1. Institute of Metallurgy, Ural Division of Russian Academy of Sciences, 620016 Yekaterinburg, Russia
2. L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russia
3. Moscow Institute of Physics and Technology, 141700 Moscow, Russia
4. Institute for High Pressure Physics, Russian Academy of Sciences, 142190 Troitsk, Russia
5. Department of Physics and Astronomy, California State University Northridge, Northridge, California 91330, USA