Three-band superconductivity and the order parameter that breaks time-reversal symmetry

TL;DR

This paper explores a three-band superconductivity model inspired by iron pnictides, revealing a novel time-reversal symmetry breaking state due to frustrated interactions, with implications for high-temperature superconductivity.

Contribution

It introduces a three-band model with repulsive interactions that predicts a new time-reversal symmetry breaking superconducting state, extending understanding beyond two-band models.

Findings

Identification of three distinct superconducting states including a time-reversal symmetry breaking state.

Construction of the phase diagram relevant to iron pnictides.

Analysis of Josephson coupling effects between different superconducting states.

Abstract

We consider a model of multiband superconductivity, inspired by iron pnictides, in which three bands are connected via repulsive pair-scattering terms. Generically, three distinct superconducting states arise within such a model. Two of them are straightforward generalizations of the two-gap order parameter while the third one corresponds to a time-reversal symmetry breaking order parameter, altogether absent within the two-band model. Potential observation of such a genuinely frustrated state would be a particularly vivid manifestation of the repulsive interactions being at the root of iron-based high temperature superconductivity. We construct the phase diagram of this model and discuss its relevance to the iron pnictides family of high temperature superconductors. We also study the case of the Josephson coupling between a two-band s' (or extended s-wave) superconductor and a single-gap s-wave superconductor, and the associated phase diagram.