1. Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw, Poland, Institute of High Pressure Physics (UNIPRESS), Polish Academy of Sciences, ul. Sokołowska 29/37, 01-142 Warsaw, Poland, Institut des Nanosciences de Paris, Université Paris VI et Paris VII, CNRS UMR 7588, 140 rue de Lourmel, Paris 75015, France, Humboldt-Universität zu Berlin, Institut für Physik, Newtonstrasse 15, D-12489 Berlin, Germany