SUPPRESSION OF SUPERCONDUCTIVITY BY MAGNETIC-FIELD IN QUENCH-CONDENSED ULTRATHIN FILMS OF INDIUM

Current-voltage characteristics and magnetoresistance are measured in an ultrathin film of indium with a mean-field transition temperature T (c0) = 4.3 K. They show similar power-law behaviors of the forms V is- proportional-to I(a) and R is-proportional-to B(b). The results are ex plained in terms of vortex unbinding by a current and a magnetic field , implying that the superconducting transition is of the Kosterlitz-Th ouless type. A magnetic field is also used to tune a thinner film with T(c0) almost-equal-to 3.9 K through the superconductor-insulator tran sition. The temperature- and magnetic-field-dependent resistance obeys the scaling function proposed by Fisher with a critical exponent z(B) nu(B) almost-equal-to 0.5, which is somewhat smaller than has been pre dicted.