Abstract
Above and below the Verwey transition in Fe3O4 the influence of the short-and long-range order of the extra B-site electrons on the density of states, the d.c conductivity and the optical absorption for infra-red frequencies is investigated. Our theory takes into account the Coulomb interaction between nearest (U1) and next-nearest neighbours (U2), the nearest-neighbour hopping (t), and a bilinear electron–phonon interaction, where U1≫t>U2 is assumed. Good agreement with experimental data is found.
The Verwey transition is treated as the condensation of a coupled charge-density phonon mode with Δ5 (1) symmetry. A new charge ordering scheme is obtained: combination of the Δ5 (1) Yamada order (along the a axis) and charge order along the b axis due to U2.