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Updated: Jan 2, 2026

High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
Published on: June 28, 2016
Coherent charge-phonon correlations and exciton dynamics in orthorhombic CH3NH3PbI3 measured by ultrafast multi-THz
Yang Lan1, Xixi Tao1, Xianghua Kong1
1Department of Physics, McGill University, Montreal, Quebec H3A 2T8, Canada.
Abstract:
We use time-resolved multi-terahertz spectroscopy for the range 4-40 meV to probe coherent and incoherent ultrafast charge carrier and exciton dynamics in the low temperature orthorhombic phase of the hybrid metal halide perovskite CH3NH3PbI3. Time- and energy-resolved terahertz reflectivity maps reveal strongly damped but coherent oscillations in the 2-4 THz reststrahlen band, indicating charge coupling to a distribution of low energy phonon modes centered at 0.9 THz (3.7 meV or 30 cm-1). First-principles calculations reveal that these modes are entirely of mixed organic/inorganic sublattice character, with the power spectrum of the coherent oscillations showing a high frequency cutoff just at the onset of organic cation-only vibrations. Two anomalous reflectivity signatures are observed which are not phonon related, which we assign to a free exciton at 12 meV appearing on a 0.5 ps time scale and a defect bound exciton at 29-32 meV appearing on slower 1 ps time scale. Our measurements reveal the coherent coupling of charges to low energy vibrations of mixed sublattice character and the presence of two distinct populations of free and bound excitons at low temperatures.
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