Family of magnetic field-boosted superconductors in rhombohedral graphene.

Abstract

In some unconventional superconductors, time-reversal symmetry can be broken in addition to the gauge symmetry¹, resulting in superconductivities that can be enhanced or induced by magnetic fields². However, field-enhanced superconductors are more vulnerable to impurities than Bardeen-Cooper-Schrieffer counterparts³. Crystalline rhombohedral multilayer graphene is a promising platform to explore them due to its superior material quality and gate-tunable strong correlation effects^4,5. Here we report transport measurements of rhombohedral tetralayer and pentalayer graphene, demonstrating a spectrum of clean-limit superconductivities. We found three different types of field-enhanced and field-induced superconductivities in the pentalayer. They are all robust against an in-plane field up to 8.5 Tesla, exceeding the Pauli limit by tens of times. Compared to Bernal bilayer graphene showing only in-plane field-enhancement⁶, pentalayer graphene features superconductors enhanced by out-of-plane as well as in-plane fields. They also reside at much lower gate electric fields owing to the intrinsically flatter band dispersion-facilitating their study and further engineering. Additionally, we observed that proximitized spin-orbit coupling (SOC) generates multiple new superconductors without introducing additional disorder effects. Our work establishes a new family of magnetic field-boosted superconductors in rhombohedral graphene. Utilizing the high accessibility with moderate gate voltages, this will pave the way for realizing non-Abelian quasiparticles through interfacial engineering⁷ in the extreme clean limit, in that proximitized SOC leads to topological states⁸ and maintains the ultrahigh quality of crystalline graphene.