1. State Key Laboratory for Artificial Microstructure and Mesoscopic Physics; School of Physics; Peking University; Beijing 100871 China
2. Materials Sciences Division; Lawrence Berkeley National Laboratory; CA 94720 USA
3. Advanced Light Source; Lawrence Berkeley National Laboratory; CA 94720 USA
4. International Center for Quantum Materials; School of Physics; Peking University; Beijing 100871 China
5. Department of Polymer Science and Engineering; University of Massachusetts; Amherst MA 01003 USA
6. Collaborative Innovation Center of Quantum Matter; Beijing 100871 China
7. Collaborative Innovation Center of Extreme Optics; Shanxi University; Taiyuan Shanxi 030006 China