[Paper Review] Observation of Chern insulator in crystalline ABCA-tetralayer graphene with spin-orbit coupling

Yating Sha, Jian Zheng+8 more|arXiv (Cornell University)|Oct 27, 2023

Graphene research and applications8 citations

TL;DR

The paper reports a ferromagnetic state in charge-neutral ABCA-tetralayer graphene induced by proximity-enabled spin-orbit coupling from WSe2, identified as a Chern insulator with Chern number 4 and quantized Hall responses.

ABSTRACT

Degeneracies in multilayer graphene, including spin, valley, and layer degrees of freedom, are susceptible to Coulomb interactions and can result into rich broken-symmetry states. In this work, we report a ferromagnetic state in charge neutral ABCA-tetralayer graphene driven by proximity-induced spin-orbit coupling from adjacent WSe2. The ferromagnetic state is further identified as a Chern insulator with Chern number of 4, and its Hall resistance reaches 78% and 100% quantization of h/4e2 at zero and 0.4 tesla, respectively. Three broken-symmetry insulating states, layer-antiferromagnet, Chern insulator and layer-polarized insulator and their transitions can be continuously tuned by the vertical displacement field. Remarkably, the magnetic order of the Chern insulator can be switched by three knobs, including magnetic field, electrical doping, and vertical displacement field.

Motivation & Objective

• Motivate exploration of interaction-driven broken-symmetry states in multilayer graphene with spin-orbit coupling proximity.
• Demonstrate a ferromagnetic, Chern-insulating phase in ABCA-tetralayer graphene at charge neutrality.
• Show controllability of distinct insulating phases via vertical displacement field and external parameters.

Proposed method

• Use crystalline ABCA-tetralayer graphene in proximity to WSe2 to induce spin-orbit coupling.
• Identify ferromagnetic/Chern-insulating state through transport measurements and Hall resistance quantization.
• Characterize transitions between layer-antiferromagnet, Chern insulator, and layer-polarized insulator as a function of vertical displacement field.
• Demonstrate switchability of the Chern insulator's magnetic order via magnetic field, electrical doping, and displacement field.

Experimental results

Research questions

• RQ1 Can proximity-induced spin-orbit coupling stabilize a ferromagnetic, Chern-insulating phase in ABCA-tetralayer graphene at charge neutrality?
• RQ2 What are the Hall resistance quantization values and Chern number associated with the observed insulating states?
• RQ3 How do vertical displacement field, magnetic field, and carrier density tune transitions among layer-antiferromagnet, Chern insulator, and layer-polarized insulator?

Key findings

• A ferromagnetic state in charge-neutral ABCA-tetralayer graphene is realized via proximity-induced spin-orbit coupling from WSe2.
• The ferromagnetic state is identified as a Chern insulator with Chern number 4.
• Hall resistance reaches 78% quantization of h/4e2 at zero field and 100% quantization at 0.4 T.
• Three broken-symmetry insulating states (layer-antiferromagnet, Chern insulator, layer-polarized insulator) are continuously tunable by a vertical displacement field.
• The magnetic order of the Chern insulator can be switched by magnetic field, electrical doping, and vertical displacement field.