Temperature and doping dependence of the penetration depth in Bi2Sr2CaCu2O8+delta

Using torque magnetometry in the Shubnikov state, we have studied the London penetration depth lambda(ab)(T) of Bi2Sr2CaCu2O8+delta and (PbxBi1-x)(2)Sr2CaCu2O8+delta single crystals with different oxygen excess delta. With increasing charge carrier density n(s)/m*proportional to 1/lambda(ab)(2)(0) the transition temperature at first increases, then approaches a maximum, and finally decreases. The sample independent, universal behavior found in the 1:2:3 family is not confirmed. Dependent on preparation prehistory of the samples, either linear or quadratic low temperature behavior of lambda(ab)(T) was observed. A linear term is seen for samples with high maximum T-c approximate to 94 K, while samples with quadratic behavior show a significantly reduced T-c. The results are discussed in terms of d-wave superconductivity with resonant impurity scattering.