Superconducting Transition and Vortex Pinning in Nb Films Patterned with Nano-scale Hole-arrays

U. Welp^a, Z. L. Xiao^a, J. S. Jiang^a, V. K. Vlasko-Vlasov^a, S. D. Bader^a, G. W. Crabtree^a, J. Liang^b, H. Chik^b, J. M. Xu^b

^aMaterials Science Division, Argonne National Laboratory, Argonne, IL 60439

^bDivision of Engineering and Department of Physics, Brown University, Providence, RI 02912

Nb films containing extended arrays of holes with 45-nm diameter and 100-nm spacing have been fabricated using anodized aluminum oxide (AAO) as substrate. Pronounced matching effects in the magnetization and Little-Parks oscillations of the superconducting critical temperature are seen in fields up to 9 kOe. Flux pinning in the patterned samples is enhanced by two orders of magnitude as compared to unpatterned reference samples in applied fields exceeding 5 kOe. Matching effects are a dominant contribution to vortex pinning at temperatures as low as 4.2 K due to the small spacing of the holes.

Vortex Matter in Nanostructured Superconductors

Victor V. Moshchalkov

Laboratory for Solid State Physics and Magnetism, K. U. Leuven, Celestijnenlaan 200 D, B-3001 Leuven, Belgium

Flux confinement has been studied in individual superconducting nanoplaquettes, their clusters and huge arrays (films with nanoengineered periodic pinning arrays (PPA)). In individual nanoplaquettes of the different form (loops, discs, triangles and squares) the superconducting critical temperature T_c(H) was measured resistively and also calculated from the linearized Ginzburg-Landau equations. Novel symmetry consistent vortex-antivortex patterns have been found for triangles and squares. In films with the PPA (lattices of antidots or magnetic dots) the combination of the local probe techniques with the bulk probes has made it possible to identify correctly all vortex patterns responsible for the strong enhancement of the critical current.

Irradiation Induced Changes in the Vortex Phase Diagram of YBCO

L. M. Paulius^a, C. Marcenat^b, V. Tobos^a, L. Undreiu^a, W. Kwok^c, T. Klein^d, G. W. Crabtree^c

^aDept. of Physics, Western Michigan University, Kalamazoo, Michigan 49008, USA

^bCommissariat d'Energie Atomique-DRFMC/SPSMS/LCP, 17 Rue des Martyrs, 38042 Grenoble, France

^cMSD, Argonne National Laboratory, Argonne, IL 60439, USA

^dCentre Nationale de la Recherche Scientifique B.P.166 38042 Grenoble, France

The vortex phase diagram of YBCO was explored with electrical transport and ac specific heat measurements. The evolution of the phase diagram with increasing defect density and varying defect geometry is discussed, with a particular emphasis on the critical points of the first order vortex melting line.