Upper critical magnetic field in K0.83Fe1.83Se2 and Eu0.5K0.5Fe2As2 single crystals

TL;DR

This study maps the upper critical magnetic fields in various iron-based superconductors, revealing anisotropic behaviors and the influence of magnetic ordering, with implications for understanding their superconducting mechanisms.

Contribution

It provides detailed Hc2(T) phase diagrams for K0.83Fe1.83Se2, K0.8Fe2Se2, and Eu0.5K0.5Fe2As2, highlighting the role of two-gap effects and anisotropic Pauli paramagnetism.

Findings

Hc2(T) fits Pauli model with anisotropic paramagnetic contribution.

Hc2(T) shows upward curvature for H//c in some compounds, indicating two-gap behavior.

Magnetic ordering does not affect Hc2(T) dependence.

Abstract

The H-T phase diagrams of single crystalline electron-doped K0.83Fe1.83Se2 (KFS1), K0.8Fe2Se2 (KFS2) and hole-doped Eu0.5K0.5Fe2As2 (EKFA) have been deduced from tunnel diode oscillator-based contactless measurements in pulsed magnetic fields up to 57 T for the inter-plane (H//c) and in-plane (H//ab) directions. The temperature dependence of the upper critical magnetic field Hc2(T) relevant to EFKA is accounted for by the Pauli model including an anisotropic Pauli paramagnetic contribution (\mu_BHp=114 T for H//ab and 86 T for H//c). This is also the case of KFS1 and KFS2 for H//ab whereas a significant upward curvature, accounted for by a two-gap model, is observed for H//c. Despite the presence of antiferromagnetic lattice order within the superconducting state of the studied compounds, no influence of magnetic ordering on the temperature dependence of Hc2(T) is observed.