1. Institute of Physics, Chinese Academy of Sciences/Beijing National Laboratory for Condensed; Matter Physics; Beijing 100190 P. R. China
2. Collaborative Innovation Center of Quantum Matter; Beijing 100190 P. R. China
3. WPI Advanced Institute for Materials Research; Tohoku University; Sendai 980-8577 Japan
4. Nanostructures Research Laboratory; Japan Fine Ceramic Centre; Nagoya 456-8587 Japan
5. Institute of Engineering Innovation; The University of Tokyo; Tokyo 113-8654 Japan