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Condensed Matter

New submissions

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New submissions for Thu, 22 Feb 18

[1]  arXiv:1802.07265 [pdf, ps, other]
Title: Hydrodynamic electron flow in a Weyl semimetal slab: The role of Chern--Simons terms
Comments: 21 pages, 5 multi-panel figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); High Energy Physics - Theory (hep-th)

The hydrodynamic flow of the chiral electron fluid in a Weyl semimetal slab of finite thickness is studied by using the consistent hydrodynamic theory. The latter includes viscous, anomalous, and vortical effects, as well as accounts for dynamical electromagnetism. The energy and momentum separations between the Weyl nodes are taken into account via the topological Chern--Simons contributions in the electric current and charge densities in the Maxwell's equations. When an external electric field is applied parallel to the slab, it is found that the electron fluid velocity has a nonuniform profile determined by the viscosity and the no-slip boundary conditions. Most remarkably, the fluid velocity field develops a nonzero component across the slab that gradually dissipates when approaching the surfaces. This abnormal component of the flow arises due to the anomalous Hall voltage induced by the topological Chern--Simons current. Another signature feature of the hydrodynamics in Weyl semimetals is a strong modification of the anomalous Hall current along the slab in the direction perpendicular to the applied electric field. Additionally, it is found that the topological current induces an electric potential difference between the surfaces of the slab that is strongly affected by the hydrodynamic flow.

[2]  arXiv:1802.07268 [pdf, other]
Title: Scrambling in the Quantum Lifshitz Model
Comments: 15 pages + appendices. 12 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Statistical Mechanics (cond-mat.stat-mech)

We study signatures of chaos in the quantum Lifshitz model through out-of-time ordered correlators (OTOC) of current operators. This model is a free scalar field theory with dynamical critical exponent $z=2$. It describes the quantum phase transition in 2D systems, such as quantum dimer models, between a phase with an uniform ground state to another one with a spontaneously translation invariance. At the lowest temperatures the chaotic dynamics are dominated by a marginally irrelevant operator which induces a temperature dependent stiffness term. The numerical computations of OTOC exhibit a non-zero Lyapunov exponent (LE) in a wide range of temperatures and interaction strengths. The LE (in units of temperature) is a weakly temperature-dependent function; it vanishes at weak interaction and saturates for strong interaction. The Butterfly velocity increases monotonically with interaction strength in the studied region while remaining smaller than the interaction-induced velocity/stiffness.

[3]  arXiv:1802.07270 [pdf, other]
Title: Photoemission signature of excitons
Comments: 6 pages, 5 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)

Excitons - the particle-hole bound states - composed of localized electron-hole states in semiconducting systems are crucial to explaining the optical spectrum. Spectroscopic measurements can contain signatures of these two particle bound states and can be particularly useful in determining the characteristics of these excitons. We formulate an expression for evaluating the angle-resolved photoemission spectrum arising from the ionization of excitons given their steady-state distribution in a semiconductor. We show that the spectrum contains information about the direct/indirect band gap nature of the semiconductor and is located below the conduction band minimum displaced by the binding energy. The dispersive features of the spectrum contains remnants of the valence band. Our results indicate that for most exciton probability distributions, the energy integrated photoemission spectrum provides an estimate of the exciton Bohr radius.

[4]  arXiv:1802.07282 [pdf, ps, other]
Title: Phase diagram of Hubbard-Holstein model on 4-leg tube system at quarter-filling
Comments: 6 pages, 7 figs
Subjects: Strongly Correlated Electrons (cond-mat.str-el)

We derive an effective electronic Hamiltonian for square lattice Hubbard-Holstein model (HHM) in the strong electron-electron (e-e) and electron-phonon (e-ph) coupling regime and under non-adiabatic conditions ($t/\omega_0 \leq 1$), $t$ and $\omega_0$ being the electron hopping and phonon frequency respectively. Using Density Matrix Renormalization Group method, we simulate this effective electronic model on $4-$Leg cylinder system at quarter-filling and present a phase diagram in $g-U$ plane where $g$ and $U$ are being the e-ph coupling constant and Hubbard on-site interaction respectively. For larger $g$, we find cluster of spins i.e. phase separation (PS) gives way to a charge density wave (CDW) phase made of NN singlets which abruptly goes to another CDW phase as we increase $U$. But for smaller $g$, we find a metallic phase sandwiched between PS and singlet CDW phase. This phase is characterized by vanishing charge gap but finite spin gap -- suggesting a singlet superconducting phase.

[5]  arXiv:1802.07283 [pdf, ps, other]
Title: Nonuniversality and strongly interacting two-level systems in glasses at low temperatures
Comments: 12 pages, 4 figures
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn)

Recent experimental results showing untypical nonlinear absorption and marked deviations from well known universality in the low temperature acoustic and dielectric losses in amorphous solids prove the need for improving the understanding of the nature of two-level systems (TLSs) in these materials. Here we suggest the study of TLSs focused on their properties which are nonuniversal. Our theoretical analysis shows that the standard tunneling model and the recently suggested Two-TLS model provide markedly different predictions for the experimental outcome of these studies. Our results may be directly tested in disordered lattices, e.g KBr:CN, where there is ample theoretical support for the validity of the Two-TLS model, as well as in amorphous solids. Verification of our results in the latter will significantly enhance understanding of the nature of TLSs in amorphous solids, and the ability to manipulate them and reduce their destructive effect in various cutting edge applications including superconducting qubits.

[6]  arXiv:1802.07307 [pdf]
Title: Unsupervised Phase Mapping of X-ray Diffraction Data by Nonnegative Matrix Factorization Integrated with Custom Clustering
Comments: 26 pages, 9 figures
Subjects: Materials Science (cond-mat.mtrl-sci); Machine Learning (stat.ML)

Analyzing large X-ray diffraction (XRD) datasets is a key step in high-throughput mapping of the compositional phase diagrams of combinatorial materials libraries. Optimizing and automating this task can help accelerate the process of discovery of materials with novel and desirable properties. Here, we report a new method for pattern analysis and phase extraction of XRD datasets. The method expands the Nonnegative Matrix Factorization method, which has been used previously to analyze such datasets, by combining it with custom clustering and cross-correlation algorithms. This new method is capable of robust determination of the number of basis patterns present in the data which, in turn, enables straightforward identification of any possible peak-shifted patterns. Peak-shifting arises due to continuous change in the lattice constants as a function of composition, and is ubiquitous in XRD datasets from composition spread libraries. Successful identification of the peak-shifted patterns allows proper quantification and classification of the basis XRD patterns, which is necessary in order to decipher the contribution of each unique single-phase structure to the multi-phase regions. The process can be utilized to determine accurately the compositional phase diagram of a system under study. The presented method is applied to one synthetic and one experimental dataset, and demonstrates robust accuracy and identification abilities.

[7]  arXiv:1802.07317 [pdf, other]
Title: Transport through a network of topological states in twisted bilayer graphene
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

Minimally twisted bilayer graphene exhibits a lattice of AB and BA stacked regions. At small carrier densities and large displacement field, topological channels emerge and form a network. We fabricate small-angle twisted bilayer graphene and tune it with local gates. In our transport measurements we observe Fabry-P\'erot and Aharanov-Bohm oscillations which are robust in magnetic fields ranging from 0 to 8T. The Fabry-P\'erot trajectories in the bulk of the system cannot be bent by the Lorentz force. By extracting the enclosed length and area we find that the major contribution originates from trajectories encircling one row of AB/BA regions. The robustness in magnetic field and the linear spacing in density testifies to the fact that charge carriers flow in one-dimensional, topologically protected channels.

[8]  arXiv:1802.07318 [pdf]
Title: High-temperature structural phase transition and infrared dielectric features of La2CoMnO6
Comments: 23 pages; 6 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

Temperature-dependent FAR-infrared reflectivity spectra of partially ordered magnetodielectric La2CoMnO6 is presented, from room temperature up to 675 K. A clear first-ordered structural phase transition (SPT) from a monoclinic structure with P2_1/n symmetry to a rhombohedral phase with R-3 symmetry was evidenced from the behaviour of polar phonon modes at TC~590 K. The temperature dependences of the transversal and longitudinal phonon branches, dielectric strengths, and damping of the strongest dielectric modes confirm the significant contribution of the phonon modes on the SPT, and revealed an important lattice anharmonicity, particularly for the low frequency modes. In addition, these investigations showed that structural ordering does not inhibit the SPT, and provided valuable information towards the polar phonons, their implications on intrinsic dielectric constant in double perovskites and in related compounds.

[9]  arXiv:1802.07323 [pdf, other]
Title: Parametric amplification and squeezing with ac- and dc-voltage biased superconducting junction
Comments: 8 pages, 5 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We theoretically investigate a near-quantum-limited parametric amplifier based on the non-linear dynamics of quasiparticles flowing through a superconducting-insulator-superconducting junction. Photon-assisted tunneling, resulting from the combination of dc- and ac-voltage bias, gives rise to a strong parametric interaction for the electromagnetic modes reflected by the junction coupled to a transmission line. We show phase-sensitive and phase-preserving amplification, together with single- and two-mode squeezing. For an Aluminum junction pumped at 8 GHz, we predict narrow-band phase-sensitive amplification of microwaves signals to more than 30 dB, and broadband phase-preserving amplification larger than 15 dB over a 4 GHz band. We also predict single-mode squeezing reaching -20 dB and two-mode squeezing of -14 dB over a 4 GHz band. A key feature is that the device parameters can be tuned in-situ by the applied dc- and ac-voltage biases.

[10]  arXiv:1802.07326 [pdf]
Title: Anti-ferromagnetic interaction in double perovskites probed by Raman Spectroscopy
Comments: 18 pages; 3 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

In this paper we show that Raman spectroscopy is a powerfull technique to detect antisite disorder into A2B'B"O6 magnetic double poerovskites whose ferromagnetic properties are driven by superexchange interactions. We could detect low antisite disorder levels by monitoring the coupling between the magnetic order and the phonons in low-level disordered La2CoMnO6 double perovskite.

[11]  arXiv:1802.07327 [pdf, other]
Title: Asymmetric Skyrmion Hall Effect in Systems with Hybrid Dzyaloshinskii-Moriya Interaction
Comments: 7 pages, 3 figures, 1 table
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)

We examine the current-induced dynamics of a skyrmion that is subject to both interfacial and bulk Dzyaloshinskii-Moriya interactions (DMIs), arising in magnetic multilayers composed of chiral magnets with noncentrosymmetric crystal and nonmagnets with strong spin-orbit coupling. As a striking result, we find that, in systems with a hybrid DMI, the spin-orbit-torque-induced skyrmion Hall angle is asymmetric for the two different skyrmion polarities, even allowing one of them to be tuned to zero. We propose several experimental ways to achieve the necessary straight skyrmion motion (with zero Hall angle) for racetrack memories, even without any interaction with another magnet or an antiferromagnetic interaction. Our results can be understood within a simple picture by using a global spin rotation which maps the hybrid DMI model to an effective model containing purely interfacial DMI. In this sense, the formalism directly reveals the effective spin torque and effective current acting on systems with a hybrid DMI.

[12]  arXiv:1802.07331 [pdf, other]
Title: Strongly enhanced tunneling at total charge neutrality in double bilayer graphene-WSe$_2$ heterostructures
Comments: 5 pages, 5 figures, one supplementary figure
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We report the experimental observation of strongly enhanced tunneling between graphene bilayers through a WSe$_2$ barrier when the graphene bilayers are populated with carriers of opposite polarity and equal density. The enhanced tunneling increases sharply in strength with decreasing temperature, and the tunneling current exhibits a vertical onset as a function of interlayer voltage at a temperature of 1.5 K. The strongly enhanced tunneling at overall neutrality departs markedly from single-particle model calculations that otherwise match the measured tunneling current-voltage characteristics well, and suggest the emergence of a many-body state with condensed interbilayer excitons, when electrons and holes of equal densities populate the two layers.

[13]  arXiv:1802.07334 [pdf, other]
Title: Multigap superconductivity in RbCa2Fe4As4F2 investigated using muSR measurements
Comments: 10 pages, 7 figures. arXiv admin note: text overlap with arXiv:1706.03641
Subjects: Superconductivity (cond-mat.supr-con)

The superconducting properties of the recently discovered double Fe$_2$As$_2$ layered high-$T_c$ superconductor RbCa$_2$Fe$_4$As$_4$F$_2$ with $T_c\approx$ 30~K have been investigated using magnetization, heat capacity, transverse-field (TF) and zero-field (ZF) muon-spin rotation/relaxation ($\mu$SR) measurements. Our low field magnetization measurements and heat capacity (C$_p$) reveal an onset of bulk superconductivity with $T_{\bf c}\sim$ 30.0(4) K. Furthermore, the heat capacity exhibits a jump at $T_{\bf c}$ of $\Delta$C$_p$/$T_{\bf c}$=94.6 (mJ/mole-K$^2$) and no clear effect of applied magnetic fields was observed on C$_p$(T) up to 9 T between 2 K and 5 K. Our analysis of the TF-$\mu$SR results shows that the temperature dependence of the magnetic penetration depth is better described by a two-gap model, either isotropic $s$+$s$-wave or $s$+$d$-wave than a single gap isotropic $s$-wave or $d$-wave model for the superconducting gap. The presence of two superconducting gaps in RbCa$_2$Fe$_4$As$_4$F$_2$ suggests a multiband nature of the superconductivity, which is consistent with the multigap superconductivity observed in other Fe-based superconductors, including ACa$_2$Fe$_4$As$_4$F$_2$ (A=K and Cs). Furthermore, from our TF-$\mu$SR study we have estimated an in-plane penetration depth $\lambda_{\mathrm{ab}}$$(0)$ =231.5(3) nm, superconducting carrier density $n_s = 7.45 \times 10^{26}~ $m$^{-3}$, and carrier's effective-mass $m^*$ = 2.45\textit{m}$_{e}$. Our ZF $\mu$SR measurements do not reveal a clear sign of time reversal symmetry breaking at $T_{\bf c}$, but the temperature dependent relaxation between 150 K and 1.2 K might indicate the presence of spin-fluctuations. The results of our present study have been compared with those reported for other Fe pnictide superconductors.

[14]  arXiv:1802.07355 [pdf]
Title: Controlling magnetism in 2D CrI3 by electrostatic doping
Comments: 12 pages and 4 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

The atomic thickness of two-dimensional (2D) materials provides a unique opportunity to control material properties and engineer new functionalities by electrostatic doping. Electrostatic doping has been demonstrated to tune the electrical and optical properties of 2D materials in a wide range, as well as to drive the electronic phase transitions. The recent discovery of atomically thin magnetic insulators has opened up the prospect of electrical control of magnetism and new devices with unprecedented performance. Here we demonstrate control of the magnetic properties of monolayer and bilayer CrI3 by electrostatic doping using a dual-gate field-effect device structure. In monolayer CrI3, doping significantly modifies the saturation magnetization, coercive force and Curie temperature, showing strengthened (weakened) magnetic order with hole (electron) doping. Remarkably, in bilayer CrI3 doping drastically changes the interlayer magnetic order, causing a transition from an antiferromagnetic ground state in the pristine form to a ferromagnetic ground state above a critical electron density. The result reveals a strongly doping-dependent interlayer exchange coupling, which enables robust switching of magnetization in bilayer CrI3 by small gate voltages.

[15]  arXiv:1802.07356 [pdf, other]
Title: Hydrodynamic fluctuations in quasi-two dimensional diffusion
Comments: Submitted to J. Stat. Mech. (JSTAT)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)

We study diffusion of colloids on a fluid-fluid interface using particle simulations and fluctuating hydrodynamics. Diffusion on a two-dimensional interface with three-dimensional hydrodynamics is known to be anomalous, with the collective diffusion coefficient diverging like the inverse of the wavenumber. This unusual collective effect arises because of the compressibility of the fluid flow in the plane of the interface, and leads to a nonlinear nonlocal convolution term in the diffusion equation for the ensemble-averaged concentration. We extend the previous hydrodynamic theory to account for a species/color labeling of the particles, as necessary to model experiments based on fluorescent techniques. We study the magnitude and dynamics of density and color density fluctuations using a novel Brownian dynamics algorithm, as well as fluctuating hydrodynamics theory and simulation. We find that hydrodynamic coupling between a single tagged particle and collective density fluctuations leads to a reduction of the long-time self-diffusion coefficient, even for an ideal gas of non-interacting particles. Using linearized fluctuating hydrodynamics theory, we show that for diffusion on a fluid-fluid interface, nonequilibrium fluctuations of the total density are small compared to the equilibrium fluctuations, but fluctuations of color density are giant and exhibit a spectrum that decays as the inverse cubed power of the wavenumber. We confirm these predictions through Brownian dynamics simulations of diffusive mixing with two indistinguishable species. We also examine nonequilibrium fluctuations in systems with two-dimensional hydrodynamics, such as thin smectic films in vacuum. We find that nonequilibrium fluctuations are colossal and comparable in magnitude to the mean, and can be accurately modeled using numerical solvers for the nonlinear equations of fluctuating hydrodynamics.

[16]  arXiv:1802.07358 [pdf]
Title: Magnetization of Topological Surface States of Topological Insulators by Two-dimensional Ferromagnetism
Comments: 4 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)

Magnetization of the topological surface states of topological insulators is critical to designing and creating next-generation innovative and novel spintronic devices. Here we discover through density functional calculations that the emerging two-dimensional (2D) ferromagnetism discovered in the insulating monolayer CrI3 by recent experiments [B. Huang et al., Nature (London) 546, 270 (2017)] can magnetize the topological surface states of the prototypical three-dimensional (3D) topological insulator Bi2Se3 by building van der Waals (vdW) heterostructures CrI3/Bi2Se3/CrI3. Excitingly, such heterostructures with six and more quintuple layers of Bi2Se3 are the long-term sought Chern insulators. Moreover, the band gaps of these Chern insulators are noticeably increased by reducing their vdW gaps. Our work demonstrates contacting 3D topological insulators with the emerging 2D ferromagnetism is a highly promising frontier to realize the high-temperature quantum anomalous Hall effect experimentally in the future.

[17]  arXiv:1802.07360 [pdf]
Title: Comparison of the Magnetic properties of Mn3Fe2Si3O12 as a crystalline garnet and as a glass
Comments: 14 pages, 7 figures, 2 tables
Subjects: Materials Science (cond-mat.mtrl-sci)

The crystalline garnet Mn3Fe2Si3O12 and an amorphous phase of the same nominal composition are synthesized at high pressure. The magnetic properties of the two forms are reported. Both phases order antiferromagnetically. The crystalline phase exhibits a Curie-Weiss theta of -47.2 K, with a sharp ordering transition at 12 K. The glassy phase exhibits a larger antiferromagnetic Curie-Weiss theta, of -83.0 K, with a broad ordering transition observed at 2.5 K. Both phases can be classified as magnetically frustrated, although the amorphous phase shows a much higher degree of frustration. The amorphous phase exhibits spin-glass behavior and is determined to have an actual composition of Mn3Fe2Si3O13.

[18]  arXiv:1802.07364 [pdf, other]
Title: Controlling stability and transport of magnetic microswimmers by an external field
Subjects: Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Pattern Formation and Solitons (nlin.PS)

We investigate the hydrodynamic stability and transport of magnetic microswimmers in an external field using a kinetic theory framework. Combining linear stability analysis and nonlinear 3D continuum simulations, we show that for sufficiently large activity and magnetic field strengths, a homogeneous polar steady state is unstable for both puller and pusher swimmers. This instability is caused by the amplification of anisotropic hydrodynamic interactions due to the external alignment and leads to a partial depolarization and a reduction of the average transport speed of the swimmers in the field direction. Notably, at stronger field strengths, a reentrant hydrodynamic stability emerges where the homogeneous polar state is stable and a transport efficiency identical to that of active particles without hydrodynamic interactions is restored.

[19]  arXiv:1802.07367 [pdf, other]
Title: Strain Fields in Repulsive Colloidal Crystals
Subjects: Soft Condensed Matter (cond-mat.soft)

The concept of a local linear elastic strain field is commonly used in the metallurgical research community to approximate the collective effect of atomic displacements around crystalline defects. Here we show that the elastic strain field approximation is a useful tool in colloidal systems. For colloidal crystals with repulsive particle interaction potentials, given similar mechanical properties, sharper potentials lead to: 1) free energies of deformation dominated by entropy, 2) lower variance in strain field fluctuations, 3) increased tension-compression asymmetry near dislocation core regions, and 4) smaller windows of applicability of the linear elastic approximation. We show that the window of linear behavior for entropic colloidal crystals is broadened for pressures at which the inter-particle separation sufficiently exceeds the range of steep repulsive interactions.

[20]  arXiv:1802.07378 [pdf, other]
Title: Perturbation theories behind thermal mode spectroscopy for high-accuracy measurement of thermal diffusivity of solids
Comments: This version was submitted in Philosophical Magazine on 28 May, 2017
Subjects: Materials Science (cond-mat.mtrl-sci)

Thermal mode spectroscopy (TMS) has been recently proposed for accurately measuring thermal diffusivity of solids from a temperature decay rate of a specific thermal mode selected by three- dimensional (anti)nodal information [Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the following advantages of TMS by use of perturbation analyses. First, TMS is applicable to the measurement of high thermal diffusivity with a small size specimen. Second, it is less affected by thermally resistive films on a specimen in the sense that the resistance at the interface does not affect the first-order correction of thermal diffusivity. Third, it can perform doubly accurate measurement of the thermal diffusivity specified at a thermal equilibrium state even if the diffusivity depends on temperature in the sense that the measurement can be performed within tiny temperature difference from the given state and that the decay rate of the slowest decaying mode is not affected by the dependence.

[21]  arXiv:1802.07387 [pdf]
Title: Dynamics of Viscous Entrapped Saturated Zones in Partially Wetted Porous Media
Comments: 18 pages, 6 figures
Subjects: Soft Condensed Matter (cond-mat.soft)

As a typical multiphase fluid flow process, drainage in porous media is of fundamental interest in nature and industrial applications. During drainage processes in unsaturated soils and porous media in general, saturated clusters, in which a liquid phase fully occupies the pore space between solid grains, affect the relative permeability and effective stress of the system. In this study, we experimentally studied drainage processes in unsaturated granular media as a model porous system. The distribution of saturated clusters is analysed by an optical imaging method under different drainage conditions, in which pore-scale information from Voronoi and Delaunay tessellation was used to characterise the topology of saturated cluster distributions. By employing statistical analyses, the observed spatial and temporal information of multiphase flow and fluid entrapment in porous media are described. The results indicate that the distributions of both the crystallised cell size and pore size are positively correlated to the spatial and temporal distribution of saturated cluster sizes. The saturated cluster size is found to follow a lognormal distribution, in which the generalised Bond number correlates negatively to the scale parameter and positively to the shape parameter. These findings can be used to connect pore-scale behaviour with overall hydro-mechanical characteristics in partially saturated porous media, using both the degree of saturation and generalised Bond number.

[22]  arXiv:1802.07391 [pdf, other]
Title: Gardner Phenomenology in Minimally Polydisperse Crystalline Systems
Comments: 5 pages, 3 figures
Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci)

We study the structure and dynamics of crystals of minimally polydisperse hard spheres at high pressures. Structurally, they exhibit a power-law scaling in their probability distribution of weak forces and small interparticle gaps as well as a flat density of vibrational states. Dynamically, they display anomalous aging beyond a characteristic pressure. Although essentially crystalline, these solids thus display features reminiscent of the Gardner phase observed in certain amorphous solids. Because preparing these materials is fast and facile, they are ideal for testing a theory of amorphous materials. They are also amenable to experimental realizations in commercially-available particulate systems.

[23]  arXiv:1802.07409 [pdf, other]
Title: Metastable state en route to traveling-wave synchronization state
Authors: Jinha Park, B. Kahng
Journal-ref: Phys. Rev. E 97, 020203(R) (2018)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Disordered Systems and Neural Networks (cond-mat.dis-nn); Chaotic Dynamics (nlin.CD); Biological Physics (physics.bio-ph)

The Kuramoto model with mixed signs of couplings is known to produce a traveling-wave synchronized state. Here, we consider an abrupt synchronization transition from the incoherent state to the traveling-wave state through a long-lasting metastable state with large fluctuations. Our explanation of the metastability is that the dynamic flow remains within a limited region of phase space and circulates through a few active states bounded by saddle and stable fixed points. This complex flow generates a long-lasting critical behavior, a signature of a hybrid phase transition. We show that the long-lasting period can be controlled by varying the density of inhibitory/excitatory interactions. We discuss a potential application of this transition behavior to the recovery process of human consciousness.

[24]  arXiv:1802.07411 [pdf, other]
Title: Design of Chern Insulating Phases in Honeycomb Lattices
Comments: 4 pages
Subjects: Materials Science (cond-mat.mtrl-sci); Strongly Correlated Electrons (cond-mat.str-el)

The search for robust examples of the magnetic version of topological insulators, referred to as quantum anomalous Hall insulators or simply Chern insulators, so far lacks success. Our groups have explored two distinct possibilities based on multiorbital 3d oxide honeycomb lattices. Each has a Chern insulating phase near the ground state, but materials parameters were not appropriate to produce a viable Chern insulator. Further exploration of one of these classes, by substituting open shell 3d with 4d and 5d counterparts, has led to realistic prediction of Chern insulating ground states. Here we recount the design process, discussing the many energy scales that are active in participating (or resisting) the desired Chern insulator phase.

[25]  arXiv:1802.07414 [pdf]
Title: Tunable Lifshitz Transitions and Multiband Transport in Tetralayer Graphene
Comments: accepted to PRL
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

As the Fermi level and band structure of two-dimensional materials are readily tunable, they constitute an ideal platform for exploring Lifshitz transition, a change in the topology of a material's Fermi surface. Using tetralayer graphene that host two intersecting massive Dirac bands, we demonstrate multiple Lifshitz transitions and multiband transport, which manifest as non-monotonic dependence of conductivity on charge density n and out-of-plane electric fieldD, anomalous quantum Hall sequences and Landau level crossings that evolve with n, D and B.

[26]  arXiv:1802.07424 [pdf, ps, other]
Title: On the vibron-polaron damping in quasi 1D macromolecular chains
Comments: 8 pages, 6 figures, contribution to the Proceedings of the XXV Int. Conference on Integrable Systems and Quantum symmetries (ISQS-25), Prague, Czech Republic, 6-10, June, 2017
Journal-ref: IOP Conf. Series: Journal of Physics: Conf. Series 965 (2018) 012011
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Theory (hep-th)

The properties of the intramolecular vibrational excitation (vibron) in a quasi 1D macromolecular structure are studied. It is supposed that due to the vibron interaction with optical phonon modes, a vibron might form partially dressed small polaron states. The properties of these states are investigated in dependence on the basic system parameters and temperature of a thermal bath. We also investigate the process of damping of the polaron amplitude as a function of temperature and vibron-phonon coupling strength. Two different regimes of the polaron damping are found and discussed.

[27]  arXiv:1802.07431 [pdf, ps, other]
Title: Tracking the spin properties of single nitrogen-vacancy centers in nanodiamonds in aqueous buffer solutions
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We report on the sensing stability of quantum nanosensors in aqueous buffer solutions for the two detection schemes of quantum decoherence spectroscopy and nanoscale thermometry. The electron spin properties of single nitrogen-vacancy (NV) centers in 25-nm-sized nanodiamonds have been characterized by tracking individual nanodiamonds during a continuous change in pH from 4 to 11. We have determined the stability of the NV quantum sensors during the pH change, which provides the fluctuations of $\pm$13\% and $\pm$0.3 MHz for $T_2$ and $\omega_0$ of their mean values. The observed fluctuations are significant when performing quantum decoherence spectroscopy and thermometry in various biological contexts. We discuss how the present observation affects the measurement scheme of nanodiamond-based NV quantum sensing.

[28]  arXiv:1802.07464 [pdf, other]
Title: Meta-screening and permanence of polar distortion in metallized ferroelectrics
Comments: 13 pages, 9 figures
Journal-ref: Phys. Rev. B 97, 054107 (2018)
Subjects: Materials Science (cond-mat.mtrl-sci)

Ferroelectric materials are characterized by a spontaneous polar distortion. The behavior of such distortions in the presence of free charge is the key to the physics of metallized ferroelectrics in particular, and of structurally-polar metals more generally. Using first-principles simulations, here we show that a polar distortion resists metallization and the attendant suppression of long-range dipolar interactions in the vast majority of a sample of 11 representative ferroelectrics. We identify a meta-screening effect, occurring in the doped compounds as a consequence of the charge rearrangements associated to electrostatic screening, as the main factor determining the survival of a non-centrosymmetric phase. Our findings advance greatly our understanding of the essentials of structurally-polar metals, and offer guidelines on the behavior of ferroelectrics upon field-effect charge injection or proximity to conductive device elements.

[29]  arXiv:1802.07467 [pdf]
Title: Thermodynamics analysis on BaF2 intermediate phase in solution-derived YBCO superconducting film deposition
Comments: 5 pages, 1 figures, 5 tables
Subjects: Superconductivity (cond-mat.supr-con)

In the YBa2Cu3O7-{\delta} (YBCO) high temperature superconducting thin film fabrication via the chemical solution deposition method, BaF2 is an important intermediate phase during heat treatment. In this paper, BaF2 thermodynamics stability was analyzed through calculating the standard Gibbs free energy change ({\Delta}GT) of the reactions related to other intermediate phases within the temperature range of 700-1000 K. Two thermodynamics methods, the Gibbs free energy function method and standard formation molar Gibbs free energy method, were utilized to obtain the {\Delta}GT values. The formation priority of BaF2 relative to other intermediate phases were verified at higher temperatures, while the possibility of BaCO3 formation was found at 700 K.

[30]  arXiv:1802.07497 [pdf, other]
Title: Landau theory of the short-time dynamical phase transition of the Kardar-Parisi-Zhang interface
Comments: 12 pages, 8 figures
Subjects: Statistical Mechanics (cond-mat.stat-mech)

We study the short-time distribution $\mathcal{P}\left(H,L,t\right)$ of the two-point two-time height difference $H=h(L,t)-h(0,0)$ of a stationary Kardar-Parisi-Zhang (KPZ) interface in 1+1 dimension. Employing the optimal-fluctuation method, we develop an effective Landau theory for the second-order dynamical phase transition found previously for $L=0$ at a critical value $H=H_c$. We show that $|H|$ and $L$ play the roles of inverse temperature and external magnetic field, respectively. In particular, we find a first-order dynamical phase transition when $L$ changes sign, at supercritical $H$. We also determine analytically $\mathcal{P}\left(H,L,t\right)$ in several limits away from the second-order transition. Typical fluctuations of $H$ are Gaussian, but the distribution tails are highly asymmetric. The tails $-\ln\mathcal{P}\sim\left|H\right|^{3/2} \! /\sqrt{t}$ and $-\ln\mathcal{P}\sim\left|H\right|^{5/2} \! /\sqrt{t}$, previously found for $L=0$, are enhanced for $L \ne 0$. At very large $|L|$ the whole height-difference distribution $\mathcal{P}\left(H,L,t\right)$ is time-independent and Gaussian in $H$, $-\ln\mathcal{P}\sim\left|H\right|^{2} \! /|L|$, describing the probability of creating a ramp-like height profile at $t=0$.

[31]  arXiv:1802.07506 [pdf, other]
Title: High Temperature Superconductivity: A Simple Model Exploiting Hydrogen Bonds
Comments: 13 pages, 5 figures
Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Lately, there has been much interest in high temperature superconductors, and more recently hydrogen-based superconductors. This work offers a simple model which explains the behavior of the superconducting gap based on BCS theory, and reproduces most effects seen in experiments, including the isotope effect and T_c enhancement as a function of pressure. We show that this is due to a combination of the factors appearing in the gap equation: the matrix element between the proton states, and the level splitting of the proton.

[32]  arXiv:1802.07511 [pdf]
Title: Spin-fluctuations drive the inverse magnetocaloric effect in Mn5Si3
Subjects: Materials Science (cond-mat.mtrl-sci)

Inelastic neutron scattering measurements were performed on single crystals of the antiferromagnetic compound Mn5Si3 in order to investigate the relation between the spin dynamics and the magneto-thermodynamic properties. It is shown that among the two stable antiferromagnetic phases of this compound, the high temperature one has an unusual magnetic excitation spectrum where propagative spin-waves and diffuse spin-fluctuations coexist. Moreover, it is evidenced that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic magnetization, is associated with field induced spin-fluctuations.

[33]  arXiv:1802.07530 [pdf, ps, other]
Title: Topological phase transitions in tilted optical lattices
Comments: 3 pages, 4 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

We analyze the energy spectrum and eigenstates of cold atoms in a tilted brick-wall optical lattice. When the tilt is applied, the system exhibits a sequence of topological phase transitions reflected in an abrupt change of the eigenstates. It is demonstrated that these topological phase transitions can be easily detected in a laboratory experiment by observing Bloch oscillations of cold atoms.

[34]  arXiv:1802.07531 [pdf, ps, other]
Title: Phonon mode softening and elastic properties of hafnium under pressure
Comments: 8 pages, 12 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

The effect of pressure on the zone-center optical phonon modes and the elastic properties of hafnium has been studied by both experimental (Raman scattering) and theoretical (DFT) approaches. It was found an anomaly dependence of the phonon frequency of E$_{2g}$ mode in the pressure range from 0 to 67 GPa. The calculated electronic structure of hafnium shows significant changes under pressure, which have a pronounced spatial anisotropy similar to the anisotropy of the observed phonon properties. The dependencies of the elastic properties on pressure including the components of the elasticity tensor, bulk and shear modulus, Poisson ratio and Universal anisotropy index obtained during the calculations has characteristic features indicating the occurrence of the structural phase transition.

[35]  arXiv:1802.07570 [pdf, ps, other]
Title: Influence of chemical potential on the Casimir-Polder interaction between an atom and gapped graphene or graphene-coated substrate
Comments: 22 pages, 9 figures; accepted for publication in Phys. Rev. A
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We present a formalism based on first principles of quantum electrodynamics at nonzero temperature which permits to calculate the Casimir-Polder interaction between an atom and a graphene sheet with arbitrary mass gap and chemical potential, including graphene-coated substrates. The free energy and force of the Casimir-Polder interaction are expressed via the polarization tensor of graphene in (2+1)-dimensional space-time in the framework of the Dirac model. The obtained expressions are used to investigate the influence of the chemical potential of graphene on the Casimir-Polder interaction. Computations are performed for an atom of metastable helium interacting with either a free-standing graphene sheet or a graphene-coated substrate made of amorphous silica. It is shown that the impacts of the nonzero chemical potential and the mass gap on the Casimir-Polder interaction are in opposite directions by increasing and decreasing the magnitudes of the free energy and force, respectively. It turns out, however, that the temperature-dependent part of the Casimir-Polder interaction is decreased by a nonzero chemical potential, whereas the mass gap increases it compared to the case of undoped, gapless graphene. The physical explanation for these effects is provided. Numerical computations of the Casimir-Polder interaction are performed at various temperatures and atom-graphene separations.

[36]  arXiv:1802.07579 [pdf, ps, other]
Title: Spin Hartree-Fock approach to quantum Heisenberg antiferromagnets in low dimensions
Comments: 5 pages, 2 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)

We construct a new mean-field theory for quantum (spin-1/2) Heisenberg antiferromagnet in one (1D) and two (2D) dimensions using a Hartree-Fock decoupling of the four-point correlation functions. We show that the solution to the self-consistency equations based on two-point correlation functions does not produce any unphysical finite-temperature phase transition in accord with Mermin-Wagner theorem, unlike the common approach based on the mean-field equation for the order parameter. The next-neighbor spin-spin correlation functions, calculated within this approach, reproduce closely the strong renormalization by quantum fluctuations obtained via Bethe ansatz in 1D and a small renormalization of the classical antiferromagnetic state in 2D. The heat capacity approximates with reasonable accuracy the full Bethe ansatz result at all temperatures in 1D. In 2D, we obtain a reduction of the peak height in the heat capacity at a finite temperature that is accessible by high-order $1/T$ expansions.

[37]  arXiv:1802.07605 [pdf, other]
Title: Accelerating crystal structure prediction by machine-learning interatomic potentials with active learning
Subjects: Materials Science (cond-mat.mtrl-sci)

In this letter we propose a new methodology for crystal structure prediction, which is based on the evolutionary algorithm USPEX and the machine-learning interatomic potentials (MLIPs) actively learning on-the-fly. Our methodology allows for an automated construction of an interatomic interaction model from scratch replacing the expensive DFT with a speedup of several orders of magnitude. Those structures are then tested on DFT, ensuring that our machine-learning model does not introduce any prediction error. We tested our methodology on a very challenging problem of prediction of boron allotropes including those which have more than 100 atoms in the primitive cell. All the the main allotropes have been reproduced and a new 54-atom structure have been found at very modest computational efforts.

[38]  arXiv:1802.07614 [pdf, other]
Title: Light Scattering by Cholesteric Skyrmions
Comments: 18 pages, 14 figures
Subjects: Soft Condensed Matter (cond-mat.soft)

We study the light scattering by localized quasi planar excitations of a Cholesteric Liquid Crystal known as spherulites. Due to the anisotropic optical properties of the medium and the peculiar shape of the excitations, we quantitatively evaluate the cross section of the axis-rotation of polarized light. Because of the complexity of the system under consideration, first we give a simplified, but analytical, description of the spherulite and we compare the Born approximation results in this setting with those obtained by resorting to a numerical exact solution. The effects of changing values of the driving external static electric (or magnetic) field is considered. Possible applications of the phenomenon are envisaged.

[39]  arXiv:1802.07627 [pdf, other]
Title: Readout Of Singlet-Triplet Qubits At Large Magnetic Field Gradients
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Visibility of singlet-triplet qubit readout is reduced to almost zero in large magnetic field gradients due to relaxation processes. Here we present a new readout technique that is robust against relaxation and allows for measurement when previously studied methods fail. This technique maps the qubit onto spin states that are immune to relaxation using a spin dependent electron tunneling process between the qubit and the lead. We probe this readout's performance as a function of magnetic field gradient and applied magnetic field, and optimize the pulse applied to the qubit through experiment and simulation.

[40]  arXiv:1802.07629 [pdf, other]
Title: Extreme cooperative swelling in topologically disordered fibre entanglements
Comments: 17 pages, 4 figures
Subjects: Soft Condensed Matter (cond-mat.soft); Materials Science (cond-mat.mtrl-sci)

Entangled states are ubiquitous amongst fibrous materials, whether naturally occurring (keratin, collagen, DNA) or synthetic (nanotube assemblies, elastane). A key mechanical characteristic of these systems is their ability to reorganise in response to external stimuli, as implicated in e.g. hydration-induced swelling of keratin fibrils in human skin. During swelling, the curvature of individual fibres changes to give a cooperative and reversible structural reorganisation that opens up a pore network. The phenomenon is known to be highly dependent on topology, even if the nature of this dependence is not well understood: certain ordered entanglements (`weavings') can swell to many times their original volume while others are entirely incapable of swelling at all. Given this sensitivity to topology, it is puzzling how the disordered entanglements of many real materials manage to support cooperative dilation mechanisms. Here we use a combination of geometric and lattice-dynamical modelling to study the effect of disorder on swelling behaviour. The model system we devise spans a continuum of disordered topologies and is bounded by ordered states whose swelling behaviour is already known to be either vanishingly small or extreme. We find that while topological disorder often quenches swelling behaviour, certain disordered states possess a surprisingly large swelling capacity. Crucially, we show that the extreme swelling response previously observed only for certain specific weavings can be matched---and even superseded---by that of disordered entanglements. Our results establish a counterintuitive link between topological disorder and mechanical flexibility that has implications not only for polymer science but also for our broader understanding of collective phenomena in disordered systems.

[41]  arXiv:1802.07657 [pdf, other]
Title: DNA-Graphene Interactions During Translocation Through Nanogaps
Comments: 13 pages, 6 figures
Journal-ref: Patel HN, Carroll I, Lopez R Jr, Sankararaman S, Etienne C, Kodigala SR, et al. (2017) DNA-graphene interactions during translocation through nanogaps. PLoS ONE 12(2): e0171505
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

We study how double-stranded DNA translocates through graphene nanogaps. Nanogaps are fabricated with a novel capillary-force induced graphene nanogap formation technique. DNA translocation signatures for nanogaps are qualitatively different from those obtained with circular nanopores, owing to the distinct shape of the gaps discussed here. Translocation time and conductance values vary by $\sim 100$%, which we suggest are caused by local gap width variations. We also observe exponentially relaxing current traces. We suggest that slow relaxation of the graphene membrane following DNA translocation may be responsible. We conclude that DNA-graphene interactions are important, and need to be considered for graphene-nanogap based devices. This work further opens up new avenues for direct read of single molecule activitities, and possibly sequencing.

[42]  arXiv:1802.07685 [pdf]
Title: Non-equilibrium Solute Capture in Passivating Oxide Films
Comments: 29 pages total, 12 figures
Subjects: Materials Science (cond-mat.mtrl-sci)

If all humans vanished tomorrow, almost every metal structure would collapse within a century or less, the metal converting to an oxide. In applications ranging from the mature technology of nuts and bolts to high technology batteries, nuclear fuels and turbine engines, protective oxide films are critical to limiting oxidation. To date models of these oxide films have assumed that they form thermodynamic equilibrium stable or metastable phases doped within thermodynamic solubility limits. Here we demonstrate experimentally and theoretically the formation of unusual non-equilibrium oxide phases, that can be predicted using a scientific framework for solute capture at a moving oxide/substrate interface. The theory shows that solute capture is likely a generic process for many electrochemical processes, and suggests that similar phenomena yielding non-equilibrium phases can occur and be predicted for a wide range of other processes involving solid-fluid and solid-solid chemical reactions.

[43]  arXiv:1802.07698 [pdf, ps, other]
Title: Gaussian Free Field in the background of correlated random clusters, formed by metallic nanoparticles
Subjects: Statistical Mechanics (cond-mat.stat-mech)

The effect of metallic nano-particles (MNPs) on the electrostatic potential of a disordered 2D dielectric media is considered. The disorder in the media is assumed to be white-noise Coulomb impurities with normal distribution. To realize the correlations between the MNPs we have used the Ising model with an artificial temperature $T$ that controls the number of MNPs as well as their correlations. In the $T\rightarrow 0$ limit, one retrieves the Gaussian free field (GFF), and in the finite temperature the problem is equivalent to a GFF in iso-potential islands. The problem is argued to be equivalent to a scale-invariant random surface with some critical exponents which vary with $T$ and correspondingly are correlation-dependent. Two type of observables have been considered: local and global quantities. We have observed that the MNPs soften the random potential and reduce its statistical fluctuations. This softening is observed in the local as well as the geometrical quantities. The correlation function of the electrostatic and its total variance are observed to be logarithmic just like the GFF, i.e. the roughness exponent remains zero for all temperatures, whereas the proportionality constants scale with $T-T_c$. The fractal dimension of iso-potential lines ($D_f$), the exponent of the distribution function of the gyration radius ($\tau_r$), and the loop lengths ($\tau_l$), and also the exponent of the loop Green function $x_l$ change in terms of $T-T_c$ in a power-law fashion, with some critical exponents reported in the text. Importantly we have observed that $D_f(T)-D_f(T_c)\sim\frac{1}{\sqrt{\xi(T)}}$, in which $\xi(T)$ is the spin correlation length in the Ising model.

[44]  arXiv:1802.07699 [pdf, other]
Title: Splay--density coupling in semiflexible main-chain nematic polymers with hairpins
Comments: 6 pages, 5 figures
Subjects: Soft Condensed Matter (cond-mat.soft)

We establish a macroscopic description of the splay--density coupling in semiflexible main-chain nematic polymers with hairpins, using a vectorial continuity constraint for the "recovered" polar order of the chain tangents and introducing chain backfolds (hairpins) as its new type of sources besides chain ends. We treat both types of sources on a unified basis as a mixture of two ideal gases with fixed composition. Performing detailed Monte Carlo simulations of nematic monodomain melts of "soft" worm-like chains with variable length and flexibility, we show via their structure factors that the chain backfolding weakens the splay--density coupling, and demonstrate how this weakening can be consistently quantified on the macroscopic level. We also probe and discuss the deviations from the noninteracting gas idealization of the chain ends and backfolds.

[45]  arXiv:1802.07709 [pdf, other]
Title: Antiferromagnet-Based Magnonic Spin-Transfer Torque
Authors: Ran Cheng, Di Xiao, Jian-Gang (Jimmy)Zhu
Comments: submitted to PRL
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)

In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down magnon excitations coexist and form an internal degree of freedom. A magnon spin current can be thermally generated near an exchange-coupled ferromagnet (F)/AF interface where the degeneracy is lifted. Here we investigate thermal magnon spin transport in an F/AF/F heterostructure. We find that a sufficiently large temperature gradient can switch the downstream F via magnonic spin-transfer torque if it is initially antiparallel with the upstream F. Reciprocal switching from the parallel to the antiparallel state can be achieved by reversing the temperature gradient. The threshold temperature gradient decreases with an increasing interfacial exchange coupling and an increasing temperature.

[46]  arXiv:1802.07717 [pdf, other]
Title: Resummation of diagrammatic series with zero convergence radius for strongly correlated fermions
Subjects: Quantum Gases (cond-mat.quant-gas)

We demonstrate that summing up series of Feynman diagrams can yield unbiased accurate results for strongly-correlated fermions even when the convergence radius vanishes. We consider the unitary Fermi gas, a model of non-relativistic fermions in three-dimensional continuous space. Diagrams are built from partially-dressed or fully-dressed propagators of single particles and pairs. The series is resummed by a conformal-Borel transformation that incorporates the large-order behavior and the analytic structure in the Borel plane, which are found by the instanton approach. We report highly accurate numerical results for the equation of state in the normal unpolarized regime, and reconcile experimental data with the theoretically conjectured fourth virial coefficient.

Cross-lists for Thu, 22 Feb 18

[47]  arXiv:1802.07261 (cross-list from physics.soc-ph) [pdf, ps, other]
Title: The Mathematics of Human Contact: Developing a Model for Social Interaction in School Children
Comments: 18 pages, 5 figures, 5 tables
Subjects: Physics and Society (physics.soc-ph); Statistical Mechanics (cond-mat.stat-mech)

In this paper, we provide a statistical analysis of high-resolution contact pattern data within primary and secondary schools as collected by the SocioPatterns collaboration. Students are graphically represented as nodes in a temporally evolving network, in which links represent proximity or interaction between students. This article focuses on link- and node-level statistics, such as the on- and off-durations of links as well as the activity potential of nodes and links. Parametric models are fitted to the on- and off-durations of links, inter-event times and node activity potentials and, based on these, we propose a number of theoretical models that are able to reproduce the collected data within varying levels of accuracy. By doing so, we aim to identify the minimal network-level properties that are needed to closely match the real-world data, with the aim of combining this contact pattern model with epidemic models in future work.

[48]  arXiv:1802.07333 (cross-list from physics.comp-ph) [pdf, ps, other]
Title: Modeling of Supersonic Radiative Marshak waves using Simple Models and Advanced Simulations
Comments: 12 pages, 8 figures
Subjects: Computational Physics (physics.comp-ph); Statistical Mechanics (cond-mat.stat-mech); Plasma Physics (physics.plasm-ph)

We study the problem of radiative heat (Marshak) waves using advanced approximate approaches. Supersonic radiative Marshak waves that are propagating into a material are radiation dominated (i.e. hydrodynamic motion is negligible), and can be described mainly by the Boltzmann equation. However, the exact thermal radiative transfer problem is a nontrivial one, and there still exists a need for approximations that are simple to solve. The discontinuous asymptotic $P_1$ approximation, which is a combination of the asymptotic $P_1$ and the discontinuous asymptotic diffusion approximations, was tested in previous work via theoretical benchmarks. Here we analyze a fundamental and typical experiment of a supersonic Marshak wave propagation in a low-density $\mathrm{SiO_2}$ foam cylinder, embedded in gold walls. First, we offer a simple analytic model, that grasps the main effects dominating the physical system. We find the physics governing the system to be dominated by a simple, one-dimensional effect, based on the careful observation of the different radiation temperatures that are involved in the problem. The model is completed with the main two-dimensional effect which is caused by the loss of energy to the gold walls. Second, we examine the validity of the discontinuous asymptotic $P_1$ approximation, comparing to exact simulations with good accuracy. Specifically, the heat front position as a function of the time is reproduced perfectly.

[49]  arXiv:1802.07347 (cross-list from quant-ph) [pdf, ps, other]
Title: Electron-Phonon Systems on a Universal Quantum Computer
Subjects: Quantum Physics (quant-ph); Strongly Correlated Electrons (cond-mat.str-el)

We present an algorithm that extends existing quantum algorithms for simulating fermion systems in quantum chemistry and condensed matter physics to include phonons. The phonon degrees of freedom are represented with exponential accuracy on a truncated Hilbert space with a size that increases linearly with the cutoff of the maximum phonon number. The additional number of qubits required by the presence of phonons scales linearly with the size of the system. The additional circuit depth is constant for systems with finite-range electron-phonon and phonon-phonon interactions and linear for long-range electron-phonon interactions. Our algorithm for a Holstein polaron problem was implemented on an Atos Quantum Learning Machine (QLM) quantum simulator employing the Quantum Phase Estimation method. The energy and the phonon number distribution of the polaron state agree with exact diagonalization results for weak, intermediate and strong electron-phonon coupling regimes.

[50]  arXiv:1802.07402 (cross-list from quant-ph) [pdf, other]
Title: Microwave device characterisation using a widefield diamond microscope
Subjects: Quantum Physics (quant-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Applied Physics (physics.app-ph)

Devices relying on microwave circuitry form a cornerstone of many classical and emerging quantum technologies. A capability to provide in-situ, noninvasive and direct imaging of the microwave fields above such devices would be a powerful tool for their function and failure analysis. In this work, we build on recent achievements in magnetometry using ensembles of nitrogen vacancy centres in diamond, to present a widefield microwave microscope with few-micron resolution over a millimeter-scale field of view, 130nT/sqrt-Hz microwave amplitude sensitivity, a dynamic range of 48 dB, and sub-ms temporal resolution. We use our microscope to image the microwave field a few microns above a range of microwave circuitry components, and to characterise a novel atom chip design. Our results open the way to high-throughput characterisation and debugging of complex, multi-component microwave devices, including real-time exploration of device operation.

[51]  arXiv:1802.07480 (cross-list from physics.bio-ph) [pdf, other]
Title: Collective Dynamics of Self-propelled Semiflexible Filaments
Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Subcellular Processes (q-bio.SC)

The collective behavior of active semiflexible filaments is studied with a model of tangentially driven self-propelled worm-like chains. The combination of excluded-volume interactions and self-propulsion leads to several distinct dynamic phases as a function of bending rigidity, activity, and aspect ratio of individual filaments. We consider first the case of intermediate filament density. For high-aspect-ratio filaments, we identify a transition with increasing propulsion from a state of free-swimming filaments to a state of spiraled filaments with nearly frozen translational motion. For lower aspect ratios, this gas-of-spirals phase is suppressed with growing density due to filament collisions; instead, filaments form clusters similar to self-propelled rods, as activity increases. Finite bending rigidity strongly effects the dynamics and phase behavior. Flexible filaments form small and transient clusters, while stiffer filaments organize into giant clusters, similarly as self-propelled rods, but with a reentrant phase behavior from giant to smaller clusters as activity becomes large enough to bend the filaments. For high filament densities, we identify a nearly frozen jamming state at low activities, a nematic laning state at intermediate activities, and an active-turbulence state at high activities. The latter state is characterized by a power-law decay of the energy spectrum as a function of wave number. The resulting phase diagrams encapsulate tunable non-equilibrium steady states that can be used in the organization of living matter.

[52]  arXiv:1802.07488 (cross-list from physics.bio-ph) [pdf, other]
Title: From jamming to collective cell migration through a boundary induced transition
Comments: 6 figures
Subjects: Biological Physics (physics.bio-ph); Soft Condensed Matter (cond-mat.soft); Cell Behavior (q-bio.CB)

Cell monolayers provide an interesting example of active matter, exhibiting a phase transition from a flowing to jammed state as they age. Here we report experiments and numerical simulations illustrating how a jammed cellular layer rapidly reverts to a flowing state after a wound. Quantitative comparison between experiments and simulations shows that cells change their self-propulsion and alignement strength so that the system crosses a phase transition line, which we characterize by finite-size scaling in an active particle model. This wound-induced unjamming transition is found to occur generically in epithelial, endothelial and cancer cells.

[53]  arXiv:1802.07599 (cross-list from physics.app-ph) [pdf]
Title: Graphene-enabled, directed nanomaterial placement from solution for large-scale device integration
Comments: 17 pages, 5 figures
Subjects: Applied Physics (physics.app-ph); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)

Controlled placement of nanomaterials at predefined locations with nanoscale precision remains among the most challenging problems that inhibit their large-scale integration in the field of semiconductor process technology. Methods based on surface functionalization have a drawback where undesired chemical modifications can occur and deteriorate the deposited material. The application of electric-field assisted placement techniques eliminates the element of chemical treatment; however, it requires an incorporation of conductive placement electrodes that limit the performance, scaling, and density of integrated electronic devices. Here, we report a method for electric-field assisted placement of solution-processed nanomaterials by using large-scale graphene layers featuring nanoscale deposition sites. The structured graphene layers are prepared via either transfer or synthesis on standard substrates, then are removed without residue once nanomaterial deposition is completed, yielding material assemblies with nanoscale resolution that cover surface areas larger than 1mm2. In order to demonstrate the broad applicability, we have assembled representative zero-, one-, and two-dimensional semiconductors at predefined substrate locations and integrated them into nanoelectronic devices. This graphene-based placement technique affords nanoscale resolution at wafer scale, and could enable mass manufacturing of nanoelectronics and optoelectronics involving a wide range of nanomaterials prepared via solution-based approaches.

[54]  arXiv:1802.07681 (cross-list from quant-ph) [pdf, other]
Title: Quantum heat engine using energy quantization and resources of ignorance
Comments: 6 pages, 5 figures, comments welcome
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)

We study a quantum Stirling cycle which extracts work using quantized energy levels. The work and the efficiency of the engine depend on the length of the potential well, and the Carnot efficiency is achieved in a low temperature limiting case. We show that the lack of information about the position of the particle inside the potential well can be converted into useful work without resorting to any measurement. In the low temperature limit, we calculate the amount of work extractable from distinguishable particles, fermions and bosons.

[55]  arXiv:1802.07703 (cross-list from quant-ph) [pdf, other]
Title: Verifying Detailed Fluctuation Relations for Discrete Feedback Controlled Quantum Dynamics
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)

Discrete quantum feedback control consists of a managed dynamics according to the information acquired by a previous measurement. Energy fluctuations along such dynamics satisfy generalized fluctuation relations, which are useful tools to study the thermodynamics of systems far away from equilibrium. Due to the practical challenge to assess energy fluctuations in the quantum scenario, the experimental verification of detailed fluctuation relations in the presence of feedback control remains elusive. We present a feasible method to experimentally verify detailed fluctuation relations for discrete feedback control quantum dynamics. Two new detailed fluctuation relations are developed and employed. The method is based on a quantum interferometric strategy that yields for the verification of fluctuation relations in the presence of feedback control. An analytical example to illustrate the applicability of the method is discussed. The comprehensive technique introduced here can be experimentally implemented at micro-scale with the current technology in a variety of experimental platforms.

[56]  arXiv:1802.07715 (cross-list from quant-ph) [pdf, ps, other]
Title: Theory of open quantum dynamics with hybrid noise
Comments: 24 pages, 9 figures
Subjects: Quantum Physics (quant-ph); Statistical Mechanics (cond-mat.stat-mech)

We develop a theory to describe dynamics of a nonstationary open quantum system interacting with a hybrid environment, which includes high-frequency and low-frequency noise components. One part of the system-bath interaction is treated in a perturbative manner, whereas the other part is considered exactly. This approach allows us to derive a set of master equations where the relaxation rates are expressed as convolutions of the Bloch-Redfield and Marcus formulas. Our theory enables analysis of systems that have extremely small energy gaps in the presence of a realistic environment. We apply the theory to an example of the 16-qubit quantum annealing problem with dangling qubits and show qualitative agreement with experimental results.

Replacements for Thu, 22 Feb 18

[57]  arXiv:1609.03483 (replaced) [pdf, other]
Title: Generalized Thermodynamics of Phase Equilibria in Scalar Active Matter
Journal-ref: Phys. Rev. E 97, 020602(R) (2018)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Soft Condensed Matter (cond-mat.soft)
[58]  arXiv:1706.06499 (replaced) [pdf, other]
Title: The splitting of electrons
Authors: Eoin Quinn
Comments: Focus switched to the purely electronic model. Derivation of an expansion in the strength of correlated hopping included. Notations and conventions improved. Discussion of large-S limit postponed, previous versions implicitly suppress spin correlations which drive ordering
Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)
[59]  arXiv:1708.02270 (replaced) [pdf, ps, other]
Title: Excitonic insulators as a model of $d-d$ and Mott transitions in strongly correlated materials
Comments: 11 pages, 5 figures
Subjects: Strongly Correlated Electrons (cond-mat.str-el)
[60]  arXiv:1709.06086 (replaced) [pdf, ps, other]
Title: Log-rise of the Resistivity in the Holographic Kondo Model
Comments: v2: 15 pages, typos corrected, few more clarifications added
Subjects: High Energy Physics - Theory (hep-th); Strongly Correlated Electrons (cond-mat.str-el)
[61]  arXiv:1710.01875 (replaced) [pdf, ps, other]
Title: Stationary mass distribution and nonlocality in models of coalescence and shattering
Comments: Published version
Journal-ref: Phys. Rev. E 97, 022137 (2018)
Subjects: Statistical Mechanics (cond-mat.stat-mech)
[62]  arXiv:1710.03680 (replaced) [pdf, ps, other]
Title: Computing diffusivities from particle models out of equilibrium
Subjects: Statistical Mechanics (cond-mat.stat-mech)
[63]  arXiv:1710.06769 (replaced) [pdf, ps, other]
Title: One-dimensional p-wave superconductor toy-model for Majorana fermions in multiband semiconductor nanowires
Comments: 4 pages, 2 figures. IEEE Transactions on Applied Superconductivity accepted version
Subjects: Superconductivity (cond-mat.supr-con)
[64]  arXiv:1710.08866 (replaced) [pdf, other]
Title: Decaying spectral oscillations in a Majorana wire with finite coherence length
Comments: 9 pages, 8 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[65]  arXiv:1710.09559 (replaced) [pdf, other]
Title: From global scaling to the dynamics of individual cities
Comments: Revised version 8 pages, 9 figures+5 pages of Supp. Information. Accepted for publication in PNAS
Subjects: Physics and Society (physics.soc-ph); Disordered Systems and Neural Networks (cond-mat.dis-nn)
[66]  arXiv:1711.01284 (replaced) [pdf, other]
Title: Quantum Quenches and Relaxation Dynamics in the Thermodynamic Limit
Comments: 5 pages, 3 figures, as published
Journal-ref: Phys. Rev. Lett. 120, 070603 (2018)
Subjects: Statistical Mechanics (cond-mat.stat-mech); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Quantum Physics (quant-ph)
[67]  arXiv:1711.02704 (replaced) [pdf]
Title: Vowel recognition with four coupled spin-torque nano-oscillators
Subjects: Neurons and Cognition (q-bio.NC); Disordered Systems and Neural Networks (cond-mat.dis-nn)
[68]  arXiv:1711.08886 (replaced) [pdf, ps, other]
Title: Bogoliubov-Cherenkov Radiation in an Atom Laser
Comments: 14 pages. 9 figures
Subjects: Quantum Gases (cond-mat.quant-gas); Pattern Formation and Solitons (nlin.PS)
[69]  arXiv:1711.10513 (replaced) [pdf, other]
Title: Optical nonlinearities of excitons in monolayer MoS2
Comments: 19 pages
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[70]  arXiv:1712.00259 (replaced) [pdf, other]
Title: Solitonic Josephson thermal transport
Comments: 8 pages, 6 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Superconductivity (cond-mat.supr-con)
[71]  arXiv:1712.01005 (replaced) [pdf, other]
Title: Renormalization of single-ion magnetic anisotropy in the absence of Kondo effect
Authors: D. Jacob
Comments: Replaced with revised version published in Phys. Rev. B; 9 pages, 7 figures
Journal-ref: Phys. Rev. B 97, 075428 (2018)
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)
[72]  arXiv:1712.01778 (replaced) [pdf, ps, other]
Title: Mutual friction in superfluid $^3$He-B in the low-temperature regime
Comments: 6 pages, 6 figures
Journal-ref: Phys. Rev. B 97, 014527 (2018)
Subjects: Other Condensed Matter (cond-mat.other)
[73]  arXiv:1712.02131 (replaced) [pdf, other]
Title: Landau levels, response functions and magnetic oscillations from a generalized Onsager relation
Comments: 31 pages, 8 figures; v2: SciPost style; v3: several references added, small corrections, typos fixed
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[74]  arXiv:1712.03489 (replaced) [pdf, ps, other]
Title: Effective gauge field theory of spintronics
Authors: Gen Tatara
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[75]  arXiv:1712.04439 (replaced) [pdf, other]
Title: Two-level Chebyshev filter based complementary subspace method: pushing the envelope of large-scale electronic structure calculations
Comments: Resubmitted version (version 2)
Subjects: Computational Physics (physics.comp-ph); Materials Science (cond-mat.mtrl-sci); Quantum Physics (quant-ph)
[76]  arXiv:1712.05648 (replaced) [pdf, other]
Title: Impact of Many-Body Effects on Landau Levels in Graphene
Comments: 10 pages, 6 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[77]  arXiv:1712.07679 (replaced) [pdf, ps, other]
Title: Information entropy of liquid metals
Authors: M. C. Gao, M. Widom
Subjects: Statistical Mechanics (cond-mat.stat-mech); Materials Science (cond-mat.mtrl-sci)
[78]  arXiv:1712.09190 (replaced) [pdf, ps, other]
Title: Orbital Order in Two-orbital Hubbard Model
Comments: 11 pages, 5 figures
Journal-ref: J. Phys. Soc. Jpn. 87, 034703 (2018)
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)
[79]  arXiv:1801.01939 (replaced) [pdf, other]
Title: Canonical Schottky barrier heights of the transition metal dichalcogenide monolayers in contact with a metal
Comments: 7 pages, 2 figures
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
[80]  arXiv:1801.03273 (replaced) [pdf, other]
Title: Prediction of a magnetic Weyl semimetal without spin-orbit coupling and strong anomalous Hall effect in the Heusler compensated ferrimagnet Ti2MnAl
Comments: 6 pages, 4 figures
Journal-ref: Phys. Rev. B 97, 060406(R), 2018
Subjects: Materials Science (cond-mat.mtrl-sci)
[81]  arXiv:1801.09233 (replaced) [pdf, other]
Title: Random matrix approach to plasmon resonances in the random impedance network model of disordered nanocomposites
Comments: 6 pages, 3 figures; References added
Subjects: Disordered Systems and Neural Networks (cond-mat.dis-nn); Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Optics (physics.optics)
[82]  arXiv:1802.03588 (replaced) [pdf, other]
Title: Single SiV$^-$ centers in low-strain nanodiamonds with bulk-like spectral properties and nano-manipulation capabilities
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci); Optics (physics.optics); Quantum Physics (quant-ph)
[83]  arXiv:1802.04341 (replaced) [pdf, other]
Title: Freezing on a Sphere
Subjects: Soft Condensed Matter (cond-mat.soft)
[84]  arXiv:1802.04810 (replaced) [pdf, other]
Title: The Hall Number of Strongly Correlated Metals
Authors: Assa Auerbach
Comments: 2 Figures, including supplementary material
Subjects: Strongly Correlated Electrons (cond-mat.str-el)
[85]  arXiv:1802.04952 (replaced) [pdf, other]
Title: Spin-state ice in geometrically frustrated spin-crossover materials
Comments: The scale on the right-hand side of Fig. 4b was incorrect. This has been corrected. No other changes from v1
Subjects: Strongly Correlated Electrons (cond-mat.str-el); Soft Condensed Matter (cond-mat.soft); Statistical Mechanics (cond-mat.stat-mech); Chemical Physics (physics.chem-ph)
[86]  arXiv:1802.06126 (replaced) [pdf, ps, other]
Title: The Mean-Field Approximation: Information Inequalities, Algorithms, and Complexity
Comments: Updated bibliography
Subjects: Learning (cs.LG); Statistical Mechanics (cond-mat.stat-mech); Mathematical Physics (math-ph); Combinatorics (math.CO)
[87]  arXiv:1802.07157 (replaced) [pdf, ps, other]
Title: Comment on "A structural test for the conformal invariance of the critical 3d Ising model" by S. Meneses, S. Rychkov, J. M. Viana Parente Lopes and P. Yvernay. arXiv:1802.02319
Comments: 6 pages, typo corrected in the title
Subjects: High Energy Physics - Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics - Lattice (hep-lat)
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