Energy dependent counting statistics in diffusive superconducting tunnel junctions

TL;DR

This paper investigates how energy influences charge transfer statistics in diffusive superconducting junctions, revealing correlated electron pair transfer and voltage-dependent noise features, especially near the Thouless energy.

Contribution

It introduces an analysis of energy-dependent full counting statistics in diffusive superconducting junctions, highlighting conditions for correlated pair transfer and noise characteristics.

Findings

Current is mainly transported via correlated electron pairs.

Uncorrelated pair transfer occurs only with strong asymmetry or high energies.

Differential shot noise exhibits a double peak near the Thouless energy.

Abstract

We present an investigation of the energy dependence of the full charge counting statistics in diffusive normal-insulating-normal-insulating-superconducting junctions. It is found that the current in general is transported via a correlated transfer of pairs of electrons. Only in the case of strongly asymmetric tunnel barriers or energies much larger than the Thouless energy is the pair transfer uncorrelated. The second cumulant, the noise, is found to depend strongly on the applied voltage and temperature. For a junction resistance dominated by the tunnel barrier to the normal reservoir, the differential shot noise shows a double peak feature at voltages of the order of the Thouless energy, a signature of an ensemble averaged electron-hole resonance.