Stepanov V. Transport properties and thermoEMF of copper and copper-oxide HTSCs, the role of defects

The dissertation is devoted to the research of the basic electronic processes occuring in polycrystalline copper and copper-oxide high-temperature superconductors (HTSCs) YBa2Cu3O7-δ under the influence of various defects resulting from deformation of copper, as well as oxygen-free annealing of polycrystals and depending on the method of preparation of films in order to obtain information about the physical nature of the interaction of superconductivity and defects and their possible impact on the Fermi surface (FS). For the first time a comparative analysis of temperature dependences of electrical resistance and thermoEMF, S(T), in copper was performed and resistance anomalies at low T were revealed correlated with features of S(T), most likely related to the possible resonant scattering of free electrons and thermal phonons on localized near electron dislocations. It is shown for the first time that the slope of S(T) in YBa2Cu3O7-δ changes at T = T *, confirming the possibility of FS rearrangement at the opening temperature of the pseudogap. Accordingly, the dependence of S(T)/T on logT changes from linear to nonlinear with decreasing charge carrier density nf below the critical doping p*, which indicates the expected change in FS at the transition nf through the quantum critical point. It is shown for the first time that the model of low-angle crystalline block interfaces, developed for critical currents in well-structured films, does not work with increasing number of defects, and the slope of logjc on log(1–T/Tc) changes markedly at 3D-2D crossover temperature, confirms the change in the electronic dimension of HTSCs below Tc.