a
National Centre for Nanoscience and Technology, Beijing 100190, China
E-mail: slf@nanoctr.cn
;
Fax: +86-10-62656765
;
Tel: +86-10-82545584
b
Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
c
College of Physics and Information Science, Hunan Normal University, Changsha 410081, China
E-mail: dstang@hunnu.edu.cn
;
Tel: +86-731-88873055
d
Graduate School of Chinese Academy of Sciences, Beijing 100049, China