Berlin 2015 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 96: Ultrafast Electron Dynamics at Surfaces and Interfaces
O 96.2: Vortrag
Freitag, 20. März 2015, 11:00–11:15, MA 004
Electron dynamics across the charge-transfer gap of NiO ultrathin films — •Konrad Gillmeister1, Mario Kiel1, and Wolf Widdra1,2 — 1Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, 06120 Halle, Germany — 2Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle, Germany
NiO is known as a prototype system for a strongly correlated oxide. Despite of numerous scientific investigations of its electronic structure, studies of the electron dynamics of NiO are rare. This contribution deals with the unoccupied Ni 3d states at the upper edge of the charge-transfer gap. For the study, ultrathin well-ordered films from 1–20 monolayers (ML) thickness have been grown on Ag(001) via molecular beam epitaxy.
The unoccupied Ni 3d states have been investigated by time-resolved two-photon photoemission spectroscopy. While interface effects dominate the electronic structure for films up to 3 ML, films of 4 ML and beyond show bulk-like behavior. For these thicknesses we find the upper Hubbard band (UHB) at 2.5 eV above EF. Electrons excited into the UHB decay on a timescale of less than 15 fs. The surprisingly short lifetimes are explained by correlation effects within the oxide film. Ultrafast decay via additional intra-gap states and strong electron-phonon coupling is also considerable.