Ultrafast carrier dynamics in thin-films of the topological insulator Bi2Se3

Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in thickness, of the topological insulator Bi2Se3 reveal a strong dependence of the carrier relaxation time on the film thickness. For thicker films, the relaxation dynamics are similar to those of bulk Bi2Se3, where the contribution of the bulk insulating phase dominates over that of the surface metallic phase. The carrier relaxation time shortens with decreasing film thickness, reaching values comparable to those of noble metals. This effect may result from the hybridization of Dirac cone states at the opposite surfaces for the thinnest films.