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

Recently, superlattices in graphene have gained much interest due to its ability to tune its band structure. In particular, it has been demonstrated that when two copies of monolayer graphene are stacked with a ‘magic’ angle twist between them, flat bands appear. Flat bands give birth to a plethora of electronic interaction governed phenomena like superconductivity, ferromagnetism, etc.

When two copies of bilayer graphene are put on top of each other with a relative twist, it allows electrical control over the flatness of the bands and the gaps between them. Even before studying interaction driven physics, it is useful to study the tunability of bands in such a system. We perform transport measurements on dual gated twisted double bilayer graphene device (TDBG) and use simple model calculations to understand important experimentally observed features. Specifically, we will discuss how the bandwidth of the bands can be tuned electrically and how an electron-hole asymmetric model can explain some observations. A discussion on some observations which may be precursors to correlation will conclude the presentation.