Charge transfer excitons in HTSC cuprates and nickelates

Abstract

An analysis of the optical properties of compounds based on 3d elements provides valuable information about
the electronic structure of the ground state and low-energy excitations. Thus, we show that the analysis of
charge-transfer d-d excitons in the dielectric antiferromagnetic phase of cuprates and metastable low-energy
electron-hole EH dimers being a result of their evolution after electron-lattice relaxation, turns out to be
very fruitful not only for describing linear and nonlinear optical properties and photoinduced effects,
but also to develop a promising model of charge triplets to describe the low-energy electronic structure
and $T-x$ phase diagrams of active CuO$_2$ planes in cuprates of the $T$-La$_2$CuO$_4$ or $T^{\prime}$-Nd$_2$CuO$_4$
type, as well as NiO$_2$ planes in nickelates of the RNiO$_2$ type, and their evolution with changes in the main energy parameters. The research was supported by the Ministry of Education and Science of the Russian Federation, project № FEUZ-2023-0017.