1. International Joint Research Laboratory of New Energy Materials and Devices of Henan Province, School of Physics and Electronics, Academy for Advanced Interdisciplinary Studies, Henan University, Kaifeng475004, P.R. China
2. State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an710049, P.R. China
3. School of Materials, Sun Yat-sen University, Shenzhen518107, P.R. China
4. Department of Materials Science and Engineering, Chonnam National University, Gwangju500-757, South Korea
5. Department of Physics, Chalmers University of Technology, SE 412 96Göteborg, Sweden