Triplet superconductivity in a nutshell

Abstract

The triplet superconductors have been around us since 1980, when Jerome et al. discovered the Bechgaard salts (TMTSF) 2PF 6 and (TMTSF) 2ClO 4. Now there are more than 20 or so triplet superconductors discovered. Recently we found that most of them with the known gap symmetries can be mapped to the superfluid phase of 3He-A and 3He-A 1. Further, in most of them, hat{l} (the chiral vector, i.e. the quantization axis of the pair angular momentum) is fixed parallel to one of the crystal axes and all the topological defects are considered in terms of \hat{d} -textures, where \hat{d} is the spin vector. Then Sr 2RuO 4, UPt 3, PrOs 4Sb 12 and (TMTSF) 2ClO 4 belong to type-A, which is an analog of superfluid 3He-A. In these superconductors, a vortex splits into a pair of half quantum vortices (HQVs) at low temperatures. On the other hand, CePt 3Si, CeIrSi 3, CeRhSi 3, UIr and Li 2Pt 3B (those in non-centrosymmetric crystals) belong to type-A 1, which is an analog of superfluid 3He-A 1. In all of these triplet superconductors, vortices harbor the zero mode or the Majorana fermions, the implications of which deserves further exploration. © 2008 The Author(s).