Voitenko A. Influence of mesoscopic heterogeneities on thermodynamic and kinetic properties of superconductors

The dissertation deals with the influence of the spatial nonuniformity in the electronic subsystem of low- and high-temperature superconductors on the superconductor properties. First, heterogeneities ( e.g., admixtures or irregularities in the crystal lattice structure) can affect the character of microscopic motion of charge carriers. Second, the response of spatially nonuniform system to an external signal is an integrated responses of an ensemble of elementary volumes with individual temperature characteristics associated with the local value of the order parameter or the energy gap. In both cases, s-superconductors can mimic the properties of homogeneous and heterogeneous d-superconductors or superconductors with a combined pairing symmetry. At the same time, the spatial heterogeneity of electronic subsystem modifies the manifestations of other collective phenomena different from the superconducting one. To show it, a self-consistent theory of uniform superconductors with charge density waves (CDWs) and partial dielectric gapping of their Fermi surface has been developed, as well as the theory of their thermodynamic properties. A theory of tunnel currents through junctions with CDW superconductors has been built. As examples of this theory, the symmetry violation in junctions with CDW electrodes has been considered, and the theory of spin-dependent tunneling in an external magnetic field through such junctions has been developed. The presentation of high-temperature oxides as spatially inhomogeneous CDW s-superconductors allows both the dip-hump structure and the pseudogap feature in the current-voltage characteristics (CVCs) of high-temperature oxides to be identified as a distorted CDW manifestation at different temperatures, with the temperature behavior of those features being adequately reproduced in the whole temperature range and for different junction geometries. At the same time, the results obtained show that other types of superconducting pairing (in particular, the d-wave one) should be taken into consideration to explain the CVCs in the whole range of bias voltages.