发表机构
University of California, Santa Barbara; University of Houston; SLAC National Accelerator Laboratory（加州大学圣塔芭芭拉分校; 休斯顿大学; 斯坦福直线加速器中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过时间分辨X射线漫散射揭示BAs中声学声子支的慢热化（TA为29.2皮秒，LA为13.9皮秒）及长寿命相干性，直接证明了其弱声子散射机制，解释了其超高热导率。
AI 中文摘要
立方砷化硼（BAs）的超高热导率源于其大的声学-光学间隙所抑制的三声子散射。在此机制下，四声子过程变得不可忽略，形成了一种不寻常的散射层级，其对非平衡声子动力学具有尚未探索的后果。本文中，时间分辨X射线漫散射揭示了异常缓慢的、依赖于声子支的声学声子热化以及长寿命相干性。利用单声子漫散射中的支灵敏度，我们分别解析出横声学（TA）和纵声学（LA）声子热化时间为29.2皮秒和13.9皮秒；即使是LA时间尺度也至少是普通半导体中的三倍。声子色散计算将0.19太赫兹和0.27太赫兹处的相干振荡分别归属于TA和LA模式；两者在50皮秒内几乎没有衰减地持续存在，仅在金刚石中观察到相当的相干性。这些发现直接动力学地体现了支撑BAs优异热输运的弱声子散射。
英文摘要
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.
