Phonon thermal Hall effect in Mott insulators via skew-scattering by the scalar spin chirality

TL;DR

This paper proposes a novel mechanism for the phonon thermal Hall effect in Mott insulators, driven by skew scattering via scalar spin chirality, independent of spin-orbit coupling, and predicts observable effects in various lattice structures.

Contribution

It introduces a new phonon-spin coupling mechanism via scalar spin chirality that explains the thermal Hall effect without relying on spin-orbit interaction.

Findings

Predicts a thermal Hall angle of 10^{-3} to 10^{-2} in Mott insulators.

Demonstrates the mechanism in YMnO3 and predicts effects in Kagome and square lattices.

Shows the effect is ubiquitous and does not require time-reversal symmetry breaking.

Abstract

Thermal transport is a crucial probe for studying excitations in insulators. In Mott insulators, the primary candidates for heat carriers are spins and phonons, and which dominates the thermal conductivity is a persistent issue. Typically, phonons dominate the longitudinal thermal conductivity while the thermal Hall effect (THE) is primarily associated with spins, which requires time-reversal symmetry breaking. The coupling between phonons and spins usually depends on spin-orbit interaction and is relatively weak. Here, we propose a new mechanism for this coupling and the associated THE: the skew scattering of phonons via spin fluctuations by the scalar spin chirality. This coupling does not require spin-orbit interaction and is ubiquitous in Mott insulators, leading to a thermal Hall angle on the order of $10^{-3}$ to $10^{-2}$. Based on this mechanism, we investigate the THE in YMnO$_3$ with a trimerized triangular lattice where the THE beyond spins was recognized, and predict the THE in the Kagome and square lattices.