Effect of Nonstoichiometric Disorder on the Upper Critical Field in Electron Doped Nd2−xCexCuO4+δ Single Crystals

Temperature dependences of the electrical resistivity measured in different magnetic fields (B∥c, J∥ab) of electron doped Nd2−xCexCuO4+δ single crystals with different cerium concentration (x=0.15, 0.17, and 0.20) and oxygen content (δ) were studied in a temperature range of 1.8–40 K. It was found that the slope of the upper critical field \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$(dB_{c2}/dT)|_{T_{c}}$\end{document} decreases with the increase of the disorder in the system. So, we can distinguish experimentally d-wave and anisotropic s-wave superconductors. Moreover, the slope of the upper critical field and critical temperature decrease with increase of the disorder parameter like in d-wave superconductors with anisotropic scattering.