Effect of the nonstoichiometric disorder on the temperature dependence of the upper critical field in Nd2− x Ce x CuO4+δ electron superconductors

The temperature dependences of the resistance of the Nd_2−x Ce _x CuO_4+δ single crystal with x = 0.15 and various disorder parameters δ have been investigated in various magnetic fields (B ‖ c, J ‖ ab) in the temperature range T = 1.8–40 K. It has been shown that the slope of the upper critical field, (dB _c2/dT)|T _c, in the electron superconductor decreases with an increase in the disorder parameter. This dependence makes it possible to experimentally distinguish between d-pairing superconductors and s-pairing superconductors. The dependence of the superconducting transition temperature on the disorder parameter in the system is investigated in the model of the superconductors with anisotropic impurity scattering.