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

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.