1. Institut für Physik, Martin-Luther-Universität Halle-Wittenberg, Karl-Freiherr-von-Fritsch Str. 3, 06120 Halle (Saale), Germany
2. Department of Physics, Rzeszów University of Technology, al. Powstańców Warszawy 6, 35-959 Rzeszów, Poland
3. Departamento de Física and CeFEMA, Instituto Superior Técnico, Universidade de Lisboa, av. Rovisco Pais, 1049-001 Lisbon, Portugal