1. College
of Physics and Information Science and Key Laboratory of Low-Dimensional
Quantum Structures and Quantum Control of the Ministry of Education, Hunan Normal University, Changsha, Hunan 410081, People’s Republic of China
2. Faculty
of Materials, Optoelectronics and Physics, Key Laboratory of Low-Dimensional
Materials and Application Technology (Ministry of Education), Xiangtan University, Xiangtan 411105, People’s Republic of China
3. Department
of Applied Physics and Materials Research Center, The Hong Kong Polytechnic University, Hong Kong