Theory of correlated insulating behaviour and spin-triplet superconductivity in twisted double bilayer graphene

Understand

Two monolayers of graphene twisted by a small `magic' angle exhibit nearly flat bands leading to correlated electronic states and superconductivity, whose precise nature including possible broken symmetries, remain under debate.

• Here we theoretically study a related but different system with reduced symmetry - twisted {\em double} bilayer graphene (TDBLG), consisting of {\em two} Bernal stacked bilayer graphene sheets, twisted with respect to one another.
• Unlike the monolayer case, we show that isolated flat bands only appear on application of a vertical displacement field $D$.
• We construct a phase diagram as a function of twist angle and $D$, incorporating interactions via a Hartree-Fock approximation.