1. Department of Mechanical Engineering, The University of Hong Kong, Pok Fu Lam Road, Pokfulam, Hong Kong
2. School of Physics, Southeast University, Nanjing, Jiangsu 211189, P. R. China
3. Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, United States
4. Synergetic Innovation Center for Quantum Effects and Applications (SCIQEA), Hunan Normal University, Changsha, Hunan 410081, P. R. China