CARRIER CONCENTRATION-DEPENDENCE AND IMPURITY EFFECTS OF MICROWAVE RESPONSE IN BI2SR2CACU2O8+Y

We report the surface impedance (Z(s)) measurements in high quality si ngle crystals of Bi2Sr2CaCu2O8+y. At relatively low oxygen content, th e change of the penetration depth, Delta lambda(T) = lambda(T) - lambd a(O), of the pure single crystals exhibits linear temperature dependen ce both parallel to the CuO2 planes and in the c direction. In contras t to this behavior, by further oxygenation or 0.6% Zn substitution, th e T-linear dependence is disrupted and T-2 dependence of Delta lambda is observed. We also found that 0.9% Ni-substitution induces no pair-b reaking effect. The present results suggest that the low-lying excitat ion spectrum of quasiparticles depends on the carrier concentration an d is easily changed by a small amount of Zn substitution.