1. Department of Mathematics and Natural Sciences, RWTH Aachen University, Templergraben 59, 52062 Aachen, Germany
2. The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwano-ha, Kashiwa 277-8581, Chiba, Japan
3. Department of Physics, University of Guelph, 488 Gordon Street, Guelph, Ontario N1G 2W1, Canada
4. Institute of Computational Biomedicine, Forschungszentrum Jülich, IAS-5/INM-9, Wilhelm-Johnen Straße, 5428 Jülich, Germany
5. Faculty of Physics, University of Bucharest, Atomiştilor 405, 077125 Măgurele, Romania