1. Department of Physics, The University of Texas at Arlington, Arlington, Texas 76019-0059, United States
2. School of Physics, Huazhong University of Science and Technology, Wuhan, People's Republic of China 430074
3. Pacific Northwest National Laboratory, Richland, Washington 99352, United States
4. Department of Material and Chemical Engineering, Hainan University, Haikou, People's Republic of China 570228