Defect-unbinding transition in layered superconductors

We establish a new interstitial-vacancy unbinding transition of the Berezin skii-Kosterlitz-Thouless type, transforming the three-dimensional pancake-v ortex lattice of a magnetically coupled layered superconductor into a defec ted solid. This transition is the finite-field extension of the vortex-anti vortex unbinding transition establishing the zero-field superfluid stiffnes s. At finite Josephson coupling, the defect unbinding transition turns into a topological decoupling transition.