Spectral and transport properties of doped Mott-Hubbard systems with incommensurate magnetic order

We present spectral and optical properties of the Hubbard model on a two-di mensional square lattice using a generalization of dynamical mean-field the ory to magnetic states in a finite dimension. The self-energy includes the effect of spin fluctuations and screening of the Coulomb interaction due to particle-particle scattering. At half-tilling the quasiparticles reduce th e width of the Mott-Hubbard ''gap'' and have dispersions and spectral weigh ts that agree remarkably well with quantum Monte Carlo and exact diagonaliz ation calculations. Away from half-filling we consider incommensurate magne tic order with a varying local spin direction, and derive the photoemission and optical spectra. The incommensurate magnetic order leads to a pseudoga p which opens at the Fermi energy and coexists with a large Mott-Hubbard ga p. The quasiparticle states survive in the doped systems, but their dispers ion is modified by the doping, and a rigid-band picture does not apply. Spe ctral weight in the optical conductivity is transferred to lower energies, and the Drude weight increases linearly with increasing doping. We show tha t incommensurate magnetic order also leads to midgap states in the optical spectra and to decreased scattering rates in the transport processes, in qu alitative agreement with the experimental observations in doped systems. Th e gradual disappearence of the spiral magnetic order and the vanishing pseu dogap with increasing temperature is found to be responsible for the linear resistivity. We discuss the possible reasons why these results may only pa rtially explain the features observed in the optical spectra of high-temper ature superconductors. [S0163-1829(99)04632-9].