Anisotropy of the penetration depth inYBa2Cu3O7−δ: Josephson-tunneling studies

Abstract

The modulation of the Josephson critical current between two superconductors in a magnetic field provides a direct, low-field dc measurement of the penetration depth of the two superconductors. To measure the in-plane penetration depth anisotropy of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$, we have fabricated low leakage $\mathrm{Pb}/\mathrm{Insulator}/\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ tunnel junctions on detwinned $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ single crystals with tunneling along the $c$ axis. By applying the magnetic field along the $b$ and $a$ crystalline axes of $\mathrm{Y}{\mathrm{Ba}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$, ${\lambda }_a$ and ${\lambda }_b$ are extracted from the respective field modulation patterns. We find a large anisotropy [${\left(\frac{{\lambda }_a}{{\lambda }_b}\right)}^2>~2$] of the penetration depths along the $a$ and $b$ axes.