Electrical properties of SN contracts with cleaved oxide superconductor films

The authors have studied the feasibility of making sharp and clean electrical contacts with high-temperature superconductors by cleaving single-crystal Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films in a stream of evaporated noble metals forming SN (superconductor/normal metal) contacts at the revealed cross-sectional edge surfaces of the films. With this technique, contact resistances on the order of 10^-9 to 10^-8 Ωcm² have been consistently obtained. For a structure with an oxide/Au/oxide configuration, the interface resistance was found to show a flat temperature dependence below T_c. Material dependence and anisotropy were observed in the contact resistance. When (110)-oriented films were cleaved in two perpendicular directions, surfaces normal to the c-axis gave interfaces with resistance more than one order of magnitude larger than the other direction. Bi-Sr-Ca-Cu-O/Au interfaces showed a tendency of giving slightly lower resistance than Y-Ba-Cu-O/Au interfaces