1. State Key Laboratory of Optoelectronic Materials and Technologies, Institute of Optoelectronic and Functional Composite Materials, Nanotechnology Research Center, School of Physics & 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