1. Department of Physics, University of Central Florida, Orlando, FL 32765, USA.
2. Department of Physics, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
3. National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
4. College of Sciences, Northeastern University, Shenyang, Liaoning, China.
5. Department of Electrical and Computer Engineering and Department of Physics and Astronomy, University of California, Riverside, CA 92521, USA.
6. Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.