Real-space study of zero-field correlation in tetralayer rhombohedral graphene

TL;DR

This study uses scanning probe techniques to reveal a magnetic correlated insulating state in tetralayer rhombohedral graphene, showing how it can be manipulated and characterized at the atomic scale, advancing understanding of exotic quantum phenomena.

Contribution

It provides the first atomic-scale evidence of zero-field correlations and magnetic ordering in tetralayer rhombohedral graphene, highlighting a symmetry-broken state absent in trilayer configurations.

Findings

Identification of a 17 meV gap at charge neutrality in tetralayer RG

Observation of a bound state around non-magnetic impurities within the correlated regime

Detection of Friedel oscillations enabling band dispersion measurement

Abstract

Rhombohedral graphene (RG) has emerged as a promising platform for exploring exotic quantum phenomena, such as quantum magnetism, unconventional superconductivity, and fractional quantum anomalous Hall effects. Despite its potential, atomic-scale investigations of RG remain limited, hindering a detailed microscopic understanding of the origins of these correlated states. In this study, we employ scanning probe microscopy and spectroscopy to probe the intrinsic electronic states in trilayer and tetralayer RG. We identify a correlated insulating state with a 17 meV gap at the charge neutrality point in tetralayer RG, which is absent in the trilayer configuration. This gap is suppressed by applying a perpendicular magnetic field or doping the charge carrier density and does not exhibit inter-valley coherence patterns. We attribute this phenomenon to a symmetry-broken layer antiferromagnetic state, characterized by ferrimagnetic ordering in the outermost layers and antiferromagnetic coupling between them. To further investigate this magnetic correlated state, we conduct local scattering experiments. Within the correlated regime, a bound state emerges around a non-magnetic impurity but is absent near magnetic impurities, suggesting that non-magnetic doping induces a spin texture in the ferrimagnetic surface layers. Outside the correlated regime, Friedel oscillations are observed, allowing precise determination of the band dispersion in tetralayer RG. These findings provide atomic-scale evidences of zero-field correlations in RG and may be extended to study other exotic phases in RG.