Ëøöööò Òò Èèóòóò Óò¬òòññòø Ò Ëëðð¹¹×××ñððð Éùùòøùñ Óø Ëùôöððøøøøø×

YANG Zheng( ), SHI Yi( ), LIU Jian-Lin( ), YAN Bo( ), HUANG Zhuang-Xiong( ), PU Lin( ), ZHENG You-Dou(Æ ), WANG Kang-Long( ) Department of Physics and National Laboratory of Solid State Microstructure, Nanjing University, Nanjing 210093 Department of Electrical Engineering, University of California at Riverside, Riverside, California 92521, USA Department of Electrical Engineering, University of California at Los Angeles Los Angeles, California 90095-1594, USA