V. I. Belinicher

This review presents the fundamental theoretical concepts concerning the photogalvanic effect (PGE)—the phenomenon of appearance of a direct current in a homogeneous medium under uniform illumination. This effect can occur in all media lacking a center of symmetry, in particular, in ferroelectrics, piezoelectrics, gyrotropic crystals, and in gases and liquid possessing natural optical activity. The starting point of a systematic microscopic theory is the asymmetry of the elementary electronic processes—their noninvariance with respect to spatial reflection. Within the framework of the theory, we study the most important mechanisms of the PGE in the regions of impurity, interband, and intraband light absorption. Possible observable manifestations of the PGE are discussed. Theoretical results are compared with experimental data.

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A full three-band model for the ${\mathrm{CuO}}_{2}$ plane with inclusion of all essential interactions---Cu-O and O-O hopping, repulsion at the copper and oxygen and between them---is considered. A general procedure of the low-energy reduction of the primary Hamiltonian to the Hamiltonian of the generalized t-t'-J model is developed. An important role of the direct O-O hopping is discussed. Parameters of the effective low-energy model (the hopping integral, the band position, and the superexchange constant J) are calculated. An analysis of the obtained data shows that the experimental value of J fixes the charge-transfer energy \ensuremath{\Delta}=(${\mathrm{\ensuremath{\epsilon}}}_{\mathit{p}}$-${\mathrm{\ensuremath{\epsilon}}}_{\mathit{d}}$) in a narrow region of energies.

Dispersion relation for the Cu${\mathrm{O}}_{2}$ hole is calculated based on the generalized $t\ensuremath{-}{t}^{\ensuremath{'}}\ensuremath{-}J$ model, recently derived from the three-band one. Numerical ranges for all model parameters, $\frac{t}{J}=2.4\ensuremath{-}2.7$, $\frac{{t}^{\ensuremath{'}}}{t}=0.0 \mathrm{to} \ensuremath{-}0.25$, $\frac{{t}^{\ensuremath{'}\ensuremath{'}}}{t}=0.1\ensuremath{-}0.15$, and three-site terms $2{t}_{N}\ensuremath{\sim}{t}_{S}\ensuremath{\sim}\frac{J}{4}$ have been strongly justified previously. Physical reasons for their values are also discussed. A self-consistent Born approximation is used for the calculation of the hole dispersion. Good agreement between calculated ${E}_{\mathrm{k}}$ and one obtained from the angle-resolved photoemission experiments is found. A possible explanation of the broad peaks in the experimental energy distribution curves at the top of the hole band is presented.