Research: Effect of hydrogen order on Kitaev exchange in H3LiIr2O6

Very recently it was reported by Kitagawa et al. in Nature, 554, 341 (2018)
that the iridate H₃LiIr₂O₆ exhibits a Kitaev spin-liquid (SL) state. To test the
possibility for Kitaev-type SL formation in this system, we performed detailed
quantum chemistry calculations to determine the magnetic interactions between
neighbouring Ir moments in H₃LiIr₂O₆ and computed the magnetic phase diagram.
We find that the nearest-neighbor Kitaev exchange indeed dominates
over other couplings. However the calculations also show a very strong dependence
of the magnetic interactions on the position of hydrogen cations next to
a Ir₂O₂ plaquettes. For example, spreading out the charges of hydrogen cations
in between the honeycomb planes increases the in-plane Kitaev exchange by
more than a factor of three - an extremely strong effect indeed. Our results
show that hydrogen vacancies and misalignment of honeycomb layers will very
strongly affect the magnetic interactions in H₃LiIr₂O₆ and can strongly enhance
spin-disordering.

R. Yadav, R. Ray, M. S. Eldeeb, S. Nishimoto, L. Hozoi, J. van den Brink,
Strong effect of hydrogen order on magnetic Kitaev interactions in H₃LiIr₂O₆,
Phys. Rev. Lett. 121, 197203 (2018)