1. College of Materials Science and EngineeringZhengzhou University Zhengzhou 450052 P. R. China
2. International Laboratory for Quantum Functional Materials of Henan School of Physics and EngineeringZhengzhou University Zhengzhou 450052 P. R. China
3. Key Laboratory for Special Functional Materials of Ministry of Education School of Materials and EngineeringHenan University Kaifeng 475004 P. R. China