We report on temperature dependent scanning tunneling microscopy and spectroscopy studies of undoped SrFe$_{2}$As$_{2}$ single crystals from 6 K to 292 K. Resistivity data show spin density wave (SDW) transition at T$_{SDW}$ $\approx$ 205 K and the superconducting transition at $\sim$ 21 K while magnetic susceptibility does not show any superconductivity. Conductance maps and local tunneling spectra show an electronically homogeneous surface at all studied temperatures. Tunnel spectra correlate well with the SDW transition with a depression in the density of states near the Fermi energy below T$_{SDW}$. On further lowering the temperature, the width of this partial energy gap associated with the SDW decreases. Using the anti-correlation of superconducting phase with SDW, we interpret this gap weakening as a precursor to superconductivity. This may give rise to a facile nucleation of superconductivity near defects.
Physical properties in hole-doped SrFe$_{2-x}$Cu$_x$As$_2$ single crystals
本文报道了用自熔法生长的SrFe $_{2-x}$ Cu $_x$ As $_2$单晶的结构、磁性和电子输运性质。SrCu $_2$ As $_2$和SrFe $_2$ As $_2$在室温下均为ThCr $_2$ Si $_2$型（122型）结构，但表现出不同的磁性和电子输运性质。X射线光电子能谱学（XPS）Cu-2 p芯线位置、电阻率、磁化率和正霍尔系数表明SrCu $_2$ As $_2$是一种sp带金属，Cu处于3d $^{10}$电子构型，对应于价态Cu $^{1+}$。与SrCu $_2$ As $_2$相比，SrFe $_{2-x}$ Cu $_x$ As $_2$中几乎不变的Cu-2 p芯线位置表明，部分Cu取代了SrFe $_2$ As $_2$中的Fe，可能导致空穴掺杂，而不是预期的电子掺杂。没有超导电性诱导Cu取代Fe网站，即使结构/自旋密度波（SDW）的转变逐渐抑制Cu掺杂。
Anisotropy in the thermal hysteresis of resistivity and charge density wave nature of single crystal SrFeO3-delta: X-ray absorption and photoemission studies
Evidence for Coexistence of Superconductivity and Magnetism in Single Crystals of Co-doped SrFe$_2$As$_2$
为了研究Co掺杂SrFe $_2$ As $_2$中磁性和超导电性是否共存，我们制备了SrFe $_{2-x}$ Co $_x$ As $_2$，$x$ = 0和0.4的单晶，并通过X射线衍射、零场和外加场（最高达9 T）以及常压和外加压力（最高达1.6 GPa）下的电阻率和磁化率对其进行了表征。当$x$ = 0.4时，在120 K下存在自旋密度波跃迁的磁性和电阻证据，而$T_c$ = 19.5 K -表明磁性和超导性共存。讨论这些结果如何与报道的结果相比，无论是在SrFe $_{2-x}$ Co $_x$作为$_2$和其他掺杂122化合物，给出。
Effect of pressure on the structural phase transition and superconductivity in (B$_{1-x}K_x)Fe_2As_2 (x = 0 and 0.45) and SrFe_2As_2 single crystals
本文研究了高压对SrFe $\sim 20$ As $_2$和轻掺Sn的BaFe $_2$ As $_2$结构相变以及（Ba $_{0.55}$ K $_{0.45}$）Fe $_2$ As $_2$单晶超导转变温度和上临界场的影响。所有的转变温度随压力几乎呈线性下降。在压力下，（Ba $_{0.55}$ K $_{0.45}$）Fe $_2$的上临界场曲线$H_{c2}(T)$随着温度下降而跟随零场$T_c$，斜率变化很小。复合$P - T$相图的三个母体化合物，AFe $_2$作为$_2$（A = Ba，Sr，Ca），构建和似乎是非常相似的：（i）具有结构（反铁磁）相变线与负斜率和（ii）显示出新兴的超导状态的迹象，在中压。
Transport and anisotropy in single-crystalline SrFe$_2$As$_2$ and $A_{0.6}$K$_{0.4}$Fe$_2$As$_2$ ($A$ = Sr, Ba) superconductors
我们用助熔剂法成功地生长了高质量的SrFe $_2$ As $_2$和A $_{0.6}$ K $_{0.4}$ Fe $_2$ As $_2$（A=Sr，Ba）单晶。测量了电阻率、比热容和霍尔系数。对于母体化合物SrFe $_2$ As $_2$，在低温下获得$ρ_c$ / $ρ_{ab}$高达130的各向异性电阻率。在200 K以下，由于SDW的不稳定性，观察到面内和面外电阻率的急剧下降。面内磁电阻的角度依赖性在低于SDW转变温度的ab平面内与场旋转呈现2重对称性。这与SDW态中的条纹型自旋有序相一致。在K掺杂的A $_{0.6}$ K $_{0.4}$ Fe $_2$ As $_2$（A= Sr. Ba）中，SDW不稳定性被抑制，在35 K以上出现超导电性，T $_c$。H $\parallel$ ab和H $\parallel$ c的上临界场各向异性很小，表明面间耦合在空穴掺杂铁基超导体中起着重要作用。
Effect of Uniaxial Stress for Pressure-Induced Superconductor SrFe_2As_2
我们报道了单晶SrFe $_2$ As $_2$的压温相图容易受到传压介质流体静力学的影响。对于我们使用的所有三种介质，超导性与零电阻出现，伴随着反铁磁（正交）相的抑制，但临界压力$P_c$被发现依赖于介质的类型。在几乎流体静力学条件下，$P_c$估计为4.4 GPa，但使用在室温下已经固化的介质，其降低至$3.4-3.7$ GPa。建议沿c轴的单轴应力有助于抑制反铁磁（正交）相。本文还报道了BaFe $_2$ As $_2$的压力效应。
Measurement of the c-axis optical reflectance of AFe$_2$As$_2$ (A=Ba, Sr) single crystals: Evidence of different mechanisms for the formation of two energy gaps
本文测量了FeAs基超导体的母体化合物BaFe $_2$ As $_2$和SrFe $_2$ As $_2$的c轴光学反射率。与在SDW态中观察到两个不同能隙的ab平面光学响应不同，\textbf{E} $\parallel$ c轴只能清楚地看到较小的能隙。对于\textbf{E} $\parallel$ ab-平面，在较高能量标度下看到的非常明显的能隙结构几乎不可见。我们提出了一个新的图片的能带结构演变跨越SDW过渡，并提出了不同的驱动机制形成的两个能隙。
Pairing Symmetry Crossover from $d$-wave to $s_{\pm}$-wave in a Bilayer Nickelate Driven by Hund's Coupling and Crystal Field Splitting
School of Physics and Astronomy, Beijing Normal University（北京师范大学物理学院）；Key Laboratory of Multiscale Spin Physics (Ministry of Education), Beijing Normal University（北京师范大学多尺度自旋物理教育部重点实验室）
Probing magnetic anisotropy and spin-reorientation transition in 3D antiferromagnet, Ho$_{0.5}$Dy$_{0.5}$FeO$_{3}\vert$Pt using spin Hall magnetoresistance
