Imaging of vortices and 1/f noise sources in YBCO dc SQUIDs using low-temperature scanning electron microscopy

Abrikosov- and Josephson-Vortices trapped in bicrystalline YBa2Cu3O7 washer de SQUIDs containing regular arrays of micrometer holes (anti-dots) have b een directly imaged using a standard scanning electron microscope equipped with a liquid nitrogen cryostage. The signal generation is based on the ele ctron-beam-induced local displacement of vortices, which is detected as a f lux change in the SQUID loop. This technique allows one a simple visualizat ion of vortices with a spatial resolution of approximate to 1 mu m, at vari able temperature and magnetic field. The magnitude of the vortex signal is a direct measure of the amount of flux a vortex couples into the SQUID hole . In addition to the static local distribution of vortices, this technique can provide information on the dynamic behavior of vortices trapped in the SQUID loop, by using the beam as a local perturbation and measuring the low -frequency noise induced by vortex motion.