Fast Suppression of Superconductivity with Fe Site Ni Substitution in Fe1−xNixSe0.5Te0.5 (x = 0.0 to 0.20) Single Crystals

We report the effect of Ni doping on the superconductivity of FeSe0.5Te0.5. The single crystal samples of Fe1−xNixSe0.5Te0.5 (x = 0.0 to 0.20) series are synthesized via vacuum shield solid-state reaction route and high-temperature heating followed by slow cooling. All the crystals of Fe1−xNixSe0.5Te0.5 series with x up to 0.20, i.e., 20 % substitution of Ni at Fe site, are crystallized in single-phase tetragonal structure with the space group P4/nmm. The electrical resistivity measurements revealed that Tc decreases fast with an increase of Ni concentration in Fe1−xNixSe0.5Te0.5, namely the superconducting transition temperature (Tc) being defined as resistivity (ρ) = 0 decrease from 12 K to around 4 K and 2 K for x = 0.01 and 0.03 samples, respectively. For x = 0.05 (5 at.% Ni at Fe site), Tconset\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$T_{\mathrm {c}}^{\text {onset}}$\end{document} is observed in resistivity (ρ–T) measurements but ρ = 0 is not seen down to 2 K. For x ≥ 0.07, neither Tconset\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$T_{\mathrm {c}}^{\text {onset}}$\end{document} nor Tcρ=0\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$T_{\mathrm {c}}^{\rho = 0}$\end{document} is seen down 2 K in ρ–T measurements. It is demonstrated that Ni doping at Fe site in FeSe0.5Te0.5 superconductor suppresses superconductivity fast. The rate of Tc depression is albeit non-monotonic. Summarily, a systematic study on suppression of superconductivity with Fe site Ni doping in flux-free gown FeSe0.5Te0.5 single crystals is presented in the current communication.