1 State Key Laboratory of Powder Metallurgy, School of Physics and Electronics, Central South University, Changsha 410083, China.
2 State Key Laboratory of Powder Metallurgy, School of Physics and Electronics, Central South University, Changsha 410083, China; Department of Physics and Astronomy, University of Rochester, New York, NY 14627, USA.
4 State Key Laboratory of Powder Metallurgy, School of Physics and Electronics, Central South University, Changsha 410083, China. Electronic address: junliang.yang@csu.edu.cn.