Phenomenology of the normal and superconducting states of a marginal Fermi liquid (invited)

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Abstract
A metal with scattering from a flat frequency spectrum of particle-hole pairs is a ‘‘marginal’’ Fermi liquid, with infinite quasiparticle lifetime but a logarithmically vanishing spectral weight. In the superconducting state, the scattering spectrum should acquire a gap, and the quasiparticle character will be restored at low energies. Unless the scattering spectrum results from interband processes, the Drude-like component of the optical conductivity will then have an onset at 4Δ in the clean limit, twice the superconducting gap. Other experimental ramifications, in particular for tunnelling, NMR relaxation rate, thermal conductivity, and photoemission spectra are considered.