1. Ministry of Education Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Shaanxi Province Key Laboratory of Quantum Information and Quantum Optoelectronic Devices, School of Physics, Xi’an Jiaotong University 1 , Xi’an 710049, China
2. Department of Nuclear Physics, China Institute of Atomic Energy 2 , P.O. Box 275(7), Beijing 102413, China