Pairing type change upon an increase in the cerium doping level in the [Nd.sub.2-x][Ce.sub.x]Cu[O.sub.4+[delta]] electronic superconductor

We report on the results of analyzing the temperature dependences of the resistivity of the [Nd.sub.2-x][Ce.sub.x]Cu[O.sub.4+[delta]] 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[parallel] c, J[parallel] 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 (d[H.sub.c2]/dT)[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] on the degree of disorder in the [Nd.sub.2-x][Ce.sub.x]Cu[O.sub.4+[delta]] system upon a change in the cerium doping level indicate a change in the symmetry of d-type pairing to anisotropic s pairing.