| 1. |
- Turenne, Diego, et al.
(författare)
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Nonequilibrium sub–10 nm spin-wave soliton formation in FePt nanoparticles
- 2022
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:13
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic nanoparticles such as FePt in the L10 phase are the bedrock of our current data storage technology. As the grains become smaller to keep up with technological demands, the superparamagnetic limit calls for materials with higher magnetocrystalline anisotropy. This, in turn, reduces the magnetic exchange length to just a few nanometers, enabling magnetic structures to be induced within the nanoparticles. Here, we describe the existence of spin-wave solitons, dynamic localized bound states of spin-wave excitations, in FePt nanoparticles. We show with time-resolved x-ray diffraction and micromagnetic modeling that spin-wave solitons of sub–10 nm sizes form out of the demagnetized state following femtosecond laser excitation. The measured soliton spin precession frequency of 0.1 THz positions this system as a platform to develop novel miniature devices.
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| 2. |
- Li, Xin, et al.
(författare)
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Innovation of International Logistics Talent Training Mode in Applied Undergraduate Colleges and Universities Based on the ‘Belt and Road’
- 2023
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Ingår i: Advances in Artificial Systems for Medicine and Education VI. - Cham : Springer Nature. ; , s. 624-633
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Under the tide of world multi polarization and economic globalization, the internationalization of higher education has become the general trend. Implementing the ‘going out’ strategy and cultivating international logistics talents are the internal needs of Application-oriented Undergraduate Colleges and universities to adapt to the development trend of higher education, and also the internal needs of Application-oriented Undergraduate Colleges and universities to improve the level of running a school. At present, in terms of international logistics talent training, there are some problems in the undergraduate of application-oriented universities, such as the lack of international logistics talent training platform and funds, the lack of international teaching staff, and the imperfect teaching system of international logistics talent training. In view of these problems, this topic introduces the guiding ideology of the ‘the Belt and Road’ and builds an application-oriented undergraduate university, which can explore the cultivation of international logistics talents from the aspects of the construction of an international logistics talent training platform, giving full play to its own characteristics and advantages, improving the curriculum, teaching and evaluation system, and promoting the internationalization of professional construction, so as to continuously improve the cultivation level of international logistics talents.
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| 3. |
- Wang, Xiaocui, et al.
(författare)
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Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation
- 2022
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Ingår i: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 237:0, s. 300-316
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Tidskriftsartikel (refereegranskat)abstract
- Wide-band-gap insulators such as NiO offer the exciting prospect of coherently manipulating electronic correlations with strong optical fields. Contrary to metals where rapid dephasing of optical excitation via electronic processes occurs, the sub-gap excitation in charge-transfer insulators has been shown to couple to low-energy bosonic excitations. However, it is currently unknown if the bosonic dressing field is composed of phonons or magnons. Here we use the prototypical charge-transfer insulator NiO to demonstrate that 1.5 eV sub-gap optical excitation leads to a renormalised NiO band-gap in combination with a significant reduction of the antiferromagnetic order. We employ element-specific X-ray reflectivity at the FLASH free-electron laser to demonstrate the reduction of the upper band-edge at the O 1s-2p core-valence resonance (K-edge) whereas the antiferromagnetic order is probed via X-ray magnetic linear dichroism (XMLD) at the Ni 2p-3d resonance (L-2-edge). Comparing the transient XMLD spectral line shape to ground-state measurements allows us to extract a spin temperature rise of 65 +/- 5 K for time delays longer than 400 fs while at earlier times a non-equilibrium spin state is formed. We identify transient mid-gap states being formed during the first 200 fs accompanied by a band-gap reduction lasting at least up to the maximum measured time delay of 2.4 ps. Electronic structure calculations indicate that magnon excitations significantly contribute to the reduction of the NiO band gap.
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| 4. |
- Bengtsson, Å U J, et al.
(författare)
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Repetitive non-thermal melting as a timing monitor for femtosecond pump/probe X-ray experiments
- 2020
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 7:5, s. 054303-054303
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved optical pump/X-ray probe experiments are often used to study structural dynamics. To ensure high temporal resolution, it is necessary to monitor the timing between the X-ray pulses and the laser pulses. The transition from a crystalline solid material to a disordered state in a non-thermal melting process can be used as a reliable timing monitor. We have performed a study of the non-thermal melting of InSb in single-shot mode, where we varied the sample temperature in order to determine the conditions required for repetitive melting. We show how experimental conditions affect the feasibility of such a timing tool.
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| 5. |
- Enquist, Henrik, et al.
(författare)
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FemtoMAX - An X-ray beamline for structural dynamics at the short-pulse facility of MAX IV
- 2018
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495. ; 25:2, s. 570-579
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Tidskriftsartikel (refereegranskat)abstract
- The FemtoMAX beamline facilitates studies of the structural dynamics of materials. Such studies are of fundamental importance for key scientific problems related to programming materials using light, enabling new storage media and new manufacturing techniques, obtaining sustainable energy by mimicking photosynthesis, and gleaning insights into chemical and biological functional dynamics. The FemtoMAX beamline utilizes the MAX IV linear accelerator as an electron source. The photon bursts have a pulse length of 100fs, which is on the timescale of molecular vibrations, and have wavelengths matching interatomic distances (Å). The uniqueness of the beamline has called for special beamline components. This paper presents the beamline design including ultrasensitive X-ray beam-position monitors based on thin Ce:YAG screens, efficient harmonic separators and novel timing tools.The FemtoMAX beamline facilitates studies of the structural dynamics of materials on the femtosecond timescale. The first commissioning results are presented.
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| 6. |
- Jarnac, A., et al.
(författare)
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Communication : Demonstration of a 20 ps X-ray switch based on a photoacoustic transducer
- 2017
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 4:5
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Tidskriftsartikel (refereegranskat)abstract
- We have studied an X-ray switch based on a gold coated indium antimonide crystal using time-resolved X-ray diffraction and demonstrated that the switch could reduce the pulse duration of a 100 ps X-ray pulse down to 20 ps with a peak reflectivity of 8%. We have used a dynamical diffraction code to predict the performance of the switch, which was then confirmed experimentally. The experiment was carried out at the FemtoMAX beamline at the short-pulse facility of the MAX IV laboratory. The performance and limitation of the switch are discussed in terms of acoustic transport properties between the two materials and the electron transport properties of gold.
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| 7. |
- Persson, A. I H, et al.
(författare)
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Studies of electron diffusion in photo-excited Ni using time-resolved X-ray diffraction
- 2016
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 109:20
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Tidskriftsartikel (refereegranskat)abstract
- We show that the heat deposition profile in a laser-excited metal can be determined by time-resolved X-ray diffraction. In this study, we investigated the electron diffusion in a 150 nm thick nickel film deposited on an indium antimonide substrate. A strain wave that mimics the heat deposition profile is generated in the metal and propagates into the InSb, where it influences the temporal profile of X-rays diffracted from InSb. We found that the strain pulse significantly deviated from a simple exponential profile, and that the two-temperature model was needed to reproduce the measured heat deposition profile. Experimental results were compared to simulations based on the two-temperature model carried out using commercial finite-element software packages and on-line dynamical diffraction tools. To reproduce the experimental data, the electron-phonon coupling factor was lowered compared to previously measured values. The experiment was carried out at a third-generation synchrotron radiation source using a high-brightness beam and an ultrafast X-ray streak camera with a temporal resolution of 3 ps.
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| 8. |
- Shokeen, Vishal, et al.
(författare)
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Real-time observation of non-equilibrium phonon-electron energy and angular momentum flow in laser-heated nickel
- 2024
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Ingår i: Science Advances. - : American Association For Cancer Research (AACR). - 2375-2548. ; 10:5
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Wang, Xiaocui, et al.
(författare)
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Generation of a large compressive strain wave in graphite by ultrashort-pulse laser irradiation
- 2019
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Ingår i: Structural Dynamics. - : AIP Publishing. - 2329-7778. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- We have studied strain wave generation in graphite induced by an intense ultrashort laser pulse. The study was performed in the intensity regime above the ablation threshold of graphite. The aim was to maximize the strain and, thus, also the internal pressure (stress). Laser pulses with a 1 ps temporal duration melt the surface of graphite resulting in a molten material which initially exists at the solid density. As the molten material expands, a compressive strain wave starts propagating into the crystal below the molten layer. The strain pulse was studied with time-resolved X-ray diffraction. At a temporal delay of 100 ps after laser excitation, we observed >10% compressive strain, which corresponds to a pressure of 7.2 GPa. This strain could be reproduced by hydrodynamic simulations, which also provided a temperature map as a function of time and depth.
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| 10. |
- Wang, Xiaocui, et al.
(författare)
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Role of Thermal Equilibrium Dynamics in Atomic Motion during Nonthermal Laser-Induced Melting
- 2020
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Ingår i: Physical Review Letters. - 1079-7114. ; 124:10
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that initial atomic velocities as given by thermodynamics play an important role in the dynamics of phase transitions. We tracked the atomic motion during nonthermal laser-induced melting of InSb at different initial temperatures. The ultrafast atomic motion following bond breaking can in general be governed by two mechanisms: the random velocity of each atom at the time of bond breaking (inertial model), and the forces acting on the atoms after bond breaking. The melting dynamics was found to follow the inertial model over a wide temperature range.
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| 11. |
- Wang, Xiaocui, et al.
(författare)
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Seven Questions on the Chemical Ecology and Neurogenetics of Resource-Mediated Speciation
- 2021
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Ingår i: Frontiers in Ecology and Evolution. - : Frontiers Media SA. - 2296-701X. ; 9
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Forskningsöversikt (refereegranskat)abstract
- Adaptation to different environments can result in reproductive isolation between populations and the formation of new species. Food resources are among the most important environmental factors shaping local adaptation. The chemosensory system, the most ubiquitous sensory channel in the animal kingdom, not only detects food resources and their chemical composition, but also mediates sexual communication and reproductive isolation in many taxa. Chemosensory divergence may thus play a crucial role in resource-mediated adaptation and speciation. Understanding how the chemosensory system can facilitate resource-mediated ecological speciation requires integrating mechanistic studies of the chemosensory system with ecological studies, to link the genetics and physiology of chemosensory properties to divergent adaptation. In this review, we use examples of insect research to present seven key questions that can be used to understand how the chemosensory system can facilitate resource-mediated ecological speciation in consumer populations.
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| 12. |
- Wang, Xiaocui
(författare)
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Time-Resolved Diffraction Studies of Structural Dynamics in Solids
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Studies of the structural dynamics of solids can improve our understanding of atomic motion in materials, and may thus help in the manufacture of new devices or the development of materials with novel structures and properties. Ultrashort laser pulses, a few tens of femtoseconds long, can deliver high energies (mJ–kJ). This energy is absorbed by the electrons in a solid material, leading to a rapid increase in the electron temperature within the duration of the laser pulse. The energy will then be transferred to the crystal lattice, resulting in an increase in the lattice temperature, which triggers lattice motion such as vibrations (phonons) and disordering (melting of solids). The distance between neighboring atoms in solids is on the order of 10^(-10) m (Ångström). Since the wavelength of X-rays is in the range of nanometers to Ångströms, which is of the same order as the interatomic distances in solids, X-rays can be used to detect structural changes in solids. The structural dynamics in solids can then be monitored as a function of time by combining ultrashort laser pulses with X-ray techniques. This thesis focuses on the structural dynamics of solids on the time scale of femtoseconds to picoseconds. The studies described in this thesis were divided into two categories based on the laser excitation fluence: below the damage threshold of the sample, and above the damage threshold of the sample. The electron diffusion in a Ni film was studied at fluences below the damage threshold, using a Ni/InSb photo-acoustic transducer. An X-ray switch based on a Au/InSb photo-acoustic transducer was designed and tested as part of the commissioning of the FemtoMAX beamline at the MAX IV Laboratory in Lund. Using fluences above the damage threshold, pressure waves were generated in an Al/InSb photo-acoustic transducer due to the melting of the Al film. The pressure waves were probed and characterized in the InSb substrate. The pressure was in the region of the phase diagram where phase transition could occur. Pressure waves with a similar amplitude were also generated and characterized in graphite. Non-thermal melting was also studied in InSb at fluences above the damage threshold. The findings presented in this thesis contribute to both applications of physics for the manufacture of new devices, and to fundamental physics, by improving our understanding of hydrodynamic pressure waves and phase transitions. The study involving the Ni/InSb photo-acoustic transducer demonstrated an alternative method of characterizing the basic physical properties of a metallic film, while the Au/InSb switch provides a potential means of generating short X-ray pulses at storage rings. The characterization of the pressure waves in the Al/InSb photo-acoustic transducer and graphite extend the current knowledge on the generation of short pressure pulses in solids on the picosecond time scale, which attracts more attention to understand the phase transition process on the ultrafast time scale. The study of non-thermal melting provided new approaches for timing diagnostics at free-electron laser facilities.
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