| 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. |
- John Mukkattukavil, Deepak, 1993-
(författare)
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Resonant Inelastic X-ray Scattering Studies on Quasi-Two-Dimensional Superconducting Materials
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Unconventional superconductivity is one of the many fascinating research areas of condensed matter physics. Understanding the superconducting pairing mechanism and its connection with other competing states remains unclear. This thesis investigates electronic transitions, charge, and spin fluctuations of various single-crystalline superconductors using a combination of x-ray absorption, x-ray emission, and resonant inelastic x-ray scattering techniques. Room temperature x-ray absorption, x-ray emission, and partial fluorescence yield measurements were carried out on LaPt2Si2 single crystal at the Si 2p and La 4d edges. Atomic-like transitions from La 4d to 4f are observed in x-ray absorption and x-ray emission measurements. The x-ray emission spectrum of LaPt2Si2 at the Si 2p edge is compared to the Si p and d local partial density of states. Resonant inelastic x-ray scattering measurements on YFe2Ge2 single crystal are also presented in this thesis. Magnon dispersion in YFe2Ge2 crystal along (h,0) and (h,h) directions are extracted from resonant inelastic x-ray scattering spectra and inelastic neutron scattering experiments. The magnon dispersion is fitted with the dispersion relation for a square lattice using the nearest and next-nearest neighbor exchange interaction. In YFe2Ge2, the ferromagnetic exchange interaction is higher than the antiferromagnetic interaction. High-resolution resonant inelastic x-ray scattering spectra were measured on La1.675Eu0.2Sr0.125CuO4 superconductor at various temperatures. Charge density fluctuations with shorter correlation lengths have been shown to exist above the structural transition up to 200 K in La1.675Eu0.2Sr0.125CuO4. Phonon dispersion relation has also been mapped from high-resolution resonant inelastic x-ray scattering spectra. Softening of optical phonon mode in La1.675Eu0.2Sr0.125CuO4 is observed at low and high temperatures coinciding with the charge density wave vector.
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| 3. |
- Mukkattukavil, Deepak John, 1993-, et al.
(författare)
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Resonant inelastic soft x-ray scattering on LaPt2Si2
- 2022
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 34:32
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Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and resonant inelastic x-ray scattering spectra of LaPt2Si2 single crystal at the Si 2p and La 4d edges are presented. The data are interpreted in terms of density functional theory, showing that the Si spectra can be described in terms of Si s and d local partial density of states (LPDOS), and the La spectra are due to quasi-atomic local 4f excitations. Calculations show that Pt d-LPDOS dominates the occupied states, and a sharp localized La f state is found in the unoccupied states, in line with the observations.
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| 4. |
- Wang, Q., et al.
(författare)
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Charge order lock-in by electron-phonon coupling in La 1.675 Eu 0.2 Sr 0.125 CuO 4
- 2021
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Ingår i: Science advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:27
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Tidskriftsartikel (refereegranskat)abstract
- Charge order is universal to all hole-doped cuprates. Yet, the driving interactions remain an unsolved problem. Electron-electron interaction is widely believed to be essential, whereas the role of electron-phonon interaction is unclear. We report an ultrahigh-resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La1.675Eu0.2Sr0.125CuO4. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that, in addition to electronic correlations, electron-phonon coupling contributes substantially to the emergence of long-range charge-stripe order in cuprates.
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| 5. |
- Wang, Qisi, et al.
(författare)
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Ferromagnetic exchange interaction probed in YFe2Ge2 by resonant inelastic x-ray scattering
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report a combined resonant inelastic x-ray scattering and inelastic neutron scattering study of YFe2Ge2. Our data reveal that the A-type magnetic excitations are dominating over the whole energy range suggestive of a ferromagnetic fluctuation mediated p-wave Cooper pairing in this compound. As the magnetic frustration is mediated by conduction electrons which could be highly tunable, for example by doping (pressure), Our results, therefore, suggest the possibility of enhancing Tc in this system.
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