[1] Natl Ctr Nanosci & Technol, CAS Ctr Excellence Nanosci, Div Nanophoton, Beijing 100190, Peoples R China
[2] Univ Chinese Acad Sci, Beijing 100049, Peoples R China
[3] Aalto Univ, Dept Elect & Nanoengn, Tietotie 3, FI-02150 Espoo, Finland
[4] Aalto Univ, Dept Appl Phys, QTF Ctr Excellence, FI-00076 Espoo, Finland
[5] Univ Minnesota, Dept Elect & Comp Engn, Keller Hall 200 Union St S-E, Minneapolis, MN 55455 USA
[6] Barcelona Inst Sci & Technol, ICFO Inst Photon Sci, Barcelona 08860, Spain
[7] ICREA, Passeig Lluis Co 23, Barcelona 08010, Spain
[8] IBM TJ Watson Res Ctr, Yorktown Hts, NY 10598 USA