Effects of excess Fe on upper critical field and magnetotransport in Fe1+y(Te1-xSx)z

TL;DR

This study explores how excess Fe influences the upper critical field anisotropy and magnetotransport in Fe1+y(Te1-xSx)z single crystals, revealing nearly isotropic behavior at low temperatures and the role of Fe as Kondo-type impurities.

Contribution

It provides new insights into the effects of excess Fe on superconducting and normal state properties, highlighting the importance of spin-paramagnetic pair-breaking and impurity scattering.

Findings

u0Hc2(T) saturates at low temperatures

Anisotropy decreases and becomes nearly isotropic at T->0

Excess Fe acts as Kondo-type impurities affecting properties

Abstract

We have investigated the upper critical field anisotropy and magnetotransport properties of Fe1.14(1)Te0.91(2)S0.09(2) single crystals in stable magnetic fields up to 35 T. The results show that u0Hc2(T) along the c axis and in the ab-plane exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic for T->0. Our analysis indicates that the spin-paramagnetic pair-breaking with spin-orbital scattering is responsible for the behavior of u0Hc2(T). Furthermore, from analysis of the normal state properties, we show evidence that the excess Fe acting as Kondo-type impurities is a key factor determining the normal and superconducting state physical properties.