Speaker
Description
Here we investigate the magnetic phase behaviour of an impure superconductor, and predict the critical fields of the Meissner/vortex state in the presence of impurities. To do this, we derive the Gibbs free energy of an impure superconductor immersed in an external magnetic field. We then use this Gibbs free energy to derive modified Ginzberg-Landau equations, which if solved describe the equilibrium state of the superconductor. We go on to solve these modified Ginzberg-Landau equations numerically, and use these solutions to predict the energy barrier for transition between the Meissner and vortex states. We perform this calculation in the case of a superconductor-insulator boundary, which has practical applications in superconducting radio frequency cavities. Operating in the Meissner state is critical for superconducting radio frequency cavities, thus calculating this state's stability is an important practical problem. Additionally, it has been theorized that some of the most promising surface treatments for cavities work due to diffusion of oxygen impurities into the superconductor, which "dirty" the material. Understanding the action of some general impurity distribution on the stability of the Meissner state could then lead to higher critical fields and more efficient superconducting radio frequency cavities.
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