arXiv:cond-mat/0603603 · Physical Review B

Stability conditions and Fermi surface topologies in a superconductor

Elena Gubankova, Andreas Schmitt, Frank A. Wilczek

Published Aug 11, 2006• 43 citations

Abstract

Candidate homogeneous, isotropic superfluid or superconducting states of paired fermion species with different chemical potentials, can lead to quasiparticle excitation energies that vanish at either 0, 1, or 2 spheres in momentum space. With no zeros, we have a conventional BCS superconductor. The other two cases, ``gapless'' superconductors, appear in mean- field theory for sufficiently large mismatches and/or sufficiently large coupling strengths. Here we examine several stability criteria for those candidate phases. Positivity of number susceptibility appears to provide the most powerful constraint, and renders all the two-zero states that we have examined mechanically unstable. Our results should apply directly to ultracold fermionic atom systems.

DOI: 10.1103/physrevb.74.064505

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