Relevance of on-site and intersite Coulomb interactions in the Kitaev-Heisenberg magnet Na$_3$Co$_2$SbO$_6$

TL;DR

This study investigates the microscopic origins of Kitaev and related interactions in Na$_3$Co$_2$SbO$_6$, revealing significant Coulomb contributions and suggesting pathways to tune the material towards a Kitaev spin liquid state.

Contribution

It provides a detailed quantum chemical analysis of the Coulomb interactions and their role in Kitaev-Heisenberg magnetism in Na$_3$Co$_2$SbO$_6$, highlighting mechanisms previously overlooked.

Findings

Kitaev and off-diagonal $ ext{Gamma}$ interactions are substantial and antiferromagnetic.

Direct Coulomb exchange and multiconfigurational effects significantly contribute to nearest-neighbor couplings.

These mechanisms differ from traditional models and suggest new avenues for tuning magnetic interactions.

Abstract

The detection of considerable spin frustration in honeycomb cobalt oxide compounds indicates the presence of sizable Kitaev interactions in these systems, enlarging the pool of Kitaev spin liquid candidates. Several key questions remain to be answered, as basic as the mechanisms behind Kitaev couplings in Co$^{2+}$ $t_{2g}^5e_g^2$ magnets. Analyzing the quantum chemistry of interacting magnetic moments in Na$_3$Co$_2$SbO$_6$, a representative $LS$-coupled $t_{2g}^5e_g^2$ oxide, we find that the Kitaev and off-diagonal $\Gamma$ interactions are substantial and antiferromagnetic but somewhat weaker than the Heisenberg contribution. All nearest-neighbor couplings feature massive contributions from direct Coulomb exchange and/or on-site multiconfigurational dressing, mechanisms not considered so far in descriptive models of Kitaev-Heisenberg magnetism. These findings call for systematic wave-function quantum chemical studies in order to understand direct-indirect exchange synergies in Kitaev-Heisenberg magnets and how to possibly tune intersite couplings towards the Kitaev spin liquid ground state.