PHENOMENOLOGY OF THE NORMAL AND SUPERCONDUCTING STATES OF A MARGINAL FERMI-LIQUID (INVITED)

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 4-DELTA 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.