Metal-insulator transition and tunable Dirac-cone surface state in the topological insulator TlBi1-xSbxTe2 studied by angle-resolved photoemission

TL;DR

This study systematically investigates the electronic structure of TlBi1-xSbxTe2 topological insulators, revealing a tunable metal-insulator transition, Dirac cone evolution, and high Dirac velocity, offering a platform for Dirac-engineering.

Contribution

It provides the first detailed ARPES analysis of TlBi1-xSbxTe2, demonstrating controllable surface states and Dirac velocity enhancement in a solid-solution topological insulator.

Findings

Metal-insulator-metal transition with Sb content

Systematic hole doping and Fermi level shifts

Largest Dirac velocity among known TIs

Abstract

We report a systematic angle-resolved photoemission spectroscopy on topological insulator (TI) TlBi1-xSbxTe2 which is bulk insulating at 0.5 < x < 0.9 and undergoes a metal-insulator-metal transition with the Sb content x. We found that this transition is characterized by a systematic hole doping with increasing x, which results in the Fermi-level crossings of the bulk conduction and valence bands at x~ 0 and x~1, respectively. The Dirac point of the topological surface state is gradually isolated from the valence-band edge, accompanied by a sign reversal of Dirac carriers. We also found that the Dirac velocity is the largest among known solid-solution TI systems. The TlBi1-xSbxTe2 system thus provides an excellent platform for Dirac-cone engineering and device applications of TIs.