1. Condensed Matter Science and Technology Institute and Department of Physics
2. Harbin Institute of Technology
3. Harbin 150080
4. China
5. Electronic Materials Research Laboratory
6. Key Laboratory of the Ministry of Education
7. Xi'an Jiaotong University
8. Xi'an 710049
9. National Laboratory of Solid State Microstructures
10. Department of Materials Science and Engineering
11. Nanjing University
12. Nanjing 210093
13. Materials Research Institute and Department of Mathematics