Superlattice-induced insulating states and valley-protected orbits in twisted bilayer graphene

Abstract

Twisted bilayer graphene (TwBLG) 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 TwBLG 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 wavevector.

5 pages, 4 figures

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• High-temperature quantum oscillations caused by recurring Bloch states in graphene superlattices
• New generation of moiré superlattices in doubly aligned hBN/graphene/hBN heterostructures
• Flat bands and perfect metal in trilayer moiré graphene
• Landau levels in twisted bilayer graphene and semiclassical orbits
• Nano-photocurrent mapping of local electronic structure in twisted bilayer graphene
• Topological charge pumping by sliding moiré pattern
• Possible nodeless $s^{\pm }$-wave superconductivity in twisted bilayer graphene
• Twisted bilayer graphene fabricated by direct bonding in a high vacuum
• Excess entropy and breakdown of semiclassical description of thermoelectricity in twisted bilayer graphene close to half filling
• Crystallographic orientation errors in mechanical exfoliation
• PhD Thesis: Electronic correlations in multiorbital systems