Dresden 2009 – scientific programme

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O: Fachverband Oberflächenphysik

O 30: Metal substrates: Adsorption of organic / bio molecules IV

O 30.10: Talk

Wednesday, March 25, 2009, 12:45–13:00, SCH A118

Vibrational Kondo effect in a metal-free organic self-assembled molecular layer — •Isabel Fernandez-Torrente, Katharina Jennifer Franke, and Jose Ignacio Pascual — Institut für Experimentalphysik, Freie Universität Berlin, Germany

Molecular magnetism is achieved by localising unpaired electrons within molecules. The traditional approach entails the synthesis of metal-organic coordination compounds, where the unpaired spin is provided by paramagnetic transition metal atoms. Here we show that localization of a spin also occurs in a molecular layer of a pure organic charge transfer compound, TTF-TCNQ, self-assembled on a metal surface. The structure adopted by this salt on Au(111) leads to localization of an unpaired electron in a pi-molecular orbital (LUMO) of the acceptor molecule. This free radical state can be demonstrated by the observation of the Kondo effect, obtained in transport experiments carried out in a low temperature scanning tunneling microscope. The unpaired electron is also coupled with molecular vibrations. This phonon-assisted spin flip induces splitting of the Kondo resonance in vibrational sidebands that exhibit different intensities across the TCNQ molecule. These variations arise from intramolecular alterations of the electron-phonon coupling. The analysis of STS curves taken along individual TCNQ molecules allows us to identify the atomic motion involved in the vibrations.