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

Abstract

Using torque magnetometry in the Shubnikov state, we have studied the London penetration depth {lambda}{sub {ital ab}}({ital T}) of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} and (Pb{sub {ital x}}Bi{sub 1{minus}{ital x}}){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} single crystals with different oxygen excess {delta}. With increasing charge carrier density {ital n}{sub {ital s}}/{ital m}{sup {asterisk}}{proportional_to}1/{lambda}{sub {ital ab}}{sup 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}{sub {ital ab}}({ital T}) was observed. A linear term is seen for samples with high maximum {ital T}{sub {ital c}}{approx_equal}94 K, while samples with quadratic behavior show a significantly reduced {ital T}{sub {ital c}}. The results are discussed in terms of {ital d}-wave superconductivity with resonant impurity scattering. {copyright} {ital 1996 The American Physical Society.}