Combined time-resolved magnetooptical and electrical flux detection in thin-film superconductors

The dynamic behavior of the current-induced dissipative flux-flow state in a thin-film type I superconductor was studied by simultaneous stroboscopic magnetooptical flux detection and direct recording of the time-resolved flux-flow voltage. Employing high-resolution magnetooptical flux detection with a high-speed stroboscope, it was possible to visualize globally individual multiquantum flux tubes during their rapid motion across the superconducting Pb film, yielding spatial and temporal resolution of better than 1 µm and 0.1 µsec, respectively. Simultaneously, the temporal structure of the flux-flow voltage was recorded using a highly sensitive signal-averaging procedure, thereby yielding a voltage resolution of about 30 nV at a time resolution of 10 nsec (corresponding to a recording bandwidth of 25 MHz). The recorded temporal voltage structures agreed well with the voltages expected from the velocity profiles of all flux tubes existing simultaneously obtained from the magnetooptical data. The experiments are the first to demonstrate full agreement between both independent flux-detection measurements, clearly confirming the existing theory.