Characterization of bilayer-metal contacts to high Tc superconducting films

Low resistivity normal metal contacts to YBa2Cu3O7-x (YBCO) films have been investigated. It has previously shown that the contact resistivity of Au contact exhibits a strong temperature dependence, decreasing 2--3 orders of magnitude at a transition temperature near Tc of YBCO film. Other metal contacts, including Pd and Nb, do not show this effect. The contact resistivity of metal contacts has been correlated with interfacial reactions and disruption studied by x-ray photoelectron spectroscopy (XPS). In this work we demonstrate that a thin interlayer, specifically 10 A of Au, between the YBCO and a metal contact such as Nb can allow the formation of a low resistance contact. XPS of the effect of the interlayer is presented, and the implications for carrier coupling are discussed. These results indicate a methodology for low contact resistance bilayer-metal structures for supercondcuting device applications