In recent years, researchers have successfully produced an array of crystalline materials only one or a few atoms thick with nearly perfect structure. It has also become possible to manipulate these crystals and select where they are placed. A question that is attracting increasing attention pertains to how electrons move when two such atomically thin crystals are placed in direct contact (i.e., on top of each other) to form an interface. Here, we show that the interaction at the interface can be so strong that it affects not only how the electrons move in space but also their internal quantum degree of freedom, known as spin.
At interfaces formed between graphene and materials known as transition metal dichalcogenides, we find that electrons experience an extremely strong interaction between their orbital motion and spin degree of freedom. Such a phenomenon is called a spin-orbit interaction, and it is at the basis of many new counterintuitive physical effects that are the subject of current research. One example is the occurrence of so-called two-dimensional topological insulators, systems that are conducting at their edges and insulating in their interiors. These systems have been predicted to exist by theoretically studying how spin-orbit interactions influence the properties of graphene. In bare graphene, however, the spin-orbit interaction is too weak to observe the effect experimentally. We recover unexpected findings when interfaces are formed with transition metal dichalcogenides (e.g., , , and ), and we find that spin-orbit interactions are extremely strong and independent of the thickness of the graphene multilayer. Furthermore, the presence of large spin-orbit interactions does not damage the electronic properties of graphene.
We expect that our results will pave the way for future studies of spin-dependent transport phenomena such as topological insulating states.
