Realizing Pure Spin Current With Photogalvanic Effect in Zigzag Graphene Nanoribbon Junctions: The Roles of Tetragon and Hexagon Connectors

Abstract

We construct zigzag graphene nanoribbon junctions for generating pure spin current through the photogalvanic effect (PGE) by first-principles calculations. Two devices with spatial inversion symmetry are designed, both consisting of three zigzag graphene nanoribbons (ZGNRs) that introduce either two carbon tetragons (“2-C4”) or two carbon hexagons (“2-C6”) as connectors. The results show that robust pure spin current without charge current can be generated in both structures. The mechanism originates from the spatial inversion antisymmetric spin density as well as the spatial inversion symmetry of the geometrical structures. Furthermore, when more connectors are involved, we generalize that for structures with carbon tetragons as connectors, an even number of connectors are required to generate pure spin currents, while for structures with carbon hexagon connectors, any number of connectors can form pure spin currents. In addition, we find that larger pure spin currents can be obtained in the case of using hexagons as connectors. These findings provide a scheme for obtaining pure spin currents based on graphene nanoribbons, which has important reference implications for the design of spintronic devices with composite nanostructures.