Fig. 4: Lattice dynamics predictions for diffuson thermal conductivity and visualization of localization effects.

Allen–Feldman thermal conductivity accumulation as a function of vibrational modes frequency for a amorphous silicon, a-Si, with inset showing Si-Si bond between two tetrahedrons, b amorphous silicon heavy-oxide, a-Si¹²⁷O₂, with inset showing Si-¹²⁷O-Si bond between two tetrahedrons, and c amorphous silicon telluride, a-Si₂₀Te₈₀, with inset showing Si-Te-Te-Si bond between two tetrahedrons. Projection of eigenvectors associated with each mode on a xy-plane, indicating the degree of spatial and energetic overlap at two consecutive frequencies, d delocalized: 41.4 cm⁻¹ (black arrows) and 41.6 (red arrows) cm⁻¹, and e localized: 240.4 cm⁻¹ (black arrows) and 242.5 (red arrows) cm⁻¹ in a-Si₂₀Te₈₀. The few high amplitude eigenvectors at localized frequencies are an indication of strong localization showing the energy associated with these modes is confined in a small geometric region. f, e Histogram indicating the population of modes based on their eigenvector amplitude at delocalized and localized frequencies.