Acknowledgements

This work is supported by the National Natural Science Foundation of China (Grant Nos. 51601012, U1637210, 11775018, 51571021). The authors gratefully

acknowledge the HVEM laboratory in Hokkaido University, Japan. The help and suggestions from Professor Q. Zhan and F.R. Wan at University of Science and Technology Beijing and Professor S. Ohnuki at Hokkaido University were highly appreciated.
