Josephson effect above 77 K in a YBaCuO break junction

Abstract
We have observed the Josephson effect in a YBaCuO break junction. Critical currents as high as 10 mA were measured at 4 K for break junctions with a point contact within the fracture of a sample. The junction was susceptible to microwave radiation showing Shapiro steps with the ratio of V/f of 2.04±0.05 μV/GHz compared to the pair tunneling value of h/2e=2.068 μV/GHz. These steps were clearly visible in the current-voltage characteristics at tempertures up to 85±5 K.