arXiv subjects

Joel E. Moore

Publications and source records attributed to Joel E. Moore.

At least 91 records · Page 5Linked to original sources

arXiv2018

Boundary edge networks induced by bulk topology

We introduce an effective edge network theory to characterize the boundary topology of coupled edge states generated from various types of topological insulators. Two examples studied are a two-dimensional second-order topological insulator and three-dimensional topological fullerenes, which involve multi-leg junctions. As a consequence of bulk-edge correspondence, these edge networks can faithfully predict properties such as the energy and fractional charge related to the bound states (edge solitons) in the aforementioned systems, including several aspects that were previously complicated or obscure.

cond-mat.mes-hall↗

arXiv2018

Spin Wave Analysis of Low-Temperature Thermal Hall Effect in the Candidate Kitaev Spin Liquid $α$-RuCl${}_3$

Proposed effective Hamiltonians from the literature for the material $α$-RuCl${}_3$ are used to compute the magnon thermal Hall conductivity, $κ_{xy}$, using linear spin wave theory for the magnetically ordered state. No model previously proposed that was tested explains published experimental data. Models with Kitaev interaction $K>0$ are seen to predict $κ_{xy}\gtrsim 0$, which is inconsistent with the data. Fluctuations toward a Kitaev-type spin liquid would have the wrong sign to explain the data. However, a slight variant of a previously proposed model predicts a large $κ_{xy}$, demonstrating that the low-temperature thermal Hall effect could be generated exclusively by the Berry curvature of the magnon bands. The experimental data of $κ_{xy}$ can therefore serve as another method to constrain a proposed effective Hamiltonian.

cond-mat.str-el↗

arXiv2018

Anisotropy in the Magnetoresistance Scaling of BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$

Theories of the strange metal, the parent state of many high temperature superconductors, invariably involve an important role for correlations in the spin and charge degrees of freedom. The most distinctive signature of this state in the charge transport sector is a resistance that varies linearly in temperature, but this phenomenon does not clearly point to one mechanism as temperature is a scalar quantity that influences every possible mechanism for momentum relaxation. In a previous work we identified an unusual scaling relationship between magnetic field and temperature in the in-plane resistivity of the unconventional superconductor BaFe$_2$(As$_{1-x}$P$_{x}$)$_2$, providing an opportunity to use the vector nature of the magnetic field to acquire additional clues about the mechanisms responsible for scattering in the strange metal state. Here we extend this work by investigating other components of the conductivity tensor under different orientations of the magnetic field. We find that the scaling phenomenon involves only the out-of-plane component of the magnetic field and is, strikingly, independent of the direction of the applied current. This suggests that the origin of the strange magnetotransport is in the action of the magnetic field on the correlated behavior of spin and charge degrees of freedom, rather than on the simple cyclotron motion of individual quasiparticles.

cond-mat.str-el↗

arXiv2018

Interplay of superconductivity and bosonic coupling in the peak-dip-hump structure of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Because of the important role of electron-boson interactions in conventional superconductivity, it has long been asked whether any similar mechanism is at play in high-temperature cuprate superconductors. Evidence for strong electron-boson coupling is observed in cuprates with angle-resolved photoemission spectroscopy (ARPES), in the form of a dispersion kink and peak-dip-hump structure. What is missing is evidence of a causal relation to superconductivity. Here we revisit the problem using the technique of time-resolved ARPES on Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. We focus on the peak-dip-hump structure, and show that laser pulses shift spectral weight into the dip as superconductivity is destroyed on picosecond time scales. We compare our results to simulations of Eliashberg theory in a superconductor with an Einstein boson, and find that the magnitude of the shift in spectral weight depends on the degree to which the bosonic mode contributes to superconductivity. Further study could address one of the longstanding mysteries of high-temperature superconductivity.

cond-mat.supr-con↗

arXiv2018

Unconventional magneto-transport in ultrapure PdCoO2 and PtCoO2

We have studied magneto transport in the single-band, quasi-two-dimensional metals PdCoO2 and PtCoO2, which have extremely long mean free paths. We observer a strong temperature dependence of the Hall resistivity in small applied, fields, linked to a large violation of Kohler's rule in the magnetoresistance. We discuss the extent to which these observations can be accounted for by standard transport theory, and describe other possible, unconventional contributions to magnetotransport in very high purity metals.

cond-mat.mes-hall↗

arXiv2018

Incomplete thermalization from trap-induced integrability breaking: lessons from classical hard rods

We study a one-dimensional gas of hard rods trapped in a harmonic potential, which breaks integrability of the hard-rod interaction in a non-uniform way. We explore the consequences of such broken integrability for the dynamics of a large number of particles and find three distinct regimes: initial, chaotic, and stationary. The initial regime is captured by an evolution equation for the phase-space distribution function. For any finite number of particles, this hydrodynamics breaks down and the dynamics become chaotic after a characteristic time scale determined by the inter-particle distance and scattering length. The system fails to thermalize over the time-scale studied ($10^4$ natural units), but the time-averaged ensemble is a stationary state of the hydrodynamic evolution. We close by discussing logical extensions of the results to similar systems of quantum particles.

cond-mat.stat-mech↗

arXiv2018

Bethe-Boltzmann Hydrodynamics and Spin Transport in the XXZ Chain

Quantum integrable systems, such as the interacting Bose gas in one dimension and the XXZ quantum spin chain, have an extensive number of local conserved quantities that endow them with exotic thermalization and transport properties. We discuss recently introduced hydrodynamic approaches for such integrable systems from the viewpoint of kinetic theory and extend the previous works by proposing a numerical scheme to solve the hydrodynamic equations for finite times and arbitrary locally equilibrated initial conditions. We then discuss how such methods can be applied to describe non-equilibrium steady states involving ballistic heat and spin currents. In particular, we show that the spin Drude weight in the XXZ chain, previously accessible only by rigorous techniques of limited scope or controversial thermodynamic Bethe ansatz arguments, may be evaluated from hydrodynamics in very good agreement with density-matrix renormalization group calculations.

cond-mat.stat-mech↗

arXiv2018

Solvable Hydrodynamics of Quantum Integrable Systems

The conventional theory of hydrodynamics describes the evolution in time of chaotic many-particle systems from local to global equilibrium. In a quantum integrable system, local equilibrium is characterized by a local generalized Gibbs ensemble or equivalently a local distribution of pseudo-momenta. We study time evolution from local equilibria in such models by solving a certain kinetic equation, the "Bethe-Boltzmann" equation satisfied by the local pseudo-momentum density. Explicit comparison with density matrix renormalization group time evolution of a thermal expansion in the XXZ model shows that hydrodynamical predictions from smooth initial conditions can be remarkably accurate, even for small system sizes. Solutions are also obtained in the Lieb-Liniger model for free expansion into vacuum and collisions between clouds of particles, which model experiments on ultracold one-dimensional Bose gases.

cond-mat.stat-mech↗

arXiv2017

Topological Floquet-Thouless energy pump

We explore adiabatic pumping in the presence of periodic drive, finding a new phase in which the topologically quantized pumped quantity is energy rather than charge. The topological invariant is given by the winding number of the micromotion with respect to time within each cycle, momentum, and adiabatic tuning parameter. We show numerically that this pump is highly robust against both disorder and interactions, breaking down at large values of either in a manner identical to the Thouless charge pump. Finally, we suggest experimental protocols for measuring this phenomenon.

cond-mat.quant-gas↗

arXiv2017

Large bulk photovoltaic effect and spontaneous polarization of single-layer monochalcogenides

We use a first-principles density functional theory approach to calculate the shift current and linear absorption of uniformly illuminated single-layer Ge and Sn monochalcogenides. We predict strong absorption in the visible spectrum and a large effective three-dimensional shift current ($\sim$100 $μ$A/V$^2$), larger than has been previously observed in other polar systems. Moreover, we show that the integral of the shift-current tensor is correlated to the large spontaneous effective three-dimensional electric polarization ($\sim$1.9 C/m$^2$). Our calculations indicate that the shift current will be largest in the visible spectrum, suggesting that these monochalcogenides may be promising for polar optoelectronic devices. A Rice-Mele tight-binding model is used to rationalize the shift-current response for these systems, and its dependence on polarization, in general terms with implications for other polar materials

cond-mat.mes-hall↗

arXiv2017

Quantitative relationship between polarization differences and the zone-averaged shift photocurrent

A relationship is derived between differences in electric polarization between bands and the "shift vector" that controls part of a material's bulk photocurrent, then demonstrated in several models. Electric polarization has a quantized gauge ambiguity and is normally observed at surfaces via the surface charge density, while shift current is a bulk property and is described by shift vector gauge invariant at each point in momentum space. They are connected because the same optical transitions that are described in shift currents pick out a relative gauge between valence and conduction bands. We also discuss subtleties arising when there are points at the Brillouin zone where optical transitions are absent. We conclude that two-dimensional materials with significant interband polarization differences should have high bulk photocurrent, meaning that the modern theory of polarization can be used as a straightforward way to search for bulk photovoltaic material candidates.

cond-mat.mes-hall↗

arXiv2017

Quantized circular photogalvanic effect in Weyl semimetals

The circular photogalvanic effect (CPGE) is the part of a photocurrent that switches depending on the sense of circular polarization of the incident light. It has been consistently observed in systems without inversion symmetry and depends on non-universal material details. Here we find that in a class of Weyl semimetals (e.g. SrSi$_2$) and three-dimensional Rashba materials (e.g. doped Te) without inversion and mirror symmetries, the injection contribution to the CPGE trace is effectively quantized in terms of the fundamental constants $e, h, c$ and $ε_0$ with no material-dependent parameters. This is so because the CPGE directly measures the topological charge of Weyl points, and non-quantized corrections from disorder and additional bands can be small over a significant range of incident frequencies. Moreover, the magnitude of the CPGE induced by a Weyl node is relatively large, which enables the direct detection of the monopole charge with current techniques.

cond-mat.str-el↗

arXiv2017

Floquet Dynamics of Boundary-Driven Systems at Criticality

A quantum critical system described at low energy by a conformal field theory (CFT) and subjected to a time-periodic boundary drive displays multiple dynamical regimes depending on the drive frequency. We compute the behavior of quantities including the entanglement entropy and Loschmidt echo, confirming analytic predictions from field theory by exact numerics on the transverse field Ising model, and demonstrate universality by adding non-integrable perturbations. The dynamics naturally separate into three regimes: a slow-driving limit, which has an interpretation as multiple quantum quenches with amplitude corrections from CFT; a fast-driving limit, in which the system behaves as though subject to a single quantum quench; and a crossover regime displaying heating. The universal Floquet dynamics in all regimes can be understood using a combination of boundary CFT and Kibble-Zurek scaling arguments.

cond-mat.str-el↗

arXiv2017

Entanglement Entropy in Excited States of the Quantum Lifshitz Model

We investigate the entanglement properties of an infinite class of excited states in the quantum Lifshitz model (QLM). The presence of a conformal quantum critical point in the QLM makes it unusually tractable for a model above one spatial dimension, enabling the ground state entanglement entropy for an arbitrary domain to be expressed in terms of geometrical and topological quantities. Here we extend this result to excited states and find that the entanglement can be naturally written in terms of quantities which we dub "entanglement propagator amplitudes" (EPAs). EPAs are geometrical probabilities that we explicitly calculate and interpret. A comparison of lattice and continuum results demonstrates that EPAs are universal. This work shows that the QLM is an example of a 2+1d field theory where the universal behavior of excited-state entanglement may be computed analytically.

cond-mat.stat-mech↗

arXiv2017

Hydrodynamic Electron Flow and Hall Viscosity

In metallic samples of small enough size and sufficiently strong momentum-conserving scattering, the viscosity of the electron gas can become the dominant process governing transport. In this regime, momentum is a long-lived quantity whose evolution is described by an emergent hydrodynamical theory. Furthermore, breaking time-reversal symmetry leads to the appearance of an odd component to the viscosity called the Hall viscosity, which has attracted considerable attention recently due to its quantized nature in gapped systems but still eludes experimental confirmation. Based on microscopic calculations, we discuss how to measure the effects of both the even and odd components of the viscosity using hydrodynamic electronic transport in mesoscopic samples under applied magnetic fields.

cond-mat.str-el↗

arXiv2017

Electrical and thermal transport in the quasi-atomic limit of coupled Luttinger liquids

We introduce a new model for quasi one-dimensional materials, motivated by intriguing but not yet well-understood experiments that have shown two-dimensional polymer films to be promising materials for thermoelectric devices. We consider a two-dimensional material consisting of many one-dimensional systems, each treated as a Luttinger liquid, with weak (incoherent) coupling between them. This approximation of strong interactions within each one-dimensional chain and weak coupling between them is the "quasi-atomic limit." We find integral expressions for the (interchain) transport coefficients, including the electrical and thermal conductivities and the thermopower, and we extract their power law dependencies on temperature. Luttinger liquid physics is manifested in a violation of the Wiedemann-Franz law; the Lorenz number is larger than the Fermi liquid value by a factor between $γ^2$ and $γ^4$, where $γ\geq 1$ is a measure of the electron-electron interaction strength in the system.

cond-mat.str-el↗

arXiv2017

Design principles for shift current photovoltaics

While the basic principles and limitations of conventional solar cells are well understood, relatively little attention has gone toward maximizing the potential efficiency of photovoltaic devices based on shift currents. In this work, we outline simple design principles for the optimization of shift currents for frequencies near the band gap, derived from the analysis of a general effective model. The use of a novel sum rule allows us to express the band edge shift current in terms of a few model parameters and to show it depends explicitly on wavefunctions via Berry connections in addition to standard band structure. We use our approach to identify two new classes of shift current photovoltaics, ferroelectric polymer films and single-layer orthorhombic monochalcogenides such as GeS. We introduce tight-binding models for these systems, and show that they exhibit the largest shift current responsivities at the band edge reported so far. Moreover, exploring the parameter space of these models we find photoresponsivities that can exceed $100$ mA/W. Our results show how the study of the shift current via effective models allows one to improve the possible efficiency of devices based on this mechanism and better grasp their potential to compete with conventional solar cells.

cond-mat.mes-hall↗

arXiv2017

Dynamical piezoelectric and magnetopiezoelectric effects in polar metals from Berry phases and orbital moments

The polarization of a material and its response to applied electric and magnetic fields are key solid-state properties with a long history in insulators, although a satisfactory theory required new concepts such as Berry-phase gauge fields. In metals, quantities such as static polarization and magnetoelectric $θ$-term cease to be well-defined. In polar metals there can be analogous dynamical current responses, which we study in a common theoretical framework. We find that current responses to dynamical strain in polar metals depend on both the first and second Chern forms, related to polarization and magnetoelectricity in insulators, as well as the orbital magnetization on the Fermi surface. We provide realistic estimates that predict that the latter contribution will dominate and investigate the feasibility of experimental detection of this effect.

cond-mat.mes-hall↗