Broken Inversion Symmetry in Van Der Waals Topological Ferromagnetic Metal Iron Germanium Telluride,Advanced Materials

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Broken Inversion Symmetry in Van Der Waals Topological Ferromagnetic Metal Iron Germanium Telluride
Advanced Materials ( IF 27.4 ) Pub Date : 2023-12-31 , DOI: 10.1002/adma.202312824
Kai-Xuan Zhang _{1,

2,

3} , Hwiin Ju ₄ , Hyuncheol Kim _{1,

2} , Jingyuan Cui _{1,

2} , Jihoon Keum _{1,

2} , Je-Geun Park _{1,

2,

3} , Jong Seok Lee ₄

Affiliation

Inversion symmetry breaking is critical for many quantum effects and fundamental for spin-orbit torque, which is crucial for next-generation spintronics. Recently, a novel type of gigantic intrinsic spin-orbit torque is established in the topological van der Waals (vdW) magnet iron germanium telluride. However, it remains a puzzle because no clear evidence exists for interlayer inversion symmetry breaking. Here, the definitive evidence of broken inversion symmetry in iron germanium telluride directly measured by the second harmonic generation (SHG) technique is reported. The data show that the crystal symmetry reduces from centrosymmetric P6₃/mmc to noncentrosymmetric polar P3m1 space group, giving the threefold SHG pattern with dominant out-of-plane polarization. Additionally, the SHG response evolves from an isotropic pattern to a sharp threefold symmetry upon increasing Fe deficiency, mainly due to the transition from random defects to ordered Fe vacancies. Such SHG response is robust against temperature, ensuring unaltered crystalline symmetries above and below the ferromagnetic transition temperature. These findings add crucial new information to the understanding of this interesting vdW metal, iron germanium telluride: band topology, intrinsic spin-orbit torque, and topological vdW polar metal states.

中文翻译：

范德华拓扑铁磁金属碲化铁锗中破缺反演对称性

反演对称性破缺对于许多量子效应至关重要，也是自旋轨道扭矩的基础，而自旋轨道扭矩对于下一代自旋电子学至关重要。最近，在拓扑范德华（vdW）磁体碲化铁锗中建立了一种新型的巨大本征自旋轨道扭矩。然而，这仍然是一个谜，因为没有明确的证据表明层间反演对称性破缺。在这里，报告了通过二次谐波发生（SHG）技术直接测量的碲化铁锗中反演对称性破缺的明确证据。数据表明，晶体对称性从中心对称的P 6 ₃ / mmc降低到非中心对称的极性P 3 m 1 空间群，给出了以面外偏振为主的三重 SHG 图案。此外，随着 Fe 缺乏的增加，SHG 响应从各向同性模式演变为尖锐的三重对称性，这主要是由于从随机缺陷到有序 Fe 空位的转变。这种二次谐波响应对温度具有鲁棒性，确保在铁磁转变温度之上和之下晶体对称性不改变。这些发现为理解这种有趣的 vdW 金属、碲化铁锗提供了重要的新信息：能带拓扑、本征自旋轨道扭矩和拓扑 vdW 极性金属态。

更新日期：2023-12-31

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