In-Plane Critical Magnetic Fields in Magic-Angle Twisted Trilayer Graphene

It has recently been shown [Y. Cao, J. M. Park, K. Watanabe, T. Taniguchi, and P. Jarillo-Herrero, Paulilimit violation and re-entrant superconductivity in moir ' e graphene, Nature (London) 595, 526 (2021).] that superconductivity in magic-angle twisted trilayer graphene survives to in-plane magnetic fields that are well in excess of the Pauli limit, and much stronger than the in-plane critical magnetic fields of magic-angle twisted bilayer graphene. The difference is surprising because twisted bilayers and trilayers both support the magic-angle flat bands thought to be the fountainhead of twisted graphene superconductivity. We show here that the difference in critical magnetic fields can be traced to a C2Mh symmetry in trilayers that survives in-plane magnetic fields, and also relative displacements between top and bottom layers that are not under experimental control at present. An gate electric field breaks the C2Mh symmetry and therefore limits the in-plane critical magnetic field.

Automated summary

Recent research has shown that superconductivity in magic-angle twisted trilayer graphene can survive in in-plane magnetic fields well beyond the Pauli limit, unlike magic-angle twisted bilayer graphene. The difference is attributed to the symmetry and relative displacements present in trilayers, which are not under experimental control at present. An gate electric field can break the symmetry and limit the in-plane critical magnetic field.