Dynamic Hubbard model.

The Hubbard on-site repulsion U between opposite spin electrons on the same atomic orbital is widely regarded to be the most important source of electronic correlation in solids. Here we extend the Hubbard model to account for the fact that the experimentally measured atomic U is different from the one obtained by calculation of the atomic Coulomb integral. The resulting model describes quasiparticles that become increasingly dressed as the number of electrons in the band increases. Superconductivity can result in this model through quasiparticle undressing. Various signatures of this physics in spectroscopies in the normal and superconducting states are discussed. A novel effect in the normal state is predicted to be electroluminescence at the sample-positive counterelectrode boundary.