  The analogy between magnetism and electricity has long been established by
Maxwell in the 19th century, in spite of their subtle difference. While
magnetic materials display paramagnetism, ferromagnetism, antiferromagnetism,
and diamagnetism, only paraelectricity, ferroelectricity, and
antiferrolelectricity have been found in dielectric materials. The missing
`diaelectricity' may be found if there exists a material that has a
dc-polarization opposing the electric field or a negative dielectric
susceptibility epsilon'-1, with epsilon' being the real part of the relative
dielectric constant. Both of these properties have been observed in
nano-particle aggregates under a dc electric bias field at room temperature. A
possible collective effect in the nano-particle aggregates is proposed to
account for the observation. `Diaelectricity' implies overscreening by
polarization to the external charges. Materials with a negative static epsilon'
are expected to provide attraction to similar charges and unusual scattering to
electromagnetic waves with possible profound implications for high temperature
superconductivity and communication.
