Internal electric fields and resonant Fermi-level pinning in anionic metals

In the normal Jahn-Teller effect a molecular distortion at low temperatures reduces total energy by splitting electronic states which are highly degenerate at the Fermi energy. Thomas et al. have discovered in layered Bi₂{Te}₃$:Bi an anti-Jahn-Teller effect in the density of conduction electrons, which effectively doubles between room and low temperatures. This effect is explained by the presence of large internal electric fields induced by dopant configurational distortions which are screened by resonant states pinning the Fermi level. Such states have been supposed previously to be the novel electronic mechanism responsible for high-temperature superconductivity in the layered cuprates.