1. State Key Laboratory for Mesoscopic Physics and School of Physics; Peking University; Beijing 100871 P. R. China
2. Collaborative Innovation Center of Quantum Matter; Beijing 100871 P. R. China
3. Collaborative Innovation Center of Extreme Optics; Taiyuan 030006 Shanxi P. R. China
4. Department of Electrical and Systems Engineering; Washington University; St. Louis MO USA 63130