Hall bar measurements of topological surface states of (001) cadmium arsenide thin films interfaced with superconductors

Abstract

Hybrid structures consisting of a topological insulator brought in proximity to an $s$-wave superconductor are one of the most promising routes to topological superconductivity and Majorana quasiparticles. A key challenge is the superconductor/topological insulator interface, which must be transparent to Cooper pairs while also preserving high-mobility topological states. Here, we investigate Hall bar devices fabricated on the topological insulator-like surfaces of (001) cadmium arsenide films, which we partially cover with different superconductors. We show that, depending on the magnitude of a perpendicular magnetic field, devices with sputter-deposited Nb exhibit superconductivity and the quantum Hall effect from the topological surface states, respectively. By contrast, devices with thermally evaporated Sn do not show superconductivity, indicating poor interface transparency. We discuss the coupling between the superconductor and the surface states.