Active orbital degree of freedom and potential spin-orbit-entangled moments in Kitaev magnet candidate BaCo${}_2$(AsO${}_4$)${}_2$

Abstract

Candidate materials for 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 4$d$ and 5$d$ based transition metal compounds, recently there has been a growing research interest in Co-based quasi-two-dimensional honeycomb magnets, such as BaCo${}_2$(AsO${}_4$)${}_2$ because of formation of spin-orbit-entangled $J_{\mathrm{eff}}$ = 1/2 pseudospin moments at Co${}^{2+}$ sites and potential realizations of Kitaev-like magnetism therein. Here, we obtain high-accuracy crystal and electronic structure of BaCo${}_2$(AsO${}_4$)${}_2$ by employing a combined density functional and dynamical mean-field theory calculations, which correctly capture the Mott-insulating nature of the target system. We show that Co${}^{2+}$ ions form a high spin configuration, $S=3/2$, with an active $L_{\mathrm{eff}}=1$ orbital degree of freedom, in the absence of spin-orbit coupling. The size of trigonal distortion within CoO${}_6$ 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.

10 pages, 10 figures

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Cited by in corpus (3)

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• Proximate Dirac spin liquid in honeycomb lattice $J_1$-$J_3$ XXZ model: Numerical study and application to cobaltates
• Spin-orbit entangled moments and magnetic exchange interactions in cobalt-based honeycomb magnets BaCo${}_2$($X$O${}_4$)${}_2$ ($X$ = P, As, Sb)