Abstract. The anisotropic resistivities of Bi 2 Sr 2 Ca 1−x Er x Cu 2 O 8 single crystals were measured and analyzed from 4.2 to 500 K with special interest taken in the parent antiferromagnetic insulator with x=1.0. Although the resistivity is semiconducting along both the in-plane and out-of-plane directions, the temperature dependences are found to be significantly different. As a result, the resistivity ratio for x=1.0 exhibits a broad maximum near room temperature. The electric conduction in the parent antiferromagnetic insulators is different from that in other semiconductors, and is as unconventional as that in high-temperature superconductors.

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The out-of-plane dielectric constant of the parent insulator of the high-temperature superconductor Bi2Sr2Dy1-xErxCu2O8 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 Bi2Sr2Ca0.75Pr0.25Cu2O8 also shows a similar dielectric constant, the charge inhomogeneity plays an important role in the insulator-superconductor transition.

The anisotropic dielectric constants of the parent antiferromagnet Bi 2 Sr 2 M Cu 2 O 8 (M =Dy, Y and Er) single crystals were measured from 80 to 300 K. The in-plane dielectric constant is found to be very huge (10 4 -10 5 ). This suggests a remnant of the Fremi surface of the parent antiferromagnet. The out-of-plane dielectric constant is 50-200, which is three orders of magnitude smaller than the in-plane one. A significant anomaly is that a similar out-of-plane dielectric constant is observed in superconducting samples.

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