Regensburg 2010 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 46: Density functional theory and beyond for real materials I

O 46.7: Vortrag

Mittwoch, 24. März 2010, 12:00–12:15, H34

Optical Absorption and Bound Excitons in MnO, FeO, CoO, and NiO — •Claudia Rödl, Frank Fuchs, and Friedhelm Bechstedt — Institut für Festkörpertheorie und -optik and European Theoretical Spectroscopy Facility (ETSF), Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

Since magnetic materials gain more and more importance also for technological applications, we calculate the optical properties of the row of antiferromagnetic oxides from MnO to NiO from first principles.

We present optical absorption spectra solving the Bethe-Salpeter equation (BSE), thus including excitonic and local-field effects (LFE). It turns out that the main absorption peaks are due to d-d excitations which are dipole forbidden at the Γ point. It is shown that the influence of LFE is almost vanishing for the materials under investigation, while the electron-hole attraction leads to a significant redistribution of spectral weight to lower energies.

Besides the dipole allowed excitations which contribute to the absorption spectra, also optically forbidden excitations within the fundamental gap occur. The latter are related to Frenkel-like bound excitonic states. These excitons have their origin in transitions between the occupied and empty d states of the transition-metal cations. Due to the separation of the excitonic Hamiltonian into the independent subspaces of spin-allowed and spin-forbidden transitions, they can be split into two groups: excitons which involve a flip of the one-particle spin between valence and conduction bands and excitons without spin flip.