| 1. |
|
|
| 2. |
- Ryan, Sinéad A., et al.
(författare)
-
Optically controlling the competition between spin flips and intersite spin transfer in a Heusler half-metal on sub-100-fs time scales
- 2023
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 9:45, s. 1428-
-
Tidskriftsartikel (refereegranskat)abstract
- The direct manipulation of spins via light may provide a path toward ultrafast energy-efficient devices. However, distinguishing the microscopic processes that can occur during ultrafast laser excitation in magnetic alloys is challenging. Here, we study the Heusler compound Co2MnGa, a material that exhibits very strong light-induced spin transfers across the entire M-edge. By combining the element specificity of extreme ultraviolet high-harmonic probes with time-dependent density functional theory, we disentangle the competition between three ultrafast light-induced processes that occur in Co2MnGa: same-site Co-Co spin transfer, intersite Co-Mn spin transfer, and ultrafast spin flips mediated by spin-orbit coupling. By measuring the dynamic magnetic asymmetry across the entire M-edges of the two magnetic sublattices involved, we uncover the relative dominance of these processes at different probe energy regions and times during the laser pulse. Our combined approach enables a comprehensive microscopic interpretation of laser-induced magnetization dynamics on time scales shorter than 100 femtoseconds.
|
|
| 3. |
- Fan, Tingting, et al.
(författare)
-
Bright circularly polarized soft X-ray high harmonics for X-ray magnetic circular dichroism
- 2015
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 112:46, s. 14206-14211
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate, to our knowledge, the first bright circularly polarized high-harmonic beams in the soft X-ray region of the electromagnetic spectrum, and use them to implement X-ray magnetic circular dichroism measurements in a tabletop-scale setup. Using counterrotating circularly polarized laser fields at 1.3 and 0.79 mu m, we generate circularly polarized harmonics with photon energies exceeding 160 eV. The harmonic spectra emerge as a sequence of closely spaced pairs of left and right circularly polarized peaks, with energies determined by conservation of energy and spin angular momentum. We explain the single-atom and macroscopic physics by identifying the dominant electron quantum trajectories and optimal phase-matching conditions. The first advanced phase-matched propagation simulations for circularly polarized harmonics reveal the influence of the finite phase-matching temporal window on the spectrum, as well as the unique polarization-shaped attosecond pulse train. Finally, we use, to our knowledge, the first tabletop X-ray magnetic circular dichroism measurements at the N-4,N-5 absorption edges of Gd to validate the high degree of circularity, brightness, and stability of this light source. These results demonstrate the feasibility of manipulating the polarization, spectrum, and temporal shape of high harmonics in the soft X-ray region by manipulating the driving laser waveform.
|
|
| 4. |
- Hickstein, Daniel D., et al.
(författare)
-
Direct Visualization of Laser-Driven Electron Multiple Scattering and Tunneling Distance in Strong-Field Ionization
- 2012
-
Ingår i: Physical Review Letters. - 1079-7114. ; 109:7
-
Tidskriftsartikel (refereegranskat)abstract
- Using a simple model of strong-field ionization of atoms that generalizes the well-known 3-step model from 1D to 3D, we show that the experimental photoelectron angular distributions resulting from laser ionization of xenon and argon display prominent structures that correspond to electrons that pass by their parent ion more than once before strongly scattering. The shape of these structures can be associated with the specific number of times the electron is driven past its parent ion in the laser field before scattering. Furthermore, a careful analysis of the cutoff energy of the structures allows us to experimentally measure the distance between the electron and ion at the moment of tunnel ionization. This work provides new physical insight into how atoms ionize in strong laser fields and has implications for further efforts to extract atomic and molecular dynamics from strong-field physics.
|
|
| 5. |
- Hickstein, Daniel D., et al.
(författare)
-
Non-collinear generation of angularly isolated circularly polarized high harmonics
- 2015
-
Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 9:11, s. 743-750
-
Tidskriftsartikel (refereegranskat)abstract
- We generate angularly isolated beams of circularly polarized extreme ultraviolet light through the first implementation of non-collinear high harmonic generation with circularly polarized driving lasers. This non-collinear technique offers numerous advantages over previous methods, including the generation of higher photon energies, the separation of the harmonics from the pump beam, the production of both left and right circularly polarized harmonics at the same wavelength and the capability of separating the harmonics without using a spectrometer. To confirm the circular polarization of the beams and to demonstrate the practicality of this new light source, we measure the magnetic circular dichroism of a 20 nm iron film. Furthermore, we explain the mechanisms of non-collinear high harmonic generation using analytical descriptions in both the photon and wave models. Advanced numerical simulations indicate that this non-collinear mixing enables the generation of isolated attosecond pulses with circular polarization.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
- Rudolf, Dennis, et al.
(författare)
-
Element Selective Investigation of Spin Dynamics in Magnetic Multilayers
- 2015
-
Ingår i: Ultrafast Magnetism I. - Cham : Springer International Publishing. - 9783319077437 - 9783319077420 ; , s. 307-309
-
Konferensbidrag (refereegranskat)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.
|
|
| 9. |
- Rudolf, Dennis, et al.
(författare)
-
Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current
- 2012
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 1037-
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 10. |
- Tao, Zhensheng, et al.
(författare)
-
The nature of non-equilibrium ultrafast demagnetization in ferromagnetic nickel
- 2019
-
Ingår i: Eleventh International Conference On Information Optics And Photonics (CIOP 2019). - : SPIE. - 9781510631748
-
Konferensbidrag (refereegranskat)abstract
- It has long been known that ferromagnets undergo a phase transition from ferromagnetic to paramagnetic at the Curie temperature, associated with critical phenomena such as a divergence in the heat capacity. A ferromagnet can also be transiently demagnetized by heating it with an ultrafast laser pulse. However, to date the connection between out-of-equilibrium and equilibrium phase transitions was not known, nor how fast the out-of-equilibrium phase transitions can proceed. In this work, by combining time- and angle-resolved photoemission (Tr-ARPES) with time-resolved transverse magneto-optical Kerr (Tr-TMOKE) spectroscopies, we show that the same critical behavior also governs the ultrafast magnetic phase transition in nickel. This is evidenced by several observations. First, we observe a divergence of the transient heat capacity of the electron spin system preceding material demagnetization. Second, when the electron temperature is transiently driven above the Curie temperature, we observe an extremely rapid change in the material response: the spin system absorbs sufficient energy within the first 20 fs to subsequently proceed through the phase transition, while demagnetization and the collapse of the exchange splitting occur on much longer timescales. Third, we find that the transient electron temperature alone dictates the magnetic response. By comparing results obtained from different methods, we show that the critical behaviors are essential for fully explaining the fluence-dependent magnetization dynamics measured using magneto-optical spectroscopy.
|
|
