In-Plane and c^-Axis Microwave Penetration Depth of Bi2Sr2Ca1Cu2O8+δ Crystals

Abstract

The complete temperature dependences of the in-plane and $\hat{c}$-axis microwave (10 GHz) penetration depth $\lambda \mathrm{}\left(T\right)\mathrm{}$ and the surface resistance $R_s\mathrm{}\left(T\right)\mathrm{}$ of high quality ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{Ca}}_1{\mathrm{Cu}}_2{\mathrm{O}}_{8+\delta }$ crystals are reported. In contrast to earlier measurements, a leading ${\lambda }_{\mathrm{ab}}\propto T$ dependence is observed at low temperatures, consistent with nodes in the in-plane gap. The overall behavior of ${\lambda }_{\mathrm{ab}}\mathrm{}\left(T\right)\mathrm{}$ and $R_{\mathrm{sab}}\mathrm{}\left(T\right)\mathrm{}$ is similar to that of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_y$ at low $T$, but differs at temperatures near $T_c$. The $\hat{c}$-axis penetration depth ${\lambda }_c\mathrm{}\left(T\right)\mathrm{}$ is shown to best agree with a model of weakly coupled superconducting layers with nodes in the gap.