Magnetic and spin-orbit exciton excitations in the honeycomb lattice compound RuBr3

Abstract

RuX3 trihalides (X=halogen atoms) offer a prominent platform for exploring the Kitaev spin liquid. Using polarization-resolved Raman spectroscopy, we report a comparative study of lattice, magnetic, and electronic excitations on X=Cl and Br. Our phonon Raman spectra show that RuBr3 retains a three-layer honeycomb lattice without structural transition, unlike ?-RuCl3 that undergoes a monoclinic-to-rhombohedral structural transition at ?150K. In addition, both RuX3 compounds commonly feature single and double spin-orbit excitons of almost identical energies, alluding to the realization of a jeff=1/2 state to the same degree. In contrast to ?-RuCl3 two-magnon scattering dominates over fractionalized excitations in RuBr3. Our results suggest that a Br-for-Cl substitution moves RuX3 further away from a pure Kitaev phase despite enhanced p-d hybridization. © 2022 American Physical Society.