Aharonov-Bohm Interference in Even-Denominator Fractional Quantum Hall States

TL;DR

This study demonstrates Aharonov-Bohm interference in even-denominator fractional quantum Hall states using bilayer graphene, revealing insights into quasiparticle charges and potential non-Abelian anyon behavior through interference patterns.

Contribution

First observation of coherent interference at even-denominator FQH states in bilayer graphene, with analysis of quasiparticle charges and non-Abelian anyon signatures via Fabry-Pérot interferometry.

Findings

Oscillation period of 2 flux quanta observed, not the expected 4, suggesting specific quasiparticle charges.

Interference patterns indicate quasiparticles with charge e*/2 or e*/4, depending on conditions.

Controlled deviations in filling factor reveal bulk quasiparticles with charge e*/4, consistent with non-Abelian anyons.

Abstract

Position exchange of non-Abelian anyons affects the quantum state of their system in a topologically-protected way. Their expected manifestations in even-denominator fractional quantum Hall (FQH) systems offer the opportunity to directly study their unique statistical properties in interference experiments. In this work, we present the observation of coherent Aharonov-Bohm interference at two even-denominator states in high-mobility bilayer graphene-based van der Waals heterostructures by employing the Fabry-P\'erot interferometry (FPI) technique. Operating the interferometer at a constant filling factor, we observe an oscillation period corresponding to two flux quanta inside the interference loop, $\Delta\Phi=2\Phi_0$, at which the interference does not carry signatures of non-Abelian statistics. The absence of the expected periodicity of $\Delta\Phi=4\Phi_0$ may indicate that the interfering quasiparticles carry the charge $e^* = \frac{1}{2}e$ or that interference of $e^* = \frac{1}{4}e$ quasiparticles is thermally smeared. Interestingly, at two hole-conjugate states, we also observe oscillation periods of half the expected value, indicating interference of $e^* = \frac{2}{3}e$ quasiparticles instead of $e^* = \frac{1}{3}e$. To probe statistical phase contributions, we operated the FPI with controlled deviations of the filling factor, thereby introducing fractional quasiparticles inside the interference loop. The resulting changes to the interference patterns at both half-filled states indicate that the additional bulk quasiparticles carry the fundamental charge $e^*=\frac{1}{4}e$, as expected for non-Abelian anyons.