1. National Laboratory of Solid State Microstructures; Collaborative Innovation Center of Advanced Microstructures; School of Electronic Science and Engineering; Nanjing University; Nanjing 210093 P. R. China
2. School of Physics; Nanjing University; Nanjing 210093 P. R. China
3. School of Physical Science and Technology; ShanghaiTech University; CAS-Shanghai Science Research Center; Shanghai 200031 P. R. China
4. Wuhan National High Magnetic Field Center; Huazhong University of Science and Technology; Wuhan 430074 P. R. China