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Anomalous Second Harmonic Generation from Atomically Thin MnBi2Te4
Jordan Fonseca1, Geoffrey M Diederich1,2, Dmitry Ovchinnikov1
1Department of Physics, University of Washington, Seattle, Washington98195, United States.
Nano Letters
|December 8, 2022
Summary
Magnetic van der Waals topological insulators like MnBi2Te4 exhibit complex magnetic ordering. Unexpectedly, second harmonic generation (SHG) signals in MnBi2Te4 are independent of magnetic state and layer number, suggesting surface effects dominate.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Quantum Materials
Background:
- Manganese bismuth telluride (MnBi2Te4) is a van der Waals topological insulator with intrinsic ferromagnetic and antiferromagnetic ordering.
- Its centrosymmetric crystal structure theoretically allows layered antiferromagnetism to break inversion symmetry, making it suitable for optical second harmonic generation (SHG) studies.
- SHG is a sensitive probe for detecting broken inversion symmetry, crucial for understanding magnetic and crystal structure coupling.
Purpose of the Study:
- To investigate the relationship between magnetic ordering, layer number, and SHG response in MnBi2Te4 flakes.
- To explore the potential of SHG as a tool for probing the interplay of magnetism and structure in layered materials.
- To determine the origin of the SHG signal in MnBi2Te4, considering both bulk and surface contributions.
Main Methods:
- Magnetic field and temperature-dependent SHG measurements were performed on MnBi2Te4 flakes of varying thicknesses (bulk to monolayer).
- Analysis focused on correlating changes in SHG intensity and symmetry with magnetic phase transitions and layer-dependent structural properties.
- Comparative analysis of experimental SHG data with theoretical predictions for bulk and surface phenomena.
Main Results:
- The dominant SHG signal in MnBi2Te4 was found to be unexpectedly independent of the material's magnetic state (ferromagnetic/antiferromagnetic).
- The SHG response did not correlate with the number of layers in the MnBi2Te4 flakes, contrary to theoretical expectations for bulk inversion symmetry breaking.
- A strong SHG signal was observed, consistent with surface effects at the MnBi2Te4-vacuum interface, whose symmetry aligns with the experimental observations.
Conclusions:
- The primary source of the strong SHG signal in MnBi2Te4 is likely the surface, not the bulk magnetic or structural properties.
- Surface contributions to inversion symmetry breaking are significant in van der Waals centrosymmetric magnets like MnBi2Te4.
- Future studies on similar materials should carefully consider and potentially isolate surface effects when using SHG to probe bulk properties.
Keywords:
2D magnetscentrosymmetric magnetssecond harmonic generationsurface symmetry-breakingtopological magnetsMore Related Videos
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