Department of Mechanical Engineering, §Department of Materials Science and Engineering, and ‡Department of Nuclear Science and Engineering Massachusetts Institute of Technology , Cambridge, Massachusetts 02139, United States.
Nano Lett. 2018 Jan 10;18(1):638-649. doi: 10.1021/acs.nanolett.7b04932. Epub 2017 Dec 20.
In the hydrodynamic regime, phonons drift with a nonzero collective velocity under a temperature gradient, reminiscent of viscous gas and fluid flow. The study of hydrodynamic phonon transport has spanned over half a century but has been mostly limited to cryogenic temperatures (∼1 K) and more recently to low-dimensional materials. Here, we identify graphite as a three-dimensional material that supports phonon hydrodynamics at significantly higher temperatures (∼100 K) based on first-principles calculations. In particular, by solving the Boltzmann equation for phonon transport in graphite ribbons, we predict that phonon Poiseuille flow and Knudsen minimum can be experimentally observed above liquid nitrogen temperature. Further, we reveal the microscopic origin of these intriguing phenomena in terms of the dependence of the effective boundary scattering rate on momentum-conserving phonon-phonon scattering processes and the collective motion of phonons. The significant hydrodynamic nature of phonon transport in graphite is attributed to its strong intralayer sp hybrid bonding and weak van der Waals interlayer interactions. More intriguingly, the reflection symmetry associated with a single graphene layer is broken in graphite, which opens up more momentum-conserving phonon-phonon scattering channels and results in stronger hydrodynamic features in graphite than graphene. As a boundary-sensitive transport regime, phonon hydrodynamics opens up new possibilities for thermal management and energy conversion.
在动力学状态下，声子在温度梯度下会以非零的集体速度漂移，这类似于粘性气体和流体的流动。对动力学声子输运的研究已经跨越了半个多世纪，但主要局限于低温（约 1 K），最近才扩展到低维材料。在这里，我们基于第一性原理计算确定石墨是一种在更高温度（约 100 K）下支持声子动力学的三维材料。具体而言，通过求解石墨带状物中声子输运的玻尔兹曼方程，我们预测声子泊肃叶流动和克努森最小值可以在液氮温度以上实验观测到。此外，我们揭示了这些有趣现象的微观起源，即有效边界散射率随动量守恒的声子-声子散射过程和声子的集体运动的依赖性。石墨中声子输运的显著动力学性质归因于其强烈的层内 sp 杂化键合和较弱的范德华层间相互作用。更有趣的是，石墨中与单个石墨烯层相关的反射对称性被打破，这开辟了更多的动量守恒的声子-声子散射通道，并导致石墨中比石墨烯更强的动力学特征。作为一种边界敏感的输运状态，声子动力学为热管理和能量转换开辟了新的可能性。
