Josephson supercurrent in a topological insulator without a bulk shunt

TL;DR

This study demonstrates the induction of a Josephson supercurrent in a topological insulator, Bi1.5Sb0.5Te1.7Se1.3, with surface states dominating transport and negligible bulk contribution, confirmed through low-temperature measurements and Fraunhofer patterns.

Contribution

It provides experimental evidence of surface-state-dominated supercurrent in a topological insulator without bulk shunt, using nanoscale Josephson junctions and detailed transport analysis.

Findings

Supercurrent is surface-state dominated

Fraunhofer patterns confirm Josephson supercurrent

Critical current behavior matches diffusive models

Abstract

A Josephson supercurrent has been induced into the three-dimensional topological insulator Bi1.5Sb0.5Te1.7Se1.3. We show that the transport in Bi1.5Sb0.5Te1.7Se1.3 exfoliated flakes is dominated by surface states and that the bulk conductivity can be neglected at the temperatures where we study the proximity induced superconductivity. We prepared Josephson junctions with widths in the order of 40 nm and lengths in the order of 50 to 80 nm on several Bi1.5Sb0.5Te1.7Se1.3 flakes and measured down to 30 mK. The Fraunhofer patterns unequivocally reveal that the supercurrent is a Josephson supercurrent. The measured critical currents are reproducibly observed on different devices and upon multiple cooldowns, and the critical current dependence on temperature as well as magnetic field can be well explained by diffusive transport models and geometric effects.