Rashba Spin-Orbit Driven Topological Phase Transitions in Graphene Nanoribbon Heterostructures

We demonstrate that the interplay between structural geometry and Rashba spin-orbit coupling generates nontrivial topological phases in honeycomb nanoribbon heterostructures. We consider an armchair nanoribbon in which a Rashba spin-orbit coupled region is embedded between pristine segments. Increasing the Rashba coupling induces symmetry-protected interface states localized at the junction between topologically distinct regions, which remain robust against edge perturbations. For finite ribbon widths, Rashba spin-orbit coupling drives a gap closing and reopening, signaling a topological phase transition without modifying the lattice structure. Our results reveal a mechanism by which interfacial geometry and spin-orbit interaction cooperatively engineer tunable topological states in graphene-based nanostructures.