1. Nanophotonics Research Division; CAS Center for Excellence in Nanoscience; National Center for Nanoscience and Technology; Beijing 100190 China
2. School of Physics; Academy for Advanced Interdisciplinary Studies; Collaborative Innovation Center of Quantum Matter; Peking University; Beijing 100871 China
3. Department of Physics; Zhejiang Normal University; Jinhua 321004 China
4. Department of Electronics and Nanoengineering; Aalto University; Tietotie 3 FI-02150 Espoo Finland