Quantum Hall Effect-Mediated Josephson Junctions in Graphene

Abstract

Evidence supporting the existence of Majorana bound states has been observed in systems such as superconducting proximitized semiconducting nanowires, atomic chains and topological insulators. This dissertation explores the possibility of engineering these states in graphene quantum Hall states hybridized with superconducting niobium nitride (NbN) one-dimensional wires. Stepwise modulations of the critical current of graphene Josephson junctions in the quantum Hall regime were observed, with the origin being attributed to the change in the number of underlying quantum Hall edge states in graphene. This is the first observation of the superconducting coupling between a superconductor and quantum Hall edge states showing up as changes in the critical current of a Josephson junction. Further theoretical calculations corroborated the conjecture that topological gaps would open up in quantum Hall-superconductor systems, allowing for the generation of not only Majorana bound states, but a myriad of topological states that are inaccessible in other systems mentioned above.