Spin-polarized superconductivity in semimetallic rhombohedral graphene: Part I

In rhombohedrally stacked graphene, SSH-like (Su-Schrieffer-Heeger) interlayer dimerization localizes the low energy electronic wavefunction to the outer crystal faces. As the number of graphene layers increases, the low-energy bands flatten and the density of states near charge neutrality grows, making rhombohedral graphene well suited to hosting symmetry-breaking phases. We study an eight-layer rhombohedral graphene sample and report the observation of five distinct superconducting pockets for each sign of an applied displacement field. This is the first observation of superconductivity in a sample thicker than six layers, suggesting that it may persist into bulk rhombohedral graphite. The superconducting pockets in octalayer graphene emerge from a semimetallic normal state in which the valence and conduction bands are localized to opposite crystal faces. Although superconductivity has been observed in several multilayer graphene-based systems, the universality of the pairing mechanism remains under question. Our results extend flat-band superconductivity into a new regime, where pairing is mediated by spatially separated dual-surface electronic reservoirs.