Superconductivity and Intercalation Statein the Lithium-Hexamethylenediamine-Intercalated Superconductor Li$_x$(C$_6$H$_{16}$N$_2$)$_y$Fe$_{2-z}$Se$_2$: Dependence on the Intercalation Temperature and Lithium Content

TL;DR

This study explores how intercalation temperature and lithium content affect superconductivity and intercalation states in Li$_x$(C$_6$H$_{16}$N$_2$)$_y$Fe$_{2-z}$Se$_2$, revealing diffusion behaviors and Tc variations.

Contribution

It provides new insights into the diffusion mechanisms and superconducting properties of lithium and HMDA intercalated FeSe, depending on intercalation temperature.

Findings

Li and HMDA co-intercalate stably up to x=2.

Higher intercalation temperature promotes diffusion into FeSe crystals.

Superconducting transition temperature increases with lithium content at higher temperature.

Abstract

The superconductivity and intercalation statein the lithium-and hexamethylenediamine (HMDA)-intercalated superconductor Li$_x$(C$_6$H$_{16}$N$_2$)$_y$Fe$_{2-z}$Se$_2$ have been investigated from powder x-ray diffraction, thermogravimetric and magnetic susceptibility measurements, changing the intercalation temperature, $T_i$, and the Li content, $x$. Both Li and HMDA have been co-intercalated stably up to $x$ = 2 roughly in the molar ratio of $x : y = 2 : 1$. In the case of $T_i$ = 45$^\circ$C, it has been found that both Li and HMDA are co-intercalated locally at the edge of FeSe crystals, indicating that both Li and HMDA are hard to diffuse into the inside of FeSe crystals at 45$^\circ$C. In the case of $T_i$ = 100$^\circ$C, on the other hand, it has been found that both Li and HMDA diffuse into the inside of FeSe crystals, so that $T_c$ tends to increase with increasing $x$ from ~30 K at $x$ = 1 up to 38 K at $x$ = 2 owing to the increase of electron carriers doped from Li into the FeSe layers.