本文系统地研究了KCa ${_2}$ Fe ${_4}$ As ${_4}$ F ${_2}$单晶的电阻率、霍尔系数、磁光成像、磁化强度和STEM分析。尖锐的抗磁性转变和磁光成像显示单晶的均匀性和突出的豆状穿透的漩涡。电阻率的大的各向异性，其中${ρ_c / ρ_{ab}}$ > 100，和类磁阻${ρ_c}$表明电子态是准二维的。霍尔效应测量表明，KCa ${_2}$ Fe ${_4}$ As ${_4}$ F ${_2}$是一个以空穴为主载流子的多带体系.磁化强度测量结果表明，与其他铁基超导体相比，J $_c$显着更大，J $_c$值取决于磁场的方向。这些J $_c$特性的起源进行了讨论的基础上使用STEM显微结构观察。此外，在重离子辐照方面证明了在KCa ${_2}$ Fe ${_4}$ As ${_4}$ F ${_2}$中J $_c$的进一步增强以用于未来的应用。
英文摘要：
We present a systematic study of electrical resistivity, Hall coefficient, magneto-optical imaging, magnetization, and STEM analyses of KCa${_2}$Fe${_4}$As${_4}$F${_2}$ single crystals. Sharp diamagnetic transition and magneto-optical imaging reveal homogeneity of single crystal and prominent Bean-like penetrations of vortices. Large anisotropy of electrical resistivity, with ${ρ_c / ρ_{ab}}$ > 100, and semiconductor-like ${ρ_c}$ suggest that the electronic state is quasi two-dimensional. Hall effect measurements indicate that KCa${_2}$Fe${_4}$As${_4}$F${_2}$ is a multiband system with holes as main carriers. Magnetization measurements reveal significantly larger J$_c$ compared with that in other iron-based superconductors with different values of J$_c$ depending on the direction of magnetic field. Origin of these J$_c$ characteristics is discussed based on microstructural observations using STEM. In addition, further enhancement of J$_c$ in KCa${_2}$Fe${_4}$As${_4}$F${_2}$ for future application is demonstrated in terms of heavy-ion irradiation.
Low temperature specific heat of 12442-type KCa_2Fe_4As_4F_2 single crystals
测量了12442型KCa $_2$ Fe $_4$ As $_4$ F $_2$单晶在不同磁场下的低温比热。在超导转变温度$T_c$观察到一个明显的SH跳跃，其高度为$ΔC/T|_{T_c}$ = 130 mJ/mol K $^2$.结果表明，电子SH系数$Δγ(H)$在低于3 T的低场区迅速增大，随着场的进一步增大，其增大速度明显减慢，这表明超导体具有较强的各向异性或多能隙特征，在超导能隙中存在一个极小值.与温度相关的SH数据表明存在$T^2$项，该项提供了进一步的信息，并支持具有线节间隙结构的图像。此外，SH转变的起始点在高达9 T的磁场下几乎保持不变，这与在铜酸盐中观察到的相似，并且将该系统置于BCS极限和玻色-爱因斯坦凝聚之间。
Superconductivity in KCa$_2$Fe$_4$As$_4$F$_2$ with Separate Double Fe$_2$As$_2$ Layers
本文报道了五元铁砷氟化物KCa $_2$ Fe $_4$ As $_4$ F $_2$的合成、晶体结构和物理性质。这种新化合物以体心四元晶格（空间群为$I4/mmm$，$a$ = 3.8684（2），c = 31.007（1），$Z$ = 2）结晶，其中含有双Fe $_2$ As $_2$导电层，由绝缘Ca $_2$ F $_2$层隔开。我们的电阻率，直流磁化率和热容量的测量表明，在33 K的KCa $_2$ Fe $_4$作为$_4$ F $_2$的体超导性。
Strong Pauli paramagnetic effect in the upper critical field of KCa$_2$Fe$_4$As$_4$F$_2$
近年来，12442系统铁基超导体由于其独特的双FeAs层结构而引起了人们的广泛关注。在KCa $_2$ Fe $_4$ As $_4$ F $_2$单晶中，在超导转变温度$T_c$附近，观察到面内上临界场随冷却而急剧增加.本文报道了在宽温度范围内对该材料上临界场的高场研究，测量了面外（$H\|c$，$H_{c2}^{c}$）和面内（$H\|ab$，$H_{c2}^{ab}$）方向。一个次线性的温度依赖性行为观察到的平面外$H_{c2}^{c}$，而强烈的凸曲率与冷却观察到的平面内$H_{c2}^{ab}$。这种行为不能用传统的Werthamer-Helfand-Hohenberg（WHH）模型来描述。基于WHH模型考虑自旋方面的数据分析揭示了大的Maki参数$α=9$，表明面内上临界场受到非常强的泡利顺磁效应的影响。
Observation of anisotropic diamagnetism above the superconducting transition in iron-pnictide Ba_(1-x)K_xFe2As2 single crystals due to thermodynamic fluctuations
Three-dimensional anisotropic fluctuation diamagnetism around the superconducting transition of Ba(1-x)KxFe2As2 single crystals in the finite-field (or Prange) regime
Weakly anisotropic superconductivity of Pr4Ni3O10 single crystals
ShanghaiTech University（上海科技大学）；Center for High Pressure Science and Technology Advanced Research（高压科学与技术先进研究中心）；Institute for Shanghai Advanced Research in Physical Sciences (SHARPS)（上海物理科学研究院）；Songshan Lake Materials Laboratory（松山湖材料实验室）；Qufu Normal University（曲阜师范大学）；University of Oxford（牛津大学）；Southeast University（东南大学）；Tsinghua University（清华大学）
