Increasing the Transition Temperature of High-T_C Superconductor Thin Films by Organic Linking of Gold Nanoparticles

The transition temperature, T_C, of two types of optimally doped cuprate high-T_C superconductor films, YBa₂Cu₃O_7-δ and La_1.85Sr_0.15CuO₄, is found to increase upon linking Au nanoparticles to their surface via organic molecules. At the same time, and quite surprisingly, the critical current is reduced. We attribute these results to screening of the Coulomb interactions and smearing the pinning potential landscape. The transition temperature was increased also when the Au NPs were not chemically linked to the surface, consistent with the screening scenario. The linking molecules, however, enable selective adsorption of the gold nanoparticles and their separation from the surface, thus eliminating the conventional proximity effect.