Tunnelling Spectroscopy of Kondo adatoms and single molecules on a magnetic surface
Spectroscopie à effet tunnel d'adatomes Kondo et de molécules uniques sur une surface magnétique
Résumé
This work deals with two spintronics problems. In a first part, the Kondo effect induced by a 3d single atom adsorbed on a ferromagnetic surface is investigated using tunneling spectroscopy. The tunneling spectra above Co adatoms on Fe/Au(111) self-organized clusters can be split by the interaction with the substrate. The spectroscopic signatures were fit using a two levels Fano resonance, which allows to extract the Kondo temperature and the magnetic field within a Zeeman effect scheme. In a second part, we investigate the spin-polarization of the local density of states of single C60 molecules adsorbed on a Cr(001) surface using spin-polarized scanning tunneling spectroscopy. The spin-resolved conductance maps and spectra show a significant tunneling magnetoresistance above the molecules. Tight-binding and ab initio simulations allow the identification of the involved molecular polarized state, which derives from the lifting of degeneracy of a free molecule orbital. The magnetoresistance is ascribed to a spin-splitting of this molecular state and its spin-dependent hybridization with the chromium surface. This remarkable effect arises in the experiment as well as in the ab initio modeling despite the intrinsic complex electronic structure of the (001) surface, which is not yet theoretically clarified. The magnetoresistance following Jullière's model reaches very high values at high biases that usually annihilate such effects.
Spectroscopie à effet tunnel d'adatomes Kondo et de molécules uniques sur une surface magnétique. English abstract.