EXCESS-CONDUCTIVITY ANALYSIS OF ALPHA-IRRADIATED POLYCRYSTALLINE BI-2212 SUPERCONDUCTOR

Excess conductivities of polycrystalline samples irradiated with alpha particles at various doses and of unirradiated ones have been studied from the data of resistivity versus temperature. The range of tempera ture chosen was from around 2T(c) to T-c onset taken as T-c(mf), the m ean-field transition temperature phenomenologically. The logarithmic p lots of excess conductivity and reduced temperatures [(T - T-c(mf))/T- c(mf)] reveal two cross-over temperatures with three exponents. Except for the unirradiated sample, which shows a distinct cross-over from t wo-dimensional to three-dimensional conductivity, all the irradiated s amples fit only with the two-dimensional Aslamazov-Larkin equation abo ve the cross-over temperature T-0. Apparently, there is an onset of cr itical fluctuation around T-0 in the case of the irradiated samples. I nterlayer-coupling strengths estimated show a decreasing trend with th e increase in dose, corresponding to a decrease in carrier concentrati on.