Quantum point contact in bilayer graphene

Edge state interferometry has been an important tool in probing the charge and statistics of elementary excitations of the quantum Hall and fractional quantum Hall effect of a two-dimensional electron gas. The recent observations of a plethora of fractional quantum Hall states in bilayer graphene, especially a series at even denominators, made this technique all the more appealing. A quantum point contact (QPC) is a key component of an interferometer, the realization of which is difficult in graphene owing to its gapless nature. In bilayer graphene, a pair of aligned top and bottom gates[1, 2] can be used to open a band gap and therefore construct a QPC. Here we report on our effort in fabricating QPC devices using high-quality h-BN encapsulated bilayer graphene. Because of the thin gating profile, the confining potential of the QPC in bilayer graphene is much sharper than what can be achieved in GaAs 2D systems. We observed well-developed quantum Hall states across QPCs with large openings and gate-controlled backscattering of edge states in QPCs with smaller openings. We discuss our fabrication processes, challenges and progress towards a Fabry-Perot interferometer in bilayer graphene.

[1] J. Li, et al. Nat Nanotechnol 11, 1060 (2016)
[2] J. Li, et al. PRL 120, 057701 (2018)