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Matej Hudak

Publications and source records attributed to Matej Hudak.

15 recordsLinked to original sources
arXiv2021

Landau theory of 180 degrees domain walls in BaTiO3 type ferroelectric particles: microcomposite materials

The Landau theory of 180 degrees domain walls in BaTiO3 type ferroelectric particles is presented. Results of exact description of domain walls in bulk enabled us to formulate variational approach to theory of domain walls in corresponding small particles. The depolarization field effects and the space-charge layers are taken into account in the samples of the cube form. It was found that at low temperatures well known hyperbolic tangent wall profile is a good approximation for description of domain walls. Near the transition temperature it is more appropriate to speak about two walls separating ferroelectric-paraelectric-ferroelectric domains correspondingly as a result of splitting of a single ferroelectric wall in small BaTiO3 particles. Domain wall energy density, average interwall distance and change of the dielectric response of thick walls in small ferroelectric particles in microcomposites is found. Our results describe observed dependencies better than those theories which exist up to date. In temperature region near transition from the ferroelectric to paraelectric phase in micrcomposites our new quantitative results for response, for Curie-like transition temperature and other properties may be verified.

cond-mat.mtrl-sci↗
arXiv2021

Anisotropic Vortices in High-Temperature Superconductors and the Onset of Vortex-like Excitations above the Critical Temperature

Recently we have found that a three-dimensional superconducting state with anisotropic vortices localized at the vortex-lattice points is a stable state in zero external magnetic field for the layered high temperature uperconductivity materials. There exists a phase transition at the temperature $T_{c}^{v}$ from the normal phase to the vortex superconducting state which is of the first order. The first order phase transition shows overheating and overcooling effects. Nucleation of the superconducting phase in the normal phase thus may occur at temperatures higher than the transition temperature $T_{c}^{v}$. Then the onset of the vortex-like excitations above the transition temperature $T_{c}^{v}$ occurs in our theory. The onset of the vortex-like excitations in Nerst signal and some other experimental evidence for these excitations above the transition temperature $T_{c}^{v}$ in LSCO, YBCO and in other high-temperature materials may be explained thus by our theory. The vortex-like excitations above and below the transition temperature $T_{c}^{v}$ in high temperature materials continuously evolve. This fact may be explained within our theory.

cond-mat.supr-con↗
arXiv2020

Graphane -- material for hydrogen storage, breathers and kinks

In this paper we study the graphane. The Frenkel-Kontorova model on hexagonal lattice was used. We studied the case of one H atom above the C atom in the plane of graphane (we used the approximation of the hexagonal lattice in the plane). Continuous limit of the Lagrange-Euler equations is found from the Hamiltonian for $H$ atoms motion, they enabled us to study kink and breather excitations of $H$ atoms in the $H$ plane above the $C$ plane. We have found that there are three cases in the one $H$ atom motion The case $1$, when the $H$ atom is at the position which is below the position at which it is desorbed. Then the motion of this $H$ atom at time $t_{h}$ is described. The case $2$, when the $H$ atom is at the position of the suppressed atom $H$ in the direction to the $C$ (nearer) atom. This $H$ atom will be desorbed from the graphane going through the minimum of the potential energy and then through the point of desorption. Its motion of at time $t_{h}$ is described. The case $3$, when the $H$ atom is near the position of small oscillations near the potential energy minimum. The position of the atom $H$ at the time $t_{0}$ is the position to which the atom $H$ was excited with external force. The lattice of $H$ atoms in graphane may be excited as described by the kink solution of the Sine-Gordon equation. The kink has its velocity $U$, $ U^{2} < 1$, and in time $T$ and in $X^{'}$ coordinate direction localization. The Sine-Gordon equation has the breather solution in the $X^{'}$ direction. There $ω$ is the frequency of the breather, $T_{0}$ and $X^{'}_{0}$ are in time $T$ and in $X^{'}$ direction localization.

cond-mat.mtrl-sci↗
arXiv2018

Nonlinear Dielectric Response of Microcomposite Ferroelectrics

A dielectric nonlinear response in model two-phase composites, prepared from a displacive ferroelectric material with a dominant dielectric response due to a single oscillator ferroelectric mode and a dielectric material, is characterized by the existence of new modes due to geometric resonances below the percolation threshold in the ferroelectric matrix. The geometric nature of oscilations depends on composition and geometric properties of the mixture. Generation of higher frequency modes is studied within our model and discussed for displacive ferroelectric materials of the $BaTiO_{3}$ type. The Bergman Representation of the effective dielectric function together with our model for spectral function recently introduced are used simultaneously with theory of absorption in finite displacive ferroelectric crystals in quasistatic approximation to describe the physics of the composite. The boundaries of the present study are within this quasistatic approximation. New ways how to optimize material properties for nonlinear optics is outlined.

cond-mat.mtrl-sci↗
arXiv2018

Inverse Scattering Method II.: Methodological part with an example: Breather solution of the Sine-Gordon Equation

Recently it was discussed the Inverse Scattering Method, Part I. (paper I.) . It was a methodological Part with an example - soliton (kink) solution of the Sine-Gordon Equation. The aim of the paper I. was to introduce the Inverse Scattering Method for later studies of some problems in nonlinear dynamics. As a methodological example we described how to solve the Sine-Gordon Equation using the Inverse Scattering Method to obtain a soliton. This soliton solution is well known. In this paper we discuss another methodological example: the solution of the Sine-Gordon Equation using the Inverse Scattering Method to obtain description of a breather. While this breather solution is also well known, we will discuss later breather solutions in some physical systems. Thus we will have in the Part I. and in this Part II. seeds for solving problems with the Inverse Scattering Method, and in case of the Sine-Gordon Equation solutions describing the soliton and the breather.

nlin.SI↗
arXiv2018

Social Behavior of Drivers and Traffic

Drivers are agents, they are members of the group of drivers. Human groupings have hierarchical structure. The civilization consists of societies, societies consist of groups, and groups consist of individuals. We will consider the group of drivers. Every social group has power to organize individuals and use them for its own purposes. This is true also for the group of drivers. An agent, a driver, we call a member of a social group of drivers, we assume that his-her special properties are defined: they are agents driving a car. A driver-s behavior is influenced to some degree by the need to associate with other drivers and to obtain the approval of other drivers in the group, this is a general property of agents in a group. A driver equates his-her needs with those of the other drivers from the group. From this we explain how three empirically observed dependencies of personal driver radius dependence on some factors enabled us to identify quantity which characterizes verification of information by a driver. The smaller personal radius the larger process of verification of verbal and non-verbal information about the other person in other to accept the risk that this person will be closer to us as a person (driver). We expect that this conclusion is a general conclusion.

physics.soc-ph↗
arXiv2018

NMR and the antiferromagnetic crystal phase regions in rapidly quenched ribbons and in alloys of the type $Cu-Mn-Al$

It was shown that anomalous resistivity behavior of the $Cu-Mn-Al$ ribbons is explained by the s-d interaction between conduction electrons and the clustered Mn atoms. While nuclear magnetic resonance measurements show the antiferromagnetic and ferromagnetic clusters of Mn atom coexisting without long-range order, it is an interesting problem to study magnetic resonance properties also for the antiferromagnetic crystal phase regions (which have long-range order for larger regions) and which may also occur in these ribbons. The Heusler Type $Cu-Mn-Al$ Alloy has a composition half way between $Cu_{2}MnAl$ and $Cu_{3}Al$. Electron microscopy of the premartensitic $βCu-Zn-Al$ alloy has shown that the $βCu-Zn-Al$ alloy quenched from high temperature has the electron diffraction patterns of this alloy well explained by the model with the existence of small particles with an orthorhombic structure. It was noted that an important aspect of improvement in the material properties is to create a nanostructured state in matrix, which has significant advantages in magnetic and mechanical characteristics in contrast to the bulk materials in crystalline or amorphous state. It is an interesting problem to study magnetic resonance properties not only for the Mn atoms and clusters without long-range order but also for the antiferromagnetic crystal phase regions (which have long-range order for larger regions) which may also occur in ribbons. This is the aim of our paper.

cond-mat.mtrl-sci↗
arXiv2018

Displays and antiferroelectric liquid crystals

Recently we have formulated theory of bi-layer-dimerized chiral liquid antiferroelectric crystals. The spontaneous polarization has been increased owing to the strong interaction of the aromatic cores of the rod like liquid crystal molecules with the honey-comb pattern of the CNT walls The SmC*A ordering is improved around the CNTs. All relaxation modes in each phase are facilitated by dispersion of nanotubes whicg enhances the relaxation frequencies. This composite system with improvement in electro-optical properties can be exploited in modern display applications. SmC* LC were studied by one of t he authors (OH), namely their transition from the SmC phase. The role of disclinations in an applied electric field was studied by O. Hudak in the SmC* structure. While the role of fluctuations and of disclinations in the SmC* (FLC)was studied in the above papers, the role of fluctuations and disclinations in SmC*A and the role of addition of MWCNTs in SmC*A phaseis not well understood. Our theoretical description of (AFLC) including SmC*A introduced in may thus be used to study these effects.

cond-mat.soft↗
arXiv2017

On composites of the type: metal - dielectrics and superconductor - dielectrics

Composites of the type: metal - dielectrics and superconductor - dielectrics are studied in the quasistatic approximation. The dielectric response is described by the spectral function $G(n,x)$, which contains effects of the concentration x (of metallic resp. superconductive particles) on the dielectric function,and effects of the shape. The parameter n plays the role of the depolarisation factor for dielectric materials, in metals it is a factor which includes effects like shape, and a topology of the composite. There exists a percolation transition at $ x_{c}= \frac{1}{3} $ which leads to a metallic-like for the composite with the concentration $ x > x_{c}$. At low frequencies divergence with frequency remains even when there are present dielectric particles above the percolation concentration. In superconductor case the spectral function $G(n,x)$ may include also Josephson junction effects. We assume in both cases of composites two types of spheroidal particles, metal (superconducting) ones and dielectric ones. A dielectric function is constant in both cases for the dielectric material, and a dielectric function for the metal and for the superconductor are used with well known form for metals and a classical superconductor. A percolation transition at $ x_{c}$ leads to a metallic-like absorption for the composite with $x>x_{c}$. Note that at low frequencies divergence in frequency remains even when there are present dielectric particles above $x_{c}$. Below the percolation threshold dielectric properties are modified by metalic particles. We obtain at very low temperatures and low concentrations x of the superconductor the effective dielectric constant. The absorption part is zero in our simple case. The real part of the dielectric function increases with the concentration of the superconducting spheres. The frequency dependence is quadratic, it gives low frequency tail.

cond-mat.mtrl-sci↗
arXiv2017

Bi-layer-dimerized chiral liquid crystals

There is a large variety of bi-layered structures with smectic A type ordering. Results of this paper contribute to a theory of bi-layered phases. The difference between the \( SmC^{*}_{A} \) and \( SmC_α^{*} \) phases is described in this latter paper and it is explained by existence and non-existence of the dipole moment pairs.

cond-mat.soft↗
arXiv2017

Diamagnetism of 2D-Fermions in the Strong Nonhomogeneous Static Magnetic Field $( {\bf B} =B( 0, 0, 1/cosh^{2}( \frac{x-x_{0} }{ δ})))$ : gas magnetization, ... and gas compressibility

We study diamagnetism of a gas of fermions moving in a nonhomogeneous magnetic field $( {\bf B} =B( 0, 0, 1/cosh^{2}( \frac{x-x_{0} }{ δ})))$ The gas magnetization, the static magnetic susceptibility, the chemical potential and the gas compressibility are discussed and compared with the uniform field case. General need to study dynamics of electrons in different types of magnetic fields follows from a large number of experimental situations in which its understanding enables physicists to obtain new information.

cond-mat.mes-hall↗
arXiv2017

Transition of the uniform statistical field anyon state to the nonuniform one ar low particle densities

Using results of our exact description of the spinless fermion motion in a nonhomogeneous magnetic field \( {\bf B} = B( 0, 0, 1/cosh^{2}( \frac{x-x_{0}}{ δ})) \) we study a gas of these particles moving in this field. For lower densities \( ν< ν_{c}(B, δ) \) the corresponding total energy is lower than that of the uniform field state. Thus when the density of anyons decreases a transition from the uniform statistical field state to the nonhomogeneous field state is predicted.

cond-mat.mes-hall↗
arXiv2017

On Mechanical Response of Macro- and Microfiller-Reinforced Polymer: Young Modulus and Shear Wave Velocity

The problem of effective shear and bulk moduli, of an effective Poison's ratio and of an effective dielectric response in microcomposites of the ferroelastic-dielectric type was studied by us recently. Recently one of us, M. Hudak, studied static mechanical properties of the EVA material theoretically and experimentally. We extend our mentioned study of mechanical response of microcomposites of the type ferrolastics - dielectrics to study of Young modulus and shear wave velocity.

cond-mat.soft↗