Phase: Correlated Metal
Dynamical Mean-Field Theory (DMFT) maps a lattice of interacting electrons (Hubbard model) onto a single impurity coupled to a self-consistent bath. The key quantity is the spectral function A(ω) = −(1/π)Im G(ω+iη). For weak Hubbard U: a broad quasiparticle peak (metal). As U increases past W/2 (half-bandwidth), a Mott-Hubbard transition occurs: the peak splits into lower and upper Hubbard bands, and the system becomes an insulator. This metal-insulator transition is one of DMFT's major achievements (Georges et al 1996).