Excitons in one-dimensional Mott insulators - art. no. 125119

We employ dynamical density-matrix renormalization-group (DDMRG) and field- theory methods to determine the frequency-dependent optical conductivity in one-dimensional extended. half-filled Hubbard models. The field-theory app roach is applicable to the regime of "small" Mott gaps which is the most di fficult to access by DDMRG. For very large Mott gaps the DDMRG recovers ana lytical results obtained previously by means of strong-coupling techniques. We focus on exciton formation at energies below the onset of the absorptio n continuum. As a consequence of spin-charge separation, these Mott-Hubbard excitons are bound states of spinless, charged excitations ("holon-antihol on" pairs). We also determine exciton binding energies and sizes. In contra st to simple band insulators, we observe that excitons exist in the Mott-in sulating phase only for a sufficiently strong intersite Coulomb repulsion. Furthermore, our results show that the exciton binding energy and size are not related in a simple way to the strength of the Coulomb interaction.