{
  "id": "1604.07079",
  "version": "v1",
  "published": "2016-04-24T20:34:30.000Z",
  "updated": "2016-04-24T20:34:30.000Z",
  "title": "Measuring Chern numbers above the Fermi level in the Type II Weyl semimetal Mo$_x$W$_{1-x}$Te$_2$",
  "authors": [
    "Ilya Belopolski",
    "Su-Yang Xu",
    "Yukiaki Ishida",
    "Xingchen Pan",
    "Peng Yu",
    "Daniel S. Sanchez",
    "Madhab Neupane",
    "Nasser Alidoust",
    "Guoqing Chang",
    "Tay-Rong Chang",
    "Yun Wu",
    "Guang Bian",
    "Hao Zheng",
    "Shin-Ming Huang",
    "Chi-Cheng Lee",
    "Daixiang Mou",
    "Lunan Huang",
    "You Song",
    "Baigeng Wang",
    "Guanghou Wang",
    "Yao-Wen Yeh",
    "Nan Yao",
    "Julien E. Rault",
    "Patrick Le Fèvre",
    "François Bertran",
    "Horng-Tay Jeng",
    "Takeshi Kondo",
    "Adam Kaminski",
    "Hsin Lin",
    "Zheng Liu",
    "Fengqi Song",
    "Shik Shin",
    "M. Zahid Hasan"
  ],
  "comment": "Incorporates earlier results presented in arXiv:1512.09099, by the same authors",
  "categories": [
    "cond-mat.mes-hall"
  ],
  "abstract": "It has recently been proposed that electronic band structures in crystals give rise to a previously overlooked type of Weyl fermion, which violates Lorentz invariance and, consequently, is forbidden in particle physics. It was further predicted that Mo$_x$W$_{1-x}$Te$_2$ may realize such a Type II Weyl fermion. One crucial challenge is that the Weyl points in Mo$_x$W$_{1-x}$Te$_2$ are predicted to lie above the Fermi level. Here, by studying a simple model for a Type II Weyl cone, we clarify the importance of accessing the unoccupied band structure to demonstrate that Mo$_x$W$_{1-x}$Te$_2$ is a Weyl semimetal. Then, we use pump-probe angle-resolved photoemission spectroscopy (pump-probe ARPES) to directly observe the unoccupied band structure of Mo$_x$W$_{1-x}$Te$_2$. For the first time, we directly access states $> 0.2$ eV above the Fermi level. By comparing our results with $\\textit{ab initio}$ calculations, we conclude that we directly observe the surface state containing the topological Fermi arc. Our work opens the way to studying the unoccupied band structure as well as the time-domain relaxation dynamics of Mo$_x$W$_{1-x}$Te$_2$ and related transition metal dichalcogenides.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2016-04-24T20:34:30.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "fermi level",
      "weyl semimetal mo",
      "measuring chern numbers",
      "unoccupied band structure",
      "weyl fermion"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2016arXiv160407079B"
    }
  }
}