Low-energy modeling of three-dimensional topological insulator nanostructures

TL;DR

This paper presents a new modeling approach for three-dimensional topological insulator nanostructures, accurately capturing low-energy surface states and their dependence on material parameters, thickness, and anisotropy.

Contribution

It introduces a fitting strategy based on ab initio calculations to derive effective parameters, improving the accuracy of low-energy state predictions in topological insulator nanostructures.

Findings

Accurate low-energy surface state spectra for Bi2Se3, Bi2Te3, Sb2Te3.

Thickness-dependent model parameters match experimental band structures.

Band anisotropy and electron-hole asymmetry affect surface state localization.

Abstract

We develop an accurate nanoelectronic modeling approach for realistic three-dimensional topological insulator nanostructures and investigate their low-energy surface-state spectrum. Starting from the commonly considered four-band $\boldsymbol{\mathrm{k\cdot p}}$ bulk model Hamiltonian for the Bi$_2$Se$_3$ family of topological insulators, we derive new parameter sets for Bi$_2$Se$_3$, Bi$_2$Te$_3$ and Sb$_2$Te$_3$. We consider a fitting strategy applied to \emph{ab initio} band structures around the $\Gamma$ point that ensures a quantitatively accurate description of the low-energy bulk and surface states, while avoiding the appearance of unphysical low-energy states at higher momenta, something that is not guaranteed by the commonly considered perturbative approach. We analyze the effects that arise in the low-energy spectrum of topological surface states due to band anisotropy and electron-hole asymmetry, yielding Dirac surface states that naturally localize on different side facets. In the thin-film limit, when surface states hybridize through the bulk, we resort to a thin-film model and derive thickness-dependent model parameters from \emph{ab initio} calculations that show good agreement with experimentally resolved band structures, unlike the bulk model that neglects relevant many-body effects in this regime. Our versatile modeling approach offers a reliable starting point for accurate simulations of realistic topological material-based nanoelectronic devices.