Description:

Title: Time-reversal symmetry breaking in multiband superconductors with frustration: the soft Leggett mode and spontaneous magnetization

Speaker: Dr. Shizeng Lin, Los Alamos National Lab

Abstract:

The discovery of MgB2 and iron-based superconductors has reopened intense and exciting discussions on multiband superconductors. The multiband superconductors can support novel phenomena, without counterparts in single-band superconductors. The presumably sign-reversal pairing symmetry (s+-) in iron-based superconductors is particularly interesting, because it can induce frustration among different bands for more-than-two bands systems. When the superconductor is optimally frustrated, the time-reversal symmetry breaking (TRSB) transition occurs even in conventional multiband BCS superconductors. This results in a new state with s+is pair symmetry. In the vicinity of TRSB, the neutral Leggett mode associated with out-of-phase oscillations of the superconductivity phases becomes soft. In the state with TRSB, magnetic flux is induced in the presence of non-magnetic impurities.

In this talk, I will briefly introduce the novel physics associated with multiband superconductors. I will present our results on the TRSB state and the soft collective modes in conventional multiband BCS superconductors. Possible experimental realization of TRSB in iron-based superconductors will also be discussed. Finally I will discuss a way to distinguish the s+is from the s+id pairing symmetry by checking the pattern of the spontaneous magnetization induced by impurities.

Keywords: Physics, Astronomy, CMP