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.
Destruction of superconductivity in disordered materials : a dimensional crossover
通过改变样品厚度$d$，研究了不同Nb组分$x$的非晶Nb $_{x}$ Si $_{1-x}$二维薄膜中无序诱导的超导体-绝缘体转变.我们表明，临界厚度$d_c$，从绝缘的超导制度，随着减少$x$强烈增加，从而达到超过100欧姆的值。相应的相图中的$(d, x)$平面推断和相关的三维情况。二维的超导体到绝缘体的转变与三维的超导体到金属的转变良好连接。
Interplay of Anisotropy and Disorder in the Doping-Dependent Melting and Glass Transitions of Vortices in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$
我们研究了Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$中平衡一级熔融和二级玻璃转变的氧掺杂依赖性。掺杂影响各向异性和无序。各向异性缩放被示出崩溃的熔化线，只有在热波动占主导地位。然而，在无序打破这种缩放的区域，玻璃线仍然崩溃。定量拟合熔化和复本对称性破缺线的2D Ginzburg-Landau模型进一步揭示，无序振幅减弱掺杂，但在较小的程度上比热波动，提高了相对的作用的障碍。
Experimental study of the correlation length of critical-current fluctuations in the presence of surface disorder: Probing vortex long-range interactions
我们报告的临界电流和电压噪声测量铌条在超导状态下，在存在的体积涡旋晶格（$B < B_{C2}$）和在表面超导状态（$B_{c2}< B < B_{C3}$）。对于均匀表面，电流波动的相关长度可以与涡流表面不稳定性的电磁趋肤深度相关联。通过低能量照射对表面状态的改变会引起临界电流和噪声的强烈改变。在频谱域中出现的拐角频率可以与人工噪声的低波矢量相联系。由于后者只发生在$B < B_{C2}$，我们建议，长程相互作用允许的相关长度延伸到由表面形貌施加的值。
Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning
我们研究了一个流形的相互作用的弹性线的空间相关性的强烈影响随机和有序钉扎之间的竞争的一般问题。这是通过磁输运实验与YBa 2 Cu 3 O 7-d薄膜，包含一个周期性的涡旋钉扎阵列通过掩蔽离子照射，除了本地随机钉扎。我们观察到的强场匹配效应表明周期性钉扎的普遍存在，并表明在匹配场中每条涡旋线都束缚在人为钉扎位点上。然而，涡玻璃化转变的维度，准2D而不是通常的3D，证据减少沿涡线的涡玻璃相关性。这也支持了一个不寻常的角度依赖的磁阻，这大大不同于玻色玻璃系统。角磁阻的定量分析使我们能够将这种行为与系统各向异性的增强联系起来，这是离子辐照的附带效应。
Microscopic structure of the vortex cores in granular niobium: A coherent quantum puzzle
LPEM, UMR-8213, ESPCI Paris, PSL, CNRS, Sorbonne University（巴黎高等物理化工学院）；Moscow Institute of Physics and Technology（莫斯科物理技术学院）；HSE University（俄罗斯国立高等经济大学）；Lobachevsky State University of Nizhny Novgorod（下诺夫哥罗德罗巴切夫斯基州立大学）；Institute for Physics of Microstructures RAS（俄罗斯科学院微结构物理研究所）；Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University（莫斯科国立大学索别尔茨因核物理研究所）；Institut des Nanosciences de Paris, UMR-7588, Sorbonne University, CNRS（巴黎纳米科学研究所）
