Spin-phonon coupling and phonon(-Hall) transport in α-RuCl3 from first principles*

Recent experimental studies on α-RuCl3 have pointed to the presence of significant magnetoelastic coupling. For example, the longitudinal thermal conductivity, which is expected to be dominated by phonons, shows a strong dependence on magnetic field strength and on the presence/absence of the magnetic order. This raises the question whether the heavily discussed thermal Hall conductivity in α-RuCl3 could contain a significant contribution from a phonon-Hall effect. 

In this study we first derive the pseudospin-phonon couplings of α-RuCl3 from first principles. 

With these, we evaluate the thermal (Hall) conductivity from bulk phonons coupled to the magnetic system. This is done by employing results from exact diagonalization methods within the framework of Boltzmann's equation.