Fabry-P\'erot interference in gapped bilayer graphene with broken anti-Klein tunneling

TL;DR

This study demonstrates Fabry-Pérot interference in high-quality dual-gated bilayer graphene, revealing how a tunable bandgap affects electron reflection and Berry phase, with experimental results aligning closely with theoretical calculations.

Contribution

It provides the first experimental observation of FP interference in gapped bilayer graphene and confirms the impact of a tunable bandgap on anti-Klein tunneling and Berry phase.

Findings

Ballistic phase-coherent transport observed in a 1 μm cavity.

Tight-binding calculations confirm the opening of a tunable bandgap.

Broken anti-Klein tunneling affects electron reflection and Berry phase behavior.

Abstract

We report the experimental observation of Fabry-P\'erot (FP) interference in the conductance of a gate-defined cavity in a dual-gated bilayer graphene (BLG) device. The high quality of the BLG flake, combined with the device's electrical robustness provided by the encapsulation between two hexagonal boron nitride layers, allows us to observe ballistic phase-coherent transport through a $1${\mu}m-long cavity. We confirm the origin of the observed interference pattern by comparing to tight-binding calculations accounting for the gate-tunable bandgap. The good agreement between experiment and theory, free of tuning parameters, further verifies that a gap opens in our device. The gap is shown to destroy the perfect reflection for electrons traversing the barrier with normal incidence (anti-Klein tunneling). The broken anti-Klein tunneling implies that the Berry phase, which is found to vary with the gate voltages, is always involved in the FP oscillations regardless of the magnetic field, in sharp contrast with single-layer graphene.