Ab initio study for heterostructures of a Kitaev magnet α-RuCl₃ and CrX₃ (X=Cl and I)

The Kitaev model is a honeycomb spin model with bond-dependent anisotropic interactions, whose ground state features a quantum spin liquid with fractional excitations. Beyond the theoretical interest, it has also attracted much attention for the feasibility in real materials toward topological quantum computing. However, it remains a challenge to materialize the Kitaev spin liquid, especially at zero magnetic field, due to parasitic interactions beyond the Kitaev model. For instance, a prime candidate α-RuCl₃ exhibits a zigzag-type antiferromagnetic order at low temperature, albeit the hallmarks of the Kitaev spin liquid were observed only within a specific region in an applied magnetic field. Here, we propose a possible realization of the Kitaev spin liquid at zero field, by making van der Waals heterostructures of α-RuCl₃ and a ferromagnet CrX₃ (X=Cl and I). Using ab initio calculations, we find that in the case of X=Cl, the spin-orbit coupled Mott insulating state, which is a key to realizing the Kitaev-type interactions, is preserved in the heterostructure and the zigzag order is suppressed at zero field by the proximity of the XY ferromagnet CrX₃. In contrast, in the case of X=I, the Mott gap is almost closing, suggesting that the α-RuCl₃ layer is on the verge of an insulator-metal transition in the spin-orbit coupled bands. Our results indicate that van der Waals heterostructures provide a new platform for studying not only magnetic but also electronic properties of the Kitaev spin liquids.