本文报道了高质量磷属元素化物超导体BaFe $_{1.84}$ Co $_{0.16}$ As $_2$薄膜的时域THz光谱研究。近T $_c$，我们发现的相干峰和定性协议的证据与弱耦合的马蒂斯-Barbarian形式的导电性。在低温下，我们发现THz电导率的实部没有被完全抑制，并且$σ_2$明显小于Matthis-Barthanson期望。穿透深度$λ$的温度依赖性遵循具有异常高的指数3.1的幂律。我们解释这些结果与杂质散射诱导的对断裂一致。总之，我们的结果是一个扩展的s $\pm$对称序参量的强有力的证据。
英文摘要：
We report a study of high quality pnictide superconductor BaFe$_{1.84}$Co$_{0.16}$As$_2$ thin films using time-domain THz spectroscopy. Near T$_c$ we find evidence for a coherence peak and qualitative agreement with the weak-coupling Mattis-Bardeen form of the conductivity. At low temperature, we find that the real part of the THz conductivity is not fully suppressed and $σ_2$ is significantly smaller than the Matthis-Bardeen expectation. The temperature dependence of the penetration depth $λ$ follows a power law with an unusually high exponent of 3.1. We interpret these results as consistent with impurity scattering induced pair-breaking. Taken together our results are strong evidence for an extended s$\pm$ symmetry order parameter.
Ultralow-dissipative conductivity by Dirac fermions in BaFe$_2$As$_2$
报道了BaFe $_{2}$ As $_{2}$在太赫兹（THz）频率范围内与狄拉克锥有关的复电导率的反常行为.在自旋密度波（SDW）转变温度以上，电导率谱遵循Drude模型。在SDW状态下，与根据Drude模型预期的情况相比，复电导率的虚部$σ_2$被抑制。真正的部分，$σ_1$，表现出几乎像德鲁德一样的行为。这种行为（即，$σ_1$几乎没有变化和$σ_2$的降低）可以被认为是额外电导率的增加，而在Drude型电导率中没有任何耗散。这种超低耗散电导率的起源被认为是由于狄拉克锥内的准粒子的电导率贡献。也就是说，我们可以通过BaFe $_2$ As $_2$的电导谱，清晰而直接地观察到狄拉克费米子的动力学过程。
The temperature dependences of the plasma frequency, superfluid density and London penetration depth were determined from terahertz spectra of conductivity and dielectric permittivity of BaFe$_{1.91}$Ni$_{0.09}$As$_{2}$ film with critical temperature $T_c=19.6$~K. Part of experimental data were analyzed within a simple three-band Eliashberg model where the mechanism of superconducting coupling is mediated by antiferromagnetic spin fluctuations, whose characteristic energy $Ω_{0}$ scales with $T_{c}$ according to the empirical law $Ω_{0} = 4.65k_{B}T_{c}$, and with a total electron-boson coupli…
Line nodes in the energy gap of high-temperature superconducting BaFe_2(As_{1-x}P_x)_2 from penetration depth and thermal conductivity measurements
本文报道了高质量BaFe $_2$（As $_{1-x}$ P $_{x}$）$_2$（$T_c=30$ \，K）单晶的磁穿透深度和热导率数据，为该材料的能隙中存在线节点提供了有力的证据。这与（Ba，K）Fe $_2$ As $_2$中发现的无节能隙明显不同，后者具有相似的$T_c$和相图。我们的研究结果表明，排斥电子相互作用的Fe基高$T_c$超导性发挥了至关重要的作用，但独特的是有明显不同的配对状态，有和没有节点，具有可比的$T_c$。
Thermal conductivity of overdoped BaFe$_{1.73}$Co$_{0.27}$As$_2$ single crystal: Evidence for nodeless multiple superconducting gaps and interband interactions
测量了过掺杂的FeAs基超导体BaFe $_{1.73}$ Co $_{0.27}$ As $_2$（$T_c$ = 8.1 K）单晶的面内热导率$κ$，其热导率低至80 mK。在零磁场下，剩余的线性项$κ_0/T$可以忽略不计，表明在$ab$平面上存在无结超导能隙.在磁场中，$κ_0/T$迅速增加，与传统的s波超导体有很大不同。这种反常的$κ_0/T(H)$可能揭示了在过掺杂BaFe $_{1.73}$ Co $_{0.27}$ As $_2$中的一种奇异的超导能隙结构：消失空穴（$β$）的能隙比包含大部分载流子的电子（$γ$和$δ$）的能隙大得多。这种奇异的带隙结构是由带间相互作用诱导的超导态的证据，其中具有{ \it较小}态密度的带具有{ \it较大}带隙。
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…
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。
Measurements of the superconducting fluctuations in optimally-doped BaFe$_{2-x}$Ni$_x$As$_2$ under high magnetic fields: Probing the 3D anisotropic Ginzburg-Landau approach
通过对几种高质量优化掺杂的BaFe $_{2-x}$ Ni $_x$ As $_2$晶体的面内介导率的测量，研究了铁基超导体正常态内的超导涨落。这些测量是在振幅高达14 T的磁场中进行的，并且相对于晶体c轴具有不同的取向（0、53和90度）。结果允许严格检查的适用性最近提出的Ginzburg-Landau方法的波动电导率的三维各向异性材料中存在的有限施加磁场。
Signatures of Dynes superconductivity in the THz response of ALD-grown NbN thin films
Universität Stuttgart（斯图加特大学）；Center for Integrated Quantum Science and Technology (IQST), Universität Stuttgart（斯图加特大学集成量子科学与技术中心）；Universität Ulm（乌尔姆大学）；Institute for Complex Quantum Systems and IQST, Universität Ulm（乌尔姆大学复杂量子系统与集成量子科学与技术中心）；Leibniz Institute of Photonic Technology（莱布尼茨光子技术研究所）；Friedrich-Schiller Universität Jena（耶拿弗里德里希·席勒大学）；Institute for Solid State Physics, Friedrich-Schiller Universität Jena（耶拿弗里德里希·席勒大学固体物理研究所）
Using a combination of time-domain THz spectroscopy (TDTS) and mutual inductance measurements, we have investigated the low-energy electrodynamic response of overdoped La$_{2-x}$Sr$_x$CuO$_4$ films that have been exposed to ion irradiation. Films went through three rounds of irradiation (2, 4, and 6 $\times 10^{13}$ ions/cm$^2$) and mutual inductance and TDTS experiments were performed between each step. Together with the as-grown film, this gives four different levels of disorder. The transport scattering rate that is measured directly in the THz experiments is an approximately linear functio…
Systematic modulation of superconducting gap dynamics in YBCO|BNT|YBCO Josephson Junctions through THz field interaction and BNT ferroelectric barrier
Chiang Mai University（清迈大学）；Universität Stuttgart（斯图加特大学）；University of Zambia（赞比亚大学）；Khon Kaen University（孔敬大学）；Institute of Nanomaterials Research and Innovation for Energy (IN-RIE), Research Network of NANOTEC- KKU (RNN)（纳米材料研究与能源创新研究所（IN-RIE），NANOTEC-孔敬大学研究网络（RNN））；University of Macau（澳门大学）；Macau University of Science and Technology（澳门科技大学）
Superconducting (SC) fluctuations in cuprate superconductors have been extensively studied to gain a deep insight into preformed Cooper pairs above the SC transition temperature $T_{\text{c}}$. While the various measurements, such as the terahertz (THz) optical conductivity, Nernst effect, angle-resolved photoemission spectroscopy (ARPES), and scanning tunneling microscopy (STM) measurements have provided the signature of the SC fluctuations, the onset temperature of the SC fluctuations depends on the measurement scheme. Here, we shed light on the Higgs mode to investigate the SC fluctuations,…
