Electron tunneling transport through single transition-metal complexes

•Romeike Christian1, Wegewijs Maarten1, Wenzel Wolfgang2 und Schoeller Herbert1
1Institut für Theoretische Physik - Lehrstuhl A, RWTH Aachen, 52056 Aachen, Germany
2Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021 Karlsruhe, Germany

We theoretically describe electron tunneling transport through a transition-metal complex coupled to metallic electrodes. Recently such a system containing a single cobalt ion has been investigated experimentally [1]. Upon increasing the coupling of the electrodes to the complex in a chemically controlled way, a strong Kondo effect in the current was observed at low temperatures.

In order to describe such an experiment, one has to formulate a interacting electronic model for the transport. We first perform electronic structure calculations on the isolated cobalt-complex. The symmetry restrictions on the tunneling from particular types of ligands onto the metal ion are carefully analysed. We next address the question of which states on the ion and ligands are to be included in a minimal model for the transport. Next, the coupling to the leads is taken into account in a phenomenological way by assuming a tunneling Hamiltonian with tunneling matrix elements which enter as parameters of our model through electron-tunneling rates. We address the possible transport situations which may be realized in such systems when different transition-metals are substituted for the cobalt.