Superconductivity in nonsymmetric epitaxial YBa2Cu3O7−x/PrBa2Cu3O7−x superlattices: The superconducting behavior of Cu-O bilayers

Abstract

We have fabricated epitaxial, nonsymmetric M×N superlattices in which ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (YBCO) layers either M=1, 2, 3, 4, or 8 c-axis unit cells thick are separated by insulating ${\mathrm{PrBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ (PrBCO) layers N unit cells thick (N=1 to ∼16). The zero-resistance transition temperature, ${\mathit{T}}_{\mathit{c}0}$, initially decreases rapidly with increasing PrBCO thickness but saturates at ${\mathit{T}}_{\mathit{c}0}$∼19 K or ${\mathit{T}}_{\mathit{c}0}$∼54 K for 1- and 2-cell-thick YBCO layers, respectively. We conclude that although intercell coupling may enhance ${\mathit{T}}_{\mathit{c}0}$, it is necessary for superconductivity of single-cell-thick YBCO layers in PrBCO matrix.