Evolution of correlation strength in KxFe(2-y)Se2 superconductor doped with S

TL;DR

This study investigates how sulfur doping affects the thermal transport and electronic properties of the KxFe(2-y)Se2 superconductor, revealing a suppression of superconductivity and electronic correlations with increased sulfur content.

Contribution

It provides new insights into how sulfur substitution alters the electronic structure and correlation strength in KxFe(2-y)Se2 superconductors.

Findings

Sulfur doping suppresses superconducting transition temperature (Tc).

Seebeck coefficient and Sommerfeld coefficient decrease with sulfur content.

Electronic correlations weaken as sulfur content increases.

Abstract

We report the evolution of thermal transport properties of iron-based superconductor K$_x$Fe$_{2-y}$Se$_2$ with sulfur substitution at Se sites. Sulfur doping suppresses the superconducting $T_c$ as well as the Seebeck coefficient. The Seebeck coefficient of all crystals in the low temperature range can be described very well by diffusive thermoelectric response model. The zero-temperature extrapolated value of Seebeck coefficient divided by temperature $S/T$ gradually decreases from $-0.48 \mu V/K^2$ to a very small value $\sim$ 0.03 $\mu$V/K$^2$ where $T_c$ is completely suppressed. The normal state electron Sommerfeld term ($\gamma_n$) of specific heat also decreases with the increase of sulfur content. The dcrease of $S/T$ and $\gamma_n$ reflects a suppression of the density of states at the Fermi energy, or a change in the Fermi surface that would induce the suppression of correlation strength.