Importance of structural distortions in enhancement of transition temperature in FeSe$_{1-x}$Te$_{x}$ superconductors

TL;DR

This study investigates how structural distortions, especially variations in anion height, influence the increase in superconducting transition temperature in FeSe$_{1-x}$Te$_x$ compounds through temperature-dependent EXAFS analysis.

Contribution

It reveals the role of local distortions and anion height variations in enhancing T$_C$ in FeSe$_{1-x}$Te$_x$, highlighting the importance of Fe-chalcogen hybridization.

Findings

Local distortions are present near superconducting onset in FeSe and FeSe$_{0.5}$Te$_{0.5}$.

Anion height variations correlate with superconducting transition temperature.

Opposite behavior of $h_{Fe-Se}$ and $h_{Fe-Te}$ near T$_C$ in FeSe$_{0.5}$Te$_{0.5}$.

Abstract

Temperature (12K $\le$ T $\le$ 300K) dependent extended X-ray absorption fine structure (EXAFS) studies at the Fe K edge in FeSe$_{1-x}$Te$_x$ (x = 0, 0.5 and 1.0) compounds have been carried out to understand the reasons for increase in T$_C$ upon Te doping in FeSe. While local distortions are present near superconducting onset in FeSe and FeSe$_{0.5}$Te$_{0.5}$, they seem to be absent in non superconducting FeTe. Of crucial importance is the variation of anion height. In FeSe$_{0.5}$Te$_{0.5}$, near superconducting onset, the two heights, $h_{Fe-Se}$ and $h_{Fe-Te}$ show a nearly opposite behaviour. These changes indicate a possible correlation between Fe-chalcogen hybridization and the superconducting transition temperature in these Fe-chalcogenides.