Halogen control of magnetic competition in Kitaev candidate Ru$X_3$ ($X=$ Cl, Br)

Abstract

The spin-orbital Mott insulators Ru$X_3$ ($X=$ Cl, Br) have attracted considerable attention as promising candidate materials for realizing a Kitaev spin liquid. In this study, we construct effective pseudospin models from multiorbital Hubbard models derived from first-principles calculations and investigate the magnetic states of RuCl${}_3$ and RuBr${}_3$. From the constructed effective models, we find that RuBr${}_3$ has more extended Wannier orbitals and stronger interlayer exchange interactions than RuCl${}_3$. These interactions enhance three-dimensional correlations, consistent with the stronger antiferromagnetic tendency experimentally inferred for RuBr${}_3$. Orbital-dependent Coulomb anisotropy further reduces the energy difference between ferromagnetic and zigzag states. Our results clarify how halogen substitution controls magnetic competition in Ru$X_3$ through interlayer exchange interactions and effects of orbital-dependent Coulomb interactions.

17 pages, 11 figures