Observation of competing, correlated ground states in the flat band of rhombohedral graphite

Abstract

In crystalline solids the interactions of charge and spin can result in a variety of emergent quantum ground states, especially in partially filled, topological flat bands such as Landau levels or in 'magic-angle' bilayer graphene. Much less explored is rhombohedral graphite (RG), perhaps the simplest and structurally most perfect condensed matter system to host a flat band protected by symmetry. By scanning tunneling microscopy we map the flat band charge density of 8, 10 and 17 layers and identify a domain structure emerging from a competition between a sublattice antiferromagnetic insulator and a gapless correlated paramagnet. Our density-matrix renormalization group calculations explain the observed features and demonstrate that the correlations are fundamentally different from graphene based magnetism identified until now, forming the ground state of a quantum magnet. Our work establishes RG as a new platform to study many-body interactions beyond the mean-field approach, where quantum fluctuations and entanglement dominate.

supplementary information included

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• Layer-dependent evolution of electronic structures and correlations in rhombohedral multilayer graphene
• Superconductivity and magnetism in the surface states of ABC-stacked multilayer graphene
• Nodal pair density waves from a quarter-metal in crystalline graphene multilayers
• Competing magnetic states on the surface of multilayer ABC-stacked graphene
• Identification of graphite with perfect rhombohedral stacking by electronic Raman scattering
• Promoting and imaging intervalley coherent order in rhombohedral tetralayer graphene on MoS2
• Real-space study of zero-field correlation in tetralayer rhombohedral graphene
• Solitons induced by an in-plane magnetic field in rhombohedral multilayer graphene
• Ideal quantum geometry of the surface states of rhombohedral graphite and its effects on the surface superconductivity
• Surface magnon spectra of nodal loop semimetals
• Solitons in binary compounds with stacked two-dimensional honeycomb lattices