Thermal spin dynamics of Kitaev magnets $-$ scattering continua and magnetic field induced phases within a stochastic semiclassical approach

TL;DR

This study uses a stochastic semiclassical approach to analyze the temperature-dependent spin dynamics of Kitaev magnets under magnetic fields, revealing broad continua in intermediate phases that mimic quantum spin liquid signatures.

Contribution

It introduces a finite-temperature semiclassical model to interpret the spin excitation continua in Kitaev magnets, emphasizing the role of thermal fluctuations.

Findings

Broadening of spin excitations at finite temperature

Similar continuum responses across different intermediate phases

Finite temperature effects can mimic quantum fractionalization signatures

Abstract

The honeycomb magnet $\alpha-$RuCl$_3$ is a prime candidate material for realizing the Kitaev quantum spin liquid (QSL), but it shows long-range magnetic order at low temperature. Nevertheless, its broad inelastic neutron scattering (INS) response at finite frequency has been interpreted as that of a 'proximate QSL'. A moderate in-plane magnetic field indeed melts the residual zigzag order, giving rise to peculiar intermediate field phases before the high-field polarized state. In INS measurements the low-frequency spin waves disappear, leading to a broad scattering continuum in the field-induced intermediate regime, whose nature is currently under debate. Here, we study the magnetic field dependent spin dynamics of the $K-\Gamma-\Gamma'-$model within a stochastic semiclassical treatment, which incorporates the effect of finite-temperature fluctuations. At temperatures relevant for INS experiments, we show how the excitations of the zigzag phase broaden and that the different intermediate phases all show a similar continuum response. We discuss the implications of our results for experiments and highlight the importance of distinguishing finite temperature fluctuations from genuine quantum fractionalization signatures in frustrated magnets.