Fermi Surfaces, Fermi Liquids, and High-Temperature Superconductors

Recent experimental results are beginning to limit seriously the theories that can be considered to explain high-temperature superconductivity. The unmistakable observations of a Fermi surface, by several groups and methods, make it the focus of realistic theories of the metallic phases. Data from angle-resolved photoemission, positron annihilaton, and de Haas-van Alphen experiments are in agreement with band theory predictions, implying that the metallic phases cannot be pictured as doped insulators. The character of the low energy excitations ("quasiparticles"), which interact strongly with atomic motions, with magnetic fluctuations, and possibly with charge fluctuations, must be sorted out before the superconducting pairing mechanism can be given a microscopic basis.