1. School
of Physics, State Key Lab for Mesoscopic Physics, Peking University, Beijing 100871, China
2. Collaborative Innovation Center of Quantum Matter, Beijing 100871, China
3. Department
of Electrical and Computer Engineering, and the Laboratory for Nanophotonics, Rice University, 6100 Main Street, Houston, Texas 77005, United States
4. Department
of Chemistry, Rice University, 6100 Main Street, Houston, Texas 77005, United States
5. School
of Materials Science and Engineering, School of Electrical and Electronic
Engineering, Nanyang Technological University, 50 Nanyang Ave., Singapore 639798
6. Mechanical
Engineering and Materials Science Department, Rice University, Houston, Texas 77005, United States
7. ICFO—Institut de Ciencies Fotoniques, Mediterranean
Technology Park, 08860 Castelldefels, Barcelona, Spain
8. ICREA—Institució Catalana de Reserca i Estudis Avançats, Passeig Lluı́s Companys,
23, 08010 Barcelona, Spain
9. Department
of Physics and Astronomy, Rice University, Houston, Texas 77005, United States