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Physics Colloquium – Carlos Silva
January 27, 2020 | 4:00 pm - 5:00 pm
Title:Excitonpolarons in two-dimensional hybrid metal-halide perovskites
Abstract: While polarons — charges bound to a lattice deformationinduced by electron-phonon coupling — are primary photoexcitations at roomtemperature in bulk metal-halide hybrid organic-inorganic perovskites (HOIP),excitons — Coulomb-bound electron-hole pairs — are the stablequasi-particles in their two-dimensional (2D) analogues. Here we address thefundamental question: are polaronic effects consequential for excitons in2D-HIOPs? Based on our recent work, we argue that polaronic effects aremanifested intrinsically in the exciton spectral structure, which is comprisedof multiple non-degenerate resonances with constant inter-peak energy spacing.We highlight measurements of population and dephasing dynamics that point tothe apparently deterministic role of polaronic effects in excitonic properties.We contend that an interplay of long-range and short-range exciton-latticecouplings give rise to exciton polarons, a character that fundamentallyestablishes their effective mass and radius, and consequently, their quantumdynamics. Given this complexity, afundamentally far-reaching issue is how Coulomb-mediated many-bodyinteractions—elastic scattering such as excitation-induced dephasing,inelastic exciton bimolecular scattering, and multi-exciton binding—dependupon the specific exciton-lattice coupling within the structured excitationlineshape. We measure the intrinsic and density-dependent exciton dephasingrates of the multiple excitons and their dependence on temperature by means oftwo-dimensional coherent excitation spectroscopy. We find that diverse excitonsdisplay distinct intrinsic dephasing rates mediated by phonon scatteringinvolving different effective phonons, and contrasting rates of exciton-excitonelastic scattering. These findings establish specifically the consequence ofdistinct lattice dressing on exciton many-body quantum dynamics, whichcritically define fundamental optical properties that underpin photonics andquantum optoelectronics.
Host: Dali Sun