[1] Beijing Inst Technol, Beijing Key Lab Nanophoton & Ultrafine Optoelect, Beijing 100081, Peoples R China
[2] Beijing Inst Technol, Sch Phys, Beijing 100081, Peoples R China
[3] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Liaoning, Peoples R China
[4] Univ Ulsan, Dept Phys, Ulsan 44610, South Korea