Searching for a quantum spin liquid in a two-dimensional magnet

Alpha-ruthenium(III) chloride (α-RuCl3) is a layered magnetic insulator that can be cleaved down to a single molecular sheet. This material is a promising candidate to host the Kitaev quantum spin liquid, an intriguing phase of matter expected to be an ideal platform for topological quantum computation. We use electronic and optical probes to investigate α-RuCl3 as a function of temperature, external magnetic field, and sample thickness to gain information about its physical structure and magnetism down to the single layer limit. Remarkably, we find that when we place α-RuCl3 in contact with a sheet of the single-atom-thick carbon-based semimetal graphene, we observe evidence of charge transfer between the two materials, despite the electrically insulating nature of α-RuCl3. When we physically separate α-RuCl3 from graphene with the atomically-thin insulator boron nitride, we detect signatures of a magnetic phase transition in α-RuCl3 electronically via the proximate graphene layer. We discuss how these layered material heterostructures present novel platforms to explore magnetism and quantum spin liquid physics in two-dimensional materials.