Nearly isotropic upper critical fields in a SrFe$_{1.85}$Co$_{0.15}$As$_{2}$ single crystal

TL;DR

This study investigates the temperature dependence of the upper critical field in a SrFeCoAs superconductor, revealing nearly isotropic behavior at low temperatures and explaining it through orbital, Pauli, and two-band effects.

Contribution

It provides new insights into the anisotropy of upper critical fields in iron-based superconductors, highlighting the near isotropy at low temperatures and the interplay of multiple limiting mechanisms.

Findings

$H_{c2}$ reaches ~48 T at zero temperature for both directions.

$H_{c2}$ becomes nearly isotropic at low temperatures.

The behavior is explained by orbital, Pauli, and two-band effects.

Abstract

We study temperature dependent upper critical field $H_{\rm c2}$ of a SrFe$_{1.85}$Co$_{0.15}$As$_{2}$ single crystal (\textit{T$_c$}=20.2 K) along \textit{ab}-plane and \textit{c}-axis through resistivity measurements up to 50 T. For the both crystalline directions, $H_{\rm c2}$ becomes nearly isotropic at zero temperature limit, reaching $\sim$ 48 T. The temperature dependence of the $H_{\rm c2}$ curves is explained by interplay between orbital and Pauli limiting behaviors combined with the two band effects.