Anisotropic penetration depth in ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_4$

The surface impedance at 10 GHz was measured systematically in single-crystal ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ for carrier concentrations 0.09≤x≤0.19, from which penetration depth λ was determined. The anisotropy and the depencences on x and temperature T of λ are extensively studied for the first time. The anisotropy of λ(T=0) decreases with increasing x, and still remains larger than 10 for x=0.19. The out-of-plane penetration depth (${\lambda }_{\mathit{c}}$) has a different temperature dependence from the in-plane one (${\lambda }_{\mathit{a}\mathit{b}}$). These results suggest that the electrodynamic properties in the superconducting state along the c axis can be explained by a Josephson-coupled layer model.