Dynamics of optical phonons in Bi2Se3 crystal studied using femtosecond time-resolved reflection measurement

The dynamics of coherent optical phonons (A1g1, A1g2 and Eg2) in Bi2Se3 single crystal have been observed by using femtosecond time-resolved reflection measurement. The phonons with the higher frequency have the faster damping rate (decay faster). The A1g2 phonons show cosine-like oscillation, while the A1g1 and Eg2 phonons show cosine-like oscillation. The difference in the initial phase suggests that the potential energy surface may shift significantly along the A1g2 eigenvector and little along the A1g1 and Eg2 eigenvectors in the excited state.