Temperature dependence of the anisotropic magnetic penetration depth and lower critical field of single-crystal ${\mathrm{Pb}}_2$${\mathrm{Sr}}_2$(Y,Ca)${\mathrm{Cu}}_3$${\mathrm{O}}_{8+\mathrm{\delta }}$

The temperature dependence of the penetration depth of single-crystal ${\mathrm{Pb}}_2$ ${\mathrm{Sr}}_2$(Y,Ca)${\mathrm{Cu}}_3$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ has been determined in the vicinity of ${\mathit{T}}_{\mathit{c}}$ (∼75 K) using intermediate-field reversible-magnetization measurements. The ab-plane penetration depth in the restricted region near ${\mathit{T}}_{\mathit{c}}$ was found to follow clean-limit BCS behavior from which an estimate of 2575 Å for ${\lambda }_{\mathit{a}\mathit{b}}$(0) was obtained. The effective-mass anisotropy parameter, γ=(${\mathit{m}}_{\mathit{c}}$/${\mathit{m}}_{\mathit{a}\mathit{b}}$ ${)}^{1/2}$, was found to be 2.5, which together with the former result yields a value of 6425 Å for ${\lambda }_{\mathit{c}}$(0). In addition, the temperature dependence of the anisotropic lower critical field was determined from observations of the onset of deviation from perfect diamagnetism. The estimates obtained for the zero-temperature lower critical field, ${\mathit{H}}_{\mathit{c}1}$(0), were 95±10 G for H⊥c and 505±20 G for H∥c.