1. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, College of Physics, Nanjing University, Nanjing 210093, People's Republic of China
2. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Electronic Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China
3. National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, Department of Material Science and Engineering, Nanjing University, Nanjing 210093, People's Republic of China
4. Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, People's Republic of China