Electrically-tunable ultra-flat bands and $\pi$-electron magnetism in graphene nanoribbons

TL;DR

This paper predicts that applying a transverse electric field to chevron graphene nanoribbons can reversibly create ultra-flat electronic bands and induce $\pi$-electron magnetism, offering new ways to explore correlated phases in carbon nanostructures.

Contribution

It introduces a novel method to generate ultra-flat bands and magnetic phases in chevron graphene nanoribbons using electric fields, expanding the scope of flat band engineering.

Findings

Electric fields produce nearly perfect flat bands around the Fermi level.

Charge doping induces magnetic moments via a Stoner-like instability.

The results suggest new pathways for correlated electronic phases in carbon nanostructures.

Abstract

Atomically thin crystals hosting flat electronic bands have been recently identified as a rich playground for exploring and engineering strongly correlated phases. Yet, their variety remains limited, primarily to two-dimensional moir\'e superlattices. Here, we predict the formation of reversible, electrically-induced ultra-flat bands and $\pi$-electron magnetism in one-dimensional chevron graphene nanoribbons. Our $ab$ $initio$ calculations show that the application of a transverse electric field to these nanoribbons generates a pair of isolated, nearly perfectly flat bands with widths of approximately 1 meV around the Fermi level. Upon charge doping, these flat bands undergo a Stoner-like electronic instability, resulting in the spontaneous emergence of local magnetic moments at the edges of the otherwise non-magnetic nanoribbon, akin to a one-dimensional spin-$\frac{1}{2}$ chain. Our findings expand the class of carbon-based nanostructures exhibiting flat bands and establish a novel route for inducing correlated electronic phases in chevron graphene nanoribbons.