Yale University

High temperature metals and insulators

Abstract: It is a common belief that low frequency dynamics and thermodynamics of macroscopic collections of interacting quantum particles at finite temperature should quite generally be describable in terms of effective classical models, e.g. possess finite transport coefficients and be capable of equilibrating. One known exception from this rule is the superconductor. Another was recently proposed by Basko and collaborators(cond-mat/0506617). Specifically, they argue that strongly disordered but weakly interacting electrons can have an insulating phase (with DC conductivity strictly zero) terminating in a phase transition to a metal at some finite temperature, Tc. Existence of a true insulator in this system is a manifestation of quantum interference over macroscopic length scales.

Armed with results of exact diagonalization on finite lattices and high temperature expansion for dynamic correlations we study emergence of dissipation in a simple model system of interacting spinless fermions in the presence of quenched impurities. The phase transition of Basko et.al. can be accessed here already at infinite temperature by varying disorder strength. First, we find that for sufficiently weak disorder the system is metallic and finite size analysis allows for an accurate extrapolation of dynamic properties (e.g. conductivity) in the infinite volume limit. When disorder is strong we find an apparently insulating phase with vanishingly small conductivity. We also study the transition between these two regimes.