A new interstitial-vacancy unbinding transition of Berezinskii-Kosterlitz-Thouless type was established which transformed the 3-dimensional pancake-vortex lattice of a magnetically coupled layered superconductor into a defected solid. This transition was a finite-field extension of the vortex-antivortex unbinding transition which led to zero-field super-fluid stiffness. For finite Josephson coupling, the defect unbinding transition turned into a topological decoupling transition.

Defect-Unbinding Transition in Layered Superconductors. M.J.W.Dodgson, V.B.Geshkenbein, G.Blatter: Physical Review Letters, 1999, 83[25], 5358-61