Long-lived Coherent Phonons Reveal Competing Thermal and Many-Body Dynamics in α-In2Se3
Abstract
The fate of quantum coherence following photoexcitation is a central problem in nonequilibrium condensed-matter physics, especially in low-dimensional solids where electronic, structural and many-body energy scales are strongly coupled. Here, we investigate this interplay in ferroelectric α-In2Se3 using broadband transient-grating spectroscopy with ∼5 fs laser pulses. Photoexcitation launches pronounced oscillations dominated by a ∼104 cm−1 mode that persists for several picoseconds. Measurements from 10 to 300 K show that its frequency remains nearly unchanged while its coherence is progressively suppressed, distinguishing the lattice coordinate from thermally activated dephasing. Varying excitation energy reveals a distinct crossover in which increasing photoexcitation progressively modifies and damps the coherent response. First-principles calculations assign the dominant oscillation to a 101.47 cm−1 Γ-point optical phonon involving collective In-Se displacement, while quantum-dynamical simulations reproduce the main transient-grating oscillations. These results establish α-In2Se3 as a model system for independently probing lattice coherence, thermal fluctuations and carrier-density-dependent interactions, revealing how a polar van der Waals semiconductor evolves from coherent lattice motion toward an incoherent many-body state after ultrafast excitation.
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BibTeX
@misc{zhang2026longlived,
title = {{Long-lived Coherent Phonons Reveal Competing Thermal and Many-Body Dynamics in $α$-In$_2$Se$_3$}},
author = {Xuanchao Zhang and Dehao Yuan and Junhua Zhou and Vandana Tiwari and Fulu Zheng and Ajay Jha and Hong-Guang Duan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.04863},
eprint = {2610.04863},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.04863},
}
RIS
TY - UNPB
TI - Long-lived Coherent Phonons Reveal Competing Thermal and Many-Body Dynamics in α-In_2Se_3
AU - Xuanchao Zhang
AU - Dehao Yuan
AU - Junhua Zhou
AU - Vandana Tiwari
AU - Fulu Zheng
AU - Ajay Jha
AU - Hong-Guang Duan
PY - 2026
DA - 2026/10/04
PB - arXiv
DO - 10.48550/arxiv.2610.04863
UR - https://arxiv.org/abs/2610.04863
AB - The fate of quantum coherence following photoexcitation is a central problem in nonequilibrium condensed-matter physics, especially in low-dimensional solids where electronic, structural and many-body energy scales are strongly coupled. Here, we investigate this interplay in ferroelectric α-In_2Se_3 using broadband transient-grating spectroscopy with ∼5 fs laser pulses. Photoexcitation launches pronounced oscillations dominated by a ∼104 cm^−1 mode that persists for several picoseconds. Measurements from 10 to 300 K show that its frequency remains nearly unchanged while its coherence is progressively suppressed, distinguishing the lattice coordinate from thermally activated dephasing. Varying excitation energy reveals a distinct crossover in which increasing photoexcitation progressively modifies and damps the coherent response. First-principles calculations assign the dominant oscillation to a 101.47 cm^−1 Γ-point optical phonon involving collective In-Se displacement, while quantum-dynamical simulations reproduce the main transient-grating oscillations. These results establish α-In_2Se_3 as a model system for independently probing lattice coherence, thermal fluctuations and carrier-density-dependent interactions, revealing how a polar van der Waals semiconductor evolves from coherent lattice motion toward an incoherent many-body state after ultrafast excitation.
ER -