Spin transport of polyacetylene chains bridging zigzag graphene nanoribbon electrodes: A nonequilibrium treatment of structural control and spin filtering

We investigate spin transport properties in a junction composed of a polyacetylene chain bridging two zigzag graphene nanoribbon (ZGNR) electrodes with antiferromagnetic (AF) and ferromagnetic (FM) ordering. The transport calculations are carried out using a nonequilibrium Green's function (NEGF) technique combined with density functional theory (DFT). Previous studies have demonstrated that the ZGNRs exhibit a special AF ordering and half-metallicity at edge states, both of which can be destroyed by applying a strong external electric field. Moreover a stable FM state can be found in ZGNRs under an electric field. Here we demonstrate that the connection between the molecular bridge and nonequivalent carbon atoms (A/B) in the graphene sublattice of ZGNRs may occur in two bonding arrangements and can produce either metallic or semiconducting systems depending on the local coupling. By considering the carbon ring where the chain is attached, one connection resembles a para-linkage in benzene while the other connection is similar to a meta-linkage. This results in different conductances for these configurations, which may be controlled by field-effect gating. Finally, the spin filter efficiency as a function of electric field for these systems, which exhibit intrinsic AF ordering coupled to FM electrodes, is discussed.