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

TL;DR

This study combines microscopy and SQUID detection to analyze microscopic vortex behavior and flux noise in YBa₂Cu₃O₇ superconducting devices, revealing surface barrier effects and vortex dynamics at nanometer scales.

Contribution

It introduces a method to correlate vortex spatial distribution with flux noise, providing new insights into microscopic vortex fluctuations in high-temperature superconductor SQUIDs.

Findings

Flux noise increases nonlinearly with magnetic field up to 60 μT.

Surface potential barrier influences flux noise behavior.

Average vortex hopping length is approximately 10 nm.

Abstract

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