4.8 Article

Anomalous Second Harmonic Generation from Atomically Thin MnBi2Te4

Journal

NANO LETTERS
Volume 22, Issue 24, Pages 10134-10139

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.2c04010

Keywords

topological magnets; second harmonic generation; surface symmetry-breaking; centrosymmetric magnets; 2D magnets

Funding

  1. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division [DESC0012509]
  2. Programmable Quantum Materials, an Energy Frontier Research Center - U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) [DE-SC0019443]
  3. AFOSR [FA9550-21-10460]
  4. U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division
  5. NSF MRSEC [DMR-1719797]
  6. State of Washington

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Magnetic field and temperature-dependent second harmonic generation (SHG) measurements were performed on MnBi2Te4 flakes with varying thickness. The dominant SHG signal was unexpectedly unrelated to both the magnetic state and layer number, suggesting a possible contribution from surface SHG. This study highlights the importance of considering surface contribution to inversion symmetry-breaking in van der Waals centrosymmetric magnets.
MnBi2Te4 is a van der Waals topological insulator with intrinsic intralayer ferromagnetic exchange and A- type antiferromagnetic interlayer coupling. Theoretically, it belongs to a class of structurally centrosymmetric crystals whose layered antiferromagnetic order breaks inversion symmetry for even layer numbers, making optical second harmonic generation (SHG) an ideal probe of the coupling between the crystal and magnetic structures. Here, we perform magnetic field and temperature-dependent SHG measurements on MnBi(2)T(e)4 flakes ranging from bulk to monolayer thickness. We find that the dominant SHG signal from MnBi2Te4 is unexpectedly unrelated to both magnetic state and layer number. We suggest that surface SHG is the likely source of the observed strong SHG, whose symmetry matches that of the MnBi2Te4-vacuum interface. Our results highlight the importance of considering the surface contribution to inversion symmetry-breaking in van der Waals centrosymmetric magnets.

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