Ground state, collective mode, phase soliton and vortex in multiband superconductors

Abstract

This article reviews theoretical and experimental work on the novel physics in multiband superconductors. Multiband superconductors are characterized by multiple superconducting energy gaps in different bands with interaction between Cooper pairs in these bands. The discovery of prominent multiband superconductors MgB2 and later iron-based superconductors, has triggered enormous interest in multiband superconductors. The most recently discovered superconductors exhibit multiband features. The multiband superconductors possess novel properties that are not shared with their single-band counterpart. Examples include: the time-reversal symmetry broken state in multiband superconductors with frustrated interband couplings; the collective oscillation of number of Cooper pairs between different bands, known as the Leggett mode; and the phase soliton and fractional vortex, which are the main focus of this review. This review presents a survey of a wide range of theoretical exploratory and experimental investigations of novel physics in multiband superconductors. A vast amount of information derived from these studies is shown to highlight unusual and unique properties of multiband superconductors and to reveal the challenges and opportunities in the research on the multiband superconductivity.

Spectroscopic signatures of time-reversal symmetry breaking superconductivity

“…Given the relative phase is pinned to a fixed value, one expects the collective mode spectrum to include a massive mode corresponding to fluctuations of ϕ around 0, π. This expectation is correct, and the mode in question is the well-known Leggett mode [33], the properties of which have been thoroughly established from microscopic calculations [34].…”

Superconducting junction with tri-component pairing gap functions

“…Mixed gap function symmetries breaking time-reversal symmetry have also been proposed in the iron-based superconductors 62,63 and other related systems, such as s+id 62,[64][65][66][67][68][69] , s+is 63,[69][70][71][72][73][74][75][76] . On the other hand, the interplays among three or more different superconducting order parameters remain less explored [77][78][79] .…”

Quasiparticle Bound States around Fractional Vortices in s-wave Superconductor

“…In both cases, the magnetic flux of a vortex is fractionally quantized. Fractionally-quantizedflux vortices have been discussed in multi-component superconductors [2,5,6]. Machida et al suggested that half fractionally-quantized-flux vortices spontaneously emerge in corners of d-wave superconductor dot embedded in s-wave superconducting matrix due to the phase interference between superconducting order parameters with different symmetries.…”