Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K

TL;DR

This study investigates how intercalation with Li/NH3 affects the hyperfine parameters of Fe in FeSe superconductors, revealing a link between charge transfer, hyperfine parameters, and increased critical temperature up to 42 K.

Contribution

It provides new insights into the relationship between intercalation, hyperfine parameters, and superconducting transition temperature in FeSe.

Findings

Intercalation increases the isomer shift due to charge transfer.

Hyperfine parameters correlate with Tc in FeSe phases.

Li+ ion diffusion affects quadrupole splitting at high temperatures.

Abstract

57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate product and a subsequent sample of this intercalate treated with moist He gas have been measured in temperature range 4.7 - 290 K. A correlation is established between hyperfine parameters and critical temperature Tc in these phases. A strong increase of isomer shift upon intercalation is explained by a charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an increase of Tc up to 42 K. A significant decrease of the quadrupole splitting above 240 K has been attributed to diffusive motion of Li+ ions within the interlamellar space.