Transport Properties of the Iron-based Superconductor SrFe2(As,P)2 in High Magnetic Fields

We have investigated the resistive upper critical field (μ0Hc2) of the iron-based superconductor SrFe2(As1−xPx)2 (x=0.35, Tc∼29 K) in pulsed high magnetic fields of up to 52 T. For H∥ab, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mu_{0}H_{\mathrm{c}2}^{ab}(T)$\end{document} exhibits the Werthamer-Helfand-Hohenberg (WHH) like behavior. While, for H∥c, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\mu_{0}H_{\mathrm {c}2}^{c}(T)$\end{document} is almost linear against T and exhibits a slightly upward curvature near Tc. The anisotropy of μ0Hc2 decreases from 2.5 near Tc to ∼1.2 at T=0 K monotonically. Similar isotropic behavior of μ0Hc2 at low temperatures has also been observed in the Fe1+δ(Te,Se). We demonstrate the results of the two-band analysis for μ0Hc2(T) on the present sample and discuss the anisotropy of μ0Hc2 by comparing with those in some kinds of iron-based superconductors.