Unconventional Superconductivity and Moderate Spin Fluctuations with Gap at Low Energies in Intercalated Iron Selenide Superconductor Li_x(NH₃)_yFe_2−δSe₂ Probed by ⁷⁷Se NMR

75As NMR studies on iron-based La1111 superconductors in lightly and heavily electron doped states

“…Although the types of AFMSFs is different in doping levels, it is suggested that the spin fluctuations may play an indispensable role on the La1111-based compounds in wide electron-doping regimes. Recently, the similar spin fluctuations suppressed moderately at low-energies was reported in the HED state of the intercalated FeSe-based compounds [16]. Toward understanding of the SC mechanism over various Fe-based families, further spectroscopic experiments across the Fe-based compound families should be performed to clarify possible roles of nematic fluctuations due to the orbital degrees in the future.…”

“…Here, the subtle variation in 75 ν Q for x ≥ 0.3 is owing to that in h P n [6]. Figure 1 (c) shows the temperature(T ) dependences of K. The monotonic decrease of K upon cooling is observed in these compounds, which is universally seen in many electron-doped Fe-based systems, not only in La1111 compounds but also in FeSe-based compounds [16]. Figure 1(d) shows the T dependence of (1/T 1 T ) in these samples, which also exhibits the decrease from high temperatures to low temperatures.…”