1. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; Beijing 100190 China
2. School of Physical Sciences; University of Chinese Academy of Sciences; Beijing 100190 China
3. Department of Electronics and Electrical Engineering; University College London; London WC1E 7JE UK
4. National Centre for Nanoscience and Technology; Chinese Academy of Sciences; Beijing 100190 China
5. Department of Physics; University of the Punjab; Quaid-e-Azam Campus Lahore 54000 Pakistan
6. Department of Physics; University of Warwick; Coventry CV4 7AL UK
7. CAS Center for Excellence in Topological Quantum Computation; University of Chinese Academy of Sciences; Beijing 100190 China