Anisotropic Band Structure in Short Period Superlattices in Graphene

In the first phase of this project, we successfully prepared state-of-the-art devices containing gate-controlled short period lateral superlattices (LSL) in high-mobility graphene, and detected anisotropic transport in both monolayer graphene and bilayer graphene based devices. We will search for unambiguous proof of the anisotropic band structure in graphene with a one-dimensional superlattice. To achieve this, we will perform transverse magnetic focusing experiments, where the electron or hole trajectories in a magnetic field reflect the shape of the Fermi contour, which, for 1D LSLs, was predicted to be elliptically deformed. In addition, the creation of additional Dirac peaks in the band structure should not only be reflected in satellite resistance peaks (which we observed in the first phase of this project), but also in a modified sequence of the quantum Hall plateaus. The observation of those requires fine-tuning of the electrostatics of the gate coupling to the graphene transport layer, which we will address by finite element modelling. The band structure generated by the lateral superlattice should also lead to electron-electron scattering in the Umklapp process, which has been found in moiré lattices, but has yet to be detected in lithographically defined superlattices. Finally, THz radiation impinging on a superlattice with reduced symmetry leads to ratchet effects, which we presently study. We will continue to provide samples for this joint effort.