Alloys of hexagonal $δ$-phase UZr$_2$ have been synthesized and studied by means of heat capacity, magnetic susceptibility, magnetization, electrical resistivity, magnetoresistance, thermoelectric power, thermal conductivity measurements, for the first time, at temperatures from 1.8 to 300 K and in magnetic fields up to 8 T. The weak temperature dependence of the magnetic susceptibility and the small value of both Seebeck (0.75 $μ$V/K at room temperature) and of the Sommerfeld coefficient (13.5 mJ mol$^{-1}$ K$^{-2}$) point to 5$f$-electrons in this material having a delocalized nature. The electrical resistivity and magnetoresistance indicate the presence of significant electronic disorder in $δ$-UZr$_2$, consistent with the disorder in its crystal structure. Density functional theory calculations have been performed and compared to experimental results.
Thermal transport is less appreciated in probing quantum materials in comparison to electrical transport. This article aims to show the pivotal role that thermal transport may play in understanding quantum materials: the longitudinal thermal transport reflects the itinerant quasiparticles even in an electrical insulating phase, while the transverse thermal transport such as thermal Hall and Nernst effect are tightly linked to nontrivial topology. We discuss three types of examples: quantum spin liquids where thermal transport identifies its existence, superconductors where thermal transport re…
Transport currents in solids decay through collisions of quasiparticles with each other and with defects or boundaries. Since information about collisional lifetimes is difficult to obtain, most calculations of transport properties rely on parameters that are not known independently. Here, we use magnon lifetime data for the two-dimensional antiferromagnet Rb2MnF4 to calculate the magnon-mediated thermal conductivity without any adjustable parameters, thereby quantifying the influence of scattering from domain boundaries on transport. Related strategies have the potential to enhance our unders…
Breaking of spatial inversion symmetry (SIS) induces unique phenomena in condensed matter. Besides the classic examples such as natural optical activity and piezoelectricity, the spin-orbit interaction further enriches the effect of SIS breaking, as exemplified by the Rashba effect. In particular, by combining this symmetry with magnetic fields or another type of time-reversal symmetry (TRS) breaking, noncentrosymmetric materials can be made to exhibit nonreciprocal responses, which are responses that differ for rightward and leftward stimuli. For example, resistivity becomes directionally dep…
In low-dimensional systems, the combination of reduced dimensionality, strong interactions, and topology has led to a growing number of many-body quantum phenomena. Thermal transport, which is sensitive to all energy-carrying degrees of freedom, provides a discriminating probe of emergent excitations in quantum materials and devices. However, thermal transport measurements in low dimensions are dominated by the phonon contribution of the lattice, requiring an experimental approach to isolate the electronic thermal conductance. Here, we show how the measurement of nonlocal voltage fluctuations …
The purpose of this note is to connect early work on thermal transport in spin-1/2 Heisenberg chains with uniaxial exchange anisotropy and nearest-neighbor interactions that was based on a moment analysis of the Fourier transform of the energy density correlation function with subsequent studies that make use of thermal current correlation functions.
Phononless plasmon assisted transport through a long disordered array of finite length quantum wires is investigated analytically. Two temperature regimes, the low- and the high-temperature ones, with qualitatively different temperature dependencies of thermally activated resistance are identified. The characteristics of plasmon assisted and phonon assisted transport mechanisms are compared. Generically strong electron-electron interaction in quantum wires results in a qualitative change of the temperature dependence of thermally activated resistance in comparison to phonon assisted transport.…
The formalism for a linear-response many-body treatment of the electronic contributions to thermal transport is developed for multilayered nanostructures. By properly determining the local heat-current operator, it is possible to show that the Jonson-Mahan theorem for the bulk can be extended to inhomogeneous problems, so the various thermal-transport coefficient integrands are related by powers of frequency (including all effects of vertex corrections when appropriate). We illustrate how to use this formalism by showing how it applies to measurements of the Peltier effect, the Seebeck effect,…
We report measurements of the specific heat and the thermal conductivity of the model Heisenberg spin-1/2 chain cuprate Sr$_{2}$CuO$_{3}$ at low temperatures. In addition to a nearly isotropic phonon heat transport, we find a quasi one-dimensional excess thermal conductivity along the chain direction, most likely associated with spin excitations (spinons). The spinon energy current is limited mainly by scattering on defects and phonons. Analyzing the specific heat data, the intrachain magnetic exchange $J/k_{B}$ is estimated to be 2650 K.
We study the transport properties of long quantum wires by generalizing the Luttinger liquid approach to allow for the finite lifetime of the bosonic excitations. Our theory accounts for long-range disorder and strong electron interactions, both of which are common features of experiments with quantum wires. We obtain the electrical and thermal resistances and thermoelectric properties of such quantum wires. We cast our results in terms of the thermal conductivity and bulk viscosity of the electron liquid and give the temperature scale above which the transport can be described by classical hy…
We present a formula for thermal transport in the bulk of Bose systems based on the quantum Boltzmann equation (QBE). First, starting from the quantum kinetic equation and using the Born approximation for impurity scattering, we derive the QBE of Bose systems and provide a formula for thermal transport subjected to a temperature gradient. Next, we apply the formula to magnons. Assuming a relaxation time approximation and focusing on the linear response regime, we show that the longitudinal thermal conductivity of the QBE exhibits the different behavior from the conventional. The thermal conduc…
This work studies heat transport of bond-disordered spin-1/2 chains. As an example, the XX case is analyzed, which corresponds to a model of noninteracting spinless fermions. Within the fermion representation, the single-particle eigenenergies are determined numerically, which allow one to compute transport coefficients. Since the ballistic transport properties of a clean chain are destroyed by disorder, the focus is on the frequency dependence of the thermal conductivity and on a qualitative comparison with the spin conductivity, both at finite temperatures.
We derive and calculate thermal transport coefficient for a quantum Hall system in the linear response regime, and show that they are exponentially small in the bulk, in contrast to the quantized value of the charge Hall coefficient, thus violating Wiedemann-Franz law. This corroborates earlier reports about the essential difference between the charge and thermal quantum Hall effect, that originates from the different behavior of the corresponding $U(1)$ and gravitational anomalies. We explicitly calculate the bulk currents when a temperature profile is applied within the bulk, and show that t…
We clarify some aspects of the calculation of the thermal transport coefficients. For a tight-binding Hamiltonian we discuss the approximate nature of the charge current and the thermal current obtained by Peierls substitution which is also identical to the equation of motion technique. We address the issue of choosing an appropriate basis for making the Peierls construction for transport calculations. We propose a criteria for finding an optimum Wannier basis where the difference between the exact current and the approximate one is minimum. Using the equations of motion we derive the thermal …
The celebrated Wiedemann-Franz (WF) law is believed to be robust in metals as long as interactions between electrons preserve their fermion-quasiparticle character. We study thermal transport and the fate of the WF law close to a continuous metal-insulator transition (MIT) in the Falicov-Kimball model (FKM) using cluster-dynamical mean-field theory (CDMFT). Surprisingly, as for electrical transport, we find robust and novel quantum critical scaling in thermal transport across the MIT. We unearth the deeper reasons for these novel findings in terms of (i) the specific structure of energy-curren…
ErTe$_3$ is studied as a model system to explore thermal transport in a layered charge density wave (CDW) material. We present data from thermal diffusivity, resistivity, and specific heat measurements: There is a sharp decrease in thermal conductivity both parallel and perpendicular to the primary CDW at the CDW transition temperature. At the same time, the resistivity changes more gradually. Correspondingly, while well above and below $T_c$, a consistent description of the thermal transport applies with essentially independent electron and phonon contributions (estimated using the Wiedemann …
We present a new framework for computing low frequency transport properties of strongly correlated, ergodic systems. Our main assumption is that, when a thermalizing diffusive system is driven at frequency $ω$, domains of size $ξ\sim\sqrt{D/ω}$ can be considered as internally thermal, but weakly coupled with each other. We calculate the transport coefficients to lowest order in the coupling, assuming incoherent transport between such domains. Our framework naturally captures the sub-leading non analytic corrections to the transport coefficients, known as hydrodynamic long time tails. In additi…
We discuss the violation of spin-charge separation in generic nonlinear Luttinger liquids and investigate its effect on the relaxation and thermal transport of genuine spin-1/2 electron liquids in ballistic quantum wires. We identify basic scattering processes compatible with the symmetry of the problem and conservation laws that lead to the decay of plasmons into the spin modes. We derive a closed set of coupled kinetic equations for the spin-charge excitations and solve the problem of thermal conductance of interacting electrons for an arbitrary relation between the quantum wire length and s…
Motivated by recent experiments on the phonon contribution to the thermal Hall effect in the cuprates, we present an analysis of chiral phonon transport. We assume the chiral behavior arises from a non-zero phonon Hall vicosity, which is likely induced by the coupling to electrons. Phonons with a non-zero phonon Hall viscosity have an intrinsic thermal Hall conductivity, but Chen et al. (Phys. Rev. Lett. 124, 167601 (2020)) have argued that a significantly larger thermal Hall conductivity can arise from an extrinsic contribution which is inversely proportional to the density of impurities. We …
We study thermal transport in strongly disordered, strongly interacting quantum field theories without quasiparticles using gauge-gravity duality. We analyze linear perturbations of black holes with broken translational symmetry in Einstein-Maxwell-dilaton theories of gravity. Using general geometric arguments in the bulk, we derive bounds on thermal conductivity for the dual disordered field theories in one and two spatial dimensions. In the latter case, the thermal conductivity is always non-zero at finite temperature, so long as the dilaton potential is bounded from below. Hence, generic ho…
