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Atoms, Volume 10, Issue 3 (September 2022) – 18 articles

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Article
Non-Monotonic dc Stark Shifts in the Rapidly Ionizing Orbitals of the Water Molecule
Atoms 2022, 10(3), 84; https://doi.org/10.3390/atoms10030084 (registering DOI) - 18 Aug 2022
Abstract
We extend a previously developed model for the Stark resonances of the water molecule. The method employs a partial-wave expansion of the single-particle orbitals using spherical harmonics. To find the resonance positions and decay rates, we use the exterior complex scaling approach which [...] Read more.
We extend a previously developed model for the Stark resonances of the water molecule. The method employs a partial-wave expansion of the single-particle orbitals using spherical harmonics. To find the resonance positions and decay rates, we use the exterior complex scaling approach which involves the analytic continuation of the radial variable into the complex plane and yields a non-hermitian Hamiltonian matrix. The real part of the eigenvalues provides the resonance positions (and thus the Stark shifts), while the imaginary parts Γ/2 are related to the decay rates Γ, i.e., the full-widths at half-maximum of the Breit–Wigner resonances. We focus on the three outermost (valence) orbitals, as they dominate the ionization process. We find that for forces directed along the three Cartesian co-ordinates, the fastest ionizing orbital always displays a non-monotonic Stark shift. For the case of fields along the molecular axis we show results as a function of the number of spherical harmonics included (max=3,4). Comparison is made with total molecule resonance parameters from the literature obtained with Hartree–Fock and coupled cluster methods. Full article
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Review
Nonlinear Dynamics in Isotropic and Anisotropic Magneto-Optical Traps
Atoms 2022, 10(3), 83; https://doi.org/10.3390/atoms10030083 - 12 Aug 2022
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Abstract
We briefly review some recent advances in the field of nonlinear dynamics of atomic clouds in magneto-optical traps. A hydrodynamical model in a three-dimensional geometry is applied and analyzed using a variational approach. A Lagrangian density is proposed in the case where thermal [...] Read more.
We briefly review some recent advances in the field of nonlinear dynamics of atomic clouds in magneto-optical traps. A hydrodynamical model in a three-dimensional geometry is applied and analyzed using a variational approach. A Lagrangian density is proposed in the case where thermal and multiple scattering effects are both relevant, where the confinement damping and harmonic potential are both included. For generality, a general polytropic equation of state is assumed. After adopting a Gaussian profile for the fluid density and appropriate spatial dependencies of the scalar potential and potential fluid velocity field, a set of ordinary differential equations is derived. These equations are applied to compare cylindrical and spherical geometry approximations. The results are restricted to potential flows. Full article
(This article belongs to the Special Issue Cold and Rydberg Atoms for Quantum Technologies)
Article
Electron and Positron Scattering from Precious Metal Atoms in the eV to MeV Energy Range
Atoms 2022, 10(3), 82; https://doi.org/10.3390/atoms10030082 - 11 Aug 2022
Viewed by 232
Abstract
This article reports on the scattering of unpolarized and spin polarized electrons and positrons from 28Ni58,29Cu63,46Pd108, and 78Pt196, covering light to heavy precious metal targets. To cover the wide [...] Read more.
This article reports on the scattering of unpolarized and spin polarized electrons and positrons from 28Ni58,29Cu63,46Pd108, and 78Pt196, covering light to heavy precious metal targets. To cover the wide energy domain of 1 eV Ei300 MeV, Dirac partial-wave phase-shift analysis is employed, using a complex optical potential for Ei1 MeV and a potential derived from the nuclear charge distribution for Ei>1 MeV. Results are presented for the differential and integral cross-sections, including elastic, momentum transfer, and viscosity cross-sections. In addition, the inelastic, ionization, and total (elastic + inelastic) cross-section results are provided, together with mean free path estimates. Moreover, the polarization correlations S,T, and U, which are sensitive to phase-dependent interference effects, are considered. Scaling laws with respect to collision energy, scattering angle, and nuclear charge number at ultrahigh energies are derived using the equivalence between elastic scattering and tip bremsstrahlung emission. In addition, a systematic analysis of the critical minima in the differential cross-section and the corresponding total polarization points in the Sherman function S is carried out. A comparison with existing experimental data and other theoretical findings is made in order to test the merit of the present approach in explaining details of the measurements. Full article
Article
Generating Sustained Coherence in a Quantum Memory for Retrieval at Times of Quantum Revival
Atoms 2022, 10(3), 81; https://doi.org/10.3390/atoms10030081 (registering DOI) - 10 Aug 2022
Viewed by 209
Abstract
We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration is comprised of an optomechanical system with additional Kerr nonlinearity in the [...] Read more.
We study the time degradation of quantum information stored in a quantum memory device under a dissipative environment in a parameter range which is experimentally relevant. The quantum memory under consideration is comprised of an optomechanical system with additional Kerr nonlinearity in the optical mode and an anharmonic mechanical oscillator with quadratic nonlinearity. Time degradation is monitored, both in terms of loss of coherence, which is analyzed with the help of Wigner functions, as well as in terms of loss of amplitude of the original state, studied as a function of time. While our time trajectories explore the degree to which the stored information degrades depending upon the variation in values of various parameters involved, we suggest a set of parameters for which the original information can be retrieved without degradation. We identify a very interesting situation where the role played by the nonlinearity is insignificant, and the system behaves as if the information is stored in a linear medium. For this case, the information retrieval is independent of the coherence revival time and can be retrieved at any instant during the time evolution. Full article
(This article belongs to the Section Atom Based Quantum Technology)
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Article
Relativistic Two-Photon Matrix Elements for Attosecond Delays
Atoms 2022, 10(3), 80; https://doi.org/10.3390/atoms10030080 - 02 Aug 2022
Viewed by 198
Abstract
The theory of one-photon ionization and two-photon above-threshold ionization is formulated for applications to heavy atoms in attosecond science by using Dirac–Fock formalism. A direct comparison of Wigner–Smith–Eisenbud delays for photoionization is made with delays from the Reconstruction of Attosecond Beating By Interference [...] Read more.
The theory of one-photon ionization and two-photon above-threshold ionization is formulated for applications to heavy atoms in attosecond science by using Dirac–Fock formalism. A direct comparison of Wigner–Smith–Eisenbud delays for photoionization is made with delays from the Reconstruction of Attosecond Beating By Interference of Two-photon Transitions (RABBIT) method. Photoionization by an attosecond pulse train, consisting of monochromatic fields in the extreme ultraviolet range, is computed with many-body effects at the level of the relativistic random phase approximation (RRPA). Subsequent absorption and emission processes of infrared laser photons in RABBIT are evaluated by using static ionic potentials as well as asymptotic properties of relativistic Coulomb functions. As expected, light elements, such as argon, show negligible relativistic effects, whereas heavier elements, such a krypton and xenon, exhibit delays that depend on the fine-structure of the ionic target. The relativistic effects are notably close to ionization thresholds and Cooper minima with differences in fine-structure delays predicted to be as large as tens of attoseconds. The separability of relativistic RABBIT delays into a Wigner–Smith–Eisenbud delay and a universal continuum–continuum delay is studied with reasonable separability found for photoelectrons emitted along the laser polarization axis in agreement with prior non-relativistic results. Full article
Review
Recent Progress in Low-Energy Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules
Atoms 2022, 10(3), 79; https://doi.org/10.3390/atoms10030079 - 29 Jul 2022
Viewed by 227
Abstract
We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima [...] Read more.
We briefly review recent applications of the Regge pole analysis to low-energy 0.0 ≤ E ≤ 10.0 eV electron elastic collisions with large multi-electron atoms and fullerene molecules. We then conclude with a demonstration of the sensitivity of the Regge pole-calculated Ramsauer–Townsend minima and shape resonances to the electronic structure and dynamics of the Bk and Cf actinide atoms, and their first time ever use as novel and rigorous validation of the recent experimental observation that identified Cf as a transitional element in the actinide series. Full article
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Article
Cross Sections for Electron Scattering from Atomic Tin
Atoms 2022, 10(3), 78; https://doi.org/10.3390/atoms10030078 - 27 Jul 2022
Viewed by 251
Abstract
The relativistic convergent close-coupling method is applied to calculate cross sections for electron scattering from atomic tin. We present integrated and momentum-transfer cross sections for elastic scattering from the ground and the first four excited states of tin for projectile energies ranging from [...] Read more.
The relativistic convergent close-coupling method is applied to calculate cross sections for electron scattering from atomic tin. We present integrated and momentum-transfer cross sections for elastic scattering from the ground and the first four excited states of tin for projectile energies ranging from 0.1 to 500 eV. Integrated and selected differential cross sections are presented for excitation to the 5p2, 5p6s, 5p5d and 5p6p manifolds from the ground state. The total ionisation cross sections are calculated from the ground and the first four excited states, accounting for the direct ionisation of the 5p valence shell and the closed 5s shell and the indirect contributions from the excitation–autoionisation. The presented results are compared with previous theoretical predictions and an experiment where available. For the total ionisation cross sections, we find good agreement with the experiment and other theories, while for excitation cross sections, the agreement is mixed. Full article
(This article belongs to the Special Issue Electron Scattering from Atoms, Ions and Molecules)
Article
An Investigation of the Resonant and Non-Resonant Angular Time Delay of e-C60 Elastic Scattering
Atoms 2022, 10(3), 77; https://doi.org/10.3390/atoms10030077 - 25 Jul 2022
Viewed by 248
Abstract
Time delay in electron scattering depends on both the scattering angle θ and scattered electron energy E. A study on the angular time delay of e-C60 elastic scattering was carried out in the present work. We employed the annular square well [...] Read more.
Time delay in electron scattering depends on both the scattering angle θ and scattered electron energy E. A study on the angular time delay of e-C60 elastic scattering was carried out in the present work. We employed the annular square well (ASW) potential to simulate the C60 environment. The contribution from different partial waves to the total angular time delay profile was examined in detail. The investigation was performed for both resonant and non-resonant energies, and salient characteristics in the time delay profile for each case were studied. Full article
(This article belongs to the Special Issue Electron Scattering from Atoms, Ions and Molecules)
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Article
On Producing Long-Lived Spin Polarized Metastable Atoms—Feasibility of Storing Electric Energy
Atoms 2022, 10(3), 76; https://doi.org/10.3390/atoms10030076 - 18 Jul 2022
Viewed by 356
Abstract
We describe a method of producing long-lived multiply excited spin polarized atoms or ions, the decay of which is strongly delayed or even blocked by intra-ionic magnetic stabilization. Special configurations with huge internal magnetic fields capture only spin polarized electrons in collisions with [...] Read more.
We describe a method of producing long-lived multiply excited spin polarized atoms or ions, the decay of which is strongly delayed or even blocked by intra-ionic magnetic stabilization. Special configurations with huge internal magnetic fields capture only spin polarized electrons in collisions with spin aligned atomic hydrogen gas targets. It is expected that the spin aligned configuration yields an extremely high internal magnetic field which will effectively block spin flip transitions. By this the lifetime of inner shell vacancies is expected to strongly increase. Full article
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Perspective
Probing C60 Fullerenes from within Using Free Electron Lasers
Atoms 2022, 10(3), 75; https://doi.org/10.3390/atoms10030075 - 14 Jul 2022
Viewed by 329
Abstract
Fullerenes, such as C60, are ideal systems to investigate energy redistribution following substantial excitation. Ultra-short and ultra-intense free electron lasers (FELs) have allowed molecular research in a new photon energy regime. FELs have allowed the study of the response of fullerenes [...] Read more.
Fullerenes, such as C60, are ideal systems to investigate energy redistribution following substantial excitation. Ultra-short and ultra-intense free electron lasers (FELs) have allowed molecular research in a new photon energy regime. FELs have allowed the study of the response of fullerenes to X-rays, which includes femtosecond multi-photon processes, as well as time-resolved ionization and fragmentation dynamics. This perspective: (1) provides a general introduction relevant to C60 research using photon sources, (2) reports on two specific X-ray FEL-based photoionization investigations of C60, at two different FEL fluences, one static and one time-resolved, and (3) offers a brief analysis and recommendations for future research. Full article
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Article
Mass Spectrometry-Based Approach to Compute Electron-Impact Partial Ionization Cross-Sections of Methane, Water and Nitromethane from Threshold to 5 keV
Atoms 2022, 10(3), 74; https://doi.org/10.3390/atoms10030074 - 14 Jul 2022
Viewed by 310
Abstract
The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the [...] Read more.
The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the orbitals and the scaling of cross-sections using the electron ionization mass spectrometry data. The computed partial ionization cross-sections are consistent with the recommended data and are better than several experimental and theoretical results. The summed partial ionization cross-sections of different fragments also agree with the total ionization cross-sections obtained from BEB and the experimental data. This work highlights the utility of mass spectrometry in the modeling and interpretation of the ionization cross-section data. The limitations and the advantages of the modified form of the BEB model are also discussed. Full article
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Article
Satellite Excitations and Final State Interactions in Atomic Photoionization
Atoms 2022, 10(3), 73; https://doi.org/10.3390/atoms10030073 - 14 Jul 2022
Viewed by 252
Abstract
Satellite excitations and final state configuration interactions appear due to the many-electron correlations and result in a photoelectron spectrum complex final state structure instead of single lines corresponding to one-hole states. In the present work, both processes are considered in a framework of [...] Read more.
Satellite excitations and final state configuration interactions appear due to the many-electron correlations and result in a photoelectron spectrum complex final state structure instead of single lines corresponding to one-hole states. In the present work, both processes are considered in a framework of the many-body perturbation theory, and two techniques, namely the spectral function and CI (configuration interaction) methods are considered. It is shown that for the calculation of satellite lineshapes and low-energy Auger decay, the spectral function method is more appropriate, but in the case of strong final state interactions, the methods of solution of Dyson equation or secular matrix are superior. The results obtained for satellites and low energy Auger decay in the Ne 1s, Ne 2p photoelectron spectra, the Co 3s, and the Th 5p photoelectron spectra are in agreement with the experimental data. Full article
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Article
Magnetic Sublevel Independent Magic and Tune-Out Wavelengths of the Alkaline-Earth Ions
Atoms 2022, 10(3), 72; https://doi.org/10.3390/atoms10030072 - 11 Jul 2022
Viewed by 333
Abstract
Light shift in a state due to the applied laser in an atomic system vanishes at tune-out wavelengths (λTs). Similarly, differential light shift in a transition vanishes at the magic wavelengths (λmagics). In [...] Read more.
Light shift in a state due to the applied laser in an atomic system vanishes at tune-out wavelengths (λTs). Similarly, differential light shift in a transition vanishes at the magic wavelengths (λmagics). In many of the earlier studies, values of the electric dipole (E1) matrix elements were inferred precisely by combining measurements and calculations of λmagic. Similarly, the λT values of an atomic state can be used to infer the E1 matrix element, as it involves dynamic electric dipole (α) values of only one state whereas the λmagic values require evaluation of α values for two states. However, both the λmagic and λT values depend on angular momenta and their magnetic components (M) of states. Here, we report the λmagic and λT values of many S1/2 and D3/2,5/2 states, and transitions among these states of the Mg+, Ca+, Sr+ and Ba+ ions that are independent of M values. It is possible to infer a large number of E1 matrix elements of the above ions accurately by measuring these values and combining with our calculations. Full article
(This article belongs to the Special Issue Electron Scattering from Atoms, Ions and Molecules)
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Article
Photoionization of Atomic Systems Using the Random-Phase Approximation Including Relativistic Interactions
Atoms 2022, 10(3), 71; https://doi.org/10.3390/atoms10030071 - 11 Jul 2022
Viewed by 272
Abstract
Approximation methods are unavoidable in solving a many-electron problem. One of the most successful approximations is the random-phase approximation (RPA). Miron Amusia showed that it can be used successfully to describe atomic photoionization processes of many-electron atomic systems. In this article, the historical [...] Read more.
Approximation methods are unavoidable in solving a many-electron problem. One of the most successful approximations is the random-phase approximation (RPA). Miron Amusia showed that it can be used successfully to describe atomic photoionization processes of many-electron atomic systems. In this article, the historical reasons behind the term “random-phase approximation” are revisited. A brief introduction to the relativistic RPA (RRPA) developed by Walter Johnson and colleagues is provided and some of its illustrative applications are presented. Full article
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Article
Strong-Field Ionization Amplitudes for Atomic Many-Electron Targets
Atoms 2022, 10(3), 70; https://doi.org/10.3390/atoms10030070 - 30 Jun 2022
Viewed by 322
Abstract
The strong-field approximation (SFA) has been widely applied in the literature to model the ionization of atoms and molecules by intense laser pulses. A recent re-formulation of the SFA in terms of partial waves and spherical tensor operators helped adopt this approach to [...] Read more.
The strong-field approximation (SFA) has been widely applied in the literature to model the ionization of atoms and molecules by intense laser pulses. A recent re-formulation of the SFA in terms of partial waves and spherical tensor operators helped adopt this approach to account for realistic atomic potentials and pulses of different shape and time structure. This re-formulation also enables one to overcome certain limitations of the original SFA formulation with regard to the representation of the initial-bound and final-continuum wave functions of the emitted electrons. We here show within the framework of Jac, the Jena Atomic Calculator, how the direct SFA ionization amplitude can be readily generated and utilized in order to compute above-threshold ionization (ATI) distributions for many-electron targets and laser pulses of given frequency, intensity, polarization, pulse duration and carrier–envelope phase. Examples are shown for selected ATI energy, angular as well as momentum distributions in the strong-field ionization of atomic krypton. We also briefly discuss how this approach can be extended to incorporate rescattering and high-harmonic processes into the SFA amplitudes. Full article
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Article
Semiempirical Calculations on Low-Energy Electron Scattering by Zn and Cd Atoms
Atoms 2022, 10(3), 69; https://doi.org/10.3390/atoms10030069 - 29 Jun 2022
Viewed by 437
Abstract
Since total cross section measurements for electron scattering by Zn and Cd performed in the 1970s, the existence of p-wave shape resonances below 1 eV are well established in the literature. It was suggested that a second d-wave shape resonance could exist in [...] Read more.
Since total cross section measurements for electron scattering by Zn and Cd performed in the 1970s, the existence of p-wave shape resonances below 1 eV are well established in the literature. It was suggested that a second d-wave shape resonance could exist in both systems at an energy slightly higher than the one recorded for the p-wave but still below the inelastic threshold. We report elastic scattering calculations for electron collisions with Zn and Cd atoms below 4 eV using a semiempirical approach, as well the scattering length for both targets. Our results show that, indeed, the d-wave shape resonance is found in Zn but absent in Cd. In fact, our cross sections and the few other ones available for this energy range are in discrepancy with the available experimental total cross sections for Cd. Full article
(This article belongs to the Special Issue Electron Scattering from Atoms, Ions and Molecules)
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Article
Quasifree Photoionization under the Reaction Microscope
Atoms 2022, 10(3), 68; https://doi.org/10.3390/atoms10030068 - 28 Jun 2022
Viewed by 395
Abstract
We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H2 at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by [...] Read more.
We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H2 at 800 eV photon energy and circular polarization with a COLTRIMS reaction microscope. Our work provides new insight into this elusive photoionization mechanism that was predicted by Miron Amusia more than four decades ago. We found the distinct four-fold symmetry in the angular emission pattern of QFM electrons from H2 double ionization that has previously only been observed for He. Furthermore, we provide experimental evidence that the photon momentum is not imparted onto the center of mass in quasifree photoionization, which is in contrast to the situation in single ionization and in double ionization mediated by the shake-off and knock-out mechanisms. This finding is substantiated by numerical results obtained by solving the system’s full-dimensional time-dependent Schrödinger equation beyond the dipole approximation. Full article
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Review
Peculiar Physics of Heavy-Fermion Metals: Theory versus Experiment
Atoms 2022, 10(3), 67; https://doi.org/10.3390/atoms10030067 - 23 Jun 2022
Cited by 1 | Viewed by 485
Abstract
This review considers the topological fermion condensation quantum phase transition (FCQPT) that leads to flat bands and allows the elucidation of the special behavior of heavy-fermion (HF) metals that is not exhibited by common metals described within the framework of the Landau Fermi [...] Read more.
This review considers the topological fermion condensation quantum phase transition (FCQPT) that leads to flat bands and allows the elucidation of the special behavior of heavy-fermion (HF) metals that is not exhibited by common metals described within the framework of the Landau Fermi liquid (LFL) theory. We bring together theoretical consideration within the framework of the fermion condensation theory based on the FCQPT with experimental data collected on HF metals. We show that very different HF metals demonstrate universal behavior induced by the FCQPT and demonstrate that Fermi systems near the FCQPT are controlled by the Fermi quasiparticles with the effective mass M* strongly depending on temperature T, magnetic field B, pressure P, etc. Within the framework of our analysis, the experimental data regarding the thermodynamic, transport and relaxation properties of HF metal are naturally described. Based on the theory, we explain a number of experimental data and show that the considered HF metals exhibit peculiar properties such as: (1) the universal T/B scaling behavior; (2) the linear dependence of the resistivity on T, ρ(T)A1T (with A1 is a temperature-independent coefficient), and the negative magnetoresistance; (3) asymmetrical dependence of the tunneling differential conductivity (resistivity) on the bias voltage; (4) in the case of a flat band, the superconducting critical temperature Tcg with g being the coupling constant, while the M* becomes finite; (5) we show that the so called Planckian limit exhibited by HF metals with ρ(T)T is defined by the presence of flat bands. Full article
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