First-Principles Study of Anharmonic Lattice Dynamics in Low Thermal Conductivity AgCrSe2 : Evidence for a Large Resonant Four-Phonon Scattering

We report a study of the anharmonic lattice dynamics in low lattice thermal conductivity (${\mathbit{\ensuremath{\kappa}}}_{\mathbit{l}}$) material ${\mathrm{AgCrSe}}_{2}$ by many-body perturbation theory. We demonstrate surprisingly giant four-phonon scattering exclusive for the heat-carrying transverse acoustic phonons due to large quartic anharmonicity and nondispersive phonon band structure, which lead to four-phonon Fermi resonance and breaks the classical ${\mathbit{\ensuremath{\tau}}}^{\ensuremath{-}1}\ensuremath{\sim}{\mathbit{\ensuremath{\omega}}}^{\mathbit{m}}{\mathbit{T}}^{\mathbit{n}}$ relation for phonon-phonon interactions. This strong resonant scattering extends over the Brillouin zone and substantially suppresses the thermal transport, even down to a low temperature of 100 K. The present results provide fundamental insights into the four-phonon resonant dynamics in the low-${\mathbit{\ensuremath{\kappa}}}_{\mathbit{l}}$ system with flat phonon dispersions, i.e., cuprous halides and skutterudites.