Chiral-edge engineering of M-graphene nanoribbons: edge-localized states, suppressed transmission and width-tunable transport device

Abstract

We report an atomistic investigation of M-graphene nanoribbons with chiral (mixed-topology) edges, focusing on how alternating zigzag-like and armchair-like motifs determine low-energy electronic structure and quantum transport. Using first-principles electronic-structure calculations combined with atomistic quantum-transport simulations, we find that M-graphene ribbons maintain an overall metallic density of states while exhibiting a narrow, motif-specific “forbidden subband” located near the Fermi level that arises from edge-localized states. In narrow ribbons this forbidden subband produces pronounced resonant scattering and a clear suppression of low-bias conductance; increasing ribbon width progressively populates additional propagating subbands, broadens transmission features, and restores more continuous, near-linear low-bias I–V behavior. The contrast between edge-dominated resonances and bulk-like conduction is robust across the width series studied and indicates that chiral/mixed edges provide an effective structural handle to tune energy-selective transport. These properties make chiral M-graphene nanoribbons promising candidates for resonance-based electronic elements and edge-engineered sensors. Under conditions where edge magnetism can be stabilized (for example via chemical functionalization, substrate effects, or explicit inclusion of strong correlations), the motif-localized states identified here could in principle enable spin-selective behavior; however, spin effects are not modeled in the present work and would require a dedicated spin-resolved study.