| 1. |
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| 2. |
- Balaz, Pavel, et al.
(author)
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Domain wall dynamics due to femtosecond laser-induced superdiffusive spin transport
- 2020
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:17
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Journal article (peer-reviewed)abstract
- Manipulation of magnetic domain walls via a helicity-independent laser pulse has recently been experimentally demonstrated and various physical mechanisms leading to domain wall dynamics have been discussed. Spin-dependent superdiffusive transport of hot electrons has been identified as one of the possible ways to affect a magnetic domain wall. Here, we develop a model based on superdiffusive spin-dependent transport to study the laser-induced transport of hot electrons through a smooth magnetic domain wall. We show that the spin transfer between neighboring domains can enhance ultrafast demagnetization in the domain wall. More importantly, our calculations reveal that when the laser pulse is properly focused onto the vicinity of the domain wall, it can excite sufficiently strong spin currents to generate a spin-transfer torque that can rapidly move the magnetic domain wall by several nanometers in several hundred femtoseconds, leading to a huge nonequilibrium domain wall velocity.
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| 3. |
- Balaz, Pavel, et al.
(author)
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Theory of superdiffusive spin transport in noncollinear magnetic multilayers
- 2023
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:17
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Journal article (peer-reviewed)abstract
- Ultrafast demagnetization induced by femtosecond laser pulses in thin metallic layers is caused by the outflow of spin-polarized hot-electron currents describable by the superdiffusive transport model. These laser-generated spin currents can cross the interface into another magnetic layer and give rise to magnetization dynamics in magnetic spin valves with noncollinear magnetizations. To describe ultrafast transport and spin dynamics in such nanostructures, we develop here the superdiffusive theory for general noncollinear magnetic multilayers. Specifically, we introduce an Al/Ni/Ru/Fe/Ru multilayer system with noncollinear Ni and Fe magnetic moments and analyze how the ultrafast demagnetization and spin-transfer torque depend on the noncollinearity. We employ ab initio calculations to compute the spin-and energy-dependent transmissions of hot electrons at the interfaces of the multilayer. Taking into account multiple electron scattering at interfaces and spin mixing in the spacer layer, we find that the laser-induced demagnetization of the Ni layer and the magnetization change of the Fe layer strongly depend on the angle between their magnetizations. Similarly, the spin-transfer torques on the Ni and Fe layers and the total spin momentum absorbed in the Ni and Fe layer are found to vary markedly with the amount of noncollinearity. These results suggest that by changing the amount of noncollinearity in magnetic multilayers, one can efficiently control the hot-electron spin transport, which may open a way toward achieving fast, laser-driven spintronic devices.
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| 4. |
- Balaz, Pavel, et al.
(author)
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Transport theory for femtosecond laser-induced spin-transfer torques
- 2018
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In: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 30:11
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Journal article (peer-reviewed)abstract
- Ultrafast demagnetization of magnetic layers pumped by a femtosecond laser pulse is accompanied by a nonthermal spin-polarized current of hot electrons. These spin currents are studied here theoretically in a spin valve with noncollinear magnetizations. To this end, we introduce an extended model of superdiffusive spin transport that enables the treatment of noncollinear magnetic configurations, and apply it to the perpendicular spin valve geometry. We show how spin-transfer torques arise due to this mechanism and calculate their action on the magnetization present, as well as how the latter depends on the thicknesses of the layers and other transport parameters. We demonstrate that there exists a certain optimum thickness of the out-of-plane magnetized spin-current polarizer such that the torque acting on the second magnetic layer is maximal. Moreover, we study the magnetization dynamics excited by the superdiffusive spin-transfer torque due to the flow of hot electrons employing the Landau-Lifshitz-Gilbert equation. Thereby we show that a femtosecond laser pulse applied to one magnetic layer can excite small-angle precessions of the magnetization in the second magnetic layer. We compare our calculations with recent experimental results.
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| 5. |
- Battiato, Marco, et al.
(author)
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Treating the effect of interface reflections on superdiffusive spin transport in multilayer samples (invited)
- 2014
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 115:17, s. 172611-
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Journal article (peer-reviewed)abstract
- Femtosecond laser-induced magnetization dynamics has recently been related to superdiffusive spin transport. With the aim to accurately compute spin superdiffusion in the complex geometries of layered heterostructures and free standing layers, we develop here a dedicated numerical scheme. We introduce a discretization technique to solve the superdiffusive equation numerically on a time and space grid. The discretization scheme facilitates an explicit treatment of the total reflection at the vacuum-material surfaces as well as of partial reflections at the interfaces between two different materials. The advantages of the numerical technique are discussed. (C) 2014 AIP Publishing LLC.
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| 6. |
- Breznau, Nate, et al.
(author)
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Observing many researchers using the same data and hypothesis reveals a hidden universe of uncertainty
- 2022
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In: Proceedings of the National Academy of Sciences of the United States of America. - : National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 119:44
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Journal article (peer-reviewed)abstract
- This study explores how researchers analytical choices affect the reliability of scientific findings. Most discussions of reliability problems in science focus on systematic biases. We broaden the lens to emphasize the idiosyncrasy of conscious and unconscious decisions that researchers make during data analysis. We coordinated 161 researchers in 73 research teams and observed their research decisions as they used the same data to independently test the same prominent social science hypothesis: that greater immigration reduces support for social policies among the public. In this typical case of social science research, research teams reported both widely diverging numerical findings and substantive conclusions despite identical start conditions. Researchers expertise, prior beliefs, and expectations barely predict the wide variation in research outcomes. More than 95% of the total variance in numerical results remains unexplained even after qualitative coding of all identifiable decisions in each teams workflow. This reveals a universe of uncertainty that remains hidden when considering a single study in isolation. The idiosyncratic nature of how researchers results and conclusions varied is a previously underappreciated explanation for why many scientific hypotheses remain contested. These results call for greater epistemic humility and clarity in reporting scientific findings.
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| 7. |
- Buendia, E., et al.
(author)
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Dynamical correlation effects in the transition probability : A study for the atoms Li to Ar
- 2012
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 548, s. 1-6
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Journal article (peer-reviewed)abstract
- Explicitly correlated wave functions constructed as a Jastrow correlation factor times a model function have been obtained for the ground and the first excited state of opposite parity of the atoms Li to Ar. Single and restricted multi-configuration model functions are employed. Line strength, oscillator strength and transition probabilities have been obtained. An analysis of the different correlation mechanisms considered, single particle excitations and dynamical correlations, on these quantities is carried out. All calculations have been done by using Variational Monte Carlo, except when no Jastrow is involved where calculations have been performed using the Optimized Effective Potential method. (C) 2012 Elsevier B. V. All rights reserved.
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| 8. |
- Buendia, E., et al.
(author)
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Explicitly correlated wave functions for atoms and singly charged ions from Li through Sr : Variational and Diffusion Monte Carlo results
- 2014
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 615, s. 21-25
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Journal article (peer-reviewed)abstract
- Total energies calculated from explicitly correlated wave functions for the ground state of the atoms Li to Sr and their singly charged anions and cations are obtained. Accurate all electron, non-relativistic Variational and Diffusion Monte Carlo energies are reported. The quality of the results, when comparing with exact estimations and experimental electron affinities and ionization potential is similar for all of the atoms studied. The parameterization of the explicitly correlated wave functions for all of the atomic systems studied is provided.
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| 9. |
- Buendia, E., et al.
(author)
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Quantum Monte Carlo ionization potential and electron affinity for transition metal atoms
- 2013
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 559, s. 12-17
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Journal article (peer-reviewed)abstract
- Non-relativistic all-electron Quantum Monte Carlo ground state energies of the neutral atoms K to Zn and positive and negative ions are calculated starting from explicitly correlated wave functions. The accuracy obtained for these atoms and ions in the fourth period is similar to that reached for those in the second and third periods. For the atoms and ions for which the 4s-4p near degeneracy effect can be important a restricted multi-configuration expansion has been employed. Ionization potentials and electron affinities have been calculated showing a good agreement with the experimental values.
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| 10. |
- Buzzi, Michele, et al.
(author)
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Single-shot Monitoring of Ultrafast Processes via X-ray Streaking at a Free Electron Laser
- 2017
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In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7
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Journal article (peer-reviewed)abstract
- The advent of x-ray free electron lasers has extended the unique capabilities of resonant x-ray spectroscopy techniques to ultrafast time scales. Here, we report on a novel experimental method that allows retrieving with a single x-ray pulse the time evolution of an ultrafast process, not only at a few discrete time delays, but continuously over an extended time window. We used a single x-ray pulse to resolve the laser-induced ultrafast demagnetisation dynamics in a thin cobalt film over a time window of about 1.6 ps with an excellent signal to noise ratio. From one representative single shot measurement we extract a spin relaxation time of (130 +/- 30) fs with an average value, based on 193 single shot events of (113 +/- 20) fs. These results are limited by the achieved experimental time resolution of 120 fs, and both values are in excellent agreement with previous results and theoretical modelling. More generally, this new experimental approach to ultrafast x-ray spectroscopy paves the way to the study of non-repetitive processes that cannot be investigated using traditional repetitive pump-probe schemes.
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| 11. |
- Ciuciulkaite, Agne, MSc, 1991-
(author)
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The interaction of light and magnetism in the TbxCo100-x system
- 2019
-
Licentiate thesis (other academic/artistic)abstract
- Development of the faster and denser magnetic memory storage elements has been an active area of research since early 20th century. The path of research on magnetization manipulation began with firstly changing the magnetization state of a medium in an external magnetic field, then heating of a medium and magnetizing with a permanent magnet was explored, while the latest efforts have been focused on switching the magnetization only by a polarized laser light. Nowadays due to the technological advancement of lasers and material fabrication methods, the search and development process of magnetic memory elements is much faster. The implementation of such technologies, however, relies on finding suitable magnetic materials which would allow for a fast magnetization writing and read-out processes and would remain magnetized, even with the reduced dimensions. Ferrimagnetic rare Earth - transition metal (RE-TM) alloys have been used for fabricating magneto-optical recording media already since the 1990’s. Relatively recently, in 2007, it was demonstrated that the ferrimagnetic GdFeCo alloy magnetization state can be switched using only circularly polarized laser light. Hence, ferrimagnetic RE-TMalloys could be suitable candidates for all-optical light-induced magnetization switching (AOS), without any external magnetic field. Another combination of RE-TM alloys that was shown to exhibit AOS is ferrimagnetic amorphous alloys containing terbium and cobalt (Tb:Co). They have attracted attention due to their strong out-of-plane magnetic anisotropy, high magneto-optical activity and amorphicity, which makes them attractive from a fabrication point of view since a variety of substrates and buffer layers could be used for growing such layers. In this Thesis, TbCo alloys are investigated in order to examine how the magnetic, optical and magneto-optical properties could be tuned by varying the elemental ratio and film thickness. The main question that was addressed here was whether such a system is suitable for fabrication of nanosized magnetic elements as the building blocks for the magnetic memory applications. TbCo alloys were prepared as thin films by magnetron co-sputtering method onto different substrates and buffer layers. Films were characterized using a variety of techniques such as an ion beam analysis, an x-ray reflectivity and diffraction, and magneto-optical characterization techniques. It was observed that the properties of such alloys depend not only on the Tb:Co ratio but also on the film thickness and an underlying buffer layer. Magnetization compensation point, at which the magnetization of a film is zero, as in an antiferromagnet, can be modified depending on the buffer layer. All-optical switching (AOS) of magnetization experiments were performed on the fabricated samples. It was determined that AOS with at least 50-100 laserpulses can be achieved for the films grown directly onto fused silica substrates and with the compositions above the magnetization compensation point at room temperature, in the range of 24 - 30 at.% Tb. In the Outlook, the initial efforts of patterning the films into the arrays of nanosized elements are presented. It is demonstrated that after the lithographic patterning of the films, the resulting nanosized elements remained out-of-plane magnetized. In this work it is shown that the ferrimagnetic TbCo alloy system is a potential candidate material for bothfacilitating AOS and the fabrication of arrays of nanomagnets. Combining the TbCo alloys,which show AOS, together with a suitable buffer layer and patterning the hybrid structure,could enable selective element-by-element magnetization switching for the magnetic memorystorage devices.
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| 12. |
- Conradson, Steven D., et al.
(author)
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Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation
- 2015
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Journal article (peer-reviewed)abstract
- Bose-Einstein condensates (BECs) composed of polarons would be an advance because they would combine coherently charge, spin, and a crystal lattice. Following our earlier report of unique structural and spectroscopic properties, we now identify potentially definitive evidence for polaronic BECs in photo-and chemically doped UO2(+x) on the basis of exceptional coherence in the ultrafast time dependent terahertz absorption and microwave spectroscopy results that show collective behavior including dissipation patterns whose precedents are condensate vortex and defect disorder and condensate excitations. That some of these signatures of coherence in an atom-based system extend to ambient temperature suggests a novel mechanism that could be a synchronized, dynamical, disproportionation excitation, possibly via the solid state analog of a Feshbach resonance that promotes the coherence. Such a mechanism would demonstrate that the use of ultra-low temperatures to establish the BEC energy distribution is a convenience rather than a necessity, with the actual requirement for the particles being in the same state that is not necessarily the ground state attainable by other means. A macroscopic quantum object created by chemical doping that can persist to ambient temperature and resides in a bulk solid would be revolutionary in a number of scientific and technological fields.
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| 13. |
- Corkhill, Claire L., et al.
(author)
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Contribution of Energetically Reactive Surface Features to the Dissolution of CeO2 and ThO2 Analogues for Spent Nuclear Fuel Microstructures
- 2014
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:15, s. 12279-12289
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Journal article (peer-reviewed)abstract
- In the safety case for the geological disposal of nuclear waste, the release of radioactivity from the repository is controlled by the dissolution of the spent fuel in groundwater. There remain several uncertainties associated with understanding spent fuel dissolution, including the contribution of energetically reactive surface sites to the dissolution rate. In this study, we investigate how surface features influence the dissolution rate of synthetic CeO2 and ThO2, spent nuclear fuel analogues that approximate as closely as possible the microstructure characteristics of fuel-grade UO2 but are not sensitive to changes in oxidation state of the cation. The morphology of grain boundaries (natural features) and surface facets (specimen preparation-induced features) was investigated during dissolution. The effects of surface polishing on dissolution rate were also investigated. We show that preferential dissolution occurs at grain boundaries, resulting in grain boundary decohesion and enhanced dissolution rates. A strong crystallographic control was exerted, with high misorientation angle grain boundaries retreating more rapidly than those with low misorientation angles, which may be due to the accommodation of defects in the grain boundary structure. The data from these simplified analogue systems support the hypothesis that grain boundaries play a role in the so-called "instant release fraction" of spent fuel, and should be carefully considered, in conjunction with other chemical effects, in safety performance assessements for the geological disposal of spent fuel. Surface facets formed during the sample annealing process also exhibited a strong crystallographic control and were found to dissolve rapidly on initial contact with dissolution medium. Defects and strain induced during sample polishing caused an overestimation of the dissolution rate, by up to 3 orders of magnitude.
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| 14. |
- Daza-Caicedo, Sandra, et al.
(author)
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Measuring the impact of practices of social appropriation of science and technology: a proposal for a set of indicators
- 2017
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In: História, Ciências, Saúde-Manguinhos. - : FUNDACO OSWALDO CRUZ. - 0104-5970 .- 1678-4758. ; 24:1, s. 145-164
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Journal article (peer-reviewed)abstract
- We propose a set of qualitative indicators for monitoring practices of social appropriation of science and technology. The design of this set is based on the Maloka case, but it can be of use to multiple actors involved in the social appropriation of science and technology (referred to by its Spanish acronym, ASCyT). The introduction discusses the concept of ASCyT. The first section provides a review of the literature about measuring activities that link science and society. The second section explains why it is important to develop this type of measurement. The third section lays out the methodology used in designing the indicators. The fourth section explains the set of indicators and the fifth reflects on that process.
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| 15. |
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| 16. |
- Emanuel, Robyn M, et al.
(author)
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Myeloproliferative Neoplasm (MPN) Symptom Assessment Form Total Symptom Score : Prospective International Assessment of an Abbreviated Symptom Burden Scoring System Among Patients With MPNs
- 2012
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In: Journal of Clinical Oncology. - 0732-183X .- 1527-7755. ; 30:33, s. 4098-4103
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Journal article (peer-reviewed)abstract
- PURPOSE Myeloproliferative neoplasm (MPN) symptoms are troublesome to patients, and alleviation of this burden represents a paramount treatment objective in the development of MPN-directed therapies. We aimed to assess the utility of an abbreviated symptom score for the most pertinent and representative MPN symptoms for subsequent serial use in assessing response to therapy.PATIENTS AND METHODSThe Myeloproliferative Neoplasm Symptom Assessment Form total symptom score (MPN-SAF TSS) was calculated as the mean score for 10 items from two previously validated scoring systems. Questions focus on fatigue, concentration, early satiety, inactivity, night sweats, itching, bone pain, abdominal discomfort, weight loss, and fevers.RESULTS MPN-SAF TSS was calculable for 1,408 of 1,433 patients with MPNs who had a mean score of 21.2 (standard deviation [SD], 16.3). MPN-SAF TSS results significantly differed among MPN disease subtypes (P < .001), with a mean of 18.7 (SD, 15.3), 21.8 (SD, 16.3), and 25.3 (SD, 17.2) for patients with essential thrombocythemia, polycythemia vera, and myelofibrosis, respectively. The MPN-SAF TSS strongly correlated with overall quality of life (QOL; r = 0.59; P < .001) and European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire C30 (EORTC QLQ-C30) functional scales (all P < .001 and absolute r ≥ 0.50 except social functioning r = 0.48). No significant trends were present when comparing therapy subgroups. The MPN-SAF TSS had excellent internal consistency (Cronbach's α = .83). Factor analysis identified a single underlying construct, indicating that the MPN-SAF TSS is an appropriate, unified scoring method.CONCLUSIONThe MPN-SAF TSS is a concise, valid, and accurate assessment of MPN symptom burden with demonstrated clinical utility in the largest prospective MPN symptom study to date. This new prospective scoring method may be used to assess MPN symptom burden in both clinical practice and trial settings.
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| 17. |
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| 18. |
- Eschenlohr, A., et al.
(author)
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Ultrafast spin transport as key to femtosecond demagnetization
- 2013
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In: Nature Materials. - 1476-1122 .- 1476-4660. ; 12:4, s. 332-336
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Journal article (peer-reviewed)abstract
- Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a Au/Ni layered structure in which the 30 nm Au capping layer absorbs the incident laser pump pulse and subsequently use the X-ray magnetic circular dichroism technique to probe the femtosecond demagnetization of the adjacent 15 nm Ni layer. A demagnetization effect corresponding to the scenario in which the laser directly excites the Ni film is observed, but with a slight temporal delay. We explain this unexpected observation by means of the demagnetizing effect of a superdiffusive current of non-equilibrium, non-spin-polarized electrons generated in the Au layer.
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| 19. |
- Gang, Seung-gi, et al.
(author)
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Element-selective investigation of femtosecond spin dynamics in NiPd magnetic alloys using extreme ultraviolet radiation
- 2018
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:6
-
Journal article (peer-reviewed)abstract
- We studied femtosecond spin dynamics in NixPd1-x magnetic thin films by optically pumping the system with infrared (1.55 eV) laser pulses and subsequently recording the reflectivity of extreme ultraviolet (XUV) pulses synchronized with the pump pulse train. XUV light in the energy range from 20 to 72 eV was produced by laser high-harmonic generation. The reflectivity of XUV radiation at characteristic resonant energies allowed separate detection of the spin dynamics in the elemental subsystems at the M-2,M-3 absorption edges of Ni (68.0 and 66.2 eV) and N-2,N-3 edges of Pd (55.7 and 50.9 eV). The measurements were performed in transversal magneto-optical Kerr effect geometry. In static measurements, we observed a magnetic signature of the Pd subsystem due to an induced magnetization. Calculated magneto-optical asymmetries based on density functional theory show close agreement with the measured results. Femtosecond spin dynamics measured at the Ni absorption edges indicates that increasing the Pd concentration, which causes a decrease in the Curie temperature T-C, results in a drop of the demagnetization time tau(M), contrary to the tau(M) similar to 1/T-C scaling expected for single-species materials. This observation is ascribed to the increase of the Pd-mediated spin-orbit coupling in the alloy.
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| 20. |
- Geyer, Holly L., et al.
(author)
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Associations between gender, disease features and symptom burden in patients with myeloproliferative neoplasms : an analysis by the MPN QOL International Working Group
- 2017
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In: Haematologica. - : Ferrata Storti Foundation (Haematologica). - 0390-6078 .- 1592-8721. ; 102:1, s. 85-93
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Journal article (peer-reviewed)abstract
- The myeloproliferative neoplasms, including polycythemia vera, essential thrombocythemia and myelofibrosis, are distinguished by their debilitating symptom profiles, life-threatening complications and profound impact on quality of life. The role gender plays in the symptomatology of myeloproliferative neoplasms remains under-investigated. In this study we evaluated how gender relates to patients' characteristics, disease complications and overall symptom expression. A total of 2,006 patients (polycythemia vera=711, essential thrombocythemia=830, myelofibrosis=460, unknown=5) were prospectively evaluated, with patients completing the Myeloproliferative Neoplasm-Symptom Assessment Form and Brief Fatigue Inventory Patient Reported Outcome tools. Information on the individual patients' characteristics, disease complications and laboratory data was collected. Consistent with known literature, most female patients were more likely to have essential thrombocythemia (48.6% versus 33.0%; P<0.001) and most male patients were more likely to have polycythemia vera (41.8% versus 30.3%; P<0.001). The rate of thrombocytopenia was higher among males than females (13.9% versus 8.2%; P<0.001) and males also had greater red-blood cell transfusion requirements (7.3% versus 4.9%; P=0.02) with shorter mean disease duration (6.4 versus 7.2 years, P=0.03). Despite there being no statistical differences in risk scores, receipt of most therapies or prior complications (hemorrhage, thrombosis), females had more severe and more frequent symptoms for most individual symptoms, along with overall total symptom score (22.8 versus 20.3; P<0.001). Females had particularly high scores for abdominal-related symptoms (abdominal pain/discomfort) and microvascular symptoms (headache, fatigue, insomnia, concentration difficulties, dizziness; all P<0.01). Despite complaining of more severe symptom burden, females had similar quality of life scores to those of males. The results of this study suggest that gender contributes to the heterogeneity of myeloproliferative neoplasms by influencing phenotypic profiles and symptom expression.
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| 21. |
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| 22. |
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| 23. |
- Geyer, Holly, et al.
(author)
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Symptomatic Profiles of Patients With Polycythemia Vera : Implications of Inadequately Controlled Disease
- 2016
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In: Journal of Clinical Oncology. - 0732-183X .- 1527-7755. ; 34:2, s. 151-
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Journal article (peer-reviewed)abstract
- PURPOSE: Polycythemia vera (PV) is a myeloproliferative neoplasm (MPN) associated with disabling symptoms and a heightened risk of life-threatening complications. Recent studies have demonstrated the effectiveness of JAK inhibitor therapy in patients with PV patients who have a history of prior hydroxyurea (HU) use (including resistance or intolerance), phlebotomy requirements, and palpable splenomegaly. We aimed to determine how these features contribute alone and in aggregate to the PV symptom burden.PATIENTS AND METHODS: Through prospective evaluation of 1,334 patients with PV who had characterized symptom burden, we assessed patient demographics, laboratory data, and the presence of splenomegaly by disease feature (ie, known HU use, known phlebotomy requirements, splenomegaly).RESULTS: The presence of each feature in itself is associated with a moderately high symptom burden (MPN symptom assessment form [SAF] total symptom score [TSS] range, 27.7 to 29.2) that persists independent of PV risk category. In addition, symptoms incrementally increase in severity with the addition of other features. Patients with PV who had all three features (PV-HUPS) faced the highest total score (MPN-SAF TSS, 32.5) but had similar individual symptom scores to patients with known HU use (PV-HU), known phlebotomy (PV-P), and splenomegaly (PV-S).CONCLUSION: The results of this study suggest that patients with PV who have any one of the features in question (known HU use, known phlebotomy, or splenomegaly) have significant PV-associated symptoms. Furthermore, it demonstrates that many PV symptoms remain severe independent of the number of features present.
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| 24. |
- Henighan, T., et al.
(author)
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Generation mechanism of terahertz coherent acoustic phonons in Fe
- 2016
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In: PHYSICAL REVIEW B. - 2469-9950. ; 93:22
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Journal article (peer-reviewed)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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| 25. |
- Hofherr, M., et al.
(author)
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Speed and efficiency of femtosecond spin current injection into a nonmagnetic material
- 2017
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In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:10
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Journal article (peer-reviewed)abstract
- We investigate femtosecond spin injection from an optically excited Ni top layer into an Au bottom layer using time-resolved complex magneto-optical Kerr effect (C-MOKE) measurements. Employing the C-MOKE formalism, we are able to follow layer-resolved demagnetization in Ni and the simultaneous spin injection into the adjacent Au film, both occurring within similar to 40 fs. We confirm the ballistic to diffusive propagation of the spin transfer process with ab initio theory and superdiffusive transport calculations. In particular, our combined experimental-theoretical effort does allow us to quantify the so far elusive amount of spin injection, and therefore the spin injection efficiency at the interface.
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| 26. |
- Hosen, M. Mofazzel, et al.
(author)
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Discovery of topological nodal-line fermionic phase in a magnetic material GdSbTe
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Journal article (peer-reviewed)abstract
- Topological Dirac semimetals with accidental band touching between conduction and valence bands protected by time reversal and inversion symmetry are at the frontier of modern condensed matter research. A majority of discovered topological semimetals are nonmagnetic and conserve time reversal symmetry. Here we report the experimental discovery of an antiferromagnetic topological nodal-line semimetallic state in GdSbTe using angle-resolved photoemission spectroscopy. Our systematic study reveals the detailed electronic structure of the paramagnetic state of antiferromagnetic GdSbTe. We observe the presence of multiple Fermi surface pockets including a diamond-shape, and small circular pockets around the zone center and high symmetry X points of the Brillouin zone (BZ), respectively. Furthermore, we observe the presence of a Dirac-like state at the X point of the BZ and the effect of magnetism along the nodal-line direction. Interestingly, our experimental data show a robust Dirac-like state both below and above the magnetic transition temperature (TN = 13 K). Having a relatively high transition temperature, GdSbTe provides an archetypical platform to study the interaction between magnetism and topological states of matter.
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| 27. |
- Hosen, M. Mofazzel, et al.
(author)
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Distinct multiple fermionic states in a single topological metal
- 2018
-
In: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Journal article (peer-reviewed)abstract
- Among the quantum materials that have recently gained interest are the topological insulators, wherein symmetry-protected surface states cross in reciprocal space, and the Dirac nodal-line semimetals, where bulk bands touch along a line in k-space. However, the existence of multiple fermion phases in a single material has not been verified yet. Using angle-resolved photoemission spectroscopy (ARPES) and first-principles electronic structure calculations, we systematically study the metallic material Hf2Te2P and discover properties, which are unique in a single topological quantum material. We experimentally observe weak topological insulator surface states and our calculations suggest additional strong topological insulator surface states. Our first-principles calculations reveal a one-dimensional Dirac crossing—the surface Dirac-node arc—along a high-symmetry direction which is confirmed by our ARPES measurements. This novel state originates from the surface bands of a weak topological insulator and is therefore distinct from the well-known Fermi arcs in semimetals.
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| 28. |
- Hosen, M. Mofazzel, et al.
(author)
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Observation of gapless Dirac surface states in ZrGeTe
- 2018
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In: Physical Review B. - : American Physical Society. ; 97:12
-
Journal article (peer-reviewed)abstract
- The experimental discovery of the topological Dirac semimetal establishes a platform to search for various exotic quantum phases in real materials. ZrSiS-type materials have recently emerged as topological nodal-line semimetals where gapped Dirac-like surface states are observed. Here, we present a systematic angle-resolved photoemission spectroscopy (ARPES) study of ZrGeTe, a nonsymmorphic symmetry protected Dirac semimetal. We observe twoDirac-like gapless surface states at the same X point of the Brillouin zone. Our theoretical analysis and first-principles calculations reveal that these are protected by crystalline symmetry. Hence, ZrGeTe appears as a rare example of a naturally fine tuned system where the interplay between symmorphic and nonsymmorphic symmetry leads to rich phenomenology and thus opens up opportunities to investigate the physics of Dirac semimetallic and topological insulating phases realized in a single material.
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| 29. |
- Hosen, M. Mofazzel, et al.
(author)
-
Tunability of the topological nodal-line semimetal phase in ZrSiX-type materials (X = S, Se, Te)
- 2017
-
In: Physical Review B. - 2469-9950 .- 2469-9969. ; 95:16
-
Journal article (peer-reviewed)abstract
- The discovery of a topological nodal-line (TNL) semimetal phase in ZrSiS has invigorated the study of other members of this family. Here, we present a comparative electronic structure study of ZrSiX (where X = S, Se, Te) using angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Our ARPES studies show that the overall electronic structure of ZrSiX materials comprises the diamond-shaped Fermi pocket, the nearly elliptical-shaped Fermi pocket, and a small electron pocket encircling the zone center (Gamma) point, the M point, and the X point of the Brillouin zone, respectively. We also observe a small Fermi surface pocket along the M-Gamma-M direction in ZrSiTe, which is absent in both ZrSiS and ZrSiSe. Furthermore, our theoretical studies show a transition from nodal-line to nodeless gapped phase by tuning the chalcogenide from S to Te in these material systems. Our findings provide direct evidence for the tunability of the TNL phase in ZrSiX material systems by adjusting the spin-orbit coupling strength via the X anion.
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| 30. |
- Kampfrath, T., et al.
(author)
-
Terahertz spin current pulses controlled by magnetic heterostructures
- 2013
-
In: Nature Nanotechnology. - 1748-3387 .- 1748-3395. ; 8:4, s. 256-260
-
Journal article (peer-reviewed)abstract
- In spin-based electronics, information is encoded by the spin state of electron bunches(1-4). Processing this information requires the controlled transport of spin angular momentum through a solid(5,6), preferably at frequencies reaching the so far unexplored terahertz regime(7-9). Here, we demonstrate, by experiment and theory, that the temporal shape of femtosecond spin current bursts can be manipulated by using specifically designed magnetic heterostructures. A laser pulse is used to drive spins(10-12) from a ferromagnetic iron thin film into a non-magnetic cap layer that has either low (ruthenium) or high (gold) electron mobility. The resulting transient spin current is detected by means of an ultrafast, contactless amperemeter(13) based on the inverse spin Hall effect(14,15), which converts the spin flow into a terahertz electromagnetic pulse. We find that the ruthenium cap layer yields a considerably longer spin current pulse because electrons are injected into ruthenium d states, which have a much lower mobility than gold sp states(16). Thus, spin current pulses and the resulting terahertz transients can be shaped by tailoring magnetic heterostructures, which opens the door to engineering high-speed spintronic devices and, potentially, broadband terahertz emitters(7-9).
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| 31. |
- Maehrlein, Sebastian F., et al.
(author)
-
Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation
- 2018
-
In: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 4:7
-
Journal article (peer-reviewed)abstract
- To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. Here, we directly probe the flow of energy and angular momentum in the model insulating ferrimagnet yttrium iron garnet. After ultrafast resonant lattice excitation, we observe that magnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependent measurements, a spin-coupling analysis, and simulations show that the two dynamics directly reflect two stages of spin lattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet's two spin sublattices and to a previously inaccessible ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.
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| 32. |
- Maldonado, Pablo, et al.
(author)
-
Ab Initio Atomistic Thermodynamics of Water Reacting with Uranium Dioxide Surfaces
- 2014
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:16, s. 8491-8500
-
Journal article (peer-reviewed)abstract
- Using first-principles simulations, we study the temperature- and pressure-dependent adsorption reaction of water on the flat (111) and (211) and (221) stepped surfaces of uranium dioxide. Our calculations are based on the density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U) for describing the chemical interaction of water with UO2, in combination with ab initio molecular dynamics simulations to capture the temperature dependence of the reaction. We compute the pressure-temperature phase diagrams and establish the thermodynamic boundaries which govern the feasibility of water adsorption at these surfaces. Effects of water coverage on the surface adsorption reaction have been taken into account. We find that the dissociative adsorption reaction of water on stepped surfaces can be analyzed as two separated reactions, the dissociative water adsorption on the step edge and the water adsorption on the terrace. The most stable water adsorption upon modification of the water partial pressure and temperature is adsorption on the (211) step edge, followed by adsorption on the (221) step edge and being the least favorable for the (111) surface. We conclude that these UO2 surfaces will always react with water at room temperature and atmospheric pressure, leading to water dissociation and a modification of the step morphology.
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| 33. |
- Maldonado, Pablo, et al.
(author)
-
Ab Initio Prediction of Surface Stability of Fluorite Materials and Experimental Verification
- 2013
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:13, s. 6639-6650
-
Journal article (peer-reviewed)abstract
- Utilizing first-principle simulations [based on density functional theory (DFT) corrected for on-site Coulomb interactions (DFT+U)], we develop a model to explain the experimental stability in solution of materials having the fluorite structure, such as CaF2 and CeO2. It is shown that the stability of a surface is mainly dependent on its atomic structure and the presence of sites where atoms are deficiently bonded. Using as reference planes the surfaces with low surface formation energies, viz., (111), (100), and (110), our results reveal the relation between the surface energy of any Miller-indexed plane and the surface energy of those reference planes, being dependent on the fluorite surface structure only. Therefore, they follow the same trend for CaF2 and CeO2. Comparison with experimental results shows a correlation between the trends of dry surface energies and surface stabilities during dissolution of both CaF2 and CeO2, even though the chemical processes of dissolution of CeO2 and CaF2 are different. A deviation between ab initio predictions and experiments for some surfaces highlights the sensitivity of the developed model to the treatment of surface dipolar moments.
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| 34. |
- Maldonado, Pablo, et al.
(author)
-
Crystal dynamics and thermal properties of neptunium dioxide
- 2016
-
In: PHYSICAL REVIEW B. - 2469-9950. ; 93:14
-
Journal article (peer-reviewed)abstract
- We report an experimental and theoretical investigation of the lattice dynamics and thermal properties of the actinide dioxide NpO2. The energy-wave-vector dispersion relation for normal modes of vibration propagating along the [001], [110], and [111] high-symmetry lines in NpO2 at room temperature has been determined by measuring the coherent one-phonon scattering of x rays from an similar to 1.2-mg single-crystal specimen, the largest available single crystal for this compound. The results are compared against ab initio phonon dispersions computed within the first-principles density functional theory in the generalized gradient approximation plus Hubbard U correlation (GGA+U) approach, taking into account third-order anharmonicity effects in the quasiharmonic approximation. Good agreement with the experiment is obtained for calculations with an on-site Coulomb parameter U = 4 eV and Hund's exchange J = 0.6 eV in line with previous electronic structure calculations. We further compute the thermal expansion, heat capacity, thermal conductivity, phonon linewidth, and thermal phonon softening, and compare with available experiments. The theoretical and measured heat capacities are in close agreement with another. About 27% of the calculated thermal conductivity is due to phonons with energy higher than 25 meV (similar to 6 THz), suggesting an important role of high-energy optical phonons in the heat transport. The simulated thermal expansion reproduces well the experimental data up to about 1000 K, indicating a failure of the quasiharmonic approximation above this limit.
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| 35. |
- Maldonado, Pablo, et al.
(author)
-
Microscopic theory of ultrafast out-of-equilibrium magnon-phonon dynamics in insulators
- 2019
-
In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 100:1
-
Journal article (peer-reviewed)abstract
- The interaction between lattice and spins is at the heart of an extremely intriguing ultrafast dynamics in magnetic materials. In this paper, we formulate a general nonequilibrium theory that disentangles the complex interplay between phonons and magnons in a THz laser-excited antiferromagnetic insulator. The theory provides a quantitative description of the transient energy flow between the spin and lattice subsystems, subject to magnon-phonon and phonon-phonon scatterings, giving rise to finite lifetimes of the quasiparticles and to the equilibration time of the system. We predict a kind of scattering process where two magnons of opposite polarizations decay into a phonon, previously omitted in the literature. The theory is combined with first-principles calculations and then applied to simulate realistic dynamics of NiO. The main relaxation channels and hot spots in the reciprocal space, giving the strongest contribution to the energy transfer between phonons and magnons are identified. The diverse interaction strengths lead to distinct coupled dynamics of the lattice and spin systems and subsequently to different equilibration timescales.
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| 36. |
- Maldonado, Pablo, et al.
(author)
-
Theory of out-of-equilibrium ultrafast relaxation dynamics in metals
- 2017
-
In: Physical Review B. - 2469-9950 .- 2469-9969. ; 96:17
-
Journal article (peer-reviewed)abstract
- Ultrafast laser excitation of a metal causes correlated, highly nonequilibrium dynamics of electronic and ionic degrees of freedom, which are, however, only poorly captured by the widely used two-temperature model. Here we develop an out-of-equilibrium theory that captures the full dynamic evolution of the electronic and phononic populations and provides a microscopic description of the transfer of energy delivered optically into electrons to the lattice. All essential nonequilibrium energy processes, such as electron-phonon and phonon-phonon interactions are taken into account. Moreover, as all required quantities are obtained from first-principles calculations, the model gives a realistic and material-dependent description of the relaxation dynamics without the need for fitted parameters. We apply the model to FePt and show that the detailed relaxation is out-of-equilibrium for ps.
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| 37. |
- Maldonado, Pablo, et al.
(author)
-
Tracking the ultrafast nonequilibrium energy flow between electronic and lattice degrees of freedom in crystalline nickel
- 2020
-
In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:10
-
Journal article (peer-reviewed)abstract
- Femtosecond laser excitation of solid-state systems creates out-of-equilibrium hot electrons that cool down by transferring their energy to other degrees of freedom and ultimately to lattice vibrations of the solid. By combining ab initio calculations with ultrafast diffuse electron scattering, we gain a detailed understanding of the complex nonequilibrium energy transfer between electrons and phonons in laser-excited Ni metal. Our experimental results show that the wave-vector-resolved population dynamics of phonon modes is distinctly different throughout the Brillouin zone and are in remarkable agreement with our theoretical results. We find that zone-boundary phonon modes become occupied first. As soon as the energy in these modes becomes larger than the average electron energy, a backflow of energy from lattice to electronic degrees of freedom occurs. Subsequent excitation of lower-energy phonon modes drives the thermalization of the whole system on the picosecond time scale. We determine the evolving nonequilibrium phonon occupations, which we find to deviate markedly from thermal occupations.
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| 38. |
- Maldonado, Pablo, et al.
(author)
-
Two-step spin-switchable tetranuclear Fe(II) molecular solid : Ab initio theory and predictions
- 2013
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 88:2, s. 020408-
-
Journal article (peer-reviewed)abstract
- Using density functional theory supplemented with on-site Coulomb U interaction in combination with ab initio molecular dynamics simulations, we investigate the spin-crossover (SCO) properties of a Fe(II) based cyanide-bridged square molecular system, [Fe-4(II)(mu-CN)(4)(bpy)(4)(tpa)(2)](PF6)(4) (where bpy = 2,2'-bipyridine and tpa = tris(2-pyridylmethyl) amine], exhibiting a two-step SCO transition. The ab initio calculated SCO temperatures are found to show remarkably good agreement with experimentally measured spin conversion temperatures [M. Nihei et al., Angew. Chem., Int. Ed. 44, 6484 (2005)]. Our theoretical study predicts further chemo switching of the spin state by introduction of guest molecules such as CO2, CS2, and H2O into the porous topology of the system, which would add another dimensionality to this interesting material.
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| 39. |
- Neupane, Madhab, et al.
(author)
-
Observation of topological nodal fermion semimetal phase in ZrSiS
- 2016
-
In: PHYSICAL REVIEW B. - 2469-9950. ; 93:20
-
Journal article (peer-reviewed)abstract
- Unveiling new topological phases of matter is one of the current objectives in condensed matter physics. Recent experimental discoveries of Dirac and Weyl semimetals prompt the search for other exotic phases of matter. Here we present a systematic angle-resolved photoemission spectroscopy study of ZrSiS, a prime topological nodal semimetal candidate. Our wider Brillouin zone (BZ) mapping shows multiple Fermi surface pockets such as the diamond-shaped Fermi surface, elliptical-shaped Fermi surface, and a small electron pocket encircling at the zone center (Gamma) point, the M point, and the X point of the BZ, respectively. We experimentally establish the spinless nodal fermion semimetal phase in ZrSiS, which is supported by our first-principles calculations. Our findings evidence that the ZrSiS-type of material family is a new platform on which to explore exotic states of quantum matter; these materials are expected to provide an avenue for engineering two-dimensional topological insulator systems.
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| 40. |
- Noguere, G., et al.
(author)
-
Doppler broadening of neutron-induced resonances using ab initio phonon spectrum
- 2018
-
In: The European Physical Journal Plus. - : Springer Berlin/Heidelberg. - 2190-5444. ; 133:5
-
Journal article (peer-reviewed)abstract
- Neutron resonances observed in neutron cross section data can only be compared with their theoretical analogues after a correct broadening of the resonance widths. This broadening is usually carried out by two different theoretical models, namely the Free Gas Model and the Crystal Lattice Model, which, however, are only applicable under certain assumptions. Here, we use neutron transmission experiments on UO2 samples at T = 23.7 K and T = 293.7 K, to investigate the limitations of these models when an ab initio phonon spectrum is introduced in the calculations. Comparisons of the experimental and theoretical transmissions highlight the underestimation of the energy transferred at low temperature and its impact on the accurate determination of the radiation widths Gamma(gamma lambda) of the U-238 resonances lambda. The observed deficiency of the model represents an experimental evidence that the Debye-Waller factor is not correctly calculated at low temperature near the Neel temperature (T-N = 30.8 K).
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| 41. |
- Prasad, Amit Kumar, et al.
(author)
-
Nonequilibrium Phonon Dynamics and Its Impact on the Thermal Conductivity of the Benchmark Thermoelectric Material SnSe
- 2023
-
In: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 17:21, s. 21006-21017
-
Journal article (peer-reviewed)abstract
- Thermoelectric materials play a vital role in the pursuit of a sustainable energy system by allowing the conversion of waste heat to electric energy. Low thermal conductivity is essential to achieving high-efficiency conversion. The conductivity depends on an interplay between the phononic and electronic properties of the nonequilibrium state. Therefore, obtaining a comprehensive understanding of nonequilibrium dynamics of the electronic and phononic subsystems as well as their interactions is key for unlocking the microscopic mechanisms that ultimately govern thermal conductivity. A benchmark material that exhibits ultralow thermal conductivity is SnSe. We study the nonequilibrium phonon dynamics induced by an excited electron population using a framework combining ultrafast electron diffuse scattering and nonequilibrium kinetic theory. This in-depth approach provides a fundamental understanding of energy transfer in the spatiotemporal domain. Our analysis explains the dynamics leading to the observed low thermal conductivity, which we attribute to a mode-dependent tendency to nonconservative phonon scattering. The results offer a penetrating perspective on energy transport in condensed matter with far-reaching implications for rational design of advanced materials with tailored thermal properties.
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| 42. |
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| 43. |
- Reid, A. H., et al.
(author)
-
Beyond a phenomenological description of magnetostriction
- 2018
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
-
Journal article (peer-reviewed)abstract
- Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction-the underlying magnetoelastic stress-can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the subpicosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.
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| 44. |
- Ritzmann, Ulrike, et al.
(author)
-
High-frequency magnon excitation due to femtosecond spin-transfer torques
- 2020
-
In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 101:17
-
Journal article (peer-reviewed)abstract
- Femtosecond laser pulses can induce ultrafast demagnetization as well as generate bursts of hot-electron spin currents. In trilayer spin valves consisting of two metallic ferromagnetic layers separated by a nonmagnetic one, hot-electron spin currents excited by an ultrashort laser pulse propagate from the first ferromagnetic layer through the spacer, reaching the second magnetic layer. When the magnetizations of the two magnetic layers are noncollinear, this spin current exerts a torque on magnetic moments in the second ferromagnet. Since this torque is acting only within the subpicosecond timescale, it excites coherent high-frequency magnons, as recently demonstrated in experiments. Here, we calculate the temporal shape of the hot-electron spin currents using the superdiffusive transport model and simulate the response of the magnetic system to the resulting ultrashort spin-transfer torque pulse by means of atomistic spin-dynamics simulations. Our results confirm that the acting spin-current pulse is short enough to excite magnons with frequencies beyond 1 THz, a frequency range out of reach for current-induced spin-transfer torques. We demonstrate the formation of thickness-dependent standing spin waves during the first picoseconds after laser excitation. In addition, we vary the penetration depth of the spin-transfer torque to reveal its influence on the excited magnons. Our simulations clearly show a suppression effect of magnons with short wavelengths already for penetration depths in the range of 1 nm, confirming experimental findings reporting penetration depths below 2 nm.
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| 45. |
- Ritzmann, Ulrike, et al.
(author)
-
Theory of out-of-equilibrium electron and phonon dynamics in metals after femtosecond laser excitation
- 2020
-
In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:21
-
Journal article (peer-reviewed)abstract
- The dynamics of electrons and phonons in metals upon laser excitation are often described by the two-temperature model, which assumes that both subsystems are individually in thermal equilibrium. However, recent experiments show that this description is not sufficient to describe the out-of-equilibrium dynamics on ultrashort timescales. Here, assuming a thermalized electronic system, we extend and apply a parameter-free microscopic out-of-equilibrium model to describe the ultrafast laser-induced phonon and electron temperature dynamics of various metallic systems such as gold, aluminum, iron, nickel, and cobalt. We report strong deviations from the two-temperature model on the picosecond timescale for all the materials studied, even for those where the assumption of separate thermal equilibrium seemed less restrictive, like in gold. Furthermore, we demonstrate the importance of the mode dependence of the electron-phonon coupling for the relaxation process and reveal the significance of this channel in the lattice equilibration.
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| 46. |
- Rudolf, Dennis, et al.
(author)
-
Element Selective Investigation of Spin Dynamics in Magnetic Multilayers
- 2015
-
In: Ultrafast Magnetism I. - Cham : Springer International Publishing. - 9783319077437 - 9783319077420 ; , s. 307-309
-
Conference paper (peer-reviewed)abstract
- Our understanding of ultrafast switching processes in novel spin-based electronics depends on our detailed knowledge of interactions between spin, charge and phonons in magnetic structures. We present element-selective studies, using extreme ultraviolet (XUV) light, to gain insight into spin dynamics in exchange coupled magnetic multilayers on the femtosecond time scale.
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| 47. |
- Rudolf, Dennis, et al.
(author)
-
Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current
- 2012
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 1037-
-
Journal article (peer-reviewed)abstract
- Uncovering the physical mechanisms that govern ultrafast charge and spin dynamics is crucial for understanding correlated matter as well as the fundamental limits of ultrafast spin-based electronics. Spin dynamics in magnetic materials can be driven by ultrashort light pulses, resulting in a transient drop in magnetization within a few hundred femtoseconds. However, a full understanding of femtosecond spin dynamics remains elusive. Here we spatially separate the spin dynamics using Ni/Ru/Fe magnetic trilayers, where the Ni and Fe layers can be ferroor antiferromagnetically coupled. By exciting the layers with a laser pulse and probing the magnetization response simultaneously but separately in Ni and Fe, we surprisingly find that optically induced demagnetization of the Ni layer transiently enhances the magnetization of the Fe layer when the two layer magnetizations are initially aligned parallel. Our observations are explained by a laser-generated superdiffusive spin current between the layers.
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| 48. |
- Scotch, Allison H, et al.
(author)
-
Symptom burden profile in myelofibrosis patients with thrombocytopenia : Lessons and unmet needs
- 2017
-
In: Leukemia Research. - : Elsevier BV. - 0145-2126 .- 1873-5835. ; 63, s. 34-40
-
Journal article (peer-reviewed)abstract
- Myelofibrosis is a myeloproliferative neoplasm associated with progressive cytopenias and high symptom burden. MF patients with thrombocytopenia have poor prognosis but the presence of thrombocytopenia frequently precludes the use of JAK2 inhibitors. In this study, we assessed quality of life and symptom burden in 418 MF patients with (n = 89) and without (n = 329) thrombocytopenia using prospective data from the MPN-QOL study group database, including the Myeloproliferative Neoplasm Symptom Assessment Form (MPN-SAF) and Total Symptom Score (MPN10). Thrombocytopenia, defined as platelet count < 100 x10(9)/L (moderate 51-100 x 10(9)/L; severe <= 50 x10(9)/L), was associated with anemia (76% vs. 45%, p < 0.001), leukopenia (29% vs. 11%, p < 0.001), and need for red blood cell transfusion (35% vs. 19%, p = 0.002). Thrombocytopenic patients had more fatigue, early satiety, inactivity, dizziness, sad mood, cough, night sweats, itching, fever, and weight loss; total symptom scores were also higher (33 vs. 24, p < 0.001). Patients with severe thrombocytopenia were more likely to have anemia (86% vs. 67%, p = 0.04), leukopenia (40% vs. 20%, p = 0.04), and transfusion requirements (51% vs. 20%, p = 0.002) but few differences in symptoms when compared to patients with moderate thrombocytopenia. These results suggest that MF patients with thrombocytopenia experience greater symptomatic burden than MF patients without thrombocytopenia and may benefit from additional therapies.
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| 49. |
- Seifert, T., et al.
(author)
-
Efficient metallic spintronic emitters of ultrabroadband terahertz radiation
- 2016
-
In: Nature Photonics. - 1749-4885 .- 1749-4893. ; 10:7, s. 483-
-
Journal article (peer-reviewed)abstract
- Terahertz electromagnetic radiation is extremely useful for numerous applications, including imaging and spectroscopy. It is thus highly desirable to have an efficient table-top emitter covering the 1-30 THz window that is driven by a low-cost, low-power femtosecond laser oscillator. So far, all solid-state emitters solely exploit physics related to the electron charge and deliver emission spectra with substantial gaps. Here, we take advantage of the electron spin to realize a conceptually new terahertz source that relies on three tailored fundamental spintronic and photonic phenomena in magnetic metal multilayers: ultrafast photoinduced spin currents, the inverse spin-Hall effect and a broadband Fabry-Perot resonance. Guided by an analytical model, this spintronic route offers unique possibilities for systematic optimization. We find that a 5.8-nm-thick W/CoFeB/Pt trilayer generates ultrashort pulses fully covering the 1-30 THz range. Our novel source outperforms laser-oscillator-driven emitters such as ZnTe(110) crystals in terms of bandwidth, terahertz field amplitude, flexibility, scalability and cost.
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| 50. |
- Shokeen, Vishal, et al.
(author)
-
Real-time observation of non-equilibrium phonon-electron energy and angular momentum flow in laser-heated nickel
- 2024
-
In: Science Advances. - : American Association For Cancer Research (AACR). - 2375-2548. ; 10:5
-
Journal article (peer-reviewed)abstract
- Identifying the microscopic nature of non-equilibrium energy transfer mechanisms among electronic, spin, and lattice degrees of freedom is central to understanding ultrafast phenomena such as manipulating magnetism on the femtosecond timescale. Here, we use time- and angle-resolved photoemission spectroscopy to go beyond the often-used ensemble-averaged view of non-equilibrium dynamics in terms of quasiparticle temperature evolutions. We show for ferromagnetic Ni that the non-equilibrium electron and spin dynamics display pronounced variations with electron momentum, whereas the magnetic exchange interaction remains isotropic. This highlights the influence of lattice-mediated scattering processes and opens a pathway toward unraveling the still elusive microscopic mechanism of spin-lattice angular momentum transfer.
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