Regensburg 1998 – wissenschaftliches Programm

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PV: Plenarvorträge

PV II

PV II: Plenarvortrag

Dienstag, 24. März 1998, 08:30–09:15, H18

Tunneling into Gold: from Superlattices to Magnetic Impurities^⋆ — •M.F. Crommie — Boston University, Physics Dept., Boston, MA, U.S.

We have used low temperature STM spectroscopy to study the local electronic properties of Au(111) in the pristine state as well as in the presence of cobalt adatoms. On clean Au(111) we find that the long-range herringbone reconstruction acts as a superlattice for surface state electrons, creating a new band-structure and modulated electronic density. Our spectroscopic results are quantitatively explained by an extended Kronig-Penney model, from which we estimate that surface state electrons in the hcp region of the reconstruction experience a potential offset 25 meV lower than in the fcc region. Cobalt atoms added to the Au(111) surface display a narrow spectroscopic resonance that lies almost exactly at the Fermi energy. The resonance is only 15 meV wide, and is spatially localized to within 8 Å of the center of a cobalt atom. The lineshape of the resonance is surprisingly not Lorentzian, but rather displays the ’anti-resonance’ lineshape typical of a Fano resonance. We believe that this spectroscopic feature is due to the Kondo effect, a cooperative electronic phenomena known to arise from spin- dependent electronic scattering.

^⋆Work done in collaboration with W. Chen, V. Madhavan, and T. Jamneala. Supported by NSF awards DMR-9457955, DMR- 9503837, and the Keck Foundation.