In a quasi-one-dimensional metal a density wave gaps the nested parts of the Fermi surface, but an antinesting term leaves ungapped pockets (imperfect nesting). This concept covers how, at arbitrary antinesting, the quasiparticle density of states develops a step singularity and a logarithmic van Hove divergence, which renormalize the superconducting transition temperature only through the BCS pre-exponential factor (a power law, not an added exponential suppression) and produce only a small resistivity increment across the density-wave transition.
In a quasi-one-dimensional metal, a density wave (DW) opens a gap on the nested parts of the Fermi surface, but a small 'antinesting' term in the electron dispersion leaves ungapped Fermi-surface poc…