Phonon Coherence in Heat Conduction

Abstract

The lecture presents a recent conceptual frame and its implications regarding phonon coherence. The speaker's proposition introduces a revised heat conduction formalism that incorporates both particle-like and wave-like behaviors of thermal phonons, integrating intrinsic and mutual coherence times into a new thermal conductivity expression [1]. This approach, validated through direct atomic simulations and theoretical arguments, is particularly relevant in complex crystals but also amorphous systems, where coherence effects dominate thermal transport.

The lecture further examines the role of short-range spatial phonon coherence in resonant systems, revealing that this coherence length—largely independent of atomic interactions—can be tuned by adjusting resonance strength and frequency, thereby offering a robust method for engineering couplings between quasi-particles [2].

Additionally, the spatiotemporal coherence of lattice vibrations is shown to govern thermal conductivity across different phases of matter, diminishing from solid to liquid but increasing from liquid to gas, a behavior linked to atomic diffusion that provides a unified understanding of thermal transport [3].

References:

[1] Z. Zhang, Heat Conduction Theory Including Phonon Coherence, Phys. Rev. Lett. 128, 015901 (2022).

[2] Z. Zhang, et al., Spatial phonon coherence in resonant systems (2026).

[3] Z. Zhang, et al., Coherence of lattice vibrations across phases of matter (2025)

About the Speaker

Prof. Sebastian VOLZ is a distinguished research professor at French National Centre for Scientific Research (CNRS), currently serving as the Director of the Laboratoire des Solides Irradiés, a joint research unit of the French Alternative Energies and Atomic Energy Commission (CEA), CNRS and École Polytechnique. He received his Engineering degree from ISAE-ENSMA in 1993, followed by a Master's degree in Heat Transfer from Poitiers University in the same year. He obtained his PhD from ISAE-ENSMA in 1996 and completed his Professor thesis (HDR) at ISAE-ENSMA – University of Poitiers in 2004. Prior to his current directorship, Prof. Volz held various academic positions, including Associate Professor at the National Engineering School of Mechanics and Aerotechnics (ISAE-ENSMA), and CNRS Senior Research Fellow at Ecole Centrale Paris and the University of Tokyo.

Prof. Volz has been developing direct simulations and characterizations to understand heat in solids at the carrier's level. His group was involved in large european projects on thermoelectricity and thermal interface materials. He has led the european Thermal NanoSciences and NanoEngineering CNRS network (2001-2018) and the CNRS-University of Tokyo joint Laboratory for Integrated Micro-Mechatronic Systems (2018-2025). He also serves as an associate editor for several journals, including Nanoscale and Microscale Thermophysical Engineering, ES Energy & Environment, and Journal of Nanoelectronics and Optoelectronics. He has authored a book published by Springer in their Mechanical Engineering Series in 2024.

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