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 (kappa(iota)) material AgCrSe2 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 tau(-1) similar to omega T-m(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-kappa(iota) system with flat phonon dispersions, i.e., cuprous halides and skutterudites.