论文标题
各向异性和障碍对niobium超导性能的影响
Effects of anisotropy and disorder on the superconducting properties of Niobium
论文作者
论文摘要
我们报告了基于Eliashberg的方程以及根据密度功能理论计算出的Eliashberg的方程以及电子和声子条带结构的超导过渡温度和各向异性能量差距的结果。电子带结构用于构建费米表面并计算费米表面上每个点的费米速度。声子条带与非弹性中子中子散射数据非常吻合。状态和电子音波耦合的相应声子密度定义了电子光谱函数，$α^2f（{\ bf p}，{\ bf p}';ω）$，以及相应的电子 - phonon配对交互作用，这是计算超管属性的基础。电子 - 音波光谱函数与现有的隧道光谱数据是很好的一致性，除了在$ \hbarω_ {\ text {lo}} = 23 \，\ mbox {mev {mev} $处的纵向声子峰的光谱重量。我们获得了$λ= 1.057 $的电子偶联常数，重新归一化的库仑相互作用，$μ^{\ star} = 0.218 $和过渡温度$ t_c = 9.33 \，\ mbox {k k} $。与弱耦合BCS值$δ_0^{\ text {\ text {wc}} = 1.78 \ \，k _ {bbox {bbox { 1.43 \，\ mbox {mev} $。超导间隙函数在费米表面表现出很大的各向异性。我们使用自洽的T-Matrix理论来分析差距各向异性的分布，并计算出超导过渡温度的抑制，用于准粒子障碍性散射，以描述掺有非磁杂质的尼伯群。我们将这些结果与氮杂质掺杂的niobium srf腔的实验结果进行了比较。
We report results for the superconducting transition temperature and anisotropic energy gap for pure Niobium based on Eliashberg's equations and electron and phonon band structures computed from density functional theory. The electronic band structure is used to construct the Fermi surface and calculate the Fermi velocity at each point on the Fermi surface.The phonon bands are in excellent agreement with inelastic neutron scattering data. The corresponding phonon density of states and electron-phonon coupling define the electron-phonon spectral function, $α^2F({\bf p},{\bf p}';ω)$, and the corresponding electron-phonon pairing interaction, which is the basis for computing the superconducting properties. The electron-phonon spectral function is good agreement with existing tunneling spectroscopy data except for the spectral weight of the longitudinal phonon peak at $\hbarω_{\text{LO}}=23\,\mbox{meV}$. We obtain an electron-phonon coupling constant of $λ=1.057$, renormalized Coulomb interaction, $μ^{\star}=0.218$ and transition temperature $T_c=9.33\,\mbox{K}$. The corresponding strong-coupling gap at $T=0$ is modestly enhanced, $Δ_0=1.55\,\mbox{meV}$, compared to the weak-coupling BCS value $Δ_0^{\text{wc}}=1.78\,k_{\mbox{b}}\,T_c= 1.43\,\mbox{meV}$. The superconducting gap function exhibits substantial anisotropy on the Fermi surface. We analyze the distribution of gap anisotropy and compute the suppression of the superconducting transition temperature using a self-consistent T-matrix theory for quasiparticle-impurity scattering to describe Niobium doped with non-magnetic impurities. We compare these results with experimental results on Niobium SRF cavities doped with Nitrogen impurities.
