1. Physical Science and Engineering Division, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia
2. Key Laboratory for Magnetism and Magnetic Materials of Ministry of Education, Lanzhou University, Lanzhou 730000, P. R. China
3. School of Integrated Circuits, Guangdong University of Technology, Guangzhou 510006, China
4. School of Physics, Engineering and Technology, University of York, York YO10 5DD, U.K.
5. School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin 541004, P. R. China
6. Guangdong Provincial Key Laboratory of Optical Information Materials and Technology & Institute for Advanced Materials, South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, P. R. China
7. Physics Department, Georgetown University, Washington, D.C. 20057, United States
8. Department of Physics, University of California at Berkeley, Berkeley, California 94720, United States
9. Laboratory of Solid State Microstructures and Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 211102, P. R. China