Anomalous Second Harmonic Generation from Atomically Thin MnBi2Te4,Nano Letters

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Anomalous Second Harmonic Generation from Atomically Thin MnBi2Te4
Nano Letters ( IF 9.6 ) Pub Date : 2022-12-07 , DOI: 10.1021/acs.nanolett.2c04010
Jordan Fonseca ₁ , Geoffrey M Diederich _{1,

2} , Dmitry Ovchinnikov ₁ , Jiaqi Cai ₁ , Chong Wang ₃ , Jiaqiang Yan _{4,

5} , Di Xiao _{1,

3} , Xiaodong Xu _{1,

3}

Affiliation

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.

中文翻译：

原子级薄的 MnBi2Te4 异常二次谐波的产生

MnBi ₂ Te ₄是一种具有本征层内铁磁交换和A型反铁磁层间耦合的范德华拓扑绝缘体。从理论上讲，它属于一类结构中心对称的晶体，其层状反铁磁序打破了偶数层的反转对称性，使光学二次谐波产生 (SHG) 成为晶体与磁结构之间耦合的理想探针。在这里，我们对从块状到单层厚度的 MnBi ₂ Te ₄薄片执行磁场和温度相关的 SHG 测量。我们发现来自 MnBi ₂ Te _{4的主要 SHG 信号}意外地与磁性状态和层数无关。我们认为表面 SHG 可能是观测到的强 SHG 的来源，其对称性与 MnBi ₂ Te ₄ -真空界面的对称性相匹配。我们的结果强调了考虑表面对范德瓦尔斯中心对称磁体中反演对称性破坏的贡献的重要性。

更新日期：2022-12-07

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