1. State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, People’s Republic of China.
2. University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China.
3. State Key Laboratory of Low-Dimensional Quantum Physics, Department of Physics, Tsinghua University, Beijing 100084, China.
4. Department of Physics, College of William and Mary, Williamsburg, VA 23187, USA.