Probing phonon hydrodynamics in 2D materials

探测二维材料中的声子流体动力学

• 批准号: RGPIN-2021-02957
• 负责人: Huberman, Samuel
• 金额: $ 2.11万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2021
• 资助国家: 加拿大
• 起止时间: 2021-01-01 至 2022-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=742298
• 关键词: Probing; phonon; hydrodynamics; 2D; materials

It is strange that, given heat's inseparable connection with every physical process, a complete picture of thermal physics has continued to elude scientists and engineers. Pushing our fundamental understanding of thermal physics is critical to increasing energy conversion efficiency in clean energy technologies (i.e., thermoelectrics and photovoltaics), improving the cooling of electronic devices (i.e., CPUs) and addressing the challenges of qubit decoherence in quantum computers. The typical textbook understanding of thermal transport in a solid is described phenomenologically by the diffusive equation or, equivalently, Fourier's Law. However, as the size of the system shrinks to the order of the length scale of the scattering between the microscopic carriers of heat (i.e., phonons), this picture breaks down and an atomistic description is required. We developed a bottom-up theoretical approach that took material properties obtained from first principles quantum mechanical calculations (i.e., density functional theory) as input to the Boltzmann transport equation to predict the experimental observable (i.e., temperature). This framework was extended and found to be capable of capturing what was previously considered to be an exotic thermal transport regime: phonon hydrodynamics. A signature of this regime is that temperature does not evolve according to the diffusion equation, but rather obeys the wave equation. Applying this theory, we reported the experimental confirmation of second sound in graphite at temperatures above 100 K, setting the current record for high temperature phonon hydrodynamics. Prior to this result, second sound had only been observed in a handful of materials at temperatures below 20 K, with active research ceasing in the 1970s. Our result revitalizes a nearly forgotten idea and opens up multiple paths forward for fundamental and applied research, which will be the focus of the proposed Discovery Grant research program. We will begin by extending our numerical framework that will take data obtained from first principles and machine learning calculations as input and predict experimental hydrodynamic signatures. We will then use this framework to guide our experimental efforts to observe phonon hydrodynamics in 2D materials and van der Waals heterostructures. Using our validated theoretical and experimental tools, we will engineer the microscopic properties materials to control phonon hydrodynamics for specific technological applications. To push the limits of our clean energy conversion and storage technologies as well as our computing power, we must push our understanding of the concomitant thermal processes. This research program will establish a state of the art platform for the future study of phonon hydrodynamics that will benefit Canada's efforts to adopt clean energy technologies and train the next generation of world class scientists and engineers.

奇怪的是，鉴于Heat与每个物理过程的密不可分的联系，热物理学的完整图片继续避免了科学家和工程师。推动对热物理学的基本理解对于提高清洁能源技术的能量转换效率（即热电学和光伏）至关重要，从而改善了电子设备的冷却（即CPU），并解决量子计算机中Qubit倒置的挑战。典型的教科书理解是通过扩散方程式或等效地说明傅立叶定律在现象学上对热运输的理解。但是，随着系统的大小缩小到微观载体（即声子）之间散射的长度尺度的顺序，此图片会分解并需要一个原子描述。我们开发了一种自下而上的理论方法，该方法采用了从第一原理量子机械计算（即密度函数理论）获得的材料特性，作为对玻尔兹曼传输方程的输入，以预测可观察到的实验性观察（即温度）。该框架被扩展并发现能够捕获以前被认为是异国情调的热运输方式：声子流体动力学。该制度的一个签名是温度不会根据扩散方程而发展，而是遵守波动方程。在应用该理论时，我们报告了在100 K以上的温度下在石墨中对第二种声音的实验确认，从而为高温声子流体动力学创造了当前记录。在此结果之前，仅在低于20 K的温度下在少数材料中观察到第二种声音，1970年代的主动研究停止。我们的结果振兴了一个几乎被遗忘的想法，并为基本和应用研究开辟了多个途径，这将是拟议的发现赠款研究计划的重点。我们将首先扩展我们的数值框架，该框架将从第一原理和机器学习计算获得的数据作为输入并预测实验性流体动力学特征。然后，我们将使用此框架来指导我们的实验工作，以观察2D材料和范德华异质结构中的声子流体动力学。使用我们经过验证的理论和实验工具，我们将设计微观特性材料来控制特定技术应用的声子水动力学。为了突破清洁能源转换和存储技术的限制以及计算能力，我们必须推动对伴随的热过程的理解。该研究计划将建立一个最先进的平台，用于对声子流体动力学的未来研究，这将使加拿大采用清洁能源技术并培训下一代世界一流的科学家和工程师的努力。