Effect of Fe excess on structural, magnetic and superconducting properties of single-crystalline Fe(1+x)Te(1-y)Se(y)

TL;DR

This study explores how excess iron and selenium doping influence the structural, magnetic, and superconducting properties of Fe(1+x)Te(1-y)Se(y) single crystals, revealing how these factors drive the material into different ground states.

Contribution

It provides a systematic analysis of how Fe excess and Se doping affect the phase diagram and ground states of Fe(1+x)Te(1-y)Se(y) crystals, highlighting the role of Fe site occupation.

Findings

Fe excess enhances spin localization.

Reducing Fe excess weakens antiferromagnetism and promotes superconductivity.

Se doping and Fe excess together shape the phase diagram.

Abstract

Single crystals of Fe(1+x)Te(1-y)Se(y) have been grown with a controlled Fe excess and Se doping, and the crystal structure has been refined for various compositions. The systematic investigation of magnetic and superconducting properties as a function of the structural parameters shows how the material can be driven into various ground states, depending on doping and the structural modifications. Our results prove that the occupation of the additional Fe site, Fe2, enhances the spin localization. By reducing the excess Fe, the antiferromagnetic ordering is weakened, and the superconducting ground state is favored. We have found that both Fe excess and Se doping in synergy determine the properties of the material and an improved 3-dimensional phase diagram is proposed.