Interaction-driven spontaneous broken-symmetry insulator and metals in ABCA tetralayer graphene

TL;DR

This paper investigates how Coulomb interactions in ABCA tetralayer graphene induce various spontaneous broken-symmetry states, including insulators and metals, with tunable phase transitions driven by carrier density and electric displacement.

Contribution

It demonstrates the experimental observation of multiple broken-symmetry states and their transitions in tetralayer graphene, highlighting the role of Coulomb interactions in these phenomena.

Findings

Observation of a layer antiferromagnetic insulator at zero doping and displacement.

Identification of continuous phase transitions driven by electric displacement.

Detection of isospin polarized metals with tunable spin and valley polarization.

Abstract

Interactions among charge carriers in graphene can lead to the spontaneous breaking of multiple degeneracies. When increasing the number of graphene layers following rhombohedral stacking, the dominant role of Coulomb interactions becomes pronounced due to the significant reduction in kinetic energy. In this study, we employ phonon-polariton assisted near-field infrared imaging to determine the stacking orders of tetralayer graphene devices. Through quantum transport measurements, we observe a range of spontaneous broken-symmetry states and their transitions, which can be finely tuned by carrier density n and electric displacement field D. Specifically, we observe a layer antiferromagnetic insulator at n = D = 0 with a gap of approximately 15 meV. Increasing D allows for a continuous phase transition from a layer antiferromagnetic insulator to a layer polarized insulator. By simultaneously tuning n and D, we observe isospin polarized metals, including spin-valley-polarized and spin-polarized metals. These transitions are associated with changes in Fermi surface topology and are consistent with the Stoner criteria. Our findings highlight the efficient fabrication of specially stacked multilayer graphene devices and demonstrate that crystalline multilayer graphene is an ideal platform for investigating a wide range of broken symmetries driven by Coulomb interactions.