Geometry dependence of the thermal Hall effect in chiral spin liquids

TL;DR

This paper proposes a geometry-based method to distinguish chiral quantum spin liquids from other materials by analyzing how constrictions affect the thermal Hall effect, aiding experimental identification.

Contribution

It introduces a novel approach using sample geometry variations to identify chiral spin liquids through their thermal Hall response.

Findings

Thermal Hall effect from chiral edge modes is enhanced by constrictions at low temperatures.

Conventional thermal Hall effects from phonons or magnons are geometry independent.

The method provides a practical way to identify chiral spin liquids in experiments.

Abstract

Recent thermal-transport experiments on the Kitaev magnet $\alpha$-RuCl$_3$ highlight the challenge in identifying chiral quantum spin liquids through their quantized thermal Hall effect. Here, we propose that variations in the underlying sample geometry -- for example, the introduction of appropriate constrictions -- reveal unique aspects of the thermal Hall effect and can be used to determine its origin. By studying standard phenomenological heat-transport equations based on minimal assumptions, we show that, whereas a conventional thermal Hall effect due to, e.g., phonons or magnons is completely geometry independent, a thermal Hall effect originating from a chiral fermion edge mode is significantly enhanced by constrictions at low temperatures. This unique geometry-dependent signature provides a practical approach for identifying chiral spin liquids in candidate materials like $\alpha$-RuCl$_3$ using currently available thermal-transport experiments.