Pseudogaps in strongly correlated metals: Optical conductivity within the generalized dynamical mean-field theory approach

The optical conductivity of the weakly doped two-dimensional repulsive Hubbard model on the square lattice with the nearest and next-nearest hoppings is calculated within the generalized dynamical mean-field (DMFT+Sigma(p)) approach, which includes correlation length scale xi into the standard DMFT equations via the momentum dependent self-energy Sigma(p), with a full account of appropriate vertex corrections. This approach takes into consideration the nonlocal dynamical correlations induced, e.g., by short-ranged collective spin-density-wavelike antiferromagnetic spin fluctuations, which (at high enough temperatures) can be viewed as a quenched Gaussian random field with finite correlation length xi. The DMFT effective single-impurity problem is solved by numerical renormalization group. We consider both the case of correlated metal with the bandwidth W less than or similar to U and that of doped Mott insulator with U > W (U-the value of local Hubbard interaction). The optical conductivity calculated within DMFT+Sigma(p) demonstrates typical pseudogap behavior within the quasiparticle band, in qualitative agreement with experiments in copper oxide superconductors. For large values of U, pseudogap anomalies are effectively suppressed.