1. a Geballe Laboratory for Advanced Materials and Department of Applied Physics, Stanford University , California , 94304 , USA
2. b Ames Laboratory and Department of Physics and Astronomy, Iowa State University , Ames , Iowa , 50011 , USA
3. e Department of Physics , Pohang University of Science and Technology , Pohang , 790 784 , South Korea
4. c Ames Laboratory and Department of Geological and Atmospheric Sciences, Iowa State University , Ames , Iowa , 50011 , USA
5. d Ames Laboratory and Department of Materials Science and Engineering, Iowa State University , Ames , Iowa , 50011 , USA