Strong four-phonon interactions in α-GeTe

High-order phonon interactions have recently garnered significant attention due to their critical role in understanding anharmonic phonon decay and accurately predicting lattice thermal conductivity κL. Here, we report a pronounced four-phonon scattering effect in α-GeTe by the inelastic neutron scattering experiment and temperature dependent molecular dynamic simulation. Strong four-phonon interactions lead to remarkably reduced intensities of imaginary dynamical susceptibility at elevated temperatures and a strong temperature dependence of phonon linewidths. The phonon dispersion nesting and strong anharmonicity at high temperatures contribute to the significant four-phonon interactions in α-GeTe. These interactions result in a deviation from the typical κL ~ T⁻¹ trend in α-GeTe, attributed to an increased scattering rate caused by the enlarged four-phonon scattering phase space at high temperature. Our work provides a detailed microscopic insight to the thermal transport of α-GeTe, offering valuable guidance for the design of advanced thermoelectric materials, and highlights the critical role of four-phonon interactions in solids at high temperatures.