Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 37: Joint Focussed Session: Theory and Computation of Electronic Structure: New Frontiers II

HL 37.1: Topical Talk

Tuesday, March 15, 2011, 11:15–11:45, TRE Phy

Electronic and Optical Excitations in Magnetic Insulators — •Claudia Rödl, Frank Fuchs, and Friedhelm Bechstedt — Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany

With the advent of electronic devices exploiting also the spin degree of freedom, magnetic materials attract more and more interest due to potential technological applications. However, describing the excitation properties of insulators with strongly localized and partially occupied d states by means of ab-initio methods remains a considerable challenge. Here, we focus on the antiferromagnetic transition-metal oxides (TMO) MnO, FeO, CoO, and NiO and ferromagnetic CrBr₃ as prototypical representatives for the class of magnetic insulators.

A perturbative treatment of Hedin’s GW approximation based on (semi)local approaches to exchange and correlation in the subjacent density-functional calculation fails to reproduce the experimental photoemission spectra. Instead, we use the non-local HSE03 exchange-correlation functional to obtain a reasonable starting point for the GW calculation. The spin-polarized extension of the Bethe-Salpeter equation (BSE) is solved to calculate optical absorption spectra including excitonic and local-field effects. The spectra are analyzed in terms of dipole-allowed and dipole-forbidden transitions. For instance, it turns out that the main absorption peaks in the TMOs are due to d-d excitations which are dipole-forbidden at the Γ point. Further, the occurrence of spin-allowed and spin-forbidden Frenkel-like bound excitonic states within the fundamental band gap is investigated.