Built-in Bernal gap in large-angle-twisted monolayer-bilayer graphene
arxiv(2024)
Abstract
Atomically thin materials offer multiple opportunities for layer-by-layer
control of their electronic properties. While monolayer graphene (MLG) is a
zero-gap system, Bernal-stacked bilayer graphene (BLG) acquires a finite band
gap when the symmetry between the layers' potential energy is broken, usually,
via a large electric field applied in double-gate devices. Here, we introduce
an asymmetric twistronic stack comprising both MLG and BLG, synthesized via
low-pressure chemical vapor deposition (LP-CVD) on Cu. Although a large
(∼30^∘) twist angle decouples the MLG and BLG electronic bands near
Fermi level, we find that the layer degeneracy in the BLG subsystem is lifted,
producing a gap in the absence of external fields. The built-in interlayer
asymmetry originates from proximity-induced energy shifts in the outermost
layers and requires a displacement field of 0.14 V/nm to be compensated. The
latter corresponds to a ∼10 meV intrinsic BLG gap, a value confirmed by
our thermal-activation measurements. The present results highlight the role of
structural asymmetry and encapsulating environment, expanding the engineering
toolbox for monolithically-grown graphene multilayers.
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