1. College of Physics and Information Technology, Shaanxi Normal University, Xian 710062, Shaanxi, PR China, State-Key Laboratory for Mechanical Behavior of Materials, Xian Jiaotong University, Xian 710049, Shaanxi, PR China, and ICMMO/LEMHE UMR CNRS 8182, Université Paris-Sud 11, 91405 Orsay Cedex, France