Unconventional sequence of correlated Chern insulators in magic-angle twisted bilayer graphene

Abstract

The interplay between strong electron-electron interactions and band topology can lead to novel electronic states that spontaneously break symmetries. The discovery of flat bands in magic-angle twisted bilayer graphene (MATBG) with nontrivial topology has provided a unique platform in which to search for new symmetry-broken phases. Recent scanning tunneling microscopy and transport experiments have revealed a sequence of topological insulating phases in MATBG with Chern numbers $C=\pm 3,\pm 2,\pm 1$ near moiré band filling factors $\nu =\pm 1,\pm 2,\pm 3$, corresponding to a simple pattern of flavor-symmetry-breaking Chern insulators. Here, we report high-resolution local compressibility measurements of MATBG with a scanning single electron transistor that reveal a new sequence of incompressible states with unexpected Chern numbers observed down to zero magnetic field. We find that the Chern numbers for eight of the observed incompressible states are incompatible with the simple picture in which the $C=\pm 1$ bands are sequentially filled. We show that the emergence of these unusual incompressible phases can be understood as a consequence of broken translation symmetry that doubles the moiré unit cell and splits each $C=\pm 1$ band into a $C=\pm 1$ band and a $C=0$ band. Our findings significantly expand the known phase diagram of MATBG, and shed light onto the origin of the close competition between different correlated phases in the system.

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• Dirac cone spectroscopy of strongly correlated phases in twisted trilayer graphene
• Selective and Quasi-continuous Switching of Ferroelectric Chern Insulator Device for Neuromorphic Computing
• Does filling-dependent band renormalization aid pairing in twisted bilayer graphene?
• Kekulé spiral order at all nonzero integer fillings in twisted bilayer graphene