J = 12 pseudospins and d-p hybridization in the Kitaev spin liquid candidates RuX3 (X =Cl, Br, I)

The recent synthesis of ruthenium trihalides RuX3 (X = Cl, Br, I) has enlarged the set of material candidates for Kitaev spin liquids. The realization of the Kitaev model necessitates the formation of J=1/2 pseudospins in the octahedral crystal field. We use Ru L3-edge resonant inelastic x-ray scattering to investigate the evolution of multiplet structures in RuX3. We identified quasielastic magnetic correlations and spin-orbit transitions to the J=3/2 states without discernible trigonal splitting, thereby validating the J=1/2 description of magnetism in the RuX3 family. Lineshape broadening in RuI3 provides evidence for its bulk metallicity in the vicinity of a bandwidth-controlled metal-insulator transition. Our results highlight the pivotal role of halogen p orbitals in controlling the electronic properties of RuX3.