1. Department of Chemical Physics, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, P. R. China.
2. Faculty of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, P. R. China.
3. Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200, Australia.