Slow Dephasing of Coherent\nOptical Phonons in Two-Dimensional\nLead Organic Chalcogenides

Hybrid organic–inorganic semiconductors with strong\nelectron–phonon\ninteractions provide a programmable platform for developing a variety\nof electronic, optoelectronic, and quantum materials by controlling\nthese interactions. However, in current hybrid semiconductors such\nas halide perovskites, anharmonic vibrations with rapid dephasing\nhinder the ability to coherently manipulate phonons. Here, we report\nthe observation of long-lived coherent phonons in lead organic chalcogenides\n(LOCs), a new family of hybrid two-dimensional semiconductors. These\nmaterials feature harmonic phonon dynamics despite distorted lattices,\ncombining long phonon dephasing times with tunable semiconducting\nproperties. A dephasing time -up to 75 ps at 10 K, with up to ∼500\ncycles of phonon oscillation between scattering events, was observed,\ncorresponding to a dimensionless harmonicity parameter that is more\nthan an order of magnitude larger than that of halide perovskites.\nThe phonon dephasing time is significantly influenced by anharmonicity\nand centrosymmetry, both of which can be tuned through the design\nof the organic ligands enabled by the direct bonding between the organic\nand inorganic motifs. This research opens new opportunities for the\nmanipulation of electronic properties with coherent phonons in hybrid\nsemiconductors.