1. School of Physics and Electronics, Key Laboratory of Low-dimensional Quantum Structures and Quantum Control of Ministry of Education, Key Laboratory for Matter Microstructure and Function of Hunan Province, Synergetic Innovation Center for Quantum Effects and Application, Hunan Normal University, Changsha 410081, Hunan, P. R. China
2. School of Materials Science and Engineering, Jiangxi Engineering Laboratory for Advanced Functional Thin Films, Jiangxi Key Laboratory for Two-Dimensional Materials, Nanchang University, Nanchang 330031, Jiangxi, P. R. China
3. School of Physical Science and Technology, MOE Key Laboratory of New Processing Technology for Non-ferrous Metals and Materials, Guangxi Key Laboratory of Processing for Non-ferrous Metals and Featured Materials, Guangxi University, Nanning 530004, Guangxi, P. R. China