Band structure engineering in (Bi1-xSbx)2Te3 ternary topological insulators

TL;DR

This paper demonstrates a method to engineer the band structure of (Bi1-xSbx)2Te3 topological insulators, achieving bulk insulation and tunable surface states, advancing the development of TI-based quantum devices.

Contribution

It introduces a novel molecular beam epitaxy growth technique to systematically control the band structure of (Bi1-xSbx)2Te3 TIs, enabling ideal insulating bulk and tunable surface states.

Findings

Topological surface states are robust across the entire composition range.

Systematic band engineering results in TIs with insulating bulk and tunable surface states.

Surface states behave like one quarter of graphene, facilitating quantum transport.

Abstract

Three-dimensional (3D) topological insulators (TI) are novel quantum materials with insulating bulk and topologically protected metallic surfaces with Dirac-like band structure. The spin-helical Dirac surface states are expected to host exotic topological quantum effects and find applications in spintronics and quantum computation. The experimental realization of these ideas requires fabrication of versatile devices based on bulk-insulating TIs with tunable surface states. The main challenge facing the current TI materials exemplified by Bi2Se3 and Bi2Te3 is the significant bulk conduction, which remains unsolved despite extensive efforts involving nanostructuring, chemical doping and electrical gating. Here we report a novel approach for engineering the band structure of TIs by molecular beam epitaxy (MBE) growth of (Bi1-xSbx)2Te3 ternary compounds. Angle-resolved photoemission spectroscopy (ARPES) and transport measurements show that the topological surface states exist over the entire composition range of (Bi1-xSbx)2Te3 (x = 0 to 1), indicating the robustness of bulk Z2 topology. Most remarkably, the systematic band engineering leads to ideal TIs with truly insulating bulk and tunable surface state across the Dirac point that behave like one quarter of graphene. This work demonstrates a new route to achieving intrinsic quantum transport of the topological surface states and designing conceptually new TI devices with well-established semiconductor technology.