Rhombohedral Tetralayer Graphene/Boron Nitride Moire Superlattices for High-Temperature Quantum Anomalous Hall and Fractional Chern Insulator
Abstract
This project aims to realize high-temperature quantum anomalous Hall insulator (i.e. integer Chern insulator) and fractional Chern insulator by controlling the electron correlation and topology in tetralayer graphene/hBN moire superlattices. Haldane first theorized that Chern insulators with integer quantum Hall effects could appear even at zero magnetic field in lattice models with broken time-reversal symmetry and complex hopping parameters. Such an intrinsic integer Chern insulator state requires two important ingredients: strong electron-electron correlation and non-trivial band topology. The strong electron correlation is needed for spontaneous time-reversal symmetry breaking, and the topological band is necessary for anomalous Hall conductance. Recent theoretical studies reveal that even fractional Chern insulator can be realized in lattice models with sufficiently strong electron correlation, where fascinating fractional quantum Hall physics emerges in zero magnetic field. Moire superlattices of rhombohedral few-layer graphene/hexagonal boron nitride (hBN) provide an attractive platform to explore high-temperature quantum anomalous Hall insulator and possible fractional Chern insulator, because both the electron-electron correlation and the band topology can be controlled in-situ by a vertical electrical field in these moire systems. For example, previous studies of rhombohedral trilayer graphene/hBN moire superlattices have demonstrated the existence of electrically tunable quantum anomalous Hall state up to 2 Kelvin. Here the PI plans to exploit the super flat and topological moire minibands in rhombohedral tetralayer graphene/hBN moire superlattice to realize high-temperature quantum anomalous Hall and fraction Chern insulator state. Rhombohedral tetralayer graphene/hBN is predicted to feature a super flat moire miniband, which will greatly enhance electron-electron correlation than that observed in trilayer graphene /hBN system. This extremely strong electron-electron correlation will stabilize the time-reversal-symmetry broken state and the orbital ferromagnetism against thermal fluctuation. Consequently, it offers exciting opportunity to achieve high-temperature quantum anomalous Hall insulator. In addition, the super flat topological band in rhombohedral tetralayer graphene/hBN moire superlattice could be enabling for the realization of the fractional Chern insulator, a completely new topological state with fractional quantum Hall effect at zero magnetic field. The PI will combine near-field nanoscopy imaging, advanced device fabrication, and magneto-transport characterization to systematically engineer the flat topological minibands in rhombohedral tetralayer graphene/hBN moire superlattices for the discovery of such high-temperature quantum amomalous Hall insulator and fractional Chern insulator.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF2110176
Entities
People
- Feng Wang
Organizations
- Army Contracting Command
- United States Army
- University of California, Berkeley