1. College of Electronic Science and TechnologyShenzhen University Shenzhen 518060 P. R. China
2. Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong ProvinceCollege of Optoelectronic EngineeringShenzhen University Shenzhen 518060 P. R. China
3. Institute for Advanced StudyShenzhen University Shenzhen 518060 P. R. China
4. Department of Physics and Materials ScienceCity University of Hong Kong Hong Kong SAR 999077 P. R. China