Theory of scanning gate microscopy imaging of the supercurrent distribution in a planar Josephson junction

TL;DR

This paper presents a theoretical study on how scanning gate microscopy can map supercurrent distributions in Josephson junctions under magnetic fields, revealing vortex structures and asymmetries.

Contribution

It introduces a model explaining how scanning gate microscopy detects supercurrent patterns and vortex formations in Josephson junctions with magnetic fields.

Findings

Supercurrent distribution can be mapped near Fraunhofer pattern maxima.

Magnetic field induces Josephson vortices affecting supercurrent flow.

Asymmetries in supercurrent distribution are revealed by scanning gate microscopy.

Abstract

We theoretically investigate the mapping of the supercurrent distribution in a planar superconductor-normal-superconductor junction in the presence of a perpendicular magnetic field via the scanning gate microscopy technique. We find that the distribution of counter-propagating supercurrents aligned in Josephson vortices can be mapped by the change of the critical current induced by the tip of the scanning probe, if the flux in the junction is set close to maxima of the Fraunhofer pattern. Instead, when the magnetic field drives the junction to a supercurrent minimum in the Fraunhofer pattern, the superconducting phase adapts, and the tip always increases the supercurrent. The perpendicular magnetic field leads to the formation of Josephson vortices, whose extension for highly transparent junctions depends on the current circulation direction. We show that this leads to an asymmetric supercurrent distribution in the junction and that this can be revealed by scanning gate microscopy. We explain our findings on the basis of numerical calculations for both short- and long-junction limits and provide a phenomenological model for the observed phenomena.