Abstract
Twisted bilayer graphene (TBLG) is one of the simplest van der Waals heterostructures, yet it yields a complex electronic system with intricate interplay between moiré physics and interlayer hybridization effects. We report on electronic transport measurements of high mobility small angle TBLG devices showing clear evidence for insulating states at the superlattice band edges, with thermal activation gaps several times larger than theoretically predicted. Moreover, Shubnikov-de Haas oscillations and tight binding calculations reveal that the band structure consists of two intersecting Fermi contours whose crossing points are effectively unhybridized. We attribute this to exponentially suppressed interlayer hopping amplitudes for momentum transfers larger than the moiré wave vector.
Highlights
Twisted bilayer graphene (TwBLG) is one of the simplest van der Waals heterostructures, yet it yields a complex electronic system with intricate interplay between moire physics and interlayer hybridization effects
We report on electronic transport measurements of high mobility small angle TwBLG devices showing clear evidence for insulating states at the superlattice band edges, with thermal activation gaps several times larger than theoretically predicted
An intricate interplay between moire physics and interlayer hybridization effects exists in TwBLG — one striking consequence is that the heterostructure can host an insulating state even though it comprises two sheets of high quality conductors
Summary
FIG. 1. (color online). (a) Schematic of TwBLG and its superlattice unit cell. λ2SL is the unit cell area. (b) The orange and blue hexagons denote the original Brillouin zones of graphene layer 1 and 2 respectively. In both samples, the conductivity minimum centered at zero density corresponds to the degenerate Dirac points in both layers of graphene. For the small angle sample S1, we observe two insulating states occurring at total carrier densities of n ≈ ±7.5 × 1012 cm−2, which are σxx (mS)
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