Field induced decoupling of superconducting bands in oxygen deficient melt-textured YBa2Cu3O7−x

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Abstract
A layered melt‐textured YBa2Cu3O7−x superconductor has been prepared consisting of alternate fully oxygenated and oxygen deficient bands stacked parallel to a‐b planes. An anomalous decrease of Jcc(H∥ab) with field is observed at high temperatures. We show that this behavior is a signature of a field induced decoupling of the strong superconducting bands, and provides evidence of a decrease of vortex pinning energy in oxygen deficient regions of melt‐textured YBa2Cu3O7−x. A large downwards shift of the irreversibility line results as a consequence of the substantially smaller area where a critical state sets in. When vortices are parallel to the c‐axis Jcab(H∥c) decreases due to the smaller condensation energy of the oxygen deficient bands.