Effect of Phase Fluctuations on the Low-Temperature Penetration Depth of High-TcSuperconductors

We describe a simple model to estimate the effects of order parameter phase fluctuations on the penetration depth $\lambda \left(T\right)$ of high- $T_c$ superconductors. When treated classically, such fluctuations are found to produce a linear temperature dependence of $\lambda \left(T\right)$, which may be comparable to the experimentally observed magnitude. This dependence persists when the combined effects of charging interactions and dissipation are included in the model. Hence, such a dependence may not be a unique signature of a superconductor with line nodes at the Fermi surface.