Direct Observation of Gate-Tunable Dark Trions in Monolayer WSe2

Zhipeng Li, Tianmeng Wang, Zhengguang Lu, Mandeep Khatoniar, Zhen Lian, Yuze Meng, Mark Blei, Takashi Taniguchi, Kenji Watanabe, Stephen A. McGill, Sefaattin Tongay, Vinod M. Menon, Dmitry Smirnov, Su Fei Shi

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


Spin-forbidden intravalley dark excitons in tungsten-based transition-metal dichalcogenides (TMDCs), because of their unique spin texture and long lifetime, have attracted intense research interest. Here, we show that we can control the dark exciton electrostatically by dressing it with one free electron or free hole, forming the dark trions. The existence of the dark trions is suggested by the unique magneto-photoluminescence spectroscopy pattern of the boron nitride (BN)-encapsulated monolayer WSe2 device at low temperature. The unambiguous evidence of the dark trions is further obtained by directly resolving the radiation pattern of the dark trions through back focal plane imaging. The dark trions possess a binding energy of ∼15 meV, and they inherit the long lifetime and large g-factor from the dark exciton. Interestingly, under the out-of-plane magnetic field, dressing the dark exciton with one free electron or hole results in distinctively different valley polarization of the emitted photon, as a result of the different intervalley scattering mechanism for the electron and hole. Finally, the lifetime of the positive dark trion can be further tuned from ∼50 ps to ∼215 ps by controlling the gate voltage. The gate-tunable dark trions usher in new opportunities for excitonic optoelectronics and valleytronics.

Original languageEnglish (US)
Pages (from-to)6886-6893
Number of pages8
JournalNano Letters
Issue number10
StatePublished - Oct 9 2019


  • Fourier plane imaging
  • TRPL
  • dark trion
  • magneto-PL
  • valley polarization

ASJC Scopus subject areas

  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanical Engineering


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