1. School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing, People’s Republic of China
2. College of Physics, Nanjing University of Aeronautics and Astronautics, Nanjing, People’s Republic of China
3. Department of Physics, Bielefeld University, Bielefeld, Germany
4. Helmholtz-Zentrum Berlin für Materialien und Energie, Berlin, Germany