Anisotropic dielectric constant of the parent antiferromagnet Bi2Sr2MCu2O8 (M=Dy, Y and Er) single crystals

The anisotropic dielectric constants of the parent antiferromagnet Bi2Sr2MCu2O8 (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.