Type-IV Superconductivity: Cooper Pairs with Broken Inversion and Time-Reversal Symmetries in Conventional Superconductors

TL;DR

This paper predicts a new type of superconductivity, called type-IV, where Cooper pairs break inversion and time-reversal symmetries, leading to mixed singlet-triplet states in vortex phases of clean superconductors.

Contribution

It introduces the concept of type-IV superconductivity with symmetry-breaking triplet components in vortex phases of conventional superconductors.

Findings

Triplet components destabilize vortex phases in clean superconductors.

Symmetry breaking effects are significant when Hc2(0) is comparable to Hp.

Type-IV superconductivity may be observable in organic, high-Tc, and MgB2 superconductors.

Abstract

Vortex phase in a singlet superconductor in the absence of impurities is shown to be absolutely unstable with respect to the appearance of a triplet component which breaks both inversion and time-reversal symmetries of Cooper pairs. Symmetry breaking paramagnetic effects are demonstrated to be of the order of unity if the orbital upper critical field, Hc2(0), is of the order of Clogston paramagnetic limiting field, Hp. We suggest a generic phase diagram of such type-IV superconductor, which is singlet one at H=0 and characterized by mixed singlet-triplet order parameter with broken time-reversal symmetry in vortex phase. A possibility to observe type-IV superconductivity in clean organic, high-Tc, MgB2, and other superconductors is discussed.