Superconductive Coupling Effects in Selectively Grown Topological Insulator-Based Three-Terminal Junctions

The combination of an ordinary s-type superconductor with three-dimensional topological insulators creates a promising platform for fault-tolerant topological quantum computing circuits based on Majorana braiding. The backbone of the braiding mechanism are three-terminal Josephson junctions. It is crucial to understand the transport in these devices for further use in quantum computing applications. We present low-temperature measurements of topological insulator-based three-terminal Josephson junctions fabricated by a combination of selective-area growth of Bi0.8Sb1.2Te3 and shadow mask evaporation of Nb. This approach allows for the in situ fabrication of Josephson junctions with an exceptional interface quality, important for the study of the proximity-effect. We map out the transport properties of the device as a function of bias currents and prove the coupling of the junctions by the observation of a multiterminal geometry-induced diode effect. We find good agreement of our findings with a resistively and capacitively shunted junction network model.