Localization and Superconductivity in Thin Films and Narrow Wires of Aluminum

The theory of localization predicts that constructive interference between electron waves scattered by impurities results in a quantum correction to the electrical resistance. The study of changes in resistance as a function of temperature and magnetic field can help us verify the theory of localization. A comprehensive set of experiments were performed on thin films of aluminum for testing the localization theory. Experiments on wide thin films in the quasi-two -dimensional regime confirm the theoretical predictions. These experiments have also yielded considerable quantitative insight about inelastic mechanisms and spin-orbit scattering rates in these films. The inelastic mechanisms that cause delocalization of electrons in our films are electron-phonon scattering and electron-electron scattering. The inferred inelastic rates we obtain are in good agreement with those obtained for films with comparable properties, from other types of experiments, done in the superconducting state. In our films, the spin-orbit scattering rate is observed to scale with the elastic scattering rate. The study of localization in quasi-one-dimensional systems requires metallic wires which are less than a micrometer in width. A new lithographic process involving a three -dimensional shadowing technique was developed, but had limited success. An alternate method using x-ray lithography has proved more successful in the fabrication of submicron -width samples. We have extended the existing theory for quasi -one-dimensional systems to include spin-orbit scattering and Maki-Thompson superconducting fluctuations. Our experiments on narrow aluminum wires have verified this new theory successfully. The prediction of the localization theory of a crossover from two-dimensional behavior to one-dimensional behavior is also confirmed. Furthermore, we infer electron inelastic scattering rates in narrow wires that are identical to those in two-dimensional films. Our analysis of the previous experiments by other workers on narrow metallic wires indicates that the resistance changes observed in those experiments were probably not due to electron localization.