Effects of low temperature irradiation with heavy ions on superconductor niobium

Abstract

To study the effects of heavy ion irradiation at low temperature on type II superconductor Nb, the transition temperatureT c , the normal state residual resistivityρ B , the transition widthΔT ph using oxygen ions of 25 MeV and subsequent thermal annealing were measured. The samples were held at temperatures <20 K during irradiation in a cryostat for in situ measurements. The maximum oxygen fluence was about 2·1015 cm−2 corresponding a relatively high defect concentration. The heavy ion irradiation experiments are described. The critical temperatureT c decreases with increasing residual resistivityρ B . In agreement with the theory and experiments, the gap anisotropy parameter is 〈a2〉=0.008, subsequent annealing shows a hysteresis ofT c versusρ B . The resistivity saturation value ΔρBS = 2.55 μΩ cm was obtained and different recovery stages were found. Significant broadening of transition width during irradiation was observed.T c andΔT ph anneal to 60% in the temperature interval of (60–90) K. Oxygen induced effects as a simulation method of high neutron damage are compared with irradiation measurements using neutrons and deuterons.