Spin-Orbit induced phase-shift in Bi$_{2}$Se$_{3}$ Josephson junctions

TL;DR

This paper reports the observation of an anomalous phase shift in Bi$_2$Se$_3$ Josephson junctions caused by spin-orbit coupling and magnetic field, revealing new ways to control superconducting phases in topological insulators.

Contribution

It demonstrates the direct measurement of an anomalous phase shift in topological insulator-based Josephson junctions, linking it to spin-orbit coupling effects.

Findings

Observation of an anomalous phase shift $$ in Bi$_2$Se$_3$ junctions

Direct measurement of spin-orbit coupling strength

Potential for phase-controlled Josephson devices

Abstract

The transmission of Cooper pairs between two weakly coupled superconductors produces a superfluid current and a phase difference; the celebrated Josephson effect. Because of time-reversal and parity symmetries, there is no Josephson current without a phase difference between two superconductors. Reciprocally, when those two symmetries are broken, an anomalous supercurrent can exist in the absence of phase bias or, equivalently, an anomalous phase shift $\varphi_0$ can exist in the absence of a superfluid current. We report on the observation of an anomalous phase shift $\varphi_0$ in hybrid Josephson junctions fabricated with the topological insulator Bi$_2$Se$_3$ submitted to an in-plane magnetic field. This anomalous phase shift $\varphi_0$ is observed directly through measurements of the current-phase relationship in a Josephson interferometer. This result provides a direct measurement of the spin-orbit coupling strength and open new possibilities for phase-controlled Josephson devices made from materials with strong spin-orbit coupling.