Measurement of laser-induced voltages of superconducting Bi-Sr-Ca-Cu-O

We report an experimental investigation of laser-induced voltages across point-contact junctions of Pt tips and superconductiong Bi compounds. It has been observed that the laser-induced voltages of all 2:2:2:3 granular samples and 2:2:1:2 single-crystal samples are converted with increasing temperature from positive to negative sign, passing through a zero point. The signs for 2:2:1:2 granular samples and n-type Nd 1.85 Ce 0.15 CuO 4+y sample are always positive