Anomalous Josephson current in superconducting topological insulator

TL;DR

This paper explores how helical Majorana fermions on the surface of superconducting topological insulators influence Josephson currents, revealing unique current-phase relations and temperature behaviors that serve as experimental signatures.

Contribution

It demonstrates the impact of surface helical Majorana fermions on Josephson effects in superconducting topological insulators, highlighting distinctive current-phase relations and temperature dependence.

Findings

Robust sin(2φ) current-phase relation in STI/s-wave junctions

Nonmonotonic temperature dependence of maximum Josephson current in STI/STI junctions

Potential experimental signatures for detecting helical Majorana fermions

Abstract

We investigate the effect of helical Majorana fermions at the surface of superconducting topological insulators (STI) on the Josephson current by referring to possible pairing states of Cu-doped Bi2Se3. The surface state in the present STI has a spin helicity because the directions of spin and momentum are locked to each other. The Josephson current-phase relation in an STI/s-wave superconductor junction shows robust sin(2{\phi}) owing to mirror symmetry, where \phi denotes the macroscopic phase difference between the two superconductors. In contrast, the maximum Josephson current in an STI/STI junction exhibits a nonmonotonic temperature dependence depending on the relative spin helicity of the two surface states. Detecting these features qualifies as distinct experimental evidence for the identification of the helical Majorana fermion in STIs.