1. Key Laboratory of Advanced Materials (MOE), School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
2. Department of Physics, and Lab of Solid State Microstructures and Quantum Control, School of Electronic Science and Applied Physics, Hefei University of Technology, Hefei, Anhui 230009, People's Republic of China
3. Institute of Microelectronics, Tsinghua University, Beijing 100084, China
4. Division of Physical Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 239955, Kingdom of Saudi Arabia