The recent prediction that honeycomb lattices of ${\mathrm{Co}}^{2+}$ $\left(3d^7\right)$ ions could host dominant Kitaev interactions provides an exciting direction for exploration of new routes to stabilizing Kitaev's quantum spin liquid in real materials. ${\mathrm{Na}}_3{\mathrm{Co}}_2{\mathrm{SbO}}_6$ has been singled out as a potential material candidate provided that spin and orbital moments couple into a $J_{\mathrm{eff}}=\frac{1}{2}$ ground state, and that the relative strength of trigonal crystal field and spin-orbit coupling acting on Co ions can be tailored. Using x-ray linear dichroism (XLD) and x-ray magnetic circular dichroism (XMCD) experiments, alongside configuration interaction calculations, we confirm the counterintuitive positive sign of the trigonal crystal field acting on ${\mathrm{Co}}^{2+}$ ions and test the validity of the $J_{\mathrm{eff}}=\frac{1}{2}$ description of the electronic ground state. The results lend experimental support to recent theoretical predictions that a compression (elongation) of ${\mathrm{CoO}}_6$ octahedra along (perpendicular to) the trigonal axis would drive this cobaltate toward the Kitaev limit, assuming the $J_{\mathrm{eff}}=\frac{1}{2}$ character of the electronic ground state is preserved.

• Received 27 March 2023
• Revised 23 May 2023
• Accepted 7 June 2023

DOI:https://doi.org/10.1103/PhysRevB.107.214443