Our manuscript studying local current flow in a Josephson junction just appeared online! You can view the arXiv pre-print here.
This work was led by Shaowen Chen and Seunghyun Park in the group of Amir Yacoby at Harvard University. We use a cryogenic scanning probe based on the nitrogen-vacancy center to image the local magnetic field generated by superconducting currents in a NbN/Au/NbN Josephson junction. An applied magnetic field creates a phase gradient along the junction, leading to the formation of vortices which we image directly. The shape and dynamics of the vortex reveal a hidden local structure that is invisible in standard transport measurements. Most notably, in an intermediate regime the junction can switch between having a vortex and no vortex by applying a bias current.
This measurement improves our understanding of the microscopic structure of the Josephson effect, and is a great showcase of NV magnetometry as a sensitive probe of local current flow.
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