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- Lytvynenko, Y., et al.
(author)
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Control of the asymmetric band structure in Mn2Au by a ferromagnetic driver layer
- 2023
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In: Physical Review B. - 2469-9950 .- 2469-9969. ; 108:10
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Journal article (peer-reviewed)abstract
- Hard x-ray angle-resolved photoemission spectroscopy reveals the momentum-resolved band structure in an epitaxial Mn2Au(001) film capped by a 2-nm-thick ferromagnetic permalloy layer. By magnetizing the permalloy capping layer, the exceptionally strong exchange bias aligns the Néel vector in the Mn2Au(001) film accordingly. Uncompensated interface Mn magnetic moments in Mn2Au were identified as the origin of the exchange bias using x-ray magnetic circular dichroism in combination with photoelectron emission microscopy. Using time-of-flight momentum microscopy, we measure the asymmetry of the band structure, E(k)≠E(-k), in Mn2Au resulting from the homogeneous orientation of the Néel vector. Comparison with theory shows that the Néel vector, determined by the magnetic moment of the top Mn layer, is antiparallel to the permalloy magnetization. The experimental results demonstrate that hard x-ray photoemission spectroscopy can measure the band structure of epitaxial layers beneath a metallic capping layer and corroborate the asymmetric band structure in Mn2Au that was previously inferred only indirectly.
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- Schönhense, G., et al.
(author)
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Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens
- 2021
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In: Review of Scientific Instruments. - : American Institute of Physics (AIP). - 0034-6748 .- 1089-7623. ; 92:5
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Journal article (peer-reviewed)abstract
- The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e-e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from -20 to -1100 V/mm for E-kin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 mu m above the sample surface for E-kin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at E-kin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm(2) (retarding field -21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm(2), it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at E-kin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments.
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- Schönhense, G., et al.
(author)
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Time-of-flight photoelectron momentum microscopy with 80-500 MHz photon sources : Electron-optical pulse picker or bandpass pre-filter
- 2021
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In: Journal of Synchrotron Radiation. - 0909-0495. ; 28, s. 1891-1908
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Journal article (peer-reviewed)abstract
- The small time gaps of synchrotron radiation in conventional multi-bunch mode (100-500 MHz) or laser-based sources with high pulse rate (∼80 MHz) are prohibitive for time-of-flight (ToF) based photoelectron spectroscopy. Detectors with time resolution in the 100 ps range yield only 20-100 resolved time slices within the small time gap. Here we present two techniques of implementing efficient ToF recording at sources with high repetition rate. A fast electron-optical beam blanking unit with GHz bandwidth, integrated in a photoelectron momentum microscope, allows electron-optical 'pulse-picking' with any desired repetition period. Aberration-free momentum distributions have been recorded at reduced pulse periods of 5 MHz (at MAX II) and 1.25 MHz (at BESSY II). The approach is compared with two alternative solutions: A bandpass pre-filter (here a hemispherical analyzer) or a parasitic four-bunch island-orbit pulse train, coexisting with the multi-bunch pattern on the main orbit. Chopping in the time domain or bandpass pre-selection in the energy domain can both enable efficient ToF spectroscopy and photoelectron momentum microscopy at 100-500 MHz synchrotrons, highly repetitive lasers or cavity-enhanced high-harmonic sources. The high photon flux of a UV-laser (80 MHz, <1 meV bandwidth) facilitates momentum microscopy with an energy resolution of 4.2 meV and an analyzed region-of-interest (ROI) down to <800 nm. In this novel approach to 'sub-μm-ARPES' the ROI is defined by a small field aperture in an intermediate Gaussian image, regardless of the size of the photon spot.
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- Giang, Kok Wai, 1984, et al.
(author)
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Congenital heart disease: changes in recorded birth prevalence and cardiac interventions over the past half-century in Sweden
- 2023
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In: European Journal of Preventive Cardiology. - : Oxford University Press (OUP). - 2047-4873 .- 2047-4881. ; 30:2, s. 169-176
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Journal article (peer-reviewed)abstract
- Aims Our objective was to assess changes in the birth prevalence of CHD over a half-century in a high-resource, nationwide setting, as well as changes in the prevalence of cardiac interventions in this population. Methods and results The Swedish National Patient and Cause of Death registers were linked to estimate the annual rates of CHD and cardiac interventions among live-born infants from 1970 to 2017. Additionally, separate estimates were obtained by lesion complexity, from mild to the most complex forms of CHD. Overall, the numbers of live-born infants with a CHD identified varied from 624 to 2459 annual cases, with rates increasing steadily from 5.7 to an average of 20 per 1000 live births at the end of the study period, and with a more pronounced increase from 1996 to 2005. The largest increase over time was observed for mild CHD lesions. Overall, the proportion of cardiac interventions among patients with CHD declined from 40.7% in 1970 to below 15.0% after 2014. However, in the most complex CHD lesion groups, overall cardiac interventions increased from 57.1 to 76.8% in patients with conotruncal defects and from 32.8 to 39.5% in those with severe non-conotruncal defects. Conclusion The live-birth prevalence of CHD in Sweden more than tripled during the past half-century, most likely resulting from more accurate diagnostic capabilities. The largest increase over time was observed among patients with simple defects. During the same period, overall cardiac interventions decreased whereas interventions for the most complex CHD groups increased.
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- Holm, M, et al.
(author)
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The MOVEMENT Trial
- 2019
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In: Journal of the American Heart Association. - 2047-9980. ; 8:2, s. e010152-
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Journal article (peer-reviewed)
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- Medjanik, K., et al.
(author)
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Site-specific atomic order and band structure tailoring in the diluted magnetic semiconductor (In,Ga,Mn)As
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:7
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Journal article (peer-reviewed)abstract
- Diluted ferromagnetic semiconductors combining ferromagnetic and semiconducting properties in one material provide numerous new functionalities, attractive for basic studies and potentially useful for novel device applications. The tailoring of the electronic structure in analogy to conventional semiconductors has yet to be explored. Here, we demonstrate the conservation of broken inversion symmetry and band structure tailoring for high-quality molecular-beam-epitaxy-grown (In,Ga,Mn)As films with 3% In plus 2.5% or 5.6% Mn using hard-x-ray photoelectron diffraction (hXPD) and momentum microscopy. Photon energies of 3-5 keV ensure that the results are not corrupted by surface effects, which are known to be strong in semiconductors. The missing inversion center of the GaAs host lattice leads to fingerprint-like hXPD signatures of As and Ga sites. For both concentrations, Mn predominantly occupies Ga substitutional sites. Momentum microscopy reveals a shift of the chemical potential with increasing Mn doping and a highly dispersing band, crossing the Fermi level for high Mn concentration. The Mn doping induces a pronounced modification of the spin-orbit split-off band.
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- Preston, Markus, et al.
(author)
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Methodology for Multiparameter Evaluation of Barriers Against Proliferation of Minor Actinides
- 2024
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In: Nuclear Technology. - 0029-5450 .- 1943-7471.
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Journal article (peer-reviewed)abstract
- There exist elements apart from uranium and plutonium that could potentially be used to construct the core of a nuclear explosive device. These belong to the so-called minor actinides (MAs), which exist in nonnegligible amounts in spent nuclear fuel (SNF) and are in nearly all cases not covered by international safeguards. Future reprocessing of SNF could result in significant separation of these elements, potentially leading to new proliferation concerns. In this work, a methodology for a transparent assessment of the barriers against proliferation of MAs has been developed and applied to the case of neptunium, americium, and curium separated from spent fuel from pressurized water reactors. In this methodology, openly available data and Monte Carlo simulations have been used to assess the barriers posed by a number of parameters relevant to the production of a nuclear explosive device from SNF. The evaluation shows that the properties of neptunium present low barriers to proliferation and that it should be discussed within the context of future nonproliferation treaties and possibly be placed under international safeguards. The properties of americium and curium present higher barriers to proliferation, meaning that these elements require less focus in the nonproliferation context.
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