{
  "id": "2009.09602",
  "version": "v1",
  "published": "2020-09-21T04:06:16.000Z",
  "updated": "2020-09-21T04:06:16.000Z",
  "title": "Long-lived populations of momentum- and spin-indirect excitons in monolayer WSe$_2$",
  "authors": [
    "Shao-Yu Chen",
    "Maciej Pieczarka",
    "Matthias Wurdack",
    "Eliezer Estrecho",
    "Takashi Taniguchi",
    "Kenji Watanabe",
    "Jun Yan",
    "Elena A. Ostrovskaya",
    "Michael S. Fuhrer"
  ],
  "categories": [
    "cond-mat.mes-hall",
    "cond-mat.mtrl-sci"
  ],
  "abstract": "Monolayer transition metal dichalcogenides are a promising platform to investigate many-body interactions of excitonic complexes. In monolayer tungsten diselenide, the ground-state exciton is dark (spin-indirect), and the valley degeneracy allows low-energy dark momentum-indirect excitons to form. Interactions between the dark exciton species and the optically accessible bright exciton (X) are likely to play significant roles in determining the optical properties of X at high power, as well as limiting the ultimate exciton densities that can be achieved, yet so far little is known about these interactions. Here, we demonstrate long-lived dense populations of momentum-indirect intervalley ($X_K$) and spin-indirect intravalley (D) dark excitons by time-resolved photoluminescence measurements (Tr-PL). Our results uncover an efficient inter-state conversion between X to D excitons through the spin-flip process and the one between D and $X_K$ excitons mediated by the exchange interaction (D + D to $X_K$ + $X_K$). Moreover, we observe a persistent redshift of the X exciton due to strong excitonic screening by $X_K$ exciton with a response time in the timescale of sub-ns, revealing a non-trivial inter-state exciton-exciton interaction. Our results provide a new insight into the interaction between bright and dark excitons, and point to a possibility to employ dark excitons for investigating exciton condensation and the valleytronics.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2020-09-21T04:06:16.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "spin-indirect excitons",
      "monolayer wse",
      "long-lived populations",
      "monolayer transition metal dichalcogenides",
      "low-energy dark momentum-indirect excitons"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}