Current transport along the [001] axis of YBCO in low-temperature superconductor-normal metal-high-temperature superconductor heterostructures

The electrophysical properties of heterojunctions several microns in size, obtained by successive deposition of the metal-oxide high-temperature superconductor YBa2Cu3Ox, a normal metal Au, and the low-temperature superconductor Nb, were studied experimentally. Current flows in the [001] direction of the epitaxial YBa2Cu3Ox film. It is shown, by comparing the experimental data with existing theoretical calculations, that for the experimentally realizable transmittances (D̄=10−5–10−6) of the YBa2Cu3Ox—normal metal boundary the critical current of the entire heterostructure is low (of the order of the fluctuation current) because of a sharp change in the amplitude of the potential of the superconducting carriers at this boundary. The current-voltage characteristics of the heterostructure studied correspond to tunnel junctions consisting of a superconductor with dx² - y² type symmetry of the superconducting wave function and a normal metal.