Phonons, the quanta of lattice vibrations, can exhibit unconventional transport behavior at microscopic scales such as nanostructured regions or interfaces, which cannot be explained by conventional thermal diffusion or particle pictures. This research topic aims to develop novel techniques for analyzing and measuring such phonon transport, with a particular focus on these non-conventional transport regimes. Furthermore, it seeks to advance a fundamental understanding of thermal transport and to establish next-generation thermal control strategies, for example, by developing methods that directly probe the spectral characteristics of phonon transport.

Outcome：

2025
n this paper, we demonstrate that the thermal conductivity of two-dimensional amorphous graphene can be predicted with high accuracy using persistent homology, a topological data analysis method. By performing an inverse analysis of the regression results, we identify key local atomic-structure features—distorted hexagonal and triangular motifs—that are strongly associated with reduced thermal conductivity. These features spatially correlate with low-frequency localized vibrational modes, supporting a physical interpretation in which they suppress heat transport.

2025
In this paper, we demonstrate the possibility of modulating phonon reflection at the boundaries of single-crystal diamond nanobeams by using temperature as a control parameter. Thermal conductivity measurements from room temperature down to ~140 K show that the thermal conductivity decreases monotonically with decreasing temperature, whereas the results increasingly and systematically deviate at lower temperatures from a “fully diffusive boundary scattering” model based on first-principles calculations and the Boltzmann transport equation. By analyzing this discrepancy, we reveal that the contribution of specular phonon–boundary scattering becomes more significant in the low-temperature regime, and that its temperature sensitivity is larger in diamond than in silicon.

2025
In this paper, we systematically investigate phonon thermal transport in indium iodides that adopt either layered (InI) or molecular-crystal-like (InI3) structures, using first-principles anharmonic lattice dynamics. By comparing particle-like transport (Peierls–Boltzmann contribution) and wave-like transport (interband-tunneling-related contribution), we show that the lattice thermal conductivities of both materials remain below 1 W m-1 K-1 over a broad temperature range. We further clarify that the wave-like contribution becomes comparable to the particle-like contribution in InI3, whereas it remains negligible in InI. We also examine the experimentally reported high-pressure phase of InI3. Motivated by indications of stacking faults and partial disorder in indium-site occupancy, we construct several ordered structural models with different stacking sequences and evaluate their energetics and thermal transport properties. The results indicate that the energetic preference among stacking sequences is small and the lattice thermal conductivities are similar across models, suggesting that in-plane thermal transport is governed primarily by the vibrational properties of the In2I6 layers themselves rather than by the specific stacking sequence.