Ultrafast, high resolution spatiotemporal mapping of energy transport dynamics for determination of energy transport properties in silicon

Segovia, Mauricio; Xu, Xianfan

doi:10.1103/PhysRevB.108.125202

The temperature dependence of the thermal conductivity is linked to the nature of the energy transport at a frequency ω , which is quantified by thermal diffusivity d ( ω ). Here we study d ( ω ) for a poorly annealed glass and a highly stable glass prepared using the swap Monte Carlo algorithm. To calculate d ( ω ), we excite wave packets and find that the energy moves diffusively for high frequencies up to a maximum frequency, beyond which the energy stays localized. At intermediate frequencies, we find a linear increase of the square of the width of the wave packet with time, which allows for a robust calculation of d ( ω ), but the wave packet is no longer well described by a Gaussian as for high frequencies. In this intermediate regime, there is a transition from a nearly frequency independent thermal diffusivity at high frequencies to d ( ω ) ∼ ω −4 at low frequencies. For low frequencies the sound waves are responsible for energy transport and the energy moves ballistically. The low frequency behavior can be predicted using sound attenuation coefficients.

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