Testing the Nanotribology Theories on Twisted Bilayer Graphene*

Friction is a ubiquitous force that appears in all length scales, and it has to be dealt with in a wide variety of circumstances ranging from daily life applications to high technology products. Depending on the circumstances it could be desirable or disadvantageous. In any case a solid theoretical understanding of the physical origin is most essential. However, since friction is not itself a fundamental force and instead arises from a combination of factors like inter-surface adhesion, surface roughness, surface deformation, contamination, etc. it is very challenging to calculate it from the first principles leaving aside developing a fundamental theory. The studies tackling this challenge mainly suffers from the fact that multiple variables come to play all at once during the experiments making it very difficult to pinpoint the individual contributions from different factors. One such study which was conducted by us previously showed that the charge distribution on the surface of a single layer graphene was dramatically affected from a minor topographical change in the substrate causing a big difference in the coefficient of friction. Here we will be presenting and discussing our preliminary results of our new research project where we have been studying the tribological properties of twisted bilayer graphene trying to exploit the fact that the surface periodicity of such systems is relatively easy to modify by a single parameter hence could contribute to the fundamental understanding of friction.