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  • 31551.
    Le Guyader, Loic
    et al.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;European XFEL, Holzkoppel 4, D-22869 Schenefeld, Germany..
    Higley, Daniel J.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Pancaldi, Matteo
    Stockholm Univ, Dept Phys, S-10691 Stockholm, Sweden..
    Liu, Tianmin
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Chen, Zhao
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Chase, Tyler
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA..
    Granitzka, Patrick W.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Univ Amsterdam, van der Waals Zeeman Inst, NL-1018 XE Amsterdam, Netherlands..
    Coslovich, Giacomo
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Lutman, Alberto A.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Dakovski, Georgi L.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Schlotter, William F.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Shafer, Padraic
    Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA..
    Arenholz, Elke
    Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA..
    Hellwig, Olav
    HGST, San Jose Res Ctr, 3403 Yerba Buena Rd, San Jose, CA 95135 USA.;Tech Univ Chemnitz, Inst Phys, D-09107 Chemnitz, Germany.;Helmholtz Zent Dresden Rossendorf, Inst Ion Beam Phys & Mat Res, Bautzner Landstr 400, D-01328 Dresden, Germany..
    Lalieu, Mark L. M.
    Eindhoven Univ Technol, Inst Photon Integrat, Dept Appl Phys, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Koopmans, Bert
    Eindhoven Univ Technol, Inst Photon Integrat, Dept Appl Phys, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Reid, Alexander H.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Bonetti, Stefano
    Stockholm Univ, Dept Phys, S-10691 Stockholm, Sweden..
    Stöhr, Joachim
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Dürr, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    State-resolved ultrafast charge and spin dynamics in [Co/Pd] multilayers2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 3, article id 032401Article in journal (Refereed)
    Abstract [en]

    We use transient absorption spectroscopy with circularly polarized x rays to detect laser-excited hole states below the Fermi level and compare their dynamics with that of unoccupied states above the Fermi level in ferromagnetic [Co/Pd] multilayers. While below the Fermi level, an instantaneous and significantly stronger demagnetization is observed, above the Fermi level, the demagnetization is delayed by 35 +/- 10 fs. This provides a direct visualization of how ultrafast demagnetization proceeds via initial spin-flip scattering of laser-excited holes to the subsequent formation of spin waves.

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    FULLTEXT01
  • 31552. Le Guyader, Loïc
    et al.
    Higley, Daniel J.
    Pancaldi, Matteo
    Stockholm University, Faculty of Science, Department of Physics.
    Liu, Tianmin
    Chen, Zhao
    Chase, Tyler
    Granitzka, Patrick W.
    Coslovich, Giacomo
    Lutman, Alberto A.
    Dakovski, Georgi L.
    Schlotter, William F.
    Shafer, Padraic
    Arenholz, Elke
    Hellwig, Olav
    Lalieu, Mark L. M.
    Koopmans, Bert
    Reid, Alexander H.
    Bonetti, Stefano
    Stockholm University, Faculty of Science, Department of Physics.
    Stöhr, Joachim
    Dürr, Hermann A.
    State-resolved ultrafast charge and spin dynamics in [Co/Pd] multilayers2022In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 120, no 3, article id 032401Article in journal (Refereed)
    Abstract [en]

    We use transient absorption spectroscopy with circularly polarized x rays to detect laser-excited hole states below the Fermi level and compare their dynamics with that of unoccupied states above the Fermi level in ferromagnetic [Co/Pd] multilayers. While below the Fermi level, an instantaneous and significantly stronger demagnetization is observed, above the Fermi level, the demagnetization is delayed by 35 ± 10 fs. This provides a direct visualization of how ultrafast demagnetization proceeds via initial spin-flip scattering of laser-excited holes to the subsequent formation of spin waves. 

  • 31553. Le Lay, G.
    et al.
    Aristov, V.Yu.
    Seehofer, L.
    Buslaps, T.
    Johnson, R. L.
    Gothelid, M.
    Hammar, M.
    KTH, Superseded Departments (pre-2005), Physics.
    Karlsson, U. O.
    Flodström, S. A.
    Feidenhans'l, R.
    Nielsen, M.
    Findeisen, E.
    Uhrberg, R. I. G.
    STM and synchrotron radiation studies of "prototypical" metal{plus 45 degree rule}semiconductor systems1994In: Surface Science, ISSN 0039-6028, Vol. 307-309, no PART A, p. 280-294Article in journal (Refereed)
    Abstract [en]

    Since the origin of surface science noble metal{plus 45 degree rule}elemental semiconductor couples have been considered as "prototypical" systems. After three decades of research their structural and electronic properties remain an intriguing maze despite recent advances made, especially thanks to the development of the near-field microscopies and the extensive use of synchrotron radiation in surface crystallography and in high-resolution photoelectron spectroscopy. In the last few years, lead, as a replacement inert metal, has nearly gained the pole position in the display of exotic behaviour. This paper gives a flavour of this mystery story and highlights some puzzling questions. © 1994.

  • 31554.
    Le, Linda
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
    Modelling Magnetism of hcp Iron under Earth’s Inner Core Conditions: Based on first-principle DFT calculations and Machine Learning2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The structure of Earth’s core remains largely a mystery. The solid inner core is believed to exist in extreme pressure and temperature conditions comparable to 300 GPa and 6000 K and consists mainly of iron, Fe. Physical samples evidently cannot be collected, thereby making theoretical models increasingly vital in the pursuit of expanding our understanding of the Earth’s core. In this study the hexagonal close-packed (hcp) structure of Fe is investigated at 300 GPa and 6000 K, conditions comparable to Earth’s inner core conditions. Accurately modelling the dynamics of hcp Fe under Earth’s core conditions with careful inclusion of electronic structure magnetism and vibrational effects is a very difficult task and has not been done before. This master thesis provides results derived from a methodology which includes temperature induced magnetic moments, where vibrational effects are appropriately coupled with all magnetic degrees of freedom in a final dynamic simulation, called ASD-AIMD-MLLSF simulation. An interstitial step in this process includes the training of a machine learning (ML) model, utilizing kernel ridge regression (KRR). 

    Local magnetic moments, their arrangements including long and short range order are the basis for the magnetic properties of most materials. To fully model the dynamics of a magnetic system it is necessary to couple the magnetic degrees of freedom, described in terms of transversal spin fluctuations (TSF) and longitudinal spin fluctuations (LSF), and the vibrational degrees of freedom. In practice, due to the computationally expensive nature of the problem, this work includes a proposed machine learning interstitial step to predict the interaction between LSF and lattice vibrations. 

    The initial part of this work has demonstrated, via first-principle calculations based on density functional theory (DFT), that if temperature is neglected, iron converges to non- magnetic solutions at extreme pressures similar to Earth’s core conditions. However, this approach does not consider the temperature induced local magnetic moments. After inclusion of such contributions in addition to all other magnetic degrees of freedom coupled with vibrational degrees of freedom the ASD-AIMD-MLLSF simulation reveals a significant nonzero local magnetic moment of roughly 1.54 μB to 1.56 μB in magnitude. Where, based on calculated LSF landscapes for some geometrical snapshots on average, an expected local magnetic moment size of 1.43 μB is estimated. In addition, this work predicts a density of 13.04 g/cm3 for hcp Fe at 300 GPa and 6000 K (based on nonmagnetic ab initio molecular dynamics calculations). This density is close to the expected density in literature for Earth’s inner core, with a difference of around 9.8% higher than the density according to preliminary reference earth model (PREM) at 300 GPa. Furthermore, the ASD-AIMD-MLLSF simulation predicts a density lower than this value, which may be in better agreement with PREM. This result supports that hcp Fe is a relevant candidate in Earth’s inner core. The optimal ML models developed in relation to this thesis work generate a prediction of local magnetic moment magnitudes with a mean absolute error of 0.0667 μB. Finally, the LSF energy landscapes for some geometrical snapshots of hcp Fe under 300 GPa and 6000 K are found to be very similar and also matches in shape with results for bcc Fe at 300 GPa and 6000 K. 

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    Modelling_magnetism_of_hcp_Iron.pdf
  • 31555.
    Le Parc, Samuel
    KTH, School of Engineering Sciences (SCI), Physics.
    Containment during the decommissioning of nuclear power plant: calculation and approach associated​2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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    fulltext
  • 31556. Le, Phu Tran Phong
    et al.
    Hofhuis, Kevin
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Rana, Abhimanyu
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Huijben, Mark
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Hilgenkamp, Hans
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Rijnders, Guus A. J. H. M.
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    ten Elshof, Johan E.
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Koster, Gertjan
    Univ Twente, MESA Inst Nanotechnol, POB 217, NL-7522 NH Enschede, Netherlands.
    Gauquelin, Nicolas
    Univ Antwerp, Electron Microscopy Mat Sci EMAT, B-2020 Antwerp, Belgium.
    Lumbeeck, Gunnar
    Univ Antwerp, Electron Microscopy Mat Sci EMAT, B-2020 Antwerp, Belgium.
    Schuessler-Langeheine, Christian
    Helmholtz Zentrum Berlin Mat & Energie, BESSY 2,Albert Einstein Str 15, D-12489 Berlin, Germany.
    Popescu, Horia
    Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France.
    Fortuna, Franck
    Univ Paris Sud, CSNSM, Batiments 104 & 108, F-91405 Orsay, France;CNRS IN2P3, Batiments 104 & 108, F-91405 Orsay, France.
    Smit, Steef
    Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.
    Verbeek, Xanthe H.
    Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.
    Araizi-Kanoutas, Georgios
    Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.
    Mishra, Shrawan
    Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands;Indian Inst Technol BHU, Sch Mat Sci & Technol, Varanasi 221005, Uttar Pradesh, India.
    Vaskivskyi, Igor
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Univ Calif San Diego, Ctr Memory & Recording Res, 9500 Gilman Dr, La Jolla, CA 92093 USA.
    Dürr, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.
    Golden, Mark S.
    Van der Waals Zeeman Inst, Inst Phys, Sci Pk 904, NL-1098 XH Amsterdam, Netherlands.
    Tailoring Vanadium Dioxide Film Orientation Using Nanosheets: a Combined Microscopy, Diffraction, Transport, and Soft X-Ray in Transmission Study2020In: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 30, no 1, article id 1900028Article in journal (Refereed)
    Abstract [en]

    Vanadium dioxide (VO2) is a much-discussed material for oxide electronics and neuromorphic computing applications. Here, heteroepitaxy of VO2 is realized on top of oxide nanosheets that cover either the amorphous silicon dioxide surfaces of Si substrates or X-ray transparent silicon nitride membranes. The out-of-plane orientation of the VO2 thin films is controlled at will between (011)(M1)/(110)(R) and (-402)(M1)/(002)(R) by coating the bulk substrates with Ti0.87O2 and NbWO6 nanosheets, respectively, prior to VO2 growth. Temperature-dependent X-ray diffraction and automated crystal orientation mapping in microprobe transmission electron microscope mode (ACOM-TEM) characterize the high phase purity, the crystallographic and orientational properties of the VO2 films. Transport measurements and soft X-ray absorption in transmission are used to probe the VO2 metal-insulator transition, showing results of a quality equal to those from epitaxial films on bulk single-crystal substrates. Successful local manipulation of two different VO2 orientations on a single substrate is demonstrated using VO2 grown on lithographically patterned lines of Ti0.87O2 and NbWO6 nanosheets investigated by electron backscatter diffraction. Finally, the excellent suitability of these nanosheet-templated VO2 films for advanced lensless imaging of the metal-insulator transition using coherent soft X-rays is discussed.

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    fulltext
  • 31557.
    Le, Quang Tuan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Magnetodynamics in Spin Valves and Magnetic Tunnel Junctions with Perpendicular and Tilted Anisotropies2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spin-torque transfer (STT) effects have brought spintronics ever closer to practical electronic applications, such as MRAM and active broadband microwave spin-torque oscillator (STO), and have emerged as an increasingly attractive field of research in spin dynamics. Utilizing materials with perpendicular magnetic anisotropy (PMA) in such applications offers several great advantages such as low-current, low-field operation combined with high thermal stability. The exchange coupling that a PMA thin film exerts on an adjacent in-plane magnetic anisotropy (IMA) layer can tilt the IMA magnetization direction out of plane, thus creating a stack with an effective tilted magnetic anisotropy. The tilt angle can be engineered via both intrinsic material parameters, such as the PMA and the saturation magnetization, and extrinsic parameters, such as the layer thicknesses.

          STOs can be fabricated in one of a number of forms—as a nanocontact opening on a mesa from a deposited pseudospin-valve (PSV) structure, or as a nanopillar etching from magnetic tunneling junction (MTJ)—composed of highly reproducible PMA or predetermined tilted magnetic anisotropy layers.

          All-perpendicular CoFeB MTJ STOs showed high-frequency microwave generation with extremely high current tunability, all achieved at low applied biases. Spin-torque ferromagnetic resonance (ST-FMR) measurements and analysis revealed the bias dependence of spin-torque components, thus promise great potential for direct gate-voltage controlled STOs.

          In all-perpendicular PSV STOs, magnetic droplets were observed underneath the nanocontact area at a low drive current and low applied field. Furthermore, preliminary results for microwave auto-oscillation and droplet solitons were obtained from tilted-polarizer PSV STOs. These are promising and would be worth investigating in further studies of STT driven spin dynamics.

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    Tuan Le - Thesis
  • 31558.
    Le, Quang Tuan
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Mazraati, Hamid
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Chung, Sunjae
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Univ Gothenburg, Sweden.
    Nguyen, Thi Ngoc Anh
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Institute of Materials Science, Vietnam Academy of Science and Technology.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. Univ Gothenburg, Sweden; NanOsc AB, Sweden.
    Bias dependence of parallel spin torque in all-perpendicular magnetic tunnel junction nanodevicesManuscript (preprint) (Other (popular science, discussion, etc.))
    Abstract [en]

    We performed spin-torque ferromagnetic resonance measurements on spin-torque oscillators based on CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs), with both free and fixed layers having perpendicular magnetic anisotropy, under the application of an in-plane field. A dc current between near-zero and -250 $\mu{A}$ was introduced to investigate the influence of spin-transfer torque effects on the asymmetric and symmetric components of the output voltage. Both components showed a minimum at a misalignment of about 30$^\circ$ between the magnetization of the two CoFeB layers, indicating a strong electric-field effect. We also found that the bias dependence of the spin-torque terms is in contrast to that of in-plane anisotropy CoFeB MTJs.

  • 31559.
    Le Reste, Alexandra
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Global 21cm HI properties of Lyman-α emitting galaxiesManuscript (preprint) (Other academic)
  • 31560.
    Le Reste, Alexandra
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ionizing radiation escape enabled by galaxy merger in reionization-era analog galaxyManuscript (preprint) (Other academic)
  • 31561.
    Le Reste, Alexandra
    Stockholm University, Faculty of Science, Department of Astronomy.
    Neutral gas properties of high-redshift analog galaxies: 21cm observations of Lyα and LyC-emitting galaxies2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Neutral hydrogen (HI) is the most abundant baryonic element and a crucial component of galaxies. In the early universe, the interaction between neutral gas and the light produced by galaxies is thought to have given rise to cosmological reionization. During this last major phase transition of the Universe, the bulk of HI within the intergalactic medium (IGM) was ionized. However, observational constraints limit our understanding of the interplay between the radiation produced by galaxies and their neutral gas, and that of the physical processes that caused this important cosmological period. Another poorly understood mechanism is the one that drives the escape of Lyman-α (Lyα) emission from star-forming galaxies and shapes the line profile of this well-used tracer of galaxies at high redshift. To fully answer these questions, direct observations of the neutral gas content and distribution of Lyα emitters are needed.

    This thesis presents 21cm observations of the neutral gas reservoirs of rare local galaxies that are analogous to objects in the early universe. We have observed the neutral gas of Haro 11, the closest known ionizing radiation (Lyman Continuum, LyC) leaking galaxy. This 21cm observation was the first to successfully map the neutral gas distribution of a confirmed LyC emitter. We observed a strongly asymmetric neutral gas distribution resulting from a merger event, with the bulk of the HI mass offset from the regions producing LyC radiation in the galaxy. By decreasing the column density of gas on large scales, this HI distribution has facilitated the escape of ionizing radiation from the center of the galaxy to the IGM.

    We have also observed the neutral gas content and distribution of local Lyα-emitting galaxies on a variety of angular scales. We mapped the neutral gas at scales that can be compared to those characterizing Lyα emission in two galaxies, and supplemented the data with integral field spectroscopic observations tracing ionized gas and dust. Additionally, we reduced low angular resolution 21cm observations of 37 galaxies in the Lyman Alpha Reference Samples. We found clear evidence of interaction in most of the galaxies in the samples (~60%), indicating that mergers play an important role in the Lyα escape from galaxies. We found that global HI properties did not correlate well with any metric quantifying Lyα emission, although different classes of Lyα-emitters were distributed differently around HI scaling relations. This indicates that star-forming galaxies with low neutral gas content have a higher chance of emitting strongly in Lyα, but ultimately, neutral gas regulates the escape of Lyα emission on small scales.

    21cm studies of both Lyα and LyC emitters conducted in this thesis have demonstrated that galaxy interactions play an important role in the escape of ultraviolet (UV) radiation from local galaxies. By perturbing the neutral gas content of galaxies and enhancing their star formation rate, these interactions are interesting mechanisms that facilitate the escape of UV radiation. According to cosmological models, galaxy mergers occurred more frequently in the early universe. Assessing the contribution of environment and galaxy interactions at high redshift will be essential to fully understand the first billion years of our universe.

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    Neutral gas properties of high-redshift analog galaxies: 21cm observations of Lyα and LyC-emitting galaxies
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    Omslagsframsida
  • 31562.
    Le Reste, Alexandra
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hayes, Matthew J.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cannon, John M.
    Herenz, Edmund Christian
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Menacho, Veronica
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Puschnig, Johannes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Argelander-Institut für Astronomie, Germany.
    Rivera-Thorsen, Thøger Emil Juul
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kunth, Daniel
    Velikonja, Nick
    LARS XIII: High Angular Resolution 21 cm H ı Observations of Lyα Emitting Galaxies2022In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 934, no 1, article id 69Article in journal (Refereed)
    Abstract [en]

    The Lyα emission line is one of the main observables of galaxies at high redshift, but its output depends strongly on the neutral gas distribution and kinematics around the star-forming regions where UV photons are produced. We present observations of Lyα and 21 cm H ı emission at comparable scales with the goal to qualitatively investigate how the neutral interstellar medium (ISM) properties impact Lyα transfer in galaxies. We have observed 21 cm H ı at the highest possible angular resolution (≈3'' beam) with the Very Large Array in two local galaxies from the Lyman Alpha Reference Sample. We compare these data with Hubble Space Telescope Lyα imaging and spectroscopy, and Multi Unit Spectroscopic Explorer and Potsdam MultiAperture Spectrophotometer ionized gas observations. In LARS08, high-intensity Lyα emission is cospatial with high column density H ı where the dust content is the lowest. The Lyα line is strongly redshifted, consistent with a velocity redistribution that allows Lyα escape from a high column density neutral medium with a low dust content. In eLARS01, high-intensity Lyα emission is located in regions of low column density H ı, below the H ı data sensitivity limit ( < 2 × 1020 cm−2). The perturbed ISM distribution with low column density gas in front of the Lyα emission region plays an important role in the escape. In both galaxies, the faint Lyα emission (∼1×10−16 erg s−1cm−2 arcsec−2) traces intermediate Hα emission regions where H ı is found, regardless of the dust content. Dust seems to modulate, but not prevent, the formation of a faint Lyα halo. This study suggests the existence of scaling relations between dust, Hα, H ı, and Lyα emission in galaxies.

  • 31563.
    Le, Son Phuong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Hsu, Chih-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Martinovic, Ivan
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    GaN-based pyramidal quantum structures for micro-size light-emitting diode applications2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 14, article id 142102Article in journal (Refereed)
    Abstract [en]

    GaN-based pyramidal quantum structures, InGaN nanostructures located on top of micro-sized GaN pyramids, were fabricated by selective-area growth on SiC substrates by means of hot-wall metal-organic chemical vapor deposition. Arrays of GaN-based pyramidal structures exhibit micro-size pyramids possessing high uniformity, precise hexagonal bases, and InGaN/GaN quantum-well layers with well-defined interfaces. Each pyramid comprises a p-i-n InGaN/GaN structure, which is separated from that of other pyramids by a dielectric layer, serving as a building block for micro-emitters. Moreover, interconnected micro-size light-emitting diodes (microLEDs) built on the GaN-based pyramidal quantum structures were demonstrated, resulting in well-determined electroluminescence in the near-ultraviolet regime with negligible spectral shifts at high current levels. The results elucidated the rewards for development of these light-emitting designs and their potential for microLED applications.

  • 31564.
    Le, Son Phuong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Polar Light Technol AB, Linkoping Sci Pk, S-58330 Linkoping, Sweden.
    Hsu, Chih-Wei
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Polar Light Technol AB, Linkoping Sci Pk, S-58330 Linkoping, Sweden.
    Martinovic, Ivan
    Polar Light Technol AB, Linkoping Sci Pk, S-58330 Linkoping, Sweden.
    Ivanov, Ivan Gueorguiev
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Holtz, Per-Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Polar Light Technol AB, Linkoping Sci Pk, S-58330 Linkoping, Sweden.
    GaN-based light-emitting materials prepared by hot-wall metal-organic chemical vapor deposition2022In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 128, no 9, article id 801Article in journal (Refereed)
    Abstract [en]

    GaN-based structures grown on SiC substrates by means of horizontal hot-wall metal-organic chemical vapor deposition (MOCVD) were systematically characterized, revealing high crystal quality. The hot-wall MOCVD grown GaN, doped by Mg and Si, respectively showed low-resistivity hole and electron transport, competitive with the state-of-the-art GaN. High concentrations of free holes (similar to 2 x 10(17) cm(-3)) were achieved for the as-grown Mg-doped GaN without thermal annealing, thanks to advantageous heating characteristics of the "hot-wall" reactor. The analysis of optical and electrical properties brought a picture, where Mg is the only impurity defining energy levels in the hot-wall MOCVD p-type doped GaN. Besides, InGaN/GaN light-emitting diodes employing such doped GaN materials in the carrier-transport layers were fabricated, resulting in high device performances. The devices exhibited bright electroluminescence with very narrow full widths at half maximum as well as negligible spectral shifts at high current levels (greater than or similar to 10 A/cm(2)). These results exemplified the rewards of the hot-wall MOCVD for development of high-quality nitrides-based structures, providing an attractive growth method to realize the demonstration of light-emitting devices with favorable properties.

  • 31565.
    Le, Son Phuong
    et al.
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Nguyen, Duong Dai
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Toshi-kazu, Suzuki
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor devices with Al2O3 or AlTiO gate dielectrics2018In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 123, no 3, p. 7p. 034504-1-034504-7, article id 034504Article in journal (Refereed)
    Abstract [en]

    We have investigated insulator-semiconductor interface fixed charges in AlGaN/GaN metal-insulator-semiconductor (MIS) devices with Al2O3 or AlTiO (an alloy of Al2O3 and TiO2) gate dielectrics obtained by atomic layer deposition on AlGaN. Analyzing insulator-thickness dependences of threshold voltages for the MIS devices, we evaluated positive interface fixed charges, whose density at the AlTiO/AlGaN interface is significantly lower than that at the Al2O3/AlGaN interface. This and a higher dielectric constant of AlTiO lead to rather shallower threshold voltages for the AlTiO gate dielectric than for Al2O3. The lower interface fixed charge density also leads to the fact that the two-dimensional electron concentration is a decreasing function of the insulator thickness for AlTiO, whereas being an increasing function for Al2O3. Moreover, we discuss the relationship between the interface fixed charges and interface states. From the conductance method, it is shown that the interface state densities are very similar at the Al2O3/AlGaN and AlTiO/AlGaN interfaces. Therefore, we consider that the lower AlTiO/AlGaN interface fixed charge density is not owing to electrons trapped at deep interface states compensating the positive fixed charges and can be attributed to a lower density of oxygen-related interface donors.

  • 31566.
    Le, Son Phuong
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Suzuki, Toshi-kazu
    Japan Adv Inst Sci & Technol JAIST, Japan.
    Electron mobility anisotropy in InAs/GaAs(001) heterostructures2021In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 118, no 18, article id 182101Article in journal (Refereed)
    Abstract [en]

    Electron transport properties in InAs films epitaxially grown on GaAs(001), InAs/GaAs(001) heterostructures, were systematically investigated through the dependence on crystal direction, thickness, and temperature. As a result, we found a pronounced electron mobility anisotropy, in which the mobility is highest and lowest along [1 (1) over bar0] and [110] crystal directions, respectively. The mobility anisotropy intensifies as the InAs thickness decreases, while it diminishes in thick regimes, where the InAs films are relatively immune to effects from the epitaxial heterointerface. We observed the anisotropy in a wide temperature range, 5-395 K, with an enhancement at high temperatures. Our analysis indicates that the electron mobility anisotropy can be attributed to anisotropic electron scatterings by both interface roughness and random piezoelectric polarization near the interface. Published under license by AIP Publishing.

  • 31567.
    Le, Son Phuong
    et al.
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Toshimasa, Ui
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Toshi-kazu, Suzuki
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Low-frequency noise in InAs films bonded on low-k flexible substrates.2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 19, p. 4p. 192103-1-192103-4, article id 192103Article in journal (Refereed)
    Abstract [en]

    We have systematically investigated low-frequency noise (LFN) in InAs films with several thicknesses (≃10-100 nm) bonded on low-k flexible substrates (InAs/FS), comparing with that in InAs films epitaxially grown on GaAs(001) substrates (InAs/GaAs). We obtain current LFN spectra exhibiting approximate 1/f characteristics and consequent effective Hooge parameters α depending on the thickness, where we find that α in the InAs/FS is larger than that in the InAs/GaAs. The behavior of α can be attributed to the fluctuation of the electron mobility dominated by surface/interface charge scattering and by thickness fluctuation scattering. [ABSTRACT FROM AUTHOR]

  • 31568.
    Le, Son Phuong
    et al.
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Toshimasa, Ui
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Tuan Quy, Nguyen
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Hong-An, Shih
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Toshi-kazu, Suzuki
    Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan.
    Low-frequency noise in AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors.2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 20, p. 6p. 204503-1-204503-6, article id 204503Article in journal (Refereed)
    Abstract [en]

    Using aluminum titanium oxide (AlTiO, an alloy of Al2O3 and TiO2) as a high-k gate insulator, we fabricated and investigated AlTiO/AlGaN/GaN metal-insulator-semiconductor heterojunction field-effect transistors. From current low-frequency noise (LFN) characterization, we find Lorentzian spectra near the threshold voltage, in addition to 1/f spectra for the well-above-threshold regime. The Lorentzian spectra are attributed to electron trapping/detrapping with two specific time constants, ~25 ms and ~3ms, which are independent of the gate length and the gate voltage, corresponding to two trap level depths of 0.5-0.7 eV with a 0.06 eV difference in the AlTiO insulator. In addition, gate leakage currents are analyzed and attributed to the Poole-Frenkel mechanism due to traps in the AlTiO insulator, where the extracted trap level depth is consistent with the Lorentzian LFN. [ABSTRACT FROM AUTHOR]

  • 31569.
    Le Yang, Gao
    et al.
    Shandong Univ, Inst Space Sci, Sch Space Sci & Phys, Weihai 264209, Peoples R China..
    Qi, Bin
    Shandong Univ, Inst Space Sci, Sch Space Sci & Phys, Weihai 264209, Peoples R China..
    Wang, Xu Dong
    Shandong Univ, Inst Space Sci, Sch Space Sci & Phys, Weihai 264209, Peoples R China..
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Neutron-proton interaction in odd-odd nuclei from statistical analysis2022In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 106, no 2, article id 024325Article in journal (Refereed)
    Abstract [en]

    The statistical distribution and correlation relationship of the empirical neutron-proton (np) interaction are analyzed, whereby the interaction strengths are extracted from the binding energies using a known four-point formula. By comparing the correlations of the data and those from numerical simulations of the random number method, it is shown that an additional attractive np interaction persists between the last proton and last neutron in odd-odd nuclei. It provides evidence of the residual np interaction from statistical analysis. The adopted new analytical method might be a useful way to clarify the inherent correlation.

  • 31570.
    Leal Flores, Angelica
    et al.
    Malmö högskola, School of Teacher Education (LUT).
    Höglund, Karin
    Malmö högskola, School of Teacher Education (LUT).
    Jag bryr mig inte om genus, jag undervisar bara2007Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Sammanfattning Syftet med vår undersökning har varit att se hur två lärare på en skola i skolår 2 interagerar med sina elever under matematiklektioner ur ett genusperspektiv. Behandlas eleverna annorlunda utifrån deras kön? Vi vill även se hur talutrymmet fördelas i klassrummet och om lärarna är genusmedvetna i sin matematikundervisning. Vi har valt att genomföra både observationer och intervjuer. Observationerna har vi gjort för att få en inblick i samspelet mellan lärare och elev. För att få en inblick i hur lärarna tänker kring genus och matematik valde vi att genomföra intervjuer. Våra resultat visar att lärarna lägger mer tid på pojkarna och att de tillåts mera frihet i klassrummet. Talutrymmet är inte jämnt fördelat mellan flickor och pojkar. Pojkarna tar en betydligt större del. Flickorna räcker upp handen för att få ordet i större utsträckning än pojkarna, men får ordet färre gånger av läraren. Den ena läraren anser sig inte prioritera genus, utan lägger fokus på svenska språket. Den andra läraren anser att genus är överdimensionerat och att man inte bör lägga för mycket energi på det.

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  • 31571. Leal-Cidoncha, E.
    et al.
    Duran, I.
    Paradela, C.
    Tarrío, Diego
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Leong, L. S.
    Tassan-Got, L.
    Audouin, L.
    Altstadt, S.
    Andrzejewski, J.
    Barbagallo, M.
    Bécares, V.
    Bečvář, F.
    Belloni, F.
    Berthoumieux, E.
    Billowes, J.
    Boccone, V.
    Bosnar, D.
    Brugger, M.
    Calviani, M.
    Calviño, F.
    Cano-Ott, D.
    Carrapiço, C.
    Cerutti, F.
    Chiaveri, E.
    Chin, M.
    Colonna, N.
    Cortés, G.
    Cortés-Giraldo, M. A.
    Diakaki, M.
    Domingo-Pardo, C.
    Dressler, R.
    Dzysiuk, N.
    Eleftheriadis, C.
    Ferrari, A.
    Fraval, K.
    Ganesan, S.
    García, A. R.
    Giubrone, G.
    Gómez-Hornillos, M. B.
    Gonçalves, I. F.
    González-Romero, E.
    Griesmayer, E.
    Guerrero, C.
    Gunsing, F.
    Gurusamy, P.
    Hernández-Prieto, A.
    Jenkins, D. G.
    Jericha, E.
    Kadi, Y.
    KÀppeler, F.
    Karadimos, D.
    Kivel, N.
    Koehler, P.
    Kokkoris, M.
    Krtička, M.
    Kroll, J.
    Lampoudis, C.
    Langer, C.
    Lederer, C.
    Leeb, H.
    Lo Meo, S.
    Losito, R.
    Mallick, A.
    Manousos, A.
    Marganiec, J.
    Martínez, T.
    Massimi, C.
    Mastinu, P. F.
    Mastromarco, M.
    Meaze, M.
    Mendoza, E.
    Mengoni, A.
    Milazzo, P. M.
    Mingrone, F.
    Mirea, M.
    Mondelaers, W.
    Pavlik, A.
    Perkowski, J.
    Plompen, A.
    Praena, J.
    Quesada, J. M.
    Rauscher, T.
    Reifarth, R.
    Riego, A.
    Robles, M. S.
    Roman, F.
    Rubbia, C.
    Sabaté-Gilarte, M.
    Sarmento, R.
    Saxena, A.
    Schillebeeckx, P.
    Schmidt, S.
    Schumann, D.
    Tagliente, G.
    Tain, J. L.
    Tsinganis, A.
    Valenta, S.
    Vannini, G.
    Variale, V.
    Vaz, P.
    Ventura, A.
    Versaci, R.
    Vermeulen, M. J.
    Vlachoudis, V.
    Vlastou, R.
    Wallner, A.
    Ware, T.
    Weigand, M.
    Weiß, C.
    Wright, T.
    Åœugec, P.
    Fission Fragment Angular Distribution measurements of 235U and 238U at CERN n_TOF facility2016Conference paper (Refereed)
    Abstract [en]

    Neutron-induced fission cross sections of U-238 and U-235 are used as standards in the fast neutron region up to 200 MeV. A high accuracy of the standards is relevant to experimentally determine other neutron reaction cross sections. Therefore, the detection efficiency should be corrected by using the angular distribution of the fission fragments (FFAD), which are barely known above 20 MeV. In addition, the angular distribution of the fragments produced in the fission of highly excited and deformed nuclei is an important observable to investigate the nuclear fission process. In order to measure the FFAD of neutron-induced reactions, a fission detection setup based on parallel-plate avalanche counters (PPACs) has been developed and successfully used at the CERN-n_TOF facility. In this work, we present the preliminary results on the analysis of new U-235(n,f) and U-238(n,f) data in the extended energy range up to 200 MeV compared to the existing experimental data.

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  • 31572. Leal-Cidoncha, E.
    et al.
    Duran, I.
    Paradela, C.
    Tassan-Got, L.
    Audouin, L.
    Leal, L. C.
    Naour, C. Le
    Noguere, G.
    Tarrio, Diego
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Leong, L. S.
    Altstadt, S.
    Andrzejewski, J.
    Barbagallo, M.
    Bécares, V.
    Bečvář, F.
    Belloni, F.
    Berthoumieux, E.
    Billowes, J.
    Boccone, V.
    Bosnar, D.
    Brugger, M.
    Calviani, M.
    Calviño, F.
    Cano-Ott, D.
    Carrapiço, C.
    Cerutti, F.
    Chiaveri, E.
    Chin, M.
    Colonna, N.
    Cortés, G.
    Cortés-Giraldo, M. A.
    Diakaki, M.
    Domingo-Pardo, C.
    Dressler, R.
    Eleftheriadis, C.
    Ferrari, A.
    Fraval, K.
    Ganesan, S.
    García, A. R.
    Giubrone, G.
    Gómez-Hornillos, M. B.
    Gonçalves, I. F.
    González-Romero, E.
    Griesmayer, E.
    Guerrero, C.
    Gunsing, F.
    Gurusamy, P.
    Hernández-Prieto, A.
    Jenkins, D. G.
    Jericha, E.
    Kadi, Y.
    Käppeler, F.
    Karadimos, D.
    Kivel, N.
    Kokkoris, M.
    Krtička, M.
    Kroll, J.
    Lampoudis, C.
    Langer, C.
    Lederer, C.
    Leeb, H.
    Losito, R.
    Mallick, A.
    Manousos, A.
    Marganiec, J.
    Martínez, T.
    Massimi, C.
    Mastinu, P. F.
    Mastromarco, M.
    Meaze, M.
    Mendoza, E.
    Mengoni, A.
    Milazzo, P. M.
    Mingrone, F.
    Mirea, M.
    Mondelaers, W.
    Pavlik, A.
    Perkowski, J.
    Plompen, A.
    Praena, J.
    Quesada, J. M.
    Rauscher, T.
    Reifarth, R.
    Riego, A.
    Robles, M. S.
    Roman, F.
    Rubbia, C.
    Sabaté-Gilarte, M.
    Sarmento, R.
    Saxena, A.
    Schillebeeckx, P.
    Schmidt, S.
    Schumann, D.
    Tagliente, G.
    Tain, J. L.
    Tsinganis, A.
    Valenta, S.
    Vannini, G.
    Variale, V.
    Vaz, P.
    Ventura, A.
    Versaci, R.
    Vermeulen, M. J.
    Vlachoudis, V.
    Vlastou, R.
    Wallner, A.
    Ware, T.
    Weigand, M.
    Weiß, C.
    Wright, T.
    Žugec, P.
    High accuracy 234U(n,f) cross section in the resonance energy region2017In: ND 2016: INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY / [ed] Plompen, A; Hambsch, FJ; Schillebeeckx, P; Mondelaers, W; Heyse, J; Kopecky, S; Siegler, P; Oberstedt, S, Les Ulis: EDP Sciences, 2017, Vol. 146, article id 04057Conference paper (Refereed)
    Abstract [en]

    New results are presented of the 234U neutron-induced fission cross section, obtained with high accuracy in the resonance region by means of two methods using the 235U(n,f) as reference. The recent evaluation of the 235U(n,f) obtained with SAMMY by L. C. Leal et al. (these Proceedings), based on previous n_TOF data [1], has been used to calculate the 234U(n,f) cross section through the 234U/235U ratio, being here compared with the results obtained by using the n_TOF neutron flux.

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  • 31573.
    Leandro, Lorenzo
    et al.
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Gunnarsson, Christine P.
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Reznik, Rodion
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia.;ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Shtrom, Igor
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia..
    Khrebtov, Artem
    ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Kasama, Takeshi
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. Delft Univ Technol, Kavli Inst Nanosci, NL-2628CJ Delft, Netherlands..
    Cirlin, George
    St Petersburg Acad Univ, RAS, St Petersburg 194021, Russia.;ITMO Univ, Kronverkskiy Pr 49, St Petersburg 197101, Russia..
    Akopian, Nika
    Tech Univ Denmark, DTU Dept Photon Engn, DK-2800 Lyngby, Denmark..
    Nanowire Quantum Dots Tuned to Atomic Resonances2018In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 18, no 11, p. 7217-7221Article in journal (Refereed)
    Abstract [en]

    Quantum dots tuned to atomic resonances represent an emerging field of hybrid quantum systems where the advantages of quantum dots and natural atoms can be combined. Embedding quantum dots in nanowires boosts these systems with a set of powerful possibilities, such as precise positioning of the emitters, excellent photon extraction efficiency and direct electrical contacting of quantum dots. Notably, nanowire structures can be grown on silicon substrates, allowing for a straightforward integration with silicon-based photonic devices. In this work we show controlled growth of nanowire-quantum-dot structures on silicon, frequency tuned to atomic transitions. We grow GaAs quantum dots in AlGaAs nanowires with a nearly pure crystal structure and excellent optical properties. We precisely control the dimensions of quantum dots and their position inside nanowires and demonstrate that the emission wavelength can be engineered over the range of at least 30 nm around 765 nm. By applying an external magnetic field, we are able to fine-tune the emission frequency of our nanowire quantum dots to the D-2 transition of Rb-87. We use the Rb transitions to precisely measure the actual spectral line width of the photons emitted from a nanowire quantum dot to be 9.4 +/- 0.7 mu eV, under nonresonant excitation. Our work brings highly desirable functionalities to quantum technologies, enabling, for instance, a realization of a quantum network, based on an arbitrary number of nanowire single-photon sources, all operating at the same frequency of an atomic transition.

  • 31574. Leane, Rebecca K.
    et al.
    Linden, Tim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter2023In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 131, no 7, article id 071001Article in journal (Refereed)
    Abstract [en]

    We present the first dedicated & gamma;-ray analysis of Jupiter, using 12 years of data from the Fermi Telescope. We find no robust evidence of & gamma;-ray emission, and set upper limits of & SIM;10-9 GeV cm-2 s-1 on the Jovian & gamma;-ray flux. We point out that Jupiter is an advantageous dark matter (DM) target due to its large surface area (compared with other solar system planets), and cool core temperature (compared with the Sun). These properties allow Jupiter to both capture and retain lighter DM, providing a complementary probe of subGeV DM. We therefore identify and perform a new search for DM-sourced & gamma;-rays in Jupiter, where DM annihilates to long-lived particles, which can escape the Jovian surface and decay into & gamma; rays. We consequently constrain DM-proton scattering cross sections as low as about 10-40 cm2, showing Jupiter is up to 10 orders of magnitude more sensitive than direct detection. This sensitivity is reached under the assumption that the mediator decay length is sufficient to escape Jupiter, and the equilibrium between DM capture and annihilation; sensitivities can be lower depending on the DM model. Our work motivates follow-up studies with upcoming MeV telescopes such as AMEGO and e-ASTROGAM.

  • 31575. Leane, Rebecca K.
    et al.
    Linden, Tim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mukhopadhyay, Payel
    Toro, Natalia
    Celestial-body focused dark matter annihilation throughout the Galaxy2021In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 103, no 7, article id 075030Article in journal (Refereed)
    Abstract [en]

    Indirect detection experiments typically measure the flux of annihilating dark matter (DM) particles propagating freely through galactic halos. We consider a new scenario where celestial bodies focus DM annihilation events, increasing the efficiency of halo annihilation. In this setup, DM is first captured by celestial bodies, such as neutron stars or brown dwarfs, and then annihilates within them. If DM annihilates to sufficiently long-lived particles, they can escape and subsequently decay into detectable radiation. This produces a distinctive annihilation morphology, which scales as the product of the DM and celestial body densities, rather than as DM density squared. We show that this signal can dominate over the halo annihilation rate in gamma-ray observations in both the Milky Way Galactic center and globular clusters. We use Fermi and H.E.S.S. data to constrain the DM-nucleon scattering cross section, setting powerful new limits down to similar to 10(-39) cm(2) for sub-GeV DM using brown dwarfs, which is up to 9 orders of magnitude stronger than existing limits. We demonstrate that neutron stars can set limits for TeV-scale DM down to about 10(-47) cm(2).

  • 31576. Learmonth, T.
    et al.
    McGuinness, C.
    Glans, P. -A
    Downes, J. E.
    Schmitt, Thorsten
    Swiss Light Source, Paul Scherrer Institute.
    Duda, Laurent-Claudius
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Guo, J. -H
    Chou, F. C.
    Smith, K. E.
    Observation of multiple Zhang-Rice excitations in a correlated solid: Resonant inelastic X-ray scattering study of Li2CuO22007In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 79, no 4, p. 47012-Article in journal (Refereed)
    Abstract [en]

    Multiple Zhang-Rice type spectral features have been observed in resonant inelastic X-ray scattering (RIXS) from the quasi -one-dimensional cuprate charge transfer insulator Li2CuO2. The first feature appears at constant emission energy, and is associated with a Zhang-Rice singlet final state. The second is an interplaquette charge transfer excitation that results in a novel triplet Zhang-Rice -type final state. It is accompanied by the presence of a O 2p nonbonding to upper Hubbard band excitation at an energy close to that of a calculated triplet charge transfer Zhang-Rice -type excitation. The site selectivity and polarization rules associated with RIXS allows these two excitations to be distinguished.

  • 31577.
    Lebas, Elise
    KTH, School of Engineering Sciences (SCI), Physics.
    Analysis of fire risk aspects and development of the  fire protection strategy for the European Pressurized Reactor at Hinkley Point C, United Kingdom2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
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  • 31578. Lebedev, A. V.
    et al.
    Leites, Dimitri A.
    Stockholm University, Faculty of Science, Department of Mathematics.
    Shapovalov determinant for loop superalgebras2008In: Theoretical and mathematical physics, ISSN 0040-5779, E-ISSN 1573-9333, Vol. 156, no 3, p. 1292-1307Article in journal (Refereed)
    Abstract [en]

    For the Kac-Moody superalgebra associated with the loop superalgebra with values in a finite-dimensional Lie superalgebra g, we show what its quadratic Casimir element is equal to if the Casimir element for g is known (if g has an even invariant supersymmetric bilinear form). The main tool is the Wick normal form of the even quadratic Casimir operator for the Kac-Moody superalgebra associated with g; this Wick normal form is independently interesting. If g has an odd invariant supersymmetric bilinear form, then we compute the cubic Casimir element. In addition to the simple Lie superalgebras g = g(A) with a Cartan matrix A for which the Shapovalov determinant was known, we consider the Poisson Lie superalgebra poi(0 vertical bar n) and the related Kac-Moody superalgebra.

  • 31579. Lebedev, Alexander
    et al.
    Olmos, JJ Vegas
    Pang, Xiaodan
    RISE ACREO AB.
    Monroy, Idelfonso Tafur
    Larsen, Knud J
    Forchhammer, Søren
    Low complexity source and channel coding for mm-wave hybrid fiber-wireless links2014In: Optics Communications, ISSN 0030-4018, E-ISSN 1873-0310, Vol. 318, p. 142-146Article in journal (Refereed)
  • 31580. Lebedev, Alexander
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Olmos, JJ Vegas
    Beltran, Marta
    Llorente, Roberto
    Forchhammer, Søren
    Monroy, Idelfonso Tafur
    Feasibility study and experimental verification of simplified fiber-supported 60-GHz picocell mobile backhaul links2013In: IEEE Photonics Journal, E-ISSN 1943-0655, Vol. 5, no 4, p. 7200913-7200913Article in journal (Refereed)
    Abstract [en]

    We propose and experimentally demonstrate a fiber-wireless transmission system for optimized delivery of 60-GHz radio frequency (RF) signals through picocell mobile backhaul connections. We identify advantages of 60-GHz links for utilization in short-range mobile backhaul through feasibility analysis and comparison with an alternative E-band (60-90 GHz) technology. The 60-GHz fiber-wireless-fiber setup is then introduced: two spans of up to 20 km of optical fiber are deployed and bridged by up to 4 m of wireless distance. The 60-GHz radio-over-fiber technology is utilized in the first span of fiber transmission. The system is simplified and tailored for delivery of on-off keying data signals by employing a single module for lightwave generation and modulation combined with a simplified RF downconversion technique by envelope detection. Data signals of 1.25 Gb/s are transmitted, and a bit-error-rate performance below the 7% overhead forward-error-correction limit is achieved for a range of potential fiber deployment scenarios. A spurious free dynamic range of 73 dB-Hz2/3 is attained for a frequency-doubling photonic RF upconversion technique. The power budget margin that is required to extend the wireless transmission distance from 4 m to a few hundred meters has been taken into account in the setup design, and the techniques to extend the wireless distance are analyzed.

  • 31581. Lebedev, Alexander
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Olmos, JJ Vegas
    Forchhammer, Søren
    Monroy, Idelfonso Tafur
    Gigabit close-proximity wireless connections supported by 60 GHz RoF links with low carrier suppression2013In: Optics Express, E-ISSN 1094-4087, Vol. 21, no 21, p. 24574-24581Article in journal (Refereed)
  • 31582. Lebedev, Alexander
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Olmos, JJ Vegas
    Forchhammer, Søren
    Monroy, Idelfonso Tafur
    Beltrán, Marta
    Llorente, Roberto
    Fiber-supported 60 GHz mobile backhaul links for access/metropolitan deployment2013In: Optical Network Design and Modeling (ONDM), 2013 17th International Conference on, 2013, p. 190-193Conference paper (Refereed)
  • 31583. Lebedev, Alexander
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Olmos, Juan J Vegas
    Forchhammer, Soren
    Monroy, Idelfonso Tafur
    Simultaneous 60-GHz RoF transmission of lightwaves emitted by ECL, DFB, and VCSEL2014In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 26, no 7, p. 733-736Article in journal (Refereed)
    Abstract [en]

    Simultaneous 60-GHz radio over fiber upconversion and fiber transmission of lightwaves produced by an external cavity laser, a distributed feedback laser, and a C-band vertical cavity surface emitting laser are demonstrated. The 1.25-Gb/s data are transmitted concurrently on each of the lightwaves attaining a bit error rate performance <;10 -9 level. Carrier suppression of 20 dB is achieved for all three lightwaves placed in a wide wavelength range. The 10 -9 receiver sensitivity level for detection of three lightwaves falls in a <;3-db region. Reported close performance of the investigated techniques enables diversification of options for lightwave generation in millimeter-wave fiber-wireless networks.

  • 31584. Lebedev, Alexander
    et al.
    Pang, Xiaodan
    RISE ACREO AB.
    Olmos, Juan Jose Vegas
    Monroy, Idelfonso Tafur
    Forchhammer, Soren
    Tunable photonic RF generator for dynamic allocation and multicast of 1.25 Gbps channels in the 60 GHz unlicensed band2013In: Microwave Symposium Digest (IMS), 2013 IEEE MTT-S International, 2013, p. 1-3Conference paper (Refereed)
  • 31585.
    Lebedev, Alexander
    et al.
    DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, 2800, Denmark.
    Vegas Olmos, J J
    DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, 2800, Denmark.
    Pang, Xiaodan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics. DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, 2800, Denmark.
    Forchhammer, Søren
    DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, 2800, Denmark.
    Tafur Monroy, Idelfonso
    DTU Fotonik, Department of Photonics Engineering, Technical University of Denmark, Kongens Lyngby, 2800, Denmark.
    Demonstration and comparison study for V-and W-band real-time high-definition video delivery in diverse fiber-wireless infrastructure2013In: Fiber and Integrated Optics, ISSN 10964681, Vol. 32, no 2, p. 93-104Article in journal (Refereed)
    Abstract [en]

    This article experimentally demonstrates uncompressed high-definition video distribution in V-band (50-75 GHz) and W-band (75-110 GHz) fiber-wireless links achieving 3 m of wireless transmission in both cases. Access architecture is experimentally emulated by deploying single/multi-mode fibers. For the W-band, experimental assessment of passive and active approaches for implementation of remote antenna units is reported. The bit error rate performance of the optical and wireless channels is reported. A successful transmission of real-time uncompressed high-definition video in the V- and W-band fiber-wireless systems is demonstrated with prospects to pave the way for application-focused fiber-wireless connectivity.

  • 31586. Lebedeva, Natalia F.
    Одномерные нестационарные задачи об ударном нагружении несжимаемых упругих сред[One-dimensional non-stationary problems of shock loading uncompressible elastic solids]1997Doctoral thesis, monograph (Other academic)
  • 31587. Lebedkin, S.
    et al.
    Hull, W.E.
    Soldatov, Alexander
    Renker, B.
    Kappes, M. M.
    Structure and properties of the fullerene dimer C140 produced by pressure treatment of C702000In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 104, no 17, p. 4101-4110Article in journal (Refereed)
    Abstract [en]

    A [2+2] cycloaddition cap-to-cap C70 dimer with C2h molecular symmetry was synthesized in high yield by pressure treatment of polycrystalline C70 at 1 GPa and 200° C. It was separated from unreacted monomers by chromatography and characterized by 13C NMR, Raman, and infrared spectroscopy, and other methods. Remarkably, only one isomer was produced out of the five possible [2+2] cycloaddition products which have equally low formation energies according to semiempirical modeling calculations. The dimer obtained is the one favored when C70 molecules adopt an ordered packing with parallel D5 axes. The intercage bonding in C140, its thermal stability, and intercage vibrational modes are similar to those found for the C60 dimer, C120. Both dimers photodissociate to the monomers in solution, probably via excited triplet states. The UV absorption and fluorescence properties of C140 are not very different from those of C70, suggesting only weak electronic interactions between the two cages of C140. In comparison, the pressure-induced dimerization of C60, under the conditions used for C70, results mainly in C60 oligomers and polymeric chains, but the dimer C120 could be isolated at low yield when short reaction times (≤5 min) were used.

  • 31588.
    Lebedkin, S.
    et al.
    Forschungszentrum Karlsruhe.
    Hull, W.E.
    Central Spectroscopy Department, German Cancer Research Center, Heidelberg.
    Soldatov, Alexander
    Renker, B.
    Forschungszentrum Karlsruhe.
    Kappes, M.M.
    Forschungszentrum Karlsruhe.
    Dimerization of C70 under high pressure: thermal dissociation and photophysical properties of the dimer C1402000In: Electronic properties od novel materials-molecular nanostructures: XIV International Winterschool/Euroconference / [ed] Hans Kuzmany, Meville, NY: American Institute of Physics (AIP), 2000, p. 77-80Conference paper (Refereed)
    Abstract [en]

    We have recently shown that solid C70 efficiently converts into a cap-to-cap dimer C2hC140 at pressure of ~1 GPa and temperature of ~200 °C [1]. Here we report on measurements of the thermal dissociation of C140 (purified by chromatography) at ambient pressure and its photophysical properties, in particular photogeneration of singlet oxygen (1O2). The kinetics of dissociation of C140 in the solid state between 130 and 200 °C is well described by a simple first-order process, with an activation energy of 1.6±0.03 eV (compare to 1.75±0.05 eV for the C60 dimer C120 [2]). In contrast, the thermal dissociation of C140 dissolved in o-dichlorobenzene shows different, non-Arrhenius behavior, suggesting a strong influence of the molecular surroundings. The quantum efficiency of 1O2 generation in solutions of C140 and C120 is close to unity, i.e. similar to that of C70 and C60.

  • 31589. Lebegue, S
    et al.
    Eriksson, O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Electronic structure of two-dimensional crystals from ab initio theory2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 11, p. 115409-Article in journal (Refereed)
    Abstract [en]

    We report on ab initio calculations of the two-dimensional systems MoS2 and NbSe2, which recently were synthesized. We find that two-dimensional MoS2 is a semiconductor with a gap which is rather close to that of the three-dimensional analog, and that NbSe2 is a metal, which is similar to the three-dimensional analog of this compound. We further computed the electronic structure of the two-dimensional hexagonal (graphene-like) lattices of Si and Ge and compared them with the electronic structure of graphene. It is found that the properties related to the Dirac cone do not appear in the case of two-dimensional hexagonal germanium, which is metallic, contrary to two-dimensional hexagonal silicon, also known as silicene, which has an electronic structure very similar to the one of graphene, making them possibly equivalent.

  • 31590. Lebegue, S
    et al.
    Klintenberg, Mattias
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Katsnelson, M.I.
    Accurate electronic band gap of pure and functionalized graphane from GW calculations2009In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 24, p. 245117-Article in journal (Refereed)
    Abstract [en]

    Using the GW approximation, we study the electronic structure of the recently synthesized hydrogenated graphene, named graphane. For both conformations, the minimum band gap is found to be direct at the Gamma point, and it has a value of 5.4 eV in the stable chair conformation, where H atoms attach C atoms alternatively on opposite sides of the two-dimensional carbon network. In the metastable boat conformation the energy gap is 4.9 eV. Then, using a supercell approach, the electronic structure of graphane was modified by introducing either a hydroxyl group or an H vacancy. In this last case, an impurity state appears at about 2 eV above the valence-band maximum.

  • 31591. Lebegue, Sebastien
    et al.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kim, Duck Young
    Ramzan, Muhammad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mao, Ho-kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Semimetallic dense hydrogen above 260 GPa2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 25, p. 9766-9769Article in journal (Refereed)
    Abstract [en]

    Being the lightest and the most abundant element in the universe, hydrogen is fascinating to physicists. In particular, the conditions of its metallization associated with a possible superconducting state at high temperature have been a matter of much debate in the scientific community, and progress in this field is strongly correlated with the advancements in theoretical methods and experimental techniques. Recently, the existence of hydrogen in a metallic state was reported experimentally at room temperature under a pressure of 260-270 GPa, but was shortly after that disputed in the light of more experiments, finding either a semimetal or a transition to an other phase. With the aim to reconcile the different interpretations proposed, we propose by combining several computational techniques, such as density functional theory and the GW approximation, that phase III at ambient temperature of hydrogen is the Cmca-12 phase, which becomes a semimetal at 260 GPa. From phonon calculations, we demonstrate it to be dynamically stable; calculated electron-phonon coupling is rather weak and therefore this phase is not expected to be a high-temperature superconductor.

  • 31592.
    Lebegue, Sebastien
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk Magnetism.
    Oppeneer, Peter
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk Magnetism.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk Magnetism.
    Ab initio study of the electronic properties and Fermi surface of the uranium dipnictides2006In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 73, no 4, p. 045119-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the uranium dipnictides UX2 (X=As, Sb, and Bi) is investigated by means of ab initio calculations based on density functional theory. The calculated Fermi surfaces are presented and compared to available experimental models obtained from de Haas-van Alphen experiments. In agreement with experiments they are found to have a significant two-dimensional character. Also, the change of the electronic properties through the series is discussed.

  • 31593.
    Lebegue, Sebastien
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk Magnetism.
    Santi, Gilles
    Svane, Axel
    Bengone, Olivier
    Katsnelson, Mikhail
    Lichtenstein, A. I.
    Eriksson, Olle
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Theoretical Magnetism. Teoretisk Magnetism.
    Electronic structure and spectroscopic properties of thulium monochalcogenides2005In: PHYSICAL REVIEW B, ISSN 1098-0121, Vol. 72, no 24, p. 245102-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the thulium monochalcogenides TmS, TmSe, and TmTe is studied with several theoretical approaches. The total energy is evaluated with the self-interaction corrected local-spin density approximation, whereby the Tm ions are described with either twelve or thirteen localized f electrons with the remaining electrons forming bands. The comparisons of these two scenarios reveal the valency shift of the Tm ion through the series. The spectral functions of TmX compounds are calculated including multiplet effects, and they are compared to experimental x-ray photoemission spectra. The basic tool is the Hubbard-I approximation in which the embedding of an isolated f(n) ion in a solid is performed by modifying the crystal Hamiltonian as obtained from the local-density approximation with the atomic self-energy of the ion. The parameters of the model are obtained from the self-consistent band structure calculation. The agreement with experiment is excellent, reproducing all significant multiplet structures.

  • 31594.
    Lebek, Maciej
    et al.
    Polish Acad Sci, Ctr Theoret Phys, Aleja Lotnikow 32-46, PL-02668 Warsaw, Poland.;Univ Warsaw, Inst Theoret Phys, Pasteura 5, PL-02093 Warsaw, Poland..
    Syrwid, Andrzej
    KTH, School of Engineering Sciences (SCI), Physics.
    Grochowski, Piotr T.
    Polish Acad Sci, Ctr Theoret Phys, Aleja Lotnikow 32-46, PL-02668 Warsaw, Poland..
    Rzazewski, Kazimierz
    Polish Acad Sci, Ctr Theoret Phys, Aleja Lotnikow 32-46, PL-02668 Warsaw, Poland..
    Repulsive dynamics of strongly attractive one-dimensional quantum gases2022In: Physical Review A: covering atomic, molecular, and optical physics and quantum information, ISSN 2469-9926, E-ISSN 2469-9934, Vol. 105, no 1, article id L011303Article in journal (Refereed)
    Abstract [en]

    We analyze the dynamics of one-dimensional quantum gases with strongly attractive contact interactions. We specify a class of initial states for which attractive forces effectively act as strongly repulsive ones during the time evolution. Our findings extend the theoretical results on the super-Tonks-Girardeau gas to a highly nonequilibrium dynamics. The mechanism is illustrated on the prototypical problem of the domain stability in a two-component Fermi gas. We also discuss finite-range interactions and analyze the universality of the presented results. Moreover, we use our conclusions to argue for the existence of metastable quantum droplets in the regime of strongly attractive contact and attractive dipolar interactions.

  • 31595. Lebiedowicz, P.
    et al.
    Pasechnik, Roman
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Szczurek, A.
    Exclusive production of chi(c)(0(+)) meson and its measurement in the pi(+)pi(-) channel2011In: Nuclear physics B, Proceedings supplements, ISSN 0920-5632, E-ISSN 1873-3832, Vol. 219-220, p. 284-287Article in journal (Refereed)
    Abstract [en]

    We report on the results of a theoretical study of the central exclusive production of scalar chi(c)(0(+)) meson via chi(c0) -> pi(+)pi(-) decay in high-energy hadron collisions at the RHIC, Tevatron and LHC. The corresponding amplitude for exclusive double-diffractive chi(c0) meson production was obtained within the k(t)-factorization approach including virtualities of active gluons and the cross section is calculated with unintegrated gluon distribution functions (UGDFs) known from the literature. The four-body pp -> pp pi(+)pi(-) reaction constitutes an irreducible background to the exclusive chi(c0) meson production. We include the absorption effects due to proton-proton interaction and pion-pion rescattering. Several differential distributions for pp((p) over bar) -> pp((p) over bar)chi(c0) process, including the absorptive corrections, were calculated. The influence of kinematical cuts on the signal-to-background ratio is investigated.

  • 31596. Lebiedowicz, P.
    et al.
    Pasechnik, Roman
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
    Szczurek, A.
    Measurement of exclusive production of scalar chi(c0) meson in proton-(anti)proton collisions via chi(c0) -> pi(+)pi(-) decay2011In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, no 4, p. 434-444Article in journal (Refereed)
    Abstract [en]

    We consider a measurement of exclusive production of scalar chi(c)(0(++)) meson in the proton-proton collisions at LHC and RHIC and in the proton-antiproton collisions at the Tevatron via chi(c0) -> pi(+)pi(-) decay. The corresponding amplitude for exclusive double-diffractive chi(c0) meson production was obtained within the k(t)-factorization approach including virtualities of active gluons and the corresponding cross section is calculated with unintegrated gluon distribution functions (UGDFs) known from the literature. The four-body pp -> pp pi(+)pi(-) reaction constitutes an irreducible background to the exclusive chi(c0) meson production. We include absorption effects due to proton-proton interaction and pion-pion rescattering. We calculate several differential distributions for pp((p) over bar) -> pp((p) over bar)chi(c0) process including the absorptive corrections. The influence of kinematical cuts on the signal-to-background ratio is investigated. Corresponding experimental consequences are discussed.

  • 31597.
    Leblanc, F.
    et al.
    Sorbonne Univ, LATMOS, CNRS, UVSQ, Paris, France..
    Roth, Lorenz
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Chaufray, J. Y.
    Sorbonne Univ, LATMOS, CNRS, UVSQ, Paris, France..
    Modolo, R.
    Sorbonne Univ, LATMOS, CNRS, UVSQ, Paris, France..
    Galand, M.
    Imperial Coll London, Dept Phys, London, England..
    Ivchenko, Natalya
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Carnielli, G.
    Imperial Coll London, Dept Phys, London, England..
    Baskevitch, C.
    Sorbonne Univ, LATMOS, CNRS, UVSQ, Paris, France..
    Oza, A.
    CALTECH, Jet Prop Lab, Pasadena, CA USA..
    Werner, A. L. E.
    Sorbonne Univ, LATMOS, CNRS, UVSQ, Paris, France.;Swedish Inst Space Phys, Uppsala, Sweden..
    Ganymede's atmosphere as constrained by HST/STIS observations2023In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 399, article id 115557Article in journal (Refereed)
    Abstract [en]

    A new analysis of aurora observations of Ganymede's atmosphere on the orbital leading and trailing hemispheres has been recently published by Roth et al. (2021), suggesting that water is its main constituent near noon. Here, we present two additional aurora observations of Ganymede's sub-Jovian and anti-Jovian hemispheres, which suggest a modulation of the atmospheric H2O/O-2 ratio on the moon's orbital period, and analyze the orbital evolution of the atmosphere. For this, we propose a reconstruction of aurora observations based on a physical modelling of the exosphere taking into account its orbital variability (the Exospheric Global Model; Leblanc et al., 2017). The solution described in this paper agrees with Roth et al. (2021) that Ganymede's exosphere should be dominantly composed of water molecules. From Ganymede's position when its leading hemisphere is illuminated to when it is its trailing hemisphere, the column density of O-2 may vary between 4.3 x 10(14) and 3.6 x 10(14) cm(-2) whereas the H2O column density should vary between 5.6 x 10(14) and 1.3 x 10(15) cm(-2). The water content of Ganymede's atmosphere is essentially constrained by its sublimation rate whereas the O-2 component of Ganymede's atmosphere is controlled by the radiolytic yield. The other species, products of the water molecules, vary in a more complex way depending on their sources, either as ejecta from the surface and/or as product of the dissociation of the other atmospheric constituents. Electron impact on H2O and H-2 molecules is shown to likely produce H Lyman-alpha emissions close to Ganymede, in addition to the observed extended Lyman-alpha corona from H resonant scattering. All these conclusions being highly dependent on our capability to accurately model the origins of the observed Ganymede auroral emissions, modelling these emissions remains poorly constrained without an accurate knowledge of the Jovian magnetospheric and Ganymede ionospheric electron populations.

  • 31598.
    Lebrun, Delphine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Multi-electron correlation spectroscopy of atoms and molecules: Focus on buckminsterfullerene2011Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Correlated many-particle dynamics in Coulombic systems is one of today‟s grand challenges in physics. In order to address this task, the electronic structure and electron correlations of multiply ionised systems are studied in this thesis, aiming to obtain information on the dynamics of electron emission processes at unprecedented ease and high resolution. State-of-the-art multi-electron correlation spectrometers are used, which were originally developed at Oxford University, UK, and which are now frequently in use at the Ångström laboratory in Uppsala, Sweden.The research is so far based mainly on single-photon excitations using laboratory light sources and synchrotron radiation facilities, and expands now gradually into non-linear and time-resolved studies of atoms, molecules and clusters using high intensive Free Electron Lasers (FEL) in the Vacuum Ultra-Violet (VUV) and X-ray spectral region. This development is highly relevant for even more deep-going applications regarding the ion and excited-state balance in the Earth‟s outer atmosphere and in astrophysical contexts, for photochemistry and biochemistry, for materials science, and to test current atomic and molecular structure theories to their limits.We will focus on the multiple ionization of the buckminsterfullerene (C60) which is of scientific interest as an exceptionally stable and symmetric cluster. Its applications are quite large in nanotechnologies.

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    correlationspectroscopy
  • 31599.
    Lebrun, Delphine
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Thiolsulfinates/Thiolsulfonates  formation:  X-ray photoelectron spectroscopy (XPS) of oxidized thiols on flat surfaces2010Independent thesis Advanced level (degree of Master (One Year)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    In order  to  find  another way to fix peptides      on      surfaces      we      study      the      chemical      and      electro      oxidation       of      a      Silicon      flat      surface      after      silanization.      Traditional      experimental      setup      is      used      to      make      the       oxidations      and      Xray      photoelectron      spectroscope      (XPS)      is      used      to      analyze      the      surfaces.      We      find      that       chemical      oxidation      works      well      but      we      cannot      fix      the      Alanine      molecule      on      the      surface,      unlike      the       electro      oxidation      which      works      for      peptides      fixation.            We      need      to      focus      on      the      electro      oxidation       process,      use      a      more      accurate      method      to      analyze      the      samples      and      probably      used      a      higher      Alanine       concentration.   

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    thiols
  • 31600.
    Lebrun, Delphine Misao
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Photonic crystals and photocatalysis: Study of titania inverse opals2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    Due to an increase of human activity, an increase health risk has emerged from the presence of pollutants in the environment. In the transition to renewable and sustainable life style, treatment of pollutants could support the shifting societies. A motivation behind material research for environmental applications is to maximize the efficiency of the materials to alleviate environmental pollution.

    In the case of titania, an increase of ultra-violet light absorption is needed to overcome its bandgap to produce reactive radicals, which is the basis for photocatalysis. It has been hypothesized that photonic crystal can enhance titania photocatalysis. They are structures made of at least two dielectrics with a high refractive index contrast, ordered in a periodic fashion. For a strong contrast, photonic band gaps emerge. The effect of the photonic band gap is to force complete reflection of the incoming light within its range and multiple internal reflections at its edges. By combining photonic and electronic band gap positions, it is possible to increase the absorption at the photonic band gap edges.

    In this thesis, fabrication method and structural analysis of titania and alumina/titania photonic structures were presented. A thorough optical analysis was performed at all steps of fabrication – beyond what previously has been reported. The photocatalytic activity was measured with two setups. Fourier Transform Infrared spectroscopy combined with arc lamps and bandpass filters was used to monitor the degradation of stearic acid in ambient air. A home-built setup was used to degrade methylene blue in solution with ultra-violet illumination.

    The results in this thesis show in general no correlation of the photocatalytic activity to the photonic band gap position, even though absorbance data displayed an increase absorption in this energy range. A more controlled environment might show the effect of the structure, as seen in some of the experiments.

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