Pauli-limited upper critical field in Fe1+yTe1-xSex

TL;DR

This study measures the upper critical magnetic field in Fe-based superconductors, revealing saturation at low temperatures and the dominance of spin-paramagnetic effects, with deviations from traditional theoretical models.

Contribution

It provides detailed experimental data on the temperature dependence of the upper critical field in Fe1+yTe1-xSex crystals and highlights the role of spin-paramagnetic pair-breaking effects.

Findings

u0Hc2(T) saturates at low temperatures

Anisotropy decreases with temperature, becoming nearly isotropic at T->0

Deviates from WHH theoretical predictions

Abstract

In this work we investigated the temperature dependence of the upper critical field u0Hc2(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2) single crystals by measuring the magnetotransport properties in stable dc magnetic fields up to 35 T. Both crystals show that u0Hc2(T) in the ab-plane and along the c-axis exhibit saturation at low temperatures. The anisotropy of u0Hc2(T) decreases with decreasing temperature, becoming nearly isotropic when the temperature T->0. Furthermore, u0Hc2(0) deviates from the conventional Werthamer-Helfand-Hohenberg (WHH) theoretical prediction values for both field directions. Our analysis indicates that the spin-paramagnetic pair-breaking effect is responsible for the temperature-dependent behavior of u0Hc2(T) in both field directions.