TRANSPORT-PROPERTIES OF THE DISORDERED CHARGED BOSE CONDENSATE IN 2 DIMENSIONS

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 density N(c)) the condensate exhibits metallic transport properties. An Ioffe-Regel criterion for the transition point is derived. The conductivity at the transition point is of order e2/h (h is Planck's constant) and depends on the kind of disorder. For charged impurities (with impurity density N(i)) the conductivity (for a condensate of particles with charge 2e and for N(i) = 2N(c)) at the transition point is given by sigma-c = 0.26 x (2e)2/h. We discuss recent experiments on superconducting ultra-thin films and on high-T(c) superconductors.