Regensburg 2022 – scientific programme

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DS: Fachverband Dünne Schichten

DS 17: 2D Materials 6 (joint session DS/CPP)

DS 17.6: Talk

Wednesday, September 7, 2022, 12:30–12:45, H17

Probing excitonic population dynamics by nonlinear optical wave mixing in monolayer WSe2 — •Jonas M. Bauer, Lijue Chen, Philipp Wilhelm, Sebastian Bange, John M. Lupton, and Kai-Qiang Lin — Department of Physics, University of Regensburg, 93053 Regensburg, Germany

Monolayer semiconductors are emerging platforms for strong nonlinear light-matter interaction, due to their giant oscillator strength of tightly bound excitons. Recently, we reported the existence of a new excitonic species, the high-lying exciton (HX), in monolayer WSe2. The HX appears at around twice the energy of the band-edge A-exciton, forming a ladder-type excitonic three-level system. We demonstrate excitonic quantum interference in monolayers [1] and twisted bilayers [2]. Here, we apply time-resolved nonlinear spectroscopy to probe the excitonic dynamics. We find that a significant time difference between two light pulses is necessary for optimal sum-frequency generation (SFG) and four-wave mixing (FWM) if one of the pulses is in resonance with an excitonic transition. The experimental results are rationalized by numerical calculations based on a density-matrix approach and provide insights into coherent exciton dynamics on a femtosecond scale.

[1] K.-Q. Lin, S. Bange, & J. M. Lupton, Nat. Phys. 15, 242-246 (2019).

[2] K.-Q. Lin, J.M. Bauer et al., Nat. Commun. 12, 1553 (2021).