1. Department of Electrical and Computer Engineering, University of California, Los Angeles, California 90095, United States
2. Microsystems Technology Laboratories, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
3. Fert Beijing Institute, BDBC, and School of Electronic and Information Engineering, Beihang University, Beijing 100191, China
4. Department of Physics and Center for Complex Quantum Systems, University of Texas at Austin, Austin, Texas 78712-0264, United States