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Probing Excitonic Rydberg States by Plasmon Enhanced Nonlinear Optical Spectroscopy in Monolayer WS2 at Room
Jia Shi1, Zexin Lin1, Ziyu Zhu1
1Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
ACS Nano
|September 28, 2022
Summary
This study demonstrates plasmon-enhanced nonlinear optical (NLO) spectroscopy for precisely characterizing high-order Rydberg excitonic states in two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers like WS2 at room temperature.
Area of Science:
- Optoelectronics
- Materials Science
- Quantum Physics
Background:
- Excitons dominate optoelectronic properties in 2D transition metal dichalcogenide (TMDC) monolayers due to strong Coulomb interactions.
- High-order Rydberg excitonic states are crucial for fundamental understanding and applications in optical switching and quantum information.
- Probing dark excitonic states typically requires nonlinear optical (NLO) spectroscopy, often at cryogenic temperatures.
Purpose of the Study:
- To investigate the NLO properties of monolayer WS2 integrated with a plasmonic cavity at the single-particle level.
- To achieve giant enhancement in NLO responses and improved spectral resolution for probing excitonic states at room temperature.
- To accurately determine the energies of high-order Rydberg excitonic states in monolayer WS2.
Main Methods:
- Designed a hybrid nanostructure of monolayer WS2 integrated with a plasmonic cavity.
- Investigated nonlinear optical (NLO) properties using techniques such as two-photon photoluminescence (2PPL), second harmonic generation (SHG), and third harmonic generation (THG).
- Combined NLO spectroscopy with linear optical spectroscopy for comprehensive analysis.
Main Results:
- Observed giant enhancement (up to 3800-fold) in NLO responses and narrowed spectral line widths (from 43 to 15 meV for SHG).
- Achieved improved signal-to-noise ratio (SNR) and spectral resolution, enabling room-temperature observation of discrete excitonic states.
- Accurately determined energies of Rydberg excitonic states (A, B, C, D excitons) and confirmed theoretical predictions of nonlocal dielectric screening effects.
Conclusions:
- Plasmon-enhanced NLO spectroscopy significantly boosts SNR and spectral resolution, allowing detailed characterization of excitonic states at room temperature.
- This technique provides accurate determination of exciton binding energies and quasiparticle bandgaps in 2D materials.
- Plasmon-enhanced NLO spectroscopy offers a general and powerful method for probing high-order Rydberg excitonic states in 2D materials.
