On the Emergence of Topologically Protected Boundary States in Topological/Normal Insulator Heterostructures

TL;DR

This study systematically investigates the formation of topologically protected boundary states in topological/normal insulator heterostructures using ab-initio tight-binding models derived from DFT, highlighting critical thickness and band alignment effects.

Contribution

It introduces a new ab-initio tight-binding approach to analyze TPBS in TI/NI heterostructures, emphasizing the role of NI thickness and band alignment.

Findings

Existence of a critical NI thickness for TPBS emergence

Band alignment influences TPBS appearance

Validated model with relativistic DFT calculations

Abstract

We have performed a systematic investigation of the formation of topologically protected boundary states (TPBS) in topological/normal insulators (TI/NI) heterostructures. Using a recently developed scheme to construct {\it ab-initio} tight-binding Hamiltonian matrices from density functional theory (DFT) calculations, we studied systems of realistic size with high accuracy and control over the relevant parameters such as TI and NI band alignment, NI gap and spin-orbit coupling strength. Our findings point to the existence of an NI critical thickness for the emergence of TPBS and to the importance of the band alignment between the TI and NI for the appearance of the TPBS. We chose Bi$_{2}$Se$_{3}$ as a prototypical case where the topological/normal insulator behavior is modeled by regions with/without spin-orbit coupling. Finally, we validate our approach comparing our model with fully relativistic DFT calculations for TI/NI heterostructures of Bi$_{2}$Se$_{3}$/Sb$_{2}$Se$_{3}$.