In two-dimensional hybrid organic-inorganic metal-halide perovskites, the intrinsic optical excitation lineshape reflects multiple excitons with distinct binding energies, which are dressed differently by the hybrid lattice. Given this complexity, a fundamentally far-reaching issue is how Coulomb-mediated many-body interactions -- elastic scattering such as excitation-induced dephasing, inelastic exciton bimolecular scattering, and multi-exciton binding -- depend upon the specific exciton-lattice coupling within the structured excitation lineshape. We measure the intrinsic and density-dependent exciton dephasing rates of the multiple excitons and their dependence on temperature by means of two-dimensional coherent excitation spectroscopy. We find that diverse excitons display distinct intrinsic dephasing rates mediated by phonon scattering involving different effective phonons, and contrasting rates of exciton-exciton elastic scattering. These findings establish specifically the consequence of distinct lattice dressing on exciton many-body quantum dynamics, which critically define fundamental optical properties that underpin photonics and quantum optoelectronics. We furthrt examine the evolution of the two-dimensional coherent exciton lineshape at 5 Kwith population waiting time (τp) in a two-dimensional lead-iodide perovskite derivative. At τp= 0, signatures of excitation-induced dephasing — the manifestation ofmany-body elastic scattering — are present in the spectral lineshape. We find that this lineshape evolves with τp over time windows in which the population itself is static, in a manner that indicates time-dependent excitation-induced dephasing. Specifically, we find that the dephasing slows down with τp. This spectral evolution invokes time-varying inter-exciton coherences, and we discuss the possible role of dark exciton states in these quantum dynamics.

Excitonic many-body effects in two-dimensional metal-halide perovskites

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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