Atome exotique

Un atome exotique se représente comme un atome « normal » dans lequel au moins une particule subatomique a été remplacée par une autre particule de même charge électrique : par exemple un pion négatif π− ou un muon à la place d'un électron. De telles configurations sont très instables, de sorte que ces atomes exotiques n'ont qu'une durée de vie très brève. Atome muonique Un atome muonique résulte du remplacement d'un électron par un muon, qui est un lepton comme l'électron. Ces « atomes » sont plus petits que les atomes normaux car les muons sont plus massifs que les électrons et demeurent donc plus proches du noyau. L'électrodynamique quantique joue un rôle central dans la distribution des niveaux d'énergie des muons dans ce type de structure. Les muons n'étant pas sensibles à l'interaction forte, leurs propriétés à l'intérieur de « l'atome » résultant sont étroitement déterminées par l'interaction électromagnétique seule. Atome hadronique Un atome hadron

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Nuclear Excitation by Free Muon Capture

Fabrizio Carbone, Simone Gargiulo, Ivan Madan

Efficient excitation of nuclei via exchange of a real or virtual photon has a fundamental importance for nuclear science and technology development. Here, we present a mechanism of nuclear excitation based on the capture of a free muon into the atomic orbits (NE mu C). The cross section of such a proposed process is evaluated using the Feshbach projection operator formalism and compared to other known excitation phenomena, i.e., photoexcitation and nuclear excitation by electron capture (NEEC), showing up to 10 orders of magnitude increase in cross section. NE mu C is particularly interesting for MeV excitations that become accessible thanks to the stronger binding of muons to the nucleus. The binding energies of muonic atoms have been calculated introducing a state of the art modification to the Flexible Atomic Code. An analysis of experimental scenarios in the context of modern muon production facilities shows that the effect can be detectable for selected isotopes. The total probability of NE mu C is predicted to be P approximate to 1 x 10-6 per incident muon in a beam-based scenario. Given the high transition energy provided by muons, NE mu C can have important consequences for isomer feeding and particle-induced fission.

AMER PHYSICAL SOC2022

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Local structural investigation of hafnia-zirconia polymorphs in powders and thin films by X-ray absorption spectroscopy

Reinis Ignatans

Despite increasing attention for the recently found ferro- and antiferroelectric properties, the polymorphism in hafnia- and zirconia-based thin films is still not sufficiently understood. In the present work, we show that it is important to have a good quality X-ray absorption spectrum to go beyond an analysis of the only the first coordination shell. Equally important is to analyze both EXAFS and XANES spectra in combination with theoretical modelling to distinguish the relevant phases even in bulk materials and to separate structural from chemical effects. As a first step toward the analysis of thin films, we start with the analysis of bulk references. After that, we successfully demonstrate an approach that allows us to extract high-quality spectra also for 20 nm thin films. Our analysis extends to the second coordination shell and includes effects created by chemical substitution of Hf with Zr to unambiguously discriminate the different polymorphs. The trends derived from X-ray absorption spectroscopy agree well with X-ray diffraction measurements. In this work we clearly identify a gradual transformation from monoclinic to tetragonal phase as the Zr content of the films increases. We separated structural effects from effects created by chemical disorder when ration of Hf:Zr is varied and found differences for the incorporation of the substitute atoms between powders and thin films, which we attribute to the different fabrication routes. This work opens the door for further in-depth structural studies to shine light into the chemistry and physics of these novel ferroelectric thin films that show high application relevance. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

PERGAMON-ELSEVIER SCIENCE LTD2019

Chargement

Emergent magnetic anisotropy in the cubic heavy-fermion metal CeIn3

Philip Johannes Walter Moll

Metals containing cerium exhibit a diverse range of fascinating phenomena including heavy fermion behavior, quantum criticality, and novel states of matter such as unconventional superconductivity. The cubic system CeIn3 has attracted significant attention as a structurally isotropic Kondo lattice material possessing the minimum required complexity to still reveal this rich physics. By using magnetic fields with strengths comparable to the crystal field energy scale, we illustrate a strong field-induced anisotropy as a consequence of non-spherically symmetric spin interactions in the prototypical heavy fermion material CeIn3. This work demonstrates the importance of magnetic anisotropy in modeling f-electron materials when the orbital character of the 4f wavefunction changes (e.g., with pressure or composition). In addition, magnetic fields are shown to tune the effective hybridization and exchange interactions potentially leading to new exotic field tuned effects in f-based materials.

2017

Chargement

Muon

Le muon est, selon le modèle standard de la physique des particules, une particule élémentaire de charge électrique négative, instable. Le muon a pour spin 1/2 et a les mêmes propriétés physiques qu

Proton

Le proton est une particule subatomique portant une charge électrique élémentaire positive. Les protons sont présents dans les noyaux atomiques, généralement liés à des neutrons par l'interaction fo

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La physique des particules ou la physique subatomique est la branche de la physique qui étudie les constituants élémentaires de la matière et les rayonnements, ainsi que leurs interactions. On l'app

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