Lateral electron tunneling through single self-assembled InAs quantum dots coupled to superconducting nanogap electrodes

TL;DR

This paper reports on the fabrication and characterization of superconductor-quantum dot-superconductor junctions using InAs quantum dots and aluminum electrodes, revealing Coulomb effects and conductance suppression at very low temperatures.

Contribution

It introduces a novel method to create SC-QD-SC junctions with lateral contacts and provides experimental insights into their Coulomb and superconducting properties.

Findings

Observation of Coulomb staircases and oscillations at 40 mK

Conductance suppression for voltages below the superconducting gap

Absence of Josephson current due to Coulomb interaction and thermal fluctuations

Abstract

We have fabricated superconductor-quantum dot-superconductor (SC-QD-SC) junctions by using SC aluminum electrodes with narrow gaps laterally contacting a single self-assembled InAs QD. The fabricated junctions exhibited clear Coulomb staircases and Coulomb oscillations at 40 mK. Furthermore, clear suppression in conductance was observed for the source-drain voltage $|V_{\rm SD}| < 2\Delta/e$, where $\Delta$ is the SC energy gap of Al. The absence of Josephson current that flows through QDs is due to the strong Coulomb interaction and non-negligible thermal fluctuation in our measurement system.