1. National Laboratory of Solid State Microstructures and Jiangsu Provincial Key Laboratory for Nanotechnology College of Engineering and Applied Sciences Nanjing University Nanjing 210093 P. R. China
2. Department of Chemistry Shantou University Guangdong 515063 P. R. China
3. College of Materials and Environmental Engineering Hangzhou Dianzi University Hangzhou Zhejiang 310018 P. R. China
4. College of Materials Science and Optoelectronic Technology CAS Center for Excellence in Topological Quantum Computation Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences, Yanqi Lake, Huairou District Beijing 101408 P. R. China