Alexander Zarubin | Ural Branch of Russian Academy of Sciences (original) (raw)

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Papers by Alexander Zarubin

Solid State Phenomena, 2011

The Hubbard model with strong correlations is treated in the many-electron representation of Hubb... more The Hubbard model with strong correlations is treated in the many-electron representation of Hubbard's operators. The regions of stability of saturated and non-saturated ferromagnetism in the n-U plane for the square and simple cubic lattices are calculated. The role of the bare density of states singularities for the magnetic phase diagram is discussed. A comparison with the results of previous works is performed.

Physical Review B, 2004

The problem of stability of saturated and non-saturated ferromagnetism in the Hubbard model is co... more The problem of stability of saturated and non-saturated ferromagnetism in the Hubbard model is considered in terms of the one-particle Green's functions. Approximations by Edwards and Hertz and some versions of the self-consisten approximations based on the 1/z-expansion are considered. The account of longitudinal fluctuations turns out to be essential for description of the non-saturated state. The corresponding pictures of density of states are obtained. "Kondo" density-of-states singularities owing to spin-flip processes are analyzed. The critical electron concentrations for instabilities of saturated ferromagnetism and paramagnetic state are calculated for various lattices. Drawbacks of various approximations are discussed. A comparison with the results of previous works is performed. 71.10.Fd Lattice fermion models (Hubbard model, etc.), 71.28.+d Narrow-band systems; intermediate-valence solids,

Journal of Magnetism and Magnetic Materials, 2006

ABSTRACT The stability of saturated and non-saturated ferromagnetism in the Hubbard model is cons... more ABSTRACT The stability of saturated and non-saturated ferromagnetism in the Hubbard model is considered in terms of the Green's functions for the Hubbard's many-electron operators. An analysis of earlier approximations and their shortcomings is performed. Various versions of the self-consistent approximations based on the 1/z-expansion in the X-operator formalism are considered. It is demonstrated that the account of longitudinal fluctuations turns out to be essential for description of the non-saturated state. The corresponding pictures of density of states are obtained, “Kondo” density-of-states singularities owing to spin-flip processes being analyzed.

Journal of Experimental and Theoretical Physics, 2013

Journal of Experimental and Theoretical Physics, 2012

ABSTRACT The Hubbard model for a metal with strong correlations is considered in the representati... more ABSTRACT The Hubbard model for a metal with strong correlations is considered in the representation of many-electron X-operators. General self-consistent expressions are obtained for the one-particle Green function taking into account fluctuation corrections. The stability regions of the saturated and unsaturated ferromagnetism in the ground state on the n-U plane (n is the electron concentration and U is the Coulomb interaction parameter) are determined for various bare densities of states (semi-elliptic band and the square, cubic, and hypercubic lattices).

Journal of Magnetism and Magnetic Materials, 2012

The quasistatic approximation and equation-of-motion decoupling for the electron Green's function... more The quasistatic approximation and equation-of-motion decoupling for the electron Green's functions are applied to trace the effect of electronic dispersion and electron correlations on the ferromagnetism of two-dimensional itinerant-electron systems. It is found that next-nearest-neighbor hopping t ′ is of crucial importance for ferromagnetism formation yielding the magnetic phase diagram which is strongly asymmetric with respect to half-filling. At small t ′ in the vicinity of half-filling the ferromagnetic phase region is restricted by the spin-density wave instability, and far from half-filling by one-particle (spin-polaron) instability. At t ′ close to t/2 ferromagnetism is stabilized at moderate Hubbard U due to substantial curvature of the Fermi surface which passes in the vicinity of the van Hove singularity points. The results obtained are of possible importance for high-T c compounds and layered ruthenates.

In this paper, we investigated the magnetocaloric effect (MCE) in one-dimensional magnets with di... more In this paper, we investigated the magnetocaloric effect (MCE) in one-dimensional magnets with different types of ordering in the Ising model, Heisenberg, XY-model, the standard, planar, and modified Potts models. Exact analytical solutions to MCE as functions of exchange parameters, temperature, values and directions of an external magnetic field are obtained. The temperature and magnetic field dependences of MCE in the presence of frustrations in the system in a magnetic field are numerically computed in detail.

Materials Science Forum, 1996

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EPJ Web of Conferences

The aim of this work was to study critical phenomena taking place in 1D Ising model with differen... more The aim of this work was to study critical phenomena taking place in 1D Ising model with different exchange interactions signs and arbitrary spin values in a magnetic field. Exact analytical formulas for frustration fields, zero temperature magnetization and entropy at these fields are obtained. The general behavior of pair spin correlation function with the accounting of only interactions between nearest neighbors is examined.

Bulletin of the Russian Academy of Sciences: Physics, 2013

Physics Letters A - PHYS LETT A, 2006

The problem of motion of a single electron interacting with a periodic lattice of two-level syste... more The problem of motion of a single electron interacting with a periodic lattice of two-level systems is investigated within a spinless fermion model. The Green's function is calculated in a single-site dynamical coherent potential approximation which is equivalent to DMFT. The picture of one-electron density of states is obtained for various values of the tunnel splitting and coupling between the electron and two-level system. The occurrence of a band splitting with increase of the coupling is demonstrated.

Materials Science Forum, 2016

We considered the Ising 1D chain in an external magnetic field taking into account the nearest an... more We considered the Ising 1D chain in an external magnetic field taking into account the nearest and next-nearest interactions. By the method of Kramers–Wannier transfer-matrix, the rigorous analytical expression for Fourier-transform of pair spin-spin correlation function was obtained, and the temperature evolution of the scattering was analyzed for various relations of exchange parameters.

The Physics of Metals and Metallography, 2015

ABSTRACT In this work, we have obtained an exact solution to the one-dimensional modified 12-stat... more ABSTRACT In this work, we have obtained an exact solution to the one-dimensional modified 12-state Potts model using the Kramers-Wannier transfer matrix with allowance for the exchange interaction between nearest neighbors in an external magnetic field. Analytical expressions have been derived for the heat capacity, magnetization, magnetic susceptibility, magnetic entropy, and magnetocaloric effect as functions of temperature, magnitude and sign of exchange interaction, and the magnitude and direction of the magnetic field. The behavior of all of these parameters has been investigated in detail using numerical methods. The possibility of applying the results obtained to explain the observed magnetic properties of real cubic magnets with a NaCl structure and easy axes oriented along the [110] crystallographic directions has been discussed.

The Physics of Metals and Metallography, 2012