Superconductivity and Phase Diagram in (Li$_{0.8}$Fe$_{0.2}$)OHFeSe$_{1-x}$S$_x$

TL;DR

This study explores how sulfur substitution affects superconductivity and magnetic properties in (Li$_{0.8}$Fe$_{0.2}$)OHFeSe$_{1-x}$S$_x$, revealing a suppression of T$_c$ with S doping and unique structural dependencies.

Contribution

The paper provides the first detailed phase diagram of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe$_{1-x}$S$_x$ and investigates the effects of S doping on its superconducting and magnetic properties.

Findings

Superconductivity is suppressed with increasing S content.

Antiferromagnetism coexists with superconductivity across doping levels.

T$_c$ vanishes at x=0.90 due to chemical pressure effects.

Abstract

A series of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe$_{1-x}$S$_x$ (0 $\leq$ x $\leq$ 1) samples were successfully synthesized via hydrothermal reaction method and the phase diagram is established. Magnetic susceptibility suggests that an antiferromagnetism arising from (Li$_{0.8}$Fe$_{0.2}$)OH layers coexists with superconductivity, and the antiferromagnetic transition temperature nearly remains constant for various S doping levels. In addition, the lattice parameters of the both a and c axes decrease and the superconducting transition temperature T$_c$ is gradually suppressed with the substitution of S for Se, and eventually superconductivity vanishes at $x$ = 0.90. The decrease of T$_c$ could be attributed to the effect of chemical pressure induced by the smaller ionic size of S relative to that of Se, being consistent with the effect of hydrostatic pressure on (Li$_{0.8}$Fe$_{0.2}$)OHFeSe. But the detailed investigation on the relationships between $T_{\rm c}$ and the crystallographic facts suggests a very different dependence of $T_{\rm c}$ on anion height from the Fe2 layer or $Ch$-Fe2-$Ch$ angle from those in FeAs-based superconductors.