Correlation of nematic fluctuations and superconductivity with the interlayer separation in high-Tc LiPyH5FeSe

In the iron-based superconductors (FeSCs), the emergence of the electronically-driven nematic state is argued to be a precursor of superconductivity (SC). We propose to reveal signatures of such correlation-driven electronic instability in the lattice dynamics of FeSCs derived by co-intercalating alkali and molecule species (guests) in the interlayer space of the β-FeSe layered host. These intercalates demonstrate a remarkable linear scaling of the critical temperature (Tc) with the Fe-square plane separation (d). As the Fe atoms play an active role in the growth of Tc (cf., from 8 to 45 K), 57-Fe nuclear (resonance) inelastic scattering (NIS) spectroscopy is sought to deliver the Fe-partial phonon density of states (pDOS) across Tc. Uncovering the renormalization of excitations due of the coupling of electronic to lattice degrees of freedom, will add knowledge on interactions required to delineate high-Tc SC in Fe-based phases.