Navigation and service

Electronic Properties of Metals and Semiconductors

Large-Scale Electronic-Structure Calculations

The development of advanced 21st century applications increasingly profits from a basic quantum mechanical understanding 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 the number of atoms in the system [1] and thus overcome the unfavourable, higher scaling in normal density functional calculations.

KKRnano enables us to treat systems with many thousands of atoms with up to more than a million parallel tasks. [2] The calculations can be made very precisely, because the Green function can be determined virtually exactly if non-local angular 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.

A. Thiess, P. H. Dederichs, R. Zeller, S. Blügel, and W. R. L. Lambrecht, Phys. Rev. B 86, 180401 (2012).
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 the physical properties of their crystalline and amorphous phases.

We investigated the role of vacancies on the experimentally observed metal-insulator transition and found that vacancy clusters 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 and Cr 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).