1. Faculty of Physics, Institute of Experimental Physics, University of Warsaw, 02-093 Warsaw, Poland
2. Institute of High Pressure Physics “Unipress,” 01-142 Warsaw, Poland
3. State Key Laboratory of Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
4. Materials Department, University of California, Santa Barbara, California 93106, USA