Ajibade, Adeoluwa Afolabi; (2020) Electron Transport through Ringed Organic Molecules Hosting Magnetic Atoms. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis gives the result of three projects on the behaviour of spins in organic molecules interacting with tunnelling currents. The first project investigates a toy model of a six-membered carbon ring acting as a ligand to a central metal atom. We modelled the interactions inside the molecule and transport across the molecule. We used the sequential tunnelling method which is valid for arbitrarily strong interactions, against the coherent method where the interactions are treated using self-consistent field and the transport is coherent using the Green’s function to calculate the transport across the molecule. The second project looks at a scanning tunnelling microscopy (STM) experi- ment probing iron phthalocyanine on a copper nitride surface, and the explana- tion of the steps in the differential conductance spectrum only appearing for iron phthalocyanine on specific sites on the copper nitride surface. We proposed a co- tunnelling mechanism to explain the appearance of the co-tunnelling steps. We provide a decomposition of the co-tunnelling matrix as a set of products of spin matrices describing multiple spin in- teractions. We calculated the cotunnelling matrix elements exactly and using perturbation theory. The perturbation theory allowed the coefficients to be expresses analytically with respect to: (a) the pseu- dogate voltage, (b) the crystal field anisotropy terms, (c) the isotropic exchange coupling between the molecule and the tunnelling electron and (d) the anisotropic exchange coupling between the molecule and tunnelling electron.

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