Controlling thermal conductivity of materials is very important in various applications, such as thermal management and energy conversion. We have been utilizing femtosecond phonon spectroscopy to excite and detect coherent phonons in various materials. However, the impact of coherent phonons to overall heat transport is still unknown. In this paper, we developed a small perturbation model in molecular dynamics (MD) to simulate coherent phonons and investigate the effect on thermal conductivity in bismuth telluride. The phonon frequency and lifetime predicted by our model agree very well with experimental results. It is found that at very low temperature, the lattice thermal conductivity, predicted by quasi-equilibrium Green-Kubo method, can be greatly enhanced upon coherent phonon generation. Our results suggest that it is possible to control lattice thermal conductivity effectively via manipulating coherent phonons.
Influence of pulse width and detuning on coherent phonon generation