Superconducting proximity effect in interacting quantum dots revealed by shot noise

TL;DR

This paper investigates how the superconducting proximity effect influences charge transport and shot noise in a quantum dot system, revealing a transition from Cooper pair to single-electron transport through full counting statistics analysis.

Contribution

It demonstrates how the superconducting proximity effect alters shot noise and full counting statistics, providing a new way to detect this effect via noise measurements.

Findings

Full counting statistics shifts from charge 2e to charge e with proximity effect.

Fano factor decreases from 2 to 1 indicating the onset of the proximity effect.

Transition observed as a function of level detuning in the quantum dot.

Abstract

We study the full counting statistics of charge transport through a quantum dot tunnel-coupled to one normal and one superconducting lead with a large superconducting gap. As function of the level detuning, there is a crossover from a regime with strong superconducting correlations in the quantum dot to a regime in which the proximity effect on the quantum dot is suppressed. We analyze the current fluctuations of this crossover in the shot-noise regime. In particular, we predict that the full counting statistics changes from Poissonian with charge 2e, typical for Cooper pairs, to Poissonian with charge e, when the superconducting proximity effect is present. Thus, the onset of the superconducting proximity effect is revealed by the reduction of the Fano factor from 2 to 1.