Abnormal oscillatory conductance and strong odd-even dependence of a perfect spin-filtering effect in a carbon chain-based spintronic device

By using nonequilibrium Green's functions in combination with the density functional theory, the transport properties of a carbon chain-based spintronic device are investigated. Previous reports show that when the carbon chains are sandwiched between metal electrodes or perfect zigzag graphene nanoribbons, the conductance of odd-n carbon chain systems is higher than that of even-n ones [Phys. Rev. Lett., 1998, 81, 3515; J. Am. Chem. Soc., 2010, 132, 11481-11486]. However, when the carbon chains are connected with Fe-porphyrin-like armchair graphene nanoribbons, we find that low conductance states belong to odd-n carbon chain systems while large conductance states belong to even-n carbon chain systems, indicating abnormal oscillatory conductance. Moreover, we also find that when the spin polarization is considered, the oscillatory characteristic of conductance in the spin-up state is opposite to that in the spin-down state. Especially, the perfect spin-filtering effect appears only in the odd-n carbon chain systems, showing a strong odd-even dependence characteristic. The mechanisms are suggested for these interesting phenomena.