Upper critical fields and two-band superconductivity in Sr1-xEux(Fe0.89Co0.11)2As2 (x=0.203 and 0.463)

TL;DR

This study investigates the upper critical magnetic fields of Sr1-xEux(Fe0.89Co0.11)2As2 single crystals, revealing two-band superconductivity features and anisotropy reduction through RF measurements and theoretical modeling.

Contribution

It provides new insights into the two-band superconductivity and anisotropy behavior in Sr1-xEux(Fe0.89Co0.11)2As2, supported by experimental data and theoretical analysis.

Findings

Hc2 approaches Pauli limit with upward curvature

Enhanced Hc2 beyond orbital limiting field

Decreasing anisotropy with temperature

Abstract

The upper critical fields, Hc2 of single crystals of Sr1-xEux(Fe0.89Co0.11)2As2(x=0.203 and 0.463) were determined by radio frequency penetration depth measurements in pulsed magnetic fields. Hc2 approaches the Pauli limiting field but shows an upward curvature with an enhancement from the orbital limited field as inferred from Werthamer-Helfand-Hohenberg theory. We discuss the temperature dependence of the upper critical fields and the decreasing anisotropy using a two-band BCS model.