1. School of Chemical Engineering, Sichuan University, Chengdu 610065, China
2. Institut für Informatik VI, Technische Universität München, Schleißheimer Str. 90a, Garching b. München 85748, Germany
3. Max Planck-EPFL Laboratory for Molecular Nanoscience and Technology, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
4. Institute of Physics (IPHYS), École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
5. School of Physics and Optoelectronics, South China University of Technology, Wushan Road 381, Guangzhou, Guangdong 510640, China
6. Department of Physics E19, Technische Universität München, James-Franck-Str.1, Garching b. München 85748, Germany