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

TL;DR

This study investigates how the ultrafast carrier relaxation dynamics in Bi2Se3 thin films vary with thickness, revealing a transition from bulk-like to metal-like behavior as films become thinner, likely due to surface state hybridization.

Contribution

It provides the first detailed analysis of thickness-dependent carrier relaxation times in Bi2Se3 thin films using transient reflectivity measurements.

Findings

Carrier relaxation time decreases with film thinning.

Thinner films exhibit relaxation times similar to noble metals.

Hybridization of surface states likely causes the observed effects.

Abstract

Transient reflectivity measurements of thin films, ranging from 6 to 40 nm in thickness, of the topological insulator Bi2Se3 revealed 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.