Josephson effect between a two-band superconductor with the s++ or s+- pairing symmetry and a conventional s-wave superconductor

TL;DR

This paper explores the Josephson effect between two-band superconductors with s++ or s± pairing symmetries and conventional s-wave superconductors, revealing new plasma modes, TRS breaking, and signatures of pairing symmetry.

Contribution

It introduces the analysis of plasma modes, flux dynamics, and TRS breaking in Josephson junctions with different pairing symmetries, highlighting novel phenomena and experimental signatures.

Findings

Discovery of a new plasma mode in charge neutrality breaking junctions.

Identification of TRS breaking states with non-trivial phase differences.

Observation of spontaneous magnetic flux as evidence of pairing symmetry.

Abstract

In this work, we investigate the Josephson effect between a two-band superconductor either with the $s++$ (two energy gaps have the same sign and are fully gapped) pairing symmetry or $s\pm$ (two energy gaps have $\pi$ phase difference and are fully gapped) pairing symmetry and a conventional s-wave superconductors. The ground state, critical current, plasma modes, flux flow dynamics, and response to external ac electric field, possible soliton solutions are investigated. For junctions with the charge neutrality breaking, we find a new plasma mode for junctions, which gives rise to new resonance peaks in the Josephson flux flow region. Because of the frustrated interaction in junctions with $s\pm$ pairing symmetry, time-reversal-symmetry (TRS) can be broken if the frustration is optimized. In the TRS broken (TRSB) state, there is a non-trivial phase difference between the two Josephson tunnelling channels, which results in a non-trivial interference. Furthermore, we find a novel massless plasma mode at the TRSB transition for junctions with the charge neutrality breaking. In the TRSB state, a spontaneous magnetic flux appears where there is a spatial inhomogeneity in the Josephson coupling, thus provides a possible smoking-gun evidence for the underlying pairing symmetry.