Optical study on topological superconductor candidate Sr-doped Bi2Se3

Utilizing infrared spectroscopy, we study the charge dynamics of the topological superconductor candidate Sr x Bi2Se3. The frequency-dependent reflectivity R(omega) demonstrates metallic feature and the scattering rate of the free carriers decreases with temperature decreasing. The plasma edge shows a slight blue shift upon cooling, similar to the behavior of Cu x Bi2Se3. As the carrier concentration n obtained by Hall resistivity increases slightly with the decreasing temperature, the effective mass is proved to increase as well, which is in contrast with that of Cu x Bi2Se3. We also perform the ultrafast pump-probe study on the Sr0.2Bi2Se3 compounds. Resembling its parent compound Bi2Se3, three distinct relaxation processes are found to contribute to the transient reflectivity. However, the deduced relaxation times are quite different. In addition, the electron-optical-phonon coupling constant is identified to be lambda = 0.88.