LOW-TEMPERATURE INSULATING PHASES OF UNIFORMLY DISORDERED 2-DIMENSIONAL SUPERCONDUCTORS

Temperature- and magnetic-field-dependent measurements of the longitudinal R(xx) and transverse R(xy) resistance of amorphous indium oxide thin-film superconductors reveal the presence of distinct insulating phases for sufficiently high disorder and/or magnetic field. For field-swept transitions at fixed disorder and low temperatures there is a critical field where R(xx) diverges and the superconductor is transformed into a Bose-glass insulator with localized Cooper pairs. At higher fields there is a second critical field where R(xy) appears to diverge, the pairs unbind, and localized single electrons characterizing a Fermi-glass insulator dominate.