Low-frequency flux noise and visualization of vortices in a YBa2Cu3O7 dc superconducting quantum interference device washer with an integrated input coil

We used low-temperature scanning electron microscopy (LTSEM) for imaging quantized magnetic flux (vortices) in dc superconducting quantum interference devices (SQUIDs) with approximately 1 mum spatial resolution at temperature T=77 K in a controllable magnetic field up to 20 muT. We demonstrate that LTSEM allows to image the spatial distribution of vortices in a YBa2Cu3O7/SrTiO3/YBa2Cu3O7 multilayer thin-film structure consisting of a dc SQUID washer with an integrated input coil on top. Simultaneously, we are able to measure the low-frequency noise of the sample under test, which allows to correlate the spatial distribution of vortices with low-frequency noise in the SQUID. (C) 2001 American Institute of Physics.