1. Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
2. Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering, South China Normal University, Guangzhou 510006, China
3. Materials Science and Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
4. School of Physics and Technology, and Institute for Advanced Studies, Wuhan University, Wuhan 430072, China
5. Department of Electrical and Computer Engineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093, United States
6. Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China