Tunable bandwidths and gaps in twisted double bilayer graphene on the verge of correlations

Abstract

We use temperature-dependent resistivity in small-angle twisted double bilayer graphene to measure bandwidths and gaps of the bands. This electron-hole asymmetric system has one set of nondispersing bands that splits into two flat bands with the electric field—distinct from the twisted bilayer system. With electric field, the gap between two emergent flat bands increases monotonically and bandwidth is tuned from 1 to 15 meV. These two flat bands with gap result in a series of thermally induced insulator to metal transitions—we use a model, at charge neutrality, to measure the bandwidth using only transport measurements. Having two flat bands with tunable gap and bandwidth offers an opportunity to probe the emergence of correlations.