Abstract
Using ab-initio calculations, we argue that the apparent frequency dependence of the thermal conductivity measured by time-domain thermoreflectance (TDTR) is majorly determined by the balance between harmonic (elastic) and anharmonic (inelastic) phonon channels, and not by ballistic phonons. The match between this theory and experiment is closer than that obtained with previous models. Concrete trends in frequency and temperature dependence are predicted. Reinterpreting frequency modulated time-domain thermoreflectance in terms of elastic vs. inelastic channels explains the markedly different behavior between alloys and non-alloys, and the approach can in principle be applied to other nanostructured material systems.
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