1. Materials Genome Institute and Department of Physics Shanghai University Shanghai 200444 China
2. Department of Physics The Ohio State University Columbus OH 43210 USA
3. Shenyang National Laboratory for Materials Science Institute of Metal Research Chinese Academy of Science Shenyang Liaoning 110016 P. R. China
4. School of Physics University of Electronic Science and Technology of China Chengdu 610054 PR China
5. Key Laboratory of Interface Science and Engineering in Advanced Materials of Ministry of Education Taiyuan University of Technology Taiyuan 030024 P. R. China
6. School of Physical Science & Technology Lanzhou University Lanzhou 730000 P. R. China
7. National Laboratory for Infrared Physics Shanghai Institute of Technical Physics Chinese Academy of Sciences Shanghai 200083 P. R. China
8. Department of Physics and Astronomy University of Missouri Columbia MO 65211‐7010 USA