Hanbury-Brown and Twiss exchange effects in a four-terminal tunnel junction

TL;DR

This paper studies current correlations in a four-terminal tunnel junction, revealing that Hanbury-Brown and Twiss type correlations are significantly enhanced by voltage fluctuations, with results aligning with a generalized shot noise theory.

Contribution

It demonstrates the enhancement of cross-correlations in a four-terminal junction due to voltage fluctuations, extending shot noise theory to multi-terminal conductors.

Findings

Cross-correlations are approximately twice as strong with two bias sources.

Voltage fluctuations of the central island increase current-current correlations.

Experimental results agree with a generalized shot noise theoretical model.

Abstract

We investigate the current-current correlations in a four-terminal Al-AlOx-Al tunnel junction where shot noise dominates. We demonstrate that cross-correlations in the presence of two biasing sources of the Hanbury-Brown and Twiss type are much stronger (approximately twice) than an incoherent sum of correlations generated by single sources. The difference is due to voltage fluctuations of the central island that give rise to current-current correlations in the four contacts of the junction. Our measurements are in close agreement with results obtained using a simple theoretical model based on the theory of shot noise in multi-terminal conductors, generalized here to arbitrary contacts.