Robust Interlayer-Coherent Quantum Hall States in Twisted Bilayer Graphene

Abstract

We introduce a novel two-dimensional electronic system with ultrastrong interlayer interactions, namely twisted bilayer graphene with a large twist angle, as an ideal ground for realizing interlayer-coherent excitonic condensates. In these systems, subnanometer atomic separation between the layers allows significant interlayer interactions, while interlayer electron tunneling is geometrically suppressed due to the large twist angle. By fully exploiting these two features we demonstrate that a sequence of odd-integer quantum Hall states with interlayer coherence appears at the second Landau level (N = 1). Notably the energy gaps for these states are of order 1 K, which is several orders of magnitude greater than those in GaAs. Furthermore, a variety of quantum Hall phase transitions are observed experimentally. All the experimental observations are largely consistent with our phenomenological model calculations. Hence, we establish that a large twist angle system is an excellent platform for high-temperature excitonic condensation.

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• Orbitally controlled quantum Hall states in decoupled two-bilayer graphene sheets
• Observation of 1/3 fractional quantum Hall physics in balanced large angle twisted bilayer graphene
• Uncovering the spin ordering in magic-angle graphene via edge state equilibration
• Milli-Tesla Quantization enabled by Tuneable Coulomb Screening in Large-Angle Twisted Graphene
• Quantum Hall Effect at 0.002T
• Ferroelectric switching of interfacial dipoles in $\alpha$-RuCl${}_3$/graphene heterostructure
• Correlated interlayer quantum Hall state in large-angle twisted trilayer graphene
• Skyrmionic Transport and First Order Phase Transitions in Twisted Bilayer Graphene Quantum Hall Ferromagnet