1. Experimentalphysik II, Universität Bayreuth, 95440 Bayreuth, Germany
2. Institut für Festkörperphysik, TU Darmstadt, Hochschulstrasse 6, 64289 Darmstadt,
Germany
3. Faculty of Mathematics & Computer Science, University of Warmia & Mazury Olsztyn, Sloneczna 54, 10710 Olsztyn, Poland
4. Institute of Physics, Kazan Federal University, Kazan 420008, Tatarstan, Russia