Stable topological insulators achieved using high energy electron beams

TL;DR

This paper demonstrates that high-energy electron beam irradiation can effectively compensate bulk defects in topological insulators, restoring the Fermi level within the bulk gap and enabling access to surface states for quantum transport studies.

Contribution

The study introduces a novel method of using swift electron beams to tune the electronic properties of topological insulators, achieving stable topological surface states.

Findings

Fermi level can be shifted into the bulk gap using electron irradiation.

Bulk conductivity can be tuned from p-type to n-type crossing the Dirac point.

Surface conductance exhibits quantum behavior consistent with two topological channels.

Abstract

Topological insulators are transformative quantum solids with immune-to-disorder metallic surface states having Dirac band structure. Ubiquitous charged bulk defects, however, pull the Fermi energy into the bulk bands, denying access to surface charge transport. Here we demonstrate that irradiation with swift ($\sim 2.5$ MeV energy) electron beams allows to compensate these defects, bring the Fermi level back into the bulk gap, and reach the charge neutrality point (CNP). Controlling the beam fluence we tune bulk conductivity from \textit{p}- (hole-like) to \textit{n}-type (electron-like), crossing the Dirac point and back, while preserving the Dirac energy dispersion. The CNP conductance has a two-dimensional (2D) character on the order of ten conductance quanta $G_0 =e^2/h$, and reveals, both in Bi$_2$Te$_3$ and Bi$_2$Se$_3$, the presence of only two quantum channels corresponding to two topological surfaces. The intrinsic quantum transport of the topological states is accessible disregarding the bulk size.