Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 21: Elektronische Struktur II
O 21.7: Vortrag
Samstag, 5. März 2005, 12:15–12:30, TU EB107
The Si(111)-(7×7) surface: a correlated electronic Hubbard system? — •Richard Schillinger, C. Bromberger, H. J. Jänsch, H. Kleine, O. Kühlert, C. Weindel, and D. Fick — Philipps-Universität, Fachbereich Physik and Zentrum für Materialwissenschaften 35032 Marburg, Germany
Li adsorption at extremely low coverages (10−3 ML and below) on the metallic Si(111)(7×7) surface has been studied by β-NMR experiments (measurement of T1-times). Instead of increasing linearly with sample temperature, as expected for a metallic system, the relaxation rates α=1/T1 are quite surprisingly constant in between 50 K and 300 K and rise considerably above. This temperature dependence points to an extremely localized and thus narrow band (width below 5 meV) which pins the Fermi energy. It is energetically located within an approximately 600 meV wide gap in between a lower filled and an upper empty Hubbard band. Due to its extremely narrow width it cannot be detected in photo emission experiments. In Dynamic Mean Field Theory (DMFT) based on Hubbard Hamiltonians [1,2] this kind of density of states is typical for correlated electron systems being close to a Hubbard metal-insulator transition.
[1] G. Kotliar and G. Vollard, Physics Today, March 2004
[2] Pou et al., Phys. Rev. Lett. 63 4309 (2000)