1. The Key Laboratory for Magnetism and Magnetic Materials of MOE, Lanzhou University, Lanzhou 730000, China
2. Quantum Structures Laboratory, Department of Electrical Engineering, University of California, Riverside, California 92521, United States
3. School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024, China
4. The Laboratory for Electron and X-ray Instrumentation, California Institute for Telecommunication and Information Technology (Calit2), University of California, Irvine, California 92697, United States