我们提出了详细的温度依赖的光学数据BaFe $_{2-x}$ Co $_{x}$作为$_{2}$（BCFA），与x = 0.14，在4 meV和6.5 eV之间。我们分析我们的光谱，以确定主要的光学参数，并表明，在这种材料的带间电导率已经开始约10毫电子伏。我们确定超流密度为2.2 × 10^{7} $ cm^{-2}, which places optimally doped BFCA close to the Uemura line. Our experimental data shows clear signs of a superconducting gap with 2$ Δ_{1} $ = 6.2 $ \pm $ 0.8 meV. In addition we show that the optical spectra are consistent with the presence of an additional band of strongly scattered carriers with a larger gap, 2$ Δ_{2} $ = 14 $ \pm $2 meV.
英文摘要：
We present detailed temperature dependent optical data on BaFe$_{2-x}$Co$_{x}$As$_{2}$ (BCFA), with x = 0.14, between 4 meV and 6.5 eV. We analyze our spectra to determine the main optical parameters and show that in this material the interband conductivity already starts around 10 meV. We determine the superfluid density to be 2.2 10^{7}$ cm^{-2}, which places optimally doped BFCA close to the Uemura line. Our experimental data shows clear signs of a superconducting gap with 2$Δ_{1}$ = 6.2 $\pm$ 0.8 meV. In addition we show that the optical spectra are consistent with the presence of an additional band of strongly scattered carriers with a larger gap, 2$Δ_{2}$ = 14 $\pm$ 2 meV.
We investigate coherent phonon oscillations of BaFe$_2$As$_2$ using optical pump-probe spectroscopy. Time-resolved optical reflectivity shows periodic modulations due to $A_{1g}$ coherent phonon of $c$-axis arsenic vibrations. Optical probe beams polarized along the orthorhombic $a$- and $b$-axes reveal that the initial phase of coherent oscillations shows a systematic deviation as a function of temperature, although these oscillations arise from the same $c$-axis arsenic vibrations. The oscillation-phase remains anisotropic even in the tetragonal structure, reflecting a nematic response of Ba…
The optical properties of a large, detwinned single crystal of BaFe$_2$As$_2$ have been examined over a wide frequency range above and below the structural and magnetic transition at $T_{\rm N}\simeq 138$ K. Above $T_{\rm N}$ the real part of the optical conductivity and the two infrared-active lattice modes are almost completely isotropic; the lattice modes show a weak polarization dependence just above $T_{\rm N}$. For $T<T_{\rm N}$, the optical conductivity due to the free-carrier response is anisotropic, being larger along the $a$ axis than the $b$ axis below $\simeq 30$ meV; above this en…
Uniaxial strain detwinning of CaFe2As2 and BaFe2As2: optical and transport study
砷化铁超导体的母体化合物$A$ Fe $_{2}$ As $_{2}$（$A$ =Ca，Sr，Ba）在温度$T_{\mathrm{TO}}$为135至205 K（取决于碱土元素）时经历四方晶系到正交晶系的结构转变。在$T_{\mathrm{TO}}$下方，独立式晶体分裂成相等分布的结构域，其掩盖了材料的固有的、面内的、各向异性的性质。在这里，我们演示了一种方法，机械解孪晶的CaFe $_{2}$ As $_{2}$和BaFe $_{2}$ As $_{2}$。偏振光成像和同步辐射$X$ -射线测量表明，脱孪晶几乎完全，并且是可逆的，应变释放后孪晶图案恢复。在孪晶和去孪晶状态的电阻率测量表明，电阻率，$ρ$，沿正交$a_{o}$ -轴减小，但沿正交$b_{o}$ -轴在两种化合物中增加。紧接在$T_{\mathrm{TO}}$之下，对于Ca和Ba化合物，比率$ρ_{bo}/ ρ_{ao}$分别= 1.2和1.5。与CaFe $_{2}$ As $_{2}$相反，BaFe $_{2}$ As $_{2}$在名义上的四元相中显示出各向异性，这表明在BaFe $_{2}$ As $_{2}$中波动在$T_{\mathrm{TO}}$以上起的作用比在CaFe $_{2}$ As $_{2}$中更大，或者存在更高的温度交叉或相变。
Doping evolution of antiferromagnetism and transport properties in the non-superconducting BaFe2-2xNixCrxAs2
本文报道了Ni和Cr等量掺杂的铁磷属元素化物BaFe $_{2-2x}$ Ni $_{x}$ Cr $_{x}$ As $_{2}$的弹性中子散射和输运测量结果。与电子掺杂的BaFe $_{2-x}$ Ni $_{x}$ As $_{2}$相比，BaFe $_{2-2x}$ Ni $_{x}$ Cr $_{x}$ As $_{2}$中的长程反铁磁（AF）有序逐渐被抑制，在$x= 0.20$附近的有序矩和Néel温度逐渐消失，没有出现超导电性.对BaFe $_{2-x}$ Ni $_{x}$ As和BaFe $_{2-2x}$ Ni $_{x}$ Cr $_{x}$ As $_{2}$的输运性质的详细分析表明，与作为温度的函数的线性电阻率相关的非费米液体行为可能不对应于静态AF序的消失。从温度依赖性的电阻率在过掺杂的化合物没有静态AF秩序，我们发现，实际上是由Cr杂质散射，这可能会导致一个金属到绝缘体的交叉在高掺杂BaFe $_{1.7-y}$ Ni $_{0.3}$ Cr $_{y}$ As $_{2}$的影响。
Transmittance and reflectance measurements at terahertz frequencies on a superconducting BaFe_{1.84}Co_{0.16}As_2 ultrathin film: an analysis of the optical gaps in the Co-doped BaFe_2As_2 pnictide
本文报道了40 nm的BaFe $_{1.84}$ Co $_{0.16}$ As $_2$超导薄膜在太赫兹波段的光学研究，超导转变温度T $_c$ = 17.5 K.结合反射率和透射率测量的详细分析表明，超导系统的光学性质可以用两带，两个间隙模型来描述。大间隙$Δ_B$的零温度值似乎遵循BCS类行为，结果为$Δ_B$（0）= 17 cm $^{-1}$。对于$Δ_A$（0）= 8 cm $^{-1}$的小间隙，不能清楚地建立温度依赖性。这些间隙值和文献中报道的BaFe $_{2-x}$ Co $_{x}$ As $_2$系统通过使用红外光谱，当放在一起作为T $_c$的函数时，显示出沿着两条主曲线聚集的趋势，提供了测量的光学间隙的统一观点。温度低于20 K时，禁带宽度与T_PDMATHABMP的关系呈现BCS型线性关系，但斜率不同。在此温度以上，两个间隙显示出不同的超线性行为。
We report a Raman scattering study of nematic degrees of freedom in the iron-based superconductor parent compound BaFe$_2$As$_2$ under tunable uniaxial strain. We demonstrate that the polarization resolved arsenic (As) phonon intensity can be used to monitor the nematic order parameter as a function of both temperature and strain. At low temperature in the nematic ordered phase we use it to track the continuous and reversible orientation of nematic domains under variable strain. At higher temperature, the evolution of the As phonon intensity under strain reflects an enhanced nematic susceptibi…
Anisotropic Superconducting Properties of Optimally Doped BaFe$_2$(As$_{0.65}$P$_{0.35}$)$_2$ under Pressure
在不同晶轴方向施加磁场的情况下，对BaFe $_2$（As $_{1-x}$ P $_{x}$）$_2$（$x\approx0.35$）的最佳掺杂单晶进行了压力下的磁性测量，从而跟踪了相干长度和各向异性因子的压力演化。尽管超导临界温度降低，我们的研究表明，压力下的超导性能变得更加各向异性。通过适当的缩放，我们直接将这些性质与BaFe $_2$（As $_{1-x}$ P $_{x}$）$_2$作为磷含量的函数获得的值进行比较。
Electronic correlations and unconventional spectral weight transfer in BaFe$_{2-x}$Co$_{x}$As$_{2}$
本文报道了磷属元素化物高温超导体BaFe $_{1.84}$ Co $_{0.16}$ As $_{2}$及其母体化合物BaFe $_{2}$ As $_{2}$的红外光学研究。我们表明，电子相关性是中等强度，并不改变整个自旋密度波过渡或掺杂。通过研究光谱权转移的能量尺度和方向，我们认为Hund耦合\emph{J}是产生相关性的主要机制。
Optical Study of BaFe$_2$As$_2$ under pressure: Coexistence of spin-density-wave gap and superconductivity
在高达$\sim$ 5 GPa的压力下，在85 - 7000 cm $^{-1}$的频率范围内对BaFe $_2$ As $_2$单晶进行了温度相关的反射率测量。用Drude-Lorentz模型分析了相应的压力和温度依赖的光学电导率，以提取相干和非相干贡献。在3.6GPa下，随着压力的增加，自旋密度波（SDW）态逐渐被抑制，并出现了与SDW相共存的超导相。在3.6 GPa时，反射率在$\sim$ 95 cm $^{-1}$以下达到1，表明超导能隙打开，在6 K时表现为全能隙趋势。
Possible superconductivity above 25 K in single crystalline Co-doped BaFe$_{2}$As$_{2}$
通过测量Ba（Fe $_{0.9}$ Co $_{0.1}$）$_{2}$ As $_{2}$的磁化强度、电阻率、上临界场、霍尔系数和磁光图像，研究了其超导特性。磁化强度的测量揭示了鱼尾磁滞回线在高温和相对较高的临界电流密度在$J_{c}=10^{5}$ A/cm $^{2}$在低温。由电阻转变确定的上临界场是各向异性的，各向异性参数$\sim$为3.5。霍尔效应测量表明Ba（Fe $_{0.9}$ Co $_{0.1}$）$_{2}$ As $_{2}$是多带体系，电子迁移率占主导地位.磁光成像揭示了突出的豆状渗透的漩涡，虽然有轻微的不均匀性的样品。此外，我们发现了一个明显的超导电性高于25 K，这使我们推测，更高的转变温度可以通过微调Co掺杂水平实现。
Optical spectroscopy was used to study the electrodynamics and hidden transport properties of a BaFe$_{1.91}$Ni$_{0.09}$As$_{2}$ thin superconducting film. We analyzed the normal state data using a Drude-Lorentz model with two Drude components: one narrow ($D_1$) and another broad one ($D_2$). In the superconducting state, two gaps with $2Δ_{0}^{(2)}/k_BT_c=1.9$--2.0 and $2Δ_{0}^{(1)}/k_BT_c=4.0$--4.3 are formed from the narrow component $D_1$ while the broad component $D_2$ remains ungapped. The calculated total DC resistivity of the film and the low-temperature scattering rate for the narrow…
We investigated the out-of-plane transport properties of parent and chemically substituted BaFe$_{2}$As$_{2}$ for various types of substitution. Based on the studies of Hall coefficient and chemical-substitution effect, we have clarified the origin for the unusual temperature dependence of out-of-plane resistivity $ρ_c(T)$ in the high-temperature paramagnetic-tetragonal phase. Electron (hole) carriers have an incoherent (coherent) character, which is responsible for non-metallic (metallic) $ρ_c(T)$. Although both of electron and hole contributions are almost comparable, a slightly larger contr…
Multi-gap superconductivity in a BaFe1.84Co0.16As2 film from optical measurements at terahertz frequencies
测量了高质量铁基超导体BaFe $_{1.84}$ Co $_{0.16}$ As $_2$外延薄膜的THz反射特性，T_（$_c$）=22.5 K.通过脉冲激光沉积在具有外延SrTiO $_3$中间层的DyScO $_3$衬底上生长膜。测量的$R_S/R_N$谱，即超导和正常状态反射率之间的反射率比，提供了接近15 cm $^{-1}$的超导间隙$Δ_A$的明确证据。详细的数据分析表明，一个两带，两个间隙模型是绝对必要的，以获得一个很好的描述所测量的$R_S/R_N$频谱。低能$Δ_A$能隙结果被很好地确定（$Δ_A$ =15.5 $\pm$ 0.5 cm $^{-1}$），而高能能隙$Δ_B$的值更不确定（$Δ_B$ =55 $\pm$ 7 cm $^{-1}$）.我们的研究结果提供了一个无节点的各向同性双间隙的情况下，与存在的两个光学间隙对应的2 $Δ/kT_c$值接近2和7的证据。
Electronic structure and exotic exchange splitting in spin-density-wave states of BaFe$_2$As$_2$
母体化合物的磁性通常与超导电性的微观机制密切相关。本文报道了对新发现的铁基超导体BaFe $_2$ As $_2$的电子结构的首次直接测量，为进一步的研究提供了基础。我们发现BaFe $_2$ As $_2$中的自旋密度波（SDW）的能量是通过能带结构的奇异交换劈裂而降低的，而不是通过费米表面的巡游电子嵌套。这清楚地表明，金属SDW状态可以单独由局部磁矩的相互作用引起，类似于铜酸盐母体化合物中的反铁磁序的性质。
Strange Metal Hall Effect in Underdoped BaFe$_2$(As$_{1-x}$P$_x$)$_2$
University of California, Berkeley（加州大学伯克利分校）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Max Planck Institute for the Structure and Dynamics of Matter（马克斯·普朗克物质与结构动态研究所）；National High Magnetic Field Laboratory（国家强磁场实验室）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）；Boston University（波士顿大学）
Because of their complex Fermi surfaces, the identification of the physical phenomena contributing to electronic scattering in the Fe-based superconductors is a difficult task. Here, we report on the electrical resistivity, magnetoresistance, and Hall effect in two series of BaFe$_{2-x}$T$_x$As$_2$ (T = Co, Ni) crystals with different values of $x$. The T contents were chosen so that the majority of the investigated samples present an intermediate magnetically ordered state and a superconducting ground state. We interpret the obtained results in terms of scattering of charge carriers by magnet…
The scaling of $H$-linear magnetoresistance in field and temperature was measured in under-doped (x = 0.19) and optimally-doped (x=0.31)~BaFe$_2$(As$_{1-x}$P$_x$)$_2$. We analyze the data based on an orbital model in the presence of strongly anisotropic quasiparticle spectra and scattering time due to antiferromagnetism. The magnetoresistance is dominated by the properties of small regions of the Fermi surface called `hot spots' where antiferromagnetic excitations induce a large quasiparticle scattering rate. Approximate temperature-magnetic field scaling relations are derived and shown to be …
We present a systematic study on the heavily Cr doped iron pnictides BaFe$_{1.9-x}$Ni$_{0.1}$Cr$_{x}$As$_{2}$ by using elastic neutron scattering, high-resolution synchrotron X-ray diffraction (XRD), resistivity and Hall transport measurements. When the Cr concentration increases from $x=$ 0 to 0.8, neutron diffraction experiments suggest that the collinear antiferromagnetism persists in the whole doping range, where the Néel temperature $T_N$ coincides with the tetragonal-to-orthorhombic structural transition temperature $T_s$, and both of them keeps around 35 K. The magnetic ordered moment, …
Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. While extensive photoemission results have been obtained, the surface complexity of 122 caused by its charge-non-neutral surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe$_2$(As$_{0.7}$P$_{0.3}$)$_2$, the surface-induced spectral broadening is strongly suppressed, and hence the coherent spectra that reflect the intrinsic bulk electronic state recover.…
BaFe$_2$S$_3$ is a quasi-one-dimensional antiferromagnetic insulator that becomes superconducting under hydrostatic pressure. The magnetic ordering temperature, $T_N$, as well as the presence of superconductivity have been found to be sample dependent. It has been argued that the Fe content may play a decisive role, with the use of 5%mol excess Fe being reportedly required during the synthesis to optimize the magnetic ordering temperature and the superconducting properties. However, it is yet unclear whether an Fe off-stoichiometry is actually present in the samples, and how it affects the str…
Topological properties of spin block magnetic ladders in proximity of a superconductor: application to BaFe$_{2}$S$_{3}$
Institute of Nuclear Physics, Polish Academy of Sciences（波兰科学院核物理研究所）；Université Paris-Saclay, Centre National de la Recherche Scientifique, Laboratoire de Physique des Solides（巴黎萨克雷大学，法国国家科学研究中心，固体物理实验室）
Disorder Induced Effects on the Critical Current Density of Iron Pnictide BaFe_1.8 Co_0.2 As_2 single crystals
研究无序在超导体中的作用是表征基本超导性质以及评估材料潜在应用的重要组成部分。在大多数情况下，缺陷矩阵上的信息是穷人，使这样的研究困难，但这种情况可以通过引入缺陷，在一个可控的方式，如中子辐照提供改善。在这项工作中，我们分析了中子辐照对Ba（Fe $_{1-x}$ Co $_x$）$_2$ As $_2$单晶的影响。我们主要集中在磁性能，这是由磁强计测定。通过中子辐照引入无序导致对可逆和不可逆磁性的显著影响，例如转变温度、上临界场、各向异性和临界电流密度。通过与未辐照状态下的性质进行比较，对结果进行了详细讨论。
Magneto-elastically coupled structural, magnetic and superconducting order parameters in BaFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$
我们测量了机械应变BaFe $_{2}$（As $_{1-x}$ P $_{x}$）$_{2}$单晶在宽的$x$范围内的输运性质。Néel转变对应力极其敏感，并且这种敏感性随着接近最佳掺杂而增加，即使转变本身被强烈抑制。此外，我们观察到显着的变化，超导转变温度与施加的应变，这反映了变化的组合物$x$的函数。这些实验直接说明了铁基超导体中不同自由度之间的紧密耦合，揭示了磁弹性耦合对磁性和超导转变温度的重要性。
Thermodynamic properties of Ba1-xMxFe2As2 (M = La and K)
测量了BaFe $_2$ As $_2$单晶、电子掺杂Ba $_{0.7}$ La $_{0.3}$ Fe $_2$ As $_2$和空穴掺杂Ba $_{0.5}$ K $_{0.5}$ Fe $_2$ As $_2$多晶的比热$C(T)$。对于未掺杂的BaFe $_2$ As $_2$单晶，在136 K处观察到非常尖锐的比热峰。这是由于在相同的温度下发生的结构和反铁磁转变。电子掺杂的非超导Ba $_{0.7}$ La $_{0.3}$ Fe $_2$ As $_2$的$C(T)$也在120 K处显示出小峰，表明类似但较弱的结构/反铁磁转变。对于空穴掺杂的超导Ba $_{0.5}$ K $_{0.5}$ Fe $_2$ As $_2$，在$T_c$ = 36 K处观察到$C/T$的明显峰，这是迄今为止在铁基高$T_c$超导体的超导转变处观察到的最高峰。由低温数据得到了这些化合物的电子比热系数$γ$和德拜温度$Θ_D$。
The polarization dependence of the near edge x-ray absorption spectroscopy (XANES) is an element specific probe to the real-space distribution of the density of unoccupied states in solid-state materials. In this paper, we present Fe and As $K$-edge experiments of Ba(Fe$_{1-x}$$M_{x}$)$_{2}$As$_{2}$ ($M=$ Mn, Co and $x=0.0$ and $0.08$). The experiments reveal a strong polarization dependence of the probed XANES spectra, which concerns mainly an increase of the intensity of electronic transitions when the beam polarization is set out of the sample's $ab$ crystallographic plane. The results show…
