Electronic Properties of Metals and Semiconductors

Large-Scale Electronic-Structure Calculations

The development of advanced 21st century applications increasingly profits from a basic quantum mechanicalunderstanding of material properties. To this end, we have developed a computer code (KKRnano) based on a Green-function formulation of the Korringa-Kohn-Rostoker method which requires computing times that scale linearly with thenumber of atoms in the system [1] and thus overcome the unfavourable, higher scaling in normal density functionalcalculations.

KKRnano enables us to treat systems with many thousands of atoms with up to more than a million parallel tasks. [2] Thecalculations can be made very precisely, because the Green function can be determined virtually exactly if non-localangular projection potentials are utilized and if the total-energy functional is evaluated appropriately. [3]

[1] A. Thiess, R. Zeller, M. Bolten, P. H. Dederichs, and S. Blügel, Phys. Rev. B 85, 235103 (2012)
[2] High-Q Club JUQUEEN
[3] R. Zeller, J. Phys.: Condens. Matter 25, 105505 (2013) and 27, 306301 (2015).

Dilute Magnetic Semiconductors

Semiconductors dilutely doped with magnetic impurities are interesting systems under discussion for spintronic applications.
In a systematic study of the exchange interactions in realistic models of Gd-doped GaN containing nitrogen or oxygen interstitials or Ga vacancies, we found that only Ga vacancies provide a robust path to magnetic percolated clusters which can explain the experimentally observed ferromagnetism with colossal magnetic moments per Gd atom in extremely dilute samples.

[1] A. Thiess, P. H. Dederichs, R. Zeller, S. Blügel, and W. R. L. Lambrecht, Phys. Rev. B 86, 180401 (2012).
[2] A. Thiess, S. Blügel, P. H. Dederichs, R. Zeller, and W. R. L. Lambrecht, Phys. Rev. B 92, 104418 (2015).

Phase-Change Alloys

Phase-change alloys are basic materials in DVD and Blu-Ray technology because of characteristic differences in thephysical properties of their crystalline and amorphous phases. We investigated the role of vacancies on the experimentally observed metal-insulator transition and found that vacancyclusters lead to localized electronic states in the insulating phase. [1] We also investigated the effects of doping with transition metal atoms and found that ferromagnetic states occur for V andCr doping with Curie temperatures approaching room temperature for large Cr concentrations of 15%. [2]

[1] W. Zhang, A. Thiess, P. Zalden, R. Zeller, P. H. Dederichs, J-Y. Raty, M. Wuttig, S. Blügel, and R. Mazzarello, Nat.Mater. 11, 952 (2012).
[2] T. Fukushima, H. Katayama-Yoshida, K. Sato, H. Fujii, E. Rabel, R. Zeller, P. H. Dederichs, W. Zhang, R. Mazzarello,Phys. Rev. B 90, 144417 (2014).