Superconductive coupling and Josephson diode effect in selectively-grown topological insulator based three-terminal junctions

TL;DR

This study investigates three-terminal topological insulator Josephson junctions, revealing superconductive coupling and diode effects, which are crucial for advancing topological quantum computing with Majorana modes.

Contribution

It demonstrates high-quality fabrication and detailed transport analysis of topological insulator-based three-terminal Josephson junctions, highlighting their potential for quantum computing applications.

Findings

Observation of superconductive coupling in the junctions

Detection of a multi-terminal geometry induced diode effect

Good agreement with a RCSJ network model

Abstract

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 $\mathrm{Bi_{0.8}Sb_{1.2}Te_3}$ 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 multi-terminal geometry induced diode effect. We find good agreement of our findings with a resistively and capacitively shunted junction network model.