Two Hubbard Bands: Weight Transfer in Optical and One-Particle Spectra

Abstract
We identify local kinetic-energy contributions which are responsible for the rapid weight transfer from the high- to the low-energy scale observed upon doping in strongly correlated materials. Using strong-coupling perturbation theory for the Hubbard model we derive expressions for the weights of the upper and lower Hubbard bands separately and evaluate them explicitly in one dimension. The optical conductivity is found to be a direct probe of the local spin order.