Fabry-Pérot interference in gapped bilayer graphene with broken anti-Klein tunneling

Anastasia Varlet, Ming-Hao Liu, Viktor Krueckl, Dominik Bischoff, Pauline Simonet, Kenji Watanabe, Takashi Taniguchi, Klaus Richter, Klaus Ensslin, Thomas Ihn

Published 2014-06-13, updated 2014-09-30Version 2

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.