Transport Properties for Biphenyl-Based Molecular Junction System

In the present study, the transport properties of an biphenyl-based molecule [$X$-BP-$X$ ($X$: the end-group atom),$ X$=O, S, Se, and Te] sandwiched between Au(111) electrodes are theoretically investigated using the non-equilibrium Green's function method based on the density functional theory. The end-group atom $X$ has an influence on the interaction between the molecule and electrodes and the interaction between the two phenyl rings. For $X$ =S, Se, and Te, similar transport properties are obtained, while the system with $X$ =O exhibits much different properties from the other $X$s. In case of $X$ =O, the interaction between the molecule and electrodes becomes the weakest and that between $\pi $-type orbitals of the two phenyl rings, which mainly contributes to the transmission around the Fermi energy, becomes the strongest. As a result, this system has a larger transmission around the Fermi energy. We also investigate the dependence on dihedral angle between the two phenyl rings for all $X$s. This study was supported by the RISS project and a Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese Government. The present calculations were performed by using the Numerical Materials Simulator in National Institute for Materials Science.