Anharmonicity and thermal transport in network glasses

The Nakayama model for network glasses classifies vibrational states into extended (ex), strongly localized (sl), and mesoscopically localized (ml), in increasing order of energy. Recently measured Raman spectra under hydrostatic pressure exhibit sl-mode an-harmonicity at least twenty times that for the ex and mi modes. The ex modes can induce hopping of the sl modes, leading to a contribution to the thermal conductivity kappa(T). This additional channel for heat conduction is consistent with measurements for a wide variety of glassy materials above the plateau temperature.