K. Inagaki, S. Tanda and T. Nakayama
We have observed the nonlinear current-voltage characteritics of Bi2Sr2CuO6 single crystals in the weakly localized regime (WLR), in which the conductivity indicates a logarithmic dependece both on temperature and on magnetic fields. The conductivity in low voltage remains constant (Ohmic behavior). Upon application of a voltage higher than the threshold electric field 0.1V/cm, the conductivity begins to increase. The observed threshold of the electric field is much smaller than the value of 200V/cm estimated from the model which Anderson et al. (1979) introduced to explain the nonliner conductivity shown in the WLR of thin metal films.
We have measured temperature-dependent resistivities of a set of Pb ultrathin films by repeating in situ deposition at liquid-He temperature. Observed conductance in the fermion region can be described by a single-parameter scaling function ( beta function) with a self-consistent theory for localization in two dimensions. Based on estimated values of electrical localization length ( xi /sub loc/) and superconducting coherence length ( xi /sub super/) the superconductor- insulator transition is confirmed to occur at the point where xi /sub loc/~2 xi /sub super/. Moreover, only samples exhibiting lnT dependence in the fermion region become global coherent superconductors at low temperature.
Transport properties of Bi/sub 2/Sr/sub 2/CuO/sub 6/ single crystals, including the electric conductivity magnetoresistance, and Hall coefficient, were measured. Characteristics of the conductivity in the weakly localized regime, which includes temperature, electric field, and magnetic field, were also measured. The coefficient of 1n H was found to be much smaller than the theoretical value predicted for the weakly localized regime. Measurement of the Hall coefficient indicates that the electron-electron interaction does not play a significant role in the conductivity. Rather, interplane coupling appears to play a role in the transport properties of this system.