The Study of the Proximity Effect in Mg/Nb Multilayers

Abstract

The proximity effect in multilayers of alternating superconducting and normal materials has been studied extensively over the years on various systems due to its transport properties of the entire system. In this work, Mg/Nb multilayer thin films were investigated through experimental methods and compared to the theoretical calculations. The crystal structured was studied to observe if the films followed the bi-phase diagram. Firstly, a study of the crystal structure of the films was attempted through X-ray diffraction (XRD) measurements. The XRD images obtained were compared with DFT calculations for Mg/Nb multilayers to check if the films fell into the expected regions of the bi-phase diagram. The XRD results were not conclusive. Next, the resistivity of all the films was measured to study the superconducting transition temperature of each of the films. The results were compared with calculations using the Cooper-de Gennes proximity effect model. The measured transition temperatures were a good match for the calculations, which points to Cooper-de Gennes being an appropriate model for this system, as long as the films are in the Cooper limit. The upper critical field of the films was examined both parallel and perpendicular to the film. The angular dependence of the upper critical field was also studied. Comparing the results with the theoretical calculations for 3D and 2D upper critical field, it was found that the films matched the 2D expression for the upper critical field.