CAREER: Anisotropic Suppression of Lattice Thermal Conductivity through the Interaction between Phonons and Thermal Magnetic Excitations

更好地了解磁性是如何影响热传递的，可以影响从计算机芯片设计到航天器等关键应用。该项目的总体目标是设计一种创新的热开关，它允许通过磁力控制热流。由于不存在完美的热导体或绝缘体，设计具有理想热传输性能的系统一直是一个挑战。因此，在能量的产生、传递和消耗过程中如何控制热流是一个非常重要的问题。这个职业项目将使用国家设施的创新实验研究和高性能热流计算模型的组合。首席调查员将与当地高中合作，为学生提供接触大型数据集的机会，并通过设计的课外活动学习使用软件工具进行分析。其他举措包括在针对南加州内陆帝国多样化社区的社区活动中进行科学演示，以及从附近社区学院招募优秀学生来度过暑期工作。这一职业项目利用创新的实验技术，在计算模拟的支持下，对核结构中的热激发(声子)和磁结构中的热激发(磁子)之间的相互作用提供了第一组直接测量。这些结果有望阐明这些相互作用对晶格热输运的各向异性抑制，从而能够设计和控制具有增强热输运性能的新一代多功能晶格结构。该项目以中子散射技术的最新进展为基础，利用几台非弹性中子谱仪对10-1300K温度和高达5T的外部磁场下的声子和热磁激发进行互补测量，提供各种声子模式的色散关系、群速度和寿命数据；基于第一性原理密度泛函理论的分子动力学模拟用于解释测量的声子动力学，并了解磁激发对声子散射引起的晶格热输运的影响。该项目的成功有望显著提高对热磁激发如何影响负责晶格输运的声子的基本理解；量化相互作用对各向异性热输运性质的贡献；并为利用磁结构作为额外自由度来定制晶格热输运提供指导。该项目还扩展了非弹性中子散射作为了解热传输过程的科学工具的使用。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

A better understanding of how magnetism affects heat transfer can impact key applications ranging from the design of computer chips to spacecraft. The overarching goal of this project is to design an innovative thermal switch, which allows the control of heat flow by magnetism. It has been challenging to design systems with desired thermal transport properties as no perfect thermal conductor or insulator exists. Therefore, being able to control heat flow in the generation, transfer, and consumption of energy represents a very important issue. This CAREER project will use a combination of innovative experimental research at national facilities and high-performance computing modeling of heat flow. The principal investigator will collaborate with local high schools to provide an opportunity for students to get exposure to large data sets and learn to use software tools for their analysis through designed extracurricular activities. Other initiatives include science demonstrations at community events targeted to the diverse community in Southern California's Inland Empire and recruitment of high-achieving students from nearby community colleges to spend their summer working on the project. This Career project utilizes innovative experimental techniques, supported by computational simulations, to provide the first set of direct measurements of the interactions between the thermal excitations in nuclear structure (phonons) and the thermal excitations in magnetic structure (magnons). The results are expected to illuminate the anisotropic suppression of lattice thermal transport by these interactions, which enables the design and control of a new generation of multifunctional lattice structures with enhanced thermal transport properties. This project builds upon recent advances in neutron scattering techniques by leveraging several inelastic neutron spectrometers to make complementary measurements of phonons and thermal magnetic excitations at temperatures from 10 to 1300 K and under external magnetic fields up to 5 T. The measurements provide dispersion relation, group velocities, and lifetime data for various phonon modes; molecular dynamics simulations based on first principles density functional theory is used to interpret the measured phonon dynamics and to understand the effects of magnetic excitations on lattice thermal transport due to phonon scattering. The success of the project is expected to significantly improve fundamental understanding of how thermal magnetic excitations affect the phonons responsible for the lattice transport; quantify the contribution of the interactions to the anisotropic thermal transport properties; and provide guidelines to tailor the lattice thermal transport using magnetic structure as an additional degree of freedom. The project also extends the use of inelastic neutron scattering as a scientific tool to understand thermal transport process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.