1. Condensed Matter Science and Technology Institute and Department of Physics, Harbin Institute of Technology, Harbin 150080, China
2. School of Civil Engineering, Harbin Institute of Technology, Harbin 150001, China
3. Department of Instrument Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
4. Department of Mathematics and Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA