Nonlinear Optics at Excited States of Exciton Polaritons in Two-Dimensional Atomic Crystals

Xiaoze Liu, Jun Yi, Quanwei Li, Sui Yang, Wei Bao, Chad Ropp, Shoufeng Lan, Yuan Wang, Xiang Zhang

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Exciton polaritons (EPs) are partial-light partial-matter quasiparticles in semiconductors demonstrating striking quantum phenomena such as Bose-Einstein condensation and single-photon nonlinearity. In these phenomena, the governing process is the EP relaxation into the ground states upon excitation, where various mechanisms are extensively investigated with thermodynamic limits. However, the relaxation process becomes drastically different and could significantly advance the understanding of EP dynamics for these quantum phenomena, when excited states of EPs are involved. Here, for the first time, we observe nonlinear optical responses at the EP excited states in a monolayer tungsten disulfide (WS2) microcavity, including dark excited states and dynamically metastable upper polariton bands. The nonlinear optics leads to unique emissions of ground states with prominent valley degree of freedom (DOF) via an anomalous relaxation process, which is applicable to a wide range of semiconductors from monolayer transition metal dichalcogenides (TMDs) to emerging halide perovskites. This work promises possible approaches to challenging experiments such as valley polariton condensation. Moreover, it also constructs a valley-dependent solid-state three-level system for terahertz photonics and stimulated Raman adiabatic passage.

Original languageEnglish (US)
Pages (from-to)1676-1685
Number of pages10
JournalNano Letters
Issue number3
StatePublished - Mar 11 2020
Externally publishedYes


  • Nonlinear optics
  • excited states
  • exciton polaritons
  • monolayer transition metal dichalcogenide
  • relaxation dynamics

ASJC Scopus subject areas

  • Bioengineering
  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics
  • Mechanical Engineering


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