1. Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Wrocław University of Science and Technology, 50-370 Wrocław, Poland
2. Department of Theoretical Physics, Wrocław University of Science and Technology, 50-370 Wrocław, Poland
3. Institute of High Pressure Physics, Polish Academy of Sciences, 01-142 Warsaw, Poland
4. Institute of Solid State Physics, Technische Universität Berlin, 10623 Berlin, Germany