Multi-Phase Physics of Multi-Condensate Superconductivity

Abstract

Multi-gap superconductors exhibit interesting properties. In N-gap superconductors, the U(1)N phase invariance is spontaneously broken. When N is greater than 2, N ≥ 3, several interesting phenomena will emerge due to the multi-band effect. Among them, the time-reversal symmetry breaking and the emergence of massless modes are significant. We consider a multi-band model with inter-band frustrated-Josephson couplings for general N. The conditions for the time-reversal symmetry breaking and the existence of massless modes are reduced to a simple form for the Josephson couplings in a separable form which we propose in this paper.