1. Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China; International Centre for Materials Physics, Academia Sinica, Shenyang 110015, China
2. Department of Physics, Sichuan University, Chengdu 610064, China; CCAST (World Laboratory), Box 8730, Beijing 100080; International Centre for Materials Physics, Academia Sinica, Shenyang 110015, China