Sheet-current distribution in a dc SQUID washer probed by vortices

Abstract

We present a method, based on vortex imaging by low-temperature scanning electron microscopy (LTSEM), to directly image the sheet-current distribution in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}$ dc superconducting quantum interference device washers. We show that the LTSEM vortex signals are simply related to the scalar stream function describing the vortex-free circulating sheet-current distribution $\mathbit{J}$. Unlike previous inversion methods that infer the current distribution from the measured magnetic field, our method uses pinned vortices as local detectors for $\mathbit{J}$. Our experimental results are in very good agreement with numerical calculations of $\mathbit{J}$.