Bulk-Edge Coupling in Bilayer Graphene Quantum Hall Fabry-Pérot Interferometers

Quantum Hall Fabry–Pérot interferometers provide a unique platform for probing anyons - quasiparticles in two dimensions with non-trivial braiding statistics. In bilayer graphene, even-denominator states observed in transport and capacitance are predicted to host non-Abelian anyons, and its high tunability makes it an ideal system for interferometry.

However, an experimental complication of these systems arises from the bulk-edge coupling between the bulk quasiparticles and the compressible edge around the cavity, producing phase slips that can mimic or obscure signatures of anyonic statistics. Hence, it is essential to understand the microscopic origin of bulk–edge coupling in bilayer graphene and ultimately develop strategies to mitigate it. In this talk, I will present data from a dual-gated bilayer graphene interferometer across various filling factors. At ν = ±1, we observe regular phase slips with an average amplitude of 2π × 0.7, which we attribute to the charging of individual quasiparticles - significantly larger than previously observed in monolayer devices of comparable geometry. Being able to resolve single-quasiparticle charging further allows us to perform gate spectroscopy and extract the lever arms to all gates, where we find the surprising result that the lever arms to the center and bottom gates change signs upon crossing the center of a plateau. We also performed interference measurements at ν = –2, where the observed phase slips are much smaller in magnitude. I will conclude by discussing the implications of bulk-edge coupling in our measurements, and how our data can be understood through studies of edge velocities and a characterization of coulomb effects with the relevant parameters.