LOW-FREQUENCY CONDUCTIVITY OF THE ONE-DIMENSIONAL STRONG-COUPLING HUBBARD-MODEL

The real part of the conductivity (absorption) of the Hubbard model at strong coupling is studied using exact diagonalization. The low-frequ ency absorption band which appears in the doped system is examined in both the standard t-J model and in the strong coupling limit of the Hu bbard model which includes three-site spin-dependent hopping terms. Th e conductivity is shown to differ markedly in the two models, with the three-site terms being essential to obtain reasonable agreement with the Hubbard model.