Superconducting fluctuation conductivity in granular Al-Ge films above the metal-insulator transition

Abstract

Superconducting fluctuation conductivities and magnetoconductances have been measured in thin granular Al-Ge films above the superconducting transition temperature. For very metallic films located well above the metal-insulator transition, the two-dimensional Aslamazov-Larkin and Maki-Thompson theories describe the conductivity and magnetoconductance data well. The Maki-Thompson expressions involve the temperature-dependent pair-breaking parameter delta . For films located near the metal-insulator transition, we have observed a dimensional crossover from three dimensions to two dimensions to a fractal dimension with decreasing temperatures. Values for the diffusion constant, ranging from 0.4 to 1.4 cm2 s-1, were obtained from the magnetoconductance fits, and these magnitudes compared favourably with values obtained from critical-field measurements taken below Tc.