二维2 H-NbSe $_2$中的Ising和XY顺磁
Ising and XY paramagnons in two-dimensional 2H-NbSe$_2$
摘要：
副磁振子是控制近磁性导体自旋响应的集体模式。在某些情况下，它们介导电子配对，导致超导性。这种情况可能发生在2 H-NbSe $_2$单层中，其特征在于由于自旋-轨道相互作用的自旋-谷耦合以及它们缺乏反转对称性。在这里，我们探讨顺磁子的自旋各向异性的非中心对称凯恩梅勒哈伯德模型的2 H-NbSe $_2$单分子膜与DFT推导的紧束缚模型描述。在无限波长的限制，我们发现空间均匀的顺磁子的能量约$1$ ~meV，具有巨大的离面单轴磁各向异性，淬火横向自旋响应。在有限的波矢量，纵向和横向通道颠倒的角色：XY波动占主导地位的布里渊区的重要部分。结果表明，2 H-NbSe $_2$接近于库仑驱动的平面内（XY）自旋密度波不稳定性.
英文摘要：
Paramagnons are the collective modes that govern the spin response of nearly magnetic conductors. In some cases they mediate electron pairing leading to superconductivity. This scenario may occur in 2H-NbSe$_2$ monolayers, that feature spin-valley coupling on account of spin-orbit interactions and their lack of inversion symmetry. Here we explore spin anisotropy of paramagnons both for non-centrosymmetric Kane-Mele-Hubbard models for 2H-NbSe$_2$ monolayers described with a DFT-derived tight-binding model. In the infinite wavelength limit we find spatially uniform paramagnons with energies around $1$~meV that feature a colossal off-plane uniaxial magnetic anisotropy, with quenched transversal spin response. At finite wave vectors, longitudinal and transverse channels reverse roles: XY fluctuations dominate within a significant portion of the Brillouin zone. Our results show that 2H-NbSe$_2$ is close to a Coulomb-driven in-plane (XY) spin density wave instability.
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