First principles theory of electron-magnon scattering and the spin polarized electron energy loss spectroscopy

Logo Projekt SPEELS

Magnetic solids constitute a very important class of materials as they are extensively used in everyday life, e.g., in the electric energy generation and propulsion, medical imaging, and information storage, and are essential to many new technologies currently under development. One of those new applications is the field of magnonics whose main target is to transport and process information using magnetic degrees of freedom contrary to the traditional approach based on charge currents, i.e. electronics. In spite of their high relevance, some of the basic properties of magnetic materials still remain a mystery. One of those topics not fully understood is the interaction between the magnetic and electronic degrees of freedom in such materials. It leads to spin dependent lifetimes of electronic states and inelastic electron transport to name but a few. Additionally, these interactions are believed to be driving the high critical temperatures in some superconductors, in particular in the pnictide and cuprate families.

In the first part of the project, the electron-magnon scattering is modeled as interaction between electrons and an effective dynamical field associated with bosonic magnons, similarly to Feynman’s approach to quantum electrodynamics. This approach is formulated in the framework of the formally exact many-body theory. The novelty in this approach is that quantities from linear response time dependent density functional theory (LRTDDFT) calculations are used to approximate an effective interaction between electrons and magnons. As these LRTDDFT calculations are based upon the Korringa-Kohn-Rostocker method, bulk systems as well as complex geometries can be accounted for.

Based on the same formalism, an ab inito theory of SPEELS will be developed in the second part of the project. In SPEELS, the energy and momentum loss of spin polarized electrons, upon their inelastic scattering from a magnetic material, are measured, allowing to probe the spectra of excited magnetic states of the solid. Since these high energy electrons interact with the electron gas of the magnetic material via the Coulomb interaction, it additionally offers a possibility to directly probe the exchange forces in the magnetic solids. Despite its relevance, no first-principles theory of SPEELS exists. Compared to the above-mentioned theory of electron magnon scattering, a set of modified Feynman diagrams has to be considered in the scattering amplitude.

The successful realization of this project will lead to a significant advance in the understanding of magnetic materials.

Mr. Sebastian Paischer  has been awarded the prestigious “DOC” grant  of the “Österreichische Akademie der Wissenschaften”. Mr. Paischer is pursuing his PhD jointly at the Johannes Kepler university, Linz, and HAW Hamburg under the supervision of Univ.-Prof. Dr. Arthur Ernst and Prof. Dr. Paweł Buczek, respectively.

In cooperation with
Johannes Kepler Universität Linz