{
  "id": "2306.10814",
  "version": "v1",
  "published": "2023-06-19T10:04:06.000Z",
  "updated": "2023-06-19T10:04:06.000Z",
  "title": "Spontaneous Exciton Dissociation in Transition Metal Dichalcogenide Monolayers",
  "authors": [
    "Taketo Handa",
    "Madisen A. Holbrook",
    "Nicholas Olsen",
    "Luke N. Holtzman",
    "Lucas Huber",
    "Hai I. Wang",
    "Mischa Bonn",
    "Katayun Barmak",
    "James C. Hone",
    "Abhay N. Pasupathy",
    "X. -Y. Zhu"
  ],
  "comment": "18 pages, 5 figures, SI",
  "categories": [
    "cond-mat.mes-hall"
  ],
  "abstract": "Since the seminal work on MoS2 monolayers, photoexcitation in atomically-thin transition metal dichalcogenides (TMDCs) has been assumed to result in excitons with large binding energies (~ 200-600 meV). Because the exciton binding energies are order-of-magnitude larger than thermal energy at room temperature, it is puzzling that photocurrent and photovoltage generation have been observed in TMDC-based devices, even in monolayers with applied electric fields far below the threshold for exciton dissociation. Here, we show that the photoexcitation of TMDC monolayers results in a substantial population of free charges. Performing ultrafast terahertz (THz) spectroscopy on large-area, single crystal WS2, WSe2, and MoSe2 monolayers, we find that ~10% of excitons spontaneously dissociate into charge carriers with lifetimes exceeding 0.2 ns. Scanning tunnelling microscopy reveals that photo-carrier generation is intimately related to mid-gap defect states, likely via trap-mediated Auger scattering. Only in state-of-the-art quality monolayers14, with mid-gap trap densities as low as 10^9 cm^-2, does intrinsic exciton physics start to dominate the THz response. Our findings reveal that excitons or excitonic complexes are only the predominant quasiparticles in photo-excited TMDC monolayers at the limit of sufficiently low defect densities.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-06-19T10:04:06.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "transition metal dichalcogenide monolayers",
      "spontaneous exciton dissociation",
      "atomically-thin transition metal dichalcogenides",
      "intrinsic exciton physics start",
      "tmdc monolayers"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 18,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}