OBSERVATION OF THE SKEW SUPERCURRENT IN JOSEPHSON VACUUM BARRIER TUNNEL-JUNCTIONS AS A FUNCTION OF THE JUNCTION NORMAL RESISTANCE

A mechanically controllable break junction is used to obtain the smallest possible Josephson junction, formed by two superconducting electrodes, which are separated by a thin subatomic vacuum barrier. The current voltage characteristics show a ''skew supercurrent'', a supercurrent-like feature with a finite resistance and a ''critical skew current value'' I(t) at a finite voltage V(t). The skew supercurrent is examined over a large normal resistance range by adjustment of the vacuum barrier thickness. In the studied range of six orders of magnitude of the junction normal resistance a crossover from a clear zero voltage supercurrent to a skew supercurrent is observed, for which V(t) remains constant.