Characterizing Unusual Behavior in Pristine Bi2Se3

Abstract

Bismuth Selenide is a material of great interest to physicists as it is one of the first materials proven to be a strong topological insulator (TI). Despite its promise as an ideal TI, defects in the material that have proven difficult to elminate, keep the material's conductive states at its surface hidden by metallic behavior in the bulk. The work discussed in this thesis focuses primarily on techniques aimed at improving the material quality of pure Bi2Se3 and better understanding the effects of air exposure on both the surface and bulk of the material. The goal is to reliably produce samples in which signatures of the surface states can be seen in simple, bulk measurements. Changes in sample quality were achieved through the manipulation parameters such as Se flux and environmental pressure during the growth process. Through these techniques, the intrinsic carrier concentration of Bi2Se3 samples was lowered to the lowest levels ever reported. Samples showing nonmetallic behavior were also produced and investigated. Furthermore, it was discovered that samples of Bi2Se3 with low carrier concentrations showed strong linear magnetoresistance. The nature of this linear magnetoresistance, its angular dependence, and its evolution over time were also investigated. This thesis will discuss the results of these experiments as examples of how growth techniques influence sample quality, which in turn affects the properties of Bi2Se3.