1. State Key Laboratory for Artificial Microstructure and Mesoscopic Physics, School of Physics, Peking University, Beijing 100871, China
2. Institute of Photonics, SUPA, University of Strathclyde, Glasgow G4 0NW, United Kingdom
3. Joint Laboratory of Advanced Optoelectronic Materials and Devices, State Key Laboratory, Wuhan University of Technology, China and Institute of Photonics, University of Strathclyde, Glasgow G4 0NW, United Kingdom
4. Department of Applied Physics, Tianjin University, Tianjin 300072, China