1. Lehrstuhl für Theoretische Materialphysik, Universität Paderborn, 33095 Paderborn, Germany
2. Institute of Physics—Center for Science and Education, Silesian University of Technology, S. Konarskiego Str. 22B, 44-100 Gliwice, Poland
3. Department of Physics, Durham University, South Road, Durham DH1 3LE, United Kingdom