V. Stepanyuk, O. Brovko, P. R. Diaz, S.K. Saha, C. Schmidt, T. R. Dasa, I. Sivkov
An important focus of the group focus lies in the investigation of the electronic and magnetic properties of nanostructures at surfaces. Using state-of-the-art commercial and home-made density functional theory and kinetic Monte Carlo codes (software) we study, among other things, electronic properties of nanoscale surface structures, and spin dependent effects therein, to better understand how they can be controlled, measured, and possibly applied in modern technological challenges, such as the advancement of spin electronics (spintronics) and novel data storage development. And since for success of spintronics it is not sufficient to understand the intrinsic magnetic and electronic properties of nanostructures we also strive to find adequate means of controlling those properties externally. We study various possibilities for such external control, e.g. through applied electric field or the interaction with a scanning tunneling microscope tip. Another major focus of our research lies in self-organization. While modern experimental techniques allow one to assemble complex structures in an atom-by-atom fashion, this process is very cumbersome and cannot be applied in industrial applications. By understanding the interplay between electronic properties of nanosystems and their interaction we can force the nanostructures to self-assemble on a surface under certain environmental conditions. And finally, we endeavor to understand such properties of oxidic surfaces as their vibrational (phonon) spectra and their dependence on electronic and structural properties.
Fig. 1
To understand and control magnetism of surface nanostructures one has to understand and control the electrons at the surface. Numerous interesting effects can be observed and put to use at surfaces that contain the so-called Shockley surface state - a state localized near the surface and behaving as a quasi-2-dimensional electron gas. The electrons in this state scatter at surface impurities and if the impurities form a closed geometry, the surface state electrons can become confined to that geometry. Carefully controlling the confinement shape one can deliberately channel and focus electrons.
fer the information about the magnetic (Kondo) state of a single atom residing in one of its focal points to the other focal point. Using the Korringa-Kohn-Rostoker Green's function method we can fully ab initio calculate such complex multiple scattering problems (Fig. 1) .
Fig. 2
This amazing property of quantum corrals can be used to tailor magnetic interaction between single adatoms if those are placed in the focuses of the corral or even a part of a corral. Our calculations show that by carefully adjusting the size and shape of the corral one can enhance, quench or even reverse the coupling between individual spins at the surface (Fig. 2).
