Phonon coherences reveal the polaronic character of excitons in two-dimensional lead-halide perovskites

• Published in: arXiv.org
• Main Authors: Thouin, Félix, Valverde Chávez, David A, Quarti, Claudio, Cortecchia, Daniele, Bargigia, Ilaria, Beljonne, David, Petrozza, Annamaria, Silva, Carlos, Ajay Ram Srimath Kandada
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 15.06.2019
• Subjects: Chemical bonds; Coupling (molecular); Covalent bonds; Crystal lattices; Current carriers; Density functional theory; Excitons; Lattice vibration; Organic semiconductors; Perovskites; Phonons; Physics - Chemical Physics; Physics - Materials Science; Raman spectroscopy; Semiconductor crystals; Semiconductor materials; Softness
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1807.10539

Hybrid organic-inorganic semiconductors feature complex lattice dynamics due to the ionic character of the crystal and the softness arising from non-covalent bonds between molecular moieties and the inorganic network. Here we establish that such dynamic structural complexity in a prototypical two-dimensional lead iodide perovskite gives rise to the coexistence of diverse excitonic resonances, each with a distinct degree of polaronic character. By means of high-resolution resonant impulsive stimulated Raman spectroscopy, we identify vibrational wavepacket dynamics that evolve along different configurational coordinates for distinct excitons and photocarriers. Employing density functional theory calculations, we assign the observed coherent vibrational modes to various low-frequency (\(\lesssim 50\)\,cm\(^{-1}\)) optical phonons involving motion in the lead-iodide layers. We thus conclude that different excitons induce specific lattice reorganizations, which are signatures of polaronic binding. This insight on the energetic/configurational landscape involving globally neutral primary photoexcitations may be relevant to a broader class of emerging hybrid semiconductor materials.