  Superconductivity often occurs close to broken-symmetry parent states and is
especially common in doped magnetic insulators. When twisted close to a magic
relative orientation angle near 1 degree, bilayer graphene has flat moire
superlattice minibands that have emerged as a rich and highly tunable source of
strong correlation physics, notably the appearance of superconductivity close
to interaction-induced insulating states. Here we report on the fabrication of
bilayer graphene devices with exceptionally uniform twist angles. We show that
the reduction in twist angle disorder reveals insulating states at all integer
occupancies of the four-fold spin/valley degenerate flat conduction and valence
bands, i.e. at moire band filling factors nu = 0, +(-) 1, +(-) 2, +(-) 3, and
superconductivity below critical temperatures as high as 3 K close to - 2
filling. We also observe three new superconducting domes at much lower
temperatures close to the nu = 0 and nu = +(-) 1 insulating states.
Interestingly, at nu = +(-) 1 we find states with non-zero Chern numbers. For
nu = - 1 the insulating state exhibits a sharp hysteretic resistance
enhancement when a perpendicular magnetic field above 3.6 tesla is applied,
consistent with a field driven phase transition. Our study shows that
symmetry-broken states, interaction driven insulators, and superconducting
domes are common across the entire moire flat bands, including near charge
neutrality.
