In superconductors with strong coupling between superconductivity and elasticity manifested in a strong dependence of transition temperature on pressure, there is an additional contribution to inter-vortex interactions due to the strain field generated by vortices. When vortex lines are along the $c$ axis of a tetragonal crystal, a square vortex lattice (VL) is favored at low vortex densities, because the vortex-induced strains contribution to the inter-vortex interactions is long range. At intermediate magnetic fields, the triangular lattice is stabilized. The triangular lattice evolves to the square lattice upon increasing magnetic field, and eventually the system locks to the square structure. We argue, however, that as $B$ approaches $H_{c2}$ the elastic inter-vortex interactions disappear faster than the standard London interactions, so that VL should return to the triangular structure. Our results are compared to VLs observed in the heavy fermion superconductor $\mathrm{CeCoIn_5}$.
Vortex lattice and vortex bound states in CsFe$_2$As$_2$ investigated by scanning tunneling microscopy/spectroscopy
利用扫描隧道显微镜/光谱（STM/STS）研究了不同磁场下CsFe $_2$ As $_2$单晶中的涡旋晶格和涡旋束缚态。随着磁场的增加，观察到了一种可能的涡格结构转变或交叉，即，在磁场接近0.5 T时，涡旋晶格由畸变的六角晶格转变为畸变的四角晶格。结果表明，在交叉区出现了由条形六方涡格和方形涡格组成的混合涡格。在涡心处还观察到涡束缚态。穿过涡旋的隧穿谱表明，随着STM针尖远离涡旋中心，束缚态峰位保持在零偏压附近。由涡旋束缚态能量估算的费米能很小。我们的研究为铁基超导体中的涡旋晶格和涡旋束缚态提供了实验信息。
Trends in pressure-induced layer-selective half-collapsed tetragonal phases in the iron-based superconductor family $Ae{}A$Fe$_4$As$_4$
通过对铁基超导体$Ae{}A$ Fe $_4$ As $_4$（$Ae$ = Ca，Sr，Ba，$A$ = K，Rb，Cs）的密度泛函理论进行压力模拟，我们预测在这些系统中，在压力$P_{c_1}$和$P_{c_2}$下会出现两个连续的半塌陷四元跃迁，它们对电子结构的影响具有不同的性质.我们发现，类似于以前的研究CaKFe $_4$作为$_4$，自旋涡旋磁波动的Fe亚晶格在零压力下的准确的结构预测中发挥了关键作用。我们确定了明确的趋势的临界压力，并讨论了相关的崩溃阶段连接到磁性和超导性。最后，在半塌陷相的背景下，讨论了EuRbFe $_4$ As $_4$和EuCsFe $_4$ As $_4$的有趣情况，其中Eu磁性与超导性共存。
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。
ac strain based thermodynamic criterion for vortex lattice in type-II superconductors
Chongqing University（重庆大学）；Hebei Normal University（河北师范大学）；Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；University of Science and Technology of China（中国科学技术大学）
