A negative dielectric constant in nano-particle materials under an   electric field at very low frequencies
  The significance of a negative dielectric constant has long been recognized. We report here the observation of a field-induced large negative dielectric constant of aggregates of oxide nano-particles at frequencies below ~ 1 Hz at room temperature. The accompanying induced charge detected opposes the electric field applied in the field-induced negative dielectric constant state. A possible collective effect in the nano-particle aggregates is proposed to account for the observations. Materials with a negative dielectric constant are expected to provide an attraction between similar charges and unusual scattering to electromagnetic waves with possible profound implications for high temperature superconductivity and communications. 
C. W. Chu (1 and 2 and 3), F. Chen (1), J. Shulman (1), S. Tsui (1),   Y. Y. Xue (1), W. Wen (4), P. Sheng (4) ((1) Departme...