Suppression of superconductivity in YNi2B2C at the atomic disordering

The behavior of the electrical resistivity ρ( T ), the superconducting transition temperature T c , and the upper critical field H c 2 ( T ) of a polycrystalline sample of YNi 2 B 2 C irradiated by thermal neutrons with the subsequent high-temperature isochronous annealing in the temperature interval T ann = 100–1000°C has been studied. It has been found that the irradiation of YNi 2 B 2 C 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 ρ( T ), T c , and H c 2 ( T ) values are almost completely recovered upon annealing at up to T ann = 1000°C. The quadratic dependence ρ( T ) = ρ 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 ρ 0 can be interpreted as the suppression of the two superconducting gaps, Δ 1 and Δ 2 (Δ 1 ∼ 2Δ 2 ). The degradation rate of Δ 1 is about three times higher than that of Δ 2 . The dependences dH c 2 / dT on ρ 0 and T c may be described by the relations for a superconductor in the intermediate limit (the coherence length ζ 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.