CAREER: Phonon Scattering By Electrons: From Fundamental Understanding To Thermal Transport Control

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Fundamental understanding and control of heat transport processes in our energy systems is crucial to improve the energy efficiency and sustainability of our society, as currently over 60% of our total energy consumption is rejected in the form of waste heat each year. Effective control of the heat transport remains a technological challenge because major heat carriers in solid materials are typically less sensitive to external influence. This CAREER project examines the theoretical basis and practical feasibility of a novel means to control heat transport in solids: using external electromagnetic fields to significantly alter the heat transfer processes. This project not only advances our fundamental understanding of energy transport in state-of-the-art materials and devices, but also benefits the society by providing new practical strategies to design more efficient and sustainable energy systems. This CAREER project also focuses on raising the workforce readiness for next-generation renewable energy technologies by exposing K-12 and undergraduate students to hands-on renewable energy harvesting projects, and promoting the diversity of the renewable energy field by providing research opportunities to undergraduate researchers from underrepresented minority communities.The overarching goal of this project is to understand how the interaction between phonons and electrons can modify the thermal transport properties of solid-state materials. This project is motivated by our recent finding that phonon-electron scattering can become the dominant phonon scattering mechanism in semiconductors with high electron concentrations at room temperature. Theoretically, state-of-the-art first-principles phonon-electron scattering calculation with coupled Boltzmann transport equations will be employed to understand phonon damping and amplification by phonon-electron scattering, reveal key factors that determine the strength of phonon-electron scattering and identify materials with strong phonon-electron scattering for potential thermal switching applications. Experimentally, ultrafast optical and electron spectroscopic methods will be developed and applied to characterize the phonon-electron scattering strength for phonon modes with different frequencies, momenta and polarizations and demonstrate solid-state thermal switching by modifying phonon-electron scattering via external photoexcitation and electrostatic gating. This CAREER project not only generates new insights for energy transfer processes in devices with high electron concentrations, but also provides transformative opportunities to develop novel functional energy materials and devices based on the interaction of microscopic energy carriers.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.