Periodic micron-size flux pinning centers on superconducting Nb films by lithographic techniques

It is well known that artificial pinning centers in NbTi filaments are effective for improvement of superconductor performances. In order to develop the artificial pinning centers for a high temperature superconductor (HTS) like Ag-sheathed Bi-2223 thin tape, we proposed groove and hole patterns on the HTS tape. As a first step, we formed periodical grooves and holes on Nb films instead of the HTS to establish a fabrication technique and to demonstrate performances of the artificial pinning centers. The groove and hole patterns with 4 μm periodical intervals and 0.6 to 0 9 μm in depth were projected and etched on the film with a photolithographic technique. The properties of the fabricated Nb films with the patterns were measured with a SQUID magnetometer. The Nb films with the patterns have critical temperature around 9.3 K and upper critical field of 0.45-0.5 T. The measured magnetizations of the Nb films with the patterns were larger than those of the films without the patterns. It was, moreover, observed that the pinning forces were resonated at applied magnetic field matching with flux lattice spacing at 9.10-9.15 K close to the critical temperature. These results demonstrate that the groove and hole patterns on the Nb films are useful for the improvement of pinning force