| 1. |
- Abbafati, Cristiana, et al.
(författare)
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- 2020
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Beal, Jacob, et al.
(författare)
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Robust estimation of bacterial cell count from optical density
- 2020
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Ingår i: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 3. |
- Rudolf, Dennis, et al.
(författare)
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Element Selective Investigation of Spin Dynamics in Magnetic Multilayers
- 2015
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Ingår i: Ultrafast Magnetism I. - Cham : Springer International Publishing. - 9783319077437 - 9783319077420 ; , s. 307-309
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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.
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| 4. |
- Rudolf, Dennis, et al.
(författare)
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Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current
- 2012
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 1037-
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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.
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| 5. |
- Zusin, Dmitriy, et al.
(författare)
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Direct measurement of the static and transient magneto-optical permittivity of cobalt across the entire M-edge in reflection geometry by use of polarization scanning
- 2018
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 97:2
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Tidskriftsartikel (refereegranskat)abstract
- The microscopic state of amagnetic material is characterized by its resonant magneto-optical response through the off-diagonal dielectric tensor component epsilon(xy). However, the measurement of the full complex epsilon(xy) in the extreme ultraviolet spectral region covering the M absorption edges of 3d ferromagnets is challenging due to the need for either a careful polarization analysis, which is complicated by a lack of efficient polarization analyzers, or scanning the angle of incidence in fine steps. Here, we propose and demonstrate a technique to extract the complex resonant permittivity epsilon(xy) simply by scanning the polarization angle of linearly polarized high harmonics to measure the magneto-optical asymmetry in reflection geometry. Because this technique is more practical and faster to experimentally implement than previous approaches, we can directly measure the full time evolution of epsilon(xy)(t) during laser-induced demagnetization across the entire M-2,M-3 absorption edge of cobalt with femtosecond time resolution. We find that for polycrystalline Co films on an insulating substrate, the changes in epsilon(xy) are uniform throughout the spectrum, to within our experimental precision. This result suggests that, in the regime of strong demagnetization, the ultrafast demagnetization response is primarily dominated by magnon generation. We estimate the contribution of exchange-splitting reduction to the ultrafast demagnetization process to be no more than 25%.
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| 6. |
- Hickstein, Daniel D., et al.
(författare)
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Non-collinear generation of angularly isolated circularly polarized high harmonics
- 2015
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Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 9:11, s. 743-750
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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.
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| 7. |
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| 8. |
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| 9. |
- Zusin, Dmitriy, et al.
(författare)
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Ultrafast perturbation of magnetic domains by optical pumping in a ferromagnetic multilayer
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:14
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Tidskriftsartikel (refereegranskat)abstract
- Ultrafast optical pumping of spatially nonuniform magnetic textures is known to induce far-from-equilibrium spin transport effects. Here, we use ultrafast x-ray diffraction with unprecedented dynamic range to study the laser-induced dynamics of labyrinth domain networks in ferromagnetic CoFe/Ni multilayers. We detected azimuthally isotropic, odd order, magnetic diffraction rings up to fifth order. The amplitudes of all three diffraction rings quench to different degrees within 1.6 ps. In addition, all three of the detected diffraction rings both broaden by 15% and radially contract by 6% during the quench process. We are able to rigorously quantify a 31% ultrafast broadening of the domain walls via Fourier analysis of the order-dependent quenching of the three detected diffraction rings. The broadening of the diffraction rings is interpreted as a reduction in the domain coherence length, but the shift in the ring radius, while unambiguous in its occurrence, remains unexplained. In particular, we demonstrate that a radial shift explained by domain-wall broadening can be ruled out. With the unprecedented dynamic range of our data, our results provide convincing evidence that labyrinth domain structures are spatially perturbed at ultrafast speeds under far-from-equilibrium conditions, albeit the mechanism inducing the perturbations remains yet to be clarified.
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| 10. |
- Echternach, P. M., et al.
(författare)
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Progress in the development of a single Cooper-pair box qubit
- 2009
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Ingår i: Quantum Information Processing. - : Springer Science and Business Media LLC. - 1570-0755 .- 1573-1332. ; 8:2-3, s. 183-198
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Tidskriftsartikel (refereegranskat)abstract
- We describe in this review progress in techniques for measuring the quantum states of the single Cooper-pair box (SCB) at the Jet Propulsion Laboratory, and the use of these techniques to characterize their performance as quantum bits. Initially, the Radio-Frequency-Single-Electron Transistor was used to measure conventional and differential versions of the SCB. To overcome some of the difficulties associated with the radio-frequency single-electron transistor, a transition was made to readout based on the quantum capacitance technique. Using this method, entanglement between two SCBs was demonstrated spectroscopically and with ground state characterization.
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| 11. |
- Shaw, M. D., et al.
(författare)
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Characterization of an entangled system of two superconducting qubits using a multiplexed capacitance measurement
- 2009
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 79:1
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Tidskriftsartikel (refereegranskat)abstract
- We characterize a pair of Cooper-pair boxes coupled with a fixed capacitor using spectroscopy and measurements of the ground-state quantum capacitance. We use the extracted parameters to estimate the concurrence or degree of entanglement between the two qubits. We also present a thorough demonstration of a multiplexed quantum capacitance measurement technique, which is in principle scalable to a large array of superconducting qubits.
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| 12. |
- Shaw, M. D., et al.
(författare)
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Experimental realization of a differential charge qubit
- 2007
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Ingår i: IEEE Transactions on Applied Superconductivity. - 1558-2515 .- 1051-8223. ; 17:2, s. 109-112
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the operation of a differential single Cooper-pair box, a charge qubit consisting of two aluminum islands, isolated from ground, coupled by a pair of small-area Josephson junctions. We have tested four devices, all of which show evidence of quasiparticle poisoning. The devices are characterized with microwave spectroscopy and temperature dependence studies. © 2007 IEEE.
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| 13. |
- Turgut, Emrah, et al.
(författare)
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Stoner versus Heisenberg : Ultrafast exchange reduction and magnon generation during laser-induced demagnetization
- 2016
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Ingår i: PHYSICAL REVIEW B. - 2469-9950. ; 94:22
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Tidskriftsartikel (refereegranskat)abstract
- Understanding how the electronic band structure of a ferromagnetic material is modified during laser-induced demagnetization on femtosecond time scales has been a long-standing question in condensed matter physics. Here, we use ultrafast high harmonics to measure time-, energy-, and angle-resolved M-edge magnetic asymmetry spectra for Co films after optical pumping to induce ultrafast demagnetization. This provides a complete data set that we can compare with advanced ab initio magneto-optical calculations. Our analysis identifies that the dominant mechanisms contributing to ultrafast demagnetization on time scales up to several picoseconds are a transient reduction in the exchange splitting and the excitation of ultrafast magnons. Surprisingly, we find that the magnon contribution to ultrafast demagnetization is already strong on subpicosecond time scales, while the reduction in exchange splitting persists to several picoseconds.
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| 14. |
- Zhou Hagström, Nanna, 1993-, et al.
(författare)
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Megahertz-rate Ultrafast X-ray Scattering and Holographic Imaging at the European XFEL
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence, and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, we present the results from the first megahertz repetition rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL. We illustrate the experimental capabilities that the SCS instrument offers, resulting from the operation at MHz repetition rates and the availability of the novel DSSC 2D imaging detector. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative examples, providing an ideal test-bed for operation at megahertz rates. Nevertheless, our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
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| 15. |
- Zhou Hagström, Nanna, 1993-, et al.
(författare)
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Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL
- 2022
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 29, s. 1454-1464
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Tidskriftsartikel (refereegranskat)abstract
- The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
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| 16. |
- Arora, Monika, et al.
(författare)
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Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys
- 2021
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetic damping properties of polycrystalline Fe-V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%-20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53 +/- 0.08) x 10-3, which is approximately a factor of 3 higher than our calculated value of 0.48 x 10-3. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.
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| 17. |
- Jangid, Rahul, et al.
(författare)
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Extreme Domain Wall Speeds under Ultrafast Optical Excitation
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:25
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved ultrafast EUV magnetic scattering was used to test a recent prediction of > 10 km/s domain wall speeds by optically exciting a magnetic sample with a nanoscale labyrinthine domain pattern. Ultrafast distortion of the diffraction pattern was observed at markedly different timescales compared to the magnetization quenching. The diffraction pattern distortion shows a threshold dependence with laser fluence, not seen for magnetization quenching, consistent with a picture of domain wall motion with pinning sites. Supported by simulations, we show that a speed of approximate to 66 km/s for highly curved domain walls can explain the experimental data. While our data agree with the prediction of extreme, nonequilibrium wall speeds locally, it differs from the details of the theory, suggesting that additional mechanisms are required to fully understand these effects.
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| 18. |
- Keller, Mark W., et al.
(författare)
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Near-unity spin Hall ratio in NixCu1-x alloys
- 2019
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 99:21
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Tidskriftsartikel (refereegranskat)abstract
- We report a large spin Hall effect in the 3d transition metal alloy NixCu1-x for x is an element of {0.3, 0.75}, detected via the ferromagnetic resonance of a permalloy (Py = Ni80Fe20) film deposited in a bilayer with the alloy. A thickness series at x = 0.6, for which the alloy is paramagnetic at room temperature, allows us to determine the spin Hall ratio theta(SH) approximate to 1, spin diffusion length lambda(s), spin mixing conductance G(up arrow down arrow) and damping due to spin memory loss alpha(SML). We compare our results with similar experiments on Py/Pt bilayers measured using the same method. Ab initio band structure calculations with disorder and spin-orbit coupling suggest an intrinsic spin Hall effect in NixCu1-x alloys, although the experiments here cannot distinguish between extrinsic and intrinsic mechanisms.
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| 19. |
- Kfir, Ofer, et al.
(författare)
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Generation of bright phase-matched circularly-polarized extreme ultraviolet high harmonics
- 2015
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Ingår i: Nature Photonics. - 1749-4885 .- 1749-4893. ; 9:2, s. 99-105
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Tidskriftsartikel (refereegranskat)abstract
- Circularly-polarized extreme ultraviolet and X-ray radiation is useful for analysing the structural, electronic and magnetic properties of materials. To date, such radiation has only been available at large-scale X-ray facilities such as synchrotrons. Here, we demonstrate the first bright, phase-matched, extreme ultraviolet circularly-polarized high harmonics source. The harmonics are emitted when bi-chromatic counter-rotating circularly-polarized laser pulses field-ionize a gas in a hollow-core waveguide. We use this new light source for magnetic circular dichroism measurements at the M-shell absorption edges of Co. We show that phase-matching of circularly-polarized harmonics is unique and robust, producing a photon flux comparable to linearly polarized high harmonic sources. This work represents a critical advance towards the development of table-top systems for element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution.
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| 20. |
- Locht, Inka L. M., 1986-, et al.
(författare)
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Magnetic asymmetry around the 3p absorption edge in Fe and Ni
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work is a joint theoretical and experimental study of the relation between the magneto- optical response of a material in the sub-picosecond timescale and its instantaneous magnetisation. We perform pump-probe experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry. We measure the magnetic asymmetry of elemental Fe and Ni before and after the laser pulse. The observed differences between the magnetic asymmetry curves for various photon energies suggest that the relation between asymmetry and sample magnetization is more complex than a simple proportionality. Further insight is obtained by means of theoretical simulations based on density-functional theory. Our calculations show that non-linear effects in the asymmetry are most prominent at energies corresponding to the absorption edge and that the proportionality is recovered outside of this region. In conclusion, our experimental and theoretical results emphasize the need of including the complex relation between asymmetry and magnetization in the interpretation of ultrafast magnetization experiments in terms of microscopic properties.
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| 21. |
- Shaw, Justin M., et al.
(författare)
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Magnetic damping in sputter-deposited Co2MnGe Heusler compounds with A2, B2, and L2(1) orders : Experiment and theory
- 2018
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:9
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Tidskriftsartikel (refereegranskat)abstract
- We show that very low values of the magnetic damping parameter can be achieved in sputter deposited polycrystalline films of Co2MnGe annealed at relatively low temperatures ranging from 240 degrees C to 400 degrees C. Damping values as low as 0.0014 are obtained with an intrinsic value of 0.0010 after spin-pumping contributions are considered. Of importance to most applications is the low value of inhomogeneous linewidth that yields measured linewidths of 1.8 and 5.1 mT at 10 and 40 GHz, respectively. The damping parameter monotonically decreases as the B2 order of the films increases. This trend is reproduced and explained by ab initio calculations of the electronic structure and damping parameter. Here, the damping parameter is calculated as the structure evolves from A2 to B2 to L2(1) orders. The largest decrease in the damping parameter occurs during the A2 to B2 transition as the half-metallic phase becomes established.
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| 22. |
- Shaw, Justin M., et al.
(författare)
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Quantifying Spin-Mixed States in Ferromagnets
- 2021
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 127:20
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Tidskriftsartikel (refereegranskat)abstract
- We quantify the presence of spin-mixed states in ferromagnetic 3D transition metals by precise measurement of the orbital moment. While central to phenomena such as Elliot-Yafet scattering, quantification of the spin-mixing parameter has hitherto been confined to theoretical calculations. We demonstrate that this information is also available by experimental means. Comparison of ferromagnetic resonance spectroscopy with x-ray magnetic circular dichroism results show that Kittel's original derivation of the spectroscopic g factor requires modification, to include spin mixing of valence band states. Our results are supported by ab initio relativistic electronic structure theory.
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| 23. |
- Tengdin, Phoebe, et al.
(författare)
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Direct light–induced spin transfer between different elements in a spintronic Heusler material via femtosecond laser excitation
- 2020
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Ingår i: Science Advances. - : American Association for the Advancement of Science. - 2375-2548. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions. Here, we use a femtosecond laser to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co2MnGe. This spin transfer initiates as soon as light is incident on the material, demonstrating spatial transfer of angular momentum between neighboring atomic sites on time scales < 10 fs. Using ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state of two elements during laser excitation, we find that the magnetization of Co is enhanced, while that of Mn rapidly quenches. Density functional theory calculations show that the optical excitation directly transfers spin from one magnetic sublattice to another through preferred spin-polarized excitation pathways. This direct manipulation of spins via light provides a path toward spintronic devices that can operate on few-femtosecond or faster time scales.
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| 24. |
- Zhou Hagström, Nanna, 1993-, et al.
(författare)
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Symmetry-dependent ultrafast manipulation of nanoscale magnetic domains
- 2022
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 106:22
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Tidskriftsartikel (refereegranskat)abstract
- Femtosecond optical pumping of magnetic materials has been used to achieve ultrafast switching and recently to nucleate symmetry-broken magnetic states. However, when the magnetic order parameter already presents a broken-symmetry state, such as a domain pattern, the dynamics are poorly understood and consensus remains elusive. Here, we resolve the controversies in the literature by studying the ultrafast response of magnetic domain patterns with varying degrees of translation symmetry with ultrafast x-ray resonant scattering. A data analysis technique is introduced to disentangle the isotropic and anisotropic components of the x-ray scattering. We find that the scattered intensity exhibits a radial shift restricted to the isotropic component, indicating that the far-from-equilibrium magnetization dynamics are intrinsically related to the spatial features of the domain pattern. Our results suggest alternative pathways for the spatiotemporal manipulation of magnetism via far-from-equilibrium dynamics and by carefully tuning the ground-state magnetic textures.
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| 25. |
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