▎ 摘　　要

A new and unusual type of Constructive Quantum Interference (CQI) is revealed in selected isolated armchair graphene nanoribbons (AGNRs). CQI, normally encountered in molecular junctions, occurs when two nearly isoenergetic states interfere constructively. Such almost isoenergetic states are identified here as the energy differences between two pairs of topological end states developed in "wider" AGNRs, through topological metal-insulator-like phase transition, which for 13-AGNRS occurs at a critical length L-c approximate to 50 angstrom. At L-c a sudden jump in conductivity by a factor similar to 2.5 occurs, which persists up to L approximate to 80 angstrom and is interpreted as a signature of CQI. Such unusual CQI, in which the zigzag region effectively plays the role of "linkers", is unique for 13-AGNRs. This is due to their ammaticity i.e., resonance between two different aromatic Clar-sextets, and the resulting symmetry and energy separation of the frontier orbitals. The experimental measurements for 13-AGNRs fully support our results.