Recent studies on superconductivity in ${\mathrm{NbSe}}_2$ have demonstrated a large anisotropy in the superconducting critical field when the material is reduced to a single monolayer. Motivated by this recent discovery, we use density-functional theory (DFT) calculations to quantitatively address the superconducting properties of bulk and monolayer ${\mathrm{NbSe}}_2$. We demonstrate that ${\mathrm{NbSe}}_2$ is close to a ferromagnetic instability, and analyze our results in the context of experimental measurements of the spin susceptibility in ${\mathrm{NbSe}}_2$. We show how this magnetic instability, which is pronounced in a single monolayer, can enable sizable singlet-triplet mixing of the superconducting order parameter, contrary to contemporary considerations of the pairing symmetry in monolayer ${\mathrm{NbSe}}_2$, and discuss approaches as to how this degree of mixing can be addressed quantitatively within our DFT framework. Our calculations also enable a quantitative description of the large anisotropy of the superconducting critical field, using DFT calculations of monolayer ${\mathrm{NbSe}}_2$ in the normal state.

中文翻译：

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NbSe2中的Ising超导和磁性

超导体的最新研究 ${\mathrm{铌硒}}_2$当材料被还原为单个单层时，已经证明了超导临界场中的大各向异性。受此最新发现的启发，我们使用密度泛函理论（DFT）计算来定量解决体层和单层的超导特性${\mathrm{铌硒}}_2$。我们证明${\mathrm{铌硒}}_2$ 接近铁磁不稳定性，并在实验测量自旋磁化率的背景下分析了我们的结果 ${\mathrm{铌硒}}_2$。我们展示了在单层中表现出的这种磁性不稳定性如何能够实现超导阶数参数的相当大的单重态-三重态混合，这与当代对单层中的配对对称性的考虑相反${\mathrm{铌硒}}_2$，并讨论如何在我们的DFT框架中定量解决这种混合程度的方法。我们的计算还可以通过使用单层DFT计算来定量描述超导临界场的大各向异性${\mathrm{铌硒}}_2$ 在正常状态。