arXiv subjects

R. Ya. Kezerashvili

Publications and source records attributed to R. Ya. Kezerashvili.

At least 19 recordsLinked to original sources

arXiv2026

Electronic Structure and Band-Edge Character of Ga-Substituted $α$-Al$_2$O$_3$: A First-Principles Study

We present a first-principles density functional theory study of substitutional Ga incorporation in an $α$-Al$_2$O$_3$-derived host, isolating chemical embedding effects without explicit geometric quantum confinement. Using a 30-atom $α$-Al$_2$O$_3$ supercell with two substituted Ga atoms, we examine three nonequivalent Ga-pair configurations and combine configuration-dependent energetics, local structural analysis, Ga-centered distortion metrics, and electronic-structure calculations.% to establish the relationship between local coordination distortion and band-edge modification. The energetically preferred configuration is governed not solely by Ga--O bond expansion but by the ability of the host lattice to accommodate bond-length and angular distortions around substituted Ga centers. Ga incorporation narrows the band gap relative to pristine $α$-Al$_2$O$_3$ without generating mid-gap states, primarily modifying the conduction-band manifold while preserving the oxygen-dominated valence edge. Band-edge charge densities and charge-density-difference maps show that the electronic response remains localized around the Ga-centered coordination environment. These results establish a chemically resolved baseline for understanding Ga incorporation in ultrawide-band-gap oxides and for future studies of confinement and interface effects in Ga-containing oxide nanostructures.

cond-mat.mtrl-sci↗

arXiv2026

Self-Consistent Determination of the Transition Temperature Between the $^{14}\mathrm{C}(n,γ)^{15}\mathrm{C}$ and $^{14}\mathrm{C}(p,γ)^{15}\mathrm{N}$ Reactions

We present the first self-consistent theoretical study of the competing $^{14}\mathrm{C}(n,γ)^{15}\mathrm{C}$ and $^{14}\mathrm{C}(p,γ)^{15}\mathrm{N}$ reactions within the same modified potential cluster model (MPCM). For the $^{14}$C$(p,γ_{0})^{15}$N reaction, total cross sections, astrophysical $S$ factors, and reaction rates are calculated using interaction potentials constrained by the available scattering and bound-state data. The astrophysical $S$-factor is estimated as $S(0)=4.5(1)$~keV$\cdot \text{b}$. Combining these results with our recent MPCM calculations for $^{14}\mathrm{C}(n,γ)^{15}\mathrm{C}$, we determine the transition temperature at which proton capture overtakes neutron capture in the production of $^{15}\mathrm{N}$. The self-consistent comparison predicts a transition temperature $T_9^{\rm c.p.}=2.5$ under Maxwell--Boltzmann statistics, significantly higher than previous estimates. The analysis is extended to Tsallis statistics, demonstrating that deviations from thermal equilibrium produce substantial shifts of the transition temperature. These results provide improved nuclear-physics input for astrophysical nucleosynthesis calculations.

nucl-th↗

arXiv2025

Stability of the Mott phase in excitonic double layers

We study the stability of excitonic Mott phases in the presence of a periodic potential and a non-local exciton-exciton interaction. The non-local interaction is treated in a mean-field approximation, while the local repulsion of the excitons is treated in a hopping expansion. The convergence of the latter is the criterion for the stability of the Mott phase with respect to quantum and thermal fluctuations. This hybrid approach enables us to establish a phase diagram for a bosonic Mott to superfluid transition. Our results could be useful to interpret recent experiments on electron-hole crystals in van der Waals heterostructures.

cond-mat.mtrl-sci↗

arXiv2025

Study of light $ϕ$-mesic nuclei with HAL QCD $ϕN$ interactions

We explore the possible existence of light $ϕ$-mesic nuclei using HAL QCD $ϕN$ interactions for the $^2S_{1/2}$ and $^4S_{3/2}$ channels. Particularly, using the Faddeev formalism in configuration space, the $ϕNN$ system, and $^{9}_ϕ$Be and $^{6}_{ϕϕ}$He nuclei within the framework of the three-body cluster model, are investigated. The $ϕα$ effective potential, obtained through a folding procedure, involves the HAL QCD $ϕN$ interaction in the $^4S_{3/2}$ channel which does not lead to a bound state of the $ϕN$ pair while the $ϕN$ $^2S_{1/2}$ channel yields the bound state as the $^3_ϕ$H nucleus. The $^4S_{3/2}$ potential ensures that the folding procedure is appropriate because there are no open channels like $ϕ+N$ and $ϕ+2N $ near or below the $ϕ+ 4N$ threshold, and it utilizes different matter distributions of $^4$He proposed in the literature. The folding potential is approximated by the Woods-Saxon formula. The mirror systems $ϕ$+$α$+$α$ and $ϕ$+$ϕ$+$α$ have energy ranges from 1-11 MeV and 3-10~MeV, respectively. The predicted binding energies represent the minimal values for the hypothetical $ϕ$ mesic nuclei $^{5}_ϕ$He, $^{9}_ϕ$Be and $^{6}_{ϕϕ}$He. The phenomenological $αα$ and $ϕϕ$ potentials are adopted from the literature.

nucl-th↗

arXiv2025

Examination of the lattice QCD-motivated strong attractive $ΩN$ potentials in the $Ω^- n p$ system

Within the framework of the Faddeev equations in configuration space, we examine the $Ω^{-} np$ system, employing strongly attractive lattice HAL QCD and Yukawa-type meson exchange potentials for the $ΩN$ interaction. Our formalism incorporates the attractive Coulomb force between the $Ω^{-}$ and proton, treating the system as three non-identical particle pairs (the $ABC$ model). In this study, we assess the impact of the Coulomb interaction on the system and compare our results with recent $ΩNN$ ($AAC$ model) calculations obtained using various approaches. The $ABC$ model yields low-energy characteristics for the $ΩNN$ system that differ from previous calculations. The Coulomb potential has a marginal perturbative effect on the $AAC$ system, shifting the three-body binding energy by the Coulomb energy of the two-body $BC$ subsystem, but only slightly deviating the spatial configuration from isosceles triangle symmetry. These effects are primarily driven by the strong $ΩN$ interaction. We demonstrate that the large binding energy of the $Ω^{-} np$ system arises from the short-range behavior of the $ΩN$ potentials.

nucl-th↗

arXiv2024

Comments to the paper "Detailed study of the astrophysical direct capture reaction $^6$Li($p,γ$)$^7$Be in a potential model approach" by E. M. Tursunov, S. A. Turakulov, and K. I. Tursunmakhatov, PHYSICAL REVIEW C 108, 065801 (2023)

We explicitly present the comparison of the results for the astrophysical S-factor and reaction rate for the $^6$Li($p,γ$)$^7$Be capture process at astrophysical energies, presented in Phys. Rev. Phys. Rev. C 105, 065806 (2022) and Phys. Rev. C 108. 065801 (2023) obtained within the famework of potential models. We demonstrate that both potential model approaches describe successfully the astrophysical S-factor and reaction rate simultaneously and reproduce the LUNA Collaboration [Phys. Rev. C 102, 052802(R) (2020)] results.

nucl-th↗

arXiv2024

The astrophysical $S-$factor and reaction rate for $^{15}$N($p,γ$)$^{16}$O within the modified potential cluster model

We study a radiative $p^{15}$N capture on the ground state of $^{16}$O at stellar energies within the framework of a modified potential cluster model (MPCM) with forbidden states, including low-lying resonances. The investigation of the $^{15}$N($p,γ_{0}$)$^{16}$O reaction includes the consideration of $^{3}S_{1}$ resonances due to $E1$ transitions and the contribution of $^{3}P_{1}$ scattering wave in $p$ + $^{15}$N channel due to $^{3}P_{1}\longrightarrow $ $^{3}P_{0}$ $M1$ transition. We calculated the astrophysical low-energy $S-$factor, and extrapolated $S(0)$ turned out to be within $34.7-40.4$ keV$\cdot $b. The important role of the asymptotic constant (AC) for the $^{15}$N($p,γ_{0}$)$^{16}$O process with interfering $^{3}S_{1}$(312) and $^{3}S_{1}$(962) resonances is elucidated. A comparison of our calculation for $S-$factor with existing experimental and theoretical data is addressed, and a reasonable agreement is found. The reaction rate is calculated and compared with the existing rates. It has negligible dependence on the variation of AC, but shows a strong impact of the interference of $^{3}S_{1}$(312) and $^{3}S_{1}$(962) resonances, especially at temperatures, referring to the CNO Gamow windows. We estimate the contribution of cascade transitions to the reaction rate based on the exclusive experimental data by \textit{Imbriani, et al. 2012}. The reaction rate enhancement due to the cascade transitions is observed from $T_{9} > 0.3 $ and reaches the maximum factor $\sim $\ 1.3 at $T_{9}=1.3$. We present the Gamow energy window and a comparison of rates for radiative proton capture reactions $^{12}$N($p,γ$)$^{13}$O, $^{13}$N($p,γ$) $^{14}$O, $^{14}$N($p,γ$)$^{15}$O, and $^{15}$N($p,γ$)$^{16}$O obtained in the framework of the MPCM and give temperature windows, prevalence, and significance of each process.

nucl-th↗

arXiv2024

Excitations of N$_{2 }$ and O$_{2}$ molecules due to helium ion impact and a polarization effect

We present an experimental study of the dissociative excitation in the collision of helium ions with nitrogen and oxygen molecules for collision energy of $0.7-10$ keV. Absolute emission cross sections are measured and reported for most nitrogen and oxygen atomic and ionic lines in wide, vacuum ultraviolet ($80-130$ nm) and visible ($380-800$ nm), spectral regions. Remarkable similarities of the processes realized in He$^{+}+$N$_{2}$ and He$^{+}+$O$_{2}$ collision systems are observed. We present polarization measurements for He$^{+}+$N$_{2}$ collision system. The emission of excited dissociative products was detected using an improved high-resolution optical spectroscopy method. This method incorporates the retarding potential method and a high resolution electrostatic energy analyzer to precisely measure the energy of incident particles and the energy of dispersion. The improvement in the optics resolution allows us to measure the cross section on the order of 10$^{-19}$ cm$^{2}$ or lower.

physics.atom-ph↗

arXiv2022

The $^6$Li$(p, γ)^7$Be reaction rate in the light of the new LUNA data

We present new calculations of the astrophysical $S-$factor and reaction rate for the $^{6}$Li$(p,γ)^{7}$Be reaction at energies of 10 keV to 5 MeV in the framework of a modified potential cluster model with forbidden states, including low lying resonances. The astrophysical $S(E)-$factor is compared with the available experimental data and calculations done within different models. The results for the $S-$factor are in good agreement with the data set (for $E<0.3$ MeV) and calculations (for $E<0.6$ MeV) of LUNA collaboration (Phys. Rev. C 102$,$ 052802, 2020). The recommended extrapolated zero value $S(0)$ turned out to be 101 eV $\cdot $ b. Using the theoretical total cross-sections$,$ the $^{6}$Li$(p,γ)^{7} $Be capture reaction rate is calculated at temperatures ranging from 0.01 to 10 $T_{9}$ and compared with NACRE and NACRE II. Analytical expressions for the $S-$factor and reaction rate are given, and the effect of low-lying resonances on the reaction rate is estimated. We suggest to update the NACRE and NACRE II databases in light of the new LUNA data and present calculations.

nucl-th↗

arXiv2020

Emission cross sections for energetic O$^+$($^4S,^2D,^2P$)-N$_2$ collisions

We report measurements of excitation functions for the O$^{+}-$N$_{2}$ process with the incident beam of $1-10$ keV O$^{+}$ in the ground O$^{+}(^{4}S)$ and metastable O$^{+}(^{2}D)$ and O$^{+}(^{2}P)$ states. The measurements are performed with the sufficiently high energy resolution of 0.001 eV, which allows to distinguish the excitation channels. The excitation cross section induced by incident ions in the metastable state O$^{+}(^{2}P)$ is much larger than that for the ground O$^{+}(^{4}S)$. The excitation cross section of N$_{2}^{+}$ ion for (0,0), (0,1) and (1,2) bands system is measured and the ratio of intensities for these bands is established as $10:3:1.$ It is shown that the cross sections for the N$^{+^{\ast }}$ions excitations in the dissociative charge exchange processes increase with the increase of the incident ion energy. The energy dependence of the excitation cross section of the band (0,0) $λ=391.4$ nm of the first negative system of the N$_{2}^{+}$ and degree of polarization of radiation in O$^{+}-$N$_{2}$ collision are measured for the first time. An influence of an admixture of the ion metastable state on a degree of polarization is revealed. It is demonstrated that for O$^{+}-$N$_{2}$ collision system the degree of polarization by metastable O$^{+}$($^{2}P$) ions is less compared to those that are in the ground O$^{+}$($^{4}S$) state and the sign of polarization degree of excited molecular ions does not change.

physics.atom-ph↗

arXiv2020

Electron-impact ionization and ionic fragmentation of O$_{2}$ from threshold to 120 eV energy range

We study the electron-impact induced ionization of O$_{2}$ from threshold to 120 eV using the electron spectroscopy method. Our approach is simple in concept and embodies the ion source with a collision chamber and a mass spectrometer with a quadruple filter as a selector for the product ions. The combination of these two devices makes it possible to unequivocally collect all energetic fragment ions formed in ionization and dissociative processes and to detect them with known efficiency. The ion source allows to vary and tune the electron-impact ionization energy and the target-gas pressure. We demonstrate that for obtaining reliable results of cross sections for inelastic processes and determining mechanisms for the formation of O$^{+}$($^{4}S,^2{D},^2{P}$) ions, it is crucial to control the electron-impact energy for production of ion and the pressure in the ion source. A comparison of our results with other experimental and theoretical data shows good agreement and proves the validity of our approach.

physics.atom-ph↗

arXiv2020

Three-body model for $K(1460)$ resonance

The three-body $KK\bar K$ model for the $K(1460)$ resonance is developed on the basis of the Faddeev equations in configuration space. A single-channel approach is using with taking into account the difference of masses of neutral and charged kaons. It is demonstrated that a splitting the mass of the $K(1460)$ resonance takes a place around 1460 MeV according to $K^0K^0{\bar K}^0$, $K^0K^+K^-$ and $K^+K^0{\bar K}^0$, $ K^+K^+K^-$ neutral and charged particle configurations, respectively. The calculations are performed with two sets of $KK$ and $K\bar K$ phenomenological potentials, where the latter interaction is considered the same for the isospin singlet and triplet states. The effect of repulsion of the $KK$ interaction on the mass of the $KK\bar K$ system is studied and the effect of the mass polarization is evaluated. The first time the Coulomb interaction for description of the $K(1460)$ resonance is considered. The mass splitting in the $K$(1460) resonances is evaluated to be in range of 10 MeV with taking into account the Coulomb force. The three-body model with the $K\bar K$ potential, which has the different strength of the isospin singlet and triplet parts that are related by the condition of obtaining a quasi-bound three-body state is also considered. Our results are in reasonable agreement with the experimental mass of the $K(1460)$ resonance.

nucl-th↗

arXiv2020

Reanalysis of $^{13}$N($p,γ$)$^{14}$O reaction and its role in stellar CNO cycle

Within the framework of the modified potential cluster model with forbidden states, the $^{13}$N($p,γ$)$^{14}$O reaction rate and the astrophysical $S$-factor are considered. It is shown that the first $p^{13}$% N resonance determines the $S$-factor and contributions of the $M1$ and $E2$ transitions are negligible at energies $E<1$ MeV, but are significant at high energies. The $S$-factor strongly depends on the $^{3}S_{1}$ resonance parameters. The influence of the width of \ the $^{3}S_{1}$ resonance on $S$% -factor is demonstrated. The reaction rate is calculated and an analytical approximation for the reaction rate is proposed. A comparison of our calculation with existing data is addressed. Results of our calculations for the $^{13}$N($p,γ)^{14}$O reaction rate provide the contribution to the steadily improving reaction rate database libraries. Our calculations of the $% ^{13}$N($p,γ)^{14}$O reaction rate along with results for the rates of $^{14}$N($% p,γ)^{15}$O and $^{12}$C$(p,γ)^{13}$N processes provide the temperature range $0.13<T_{9}<0.97$ for the conversion of CNO cycle to the HCNO cycle. Our results demonstrate that at early stages of a nova explosion at temperatures about $0.1$ $T_{9}$ and at late stages of evolution of supermassive stars at temperatures about $1.0$ $T_{9}$ the ignition of the HCNO cycle could occur at much lower densities of a stellar medium.

nucl-th↗

arXiv2019

Electron-hole superfluidity controlled by a periodic potential

We propose to control of an electron-hole superfluid in semiconductor coupled quantum wells and double layers of two-dimensional (2D) material by an external periodic field. This can either be created by the gates periodically located and attached to the quantum wells or double layers of 2D material or by the Moiré pattern of two twisted layers. The dependence of the electron-hole pairing order parameter on the temperature, the charge carrier density, and the gate parameters is obtained by minimization of the mean-field free energy. The second order phase transition between superfluid and electron-hole plasma, controlled by the external periodic gate field, is analyzed for different parameters.

cond-mat.mes-hall↗

arXiv2019

Integer and half-integer channel spins for elastic scattering cross sections

We present the analytical expressions for the differential cross sections and independent partial amplitudes for elastic scattering of nuclear particles for channels with a spin value of 1/2, 1, 3/2, 2 and 5/2. The independent partial amplitudes are presented for arbitrary orbital angular momentum $l$ and taking into account spin-orbit splitting. The analytical expressions allow one to carry out full phase shift analyses using experimental data for differential cross sections for processes with channel spins 1/2, 1, 3/2, 2 and 5/2.

nucl-th↗

arXiv2018

Trions and biexcitons in a nanowire

A theory of the trion and biexciton in a nanowire (NW) in the framework of the effective-mass model using the Born-Oppenheimer approximation is presented. We consider the formation of trions and biexcitons under the action of both the lateral confinement and the localization potential. The analytical expressions for the binding energy and eigenfunctions of the trion and biexciton are obtained and expressed by means of matrix elements of the effective one-dimensional cusp-type Coulomb potentials whose parameters are determined self-consistently by employing the same eigenfunctions of the confined electron and hole states. Our calculations for the ZnO/ZnMgO, CdSe/ZnS and CdSe/CdS core/shell cylindrical shaped NWs show that the trion and biexciton binding energy in NWs are size-dependent and for the same input parameters the biexciton binding energy in NWs is always larger than the binding energy of the trion. The trion and biexciton remain stable in CdSe/ZnS NW with the increase of the dielectric shell, while in ZnO/ZnMgO NW they become unstable when the surrounding dielectric shell exceeds 2.5 nm and 2 nm for each, respectively. The associative ionization of biexciton antibonding states into trion bonding states is studied. Based on the results for size dependence of biexciton binding energy and probability associative ionization an optimal radius for optoelectronic application NW is suggested.

cond-mat.mes-hall↗

arXiv2017

On mass polarization effect in three-body systems

We evaluate the mass polarization term of the kinetic-energy operator for different three-body nuclear $AAB$ systems by employing the method of Faddeev equations in configuration space. For a three-boson system this term is determined by the difference of the doubled binding energy of the $AB$ subsystem $2E_{2}$ and the three-body binding energy $E_{3}(V_{AA}=0)$ when the interaction between the identical particles is omitted. In this case: $\left\vert E_{3}(V_{AA}=0)\right\vert >2\left\vert E_{2}\right\vert$. In the case of a system complicated by isospins(spins), such as the kaonic clusters $ K^{-}K^{-}p$ and $ppK^{-}$, the similar evaluation impossible. For these systems it is found that $\left\vert E_{3}(V_{AA}=0)\right\vert <2\left\vert E_{2}\right\vert$. A model with an $AB$ potential averaged over spin(isospin) variables transforms the later case to the first one. The mass polarization effect calculated within this model is essential for the kaonic clusters. Besides we have obtained the relation $|E_3|\le |2E_2|$ for the binding energy of the kaonic clusters.

nucl-th↗

arXiv2016

Sensitive linear response of an electron-hole superfluid in a periodic potential

We consider excitons in a two-dimensional periodic potential and study the linear response of the excitonic superfluid to an electromagnetic wave at low and high densities. It turns out that the static structure factor for small wavevectors is very sensitive to a change of density and temperature. It is a consequence of the fact that thermal fluctuations play a crucial role at small wavevectors, since exchanging the order of the two limits, zero temperature and vanishing wavevector, leads to different results for the structure factor. This effect could be used for high accuracy measurements in the superfluid exciton phase, which might be realized by a gated electron-hole gas. The transition of the exciton system from the superfluid state to a non-superfluid state and its manifestation by light scattering are discussed.

cond-mat.str-el↗