# Disorder enabled band structure engineering of a topological insulator surface

## TL;DR

This paper demonstrates how defects in topological insulators can create resonance states that form a new quantum basis, enabling diffusive electrical transport despite the surface electrons' resistance to localization.

## Contribution

It reveals that defect resonance states in topological insulators can be harnessed to engineer their surface electronic structure and transport properties.

## Key findings

- Resonance states form a new quantum basis for electron gas.
- Defects enable diffusive electrical transport.
- Surface electrons resist localization but can be reshaped by defects.

## Abstract

Three dimensional topological insulators are bulk insulators with $\mathbf{Z}_2$ topological electronic order that gives rise to conducting light-like surface states. These surface electrons are exceptionally resistant to localization by non-magnetic disorder, and have been adopted as the basis for a wide range of proposals to achieve new quasiparticle species and device functionality. Recent studies have yielded a surprise by showing that in spite of resisting localization, topological insulator surface electrons can be reshaped by defects into distinctive resonance states. Here we use numerical simulations and scanning tunneling microscopy data to show that these resonance states have significance well beyond the localized regime usually associated with impurity bands. At native densities in the model Bi$_2$X$_3$ (X=Bi, Te) compounds, defect resonance states are predicted to generate a new quantum basis for an emergent electron gas that supports diffusive electrical transport.