Out-of-plane dielectric constant and insulator-superconductor transition in Bi₂Sr₂Dy_1-xEr_xCu₂O₈ single crystals

The out-of-plane dielectric constant of the parent insulator of the high-temperature superconductor Bi₂Sr₂Dy_1-xEr_xCu₂O₈ was measured and analysed from 80 to 300 K in the frequency range of 10⁶-10⁹ Hz. All the samples were found to show a fairly large value of 10-60, implying some kind of charge inhomogeneity in the CuO₂ plane. Considering that the superconducting sample Bi₂Sr₂Ca_0.75Pr_0.25Cu₂O₈ also shows a similar dielectric constant, the charge inhomogeneity plays an important role in the insulator-superconductor transition.