Finite-Momentum Pairing and Superlattice Superconductivity in Valley-Imbalanced Rhombohedral Graphene

Inspired by the recent experimental discovery of superconductivity emerging from a time-reversal symmetry-breaking normal state in tetralayer rhombohedral graphene, we here investigate superconducting instabilities in this system. We classify the possible pairing instabilities, including states with commensurate and incommensurate center of mass momenta. As rotational symmetry is broken in the latter type of pairing states, their momentum-space structure is most naturally characterized by a "valley-independent Chern number," measuring the relative chirality between the normal and superconducting state. We further demonstrate that superconductivity can condense at multiple incommensurate momenta simultaneously, leading to the spontaneous formation of a translational-symmetry-breaking superlattice superconductor. Studying multiple different pairing mechanisms and varying the degree of spin and valley polarization in the normal state, we compare the energetics of these superconductors. Our results demonstrate that valley-imbalanced rhombohedral tetralayer graphene can give rise to rich superconducting phenomenologies.