Electron Theory

For many phenomena in solid state physics there is an interplay between various scales of length, energy and time, from the electronic to the atomic and mesoscopic scale up to the macroscopic scale. Therefore, a multiscale analysis is indispensable for a comprehensive description of solid state properties. To achieve this, we combine the methods of the ab-initio density functional electron theory with phenomenological methods like statistical mechanics, micromagnetism, lattice theory and elasticity theory. In the centre of our interest are the static and dynamical properties of spin and orbital magnetism in magnetic materials with various dimensions, i.e., bulk materials and nanostructured systems (two-, one- and zero-dimensional), which are interesting both from the viewpoint of basic research and because of their potential technological applications (magnetic materials for memory devices, spintronics, etc.). Examples are the dissipative magnetization dynamics on the timescale of nanoseconds (e.g., vortex dynamics studied intensively in the department) and on the timescale of femtoseconds (demagnetization and magnetization reversal of ferromagnetic layers after optical femtosecond laserpulses). Other examples are the ab initio derived spinclusterexpansion for the description of spin interactions on the atomic level, and the atomistic simulation of magnetoelectric effects in nanostructures with an ab initio determined model operator for the description of the electric-field effect on the magnetocrystalline anisotropy energy. In addition to purely theoretical basic research it is a central objective of this research branch to deliver a theoretical basis for the main experimental activity of the depertment, i.e., spectroscopy and microscopy with polarized x-rays, and to explore possible future applications for even more intensive x-ray sources.

The experimental XMCD spectra (P. Gambardella et al., Nature 416, 301 (2002)) for monatomic Co chains at the steps of a vicinal Pt surface, for a Co monolayer on Pt and for bulk Co, in comparison with our calculated XMCD spectra (lowest part).