Penetration depth in layered high-Tcsuperconductors

Starting from the complete anisotropic Eliashberg equations valid for a layered compound, we compute the temperature variation of the London penetration depth ${\lambda }_{\mathit{L}}$(T) parallel and perpendicular to the planes. In our model we use a free-electron approximation in the planes with a hopping probability for interplane motion. The anisotropy in the pairing is expanded in Fermi-surface harmonics. It is found that anisotropy can strongly influence the temperature dependence of ${\lambda }_{\mathit{L}}$(T) but that its effect is suppressed with increasing coupling strength.