Observation of the Flux Line Lock-In Transition in Layered Superconductors

Abstract

We have investigated the vortex structure in three different representatives of highly anisotropic layered superconductors: Tl2Ba2Ca2Cu3O10, Bi2Sr2CaCu2O8 and κ-(BEDT-TTF)2-Cu[N(CN)2]Br. Based on the equilibrium part of the magnetic torque we identify the vortex lock-in transition, i.e. the perfect alignment of the magnetic induction parallel to the superconducting planes. This Meissner state for pancake vortices is quantitatively confirmed by ideal screening of the perpendicular field component.