Effective field theory of local moment formation in disordered metals.

We present a simple new effective-field theory for the metallic state of a disordered interacting Fermi liquid. The theory properly accounts for the instability of an interacting electron gas towards the formation of local moment states; such instabilities can occur even in the presence of weak disorder under conditions in which all of the mean field single-quasiparticle states are extended. The theory justifies in part the phenomenological models of the disordered state used to understand recent experiments in phosphoros-doped silicon. It should also serve as an improved starting point for a complete theory of the metal-insulator transition in disordered systems.