How coherence is governing diffuson heat transfer in amorphous solids?

Publication in Npj Computational Materials!

Thermal transport in amorphous materials has remained one of the fundamental questions in solid state physics while involving a very large field of applications. Using a heat conduction theory incorporating coherence, we demonstrate that the strong phase correlation between local and non-propagating modes, commonly named diffusons in the terminology of amorphous systems, triggers the conduction of heat. By treating the thermal vibrations as collective excitations, the significant contribution of diffusons, predominantly relying on coherence, further reveals interesting temperature and length dependences of thermal conductivity. The propagation length of diffuson clusters is found to reach the micron, overpassing the one of propagons. The explored wavelike behavior of diffusons uncovers the unsolved physical picture of mode correlation in prevailing models and further provides an interpretation of their ability to transport heat. This work introduces a framework for understanding thermal vibrations and transport in amorphous materials, as well as an unexpected insight into the wave nature of thermal vibrations.

Fig. 1: Dynamical structure factor. The calculated dynamical structure factor (DSF) of amorphous silicon for the longitudinal excitations at room-temperature. The calculated amorphous silicon contains 4 096 atoms. The solid white lines are the phonon dispersion of the longitudinal branch for crystal silicon. The dots in are the specific vibrations that applied in wave-packet simulations.

Ref : Z. Zhang, Y. Guo, M. Bescond, J. Chen, M. Nomura and S. Volz, "How coherence is governing diffuson heat transfer in amorphous solids," Npj Comput. Mater. 8, 96 (2022).