Magnetic Properties of Chiral Superconductors in Rhombohedral Multilayer Graphene

Recent experiments have uncovered unconventional superconductivity in rhombohedral multilayer graphene emerging in close proximity to magnetic phase transitions—and, in some cases, directly from a parent metallic state with a net orbital moment. This latter case, known as the chiral superconductor, originates from a parent state with single-spin and single-valley polarization that breaks time-reversal symmetry. It exhibits an exceptionally large critical magnetic field, and its ground state reverses at a finite coercive field. Given a BCS-type superconducting wavefunction, there exists no standard framework for deriving orbital magnetization—a theoretical gap that our work addresses. We develop a microscopic theory that describes how the ground-state magnetization of a time-reversal–broken metal evolves across the superconducting transition and how the resulting condensate expels magnetic fields. Our results provide new insight into the coexistence of orbital magnetization and superconductivity in a strongly correlated electron gas in multilayer graphene.