Vortex unbinding and layer decoupling in a quasi-two-dimensional superconductor

The role of thermal vortices in the absence of applied magnetic fields is studied theoretically for anisotropic layered superconductors such as the high-${\mathit{T}}_{\mathit{c}}$ cuprates. Using a quasi-two-dimensional model and a real-space renormalization-group approach, the vortices are found to Josephson-decouple the superconducting layers slightly above ${\mathit{T}}_{\mathit{c}}$. The results are consistent with recent experiments and Monte Carlo simulations.