Prof. Yangyu GUO¹

Talk: "Phonon hydrodynamics beyond linear regime"

¹School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, China

Figure 1: Thermal rectification in an asymmetric graphite micro-ribbon in nonlinear phonon hydrodynamic regime.

Phonon hydrodynamics usually occurs in dielectric crystals at very low temperatures and has been extensively investigated throughout the last century. In recent years, there has been renewed interest in phonon hydrodynamics due to its emergence in graphitic materials at elevated temperatures, for instance, the observation of phonon Poiseuille flow at ~100 K in isotopically purified graphite micro-ribbons [1].

A solid-state graphite thermal Tesla valve [2] has been recently designed in the hydrodynamic regime, indicating a nonlinear mechanism yet to be uncovered. We first demonstrate the essential physics of phonon hydrodynamics beyond the linear regime using a semi-analytic solution of the phonon Boltzmann equation under the dual relaxation model [3, 4], including the saturation of phonon drift and heat-flux reduction.

Then we unveil the correlation between nonlinear phonon hydrodynamics and thermal rectification in asymmetric graphite ribbons through a direct numerical solution of the nonlinear phonon Boltzmann equation in complex geometries [5]. Finally, we discuss the theoretical explanation of the thermal Tesla valve and existing open questions.

• [1] X. Huang, Y. Guo et al., Nat. Commun. 14, 2044 (2023).
• [2] X. Huang et al., Nature 634, 1086–1090 (2024).
• [3] Y. Guo et al., Phys. Rev. B 104, 075450 (2021).
• [4] W. Liu and Y. Guo, Phys. Rev. B 111, 125417 (2025).
• [5] W. Liu, K. Zhang and Y. Guo, Phys. Rev. Mater. 10, L053001 (2026).

Acknowledgements: The work was supported by the National Natural Science Foundation of China (Grant No. 12505043).