Unconventional pairing in anomalous superconductors

The existence of unconventional pairing (p- or d-wave) in the high T-c cupr ate and heavy fermion superconductors raises many important questions. The unusual pairing state suggests novel pairing mechanisms, and may also be re lated to other 'anomalous' normal state effects such as heavy fermion behav iour, magnetic fluctuations or the normal state pseudogap. In this context, it is interesting to ask whether other classes of anomalous superconductor s also may have p- or d-wave pairing states. Indeed there is now strong evi dence for p-wave pairing in Sr2RuO4, and some indications of d- or p-wave p airing in some organic superconductors. This article summarises some of the evidence indicating either conventional s-wave, or unconventional p- or d- wave pairing in various anomalous systems including the ruthenates, organic s, boro-carbides, bismuthates, fullerenes, and C15s. (C) 1999 Elsevier Scie nce B.V. All rights reserved.