{
  "id": "2007.03735",
  "version": "v1",
  "published": "2020-07-07T18:55:05.000Z",
  "updated": "2020-07-07T18:55:05.000Z",
  "title": "Chern Insulators and Topological Flat-bands in Magic-angle Twisted Bilayer Graphene",
  "authors": [
    "Shuang Wu",
    "Zhenyuan Zhang",
    "K. Watanabe",
    "T. Taniguchi",
    "Eva Y. Andrei"
  ],
  "comment": "29 pages, 16 figures",
  "categories": [
    "cond-mat.mes-hall"
  ],
  "abstract": "Magic-angle twisted bilayer graphene (MA-TBG) features intriguing quantum phase transitions between strongly correlated states with superconducting, ferromagnetic or nematic order. Their emergence is triggered by enhanced electron-electron interactions when the flat bands in MA-TBG are partially filled by electrostatic doping. To date however, questions concerning the nature of these states and their connection to the putative non-trivial topology of the flat bands in MA-TBG are largely unanswered. Here we report on magneto-transport and Hall density measurements that reveal a succession of doping-induced Lifshitz transitions where discontinuous changes in the Fermi surface topology are accompanied by van Hove singularity (VHS) peaks10 in the density of states (DOS). The VHSs facilitate gapping-out the highly degenerate flat bands of MA-TBG, allowing to uncover the topological nature of the emerging minibands at doping levels corresponding to filled minibands. In the presence of a magnetic field the non-trivial topology of the minibands is revealed through well quantized Hall plateaus which signal the appearance of Chern insulators with integer Chern numbers, C=1,2,3. Surprisingly, for magnetic fields exceeding 5T we observe a new Lifshitz transition at a doping level of 3.5 electrons per moir\\'e cell, suggesting the emergence in higher fields of a topological miniband at a fractional moir\\'e filling.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-07-07T18:55:05.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "magic-angle twisted bilayer graphene",
      "chern insulators",
      "topological flat-bands",
      "flat bands",
      "magnetic field"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 29,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}