Publications

2022

• Comparison of long-range corrected kernels and range-separated hybrids for excitons in solids
  
  • Maji Rita
  • Degoli Elena
  • Calatayud Monica
  • Véniard Valérie
  • Luppi Eleonora
  Physical Review B, American Physical Society, 2022, 106 (23), pp.235158. The most accurate theoretical method to describe excitons is the solution of the Bethe-Salpeter equation in the GW approximation (GW-BSE). However, because of its computation cost time-dependent density functional theory (TDDFT) is becoming the alternative approach to GW-BSE to describe excitons in solids. Nowadays, the most efficient strategy to describe optical spectra of solids in TDDFT is to use long-range corrected exchange-correlation kernels on top of GW or scissor-corrected energies. In recent years, a different strategy based on range-separated hybrid functionals started to be developed in the framework of time-dependent generalised Kohn-Sham density functional theory (TDGKSDFT). Here, we compare the performance of long-range corrected kernels with range-separated hybrid functionals for the description of excitons in solids. This comparison has the purpose to weight the pros and cons of using range-separated hybrid functionals, giving new perspectives for theoretical developments of these functionals. We illustrate the comparison for the case of Si and LiF, representative of solid state excitons. (10.1103/PhysRevB.106.235158)
  DOI : 10.1103/PhysRevB.106.235158
• Clifford algebras for SE(3) and the Poincaré group
  
  • Coddens Gerrit
  , 2022. Non-homogeneous groups like the special Euclidean group SE(3) (of the translations and rotations in R 3) or the Poincaré group of Minkowski space-time R 4 also contain translations, which seems to preclude the possibility of building a representation based on Clifford algebra for them because representations are purely based on matrix multiplication. Summing of group elements is a priori not defined, only products are. However, with the use of homogeneous coordinates, SE(3) can be obtained as the group generated by an even number of reflections with respect to hyperplanes of R 4. Similarly the Poincaré group is a group that can be generated by an even number of reflections with respect to hyperplanes of R 5. However, this leads to some normalization problems and in order to avoid these, null vectors must be introduced. We work this out for the group SE(3) and for the Poincaré group. It leads to groups noted as SO(3,1,0) for SE(3) and SO(3,1,1) or SO(1,1,3) for the Poincaré group.
• Ultrafast dynamics in hybrid perovskites
  
  • Cherasse Marie
  , 2022. Hybrid lead halide perovskites (ABX3) are an intriguing class of semiconductors with excellent optoelectronic properties and promising for photovoltaic applications. A fundamental understanding of the ultrafast dynamics in these materials is required. This work deals with two main topics: (1) The study of electron relaxation in the conduction band using time-resolved photoemission (2PPE) and angle-resolved photoemission (tr-ARPES). Here, the influence of the orientation of A-site cations and crystallographic structure on charge screening have been studied, explaining the high tolerance to electron trapping on the surface in MAPbI3 crystals. (2) Understanding the dynamic role of phonons and their influence on electrons using the THz-induced Kerr effect. We obtained coherent control over a Raman-active Pb-Br sublattice mode, which was found to dominate the ultrafast lattice polarizability in both single and complex A-site cation perovskites. This finding highlights the potential of the inorganic lattice for dynamic carrier screening and the related mechanism of charge carrier protection.
• Structure et réactivité des ferrites de calcium industriels (brownmillerite) et de leurs hydrates, vis-à-vis des solutions aqueuses sulfatées
  
  • Meriot Alexis
  , 2022. La résistance des ciments aux sulfates est restée un problème important depuis le début de leur histoire. Les sulfates sont à l’origine de gonflements qui provoquent la fissuration du matériau. Leur présence dans les environnements marins ou sols gypseux pose donc des problèmes vis-à-vis de la durabilité du ciment Portland. Le ciment Portland, contient essentiellement deux silicates de calcium, et deux aluminates de calcium, l’aluminate tricalcique et le ferrite. Le rôle de l’aluminate tricalcique dans la baisse de résistance aux sulfates est connu, cependant celui du ferrite qui n’a pas été étudié semble déterminant.C’est pourquoi nous avons travaillé sur la réactivité en milieu sulfatique du ferrite de synthèse et industriel.Néanmoins, la complexité du ciment ne permet pas de travailler directement sur ce dernier. Nous sommes parvenus à mettre au point une méthode de double extraction pour l’étudier.Le ferrite fut étudié par diffraction des rayons X, spectroscopie Mössbauer, spectroscopie de fluorescence X et microsonde de Castaing. La réactivité du ferrite fut aussi étudiée dans différents milieux réactionnels par spectroscopie d’émission atomique et conductimétrie. Les résultats montrent que la réactivité du ferrite dépend très fortement du rapport molaire Al/Fe mais aussi du milieu réactionnel. Différentes valeurs pivots ont pu être trouvées en fonction du milieu. On arrive à mesurer très finement la réactivité, même pour des ferrites très proches chimiquement.Il s’avère à travers ce travail que le ferrite ne peut plus être négligé pour les études de durabilité.
• Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrode
  
  • Clochard M.-C.
  • Oral O.
  • Wade Travis L.
  • Cavani O.
  • Castellino M.
  • Ligiero L. Medina
  • Elan T.
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.15771. Abstract Detection of Zn(II) in oil-polluted seawater via square-wave anodic stripping voltammetry (SW-ASV) utilizing thin gold electrodes sputtered onto nanoporous poly(acrylic acid)-grafted-poly(vinylidene difluoride) (PAA-g-PVDF) membrane is herein reported. Prior to SW-ASV, PAA grafted nanopores demonstrated to efficiently trap Zn(II) ions at open circuit. This passive adsorption followed a Langmuir law. An affinity constant of 1.41 L $$\upmu $$ μ mol $$^{-1}$$ - 1 and a maximum Zn(II) adsorbed mass q $$_{max}$$ max of 1.21 $$\upmu $$ μ mol g $$^{-1}$$ - 1 were found. Applied SW-ASV protocol implied an accumulation step (− 1.2 V for 120 s) followed by a stripping step (− 1.2 to 1 V; 25 Hz; step: 4 mV; amplitude: 25 mV; acetate buffer (pH 5.5)). It revealed a Zn redox potential at − 0.8 V (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of production waters exhibited a decreasing precision with the number of readings R (1.65 $$\%$$ % (R = 2) and 6.56 $$\%$$ % (R = 3)). These membrane-electrodes should be used as disposable. The intra-batch mean precision was 14 $$\%$$ % (n = 3) while inter-batches precision was 20 $$\%$$ % (n = 15). Linear and linear-log calibrations allow exploitation of Zn(II) concentrations ranging from 10 to 500 $$\upmu $$ μ g L $$^{-1}$$ - 1 and 100 to 1000 $$\upmu $$ μ g L $$^{-1}$$ - 1 respectively. The LOD was 4.2 $$\upmu $$ μ g L $$^{-1}$$ - 1 (3S/N). Thanks to obtained calibration, a detected Zn(II) content of 1 ppm in a raw production water from North Sea oil platform was determined. (10.1038/s41598-022-20067-0)
  DOI : 10.1038/s41598-022-20067-0
• Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrode
  
  • Clochard M.-C.
  • Oral O.
  • Wade T.
  • Cavani O.
  • Castellino M.
  • Ligiero L. Medina
  • Elan T.
  Scientific Reports, Nature Publishing Group, 2022, 12 (1), pp.15771. Abstract Detection of Zn(II) in oil-polluted seawater via square-wave anodic stripping voltammetry (SW-ASV) utilizing thin gold electrodes sputtered onto nanoporous poly(acrylic acid)-grafted-poly(vinylidene difluoride) (PAA-g-PVDF) membrane is herein reported. Prior to SW-ASV, PAA grafted nanopores demonstrated to efficiently trap Zn(II) ions at open circuit. This passive adsorption followed a Langmuir law. An affinity constant of 1.41 L $$\upmu $$ μ mol $$^{-1}$$ - 1 and a maximum Zn(II) adsorbed mass q $$_{max}$$ max of 1.21 $$\upmu $$ μ mol g $$^{-1}$$ - 1 were found. Applied SW-ASV protocol implied an accumulation step (− 1.2 V for 120 s) followed by a stripping step (− 1.2 to 1 V; 25 Hz; step: 4 mV; amplitude: 25 mV; acetate buffer (pH 5.5)). It revealed a Zn redox potential at − 0.8 V (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of production waters exhibited a decreasing precision with the number of readings R (1.65 $$\%$$ % (R = 2) and 6.56 $$\%$$ % (R = 3)). These membrane-electrodes should be used as disposable. The intra-batch mean precision was 14 $$\%$$ % (n = 3) while inter-batches precision was 20 $$\%$$ % (n = 15). Linear and linear-log calibrations allow exploitation of Zn(II) concentrations ranging from 10 to 500 $$\upmu $$ μ g L $$^{-1}$$ - 1 and 100 to 1000 $$\upmu $$ μ g L $$^{-1}$$ - 1 respectively. The LOD was 4.2 $$\upmu $$ μ g L $$^{-1}$$ - 1 (3S/N). Thanks to obtained calibration, a detected Zn(II) content of 1 ppm in a raw production water from North Sea oil platform was determined. (10.1038/s41598-022-20067-0)
  DOI : 10.1038/s41598-022-20067-0
• Delocalization of dark and bright excitons in flat-band materials and the optical properties of V2O5
  
  • Gorelov Vitaly
  • Reining Lucia
  • Feneberg Martin
  • Goldhahn Rüdiger
  • Schleife André
  • Lambrecht Walter
  • Gatti Matteo
  npj Computational Materials, Springer Nature, 2022, 8 (1), pp.94. Abstract The simplest picture of excitons in materials with atomic-like localization of electrons is that of Frenkel excitons, where electrons and holes stay close together, which is associated with a large binding energy. Here, using the example of the layered oxide V 2 O 5 , we show how localized charge-transfer excitations combine to form excitons that also have a huge binding energy but, at the same time, a large electron-hole distance, and we explain this seemingly contradictory finding. The anisotropy of the exciton delocalization is determined by the local anisotropy of the structure, whereas the exciton extends orthogonally to the chains formed by the crystal structure. Moreover, we show that the bright exciton goes together with a dark exciton of even larger binding energy and more pronounced anisotropy. These findings are obtained by combining first principles many-body perturbation theory calculations, ellipsometry experiments, and tight binding modelling, leading to very good agreement and a consistent picture. Our explanation is general and can be extended to other materials. (10.1038/s41524-022-00754-2)
  DOI : 10.1038/s41524-022-00754-2
• Connector theory for reusing model results to determine materials properties
  
  • Vanzini Marco
  • Aouina Ayoub
  • Panholzer Martin
  • Gatti Matteo
  • Reining Lucia
  npj Computational Materials, Springer Nature, 2022, 8, pp.98. The success of Density Functional Theory (DFT) is partly due to that of simple approximations, such as the Local Density Approximation (LDA), which uses results of a model, the homogeneous electron gas, to simulate exchange-correlation effects in real materials. We turn this intuitive approximation into a general and in principle exact theory by introducing the concept of a connector: a prescription how to use results of a model system in order to simulate a given quantity in a real system. In this framework, the LDA can be understood as one particular approximation for a connector that is designed to link the exchange-correlation potentials in the real material to that of the model. Formulating the in principle exact connector equations allows us to go beyond the LDA in a systematic way. Moreover, connector theory is not bound to DFT, and it suggests approximations also for other functionals and other observables. We explain why this very general approach is indeed a convenient starting point for approximations. We illustrate our purposes with simple but pertinent examples. (10.1038/s41524-022-00762-2)
  DOI : 10.1038/s41524-022-00762-2
• Thermal relaxation of silica phases densified under electron irradiation
  
  • Mobasher Mahinour
  • Lancry Matthieu
  • Lu Jiafeng
  • Neuville Daniel R.
  • Bellot-Gurlet Ludovic
  • Ollier Nadège
  Journal of Non-Crystalline Solids, Elsevier, 2022, 597, pp.121917. The thermal relaxation of the silica metamict phase obtained after electron irradiation of 11 GGy Suprasil SiO2 glass was characterized using Raman spectroscopy and compared to silica densified under high Pressure and high temperature irradiated at 107 Gy. In parallel, we studied the densification relaxation kinetic by step isochronal annealing treatments. Starting from the metamict phase, local density indicators, D1 and D2 bands decreased quasi-monotonously under thermal treatment together with the glass density. However, for 107 Gy samples, we evidenced an anomalous sharp increase of D1 and D2 bands between 800°C and 1000°C, which could be interpreted as a transition from low-density amorphous (LDA) to a high-density amorphous configurational state (HDA). Interestingly after an annealing at 1000°C, the overall Raman signature indicates that the “relaxed metamict phase” exhibits a higher configurational disorder than pristine silica whereas 107 Gy samples simply relaxed towards pristine silica suggesting a low density amorphous megabasin with several minima. (10.1016/j.jnoncrysol.2022.121917)
  DOI : 10.1016/j.jnoncrysol.2022.121917
• A Lorentz boost as a product of two space-time reflections and some additional results about Clifford algebra
  
  • Coddens Gerrit
  , 2022. This is a technical clarifying note consisting of two parts. In the first part we derive the expression for a boost in two representations of the homogeneous Lorentz group, viz. the two-dimensional representation SL(2,C) and the four-dimensional Dirac representation in its Cartan-Weyl form. The derivation is purely algebraic. It uses the development of a Clifford algebra for a group of isometries of a vector space, whereby the group is generated by reflections. We prove that a boost can be obtained as a product of two space-time reflections, in perfect analogy with the way a rotation in R 3 can be obtained as a product of two reflections. The derivation does therefore not rely on physical considerations as in Einstein's approach. It is purely based on symmetry arguments. The second part deals with the justification of the definition of a Clifford algebra given in certain mathematical textbooks, which immediately introduce a basis of multi-vectors 1, ej, ej 1 ∧ ej 2 , ej 1 ∧ ej 2 ∧ ej 3 , • • • for this algebra. Rather than as a bemusing "postulate" that descends from heaven, we will present the introduction of this basis as an obvious result of a logical construction of the group representation theory. This will provide the reader with a much better understanding of what is going on behind the scenes of the formalism. We prove that this basis of multi-vectors 1, ej, ej 1 ∧ ej 2 , ej 1 ∧ ej 2 ∧ ej 3 , • • • is orthogonal in terms of a scalar product whose use is very natural in vector spaces of matrices.
• Contribution des effets quantiques nucléaires au coefficient de diffusion de l’hydrogène dans BaZrO3
  
  • Dammak Hichem
  • Hayoun Marc
  , 2022.
• Normalization errors in CHSH Bell inequalities
  
  • Coddens Gerrit
  , 2022. We consider two different definitions of determinism, the traditional one and a new alternative one. The alternative definition introduces a new description of what happens during a photon correlation measurement. The CHSH Bell-type inequality is derived according to the traditional definition of determinism. It can then not be applied in the usual way to the experiments it has been designed for, when in the analysis of the experiments we follow the alternative type of definition. In fact, the usual procedure introduces then a normalization error with a confusion between absolute and conditional probabilities. Within the frame work of the alternative definition the inequality is no longer violated and determinism is not defeated.
• Resonant phonon-magnon interactions in freestanding metal-ferromagnet multilayer structures
  
  • Vernik Urban
  • Lomonosov Alexey
  • Vlasov Vladimir
  • Kotov Leonid
  • Kuzmin Dmitry
  • Bychkov Igor
  • Vavassori Paolo
  • Temnov Vasily
  Physical Review B, American Physical Society, 2022, 106 (14), pp.144420. We analyze resonant magnetoelastic interactions between standing perpendicular spin wave modes (exchange magnons) and longitudinal acoustic phonon modes in free-standing hybrid metal-ferromagnet bilayer and trilayer structures. Whereas the ferromagnetic layer acts as a magnetic cavity, all metal layers control the frequencies and eigenmodes of acoustic vibrations. The design proposed here allows for achieving and tuning the spectral and spatial mode overlap between phonons and magnons that results in their strong resonant interaction. Realistic simulations for gold-nickel multilayers show that sweeping the external magnetic field should allow for observing resonantly enhanced interactions between individual magnon and phonon modes in a broad range of frequencies spanning from tens of gigahertz up to several hundreds of gigahertz, which can be finely tuned through the multilayer design. Our results would enable the systematic study and the deep understanding of resonantly enhanced magnetoelastic coupling between individual phonon and magnon modes up to frequencies of great contemporary fundamental and applied interest. (10.1103/PhysRevB.106.144420)
  DOI : 10.1103/PhysRevB.106.144420
• Modelling and Simulation of the Magnetostriction Effect in a Magneto-sensitive Material
  
  • Saouli N.
  • Dammak H.
  • Hayoun M.
  • Bodelot L.
  , 2022.
• The 2022 Magneto-Optics Roadmap
  
  • Kimel Alexey
  • Zvezdin Anatoly
  • Sharma Sangeeta
  • Shallcross Samuel
  • Sousa Nuno De
  • Garcia-Martin Antonio
  • Salvan Georgeta
  • Hamrle Jaroslav
  • Stejskal Ondrej
  • Mccord Jeffrey
  • Tacchi Silvia
  • Carlotti Giovanni
  • Gambardella Pietro
  • Salis Gian
  • Muenzenberg Markus
  • Schultze Martin
  • Temnov Vasily
  • Bychkov Igor
  • Kotov Leonid
  • Maccaferri Nicolò
  • Ignatyeva Daria
  • Belotelov Vladimir
  • Donnelly Claire
  • Rodriguez Aurelio Hierro
  • Matsuda Iwao
  • Ruchon Thierry
  • Fanciulli Mauro
  • Sacchi Maurizio
  • Du Chunhui Rita
  • Wang Hailong
  • Armitage N. Peter
  • Schubert Mathias
  • Darakchieva Vanya
  • Liu Bilu
  • Huang Ziyang
  • Ding Baofu
  • Berger Andreas
  • Vavassori Paolo
  Journal of Physics D: Applied Physics, IOP Publishing, 2022. Magneto-optical effects, viz. magnetically induced changes in light intensity or polarization upon reflection from or transmission through a magnetic sample, were discovered over a century and a half ago. Initially they played a crucially relevant role in unveiling the fundamentals of electromagnetism and quantum mechanics. A more broad-based relevance and wide-spread use of magneto-optical methods, however, remained quite limited until the 1960s due to a lack of suitable, reliable and easy- to-operate light sources. The advent of Laser technology and the availability of other novel light sources led to an enormous expansion of magneto-optical measurement techniques and applications that continues to this day (see Section 1). The here-assembled roadmap article is intended to provide a meaningful survey over many of the most relevant recent developments, advances, and emerging research directions in a rather condensed form, so that readers can easily access a significant overview about this very dynamic research field. While light source technology and other experimental developments were crucial in the establishment of today’s magneto-optics, progress also relies on an ever-increasing theoretical understanding of magneto-optical effects from a quantum mechanical perspective (see Section 2), as well as using electromagnetic theory and modelling approaches (see Section 3) to enable quantitatively reliable predictions for ever more complex materials, metamaterials, and device geometries. The latest advances in established magneto-optical methodologies and especially the utilization of the magneto-optical Kerr effect (MOKE) are presented in effect in 2D materials). In addition, magneto-optical effects are now being investigated and utilized in spectral ranges, to which they originally seemed completely foreign, as those of synchrotron radiation X-rays (see Section 14 on 3D magnetic characterization and Section 16 on light beams carrying orbital angular momentum) and, very recently, the terahertz regime (see Section 18 on THz MOKE and Section 19 on THz ellipsometry for electron paramagnetic resonance detection). Magneto-optics also demonstrates its strength in a unique way when combined with femtosecond laser pulses (see Section 10 on ultrafast MOKE and Section 15 on magneto-optics using X-ray free electron lasers), facilitating the very active field of time- resolved magneto-optical spectroscopy that enables investigations of phenomena like spin relaxation of nonequilibrium photoexcited carriers, transient modifications of ferromagnetic order, and photo- induced dynamic phase transitions, to name a few. Recent progress in nanoscience and nanotechnology, which is intimately linked to the achieved impressive ability to reliably fabricate materials and functional structures at the nanoscale, now enables the exploitation of strongly enhanced magneto-optical effects induced by light-matter interaction at the nanoscale (see Section 12 on magnetoplasmonics and Section 13 on magneto- optical metasurfaces). Magneto-optical effects are also at the very heart of powerful magnetic characterization techniques like Brillouin light scattering and time-resolved pump-probe measurements for the study of spin waves (see Section 7), their interactions with acoustic waves (see Section 11), and ultra-sensitive magnetic field sensing applications based on Nitrogen-vacancy centers in diamond (see Section 17). Despite our best attempt to represent the field of magneto-optics accurately and do justice to all its novel developments and its diversity, the research area is so extensive and active that there remains great latitude in deciding what to include in an article of this sort, which in turn means that some areas might not be adequately represented here. However, we feel that the 20 sections that form this 2022 Magneto-Optics Roadmap article, each written by experts in the field and addressing a specific subject on only two pages, provide an accurate snapshot of where this research field stands today. Correspondingly, it should act as a valuable reference point and guideline for emerging research directions in modern magneto-optics, as well as illustrate the directions this research field might take in the foreseeable future. (10.1088/1361-6463/ac8da0)
  DOI : 10.1088/1361-6463/ac8da0
• Electron-phonon coupling and ultrafast dynamics of hot carriers in semiconductors: from interpretation of photoemission experiments to transport simulations in devices.
  
  • Sjakste Jelena
  , 2022. The progress in DFT-based description of the electron-phonon scattering allowed to describe the relaxation dynamics of hot or photoexcited electrons in several materials, in very good agreement with time-resolved spec- troscopy experiments [1-3]. As hot carriers also start to attract attention in the context of emerging concepts for energy conversion, here we present our first results related to the coupling of ab initio data with device-oriented Monte Carlo simulation methods [4]. We show that DFT-based description of the electron-phonon intervalley scattering in GaAs, coupled with stochastic Monte Carlo method, allows to describe the energy transfer from electrons to phonons in transient regime, in good agreement with previous time-resolved photoemission experiments. [1] J. Sjakste et al, J. Phys: Cond. Mat. 30, 353001 (2018). [2] Chen, Sjakste et al, PNAS 117, 21962-21967 (2020). [3] H. Tanimura et al, Phys. Rev. B 100, 035201 (2019). [4] R. Sen, N. Vast, J. Sjakste, Appl. Phys. Lett. 120, 082101 (2022).
• Preparation and behavior of grafted and ungrafted chitosan thin films: swelling and bacterial adhesion
  
  • Garreau Cyrielle
  • Diallo Mamoudou
  • Chiappisi Leonardo
  • Micciulla Samantha
  • Lairez Didier
  • Trombotto Stéphane
  • Delair Thierry
  • Sudre Guillaume
  , 2022.
• All-electron many-body approach to resonant inelastic X-ray scattering
  
  • Vorwerk Christian
  • Sottile Francesco
  • Draxl Claudia
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2022, 24 (29), pp.17439-17448. An all-electron Bethe–Salpeter equation framework reveals the interplay of correlation and coherence in the resonant inelastic X-ray scattering in solids. (10.1039/D2CP00994C)
  DOI : 10.1039/D2CP00994C
• Electron Irradiation Effects on Single‐Layer MoS 2 Obtained by Gold‐Assisted Exfoliation
  
  • Panasci Salvatore Ethan
  • Alessi Antonino
  • Buscarino Gianpiero
  • Cannas Marco
  • Gelardi Franco Mario
  • Schilirò Emanuela
  • Giannazzo Filippo
  • Agnello Simonpietro
  Physica Status Solidi A (applications and materials science), Wiley, 2022, pp.2200096. Mechanical exfoliation assisted by gold is applied to obtain good quality large lateral size single-layer MoS2. The effects of 2.5 MeV electron irradiation are investigated at room temperature on structural and electronic features by Raman and microluminescence spectroscopy. The exciton recombination emission in the direct bandgap of single-layer MoS2 is affected during irradiation starting from the minimum explored dose of 1 kGy. At higher doses, Raman bands show no relevant modifications whereas the exciton emission is quenched, suggesting that irradiation-induced point defects affect exciton dynamics. (10.1002/pssa.202200096)
  DOI : 10.1002/pssa.202200096
• Silver photochemical reactivity under electronic irradiation analysis of gallo-phosphate glasses
  
  • Alassani Fouad
  • Ollier Nadège
  • Petit Yannick
  • Cardinal Thierry
  • Ollier Nadège
  , 2022.
• Optical response of two-dimensional systems: Insights from classical electromagnetism to $ab\ initio$ calculations
  
  • Mazzei Stefano
  • Giorgetti Christine
  Physical Review B, American Physical Society, 2022, 106, pp.035431. Quasi-2D objects appear to be promising for the development of new optical devices, since their electronic properties are expected to be governed by their size. The understanding of these properties can be achieved by means of theoretical spectroscopy based on the state-of-the-art ab initio formalisms. Time-dependent density functional theory is well suited since it accounts for the local field effects, which are expected to be large at the interfaces with vacuum. This framework allows the calculation of the response function to the external potential. For bulk materials, this quantity is related to the macroscopic dielectric function following the Adler and Wiser formula. This expression contains dimensionless quantities, while for 2D object, the physical observables should be proportional to the thickness. In this paper, we propose a mixed-space approach which allows us to calculate in a direct way the out-of-plane component and to evidence how the ambiguity on the thickness of the slab affects the calculation of the macroscopic dielectric function. The classical Lorentz model adapted to a thin slab reveals how the huge change of the induced electric field, and the arising of a transverse polarization, lead to modify the expression of the macroscopic dielectric function to get the absorption spectrum. Despite the influence of the thickness of the slab on the macroscopic dielectric function, the optical response resulting from the classical electromagnetism can be unambiguously calculated from the mixed-space simulations. (10.1103/PhysRevB.106.035431)
  DOI : 10.1103/PhysRevB.106.035431
• The exact meaning of the angular-momentum and spin operators in quantum mechanics
  
  • Coddens Gerrit
  , 2022. The theory of angular momentum and spin in quantum mechanics seems to defy common-sense intuition. We render the theory intelligible again by pointing out that this apparent impenetrability merely stems from an {\em undue} parallel interpretation of the algebraic expressions for the angular-momentum and spin operators in the group representation theory of SO(3) and SU(2). E.g. the correct meaning of the quantum operator ${\hat{L}}_{z} = {\hbar\over{\imath}}\,(x{\partial\over{\partial y}} - y{\partial\over{\partial x}} )$ is not that it is the operator for the $z$-component $L_{z}$ of the angular momentum ${\mathbf{L}}$, but rather the expression of the operator for the angular momentum ${\mathbf{L}}$ when it is aligned with the $z$-axis. Hence what we are used to note (erroneously) as ${\hat{L}}_{z}$ is not a scalar but a vector operator. The same applies {\em mutatis mutandis} for the spin operators. In the correct interpretation, the whole algebraic formalism is just the group representation theory for the rotations of three-dimensional Euclidean geometry. It is thus mere, elementary high-school mathematics (in a less usual, more technical guise) and as such totally exempt of any physics, let alone quantum mysteries. The change of interpretation has no impact on the algebraic results, such that they remain in agreement with experimental data and the algebra quantum mechanics remains correct. It is all only a matter of the correct geometrical meaning of the algebra. All these statements are proved within the framework of the group representation theory for SO(3) and SU(2) which is the basic tool used to describe rotational motion in quantum mechanics.
• Magnetoresponsive Devices with Programmable Behavior Using a Customized Commercial Stereolithographic 3D Printer
  
  • Lantean Simone
  • Roppolo Ignazio
  • Sangermano Marco
  • Hayoun Marc
  • Dammak Hichem
  • Barrera Gabriele
  • Tiberto Paola
  • Pirri Candido Fabrizio
  • Bodelot Laurence
  • Rizza Giancarlo
  Advanced Materials Technologies, Wiley, 2022, pp.2200288. The revolution of 4D printing allows combining smart materials to additive processes to create behavioral objects able to respond to external stimuli, such as temperature, light, electrical or magnetic fields. Here, we used a modified commercial Digital Light Processing (DLP) 3D printer to obtain complex macroscopic remotely-controlled gear-based devices. The fabrication process is based on the printing of magneto-responsive polymers containing in situ selfassembled microstructures, i.e. composed of oriented chains of Fe3O4 nanoparticles. First, we demonstrate that we are able to print magneto-responsive hammer-like actuators with different stiffness allowing both pure rotation or/and bending motions. Then, we exploit microstructure to create a magneto-responsive gear. In particular, we showed that they can be successfully used to transfer torque to other gears, thereby converting a rotation movement into linear translation. Finally, we demonstrated that magneto-responsive gears can be also combined with other non-magnetic elements to create complex assemblies, such as gear-trains, linear actuators and grippers, that can be remotely controlled. (10.1002/admt.202200288)
  DOI : 10.1002/admt.202200288
• Inadequacy of the CHSH Bell inequality for an application to its associated photon correlation experiments
  
  • Coddens Gerrit
  , 2022. We analyse the proof of a CHSH Bell-type inequality and show that this inequality cannot be applied to the experiments it has been designed for. In the example we study, two polarization values are attributed to each of the two photons of a correlated photon pair, such that four values are assigned simultaneously to a single pair. But in the experiments these four values cannot be measured simultaneously on a single photon pair, such that the assumptions underlying the inequality do not properly translate the experimental situation into mathematics. By and large the community thinks that this objection has already been dealt with by Larsson. However, the argument used by Larsson overlooks a normalization error. The same errors occur in the derivation of other types of Bell inequalities such that none of them can be applied to the experimental data they were designed for. The violation of these Bell inequalities can therefore not be considered as a proof for the existence of entanglement.
• Photoexcited electron dynamics and energy loss rate in silicon: temperature dependence and main scattering channels
  
  • Sen Raja
  • Vast Nathalie
  • Sjakste Jelena
  Proceedings of SPIE, the International Society for Optical Engineering, SPIE, The International Society for Optical Engineering, 2022, 12132, pp.1213204. In this work, we revisit the DFT-based results for the electron-phonon scattering in highly excited silicon. Using state-of-the-art ab initio methods, we examine the main scattering channels which contribute to the total electron-phonon scattering rate and to the energy loss rate of photoexcited electrons in silicon as well as their temperature dependence. Both temperature dependence and the main scattering channels are shown to strongly differ for the total electron-phonon scattering rate and for the energy loss rate of photoexcited electrons. Whereas the total electron-phonon scattering rate increases strongly with temperature, the temperature dependence of the energy loss rate is negligible. Also, while acoustic phonons dominate the total electron-phonon scattering rate at 300 K, the main contribution to the energy loss rate comes from optical modes. (10.1117/12.2621174)
  DOI : 10.1117/12.2621174