Microscopic Analysis of Low-Frequency Flux Noise in YBa$_2$Cu$_3$O$_7$ Direct Current Superconducting Quantum Interference Devices

摘要

We use low-temperature scanning electron microscopy combined with SQUIDdetection of magnetic flux to image vortices and to investigate low-frequencyflux noise in YBa$_2$Cu$_3$O$_7$ thin film SQUIDs. The low-frequency flux noiseshows a nonlinear increase with magnetic cooling field up to 60 $\mu$T. Thiseffect is explained by the surface potential barrier at the SQUID hole. Bycorrelating flux noise data with the spatial distribution of vortices, weobtain information on spatial fluctuations of vortices on a microscopic scale,e.g. an average vortex hopping length of approximately 10 nm.