KOSTERLITZ-THOULESS SIGNATURES FROM 3D VORTEX LOOPS IN LAYERED SUPERCONDUCTORS

Layered 3D high-T(c) superconductors exhibit Kosterlitz-Thouless- (KT-) like quasi-2D signatures, and a decoupling of layers for T > T(c) has been suggested. A vortex-loop scaling approach to the layered 3D XY model, with bare anisotropic coupling ratio gamma0(-2) = J(perpendicular-to)/J(parallel-to), shows layer fluctuations are indeed effectively decoupled, but only at finite scales a less than or similar r0 approximately gamma0 much greater than 1, where rectangular loops cutting single layers dominate. Finite-scale KT-like unbinding at ''T(KT)'' (gamma-) less than or similar T(c) (gamma0) yields quasi-2D signatures outside a 3D critical region \(T - T(c))/T(c)\ = \epsilon\ = \epsilon(c)\ where multilayer, elliptical tumbling loops dominate, correlated over scales xi approximately \epsilon\-v much greater than r0.