Peter Grünberg Institute (PGI)
Theoretical Nanoelectronics (PGI2/IAS3)
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Peter Grünberg Institute (PGI)
Theoretical Nanoelectronics (PGI2/IAS3)
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 Greenfunction formulation of the KorringaKohnRostoker 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 nonlocal angular projection potentials are utilized and if the totalenergy 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] HighQ Club JUQUEEN
[3] R. Zeller, J. Phys.: Condens. Matter 25, 105505 (2013) and 27, 306301 (2015).
In a systematic study of the exchange interactions in realistic models of Gddoped 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).
We investigated the role of vacancies on the experimentally observed metalinsulator 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, JY. Raty, M. Wuttig, S. Blügel, and R. Mazzarello, Nat. Mater. 11, 952 (2012).
[2] T. Fukushima, H. KatayamaYoshida, K. Sato, H. Fujii, E. Rabel, R. Zeller, P. H. Dederichs, W. Zhang, R. Mazzarello, Phys. Rev. B 90, 144417 (2014).