Optimizing the Bi_(2-x)Sb_(x)Te_(3-y)Se_(y) solid solutions to approach the intrinsic topological insulator regime

TL;DR

This study synthesizes and characterizes Bi_(2-x)Sb_(x)Te_(3-y)Se_(y) solid solutions to identify compositions with optimal bulk-insulating properties, highlighting Bi1.5Sb0.5Te1.7Se1.3 as ideal for surface transport research.

Contribution

It identifies specific compositions of BSTS solid solutions that achieve intrinsic topological insulator behavior with minimized bulk conduction.

Findings

Resistivity reaches several Ohmcm at low temperature.

Bi1.5Sb0.5Te1.7Se1.3 has the lowest bulk carrier density.

Intrinsic compositions show balanced acceptors and donors.

Abstract

To optimize the bulk-insulating behavior in the topological insulator materials having the tetradymite structure, we have synthesized and characterized single-crystal samples of Bi_(2-x)Sb_(x)Te_(3-y)Se_(y) (BSTS) solid solution at various compositions. We have elucidated that there are a series of "intrinsic" compositions where the acceptors and donors compensate each other and present a maximally bulk-insulating behavior. At such compositions, the resistivity can become as large as several Ohmcm at low temperature and one can infer the role of the surface-transport channel in the non-linear Hall effect. In particular, the composition of Bi1.5Sb0.5Te1.7Se1.3 achieves the lowest bulk carrier density and appears to be best suited for surface transport studies.