Effects of self-assembled gold nanoparticles on YBa 2 Cu 3 O 7−δ thin films and devices

In our work we prepared YBa 2 Cu 3 O 7−δ (YBCO) thin films with self-assembled gold nanoparticles on SrTiO 3 (STO) substrates. We carried out different experiments to determine the effects on the crystallographic properties of the YBCO matrix as well as of the gold nanoparticles. Furthermore, we investigated how the particles influence the superconducting parameters of the film, e.g. the critical temperature T C and the critical current density j C . To ascertain j C we employed magneto-optical Faraday microscopy. In addition, the YBCO film was deposited and structured on STO bi-crystal substrates, thus producing grain boundary Josephson junctions. We studied those junctions with respect to the normal state resistance R N , and the dependence of the critical current I C on the temperature T as well as on the magnetic flux Φ. Finally, we prepared direct current superconducting quantum interference device (dc-SQUID) gradiometers and embedded gold nanoparticles at well-defined areas such as only the antenna or the SQUID region. We measured the flux noise in a shielded environment using an ac-bias reversal technique and compared it with that of sensors without gold nanoparticles. Thus, we demonstrate a new preparation method and an innovative application of gold nanoparticles.