Dziuba (Dzyuba) M. Transport properties of hybrid systems with strongly correlated electrons

The thesis presents the results of the investigations of the kinetic and galvanomagnetic properties of erbium and lanthanum cobaltites and heterojunctions with iron-based superconductors LaOFFeAs and FeSe. In the Er1-xSrxCoO3 system, it was found an abnormal increase of conductivity and a large magnetoresistance effect in a narrow range of Sr concentrations, which is explained by the presence of several phases with different conduction mechanisms. For low values of current, it was detected the nonlinear features of percolation transport induced by an electric field. For the first time the transition from metallic to nonmetallic behavior of the conductivity with a decrease of the temperature was obseved in the bulk granular cobaltites La0,65Sr0,35CoO3 and (La0,65Sr0,35)0,95Ag0,05CoO3. It was proposed an explanation of the nature of the phenomenon, based on the account of the intergranular mechanism of the spin-polarized tunneling of charge carriers between the nearest granules. It was found that in the mesoscopic heterojunctions Cu/LaOFFeAs in the conditions of the Andreev reflection, conductivity in the external magnetic field greater than 1 kOe, increases, causing a negative magnetoresistance. In the conditions of suppressed superconductivity, the porosity and parity of the magnetoresistance have been found, which may be a result of stripe or nematic ordering in the normal state of iron-based superconductors.