Transport properties of the disordered charged bose condensate in two dimensions

Abstract

Analytical results for the frequency-dependent conductivity of a disordered two-dimensional interacting Bose condensate are presented. Charged and uncharged impurities are considered. We find that for weak disorder the condensate is a superfluid while for strong disorder it is an insulator (a Bose glass). At the superfluid-insulator transition point (at the critical boson densityN c) the condensate exhibits metallic tranport properties. An loffe-Regel criterion for the transition point is derived. The conductivity at the transition point is of ordere 2/h (h is Planck's constant) and depends on the kind of disorder. For charged impurities (with impurity densityN i) the conductivity (for a condensate of particles with charge 2e and forN i=2N c) at the transition point is given by σ c =0.26x(2e)2/h. We discuss recent experiments on superconducting ultra-thin films and on high-T c superconductors.