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Victor D. Lakhno

Publications and source records attributed to Victor D. Lakhno.

16 recordsLinked to original sources
arXiv2025

On the comparison of models and experiments in the study of DNA open states: the problem of degrees of freedom

Simple mechanical models of DNA play an important role in studying the dynamics of its open states. The main requirement when developing a DNA model is the correct selection of its effective potentials and parameters based on experimental data. At the same time, various experiments allow us to "see" different types of DNA open states. Consideration of this feature is one of the most important conditions in the development, optimization, and parameterization of any mechanical model. Violation of this condition, i.e., the comparison of incomparable characteristics, leads to critical errors. The present investigation is devoted to the problem of degrees of freedom of DNA bases taken into account in mechanical models. Using the Peyrard-Bishop-Dauxois model as an example, two types of errors in interpreting experimental data when compared with the model are examined. The first one is a mismatch between the open state types in the model and experiment. The second one is an incorrect specification of the "threshold coordinate" of the open state. The concept of the effective total threshold coordinate of the radial separation of DNA strands for registration of opening is introduced. It is shown that correct interpretation of experimental data can actually eliminate discrepancies with theory.

cond-mat.other↗
arXiv2024

On the thermodynamics of DNA in the Peyrard-Bishop-Dauxois model

Based on the direct method of molecular dynamics, the temperature dependence of energy, partition function, entropy and free energy, describing the first-order phase transition, is calculated for the classical Peyrard-Bishop-Dauxois model of the DNA molecule. It is shown that without taking into account the quantum freezing of the degrees of freedom at low temperatures, the relationship between these quantities is not determined. An estimation was given for the number of bubbles in homogeneous DNA chains: PolyA/PolyT and PolyG/PolyC.

cond-mat.stat-mech↗
arXiv2021

Translation-Invariant Excitons in a Phonon Field

Large-radius excitons in polar crystals are considered. It is shown that translation invariant description of excitons interacting with a phonon field leads to a nonzero contribution of phonons into the exciton ground state energy only in the case of weak or intermediate electron-phonon coupling. A conclusion is made that self-trapped excitons cannot exist in the limit of strong coupling. Peculiarities of the absorption and emission spectra of translation invariant excitons in a phonon field are discussed. Conditions when the hydrogen-like exciton model remains valid in the case of electron-phonon interaction are found.

cond-mat.mes-hall↗
arXiv2020

Isotope effect in the translation-invariant bipolaron theory of high-temperature superconductivity

It is shown that the translation-invariant bipolaron theory of superconductivity can explain the dependence of the isotope coefficient in high-temperature superconductors on the critical temperature of a superconducting transition: in the case of strong electron-phonon interaction, the isotope coefficient is low when doping is optimal and high when it is weak. It is demonstrated that in the case of London penetration depth, the absolute value of the isotope coefficient behaves in the opposite way. A conclusion of the great role of non-adiabaticity in the case of weak doping is made. The criteria for d-wave phonon input into the isotope effect is established.

cond-mat.supr-con↗
arXiv2020

Dynamics of Holstein polaron in a chain with thermal fluctuations

Numerical modeling is used to investigate the dynamics of a polaron in a chain with small random Langevin-like perturbations which imitate the environmental temperature $T$ and under the influence of a constant electric field. In the semiclassical Holstein model the region of existence of polarons in the thermodynamic equilibrium state depends not only on temperature but also on the chain length. Therefore when we compute dynamics from initial polaron data, the mean displacement of the charge mass center differs for different-length chains at the same temperature. For a large radius polaron, it is shown numerically that the ``mean polaron displacement'' (which takes account only of the polaron peak and its position) behaves similarly for different-length chains during the time when the polaron persists. A similar slope of the polaron displacement enables one to find the polaron mean velocity and, by analogy with the charge mobility, assess the ``polaron mobility''. The calculated values of the polaron mobility for $T \approx 0$ are close to the value at $T=0$, which is small but not zero. For the parameters corresponding to the small radius polaron, simulations of dynamics demonstrate switching mode between immobile polaron and delocalized state. The position of the new polaron is not related to the position of the previous one; charge transfer occurs in the delocalized state.

cond-mat.stat-mech↗
arXiv2020

Translational-invariant bipolarons and superconductivity

A translation-invariant (TI) bipolaron theory of superconductivity based, like Bardeen-Cooper-Schrieffer theory, on Fröhlich Hamiltonian is presented. Here the role of Cooper pairs belongs to TI bipolarons which are pairs of spatially delocalized electrons whose correlation length of a coupled state is small. The presence of Fermi surface leads to stabilization of such states in its vicinity and a possibility of their Bose-Einstein condensation (BEC). The theory provides a natural explanation of the existence of a pseudogap phase preceding the superconductivity and enables one to estimate the temperature of a transition $T^*$ from a normal state to a pseudogap one. It is shown that the temperature of BEC of TI bipolarons determines the temperature of a superconducting transition $T_c$ which depends not on the bipolaron effective mass but on the ordinary mass of a band electron. This removes restrictions on the upper limit of $T_c$ for a strong electron-phonon interaction. A natural explanation is provided for the angular dependence of the superconducting gap which is determined by the angular dependence of the phonon spectrum. It is demonstrated that a lot of experiments on thermodynamic and transport characteristics, Josephson tunneling and angle-resolved photoemission spectroscopy (ARPES) of high-temperature superconductors does not contradict the concept of a TI bipolaron mechanism of superconductivity in these materials. Possible ways of enhancing $T_c$ and producing new room-temperature superconductors are discussed on the basis of the theory suggested.

cond-mat.supr-con↗
arXiv2019

New method of soft modes investigation by Little-Parks effect

As is known, Little-Parks effect concerned with oscillations of the critical temperature of a superconducting transition was one of the first effects which suggested the existence of Cooper pairing in conventional superconductors. It is shown that in high-temperature superconductors (HTSC) the Little-Parks effect based on bipolaron mechanism which in HTSC is the equivalent of Cooper pairing can be anomalously high. The results obtained can be used as a new method for detecting soft phonon modes in nanostructures on the basis of HTSC. The results can be also used to enhance the critical temperature of a superconducting transition.

cond-mat.supr-con↗
arXiv2019

Superconducting properties of 3D low-density TI-bipolaron gas in magnetic field

Consideration is given to thermodynamical properties of a three-dimensional Bose-condensate of translation-invariant bipolarons (TI-bipolarons) in magnetic field. The critical temperature of transition, critical magnetic fields, energy, heat capacity and the transition heat of TI-bipolaron gas are calculated. Such values as maximum magnetic field, London penetration depth and their temperature dependencies are calculated. The results obtained are used to explain experiments on high-temperature superconductors.

cond-mat.supr-con↗
arXiv2019

The way from high to room temperature superconductivity

Presently, the main method of producing new high-temperature superconductors is chemical when record temperatures of the superconducting transition $T_c$ are reached due to changes in the chemical structure of a superconductor. This paper deals with a possibility to reach room temperatures of $T_c$ in already available high-temperature superconducting materials by physical methods. It is shown that a superconducting phase corresponds to a Bose condensate moving in a thin subsurface layer and a motionless condensate in volume. We discuss a possibility to set in motion a motionless Bose condensate and enhance the temperature of superconducting transition.

physics.gen-ph↗
arXiv2017

New insight into the dynamics of rhodopsin photoisomerization from one-dimensional quantum-classical modeling

Characterization of the primary events involved in the $cis-trans$ photoisomerization of the rhodopsin retinal chromophore was approximated by a minimum one-dimensional quantum-classical model. The developed mathematical model is identical to that obtained using conventional quantum-classical approaches, and multiparametric quantum-chemical or molecular dynamics (MD) computations were not required. The quantum subsystem of the model includes three electronic states for rhodopsin: (i) the ground state, (ii) the excited state, and (iii) the primary photoproduct in the ground state. The resultant model is in perfect agreement with experimental data in terms of the quantum yield, the time required to reach the conical intersection and to complete the quantum evolution, the range of the characteristic low frequencies active within the primary events of the $11-cis$ retinal isomerization, and the coherent character of the photoreaction. An effective redistribution of excess energy between the vibration modes of rhodopsin was revealed by analysis of the dissipation process. The results confirm the validity of the minimal model, despite its one-dimensional character. The fundamental nature of the photoreaction was therefore demonstrated using a minimum mathematical model for the first time.

cond-mat.other↗
arXiv2016

Cooper pairs and bipolarons

It is shown that Cooper pairs are a solution of the bipolaron problem for model Fröhlich Hamiltonian. The total energy of a pair for the initial Fröhlich Hamiltonian is found. Differences between the solutions for the model and initial two-particle problems are discussed.

cond-mat.str-el↗
arXiv2013

Davydov's Solitons in a Homogeneous Nucleotide Chain

Charge transfer in homogeneous nucleotide chains is modeled on the basis of Holstein Hamiltonian. The path length of Davydov solitons in these chains is being studied. It is shown that in a dispersionless case, when the soliton velocity V is small, the path length grows exponentially as V decreases. In this case the state of a moving soliton is quasisteady. In the presence of dispersion determined by the dependence $Ω^2 = Ω_0^2 + V_0^2κ^2$ \, the path length in the region 0 < V < V_0 is equal to infinity. In this case the phonon environment follows the charge motion. In the region V > V_0 the soliton motion is accompanied by emission of phonons which leads to a finite path length of a soliton. The latter tends to infinity as $V \rightarrow V_0 + 0$ and $V \rightarrow \infty$. The presence of dissipation leads to a finite soliton path length. An equilibrium velocity of soliton in an external electric field is calculated. It is shown that there is a maximum intensity of an electric field at which a steady motion of a soliton is possible. The soliton mobility is calculated for the stable or ohmic brunch.

cond-mat.other↗
arXiv2013

s-f(d) exchange mechanism of magnon generation by slow spinpolarons

It is shown that in a single-axis antiferromagnetic semiconductor placed in a strong magnetic field, dispersionless magnons start emitting at any arbitrarily small velocity of an electron occurring in a spinpolaron state. If magnons are dispersed they are generated when the spinpolaron velocity exceeds the minimum phase velocity of magnons. The maximum power of magnon generation caused by the drift of spinpolarons is estimated.

cond-mat.mes-hall↗