1. School of Physics, Nankai University, Tianjin 300071, China
2. Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China
3. Department of Physics and Astronomy, Texas A&M University, College Station, Texas 77843, USA
4. Department of Physics and Astronomy and Stewart Blusson Quantum Matter Institute, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1