Finite-Frequency Optical Absorption in 1D Conductors and Mott-Hubbard Insulators

The frequency-dependent conductivity is studied for the one-dimensional Hubbard model, using a selection rule, the Bethe ansatz, and symmetries associated with conservation laws. For densities where the system is metallic the absorption spectrum has two contributions, a Drude peak at $\omega =0\mathrm{}$ separated by a pseudogap from a broad absorption band whose lower edge is characterized by a nonclassical critical exponent. Our findings shed new light on the “far infrared puzzle” and other optical properties of metallic organic chain compounds.