Excitonic metal and non-Fermi liquid behaviour in twisted double bilayer graphene

We show that twisted double bilayer graphene, whose band structure shows low energy electron and hole pockets, forms an excitonic metal near the charge neutrality point at very low temperatures ~ a few K. This leads to interesting implications for low-temperature transport in the system as a function of carrier density. Above the transition temperature, the density fluctuations in this critical metal lead to non-Fermi liquid features, which can also be seen in the temperature dependence of transport in the system. Similar features are also observed in recent experiments on these systems.