  We discuss novel transverse plasmon-polaritons that are hosted by AA- and
AB-stacked bilayer graphene due to perfect nesting. They are composed of
oscillating counterflow currents in between the layers, giving a clear
interpretation for these collective modes as magnetic excitations carrying
magnetic moment parallel to the planes. For AA-stacked bilayer graphene, these
modes can reach zero frequency at the neutrality point and we thus predict a
symmetry broken ground-state leading to in-plane orbital ferromagnetism. Even
though it could be hard to detect them in real solid-state devices, these novel
magnetic plasmons should be observable in artificial set-ups such as optical
lattices. Also, our results might be relevant for magic angle twisted bilayer
graphene samples as their electronic properties are mostly determined by
confined AA-stacked regions.
