We investigated chemical pressure effects in electron-doped (e-doped) FeSe by fabricating an electric-double-layer structure with single crystalline FeSe films on LaAlO$_3$ with Se substituted by isovalent Te and S. Our method enables transport measurements of e-doped FeSe. Electron doping by applying gate voltage of 5 V increases $T_{\mathrm c}$ of the FeSe$_{1-x}$Te$_x$ and FeSe$_{1-y}$S$_y$ films with $0 \leq x \leq 0.4$ and $0 \leq y \leq 0.25$, while the e-doped $x=0.5$ film showed lower $T_{\mathrm c}$ than that of the undoped one. Both positive and chemical pressure suppress $T_{\mathrm c}$ of the e-doped FeSe. The obtained superconducting phase diagram in the e-doped samples is rather different from that in undoped samples. This might suggest that the superconductivity mechanism is different between undoped and e-doped systems. Alternatively, this is possibly explained by the absence of the nematic order in e-doped samples.
The strong fascination exerted by the binary compound of FeSe demands reliable engineering protocols and more effective approaches towards inducing superconductivity in FeSe thin films. Our study addresses the peculiarities in pulsed laser deposition which determine FeSe thin film growth and focuses on the film/substrate interface, the tendency for domain matching epitaxial growth but also the disadvantage of chemical heterogeneity. We propose that homogenization of the substrate surface improves the control of stoichiometry, texture, and nanostrain in a way that favors superconductivity even …
Thickness dependence of superconductivity and superconductor-insulator transition in ultrathin FeSe films on SrTiO3(001) substrate
SrTiO 3（001）（STO）衬底上单胞FeSe薄膜的界面增强高温超导性是近年来凝聚态物理和材料科学研究的热点。本文利用非原位输运测量方法研究了STO衬底上不同厚度的FeSe超薄膜的超导电性。我们发现，开始超导转变温度（Tc）随FeSe薄膜厚度的增加而降低，这是在传统的超导薄膜中通常观察到的行为相反。通过对5 μ C FeSe薄膜的系统后退火，我们观察到了绝缘体到超导体的转变，根据相应的霍尔测量，在低温下伴随着占主导地位的载流子从空穴到电子的符号变化。
Superconductivity above 28 K in single unit cell FeSe films interfaced with GaO$_{2-δ}$ layer on NdGaO$_{3}$(110)
我们在以Ga O $_{2-δ}$为终端的钙钛矿型Nd Ga O $_{3}$（110）衬底上制备了单晶胞FeSe薄膜，并对FeTe保护膜进行了非原位输运和扫描透射电子显微镜测量。我们的实验测量表明，与GaO $_{2-δ}$层界面的单晶胞FeSe薄膜是通过界面电荷转移进行电子掺杂的。最重要的是，这种类型的异质结构可以主机界面增强超导性的起始温度约为28 K，这是远远高于8 K的值在体FeSe。我们的工作表明，FeSe/GaO $_{2-δ}$可以作为一个与FeSe/TiO $_{2-δ}$家族相比较的平台，用于理解界面增强高温超导性的机制。
Growth of superconducting epitaxial films of sulfur substituted FeSe via pulsed laser deposition
本文报道了用脉冲激光沉积法成功地生长了含$x \leq 0.43$的FeSe $_{1-x}$ S $_x$外延薄膜。随着S含量的增加，超导转变温度$T_{\mathrm s}$系统地降低，并且超导转变温度$T_{\mathrm c}$显示出逐渐降低，即使当$x$超过超导终点（NEP）时，类似于体样品。对于具有大$x$的膜，在$ρ$-$T$曲线中观察到新的扭结异常，这可能是由于磁性转变。FeSe $_{1-x}$ S $_x$薄膜的相图与FeSe $_{1-y}$ Te $_y$薄膜的相图相反，其显示在NEP处$T_{\mathrm c}$快速增加。结果表明，在FeSe体系中，超导电性与超有序度之间的关系并不普遍，这表明在这些材料中，超导电性与超有序度之间的关系并不是主要的.
Superconducting fluctuations in FeSe$_{0.5}$Te$_{0.5}$ thin films probed via microwave spectroscopy
我们研究了FeSe $_{0.5}$ Te $_{0.5}$在CaF $_2$上外延薄膜在超导转变附近的微波电导率谱。随着薄膜厚度的增加，我们观察到了超导涨落的临界行为，并出现了从二维到三维的空间交叉。由标度参数的温度依赖性，我们得出FeSe $_{0.5}$ Te $_{0.5}$超导转变的普适类是3D-XY模型。超导波动的起始温度的下限，Tonset，由我们的测量确定的是1.1 Tc，这表明FeSe $_{0.5}$ Te $_{0.5}$的超导波动至少与最佳和过掺杂的铜酸盐一样大。
Structural and electronic properties of ultrathin FeSe films grown on Bi$_2$Se$_3$(0001) studied by STM/STS
本文报道了在Bi $_2$ Se $_3$（0001）衬底上生长的单晶胞和双晶胞高FeSe薄膜的扫描隧道显微镜和光谱学（STM/STS）研究。在我们的薄膜中，我们发现FeSe的四方相和沿Se-Se键方向取向的哑铃形缺陷。此外，我们观察到条纹莫尔图案的周期性（$7.3\pm 0.1$）nm之间的失配FeSe晶格和Bi $_2$ Se $_3$晶格产生的。在6.5 K下，在一个和两个UC厚的FeSe岛表面上测量的隧道谱中，我们没有发现任何超导能隙的特征。光谱，而不是显示出一个不对称的行为和有限的状态密度在费米能级（$E_F$）类似于在正常状态的散装FeSe。
Orbital superconductivity, defects and pinned nematic fluctuations in the doped iron chalcogenide FeSe$_{0.45}$Te$_{0.55}$
我们表明，差分电导，$dI/dV$，通过光谱成像扫描隧道显微镜测量的掺杂铁硫属化物FeSe $_{0.45}$ Te $_{0.55}$，具有一系列的特征，允许一个提取的超导间隙的轨道结构。这在两个类空穴费米面上产生了近各向同性的超导带隙，而在类电子费米面上产生了强各向异性的带隙。此外，我们表明，钉扎由缺陷的涨落可以引起一个哑铃状的空间结构的诱导杂质束缚态，并解释了相关的$C_2$ -对称性的傅立叶变换微分电导。
Our recent year's studies of the prototypal FeSe and molecule-intercalated (Li,Fe)OHFeSe superconductor systems are briefly reviewed here, with emphasis on experimental observations of the link between the superconductivity and normal-state electronic property in the single crystals and films. These samples were successfully synthesized by our recently developed soft-chemical hydrothermal methods, which are also briefly described. Particularly in the Mn-doped high-Tc (Li,Fe)OHFeSe film, a strong enhancement of the superconducting critical current density was achieved, which is promising for pr…
Universal Substrate Effect on the Superconductivity of FeSe Monolayer Films
为了阐明单层（1 ML）FeSe在SrTiO $_3$（STO）上的$T_c$增强的机制，我们在金红石TiO $_2$的矩形（100）面上生长了高应变的1 ML FeSe，并在63 K的$T_c$下观察到了复制带和超导电性的共存。从该系统与STO（001）上的1 ML FeSe之间的相似的$T_c$，我们得出结论，在这些系统中，应变和介电常数可能对增强的$T_c$不重要。一个系统的比较1 ML FeSe的TiO $_2$与其他系统中的FeSe家庭表明，虽然单独的电荷转移可以提高$T_c$，它只是与界面的电子-声子耦合，$T_c$可以增加到在STO上的1 ML FeSe的水平。
In this study, we fabricate 5-30-nm-thick films of FeSe/STO using pulsed laser deposition (PLD). The grown films exhibit superconductivity with an onset $T_{\mathrm{c}}$ that is much higher than that of bulk FeSe under ambient pressure. The observed $T_{\mathrm{c}}$ values are exceptionally high in terms of the strain vs. $T_{\mathrm{c}}$ relationship of the same material established so far. Furthermore, $T_{\mathrm{c}}$ increases as the film thickness decreases, except for films thinner than 10 nm. This thickness dependence of $T_{\mathrm{c}}$ is in good agreement with the results reported fo…
Muon spin rotation/relaxation measurements were performed to investigate magnetic properties of FeSe$_{1-x}$S$_x$ thin films on LaAlO$_3$. A drastic decrease of the initial asymmetry was observed together with the peak structure in the temperature dependence of the relaxation rate of muon spins almost at the same temperature where kink anomalies were observed in the temperature dependent resistivity. With increasing S content, the anomaly temperature increased and the magnetic fluctuations at the lowest temperature were suppressed. These results show that the S substitution induces magnetism a…
Suppression of phase separation and giant enhancement of superconducting transition temperature in FeSe$_{1-x}$Te$_{x}$ thin films
我们证明了成功的制造与$0 \le x \le 1$的FeSe $_{1-x}$ Te $_{x}$薄膜的CaF $_2$衬底上，包括区域的$0.1 \le x \le 0.4$，这是众所周知的“相分离区”，通过脉冲激光沉积，这是一种非平衡的方法。在由此产生的薄膜中，我们观察到一个巨大的增强的超导转变温度，$T_\mathrm{c}$，在该区域的$0.1 \le x \le 0.4$：最大值达到23 K，这是大约1.5倍大的散装样品的FeSe $_{1-x}$ Te $_{x}$报告的值。我们提出了一个完整的相图FeSe $_{1-x}$ Te $_{x}$薄膜。令人惊讶的是，在$0.1<x<0.2$处观察到$T_\mathrm{c}$的突然抑制，而对于$0.2 \le x < 1$，$T_\mathrm{c}$随着$x$的降低而增加。也就是说，在$x=0-0.1$和$x \ge 0.2$中实现的超导性之间存在明显的差异。为了获得具有高$T_\mathrm{c}$的FeSe $_{1-x}$ Te $_{x}$薄膜，发现Te含量$x$和面内晶格应变的控制是关键因素。
Systematic Comparison of Eight Substrates in the Growth of FeSe$_{0.5}$Te$_{0.5}$ Superconducting Thin Films
本文研究了在八种不同衬底上生长的FeSe $_{0.5}$ Te $_{0.5}$薄膜的晶体结构和超导性质。超导性与晶格失配无关，而是与面内取向程度和晶格参数比$c/a$相关。在MgO和LaAlOPDMATHABMO（$T_\mathrm{c}^\mathrm{zero}$为9.5 K）上的薄膜中观察到最好的超导性能。TEM观察表明，在衬底表面的非晶类层的存在或不存在起着关键作用，在确定的结构和超导性能的生长薄膜。
In-plane magnetic field effect on the neutron spin resonance in optimally doped FeSe$_{0.4}$Te$_{0.6}$ and BaFe$_{1.9}$Ni$_{0.1}$As$_{2}$ superconductors
用非弹性中子散射研究了面内磁场对最佳掺杂超导体FeSe $_{0.4}$ Te $_{0.6}$（$T_c=14$ K）和BaFe $_{1.9}$ Ni $_{0.1}$ As $_{2}$（$T_c=20$ K）的磁共振的影响.虽然高达14.5特斯拉的磁场不改变共振的能量，但它部分地抑制了$T_c$和相应的超导诱导的强度增益的模式。然而，我们没有发现直接的证据，场诱导自旋1塞曼分裂的共振。因此，仍然不清楚共振是否是长期寻求的直接耦合到超导电子库珀对的单重态-三重态激发。
