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The recent prediction that honeycomb lattices of Co2+ (3d7) 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. Na3Co2SbO6 has been singled out as a potential material candidate provided that spin and
orbital moments couple into a Jeff = 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 Co2+ ions and test the validity of the
Jeff = 1/2 description of the electronic ground state. The results lend experimental support to recent theoretical predictions that a compression (elongation) of CoO6 octahedra along (perpendicular to) the trigonal axis would drive this cobaltate toward the Kitaev limit, assuming the Jeff = 1/2 character of the electronic ground state is preserved.
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