1. School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK
2. Department of Materials Science and Engineering, Shenzhen Institute for Quantum Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China
3. Department of Physics, Hong Kong Baptist University, Hong Kong, S. A. R. China
4. Department of Physics, University of Paderborn, Warburger Straße 100, D-33098 Paderborn, Germany