Critical Current Densities Through Josephson Junctions in Low Magnetic Fields

Abstract

Understanding the properties of grain boundaries in polycrystalline superconductors is essential for optimizing their critical current density. Here, we provide computational simulations of 2D Josephson junctions (JJs) in low magnetic fields using time-dependent Ginzburg-Landau theory, since they can be considered a proxy for a grain boundary between two grains. We present data for junctions with a wide range of superconducting electrodes of different Ginzburg-Landau parameter (κ) values and geometries, as well as normal barriers with different strengths of pair-breaking -characterized by the thickness of the junction and the junction condensation parameter ( αn). We describe our results using analytic solutions, and hence provide a detailed description of Josephson junctions in low fields up to that required for a single fluxon to penetrate the junction.

Numerical simulation of mechanical behaviors and intergranular fracture of polycrystalline Nb3Sn and superconducting filaments

“…Grain boundary structures are of particular importance because most technological superconductors are polycrystalline and the grain boundary defects strongly affect magnetic flux distribution and limit J c [44,45]. The superconductivity group of Durham University has constructed a framework for analytical and computational the critical current of two-dimensional (2D) and three-dimensional (3D) polycrystalline systems with grain boundaries based on the time-dependent Ginzburg-Landau theory [46][47][48][49][50]. Within this framework, the flux pinning effect can be visualized and quantified, and the in-field J c can be simulated.…”