Classification of unconventional electron-hole condensates

Abstract

Heavy Fermion metals with their very anisotropic quasiparticle states may support unconventional electron-hole (Peierls) pairing in addition to unconventional two electron (Cooper) pairs in the superconducting phase. For two different nesting Fermi surface models the possible types of electron hole condensates are classified according to the symmetries of their order parameters. This is performed within a continuum representation for the electronic states near the van Hove saddle point singularities. The quasiparticle bands and the unitary transformation to Bloch states in the condensed phase are derived for the two Fermi surface models with one and two independent nesting vectors respectively. Emphasis is put on the investigation of electron-hole condensed phases with 2Q-modulated structure. It is shown that in the continuum approximation the gap equations are all equivalent and the critical field curve is calculated in the rigid band model.