Normal and superconducting state spectral properties of cuprates are theoretically described within the extended t-J model. The method is based on the equations of motion for projected fermionic operators and the mode-coupling approximation for the self-energy matrix. The dynamical spin susceptibility at various doping is considered as an input, extracted from experiments. The analysis shows th...

The theory of the superconductivity mediated by kinematic and exchange interactions in t?J and two-band Hubbard models in a paramagnetic state is formulated. The Dyson equations for the matrix Green functions in terms of the Hubbard operators are obtained in the non-crossing approximation. To calculate superconducting T c a numerical solution of self-consistent Eliashberg equations is proposed.

We present a non-perturbative approach to the problem of quasiparticles coupled to spin-fluctuations. If the fully dressed spin-fluctuation propagator is used in the Feynman graph expansion of the single particle Green’s function, the problem of summing all spin-fluctuation exchange Feynman graphs (i.e all the graphs without fermion loops) can be cast as a functional integral over Gaussian dist...

The issue of the vertex corrections in the spin-fermion model for cuprates has attracted a substantial interest over the last few years. The fully renormalized spin-fermion vertex, g full appears as the overall factor in the effective pairing interaction mediated by spin fluctuations: G(q ,v) 5g full 2 x(q ,v) where x(q ,v) is the dynamical spin susceptibility, and q and v are transferred momen...

Hund's pairing refers to Cooper generated by onsite interactions that become attractive due large exchange $J$. This is possible in multiorbital systems even when all local bare are repulsive, since attractions specific channels given certain linear combinations of interaction parameters. On the other hand, processes such as spin fluctuations also present. We compare mean-field and spin-fluctua...

This chapter is intended as a brief overview of some of the quantum spin liquid phases with unbroken SU(2) spin symmetry available in one dimension. The main characteristics of these phases are discussed by means of the bosonization approach. A special emphasis is laid on the interplay between frustration and quantum fluctuations in one dimension.

In molecular dynamics simulations, temperature is evaluated, via the equipartition principle, by computing the mean kinetic energy of atoms. There is no similar recipe yet for evaluating temperature of a dynamic system of interacting spins. By solving semiclassical Langevin spin-dynamics equations, and applying the fluctuation-dissipation theorem, we derive an equation for the temperature of a ...