Lj. Ristovski

The unified theory of Davydov's and Fröhlich's models

Starting from the experimental facts and from quite general theoretical assumptions a theoretical model was formulated and the Hamiltonian derived which describes the possible excitations in a biological system. Davydovs and Fröhlichs models are also devoted to the same problem, although it seems that these models are not connected. Our results show that the Hamiltonians of Davydovs and Fröhlichs models can be easily obtained from the Hamiltonian of our model. More precisely, our theory could be considered as the microscopic theory of Fröhlichs model, from which Davydovs theoretical model follows as a particular case.

Free electron distribution in thin films

In this paper we analyze the electron states in metallic films. The first part of the paper is devoted to the study of the film where ion-ion interaction changes only in boundary layers. It was concluded that bulk states always appear in such film. Surface states appear only if the variation of the ion-ion interaction in the direction of the symmetry breaking in the boundary layer are neutralized. If the conditions for the creation of surface states are realized, one can obtain dense currents running along the film surface.

The similarities between thin sputtered films and high-Tc superconductive ceramics

Abstract The system which will be considered in this paper is the thin film having, in a specific way, a modulated mass distribution along a given direction as consequence of the sputtering treatment. The theoretical analysis demonstrates that this system has some particular properties, which are very similar to the properties of the high temperature superconductive ceramics. Therefore, taking into account their layered structure, we propose to consider the sputtered high temperature ceramic as a system of thin sputtered film-blocks. The blocks, depending on the film thickness as well as on the results of the sputtering treatment, could exhibit (SP-blocks) or not exhibit (N-blocks) superconductive properties. Here, the word “superconductive” has a particular meaning, because the superconductive state is in fact the normal state with no phonons, as well with no Cooper pairs. Namely, due to the freezing of the low energy acoustical modes which arises in the SP-blocks, the current in these blocks could be considered as a superconductive one because the carriers propagate in the media with no phonons. The above mentioned model assumptions lead to results which give possible explanations for the following particular properties of high Tc ceramics: the great carrier effective mass, the small value of the Fermi level, the anisotropy of the superconductive properties, the strong pressure dependence of Tc, the increasing of Tc with the increasing of the number of layers in the elementary cell, the existence of the specific heat jump and the dependence of the superconductive properties on the stoichiometric proportions x and δ.

Solitons in a molecular chain with impurities

The propagation of Davydovs soliton in the molecular chain with an impurity has been investigated. The numerical analysis demonstrates that the presence of the impurity leads to the decreasing of the soliton velocity, as well as to the localization (pinning) of the excitation in a region of space close to the impurity or even to the reflection or destruction of the soliton. The analytical results which demonstrate that the influence of the impurity is equivalent to the existence of some localized external inhomogeneous field or friction force have been obtained also.

Localized excitations in polymer chain with an isotopically substituted host

The optical properties of the molecular chain with the guest being an isotopically substituted molecule has been considered. The energies of the localized excitations are determined by the use of a particular theoretical approach.

On the problem of the exciton—phonon interaction

Abstract It is demonstrated that the theory of the exciton—phonon interaction could be formulated insuch a way that the quadratic exciton—phonon coupling terms arise which lead to the hybridization. Some consequences of the hybridization effects are pointed out.