Hydrodynamic phonon transport in solids exhibits unique thermal transport behaviors, such as second sound, the Poiseuille flow, and ultrahigh thermal conductivity. However, those have been limited up to the cryogenic temperature ($\sim 1$ K) for a few materials. In this work, by employing the phonon Boltzmann transport equation, we demonstrate hydrodynamic phonon transport in organic systems such as bulk crystalline polymers. Remarkable hydrodynamic phonon transport up to 50 K is demonstrated for both polyacene ${(-{\mathrm{C}}_4{\mathrm{H}}_2-)}_n$ and polyacetylene ${(-{\mathrm{C}}_2{\mathrm{H}}_2-)}_n$ crystals. More interestingly, a weak phonon hydrodynamic behavior takes place in crystalline polyethylene ${(-{\mathrm{C}}_2{\mathrm{H}}_4-)}_n$ in the intermediate-temperature range around 120 K, different from the observed hydrodynamics in most systems. The spectral phonon analysis reveals that the torsional motion of the $A_2$ mode causes this unique hydrodynamic behavior. A modified criterion for the emergence of hydrodynamic phonon transport is proposed which agrees quantitatively with the results from thermal conductivity and phonon drifting component calculations. This study provides physical insights into the understanding of phonon hydrodynamics in organic materials and also a reliable criterion to probe the hydrodynamic phonon transport in complex systems.

中文翻译：

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块状结晶聚合物中的流体动力声子传输

固体中的流体动力声子传输表现出独特的热传输行为，例如第二声，泊瓦流和超高导热率。但是，这些限制仅限于低温（$〜\mathrm{1个}$ K）几种材料。在这项工作中，通过使用声子玻耳兹曼输运方程，我们证明了有机体系（例如本体结晶聚合物）中的流体动力学声子输运。两种并苯均显示出高达50 K的显着水动力声子传输${（-{\mathrm{C}}_4{\mathrm{H}}_2-）}_{ñ}$ 和聚乙炔 ${（-{\mathrm{C}}_2{\mathrm{H}}_2-）}_{ñ}$晶体。更有趣的是，结晶聚乙烯中存在弱的声子流体动力学行为${（-{\mathrm{C}}_2{\mathrm{H}}_4-）}_{ñ}$在大约120 K的中间温度范围内，不同于大多数系统中观察到的流体动力学。频谱声子分析表明，${\mathrm{一种}}_2$模式导致这种独特的流体动力学行为。提出了一种修正的流体动力声子传输准则，该准则与热导率和声子漂移分量计算的结果定量地吻合。这项研究提供了对有机材料中声子流体动力学理解的物理见解，并且是探测复杂系统中流体声子传输的可靠标准。