arXiv subjects

R. G. Nazmitdinov

Publications and source records attributed to R. G. Nazmitdinov.

At least 19 recordsLinked to original sources

arXiv2026

THz-Driven Floquet Spin Valve-Modulator

Within the scattering matrix ($S$-matrix) framework adapted to the high-frequency Floquet--Magnus formalism based on the length gauge, we investigate spin-dependent quantum transport in a 1D quantum ring with an asymmetric ($π/2$) configuration of quantum point contacts. We demonstrate the realization of a contactless electromagnetic analog of the Datta--Das spin field-effect transistor with ferromagnetic leads operating at zero static magnetic field. It is shown that an off-resonance terahertz (THz) field enables high-precision switching between spin channels without altering the static parameters of the nanostructure. Driven by an electronic Vernier effect, the quantum interference in the asymmetric geometry yields a selective spin phase rotator alongside an ultra-high-contrast current-suppression regime (``optical shutter''). The proposed architecture is fundamentally robust against multiphoton leakage sidebands, offering a thermally immune, high-speed alternative to conventional semiconductor static spin transistors.

cond-mat.mes-hall↗

arXiv2026

Nuclear molecule of heavy nuclei

The model of a nuclear molecule that composed of two heavy nuclei is proposed. To this aim the Hamiltonian of a dinuclear system is derived and diagonalized in the basis of bipolar spherical functions. Analytical expressions, describing excitations of highly deformed states of a nuclear molecule, are obtained. A remarkable agreement between numerical and analytical results is demonstrated at the description of roto-vibrational excitations in $^{240}$Pu at low energies. We provide the prediction for the spectrum of hyperdeformed states of the nucleus $^{232}$Th, considering it as a nuclear molecule that consists of $^{132}$Sn+$^{100}$Zr nuclei. The angular distribution of fission fragments for the nucleus $^{240}$Pu have been analyzed as well and compared with available experimental data.

nucl-th↗

arXiv2025

Antisolvent-Assisted Growth of Centimeter-Scale CsPbBr$_3$ Perovskite Single Crystals: A Theory-Guided Approach

The fabrication of large, high-quality single crystals (SCs) of all-inorganic cesium lead bromide (CsPbBr$_3$) via accessible methods remains a significant challenge. This work presents a systematic approach to optimize the antisolvent vapor-assisted crystallization (AVC) method, where the experimental design is guided by a theoretical methods at each step. A synergistic 9:1 (v/v) DMSO/DMF binary solvent was selected to balance solubility and kinetics, a choice rationalized by an analysis of Gutmann's donor numbers. Subsequently, ethanol was selected as a promising antisolvent by evaluating its properties against key criteria of miscibility and diffusion rate using Hansen Solubility Parameters (HSP) and Fick's law expressed in terms of saturated vapor pressure. Within this rationally-defined chemical system, the "growth window" was experimentally mapped, identifying an optimal precursor concentration of 0.35 M and a preliminary titration step to induce a controlled metastable state. The optimized protocol consistently yields phase-pure, orthorhombic CsPbBr$_3$ SCs up to 1 cm in size within one week at room temperature. The resulting crystals exhibit high crystallinity and thermal stability up to \SI{550}{\celsius}

cond-mat.mtrl-sci↗

arXiv2024

Valley focusing effect in a rippled graphene superlattice

Graphene corrugations affect hybridization of $π$ and $σ$ orbitals of carbon atoms in graphene based systems. It can as well break differently the symmetry of the electron transfer integrals for different strip boundaries. Using these facts, we found that the momentum distribution of electrons in ballistically propagating beam can be selective without external electric and/or magnetic fields in the graphene strip under experimentally feasible periodic potential. Such a potential is created by means of the superlattice that consists of periodically repeated graphene elements (flat+rippled junction) with different hybridization of carbon orbits, produced by variation of the graphene surface curvature. As a result it gives rise to the valley dependent focusing effects that can be controlled by alteration of number of superlattice elements.

cond-mat.mes-hall↗

arXiv2023

On performance of thin-film meso-structured perovskite solar cell through experimental analysis and device simulation

In the last few years there is an unprecedented progress in the increase of the power conversion efficiency of perovskite solar cells. Evidently, further advances of the efficiency of these devices will depend on the constraints imposed by the optical and electronic properties of their constituents. Quite apparently that during the manufacturing process of a solar cell, there is an inevitable variation in the thicknesses of various functional layers, which affects the optoelectronic characteristics of the final sample. In this work a possible strategy of the analysis of the solar cell performance is suggested, based on statistically averaging procedure of experimental data. We present a case study, in which the optoelectronic properties of the meso-structured perovskite solar cell (with a mesoporous TiO$_2$ layer) are analysed within the method providing a deeper understanding of the device operation. This method enables an assessment of the overall quality of the device, pointing pathways towards the maximum efficiency design of a perovskite solar cell by material properties tuning.

cond-mat.mtrl-sci↗

arXiv2023

Spreading widths of giant monopole resonance in the lead region: Random matrix approach

The microscopic calculation of the decay width of giant monopole resonance (GMR) anticipates the mixing of one-phonon states with configurations of increasing complexity. To this aim we develop the effective approach for description of monopole excited states that are obtained in the quasiparticle random phase approximation (QRPA), with regard of the coupling between one- and two-phonon states. Based on the QRPA one-phonon states, we generate the coupling and two-phonon states by means of the Gaussian orthogonal ensemble (GOE) distribution. Within our approach the spreading width of the GMRs in $^{204,206,208}$Pb are described by means of a random matrix approach on two energy scales. It is demonstrated that the main contribution into the decay of the GMR is determined by a small number of two-phonon states strongly coupled to low-energy surface vibrations. While a vast majority of the coupling matrix elements (that are small in value and following the GOE distribution) are responsible for the fine structure of the GMR spreading width. A remarkable agreement between the results of the full microscopic calculations (based on QRPA phonons coupled by means of the microscopic coupling matrix elements with calculated two-phonon states) with those of the developed approach confirms the vitality of the proposed ideas.

nucl-th↗

arXiv2022

Classical conformal blocks, Coulomb gas integrals and Richardson-Gaudin models

Virasoro conformal blocks are universal ingredients of correlation functions of two-dimensional conformal field theories (2d CFTs) with Virasoro symmetry. It is acknowledged that in the (classical) limit of large central charge of the Virasoro algebra and large external, and intermediate conformal weights with fixed ratios of these parameters Virasoro blocks exponentiate to functions known as Zamolodchikovs' classical blocks. The latter are special functions which have awesome mathematical and physical applications. Uniformization, monodromy problems, black holes physics, quantum gravity, entanglement, quantum chaos, holography, N=2 gauge theory and quantum integrable systems (QIS) are just some of contexts, where classical Virasoro blocks are in use. In this paper, exploiting known connections between power series and integral representations of (quantum) Virasoro blocks, we propose new finite closed formulae for certain multi-point classical Virasoro blocks on the sphere. Indeed, combining classical limit of Virasoro blocks expansions with a saddle point asymptotics of Dotsenko-Fateev (DF) integrals one can relate classical Virasoro blocks with a critical value of the "Dotsenko-Fateev matrix model action". The latter is the "DF action" evaluated on a solution of saddle point equations which take the form of Bethe equations for certain QIS (Gaudin spin models). A link with integrable models is our main motivation for this research line. ... .

hep-th↗

arXiv2020

Potential roots of the deep sub-barrier heavy-ion fusion hindrance phenomenon

We analyse the origin of the unexpected deep sub-barrier heavy-ion fusion hindrance in 64Ni+100Mo and 28Si+64Ni recations. Our analysis is based on the improved coupled-channels approach, implemented by means of the finite element method. With the aid of the Woods-Saxon potential the experimental cross sections and the S-factors of these reactions are remarkably well reproduced. We found that the account on the non-diagonal matrix elements of the coupling matrix, traditionally neglected in the conventional coupled-channels approaches in setting the left boundary conditions inside the potential pocket, and its minimal value are crucially important for the interpretation experimental data. Within our approach we found a good agreement with the experimental data for the S-factor of the fusion reaction 12C+12C, which has no a pronounced maximum for this system.

nucl-th↗

arXiv2019

Spin-dependent electron transmission across the corrugated graphene

We study various mechanisms of electron transmission across the corrugations in the graphene sheet. The spin dependence of the electron transmission probability in the rippled graphene is found. The electrons mean free path and transmission probabilities are analysed for different distributions of ripples in the graphene sheet as well. We demonstrate that the periodically repeated rippled graphene structure (the superlattice) leads to the suppression of the transmission of the ballistic electrons with one spin orientation in contrast to the other, depending on the direction of the incoming electron flow.

cond-mat.mes-hall↗

arXiv2019

Klein collimation by rippled graphene superlattice

The hybridization of $σ$ and $π$ orbitals of carbon atoms in graphene depends on the surface curvature. Considering a single junction between flat and rippled graphene subsystems, it is found an accumulation of charge in the rippled subsystem due to Klein penetration phenomenon that gives rise to n-p junction. Using this fact, we show that the momentum distribution of electrons in ballisitically propagating beam can be selective without a waveguide, or external electric, and/or magnetic fields in graphene strip under experimentally feasible one-dimensional periodic potential. Such a potential is created with the aid of superlattice that consists of periodically repeated graphene pieces withdifferent hybridizations of carbon orbits, produced by variation of the graphene surface curvature. The charge redistribution and selected transmission of electrons, caused by the superlattice, allows to control the electron focusing in the considered system by simply changing the element properties in the superlattice

cond-mat.mes-hall↗

arXiv2018

Two-phonon structures for beta-decay theory

The $β$-decay rates of $^{60}$Ca have been studied within a microscopic model, which is based on the Skyrme interaction T45 to construct single-particle and phonon spaces. We observe a redistribution of the Gamow-Teller strength due to the phonon-phonon coupling, considered in the model. For $^{60}$Sc, the spin-parity of the ground state is found to be $1^+$. We predict that the half-life of $^{60}$Ca is 0.3 ms, while the total probability of the $βx n$ emission is 6.1%. Additionally, the random matrix theory has been applied to analyse the statistical properties of the $1^+$ spectrum populated in the $β$-decay to elucidate the obtained results.

nucl-th↗

arXiv2018

Shape transitions in two-body systems: two-electron quantum dots in a magnetic field

We present a thorough analysis of the electron density distribution (shape) of two electrons, confined in the three-dimensional harmonic oscillator potential, as a function of the perpendicular magnetic field.Explicit algebraic expressions are derived in terms of the system's parameters and the magnetic field strength to trace the shape transformations in the ground and low-lying excited states. We found that the interplay of the classical and quantum properties lead to a quantum shape transition from a lateral to a vertical localization of electrons in low-lying excited states at relatively strong Coulomb interaction with alteration of the magnetic field. In contrast, in that regime in the ground states the electrons form always a ring type distribution in the lateral plane. The analytical results demonstrate a good agreement with quantum numerical results near the transition point and at high magnetic field.

cond-mat.mes-hall↗

arXiv2017

Self-organization of charged particles in circular geometry

The basic principles of self-organization of one-component charged particles, confined in disk and circular parabolic potentials, are proposed. A system of equations is derived, that allows us to determine equilibrium configurations for an arbitrary, but finite, number of charged particles that are distributed over several rings. Our approach reduces significantly the computational effort in minimizing the energy of equilibrium configurations and demonstrates a remarkable agreement with the values provided by molecular dynamics calculations. With the increase of particle number n>180 we find a steady formation of a centered hexagonal lattice that smoothly transforms to valence circular rings in the ground state configurations for both potentials.

cond-mat.stat-mech↗

arXiv2017

Spreading widths of giant resonances in spherical nuclei: damped transient response

We propose the universal approach to describe spreading widths of monopole, dipole and quadrupole giant resonances in heavy and superheavy spherical nuclei. Our approach is based on the ideas of the random matrix distribution of the coupling between one-phonon and two-phonon states generated in the random phase approximation. We use the Skyrme interaction SLy4 as our model Hamiltonian to create a single-particle spectrum and to analyze excited states of the doubly magic nuclei $^{132}$Sn, $^{208}$Pb and $^{310}$126. Our results demonstrate that the universal approach enables to describe gross structure of the spreading widths of the considered giant resonances.

nucl-th↗

arXiv2017

Radiative breaking of conformal symmetry in the Standard Model

Radiaitve mechanism of conformal symmetry breaking in a comformal-invariant version of the Standard Model is considered. The Coleman-Weinberg mechanism of dimensional transmutation in this system gives rise to finite vacuum expectation values and, consequently, masses of scalar and spinor fields. A natural bootstrap between the energy scales of the top quark and Higgs boson is suggested.

hep-ph↗

arXiv2017

Reply to "Comment on 'Thomson rings in a disk' "

We demonstrate that our model [Phys.Rev. E91, 032312 (2015)] serves as a useful tool to trace the evolution of equilibrium configurations of one-component charged particles confined in a disk. Our approach reduces significantly the computational effort in minimizing the energy of equilibrium configurations and demonstrates a remarkable agreement with the values provided by molecular dynamics calculations. We show that the Comment misrepresents our paper, and fails to provide plausible arguments against the formation hexagonal structure for n>200 in molecular dynamics calculations.

cond-mat.stat-mech↗

arXiv2016

Random matrix analysis of the monopole strength distribution in $^{208}$Pb

We study statistical properties of the $0^+$ spectrum of $^{208}$Pb in the energy region $E_x\leq20$ MeV. We use the Skyrme interaction SLy4 as our model Hamiltonian to create a single-particle spectrum and to analyze excited states. The finite-rank separable approximation for the particle-hole interaction enables us to perform the calculations in large configuration spaces. We show that while the position of the monopole resonance centroid is determined by one phonon excitations of $0^+$, the phonon-phonon coupling is crucial for the description of a strength distribution of the $0^+$ spectrum. In fact, this coupling has an impact on the spectral rigidity $Δ_3(L)$ which is shifted towards the random matrix limit of the Gaussian orthogonal ensembles.

nucl-th↗

arXiv2016

Triplet absorption spectroscopy and electromagnetically induced transparency

Coherence phenomena in four-level atomic system, cyclicly driven by three coherent fields, are investigated thoroughly at zero and weak magnetic fields. Each strongly interacting atomic state is converted to a triplet due to a dynamical Stark effect. Two dark lines with a Fano-like profile are arising in the triplet absorption spectrum with anomalous dispersions. We provide the conditions to control the widths of the transparency windows by means of the relative phase of the driving fields and the intensity of the microwave field, that closes the optical system loop. The effect of the Doppler broadening on results of the triplet absorption spectroscopy is analysed in detail.

physics.optics↗