[1] Univ Sci & Technol Beijing, Sch Math & Phys, Beijing 100083, Peoples R China
[2] Chinese Acad Sci, Beijing Natl Lab Condensed Matter Phys, Inst Phys, Beijing 100190, Peoples R China
[3] Univ Nevada, Dept Phys & Astron, HiPSEC, Las Vegas, NV 89154 USA
[4] Northeastern Univ Qinhuangdao, Sch Resources & Mat, Qinhuangdao 066004, Peoples R China