Induced superconductivity in thin films of cadmium arsenide

Topological superconductors can host non-Abelian quasiparticles that have profound implications for fault-tolerant quantum computing. Hybrid structures between topological insulators and superconductors are an attractive route towards a topological superconductor. Here, we report on induced superconductivity in Josephson junctions fabricated on the surface of thin films of cadmium arsenide (Cd₃As₂), which are tuned into different topological and trivial states, respectively, including a two-dimensional (2D) topological insulator (TI). The junctions are in a short junction limit with no hysteresis in their current-voltage characteristic and exhibit a 20 µeV induced superconducting gap. The measured superconducting quantum interference (SQI) pattern for mesa-isolated junctions fabricated on a film that is in a 2D TI state deviates from a Fraunhofer pattern that is expected for a junction with a bulk-dominated superconducting transport. Measurements of the SQI in Josephson junction and superconducting quantum interference (SQUID) device geometries, respectively allows us to separate the contribution of bulk and edge electronic states and determine current-phase relations of the junctions. We utilize electrostatic gating to tune the films into the gap of the insulating states and demonstrate gate-tuning between the bulk- and edge-dominated transport regimes.