Superconducting studies of large-scale structure in granular aluminum films
Harrington, Scott Nelson
Dodds, Stanley A.
Master of Arts
Critical field measurements have been performed on granular aluminum films with normal state resistivities ranging from 9x1^-3 Q-cm to 6x1^-5 Q-cm. These experiments indicate the presence of thin internal layers within the films. The layer thickness generally decreases as Pjj decreases, but there is no evidence of layering in the cleanest film. From the angular dependence of the critical field, it has been determined that the layers are essentially decoupled. The perpendicular critical field, H(T), has an anomalous upward curvature, which we are unable to explain. The fluctuation conductivity of the granular films was also measured. Using the layer thickness determined from critical field data, there is good agreement with the two-dimensional Aslamazov-Larkin theory for a moderately dirty film. There is also agreement with the magnitude at intermediate reduced temperatures in very dirty films, but a marked deviation from the theoretical prediction at high t is noted, possibly due to a continuous decoupling of grains within a layer. For the cleanest film, there is fair agreement with the theory if the Maki-Thompson term is included.