Ultrafast Dynamics of Self-hybridized Exciton-Polaritons in WSe2
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Exciton-polaritons (EPs) show intriguing optoelectronic properties. Self-hybridized EPs without external cavity mitigate the complexity in cavity fabrication, and provide an open and more natural platform for exploring polariton physics and chemistry. However, ultrafast dynamics and many-body interactions in self-hybridized EPs remain unclear. In this work, we use transient reflection spectroscopy to investigate ultrafast dynamics of self-hybridized EPs in WSe 2 flakes. Above-resonance and lower-polariton-resonant excitations reveal two-step inter-branch scattering between exciton reservoir and polaritons in coherent (ultrafast, ＜100 fs) and incoherent, phonon-assisted (slow, 2-30 ps) regimes. The optical nonlinearity of self-hybridized EPs originates from the many-body interactions including Pauli blocking and bandgap renormalization of excitons. Significantly smaller blueshift is seen in the first few picoseconds under lower-polariton-resonant excitation compared to above-resonance excitation, demonstrating that polaritons experience much weaker interparticle interactions than excitons because of the photonic component. These results are valuable for developing cavity-free polaritonic devices.
