Pairing type change upon an increase in the cerium doping level in the Nd2−xCexCuO4+δ electronic superconductor

We report on the results of analyzing the temperature dependences of the resistivity of the Nd2−xCexCuO4+δ electronic superconductor with x = 0.14 (underdoped range), x = 0.15 (optimal doping), and x = 0.18 (overdoped range) and with various degrees of annealing in an oxygen-free atmosphere in magnetic fields up to H = 90 kOe (H ‖ c, J ‖ ab) in the temperature range T = (0.4–300) K. It is shown that the observed differences in the dependences of the slope of the upper critical field dHc2/dT)|Tc on the degree of disorder in the Nd2−xCexCuO4+δ system upon a change in the cerium doping level indicate a change in the symmetry of d-type pairing to anisotropic s pairing.