The construction of magnon-phonon couplings in Kitaev material candidate α-RuCl₃

Yi-Fang Tsai^1*, Yi-Ping Huang^1,2

¹Department of Physics, National Tsing Hua University, Hsinchu, Taiwan
²Institute of Physics, Academia Sinica, Taipei, Taiwan

* Presenter:Yi-Fang Tsai, email:emi19991012@gapp.nthu.edu.tw

As a Mott-Hubbard model system with strong spin-orbit coupling, α-RuCl₃ is of huge interest as a candidate of the Kitaev material. Experiments show that it doesn’t order at low temperatures and the magnetic order is suppressed when applying a range of external magnetic field. The behaviors of its low energy excitation in thermal Hall signals and Raman data also suggest that there might exist Majorana edge modes. However, there are still lots of debates on the interpretations of the experiments and their actual underlying mechanism since α-RuCl₃ is a Van der Waals material with the possible presence of stacking faults and the exact Kitaev spin liquid has only a tiny regime of stability beyond the solvable limit. One of the recent experimental data of α-RuCl₃ on thermal Hall conductivity suggests that, apart from magnon, we should also consider the effect of phonons. We first try building a minimal model of monolayer α-RuCl₃ and include the effect of phonons by twisting a bilayer α-RuCl₃. Our work on such couplings between the magnetic moments and the displacement of layers could help elucidate the microscopic picture of low-energy excitations in this material.

Keywords: Kitaev material, magnetic Van der Waals material, spin liquid, magnon-phonon coupling