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 CA 94720 USA
4. School of Chemistry Joseph Banks Laboratories University of Lincoln Beevor Street Lincoln LN6 7DL UK
5. Department of Physics Shanghai Jiao Tong University Shanghai 200240 China
6. Department of Polymer Science and Engineering University of Massachusetts Amherst MA 01003 USA
7. Collaborative Innovation Center of Extreme Optics Shanxi University Taiyuan Shanxi 030006 China