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Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides

Author

Listed:
  • Hongyi Yu

    (The University of Hong Kong)

  • Gui-Bin Liu

    (The University of Hong Kong
    School of Physics, Beijing Institute of Technology)

  • Pu Gong

    (The University of Hong Kong)

  • Xiaodong Xu

    (University of Washington
    University of Washington)

  • Wang Yao

    (The University of Hong Kong)

Abstract

In monolayer transition metal dichalcogenides, tightly bound excitons have been discovered with a valley pseudospin optically addressable through polarization selection rules. Here, we show that this valley pseudospin is strongly coupled to the exciton centre-of-mass motion through electron-hole exchange. This coupling realizes a massless Dirac cone with chirality index I=2 for excitons inside the light cone, that is, bright excitons. Under moderate strain, the I=2 Dirac cone splits into two degenerate I=1 Dirac cones, and saddle points with a linear Dirac spectrum emerge. After binding an extra electron, the charged exciton becomes a massive Dirac particle associated with a large valley Hall effect protected from intervalley scattering. Our results point to unique opportunities to study Dirac physics, with exciton’s optical addressability at specifiable momentum, energy and pseudospin. The strain-tunable valley-orbit coupling also implies new structures of exciton condensates, new functionalities of excitonic circuits and mechanical control of valley pseudospin.

Suggested Citation

  • Hongyi Yu & Gui-Bin Liu & Pu Gong & Xiaodong Xu & Wang Yao, 2014. "Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides," Nature Communications, Nature, vol. 5(1), pages 1-7, September.
    • Handle: RePEc:nat:natcom:v:5:y:2014:i:1:d:10.1038_ncomms4876
    DOI: 10.1038/ncomms4876
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    Cited by:

    1. Harley D. Scammell & Julian Ingham & Tommy Li & Oleg P. Sushkov, 2023. "Chiral excitonic order from twofold van Hove singularities in kagome metals," Nature Communications, Nature, vol. 14(1), pages 1-9, December.
    2. Kai-Qiang Lin & Jonas D. Ziegler & Marina A. Semina & Javid V. Mamedov & Kenji Watanabe & Takashi Taniguchi & Sebastian Bange & Alexey Chernikov & Mikhail M. Glazov & John M. Lupton, 2022. "High-lying valley-polarized trions in 2D semiconductors," Nature Communications, Nature, vol. 13(1), pages 1-8, December.
    3. Raul Perea-Causin & Samuel Brem & Fabian Buchner & Yao Lu & Kenji Watanabe & Takashi Taniguchi & John M. Lupton & Kai-Qiang Lin & Ermin Malic, 2024. "Electrically tunable layer-hybridized trions in doped WSe2 bilayers," Nature Communications, Nature, vol. 15(1), pages 1-8, December.

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