Evidence for atomic-scale vibron-mediated electron bunching

TL;DR

This study demonstrates that vibrational coupling at the atomic scale can induce electron bunching during tunnelling, revealing a new mechanism for electron correlation in nano-electro-mechanical systems.

Contribution

It provides experimental evidence of vibron-assisted electron bunching at atomic sites, a phenomenon previously only theoretically predicted.

Findings

Observation of vibron-assisted tunnelling signatures.

Detection of super-Poissonian shot noise indicating electron bunching.

Implication of vibronic coupling as a new electron correlation mechanism.

Abstract

Due to the Coulomb blockade effect, electrons rarely bunch during transport, a phenomenon observed only in a few specially engineered mesoscopic configurations. In this work, we introduce an atomically resolved shot-noise study to demonstrate the possibility of electron bunching through vibrational coupling which takes place in an atomically sized nano-electro-mechanical system. Using tunnelling spectroscopy, we observe signatures of vibron-assisted tunnelling on an Fe impurity in Bi$_2$Se$_3$. Notably, simultaneous shot-noise measurements at the centre of the vibrating impurity reveal super-Poissonian noise. In the absence of alternative sources of super-Poissonian noise, this implies vibronic-coupling-induced bunching of electrons during the tunnelling process through the impurity, as theoretically predicted decades ago. As a future outlook, if coherence between electrons can be implemented, vibron-mediated electron bunching at single atomic sites may be exploited as a local injection source of $N$-paired electrons.