Broadband transient reflectivity traces were measured for Bi2Se3 thin films with various substrates via a 400 nm pump-white light probe setup. We have verified the existence of a second Dirac surface state in Bi2Se3 and qualitatively located it by properly analyzing the traces acquired at different probe wavelength. Referring to the band structure of Bi2Se3, the relaxation mechanisms for photo-excited electrons with different energies are also revealed and studied. Our results show a second rise of the transient reflection signal at the time scale of several picosecond. The types of substrate can also significantly affect the dynamics of the rising signal. This phenomenon is attributed to the effect of lattice heating and coherent phonon processes. The mechanism study in this work will benefit the fabrication of high-performance photonic devices based on topological insulators.
Jiang Tian, Miao Runlin, Zhao Jie, Xu Zhongjie, Zhou Tong, Wei Ke, You Jie, Zheng Xin, Wang Zhenyu, Cheng Xiangai. The electron-phonon coupling in topological insulator Bi2Se3 thin films with different substrates[J]. Chinese Optics Letters, 2019, 17(2): .