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