Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers

摘要

Large area arrays of through-thickness nanoscale pores have been milled into superconducting Nb thin films via a process utilizing anodized aluminum oxide thin film templates. These pores act as artificial flux pinning centers, increasing the superconducting critical current, J_c, of the Nb films. By optimizing the process conditions including anodization time, pore size and milling time, J_c values approaching and in some cases matching the Ginzburg-Landau depairing current of 30MAcm~(-2) at 5K have been achieved - a J_c enhancement over as-deposited films of more than 50 times. In the field dependence of J_c, a matching field corresponding to the areal pore density has also been clearly observed. The effect of backfilling the pores with magnetic material has then been investigated. While backfilling with Co has been successfully achieved, the effect of the magnetic material on J_c has been found to be largely detrimental compared to voids, although a distinct influence of the magnetic material in producing a hysteretic J_c versus applied field behavior has been observed. This behavior has been tested for compatibility with currently proposed models of magnetic pinning and found to be most closely explained by a model describing the magnetic attraction between the flux vortices and the magnetic inclusions.