Quasiparticles in Narrow Band Systems

Abstract

When electrons are moving through a molecule or solid, two distinct features influence their motion. One is the kinetic energy gain due to the overlap of orbitais centered on different atoms. In a solid it is characterized by the band width W and results in charge fluctuations at the different atomic sites. The other one is the Coulomb repulsion between the electrons. It is minimized when the electrons stay apart as far as possible. Clearly, the kinetic energy gain and the Coulomb repulsions are competing effects, as the latter try to reduce charge fluctuations to a minimum. More precisely it is the ratio (U-K)/W which governs the size of the charge fluctuations, where U is the repulsion between two electrons at the same site and K is the one between two electrons on neighboring sites.