Thermal Hall signatures of non-Kitaev spin liquids in honeycomb Kitaev materials

Yong Hao Gao,Tao Xiang,Simon Trebst,Gang Chen,Ciarán Hickey

doi:10.1103/physrevresearch.1.013014

Abstract

Motivated by the recent surge of field-driven phenomena discussed for Kitaev materials, in particular the experimental observation of a finite thermal Hall effect and theoretical proposals for the emergence of additional spin liquid phases beyond the conventional Kitaev spin liquid, we develop a theoretical understanding of the thermal Hall effect in honeycomb Kitaev materials in magnetic fields. Our focus is on gapless U(1) spin liquids with a spinon Fermi surface, which have been shown to arise as field-induced phases. We demonstrate that in the presence of symmetry-allowed, second-neighbor Dzyaloshinskii-Moriya interactions these spin liquids give rise to a finite, non-quantized, thermal Hall conductance in a magnetic field. The microscopic origin of this thermal Hall effect can be traced back to an interplay of Dzyaloshinskii-Moriya interaction and Zeeman coupling, which generates an internal U(1) gauge flux that twists the motion of the emergent spinons. We argue that such a non-quantized thermal Hall effect is a generic response in Kitaev models for a range of couplings.

Highlights

The first experimental observation of a quantum Hall effect in two-dimensional electron systems [1] has proved to be a scientific revolution, with its exact quantization of Hall resistance raising measurement standards to unprecedented levels of precision [2]
Motivated by the recent surge of field-driven phenomena discussed for Kitaev materials, in particular the experimental observation of a finite thermal Hall effect and theoretical proposals for the emergence of additional spin liquid phases beyond the conventional Kitaev spin liquid, we develop a theoretical understanding of the thermal Hall effect in honeycomb Kitaev materials in magnetic fields
While the original motivation for the exploration of the growing family of Kitaev materials [15,16,17] might have been to discover an experimental realization of the Kitaev spin liquid [22], i.e., a non-Abelian chiral spin liquid with a gapless Majorana edge current, it is becoming increasingly clear that these materials might harbor other types of spin liquids [34,35,36,45,58]

Summary

Introduction

The first experimental observation of a quantum Hall effect in two-dimensional electron systems [1] has proved to be a scientific revolution, with its exact quantization of Hall resistance raising measurement standards to unprecedented levels of precision [2]. It has served as a blueprint for the interplay between experimental breakthroughs and deep conceptual progress on the theoretical side. For the integer quantum Hall effect, it was the seminal introduction of topological invariants [3] that explained the quantization of conductance. The more recent observation of a half-integer quantized thermal Hall effect [8,9] has caught the imagination of experimentalists and theorists alike

Objectives

Discussion

Conclusion