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: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=746794
• 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，考虑到热与每一个物理过程都有着不可分割的联系，科学家和工程师们仍然无法了解热物理学的全貌。推动我们对热物理的基本理解对于提高清洁能源技术的能量转换效率至关重要（即，热电和光电），改善电子器件的冷却（即，CPU）和解决量子计算机中量子位退相干的挑战。典型的教科书理解的热输运在固体中描述的扩散方程，或等效的，傅立叶定律的现象。然而，随着系统的尺寸缩小到微观热载体之间散射的长度尺度的量级（即，声子），这张照片打破了，需要一个原子的描述。我们开发了一种自下而上的理论方法，该方法采用从第一原理量子力学计算获得的材料性质（即，密度泛函理论）作为玻尔兹曼输运方程的输入来预测实验可观测值（即，温度）。这个框架进行了扩展，并发现能够捕获什么以前被认为是一个外来的热传输制度：声子流体动力学。这种状态的一个特征是温度不根据扩散方程发展，而是服从波动方程。应用这一理论，我们报道了在100 K以上的温度下石墨中第二声的实验确认，创下了高温声子流体力学的最新记录。在此之前，第二声只在温度低于20 K的少数材料中观察到，积极的研究在20世纪70年代停止。我们的结果振兴了一个几乎被遗忘的想法，并为基础和应用研究开辟了多条道路，这将是拟议的发现补助金研究计划的重点。我们将开始扩展我们的数值框架，将从第一原理和机器学习计算获得的数据作为输入，并预测实验流体动力学特征。然后，我们将使用这个框架来指导我们的实验工作，观察声子流体力学在二维材料和货车德瓦耳斯异质结构。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，以控制特定技术应用的声子流体力学。为了推动我们的清洁能源转换和存储技术以及我们的计算能力的极限，我们必须推动我们对伴随的热过程的理解。这项研究计划将为声子流体力学的未来研究建立一个最先进的平台，这将有利于加拿大采用清洁能源技术和培养下一代世界级科学家和工程师的努力。