1. Centre for Science at Extreme Conditions & The School of Physics and Astronomy, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, U.K.
2. Center for High Pressure Science & Technology Advanced Research, 1690 Cailun Road, Shanghai 201203, P. R. China
3. Key Laboratory of Materials Physics, Institute of Solid State Physics, HFIPS, Chinese Academy of Sciences, Hefei 230031, China