Magnetic penetration depth in single-crystal YBa2Cu3O7- delta.

We report the first measurement of the magnetic penetration depth $\ensuremath{\lambda}(T, \ensuremath{\theta})$ in single crystals of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ ($\ensuremath{\delta}\ensuremath{\sim}0.1$). Results are consistent with conventional $s$-wave pairing, and yield penetration depths of ${\ensuremath{\lambda}}_{\mathrm{ab}}(0)=1415\ifmmode\pm\else\textpm\fi{}30$ \AA{} and ${\ensuremath{\lambda}}_{c}(0)g7000$ \AA{}, parallel and perpendicular to the basal plane, respectively. Comparative data on sintered Y${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ are also shown to be consistent with the single-crystal results. The muon-spin-rotation data, together with specific-heat results, indicate a two-dimensional carrier density of ${\ensuremath{\eta}}_{2\mathrm{D}}\ensuremath{\approx}8\ifmmode\times\else\texttimes\fi{}{10}^{14}$ carriers ${\mathrm{cm}}^{\ensuremath{-}2}$ and a basal-plane effective mass of $\frac{{m}_{\mathrm{ab}}^{*}}{{m}_{e}}\ensuremath{\approx}10$.