Thermoelectric materials are significant for sustainable energy systems by allowing the conversion of waste heat to electric energy. To achieve highly efficient energy conversion, low thermal conductivity is substantial. An excellent benchmark material seems to be SnSe thanks to the demonstration of ultralow thermal conductivity [1]. Studying this material, we explored the nonequilibrium phonon dynamics induced by a laser-excited electron population using a framework combining ultrafast electron diffuse scattering [2] and nonequilibrium kinetic theory [3]. This in-depth approach provides a fundamental understanding of energy transfer in the spatio-temporal domain focusing on an interplay between the phononic and electronic properties of the nonequilibrium state. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to non-conservative phonon scattering [4]. The results offer a perspective on energy transport in condensed matter with far-reaching implications for the rational design of advanced materials with tailored thermal properties.

[1] L. D. Zhao et al.; Nature 2014, 508 (7496), 373−377.
[2] D. Filippetto et al.; Rev. Mod. Phys. 2022, 94(4) , 045004.
[3] P .Maldonado et al.; Phys. Rev. B 2017, 96(17) ,174439
[4] A. K. Prasad, JS, et al.; ACS Nano 2023 17 (21), 21006