1. School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China
2. Institute for Advanced Materials and Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China Normal University, Guangzhou 510006, China
3. School of Chemistry, Sun Yat-Sen University, Guangzhou 510275, China
4. Department of Physics, University of Texas at Arlington, Arlington, Texas 76019, USA