Kitaev exchange in new Ruthenium-based honeycomb and triangular lattice compounds

In the hunt for the realization of the celebrated Kitaev spin liquid, the (arguably) closest realization so far has been α-RuCl₃, which nevertheless orders with zigzag antiferromagnetic order.

In this ab-initio based study we consider new Ruthenium-based candidate materials: The honeycomb compounds RuBr₃, RuI₃ [1] and the triangular-lattice compound NaRuO₂. Our computed magnetic models contain large Kitaev and bond-dependent Gamma exchange in all cases, but feature different ground states. We compare to recent experimental data, which do not find magnetic order for RuI₃ and NaRuO₂.

Aside from frustrated bilinear exchange, four-spin ring exchange on the triangular lattice is an established mechanism to suppress magnetic order. In the Kitaev-candidate Ruthenates, spin-orbit coupling is expected to turn also such higher-order exchanges strongly anisotropic. We therefore systematically study the effects of such new SU(2)-breaking ring exchanges and compute them explicitly for NaRuO₂.

[1] Kaib et al., npj Quantum Materials 7, 75 (2022).