Spin-wave analysis of the low-temperature thermal Hall effect in the candidate Kitaev spin liquid α-RuCl3

Proposed effective Hamiltonians from the literature for the material alpha-RuCl3 are used to compute the magnon thermal Hall conductivity kappa(xy) using linear spin-wave theory for the magnetically ordered state. No model previously proposed that was tested explains the published experimental data. Models with Kitaev interaction K > 0 are seen to predict kappa(xy) greater than or similar to 0, which is inconsistent with the data. Fluctuations toward a Kitaev-type spin liquid would have the wrong sign to explain the data. However, a slight variant of a previously proposed model predicts a large kappa(xy), demonstrating that the low-temperature thermal Hall effect could be generated exclusively by the Berry curvature of the magnon bands. The experimental data of kappa(xy) can therefore serve as another method to constrain a proposed effective Hamiltonian.