Publications

2017

• Détection de vapeurs d'atomes métalliques par fluorescence induite par laser (LIF) : application à la propulsion solide
  
  • Vilmart Gautier
  , 2017. Cette thèse porte sur la méthode de Fluorescence Induite par Laser (LIF) à haute cadence développée sur deux atomes métalliques (Al et Fe) utilisés comme traceurs fluorescents dans les flammes de propergols solides où ils sont naturellement présents. Deux expériences d’évaporation de l’aluminium sont mises en œuvre pour mettre au point la technique dans des conditions contrôlées sur une large gamme de pressions et températures. Un modèle théorique du processus de fluorescence appliqué à ces deux atomes est élaboré pour calculer les taux de quenching du signal avec la pression et la température. Les données collisionnelles qui sont inconnues sont prédéterminées théoriquement pour Fe et expérimentalement pour Al. Les coefficients de transferts d’énergie et d’élargissements spectraux par collisions de l’atome Al sont déterminés expérimentalement en environnement d’azote pur. Une étude du comportement du signal de Al avec l’énergie laser est effectuée pour mesurer les seuils de saturation avec les gaz N₂, Ar et He en fonction de la pression. Le modèle permet de reproduire correctement les profils temporels et spectraux avec toutefois des approximations et des limitations qui sont explicitées. Une première application de l’imagerie LIF sur Al dans une flamme de propergol solide aluminisé (10 bar et 3000 K) permet de visualiser des gouttes d’aluminium réactives et observer leur évolution dans la flamme.
• Towards an improved description of spectroscopies for materials with localized electrons : Effective potentials and interactions
  
  • Tzavala Marilena
  , 2017. The aim of this thesis is to develop approximations to describe many-body effects in photoemission and optical properties of materials containing localized electrons. This is a tough problem. The full quantum-mechanical treatment is based on the solution of the Schrödinger equation for the many-body wavefunction, which is cumbersome and requires in practice some approximations. One simplified approach is given by Density Functional Theory (DFT) with the Kohn-Sham system of independent particles, but it is difficult to access properties other than the density and total energy. In this thesis we start from an in principle exact framework, the Green's functions. They are intermediate in complexity between DFT and the full wavefunction methods.For the removal or excitation of a localized electron one important point is to avoid self-interaction and self-screening. This is naturally achieved when one uses a generalized Coulomb interaction (Chap.3). Moreover, supposing that the localized electron has little overlap with the others, we can think that their interaction is classical. Then the main many-body effect is the reaction of the other electrons to the removal or excitation of the localized electron: this is screening of the hole or electron-hole pair by the other electrons. However, in many standard approximations in the Green's functions framework, such as GW or the cumulant expansion, screening appears in the linear response approximation. Instead, we can expect that the removal or excitation of a localized electron is a strong perturbation to the other electrons. Therefore, it could be that non-linear contributions to screening are important. How can we verify when this is true? And how can we include these effects? On the other hand, even in linear response one could do better than standard approximations, because the linear response screening itself is often calculated in the Random Phase Approximation (RPA). How much do things improve when one goes beyond the RPA but stays in linear response? We address these points in the thesis.Concerning the screening, in Chap.5 we first use a simple zero-dimensional model to study on one side, effects beyond the RPA within linear reponse and, on the other side, effects beyond linear response but staying within the RPA. Interestingly, we find that we have to treat both at the same time in order to find significant improvement. This means that we have to find promising ways to go beyond the RPA that are simple enough to allow us to go to the non-linear regime. Therefore we develop approximations based on perturbation theory and test some already existent ones in the model.Screening is expressed through the dielectric function, which gives us also directly absorption. This is another reason to study it. In order to be more realistic than the zero-dimensional model, in Chap.6 we study the dielectric function of a simple solid using localized Wannier functions. This allows us to highlight cancellations between self-energy and excitonic effects in the framework of Green's functions and from this derive a simple Kohn Sham exchange-correlation potential and kernel for Time-Dependent DFT (TDDFT).In Chap.7 we go back to the problem of non-linear screening and address the question: how can we make it appear explicitly in the full formulation? We show how to do this,and how to use the approximation of a localized electron in order to derive a cumulant Green's function beyond the standard linear response one. We propose two levels of approximations to evaluate the resulting expression in practice, and show some preliminary results. In both cases, TDDFT is used to describe screening.Since a combination of Green's functions and TDDFT seems to be a good strategy to simplify the many-body problem, Chap.8 contains some more considerations about possible combinations.
• Depth Profiling of Strain in Textured Tungsten Thin Films
  
  • Li Chenyi
  • Baldinozzi Gianguido
  • Lecoeur Philippe
  • Maroutian Thomas
  • Pontikis Vassilis
  , 2017. The stability of heterophase interfaces between metal systems, their kinetic, structural, and thermomechanical properties are a matter of concern for high demanding applications involved in the development of technological coatings for the first wall materials in fusion reactors and their prototypes (ITER). We would like to discuss preliminary results of X-ray experiments on model coatings made of tungsten, in particular the problems related to strain inhomogeneity in metal films on heterophase substrates. These analyses of nanostructured thin layers can be performed using laboratory grazing incidence diffraction, allows the accurate extraction of quantitative relevant information about the structure (strain and atomic positions) and the microstructure (crystallite size and microstrain), selectively probing the material on a depth of few nanometers. References Results The local strain in the three films is almost identical at a given depth. This suggests that the deposition method produce reliable microstructural characteristics for the three films. In the three films the maximum amplitude of the strain is close to the surface of the films and it decreases smoothly when the depth increases. It seems likely that the larger strain observed close to the surface could be partly related to the interaction of the films with the gases of the ambient atmosphere: nevertheless, these effects seems to remain small and do not seem to require a reassessment of the absorbance of the films. Grazing incidence X-ray diffraction can be a workhorse technique for deriving crystallite size in nanoscale systems due to its non-destructive character, the fast data collection and the relative simplicity of the experimental setup, This information is relevant for an accurate description of nanocrystalline systems prepared as thin films and it can significantly improve the knowledge of their structure-properties relationships. This work was partly supported by Laboratoire d'Excellence Physique Atomes Lumière Matière (LabEx PALM) through a French national grant of Agence Nationale de la Recherche within the "Programme Investissements d'Avenir" with
• Electronic structure and dynamics of CH3NH3PbI3 hybrid organic-inorganic perovskite
  
  • Lee Min-I
  • Chen Zhesheng
  • Barragan Ana
  • Zhang Zailan
  • Lédée F.
  • Narayanan Nair Maya
  • Jemli K.
  • Trippé-Allard G.
  • Diab Hiba
  • Fertey Pierre
  • Garrot D.
  • Papalazarou E.
  • Ponseca Carlito
  • Jacques V.
  • Bolloc'H David Le
  • Marsi M.
  • Deleporte Emmanuelle
  • Perfetti Luca
  • Taleb-Ibrahimi A.
  • Tejeda Antonio
  , 2017. Organic-inorganic hybrid perovskites are promising absorber materials for low-cost photovoltaic solar cells or optoelectronic devices [1-4]. Among these perovskites, methylammonium triiodideplumbate (CH 3 NH 3 PbI 3 , MAPbI 3 or MAPI) exhibits currently the highest efficiency. Here we have analyzed the structural transition in MAPI by X-ray diffraction at the β phase and we have correlated it to its electronic properties. Despite all the extensive work on hybrid organic-inorganic halide perovskites, their experimental band structure measured with k-resolution has remained elusive. Such an experimental determination is a necessary requirement for an accurate theoretical description and understanding of the system. The impact of the structural phase transitions on the band structure in the operation temperature range of solar cells needed also to be elucidated. Herein, we present the experimental determination of the band structure of MAPI with k resolution by angle-resolved photoemission at 170 K [5]. Our results show that the spectral weight is strongly affected by the cubic symmetry although traces of the tetragonal band structure are appreciated. Some deviations with respect to theoretical calculations are observed, which may help to reach a more precise description of this paradigmatic system of the hybrid perovskite family. On a second step, we have studied the relaxation dynamics after photoexcitation, particularly important in a photovoltaic material. Time-resolved two-photon photoemission spectroscopy allows to directly visualize the electronic cooling at early delay times. It follows that photoexcited carriers thermalize on a subpicosecond timescale, presumably because of the coupling to the vibrations of organic cations [6]. The project leading to this application has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 687008 (GOTSolar). [1] S.D. Stranks and H.J. Snaith, Nature Nanotech 10, 391 (2015). [2] M. Grätzel, Nature Materials 13, 838 (2014). [3] Y. Wei et al., J. Phys. D: Appl. Phys. 46, 135105 (2013). [4] H. Diab, G. Trippé-Allard, F. Ledee, K. Jemli, C. Vilar, G. Bouchez, V. L. R. Jacques, A. Tejeda, J. Even, J.S. Lauret, E. Deleporte, and D. Garrot, J. Phys. Chem. Lett. 7, 5093 (2016). [5] M.-I. Lee, A. Barragán, M. N. Nair, V. L. R. Jacques, D. Le Bolloc’h, P. Fertey, K. Jemli, F. Ledee, G. Trippé-Allard, E. Deleporte, A. Taleb-Ibrahimi, and A. Tejeda, J. Phys. D: Appl. Phys. 50, 26LT02 (2017). [6] Z. Chen, M.-I. Lee, Z. Zhang, H. Diab, D. Garrot, F. Ledee, P. Fertey, E. Papalazarou, M. Marsi, C. Ponseca, E. Deleporte, A. Tejeda, and L. Perfetti, Phys. Rev. Mat. 1, 045402 (2017).
• Advanced capabilities for materials modelling with Quantum ESPRESSO
  
  • Giannozzi P.
  • Andreussi Oliviero
  • Brumme T
  • Bunau O.
  • Buongiorno Nardelli M.
  • Calandra M.
  • Car R
  • Cavazzoni C
  • Ceresoli D
  • Cococcioni M
  • Colonna N
  • Carnimeo I
  • Dal Corso A.
  • Baroni S
  • de Gironcoli S.
  • Delugas P
  • Di Stasio Jr. R.A.
  • Ferretti A
  • Floris A
  • Fratesi G.
  • Fugallo G.
  • Gebauer R
  • Gerstmann U.
  • Giustino F
  • Gorni T
  • Jia J
  • Kawamura M
  • Ko H-y
  • Kokalj A
  • Küçükbenli E
  • Lazzeri M.
  • Marsili M.
  • Marzari Nicola
  • Mauri F.
  • Nguyen N.L.
  • Otero-De-La-Roza A
  • Paulatto L.
  • Poncé S
  • Rocca D.
  • Sabatini R.
  • Santra B.
  • Schlipf M.
  • Seitsonen A.P.
  • Smogunov A.
  • Timrov I.
  • Thonhauser T
  • Umari P
  • Vast N.
  • Wu X
  • Nguyen H.-V.
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2017, 29, pp.465901. Quantum ESPRESSO is an integrated suite of open-source computer codes for quantum simulations of materials using state-of-the-art electronic-structure techniques, based on density-functional theory, density-functional perturbation theory, and many-body perturbation theory, within the plane-wave pseudopotential and projector-augmented-wave approaches. Quantum ESPRESSO owes its popularity to the wide variety of properties and processes it allows to simulate, to its performance on an increasingly broad array of hardware architectures, and to a community of researchers that rely on its capabilities as a core open-source development platform to implement their ideas. In this paper we describe recent extensions and improvements, covering new methodologies and property calculators, improved parallelization, code modularization, and extended interoperability both within the distribution and with external software. (10.1088/1361-648X/aa8f79)
  DOI : 10.1088/1361-648X/aa8f79
• High intensity surface plasma waves, theory and PIC simulations
  
  • Raynaud Michèle
  • Héron Anne
  • Adam Jean-Claude
  Plasma Physics and Controlled Fusion, IOP Publishing, 2017, 60, pp.014021. With the development of intense (>1019 W cm−2) short pulses (≤25 fs) laser with very high contrast, surface plasma wave (SPW) can be explored in the relativistic regime. As the SPW propagates with a phase velocity close to the speed of light it may results in a strong acceleration of electron bunches along the surface permitting them to reach relativistic energies. This may be important e.g. for applications in the field of plasma-based accelerators. We investigate in this work the excitation of SPWs on grating preformed over-dense plasmas for laser intensities ranging from 1019 up to 1021 W cm−2. We discuss the nature of the interaction with respect to the solid case in which surface plasmon can be resonantly excited with weak laser intensity. In particular, we show the importance of the pulse duration and focalization of the laser beam on the amplitude of the SPW. (10.1088/1361-6587/aa8f13)
  DOI : 10.1088/1361-6587/aa8f13
• Irradiation and nanostructuration of piezoelectric polymers for nano-sensoring and harvesting energy applications.
  
  • Melilli Giuseppe
  , 2017. The versatility of the track-etching technique has allowed to investigate deeper the direct and inverse piezoelectric effect of a polarized Poly(vinylidene fluoride) (PVDF) film in building nanostructured hybrid Nickel nanowires (Ni NWs)/PVDF membrane. The magnetic properties of the Ni NW, such as anisotropic magneto resistance (AMR), are exploited to investigate the response of the magnetization to a mechanical deformation of the PVDF matrix. In particular, the deformations were induced either by thermo-mechanical or an electro-mechanical (inverse piezoelectric effect) stress. The sensitivity of the single NW has allowed to determine the amplitude and direction of a mechanical stress exerted at the nano-scale by the PVDF matrix. The outstanding resistance of the direct piezoelectric response of polarized PVDF film to radiation, such as SHI and e-beam, (doses range < 100kGy) was reported. Beyond the conservation of the piezoelectric response, in this dose range, irradiation defects (chain scissions, increase of the crystalline -phase, crosslinking) had a significative impact on the polymer material. All these defects, ones predominant above the gel dose (herein 10 kGy), and the other ones below, compensate their antagonistic effects towards the globally unchanged piezoelectric responses. Motivated by the high radiation resistance of the PVDF in terms of piezoelectric response, the idea was to exploit Ni NWs array embedded in the polarized PVDF membrane to study the influence of the Ni NWs on the piezoelectric response in view of harvesting energy application. The presence of the Ni NWs array leads a non-negligible increase of the piezoelectric efficiency. Related to the presence of the NWs, an increase of the dielectric permittivity in the nanostructured PVDF was also reported. An interfacial polarization between the Ni NWs and the PVDF matrix could explain the higher efficiency value respect to nanoporous PVDF, without NWs.
• Vertically Aligned Carbon Nanotube Growth on Aluminium Substrate at Low Temperature
  
  • Nassoy F.
  • Pinault M.
  • Descarpentries J.
  • Reynaud C.
  • Coulon P-E
  • Mayne-L'Hermite M.
  , 2017. This communication addresses the growth of VACNT on aluminium by a single-step process (simultaneously injecting catalyser and carbon source precursors), namely the thermal aerosol assisted CCVD. The aim is to get a scalable process to fabricate ultracapacitor electrodes exhibiting a great potential thanks to VACNT specific surface area, anisotropy and good electrical conductivity. Considering the aluminium melting temperature (c.a. 660°C), the synthesis of VACNT on such substrates requires a significant reduction in the growth temperature as compared to conventional substrates [1-3]. According to our previous work, when hydrogen is added in the gas phase, the decomposition of the catalyst precursor will be more efficient at low temperature [2]. Moreover, the use of acetylene as carbon source is more favourable for a decomposition at low temperature [4]. Our approach is first to identify the most relevant synthesis parameters to reach VACNT growth at such a low temperature by analysing the VACNT properties such as CNT length, density, diameter, … This optimization study, involving no surface pre-treatment of aluminium substrate, shows clean, long and dense VACNTs (Fig.1 A,B,C), with a growth rate (ca. 5µm/min) on par with the state of art the state of the art. Secondly, the objective is to understand VACNT growth mechanisms on Al substrate occurring at low temperature in order to optimise the VACNT synthesis process. Indeed, attention is paid on the Al surface prior and past the initial step of VACNT growth, and on the CNT/Al interface, with various analysis technics: SEM, TEM, EDX, XPS, GDOES … The results of the chemical analysis of the interface by STEM/EDX (Fig.2 D) exhibit clearly identifiable catalytic particles located at the CNT base within a well-defined oxide interface layer suggesting the crucial role of the interface for an efficient and reproducible VACNT growth.
• Manipulating refractive index, homogeneity and spectroscopy of Yb$^{3+}$-doped silica-core glass towards high-power large mode area photonic crystal fiber lasers
  
  • Fan Wang
  • Lili Hu
  • Wenbin Xu
  • Meng Wang
  • Suya Feng
  • Jinjun Ren
  • Lei Zhang
  • Danping Chen
  • Nadège Ollier
  • Guojun Gao
  • Chunlei Yu
  • And Shikai Wang
  Optics Express, Optical Society of America - OSA Publishing, 2017, 25 (21), pp.25960. Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb 3+-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb 3+ /Al 3+ /F-/P 5+-co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al 3+ /F-/P 5+ in Yb 3+doped silica glass,it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb 3+. The spectroscopic properties of Yb 3+ ions have not deteriorated by the co-doping of Fand P 5+ in YAFP glass compared with that of Yb 3+ /Al 3+ co-doped silica glass. A large-size (⌀5 mm × 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 × 10 −4 (with respect to pure silica glass), and low radial and axial RI fluctuations of ~2 × 10 −4 , was prepared. A LMA PCF with 50 µm core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M 2 of 1.4. (10.1364/oe.25.025960)
  DOI : 10.1364/oe.25.025960
• Comportement sous irradiation des verres d'aluminosilicate
  
  • Le Gac Alexandre
  , 2017. La compréhension des effets d’irradiation dans les verres d’oxyde est importante dans le domaine du conditionnement des déchets nucléaire et requière l’évaluation du rôle des formateurs de réseau, principalement le silicium, le bore et l’aluminium, mais aussi du rôle des éléments alcalins et alcalino-terreux qui peuvent agir en tant que modificateurs de réseau ou compensateurs de charge. Les verres d’aluminoborosilicates ont été très étudiés et le rôle des changements de coordinence du bore sur l’évolution structurale du verre sous irradiation a été souligné. Cependant, il n’y a que peu d’études sur les verres d’aluminosilicates et presque qu’aucune information sur l’influence de l’aluminium et de ses compensateurs de charge sur l’évolution du réseau sous irradiation. Ce travail de thèse a donc pour objectif de déterminer les effets de la teneur en aluminium et du type de compensateurs de charge (ici les ions sodium et calcium) sur l’évolution de la structure des verres d’aluminosilicates sous irradiation. Afin de comprendre les différents phénomènes dans les verres d’oxyde complexes, 13 verres simplifiés, composés d’oxydes de SiO2, Al2O3, Na2O et CaO, ont été élaborés. Ainsi, l’influence des rapports Na2O/CaO et Al2O3/SiO2 et de la teneur en Al2O3 ont été investigués. Pour simuler les désintégrations alpha et comparer les dommages électronique et balistique, des irradiations externes aux ions He2+ d’énergie 5 MeV et aux ions Au4+ d’énergie 7 MeV ont été réalisées sur les verres. Des irradiations aux électrons ont également été faites afin d’obtenir des échantillons irradiés en volume par des collisions électroniques à faible pouvoir d’arrêt.
• Etude du comportement sous irradiation γ et électronique de matrices cimentaires et de leurs hydrates constitutifs
  
  • Acher Loren
  , 2017. Afin de conditionner les déchets technologiques issus du démantèlement de l’Atelier de Vitrification de Marcoule au Commissariat à l’Energie Atomique et aux énergies alternatives (CEA), leur blocage dans une matrice cimentaire est envisagé. Dans ce contexte, l’effet des rayonnements ionisants issus des déchets nucléaires sur la matrice de confinement doit être examiné afin de garantir d’une part l’intégrité du colis, et d’autre part une production de gaz de radiolyse limitée. Ce travail de thèse s’intéresse au comportement sous irradiation gamma et électronique de trois types de matériaux cimentaires aux constituants différents et se focalise sur la production de gaz de radiolyse et sur l’évaluation de la résistance physique à travers l’observation des modifications structurales. Le sujet est traité par une double approche à la fois sur pâte de ciment et sur phases modèles, c’est-à-dire sur les hydrates constitutifs des pâtes de ciment synthétisés indépendamment. Il apparaît clairement que l’eau porale ainsi que les hydrates constitutifs contribuent à la production d’hydrogène radiolytique, avec une forte variation selon la nature des matériaux cimentaires. Ainsi, les ciments à base d’aluminates de calcium et les ciments phospho-magnésiens présentent un intérêt notable par rapport aux ciments silico-calciques usuels quant à la production d’hydrogène. Aux très fortes doses (plusieurs GGy) la résistance structurale sous irradiation électronique a été évaluée par diffraction de rayons X. Les hydrates constitutifs des trois familles de ciment étudiées présentent une bonne résistance structurale. Malgré la présence de variations dimensionnelles et microstructurales, ils ne s’amorphisent pas sous irradiation, ce qui s’avère positif en vue de l’application industrielle envisagée.
• Proton diffusion mechanisms in the double perovskite cathode material GdBaCo2O5.5 : A molecular dynamics study
  
  • Brieuc Fabien
  • Dezanneau Guilhem
  • Hayoun Marc
  • Dammak Hichem
  Solid State Ionics, Elsevier, 2017, 309, pp.187 - 191. GdBaCo2O5+x compounds have demonstrated to be very efficient cathode materials not only in solid oxide fuel cells but also in proton conducting fuel cells. In this last case, the excellent properties could be due to the presence of mixed electron-proton conduction. We study here the diffusion of the proton in this material using molecular dynamics simulations. Two different diffusion mechanisms are observed. The predominant mechanism is the standard proton transfer between two neighbouring oxygen atoms combined with the rotation of H around its first neighbour oxygen atom. The second mechanism consists in the migration of the OH group where both oxygen and hydrogen atoms diffuse together. Strong spatial correlations between successive proton jumps are evidenced. This is likely related to the presence of oxygen vacancies and to the concerted diffusion of hydrogen and oxygen atoms. (10.1016/j.ssi.2017.07.017)
  DOI : 10.1016/j.ssi.2017.07.017
• Damping Dependence of Spin-Torque Effects in Thermally Assisted Magnetization Reversal
  
  • Kalmykov Y.
  • Byrne D.
  • Coffey W. T.
  • Dowling W. J.
  • Titov S. V.
  • Wegrowe J. E.
  IEEE Transactions on Magnetics, Institute of Electrical and Electronics Engineers, 2017, 53 (10), pp.1 - 8. (10.1109/TMAG.2017.2732944)
  DOI : 10.1109/TMAG.2017.2732944
• Ab-initio description of optical nonlinear properties of semiconductors under an electrostatic field
  
  • Prussel Lucie
  , 2017. A deep understanding of the optical properties of solids is crucial for the improvement of nonlinear materials and devices.It offers the opportunity to search for new materials with specific properties.One way to tune some of those properties is to apply an electrostatic field. This gives rise to electro-optic effects.The most known among those is the Pockel or linear electro-optic effect (LEO), which is a second order response property.An important nonlinear process is the second harmonic generation (SHG), where two photons are absorbed bythe material and a photon is emitted at twice the energy of the incoming photon. While this process is sensitive tothe symmetry of the material, adding a static field would enable a nonlinear response from every material,including centrosymmetric ones. This happens through a third order process, named EFISH (Electric Field Induced Second Harmonic).We have developed a theoretical approach and a numerical tool to study these two nonlinear properties (LEO and EFISH)in the context of Time-dependent Density Functional Theory (TDDFT), and we have applied it to the case of bulk SiC andGaAs as well as layered systems such as Si/Ge.
• Radioactive waste conditioning: the choice of the cement matrix versus irradiation
  
  • Acher L
  • Chartier D
  • Dannoux-Papin A
  • Haas J
  • Courtial M
  • de Noirfontaine M-N
  • Dunstetter F
  • Gorse-Pomonti D
  • Tusseau-Nenez Sandrine
  , 2017. The aim of this study is to compare the behavior of Portland and Ciment Fondu® cement under irradiation taking into account both real cement pastes and synthetic hydrates. First, γ-irradiations were performed using a 60 Co source (dose rate: 0.17-0.25 Gy.s-1, dose: up to 500×10 3 Gy). Thermogravimetric analysis measurements were performed in order to determine the amount and the type of water involved. H2 gas production was measured by gas chromatography. Regardless of the water to cement ratio (W/C) chosen (0.2, 0.4 and 0.6), it is shown that Ciment Fondu® pastes produce less H2 under irradiation. Moreover, the H2 production of portlandite and gibbsite, constituent hydrates of Portland and Ciment Fondu® cements respectively, shows that the amount of gas produced depends on the hydrate nature. Secondly, portlandite and gibbsite were electron-irradiated up to 300 MGy and 3 GGy using the LSI SIRIUS accelerator platform. X-Ray Diffraction analyses were performed before and after irradiation in order to investigate structural damage. Only limited structural disorder was observed, which confirms the good stability of both hydrates under present irradiation conditions.
• Edge Contamination, Bulk Disorder, Flux Front Roughening, and Multiscaling in Type II Superconducting Thin Films
  
  • Geahel Michel
  • Jouanny Isabelle
  • Gorse-Pomonti Dominique
  • Poirier-Quinot Marie
  • Briatico Javier
  • Jacominus van Der Beek Cornelis
  Condensed Matter, MDPI, 2017, 2 (3), pp.27. We have investigated the effect of different types of disorder on the propagation, roughness, and scaling properties of magnetic flux fronts in a type II superconductor. A progression from the usual (Kardar-Parisi-Zhang-type) scaling to multiscaling is observed as the disorder strength is increased. A hierarchy of disorder strengths is established for YBa 2 Cu 3 O 7 d thin films. The results cast light on the physical origin of the roughening of flux fronts, and they are of interest for the design and elimination of flux noise in microscopic superconducting thin-film devices. (10.3390/condmat2030027)
  DOI : 10.3390/condmat2030027
• Eigenmodes of semiconductor spin-lasers with local linear birefringence and gain dichroism (Conference Presentation)
  
  • Fordos Tibor
  • Postava Kamil
  • Pištora Jaromír
  • Garnache Arnaud
  • Jaffrès Henri
  • Drouhin Henri
  • Wegrowe Jean-Eric
  • Razeghi Manijeh
  , 2017, pp.88. (10.1117/12.2278023)
  DOI : 10.1117/12.2278023
• Spinors for everyone
  
  • Coddens Gerrit
  , 2017. It is hard to find intuition for spinors in the literature. We provide this intuition by explaining all the underlying ideas in a way that can be understood by everybody who knows the definition of a group, complex numbers and matrix algebra. We first work out these ideas for the representation SU(2) of the three-dimensional rotation group in R 3. In a second stage we generalize the approach to rotation groups in vector spaces R n of arbitrary dimension n > 3, endowed with an Euclidean metric. The reader can obtain this way an intuitive understanding of what a spinor is. We discuss the meaning of making linear combinations of spinors.
• Photoinduced filling of near-nodal gap in Bi 2 Sr 2 CaCu 2 O 8 + δ
  
  • Zhang Zhongkai
  • Piovera C.
  • Papalazarou E.
  • Marsi M.
  • d'Astuto Matteo
  • van Der Beek C. J.
  • Taleb-Ibrahimi A.
  • Perfetti L.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2017, 96 (6). (10.1103/PhysRevB.96.064510)
  DOI : 10.1103/PhysRevB.96.064510
• Dynamics and reactivity of water in natural montmorillonites
  
  • Fourdrin Chloé
  • Hanane Aarrachi
  • Latrille Christelle
  • Bergaya Faiza
  • Renault Jean-Philippe
  • Lima Manuela
  • Le Caër Sophie
  , 2017. The radiolytic decomposition of water has significant impact in the nuclear industry. H$_2$_ radiolytically fonned by water decomposition might lead to explosion and overpressure hazards in the waste package. In the context of high level radioactive waste management, heterogeneous materials such as clay mineraIs (or concrete) are possible candidates around the waste package. For instance, bentonite, which major component is montmorillonite (Mt, the most representative swelling clay mineraI of the smectite group), is foreseen in France as backfilling material for its swelling and retention properties. However, the significant amount of water present in the interlayer space and between the particles might enhance the H$_2$ production under irradiation, and despite the environmental significance, only a few studies discuss the water radiolysis in those systems. In this context, we have decided to investigate the dynamics and the reactivity of water molecules confmed in natural montmorillonites from Camp Berteau, Marocco. Ultrafast infrared spectroscopy of the O-D stretching mode of dilute HOD in H$_2$0 probes the local environment and the hydrogen bond network of confined water [1]. The dynamics of water molecules confined in the interlayer space of montmorillonites and in interaction with two types of cations (Li$^+$ and Ca$^{2+}$) but also with the negatively charged siloxane surface was studied. The results evidenced that the OD vibrational dynamics was significantly slowed down in confined media: it went from 1.7 ps in neat water to 2.6 ps in the case of Li$^+$ cations with two water pseudolayers (2.2-2.3 ps in the case of Ca$^{2+}$ cations) and to 4.7 ps in the case of Li$^+$ cations with one water pseudo layer. No significant difference between the two cations was noticed. In this 2D confined geometry (the interlayer space being about 0.6 nm for two water pseudolayers), the relaxation time constants obtained were comparable to the ones measured in analogous concentrated salt solutions. Nevertheless, and in strong opposition to the observations perfonned in the liquid phase, anisotropy experiments evidenced the absence of rotational motions on a 5 ps time scale, proving that the hydrogen bond network in the interlayer space of the clay mineraI is locked at this time scale. Lastly, the impact of confinement on the reactivity under irradiation of confmed water molecules was investigated. The radiolysis of water confmed in natural montmorillonites was studied as a function of the composition of the montrnorillonite, the nature of the exchangeable cation, and the relative humidity by following the H$_2$ production under electron irradiation [2]. It was shown that the main factor influencing this H$_2$ production was the water amount in the interlayer space. The effect of the exchangeable cation was linked to its hydration enthalpy. When the water amount was high enough to get a basal distance higher than 1.3 nm, then a total energy transfer from the montmorillonite sheets to the interlayer space occured, and the H$_2$ production measured was very similar to the one obtained in bulk water. For a basal distance smaller than 1.3 nm, the H$_2$ production increased with the relative humidity and thus with the water amount.
• Etude des effets magneto-transverses dans les matériaux ferromagnétiques : effets Righi-Leduc planaire et anomal et géométrie Corbino.
  
  • Madon Benjamin
  , 2017. Résumé : Au cours de cette thèse nous nous sommes intéressés à différentes propriétés de transport électrique, thermique et thermoélectrique. En particulier, nous avons mis en évidence les effets Righi-Leduc anomal et planaire qui sont les équivalents thermiques des effets Hall anomal et planaire. Ces effets doivent impérativement être considérés dans l’interprétation des mesures d’effet Seebeck de Spin.Nous avons mis à profit les techniques développées dans le cadre de cette étude pour étudier l’effet Nernst dans InSb. Nous avons utilsé un modèle de distribution de porteur pour expliquer les non-linéarités de celui-ci à des champs magnétiques proches de 1T.Nous avons construit une expérience de résonance ferromagnétique dont le but sera d’étudier les implications des effets thermique et thermoélectrique dans les expérience de pompage de spin. Enfin, nous nous sommes intéréssés au transport électrique en géométrie Corbino. La géométrie Corbino est celle d’un disque dans laquelle il n’existe aucun bord libre ou des charges peuvent s’accumuler. Cela se traduit par l’apparition d’un courant de Hall ortho-radial dont la conséquence est l’augmentation de la résistance du disque. Nous avons mis en évidence une augmentation de résistance en géométrie Corbino dans CoGd et CoTb dont l’origine est l’effet Hall anomale. Bien que cet effet ne soit pas dissipatif, il a donné naissance à un courant dissipatif transverse. Nous avons également vu que cet effet entre en compétition avec la magnétorésistance anisotrope dans le permalloy.Du fait de la similitude entre l’effet Hall anomal et l’effet Hall de spin, on s’attend dans le platine à l’existence d’un fort courant de spin orthoradial sans possibilités d’accumulations dont la mise en évidence expérimentale fera l’objet de travaux futurs.
• Damping dependence of spin-transfer torque effects in thermally assisted magnetization reversal
  
  • Kalmykov Yu. P.
  • Byrne D. J.
  • Coffey W. T.
  • Dowling W. J.
  • Titov S. V.
  • Wegrowe J. -E.
  , 2017.
• Excess of topological defects induced by confinement in vortex nanocrystals
  
  • Bolecek N.
  • Dolz M.
  • Pastoriza H.
  • Konczykowski M.
  • van Der Beek C.
  • Kolton A.
  • Fasano Y.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2017, 96 (2). (10.1103/PhysRevB.96.024507)
  DOI : 10.1103/PhysRevB.96.024507
• Self-consistent Dyson equation and self-energy functionals: An analysis and illustration on the example of the Hubbard atom
  
  • Tarantino Walter
  • Romaniello Pina
  • Berger Arjan
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2017, 96 (4), pp.045124. (10.1103/PhysRevB.96.045124)
  DOI : 10.1103/PhysRevB.96.045124
• Fully gapped superconductivity with no sign change in the prototypical heavy-fermion CeCu$_2$ Si$_2$
  
  • Yamashita Takuya
  • Takenaka Takaaki
  • Tokiwa Yoshifumi
  • Wilcox Joseph
  • Mizukami Yuta
  • Terazawa Daiki
  • Kasahara Yuichi
  • Kittaka Shunichiro
  • Sakakibara Toshiro
  • Konczykowski Marcin
  • Seiro Silvia
  • Jeevan Hirale
  • Geibel Christoph
  • Putzke Carsten
  • Onishi Takafumi
  • Ikeda Hiroaki
  • Carrington Antony
  • Shibauchi Takasada
  • Matsuda Yuji
  Science Advances, American Association for the Advancement of Science (AAAS), 2017, 3 (6), pp.e1601667. In exotic superconductors, including high-T$_c$ copper oxides, the interactions mediating electron Cooper pairing are widely considered to have a magnetic rather than a conventional electron-phonon origin. Interest in this exotic pairing was initiated by the 1979 discovery of heavy-fermion superconductivity in CeCu$_2$Si$_2$, which exhibits strong antiferromagnetic fluctuations. A hallmark of unconventional pairing by anisotropic repulsive interactions is that the superconducting energy gap changes sign as a function of the electron momentum, often leading to nodes where the gap goes to zero. We report low-temperature specific heat, thermal conductivity, and magnetic penetration depth measurements in CeCu$_2$Si$_2$, demonstrating the absence of gap nodes at any point on the Fermi surface. Moreover, electron irradiation experiments reveal that the superconductivity survives even when the electron mean free path becomes substantially shorter than the superconducting coherence length. This indicates that superconductivity is robust against impurities, implying that there is no sign change in the gap function. These results show that, contrary to long-standing belief, heavy electrons with extremely strong Coulomb repulsions can condense into a fully gapped s-wave superconducting state, which has an on-site attractive pairing interaction. (10.1126/sciadv.1601667)
  DOI : 10.1126/sciadv.1601667