Pervasive spin-triplet superconductivity in rhombohedral graphene

TL;DR

This paper reports on the discovery of robust spin-triplet superconductivity in rhombohedral graphene layers that persists under high magnetic fields, revealing new properties of field-induced superconductivity in layered graphene systems.

Contribution

It demonstrates the existence of magnetic-field-induced spin-triplet superconductivity in rhombohedral graphene, a phenomenon not previously observed in such systems.

Findings

Superconductivity persists beyond the Pauli limit under in-plane magnetic fields.

Superconductivity is gate-tunable and associated with specific conduction band fillings.

Observation of a superconducting diode effect near quantum anomalous Hall states.

Abstract

Magnetic fields typically suppress superconductivity once the Zeeman energy exceeds the pairing gap, unless mechanisms such as unconventional pairing, strong spin-orbit coupling, or intrinsic magnetism intervene. Several graphene platforms realize such mitigating routes, exhibiting superconductivity resilient to magnetic fields. Here we report superconductivity in rhombohedral heptalayer graphene that is both induced and stabilized by in-plane magnetic field ($B_{\parallel}$), with critical fields far beyond the Pauli paramagnetic limit. The superconductivity spans a wide gate range and emerges from a sharp zero-field resistive ridge that tracks approximately constant conduction band filling. The presence of zero-field superconductivity and the evolution of the critical temperature with $B_{\parallel}$ are highly gate sensitive. We also observe a weak superconducting diode effect in several distinct regimes within the superconducting phase, including nearby to an integer quantum anomalous Hall state generated by a boron nitride moir\'e superlattice, indicating a potential coexistence of valley imbalance and superconductivity. These results establish several intriguing new properties of spin-triplet, field-induced superconductivity in a thick rhombohedral graphene stack.