Abstract
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 MnBi2Te4 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.
| Original language | English |
|---|---|
| Pages (from-to) | 10134-10139 |
| Number of pages | 6 |
| Journal | Nano Letters |
| Volume | 22 |
| Issue number | 24 |
| DOIs | |
| State | Published - Dec 28 2022 |
Funding
We thank Kyle Seyler for helpful discussion during the preparation of this manuscript. This work was mainly supported by the Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division (DE-SC0012509). Magento-optical measurement is partially supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award DE-SC0019443. Device fabrication is partially supported by AFOSR FA9550-21-1-0460. J.Y. acknowledges support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. The authors also acknowledge the use of the facilities and instrumentation supported by NSF MRSEC DMR-1719797. This research was supported by an appointment to the Intelligence Community Postdoctoral Research Fellowship Program at the University of Washington, administered by Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and the Office of the Director of National Intelligence. X.X. acknowledges the support from the State of Washington funded Clean Energy Institute.
Keywords
- 2D magnets
- centrosymmetric magnets
- second harmonic generation
- surface symmetry-breaking
- topological magnets