Publications

2024

• 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. (10.70675/8196c947z6ff5z48a8zad7ez57b379e39fc2)
  DOI : 10.70675/8196c947z6ff5z48a8zad7ez57b379e39fc2
• 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
• Impact of Glass Free Volume on Femtosecond Laser-Written Nanograting Formation in Silica Glass
  
  • Shchedrina Nadezhda
  • Cavillon Maxime
  • Ari Julien
  • Ollier Nadège
  • Lancry Matthieu
  Materials, MDPI, 2024, 17 (2), pp.502. In this study, we investigate the effects of densification through high pressure and temperature (up to 5 GPa, 1000 °C) in the making of nanogratings in pure silica glass, inscribed with femtosecond laser. The latter were monitored through retardance measurements using polarized optical microscopy, and their internal structure was observed under scanning electron microscopy. We reveal the difficulty in making nanogratings in densified silica glasses. Based on this observation, we propose that free volume may be a key precursor to initiate nanograting formation. (10.3390/ma17020502)
  DOI : 10.3390/ma17020502
• Single-gap isotropic s−wave superconductivity in single crystals AuSn4
  
  • Ghimire Sunil
  • Joshi Kamal R
  • Krenkel Elizabeth H
  • Tanatar Makariy A
  • Konczykowski Marcin
  • Grasset Romain
  • Canfield Paul C
  • Prozorov Ruslan
  SciPost Physics, SciPost Foundation, 2024, 17 (4), pp.116. London, λL(T), and Campbell, λC(T), penetration depths were measured in single crystals of a topological superconductor candidate AuSn4. At low temperatures, λL(T) is exponentially attenuated and, if fitted with the power law, λ(T)∼Tn, gives exponents n>4, indistinguishable from the isotropic single s−wave gap Bardeen-Cooper-Schrieffer (BCS) asymptotic. The superfluid density fits perfectly in the entire temperature range to the BCS theory. The superconducting transition temperature, Tc=2.40±0.05 K, does not change after 2.5 MeV electron irradiation, indicating the validity of the Anderson theorem for isotropic s−wave superconductors. Campbell penetration depth before and after electron irradiation shows no hysteresis between the zero-field cooling (ZFC) and field cooling (FC) protocols, consistent with the parabolic pinning potential. Interestingly, the critical current density estimated from the original Campbell theory decreases after irradiation, implying that a more sophisticated theory involving collective effects is needed to describe vortex pinning in this system. In general, our thermodynamic measurements strongly suggest that the bulk response of the AuSn4 crystals is fully consistent with the isotropic s−wave weak-coupling BCS superconductivity. (10.21468/SciPostPhys.17.4.116)
  DOI : 10.21468/SciPostPhys.17.4.116
• Non-resonant inelastic X-ray scattering for discrimination of pigments
  
  • Dalecky Lauren
  • Sottile Francesco
  • Hung Linda
  • Cazals Laure
  • Desolneux Agnès
  • Chevalier Aurélia
  • Rueff Jean-Pascal
  • Bertrand Loïc
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2024, 26 (5), pp.4363-4371. Inelastic X-ray scattering spectroscopy (IXS) has been used in many fields of solid state physics and theoretical chemistry as an accurate and quantitative probe of elementary excitations. We show that IXS spectra in the energy loss range below 100 eV exhibit a strong contrast across a wide range of commercially available pigments, opening new routes for their discrimination. These signatures combine plasmonic transitions, collective excitations and low energy absorption edges. We have performed IXS to discriminate different artists' pigments in complex mixtures and to quantitatively determine rutile and anatase polymorphs of TiO2. The combination of experimental data on pigment powders with suitable ab initio simulations shows a precise fit of the spectroscopic data both in the position of the resonances and in their relative intensity. (10.1039/D3CP04753A)
  DOI : 10.1039/D3CP04753A
• Stability under electron irradiation of some layered hydrated minerals
  
  • de Noirfontaine Marie-Noëlle
  • Courtial Mireille
  • Alessi A.
  • Tusseau-Nenez Sandrine
  • Garcia-Caurel E.
  • Cavani Olivier
  • Cau Dit Coumes Céline
  • Gorse–pomonti Dominique
  Journal of Solid State Chemistry, Elsevier, 2024, 340, pp.125033. The structural damages caused to some layered hydrated minerals by 2.5 MeV electron irradiation using the SIRIUS platform were studied by powder X-Ray diffraction and, in some cases, by 1H MAS-NMR spectroscopy. It is clearly demonstrated that the radiation damages are distinguishable from the heating effects. It is shown that: i) in all cases electron irradiation leads to distortions of the unit cell and very limited volume expansion, compared to heating; ii) radiation damages increase with increasing the structural complexity of the mineral; iii) portlandite Ca(OH)2 and brucite Mg(OH)2 remain crystalline up to high doses (a few GGy), with appearance of stacking fault disorder especially in brucite; iv) brushite CaHPO4.2H2O and gypsum CaSO4.2H2O undergo a phase transformation of type amorphization for brushite involving the strongest intralayer H bond between the acidic proton and the phosphate tetrahedral, and decomposition for gypsum involving interlayer H bonds between water molecules. (10.1016/j.jssc.2024.125033)
  DOI : 10.1016/j.jssc.2024.125033
• Total Energy beyond GW: Exact Results and Guidelines for Approximations
  
  • El-Sahili Abdallah
  • Sottile Francesco
  • Reining Lucia
  Journal of Chemical Theory and Computation, American Chemical Society, 2024, 20 (5), pp.1972-1987. The total energy and electron addition and removal spectra can in principle be obtained exactly from the one-body Green's function. In practice, the Green's function is obtained from an approximate self-energy. In the framework of many-body perturbation theory, we derive different expressions that are based on an approximate self-energy, but that yield nevertheless in principle the exact exchange-correlation contribution to the total energy for any interaction strength. Response functions play a crucial role, which explains why, for example, ingredients from time-dependent density functional theory can be used to build these approximate self-energies. We show that the key requirement for obtaining exact results is the consistent combination of ingredients. Also when further approximations are made, as it is necessary in practice, this consistency remains the key to obtain good results. All findings are illustrated using the exactly solvable symmetric Hubbard dimer. (10.1021/acs.jctc.3c01200)
  DOI : 10.1021/acs.jctc.3c01200
• Electronic excitation spectra of molecular hydrogen in phase I from quantum Monte Carlo and many-body perturbation methods
  
  • Gorelov Vitaly
  • Holzmann Markus
  • Ceperley David M
  • Pierleoni Carlo
  Physical Review B, American Physical Society, 2024, 109 (24), pp.L241111. We study the electronic excitation spectra in solid molecular hydrogen (phase I) at ambient temperature and 5to 90-GPa pressures using quantum Monte Carlo methods and many-body perturbation theory. In this range, the system changes from a wide-gap molecular insulator to a semiconductor, altering the nature of the excitations from localized to delocalized. Computed gaps and spectra agree with experiments, proving the ability to predict accurately band gaps of many-body systems in the presence of nuclear quantum and thermal effects. (10.1103/PhysRevB.109.L241111)
  DOI : 10.1103/PhysRevB.109.L241111
• Photochemistry of bismuth- and silver-containing glasses under femtosecond laser irradiation: energy transfers and 3D-localized background-free near-infrared fluorescence emission
  
  • Alassani Fouad
  • Ollier Nadège
  • Raffy Guillaume
  • Fargues Alexandre
  • del Guerzo André
  • Canioni Lionel
  • Cardinal Thierry
  • Petit Yannick
  Journal of Physical Chemistry C, American Chemical Society, 2024, 128 (20), pp.8296–8306. The tunable fluorescence property from the visible to near-infrared (NIR) region of high-localized 3D architecture down to the diffraction limit thanks to femtosecond (fs) Direct Laser Writing (DLW) in bismuth-doped, silver-containing glass is performed. Absorption and photoluminescent spectroscopy showed evidence of the homogeneous dispersion of bismuth ions (Bi3+) and silver ions in the glass matrix before DLW. High repetition rate fs DLW simultaneously inducing the photochemistry of silver ions and the photoredox reaction of bismuth ions has been obtained. Femtosecond DLW allows the creation of 3D fluorescence patterns formed by colocalization of a silver cluster and low valence bismuth ions, exhibiting an emission band covering the whole visible to the NIR wave range. The phenomena of electron transfer from silver atoms to bismuth ions and the nonradiative energy transfer from silver clusters to NIR-emitting bismuth ions are demonstrated. (10.1021/acs.jpcc.4c01036)
  DOI : 10.1021/acs.jpcc.4c01036
• Femtosecond laser activation of the photochemistry of Bismuth and associated threedimensional sub-micron fluorescence patterning
  
  • Alassani Fouad
  • Ollier Nadège
  • Canioni Lionel
  • Petit Yannick
  • Cardinal Thierry
  Journal of Luminescence, Elsevier, 2024, 275, pp.120728. Localized sub-micrometer-scale visible and near-IR fluorescence structures have been achieved in three-dimension (3D) thanks to femtosecond laser-activated photochemistry of Bismuth in a Bismuth-doped phosphate glass. These structures exhibit high fluorescence contrast with good spatial resolution with spectral emission in the red and near-IR ranges. These fluorescence properties arise from femtosecond laser-induced multi-photon absorption and the creation of free electrons, which activates local redox reactions of Bi3+ that allow for the dose-dependent formation of low valence Bismuth ions such as Bi2+ and Bi+. These new species promote not only new selective fluorescence emission properties in the VIS and near-IR spectral range but also co-localized positive refractive index changes. The thermal treatment of 3D patterns evidences the possibility of Bismuth cluster formation with good thermal stability up to the glass temperature transition. These observations open the way for laser-inscribed photonic integrated circuits for potential laser amplification devices in the second telecommunication windows around 1.3 μm. (10.1016/j.jlumin.2024.120728)
  DOI : 10.1016/j.jlumin.2024.120728
• Direct observation of electronic bandgap and hot carrier dynamics in GeAs semiconductor
  
  • Zhang Zailan
  • Zhang Jiuxiang
  • Zhou Gangqiang
  • Xu Jiyuan
  • Michel Ian-Evan
  • Dappe Yannick
  • Zhang Xiao
  • Oughaddou Hamid
  • Qi Weiyan
  • Papalazarou Evangelos
  • Perfetti Luca
  • Chen Zhesheng
  • Bendounan Azzedine
  • Marsi Marino
  Applied Physics Letters, American Institute of Physics, 2024, 125 (18). Germanium arsenide (GeAs) is a layered semiconductor with remarkably anisotropic thermoelectric and optical properties and a promising candidate for multifunctional devices based on in-plane polarization dependent response. Understanding the underlying mechanism of such devices requires knowledge of GeAs electronic band structure and of the hot carrier dynamics in its conduction band, whose details are still unclear. In this work, we investigate the properties of occupied and photoexcited states of GeAs, by combining scanning tunneling spectroscopy, angle-resolved photoemission spectroscopy (ARPES), and time-resolved ARPES. We find that GeAs is an ∼0.8 eV indirect gap semiconductor, for which the conduction band minimum (CBM) is located at the Γ ¯ point while the valence band maximum is out of Γ ¯ . A Stark broadening of the valence band is observed immediately after photoexcitation, which can be attributed to the effects of the electrical field at the surface induced by inhomogeneous screening. Moreover, the hot electron relaxation time of 1.56 ps is down to the CBM, which is dominated by electron-phonon coupling. Besides their relevance for our understanding of GeAs, these findings present general interest for the design of high performance thermoelectric and optoelectronic devices based on 2D semiconductors. (10.1063/5.0233111)
  DOI : 10.1063/5.0233111