Scanning gate microscopy of nonretracing electron-hole trajectories in a normal-superconductor junction

TL;DR

This paper theoretically investigates scanning gate microscopy of electron and hole trajectories in a normal-superconductor junction, revealing interference fringes at zero bias and a beating pattern at non-zero bias due to wavevector mismatch.

Contribution

It introduces the prediction of a beating pattern in SGM conductance at non-zero bias caused by electron-hole wavevector mismatch, and analyzes the non-retracing hole trajectories.

Findings

Interference fringes appear in SGM maps at zero bias.

A beating pattern emerges in conductance at non-zero bias.

The hole does not retrace the electron path due to wavevector mismatch.

Abstract

We theoretically study scanning gate microscopy (SGM) of electron and hole trajectories in a quantum point contact (QPC) embedded in a normal-superconductor (NS) junction. At zero voltage bias, the electrons and holes transported through the QPC form angular lobes and are subject to self-interference, which marks the SGM conductance maps with interference fringes analogously as in normal systems. We predict that for an NS junction at non-zero bias a beating pattern is to occur in the conductance probed with the use of the SGM technique owing to a mismatch of the Fermi wavevectors of electrons and holes. Moreover, the SGM technique exposes a pronounced disturbance in the angular conductance pattern, as the retroreflected hole does not retrace the electron path due to wavevector difference.