Materials science

Physics

Bilayer graphene

Nanotechnology

Quantum mechanics

Graphene

Superconductivity

Spectral line

Magic angle

Condensed matter physics

Nature

Superconductivity can occur under conditions approaching broken-symmetry parent states1. In bilayer graphene, the twisting of one layer with respect to the other at ‘magic’ twist angles of around 1 degree leads to the emergence of ultra-flat&nbsp;moiré superlattice minibands. Such bands are a rich and highly tunable source of strong-correlation physics2–5, notably superconductivity, which emerges close to interaction-induced insulating states6,7. Here we report the fabrication of magic-angle twisted bilayer graphene devices with highly uniform twist angles. The reduction in twist-angle disorder reveals the presence of insulating states at all integer occupancies of the fourfold spin–valley degenerate flat conduction and valence bands—that is, at moiré band filling factors ν&nbsp;=&nbsp;0,&nbsp;±1,&nbsp;±2,&nbsp;±3. At ν&nbsp;≈&nbsp;−2, superconductivity is observed below critical temperatures of up to 3 kelvin. We also observe three new superconducting domes at much lower temperatures, close to the ν&nbsp;=&nbsp;0 and ν&nbsp;=&nbsp;±1 insulating states. Notably, at ν&nbsp;=&nbsp;±&nbsp;1 we find states with non-zero Chern numbers. For ν&nbsp;=&nbsp;−1 the insulating state exhibits a sharp hysteretic resistance enhancement when a perpendicular magnetic field greater than 3.6 tesla is applied, which is consistent with a field-driven phase transition. Our study shows that broken-symmetry states, interaction-driven insulators, orbital magnets, states with non-zero Chern numbers and superconducting domes occur frequently across a wide range of moiré flat band fillings, including close to charge neutrality. This study provides a more detailed view of the phenomenology of magic-angle twisted bilayer graphene, adding to our evolving understanding of its emergent properties. The fabrication of magic-angle&nbsp;twisted&nbsp;bilayer graphene devices with highly uniform twist angles enables the observation of new superconducting domes, orbital magnets and Chern insulating states.

Superconductors, orbital magnets and correlated states in magic-angle bilayer graphene