Time-Dependent Ginzburg-Landau Simulations of the Critical Current in Superconducting Films and Junctions in Magnetic Fields

Understanding the magnetic field dependence of the critical current density (Jc) of superconductors is of considerable interest for optimizing their use in high field applications. Using time-dependent Ginzburg-Landau theory, we have completed simulations of the average electric field generated in thin film systems subject to transport currents in applied magnetic fields, and compared them to thin film systems containing narrow junctions of reduced critical temperature (Tc). For thin films in contact with insulating surfaces, Jc approaches the depairing current density at applied magnetic fields below the initial vortex penetration field and remains nonzero until close to Tinkham's parallel critical field. For thin films in contact with highly metallic surfaces, Jc was found to decrease to zero with decreasing film width. Adding a junction region to the film was found to broaden the transition to the normal state at all applied magnetic fields and reduce Jc of the film at zero field.