Affiliation: | 1. Department of Physics, Fudan University, 200433 Shanghai, China;2. Department of Physics, National Dong Hwa University, Shoufeng, 974 Hualien, Taiwan;3. Department of Physics, Autonomous University of Barcelona, 08193 Bellaterra, Barcelona, Spain;4. Instituto de Física, Universidade de São Paulo, CP 66318, 05315-970 São Paulo, Brazil |