Enhanced low-temperature thermal conductance by quantum dot made of material with high sound velocity in a three-dimensional semiconductor nanowire

We investigate ballistic phonon transport and thermal conductance in a three-dimensional semiconductor nanowire modulated with different materials in a single quantum dot using elastic wave continuum model. In general, the acoustic discontinuities at such system cause the decrease of the thermal conductance. However, at very low temperatures, the material with higher sound velocity in quantum dot do enhance the thermal transport, despite that phonons are scattered due to the acoustic mismatch at the interfaces. The enhancement originates from the longer wavelength of the mode (0,0) in the material with higher sound velocity.