Scattering Selection Rules of Chiral Phonons and Thermal Transport

随着现代设备的小型化，有效地散发它们产生的强烈热量已成为一项艰巨的挑战。此外，热量可以比现有的电子设备更有效地用于执行计算任务。为了解决这些问题，该项目研究了固体中的一种新型振动。原子的振动携带热量，它们之间的相互作用决定了热量的传递。科学家通常把热引起的振动看作是来回运动。然而，许多材料的振动是圆形的，人们对这种振动如何相互作用知之甚少。在这个项目中，来自同步加速器的超强x射线和超精确能量被用来测量这些振动，以配置它们相互作用的规则。这些发现的规则将为控制设备中的热量流动提供新的方法。此外，通过寻找不相互作用的振动，创新的设备可能会被创造出来，利用这些振动来携带信息和执行计算。本项目旨在研究手性声子的非弹性x射线散射，以了解它们在晶格热输运中的作用。提出的工作有望实现三个主要目标：量化具有破逆对称性的晶格的热输运性质，以便通过声子工程控制这些性质；提出了非弹性x射线散射理论和技术，并将其应用于具有角动量的声子动力学；并揭示了手性声子的物理现象，这可能导致具有与电子对应物相似拓扑行为的奇异量子态。结合实验和理论工作将使人们更好地理解声子的角动量动力学，它可以通过选择规则强烈地改变声子之间的耦合和其他自由度，如自旋。该项目还可以通过操纵mev带宽光束的偏振来帮助开发非弹性x射线散射技术的新领域。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the miniaturization of modern devices, effectively dissipating the intense heat they generate has become a daunting challenge. Also, heat can potentially be used to perform computation tasks more efficiently than existing electronics. To address these issues, the project studies a type of novel vibrations in solids. Vibrations of atoms carry heat and the interactions between them dictate heat transfer. Scientists usually treat vibrations induced by heat as back-and-forth motions. However, vibrations in many materials are circular and little is known about how such vibrations interact with each other. In the project, extremely strong X-ray with ultra-precise energy from synchrotrons is used to measure these vibrations to configure the rules of their interactions. The discovered rules will provide new ways to control the flow of heat in devices. Additionally, by finding vibrations that do not interaction with each other, innovative devices may be created to use these vibrations to carry information and perform computation.This project aims to study the inelastic X-ray scattering of chiral phonons to understand their roles in lattice thermal transport. The proposed work is expected to achieve three major objectives: quantify the thermal transport properties of lattices with broken inversion symmetry in order to control these properties by phonon engineering; advance the theory and technique of inelastic X-ray scattering and extend its usage to the dynamics of phonons with angular momentum; and reveal the physical phenomena of the chiral phonons, which may lead to exotic quantum states with topological behaviors similar to their electronic counterparts. The combined experimental and theoretical work will enable better understanding of the dynamics of phonons with angular momentum, which could strongly alter phonon couplings with each other and other degrees of freedom, such as spins, through selection rules. This project may also help develop a new field of inelastic X-ray scattering techniques through the manipulation of the polarization of a meV-bandwidth beam.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.