Broadband transient reflectivity traces were measured for Bi2 Se3 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 Bi2 Se...Broadband transient reflectivity traces were measured for Bi2 Se3 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 Bi2 Se3 and qualitatively located it by properly analyzing the traces acquired at different probe wavelengths. Referring to the band structure of Bi2 Se3, 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 picoseconds. 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.展开更多
基金the Opening Foundation of State Key Laboratory of High Performance Computing(Nos.201601-01,201601-02,and 201601-03)the Scientific Researches Foundation of National University of Defense Technology(No.zk16-03-59)+3 种基金the Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2017KF06)the Director Fund of State Key Laboratory of Pulsed Power Laser Technology(No.SKL2018ZR05)the Funds for International Cooperation and Exchange of National Natural Science Foundation of China(Nos.61120106 and 60921062)the National Natural Science Foundation of China(Nos.11802339 and 11805276).
文摘Broadband transient reflectivity traces were measured for Bi2 Se3 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 Bi2 Se3 and qualitatively located it by properly analyzing the traces acquired at different probe wavelengths. Referring to the band structure of Bi2 Se3, 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 picoseconds. 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.