d-Wave Pairing in an Ensemble of Spin Polaron Quasiparticles in the Spin-Fermion Model of the Electronic Structure of the CuO2 Plane

It is demonstrated for the first time that the strong coupling between spin moments of copper ions and oxygen holes, which arises upon hybridazation mixing of two hole subsystems in the Emery model, not only affects the formation of spin polaron quasiparticles but also ensures effective attraction between them via the exchange interaction. This results in the Cooper instability with d-wave pairing in a 2D ensemble of spin polaron quasiparticles. The T-x-phase diagram obtained using this approach agrees well with the available experimental data

The higher-order magnetic skyrmions in non-uniform magnetic fields

For 2D Hubbard model with spin-orbit Rashba coupling in external magnetic field the structure of effective spin interactions is studied in the regime of strong electron correlations and at half-filling. It is shown that in the third order of perturbation theory, the scalar and vector chiral spin-spin interactions of the same order arise. The emergence of the latter is due to orbital effects of magnetic field. It is shown that for nonuniform fields, scalar chiral interaction can lead to stabilization of axially symmetric skyrmion states with arbitrary topological charges. Taking into account the hierarchy of effective spin interactions, an analytical theory on the optimal sizes of such states -- the higher-order magnetic skyrmions -- is developed for axially symmetric magnetic fields of the form $h(r) \sim r^{\beta}$ with $\beta \in \mathbb{R}$.Comment: 20 pages, 10 figures, 75 reference

LONDON PENETRATION DEPTH IN THE ENSEMBLE OF SPIN-POLARON OF QUASIPARTICLES CUPRATE SUPERCONDUCTORS

In the work on the example of calculation London penetration depth λL is shown that the spin-polaron approach can successfully describe the electrodynamic properties of high temperature cuprate superconductors. To study concentration and temperature dependences of λL was developed a method of calculating the response of an ensemble of spinpolaron of quasiparticles in a uniform field the vector potential Aq=0. Discusses the nature of the calculated concentration and temperature dependences of λL.Исследование выполнено при финансовой поддержке Программы Президиума РАН №12 "Фундаментальные проблемы высокотемпературной сверхпроводимости", РФФИ (грант #18-02-00837). Работа К.К.К. поддержана Советом по грантам Президента РФ (проект MK-1398.2017.2)