1. Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
2. Institute for Advanced Materials Guangdong Provincial Key Laboratory of Optical Information Materials and Technology South China Academy of Advanced Optoelectronics South China Normal University Guangzhou 510006 China
3. Physical Science and Engineering Division King Abdullah University of Science and Technology Thuwal 23955‐6900 Saudi Arabia
4. School of Science and Engineering The Chinese University of Hong Kong Shenzhen Guangdong 518172 China
5. School of Materials Science and Engineering Nanjing University of Science and Technology Nanjing 210094 China
6. Department of Applied Physics The University of Tokyo 7‐3‐1 Hongo Tokyo 113‐8656 Japan
7. Department of Electrical and Computer Engineering Shinshu University 4‐17‐1 Wakasato Nagano 380‐8553 Japan