Strong gate-tunability of flat bands in bilayer graphene due to moir\'e encapsulation between hBN monolayers

TL;DR

This study demonstrates that gate-tuning in hBN-encapsulated bilayer graphene can significantly control the flatness of electronic bands, enabling the creation of isolated, strongly-correlated states through moiré pattern engineering.

Contribution

The paper introduces a new mechanism for tuning flat bands in bilayer graphene via gate control and moiré stacking, independent of vertical gating effects.

Findings

Gaps at secondary Dirac points can be opened in specific moiré configurations.

Gating can tune the principal Dirac point gap and compress the first moiré mini-band.

Achieved flat bands narrower than 10 meV, facilitating strongly-correlated electronic states.

Abstract

When using hexagonal boron-nitride (hBN) as a substrate for graphene, the resulting moir\'e pattern creates secondary Dirac points. By encapsulating a multilayer graphene within aligned hBN sheets the controlled moir\'e stacking may offer even richer benefits. Using advanced tight-binding simulations on atomistically-relaxed heterostructures, here we show that the gap at the secondary Dirac point can be opened in selected moir\'e-stacking configurations, and is independent of any additional vertical gating of the heterostructure. On the other hand, gating can broadly tune the gap at the principal Dirac point, and may thereby strongly compress the first moir\'e mini-band in width against the moir\'e-induced gap at the secondary Dirac point. We reveal that in hBN-encapsulated bilayer graphene this novel mechanism can lead to isolated bands flatter than 10~meV under moderate gating, hence presenting a convenient pathway towards electronically-controlled strongly-correlated states on demand.