1. School of Electronic Science and Engineering, National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China
2. Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
3. National Laboratory of Solid State Microstructures, School of Electronics Science and Engineering, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China