Increased flux pinning in YBa

We prepared direct-current superconducting quantum interference device (dc-SQUID) gradiometers consisting of a single YBa2Cu3O7- δ (YBCO) layer on SrTiO3 (STO) bicrystal substrates. The superconducting thin film was modified by embedding crystalline gold nanoparticles. We investigated the growth conditions of these particles as well as their influence on the properties of the YBCO thin film. In our magneto-optical measurements we found that the presence of embedded nano crystals results in a distinct enhancement of jc over the whole investigated temperature range. We attribute the higher critical current density to an increased pinning, which also results in a reduction of the flux noise of our investigated gradiometers