1. Department of Physics, Guangdong Technion-Israel Institute of Technology, Shantou 515063, Guangdong, China
2. Guangdong Provincial Key Laboratory of Materials and Technologies for Energy Conversion, Guangdong Technion-Israel Institute of Technology, Shantou 515063 Guangdong, China
3. Techion-Israel Institute of Technology, Haifa 32000, Israel