Twisting graphene layers with a twist angle larger than 10 degrees results in electronically decoupled systems. This can be used to extract the electronic thickness of graphene from transport experiments. For twisted double bilayer graphene a gap opens without applied top  and back gate voltages. The gap formation is caused by crystal fields between the layers. For tilt angles around 2 degrees the overlap between gaps and wave functions in the two double layer systems can be controlled by top and back gates. This intermediate angle is small enough for the minibands to form and large enough such  that the charge carrier gases in the layers can be tuned independently. We use this property to generate an energetic overlap between narrow isolated electron and hole bands with good nesting properties. Our measurements reveal the formation of ordered states with reconstructed Fermi surfaces, consistent with density-wave states, for equal electron and hole densities. For MATBG we observe superconductivity and demonstrate the dc and ac Jospehson effect.

This work was done in collaboration with F. De Vries, P. Rickhaus, G. Zheng, E. Portoles, A. Kurzmann, C. Tong, R. Garreis, C. Gold, and T. Ihn