New Superconducting Phase of Li$_x$(C$_6$H$_{16}$N$_2$)$_y$Fe$_{2-z}$Se$_2$ with $T_\textrm{c}$ = 41 K Obtained through the Post-Annealing

TL;DR

This study reveals a new superconducting phase of Li-intercalated FeSe with a transition temperature of 41 K, achieved through post-annealing that modifies the interlayer spacing and stabilizes a different intercalation structure.

Contribution

It demonstrates the stabilization of a new superconducting phase with higher Tc via post-annealing, highlighting the relationship between interlayer spacing and superconductivity in FeSe-based intercalates.

Findings

New phase with d=10.30 Å and Tc=41 K stabilized

Interlayer spacing reduction correlates with Tc increase

Post-annealing induces structural changes enhancing superconductivity

Abstract

Post-annealing effects on the crystal structure and superconductivity of the lithium- and hexamethylenediamine (HMDA)-intercalated superconductor Lix(C6H16N2)yFe2-zSe2 have been investigated. Through the post-annealing, a two-step reduction of the interlayer spacing between neighboring Fe layers, d, has been observed. It has been found that a new phase of Lix(C6H16N2)yFe2-zSe2 with d= 10.30(2) {\AA} and Tc = 41 K different from the as-intercalated phase is stabilized owing to the possible stable inclination of HMDA intercalated between FeSe layers. This result supports the domic relation between Tc and d in the FeSe-based intercalation superconductors. The reason why Tc increases with a decrease in d through the post-annealing is discussed.