MnNBr Monolayer: A High-Temperature Ferromagnetic Half-Metal with Type-II Weyl Fermions,Physica Status Solidi-Rapid Research Letters

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MnNBr Monolayer: A High-Temperature Ferromagnetic Half-Metal with Type-II Weyl Fermions
Physica Status Solidi-Rapid Research Letters ( IF 2.5 ) Pub Date : 2021-05-06 , DOI: 10.1002/pssr.202100115
Yongting Shi ₁ , Lingjun Li ₁ , Xin Cui ₁ , Tielei Song ₁ , Zhifeng Liu ₁

Affiliation

For spintronics, it is highly desirable to obtain stable low-dimensional materials with ferromagnetic ground state, 100% spin polarization, and high Curie temperature. Moreover, type-II Weyl fermions are also desired for realizing high-speed anisotropic transport. Herein, based on first-principles calculations, the orthorhombic MnNBr monolayer is identified as a needed ferromagnetic half-metal, which not only has a high Curie temperature (910 K), but also holds type-II Weyl state with Lorentz symmetry broken. Analysis of the stability reveals that the MnNBr monolayer is energetically, mechanically, dynamically, and thermally stable. Remarkably, in the vicinity of the Fermi level there exist both type-I and titled type-II Weyl states, whose nodes form continuously distributed Weyl loops. Under intrinsic out-of-plane magnetization, they are robust against spin–orbital coupling due to the protection of glide mirror symmetry. Moreover, near the type-II Weyl point, there is direction-dependent band dispersion: the largest fermion velocities can be found in the k path of G–X (up to 6.86 × 10⁵ m s⁻¹), while quasi-flat bands with negligible band dispersion can be found along the direction being parallel to G–Y. This indicates that MnNBr monolayer should be a promising candidate for further applications of high-speed anisotropic transport and studies of strongly correlated electronic states.

中文翻译：

MnNBr 单层：具有 II 型外尔费米子的高温铁磁半金属

对于自旋电子学，非常需要获得具有铁磁基态、100% 自旋极化和高居里温度的稳定低维材料。此外，还需要 II 型外尔费米子来实现高速各向异性输运。在此，基于第一性原理计算，正交晶系 MnNBr 单层被确定为所需的铁磁半金属，它不仅具有高居里温度（910 K），而且还具有洛伦兹对称性被破坏的 II 型外尔态。稳定性分析表明，MnNBr 单层在能量、机械、动态和热方面都是稳定的。值得注意的是，在费米能级附近，同时存在 I 型和 II 型外尔态，其节点形成连续分布的外尔环。在本征面外磁化下，由于滑翔镜对称性的保护，它们对自旋轨道耦合具有鲁棒性。此外，在 II 型外尔点附近，存在与方向相关的带色散：最大的费米子速度可以在 G-X 的k路径（高达 6.86 × 10⁵ m s^-1），而沿平行于 G-Y 的方向可以找到带色散可忽略的准平坦带。这表明 MnNBr 单层应该是高速各向异性输运的进一步应用和强相关电子态研究的有希望的候选者。

更新日期：2021-07-12

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