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L. A. Maksimov

Publications and source records attributed to L. A. Maksimov.

At least 19 recordsLinked to original sources
arXiv2009

Singlet-triplet Hamiltonian for spin excitation in the Kondo-insulator

Within the framework of periodic asymmetric Anderson model for Kondo isoulators an effective singlet-triplet Hamiltonian with indirect antiferromagnetic f-f exchange interaction is introduced which allows to study analytically the dynamic magnetic susceptibilities of f-electrons. The approach allows to describe the three-level spin excitation spectrum with a specific dispersion in $YbB_{12}$. Distinctive feature of the consideration is the introduction of small radius singlet and triplet collective f-d excitations which at movement on a lattice form low - and high-energy spin bands.

cond-mat.str-el↗
arXiv2008

Thermal Hall Effect in 2D model for paramagnetic dielectrics

Phonon polarization in a magnetic field is analyzed in 2D model. It is shown, that at presence of spin-phonon interaction phonon possess elliptic polarization which causes the appearance of heat flux component perpendicular both to temperature gradient and magnetic field.

cond-mat.other↗
arXiv2008

Thermal Hall-Senftleben Effect

This paper is devoted to a prediction of new effect - the occurrence of a heat flow perpendicular both to temperature gradient and magnetic field in molecular dielectric where rotary degrees of freedom of molecules are defrozen. The method of the moments considering processes of phonon scattering on molecules with their rotary condition changing is developed.

cond-mat.other↗
arXiv2007

On the Kinetic Equation and Electrical Resistivity in Systems with Strong Spin- Hole Interaction

The problem of constructing the kinetic equation with the description of motion of a hole in systems with strong spin- hole interaction (such as high- temperature superconductors) in terms of the spin polaron has been considered in the framework of the regular antiferromagnetic $s-d$ model. It has been shown by the example of the electrical resistivity that kinetics is determined by the properties of the bands of the spin polaron (rather than "bar hole") and their quasiparticle residues $Z_{k}$. The cases of low and optimal doping of the $CuO_{2}$ plane have been considered. It has been shown that the rearrangement of the spectrum of the lower polaron band, as well as the strong doping dependence of the quasiparticle residues $Z_{k}$ is decisive in the unified consideration of these cases.

cond-mat.str-el↗
arXiv2007

Anomalous Hall effect for the phonon heat conductivity in paramagnetic dielectric

The theory of anomalous Hall effect for the heat transfer in a paramagnetic dielectric, discovered experimentally in [1], is developed. The appearance of the phonon heat flux normal to both the temperature gradient and the magnetic field is connected with the interaction of magnetic ions with the crystal field oscillations. In crystals with an arbitrary phonon spectrum this interaction creates the elliptical polarization of phonons. The kinetics related to phonon scattering induced by the spin-phonon interaction determines an origin of the off-diagonal phonon density matrix. The combination of the both factors is decisive for the phenomenon under consideration.

cond-mat.other↗
arXiv2005

On the stability of the coherent state of a two-level atom Bose gas in the resonant laser field at zero temperature

It is shown that a Bose gas of two-level atoms in the intense resonant laser field at zero temperature is a mixture of two condensates with a definite ratio of the densities. The criteria of stability are found for the stationary states of such system against the increment of the amplitudes of quasi Bogoliubov elementary excitations. Besides the usual acoustic mode the gap mode is shown to exist and the magnitude of the gap is proportional to the laser field amplitude. The involvement of the gas nonideality under definite conditions results in an instability and decay of the condensates.

cond-mat.other↗
arXiv2005

The structure of the ground superfluid state in a gas of Fermi atoms near the Feshbach resonance

Within the framework of the variational approach the ground state is studied in a gas of Fermi atoms near the Feshbach resonance at negative scattering length. The structure of the originating superfluid state is formed by two coherently bound subsystems. One subsystem is that of quasi molecules in the closed channel and the other is a system of pairs of atoms in the open channel. The set of equations derived allows us to describe the properties of the ground state at an arbitrary magnitude of the parameters. In particular, it allows one to find a gap in the spectrum of single-particle Fermi excitations and sound velocity characterizing a branch of collective Bose excitations.

cond-mat.other↗
arXiv2003

Relaxation of the Bose-condensate oscillations in the mesoscopic system at T=0

The general system is given of nonlinear equations describing dissipationless evolution of the oscillating Bose-condensate. The relaxation of transverse oscillations of the condensate in a trap of the cylindric symmetry is considered. The evolution occurs due to parametric resonance coupling the transverse mode with the longitudinal ones. The nonlinear rescattering in the subsystem of discrete longitudinal modes results in suppression of the return of energy, yielding dissipationless nonmonotonic relaxation of transverse oscillations in the condensate.

cond-mat.stat-mech↗
arXiv2002

The nonlinear damping of Bose-Einstein condensate oscillations at ultra-low temperatures

We analyze the damping of the transverse breathing mode in an elongated trap at ultralow temperatures. The damping occurs due to the parametric resonance entailing the energy transfer to the longitudinal degrees of freedom. It is found that the nonlinear coupling between the transverse and discrete longitudinal modes can result in an anomalous behavior of the damping as a function of time with the partially reversed pumping of the breathing mode. The picture revealed explains the results observed in [16].

cond-mat.soft↗
arXiv2002

The anomalous tunneling of Bose-condensate excitations

We discuss the tunneling of phonon excitations across a potential barrier separating two condensate bulks. It is shown that the strong barrier proves to be transparent for the excitations at low energy $ε$. Moreover, the transmission is reduced with increasing $ε$ in contrast to the standard dependence. This anomalous behavior is due to an existence of the quasiresonance interaction. The origin of this interaction is a result of the formation of the special well determined by the density distribution of condensate in the vicinity of a high barrier.

cond-mat.stat-mech↗
arXiv2001

The Damping of the Bose-Condensate Oscillations in a Trap at Zero Temperature

We discuss an existence of the damping for the radial condensate oscillations in a cylindric trap at zero temperature. The damping is a result of the parametric resonance leading to energy transfer from the coherent condensate oscillations to the longitudinal sound waves within a finite frequency interval. The parametric resonance is due to the oscillations of the sound velocity. The triggering amplitudes at zero temperature are associated with the zero-point oscillations.

cond-mat.stat-mech↗
arXiv2001

"Cherenkov radiation" of a sound in a Bose-condensed gas

In terms of linearized Gross-Pitaevskii equation we have studied the process of sound emission arises from a supersonic particle motion in a Bose-condensed gas. By analogy with the method used for description of Vavilov-Cherenkov phenomenon, we have found a friction work created by the particle generated condensate polarization. For comparison we have found radiation intensity of excitations. Both methods gives the same result.

cond-mat.stat-mech↗
arXiv2000

Manifestation of superfluidity in an evolving Bose-condensed gas

We study the generation of excitations due to an ''impurity''(static perturbation) placed into an oscillating Bose-condensed gas in the time-dependent trapping field. It is shown that there are two regions for the position of the local perturbation. In the first region the condensate flows around the ''impurity'' without generation of excitations demonstrating superfluid properties. In the second region the creation of excitations occurs, at least within a limited time interval, revealing destruction of superfluidity. The phenomenon can be studied by measuring the damping of condensate oscillations at different positions of the ''impurity''.

cond-mat.supr-con↗
arXiv1998

Comparison of non-crossing perturbative approach and generalized projection method for strongly coupled spin-fermion systems at low doping

We analyze the two-dimensional spin-fermion model in the strong coupling regime relevant to underdoped cuprates. We recall the set of general sumrules that relate moments of spectral density and the imaginary part of fermion self-energy with static correlation functions. We show that two-pole approximation of projection method satisfies the sumrules for first four moments of spectral density and gives an exact upper bound for quasiparticle energy near the band bottom. We prove that non-crossing approximation that is often made in perturbative consideration of the model violates the sumrule for third moment of spectral density. This leads to wrong position of lowest quasiparticle band. On the other hand, the projection method is inadequate in weak coupling limit because of approximate treatment of kinetic energy term. We propose a generalization of projection method that overcomes this default and give the fermion self-energy that correctly behaves both in weak and strong coupling limits.

cond-mat.str-el↗
arXiv1998

Spin polaron damping in the spin-fermion model for cuprate superconductors

A self-consistent, spin rotational invariant Green's function procedure has been developed to calculate the spectral function of carrier excitations in the spin-fermion model for the CuO2 plane. We start from the mean field description of a spin polaron in the Mori-Zwanzig projection method. In order to determine the spin polaron lifetime in the self-consistent Born approximation, the self-energy is expressed by an irreducible Green's function. Both, spin polaron and bare hole spectral functions are calculated. The numerical results show a well pronounced quasiparticle peak near the bottom of the dispersion at (pi/2,pi/2), the absence of the quasiparticle at the Gamma-point, a rather large damping away from the minimum and an asymmetry of the spectral function with respect to the antiferromagnetic Brillouin zone. These findings are in qualitative agreement with photoemission data for undoped cuprates. The direct oxygen-oxygen hopping is responsible for a more isotropic minimum at (pi/2,pi/2).

cond-mat↗
arXiv1997

Redistribution of the Hole Spectral Weight due to Long-Range Spin Correlations in the Three-Band Hubbard Model

In the framework of the three-band model for CuO_2 plane in high-temperature superconductors the spectrum of the spin-polaron hole exitation is investigated. The problem is treated taking into account the coupling of a local polaron with the antiferromagnetic spin wave with Q=(pi,pi). This leads to the essential changes of the lowest polaron band E(k) and the strong redistribution of the bare electron filling.

cond-mat↗
arXiv1997

One Spin-Polaron Problem in the Two-Dimensional Kondo-Lattice

Within the frameworks of spin-polaron concept and the spherically symmetric state for the antiferromagnetic spin background, the one-particle motion is studied for two-dimensional Kondo-lattice. The elemetary excitations are represented as a Bloch superposition of four one-site electron states: two local states- a bare electron state and a local spin-polaron of small radius, and two states of delocalized polarons which correspond to the coupling of local states to the antiferromagnetic spin wave with momentum Q=(pi,pi), so called Q-polarons. As a remarkable result we show that the lowest band of elementary excitations is essentially determined by Q-polaron states in strongly coupled regime. The account of Q-polarons shifts the band bottom from (pi,pi) to (0,0). The spectral weight of a bare particle in the lowest band states can greatly differ from 1. This may lead to a large Fermi surface for relatively small particle concentration.

cond-mat.str-el↗