近日，华中科技大学的朱增伟及其研究小组与法国巴黎文理研究大学的Kamran Behnia合作并取得一项新进展。经过不懈努力，他们对WTe₂中纯度依赖洛伦兹数、电子流体力学和的电子-声子耦合进行研究。相关研究成果已于2024年7月30日在国际知名学术期刊《中国科学：物理、力学与天文学》上发表。

该研究团队探究了Weyl半金属WTe2在0.3开尔文温度下的电与热传输特性。他们发现，Wiedemann-Franz定律在2开尔文及以下温度时成立，但在超过2开尔文时开始出现向下偏离的现象。这种偏离在更纯净的样品中表现得更为显著，这与电子传输的流体动力学模型中的预期相符，即一小部分电子-电子碰撞能够保持动量。此外，研究指出声子是主要的热传导载体，并且它们的平均自由程并未展现出克努森最小值。这一现象可能归因于较弱的非谐性，正如比热的温度依赖性所表明的那样。

声子与电子之间频繁的动量交换引发了声子热导率的量子振荡现象。当Umklapp过程的声子-声子碰撞不再作为电子动量流的汇聚点时，电子-声子散射的Bloch-Grüneisen图像在低温条件下会失效。与半金属Sb的对比研究显示，正常的声子-声子碰撞效应因非谐性的增强而被放大。在这两种半金属中，低温环境下，电子-声子碰撞会降低声子的能量流，但对电子的动量流没有减弱作用。

附：英文原文

Title: Purity-dependent Lorenz number, electron hydrodynamics and electron-phonon coupling in WTe₂

Author: Xie, Wei, Yang, Feng, Xu, Liangcai, Li, Xiaokang, Zhu, Zengwei, Behnia, Kamran

Issue&Volume: 2024-07-30

Abstract: We present a study of electrical and thermal transport in Weyl semimetal WTe₂ down to 0.3 K. The Wiedemann-Franz law holds below 2 K and a downward deviation starts above. The deviation is more pronounced in cleaner samples, as expected in the hydrodynamic picture of electronic transport, where a fraction of electron-electron collisions conserve momentum. Phonons are the dominant heat carriers and their mean-free-path does not display a Knudsen minimum. This is presumably a consequence of weak anharmonicity, as indicated by the temperature dependence of the specific heat. Frequent momentum exchange between phonons and electrons leads to quantum oscillations of the phononic thermal conductivity. Bloch-Grüneisen picture of electron-phonon scattering breaks down at low temperature when Umklapp ph-ph collisions cease to be a sink for electronic flow of momentum. Comparison with semi-metallic Sb shows that normal ph-ph collisions are amplified by anharmonicity. In both semimetals, at cryogenic temperature, e-ph collisions degrade the phononic flow of energy but not the electronic flow of momentum.

DOI: 10.1007/s11433-024-2404-0

Source: https://link.springer.com/article/10.1007/s11433-024-2404-0