{
  "id": "1212.6441",
  "version": "v4",
  "published": "2012-12-28T00:23:34.000Z",
  "updated": "2015-04-21T02:00:21.000Z",
  "title": "Unexpected edge conduction in HgTe quantum wells under broken time reversal symmetry",
  "authors": [
    "Eric Yue Ma",
    "M. Reyes Calvo",
    "Jing Wang",
    "Biao Lian",
    "Mathias Muhlbauer Christoph Brune",
    "Yong-Tao Cui",
    "Keji Lai",
    "Worasom Kundhikanjana",
    "Yongliang Yang",
    "Matthias Baenninger",
    "Markus Konig",
    "Christopher Ames",
    "Hartmut Buhmann",
    "Philipp Leubner",
    "Laurens W. Molenkamp",
    "Shou-Cheng Zhang",
    "David Goldhaber-Gordon",
    "Michael K. Kelly",
    "Zhi-Xun Shen"
  ],
  "comment": "18 pages, 3 figures, accepted to Nature Communication",
  "categories": [
    "cond-mat.mes-hall"
  ],
  "abstract": "The realization of quantum spin Hall (QSH) effect in HgTe quantum wells (QWs) is considered a milestone in the discovery of topological insulators. The QSH edge states are predicted to allow current to flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction of QSH theory that remains to be experimentally verified is the breakdown of the edge conduction under broken time reversal symmetry (TRS). Here we first establish a rigorous framework for understanding the magnetic field dependence of electrostatically gated QSH devices. We then report unexpected edge conduction under broken TRS, using a unique cryogenic microwave impedance microscopy (MIM), on a 7.5 nm HgTe QW device with an inverted band structure. At zero magnetic field and low carrier densities, clear edge conduction is observed in the local conductivity profile of this device but not in the 5.5 nm control device whose band structure is trivial. Surprisingly, the edge conduction in the 7.5 nm device persists up to 9 T with little effect from the magnetic field. This indicates physics beyond simple QSH models, possibly associated with material- specific properties, other symmetry protection and/or electron-electron interactions.",
  "revisions": [
    {
      "version": "v3",
      "updated": "2013-10-29T06:28:26.000Z",
      "title": "Direct Imaging of Quantum Spin Hall Edge States in HgTe Quantum Well",
      "abstract": "To establish the central role of the helical edge states for the recently-discovered quantum spin Hall (QSH) system, direct imaging of those edge states is an important milestone. Employing a unique cryogenic microwave impedance microscope, we directly image QSH edges in a HgTe quantum well. The edge states emerge prominently when the Fermi level is tuned into the bulk gap, with the spatial width of edge conduction increasing monotonically across the bulk gap from the p-type side through the Dirac point into n-type. This monotonic evolution of edge width is counterintuitive at first glance but is in good agreement with the underlying particle-hole asymmetry of HgTe band structure. The observed dependence of edge state width on magnetic field is not expected from single-electron Landau level physics but may be understood by including band bending at the edge. Detailed agreement between theory and the imaging experiment supports the notion of HgTe being a model system for the QSH effect.",
      "comment": "This paper has been withdraw by the author. We are working on improving the quality of the experiment",
      "journal": null,
      "doi": null,
      "authors": [
        "Yue Ma",
        "Worasom Kundhikanjana",
        "Jing Wang",
        "M. Reyes Calvo",
        "Biao Lian",
        "Yongliang Yang",
        "Keji Lai",
        "Matthias Baenninger",
        "Markus König",
        "Christopher Ames",
        "Christoph Brüne",
        "Hartmut Buhmann",
        "Philip Leubner",
        "Qiaochu Tang",
        "Kun Zhang",
        "Xinxin Li",
        "Laurens W. Molenkamp",
        "Shou-Cheng Zhang",
        "David Goldhaber-Gordon",
        "Michael A. Kelly",
        "Zhi-Xun Shen"
      ]
    },
    {
      "version": "v4",
      "updated": "2015-04-21T02:00:21.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "quantum spin hall edge states",
      "hgte quantum",
      "direct imaging",
      "unique cryogenic microwave impedance microscope"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "adsabs": "2012arXiv1212.6441M"
    }
  }
}