A study conducted by Keita Funayama et al. in collaboration with Kyoto University was published in Communications Physics.
Thermal management in solid devices is a significant technology to realize high-performance electronics. In particular, high integration and quantum technology advances require a scheme to design thermal control in nanoscale structures. Recently, topological thermal diffusion has attracted attention as an approach to control directional thermal flow and robust decay by utilizing the structural design as well as material properties.
In addition to thermal diffusion, the wave-like properties of phonons affect heat transport in nanoscale leading to reflection and scattering on surfaces of the structures. Such quasi ballistic phonon regime induces the size dependence of thermal conductivity. Consequently, it is difficult for Fourier's Law, which is based on a constant thermal conductivity, to capture heat transport in nanostructures. However, heat transport depending on the size effect have not been sufficiently investigated yet.
In this study, we fabricated a one-dimensional topologically diffusive structure consisting of disk-shaped sites connected by long and short beams alternately. We obtained the thermal decay rate based on topological properties by heating the site and observing the temporal temperature through phonon transport in the narrow beams. Furthermore, we theoretically derived thermal decay based on a topological thermal transport model with the size effect. The two results agreed well, demonstrating that the topological properties can predict the thermal decay rate within nanostructures.
These results pave the way to expand the regime of thermal design utilizing topological structures even to nanostructures where the wave-like nature of phonons and the influence of structural size cannot be ignored. In the future, this approach will contribute to design for thermal management in nanoscale semiconductor and quantum devices.
Title: Design of Topological Thermal Diffusion in the Quasi Ballistic Phonon Regime
Authors: Funayama, K., Akura, Y., Tanaka, H., Hirotani, J.
Journal Name: Communications Physics
Published: July 18, 2026