标题： 超导体$Li_{1.0}(C_5H_5N)_yFe_{2-z}Se_2$中由插层驱动的掺杂所介导的局部结构和声子态 显示英文标题

标题： Local structure and phonon states mediated by intercalation-driven doping in superconducting $Li_{1.0}(C_5H_5N)_yFe_{2-z}Se_2$

摘要： 二维（2D）铁硫属化合物与分子物种的插层需要解开电子和结构贡献，以理解在长层间距离前沿超导转变温度（$T_c$）的神秘限制。 在此，同步辐射X射线吸收谱（XAS）在硒K边缘揭示了载流子掺杂对高-$T_c$（~39 K）$Li_{1.0}(C_5H_5N)_yFe_{2-z}Se_2$相局部结构的影响。 这种材料是通过退火结构相关的原位衍生物（$T_c$~ 44 K）得到的，层间由[碱金属分子]客体隔开。 诸如硒$4p$轨道填充减少和退火相中Fe-Se键缩短等指标，证实了与原位材料相比，退火相的电子掺杂水平较低。 基于关联德拜模型的金属-配体热运动分析，进一步将较高的$T_c$插层与局部Fe-Se键的软化联系起来。 除了电子效应之外，插层带来了宿主-客体相互作用，这些相互作用调节了体晶体结构的动力学。 为此，对退火衍生物进行中子飞行时间谱学研究，证实了Se-Fe-Se层对受限有机客体施加的化学压力效应敏感。 这反映在声子态密度中，与原始无机（$\beta$-FeSe）和有机（$C_5D_5N$）对应物相比，观察到了更硬的低能横向声学基质声子和分子振动。在通过$T_c$冷却时，这些激发没有集体磁共振模式——这是非常规自旋介导机制中的关键因素——引起了对最佳掺杂偏离的质疑。这项工作强调，当铁方形平面被调得较远时，通过插层实现的载流子掺杂在$T_c$参数化中起着关键作用。 显示英文摘要

摘要： Intercalation of two-dimensional (2D) iron chalcogenides with molecular species requires disentangling electronic and structural contributions to understand the puzzling limit to superconducting transition temperature ($T_c$) at the frontier of long interlayer separations. Here, synchrotron X-ray absorption spectroscopy (XAS) at the Se K-edge sheds light on the impact of carrier-doping on the local structure of the high-$T_c$ (~39 K) $Li_{1.0}(C_5H_5N)_yFe_{2-z}Se_2$ phase. This material is derived by annealing the structurally related as-made derivative ($T_c$~ 44 K), with layers being primed apart by [alkali-molecule] guests. Metrics, such as, a reduced filling of Se $4p$ orbitals and shorter Fe-Se bonds in the annealed phase, corroborate to a lower electron doping level with respect to the as-made one. Analysis of the metal-ligand thermal motion, based on the correlated Debye model, further relates the higher $T_c$ intercalates with the softening of the local Fe-Se bond. Beyond electronic effects, intercalation brings forth host-guest interactions that mediate the dynamics of the bulk crystal structure. For this, neutron time-of-flight spectroscopy on the annealed derivative, corroborates to the Se-Fe-Se layer being sensitive to chemical pressure effects imposed by the confined organic guests. This reflects in the phonon density of states, where harder low-energy transverse acoustic matrix phonons and molecular vibrations are witnessed, with respect to the pristine inorganic ($\beta$-FeSe) and organic ($C_5D_5N$) counterparts. On cooling through $T_c$, these excitations arrive without a collective magnetic-resonance mode - essential in unconventional, spin-mediated mechanisms - enquiring about deviations from optimal doping. The work highlights that when the Fe-square planes are tuned far apart, carrier-doping leveraged by intercalation plays a key role in the $T_c$ parametrization.