Rare-Earth Chalcohalides: A Family of van der Waals Layered Kitaev Spin Liquid Candidates

The Kitaev spin liquid (KSL) system has attracted tremendous attention in recent years because of its fundamental significance in condensed matter physics and promising applications in fault-tolerant topological quantum computation. Material realization of such a system remains a major challenge in the field due to the unusual configuration of anisotropic spin interactions, though great effort has been made before. Here we reveal that rare-earth chalcohalides REChX (RE = rare earth; Ch = O, S, Se, Te; X = F, Cl, Br, I) can serve as a family of KSL candidates. Most family members have the typical SmSI-type structure with a high symmetry of R\bar3m, and rare-earth magnetic ions form an undistorted honeycomb lattice. The strong spin-orbit coupling of 4f electrons intrinsically offers anisotropic spin interactions as required by the Kitaev model. We have grown the crystals of YbOCl and synthesized the polycrystals of SmSI, ErOF, HoOF and DyOF, and made careful structural characterizations. We carry out magnetic and heat capacity measurements down to 1.8 K and find no obvious magnetic transition in all the samples but DyOF. The van der Waals interlayer coupling highlights the true two-dimensionality of the family which is vital for the exact realization of Abelian/non-Abelian anyons, and the graphene-like feature will be a prominent advantage for developing miniaturized devices. The family is expected to act as an inspiring material platform for the exploration of KSL physics.