Regensburg 2025 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 11: Ultra-fast Phenomena I
HL 11.9: Talk
Monday, March 17, 2025, 18:15–18:30, H14
Phonon-driven exciton population oscillations in Methylammonium Lead Bromide Perovskites. — •Mohsin Sayar1, Katrin Winte1, Daniel Timmer1, Somayeh Souri1, Davide Ceratti2, David Cahen2, Christoph Lienau1, and Antonietta De Sio1 — 1Carl von Ossietzky Universität, Oldenburg, Germany. — 2Weizmann Institute of Science, Rehovot, Israel
Halide perovskites exhibit unique optoelectronic properties significantly influenced by electron-phonon interactions. Recent work shows that the internal fields induced by coherent lattice motions can transiently control ultrafast excitonic optical response in bulk CsPbBr3[1]. Here, we demonstrate this behaviour also in CH3NH3PbBr3 across different crystal phases, using temperature-dependent ultrafast transient reflectivity with 10 fs time resolution. Following resonant exciton excitation reveals coherent low-frequency phonon oscillations at 40cm−1 and 67cm−1, corresponding to Pb-Br-Pb bending and stretching modes[2] that most strongly couple to the exciton. Additionally, we observe faster oscillations with dominant period of 105 fs in all crystal phases, arising from coherent exciton population transfer between 1s and 2p excitonic states, off-resonantly driven by the low-frequency phonon fields. We rationalize these results by a phenomenological model accounting for the coupling of excitons to the low frequency phonon modes and coupling of 1s-2p vibronic manifolds via the phonon fields[1]. These results may have important implications for transiently modifying the optoelectronic properties of perovskites.
Keywords: Excitons; Hybrid Perovskites; Ultrafast Spectroscopy; Phonon Coupling