Optical conductivity of the Hubbard chain away from half filling

We consider the optical conductivity sigma(1)(omega) in the metallic phase of the one-dimensional Hubbard model. Our results focus on the vicinity of half filling and the frequency regime around the optical gap in the Mott insulating phase. By means of a density-matrix renormalization group implementation of the correction-vector approach, sigma(1)(omega) is computed for a range of interaction strengths and dopings. We identify an energy scale E-opt above which the optical conductivity shows a rapid increase. We then use a mobile impurity model in combination with exact results to determine the behavior of sigma(1)(omega) for frequencies just above E-opt which is in agreement with our numerical data. As a main result, we find that this onset behavior is not described by a power law.