We have fabricated two-dimensional (2D) small-Josephson-junction arrays of which each Al-AlOx-Al junction is shunted by a Cr resistor. The arrays with large junction resistance and large charging energy show a transition from insulating to superconducting behavior when the shunt resistance is lowered below a critical value, which is close to 2R(Q) ( R(Q) identical withh/4e(2) = 6.45 kOmega). The measured phase diagram is consistent with theories of quantum-fluctuation-driven and dissipation-driven phase transitions in the 2D Josephson-junction array with Ohmic shunt resistors.
We have analyzed the temperature dependence of the electrical conductivity of a series of metallic samples of Ge:Sb in the temperature range 10 mK to 1 K. We find a temperature dependence that is consistent with a sum of the behaviors predicted by Coulomb interactions and localization theories. The observed density dependence of the Coulomb contribution is consistent with theory but its magnitude differs by a factor of up to 4 if intervalley scattering is neglected. With our fitting procedure the dominant inelastic scattering process is electron-electron with a density dependence in reasonable agreement with theory. The magnitude of this scattering is enhanced by a factor of -2 over the
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