Berlin 2005 – wissenschaftliches Programm

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MA: Magnetismus

MA 20: Poster:Schichten(1-29),Spintrsp(30-45),Ex-Bias(46-63),Spindyn(64-75),Mikromat.(76-80),Cluster(81-94),Abbv.(95-99),Obflm(100-02),SpElek.(103-09),E-Theo(110-14),Mikromag.(115-16),Spin+PÜ(117-26),Mag.Mat.(127-51),Meth.(152-55),Mol.Mag(156-59),Kondo(160-65

MA 20.164: Poster

Montag, 7. März 2005, 14:00–18:00, Poster TU C

Electronic structure of NiO monolayer on Ag(100) — •L. H. Tjeng¹, C.-F. Chang¹, S. Altieri², S. Heise¹, M. W. Haverkort¹, Z. Hu¹, S. V. Streltsov³, V. I. Anisimov³, H. H. Hsieh⁴, H.-J. Lin⁵, D.-J. Huang⁵ und C.T. Chen⁵ — ¹II. Physikalisches Institut, Universität zu Köln,Zülpicher Str. 77, 50937 Köln, Germany — ²INFM, Modena,Italy — ³Institute of MetalPhysics, Ekaterinburg, Russia — ⁴Chung Cheng Institute of Technology, Taiwan — ⁵NSRRC, Taiwan

We have investigated the electronic structure of a NiO monolayer deposited on top of a Ag(100) substrate. Using x-ray absorption spectroscopy we found that the Ni ions are in the 3d⁸ (2+) valence state, with one hole in a 3d_3z²−r² orbital and another in a 3d_x²−y², very similar to bulk NiO. From the polarization dependence we observed nevertheless that the 3d_3z²−r² orbital in the NiO monolayer is somewhat less unoccupied than in bulk NiO and that there is a large 3d_3z²−r² −3d_x²−y² crystal field splitting. Our LDA+U calculations show that the unoccupied 3d_3z²−r² orbital is not pushed up so strongly above the Fermi level because in the monolayer there are no oxygens above or below it to hybridize with. This 3d_3z²−r² forms a band via the Ag sp-states, with a low energy tail extending below the Fermi level. This is confirmed by our photoemission data, which show a clear Fermi cut-off in the Ni 3d. In other words, the monolayer is metallic. Moreover, except for a rigid energy shift, the photoemission spectra of the NiO monolayer and bulk NiO look rather similar. We have more spectroscopic data to suggest that the NiO monolayer on Ag is actually a Kondo lattice system.