Microwave Conductivity of Granular Superconducting Aluminum Films

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Abstract
Measurements of the transmission amplitude and phase of 20 GHz microwaves through superconducting granular aluminum films were made as a function of temperature from 4.2° to 1.75°K. The films were fabricated by vacuum deposition in the presence of controlled amounts of oxygen, and exhibited small grain size (∼40 Å) and enhanced transition temperatures of up to 2.86°K. The temperature coefficients of resistance (TCR) for the films ranged from slightly positive to almost zero, and for several films the TCR was negative. For all films measured, the microwave transmission data agreed very well with that computed by using the Mattis and Bardeen conductivity functions.

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