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American Physical Society


We report observations of the zero-field resistive transitions of superconducting quench-condensed Bi0.97Tl0.03 films both near electrically isolated normal-metal ground planes and on clean fire-polished glass. Transition temperatures, obtained by fitting the data with the two-dimensional Aslamazov-Larkin theory of fluctuation conductance, were found to be significantly enhanced for films deposited over ground planes versus those deposited onto insulating substrates. Conductivity enhancement due to superconducting fluctuations was found to be much less than expected for the thinnest samples. This suppression was coincident with broadened superconductor transitions that are consistent with nonuniform sample thickness. Sufficiently thick films showed reasonable agreement with both the fluctuation theory and assumption of uniformity. We discuss discrepancies between our fits and the theory within the context of film morphology.

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