Effects of defects and surface roughness on the vortex penetration and vortex dynamics in superconductor–insulator–superconductor multilayer structures exposed to RF magnetic fields: numerical simulations within TDGL theory

Abstract

Vortex penetration and vortex dynamics are significantly important to superconducting devices, for example, the superconducting cavities, since vortex motions will create substantial dissipation. In experiments, different kinds of defects as well as different degrees of surface roughness were observed. By considering these in superconductor–insulator–superconductor (SIS) structures, vortex penetration and vortex dynamics are very complex due to their interactions with defects and the influence of surface roughness, especially for radio-frequency (RF) magnetic fields, which are quite different from ideal defect-free SIS multilayer structures. In this paper, within the Ginzburg–Landau theory, we perform numerical simulations to study the effects of nanoscale defects, surface roughness, and cracks in the coating layer on the vortex penetration and superheating field in Nb3Sn–I–Nb multilayer structures exposed to a quasi-static magnetic field. The validation of the numerical simulations is verified by good consistency with previous theoretical results in ideal defect-free SIS multilayer and single Nb structures. Furthermore, we explore the vortex dynamics and induced voltages in SIS multilayer structures exposed to RF magnetic fields for both ideal defect-free structures and real situations that include surface roughness. Our numerical simulations indicate that, unlike the quasi-static case, the advantage of SIS multilayer structures over a single Nb structure depends on the degree of surface roughness as well as the frequency and amplitude of the RF magnetic field. The results of this paper provide deep insight to evaluate the actual performance-limiting characteristics of next-generation superconducting RF cavities with different proposed candidate materials, which are quite susceptible to nonideal surfaces.