Slowdown of entropy generation in phonon transport by atomic-scale local resonances

Nanoscale phonon transport may exhibit both coherent and incoherent mechanisms taking place simultaneously in the same material system. Nanoscale phonon transport in crystals is influenced by the interaction of phonons with nanoscale structural constraints, such as, for example, boundaries or periodic features such as holes or cavities. While the analysis of the thermal conductivity provides insights into the different scattering mechanisms limiting the heat conduction, it does not directly elucidate the thermodynamic characteristics of thermal evolution towards equilibrium. Using nonequilibrium molecular dynamics simulations, we predict the rate of entropy generation associated with phonon transport in crystals, which provides a direct probe of the degree of irreversibility in the underlying phonon mechanisms. We examine a variety of silicon nanostructures at room temperature and show that the phonon entropic behavior is highly influenced by the type of the nanostructure. In particular, we show that the inclusion of intrinsically resonating nanostructures (such as nanopillars on a thin membrane) [1] enables a regime of ordered thermal transport to be approached, one where the randomization and thermalization of the system--rigorously quantified by the rate of entropy production--are hindered and the coherent portion of the phonon motion is distinctly prevalent [2].

[1] B.L. Davis and M.I. Hussein, Phys. Rev. Lett. 112, 055505, (2014).

[2] A. Beardo, A., P. Rawte, C.N. Tsai, and M.I. Hussein, 2404.15831v3 (2024)