作者机构:Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, China
相关基金:Project supported by the National Natural Science Foundation of China (Grant No 60771004) and the Ministry of Science and Technology of the People's Republic of China (Grant No 2006CB932402). Acknowledgment The corresponding author has benefited greatly from the discussion with Dr. Liang Xue-Lei.