Gh. Adam

Exchange and spin-fluctuation mechanisms of superconductivity in cuprates

We propose a microscopical theory of superconductivity in CuO

Reliability conditions in quadrature algorithms

_2

The boundary layer problem in Bayesian adaptive quadrature

layer within the effective two-band Hubbard model in the strong correlation limit. By applying a projection technique for the matrix Green function in terms of the Hubbard operators, the Dyson equation is derived. It is proved that in the mean-field approximation d-wave superconducting pairing mediated by the conventional exchange interaction occurs. Allowing for the self-energy corrections due to kinematic interaction, a spin-fluctuation d-wave pairing is also obtained.

Rigorous derivation of the mean-field Green functions of the two-band Hubbard model of superconductivity

T\sb{c}

The development of distributed computing technologies and BigData in LIT-JINR

dependence on the hole concentration and

Computer physics challenges in LIT-JINR

\bf k

Handling accuracy in Bayesian automatic adaptive quadrature

-dependence of the gap function are derived. The results show that the exchange interaction (which stems from the interband hopping) prevails over the kinematic interaction (which stems from the intraband hopping).A microscopic theory of superconductivity is considered in the framework of the Hubbard p-d model for the CuO2 plane. The Dyson equation is derived in the nonintersecting diagram approximation using the projection technique for the matrix Green function of the Hubbard operator. The solution of the equation for the superconducting gap shows that interband transitions for Hubbard subbands lead to antiferromagnetic exchange pairing as in the t-J model, while intraband transitions additionally lead to spin-fluctuation pairing of the d-wave type. The calculated dependences of the superconducting transition temperature on the hole concentration and of the gap on the wave vector are in qualitative agreement with experiments.

MEAN-FIELD SOLUTIONS TO SINGLET HOPPING AND SUPERCONDUCTING PAIRING WITHIN A TWO-BAND HUBBARD MODEL

The detection of insufficiently resolved or ill-conditioned integrand structures is critical for the reliability assessment of the quadrature rule outputs. We discuss a method of analysis of the profile of the integrand at the quadrature knots which allows inferences approaching the theoretical 100% rate of success, under error estimate sharpening. The proposed procedure is of the highest interest for the solution of parametric integrals arising in complex physical models.

Effective One‐Particle Crystal Field Potentials in the Point Charge Approximation

The boundary layer of a finite domain [a, b] covers mesoscopic lateral neighborhoods, inside [a, b], of the endpoints a and b. The correct diagnostic of the integrand behavior at a and b, based on its sampling inside the boundary layer, is the first from a set of hierarchically ordered criteria allowing a priori Bayesian inference on efficient mesh generation in automatic adaptive quadrature.

Effective interatomic forces from one‐particle crystal field parameters

The Green function (GF) equation of motion technique for solving the effective two-band Hubbard model of high-Tc superconductivity in cuprates (Plakida et al 1995 Phys. Rev. B 51 16599, Plakida et al 2003 JETP 97 331) rests on the Hubbard operator (HO) algebra. We show that, if we take into account the invariance to translations and spin reversal, the HO algebra results in invariance properties of several specific correlation functions. The use of these properties allows rigorous derivation and simplification of the expressions of the frequency matrix (FM) and of the generalized mean-field approximation (GMFA) Green functions (GFs) of the model. For the normal singlet-hopping and anomalous exchange pairing correlation functions which enter the FM and GMFA-GFs, an approximation procedure based on the identification and elimination of exponentially small quantities is described. It secures the reduction of the correlation order to GMFA-GF expressions.