Anharmonic phonon renormalization and two-channel thermal transport in SrTiO3 using full temperature-dependent interatomic force constant

The microscopic mechanism of lattice thermal conductivity of SrTiO3 is investigated by full temperature-dependent anharmonic phonon renormalization and two-channel thermal transport. The contribution of normal phonon is calculated by the Boltzmann transport equation, while the contribution of diffusion phonon is treated by random-walk diffusion theory and wave-like tunneling of phonon. Based on the anharmonic phonon renormalization, the full temperature-dependent interatomic force constant is utilized to calculate the thermal conductivity of normal phonon and diffusion phonon. With the combined inclusion of normal phonon and diffusion phonon, our work successfully reproduces the experimental thermal conductivity of SrTiO3 on top of full temperature-dependent anharmonic phonon renormalization. Our results show that the anharmonic phonon renormalization (a) strongly hardens the acoustic branch and softens the optical branch, (b) suppresses the weighted phase space of low-frequency phonon modes, reducing the coupling between acoustic and optical phonons, and (c) diminishes the strength of three-phonon scattering and four-phonon scattering, enlarging the lattice thermal conductivity. The anharmonic phonon renormalization plays a significant role in the thermal transport process of SrTiO3, and the diffusion phonon transport also makes an important contribution to the total thermal conductivity. The methodology may be used to resolve the discrepancies between experimental and theoretical thermal conductivity.