Anisotropic susceptibilities in the honeycomb Kitaev system $\alpha$-RuCl$_{3}$

TL;DR

This study investigates the anisotropic magnetic susceptibilities of $ ext{α-RuCl}_3$, revealing unidirectional in-plane anisotropy and the significant role of $ ext{Γ}$ spin exchange, supporting its candidacy as a Kitaev quantum spin liquid material.

Contribution

The paper provides detailed susceptibility measurements and a theoretical model that elucidates the role of bond anisotropy and $ ext{Γ}$ interactions in $ ext{α-RuCl}_3$, advancing understanding of its magnetic properties.

Findings

Unidirectional in-plane susceptibility anisotropy observed.

Strong symmetric off-diagonal $ ext{Γ}$ exchange explains susceptibility differences.

Quantified $ ext{Γ}$ couplings and other Hamiltonian parameters.

Abstract

The magnetic insulator $\alpha$-RuCl$_{3}$ is a promising candidate to realize Kitaev interactions on a quasi-2D honeycomb lattice. We perform extensive susceptibility measurements on single crystals of $\alpha$-RuCl$_{3}$, including angle-dependence of the in-plane longitudinal and transverse susceptibilities, which reveal a unidirectional anisotropy within the honeycomb plane. By comparing the experimental results to a high-temperature expansion of a Kitaev-Heisenberg-$\Gamma$ spin Hamiltonian with bond anisotropy, we find excellent agreement with the observed phase shift and periodicity of the angle-resolved susceptibilities. Within this model, we show that the pronounced difference between in-plane and out-of-plane susceptibilities as well as the finite transverse susceptibility are rooted in strong symmetric off-diagonal $\Gamma$ spin exchange. The $\Gamma$ couplings and relationships between other terms in the model Hamiltonian are quantified by extracting relevant Curie-Weiss intercepts from the experimental data.