Disorder-driven electronic localization and phase separation in superconducting Fe1+yTe0.5Se0.5 single crystals

TL;DR

This study explores how excess iron in Fe1+yTe0.5Se0.5 crystals affects their superconductivity, magnetism, and electronic localization, revealing disorder-driven phase separation and suppression of superconductivity due to magnetic interactions.

Contribution

It demonstrates the impact of Fe-excess on superconductivity and electronic localization, highlighting disorder-driven phase separation in Fe1+yTe0.5Se0.5 crystals.

Findings

Fe-excess suppresses superconductivity.

Inhomogeneous superconducting state observed.

Disorder-driven electronic localization indicated by resistivity divergence.

Abstract

We have investigated the influence of Fe-excess on the electrical transport and magnetism of Fe1+yTe0.5Se0.5 (y=0.04 and 0.09) single crystals. Both compositions exhibit resistively determined superconducting transitions (Tc) with an onset temperature of about 15 K. From the width of the superconducting transition and the magnitude of the lower critical field Hc1, it is inferred that excess of Fe suppresses superconductivity. The linear and non-linear responses of the ac-susceptibility show that the superconducting state for these compositions is inhomogeneous. A possible origin of this phase separation is a magnetic coupling between Fe-excess occupying interstitial sites in the chalcogen planes and those in the Fe-square lattice. The temperature derivative of the resistivity drho/dT in the temperature range Tc < T < Ta with Ta being the temperature of a magnetic anomaly, changes from positive to negative with increasing Fe. A log 1/T divergence of the resistivity above Tc in the sample with higher amount of Fe suggests a disorder driven electronic localization.