Scattering Selection Rules of Chiral Phonons and Thermal Transport

University Of California-Riverside, Riverside CA

Investigators

Abstract

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.