1. Beijing National Laboratory of Condensed Matter, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, P.R. China, State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080, P.R. China, Center for Nanoscience and Department für Physik, Ludwig-Maximilians-Universität München, Geschwister-School-Platz 1, 80539 München, Germany, National Center for Nanoscience and Nanotechnology, Chinese Academy of Sciences, Beijing 100080, P.R. China, and...