Suppression of superconductivity in YNi2B2C at the atomic disordering

The behavior of the electrical resistivity rho(T), the superconducting transition temperature T (c) , and the upper critical field H (c2)(T) of a polycrystalline sample of YNi2B2C irradiated by thermal neutrons with the subsequent high-temperature isochronous annealing in the temperature interval T (ann) = 100-1000A degrees C has been studied. It has been found that the irradiation of YNi2B2C with a fluence of 10(19)cm(-2) leads to the suppression of the superconductivity. The final disordered state is reversible; i.e., the initial rho(T), T (c) , and H (c2)(T) values are almost completely recovered upon annealing at up to T (ann) = 1000A degrees C. The quadratic dependence rho(T) = rho(0) + a (2) T (2) is observed for the sample in the superconducting state (T (c) = 5.5-14.5 K). The coefficient a (2) (proportional to the square of the electron mass m*) hardly changes. The form of the dependence of T (c) on rho(0) can be interpreted as the suppression of the two superconducting gaps, Delta(1) and Delta(2) (Delta(1) similar to 2 Delta(2)). The degradation rate of Delta(1) is about three times higher than that of Delta(2). The dependences dH (c2)/dT on rho(0) and T (c) may be described by the relations for a superconductor in the intermediate limit (the coherence length zeta(0) is on the order of the electron mean free path l (tr)) under the assumption of a nearly constant electron density of states on the Fermi level N(E (F)). The observed behavior of T (c) obviously does not agree with the widespread opinion about the purely electron-phonon mechanism of superconductivity in the compounds of this type supposing the anomalous type of superconducting pairing.