Electrically-tunable ultra-flat bands and π-electron magnetism in graphene nanoribbons

Atomically thin crystals with flat electronic bands have recently emerged as key platforms for exploring and engineering strongly correlated states. However, the range of low-dimensional flat-band materials remains relatively limited, primarily confined to two-dimensional moiré superlattices. In this work, we predict the formation of reversible, electrically induced ultra-flat bands and π-electron magnetism in one-dimensional chevron graphene nanoribbons using ab initio calculations. We show that applying a transverse electric field to these nanoribbons generates a pair of isolated, nearly perfectly flat bands with bandwidths of approximately 1 meV, symmetrically centered around the Fermi level. Upon charge doping, these flat bands exhibit a Stoner-like electronic instability, leading to the emergence of local magnetic moments at the edges of the otherwise non-magnetic nanoribbon, ultimately forming a one-dimensional spin-1/2 chain. Our findings broaden the range of carbon-based nanostructures exhibiting flat bands and provide new strategies for inducing correlated electronic phases in chevron graphene nanoribbons.