Geometry and Topology in van der Waals Superconducting Devices

Abstract

Non-Abelian anyons are particles that achieve unique non-commutative exchange statistics, in contrast to the typical fermionic and bosonic statistics. One route towards the observation of these anyons is the realization of topological superconductivity, which can be accomplished by interfacing certain topological states with superconductivity. In this dissertation, we develop superconducting devices based on van der Waals materials, which are designed as potential platforms to study topological superconductivity. We first present the study of a device combining superconductivity with the fractional quantum Hall effect in graphene, and our observation of a crossed Andreev reflection signal indicating the coexistence of these two effects. Our observed signal has marked differences in certain fractional fillings, signifying that the mechanism may be unique in this case. We then present the study of Josephson junctions on graphene proximitized by CrPS4. Superconducting transport shows clear hallmarks of a magnetic proximity effect, with possible applications towards tunable topological superconductivity. We finally present two studies of Corbino-geometry Josephson junctions on the surface of a three-dimensional topological insulator (3DTI). The first study showcases a novel diode effect, where the polarity robustly alternates its sign depending on the parity (even or odd) of the enclosed vortex number. This behavior is absent in devices controlling for two distinct effects, indicating that the polarity-tunable JDE is intrinsically linked to the unique combination of the proximitized topological superconductivity in the 3DTI surface and the Corbino device's closed-loop geometry. The second study showcases signatures of vortex dynamics, where controllable vortex collision leads to the suppression of AC Josephson effects. These two experiments establish the Corbino-geometry 3DTI junction as a promising platform for realizing non-Abelian exchange statistics. While many open questions remain, this work showcases the possibilities for new topological superconducting devices based on van der Waals materials.