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Open AccessArticle

Strong-Field Ionization Amplitudes for Atomic Many-Electron Targets

by

Stephan Fritzsche

and

Birger Böning

Atoms 2022, 10(3), 70; https://doi.org/10.3390/atoms10030070 - 30 Jun 2022

Viewed by 64

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

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Quasifree Photoionization under the Reaction Microscope

by

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,

,

,

,

and

Atoms 2022, 10(3), 68; https://doi.org/10.3390/atoms10030068 - 28 Jun 2022

Viewed by 142

Abstract

We experimentally investigated the quasifree mechanism (QFM) in one-photon double ionization of He and H

_{2}

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 H

_{2}

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 H

_{2}

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

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Spin Polarization of Electrons in Two-Color XUV + Optical Photoionization of Atoms

by

Nikolay M. Kabachnik

and

Irina P. Sazhina

Atoms 2022, 10(2), 66; https://doi.org/10.3390/atoms10020066 - 20 Jun 2022

Viewed by 256

Abstract

The spin polarization of photoelectrons in two-color XUV + optical multiphoton ionization is theoretically considered using strong field approximation. We assume that both the XUV and the optical radiation are circularly polarized. It is shown that the spin polarization is basically determined by [...] Read more.

The spin polarization of photoelectrons in two-color XUV + optical multiphoton ionization is theoretically considered using strong field approximation. We assume that both the XUV and the optical radiation are circularly polarized. It is shown that the spin polarization is basically determined by the XUV photoabsorption and that the sidebands are spin polarized as well. Their polarization may be larger or smaller than that of the central photoelectron line depending on the helicity of the dressing field. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Taking the Convergent Close-Coupling Method beyond Helium: The Utility of the Hartree-Fock Theory

by

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,

,

Sudhakar Pamidighantam

,

Maciej Cytowski

and

Anatoli S. Kheifets

Atoms 2022, 10(1), 22; https://doi.org/10.3390/atoms10010022 - 11 Feb 2022

Viewed by 814

Abstract

The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He

^{+}

. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and [...] Read more.

The convergent close-coupling (CCC) method was initially developed to describe electron scattering on atomic hydrogen and the hydrogenic ions such as He

^{+}

. The latter allows implementation of double photoionization (DPI) of the helium atom. For more complex single valence-electron atomic and ionic targets, the direct and exchange interaction with the inner electron core needs to be taken into account. For this purpose, the Hartree-Fock (HF) computer codes developed in the group of Miron Amusia have been adapted. In this brief review article, we demonstrate the utility of the HF technique by examples of electron scattering on Li and the DPI of the H

^{-}

and Li

^{-}

ions. We also discuss that modern-day computer infrastructure allows the associated CCC code, and others, to be readily run directly via the Atomic, Molecular and Optical Science Gateway. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Accurate Exponential Representations for the Ground State Wave Functions of the Collinear Two-Electron Atomic Systems

by

Evgeny Z. Liverts

and

Nir Barnea

Atoms 2022, 10(1), 4; https://doi.org/10.3390/atoms10010004 - 29 Dec 2021

Viewed by 656

Abstract

In the framework of the study of helium-like atomic systems possessing the collinear configuration, we propose a simple method for computing compact but very accurate wave functions describing the relevant S-state. It is worth noting that the considered states include the well-known states [...] Read more.

In the framework of the study of helium-like atomic systems possessing the collinear configuration, we propose a simple method for computing compact but very accurate wave functions describing the relevant S-state. It is worth noting that the considered states include the well-known states of the electron–nucleus and electron–electron coalescences as a particular case. The simplicity and compactness imply that the considered wave functions represent linear combinations of a few single exponentials. We have calculated such model wave functions for the ground state of helium and the two-electron ions with nucleus charge

1 \leq Z \leq 5

. The parameters and the accompanying characteristics of these functions are presented in tables for number of exponential from 3 to 6. The accuracy of the resulting wave functions are confirmed graphically. The specific properties of the relevant codes by Wolfram Mathematica are discussed. An example of application of the compact wave functions under consideration is reported. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessArticle

Time Delay in Electron Collision with a Spherical Target as a Function of the Scattering Angle

by

Miron Ya. Amusia

,

Arkadiy S. Baltenkov

and

Igor Woiciechowski

Atoms 2021, 9(4), 105; https://doi.org/10.3390/atoms9040105 - 01 Dec 2021

Viewed by 755

Abstract

We have studied the angular time delay in slow-electron elastic scattering by spherical targets as well as the average time delay of electrons in this process. It is demonstrated how the angular time delay is connected to the Eisenbud–Wigner–Smith (EWS) time delay. The [...] Read more.

We have studied the angular time delay in slow-electron elastic scattering by spherical targets as well as the average time delay of electrons in this process. It is demonstrated how the angular time delay is connected to the Eisenbud–Wigner–Smith (EWS) time delay. The specific features of both angular and energy dependencies of these time delays are discussed in detail. The potentialities of the derived general formulas are illustrated by the numerical calculations of the time delays of slow electrons in the potential fields of both absolutely hard-sphere and delta-shell potential well of the same radius. The conducted studies shed more light on the specific features of these time delays. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Review

Jump to: Research

Open AccessReview

Peculiar Physics of Heavy-Fermion Metals: Theory versus Experiment

by

Vasily R. Shaginyan

,

Alfred Z. Msezane

and

George S. Japaridze

Atoms 2022, 10(3), 67; https://doi.org/10.3390/atoms10030067 - 23 Jun 2022

Viewed by 216

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) \propto A_{1} T

(with

A_{1}

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

T_{c} \propto g

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) \propto T

is defined by the presence of flat bands. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

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Open AccessReview

ATOM Program System and Computational Experiment

by

Larissa V. Chernysheva

and

Vadim K. Ivanov

Atoms 2022, 10(2), 52; https://doi.org/10.3390/atoms10020052 - 24 May 2022

Viewed by 425

Abstract

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the [...] Read more.

The article is devoted to a brief description of the ATOM computer program system, designed to study the structure, transition probabilities and cross sections of various processes in multielectron atoms. The theoretical study was based on the concept of a computational experiment, the main provisions of which are discussed in the article. The main approximate methods used in the system of programs for taking many-electron correlations into account and determining their role in photoionization processes, elastic and inelastic electron scattering, the decay of vacancies, and many others are presented. The most significant results obtained with this software are listed. Full article

(This article belongs to the Special Issue Many-Electron and Multiphoton Atomic Processes: A Tribute to Miron Amusia)

Author	Affiliation	Title
Valeriy Dolmatov	University of North Alabama, Florence, USA	Ionization and scattering processes in encapsulated atoms
Marcus Dahlström	Lund University, Sweden	Time-delay in two-photon ionization processes
Victor Sukhorukov	Rostov University, Russia	Studying many-electron processes with fluorescence spectroscopy
Horst Schmidt-Bocking	Institut fur Kernphysik, Universitat Frankfurt, Germany	On the formation of "long living" spin-polarized metastable atoms - A chance for very efficient storage of electric-energy
Elena Gryzlova	Moscow State University Russia	Cooper minima of excited atomic states
Gleb Gribakin	Queen's University Belfast	Low-energy positron scattering

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