Aging and reduced bulk conductance in thin films of the topological insulator Bi$_2$Se$_3$

TL;DR

This study investigates how atmospheric exposure affects the THz conductivity of Bi$_2$Se$_3$ thin films, revealing decay in bulk response while surface states remain robust, with no trivial surface state features detected.

Contribution

It provides new insights into the aging effects on bulk and surface conductance in topological insulator thin films under ambient conditions.

Findings

Bulk spectral weight decays over days of exposure

Surface response remains robust and unchanged

No evidence of trivial surface state features

Abstract

We report on the effect of exposure to atmospheric conditions on the THz conductivity of thin films of the topological insulator Bi$_2$Se$_3$. We find: 1) two contributions of mobile charge carriers to the THz conductivity immediately after growth, and 2) the spectral weight of the smaller of these decays significantly over a period of several days as the film is exposed to ambient conditions, while the other remains relatively constant. We associate the former with a bulk response, and the latter with the surface. The surface response exhibits the expected robustness of the carriers from 2D topological surface states. We find no evidence for a third spectral feature derived from topologically trivial surface states.