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Collaborations: A. Bagrets1,3, V. Meded1, A. Bernand-Mantel4,
H. van der Zant5, M. Ruben1, S. Schmauss1,6, W. Wulfhekel1,6.
1 Institute of Nanotechnology, Karlsuhe Institute of Technology (KIT), Germany 2 Institut für Theorie der Kondensierten Materie, KIT, Germany 3 DFG-Center for Functional Nanostructures, KIT, Germany 4 Institut Néel - Département Nano, Grenoble, France 5 Kavli Institute of Nanosciences, Delft University of Technology, The Netherlands 6 Physikalisches Institut, KIT, Germany Single molecules realize classes of quantum dots in new parameter regimes. Phenomena specifically related to molecules typically arise when a molecular symmetry, for instance related to its geometry, is weakly broken. In such a case the molecule can be close to an instability which leaves its signature in the low energy excitations and transport properties. In our presentation we will give two examples illustrating this principle. The first example focuses on magnetism. We explain the experimental observation that a diamagnetic molecule can enhance the (giant) magneto-resistance (GMR) of an STM tunneling contact by an order of magnitude. [1] The second example addresses another transport experiment performed on a spin transition complex [FeII(bpp)2]2+. [2] The experimental observation is a splitting of the Kondo-peak in the deep Coulomb blockade regime induced by a charge reorganization. We invoke a scenario where the internal double-dot structure and the related symmetry of the molecule, the closeness of the spin transition and the spin orbit interaction cooperate in order to explain the experimenta. effect. For both examples we present an extensive set of ab-initio calculations that support our analysis. [1] S. Schmauss, A. Bagrets, Y. Nahas, T. K. Yamada, A. Bork, M. Bowen, E. Beaurepaire, F. Evers, W. Wulfhekel, Magnetoresistance through single molecules using a spin-polarized STM, accepted Nature Nanotechnology (2010). [2] A. Bernand-Mantel, J. Seldenthuis, A. Beukman, H. S. J. van der Zant, V. Meded, R. Chandrasekhar, K. Fink, M. Ruben, F. Evers, Spin-coupled double-quantum-dot behavior inside a single-molecule transistor, submitted (2010). |
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