[Paper Review] Reentrant quantum anomalous Hall effect in molecular beam epitaxy-grown MnBi2Te4 thin films

Yuanzhao Li, Yunhe Bai+17 more|arXiv (Cornell University)|Jan 21, 2024

Topological Materials and Phenomena4 citations

TL;DR

This study reports the observation of a reentrant quantum anomalous Hall (QAH) effect in molecular beam epitaxy-grown MnBi2Te4 thin films, where the QAH state emerges at zero magnetic field when the Fermi energy lies in the valence band, indicating the formation of a Chern Anderson insulator. The result highlights the interplay between Berry curvature and Anderson localization in realizing robust QAH states without external magnetic fields.

ABSTRACT

In this study, we investigate intrinsic magnetic topological insulator MnBi2Te4 thin films grown by molecular beam epitaxy. We observe a reentrant quantum anomalous Hall effect when the Fermi energy enters the valance band and magnetic field equals zero, indicating the emergence of the Chern Anderson insulator state. The discovery opens a new avenue for realizing the QAH effect and underscores the fundamental role of both Berry curvature and Anderson localization.

Motivation & Objective

• To investigate the intrinsic magnetic topological insulator behavior in molecular beam epitaxy-grown MnBi2Te4 thin films.
• To explore the emergence of the quantum anomalous Hall effect in the absence of an external magnetic field.
• To understand the role of Berry curvature and Anderson localization in stabilizing topological phases.
• To identify conditions under which a reentrant QAH effect can be realized in intrinsic magnetic topological insulators.

Proposed method

• Molecular beam epitaxy (MBE) was used to grow high-quality, single-crystalline MnBi2Te4 thin films with controlled thickness and doping.
• Transport measurements were performed at low temperatures to probe the quantized Hall resistance and longitudinal resistivity.
• The Fermi energy was tuned via back-gating to access different regions of the valence band.
• Magnetic field dependence of the Hall and longitudinal resistivity was measured to identify topological phase transitions.
• Theoretical analysis linked the observed QAH state to the interplay between nontrivial Berry curvature and disorder-induced Anderson localization.
• The emergence of a Chern Anderson insulator state was inferred from the reentrant behavior of the QAH effect at zero magnetic field.

Experimental results

Research questions

• RQ1 Can the quantum anomalous Hall effect be realized in MnBi2Te4 thin films without an external magnetic field?
• RQ2 What is the role of Fermi energy position in the valence band in stabilizing the QAH state?
• RQ3 How does Anderson localization contribute to the formation of a topological insulator phase in MnBi2Te4?
• RQ4 What is the nature of the topological phase transition observed in the reentrant QAH effect?
• RQ5 Is the observed QAH state consistent with a Chern Anderson insulator state?

Key findings

• A reentrant quantum anomalous Hall effect was observed at zero magnetic field when the Fermi energy was tuned into the valence band.
• The quantized Hall resistance reached the expected value of h/e², confirming the topological nature of the state.
• The longitudinal resistivity dropped to near zero, indicating dissipationless edge transport.
• The QAH state persisted only in a narrow window of Fermi energy near the valence band edge, indicating reentrancy.
• The observed state is attributed to the formation of a Chern Anderson insulator, where Berry curvature and disorder localization coexist.
• The results demonstrate that intrinsic magnetic topological insulators can host robust QAH states without external magnetic fields.