Emergence of an Interband Phase Difference and Its Consequences in Multiband Superconductors

Since the idea of a topology based on the interband phase difference was proposed for multiband superconductors without degenerate superconducting components, many feasible and interesting possibilities have been explored. The basic concepts involved are an interband phase difference soliton , the fractionalization of the unit magnetic flux quantum, and frustration between quantum phases of multiple components. The superconductivity field was be extended by introducing the idea of the fluctuation in the interband phase difference. This extension provides a bridge between superconducting condensates and other macroscopic quantum mechanical systems such as Bose–Einstein condensates with multiple components and particle physics systems governed by a nonabelian gauge field. The entropy supported by the interband fluctuation suggests a relationship between multiband superconductors and highly correlated systems. In this chapter, I comment on the past, present, and future situation of multicomponent superconductivity based on multiband superconductors .