Competing Zero-Field Chern Insulators in Superconducting Twisted Bilayer Graphene

The discovery of magic angle twisted bilayer graphene has unveiled a rich variety of superconducting, magnetic, and topologically nontrivial phases. Here, we show that the zero-field states at odd integer filling factors in h-BN nonaligned devices are consistent with symmetry broken Chern insulators, as is evidenced by the observation of the anomalous Hall effect near moire ' cell filling factor v = +1. The corresponding Chern insulator has a Chern number C = +1 and a relatively high Curie temperature of Tc approximate to 4.5 K. In a perpendicular magnetic field above B > 0.5 T we observe a transition of the v = +1 Chern insulator from Chern number C = +1 to C = 3, characterized by a quantized Hall plateau with Ryx = h/3e2. These observations demonstrate that interaction-induced symmetry breaking leads to zero-field ground states that include almost degenerate and closely competing Chern insulators, and that states with larger Chern numbers couple most strongly to the B field. In addition, the device reveals strong superconducting phases with critical temperatures of up to Tc approximate to 3.5 K. By providing the first demonstration of a system that allows gate-induced transitions between magnetic and superconducting phases, our observations mark a major milestone in the creation of a new generation of quantum electronics.

Automated summary

Research has shown that the odd integer filling factors in h-BN nonaligned devices correspond to symmetry broken Chern insulators with a Chern number of C = +1 and a relatively high Curie temperature. Under a perpendicular magnetic field, the Chern insulator at v = +1 transitions from C = +1 to C = 3, characterized by a quantized Hall plateau. Additionally, the device exhibits strong superconducting phases with critical temperatures up to Tc ≈ 3.5 K.