Excitonic Complexes and Emerging Interlayer Electron-Phonon Coupling in BN Encapsulated Monolayer Semiconductor Alloy: WS 0.6 Se 1.4

Yuze Meng, Tianmeng Wang, Zhipeng Li, Ying Qin, Zhen Lian, Yanwen Chen, Michael C. Lucking, Kory Beach, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Fengqi Song, Humberto Terrones, Su Fei Shi

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Monolayer transition metal dichalcogenides (TMDs) possess superior optical properties, including the valley degree of freedom that can be accessed through the excitation light of certain helicity. Although WS 2 and WSe 2 are known for their excellent valley polarization due to the strong spin-orbit coupling, the optical bandgap is limited by the ability to choose from only these two materials. This limitation can be overcome through the monolayer alloy semiconductor, WS 2x Se 2(1-x) , which promises an atomically thin semiconductor with tunable bandgap. In this work, we show that the high-quality BN encapsulated monolayer WS 0.6 Se 1.4 inherits the superior optical properties of tungsten-based TMDs, including a trion splitting of ∼6 meV and valley polarization as high as ∼60%. In particular, we demonstrate for the first time the emerging and gate-tunable interlayer electron-phonon coupling in the BN/WS 0.6 Se 1.4 /BN van der Waals heterostructure, which renders the otherwise optically silent Raman modes visible. In addition, the emerging Raman signals can be drastically enhanced by the resonant coupling to the 2s state of the monolayer WS 0.6 Se 1.4 A exciton. The BN/WS 2x Se 2(1-x) /BN van der Waals heterostructure with a tunable bandgap thus provides an exciting platform for exploring the valley degree of freedom and emerging excitonic physics in two-dimension.

Original languageEnglish (US)
Pages (from-to)299-307
Number of pages9
JournalNano Letters
Issue number1
StatePublished - Jan 9 2019


  • 2s exciton
  • WS
  • WSe
  • alloy
  • resonance Raman peak
  • valley polarization

ASJC Scopus subject areas

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


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