Natural van der Waals heterostructural single crystals with both magnetic and topological properties (1905.02385v2)

Abstract: Heterostructures having both magnetism and topology are promising materials for the realization of exotic topological quantum states while challenging in synthesis and engineering. Here, we report natural magnetic van der Waals heterostructures of (MnBi2Te4)m(Bi2Te3)n that exhibit controllable magnetic properties while maintaining their topological surface states. The interlayer antiferromagnetic exchange coupling is gradually weakened as the separation of magnetic layers increases, and an anomalous Hall effect that is well coupled with magnetization and shows ferromagnetic hysteresis was observed below 5 K. The obtained homogeneous heterostructure with atomically sharp interface and intrinsic magnetic properties will be an ideal platform for studying the quantum anomalous Hall effect, axion insulator states, and the topological magnetoelectric effect.

• The paper demonstrates successful synthesis of high-quality natural van der Waals heterostructures exhibiting exotic quantum states such as QAHE and axion insulator phases.
• It uses precise solid-state reactions combined with XRD, STEM, DFT, and ARPES to characterize alternating septuple and quintuple layers and their magnetic transitions.
• The findings reveal tunable antiferromagnetic to ferromagnetic phases, highlighting promising applications in spintronics and quantum electronic devices.

Natural van der Waals Heterostructural Single Crystals with both Magnetic and Topological Properties

The paper encompasses the synthesis and characterization of natural van der Waals heterostructures with unique magnetic and topological properties, advancing our understanding of spintronics and topotronics. Specifically, the paper focuses on MnBi2Te4, part of the ternary layered manganese bismuth tellurides, and newly synthesized MnBi4Te7, highlighting their potential for hosting exotic quantum states such as the quantum anomalous Hall effect (QAHE) and axion insulator states.

Summary of Findings

The investigators report the successful synthesis of MnBi2Te4, MnBi4Te7, and MnBi6Te10 layered compounds using a solid-state reaction method. The synthesis involved precise temperature control, critical for obtaining high-quality single crystals. The paper addresses the structural properties using techniques such as X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM), confirming the distinct alternating layers of septuple (SL) and quintuple layers (QL), characteristic of van der Waals heterostructures.

Magnetic and Electronic Properties

The research highlights a controlled modulation of magnetic properties by varying the separation of magnetic layers, resulting in materials that can transition between antiferromagnetic (AFM) and ferromagnetic (FM) states under different conditions. Below 5 K, an anomalous Hall effect was observed, coupled with magnetization and showing ferromagnetic hysteresis, thus indicating the potential for topological applications.

Density functional theory (DFT) calculations reveal the electronic structure and confirm MnBi4Te7 as an AFM topological insulator. Angle-resolved photoemission spectroscopy (ARPES) measurements provide experimental validation, indicating a surface gap consistent with the expectations of broken time-reversal symmetry.

Implications for Spintronics and Topotronics

The synthesis of homogeneous heterostructures with atomically sharp interfaces provides an ideal platform to explore QAHE, axion insulator states, and topological magnetoelectric effects. These materials exhibit promising features for novel spintronic devices, such as spin valves and two-dimensional van der Waals magnets.

Magnetic Structure and Anomalous Hall Effect

The paper explores the magnetic interactions within the heterostructures, noting the competition between interlayer exchange coupling (IEC) and additional magnetic interactions (AMI) that influence phase stability. The Hamiltonian model proposed suggests a delicate balance between AFM and FM states, reflected in temperature-dependent magnetization measurements.

The anomalous Hall resistivity and conductivity demonstrate characteristics consistent with intrinsic Berry's phase curvature, affirming the presence of nontrivial topological phenomena. The paper suggests the potential for tuning the Fermi level to optimize these effects, presenting an exciting avenue for future research.

Conclusion and Future Directions

This paper establishes a new framework for the exploration of van der Waals layered magnetic materials with topological properties, addressing challenges in synthesis while opening pathways for practical applications in quantum computing and beyond. The ability to modulate magnetic properties paves the way for tailored quantum effects, setting the stage for advancements in quantum material research and development.

Future directions could involve in-depth exploration of the interplay between topological surface states and magnetism at reduced dimensional scales, employing advanced synthesis and characterization techniques. Additionally, theoretical models need refinement to predict and exploit quantum transitions under varied conditions, facilitating the design of next-generation quantum electronic devices.