Publications

2024

• Photon emission and radiation reaction effects in surface plasma waves in ultra-high intensities
  
  • Kleij P.
  • Marini S.
  • Caetano de Sousa M.
  • Grech M.
  • Riconda C.
  • Raynaud M.
  Physics of Plasmas, American Institute of Physics, 2024, 31 (7). Manipulating and harnessing plasmonic phenomena in the ultra-relativistic regime reveal promising prospects for the use of surface plasma waves (SPW) to create high-energy particle and radiation sources in the next generation of multi-petawatt lasers. Indeed, relativistic high-charge electron bunches can be produced by SPW excited by ultra-high intensity femtosecond lasers impinging on a periodically modulated solid-density target. In this regime, there is good evidence that SPW excitation survives and that the produced electron bunches experience strong acceleration, thus emitting large amounts of electromagnetic radiation. Therefore, extending the study to ultra-high laser intensities (I>1021 W/cm2), the use of a resonant grating for SPW generation represents an interesting alternative to light sources, as the energy lost by electrons due to radiation emission is transferred to high-energy γ photons. In addition, we show that using a laser with wavefront rotation coupled with a tailored blazed grating improves photon emission in the ultra-relativistic regime of interaction. (10.1063/5.0209316)
  DOI : 10.1063/5.0209316
• Hydration in diluted solutions of brownmillerite extracted from SR cement and synthetic brownmillerite
  
  • Mériot Alexis
  • Gauffinet sandrine
  • de Noirfontaine Marie-Noëlle
  • Courtial Mireille
  • Alloncle Karen
  • Izoret Laurent
  • Dunstetter Frédéric
  Cement and Concrete Research, Elsevier, 2024, 181, pp.107518. The aim of this study is to investigate the reactivity of ferrites extracted from Sulfate Resisting (SR) Portland cement clinkers, until now often neglected. Industrial materials and synthetic materials have been studied and compared in the whole range of the Al/Fe ratio. Highly diluted aqueous suspensions were used, ranging between pure water and more complex solutions simulating the pore solution in cement. Conductimetry was combined with ICP. The reactivity of ferrite depends on the environment and the aluminum content of ferrite. The reactivity of ferrites extracted from industrial SR0 and SR3 clinkers (C3A = 0 wt% and C3A ≤ 3 wt% respectively) can be distinguished from one another. Additionally, industrial ferrite was found to be more reactive than synthetic ferrite. The iron content of katoite and ettringite was investigated using XRD. It depends on the Al/Fe ratio of ferrite and the presence of calcium hydroxide in the solution. (10.1016/j.cemconres.2024.107518)
  DOI : 10.1016/j.cemconres.2024.107518
• Assessing Pozzolanic Reactivity of Reclaimed Fired Clay Roof Tiles and Bricks in Presence of Ground Limestone
  
  • Guillaume Bernadin
  • Serbource Théodore
  • Gauffinet sandrine
  • de Noirfontaine Marie-Noëlle
  • Izoret Laurent
  , 2024, 362, pp.783-793. Due to the drastic necessity to reduce cement and binder carbon footprint and because of the increasing scarcity of traditional supplementary cementitious material, there is an increasing interest in non-traditional reactive materials with low CO2 footprint, eventually coming from the circular economy. There are several emerging opportunities that need to be investigated before confirming their aptitude to substitute clinker, alone or in combination with other materials. Among these opportunities, reclaimed fired clay roof tiles and bricks represent a good candidate not only because they were historically used by the antic Romans but also because they represent a significant part of demolition wastes. These materials, gathered from different locations in France with different ages, were chemically and mineralogically characterized. Their potential pozzolanic character was assessed by mean of R3 tests with a follow-up of the evolution of hydrates suite (consumption and precipitation), doubled with mechanical strength on mortar for different formulated binders, combining materials to simulate standardized cement types according to European standards EN197-1 and -5. The overall results indicate their reactivity was good enough to conclude that these materials can be considered as potential alternative SCMs. (10.14359/51742009)
  DOI : 10.14359/51742009
• Non-linear phononics in THz excited Bi2Te3 nanofilms
  
  • Busselez R
  • Levchuk A
  • Ruello P
  • Juvé V
  • Arnaud B
  , 2024.
• All-optical polarization switching in ferroelectrics
  
  • Temnov Vasily V
  • Vavassori Paolo
  Nature Photonics, Nature Publishing Group, 2024, 18, pp.529 - 530. Ultrafast optical experiments using narrow-bandwidth tunable IR laser pulses enable nonvolatile all-optical switching of ferroelectric polarization in BaTiO3 in the epsilon-near-zero regime. (10.1038/s41566-024-01452-9)
  DOI : 10.1038/s41566-024-01452-9
• Electron-phonon coupling and transient dynamics of hot carriers: from interpretation of photoemission experiments to transport simulations in devices
  
  • Ghanem Mohammad
  • Dollfus Philippe
  • Saint-Martin Jérôme
  • Sen Raja
  • Vast Nathalie
  • Sjakste Jelena
  Proceedings of SPIE, the International Society for Optical Engineering, SPIE, The International Society for Optical Engineering, 2024, 12992, pp.1299207. 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 spectroscopy experiments. 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. We show that DFT-based description of the electron-phonon intervalley scattering in GaAs, coupled with the 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. (10.1117/12.3022114)
  DOI : 10.1117/12.3022114
• Injection of anomalous-Hall current into a load circuit
  
  • Lacour D.
  • Hehn M.
  • Xu Min
  • Wegrowe J.-E.
  Journal of Applied Physics, American Institute of Physics, 2024, 135 (19), pp.193903. The anomalous-Hall current injection is studied in a Hall device contacted to a lateral load circuit. This anomalous-Hall current is generated inside a Co75Gd25 ferrimagnetic Hall bar and injected into a lateral load circuit contacted at the edges. The current, the voltage, and the power are measured as a function of the magnetization states, the load resistance Rl, and the temperature. It is shown that (1) the resistance associated with the anomalous-Hall current flowing inside the Hall bar is that of the portion of the ferrimagnet located between the lateral contacts, (2) the role of the non-uniformity of the current due to the lateral contacts is small, (3) the maximum power efficiency of the current injection into the load circuit corresponds to the condition of the resistance matching of the two sub-circuits, and (4) this maximum power efficiency is of the order of the square of the anomalous-Hall angle. These observations are in agreement with recent predictions based on a non-equilibrium variational approach. (10.1063/5.0205911)
  DOI : 10.1063/5.0205911
• Coupling ab-initio Description and Monte Carlo Simulation to Capture the Transport of Hot Carriers
  
  • Ghanem Mohammad
  • Sjakste Jelena
  • Sen Raja
  • Pilotto Alessandro
  • Dollfus Philippe
  • Saint-Martin Jérôme
  , 2024.
• Thermostatistics, Information, Subjectivity: Why Is This Association So Disturbing?
  
  • Lairez Didier
  Mathematics, MDPI, 2024, 12 (10), pp.1498. Although information theory resolves the inconsistencies (known in the form of famous enigmas) of the traditional approach of thermostatistics, its place in the corresponding literature is not what it deserves. This article supports the idea that this is mainly due to epistemological rather than scientific reasons: the subjectivity introduced into physics is perceived as a problem. Here is an attempt to expose and clarify where exactly this subjectivity lies: in the representation of reality and in probabilistic inference, two aspects that have been integrated into the practice of science for a long time and which should no longer frighten anyone but have become explicit with information theory. (10.3390/math12101498)
  DOI : 10.3390/math12101498
• Single-component superconductivity in UTe2 at ambient pressure
  
  • Theuss Florian
  • Shragai Avi
  • Grissonnanche Gaël
  • Hayes Ian
  • Saha Shanta
  • Eo Yun Suk
  • Suarez Alonso
  • Shishidou Tatsuya
  • Butch Nicholas
  • Paglione Johnpierre
  • Ramshaw B.
  Nature Physics, Nature Publishing Group [2005-....], 2024, 20 (7), pp.1124-1130. (10.1038/s41567-024-02493-1)
  DOI : 10.1038/s41567-024-02493-1
• The glassy structure of reactive supplementary cementitious materials (SCMs) and recycled glass: Contribution of XRD and Raman spectroscopy to their characterization
  
  • Serbource Théodore
  • Courtial Mireille
  • de Noirfontaine Marie-Noëlle
  • Tusseau-Nenez Sandrine
  • Sandt Christophe
  • Izoret Laurent
  Cement and Concrete Research, Elsevier, 2024, 179, pp.107468. This study compares thirteen natural and industrial samples of supplementary or emerging supplementary cementitious materials (SCMs): slag, fly ashes, pozzolan, obsidian, silica fume, and recycled glass. These materials are used or are under consideration for decarbonization in cement plants. XRF, XRD and Raman microspectroscopy were used in order to achieve a deeper understanding of the structural characterization of SCMs. The changes in position and shape of the XRD diffuse halos were compared. Raman spectroscopy was used to study the glass part of the SCM families, to better understand their structure in terms of depolymerization degree, angle, ring size and incorporations into the glass. The chemical composition of each glassy part was also estimated using reverse Bogue calculations. The hump position is correlated with the Raman shift, and with the XRF bulk or with the calculated glass chemical composition of SCMs, in terms of CaO/(SiO2+Al2O3) or network modifiers to formers ratios. (10.1016/j.cemconres.2024.107468)
  DOI : 10.1016/j.cemconres.2024.107468
• Reduction of native singly ionized zinc vacancies content by 2.5 MeV electron irradiation of ZnGeP$_2$ single crystals
  
  • Vernozy Charlotte
  • Alessi Antonino
  • Petit Johan
  • Courpron Audrey
  • Cavani Olivier
  • Véniard Valérie
  Physica Status Solidi A (applications and materials science), Wiley, 2024, 221 (11), pp.2300818. An experimental study on how to reduce the content of singly ionized zinc vacancy (V$^−_{Zn}$ ) in ZnGeP$_2$ crystals to improve their optical quality is presented. Their electron paramagnetic resonance signal has been studied in samples treated in different ways. The data provide a scheme of the reductions that can be obtained by the different methods or by their combinations. The adding of Sn during the synthesis phase helps the production of large‐size single crystals and the reduction of the V$^−_{Zn}$ content. Thermal treatment and electron irradiation are then needed for further reduction. At the fluence of 2 × 10$^{17}$e cm$^{−2}$ , the V$^−_{Zn}$ decrease does not reach a minimum value, so with higher fluences, additional reduction of V$^−_{Zn}$ content is expected. (10.1002/pssa.202300818)
  DOI : 10.1002/pssa.202300818
• charge density response of 2d polymorphs : borophene as a prototypical case
  
  • Osorio Delgadillo Alam Tonaltzin
  , 2024. The aim of this thesis is to elucidate the charge dynamics in 2D materials with complex atomic structures. To this end, borophene was chosen as a prototypical material that exhibits numerous allotropes, such that the influence of the atomic structure on the electronic properties can be investigated directly. Among the multiple allotropes I identified eight structures of theoretical and experimental relevance and computed their electronic band structure. I then used the shared characteristics of the electronic structure of the different polymorphs to relate them to a common parent structure, and I built a theoretical model based on a confined three-dimensional homogeneous electron gas. This model explain several findings for the electronic structure of the different polymorphs studied in this work.The electronic structure of the different polymorphs showed common features among different allotropes, but it also showed differences in the form of weakly-dispersive bands. These flat bands show up as a signature of the specific atomic structure. We refer to them as defect-like states that appear from the creation of point defects in a common borophene atomic structure. Moreover, I investigated the effect of buckling on the electronic structure and showed that we can use this parameter to tune electronic properties of the material such that semimetallicity and eventually even superconductivity might be impacted.The study of the electronic structure also showed the potential of this class of materials to be used as a transparent conductor. I described the mechanism for which certain electronic transitions do not appear in the absorption spectra by symmetry: the position of the Fermi energy in the band structure is an important parameter to determine the optical properties of borophene, and the relative positions of p-states in-plane and out-of-plane plays also an important role around the Fermi level. I therefore described nesting of the Fermi surface based on the information of the electronic transitions. The study of the nesting of the Fermi surface was complemented with the computation of the static linear response, which allowed me to we unravel the nature of two Kohn anomalies appearing in borophene delta_6.The calculation of the response functions is computationally very expensive. I addressed this problem by developing an approximated method that allows us to write the static response as an explicit functional of the density matrix. This is of both fundamental and practical interest since it is one of the few examples of explicit density matrix functionals for observables, and since it leads to an order of magnitude gain in computer time.
• On the Supposed Mass of Entropy and That of Information
  
  • Lairez Didier
  Entropy, MDPI, 2024, 26 (4), pp.337. In the theory of special relativity, energy can be found in two forms: kinetic energy and rest mass. The potential energy of a body is actually stored in the form of rest mass, the interaction energy too, but temperature is not. Information acquired about a dynamical system can be potentially used to extract useful work from it. Hence, the “mass–energy–information equivalence principle” that has been recently proposed. In this paper, it is first recalled that for a thermodynamic system made of non-interacting entities at constant temperature, the internal energy is also constant. So, the energy involved in a variation in entropy (TΔS) differs from a change in the potential energy stored or released and cannot be associated to a corresponding variation in mass of the system, even if it is expressed in terms of the quantity of information. This debate gives us the opportunity to deepen the notion of entropy seen as a quantity of information, to highlight the difference between logical irreversibility (a state-dependent property) and thermodynamical irreversibility (a path-dependent property), and to return to the nature of the link between energy and information that is dynamical. (10.3390/e26040337)
  DOI : 10.3390/e26040337
• Glass for photonics: insight in the glass properties obtained under laser fs writing via point defects analysis
  
  • Ollier Nadège
  • Alassani Fouad
  • Petit Yannick
  • Cardinal Thierry
  • Parmar Vinod
  • Bellouard Yves
  , 2024. Photonics is becoming a key enable technology for the future. In particular, the ability to use direct laser writing for shaping and inscribing functionality in glass material has open a way for the versatile production of multi-scale subwavelength photonic architectures...
• Connections between resonant inelastic x-ray scattering and complementary x-ray spectroscopies: Probing excitons at the Al K and L$_1$ edges of $\alpha$−Al$_2$O$_3$
  
  • Urquiza M. Laura
  • Gatti Matteo
  • Sottile Francesco
  Physical Review B, American Physical Society, 2024, 109 (11), pp.115157. We present an ab initio study of neutral core and valence electronic excitations in α-Al2O3 by solving the Bethe-Salpeter equation (BSE) of many-body perturbation theory within an all-electron framework. Calculated spectra at the Al K and L1 edges are in remarkable agreement with available experiments from X-ray absorption (XAS) and X-ray Raman spectroscopy once excitonic effects are taken into account. The combination of the BSE spectra for the two techniques confirms the dipole-forbidden nature of the exciton prepeak as suggested by recent calculations based on densityfunctional theory. Moreover, we make predictions for resonant inelastic X-ray scattering (RIXS) spectra at K and L1 edges, which strikingly fully overlap also beyond an independent-particle picture.The RIXS calculations reveal two distinct regimes as a function of incoming photon energy. Below and at the XAS threshold, we observe Raman-like features, characterised by strong excitonic effects, which we directly compare to peaks in the loss function. Above the XAS threshold, instead, fluorescence features become predominant: RIXS spectra can be well described and analyzed within an independent-particle approximation showing similarity with the X-ray emission spectrum. (10.1103/PhysRevB.109.115157)
  DOI : 10.1103/PhysRevB.109.115157
• Using modelling and simulation to account for magnetic-driven self-assembly and elongation of nanoparticles during in situ X-ray microscopy in liquid phase
  
  • Saouli Nathalie
  • Dammak Hichem
  • Cosola Andrea
  • Hayoun Marc
  • Rizza Giancarlo
  , 2024.
• Matter and waves
  
  • Baldovin Marco
  • Browaeys Antoine
  • de Teresa José María
  • Draxl Claudia
  • Druon Frédéric
  • Gradenigo Giacomo
  • Greffet Jean-Jacques
  • Lépine Franck
  • Lüning Jan
  • Reining Lucia
  • Salières Pascal
  • Seneor Pierre
  • Silva Luis
  • Tschentscher Thomas
  • van der Beek Kees
  • Vollmer Antje
  • Vulpiani Angelo
  , 2024, pp.3-1-3-114. (10.1088/978-0-7503-6342-6ch3)
  DOI : 10.1088/978-0-7503-6342-6ch3
• Identification of paramagnetic centers in irradiated Sn-doped silicon dioxide by first-principles
  
  • Giacomazzi L
  • Martin-Samos L
  • Richard N
  • Ceresoli D
  • Alessi A
  Journal of Physics: Condensed Matter, IOP Publishing [1989-....], 2024, 36 (21), pp.215502. We present a first-principles investigation of Sn paramagnetic centers in Sn-doped vitreous silica based on calculations of the electron paramagnetic resonance (EPR) parameters. The present investigation provides evidence of an extended analogy between the family of Ge paramagnetic centers in Ge-doped silica and the family of Sn paramagnetic centers in Sn-doped silica for SnO 2 concentrations below phase separation. We infer, also keeping into account the larger spin–orbit coupling of Sn atoms with respect to Ge atoms, that a peculiar and highly distorted three-fold coordinated Sn center (i.e. the Sn forward-oriented configuration) should give rise to an orthorhombic EPR signal of which we suggest a fingerprint in the EPR spectra recorded by Chiodini et al (2001 Phys. Rev. B 64 073102). Given its structural analogy with the E α ′ and Ge(2) centers, we here name it as the ‘Sn(2) center’. Moreover, we show that the single trapped electron at a SnO 4 tetrahedron constitutes a paramagnetic center responsible for the orthorhombic EPR signal reported in Chiodini et al (1998 Phys. Rev. B 58 9615), confuting the early assignment to a distorted variant of the Sn- E ʹ center. We hence relabel the latter orthorhombic EPR signal as the ‘Sn(1) center’ due to its analogy to the Ge(1) center in Ge-doped silica. (10.1088/1361-648X/ad2a0c)
  DOI : 10.1088/1361-648X/ad2a0c
• Nodal superconductivity in miassite Rh$_{17}$S$_{15}$
  
  • Kim Hyunsoo
  • Tanatar Makariy
  • Kończykowski Marcin
  • Grasset Romain
  • Kaluarachchi Udhara
  • Teknowijoyo Serafim
  • Cho Kyuil
  • Sapkota Aashish
  • Wilde John
  • Krogstad Matthew
  • Bud’ko Sergey
  • Brydon Philip
  • Canfield Paul
  • Prozorov Ruslan
  Communications Materials, Nature, 2024, 5 (1), pp.17. Solid state chemistry has produced a plethora of materials with properties not found in nature. For example, high-temperature superconductivity in cuprates is drastically different from the superconductivity of naturally occurring metals and alloys and is frequently referred to as unconventional. Unconventional superconductivity is also found in other synthetic compounds, such as iron-based and heavy-fermion superconductors. Here, we report compelling evidence of unconventional nodal superconductivity in synthetic samples of Rh 17 S 15 ( T c = 5.4 K), which is also found in nature as the mineral miassite. We investigated the temperature-dependent variation of the London penetration depth Δ λ ( T ) and the disorder evolution of the critical superconducting temperature T c and the upper critical field H c 2 ( T ) in single crystalline Rh 17 S 15 . We found a T − linear temperature variation of Δ λ ( T ) below 0.3 T c , which is consistent with the presence of nodal lines in the superconducting gap of Rh 17 S 15 . The nodal character of the superconducting state is supported by the observed suppression of T c and H c 2 ( T ) in samples with a controlled level of non-magnetic disorder introduced by 2.5 MeV electron irradiation. We propose a nodal sign-changing superconducting gap in the A 1 g irreducible representation, which preserves the cubic symmetry of the crystal and is in excellent agreement with the derived superfluid density. To the best of our knowledge, this establishes miassite as the only mineral known so far that reveals unconventional superconductivity in its clean synthetic form, though it is unlikely that it is present in natural crystals because of unavoidable impurities that quickly destroy nodal superconductivity. (10.1038/s43246-024-00456-w)
  DOI : 10.1038/s43246-024-00456-w
• epiq: An open-source software for the calculation of electron-phonon interaction related properties
  
  • Marini Giovanni
  • Marchese Guglielmo
  • Profeta Gianni
  • Sjakste Jelena
  • Macheda Francesco
  • Vast Nathalie
  • Mauri Francesco
  • Calandra Matteo
  Computer Physics Communications, Elsevier, 2024, 295, pp.108950. <div><p>epiq, (Electron-Phonon wannier Interpolation over k and q-points), is an open-source software for the calculation of electron-phonon interaction related properties from first principles. Acting as a post-processing tool for a DFPT code ( Quantum ESPRESSO ) and wannier90 packages, epiq exploits the localization of the deformation potential in the Wannier function basis and the stationary properties of a force-constant functional with respect to the first-order perturbation of the electronic charge density to calculate many electron-phonon related properties with high accuracy and free from convergence issues related to Brillouin zone sampling. epiq features includes: the adiabatic and non-adiabatic phonon dispersion, superconducting properties (including the superconducting band gap in the Migdal-Eliashberg formulation), double-resonant Raman spectra and lifetime of excited carriers. The possibility to customize most of its input makes epiq a versatile and interoperable tool. Particularly relevant is the interaction with the Stochatic Self-Consistent Harmonic Approximation (SSCHA) allowing anharmonic effects to be included in the calculation of electron-properties. The scalability * These authors contributed equally.</p></div> (10.1016/j.cpc.2023.108950)
  DOI : 10.1016/j.cpc.2023.108950
• Electron irradiation reveals robust fully gapped superconductivity in LaNiGa$_2$
  
  • Ghimire S.
  • Joshi K.
  • Krenkel E.
  • Tanatar M.
  • Shi Yunshu
  • Kończykowski M.
  • Grasset R.
  • Taufour V.
  • Orth P.
  • Scheurer M.
  • Prozorov R.
  Physical Review B, American Physical Society, 2024, 109 (2), pp.024515. (10.1103/PhysRevB.109.024515)
  DOI : 10.1103/PhysRevB.109.024515
• Femtosecond laser induces near-IR 3D luminescence patterns in glass
  
  • Alassani Fouad
  • Raffy Guillaume
  • Fargues Alexandre
  • del Guerzo André
  • Ollier Nadège
  • Canioni Lionel
  • Cardinal Thierry
  • Petit Yannick
  , 2024, PC128760, pp.PC128760A. We have demonstrated the co-doping of silver ions and Bi3+ in glass allowing creation of 3D structures with tuning luminescence properties from the visible to the near IR with fs DWL. The tunable luminescence arises from the fs laser triggering both the photochemistry of silver ions and the photo-redox reaction of Bi3+ forming low valence Bismuth ions (Bi2+ red emitter and Bi+ near IR emitter). Confocal hyper-spectral lifetime-resolved imaging revealed the shortening of the fluorescence lifetime of silver clusters in the presence of Bismuth revealing the energy transfer mechanism from silver clusters to Bi+. (10.1117/12.3002586)
  DOI : 10.1117/12.3002586
• From spectra to total energy : beyond the GW approximation designing effective interactions.
  
  • El Sahili Abdallah
  , 2024. The world around us is composed of interacting many-particle systems, making it essential to comprehend these systems in order to understand the nature of our reality. Throughout human history, much effort has been made to reach this goal, with consequences impacting the technological advancements that shape our modern lives. In this thesis, which is specialized in condensed matter physics, we attempt to understand the interacting electrons systems that lead to electronic properties. In particular our efforts are focused on ground state total energy (E0) calculations. The main obstacle, which is the huge many-body wave functions that can be calculated only for small number of electrons, is overcome by the current available theories such as Density Functional Theory (DFT) and Many-Body Perturbation Theory (MBPT). These theories express observables in terms of more compact quantities, which are the one-body density and one-body Green's function (GF). However, the exact expressions and/or the density and GF themselves are often not known. One important example is the ground state total energy E0, whose expression is unknown in terms of the density. On the other hand, E0 can be written exactly in terms of the GF. The same holds for electron addition and removal spectral functions. However, the exact GF, that relies on the exact self-energy, is unknown and the need for approximations to the GF itself strongly impacts the quality of the results. Still, the Green's functions framework benefits from the existence of powerful approximations. In particular, MBPT suggests a way to expand the self-energy in diagrams that carry physical meaning. For situations that show only weak to moderate interaction effects, MBPT is often considered to be a systematic way to proceed, although in practice renormalizations, such as screening of the Coulomb interaction, are needed. In particular, even the lowest order of an expansion of the self-energy in terms of the screened Coulomb interaction W, which is the widely used GW approximation, has been very successful for the calculation of the quasi-particle part of electron addition and removal spectra in finite and extended systems. However, GW suffers from some shortcomings, such as a self-screening error and violation of exact constraints. Moreover, its good performance is limited to some materials where the correlation strength lies in a weak to moderate regime, whereas the strongly correlated systems remain unreachable by GW. In this thesis, we propose three different ways to go beyond GW in order to improve the calculation of ground state total energies. The first method includes corrections in the self-energy by combining time-dependent DFT (TDDFT) with MBPT. With these corrections, the self-energy is still approximated. We, however, show that the exact exchange-correlation contribution to E0 can be obtained exactly using this approximate self-energy provided that the ingredients are combined in a consistent way. The second method is based on expanding the self-energy in terms of W. We investigated the convergence of MBPT and we explored which W is the best choice in this expansion. The third method is based on the use of exact constraints, which can be used to add corrections beyond GW at a negligible computational cost. Our findings are illustrated using the symmteric Hubbard dimer at quarter and half fillings (one and two electron system). We provide a computer code for this project that will be available online at the end of the thesis.
• β -rays induced displacement damage on epitaxial 4H-SiC revealed by exciton recombination
  
  • Migliore F.
  • Alessi A.
  • Principato F.
  • Girard S.
  • Cannas M.
  • Gelardi F.
  • Lombardo A.
  • Vecchio D.
  • Brischetto A.
  • Agnello S.
  Applied Physics Letters, American Institute of Physics, 2024, 124 (4). One of the most interesting wide-bandgap semiconductor is 4H-SiC that has an indirect wide-bandgap of 3.3 eV. This material holds great potential to develop power devices that find applications in the field of high-voltage and high-temperature electronics and harsh environments. In this study, we employed complementary noninvasive characterization techniques, including micro-Raman, optical absorption, steady-state, and time-resolved photoluminescence spectroscopy, to investigate the characteristics of a 12 μm thick epitaxial layer of 4H-SiC grown on 4H-SiC. Furthermore, we explored the impact of ionizing radiation on this material, utilizing β-rays and two x-ray sources. The doses are in the range of 1–100 kGy for electrons with energy of 2.5 MeV, 16 kGy for the first x-ray source (an x-ray tube with a W target operating at an anode bias voltage of 28 kV), and 100 kGy for the second x-ray source (an x-ray tube with a W target operating at an anode bias voltage of 100 kV). When exposed to the electron beam, the excitonic band at 3.2 eV exhibits a reduction in its lifetime as the deposited dose increases. In particular, in samples characterized by a greater amount of native defects, both extended and point defects, this effect becomes evident at lower deposited doses. Conversely, in the samples subjected to x-ray irradiation, these effects are not observed. These findings indicate that electron beam irradiation triggers the formation of defects associated with atomic displacement. Ultimately, we have examined the impact of thermal treatments in air, ranging from 100 to 900 °C, to investigate the recovery characteristics of 4H-SiC. (10.1063/5.0179556)
  DOI : 10.1063/5.0179556