1. School of Materials Science and Engineering Nanyang Technological University Singapore 639798 Singapore
2. Beijing National Laboratory for Condensed Matter Physics and Institute of Physics Chinese Academy of Sciences Beijing 100190 China
3. Key Lab of Advanced Optoelectronic Quantum Architecture and Measurement (Ministry of Education) Beijing Key Lab of Nanophotonics & Ultrafine Optoelectronic Systems, and School of Physics Beijing Institute of Technology Beijing 100081 China
4. CINTRA CNRS/NTU/THALES UMI 3288, Research Techno Plaza, 50 Nanyang Drive, Border X Block, Level 6 Singapore 637553 Singapore