Slow Thermalization and Long-Lived Coherence across Acoustic Phonon Branches in BAs
Abstract
The exceptionally high thermal conductivity of cubic boron arsenide (BAs) arises from suppressed three-phonon scattering associated with its large acoustic--optical gap. In this regime, four-phonon processes become non-negligible, creating an unusual scattering hierarchy with unexplored consequences for nonequilibrium phonon dynamics. Here, time-resolved x-ray diffuse scattering reveals exceptionally slow, branch-dependent acoustic phonon thermalization and long-lived coherence. Exploiting branch sensitivity in one-phonon diffuse scattering, we resolve transverse acoustic (TA) and longitudinal acoustic (LA) thermalization times of 29.2 and 13.9~ps, respectively; even the LA timescale is at least three times that in common semiconductors. Phonon dispersion calculations assign coherent oscillations at 0.19 and 0.27~THz to the TA and LA modes, respectively; both persist with little decay over 50~ps, with comparable coherence found only in diamond. These findings provide a direct dynamical manifestation of the weak phonon scattering underlying the exceptional thermal transport of BAs.
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BibTeX
@misc{xiang2026slow,
title = {{Slow Thermalization and Long-Lived Coherence across Acoustic Phonon Branches in BAs}},
author = {Zeyu Xiang and Ying Peng and Ange Benise Niyikiza and Fanghao Zhang and Haoyuan Li and Takahiro Sato and Thomas Linker and Yanwen Sun and Meredith Henstridge and Vincent Esposito and James F. Cotter and Diling Zhu and Zhifeng Ren and Bolin Liao},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.13541},
eprint = {2609.13541},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.13541},
}
RIS
TY - UNPB
TI - Slow Thermalization and Long-Lived Coherence across Acoustic Phonon Branches in BAs
AU - Zeyu Xiang
AU - Ying Peng
AU - Ange Benise Niyikiza
AU - Fanghao Zhang
AU - Haoyuan Li
AU - Takahiro Sato
AU - Thomas Linker
AU - Yanwen Sun
AU - Meredith Henstridge
AU - Vincent Esposito
AU - James F. Cotter
AU - Diling Zhu
AU - Zhifeng Ren
AU - Bolin Liao
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.13541
UR - https://arxiv.org/abs/2609.13541
AB - The exceptionally high thermal conductivity of cubic boron arsenide (BAs) arises from suppressed three-phonon scattering associated with its large acoustic--optical gap. In this regime, four-phonon processes become non-negligible, creating an unusual scattering hierarchy with unexplored consequences for nonequilibrium phonon dynamics. Here, time-resolved x-ray diffuse scattering reveals exceptionally slow, branch-dependent acoustic phonon thermalization and long-lived coherence. Exploiting branch sensitivity in one-phonon diffuse scattering, we resolve transverse acoustic (TA) and longitudinal acoustic (LA) thermalization times of 29.2 and 13.9~ps, respectively; even the LA timescale is at least three times that in common semiconductors. Phonon dispersion calculations assign coherent oscillations at 0.19 and 0.27~THz to the TA and LA modes, respectively; both persist with little decay over 50~ps, with comparable coherence found only in diamond. These findings provide a direct dynamical manifestation of the weak phonon scattering underlying the exceptional thermal transport of BAs.
ER -