Optical study on topological superconductor candidate Sr-doped Bi2Se3

Utilizing infrared spectroscopy, we study the charge dynamics of the topological superconductor candidate Sr x Bi 2 Se 3 . The frequency-dependent reflectivity R ( ω ) 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 Bi 2 Se 3 . 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 Bi 2 Se 3 . We also perform the ultrafast pump-probe study on the Sr 0.2 Bi 2 Se 3 compounds. Resembling its parent compound Bi 2 Se 3 , 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 λ = 0.88.