Quantized and unquantized thermal Hall conductance of Kitaev spin-liquid candidate $\alpha$-RuCl$_3$

TL;DR

This study investigates the thermal Hall conductance in $ ext{α}$-RuCl$_3$, revealing that quantization depends on sample purity, thermal conductivity, and magnetic interactions, providing insights into Majorana edge modes in quantum spin liquids.

Contribution

The paper demonstrates the relationship between thermal Hall quantization and sample-dependent properties like thermal conductivity and Néel temperature in $ ext{α}$-RuCl$_3$, highlighting the effects of impurities and interactions.

Findings

Half-integer quantum thermal Hall effect linked to thermal conductivity.

Higher Néel temperature correlates with higher magnetic field for quantization.

Impurity scattering and non-Kitaev interactions influence quantization.

Abstract

Despite extensive investigations, a topological state that hosts Majorana edge modes in the magnetic field-induced quantum disordered state of the Kitaev candidate material $\alpha$-RuCl$_3$ has been hotly debated. To gain more insight into this issue, we measured the thermal Hall conductivity $\kappa_{xy}$ of various samples grown by the Bridgman method. The results show that the half-integer quantum thermal Hall effect is intimately related to the magnitude of longitudinal thermal conductivity and the N\'{e}el temperature at zero field, both of which are sample dependent. Samples exhibiting the half-integer quantum thermal Hall effect have larger zero-field thermal conductivity values than a threshold value, implying that a long mean free path of heat carriers is an important prerequisite. In addition, we find that samples with a higher N\'{e}el temperature exhibit a higher magnetic field at which quantization starts to occur. These results indicate that the quantization phenomenon is significantly affected by the impurity scatterings and the non-Kitaev interactions.