Inequivalent layers can cause flux-lattice melting in layered superconductors

The high-Tc superconductors consist typically of superconducting (S) and nonsuperconducting (W) layers. The latter layers acquire actually a nonzero order parameter through a proximity effect. We show that the vortices fluctuate much more wildly on the W layers, than on the S layers. Consequently, flux-lattice melting can begin rather easily on the W layers, rendering then the whole system two dimensional