Spin dynamics in the expanded lattice molecule intercalated iron selenide Lix(C5D5N)yFe2-zSe2

Strongly correlated electron systems can facilitate an exotic interplay between magnetism and superconductivity, bringing them at the center of interest in the condensed matter physics community. Two-dimensional iron (Fe)-selenides display an intriguing enhancement of the superconducting transition temperature (Tc) when the Fe-square planes are spaced apart through the intercalation of electron donating species in the host FeSe lattice. Specifically, the Tc of FeSe is enhanced up to five times when large organic molecular spacers (pyridine; C5H5N) are co-intercalated with alkali metal (Li) cations in the host lattice, consequently producing a material with significant c-axis lengthening. In unconventional Fe-based systems, a spin resonance (Eres) appears below Tc as a peak in the (Q,ω) space of the inelastic neutron scattering (INS) spectra. This peak is centered at a characteristic wave-vector (Qres), which is close to the propagation vector of the antiferromagnetic correlations that border with the emerging superconducting state, thus suggesting that magnetism may couple to superconductivity. We intend to pursue INS studies to decipher the spin fluctuations in the polycrystalline Lix(C5D5N)yFe2-zSe2 (Tc~ 38 K) material by scanning the (Q,ω) space above and below Tc. The high flux capabilities of the MERLIN spectrometer will enable the assessment of the spin resonance below Tc, thus shedding light in the spin-fluctuation picture of superconductivity in high Tc materials.