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Condensed Matter (cond-mat) updates on the arXiv.org e-print archive



Published: 2017-09-25T20:30:00-05:00

 



Topological thermal Hall effect due to Weyl magnons. (arXiv:1709.07879v1 [cond-mat.str-el])

We present the first theoretical evidence of zero magnetic field topological (anomalous) thermal Hall effect due to Weyl magnons. Here we consider Weyl magnons in three-dimensional stacked frustrated kagome antiferromagnets recently proposed by the author Owerre, [arXiv:1708.04240]. The Weyl magnons in this system result from macroscopically broken time-reversal symmetry by the scalar spin chirality of noncoplanar chiral spin textures. Most importantly, they come from the lowest excitation, therefore they can be observed experimentally at low temperatures due to the population effect. Similar to electronic Weyl nodes close to the Fermi energy, Weyl magnon nodes in the lowest excitation are the most important. Indeed, we show that the topological (anomalous) thermal Hall effect in this system arises from nonvanishing Berry curvature due to Weyl magnon nodes in the lowest excitation, and it depends on their distribution (distance) in momentum space. The present result paves the way to directly probe low excitation Weyl magnons and macroscopically broken time-reversal symmetry in three-dimensional frustrated magnets with the anomalous thermal Hall effect. Moreover, our results could also be potentially applicable to the field of magnon spintronics and magnetic data storage devices.




Particle-hole symmetry and composite fermions in fractional quantum Hall states. (arXiv:1709.07885v1 [cond-mat.mes-hall])

We study fractional quantum Hall states at filling fractions in the Jain sequences using the framework of composite Dirac fermions. Synthesizing previous work, we write down an effective field theory consistent with all symmetry requirements, including Galilean invariance and particle-hole symmetry. Employing a Fermi liquid description, we demonstrate the appearance of the Girvin--Macdonlald--Platzman algebra and compute the dispersion relation of neutral excitations and various response functions. Our results satisfy requirements of particle-hole symmetry. We show that while the dispersion relation obtained from the HLR theory is particle-hole symmetric, correlation functions obtained from HLR are not. The results of the Dirac theory are shown to be consistent with the Haldane bound on the projected structure factor, while those of the HLR theory violate it.




Non-local Coulomb interactions on the triangular lattice in the high-doping regime: Spectra and charge dynamics from Extended Dynamical Mean Field Theory. (arXiv:1709.07901v1 [cond-mat.str-el])

We explore the two-dimensional extended Hubbard model on the triangular lattice in the high doping regime. On-site and nearest-neighbour repulsive interactions are treated in a non-perturbative way by means of Extended Dynamical Mean Field Theory. We compute the low-temperature phase diagram, displaying a metallic phase and a symmetry-broken phase for strong intersite repulsions. We describe the correlation effects on both single-particle and two-particle observables in the metallic phase. Whereas single-particle spectra feature a Hubbard satellite typical of strongly correlated systems, local susceptibilities remain close to their non-interacting limit, even for large on-site repulsions. We argue that this behaviour is typical of the strongly doped case. We also report a region in parameter space with negative static local screening.




Metal passivation effect on focused beam-induced nonuniform structure changes of amorphous SiOx nanowire. (arXiv:1709.07920v1 [physics.app-ph])

Passivation effect of heterogeneous Au nanoparticles (AuNPs) on the nonuniform structure changes of amorphous SiOx nanowire (a-SiOx NW) as athermally induced by focused electron beam (e-beam) irradiation is investigated in an in-situ transmission electron microscope. It is found that at room temperature the straight and uniform a-SiOx NW demonstrates an accelerated necking at the nanoscale along with a fast, plastic elongation and a local S-type deformation in the axial direction. However, once being modified with uniform AuNPs, the nanocurved sidewall surface of a-SiOx NW becomes intriguingly passivated and the processing transfers from a diffusion (or plastic flow)-dominated status to an evaporation (or ablation)-dominated status. As a result, the necking of the AuNPs-modified a-SiOx NW is greatly retarded without visible elongation and bending deformation. Two combined effects of nanocurvature and beam-induced soft mode and instability of atomic vibration are further proposed to elucidate the observed new phenomena.




Spin order and phase transitions in chains of polariton condensates. (arXiv:1709.07921v1 [cond-mat.mes-hall])

We demonstrate that multiply-coupled spinor polariton condensates can be optically tuned through a sequence of spin-ordered phases by changing the coupling strength between nearest neighbors. For closed 4-condensate chains these phases span from ferromagnetic (FM) to antiferromagnetic (AFM), separated by an unexpected crossover phase. This crossover phase is composed of alternating FM-AFM bonds. For larger 8 condensate chains, we show the critical role of spatial inhomogeneities and demonstrate a scheme to overcome them and prepare any desired spin state. Our observations thus demonstrate a fully controllable non-equilibrium spin lattice.




On heat transfer in a thermally perturbed harmonic chain. (arXiv:1709.07924v1 [cond-mat.stat-mech])

Unsteady heat transfer in a harmonic chain is analyzed. Two types of thermal perturbations are considered: 1) initial instant temperature perturbation, 2) external heat supply. Closed equations describing the heat propagation are obtained and their analytical solution is constructed.




Scaling Invariance and Characteristics of the Fragments Cloud of Spherical Projectile Fragmentation upon High-Velocity Impact on a Thin Mesh Shield. (arXiv:1709.07927v1 [physics.app-ph])

In the present paper we consider the problem of the fragmentation of an aluminum projectile on a thin steel mesh shield at high-velocity impact in a three-dimensional (3D) setting. The numerical simulations are carried out by smoothed particle hydrodynamics method applied to the equations of mechanics of deformable solids. Quantitative characteristics of the projectile fragmentation are obtained by studying statistics of the cloud of fragments. The considerable attention is given to scaling laws accompanying the fragmentation of the projectile. Scaling is carried out using the parameter K which defines the number of the mesh cells falling within the projectile diameter. It is found that the dependence of the critical velocity Vc of fragmentation on the parameter K consists of two branches that correspond to two modes of the projectile fragmentation associated with the "small" and "large" aperture of the mesh cell. We obtain the dependences of the critical velocity Vc on the projectile diameter and the mesh parameters for the both modes of the fragmentation. It is shown that the average cumulative mass distributions constructed at Vc exhibit the property of scale invariance, splitting into two groups of distributions exactly corresponding to the modes of the projectile fragmentation. In each group, the average cumulative distributions show good coincidence in the entire mass region, moreover in the intermediate mass region the each group of distributions has a power-law distribution with an exponent tau different from that in the other group. The conclusion about the dependence of the exponent of the power-law distribution tau on the fragmentation mode is made.




Parafermion supporting platform based on spin transitions in the fractional quantum Hall effect regime. (arXiv:1709.07928v1 [cond-mat.mes-hall])

We propose an experimentally-feasible system based on spin transitions in the fractional quantum Hall effect regime where parafermions, high-order non-abelian excitations, can be potentially realized. We provide a proof-of-concept experiments showing that in specially designed heterostructures spin transitions at a filling factor 2/3 can be induced electrostatically, allowing local control of polarization and on-demand formation of helical domain walls with fractionalized charge excitations, a pre-requisite ingredient for parafermions formation. We also present exact diagonalization numerical studies of domain walls formed between domains with different spin polarization in the fractional quantum Hall effect regime and show that they indeed possess electronic and magnetic structure needed for parafermion formation when coupled to an s-wave superconductor.




Elastic and viscous properties of nematic dimer CB7CB. (arXiv:1709.07931v1 [cond-mat.soft])

We present a comprehensive set of measurements of optical, dielectric, diamagnetic, elastic and viscous properties in the nematic (N) phase formed by a liquid crystalline dimer. The studied dimer, 1,7-bis-4-(4-cyanobiphenyl) heptane (CB7CB), is composed of two rigid rod-like cyanobiphenyl segments connected by a flexible aliphatic link with seven methyl groups. CB7CB and other nematic dimers are of interest due to their tendency to adopt bent configurations and to form two states possessing a modulated nematic director structure, namely, the twist bend nematic, NTB, and the oblique helicoidal cholesteric, ChOH, which occurs when the achiral dimer is doped with a chiral additive and exposed to an external electric or magnetic field. We characterize the material parameters as functions of temperature in the entire temperature range of the N phase, including the pre-transitional regions near the N-NTB and N-to-isotropic (I) transitions. The splay constant K11 is determined by two direct and independent techniques, namely, detection of the Frederiks transition and measurement of director fluctuation amplitudes by dynamic light scattering (DLS). The bend K33 and twist K22 constants are measured by DLS. K33 being the smallest of the three constants, shows a strong non-monotonous temperature dependence with a negative slope in both N-I and N-NTB pretransitional regions. The measured ratio K11/K22 is larger than 2 in the entire nematic temperature range. The orientational viscosities associated with splay, twist and bend fluctuations in the N phase are comparable to those of nematics formed by rod-like molecules. All three show strong temperature dependence, increasing sharply near the N-NTB transition.




Classical many-particle systems with unique disordered ground states. (arXiv:1709.07947v1 [cond-mat.stat-mech])

Classical ground states (global energy-minimizing configurations) of many-particle systems are typically unique crystalline structures, implying zero enumeration entropy of distinct patterns (aside from trivial symmetry operations). By contrast, the few previously known disordered classical ground states of many-particle systems are all high-entropy (highly degenerate) states. Here we show computationally that our recently-proposed "perfect glass" many-particle model [Scientific Reports, 6, 36963 (2016)] possesses disordered classical ground states with a zero entropy: a highly counterintuitive situation, which has heretofore never been identified. For all of the system sizes, parameters, and space dimensions that we have numerically investigated, the disordered ground states are unique such that they can always be superposed onto each other or their mirror image. At low energies, the density of states obtained from simulations matches those calculated from the harmonic approximation near a single ground state, further confirming ground-state uniqueness. Our discovery provides singular examples in which entropy and disorder are at odds with one another. The zero-entropy ground states provides a new perspective on the celebrated Kauzmann-entropy crisis in which the extrapolated entropy of a supercooled liquid drops below that of the crystal. We expect that our disordered unique patterns to be of value in cryptography as pseudo-random functions with tunable computational complexity.




Quantification of spin accumulation causing spin-orbit torque in Pt/Co/Ta stack. (arXiv:1709.07948v1 [cond-mat.mes-hall])

Spin accumulation induced by spin-orbit coupling is experimentally quantified in stack with in-plane magnetic anisotropy via the contribution of spin accumulation to Hall resistances. Using a biasing direct current the spin accumulation within the structure can be tuned, enabling quantification. Quantification shows the spin accumulation can be more than ten percentage of local magnetization, when the electric current is 1E11 A/m*m. The spin accumulation is dependent of the thickness of Ta layer, the trend agrees with that of spin Hall angle indicating the capability of Ta and Pt in generating spins.




Nonequilibrium distribution functions in electron transport: Decoherence, energy redistribution and dissipation. (arXiv:1709.07950v1 [cond-mat.mes-hall])

A new statistical model for the combined effects of decoherence, energy redistribution and dissipation on electron transport in large quantum systems is introduced. The essential idea is to consider the electron phase information to be lost only at randomly chosen regions with an average distance corresponding to the decoherence length. In these regions the electron's energy can be unchanged or redistributed within the electron system or dissipated to a heat bath. The different types of scattering and the decoherence leave distinct fingerprints in the energy distribution functions. They can be interpreted as a mixture of unthermalized and thermalized electrons. In the case of weak decoherence, the fraction of thermalized electrons show electrical and thermal contact resistances. In the regime of incoherent transport the proposed model is equivalent to a Boltzmann equation. The model is applied to experiments with carbon nanotubes. The excellent agreement of the model with the experimental data allows to determine the scattering lengths of the system.




Dynamics and interactions of particles in a thermophoretic trap. (arXiv:1709.07968v1 [cond-mat.soft])

We investigate dynamics and interactions of particles levitated and trapped by the thermophoretic force in a vacuum cell. Our analysis is based on footage taken by orthogonal cameras that are able to capture the three dimensional trajectories of the particles. In contrast to spherical particles, which remain stationary at the center of the cell, here we report new qualitative features of the motion of particles with non-spherical geometry. Singly levitated particles exhibit steady spinning around their body axis and rotation around the symmetry axis of the cell. When two levitated particles approach each other, repulsive or attractive interactions between the particles are observed. Our levitation system offers a wonderful platform to study interaction between particles in a microgravity environment.




Dirac and chiral quantum spin liquids on the honeycomb lattice in a magnetic field. (arXiv:1709.07990v1 [cond-mat.str-el])

Motivated by recent experimental observations in $\alpha$-RuCl$_3$, we study the $K$-$\Gamma$ model on the honeycomb lattice in an external magnetic field. By a slave-particle representation and Variational Monte Carlo calculations, we reproduce the phase transition from zig-zag magnetic order to a field-induced disordered phase. The nature of this state depends crucially on the field orientation. For particular field directions in the honeycomb plane, we find a gapless Dirac spin liquid, in agreement with recent experiments on $\alpha$-RuCl$_3$. For a range of out-of-plane fields, we predict the existence of a Kalmeyer-Laughlin-type chiral spin liquid, which would show a quantized thermal Hall effect.




Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence. (arXiv:1709.08003v1 [physics.chem-ph])

We present a perturbation approach rooted in time-dependent density-functional theory to calculate electron hole (eh)-pair excitation spectra during the non-adiabatic vibrational damping of adsorbates on metal surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111) elucidates the surprisingly strong influence of rather short electronic coherence times. We demonstrate how in the limit of short electronic coherence times, as implicitly assumed in prevalent quantum nuclear theories for the vibrational lifetimes as well as electronic friction, band structure effects are washed out. Our results suggest that more accurate lifetime or chemicurrent-like experimental measurements could characterize the electronic coherence.




Kondo Effect with Weyl Semimetal Fermi Arcs. (arXiv:1709.08008v1 [cond-mat.str-el])

We investigate the Kondo effect of the Fermi arcs in a time-reversal-invariant Weyl semimetal with the variational method. To show the consequence brought out by the nontrivial spin texture, we calculate the spatial spin-spin correlation functions. The correlation functions exhibit high anisotropy. The diagonal correlation functions are dominated by the antiferromagnetic correlation while the off-diagonal part has more complicated pattern. The correlation functions obey the same symmetry as the spin texture. Tuning chemical potential changes the pattern of the correlation functions and the correlation length. The correlation functions of the Weyl semimetal Fermi arcs and that from a Dirac semimetal show discrepancy.




Pinning of Domain Walls in thin Ferromagnetic Films. (arXiv:1709.08009v1 [cond-mat.mes-hall])

We present a quantitative investigation of magnetic domain wall pinning in thin magnets with perpendicular anisotropy. A self-consistent description exploiting the universal features of the depinning and thermally activated sub-threshold creep regimes observed in the field driven domain wall velocity, is used to determine the fundamental pinning parameters controlling the domain wall dynamics: the effective height of pinning barriers, the depinning threshold, and the velocity at depinning. Within this framework, the analysis of results published in the literature allows for a quantitative comparison of pinning properties for a large set of magnetic materials in a wide temperature range. On the basis of scaling arguments, the microscopic parameters controlling the pinning: the correlation length of pinning, the collectively pinned domain wall length (Larkin length) and the strength of pinning disorder, are estimated from the pinning parameters controlling domain wall dynamics and the micromagnetic parameters. The analysis of thermal effects reveals a crossover between different pinning length scales at low reduced temperatures.




Combining Machine Learning and Physics to Understand Glassy Systems. (arXiv:1709.08015v1 [stat.ML])

Our understanding of supercooled liquids and glasses has lagged significantly behind that of simple liquids and crystalline solids. This is in part due to the many possibly relevant degrees of freedom that are present due to the disorder inherent to these systems and in part to non-equilibrium effects which are difficult to treat in the standard context of statistical physics. Together these issues have resulted in a field whose theories are under-constrained by experiment and where fundamental questions are still unresolved. Mean field results have been successful in infinite dimensions but it is unclear to what extent they apply to realistic systems and assume uniform local structure. At odds with this are theories premised on the existence of structural defects. However, until recently it has been impossible to find structural signatures that are predictive of dynamics. Here we summarize and recast the results from several recent papers offering a data driven approach to building a phenomenological theory of disordered materials by combining machine learning with physical intuition.




Spin precession in spin-orbit coupled weak links: Coulomb repulsion and Pauli quenching. (arXiv:1709.08022v1 [cond-mat.mes-hall])

A simple model for the transmission of pairs of electrons through a weak electric link in the form of a nanowire made of a material with strong electron spin-orbit interaction (SOI) is presented, with emphasis on the effects of Coulomb interactions and the Pauli exclusion principle. The constraints due to the Pauli principle are shown to "quench" the coherent SOI-induced precession of the spins when the spatial wave packets of the two electrons overlap significantly. The quenching, which results from the projection of the pair's spin states onto spin-up and spin-down states on the link, breaks up the coherent propagation in the link into a sequence of coherent hops that add incoherently. Applying the model to the transmission of Cooper pairs between two superconductors, we find that in spite of Pauli quenching, the Josephson current oscillates with the strength of the SOI, and may even change its sign. Conditions for an experimental detection of these features are discussed.




Non-integrable dynamics of matter-wave solitons in a density-dependent gauge theory. (arXiv:1709.08037v1 [cond-mat.quant-gas])

We study interactions between bright matter-wave solitons which acquire chiral transport dynamics due to an optically-induced density-dependent gauge potential. Through numerical simulations, we find that the collision dynamics feature several non-integrable phenomena, from inelastic collisions including population transfer and radiation losses to short-lived bound states and soliton fission. An effective quasi-particle model for the interaction between the solitons is derived by means of a variational approximation, which demonstrates that the inelastic nature of the collision arises from a coupling of the gauge field to velocities of the solitons. In addition, we derive a set of interaction potentials which show that the influence of the gauge field appears as a short-range potential, that can give rise to both attractive and repulsive interactions.




Skyrmion formation in a bulk chiral magnet at zero magnetic field and above room temperature. (arXiv:1709.08047v1 [cond-mat.str-el])

We report that in a $\beta$-Mn-type chiral magnet Co$_9$Zn$_9$Mn$_2$, skyrmions are realized as a metastable state over a wide temperature range, including room temperature, via field-cooling through the thermodynamic equilibrium skyrmion phase that exists below a transition temperature $T_\mathrm{c}$ $\sim$ 400 K. The once-created metastable skyrmions survive at zero magnetic field both at and above room temperature. Such robust skyrmions in a wide temperature and magnetic field region demonstrate the key role of topology, and provide a significant step toward technological applications of skyrmions in bulk chiral magnets.




The SU(4) Kondo effect in double quantum dots with ferromagnetic leads. (arXiv:1709.08049v1 [cond-mat.mes-hall])

We investigate the spin-resolved transport properties, such as the linear conductance and the tunnel magnetoresistance, of a double quantum dot device attached to ferromagnetic leads and look for signatures of SU(4) symmetry in the Kondo regime. We show that the transport behavior greatly depends on the magnetic configuration of the device, and the spin-SU(2) as well as the orbital and spin-SU(4) Kondo effects become generally suppressed when the magnetic configuration of the leads varies from the antiparallel to the parallel one. Furthermore, a finite spin polarization of the leads lifts the spin degeneracy and drives the system from the SU(4) to an orbital-SU(2) Kondo state. We analyze in detail the crossover and show that the Kondo temperature between the two fixed points has a non-monotonic dependence on the degree of spin polarization of the leads. In terms of methods used, we characterize transport by using a combination of analytical and numerical renormalization group approaches.




Synchronization of coupled active rotators by common noise. (arXiv:1709.08058v1 [cond-mat.stat-mech])

We study the effect of common noise on coupled active rotators. While such a noise always facilitates synchrony, coupling may be attractive or repulsing. We develop an analytical approach based on a transformation to approximate angle-action variables and averaging over fast rotations. For identical rotators, we describe a transition from full to partial synchrony at a critical value of repulsive coupling. For nonidentical rotators, the most nontrivial effect occurs at moderate repulsive coupling, where a juxtaposition of phase locking with frequency repulsion (anti-entrainment) is observed. We show that the frequency repulsion obeys a nontrivial power law.




Hybrid grid/basis set discretizations of the Schr\"odinger equation. (arXiv:1709.08059v1 [physics.chem-ph])

We present a new kind of basis function for discretizing the Schr\"odinger equation in electronic structure calculations, called a gausslet, which has wavelet-like features but is composed of a sum of Gaussians. Gausslets are placed on a grid and combine advantages of both grid and basis set approaches. They are orthogonal, infinitely smooth, symmetric, polynomially complete, and with a high degree of locality. Because they are formed from Gaussians, they are easily combined with traditional atom-centered Gaussian bases. We also introduce diagonal approximations which dramatically reduce the computational scaling of two-electron Coulomb terms in the Hamiltonian.




On the magnetism of the C14 Nb0.975Fe2.025 Laves phase compound: Determination of the H-T phase diagram. (arXiv:1709.08064v1 [cond-mat.str-el])

A C14 Nb0.975Fe2.025 Laves phase compound was investigated aimed at determining the H-T magnetic phase diagram. Magnetization, M, and AC magnetic susceptibility measurements were performed. Concerning the former field-cooled and zero-field-cooled M-curves were recorded in the temperature range of 2-200K and in applied magnetic field, H, up to 1000 Oe, isothermal M(H) curves at 2 K, 5 K, 50 K, 80 K and 110 K as well as hysteresis loops at several temperatures over the field range of -10 to +10kOe. Regarding the AC susceptibility, both real and imaginary components were registered as a function of increasing temperature in the interval of 2 K - 150 K at the frequencies of the oscillating field, f, from 3 Hz up to 999 Hz. An influence of the external DC magnetic field, H, on the temperature dependence of the AC susceptibility was investigated, too. The measurements clearly demonstrated that the magnetism of the studied sample is weak, itinerant and has a reentrant character. Based on the obtained results a magnetic phase diagram has been constructed in the H-T coordinates.




Effects of the Position Reversal of Friction Pairs on the Strength of Tribocharging and Tribodischarging. (arXiv:1709.08067v1 [cond-mat.mtrl-sci])

The friction-induced charging (i.e., tribocharging) and the following discharging (referred here as tribodischarging) are always believed to have negative effects on the daily life and on the industrial production. Thus, how to inhibit the tribocharging and the tribodischarging has caused wide public concern. Because the discharge caused by the electrical breakdown of the ambient gas is generally accompanied with the generation of light, we investigated here the tribocharging and the tribodischarging by observing the light emitted during friction. We found that the position reversal of the friction pair has a dramatic impact on the intensity of the tribo-induced light. Experimental results show that an intense light is produced when a stationary Al2O3 disk is sliding on a rotating SiO2 disk, but only a weak light is observed for the case of a stationary SiO2 disk and a rotating Al2O3 disk. This means that the process of the tribocharging and the tribodischarging can be significantly influenced owing to the change in the relative position of the friction couple. The experimentally measured polarities of the tribo-induced charge on the friction surfaces further indicated that the strong discharging occurs when the rotating surface is negatively charged. The reason for the difference in the intensity of the tribocharging and tribodischarging can be attributed to the combined effects of the contact potential difference and the temperature gradient between the contacting surfaces on the charge transfer when friction. Finally, a simple, low cost, yet effective approach, i.e., just keep the friction partner whose surface is tribo-induced negatively charged as the stationary one, can be utilized to suppress the intensity of the tribocharging and the tribodischarging. This work may provide potential applications in numerous areas of science and engineering and also in the everyday life.




Propagation in media as a probe for topological properties. (arXiv:1709.08078v1 [cond-mat.quant-gas])

The central goal of this thesis is to develop methods to experimentally study topological phases. We do so by applying the powerful toolbox of quantum simulation techniques with cold atoms in optical lattices. To this day, a complete classification of topological phases remains elusive. In this context, experimental studies are key, both for studying the interplay between topology and complex effects and for identifying new forms of topological order. It is therefore crucial to find complementary means to measure topological properties in order to reach a fundamental understanding of topological phases. In one dimensional chiral systems, we suggest a new way to construct and identify topologically protected bound states, which are the smoking gun of these materials. In two dimensional Hofstadter strips (i.e: systems which are very short along one dimension), we suggest a new way to measure the topological invariant directly from the atomic dynamics.




Shape transitions in a soft incompressible sphere with residual stresses. (arXiv:1709.08081v1 [cond-mat.soft])

Residual stresses may appear in elastic bodies due to the formation of misfits in the micro-structure, driven by plastic deformations, thermal or growth processes. They are especially widespread in living matter, resulting from the dynamic remodelling processes aiming at optimizing the overall structural response to environmental physical forces. From a mechanical viewpoint, residual stresses are classically modelled through the introduction of a virtual incompatible state that collects the local relaxed states around each material point. In this work, we instead employ an alternative approach based on a strain energy function that constitutively depends only on the deformation gradient and the residual stress tensor. In particular, our objective is to study the morphological stability of an incompressible sphere, made of a neo-Hookean material and subjected to given distributions of residual stresses. Firstly, we perform a linear stability analysis on the pre-stressed solid sphere using the method of incremental deformations. The marginal stability conditions are given as a function of a control parameter, being the dimensionless variable that represents the characteristic intensity of the residual stresses. Secondly, we perform finite element simulations using a mixed formulation in order to investigate the post-buckling morphology in the fully nonlinear regime. Considering different distributions of the residual stresses, we find that different morphological transitions occur around the material domain where the hoop residual stress reaches its maximum compressive value. The results provide useful guidelines in order to design morphable soft spheres, for example by controlling the residual stresses through active deformations. They finally suggest a viable solution for the nondestructive characterization of residual stresses in soft tissues, such as solid tumors.




Classical and Quantum Factors of Channels. (arXiv:1709.08101v1 [quant-ph])

Given a classical channel, a stochastic map from inputs to outputs, can we replace the input with a simple intermediate variable that still yields the correct conditional output distribution? We examine two cases: first, when the intermediate variable is classical; second, when the intermediate variable is quantum. We show that the quantum variable's size is generically smaller than the classical, according to two different measures---cardinality and entropy. We demonstrate optimality conditions for a special case. We end with several related results: a proposal for extending the special case, a demonstration of the impact of quantum phases, and a case study concerning pure versus mixed states.




The resolvent algebra of non-relativistic Bose fields: observables, dynamics and states. (arXiv:1709.08107v1 [math-ph])

The gauge-invariant (particle number preserving) observable algebra generated by a non-relativistic Bose field is studied in the C*-algebraic framework of the resolvent algebra. It is shown that this algebra is isomorphic to the inverse limit of a system of approximately finite dimensional C*-algebras. Using this result, it is proven that the algebra is compatible with the Heisenberg picture in the sense that it is stable under the dynamics induced by Hamiltonians involving pair interactions. The argument does not require any approximations, it deals from the outset with the full dynamics. It is outlined how these results shed new light on several topics in many body theory, ranging from causality aspects over the construction of ground states and collision theory up to the determination of thermal equilibrium states. The present approach leads to conceptual simplifications and admits a unified field theoretic treatment of small and large bosonic systems.




The effect of the junction model on the anomalous diffusion in the 3D comb structure. (arXiv:1709.08109v1 [cond-mat.stat-mech])

The diffusion in the comb structures is a popular model of geometrically induced anomalous diffusion. In the present work we concentrate on the diffusion along the backbone in a system where sidebranches are planes, and the diffusion thereon is anomalous and described by continuous time random walks (CTRW). We show that the mean squared displacement (MSD) in the backbone of the comb behaves differently depending on whether the waiting time periods in the sidebranches are reset after the step in the backbone is done (a rejuvenating junction model), or not (a non-rejuvenating junction model). In the rejuvenating case the subdiffusion in the sidebranches only changes the prefactor in the ultra-slow (logarithmic) diffusion along the backbone, while in the non-rejuvenating case the ultraslow, logarithmic subdiffusion is changed to a much faster power-law subdiffusion (with a logarithmic correction) as it was found earlier by Iomin and Mendez [Chaos Solitons and Fractals 2016; 82:142]. Moreover, in the first case the result does not change if the diffusion in the backbone is itself anomalous, while in the second case it does. Two of the special cases of the considered models (the non-rejuvenating junction under normal diffusion in the backbone, and rejuvenating junction for the same waiting time distribution in the sidebranches and in junction points) were also investigated within the approach based on the corresponding generalized Fokker-Planck equations.




Atomic Structure of Domain and Interphase Boundaries in Ferroelectric HfO$_2$. (arXiv:1709.08110v1 [cond-mat.mtrl-sci])

Though the electrical responses of the various polymorphs found in ferroelectric polycrystalline thin film HfO$_2$ are now well characterized, little is currently understood of this novel material's grain sub-structure. In particular, the formation of domain and phase boundaries requires investigation to better understand phase stabilization, switching, and interconversion. Here, we apply scanning transmission electron microscopy to investigate the atomic structure of boundaries in these materials. In particular, we find orthorhombic/orthorhombic domain walls and coherent orthorhombic/monoclinic interphase boundaries formed throughout individual grains. The results inform how interphase boundaries can impose strain conditions that may be key to phase stabilization. Moreover, the atomic structure near interphase boundary walls suggests potential for their mobility under bias, which has been speculated to occur in perovskite morphotropic phase boundary systems by mechanisms similar to domain boundary motion.




Electron Mobility in Monoclinic \beta-Ga2O3 - Effect of Plasmon-phonon Coupling, Anisotropy, and Confinement. (arXiv:1709.08117v1 [cond-mat.mtrl-sci])

This work reports an investigation of electron transport in monoclinic \beta-Ga2O3 based on a combination of density functional perturbation theory based lattice dynamical computations, coupling calculation of lattice modes with collective plasmon oscillations and Boltzmann theory based transport calculations. The strong entanglement of the plasmon with the different longitudinal optical (LO) modes make the role LO-plasmon coupling crucial for transport. The electron density dependence of the electron mobility in \beta-Ga2O3 is studied in bulk material form and also in the form of two-dimensional electron gas. Under high electron density a bulk mobility of 182 cm2/ V.s is predicted while in 2DEG form the corresponding mobility is about 418 cm2/V.s when remote impurities are present at the interface and improves further as the remote impurity center moves away from the interface. The trend of the electron mobility shows promise for realizing high electron mobility in dopant isolated electron channels. The experimentally observed small anisotropy in mobility is traced through a transient Monte Carlo simulation. It is found that the anisotropy of the IR active phonon modes is responsible for giving rise to the anisotropy in low-field electron mobility.




Multiple Topological Electronic Phases in Superconductor MoC. (arXiv:1709.08143v1 [cond-mat.supr-con])

The search for a superconductor with non-s-wave pairing is important not only for understanding unconventional mechanisms of superconductivity but also for finding new types of quasiparticles such as Majorana bound states. Materials with both topological band structure and superconductivity are promising candidates as $p+ip$ superconducting states can be generated through pairing the spin-polarized topological surface states. In this work, the electronic and phonon properties of the superconductor molybdenum carbide (MoC) are studied with first-principles methods. Our calculations show that nontrivial band topology and superconductivity coexist in both structural phases of MoC, namely, the cubic $\alpha$ and hexagonal $\gamma$ phases. The $\alpha$ phase is a strong topological insulator and the $\gamma$ phase is a topological nodal line semimetal with drumhead surface states. In addition, hole doping can stabilize the crystal structure of the $\alpha$ phase and elevate the transition temperature in the $\gamma$ phase. Therefore, MoC in different structural forms can be a practical material platform for studying topological superconductivity and elusive Majorana fermions.




The Blume-Capel Model on Hierarchical Lattices: exact local properties. (arXiv:1709.08147v1 [cond-mat.stat-mech])

The local properties of the spin one ferromagnetic Blume-Capel model defined on hierarchical lattices with dimension two and three are obtained by a numerical recursion procedure and studied as functions of the temperature and the reduced crystal-field parameter. The magnetization and the density of sites in the configuration S=0 state are carefully investigated at low temperature in the region of the phase diagram that presents the phenomenon of phase reentrance. Both order parameters undergo transitions from the ferromagnetic to the ordered paramagnetic phase with abrupt discontinuities that decrease along the phase boundary at low temperatures. The distribution of magnetization in a typical profile was determined on the transition line presenting a broad multifractal spectrum that narrows towards the fractal limit (single point) as the discontinuities of the order parameters grow towards a maximum. The amplitude of the order-parameter discontinuities and the narrowing of the multifractal spectra were used to delimit the low temperature interval for the possible locus of the tricritical point.




Time-dependent Hartree-Fock study of electron-hole interaction effects on high-harmonic generation from periodic crystals. (arXiv:1709.08153v1 [physics.optics])

We investigate the multielectron effects on high-harmonic generation from solid-state materials using the time-dependent Hartree-Fock theory. We find qualitative change in harmonic spectra, in particular, multiple-plateau formation at significantly lower laser intensities than within the independent-electron approximation. We reveal its origin in terms of interband polarization, i.e, electron-hole polarization, enabling interband excitation at remote crystal momenta via Coulomb potential.




Randomness-induced quantum spin liquid on honeycomb lattice. (arXiv:1709.08156v1 [cond-mat.str-el])

We present a quantu spin liquid state in a spin-1/2 honeycomb lattice with randomness in the exchange interaction. That is, we successfully introduce randomness into the organic radial-based complex and realize a random-singlet (RS) state. All magnetic and thermodynamic experimental results indicate the liquid-like behaviors, which are consistent with those expected in the RS state. These results demonstrate that the randomness or inhomogeneity in the actual systems stabilize the RS state and yield liquid-like behavior.




Dimensional Crossover Induced Topological Hall Effect in a Magnetic Topological Insulator. (arXiv:1709.08161v1 [cond-mat.mtrl-sci])

We report transport studies of Mn-doped Bi2Te3 topological insulator (TI) films with accurately controlled thickness grown by molecular beam epitaxy. We find that films thicker than 5 quintuple-layer (QL) exhibit the usual anomalous Hall effect for magnetic TIs. When the thickness is reduced to 4 QL, however, characteristic features associated with the topological Hall effect (THE) emerge. More surprisingly, the THE vanishes again when the film thickness is further reduced to 3 QL. Theoretical calculations demonstrate that the coupling between the top and bottom surface states at the dimensional crossover regime stabilizes the magnetic skyrmion structure that is responsible for the THE.




Observation of the Dynamic Equivalence between Soft Star Polymers and Hard Spheres via Compressibility Scaling. (arXiv:1709.08179v1 [cond-mat.soft])

We propose a definition of the effective hard-sphere volume fraction (phi_HS) for liquids composed of soft repulsive particles by employing the condition of compressibility equivalence, and devise a model-independent method to determine phi_HS for soft colloids from Small-Angle Neutron Scattering (SANS) experiments. A series of star polymer dispersions are measured as a model soft colloidal liquid. It is found that as the concentration increases, the slowing of the long-time dynamics of the star polymer, normalized by the short-time self-diffusion coefficient, can be scaled to the hard-sphere behavior with phi_HS. This result agrees with the dynamic equivalence rule between the soft-repulsive and hard-sphere colloidal liquids predicted by recent theoretical and simulation work.




Characteristics of Chiral Anomaly in View of Various Applications. (arXiv:1709.08181v1 [hep-th])

In view of the recent applications of chiral anomaly to various fields beyond particle physics, we discuss some basic aspects of chiral anomaly which may help deepen our understanding of chiral anomaly in particle physics also. It is first shown that Berry's phase for the Weyl model $H =v_{F} \vec{\sigma}\cdot \vec{p}(t)$ assumes a monopole form at the exact adiabatic limit but deviates from it off the adiabatic limit and vanishes quadratically $\sim 1/\omega^{2}$ in the high frequency limit of the Fourier transform of $\vec{p}(t)$. An effective action which is consistent with the non-adiabatic limit of Berry's phase and BJL prescription gives normal equal-time space-time commutators and no chiral anomaly. In contrast, an effective action with a monopole at the origin of the momentum space, which describes Berry's phase in the precise adiabatic limit but fails off the adiabatic limit, gives anomalous space-time commutators and a covariant anomaly to the gauge current. We regard this anomaly as an artifact of the postulated monopole and not a consequence of Berry's phase. As for the recent application of the chiral anomaly to the description of effective Weyl fermions in condensed matter and nuclear physics, which is closely related to the formulation of lattice chiral fermions, we point out that the chiral anomaly for each species doubler separately vanishes for a finite lattice spacing, contrary to the common assumption. Instead a general form of pair creation associated with the spectral flow for the Dirac sea with finite depth takes place. This view is supported by the Ginsparg-Wilson fermion, which defines a single Weyl fermion without doublers on the lattice and gives a well-defined index (anomaly) even for a finite lattice spacing. A different use of anomaly in analogy to PCAC is also mentioned, which could lead to an effect without fermion number non-conservation.




Transient Heat Conduction in Fractal Media. (arXiv:1709.08191v1 [cond-mat.mes-hall])

Transient dynamics of heat conduction in isotropic fractal media is investigated. By using the Laplacian operator in non-integer dimension, we analytically and numerically study the impact of dimensionality on the evolution of the temperature profile, heat flux and excess energy under certain initial and boundary conditions. We find that larger dimension can promote the heat diffusion. Particularly, with randomly distributed absorbing heat sinks in the fractal media, we obtain a non-exponential decay behavior of the heat pulse diffusion, and an optimal dimension for efficient heat absorption depending on sink concentrations. Our results may have potential applications in controlling transient heat conduction in fractal media, which will be ubiquitous as porous, composite, networked materials.




Transverse Magnetic Susceptibility of a Frustrated Spin-$\frac{1}{2}$ $J_{1}$--$J_{2}$--$J_{1}^{\perp}$ Heisenberg Antiferromagnet on a Bilayer Honeycomb Lattice. (arXiv:1709.08205v1 [cond-mat.str-el])

We use the coupled cluster method (CCM) to study a frustrated spin-$\frac{1}{2}$ $J_{1}$--$J_{2}$--$J_{1}^{\perp}$ Heisenberg antiferromagnet on a bilayer honeycomb lattice with $AA$ stacking. Both nearest-neighbor (NN) and frustrating next-nearest-neighbor antiferromagnetic (AFM) exchange interactions are present in each layer, with respective exchange coupling constants $J_{1}>0$ and $J_{2} \equiv \kappa J_{1} > 0$. The two layers are coupled with NN AFM exchanges with coupling strength $J_{1}^{\perp}\equiv \delta J_{1}>0$. We calculate to high orders of approximation within the CCM the zero-field transverse magnetic susceptibility $\chi$ in the N\'eel phase. We thus obtain an accurate estimate of the full boundary of the N\'eel phase in the $\kappa\delta$ plane for the zero-temperature quantum phase diagram. We demonstrate explicitly that the phase boundary derived from $\chi$ is fully consistent with that obtained from the vanishing of the N\'eel magnetic order parameter. We thus conclude that at all points along the N\'eel phase boundary quasiclassical magnetic order gives way to a nonclassical paramagnetic phase with a nonzero energy gap. The N\'eel phase boundary exhibits a marked reentrant behavior, which we discuss in detail.




Ab-initio study of structural, elastic, electronic, optical and thermodynamic properties of MgV2O6. (arXiv:1709.08208v1 [cond-mat.mtrl-sci])

We have performed ab-initio calculations using plane-wave ultraviolet pseudopotential technique based on the density-functional theory (DFT) to study the structural, mechanical, electronic, optical and thermodynamic properties of orthorhombic MgV2O6. The calculated lattice parameters are in good agreement with the available experimental data. The second-order elastic constants and the other relevant quantities such as the Youngs modulus, shear modulus, Poissons ratio, compressibility, anisotropy factor, sound velocity, and Debye temperature have been calculated. After analyzing the calculated elastic constants, it is shown that the compound under study is mechanically stable. The analysis of the electronic band structure shows that this compound reveals semiconducting nature with band gap 2.195 eV and the contribution predominantly comes from O-2s states.




An analytic relation between the fractional parameter in the Mittag-Leffler function and the chemical potential in the Bose-Einstein distribution through the analysis of the NASA COBE monopole data. (arXiv:1709.08212v1 [cond-mat.stat-mech])

To extend the Bose-Einstein (BE) distribution to fractional order, we turn our attention to the differential equation, $df/dx =-f-f^2$. It is satisfied with the stationary solution, $f(x)=1/(e^{x+\mu}-1)$, of the Kompaneets equation, where $\mu$ is the constant chemical potential. Setting $R=1/f$, we obtain a linear differential equation for $R$. Then, the Caputo fractional derivative of order $p$ ($p>0$) is introduced in place of the derivative of $x$, and fractional BE distribution is obtained, where function ${\rm e}^x$ is replaced by the Mittag-Leffler (ML) function $E_p(x^p)$. Using the integral representation of the ML function, we obtain a new formula. Based on the analysis of the NASA COBE monopole data, an identity $p\simeq e^{-\mu}$ is found.




Learning crystal plasticity using digital image correlation: Examples from discrete dislocation dynamics. (arXiv:1709.08225v1 [cond-mat.mtrl-sci])

Digital image correlation (DIC) is a well-established, non-invasive technique for tracking and quantifying the deformation of mechanical samples under strain. While it provides an obvious way to observe incremental and aggregate displacement information, it seems likely that DIC data sets, which after all reflect the spatially-resolved response of a microstructure to loads, contain much richer information than has generally been extracted from them. In this paper, we demonstrate a machine-learning approach to quantifying the prior deformation history of a crystalline sample based on its response to a subsequent DIC test. This prior deformation history is encoded in the microstructure through the inhomogeneity of the dislocation microstructure, and in the spatial correlations of the dislocation patterns, which mediate the system's response to the DIC test load. Our domain consists of deformed crystalline thin films generated by a discrete dislocation plasticity simulation. We explore the range of applicability of machine learning (ML) for typical experimental protocols, and as a function of possible size effects and stochasticity. Plasticity size effects may directly influence the data, rendering unsupervised techniques unable to distinguish different plasticity regimes.




Coherent Manipulation of Spin Correlations in the Hubbard Model. (arXiv:1709.08231v1 [cond-mat.quant-gas])

We coherently manipulate spin correlations in a two-component atomic Fermi gas loaded into an optical lattice using spatially and time-resolved Ramsey spectroscopy combined with high-resolution \textit{in situ} imaging. This novel technique allows us not only to imprint spin patterns but also to probe the static magnetic structure factor at arbitrary wave vector, in particular the staggered structure factor. From a measurement along the diagonal of the $1^\mathrm{st}$ Brillouin zone of the optical lattice, we determine the magnetic correlation length and the individual spatial spin correlators. At half filling, the staggered magnetic structure factor serves as a sensitive thermometer for the spin temperature, which we employ to study the thermalization of spin and density degrees of freedom during a slow quench of the lattice depth.




Coexistence of antiferromagnetism and topological superconductivity on honeycomb lattice Hubbard model. (arXiv:1709.08232v1 [cond-mat.str-el])

Motivated by the recent numerical simulations for doped $t$-$J$ model on honeycomb lattice, we study superconductivity of singlet and triplet pairing on honeycomb lattice Hubbard model. We show that a superconducting state with coexisting spin-singlet and spin-triplet pairings is induced by the antiferromagnetic order near half-filling. The superconducting state we obtain has a topological phase transition that separates a topologically trivial state and a nontrivial state with Chern number two. Possible experimental realization of such a topological superconductivity is also discussed.




Why rare-earth ferromagnets are so rare: insights from the p-wave Kondo model. (arXiv:1709.08241v1 [cond-mat.str-el])

Magnetic exchange in Kondo lattice systems is of the Ruderman-Kittel-Kasuya-Yosida type, whose sign depends on the Fermi wave vector, $k_F$ . In the simplest setting, for small $k_F$ , the interaction is predominately ferromagnetic, whereas it turns more antiferromagnetic with growing $k_F$. It is remarkable that even though $k_F$ varies vastly among the rare-earth systems, an overwhelming majority of lanthanide magnets are in fact antiferromagnets. To address this puzzle, we investigate the effects of a p-wave form factor for the Kondo coupling pertinent to nearly all rare-earth intermetallics. We show that this leads to interference effects which for small kF are destructive, greatly reducing the size of the RKKY interaction in the cases where ferromagnetism would otherwise be strongest. By contrast, for large $k_F$, constructive interference can enhance antiferromagnetic exchange. Based on this, we propose a new route for designing ferromagnetic rare-earth magnets.




Extensile actomyosin?. (arXiv:1709.08246v1 [physics.bio-ph])

Living cells move thanks to assemblies of actin filaments and myosin motors that range from very organized striated muscle tissue to disordered intracellular bundles. The mechanisms powering these disordered structures are debated, and all models studied so far predict that they are contractile. We reexamine this prediction through a theoretical treatment of the interplay of three well-characterized internal dynamical processes in actomyosin bundles: actin treadmilling, the attachement-detachment dynamics of myosin and that of crosslinking proteins. We show that these processes enable an extensive control of the bundle's active mechanics, including reversals of the filaments' apparent velocities and the possibility of generating extension instead of contraction. These effects offer a new perspective on well-studied in vivo systems, as well as a robust criterion to experimentally elucidate the underpinnings of actomyosin activity.




Spectral properties and the Kondo effect of cobalt adatoms on silicene. (arXiv:1709.08249v1 [cond-mat.mes-hall])

In terms of the state-of-the-art first principle computational methods combined with the numerical renormalization group technique the spectroscopic properties of Co adatoms deposited on silicene are analyzed. By establishing an effective low-energy Hamiltonian based on first principle calculations, we study the behavior of the local density of states of Co adatom on external parameters, such as magnetic field and gating. It is shown that the Kondo resonance with the Kondo temperature of the order of a few Kelvins can emerge by fine-tuning the chemical potential. The evolution and splitting of the Kondo peak with external magnetic field is also analyzed. Furthermore, it is shown that the spin polarization of adatom's spectral function in the presence of magnetic field can be relatively large, and it is possible to tune the polarization and its sign by electrical means.




Elastocapillary driven assembly of particles at free-standing smectic-A films. (arXiv:1709.08253v1 [cond-mat.soft])

Colloidal particles at complex fluid interfaces and within films assemble to form ordered structures with high degrees of symmetry via interactions that include capillarity, elasticity, and other fields like electrostatic charge. Here we study microparticle interactions within free-standing smectic-A films, in which the elasticity arising from the director field distortion and capillary interactions arising from interface deformation compete to direct concomitantly the assembly of motile particles. New colloidal assemblies and patterns, ranging from 1D chains to 2D aggregates, sensitive to the initial wetting conditions of particles at the smectic film, are reported. This work paves the way to exploiting LC interfaces as a means to direct spontaneously formed, reconfigurable, and optically active materials.




Type II Nodal line Semimetal. (arXiv:1709.08287v1 [cond-mat.str-el])

Recently, topological semimetals become hot topic in condensed matter physics, including Dirac semimetal, Weyl semimetal, and nodal line semimetal (NLSM). In this paper, a new type of node- line semimetal - type-II NLSM is proposed based on a two-band cubic lattice model. For type-II NLSM, the zero energy bulk states have a closed loop in momentum space but the (local) Weyl cones on nodal line become tilted. The effect of magnetic field and that of correlation on type-II NLSM are studied. In particular, after considering repulsive interaction and additional spin degrees of freedom, different types of long range magnetic orders appear in bulk states. In addition, the interaction-induced ferromagnetic order of surface states may exist. At critical point between type-I NLSM and type-II NLSM, arbitrary tiny interaction induces ferromagnetic order due to a flat band at Fermi surface.




Orbital-Free Density-Functional Theory Simulations of Displacement Cascade in Aluminum. (arXiv:1709.08288v1 [cond-mat.mtrl-sci])

Here, we report orbital-free density-functional theory (OF DFT) molecular dynamics simulations of the displacement cascade in aluminum. The electronic effect is our main concern. The displacement threshold energies are calculated using OF DFT and classical molecular dynamics (MD) and the comparison reveals the role of charge bridge. Compared to MD simulation, the displacement spike from OF DFT has a lower peak and shorter duration time, which is attributed to the effect of electronic damping. The charge density profiles clearly display the existence of depleted zones, vacancy and interstitial clusters. And it is found that the energy exchanges between ions and electrons are mainly contributed by the kinetic energies.




Charge Separation and Dissipation in Molecular Wires under a Light Radiation. (arXiv:1709.08290v1 [cond-mat.mes-hall])

Photo-induced charge separation in nanowires or molecular wires had been studied in previous experiments and simulations. Most researches deal with the carrier diffusions with the classical phenomenological models, or the static energy levels by quantum mechanics calculations. Here we give a dynamic quantum investigation on the charge separation and dissipation in molecule wires. The method is based on the time-dependent non-equilibrium Green's function theory. Polyacetylene chain and poly-phenylene are used as model systems with a tight-binding Hamiltonian and the wide band limit approximation in this study. A light pulse with the energy larger than the band gap is radiated on the system. The evolution and dissipation of the non-equilibrium carriers in the open nano systems are studied. With an external electric potentials or impurity atoms, the charge separation is observed. Our calculations show that the separation behaviors of the electron/hole wave packets are related to the Coulomb interaction, light intensity and the effective masses of electron/hole in the molecular wire.




Nuclear Magnetic Resonance in Low-Symmetry Superconductors. (arXiv:1709.08297v1 [cond-mat.supr-con])

We consider the nuclear spin-lattice relaxation rate, $1/T_1T$ in superconductors with accidental nodes. We show that a Hebel-Slichter-like peak occurs even in the absence of an isotropic component of the superconducting gap. The logarithmic divergence found in clean, non-interacting models is controlled by both disorder and electron-electron interactions. However, for reasonable parameters, neither of these effects removes the peak altogether.




Metastable Phase Diagram and Precipitation Kinetics of Magnetic Nanocrystals in FINEMET Alloys. (arXiv:1709.08306v1 [cond-mat.mtrl-sci])

In this work, Fe-Si phase diagrams were derived to identify the composition-temperature domain where Fe$_3$Si ($\alpha{\alpha}^{''}$-(Fe, Si) D03) phase can be stabilized. Thereafter, we developed a precipitation model capable of simulating nucleation and growth of Fe$_3$Si nanocrystals via Langer-Schwartz theory. For optimum magnetic properties, prior work suggests that it is desirable to precipitate Fe$_3$Si nanocrystals with 10-15 nm diameter and with crystalline volume fraction of about 70 \%. Based on our parameterized model, we simulated nucleation and growth of Fe$_3$Si nanocrystals with the desired size range and volume fraction by isothermal annealing of a FINEMET alloy (Fe$_{72.89}$Si$_{16.21}$B$_{6.90}$Nb$_{3}$Cu$_{1}$ in atomic \%). In numerical experiments, the alloys were isothermally treated at 490, 500, 510, 520, 530, 540, and 550 \degree C for two hours to study the effect of holding time not only on mean radius and volume fraction, but also on the size distribution, nucleation rate, number density, and driving force for the growth of Fe$_3$Si nanocrystals. With increasing annealing temperature, the mean radius of Fe$_3$Si nanocrystals increases, while the volume fraction decreases. Thereafter, the composition of Fe and Si in the FINEMET alloy was varied by $\pm$ 3 \% to check the predictions of the model for nucleation and growth of Fe$_3$Si nanocrystals from different alloy compositions. As Fe content decreases, it is possible to achieve the desired mean radius and volume fraction within one hour holding time. The CALPHAD approach presented here can provide efficient exploration of the nanocrystalline morphology for most FINEMET systems, for cases in which the optimization of one or more material properties or process variable is desired.




Optical Selection Rule of Excitons in Gapped Chiral Fermion Systems. (arXiv:1709.08310v1 [cond-mat.mes-hall])

We show that the exciton optical selection rule in gapped chiral fermion systems is governed by their winding number $w$, a topological quantity of the Bloch bands. Specifically, in a $C_N$-invariant chiral fermion system, the angular momentum of bright exciton states is given by $w \pm 1 + nN$ with $n$ being an integer. We demonstrate our theory by proposing two chiral fermion systems capable of hosting dark $s$-like excitons: gapped surface states of a topological crystalline insulator with $C_4$ rotational symmetry and biased $3R$-stacked MoS$_2$ bilayers. In the latter case, we show that gating can be used to tune the $s$-like excitons from bright to dark by changing the winding number. Our theory thus provides a pathway to electrical control of optical transitions in two-dimensional material.




Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2. (arXiv:1709.08313v1 [cond-mat.mes-hall])

Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature TC ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.




Electrical control of inter-layer excitons in van der Waals heterostructures. (arXiv:1709.08315v1 [cond-mat.mes-hall])

We investigate excitons in stacked transition metal dichalcogenide (TMDC) layers under perpendicularly applied electric field, herein MoSe$_2$/WSe$_2$ van der Waals heterostructures. Band structures are obtained with density functional theory calculations, along with the electron and hole wave functions in conduction and valence bands, respectively. Although the type-II nature of the heterostructure leads to fully charge separated inter-layer excitons, charge carriers distribution among the layers is shown to be easily tunable by external field. Our results show that moderate values of electric field produce more evenly distributed wave functions along the heterostructure, thus enhancing both the inter-layer exciton binding energy and, most notably, its oscillator strength.




The Best Features of Diamond Nanothread for Nanofiber Application. (arXiv:1709.08326v1 [cond-mat.mtrl-sci])

Carbon fibers, especially those constructed from carbon nanotubes (CNTs), have attracted intensive interests from both scientific and engineering communities due to their outstanding physical properties. In this workHere we report, we find that the recently synthesized recently synthesized ultrathin diamond nanothread (DNT) not only possesses excellent torsional deformation capability, but also has excellent interfacial load transfer efficiency. Comparing with the (10,10) carbon nanotube bundles, (1) By considering a seven strand fiber, the flattening of nanotubes as observed in (10,10) CNT bundles is not observed in DNTdiamond nanothread bundle, which . This endows the DNT bundle withleads to a high torsional elastic limit that is almost three times higherfour times as obtained from the (10,10) CNT bundle. Pull-out tests reveal that (2) Pull-out tests reveal that tthe DNT diamond nanothread bundle has has an interface transfer load of more than twice that of the CNT carbon naontube bundle, corresponding to an order of magnitude higher in terms of . (3) Tthe interfacial shear strength of the DNT bundle is an order of magnitude higher than that of the CNT bundle. Such high interface load transfer efficiency is attributed to the zigzag morphology of DNT, which introduces a strong mechanical interlocking effect at the interface through the stick-slip motion (totally different from the load transfer mechanism in CNT bundle). The aforementioned three aspects are commonly used to gauge the performance of fibers. Obviously,These intriguing features enable DNT diamond nanothread as exhibits excellent potential candidate for constructing next generation carbon fibers.




Graphene helicoid as novel nanospring. (arXiv:1709.08329v1 [cond-mat.mtrl-sci])

Advancement of nanotechnology has greatly accelerated the miniaturization of mechanical or electronic devices. This work proposes a new nanoscale spring - a graphene nanoribbon-based helicoid (GH) structure by using large-scale molecular dynamics simulation. It is found that the GH structure not only possesses an extraordinary high tensile deformation capability, but also exhibits unique features not accessible from traditional springs. Specifically, its yield strain increases when its inner radius is enlarged, which can exceed 1000%, and it has three elastic deformation stages including the initial delamination, stable delamination and elastic deformation. Moreover, the failure of the GH is found to be governed by the failure of graphene nanoribbon and the inner edge atoms absorb most of the tensile strain energy. Such fact leads to a constant elastic limit force (corresponding to the yield point) for all GHs. This study has provided a comprehensive understanding of the tensile behaviors of GH, which opens the avenue to design novel nanoscale springs based on 2D nanomaterials.




Mechanical Properties of Penta-Graphene Nanotubes. (arXiv:1709.08330v1 [cond-mat.mtrl-sci])

Penta-graphene is the name given to a novel puckered monolayer of carbon atoms tightly packed into an inerratic pentagonal network, theoretically, which exhibits excellent thermal and mechanical stability and can be rolled into penta-graphene nanotubes (PGNTs). Herein, we perform the first simulation study of mechanical properties of PGNTs under uniaxial tension. In addition to comparable mechanical properties with that of carbon nanotubes (CNT), it is found that PGNTs possess promising extensibility with typical plastic behavior due to the irreversible pentagon-to-polygon structural transformation and the hexagon carbon ring becomes the dominating structural motif after the transformation. The plastic characteristic of PGNTs is inherent with strain-rate and tube-diameter independences. Moreover, within ultimate temperature (T<1100 K), tensile deformed PGNTs manifest similar phase transition with an approximate transition ratio from pentagon to hexagon. The intrinsic insight provides a fundamental understanding of mechanic properties of PGNTs, which should open up a novel perspective for the design of plastic carbon-based nanomaterials.




Strain-induced large spin splitting and persistent spin helix at LaAlO$_3$/SrTiO$_3$ interface. (arXiv:1709.08335v1 [cond-mat.mtrl-sci])

We investigated the effect of the tensile strain on the spin splitting at the n-type interface in LaAlO$_3$/SrTiO$_3$ in terms of the spin-orbit coupling coefficient $\alpha$ and spin texture in the momentum space using first-principles calculations. We found that the $\alpha$ could be controlled by the tensile strain and be enhanced up to 5 times for the tensile strain of 7%, and the effect of the tensile strain leads to a persistent spin helix, which has a long spin lifetime. These results support that the strain effect on LaAlO$_3$/SrTiO$_3$ is important for various applications such as SpinFET and spin-to-charge conversion.




Chirality in magnetic multilayers probed by the symmetry and the amplitude of dichroism in X-ray resonant magnetic scattering. (arXiv:1709.08352v1 [cond-mat.mtrl-sci])

Chirality in condensed matter is now a topic of the utmost importance because of its significant role in the understanding and mastering of a large variety of new fundamental physicals mechanisms. Versatile experimental approaches, capable to reveal easily the exact winding of order parameters are therefore essential. Here we report X-ray resonant magnetic scattering (XRMS) as a straightforward tool to identify directly the properties of chiral magnetic systems. We show that it can straight-forwardly and unambiguously determine the main characteristics of chiral magnetic distributions: i.e. its chiral nature, the quantitative winding sense (clockwise or counter-clockwise) and its type (N\'eel/cycloidal or Bloch/helical). This method is model-independent, does not require a-priori knowledge of magnetic parameters and can be applied to any system with magnetic domains ranging from few nanometers (wavelength limited) to several microns. By using prototypical multilayers with tailored magnetic chiralities based on the Co|Pt interface we illustrate the strength of this method.




Floquet topological phase transitions in a kicked Haldane-Chern insulator. (arXiv:1709.08354v1 [cond-mat.mes-hall])

We consider a periodically $\delta$-kicked Haldane type Chern insulator with the kicking applied in the $\hat{z}$ direction. This is known to behave as an inversion symmetry breaking perturbation, since it introduces a time-dependent staggered sub-lattice potential. We study here the effects of such driving on the topological phase diagram of the original Haldane model of a Hall effect in the absence of a net magnetic field. The resultant Floquet band topology is again that of a Chern insulator with the driving parameters, frequency and amplitude, influencing the inversion breaking mass $M$ of the undriven Haldane model. A family of such, periodically related, `Semenoff masses' is observed to occur which support a periodic repetition of Haldane like phase diagrams along the inversion breaking axis of the phase plots. Out of these it is possible to identify two in-equivalent masses in the reduced zone scheme of the Floquet quasienergies, which form the centres of two inequivalent phase diagrams. Further, variation in the driving amplitude's magnitude alone is shown to effect the topological properties by linearly shifting the phase diagram of the driven model about the position of the undriven case. A phenomenon that allows the study of Floquet topological phase transitions in the system. Finally, we also discuss some issues regarding the modifications to Haldane's condition for preventing band overlaps at the Dirac point touchings in the Brillouin zone, in the presence of kicking.




Doubled Shapiro Steps in a Topological Josephson Junction. (arXiv:1709.08355v1 [cond-mat.mes-hall])

We study the transport properties of a superconductor-quantum spin Hall insulator-superconductor (S-QSHI-S) hybrid system in the presence of a microwave radiation. Instead of adiabatic analysis or using the resistively shunted junction model, we start from the microscopic Hamiltonian and calculate the DC current directly with the help of the non-equilibrium Green's Functions method. The numerical results show that (i) the I-V curves of background current due to multiple Andreev reflections (MAR) exhibit a different structure with that in the conventional junctions, (ii) all Shapiro steps are visible and appear one by one at high frequency, while at low frequency, the steps evolve exactly as the Bessel functions and the odd steps are completely suppressed, implying a fractional Josephson effect.




Ferromagnetic Potts models with multi-site interaction. (arXiv:1709.08368v1 [cond-mat.stat-mech])

We provide a bound on the critical point of the $q$ states Potts models with four site interaction on the square lattice. Based on the asymptotic behaviour of lattice animals, it is argued that when $q<4$ the system exhibits a second order phase transition, and when $q>4$ the transition is first order. The $q=4$ model is borderline. When the transition if first order, the critical bound can be improved and related to the finite size correlation length. These two results can be extended to other lattices. Our theoretical predictions are confirmed numerically by an extensive study of the four site interaction model using the Wang-Landau entropic sampling method for $q=3,4,5$. In particular, the $q=4$ model shows an ambiguous finite size pseudo-critical behaviour.




Asymmetric $g$ tensor in low-symmetry two-dimensional hole systems. (arXiv:1709.08376v1 [cond-mat.mes-hall])

The complex structure of the valence band in many semiconductors leads to multifaceted and unusual properties for spin-3/2 hole systems compared to typical spin-1/2 electron systems. In particular, two-dimensional hole systems show a highly anisotropic Zeeman spin splitting. We have investigated this anisotropy in GaAs/AlAs quantum well structures both experimentally and theoretically. By performing time-resolved Kerr rotation measurements, we found a non-diagonal tensor $g$ that manifests itself in unusual precessional motion as well as distinct dependencies of hole spin dynamics on the direction of the magnetic field $\vec{B}$. We quantify the individual components of the tensor $g$ for [113]-, [111]- and [110]-grown samples. We complement the experiments by a comprehensive theoretical study of Zeeman splitting in in-plane and out-of-plane fields $\vec{B}$. To this end, we develop a detailed multiband theory for the tensor $g$. Using perturbation theory, we derive transparent analytical expressions for the components of the tensor $g$ that we complement with accurate numerical calculations based on our theoretical framework. We obtain very good agreement between experiment and theory. Our study demonstrates that the tensor $g$ is neither symmetric nor antisymmetric. Opposite off-diagonal components can differ in size by up to an order of magnitude.




Modeling and analysis of the dielectric properties of composite materials using large random RC networks. (arXiv:1709.08381v1 [cond-mat.dis-nn])

The paper proposes a simple and efficient method to study the dielectric properties of composite materials modeled using very large random resistor-capacitor (RC) networks. The algorithm is based on the Frank-Lobb reduction scheme and analyses the frequency dependent AC conductivity, permittivity and phase angle of composite materials. The simulation study is based on 1056 samples of random network containing 2*10^6 components randomly positioned in different proportion of capacitors. It has been found that these properties exhibit similarities to the universal dielectric response of dielectric materials. The results show that there is no variability between samples at low and high frequencies and across the power law.




Chiral Soliton Lattice Formation in Monoaxial Helimagnet Yb(Ni$_{1-x}$Cu$_x$)$_3$Al$_9$. (arXiv:1709.08382v1 [cond-mat.str-el])

Helical magnetic structures and its responses to external magnetic fields in Yb(Ni$_x$Cu$_{1-x}$)$_3$Al$_9$, with a chiral crystal structure of the space group $R32$, have been investigated by resonant X-ray diffraction. It is shown that the crystal chirality is reflected to the helicity of the magnetic structure by a one to one relationship, indicating that there exists an antisymmetric exchange interaction mediated via the conduction electrons. When a magnetic field is applied perpendicular to the helical axis ($c$ axis), the second harmonic peak of $(0, 0, 2q)$ develops with increasing the field. The third harmonic peak of $(0, 0, 3q)$ has also been observed for the $x$=0.06 sample. This result provides a strong evidence for the formation of a chiral magnetic soliton lattice state, a periodic array of the chiral twist of spins, which has been suggested by the characteristic magnetization curve. The helical ordering of magnetic octupole moments, accompanying with the magnetic dipole order, has also been detected.




Quenching the CME via the gravitational anomaly and holography. (arXiv:1709.08384v1 [hep-th])

In the presence of a gravitational contribution to the chiral anomaly, the chiral magnetic effect induces an energy current proportional to the square of the temperature in equilibrium. In holography the thermal state corresponds to a black hole. We numerically study holographic quenches in which a planar shell of scalar matter falls into a black hole and rises its temperature. During the process the momentum density (energy current) is conserved. The energy current has two components, a non-dissipative one induced by the anomaly and a dissipative flow component. The dissipative component can be measured via the drag it asserts on an additional auxiliary color charge. Our results indicate strong suppression very far from equilibrium.




Connectedness percolation of hard deformed rods. (arXiv:1709.08390v1 [cond-mat.soft])

Nanofiller particles, such as carbon nanotubes or metal wires, are used in functional polymer composites to make them conduct electricity. They are often not perfectly straight cylinders, but may be tortuous or exhibit kinks. Therefore we investigate the effect of shape deformations of the rodlike nanofillers on the geometric percolation threshold of the dispersion. We do this by using connectedness percolation theory within a Parsons-Lee type of approximation, in combination with Monte Carlo integration for the average overlap volume in the isotropic fluid phase. We find that a deviation from a perfect rodlike shape has very little effect on the percolation threshold, unless the particles are strongly deformed. This demonstrates that idealized rod models are useful even for nanofillers that superficially seem imperfect. In addition, we show that for small or moderate rod deformations, the universal scaling of the percolation threshold is only weakly affected by the precise particle shape.




Inter-subband Landau level couplings induced by in-plane magnetic fields in trilayer graphene. (arXiv:1709.08401v1 [cond-mat.mes-hall])

We observed broken-symmetry quantum Hall effects and level crossings between spin- and valley- resolved Landau levels (LLs) in Bernal stacked trilayer graphene. When the magnetic field was tilted with respect to sample normal from $0^{\circ}$ to $66^\circ$, the LL crossings formed at intersections of zeroth and second LLs from monolayer-graphene-like and bilayer-graphene-like subbands, respectively, exhibited a sequence of transitions. The results indicate the LLs from different subbands are coupled by in-plane magnetic fields ($B_{\parallel}$), which was explained by developing the tight-binding model Hamiltonian of trilayer graphene under $B_{\parallel}$.




An exactly solvable BCS-Hubbard Model in arbitrary dimensions. (arXiv:1709.08411v1 [cond-mat.str-el])

We introduce in this paper an exact solvable BCS-Hubbard model in arbitrary dimensions. The model describes a $p$-wave BCS superconductor with equal spin pairing moving on a bipartite (cubic, square etc.) lattice with on site Hubbard interaction $U$. We show that the model becomes exactly solvable for arbitrary $U$ when the BCS pairing amplitude $\Delta$ equals the hopping amplitude $t$. The nature of the solution is described in detail in this paper. The construction of the exact solution is parallel to the exactly solvable Kitaev honeycomb model for $S=1/2$ quantum spins and can be viewed as a generalization of Kitaev's construction to $S=1/2$ interacting lattice fermions. The BCS-Hubbard model discussed in this paper is just an example of a large class of exactly solvable lattice fermion models that can be constructed similarly.




Non-local plasticity effects on notch fracture mechanics. (arXiv:1709.08412v1 [cond-mat.mtrl-sci])

We investigate the influence of gradient-enhanced dislocation hardening on the mechanics of notch-induced failure. The role of geometrically necessary dislocations (GNDs) in enhancing cracking is assessed by means of a mechanism-based strain gradient plasticity theory. Both stationary and propagating cracks from notch-like defects are investigated through the finite element method. A cohesive zone formulation incorporating monotonic and cyclic damage contributions is employed to address both loading conditions. Computations are performed for a very wide range of length scale parameters and numerous geometries are addressed, covering the main types of notches. Results reveal a strong influence of the plastic strain gradients in all the scenarios considered. Transitional combinations of notch angle, radius and length scale parameter are identified that establish the regimes of GNDs-relevance, laying the foundations for the rational application of gradient plasticity models in damage assessment of notched components.




Higher-order topological insulators and semimetals on the breathing Kagome and pyrochlore lattices. (arXiv:1709.08425v1 [cond-mat.mes-hall])

A second-order topological insulator in $d$ dimensions is an insulator which has no $d-1$ dimensional topological boundary states but has $d-2$ dimensional topological boundary states. They have been investigated in square and cubic lattices. In this paper, we generalize them to breathing Kagome and pyrochlore lattices. First, we demonstate that a second-order topological insulator is constructed on the breathing Kagome lattice. Three topological boundary states emerge at the corner of the triangle, realizing a 1/3 fractional charge at each corner. Second, we demonstrate that a third-order topological insulator is constructed on the breathing pyrochlore lattice. Four topological boundary states emerge at the corners of the tetrahedron with a 1/4 fractional charge at each corner. We argue that they are higher dimensional extension of the Su-Schrieffer-Heager model. Finally, we study a second-order topological semimetal by stacking the breathing Kagome lattice.




Magnetothermoelectric DC conductivities from holography models with hyperscaling factor in Lifshitz spacetime. (arXiv:1709.08428v1 [hep-th])

We investigate an Einstein-Maxwell-Dilaton-Axion holographic model and obtain two branches of a charged black hole solution with a dynamic exponent and a hyperscaling violation factor when a magnetic field presents. The magnetothermoelectric DC conductivities are then calculated in terms of horizon data by means of holographic principle. We find that linear temperature dependence resistivity and quadratic temperature dependence inverse Hall angle can be achieved in our model. The well-known anomalous temperature scaling of the Nernst signal and the Seebeck coefficient of cuprate strange metals are also discussed.




The Mechanism behind Erosive Bursts in Porous Media. (arXiv:1709.08451v1 [physics.flu-dyn])

Erosion and deposition during flow through porous media can lead to large erosive bursts that manifest as jumps in permeability and pressure loss. Here we reveal that the cause of these bursts is the re-opening of clogged pores when the pressure difference between two opposite sites of the pore surpasses a certain threshold. We perform numerical simulations of flow through porous media and compare our predictions to experimental results, recovering with excellent agreement shape and power-law distribution of pressure loss jumps, and the behavior of the permeability jumps as function of particle concentration. Furthermore, we find that erosive bursts only occur for pressure gradient thresholds within the range of two critical values, independent on how the flow is driven. Our findings provide a better understanding of sudden sand production in oil wells and breakthrough in filtration.




Grand Canonical Adaptive Resolution Simulation for Molecules with Electrons: A Theoretical Framework based on Physical Consistency. (arXiv:1709.08452v1 [cond-mat.stat-mech])

A theoretical scheme for the treatment of an open molecular system with electrons and nuclei is proposed. The idea is based on the Grand Canonical description of a quantum region embedded in a classical reservoir of molecules. Electronic properties of the quantum region are calculated at constant electronic chemical potential equal to that of the corresponding (large) bulk system treated at full quantum level. Instead, the exchange of molecules between the quantum region and the classical environment occurs at the chemical potential of the macroscopic thermodynamic conditions. T he Grand Canonical Adaptive Resolution Scheme is proposed for the treatment of the classical environment; such an approach can treat the exchange of molecules according to first principles of statistical mechanics and thermodynamic. The overall scheme is build on the basis of physical consistency, with the corresponding definition of numerical criteria of control of the approximations implied by the coupling. Given the wide range of expertise required, this work has the intention of providing guiding principles for the construction of a well founded computational protocol for actual multiscale simulations from the electronic to the mesoscopic scale.




High-Tc superconductivity up to 55 K under high pressure in the heavily electron doped Lix(NH3)yFe2Se2 single crystal. (arXiv:1709.08455v1 [cond-mat.supr-con])

We report a high-pressure study on the heavily electron doped Lix(NH3)yFe2Se2 single crystal by using the cubic anvil cell apparatus. The superconducting transition temperature Tc = 44 K at ambient pressure is first suppressed to below 20 K upon increasing pressure to Pc = 2 GPa, above which the pressure dependence of Tc(P) reverses and Tc increases steadily to ca. 55 K at 11 GPa. These results thus evidenced a pressure-induced second high-Tc superconducting (SC-II) phase in Lix(NH3)yFe2Se2 with the highest Tcmax = 55K among the FeSe-based bulk materials. Hall data confirm that in the emergent SC-II phase the dominant electron-type carrier density undergoes a fourfold enhancement and tracks the same trend as Tc(P). Interesting, we find a nearly parallel scaling behavior between Tc and the inverse Hall coefficient for the SC-II phases of both Lix(NH3)yFe2Se2 and (Li,Fe)OHFeSe. The present work demonstrates that high pressure offers a distinctive means to further raising the maximum Tc of heavily electron doped FeSe-based materials by increasing the effective charge carrier concentration via a plausible Fermi surface reconstruction at Pc.




A Universal Curve of Optimum Thermoelectric Figures of Merit for Bulk and Low-dimensional Semiconductors. (arXiv:1709.08456v1 [cond-mat.mtrl-sci])

Analytical formulas for thermoelectric figure of merit and power factor are derived based on the one-band model. We find that there is a direct relationship between the optimum figures of merit and the optimum power factors of semiconductors despite of the fact that the two quantities are generally given by different values of chemical potentials. By introducing a dimensionless parameter consisting of optimum power factor and lattice thermal conductivity (without electronic thermal conductivity), it is possible to unify optimum figures of merit of both bulk and low-dimensional semiconductors into a single universal curve that covers lots of materials with different dimensionalities.




Non-adiabatic breaking of topological pumping. (arXiv:1709.08457v1 [cond-mat.quant-gas])

We study Thouless pumping out of the adiabatic limit. Our findings show that despite its topological nature, this phenomenon is not robust to non-adiabatic effects. Indeed we find that the Floquet diagonal ensemble value of the pumped charge shows a deviation from the topologically quantized limit which is quadratic in the frequency of the driving and not exponentially small as previously believed. This is reflected also in the charge pumped in a single period, which shows a non-analytic behaviour on top of an overall quadratic decrease. We also discuss thermal effects and the experimental feasibility of observing such a deviation.




Local equilibrium in the Bak-Sneppen model. (arXiv:1709.08468v1 [nlin.AO])

The Bak Sneppen (BS) model is a very simple model that exhibits all the richness of self-organized criticality theory. At the thermodynamic limit, the BS model converges to a situation where all particles have a fitness that is uniformly distributed between a critical value $p_c$ and 1. The $p_c$ value is unknown, as are the variables that influence and determine this value. Here, we study the Bak Sneppen model in the case in which the lowest fitness particle interacts with an arbitrary even number of $m$ nearest neighbors. We show that $p_{c,m}$ verifies a simple local equilibrium relationship. Based on this relationship, we can determine bounds for $p_{c,m}$.




Critical values in Bak-Sneppen type models. (arXiv:1709.08474v1 [nlin.AO])

In the Bak-Sneppen model, the lowest fitness particle and its two nearest neighbors are renewed at each temporal step with a uniform (0,1) fitness distribution. The model presents a critical value that depends on the interaction criteria (two nearest neighbors) and on the update procedure (uniform). Here we calculate the critical value for models where one or both properties are changed. We study models with non-uniform updates, models with random neighbors and models with binary fitness and obtain exact results for the average fitness and for $p_c$.




Atom Pairing in Optical Superlattices. (arXiv:1709.08484v1 [cond-mat.quant-gas])

We study the pairing of fermions in a one-dimensional lattice of tunable double-well potentials using radio-frequency spectroscopy. The spectra reveal the coexistence of two types of atom pairs with different symmetries. Our measurements are in excellent quantitative agreement with a theoretical model, obtained by extending the Green's function method of Orso et al., [Phys. Rev. Lett. 95, 060402 (2005)], to a bichromatic 1D lattice with finite harmonic radial confinement. The predicted spectra comprise hundreds of discrete transitions, with symmetry-dependent initial state populations and transition strengths. Our work provides an understanding of the elementary pairing states in a superlattice, paving the way for new studies of strongly interacting many-body systems.




The structural, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure. (arXiv:1709.08502v1 [cond-mat.mtrl-sci])

The magnetic transition-metal (TM) @ oxide nanoparticles have been of great interest due to their wide range of applications, from medical sensors in magnetic resonance imaging to photo-catalysis. Although several studies on small clusters of TM@oxide have been reported, the understanding of the physical electronic properties of TMn@(ZnO)42 is far from sufficient. In this work, the electronic, magnetic and optical properties of TMn@(ZnO)42 (TM = Fe, Co and Ni) hetero-nanostructure are investigated using the density functional theory (DFT). It has been found that the core-shell nanostructure Fe13@(ZnO)42, Co15@(ZnO)42 and Ni15@(ZnO)42 are the most stable structures. Moreover, it is also predicted that the variation of the magnetic moment and magnetism of Fe, Co and Ni in TMn@ZnO42 hetero-nanostructure mainly stems from effective hybridization between core TM-3d orbitals and shell O-2p orbitals, and a magnetic moment inversion for Fe15@(ZnO)42 is investigated. Finally, optical properties studied by calculations show a red shift phenomenon in the absorption spectrum compared with the case of (ZnO)48.




Simple analysis of scattering data with Ornstein-Zernike equation. (arXiv:1709.08507v1 [cond-mat.soft])

In this paper we propose and explore a method of analysis of the scattering experimental data for uniform liquid-like systems. In our pragmatic approach we are not trying to introduce by hands an artificial small parameter to work out a perturbation theory with respect to the known results e.g., for hard spheres or sticky-hard spheres (all the more that in the agreement with the notorious Landau statement, there is no any physical small parameter for liquids). Instead of it guided by the experimental data we are solving the the Ornstein-Zernike equation with a trial (variational) form of the inter-particle interaction potential. To find all needed correlation functions this variational input is iterated numerically to satisfy the Ornstein-Zernike equation supplemented by a closure relation. We illustrate by a number of model and real experimental examples of the X-ray and neutron scattering data how the approach works.




Coherent scattering from semi-infinite non-Hermitian potentials. (arXiv:1709.08513v1 [quant-ph])

When two identical (coherent) beams are injected at a semi-infinite non-Hermitian medium from left and right, we show that both reflection $(r_L,r_R)$ and transmission $(t_L,t_R)$ amplitudes are non-reciprocal. In a parametric domain, there exists Spectral Singularity (SS) at a real energy $E=E_*$ and the determinant of the time-reversed two port S-matrix i.e., $|\det(S)|=|t_L t_R-r_L r_R|$ vanishes sharply at $E=E_*$ displaying the phenomenon of Coherent Perfect Absorption (CPA). In the complimentary parametric domain, the potential becomes either left or right reflectionless at $E=E_z$. But we rule out the existence of Invisibility despite $r_R(E_i)=0$ and $t_R(E_i)=1$ in these new models. We present two simple exactly solvable models where the expressions for $E_*$, $E_z$, $E_i$ and the parametric conditions on the potential have been obtained in explicit and simple forms. Earlier, the novel phenomena of SS and CPA have been found to occur only in the scattering complex potentials which are spatially localized (vanish asymptotically) and having $t_L=t_R$.




Enhanced Quantum Synchronization via Quantum Machine Learning. (arXiv:1709.08519v1 [quant-ph])

We study the quantum synchronization between a pair of two-level systems inside two coupledcavities. Using a digital-analog decomposition of the master equation that rules the system dynamics, we show that this approach leads to quantum synchronization between both two-level systems. Moreover, we can identify in this digital-analog block decomposition the fundamental elements of a quantum machine learning protocol, in which the agent and the environment (learning units) interact through a mediating system, namely, the register. If we can additionally equip this algorithm with a classical feedback mechanism, which consists of projective measurements in the register, reinitialization of the register state and local conditional operations on the agent and register subspace, a powerful and flexible quantum machine learning protocol emerges. Indeed, numerical simulations show that this protocol enhances the synchronization process, even when every subsystem experience different loss/decoherence mechanisms, and give us flexibility to choose the synchronization state. Finally, we propose an implementation based on current technologies in superconducting circuits.




Entangled plasmon generation in nonlinear spaser system under action of external magnetic field. (arXiv:1709.08548v1 [cond-mat.mes-hall])

Quantum dynamics of localized plasmons in spaser systems, consisting of three or four metal nanoparticles and semiconductor quantum dots, are theoretically investigated. In the framework of the mean field approximation the conditions for observation stable stationary regimes of single-particle plasmons are established and discussed. The effect of fast destruction of initial nonclassical plasmon states via strong dipole-dipole interaction between adjacent nanoparticles is shown in the four-particle spaser system. It is proposed for the first time and demonstrated use of external magnetic field for control of the second-order plasmonic cross-correlation function in the three-particle spaser system. Generation of the entangled plasmons in the three-particle spaser system with nonlinear plasmon-bi-exciton interaction is predicted.




Entropy production and work fluctuation relations for a single particle in active bath. (arXiv:1709.08554v1 [cond-mat.stat-mech])

A colloidal particle immersed in a bath of bacteria is a typical example of a passive particle in an active bath. To model this, we take an overdamped harmonically trapped particle subjected to a thermal and a non-equilibrium noise arising from the active bath. The harmonic trap can be attributed to the laser trap or to the fact that a sedimenting colloid near the bottom of the capillary experiences a near harmonic potential. In the long time, the system reaches a non-equilibrium steady state that can be described by an effective temperature. By adopting this notion of effective temperature, we investigate whether fluctuation relations for entropy hold. In addition, when subjected to a deterministic time dependent drag, we find that transient fluctuation theorem for work cannot be applied. However, a steady state fluctuation relation for work emerges out with a renormalized temperature.




Mean field theory of the swap Monte Carlo algorithm. (arXiv:1709.08557v1 [cond-mat.dis-nn])

The swap Monte Carlo algorithm combines the translational motion with the exchange of particle species, and is unprecedentedly efficient for some models of glass former. In order to clarify the physics underlying this acceleration, we study the problem within the mean field replica liquid theory. We extend the Gaussian ansatz so as to take into account the exchange of particles of different species, and we calculate analytically the dynamical transition points corresponding to the swap and standard Monte Carlo algorithms. We show that the system evolved with the standard Monte Carlo algorithm exhibits the dynamical transition before that of the swap Monte Carlo algorithm. We also test the result by performing numerical simulations of a binary mixture of the Mari-Kurchan model, both with standard and swap Monte Carlo. This scenario provides a possible explanation for the efficiency of the swap Monte Carlo algorithm. Finally, we discuss how the thermodynamic theory of the glass transition should be modified based on our results.




Scanning gate experiments: from strongly to weakly invasive probes. (arXiv:1709.08559v1 [cond-mat.mes-hall])

An open resonator fabricated in a two-dimensional electron gas is used to explore the transition from strongly invasive scanning gate microscopy to the perturbative regime of weak tip-induced potentials. With the help of numerical simulations that faithfully reproduce the main experimental findings, we quantify the extent of the perturbative regime in which the tip-induced conductance change is unambiguously determined by properties of the unperturbed system. The correspondence between the experimental and numerical results is established by analyzing the characteristic length scale and the amplitude modulation of the conductance change. In the perturbative regime, the former is shown to assume a disorder-dependent maximum value, while the latter linearly increases with the strength of a weak tip potential.




Magnetic structure of Ba(TiO)Cu$_4$(PO$_4$)$_4$ probed using spherical neutron polarimetry. (arXiv:1709.08566v1 [cond-mat.str-el])

The antiferromagnetic compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ contains square cupola of corner-sharing CuO$_4$ plaquettes, which were proposed to form effective quadrupolar order. To identify the magnetic structure, we have performed spherical neutron polarimetry measurements. Based on symmetry analysis and careful measurements we conclude that the orientation of the Cu$^{2+}$ spins form a non-collinear in-out structure with spins approximately perpendicular to the CuO$_4$ motif. Strong Dzyaloshinskii-Moriya interaction naturally lends itself to explain this phenomenon. The identification of the ground state magnetic structure should serve well for future theoretical and experimental studies into this and closely related compounds.




Dynamics of elastically strained islands in presence of an anisotropic surface energy. (arXiv:1709.08570v1 [cond-mat.soft])

The equilibrium solutions and coarsening dynamics of strained semi-conductor islands are investigated analytically and numerically. We develop an analytical model to study the effect of surface energy anisotropy on the dynamics coarsening of islands. We propose a simple model to explain the effect of this anisotropy on the coarsening time. We find that the anisotropy slows down the coarsening. This effect is rationalised using a quasi-analytical description of the island profile.




Solvable 2D superconductors with l-wave pairing. (arXiv:1709.08576v1 [cond-mat.str-el])

We analyze a family of two dimensional BCS Hamiltonians with general l-wave pairing interactions, classifying the models in this family that are Bethe-Ansatz solvable in the finite-size regime. We show that these solutions are characterized by nontrivial winding numbers, associated to topological phases, in some part of the corresponding phase diagrams. By means of a comparative study, we demonstrate benefits and limitations of the mean-field approximation, which is the standard approach in the limit of large number of particles. The mean-field analysis also allows to extend part of the results beyond integrability, clarifying the peculiarities associable to the integrability itself.




Phase-Tunable Thermal Logic: Computation with Heat. (arXiv:1709.08609v1 [cond-mat.mes-hall])

Boolean algebra, the branch of mathematics where variables can assume only true or false value, is the theoretical basis of classical computation. The analogy between Boolean operations and electronic switching circuits, highlighted by Shannon in 1938, paved the way to modern computation based on electronic devices. The grow of computational power of such devices, after an exciting exponential -Moore trend, is nowadays blocked by heat dissipation due to computational tasks, very demanding after the chips miniaturization. Heat is often a detrimental form of energy which increases the systems entropy decreasing the efficiency of logic operations. Here, we propose a physical system able to perform thermal logic operations by reversing the old heat-disorder epitome into a novel heat-order paradigm. We lay the foundations of heat computation by encoding logic state variables in temperature and introducing the thermal counterparts of electronic logic gates. Exploiting quantum effects in thermally biased Josephson junctions (JJs), we propound a possible realization of a functionally complete dissipationless logic. Our architecture ensures high operation stability and robustness with switching frequencies reaching the GHz.




Non-fixation for conservative stochastic dynamics on the line. (arXiv:1508.05677v3 [math.PR] UPDATED)

We consider Activated Random Walk (ARW), a model which generalizes the Stochastic Sandpile, one of the canonical examples of self organized criticality. Informally ARW is a particle system on $\mathbb{Z}$ with mass conservation. One starts with a mass density $\mu>0$ of initially active particles, each of which performs a symmetric random walk at rate one and falls asleep at rate $\lambda>0$. Sleepy particles become active on coming in contact with other active particles. We investigate the question of fixation/non-fixation of the process, and show for small enough $\lambda$, the critical mass density for fixation is strictly less than one. Moreover, the critical density goes to zero as $\lambda$ tends to zero. This settles a long standing open question.




Quantifying Complexity in Quantum Phase Transitions via Mutual Information Complex Networks. (arXiv:1508.07041v4 [cond-mat.stat-mech] UPDATED)

We quantify the emergent complexity of quantum states near quantum critical points on regular 1D lattices, via complex network measures based on quantum mutual information as the adjacency matrix, in direct analogy to quantifying the complexity of EEG/fMRI measurements of the brain. Using matrix product state methods, we show that network density, clustering, disparity, and Pearson's correlation obtain the critical point for both quantum Ising and Bose-Hubbard models to a high degree of accuracy in finite-size scaling for three classes of quantum phase transitions, $Z_2$, mean field superfluid/Mott insulator, and a BKT crossover.




Statistical Approach to Tunneling Time in Attosecond Experiments. (arXiv:1512.04338v3 [quant-ph] UPDATED)

Tunneling, transport of particles through classically forbidden regions, is a pure quantum phenomenon. It governs numerous phenomena ranging from single-molecule electronics to donor-acceptor transition reactions. The main problem is the absence of a universal method to compute tunneling time. This problem has been attacked in various ways in the literature. Here, in the present work, we show that a statistical approach to the problem, motivated by the imaginary nature of time in the forbidden regions, lead to a novel tunneling time formula which is real and subluminal (in contrast to various known time definitions implying superluminal tunneling). This entropic tunneling time, as we call it, shows good agreement with the tunneling time measurements in laser-driven He ionization. Moreover, it sets an accurate range for long-range electron transfer reactions. The entropic tunneling time is general enough to extend to the photon and phonon tunneling phenomena.