1. State Key
Laboratory of Optoelectronic Materials and Technologies, Institute
of Optoelectronic and Functional Composite Materials, Nanotechnology
Research Center, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275, Guangdong People’s Republic of China
2. Key Laboratory
of Low-Dimensional Quantum Structures and Quantum Control of the Ministry
of Education, Department of Physics, Hunan Normal University, Changsha 410081, Hunan People’s Republic of China