| 1. |
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| 2. |
- Fuchs, M.a b, et al.
(författare)
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Nonlinear X-ray compton scattering
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We use XFEL pulses to observe the most fundamental nonlinear X-ray-matter interaction: nonlinear Compton scattering. In contrast to theoretical predictions, we measure an anonymous and yet to be explained red-shift in the observed photon energy.
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| 3. |
- Trigo, M., et al.
(författare)
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Fourier-transform inelastic X-ray scattering from time- and momentum-dependent phonon-phonon correlations
- 2013
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Ingår i: Nature Physics. - 1745-2473. ; 9:12, s. 790-794
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Tidskriftsartikel (refereegranskat)abstract
- The macroscopic characteristics of a material are determined by its elementary excitations, which dictate the response of the system to external stimuli. The spectrum of excitations is related to fluctuations in the density-density correlations and is typically measured through frequency-domain neutron(1) or X-ray(2-4) scattering. Time-domain measurements of these correlations could yield a more direct way to investigate the excitations of solids and their couplings both near to and far from equilibrium. Here we show that we can access large portions of the phonon dispersion of germanium by measuring the diffuse scattering from femtosecond X-ray free-electron laser pulses. A femtosecond optical laser pulse slightly quenches the vibrational frequencies, producing pairs of high-wavevector phonons with opposite momenta. These phonons manifest themselves as time-dependent coherences in the displacement correlations(5) probed by the X-ray scattering. As the coherences are preferentially created in regions of strong electron-phonon coupling, the time-resolved approach is a natural spectroscopic tool for probing low-energy collective excitations in solids, and their microscopic interactions.
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| 4. |
- Henighan, T., et al.
(författare)
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Generation mechanism of terahertz coherent acoustic phonons in Fe
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 93:22
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Tidskriftsartikel (refereegranskat)abstract
- We use femtosecond time-resolved hard x-ray scattering to detect coherent acoustic phonons generated during ultrafast laser excitation of ferromagnetic bcc Fe films grown on MgO(001). We observe the coherent longitudinal-acoustic phonons as a function of wave vector through analysis of the temporal oscillations in the x-ray scattering signal. The width of the extracted strain wave front associated with this coherent motion is similar to 100 fs. An effective electronic Gruneisen parameter is extracted within a two-temperature model. However, ab initio calculations show that the phonons are nonthermal on the time scale of the experiment, which calls into question the validity of extracting physical constants by fitting such a two-temperature model.
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| 5. |
- Kozina, M., et al.
(författare)
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Terahertz-driven phonon upconversion in SrTiO3
- 2019
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Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 15:4, s. 387-
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Tidskriftsartikel (refereegranskat)abstract
- Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high-frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower-frequency lattice modulations. Here, we drive the lowest-frequency optical phonon in the prototypical transition metal oxide SrTiO3 well into the anharmonic regime with an intense terahertz field. We show that it is possible to transfer energy to higher-frequency phonon modes through nonlinear coupling. Our observations are carried out by directly mapping the lattice response to the coherent drive field with femtosecond X-ray pulses, enabling direct visualization of the atomic displacements.
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| 6. |
- Kozina, M., et al.
(författare)
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Local terahertz field enhancement for time-resolved x-ray diffraction
- 2017
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 110:8
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Tidskriftsartikel (refereegranskat)abstract
- We report local field strength enhancement of single-cycle terahertz (THz) pulses in an ultrafast time-resolved x-ray diffraction experiment. We show that patterning the sample with gold microstructures increases the THz field without changing the THz pulse shape or drastically affecting the quality of the x-ray diffraction pattern. We find a five-fold increase in THz-induced x-ray diffraction intensity change in the presence of microstructures on a SrTiO3 thin-film sample.
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| 7. |
- Shen, L., et al.
(författare)
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Decoupling spin-orbital correlations in a layered manganite amidst ultrafast hybridized charge-transfer band excitation
- 2020
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Ingår i: Physical Review B. - 2469-9950. ; 101:20
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Tidskriftsartikel (refereegranskat)abstract
- In the mixed-valence manganites, a near-infrared laser typically melts the orbital and spin order simultaneously, corresponding to the photoinduced d1d0→d0d1 excitations in the Mott-Hubbard bands of manganese. Here, we use ultrafast methods-both femtosecond resonant X-ray diffraction and optical reflectivity-to demonstrate that the orbital response in the layered manganite Nd1-xSr1+xMnO4(x=2/3) does not follow this scheme. At the photoexcitation saturation fluence, the orbital order is only diminished by a few percent in the transient state. Instead of the typical d1d0→d0d1 transition, a near-infrared pump in this compound promotes a fundamentally distinct mechanism of charge transfer, the d0→d1L, where L denotes a hole in the oxygen band. This finding may pave a different avenue for selectively manipulating specific types of order in complex materials of this class.
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| 8. |
- Chernenkaya, A., et al.
(författare)
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Microscopic origin of the charge transfer in single crystals based on thiophene derivatives : A combined NEXAFS and density functional theory approach
- 2016
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145:3
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the charge transfer mechanism in single crystals of DTBDT-TCNQ and DTBDT-F4TCNQ (where DTBDT is dithieno[2,3-d;2′,3′-d′] benzo[1,2-b;4,5-b′]dithiophene) using a combination of near-edge X-ray absorption spectroscopy (NEXAFS) and density functional theory calculations (DFT) including final state effects beyond the sudden state approximation. In particular, we find that a description that considers the partial screening of the electron-hole Coulomb correlation on a static level as well as the rearrangement of electronic density shows excellent agreement with experiment and allows to uncover the details of the charge transfer mechanism in DTBDT-TCNQ and DTBDT-F4 TCNQ, as well as a reinterpretation of previous NEXAFS data on pure TCNQ. Finally, we further show that almost the same quality of agreement between theoretical results and experiment is obtained by the much faster Z+1/2 approximation, where the core hole effects are simulated by replacing N or F with atomic number Z with the neighboring atom with atomic number Z+1/2.
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| 9. |
- Hagberg, C. E., et al.
(författare)
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Flow Cytometry of Mouse and Human Adipocytes for the Analysis of Browning and Cellular Heterogeneity
- 2018
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Ingår i: Cell Reports. - : Elsevier BV. - 2211-1247. ; 24:10
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Tidskriftsartikel (refereegranskat)abstract
- Adipocytes, once considered simple lipid-storing cells, are rapidly emerging as complex cells with many biologically diverse functions. A powerful high-throughput method for analyzing single cells is flow cytometry. Several groups have attempted to analyze and sort freshly isolated adipocytes; however, using an adipocyte-specific reporter mouse, we demonstrate that these studies fail to detect the majority of white adipocytes. We define critical settings required for adipocyte flow cytometry and provide a rigid strategy for analyzing and sorting white and brown adipocyte populations. The applicability of our protocol is shown by sorting mouse adipocytes based on size or UCP1 expression and demonstrating that a subset of human adipocytes lacks the beta(2)-adrenergic receptor, particularly in the insulin-resistant state. In conclusion, the present study confers key technological insights for analyzing and sorting mature adipocytes, opening up numerous downstream research applications.
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| 10. |
- Odak, I., et al.
(författare)
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Teachers’ Social and Emotional Competencies : A Lever for Social and Emotional Learning in Schools
- 2023
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Ingår i: Sociologija i Prostor. - : Institute for Social Research Zagreb. - 1846-5226. ; 61:1, s. 105-122
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Tidskriftsartikel (refereegranskat)abstract
- The present paper focuses on social and emotional learning, and highlights empirical findings on its importance for teachers, students and schools. The importance of social and emotional learning in school settings has been a central focus of research for the last 30 years. The development of teachers’ social and emotional competencies has been an essential factor for improving social and emotional learning of students. Only when teachers are able to create a school climate in which students feel included and welcome, students can develop and enhance their social and emotional competencies. In this paper, we outline the main conceptual frameworks on social and emotional learning, emphasizing the CASEL framework, relevant for both young people and adults. We proceed by focusing on teachers’ social and emotional competencies, as teachers are one of the key figures for fostering and developing social and emotional competencies in school settings. Afterwards, we address the issue of development of teachers’ social and emotional competencies in various settings. The last part of the paper links teachers’ and students’ social and emotional competencies. We stress the importance of teachers’ social and emotional competencies for healthy teacher-student relationships, and students’ well-being and academic achievement. As teachers also need support for the development of these competencies, we advocate for comprehensive school-wide approach, in order to ensure the successful implementation of social and emotional learning in classrooms.
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