Strain tunable magneto-transport study of twisted bilayer graphene heterostructures

Twisting two single layer graphenes with small angle creates a moiré potential which can efficiently modify the electron band structure. At the first magic angle ~ 1.1^o, the Coulomb potential dominates over the kinetic energy. The resultant two lowest flat bands host novel electronic phenomena, such as correlated insulating states, superconductivity, ferromagnetism, etc. At lower twist angles, higher order moiré bands and Hofstadter butterfly spectra of twisted bilayer graphene provide promising platforms for fascinating quantum phases and are highly unexplored. In our work, we fabricate twisted bilayer graphene heterostructures on flexible substrates which allows us to apply strain on the heterostructures. We explore twisted bilayer graphene over various twisting angles by magneto-transport measurements. Moiré superlattice area changes dramatically with the twisting angle. By observing the required magnetic field to induce one magnetic flux quantum per unit moiré cell, we found that strain is able to change the moiré superlattice area. Our work shows that strain plays an important role in modulating the band structure of twisted bilayer graphene.