Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 40: 2D Semiconductors and van der Waals Heterostructures IV

HL 40.12: Talk

Wednesday, March 19, 2025, 18:30–18:45, H15

Inhomogeneous Broadening of Dark Rydberg Excitons in TMDC Monolayers Probed by Ultrafast Frequency-Resolved Autocorrelation Spectroscopy — •Katem Mitkong, Tom Jehle, Daniel C. Lünemann, Lukas Lackner, Juanmei Duan, Christian Schneider, and Christoph Lienau — Institute of Physics, Carl von Ossietzky University, Oldenburg, Germany

Monolayers of Transition Metal Dichalcogenides (TMDCs), as two-dimensional materials, exhibit unique optical properties influenced by their dielectric environment. The reduced dimensionality enhances the exciton binding energy, enabling the formation of Rydberg exciton series even at room temperature. In this study, broadband nonlinear Interferometric Frequency-Resolved Autocorrelation (IFRAC) spectroscopy with few-cycle time resolution is used to probe the optically dark 2p exciton state in WS2 monolayers. The result readily distinguishes coherent second harmonic generation (SHG) from incoherent two-photon photoluminescence emission (TPPLE) without requiring polarization control. We observe the 2p dark exciton state at 2.20 eV, with TPPLE linewidths that depend on excitation power. Comparison with Lindblad Master equation solutions shows significant inhomogeneous broadening of the 2p resonance, about three times greater than that of 1s excitons. This broadening, attributed to the extended spatial wavefunction of 2p excitons relative to 1s excitons, underscores their increased sensitivity to inhomogeneities such as local strain and dielectric fluctuations. This finding suggests potential applications in nanoscale sensing technologies.

Keywords: TMDC monolayers; inhomogeneous broadening; dark Rydberg excitons; nonlinear spectroscopy