1. Kirchhoff Institute of Physics, Heidelberg University, INF 227, 69120 Heidelberg, Germany
2. Institute for Solid State Physics, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
3. Physikalisches Institut, Goethe-Universität, 60323, Frankfurt am Main, Germany
4. Faculty of Science, Physics Department, Fayoum University, 63514 Fayoum, Egypt
5. Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710072, P. R. China
6. Leibniz Institute for Solid State and Materials Research IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany