Transition in the flux lattice of artificially layered superconductors

Abstract

We report a novel magnetic-field dependence of the critical-current density ${\mathit{J}}_{\mathit{c}}$ in artificially grown Ge/Pb superlattices. In these layered structures ${\mathit{J}}_{\mathit{c}}$ exhibits an unexpected minimum as a function of perpendicular applied field, unlike any ever observed in other superconductor systems. The systematic evolution of this minimum as a function of layer thicknesses, temperature and pinning strength is related to either flux-lattice decoupling or melting.