Superconductivity from dual-surface carriers in rhombohedral graphene

TL;DR

This paper reports the discovery of superconductivity in rhombohedral multilayer graphene, arising from an unusual surface-localized electronic state with coexisting Fermi pockets, and explores its relation to topological states and electric displacement fields.

Contribution

It demonstrates superconductivity originating from a charge-delocalized semimetallic state in rhombohedral graphene with coexisting surface Fermi pockets, a novel regime in multilayer graphene.

Findings

Superconductivity appears in multiple Fermi pockets at the surfaces.

Superconductivity coexists with an anomalous Hall state under certain conditions.

Enhanced density of states near charge neutrality promotes symmetry-breaking phases.

Abstract

Intrinsic rhombohedral graphene hosts an unusual low-energy electronic wavefunction, predominantly localized at its outer crystal faces with negligible presence in the bulk. Increasing the number of graphene layers amplifies the density of states near charge neutrality, greatly enhancing the susceptibility to symmetry-breaking phases. Here, we report superconductivity in rhombohedral graphene arising from an unusual charge-delocalized semimetallic normal state, characterized by coexisting valence- and conduction-band Fermi pockets split to opposite crystal surfaces. In octalayer graphene, the superconductivity appears in five apparently distinct pockets for each sign of an external electric displacement field ($D$). In a moir\'e superlattice sample where heptalayer graphene is aligned on one side to hexagonal boron nitride, two pockets of superconductivity emerge from a single sharp resistive feature. At higher $D$ the same resistive feature additionally induces an $h/e^{2}$-quantized anomalous Hall state at dopings near one electron per moir\'e unit cell. Our findings reveal a novel superconducting regime in multilayer graphene and create opportunities for coupling to nearby topological states.