Maximized K/J ratio and cubiclike jeff=12 moments in a noncubic environment in

Pritam Bhattacharyya,Liviu Hozoi, Sei‐ichi Nishimoto,Quirin Stahl, J. Geck,Nikolay A. Bogdanov

Maximization of the ratio between Kitaev and residual Heisenberg interactions is a major goal in the current research on Kitaev-Heisenberg magnets. Here we investigate Kitaev-Heisenberg exchange in a recently discovered crystalline phase of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{RuCl}}_{3}$ under pressure---it displays unusually high symmetry, with only one type of Ru-Ru links and uniform Ru-Cl-Ru bond angles of $\ensuremath{\approx}{93}^{\ensuremath{\circ}}$. Using quantum chemical calculations, we find a very small nearest-neighbor Heisenberg $J$, which yields a $K/J$ ratio between Kitaev and Heisenberg exchange as large as $\ensuremath{\sim}100$. We also find that this is associated with vanishingly small $d$-shell trigonal splittings, i.e., minimal departure from ideal ${j}_{\mathrm{eff}}=1/2$ moments. This reconfirms ${\mathrm{RuCl}}_{3}$ as a most promising platform for materializing the much sought-after Kitaev spin-liquid phase and should stimulate further experiments under strain and pressure.