1. Department of Materials Science and EngineeringCollege of EngineeringPeking University Beijing 100871 P. R. China
2. Academy for Advanced Interdisciplinary Studies and Department of PhysicsSouthern University of Sciences and Technology Shenzhen 518000 P. R. China
3. Guangdong Provincial Key Laboratory of, Energy Materials for Electric Power Shenzhen 518055 P. R. China