Permittivity of BaTiO₃ epitaxial films grown on the YBa₂Cu₃O_7−δ(001) surface

Abstract

The epitaxial heterostructures YBa₂Cu₃O_7−δ and YBa₂Cu₃O_7−δ/(5 nm)SrTiO₃/BaTiO₃/(5 nm)SrTiO₃/YBa₂Cu₃O_7−δ are grown by the laser evaporation method on an LaAlO₃(100) substrate. The permittivity of a BaTiO₃ layer is approximately doubled (T=300 K) when a SrTiO₃ thin layer is inserted between a ferroelectric layer and superconducting cuprate electrodes. A maximum in the temperature dependence of the permittivity for a barium titanate layer in the YBa₂Cu₃O_7−δ/(5 nm)SrTiO₃/BaTiO₃/(5 nm)SrTiO₃/YBa₂Cu₃O_7−δ heterostructure is shifted by 70–80 K toward the low-temperature range with respect to its location in the corresponding dependence for the BaTiO₃ bulk single crystal. The bias voltage dependence of the permittivity for the BaTiO₃ grown layers exhibits a clearly pronounced hysteresis (T=300 K). The superconducting transition temperature for the lower YBa₂Cu₃O_7−δ electrode in a superconductor/ferroelectric/superconductor heterostructure considerably depends on the rate of its cooling after the completion of the formation process.