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 YBa(2)Cu(3)O(7) washer de SQUIDs containing regular arrays of micrometer holes (anti-dots) have been directly imaged using a standard scanning electron microscope equipped with a liquid nitrogen cryostage. The signal generation is based on the electron-beam-induced local displacement of vortices, which is detected as a flux change in the SQUID loop. This technique allows one a simple visualization of vortices with a spatial resolution of approximate to 1 mu m, at variable 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.