Electronic structure of Co 3d states in the Kitaev material candidate honeycomb cobaltate Na3Co2SbO6 probed with x-ray …

The recent prediction that honeycomb lattices of ${\mathrm{Co}}^{2+}$ $(3{d}^{7})$ 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.