Polarons and transport in a half-doped lanthanum–calcium manganite with low nonstoichiometric transition-metal ion content

The influence of local electron–phonon interaction on the formation of long-range order and electron dynamics in lanthanum–calcium manganite in the first non-vanishing approximation with respect to the inverse effective radius of the interaction of the time-dependent perturbation theory is considered. This work contains a detailed analysis of the relationship between charge and spin degrees of freedom in strongly correlated electronic systems that is important in understanding the mechanism of high-temperature superconductivity. It is shown that consistent consideration of correlation contributions from strong electron–electron and electron–phonon interactions describes the dynamic phenomena in manganites correctly. The presented theory gives zeroth spectral density at the chemical potential level that allows studying the fine structure of polaron excitations. A sharp increase in conductivity below the ferromagnetic ordering temperature has been observed. It is assumed that this phenomenon is associated with the appearance of intermediate-sized mobile polarons in a certain temperature area. Using the lanthanum–calcium manganite with a weak nonstoichiometric content of iron ions as an example, a comparison of theoretical and experimental results has been made.