[1] Univ Sci & Technol China, Hefei Natl Lab Phys Sci Microscale, Int Ctr Quantum Design Funct Mat ICQD, Hefei 230026, Anhui, Peoples R China
[2] Fudan Univ, State Key Lab Surface Phys, Shanghai 200433, Peoples R China
[3] Fudan Univ, Dept Phys, Shanghai 200433, Peoples R China
[4] Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA
[5] Chinese Acad Sci, Shenzhen Inst Adv Technol, Shenzhen 518055, Peoples R China
[6] Univ New S Wales, Sch Phys, Sydney, NSW 2052, Australia
[7] Harvard Univ, Sch Appl Sci & Engn, Cambridge, MA 02138 USA