Engineering Topological Bands in Strained Covalent Organic Frameworks

TL;DR

This paper demonstrates how chemical modifications and strain in covalent organic frameworks can be used to engineer topological electronic phases, including topological insulators and higher-order topological insulators.

Contribution

It introduces a method to induce topological phases in COFs through strain and linker substitution, supported by tight-binding models and first-principles calculations.

Findings

Uniaxial strain can generate topological band structures in COFs.

Chemical substitution of linkers can drive COFs into topological phases.

Replacing biphenyl with pyrene links approaches a HOTI phase.

Abstract

The tunability of covalent organic frameworks (COFs) opens opportunities to engineer topological electronic phases, including topological insulators (TIs) and higher-order topological insulators (HOTIs)--materials that host in-gap states localized at their edges, hinges, or corners. Here we explore how chemically feasible perturbations can drive triazine-based COFs (CTFs) into topological regimes. Using a tight-binding model on the Honeycomb lattice inspired by the frontier electronic states of CTFs, we show that introducing an effective uniaxial strain--implemented as a modulation of electron hopping on a subset of bonds--can generate a series of distinct topological band structures. This effect can be realized in practice through chemical substitution of linkers along the strained bonds. First-principles calculations demonstrate that replacing biphenyl with pyrene linkers drives a CTF to the brink of a HOTI phase, suggesting a viable route toward topological band-structure engineering in COFs.