Andreev reflection of fractional quantum Hall quasiparticles

TL;DR

This paper reports the first observation of an Andreev-like reflection process involving fractional quantum Hall quasiparticles, revealing new boundary charge dynamics in topological quantum states.

Contribution

It demonstrates experimentally for the first time an Andreev-like process in a topological quantum many-body system, extending the concept beyond superconductivity.

Findings

Conductance exceeds that of the fractional state.

Observation of Andreev reflection of fractional quasiparticles.

Provides insight into boundary charge dynamics in topological states.

Abstract

Electron correlation in a quantum many-body state appears as peculiar scattering behaviour at its boundary, symbolic of which is Andreev reflection at a metal-superconductor interface. Despite being fundamental in nature, dictated by the charge conservation law, however, the process has had no analogues outside the realm of superconductivity so far. Here, we report the observation of an Andreev-like process originating from a topological quantum many-body effect instead of superconductivity. A narrow junction between fractional and integer quantum Hall states shows a two-terminal conductance exceeding that of the constituent fractional state. This remarkable behaviour, while theoretically predicted more than two decades ago but not detected to date, can be interpreted as Andreev reflection of fractionally charged quasiparticles. The observed fractional quantum Hall Andreev reflection provides a fundamental picture that captures microscopic charge dynamics at the boundaries of topological quantum many-body states.