1. Department of Physics, State Key Laboratory of Surface Physics and Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Fudan University, Shanghai 200433, China.
2. Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China.
3. Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil.
4. Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, MN 55455, USA.