Theoretical study in nano-structure-physics of magnetic atom bridges and molecular bridges

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We investigated the nano-physics of the magnetic atom bridges and molecular bridges with the aid of the first-principles calculations based on the density functional theory. After we researched the stability and magnetic properties of the magnetic atom bridge constructed between metal surface and STM-tip, we started researching the magnetic molecular bridges, which have their highly-reproducible structures supporting the magnetic atoms. We treated the tape-porphyrin with the transition metal atom, M, as a centre metal atom, in which M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. We found that in the case of M= Sc, Ti, V, Cr, Mn and Fe, the systems are the ferromagnetic metals. In the case of M=Co, Ni and Cu, the systems are insulators. In order to investigate the origin of the electronic property of these tapes, we also calculated the corresponding isolated unit of M porphyrin molecule, whose meso-and β-carbons are terminated by hydrogen atoms. As the results, The molecular orbital, which has the charge distribution on the meso-and β-carbons, becomes the wide energy bands when the molecules connect each other and construct the tape. So in the case where their Eigen energies lie near the Fermi energy, the corresponding tape-porphyrin is conductor.In addition, we found that the metal-insulator transition occurs when a CO molecule adsorbed on the Fe tape-porphyrin. We clarified that such a metal-insulator transition is caused by the hybridization of the dxz and dyz orbitals of Fe with the II^* g orbitals of CO molecule.