End-State-Controlled Quantum Transport in Armchair Graphene Nanoribbon Artificial Quantum Materials

Abstract

Artificial quantum materials based on atomically precise graphene nanostructures provide an ideal platform for exploring quantum phenomena arising from localized electronic states. Here, we develop a real-space theoretical framework to elucidate the microscopic origin of interface states in graphene architectures composed of $n$-triangulenes and armchair graphene nanoribbons (AGNRs). By continuously tuning the coupling between graphene building blocks, we reveal the evolution of triangulene zero-energy modes and AGNR end states into compact localized node orbitals at three-arm junctions. The number and chirality of these node orbitals obey a universal relation, $N_{node,δ}=|N_{es,t,A(B)}-N_{tri,0,B(A)}|$, where $N_{es,t}$ denotes the total number of AGNR end states contributed by the three AGNR arms at the junction, and $N_{tri,0}$ is the number of zero-energy modes of the attached triangulene. The chirality of the node orbitals is determined by the dominant constituent: when $N_{es,t}>N_{tri,0}$, they inherit the sublattice chirality of the AGNR end states ($δ=A(B)$), whereas for $N_{tri,0}>N_{es,t}$ they inherit that of the triangulene zero-energy modes ($δ=B(A)$). This real-space picture provides a transparent understanding of compact localized state (CLS) formation beyond conventional bulk topological descriptions. Using experimentally synthesized triangulene nanographenes as representative examples, we further explain the emergence of their zero-energy modes and quantitatively reproduce their tunneling spectra within an extended Anderson model. Finally, we demonstrate that these node orbitals can serve as elementary building blocks for constructing artificial graphene nanoribbons with highly tunable flat subbands near the Fermi energy. The resulting CLSs exhibit controllable degeneracy and strongly anisotropic quantum transport.