1. Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, 400714 Chongqing, China and National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083, China
2. Faculty of Physics and CENIDE, University of Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
3. Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätstraße 150, 44780 Bochum, Germany