CAREER: Nanoscale Phonon Spectrometer to Quantitatively Characterize Low-Dimensional Heat Transfer

*技术摘要*这个学院早期职业发展(CALEAR)项目的实验旨在研究通过纳米几何图形的热流的基础科学。该项目旨在阐明声子行为的关键模型预测，例如表面散射的波长依赖性，以及复杂纳米几何结构选择性阻止、增强或引导热流的能力。这将通过开发一种探测纳米结构中单频声子传输的设备来实现。能量可控的声子将通过超导隧道结(STJ)产生。激发态电子通过结的注入会导致声子在随后的驰豫和重组过程中发射到库珀对基态。同样的原理也将用于STJ的声子探测：入射声子破坏探测器中的库珀对，产生可测量的隧道电流。成功的测量将引起纳米材料、热传输和超导设备领域的研究人员的广泛兴趣。该项目将支持一名研究生在纳米制造、低温和敏感测量技术方面的培训。它将在当代物理研究的广泛领域对学生进行教育，包括超导设备和声子传输。这项研究还将纳入一个新的推广模块，促进学生学习科学和更广泛地了解纳米技术。*非技术摘要*在绝缘材料中，热通过原子振动(声子)传递，这种振动在固体中传播，就像水中的涟漪或空气中的声波一样，但速度要快得多。现有的物理理论很好地解释了散体材料中的热传输；然而，当相同的材料被减少到只有几千个原子宽时，这些定律就失效了。理论建模预测了纳米结构的非凡行为--例如仅根据纳米结构的形状选择性地传输热波--但这些想法还没有被实验量化。这个学院早期职业发展项目将通过建造一个纳米大小的设备来创建和探测原子振动热传输来研究纳米级的热传输。这项工作将通过开发纳米材料的不同寻常的热性能来改进热电和微电子冷却模块等设备的工程设计。由于最新可用的先进纳米制造技术，这项工作直到最近才成为可能。该项目将支持一名研究生在相关尖端纳米制造、低温和敏感测量技术方面的培训。它将在当代物理研究的广泛领域对学生进行教育，包括超导设备和声子传输。此外，这项研究将被纳入一个新的推广单元，促进学生学习科学和更广泛地了解纳米技术。

****TECHNICAL ABSTRACT****The experiments in this Faculty Early Career Development (CAREER) project aim to study the fundamental science of heat flow through nanoscale geometries. The project intends to elucidate key model predictions of phonon behavior, such as the wavelength dependence of surface scattering and the ability of complex nanoscale geometries to selectively block, enhance, or direct heat flow. This will be accomplished by developing a device for probing single-frequency phonon transmission in nanostructures. Phonons of controlled energy will be generated by using superconducting tunnel junctions (STJs). Injection of excited-state electrons through the junction causes emission of phonons during the subsequent relaxation and recombination of the electrons into the Cooper-pair ground state. The same principle will be used for phonon detection by STJs: incident phonons break Cooper pairs in the detector, creating a measurable tunnel current. Successful measurements will be of broad interest to researchers in the fields of nanomaterials, thermal transport, and superconducting devices. The project will support the training of a graduate student in nanofabrication, cryogenics, and sensitive measurement techniques. It will educate the student in a broad range of contemporary physics research areas, including superconducting devices and phonon transport. The research will also be incorporated into a new outreach module promoting science learning to students and a broader understanding of nanotechnology. ****NON-TECHNICAL ABSTRACT****In insulating materials, heat is transmitted by atomic vibrations ('phonons'), which move through a solid like ripples in water or sound waves in air, but much more rapidly. Existing physical theories explain heat transport well in bulk materials; however, these laws break down when the same material is reduced to only a few thousand atoms wide. Theoretical modeling predicts remarkable behaviors for nanostructures - such as the selective transmission of heat waves based solely on the nanostructure's shape - but these ideas have not been experimentally quantified. This Faculty Early Career Development (CAREER) project will study nanoscale heat transport by building a nano-sized device to create and probe atomic vibrational heat transfer. This work will inform improved engineering of devices like thermoelectrics and microelectronic cooling modules through the exploitation of nanomaterials' unusual thermal properties. This work has only recently been made possible due to newly available advanced nanofabrication techniques. The project will support the training of a graduate student in related cutting-edge nanofabrication, cryogenics, and sensitive measurement techniques. It will educate the student in a broad range of contemporary physics research areas, including superconducting devices and phonon transport. In addition, the research will be incorporated into a new outreach module promoting science learning to students and a broader understanding of nanotechnology.