Pseudogaps in Strongly Correlated Metals: Optical Conductivity within the Generalized Dynamical Mean-Field Theory Approach

Abstract

Optical conductivity of the weakly doped two-dimensional repulsive Hubbard model on the square lattice with nearest and next nearest hoppings is calculated within the generalized dynamical-mean field (DMFT+Σ_p) approach which includes correlation length scale ξinto the standard DMFT equations via the momentum dependent self-energy Σ_p, with full account of appropriate vertex corrections. This approach takes into consideration non-local dynamical correlations induced e.g. by short-ranged collective SDW-like antiferromagnetic spin fluctuations, which (at high enough temperatures) can be viewed as a quenched Gaussian random field with finite correlation length ξ. The effective single impurity problem is solved by numerical renormalization group (NRG). We consider both the case of correlated metal with the bandwidth W<=U and that of doped Mott insulator with U>>W (U - value of local Hubbard interaction). Optical conductivity calculated within DMFT+Σ_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.