1. Center for Nano and Micro Mechanics, School of Aerospace Engineering, Tsinghua University , Beijing 100084 , China
2. Department of Engineering Mechanics, School of Aerospace Engineering, Tsinghua University , Beijing 100084 , China
3. International School for Advanced Studies (SISSA) , Trieste 34136 , Italy
4. International Centre for Theoretical Physics (ICTP) , Trieste 34151 , Italy
5. Institute of Superlubricity Technology, Research Institute of Tsinghua University in Shenzhen , Shenzhen 518057 , China
6. Department of Mechanical Engineering, State Key Lab of Tribology in Advanced Equipment (SKLT), Tsinghua University , Beijing 10084 , China
7. Institute of Materials Research, Tsinghua Shenzhen International Graduate School , Shenzhen 518057 , China