Detection of vortex motion in high-T_c superconductor by N-S point contact

A N-S point contact (platinum tip-ab-plane of a Bi₂Sr₂CaCu₂O₈ single crystal) has been used for the first time to detect the vortex motion in a high-T_c superconductor. The sweep of an external magnetic field led to the appearance of voltage pulses on the contact (when a constant current was passed through the contact), which were associated with the passage of individual vortices through the contact. An abrupt decrease of the pulse amplitude with increasing temperature has also been observed. This fact may be explained by thermal fluctuations of the vortex lattice.