Massless Leggett Mode in Three-band Superconductors with Time-Reversal-Symmetry Breaking

TL;DR

This paper predicts a massless Leggett mode in three-band superconductors with TRSB, which could be experimentally detected and has significant thermodynamic implications.

Contribution

It introduces the existence of a massless Leggett mode in TRSB three-band superconductors, a novel phenomenon not previously identified.

Findings

Massless Leggett mode exists near TRSB transition

Mode is detectable via Raman spectroscopy

Impacts thermodynamic properties of superconductors

Abstract

The Leggett mode associated with out-of-phase oscillations of superconducting phase in multi-band superconductors usually is heavy due to the interband coupling, which makes its excitation and detection difficult. We report on the existence of a massless Leggett mode in three-band superconductors with time-reversal-symmetry-breaking (TRSB). The mass of the Leggett mode is small close to the TRSB transition and vanishes at the transition point, and thus locates within the smallest superconducting energy gap, which makes it stable and detectable. The mass of the Leggett mode can be measured by Raman spectroscopy. The thermodynamic consequences of this massless mode and possible realization in iron-based superconductors are also discussed.