A combination of high field quantum transport experiments, near-field and far-field photocurrent experiments and were performed in graphene superlattices and twisted graphene heterostructures during the project. First, a strong out-of-equilibrium electron distribution was identified generic to all graphene-based superlattices caused by Zener-tunnelling processes analogous to the Schwinger effect1. The effect demonstrated that physics related to Bloch oscillations is prominent in graphene superlattices. Specifically, the work shows that electrons in graphene superlattices can be accelerated through the entire Brillouin zone and their Fermi surface shifted to a strongly out-of-equilibrium electronic state. Second, scanning probe near-field photocurrent experiments were used to image the local structure of twisted graphene superlattices2. Using a scattering-type near-field optical microscope, the opto-electronic properties of the superlattice structure was mapped out with 50 nm spatial resolution and a strong photocurrent pattern was shown to emerge reflecting microscopic variations in the Seebeck coefficient. Third, a giant photoconductive response was demonstrated in twist-decoupled double bilayer graphene layers. The heterostructure was shown to exhibit a giant broadband response extending from visible to terahertz wavelengths with high internal quantum efficiencies thanks to strong enhancement in carrier mobilities caused by interlayer screening of Coulomb scattering.
1. A. Berdyugin, R. Krishna Kumar et al Science 375, 66579, 430-433 (2002)
2. N. C. Hesp, R. Krishna Kumar et al Nat Comm 12, 1640 (2021)
