Kelvin temperatures and high magnetic fields. The architecture of the cryo-CMOS multiplexer is discussed and performance benchmarked using few-electron quantum dots and Hall mobility-mapping measurements.

[59]  arXiv:1908.07700 (cross-list from hep-th) [pdf, other]
Title: Ishibashi States, Topological Orders with Boundaries and Topological Entanglement Entropy II -- Cutting through the boundary
Comments: 38 pages, 5 figures
Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)

We compute the entanglement entropy in a 2+1 dimensional topological order in the presence of gapped boundaries. Specifically, we consider entanglement cuts that cut through the boundaries. We argue that based on general considerations of the bulk-boundary correspondence, the "twisted characters" feature in the Renyi entropy, and the topological entanglement entropy is controlled by a "half-linking number" in direct analogy to the role played by the S-modular matrix in the absence of boundaries. We also construct a class of boundary states based on the half-linking numbers that provides a "closed-string" picture complementing an "open-string" computation of the entanglement entropy. These boundary states do not correspond to diagonal RCFT's in general. These are illustrated in specific Abelian Chern-Simons theories with appropriate boundary conditions.

[60]  arXiv:1908.07815 (cross-list from physics.app-ph) [pdf]
Title: Impact of a doping-induced space-charge region on the collection of photo-generated charge carriers in thin-film solar cells based on low-mobility semiconductors
Comments: Main text (29 pages, 7 figures) and supplemental material (7 pages, 4 figures)
Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci)

Unintentional doping of the active layer is a source for lowered device performance in organic solar cells. The effect of doping is to induce a space-charge region within the active layer, generally resulting in increased recombination losses. In this work, the impact of a doping-induced space-charge region on the current-voltage characteristics of low-mobility solar cell devices has been clarified by means of analytical derivations and numerical device simulations. It is found that, in case of a doped active layer, the collection efficiency of photo-generated charge carriers is independent of the light intensity and exhibits a distinct voltage dependence, resulting in an apparent electric-field dependence of the photocurrent. Furthermore, an analytical expression describing the behavior of the photocurrent is derived. The validity of the analytical model is verified by numerical drift-diffusion simulations and demonstrated experimentally on solution-processed organic solar cells. Based on the theoretical results, conditions of how to overcome charge collection losses caused by doping are discussed. Furthermore, the presented analytical framework provides tools to distinguish between different mechanisms leading to voltage dependent photocurrents.

[61]  arXiv:1908.07852 (cross-list from physics.app-ph) [pdf]
Title: Perfect proton selectivity in ion transport through two-dimensional crystals
Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Defect-free monolayers of graphene and hexagonal boron nitride were previously shown to be surprisingly permeable to thermal protons, despite being completely impenetrable to all gases. It remains untested whether small ions can permeate through the two-dimensional crystals. Here we show that mechanically exfoliated graphene and hexagonal boron nitride exhibit perfect Nernst selectivity such that only protons can permeate through, with no detectable flow of counterions. In the experiments, we used suspended monolayers that had few if any atomic-scale defects, as shown by gas permeation tests, and placed them to separate reservoirs filled with hydrochloric acid solutions. Protons accounted for all the electrical current and chloride ions were blocked. This result corroborates the previous conclusion that thermal protons can pierce defect-free two-dimensional crystals. Besides importance for theoretical developments, our results are also of interest for research on various separation technologies based on two-dimensional materials.

[62]  arXiv:1908.07863 (cross-list from math.PR) [pdf, other]
Title: Derivation of coupled KPZ-Burgers equation from multi-species zero-range processes
Subjects: Probability (math.PR); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph)

We consider the fluctuation fields of multi-species weakly-asymmetric zero-range interacting particle systems in one dimension, where the mass density of each species is conserved. Although such fields have been studied in systems with a single species, the multi-species setting is much less understood. Among other results, we show that, when the system starts from stationary states, with a particular property, the scaling limits of the multi-species fluctuation fields, seen in a characteristic traveling frame, solve a coupled Burgers SPDE, which is a formal spatial gradient of a coupled KPZ equation.

[63]  arXiv:1908.07913 (cross-list from nlin.SI) [pdf, ps, other]
Title: On Bethe Ansatz for a Supersymmetric Vertex Model with $\mathcal{U}_{\rm q}[{\rm osp}(2|2)^{(2)}]$
Comments: 18 pages. arXiv admin note: substantial text overlap with arXiv:hep-th/9807219
Subjects: Exactly Solvable and Integrable Systems (nlin.SI); Statistical Mechanics (cond-mat.stat-mech)

The Algebraic Bethe ansatz for a supersymmetric nineteen vertex-model constructed from a three-dimensional representation of the twisted quantum affine Lie superalgebra $\mathcal{U}_{q}[\mathrm{osp}(2|2)^{(2)}]$ is presented in detail. The eigenvalues and eigenvectors of the row-to-row transfer matrix are calculated and the corresponding Bethe Ansatz equations are obtained and analyzed numerically.

[64]  arXiv:1908.07944 (cross-list from nucl-th) [pdf, ps, other]
Title: Critical endpoint and universality class of neutron $^3P_2$ superfluids in neutron stars
Comments: 14 pages, 5 figures
Subjects: Nuclear Theory (nucl-th); Statistical Mechanics (cond-mat.stat-mech)

We study the thermodynamics and critical behavior of neutron $^3P_2$ superfluids in the inner cores of neutron stars. $^3P_2$ superfluids offer a rich phase diagram including uniaxial/biaxial nematic phases, the ferromagnetic phase, and the cyclic phase. Using the Bogoliubov-de Gennes (BdG) equation as superfluid Fermi liquid theory, we show that a strong (weak) magnetic field drives the first (second) order transition from the dihedral-two biaxial nematic phase to dihedral-four biaxial nematic phase in low (high) temperatures, and their phase boundaries are divided by the critical endpoint (CEP). We demonstrate that the set of critical exponents at the CEP satisfies the Rushbrooke, Griffiths, and Widom equalities, indicating a new universality class. At the CEP, the $^3P_2$ superfluid exhibits critical behavior with nontrivial critical exponents, indicating a new universality class. Furthermore, we find that the Ginzburg-Landau (GL) equation up to the 8th-order expansion satisfies three equalities and properly captures the physics of the CEP. This implies that the GL theory can provide a tractable way for understanding critical phenomena which may be realized in the dense core of realistic magnetars.

[65]  arXiv:1908.07954 (cross-list from nlin.AO) [pdf, other]
Title: Cross frequency coupling in next generation inhibitory neural mass models
Comments: 14 pages, 10 figures
Subjects: Adaptation and Self-Organizing Systems (nlin.AO); Disordered Systems and Neural Networks (cond-mat.dis-nn)

Coupling among neural rhythms is one of the most important mechanisms at the basis of cognitive processes in the brain. In this study we consider a neural mass model, rigorously obtained from the microscopic dynamics of an inhibitory spiking network with exponential synapses, able to autonomously generate collective oscillations (COs). These oscillations emerge via a super-critical Hopf bifurcation, and their frequencies are controlled by the synaptic time scale, the synaptic coupling and the excitability of the neural population. Furthermore, we show that two inhibitory populations in a master-slave configuration with different synaptic time scales can display various collective dynamical regimes: namely, damped oscillations towards a stable focus, periodic and quasi-periodic oscillations, and chaos. Finally, when bidirectionally coupled the two inhibitory populations can exhibit different types of theta-gamma cross-frequency couplings (CFCs): namely, phase-phase and phase-amplitude CFC. The coupling between theta and gamma COs is enhanced in presence of a external theta forcing, reminiscent of the type of modulation induced in Hippocampal and Cortex circuits via optogenetic drive.

[66]  arXiv:1908.07958 (cross-list from quant-ph) [pdf, other]
Title: Efficient Encoding of Matrix Product States into Quantum Circuits of One- and Two-Qubit Gates
Authors: Shi-Ju Ran
Comments: 6 pages, 5 figures
Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)

Matrix product state (MPS) belongs to the most important mathematical models in, for example, condensed matter physics and quantum information sciences. However, to realize an $N$-qubit MPS with large $N$ and large entanglement on a quantum platform is extremely challenging, since it requires high-level qudits or multi-body gates of two-level qubits to carry the entanglement. In this work, an efficient method that accurately encodes a given MPS into a quantum circuit with only one- and two-qubit gates is proposed. The idea is to construct the unitary matrix product operators that optimally disentangle the MPS to a product state. These matrix product operators form the quantum circuit that evolves a product state to the targeted MPS with a high fidelity. Our benchmark on the ground-state MPS's of the strongly-correlated spin models show that the constructed quantum circuits can encode the MPS's with much fewer qubits than the sizes of the MPS's themselves. This method paves a feasible and efficient path to realizing quantum many-body states and other MPS-based models as quantum circuits on the near-term quantum platforms.

[67]  arXiv:1908.07959 (cross-list from physics.comp-ph) [pdf]
Title: Inverse Structural Design of Graphene/Boron Nitride Hybrids by Regressional GAN
Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Applied Physics (physics.app-ph)

Inverse design of materials with desired properties is currently laborious and heavily relies on intuition of researchers through a trial-and-error process. The massive combinational spaces due to the constituent elements and their structural configurations are too overwhelming to be all searched even by high-throughput computations. Herein, we demonstrated a novel regressional generative adversarial network (RGAN) for inverse design of representative two-dimensional materials, graphene and boron-nitride (BN) hybrids. A significant novelty of the proposed RGAN is that it combines the supervised and regressional convolutional neural network (CNN) with the traditional unsupervised GAN, thus overcoming the common technical barrier in the traditional GANs, which cannot generate data associated with given continuous quantitative labels. The proposed RGAN enables to autonomously generate graphene/BN hybrids with any given bandgaps. Moreover, the generated structures exhibit high fidelity, yielding bandgaps within ~ 10% MAEF of the desired bandgaps as cross-validated by density functional theory (DFT) calculations. Further analysis by principle component analysis (PCA) and modified locally linear embedding (MLLE) methods on the latent features encoded by the regressor reveals that the generator has successfully generated structures that followed the statistical distribution of the real structures. It implies the possibility of the RGAN in recognizing physical rules hidden in the high-dimensional data. This new inverse design methodology would speed up the discovery and development of other 2D materials and beyond.

[68]  arXiv:1908.07971 (cross-list from physics.flu-dyn) [pdf, other]
Title: Equilibrium and stability of two-dimensional pinned drops
Comments: 5 pages, 4 figures
Subjects: Fluid Dynamics (physics.flu-dyn); Soft Condensed Matter (cond-mat.soft)

Superhydrophobicity relies on the stability of drops's interfaces pinned on sharp edges to sustain non-wetting (Cassie-Baxter) equilibrium states. Gibbs already pointed out that equilibrium is possible as long as the pinning angle at the edge falls between the equilibrium contact angles corresponding to the flanks of the edge. However, the lack of stability can restrict further the realizable equilibrium configurations. To find these limits we analyze here the equilibrium and stability of two-dimensional drops bounded by interfaces pinned on mathematically sharp edges. We are specifically interested on how the drop's stability depends on its size, which is measured with the Bond number $Bo = (\mathcal{W}_d/\ell_c)^2$, defined as the ratio of the drop's characteristic length scale $\mathcal{W}_d$ to the capillary length $\ell_c = \sqrt{\sigma/\rho g}$. Drops with a fixed volume become more stable as they shrink in size. On the contrary, open drops, i.e. capable of exchanging mass with a reservoir, are less stable as their associated Bond number decreases.

[69]  arXiv:1908.07989 (cross-list from hep-th) [pdf, ps, other]
Title: Fractional Fermion Number and Hall Conductivity of Domain Walls
Comments: 9 pages
Subjects: High Energy Physics - Theory (hep-th); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

In this letter the fractional fermion number of thick domain walls is computed. The analysis is achieved by developing the heat kernel expansion of the spectral eta functon of the Dirac Hamiltonian governing the fermionic fluctuations around the domain wall. A formula is derived showing that a non null fermion number is always accompanied by a Hall conductivity induced on the wall. In the limit of thin and impenetrable walls the chiral bag boundary conditions arise, and the Hall conductivity is computed for this case as well.

[70]  arXiv:1908.07991 (cross-list from physics.app-ph) [pdf, other]
Title: Prospects of designing gold-nanoparticles-based soft terahertz radiation sources and terahertz-to-infrared converters for concealed object detection technology
Comments: A manuscript for the SPIE Security+Defence 2019 conference, Strasbourg, Sep 9-12, 2019
Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Instrumentation and Detectors (physics.ins-det)

The two-phonon scheme of generation of terahertz (THz) photons by gold nanobars (GNBs) is considered. It is shown that in GNBs, by choosing their sizes, it is possible to provide conditions for converting the energy of longitudinal phonons with THz frequencies into the energy of THz photons. The prospects of designing GNBs-based soft THz radiation sources (frequencies: 0.14; 0.24; 0.41 and 0.70 THz) with a large flow cross-section (diameter ~40 cm) intended for detection of hidden objects under clothing to ensure security in public places (airports, railway stations, stadiums, etc.) are assessed. The choice of the above frequencies is a compromise between the requirements of low absorption of THz radiation by water vapor in air, good penetration through the fabric of clothing, favoring a sufficient resolution of the imaging system, and an abundance of corresponding longitudinal phonons, capable of exciting Fermi electrons in GNBs. Estimates of the characteristics of the terahertz-to-infrared converter based on gold nanospheres (GNSs), which could work in tandem with these sources of THz radiation -- as a means of visualization of hidden objects -- are also given.

Replacements for Thu, 22 Aug 19

[71]  arXiv:1802.08763 (replaced) [pdf, other]
Title: Berezinskii-Kosterlitz-Thouless transition of two-component Bose mixtures with inter-component Josephson coupling
Comments: 11 pages, 9 figures
Journal-ref: Phys. Rev. Lett. 123, 075303 (2019)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Superconductivity (cond-mat.supr-con); High Energy Physics - Theory (hep-th)
[72]  arXiv:1803.07282 (replaced) [pdf]
Title: Observation of Rydberg exciton polaritons and their condensate in a perovskite cavity
Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[73]  arXiv:1807.08245 (replaced) [pdf, other]
Title: Continuous transformation between ferro and antiferro circular structures in $J_1-J_2-J_3$ frustrated Heisenberg model
Comments: 9 pages, 12 figures
Journal-ref: Journal of Physics: Condensed Matter, Volume 31, Number 45 (2019)
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
[74]  arXiv:1809.07985 (replaced) [pdf, ps, other]
Title: Thermodynamic properties of ferroics described by the transverse Ising model and their applications for CoNb$_2$O$_6$
Comments: 22 pages, 16 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el)
[75]  arXiv:1810.00698 (replaced) [pdf, other]
Title: An operational approach to quantum stochastic thermodynamics
Comments: Post-final version with Eq. (28) corrected compared to the published version
Journal-ref: Phys. Rev. E 100, 022127 (2019)
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
[76]  arXiv:1810.03211 (replaced) [pdf, other]
Title: Gazing at crystal balls -- Electron backscatter diffraction indexing and cross correlation on a sphere
Comments: Re-submitted version (submitted for review 21/08/2019)
Subjects: Materials Science (cond-mat.mtrl-sci)
[77]  arXiv:1901.05201 (replaced) [pdf, other]
Title: Enhancing power grid synchronization and stability through time delayed feedback control
Subjects: Adaptation and Self-Organizing Systems (nlin.AO); Disordered Systems and Neural Networks (cond-mat.dis-nn); Chaotic Dynamics (nlin.CD)
[78]  arXiv:1901.05709 (replaced) [pdf, other]
Title: Linear response theory for quantum Gaussian processes
Comments: Close to the published version
Journal-ref: New J. Phys. 21 083036 (2019)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
[79]  arXiv:1901.11495 (replaced) [pdf, other]
Title: Modelling microgels with controlled structure across the volume phase transition
Subjects: Soft Condensed Matter (cond-mat.soft)
[80]  arXiv:1902.00210 (replaced) [pdf, other]
Title: Berezinskii-Kosterlitz-Thouless transition of spin-1 spinor Bose gases in the presence of the quadratic Zeeman effect
Comments: 15 pages, 19 figures
Journal-ref: J. Phys. Soc. Jpn. 88 094001 (2019)
Subjects: Quantum Gases (cond-mat.quant-gas); Statistical Mechanics (cond-mat.stat-mech)
[81]  arXiv:1902.06295 (replaced) [pdf, other]
Title: Electrical writing, deleting, reading, and moving of magnetic skyrmioniums in a racetrack device
Comments: This is a post-peer-review, pre-copyedit version of an article published in Scientific Reports. The final authenticated version is available online at [DOI]
Journal-ref: Scientific Reports 9, 12119 (2019)
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[82]  arXiv:1902.08540 (replaced) [pdf, other]
Title: On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4
Authors: Bodo Zibrowius, Michael Felderhoff (Max-Planck-Institut für Kohlenforschung)
Comments: 27 pages, 5 figures, final version as published in PCCP, with reviewer reports attached to the ESI
Subjects: Materials Science (cond-mat.mtrl-sci)
[83]  arXiv:1903.10499 (replaced) [pdf, other]
Title: Slow scrambling and hidden integrability in a random rotor model
Comments: 5+6 pages, 3+2 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)
[84]  arXiv:1903.10733 (replaced) [pdf, ps, other]
Title: Drastic enhancement of the thermal Hall angle in a $d$-wave superconductor
Comments: 10 pages, 11 figures
Subjects: Superconductivity (cond-mat.supr-con)
[85]  arXiv:1903.11545 (replaced) [pdf, other]
Title: Data-driven, structure-based hyperelastic manifolds: A macro-micro-macro approach
Subjects: Materials Science (cond-mat.mtrl-sci)
[86]  arXiv:1904.02042 (replaced) [pdf, other]
Title: On-the-Fly Bayesian Active Learning of Interpretable Force-Fields for Atomistic Rare Events
Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci)
[87]  arXiv:1904.05909 (replaced) [pdf]
Title: Excitonic and lattice contributions to the charge density wave in 1T-TiSe$_2$ revealed by a phonon bottleneck
Comments: 11 pages, 4 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
[88]  arXiv:1904.13152 (replaced) [pdf, other]
Title: Non-universal Transverse Electron Mean Free Path through Few-layer Graphene
Journal-ref: Phys. Rev. Lett. 123, 086802 (2019)
Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[89]  arXiv:1905.03437 (replaced) [pdf, other]
Title: Intervention Threshold for Epidemic Control in Susceptible-Infected-Recovered Metapopulation Models
Comments: 11pages, 8 figures
Journal-ref: Phys. Rev. E 100, 022302 (2019)
Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)
[90]  arXiv:1905.03898 (replaced) [pdf, other]
Title: Prediction of thermal conductivity in dielectrics using fast, spectrally-resolved phonon transport simulations
Comments: 36 pages, 13 figures
Subjects: Materials Science (cond-mat.mtrl-sci); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Computational Physics (physics.comp-ph)
[91]  arXiv:1905.05782 (replaced) [pdf, other]
Title: Disentangling Sources of Quantum Entanglement in Quench Dynamics
Comments: Updated version with minor modifications
Journal-ref: Phys. Rev. Research 1, 012007(R) (2019)
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech); Quantum Physics (quant-ph)
[92]  arXiv:1905.06901 (replaced) [pdf, ps, other]
Title: Coexistence of ferromagnetic fluctuations and superconductivity in the actinide superconductor UTe2
Comments: 5 pages, 6 figures
Subjects: Superconductivity (cond-mat.supr-con)
[93]  arXiv:1905.08906 (replaced) [pdf, other]
Title: Transport and spectral signatures of transient fluctuating superfluids in the absence of long-range order
Comments: 25 pages, 5 figures
Subjects: Superconductivity (cond-mat.supr-con)
[94]  arXiv:1905.11696 (replaced) [pdf, other]
Title: Computing three-dimensional densities from force densities improves statistical efficiency
Comments: Main paper 13 pages 8 figures. Supporting information 2 pages 4 figures. Published in the Journal of Chemical Physics
Journal-ref: J. Chem. Phys. 151 (2019) 064124
Subjects: Chemical Physics (physics.chem-ph); Statistical Mechanics (cond-mat.stat-mech)
[95]  arXiv:1906.05307 (replaced) [pdf, other]
Title: Universal shift of the fidelity susceptibility peak away from the critical point of the Berezinskii-Kosterlitz-Thouless quantum phase transition
Comments: published version, 6 pages, 2 figures
Journal-ref: Phys. Rev. B 100 081108(R) (2019)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Strongly Correlated Electrons (cond-mat.str-el)
[96]  arXiv:1907.00018 (replaced) [pdf, ps, other]
Title: Percolation of sites not removed by a random walker in $d$ dimensions
Comments: RevTex, 12 pages, 13 figures
Journal-ref: Phys. Rev. E 100, 022125 (2019)
Subjects: Statistical Mechanics (cond-mat.stat-mech)
[97]  arXiv:1907.00291 (replaced) [pdf, other]
Title: Logarithmic growth of local entropy and total correlations in many-body localized dynamics
Comments: 4 pages, 5 figures, comments are welcome
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)
[98]  arXiv:1907.08204 (replaced) [pdf, other]
Title: Topological theory of Lieb-Schultz-Mattis theorems in quantum spin systems
Comments: 27 pages + 12 pages of appendices. v2 updated references
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mathematical Physics (math-ph); Quantum Physics (quant-ph)
[99]  arXiv:1907.10784 (replaced) [pdf]
Title: Phase-Change Control of Interlayer Exchange Coupling
Subjects: Materials Science (cond-mat.mtrl-sci)
[100]  arXiv:1907.11602 (replaced) [pdf]
Title: Time Reversal Symmetry Breaking in the Fe-Chalcogenide Superconductors
Subjects: Superconductivity (cond-mat.supr-con)
[101]  arXiv:1908.03292 (replaced) [pdf, other]
Title: Out of Time Order Correlations in the Quasi-Periodic Aubry-André model
Comments: 14 pages, 10 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Quantum Physics (quant-ph)
[102]  arXiv:1908.04257 (replaced) [pdf, ps, other]
[103]  arXiv:1908.04536 (replaced) [pdf, other]
Title: Phase structure of the 1+1 dimensional massive Thirring model from matrix product states
Comments: 30 pages, 18 figures; minor stylistic changes, typos corrected, references added
Subjects: High Energy Physics - Lattice (hep-lat); Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
[104]  arXiv:1908.06101 (replaced) [pdf, other]
Title: Parallel implementation of high-fidelity multi-qubit gates with neutral atoms
Comments: 6 pages, 4 figures + Supplemental Materials (10 pages, 6 figures)
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)
[105]  arXiv:1908.06578 (replaced) [pdf, other]
Title: Ultraviolet to Near-infrared Single Photon Emitters in hBN
Comments: 5 Figures
Subjects: Applied Physics (physics.app-ph); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics)
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