Expert Profile:

Prof. Jae Hun Seol is a professor in the Department of Mechanical and Robotics Engineering at Gwangju Institute of Science and Technology (GIST), Korea. He received his Ph.D. in Mechanical Engineering from The University of Texas at Austin under the supervision of Prof. Li Shi, and subsequently conducted postdoctoral research at The University of California, Berkeley with Prof. Arun Majumdar. His research focuses on micro/nanoscale heat transfer, thermal transport in low-dimensional materials, and the development of advanced thermal measurement techniques.

Title of Presentation:

 Hydrodynamic and Anomalous Heat Transport in Two-Dimensional Materials

Please choose one Forum Theme:

I. Heat Conduction and Quantum Thermodynamics in Low-Dimensional Systems

Abstract:

 Non-classical heat transport in low-dimensional materials has emerged as an important topic beyond the conventional Fourier diffusion framework, revealing collective and unconventional phonon transport phenomena. In this presentation, we provide a unified perspective on thermal transport in two-dimensional (2D) materials, focusing on the transition from phonon hydrodynamic transport to strongly scattered yet phonon-dominated conduction regimes.

We first discuss phonon hydrodynamics in graphite through combined observations of second sound and Poiseuille phonon flow. Using ultrafast thermoreflectance measurements, we observe clear wave-like thermal propagation associated with second sound. In contrast, thickness-dependent thermal transport measurements reveal signatures of viscous phonon flow characteristic of the Poiseuille regime. A notable finding is the emergence of a Knudsen minimum in both experimental configurations, providing a robust and unifying signature of hydrodynamic phonon transport. These results establish a direct connection between distinct hydrodynamic phenomena and demonstrate the critical role of momentum-conserving phonon scattering in enabling collective heat flow.

To broaden this picture, we further examine thermal transport in metallic 2D materials, with particular attention to Ti₃C₂T_x MXene. Although the material exhibits high electrical conductivity, thermal transport is predominantly governed by phonons over a wide temperature range. The absence of a conventional Umklapp peak, together with the presence of a broad high-temperature thermal conductivity plateau, suggests strong internal scattering arising from surface terminations and structural disorder. Unlike graphite, where momentum-conserving scattering supports hydrodynamic transport, the MXene system represents a strongly scattered regime in which collective phonon behavior is suppressed, yet heat conduction remains largely phonon-dominated.