The effect of Ag or Au overlayers on underlying YBa2Cu3O7 thin films

Although Ag and Au are commonly used to provide low-resistance contacts to YBa₂Cu₃O₇ (YBCO), their effect on the electrical properties of the underlying YBCO has been largely neglected. Epitaxial YBCO thin films on LaAlO₃ substrates were used in this study. Thin (50 nm) and thick (1 μm) layers of Ag or Au were deposited as overlayers, and in some cases annealed in oxygen at 550–650°C. Compared to samples with no metal overlayers, for both Ag and Au the normal-state parameters changed (resistivity, its temperature coefficient, and the transition width), whereas the transition temperature and critical current density remained unaltered. These results are encouraging for the use of these metals as contacts and/or conducting overlayers on YBCO.