| At certain quantum critical points in metals an entire Fermi surface may disappear. A crucial question is the nature of the electronic excitations at the critical point. Here we provide arguments showing that at such quantum critical points the Fermi surface remains sharply defined even though the Landau quasiparticle is absent. The presence of such a critical Fermi surface has a number of consequences for the universal phenomena near the quantum critical point which are discussed. Scaling hypotheses appropriate to a critical fermi surface are proposed. Experiments on heavy fermion critical points, and in the normal state of the cuprates are examined from this perspective. A theory of a continuous Mott transition in two dimensions is described. The Mott critical point is explicitly shown to possess a critical Fermi surface. Several interesting phenomena near the Mott transition are found. Implications for experiments in the organics are described. |
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