Kosterlitz-Thouless signatures from 3D vortex loops in layered superconductors

Abstract

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 γ₀⁻²≡scrI_⊥/scrI_||, shows layer fluctuations are indeed effectively decoupled, but only at finite scales a≲r₀~γ₀≫1, where rectangular loops cutting single layers dominate. Finite-scale KT-like unbinding at "T_KT" (γ₀)≲T_c(γ₀) yields quasi-2D signatures outside a 3D critical region ||(T-T_c)/T_c||≡||ε||=||ε_c|| < γ₀^−1/ν, where multilayer, elliptical tumbling loops dominate, correlated over scales ξ~||ε||^−ν≫r₀.