Berlin 2024 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 36: Poster III

HL 36.14: Poster

Wednesday, March 20, 2024, 18:00–20:30, Poster E

Theory of Phonon Sidebands in the Absorption Spectra of Moiré Exciton-Polaritons — •Kevin Jürgens¹, Daniel Wigger², and Tilmann Kuhn¹ — ¹Institute of Solid State Theory, University of Münster, Germany — ²Department of Physics, University of Münster, Germany

Excitons in twisted bilayers of transition metal dichalcogenides experience a spatially varying electronic environment, which manifests in the formation of a periodic and twist-angle dependent moiré potential. For small twist angles the excitons are localized at the minima of the moiré potential, resulting in a flat band structure, whereas for large twist angles the excitons are almost entirely delocalized. When placing the heterostructure in an optical cavity, the moiré excitons interact with the photonic field, which leads to the formation of moiré exciton-polaritons. These couple to the lattice vibrations of the heterostructure giving rise to transitions between the two polariton branches that strongly depend on the twist angle.

We calculate the absorption spectra in the limit of small polariton densities. The polaritons are coupled to the same phonon bath, which results in inter- and intrabranch transitions in the polariton dispersion. We analyze the spectra and find rich phonon sidebands reflecting optical transitions assisted by phonon emission or absorption, that strongly depend on the twist angle. We identify the polariton gap and the presence of Van Hove singularities as critical parameters.

Keywords: moiré excitons; polaritons; phonons