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Abstract The interactions between charges and excitons involve complex many-body interactions at high densities. The exciton-polaron model has been adopted to understand the Fermi sea screening of charged excitons in monolayer transition metal dichalcogenides. The results provide good agreement with absorption measurements, which are dominated by dilute bright exciton responses. Here we investigate the Fermi sea dressing of spin-forbidden dark excitons in monolayer WSe2. With a Zeeman field, the valley-polarized dark excitons show distinct p-doping dependence in photoluminescence when the carriers reach a critical density. This density can be interpreted as the onset of strongly modified Fermi sea interactions and shifts with increasing exciton density. Through valley-selective excitation and dynamics measurements, we also infer an intervalley coupling between the dark trions and exciton-polarons mediated by the many-body interactions. Our results reveal the evolution of Fermi sea screening with increasing exciton density and the impacts of polaron-polaron interactions, which lay the foundation for understanding electronic correlations and many-body interactions in 2D systems.
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Low Exciton Binding Energies and Localized Exciton–Polaron States in 2D Tin Halide Perovskites
Abstract Aside from band gap reduction, little is understood about the effect of the tin‐for‐lead substitution on the fundamental optical and optoelectronic properties of metal halide perovskites (MHPs), especially when transitioning from 3D to lower dimensional structures. Herein, we take advantage of the spectroscopic isolation of excitons in 2D MHPs to study the intrinsic differences between lead and tin MHPs. The exciton's spectral fine structure indicates a larger polaron binding energy in tin MHPs. Additionally, the electroabsorption responses of the 2D MHPs demonstrates that tin MHPs have exciton binding energies 1.5–2× lower than that of their lead counterparts. Despite the lower binding energy, the excitons in tin MHPs are more Frenkel‐like with small radii, small polarizabilities, and large dipole moments. These results are interpreted as consequences of small polaron formation and disorder‐induced dipole moments. This work highlights the wide range of intrinsic differences between lead and tin MHPs as well as the complexity of excited states in these systems.
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- Award ID(s):
- 1757998
- PAR ID:
- 10446456
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Optical Materials
- Volume:
- 10
- Issue:
- 9
- ISSN:
- 2195-1071
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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