arXiv subjects

V. Fleurov

Publications and source records attributed to V. Fleurov.

At least 37 records · Page 2Linked to original sources

arXiv2005

Resonant light-light interaction in slab waveguides: angular filters and spectral hole burning

We consider the process of low-power light scattering by optical solitons in a slab waveguide with homogeneous and inhomogeneous refractive index core. We observe resonant reflection (Fano resonance) as well as resonant transmission of light by optical solitons at certain incident angles. The resonance position can be controlled experimentally by changing the soliton intensity and the relative frequency detuning between the soliton and the probe light beams.

nlin.PS↗

arXiv2005

Resonant light scattering by optical solitons

We consider the process of light scattering by optical solitons in a planar waveguide with homogeneous and inhomogeneous refractive index core. We observe resonant reflection (Fano resonances) as well as resonant transmission of light by optical solitons. All resonant effects can be controlled in experiment by changing the soliton intensity.

nlin.PS↗

arXiv2004

Classical and quantum radiation of perturbed discrete breathers

We show that the linearized phase space flow around a discrete breather solution is not capable of generating persistent energy flow away from the breather even in the case of instabilities of extended states. This holds both for the classical and quantized description of the flow. The main reason for that is the parametric driving the breather provides to the flow. Corresponding scaling arguments are derived for both classical and quantum cases. Numerical simulations of the classical flow support our findings.

cond-mat.other↗

arXiv2004

Nonlinear effects in tunnelling escape in N-body quantum systems

We consider the problem of tunneling escape of particles from a multiparticle system confined within a potential trap. The process is nonlinear due to the interparticle interaction. Using the hydrodynamic representation for the quantum equations of the multiparticle system we find the tunneling rate and time evolutions of the number of trapped particles for different nonlinearity values.

cond-mat.other↗

arXiv2003

Double exchange mechanisms for Mn doped III-V ferromagnetic semiconductors

A microscopic model of indirect exchange interaction between transition metal impurities in dilute magnetic semiconductors (DMS) is proposed. The hybridization of the impurity d-electrons with the heavy hole band states is largely responsible for the transfer of electrons between the impurities, whereas Hund rule for the electron occupation of the impurity d-shells makes the transfer spin selective. The model is applied to such systems as $n-$type GaN:Mn and $p-$type (Ga,Mn)As, $p-$type (Ga,Mn)P. In $n-$type DMS with Mn$^{2+/3+}$ impurities the exchange mechanisms is rather close to the kinematic exchange proposed by Zener for mixed-valence Mn ions. In $p-$type DMS ferromagnetism is governed by the kinematic mechanism involving the kinetic energy gain of heavy hole carriers caused by their hybridization with 3d electrons of Mn$^{2+}$ impurities. Using the molecular field approximation the Curie temperatures $T_C$ are calculated for several systems as functions of the impurity and hole concentrations. Comparison with the available experimental data shows a good agreement.

cond-mat.str-el↗

arXiv2003

Damped orbital excitations in the titanates

A possible mechanism for the removal of the orbital degeneracy in RTiO3 (where R=La, Y, ...) is considered. The calculation is based on the Kugel-Khomskii Hamiltonian for electrons residing in the t2g orbitals of the Ti ions, and uses a self-consistent pe rturbation expansion in the interaction between the orbital and the spin degrees of freedom. The latter are assumed to be ordered in a Neel state, brought about by delicate interactions that are not included in the Kugel-Khomskii Hamiltonian. Within our model calculations, each of the t2g bands is found to acquire a finite, temperature-dependent dispersion, that lifts the orbital degeneracy. The orbital excitations are found to be heavily damped over a rather wide band. Consequently, they do not participate as a separate branch of excitations in the low-temperature thermodynamics.e

cond-mat.str-el↗

arXiv2002

Fano resonances with discrete breathers

A theoretical study of linear wave scattering by time-periodic spatially localized excitations (discrete breathers (DB)) is presented. We obtain that the wave propagation is strongly influenced by a local coupling between an open and closed channels generated by the DB. A peculiar effect of total reflection occurs due to a Fano resonance when a localized state originating from closed channels resonates with the open channel. For the discrete nonlinear Schroedinger chain we provide with an analytical result for the frequency dependence of the transmission coefficient, including the possibility of resonant reflection. We extend the analysis to chains of weakly coupled anharmonic oscillators and discuss the relevance of the effect for electronic transport spectroscopy of mesoscopic systems.

cond-mat.soft↗

arXiv2002

Plasticity of Ferromagnets near the Curie Point

We propose an explanation of the anomalous growth of plasticity in ferromagnets near the Curie point. We demonstrate that this effect is caused by spin-dependent detachment of dislocations from obstacles under an influence of the internal magnetic field. Magnetization fluctuations grow in the vicinity of the Curie point, yield an increase of the detachment probability and, hence, an increase of the plasticity. We apply this model for a description of the temperature behaviour of the critical stress in nickel and of the microhardness of gadolinium. An external magnetic field suppresses the magnetization fluctuations and, hence may suppress the above singularities.

cond-mat.mtrl-sci↗

arXiv2002

On the nature of ferromagnetism in diluted magnetic semiconductors: GaAs:Mn, GaP:Mn

A microscopic Hamiltonian for interacting manganese impurities in diluted magnetic semiconductors (DMS) is derived. It is shown that in p -type III-V DMS the indirect exchange between Mn impurities has similarities with the Zener mechanism in transition metal oxides. Here the mobile holes and localized states near the top of the valence band play the role of unoccupied oxygen orbitals which induce ferromagnetism. The Curie temperature estimated from the proposed kinematic exchange agrees with recent experiments on GaAs:Mn. The model is also applicable to the GaP:Mn system.

cond-mat↗

arXiv2002

Quantum Effects in the Conductivity of a Quasi 2D Electron Gas

We consider the role of the third dimension in the conductivity of a quasi 2D electron gas. If the transverse correlation radius of the scattering potential is smaller than the width of the channel, i.e. the width of the transverse electron density distribution, then scattering to higher levels of the confinement potential becomes important, which causes a broadening of the current flow profile. The resulting conductivity is larger than that obtained from a 2D Boltzmann equation. A magnetic field, parallel to the driving electric field, effectively competes with the confining potential and, in the limit of a strong magnetic field, it is the field, which largely shapes the electron and current profile, rather than the potential. As a result the current flow profile increases and a negative longitudinal magnetoresistivity of the quasi 2D electron gas may be observed.

cond-mat.mes-hall↗

arXiv2001

Localized states in 2D semiconductors doped with magnetic impurities in quantizing magnetic field

A theory of magnetic impurities in a 2D electron gas quantized by a strong magnetic field is formulated in terms of Friedel-Anderson theory of resonance impurity scattering. It is shown that this scattering results in an appearance of bound Landau states with zero angular moment between the Landau subbands. The resonance scattering is spin selective, and it results in a strong spin polarization of Landau states, as well as in a noticeable magnetic field dependence of the $g$ factor and the crystal field splitting of the impurity $d$ levels.

cond-mat.mes-hall↗

arXiv2001

Spin-engineered quantum dots

Spatially nonhomogeneously spin polarized nuclei are proposed as a new mechanism to monitor electron states in a nanostructure, or as a means to createn and, if necessary, reshape such nanostructures in the course of the experiment. We found that a polarization of nulear spins may lift the spin polarization of the electron states in a nanostructure and, if sufficiently strong, leads to a polarization of the electron spins. Polarized nuclear spins may form an energy landscape capable of binding electrons with energy up to several meV and the localization radius $ >$ 100Å.

cond-mat.mes-hall↗

arXiv2001

Bound spin-excitons in two-dimensional electron gas

A theory of the spin exciton capture by a magnetic impurity in a 2D electron gas is developed. We consider the resonance model for electron scattering by a transition metal impurity and calculate the binding potential for spin excitons. This potential is spin selective and is capable of binding a spin exciton with zero angular momentum. In order to trap an exciton with a nonzero angular momentum m, the potential must exceed a certain threshold value, depending on m.

cond-mat.mes-hall↗

arXiv2000

Exchange Mediated Interaction of Dislocations and Deformation Hardening of Invar Alloys

We propose an explanation of anomalies observed in the behavior of deformation hardening of Invars. An extremely strong volume magnetostriction, typical of Invars, results in an enhancement of the exchange contribution to the energy of the dislocation system by about three orders of magnitude with respect to its value in conventional ferromagnetics. Both the self energy of individual dislocations and the interaction between them, determined usually only by the elastic deformation, in Invars is strongly diminished by the contribution of the exchange energy. This fact explains a strong suppression of the deformation hardening rate in the second stage as well as its strong temperature and content dependence in Invars.

cond-mat.mtrl-sci↗

arXiv2000

"Cold Melting" of Invar Alloys

An anomalously strong volume magnetostriction in Invars may lead to a situation when at low temperatures the dislocation free energy becomes negative and a multiple generation of dislocations becomes possible. This generation induces a first order phase transition from the FCC crystalline to an amorphous state, and may be called "cold melting". The possibility of the cold melting in Invars is connected with the fact that the exchange energy contribution into the dislocation self energy in Invars is strongly enhanced, as compared to conventional ferromagnetics, due to anomalously strong volume magnetostriction. The possible candidate, where this effect can be observed, is a FePt disordered Invar alloy in which the volume magnetostriction is especially large.

cond-mat.mtrl-sci↗

arXiv2000

Exchange Effects in the Invar Hardening: $Fe_{0.65}Ni_{0.35}$ as a test case

An increase of the critical resolved shear stress of Invar alloys (Invar hardening) with a lowering temperature is explained. The effect is caused by a growth of the exchange interaction between dangling $d$-electron states of dislocation cores and paramagnetic obstacles (e.g., Ni atoms in FeNi alloys) which occurs below the Curie temperature. The spins of the two electrons align along the magnetization due to the exchange interaction with the surrounding atoms of the ferromagnetic. The exchange interaction between the dislocations and obstacles is enhanced in Invars due to a strong growth of the magnetic moments of atoms under the action of elastic strains near the dislocation cores. Parameters characterizing the exchange interaction are determined for the case of the Fe$_{0.65}$Ni$_{0.35}$ Invar. The influence of the internal magnetic field on the dislocation detachment from the obstacles is taken into account. The obtained temperature dependence of the critical resolved shear stress in the Fe$_{0.65}$Ni$_{0.35}$ Invar agrees well with the available experimental data. Experiments facilitating a further check of the theoretical model are suggested.

cond-mat.mtrl-sci↗

arXiv2000

Tunneling of localized excitations: giant enhancement due to fluctuations

We consider the tunneling of localized excitations (many boson bound states) in the presence of a bosonic bath. We show both analytically and numerically that the bath influence results in a dramatical enhancement of the amplitude of the excitation tunneling. The order of the bosonic flow in the course of the tunneling process is obtained. On the background of the giant tunneling enhancement we observe and describe additional resonant enhancement and {\sl suppression} of tunneling due to avoided level crossings.

cond-mat.stat-mech↗

arXiv2000

Discrete breathers in classical spin lattices

Discrete breathers (nonlinear localised modes) have been shown to exist in various nonlinear Hamiltonian lattice systems. In the present paper we study the dynamics of classical spins interacting via Heisenberg exchange on spatial $d$-dimensional lattices (with and without the presence of single-ion anisotropy). We show that discrete breathers exist for cases when the continuum theory does not allow for their presence (easy-axis ferromagnets with anisotropic exchange and easy-plane ferromagnets). We prove the existence of localised excitations using the implicit function theorem and obtain necessary conditions for their existence. The most interesting case is the easy-plane one which yields excitations with locally tilted magnetisation. There is no continuum analogue for such a solution and there exists an energy threshold for it, which we have estimated analytically. We support our analytical results with numerical high-precision computations, including also a stability analysis for the excitations.

cond-mat↗