1. School of Science Constructor University Campus Ring 1 28759 Bremen Germany
2. Center of Single-Molecule Sciences, College of Electronic Information and Optical Engineering Nankai University 38 Tongyan Road, Jinnan District 300350 Tianjin China
3. Faculty of Physics University of Vienna Kolingasse 14–16 10905 Vienna Austria
4. The State Key Laboratory of Refractories and Metallurgy, Faculty of Materials Wuhan University of Science and Technology 430081 Wuhan, Hubei China