The superconducting series, Fe(Te,Se), has a complex structural and magnetic phase diagram that is dependent on composition and occupancy of a secondary interstitial Fe site. In this letter, we show that superconductivity in Fe1+xTe0.7Se0.3 can be enhanced by topotactic deintercalation of the interstitial iron, demonstrating the competing roles of the two iron sites. Neutron diffraction reveals a flattening of the Fe(Te,Se)4 tetrahedron on Fe removal of iron and an increase in negative thermal expansion within the ab plane that correlates with increased lattice strain. Inelastic neutron scattering shows that a gapped excitation at 6 meV, evolves into gapless paramagnetic scattering with increasing iron; similar to the fluctuations observed for non-superconducting Fe1+xTe itself.
Interstitial oxygen order and its competition with superconductivity in La$_2$PrNi$_2$O$_{7+δ}$
Tsinghua University（清华大学）；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）；New Cornerstone Science Laboratory（新 cornerstones 科学实验室）；Hefei National Laboratory（合肥国家实验室）
Ordering of Interstitial Iron Atoms and Local Structural Distortion Induced by Iron Polycomplex in Fe1+yTe1-xSex as Seen via Transmission Electron Microscopy
Inelastic neutron scattering was performed for an iron-based superconductor LaFeAsO0.9D0.1, where most of D (deuterium) replaces oxygen, while a tiny amount goes into interstitial sites. By first-principle calculation, we characterize the interstitial sites for D (and for H slightly mixed) with four equivalent potential minima. Below the superconducting transition temperature Tc = 26 K,new excitations emerge in the range 5-15 meV, while they are absent in the reference system LaFeAsO0.9F0.1. The strong excitations at 14.5 meV and 11.1 meV broaden rapidly around 15 K and 20 K, respectively, whe…
In this editorial, we first give a brief survey of the field of iron-selenide superconductivity, both in the case of bulk FeSe characterized by the co-existence of superconductivity and nematic order, and in the case of electron-doped FeSe characterized by high-temperature superconductivity. We next review the 8 contributions to the Frontiers in Physics research topic "High-Tc Superconductivity in Electron-Doped Iron Selenide and Related Compounds".
Superconductivity mediated by the antiferromagnetic spin-wave in chalcogenide iron-base superconductors
K $_{0.8+x}$ Fe $_{1.6+y}$ Se $_2$等铁基硒化物超导体的基态都是掺杂反铁磁半导体。在这些材料中，存在定义明确的铁局域矩，其能量与传导电子的能量通过大的带隙分开。我们建议，该系统的低能物理是由一个模型的相互作用的电子与现场铁磁交换相互作用和站点间的超交换相互作用的哈密顿量。我们在线性自旋波近似下导出了电子的有效配对势，并证明了这些材料中的超导性可以通过介导相干自旋波激发来驱动。我们的工作为中子散射和其他实验观察到的超导和反铁磁长程序共存提供了一个自然的解释。
The iron-based superconductor FeTe$_{1-x}$Se$_{x}$ has attracted considerable attention as a candidate topological superconductor owing to a unique combination of topological surface states and bulk high-temperature superconductivity. The superconducting properties of as-grown single crystals, however, are highly variable and synthesis dependent due to excess interstitial iron impurities incorporated during growth. Here we report a novel physicochemical process for pumping this interstitial iron out of the FeTe$_{1-x}$Se$_{x}$ matrix and achieving bulk superconductivity. Our method should have…
We report on the discovery, structural analysis, and the physical properties of Nb$_4$SiSb$_2$ -- a hitherto unknown compound crystallizing in the V$_4$SiSb$_2$-type structure with the tetragonal space group $I4/mcm$ and unit cell parameters $a$ = 10.3638(2) $\mathring{\mathrm{A}}$ and $c$ = 4.9151(2) $\mathring{\mathrm{A}}$. We find Nb$_4$SiSb$_2$ to be a metal undergoing a transition to a superconducting state at a critical temperature of $T_{\rm c} \approx$ 1.6 K. The bulk nature of the superconductivity in this material is confirmed by the observation of a well defined discontinuity in spe…
Unconventional superconductivity in the layered iron germanide YFe$_2$Ge$_2$
自从2006年在LaFePO中发现超导性以来，已经在不同的结构家族中鉴定出许多铁基超导体，所有这些都将铁与V族（磷属元素）或VI族（硫属元素）元素结合。非常规的超导性在这些层状铁系统和铜酸盐之外的过渡金属化合物中是极其罕见的，并且它几乎普遍与高度各向异性的电子性质和接近2D的费米表面几何形状相关联。铁基金属间化合物YFe $_2$ Ge $_2$具有3D费米面和强烈增强的低温热容，这表明强的电子相关性。我们目前的数据从新一代的高品质样品的YFe $_2$锗$_2$，这表明超导转变异常低于1.8 K的热力学以及运输测量，建立超导性是内在的，在这个层状铁化合物以外的已知的超导铁磷属元素化物或硫属元素化物家庭。YFe $_2$ Ge $_2$的费米面几何形状类似于KFe $_2$ As $_2$在高压下坍缩的四方相的费米面几何形状，其中最近报道了在高达10 K的温度下的超导性，这表明两个系统之间的潜在联系。
We report a comprehensive study of the Zr$_5$Pt$_3$C$_x$ superconductors, with interstitial carbon comprised between 0 and 0.3. At a macroscopic level, their superconductivity, with $T_c$ ranging from 4.5 to 6.3 K, was investigated via electrical-resistivity-, magnetic-susceptibility-, and specific-heat measurements. The upper critical fields $μ_0H_\mathrm{c2}$ $\sim$ 7 T were determined mostly from measurements of the electrical resistivity in applied magnetic fields. The microscopic electronic properties were investigated by means of muon-spin rotation and relaxation ($μ$SR) and nuclear magn…
We study the superconducting instability mediated by spin fluctuations in the Eliashberg theory for a minimal two-band model of iron-based superconductors. While antiferromagnetic spin fluctuations can drive superconductivity (SC) as is well established, we find that spin fluctuations necessarily contain a contribution to suppress SC even though SC can eventually occur at lower temperatures. This self-restraint effect stems from a general feature of the spin-fluctuation mechanism, namely the repulsive pairing interaction, which leads to phase frustration of the pairing gap and consequently the…
Electrides are unique compounds where most of the electrons reside at interstitial regions of the crystal behaving as anions, which strongly determines its physical properties. Interestingly, the magnitude and distribution of interstitial electrons can be effectively modified either by modulating its chemical composition or external conditions (e.g. pressure). Most of the electrides under high pressure are non-metallic, and superconducting electrides are very rare. In this work we report that a pressure-induced stable Li6P electride becomes superconductor with a Tc of 39.3 K, which is the high…
We establish quasi-two-dimensional thin films of iron-based superconductors (FeSCs) as a new high-temperature platform for hosting intrinsic time-reversal-invariant helical topological superconductivity (TSC). Based on the combination of Dirac surface state and bulk extended $s$-wave pairing, our theory should be directly applicable to a large class of experimentally established FeSCs, opening a new TSC paradigm. In particular, an applied electric field serves as a "topological switch" for helical Majorana edge modes in FeSC thin films, allowing for an experimentally feasible design of gate-co…
Angle-Resolved Photoemission Spectroscopy of Iron-Chalcogenide Superconductor Fe1.03Te0.7Se0.3 : Strong-Coupling Superconductivity and Universality of Inter-Band Scattering
Influence of interstitial Fe to the phase diagram of Fe$_{1+y}$Te$_{1-x}$Se$_x$ single crystals
在铁基和铜酸盐超导体的母体化合物中观察到具有长程反铁磁有序抑制的超导电性。与大多数铁磷族化合物的共线原子力显微镜序（$π$，$π$）不同，母体化合物FeTe的原子力显微镜波矢是双共线的（$π$，0）。Fe $_{1+y}$ Te $_{1-x}$ Se $_x$相图的研究是研究双共线AFM与SC竞争的最直接的方法，但间隙Fe的存在影响了Fe $_{1+y}$ Te $_{1-x}$ Se $_x$的磁性和SC，从而阻碍了真实相图的建立。在这里，我们报告的掺杂温度（$x$ - $T$）相图的Fe $_{1+y}$ Te $_{1-x}$ Se $_x$（0 $\leq$ $x$ $\leq$ 0.43）单晶去除间隙Fe之前和之后的比较。在没有间隙Fe的情况下，AFM状态仅在$x$ $<$ 0.05时存在，并且从$x$ = 0.05出现体SC，并且不与AFM状态共存。先前报道的自旋玻璃态，以及AFM和SC的共存可能源于间隙Fe的影响。Fe $_{1+y}$ Te $_{1-x}$ Se $_x$的相图与LaFeAsO $_{1-x}$ F $_x$等“1111”体系的相图相似，而与“122”体系的相图不同。
Superconductivity tuned by the iron vacancy order in K$_{\bf x}$Fe$_{\bf 2-y}$Se$_2$
结合深入的中子衍射和系统的整体研究，我们发现，$\sqrt{5}\times\sqrt{5}$ Fe空位顺序与其相关的块反铁磁顺序是基态，与不同的占有率的铁16 i和空位4d网站，整个相图的K $_{\bf x}$ Fe $_{\bf 2-y}$ Se $_2$。的正交顺序与四个Fe网站之一的空缺出现在中间温度作为竞争相。当$\sqrt{5}\times\sqrt{5}$顺序高度发展时，材料经历绝缘体到金属的交叉。超导性发生在这样的金属相中。
High-temperature iron-based superconductivity develops in a structure with unusual lattice-orbital geometry, based on a planar layer of Fe atoms with 3d orbitals and tetrahedrally coordinated by anions. Here we elucidate the electronic role of anions in the iron-based superconductors utilizing state-of-the-art scanning tunneling microscopy. By measuring the local electronic structure, we find that As anion in Ba0.4K0.6Fe2As2 has a striking impact on the electron pairing. The superconducting electronic feature can be switched off/on by removing/restoring As atoms on Fe layer at the atomic scale…
