Inducing a topological transition in graphene nanoribbons superlattices by external strain

TL;DR

This study demonstrates how external strain can induce topological transitions in graphene nanoribbon superlattices, affecting their electronic edge states while maintaining mechanical integrity, with potential implications for flexible electronic devices.

Contribution

We reveal a general strain-induced topological transition mechanism in graphene nanoribbon superlattices, characterized by sublattice polarization and robust topological states.

Findings

Topological transition occurs at 3-5% strain, below fracture strain.

Superlattice topological states are robust to strain and disorder.

Fracture in superlattices is brittle, occurring at thinner regions.

Abstract

Armchair graphene nanoribbons, when forming a superlattice, can be classified in different topological phases, with or without edge states. By means of tight-binding and classical molecular dynamics (MD) simulations, we studied the electronic and mechanical properties of some of these superlattices. MD shows that fracture in modulated superlattices is brittle, as for unmodulated ribbons, and that occurs at the thinner regions, with staggered superlattices achieving a larger fracture strain. We found a general mechanism to induce a topological transition with strain, related to the electronic properties of each segment of the superlattice, and by studying the sublattice polarization we were able to characterize the transition and the response of these states to the strain. For the cases studied in detail here, the topological transition occurred at $\sim$3-5 \% strain, well below the fracture strain. The topological states of the superlattice -- if present -- are robust to strain even close to fracture. Unlike the zero-energy edge states found in the zig-zag edges of graphene nanoribbons, the superlattice states shows signatures of being particularly insensitive to disorder, even in real space.