Superconductivity and Ferroelectric Orbital Magnetism in Semimetallic Rhombohedral Hexalayer Graphene

TL;DR

This paper explores the rich quantum phases in rhombohedral hexalayer graphene, revealing superconducting-like states, ferroelectric orbital magnetism, and electric-field-driven band inversion in its semimetallic regime.

Contribution

It uncovers a new correlated semimetal regime with dual-carrier superconductivity and switchable ferroelectric orbital magnetism, expanding understanding of quantum phases in layered graphene.

Findings

Observation of two superconducting-like states near band inversion

Identification of a ferroelectric orbital magnet with electric switching

Detection of magnetic hysteresis reversible by electric field

Abstract

Rhombohedral multilayer graphene has emerged as a promising platform for exploring correlated and topological quantum phases, enabled by its Berry-curvature-bearing flat bands. While prior work has focused on separated conduction and valence bands, we probe the extensive semimetallic regime of rhombohedral hexalayer graphene. We survey a rich phase diagram dominated by flavor-symmetry breaking and reveal an electric-field-driven band inversion by fermiology. Near this inversion, we observe two superconducting-like states confined to regions with coexisting electron and hole Fermi surfaces, suggesting a possible dual-carrier origin. In addition, we identify a ferroelectric orbital magnet that undergoes sharp switching under unipolar electric fields, signaling spontaneous electric polarization. Unlike previously reported multiferroicity near zero electric field, this new state exhibits magnetic hysteresis reversible by electric field, consistent with a phenomenological model of coupled electric and magnetic polarization. Our work elucidates the correlated semimetal regime in rhombohedral graphene and underscores its potential to host diverse quantum phases.