1. School of Physical Science and Technology, Lanzhou University 1 , Lanzhou 730000, China
2. Institute of Materials Research, Slovak Academy of Sciences 2 , Watsonova 47, 040 01 Kosice, Slovakia
3. Lanzhou Center for Theoretical Physics and Key Laboratory of Theoretical Physics of Gansu Province, Lanzhou University 3 , Lanzhou 730000, China
4. Key Laboratory of Quantum Theory and Applications of Ministry of Education, Lanzhou University 4 , Lanzhou 730000, China