New Paradigm of Triplet Superconductivity

Since 1980, more than 10 or so triplet superconductors have been discovered.Now we can put them into two separate classes.Type A consists of e.g.(TMTSF) 2 PF 6 , (TMTSF) 2 ClO 4 , UPt 3 , Sr 2 RuO 4 , PrOs 4 Sb 12 .These triplet superconductors are characterized with the extreme smallness of the spin-orbit coupling energy E so ( ∆, where ∆ is the superconducting gap).Also like superfluid 3 He-A, the order parameter of these superconductors are characterized by l (the chiral vector) and d (the spin vector).In these superconductors, an Abrikosov vortex splits into a pair of half quantum vortices at low temperatures.Type A1 comprises most of non-centrosymmetric triplet superconductors discovered recently, e.g.CePt3Si, CeIrSi3, CeRhSi3, and Li2Pt3B.They are characterized by l and d1 + i d2 like superfluid 3 He-A1.The spin-orbit coupling energy Eso is extremely large Eso ≈ 10 3 K.Therefore, as noted by Frigeri et al., the Fermi surface splits for the up-spin one and the down-spin one.However, contrary to Frigeri et al., the superconductivity should occupy only the larger Fermi surface (say for spin-up).The other Fermi surface remains in the normal state.Also in type A1 superconductors, an Abrikosov vortex does not split into a pair of half quantum vortices.Further all thase triplet superconductors (both type A and type A1) harbor the zero mode or the Majorana fermion attached to each vortex, of which implication should be further explored.