A. Palau, C. Montón, V. Rouco, X. Obradors and T. Puig Phys. Rev. B 85, 012502 (2012) DOI: http://dx.doi.org/10.1103/PhysRevB.85.012502 We investigate guided vortex motion in high-temperature YBa2Cu3O7 thin films patterned with an array of asymmetric blind antidots. A preferential vortex motion along spatial asymmetric pinning potentials has been directly observed by changing the driving current direction. Transport measurements reveal that effective ratchet potentials are created by fixed vortices strongly pinned within the antidots while the spatial asymmetry is transferred to interstitial vortices. We study a novel ratchet system that requires vortex-vortex interactions to work, in contrast with the individual vortex effects studied in conventional ratchet systems. By tuning the magnetic field and temperature, we are able to control the transition from a single vortex pinning regime to a region where collective effects become important and determine the range where the rectification effect is activated.

A. Llordes, A. Palau, J. Gazquez, M. Coll, R. Vlad, A. Pomar, J. Arbiol, R. Guzman, S. Ye, V. Rouco, F. Sandiumenge, S. Ricart, T. Puig, M. Varela, D. Chateigner, J. Vanacken, J. Gutierrez, V. Moshchalkov, G. Deutscher, C. Magen and X. Obradors Nature Materials, 11, 329-336 (2012) DOI: 10.1038/nmat3247 Boosting large-scale superconductor applications require nanostructured conductors with artificial pinning centres immobilizing quantized vortices at high temperature and magnetic fields. Here we demonstrate a highly effective mechanism of artificial pinning centres in solution-derived high-temperature superconductor nanocomposites through generation of nanostrained regions where Cooper pair formation is suppressed. The nanostrained regions identified from transmission electron microscopy devise a very high concentration of partial dislocations associated with intergrowths generated between the randomly oriented nanodots and the epitaxial YBa₂Cu₃O₇ matrix. Consequently, an outstanding vortex-pinning enhancement correlated to the nanostrain is demonstrated for four types of randomly oriented nanodot, and a unique evolution towards an isotropic vortex-pinning behaviour, even in the effective anisotropy, is achieved as the nanostrain turns isotropic. We suggest a new vortex-pinning mechanism based on the bond-contraction pairing model, where pair formation is quenched under tensile strain, forming new and effective core-pinning regions.