Evidence for correlated electron pairs and triplets in quantum Hall interferometers

TL;DR

This paper provides experimental evidence of electron pairing and tripling phenomena in graphene quantum Hall interferometers, revealing complex correlated charge transport involving multiple entangled edge channels and challenging existing theoretical models.

Contribution

It uncovers electron pairing at filling factor nu=2 and unexpected electron tripling at nu=3, involving three entangled edge channels and novel flux periodicity.

Findings

Evidence of electron pairing at nu=2

Observation of electron tripling with h/3e flux period at nu=3

Identification of correlated charge transport on multiple edge channels

Abstract

Pairing of electrons is ubiquitous in electronic systems featuring attractive inter-electron interactions, as exemplified in superconductors. Counter-intuitively, it can also be mediated in certain circumstances by the repulsive Coulomb interaction alone. Quantum Hall (QH) Fabry-P\'erot interferometers (FPIs) tailored in two-dimensional electron gas under a perpendicular magnetic field has been argued to exhibit such unusual electron pairing seemingly without attractive interaction. Here, we show evidence in graphene QH FPIs revealing not only a similar electron pairing at bulk filling factor nu=2 but also an unforeseen emergence of electron tripling characterized by a fractional Aharonov-Bohm flux period h/3e (h is the Planck constant and e the electron charge) at nu=3. Leveraging a novel plunger-gate spectroscopy, we demonstrate that electron pairing (tripling) involves correlated charge transport on two (three) entangled QH edge channels. This spectroscopy indicates a quantum interference flux-periodicity determined by the sum of the phases acquired by the distinct QH edge channels having slightly different interfering areas. While recent theory invokes the dynamical exchange of neutral magnetoplasmons -- dubbed neutralons -- as mediator for electron pairing, our discovery of three entangled QH edge channels with apparent electron tripling defies understanding and introduces a new three-body problem for interacting fermions.