HEAT-TRANSPORT AND NONTHERMAL EXCITATIONS IN VIBRATIONAL HOPPING SYSTEMS

We investigate a system-of high-frequency (optical) phonon modes which are localized due to disorder and interact with the low-frequency (acoustic) phonon modes which are extended and effectively act as a heat bath for the optical modes. Fourth-order anharmonicity is included in the subsystem of the optical modes and taken into account within a mean-held approximation. The thermal conductivity due to hopping of the optical modes is lowered by increasing the anharmonicity, but its temperature dependence is not affected. Furthermore, considering the system under the influence of an energy pump it turns out that the occupation of the localized modes is influenced by the anharmonicity in such a way as to screen off disorder.