1111.5711 (M. Yu. Kagan)
M. Yu. Kagan
In Chapters 9 and 10 we discuss non-phonon mechanisms of superconductivity of the Kohn-Luttinger type for different models in 3D and 2D electron systems at low densities including Fermi-gas model, Hubbard model and Shubin-Vonsovsky model. We complete the superconductive phase-diagrams of p-wave and d-wave superconductive pairing and discuss the possibility to increase Tc already at low density considering spin-polarized case or the two-band situation. In Chapters 15 and 16 mechanisms of electron nanoscale phase-separation in manganite-type oxide materials are analyzed using a simple Kondo-lattice model with intersite Coulomb repulsion between conductivity electrons. This model predicts the instability of magnetic (or charge) homogeneous ordering towards the formation of droplet structures (magnetic polarons) for a wide parameter range on the phase-diagram Various types of free and bound magnetic polarons are examined on regular, anisotropic and frustrated AFM-lattices. The transport properties of these materials are also discussed in the framework of the model where charge transport is due to spin-dependent tunneling of charge carriers between neighboring magnetic polarons. This model allows to analyze the temperature and magnetic field dependences of resistivity, magnetoresistance, magnetic susceptibility and 1/f-noise spectrum of phase-separated magnetic oxides in the temperature range corresponding to non-metallic behavior. The comparison of theoretical and experimental results for five families of 3D and layered magnetic oxides confirm the main predictions of the theory.We predict also the formation of various types of orbital polarons in the framework of the popular nowadays orbital t-J model.
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http://arxiv.org/abs/1111.5711
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