New Alkali-Metal- and 2-Phenethylamine-Intercalated Superconductors $A_x$(C$_8$H$_{11}$N)$_y$Fe$_{1-z}$Se ($A$ = Li, Na) with the Largest Interlayer Spacings and $T_\mathrm{c}$ $\sim$ 40 K
New FeSe-based intercalation superconductors, $A_x$(C$_8$H$_{11}$N)$_y$Fe$_{1-z}$Se ($A$ = Li, Na), with $T_\mathrm{c}$ = 39-44 K have been successfully synthesized via the intercalation of alkali metals and 2-phenethylamine into FeSe. The interlayer spacings, namely, the distances between neighboring Fe layers, $d$, of $A_x$(C$_8$H$_{11}$N)$_y$Fe$_{1-z}$Se ($A$ = Li, Na) are 19.04(6) and 18.0(1) Å, respectively. These $d$ values are the largest among those of the FeSe-based intercalation compounds and are understood to be due to the intercalation of two molecules of 2-phenethylamine in series perpendicular to the FeSe layers. It appears that the relationship between $T_\mathrm{c}$ and $d$ in the FeSe-based intercalation superconductors is not domic but $T_\mathrm{c}$ is saturated at ~ 45 K, which is comparable to the $T_\mathrm{c}$ values of single-layer FeSe films, for $d$ $\geq$ 9 Å.
Magnetic phase separation and superfluid density measurements in alkali metal-organic solvent intercalated iron selenide superconductor Lix(C5H5N)yFe2-zSe2
Elucidating the magnetic and superconducting phases in the alkali metal intercalated iron chalcogenides
复杂的叉指相极大地挫败了试图记录碱金属插层铁硫属化合物中超导性的基本特征的尝试。在这里，使用弹性中子散射，能量色散X射线光谱，和电阻率测量，我们阐明这些阶段的关系Rb $_{1-δ}$ Fe $_y$ Se $_{2-z}$ S $_z$。我们发现：i）铁含量在稳定具有菱形铁空位有序的条纹反铁磁（AF）相方面是关键的（$y\approx1.5$），具有$\sqrt{5}\times \sqrt{5}$铁空位顺序的块AF相（$y\approx1.6$）和无铁空位相（$y\approx2$）;（二）超导相（$z=0$）演变成具有硫取代的金属相（$z>1.5$），这是由于电子相关强度的逐渐降低。条AF相和块AF相都是莫特绝缘体。我们的数据表明，这三个阶段之间存在可扩展性差距。铁含量中存在的溶解间隙是理解这些复杂相之间关系的关键。
Unified picture of the doping dependence of superconducting transition temperatures in alkali metal/ammonia intercalated FeSe
在最近合成的Li $_x$（NH $_2$）$_y$（NH $_3$）$_z$ Fe $_2$ Se $_2$家族的铁硫属化物中，由锂离子、氨基锂和氨组成的分子间隔物分隔FeSe层。已经表明，在间隔层的化学成分变化时，超导转变温度可以达到$T_c\sim 44 \mathrm{K}$，但是层分离和有效掺杂对$T_c$增强的相对重要性目前尚不清楚。使用国家的最先进的能带结构展开技术，我们构建八轨道模型从头计算密度泛函理论计算这些材料。在RPA自旋涨落的方法，我们表明，电子掺杂增强的超导配对，这是$s_\pm$对称性和解释实验观察到的限制$T_c$在分子间隔插入FeSe类材料。
The iron chalcogenides FeSe and FeS are superconductors composed of two-dimensional sheets held together by van der Waals interactions, which makes them prime candidates for the intercalation of various guest species. We review the intercalation chemistry of FeSe and FeS superconductors and discuss their synthesis, structure, and physical properties. Before we review the latest work in this area, we provide a brief background on the intercalation chemistry of other inorganic materials that exhibit enhanced superconducting properties upon intercalation, which include the transition metal dichal…
The weak van der Waals interlayer interactions in the transition metal dichalcogenide (TMD) materials have created a rich platform to study their exotic electronic properties through chemical doping or physical gating techniques. We reported bulk superconductivity up to 7.6 K through careful manipulation of the charge carrier density and interlayer spacing d in the chemically intercalated two dimensional 1T-SnSe2 phase. We found, for the first time in the two dimensional SnSe2, that polar organic molecules cointercalated with the alkali metal Li into the basal layers, thus significantly enhanc…
Inspired by naturally occurring sulfide minerals, we present a new family of iron-based superconductors. A metastable form of FeS known as the mineral mackinawite forms two-dimensional sheets that can be readily intercalated by various cationic guest species. Under hydrothermal conditions using alkali metal hydroxides, we prepare three different cation and metal hydroxide-intercalated FeS phases including (Li$_{1-x}$Fe$_x$OH)FeS, [(Na$_{1-x}$Fe$_x$)(OH)$_2$]FeS, and K$_x$Fe$_{2-y}$S$_2$. Upon successful intercalation of the FeS layer, the superconducting critical temperature $T_c$ of mackinawi…
This study examines the potential of superconductivity in transition metal (TM) intercalated bilayer graphene through a systematic study of the electronic and magnetic properties. We determine the electronic structure for all first row TM elements in the stable honeycomb configuration between two layers of graphene using density functional theory (DFT). Through an analysis of the electron density, we assess the induction of the magnetic moment in each case, where a comparison of the ferromagnetic and antiferromagnetic configurations allow us to ascertain an estimated exchange coupling between …
Bulk FeSe becomes superconducting below 9\,K, but the critical temperature (T$_{c}$) is enhanced almost universally by a factor of $\sim$4-5 when it is intercalated with alkali elements. How intercalation modifies the structure is known from in-situ X-ray and neutron scattering techniques, but why T$_{c}$ changes so dramatically is not known. Here we show that there is one-to-one correspondence between the enhancement in magnetic instabilities at certain $\bf q$ vectors and superconducting pairing vertex, even while the nuclear spin relaxation rate ${1}/{(T_{1}T)}$ may not reflect this enhance…
Layered platinum tellurium (PtTe2) was recently synthesized with controllable layer numbers down to a monolayer limit. Using ab initio calculations based on anisotropic Midgal-Eliashberg formalism, we show that by rubidium (Rb) intercalation, weak superconductivity in bilayer PtTe2 can be significantly boosted with superconducting Tc = 8 K in the presence of spin-orbit coupling (SOC). The intercalant on one hand mediates the interlayer coupling and serves as an electron donor, leading to large density of states at Fermi energy. On the other hand, it increases the mass-enhancement parameter wit…
