| 1. |
- Rusydi, A., et al.
(författare)
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Metal-insulator transition in manganites: Changes in optical conductivity up to 22 eV
- 2008
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 78:12, s. 125110 (art. no.)-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic response of doped manganites at the transition from the paramagnetic insulating to the ferromagnetic metallic state in La(1-x)Ca(x)MnO(3) for x=0.3 and 0.2 was investigated by dc conductivity, ellipsometry, and vacuum ultraviolet reflectance for energies between 0 and 22 eV. A stabilized Kramers-Kronig transformation yields the optical conductivity and reveals changes in the optical spectral weight up to 22 eV at the metal-to-insulator transition. In the observed energy range, the spectral weight is conserved within 0.3%. The redistribution of spectral weight in this surprisingly broad energy range has important ramifications for the effective low-energy physics. We discuss the importance of the charge-transfer, Coulomb on-site, Jahn-Teller, and long-range Coulomb screening effects to the electronic structure.
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| 2. |
- Wendisch, M., et al.
(författare)
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Atmospheric and Surface Processes, and Feedback Mechanisms Determining Arctic Amplification: A Review of First Results and Prospects of the (AC)(3) Project
- 2023
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Ingår i: Bulletin of the American Meteorological Society. - : American Meteorological Society. - 0003-0007 .- 1520-0477. ; 104:1
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Tidskriftsartikel (refereegranskat)abstract
- Mechanisms behind the phenomenon of Arctic amplification are widely discussed. To contribute to this debate, the (AC)(3) project was established in 2016 (www.ac3-tr.de/). It comprises modeling and data analysis efforts as well as observational elements. The project has assembled a wealth of ground-based, airborne, shipborne, and satellite data of physical, chemical, and meteorological properties of the Arctic atmosphere, cryosphere, and upper ocean that are available for the Arctic climate research community. Short-term changes and indications of long-term trends in Arctic climate parameters have been detected using existing and new data. For example, a distinct atmospheric moistening, an increase of regional storm activities, an amplified winter warming in the Svalbard and North Pole regions, and a decrease of sea ice thickness in the Fram Strait and of snow depth on sea ice have been identified. A positive trend of tropospheric bromine monoxide (BrO) column densities during polar spring was verified. Local marine/biogenic sources for cloud condensation nuclei and ice nucleating particles were found. Atmospheric-ocean and radiative transfer models were advanced by applying new parameterizations of surface albedo, cloud droplet activation, convective plumes and related processes over leads, and turbulent transfer coefficients for stable surface layers. Four modes of the surface radiative energy budget were explored and reproduced by simulations. To advance the future synthesis of the results, cross-cutting activities are being developed aiming to answer key questions in four focus areas: lapse rate feedback, surface processes, Arctic mixed-phase clouds, and airmass transport and transformation.
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| 3. |
- Neuber, G., et al.
(författare)
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Temperature-dependent spectral generalized magneto-optical ellipsometry
- 2003
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 83, s. 4509-4511
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Tidskriftsartikel (refereegranskat)abstract
- We present a setup for temperature-dependent spectral generalized magneto-optical ellipsometry (SGME). This technique gives access to the electronic as well as the magnetic properties of ferromagnetic materials within one single magneto-optical measurement. It also allows the determination of the orientation of the magnetization. We show spectra of the real and the imaginary part of the refractive index N as well as the magneto-optical coupling parameter Q of permalloy and iron films for in-plane magnetization. Our findings demonstrate the relevance of SGME for the understanding of the interplay between electronic and magnetic properties of ferromagnetics. (C) 2003 American Institute of Physics.
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| 4. |
- Dicke, B., et al.
(författare)
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Transferring the entatic-state principle to copper photochemistry
- 2018
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Ingår i: Nature Chemistry. - : NATURE PUBLISHING GROUP. - 1755-4330 .- 1755-4349. ; 10:3, s. 355-362
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Tidskriftsartikel (refereegranskat)abstract
- The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.
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| 5. |
- Dicke, B., et al.
(författare)
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Transferring the entatic-state principle to copper photochemistry
- 2018
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Ingår i: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4349 .- 1755-4330. ; 10:3, s. 355-362
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Tidskriftsartikel (refereegranskat)abstract
- The entatic state denotes a distorted coordination geometry of a complex from its typical arrangement that generates an improvement to its function. The entatic-state principle has been observed to apply to copper electron-transfer proteins and it results in a lowering of the reorganization energy of the electron-transfer process. It is thus crucial for a multitude of biochemical processes, but its importance to photoactive complexes is unexplored. Here we study a copper complex-with a specifically designed constraining ligand geometry-that exhibits metal-to-ligand charge-transfer state lifetimes that are very short. The guanidine-quinoline ligand used here acts on the bis(chelated) copper(I) centre, allowing only small structural changes after photoexcitation that result in very fast structural dynamics. The data were collected using a multimethod approach that featured time-resolved ultraviolet-visible, infrared and X-ray absorption and optical emission spectroscopy. Through supporting density functional calculations, we deliver a detailed picture of the structural dynamics in the picosecond-to-nanosecond time range.
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| 6. |
- Espinoza, S., et al.
(författare)
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User oriented end-station on VUV pump-probe magneto-optical ellipsometry at ELI beamlines
- 2017
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 421, s. 378-382
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Tidskriftsartikel (refereegranskat)abstract
- A state of the art ellipsometer for user operations is being implemented at ELI Beamlines in Prague, Czech Republic. It combines three of the most promising and exotic forms of ellipsometry: VUV, pump-probe and magneto-optical ellipsometry. This new ellipsometer covers a spectral operational range from the NIR up to the VUV, with high through-put between 1 and 40 eV. The ellipsometer also allows measurements of magneto-optical spectra with a 1 kHz switchable magnetic field of up to 1.5 T across the sample combining ellipsometry and Kerr spectroscopy measurements in an unprecedented spectral range. This form of generalized ellipsometry enables users to address diagonal and off-diagonal components of the dielectric tensor within one measurement. Pump-probe measurements enable users to study the dynamic behaviour of the dielectric tensor in order to resolve the time-domain phenomena in the femto to 100 ns range.
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| 7. |
- Mazzei, Laura, 1988, et al.
(författare)
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Phonon spectra of pure and acceptor doped BaZrO3 investigated with visible and UV Raman spectroscopy
- 2020
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Ingår i: Journal of Physics Condensed Matter. - 0953-8984 .- 1361-648X. ; 32:40
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Tidskriftsartikel (refereegranskat)abstract
- We report results from visible and UV Raman spectroscopy studies of the phonon spectra of a polycrystalline sample of the prototypical perovskite type oxide BaZrO3 and a 500 nm thick film of its Y-doped, proton conducting, counterpart BaZr0.8Y0.2O2.9. Analysis of the Raman spectra measured using different excitation energies (between 3.44 eV and 5.17 eV) reveals the activation of strong resonance Raman effects involving all lattice vibrational modes. Specifically, two characteristic energies were identified for BaZrO3, one around 5 eV and one at higher energy, respectively, and one for BaZr0.8Y0.2O2.9, above 5 eV. Apart from the large difference in spectral intensity between the non-resonant and resonant conditions, the spectra are overall similar to each other, suggesting that the vibrational spectra of the perovskites are stable when investigated using an UV laser as excitation source. These results encourage further use of UV Raman spectroscopy as a novel approach for the study of lattice vibrational dynamics and local structure in proton conducting perovskites, and open up for, e.g., time-resolved experiments on thin films targeted at understanding the role of lattice vibrations in proton transport in these kinds of materials.
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| 8. |
- Neuber, G., et al.
(författare)
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Generalized magneto-optical ellipsometry in ferromagnetic metals
- 2004
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 455, s. 39-42
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Tidskriftsartikel (refereegranskat)abstract
- We present spectral generalized magneto-optical ellipsometry as an optical tool to investigate magnetic and electronic properties of ferromagnetic materials. The advantage of the simultaneous observation of the dielectric and the magnetic responses within one measurement procedure is crucial for materials with coupled degrees of freedom near a phase transition or during annealing procedures to improve the film quality by removing grain boundaries. Moreover, we show the implementation of this technique within an UHV-cryostat for a temperature range between 4.2 and 800 K and fields up to 40 mT. Examplary measurements on iron and Permalloy demonstrate the comfortable application of this technique. (C) 2003 Elsevier B.V. All rights reserved.
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| 9. |
- Rauer, R., et al.
(författare)
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Magneto-optical investigation of spin polarisation of La0.71Ca0.3MnO3 and La0.7Sr0.3MnO3
- 2005
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Ingår i: Journal of Magnetism and Magnetic Materials. ; 290, s. 948-951
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the ferromagnetic phase of thin epitaxial films of the CMR manganites La0.7Ca0.3MnO3 and La0.7Sr0.3MnO3 by temperature-dependent spectral generalised magneto-optical ellipsometry (SGME). The phase transitions from a paramagnetic insulator to a ferromagnetic metal take place at T-C ≈ 265 K and T-C ≈ 335 K, respectively. The measurements covering a spectral range of 0.5-5eV are performed in the temperature range of 25-425 K. SGME allows a complete magneto-optical characterisation consisting of the determination of the diagonal components as well as the off-diagonal components ε(xx) of the dielectric tensor within a single measurement. Upon cooling through the Curie temperature, we observe the development of a Drude-like free-carrier response in ε(xx), indicating the release of previously bound charges. Meanwhile, ε(xx) exhibits a rising magneto-optical response. This reflects, via the increasing degree of spin polarisation of the bands involved in optical transitions, the emergence of ferromagnetism. We tentatively assign spectral features between 2.5 and 4.5 eV to transitions involving the Mn-d shell, especially the e(g) and t(2g) levels. © 2004 Elsevier B.V. All rights reserved.
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| 10. |
- Rauer, R., et al.
(författare)
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Temperature-dependent spectral generalized magneto-optical ellipsometry for ferromagnetic compounds
- 2005
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Ingår i: Review of Scientific Instruments. - 0034-6748 .- 1089-7623. ; 76
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Tidskriftsartikel (refereegranskat)abstract
- Spectral generalized magneto-optical ellipsometry is presented as an optical tool for the simultaneous measurement of the complex index of refraction n=n+ik, the complex magneto-optical coupling parameter Q=Q(r)+iQ(i) (i.e., the Voigt-parameter), and the orientation of the saturation magnetization M-s of isotropic ferromagnetic bulk materials. For wavelengths between 220 nm and 790 nm and at temperatures between 4.2 K and 800 K measurements on iron and permalloy demonstrate the comfortable application of this technique in order to resolve the spectral response of spin-polarized carriers and bands, which can provide valuable insight about the formation of the ferromagnetic state. (C) 2005 American Institute of Physics.
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