1. Department of Applied Physics, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
2. Department of Electrical and Computer Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan
3. School of Physics, The University of New South Wales, Sydney 2052, Australia
4. Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-8656, Japan
5. College of Physics and Electronic Engineering, Sichuan Normal University, Chengdu 610068, China
6. School of Science and Engineering, The Chinese University of Hong Kong, Shenzhen, Guangdong 518172, China