Thermal transport of the XXZ chain in a magnetic field

TL;DR

This paper investigates the thermal transport properties of the spin-1/2 XXZ chain in magnetic fields, revealing how magnetic field strength influences the thermal Drude weight and proposing a universal behavior at quantum critical points.

Contribution

It provides a detailed analysis of the magnetic field dependence of thermal transport in the XXZ chain using exact diagonalization and mean-field theory, highlighting new universal low-temperature behavior.

Findings

Thermal Drude weight strongly depends on magnetic field strength.

Mean-field theory agrees well with exact results for small anisotropies and fields.

Universal low-temperature behavior is proposed at the quantum critical line.

Abstract

We study the heat conduction of the spin-1/2 XXZ chain in finite magnetic fields where magnetothermal effects arise. Due to the integrability of this model, all transport coefficients diverge, signaled by finite Drude weights. Using exact diagonalization and mean-field theory, we analyze the temperature and field dependence of the thermal Drude weight for various exchange anisotropies under the condition of zero magnetization-current flow. First, we find a strong magnetic field dependence of the Drude weight, including a suppression of its magnitude with increasing field strength and a non-monotonic field-dependence of the peak position. Second, for small exchange anisotropies and magnetic fields in the massless as well as in the fully polarized regime the mean-field approach is in excellent agreement with the exact diagonalization data. Third, at the field-induced quantum critical line between the para- and ferromagnetic region we propose a universal low-temperature behavior of the thermal Drude weight.