[Paper Review] Large Quantum Anomalous Hall Effect in Spin-Orbit Proximitized Rhombohedral Graphene

Tonghang Han, Zhengguang Lu+9 more|arXiv (Cornell University)|Oct 26, 2023

Graphene research and applications40 references8 citations

TL;DR

Demonstrates a large quantum anomalous Hall effect in rhombohedral pentalayer graphene/WS2 without magnetic elements or moiré patterns, achieving C = ±5 QAHE states at charge neutrality up to ~1.5 K via Ising spin-orbit coupling from spin-orbit proximitization and electron correlations.

ABSTRACT

The quantum anomalous Hall effect (QAHE) is a robust topological phenomenon featuring quantized Hall resistance at zero magnetic field. We report the QAHE in a rhombohedral pentalayer graphene/monolayer WS2 heterostructure. Distinct from other experimentally confirmed QAHE systems, this system has neither magnetic element nor moiré superlattice effect. The QAH states emerge at charge neutrality and feature Chern numbers C = +-5 at temperatures up to about 1.5 K. This large QAHE arises from the synergy of the electron correlation in intrinsic flat bands of pentalayer graphene, the gate-tuning effect, and the proximity-induced Ising spin-orbit-coupling. Our experiment demonstrates the potential of crystalline two-dimensional materials for intertwined electron correlation and band topology physics, and may enable a route for engineering chiral Majorana edge states.

Motivation & Objective

• Explore realization of QAHE in a rhombohedral graphene heterostructure without magnetic elements or moiré superlattices.
• Leverage intrinsic flat-band correlation effects and gate-tunability to induce topological states at charge neutrality.
• Investigate the role of proximity-induced Ising spin-orbit coupling from WS2 in stabilizing large Chern numbers.

Proposed method

• Fabrication of rhombohedral pentalayer graphene on monolayer WS2 to induce spin-orbit proximity effects.
• Characterization of quantum anomalous Hall states at charge neutrality and measurement of Chern numbers C = ±5.
• Utilization of gate tuning to control electronic structure and enhance correlation effects in flat bands.
• Analysis of the interplay between electron correlations, flat-band physics, and spin-orbit coupling to realize QAHE.
• Comparison with systems lacking magnetic elements or moiré superlattices to highlight the new mechanism.

Experimental results

Research questions

• RQ1 Can QAHE with large Chern numbers be realized in rhombohedral graphene heterostructures without magnetic elements or moiré patterns?
• RQ2 What is the role of proximity-induced Ising spin-orbit coupling in stabilizing high-Chern-number QAHE in correlated flat bands?
• RQ3 At what temperatures and carrier densities can C = ±5 QAHE states be observed in this system?
• RQ4 How do gate-tuning and intrinsic electronic correlations combine to produce robust topological states at charge neutrality?

Key findings

• QAHE with C = ±5 is observed at charge neutrality in a rhombohedral pentalayer graphene/WS2 heterostructure.
• The large QAHE emerges without magnetic elements and without moiré superlattice effects.
• Proximity-induced Ising spin-orbit coupling, together with electron correlations in intrinsic flat bands, enables the observed topological states.
• QAHE remains detectable up to temperatures of about 1.5 K.
• The results demonstrate a route to engineer chiral edge states and potential platforms for Majorana-related physics in crystalline 2D materials.