Active orbital degree of freedom and potential spin-orbit-entangled moments in the Kitaev magnet candidate BaCo₂(AsO₄)₂

Candidate materials for the Kitaev spin liquid phase have been intensively studied recently because of their potential applications in fault-tolerant quantum computing. Although most of the studies on Kitaev spin liquid have been done in 4d- and 5d-based transition-metal compounds, recently there has been a growing research interest in Co-based quasi-two-dimensional honeycomb magnets, such as BaCo₂(AsO₄)₂ because of formation of spin-orbit-entangled J_eff = 1/2 pseudospin moments at Co²⁺ sites and potential realizations of Kitaev-like magnetism therein. Here, we obtain high-accuracy crystal and electronic structure of BaCo₂(AsO₄)₂ by employing combined density-functional and dynamical mean-field theory calculations, which correctly capture the Mott-insulating nature of the target system. We show that Co²⁺ ions form a high-spin configuration, S = 3/2, with an active L_eff = 1 orbital degree of freedom, in the absence of spin-orbit coupling. The size of trigonal distortion within CoO₆ octahedra is found to be not strong enough to completely quench the orbital degree of freedom, so that the presence of spin-orbit coupling can give rise to the formation of spin-orbit-entangled moments and the Kitaev exchange interaction. Our finding supports recent studies on potential Kitaev magnetism in this compound and other Co-based layered honeycomb systems.