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Robust axion insulator and Chern insulator phases in a two-dimensional antiferromagnetic topological insulator (1905.00715v2)

Published 2 May 2019 in cond-mat.mes-hall and cond-mat.mtrl-sci

Abstract: The intricate interplay between nontrivial topology and magnetism in two-dimensional (2D) materials has led to the emergence of many novel phenomena and functionalities. An outstanding example is the quantum anomalous Hall (QAH) effect, which was realized in magnetically doped topological insulators (TIs) in the absence of magnetic field. Recently, the layered van der Waals compound MnBi2Te4 has been theoretically predicted and experimentally verified to be a TI with interlayer antiferromagnetic (AFM) order. It is a rare stoichiometric material with coexisting topology and magnetism, thus represents a perfect building block for complex topological-magnetic structures. Here we investigate the quantum transport behaviors of both bulk crystal and exfoliated MnBi2Te4 flakes in a field effect transistor geometry. In the 6 septuple layers (SLs) device tuned into the insulating regime, we observe a large longitudinal resistance and zero Hall plateau, which are characteristic of the axion insulator state. The robust axion insulator state occurs in zero magnetic field, over a wide magnetic field range, and at relatively high temperatures. Moreover, a moderate magnetic field drives a quantum phase transition from the axion insulator phase to a Chern insulator phase with zero longitudinal resistance and quantized Hall resistance h/e2 (h is the Plank constant and e is the elemental charge). These results pave the road for using even-number-SL MnBi2Te4 to realize the quantized topological magnetoelectric effect and axion electrodynamics in condensed matter systems.

Citations (646)

Summary

  • The paper demonstrates the realization of a robust axion insulator phase in exfoliated MnBi₂Te₄ films at zero magnetic field over a broad temperature range.
  • Experimental measurements reveal a large longitudinal resistance (~5.5 h/e) and a zero Hall plateau, confirming distinct topological states.
  • The observed quantum phase transition to the Chern insulator phase under moderate magnetic fields offers a tunable pathway for future quantum device applications.

Overview of Robust Axion and Chern Insulator Phases in 2D Antiferromagnetic Topological Insulators

This paper by Chang Liu et al. presents a comprehensive paper investigating the axion insulator and Chern insulator phases in exfoliated MnBi2_2Te4_4 films, focusing on their quantum transport behavior in a field effect transistor (FET) configuration. The research brings to light these topological phases' unique characteristics and potential applications in condensed matter physics, particularly in the context of magnetoelectric coupling and axion electrodynamics.

Key Findings

The researchers demonstrate the realization of the axion insulator phase in MnBi2_2Te4_4 under zero magnetic field conditions, over a broad temperature range. The axion insulator phase is notable for its large longitudinal resistance and zero Hall plateau, indicative of the Chern number C=0C = 0. These traits were further corroborated by a robust zero-field axion insulator state, maintained even at elevated temperatures. The paper also observes a quantum phase transition from the axion insulator phase to the Chern insulator phase triggered by a moderate external magnetic field. In this latter phase, the system exhibits zero longitudinal resistance and quantized Hall resistance, characteristic of the Chern insulator with a non-zero Chern number.

Numerical and Experimental Results

  • The material utilized, MnBi2_2Te4_4, is a stoichiometric compound showcasing a natural axion insulator state at higher temperatures compared to existing heterostructure-based systems.
  • The longitudinal resistance (ρxx\rho_{xx}) reached up to 5.5 h/e in the axion insulator state at low temperatures, which is comparable to values in known QAH systems.
  • A zero Hall plateau was observed within the range -3.5 T < μ0_0H < 3.5 T.
  • In the crossover to the Chern insulator phase, ρxx\rho_{xx} decreased significantly in high magnetic fields (up to 9 T), exhibiting values as low as 0.018 h/e.
  • The transition from the axion to the Chern insulator phase suggests an underlying quantum critical point with scaling behavior similar to quantum Hall phase transitions.

Implications and Future Prospective

These findings herald advances in the understanding of topological quantum states in 2D materials, emphasizing the role of intrinsic magnetic ordering and strong spin-orbit coupling in manifesting exotic quantum phases. The facile transition between the axion and Chern insulator phases underpins the potential of MnBi2_2Te4_4 in practical device implementations, allowing for controlled toggling of topological phases. Applications may include topological quantum computations and novel quantum devices necessitating high thermal stability and robust off-diagonal response.

Further research could investigate the effect of variable stacking layers and interface engineering in similar van der Waals compounds to explore the emergence of other quantum phases. Theoretical exploration into the interplay between antiferromagnetism and topology in such materials might yield predictive models enhancing control over phase transitions in future quantum materials. MnBi2_2Te4_4, due to its high structural and electronic compatibility, stands out as an ideal candidate for progressing in this domain.

Conclusively, this work exemplifies a significant step toward practical applications leveraging the complex interplay of magnetism and topology in 2D materials, paving the way for advancements in quantum electronics and topological phases of matter.