Bulk FeSe becomes superconducting below 9 K, but the critical temperature (T_c) is enhanced almost universally by a factor of ~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 q vectors and superconducting pairing vertex, even while the nuclear spin relaxation rate 1/(T₁T) may not reflect this enhancement. Intercalation modifies electronic screening both in the plane and also between layers. We disentangle quantitatively how superconducting pairing vertex gains from each such changes in electronic screening. Intercalated FeSe provides an archetypal example of superconductivity where information derived from the single-particle electronic structure appears to be insufficient to account for the origins of superconductivity, even when they are computed including correlation effects. We show that the five-fold enhancement in T_c on intercalation is not sensitive to the exact position of the d_xy at Γ point, as long as it stays close to E_F. Finally, we show that intercalation also significantly softens the collective charge excitations, suggesting the electron-phonon interaction could play some role in intercalated FeSe.

块状 FeSe 在 9 K 以下变得超导，但当它与碱金属元素插层时，临界温度 ( T _c ) 几乎普遍提高了约 4-5 倍。从原位 X 射线和中子散射技术可知插层如何改变结构，但尚不清楚为什么Tc_{会发生如此显着的变化。}在这里，我们表明即使核自旋弛豫率 1/ ( T ₁ T) 可能无法反映此增强功能。插层改变平面内和层间的电子屏蔽。我们定量分析了超导配对顶点如何从电子屏蔽中的每个此类变化中获益。插层 FeSe 提供了超导性的一个典型例子，其中来自单粒子电子结构的信息似乎不足以解释超导性的起源，即使计算它们包括相关效应也是如此。我们表明，插入时T _c的五倍增强对 Γ 点的 d _{x y}的确切位置不敏感，只要它保持接近E _F. 最后，我们表明嵌入也显着软化了集体电荷激发，表明电子-声子相互作用可能在嵌入的 FeSe 中发挥一定作用。