We have performed transverse- and zero-field muon spin rotation/relaxation experiments, as well as magnetometry measurements, on samples of Fe1-xVxSe and their Li+NH3 intercalates Li0.6(NH2)0.2(NH3)0.8 Fe1-x Vx Se. We examine the low vanadium substitution regime: x = 0.005, 0.01, and 0.02. The intercalation reaction significantly increases the critical temperature (Tc) and the superfluid stiffness for all x. The nonintercalated samples all exhibit Tc = 8.5 K while the intercalated samples all show an enhanced Tc > 40 K. Vanadium substitution has a negligible effect on Tc, but seems to suppress the superfluid stiffness for the nonintercalated samples and weakly enhance it for the intercalated materials. The optimal substitution level for the intercalated samples is found to be x = 0.01, with Tc = 41 K and λ_{ab}(0) = 0.18 μm. The nonintercalated samples can be modeled with either a single d-wave superconducting gap or with an anisotropic gap function based on recent quasiparticle imaging experiments, whereas the intercalates display multigap nodal behavior which can be fitted using s + d- or d + d-wave models. Magnetism, likely from iron impurities, appears after the intercalation reaction and coexists and competes with the superconductivity. However, it appears that the superconductivity is remarkably robust to the impurity phase, providing an avenue to stably improve the superconducting properties of transition metal substituted FeSe.
Investigations on the relationship between $T_c$ and the superconducting gap under magnetic and non-magnetic impurity substitutions in YBa$_2$Cu$_3$O$_{7-δ}$
Effects of disordered Ru substitution in BaFe$_2$As$_2$: Realization of superdiffusion mechanism in real materials
根据第一性原理理论，在Ru取代的BaFe $_2$ As $_2$中发现了一种出乎意料的费米面对杂质散射的不敏感性，为这种材料中高水平无序取代的输运和超导性的异常弹性提供了一种自然的解释。这种鲁棒性被证明是源于相关的现场和站点间的杂质散射的相干干涉，类似的精神在一维超扩散的微观机制。我们的结果也表明了费米面和载流子浓度的强烈的替代依赖性，并提供了一个自然的分辨率，目前的差异，在最近的光电子能谱学。这些效应提供了一个自然的解释，减少长程磁性，轨道和超导秩序与高替代。
Similarity between Ni and Zn impurity effects on the superconductivity and Cu-spin correlation in La2-xSrxCu1-yNiyO4 high-Tc cuprates: A comparison based on the hole trapping by Ni
Effect of impurity substitution on band structure and mass renormalization of the correlated FeTe$_{0.5}$Se$_{0.5}$ superconductor
用角分辨光电子能谱（ARPES）研究了杂质势对FeTe $_{0.5}$ Se $_{0.5}$超导体电子结构的影响.在FeTe $_{0.5}$ Se $_{0.5}$的情况下，我们可以分辨出靠近带中心的三个空穴袋和靠近带角的一个电子袋，而在Fe $_{0.9}$ Ni $_{0.1}$ Te $_{0.5}$ Se $_{0.5}$的情况下，只能分辨出靠近带中心的两个空穴袋和靠近带角的一个电子袋，这表明主要具有$xy$轨道特征的空穴袋对杂质散射非常敏感。在电子掺杂时，与主体化合物相比，空穴袋的尺寸减小并且电子袋的尺寸增加。然而，观察到的电子和空穴口袋的大小的变化是不符合刚性带模型。此外，与FeTe $_{0.5}$ $_{0.5}$ Se相比，在掺杂的Fe $_{0.9}$ Ni $_{0.1}$ Te $_{0.5}$ Se $_{0.5}$中，空穴袋的有效质量在区域中心附近减小，而电子袋的有效质量在区域拐角附近增加。我们将这些观察结果归因于掺杂剂的杂质势的影响所引起的光谱函数的变化。
We investigated Fe-substitution effects on ferromagnetic fluctuations in the superconducting overdoped and non-superconducting heavily overdoped regimes of the Bi-2201 cuprates by the magnetization and electrical-resistivity measurements. It was found that the spin-glass state was induced at low temperatures by the Fe substitution. The Curie constant and the effective Bohr magneton, estimated from the magnetic susceptibility, as well as the dimensionality of the ferromagnetic fluctuations from the resistivity, suggest the enhancement of the ferromagnetic fluctuations owing to the Fe substituti…
Non-magnetic impurities in iron-based superconductors can provide an important tool to understand the pair symmetry and they can influence significantly the transport and the superconducting behaviour. Here, we present a study of the role of strong impurity potential in the Fe plane, induced by Cu substitution, on the electronic and superconducting properties of single crystals of FeSe. The addition of Cu quickly suppresses both the nematic and superconducting states, and increases the residual resistivity due to enhanced impurity scattering. Using magnetotransport data up to 35 T for a small …
Gigantic Impact of Magnetic Impurity on Stripe Order in La$_{2-x}$Sr$_{x}$CuO$_4$ ($x$$\sim$1/8)
对La $_{1.88-y}$ Sr $_{0.12+y}$ Cu $_{0.99}$ R $_{0.01}$ O $_4$（当R=Cu，Zn时$y$ =0，当R=Ga，Fe时$y$ =0.01）进行了精确的中子散射实验，研究了杂质替代效应对铜氧化物条纹有序稳定性的影响。对于所有的杂质取代的样品的静态电荷密度波的顺序类似于在低温四方晶相（LTT）中报道的首次发现，在低温正交（LTO）相。Fe取代显着提高了电荷和自旋密度波的订单。这些结果表明，动态的电荷条纹可以稳定到静态的铜位缺陷周围的晶体结构的类型无关。此外，在Cu-站点的大的磁矩可能会引起周围的缺陷，这反过来又提高了静态电荷密度波秩序的Cu自旋波动的减少。
Comment on "Isoelectronic Ru substitution at Fe-site in Sm(Fe$_{1-x}$Ru$_x$)AsO$_{0.85}$F$_{0.15}$ compound and its effects on structural, superconducting and normal state properties" (arXiv:1004.1978)
基于五轨道模型，由剩余电阻率导出Sm（Fe $_{1-x}$ Ru $_{x}$）AsO $_{0.85}$ F $_{0.15}$中约化杂质散射率$g=zγ/2πT_{c0}$.在$x=0$下，转变温度为$T_{c0}=50$ K。对于$0.05<x<0.36$（$0.84>T_{c}/T_{c0}>0.3$），得到的$g$值在1.5到2.9之间，这表明$s_\pm$波态不能存在.我们指出，在关联电子系统中，磁电阻经常给出一个低估的$g$值。
Change of the Ground State upon Hole Doping Unveiled by Ni Impurity in High-$T_{\rm c}$ Cuprates
通过比热和μ子自旋弛豫测量，研究了高$T_{\rm c}$铜氧化物中超导态被Ni取代抑制的电子基态在La $_{2-x}$ Sr $_x$ Cu $_{1-y}$ Ni $_y$ O $_4$中的变化.发现随着空穴浓度的增加，基态由具有Ni强空穴俘获的磁有序态转变为具有Ni的近藤效应的金属态.此外，对结果的分析表明，在两相的边界附近发生了磁有序相和金属相的相分离。
Dependence of carrier doping on the impurity potential in transition-metal-substituted FeAs-based superconductors
为了研究类刚性带电子掺杂在何种程度上适用于过渡金属取代的铁基超导体，我们对Ba（Fe $_{1-x}$ Ni $_{x}$）$_2$ As $_2$（Ni-122）和Ba（Fe $_{1-x}$ Cu $_{x}$）$_2$ As $_2$（Cu-122），并将结果与Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$（Co-122）进行比较。结果表明，Ni 3 $\it{d}$衍生的特征形成于Fe 3 $\it{d}$能带之下，而Cu 3 $\it{d}$衍生的特征形成于更低的能带之下，电子和空穴费米面（FS）体积分别随取代量的增加和减少而增加，与刚性能带模型定性一致.然而，从FS体积（总电子FS体积减去总空穴FS体积）估计的总额外电子数被发现减少从Co-，Ni-，Cu-122为一个固定的标称额外电子数，也就是说，参与形成FS的电子数随着杂质电位的增加而减少。我们发现N $\acute{\rm{e}}$ el温度$T_{\rm{N}}$和临界温度$T_{\it{c}}$最大值是由FS体积决定的，而不是由名义额外电子浓度或取代原子浓度决定的。
Indium substitution effect on the topological crystalline insulator family (Pb$_{1-x}$Sn$_{x}$)$_{1-y}$In$_{y}$Te: Topological and superconducting properties
拓扑晶体绝缘体是凝聚态物理研究的热点。研究了铟掺杂对TCI体系（Pb $_{1-x}$ Sn $_{x}$）$_{1-y}$ In $_{y}$ Te的晶体结构和输运性质的影响。对于具有锡浓度$x\le50\%$的样品，低温电阻率显示出作为铟浓度的函数的显著变化：当铟掺杂高达~2%时，样品显示出弱金属行为，类似于它们的母体化合物;当铟掺杂~6%时，样品具有真正的体绝缘电阻率，并且呈现出非平凡拓扑表面状态的证据;在较高的铟掺杂水平下，观察到超导电性，其中转变温度Tc与铟浓度正相关并且高达4.7K。我们解决这个问题，从体电子结构的角度修改的铟诱导的杂质水平钉扎费米能级。本文综述了（Pb，Sn）Te的In替代效应，并从拓扑和超导方面进行了讨论，为今后的研究提供了指导。
Superconductivity in FeSe is strongly enhanced under applied pressure and it is proposed to emerge from anomalously coupled structural and magnetic phases. Small impurities inside the Fe plane can strongly disrupt the pair formation in FeSe at ambient pressure and can also reveal the interplay between normal and superconducting phases. Here, we investigate how an impurity inside the Fe plane induced by the Cu substitution can alter the balance between competing electronic phases of FeSe at high pressures. In the absence of an applied magnetic field, at low pressures the nematic and superconduc…
