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  • 1.
    Aperis, Alex
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab initio theory of magnetic-field-induced odd-frequency two-band superconductivity in MgB22015In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 92, no 5, article id 054516Article in journal (Refereed)
  • 2.
    Balaz, Pavel
    et al.
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Zonda, Martin
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Carva, Karel
    Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague, Czech Republic..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Transport theory for femtosecond laser-induced spin-transfer torques2018In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 30, no 11, article id 115801Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Battiato, Marco
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Treating the effect of interface reflections on superdiffusive spin transport in multilayer samples (invited)2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 115, no 17, p. 172611-Article in journal (Refereed)
    Abstract [en]

    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.

  • 4. Buendia, E.
    et al.
    Galvez, F. J.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarsa, A.
    Dynamical correlation effects in the transition probability: A study for the atoms Li to Ar2012In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 548, p. 1-6Article in journal (Refereed)
    Abstract [en]

    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.

  • 5. Buendia, E.
    et al.
    Galvez, F. J.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarsa, A.
    Explicitly correlated wave functions for atoms and singly charged ions from Li through Sr: Variational and Diffusion Monte Carlo results2014In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 615, p. 21-25Article in journal (Refereed)
    Abstract [en]

    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.

  • 6. Buendia, E.
    et al.
    Galvez, F. J.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sarsa, A.
    Quantum Monte Carlo ionization potential and electron affinity for transition metal atoms2013In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 559, p. 12-17Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Buzzi, Michele
    et al.
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Makita, Mikako
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Howald, Ludovic
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Kleibert, Armin
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Vodungbo, Boris
    Ecole Polytech, CNRS, UMR 7639, Lab Opt Appl,ENSTA ParisTech, Chemin Huniere, F-91761 Palaiseau, France.;UPMC Univ Paris 06, Sorbonne Univ, CNRS, LCPMR, F-75005 Paris, France..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Raabe, Jörg
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Jaouen, Nicolas
    Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Redlin, Harald
    DESY, HASYLAB, Notkestr 85, D-22607 Hamburg, Germany..
    Tiedtke, Kai
    DESY, HASYLAB, Notkestr 85, D-22607 Hamburg, Germany..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    David, Christian
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Nolting, Frithjof
    Paul Scherrer Inst, CH-5232 Villigen, Switzerland..
    Luning, Jan
    UPMC Univ Paris 06, Sorbonne Univ, CNRS, LCPMR, F-75005 Paris, France.;Synchrotron SOLEIL, BP 48, F-91192 Gif Sur Yvette, France..
    Single-shot Monitoring of Ultrafast Processes via X-ray Streaking at a Free Electron Laser2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 7253Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Conradson, Steven D.
    et al.
    Synchrotron Soleil, Orme Merisiers St Aubin, F-91192 Gif Sur Yvette, France..
    Gilbertson, Steven M.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Daifuku, Stephanie L.
    Univ Rochester, Dept Chem, Rochester, NY 14627 USA..
    Kehl, Jeffrey A.
    Univ Rochester, Dept Chem, Rochester, NY 14627 USA..
    Durakiewicz, Tomasz
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Andersson, David A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bishop, Alan R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Byler, Darrin D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Valdez, James A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Neidig, Michael L.
    Univ Rochester, Dept Chem, Rochester, NY 14627 USA..
    Rodriguez, George
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Possible Demonstration of a Polaronic Bose-Einstein(-Mott) Condensate in UO2(+x) by Ultrafast THz Spectroscopy and Microwave Dissipation2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 15278Article in journal (Refereed)
    Abstract [en]

    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.

  • 9. Corkhill, Claire L.
    et al.
    Myllykyla, Emmi
    Bailey, Daniel J.
    Thornber, Stephanie M.
    Qi, Jiahui
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stennett, Martin C.
    Hamilton, Andrea
    Hyatt, Neil C.
    Contribution of Energetically Reactive Surface Features to the Dissolution of CeO2 and ThO2 Analogues for Spent Nuclear Fuel Microstructures2014In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, no 15, p. 12279-12289Article in journal (Refereed)
    Abstract [en]

    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.

  • 10. Eschenlohr, A.
    et al.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pontius, N.
    Kachel, T.
    Holldack, K.
    Mitzner, R.
    Foehlisch, A.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stamm, C.
    Optical excitation of thin magnetic layers in multilayer structures Reply2014In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 13, no 2, p. 102-103Article in journal (Refereed)
  • 11. Eschenlohr, A.
    et al.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pontius, N.
    Kachel, T.
    Holldack, K.
    Mitzner, R.
    Foehlisch, A.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stamm, C.
    Ultrafast spin transport as key to femtosecond demagnetization2013In: Nature Materials, ISSN 1476-1122, E-ISSN 1476-4660, Vol. 12, no 4, p. 332-336Article in journal (Refereed)
    Abstract [en]

    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.

  • 12.
    Gang, Seung-gi
    et al.
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Adam, Roman
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Plötzing, Moritz
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    von Witzleben, Moritz
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Weier, Christian
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Parlak, Umut
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Bürgler, Daniel E.
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Schneider, Claus M.
    Res Ctr Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Element-selective investigation of femtosecond spin dynamics in NiPd magnetic alloys using extreme ultraviolet radiation2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 6, article id 064412Article in journal (Refereed)
    Abstract [en]

    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.

  • 13.
    Henighan, T.
    et al.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Trigo, M.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, Menlo Pk, CA 94025 USA.;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Bonetti, S.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Granitzka, P.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Univ Amsterdam, Van der Waals Zeeman Inst, Kruislaan 403, NL-1018 XE Amsterdam, Netherlands..
    Higley, D.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Photon Sci, Stanford, CA 94305 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Chen, Z.
    Stanford Univ, Dept Phys, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Jiang, M. P.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Kukreja, R.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Gray, A.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Reid, A. H.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Jal, E.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Hoffmann, C.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Kozina, M.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, Menlo Pk, CA 94025 USA.;SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Song, S.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Chollet, M.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Zhu, D.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA..
    Xu, P. F.
    IBM Almaden Res Ctr, 650 Harry Rd, San Jose, CA 95120 USA.;Max Planck Inst Microstruct Phys, D-06120 Halle, Saale, Germany..
    Jeong, J.
    IBM Almaden Res Ctr, 650 Harry Rd, San Jose, CA 95120 USA..
    Carva, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, Dept Condensed Matter Phys, Fac Math & Phys, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Samant, M. G.
    IBM Almaden Res Ctr, 650 Harry Rd, San Jose, CA 95120 USA..
    Parkin, S. S. P.
    IBM Almaden Res Ctr, 650 Harry Rd, San Jose, CA 95120 USA.;Max Planck Inst Microstruct Phys, D-06120 Halle, Saale, Germany..
    Reis, D. A.
    SLAC Natl Accelerator Lab, Stanford PULSE Inst, Menlo Pk, CA 94025 USA.;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Photon Sci, Stanford, CA 94305 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA..
    Durr, H. A.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Generation mechanism of terahertz coherent acoustic phonons in Fe2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 22, article id 220301Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Hofherr, M.
    et al.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany.;Grad Sch Mat Sci Mainz, Staudinger Weg 9, D-55128 Mainz, Germany..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schmitt, O.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany..
    Berritta, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bierbrauer, U.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany..
    Sadashivaiah, S.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany..
    Schellekens, A. J.
    Eindhoven Univ Technol, cNM, Dept Appl Phys, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Koopmans, B.
    Eindhoven Univ Technol, cNM, Dept Appl Phys, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Steil, D.
    Georg August Univ Gottingen, Phys Inst 1, Friedrich Hund Pl 1, D-37077 Gottingen, Germany..
    Cinchetti, M.
    Tech Univ Dortmund, Expt Phys 6, D-44221 Dortmund, Germany..
    Stadtmueller, B.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany.;Grad Sch Mat Sci Mainz, Staudinger Weg 9, D-55128 Mainz, Germany..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathias, S.
    Georg August Univ Gottingen, Phys Inst 1, Friedrich Hund Pl 1, D-37077 Gottingen, Germany.;Georg August Univ Gottingen, ICASEC, D-37077 Gottingen, Germany..
    Aeschlimann, M.
    Univ Kaiserslautern, Erwin Schroedinger Str 46, D-67663 Kaiserslautern, Germany..
    Speed and efficiency of femtosecond spin current injection into a nonmagnetic material2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 100403Article in journal (Refereed)
    Abstract [en]

    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.

  • 15. Hosen, M. Mofazzel
    et al.
    Dhakal, Gyanendra
    Dimitri, Klauss
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kabir, Firoza
    Sims, Christopher
    Riseborough, Peter
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaczorowski, Dariusz
    Durakiewicz, Tomasz
    Neupane, Madhab
    Discovery of topological nodal-line fermionic phase in a magnetic material GdSbTe2018In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, article id 13283Article in journal (Refereed)
    Abstract [en]

    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.

  • 16.
    Hosen, M. Mofazzel
    et al.
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Dimitri, Klauss
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Belopolski, Ilya
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Dhakal, Gyanendra
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Kabir, Firoza
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Sims, Christopher
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Hasan, M. Zahid
    Princeton Univ, Joseph Henry Lab, Princeton, NJ 08544 USA.
    Kaczorowski, Dariusz
    Polish Acad Sci, Inst Low Temp & Struct Res, PL-50950 Wroclaw, Poland.
    Durakiewicz, Tomasz
    Marie Curie Sklodowska Univ, Inst Phys, PL-20031 Lublin, Poland.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Neupane, Madhab
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA.
    Observation of gapless Dirac surface states in ZrGeTe2018In: Physical Review B, Vol. 97, no 12, article id 121103Article in journal (Refereed)
    Abstract [en]

    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 <overline> 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.

  • 17.
    Hosen, M. Mofazzel
    et al.
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Dimitri, Klauss
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Belopolski, Ilya
    Princeton Univ, Joseph Henry Labs, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sankar, Raman
    Acad Sinica, Inst Phys, Taipei 10617, Taiwan.;Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10617, Taiwan..
    Dhakal, Nagendra
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Dhakal, Gyanendra
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Cole, Taiason
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaczorowski, Dariusz
    Polish Acad Sci, Inst Low Temp & Struct Res, PL-50950 Wroclaw, Poland..
    Chou, Fangcheng
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10617, Taiwan..
    Hasan, M. Zahid
    Princeton Univ, Joseph Henry Labs, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA..
    Durakiewicz, Tomasz
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA.;Marie Curie Sklodowska Univ, Inst Phys, PL-20031 Lublin, Poland..
    Neupane, Madhab
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Tunability of the topological nodal-line semimetal phase in ZrSiX-type materials (X = S, Se, Te)2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 16, article id 161101Article in journal (Refereed)
    Abstract [en]

    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.

  • 18. Hosen, M. Mofazzel
    et al.
    Dimitri, Klauss
    Nandy, Ashis K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sankar, Raman
    Dhakal, Gyanendra
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kabir, Firoza
    Sims, Christopher
    Chou, Fangcheng
    Kaczorowski, Dariusz
    Durakiewicz, Tomasz
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Neupane, Madhab
    Distinct multiple fermionic states in a single topological metal2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 3002Article in journal (Refereed)
    Abstract [en]

    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.

  • 19. Kampfrath, T.
    et al.
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eilers, G.
    Noetzold, J.
    Maehrlein, S.
    Zbarsky, V.
    Freimuth, F.
    Mokrousov, Y.
    Bluegel, S.
    Wolf, M.
    Radu, I.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Muenzenberg, M.
    Terahertz spin current pulses controlled by magnetic heterostructures2013In: Nature Nanotechnology, ISSN 1748-3387, E-ISSN 1748-3395, Vol. 8, no 4, p. 256-260Article in journal (Refereed)
    Abstract [en]

    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).

  • 20.
    Maehrlein, Sebastian F.
    et al.
    Max Planck Gesell, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany;Free Univ Berlin, Dept Phys, Arnimallee 14, D-14195 Berlin, Germany;Columbia Univ, Dept Chem, 3000 Broadway, New York, NY 10027 USA.
    Radu, Ilie
    Max Born Inst Nonlinear Opt & Short Pulse Spect, Max Born Str 2A, D-12489 Berlin, Germany;Helmholtz Zentrum Berlin Mat & Energie, Albert Einstein Str 15, D-12489 Berlin, Germany;Tech Univ Berlin, Inst Opt & Atom Phys, Hardenbergstr 36, D-10623 Berlin, Germany.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Paarmann, Alexander
    Max Planck Gesell, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany.
    Gensch, Michael
    Helmholtz Zentrum Dresden Rossendorf, Bautzner Landstr 400, D-01328 Dresden, Germany.
    Kalashnikova, Alexandra M.
    Ioffe Inst, 26 Polytechnicheskaya St, St Petersburg 194021, Russia.
    Pisarev, Roman V.
    Ioffe Inst, 26 Polytechnicheskaya St, St Petersburg 194021, Russia.
    Wolf, Martin
    Max Planck Gesell, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Barker, Joseph
    Tohoku Univ, Inst Mat Res, Sendai, Miyagi 9808577, Japan.
    Kampfrath, Tobias
    Max Planck Gesell, Fritz Haber Inst, Faradayweg 4-6, D-14195 Berlin, Germany;Free Univ Berlin, Dept Phys, Arnimallee 14, D-14195 Berlin, Germany.
    Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation2018In: Science Advances, E-ISSN 2375-2548, Vol. 4, no 7, article id eaar5164Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Maldonado, Pablo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Carva, Karel
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Charles Univ Prague, Fac Math & Phys, Dept Condensed Matter Phys, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic.
    Flammer, Martina
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theory of out-of-equilibrium ultrafast relaxation dynamics in metals2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 17, article id 174439Article in journal (Refereed)
    Abstract [en]

    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.

  • 22.
    Maldonado, Pablo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Evins, L. Z.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab Initio Atomistic Thermodynamics of Water Reacting with Uranium Dioxide Surfaces2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 16, p. 8491-8500Article in journal (Refereed)
    Abstract [en]

    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.

  • 23.
    Maldonado, Pablo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Godinho, J. R. A.
    Evins, L. Z.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ab Initio Prediction of Surface Stability of Fluorite Materials and Experimental Verification2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 13, p. 6639-6650Article in journal (Refereed)
    Abstract [en]

    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.

  • 24.
    Maldonado, Pablo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kanungo, Sudipta
    Saha-Dasgupta, Tanusri
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Two-step spin-switchable tetranuclear Fe(II) molecular solid: Ab initio theory and predictions2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 2, p. 020408-Article in journal (Refereed)
    Abstract [en]

    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.

  • 25.
    Maldonado, Pablo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Paolasini, L.
    European Synchrotron Radiat Facil, BP 220, F-38043 Grenoble, France..
    Oppeneer, Peter. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Forrest, T. R.
    European Synchrotron Radiat Facil, BP 220, F-38043 Grenoble, France..
    Prodi, A.
    CNR, Ist Struttura Mat, Area Ric Roma 1,Via Salaria Km 29-300, Montelibretti, Italy..
    Magnani, N.
    Commiss European Communities, JRC, ITU, Postfach 2340, D-76125 Karlsruhe, Germany..
    Bosak, A.
    European Synchrotron Radiat Facil, BP 220, F-38043 Grenoble, France..
    Lander, G. H.
    Commiss European Communities, JRC, ITU, Postfach 2340, D-76125 Karlsruhe, Germany..
    Caciuffo, R.
    Commiss European Communities, JRC, ITU, Postfach 2340, D-76125 Karlsruhe, Germany..
    Crystal dynamics and thermal properties of neptunium dioxide2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 14, article id 144301Article in journal (Refereed)
    Abstract [en]

    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.

  • 26.
    Neupane, Madhab
    et al.
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Belopolski, Ilya
    Hosen, M. Mofazzel
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Sanchez, Daniel S.
    Princeton Univ, Joseph Henry Lab, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA..
    Sankar, Raman
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10617, Taiwan..
    Szlawska, Maria
    Polish Acad Sci, Inst Low Temp & Struct Res, POB 937, PL-50950 Wroclaw, Poland..
    Xu, Su-Yang
    Princeton Univ, Joseph Henry Lab, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA..
    Dimitri, Klauss
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Dhakal, Nagendra
    Univ Cent Florida, Dept Phys, Orlando, FL 32816 USA..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kaczorowski, Dariusz
    Polish Acad Sci, Inst Low Temp & Struct Res, POB 937, PL-50950 Wroclaw, Poland..
    Chou, Fangcheng
    Natl Taiwan Univ, Ctr Condensed Matter Sci, Taipei 10617, Taiwan..
    Hasan, M. Zahid
    Princeton Univ, Joseph Henry Lab, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA..
    Durakiewicz, Tomasz
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, POB 1663, Los Alamos, NM 87545 USA..
    Observation of topological nodal fermion semimetal phase in ZrSiS2016In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 20, article id 201104Article in journal (Refereed)
    Abstract [en]

    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.

  • 27.
    Noguere, G.
    et al.
    CEA, DEN Cadarache, Lab Phys Studies, F-13108 St Paul Les Durance, France.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    De Saint Jean, C.
    CEA, DEN Cadarache, Lab Phys Studies, F-13108 St Paul Les Durance, France.
    Doppler broadening of neutron-induced resonances using ab initio phonon spectrum2018In: The European Physical Journal Plus, ISSN 2190-5444, E-ISSN 2190-5444, Vol. 133, no 5, article id 177Article in journal (Refereed)
    Abstract [en]

    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).

  • 28.
    Reid, A. H.
    et al.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Shen, X.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chase, T.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA..
    Jal, E.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Univ Paris 06, UPMC, Sorbonne Univ, CNRS,Lab Chim Phys Matiere & Rayonnement, F-75005 Paris, France..
    Granitzka, P. W.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Univ Amsterdam, Van der Waals Zeeman Inst, NL-1018 XE Amsterdam, Netherlands..
    Carva, K.
    Charles Univ Prague, Dept Condensed Matter Phys, Fac Math & Phys, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic..
    Li, R. K.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Li, J.
    Brookhaven Natl Lab, Upton, NY 11973 USA..
    Wu, L.
    Brookhaven Natl Lab, Upton, NY 11973 USA..
    Vecchione, T.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Liu, T.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Chen, Z.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Higley, D. J.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.;Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA..
    Hartmann, N.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Coffee, R.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Wu, J.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Dakovski, G. L.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Schlotter, W. F.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Ohldag, H.
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Takahashi, Y. K.
    Natl Inst Mat Sci, Magnet Mat Unit, Tsukuba, Ibaraki 3050047, Japan..
    Mehta, V.
    HGST Western Digital Co, San Jose Res Ctr, 3403 Yerba Buena Rd, San Jose, CA 95135 USA.;Thomas J Watson Res Ctr, 1101 Kitchawan Rd, Yorktown Hts, NY 10598 USA..
    Hellwig, O.
    HGST Western Digital Co, San Jose Res Ctr, 3403 Yerba Buena Rd, San Jose, CA 95135 USA.;Tech Univ Chemnitz, Inst Phys, Reichenhainer Str 70, D-09107 Chemnitz, Germany.;Helmholtz Zentrum Dresden Rossendorf, Inst Ion Beam Phys & Mat Res, D-01328 Dresden, Germany..
    Fry, A.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Zhu, Y.
    Cao, J.
    Florida State Univ, Dept Phys, Tallahassee, FL 32310 USA.;Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32310 USA..
    Fullerton, E. E.
    Univ Calif San Diego, Ctr Memory & Recording Res, 9500 Gilman Dr, La Jolla, CA 92093 USA..
    Stohr, J.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, X. J.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Dürr, Hermann A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Beyond a phenomenological description of magnetostriction2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 388Article in journal (Refereed)
    Abstract [en]

    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.

  • 29.
    Reid, A. H.
    et al.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Shen, X.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chase, T.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA.
    Jal, E.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; UPMC Univ Paris 06, Sorbonne Univ, Lab Chim Phys Matiere & Rayonnement, CNRS, F-75005 Paris, France.
    Granitzka, P. W.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; Univ Amsterdam, Van der Waals Zeeman Inst, NL-1018 XE Amsterdam, Netherlands.
    Carva, K.
    Charles Univ Prague, Dept Condensed Matter Phys, Fac Math & Phys, Ke Karlovu 5, CZ-12116 Prague 2, Czech Republic.
    Li, R. K.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Li, J.
    Brookhaven Natl Lab, Upton, NY 11973 USA.
    Wu, L.
    Brookhaven Natl Lab, Upton, NY 11973 USA.
    Vecchione, T.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Liu, T.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; Stanford Univ, Dept Phys, Stanford, CA 94305 USA.
    Chen, Z.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; Stanford Univ, Dept Phys, Stanford, CA 94305 USA.
    Higley, D. J.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA; Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA.
    Hartmann, N.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Coffee, R.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Wu, J.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Dakowski, G. L.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Schlotter, W. F.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Ohldag, H.
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lab, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Takahashi, Y. K.
    Natl Inst Mat Sci, Magnet Mat Unit, Tsukuba, Ibaraki 3050047, Japan.
    Mehta, V.
    HGST, San Jose Res Ctr, 3403 Yerba Buena Rd, San Jose, CA 95135 USA; Thomas J Watson Res Ctr, 1101 Kitchawan Rd, Yorktown Hts, NY 10598 USA.
    Hellwig, O.
    HGST, San Jose Res Ctr, 3403 Yerba Buena Rd, San Jose, CA 95135 USA; Tech Univ Chemnitz, Inst Phys, Reichenhainer Str 70, D-09107 Chemnitz, Germany; Helmholtz Zentrum Dresden Rossendorf, Inst Ion Beam Phys & Mat Res, D-01328 Dresden, Germany.
    Fry, A.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Zhu, Y.
    Brookhaven Natl Lab, Upton, NY 11973 USA.
    Cao, J.
    Florida State Univ, Dept Phys, Tallahassee, FL 32310 USA; Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32310 USA.
    Fullerton, E. E.
    Univ Calif San Diego, Ctr Memory & Recording Res, 9500 Gilman Dr, La Jolla, CA 92093 USA.
    Stohr, J.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, X. J.
    SLAC Natl Accelerator Lab, Accelerator Div, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Dürr, Hermann A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA.
    Publisher Correction: Beyond a phenomenological description of magnetostriction2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1035Article in journal (Other academic)
  • 30.
    Rudolf, Dennis
    et al.
    Res Ctr Julich, Peter Grnberg Inst PGI 6, D-52425 Julich, Germany..
    La-O-Vorakiat, Chan
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adam, Roman
    Res Ctr Julich, Peter Grnberg Inst PGI 6, D-52425 Julich, Germany..
    Grychtol, Patrik
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Shaw, Justin M.
    NIST, Electromagnet Div, Boulder, CO 80305 USA..
    Turgut, Emrah
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathias, Stefan
    Univ Kaiserslautern, D-67663 Kaiserslautern, Germany.;Res Ctr OPTIMAS, D-67663 Kaiserslautern, Germany..
    Nembach, Hans T.
    NIST, Electromagnet Div, Boulder, CO 80305 USA..
    Silva, Thomas J.
    NIST, Electromagnet Div, Boulder, CO 80305 USA..
    Aeschlimann, Martin
    Univ Kaiserslautern, D-67663 Kaiserslautern, Germany.;Res Ctr OPTIMAS, D-67663 Kaiserslautern, Germany..
    Kapteyn, Henry C.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Murnane, Margaret M.
    Univ Colorado, Dept Phys, Boulder, CO 80309 USA.;Univ Colorado, JILA, Boulder, CO 80309 USA..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schneider, Claus M.
    Res Ctr Julich, Peter Grnberg Inst PGI 6, D-52425 Julich, Germany..
    Element Selective Investigation of Spin Dynamics in Magnetic Multilayers2015In: Ultrafast Magnetism I / [ed] Bigot, JY; Hubner, W; Rasing, T; Chantrell, R, 2015, p. 307-309Conference paper (Refereed)
    Abstract [en]

    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.

  • 31. Rudolf, Dennis
    et al.
    La-O-Vorakiat, Chan
    Battiato, Marco
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adam, Roman
    Shaw, Justin M.
    Turgut, Emrah
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mathias, Stefan
    Grychtol, Patrik
    Nembach, Hans T.
    Silva, Thomas J.
    Aeschlimann, Martin
    Kapteyn, Henry C.
    Murnane, Margaret M.
    Schneider, Claus M.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ultrafast magnetization enhancement in metallic multilayers driven by superdiffusive spin current2012In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 3, p. 1037-Article in journal (Refereed)
    Abstract [en]

    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.

  • 32.
    Seifert, T.
    et al.
    Fritz Haber Inst Max Planck Soc, Dept Phys Chem, D-14195 Berlin, Germany..
    Jaiswal, S.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany.;Singulus Technol AG, D-63796 Kahl Am Main, Germany..
    Martens, U.
    Ernst Moritz Arndt Univ Greifswald, Inst Phys, D-17489 Greifswald, Germany..
    Hannegan, J.
    Univ Maryland Baltimore Cty, Dept Phys, Baltimore, MD 21250 USA..
    Braun, L.
    Fritz Haber Inst Max Planck Soc, Dept Phys Chem, D-14195 Berlin, Germany..
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Freimuth, F.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Kronenberg, A.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Henrizi, J.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Radu, I.
    Tech Univ Berlin, Inst Opt & Atom Phys, D-12489 Berlin, Germany.;Helmholtz Zentrum Berlin Mat & Energie, D-12489 Berlin, Germany..
    Beaurepaire, E.
    Inst Phys & Chim Mat Strasbourg, F-67200 Strasbourg, France..
    Mokrousov, Y.
    Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany..
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jourdan, M.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Jakob, G.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Turchinovich, D.
    Max Planck Inst Polymer Res, D-55128 Mainz, Germany..
    Hayden, L. M.
    Wolf, M.
    Fritz Haber Inst Max Planck Soc, Dept Phys Chem, D-14195 Berlin, Germany..
    Muenzenberg, M.
    Ernst Moritz Arndt Univ Greifswald, Inst Phys, D-17489 Greifswald, Germany..
    Klaeui, M.
    Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany..
    Kampfrath, T.
    Fritz Haber Inst Max Planck Soc, Dept Phys Chem, D-14195 Berlin, Germany..
    Efficient metallic spintronic emitters of ultrabroadband terahertz radiation2016In: Nature Photonics, ISSN 1749-4885, E-ISSN 1749-4893, Vol. 10, no 7, p. 483-+Article in journal (Refereed)
    Abstract [en]

    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.

  • 33. Waeckerlin, Christian
    et al.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Arnold, Lena
    Shchyrba, Aneliia
    Girovsky, Jan
    Nowakowski, Jan
    Ali, Md. Ehesan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Haehlen, Tatjana
    Baljozovic, Milos
    Siewert, Dorota
    Kleibert, Armin
    Muellen, Klaus
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jung, Thomas A.
    Ballav, Nirmalya
    Magnetic exchange coupling of a synthetic Co(II)-complex to a ferromagnetic Ni substrate2013In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 49, no 91, p. 10736-10738Article in journal (Refereed)
    Abstract [en]

    On-surface assembly of a spin-bearing and non-aromatic porphyrin-related synthetic Co(II)-complex on a ferromagnetic Ni thin film substrate and subsequent magnetic exchange interaction across the interface were studied by scanning tunnelling microscopy (STM), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and density functional theory +U (DFT + U) calculations.

  • 34. Walker, H. C.
    et al.
    McEwen, K. A.
    Griveau, J. -C
    Eloirdi, R.
    Amador, P.
    Maldonado, Pablo
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Colineau, E.
    Magnetic, electrical, and thermodynamic properties of NpIr: Ambient and high-pressure measurements, and electronic structure calculations2015In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 19, article id 195146Article in journal (Refereed)
    Abstract [en]

    We present bulk property measurements of NpIr, a newly synthesized member of the Np-Ir binary phase diagram, which is isostructural to the noncentrosymmetric pressure-induced ferromagnetic superconductor UIr. Magnetic susceptibility, electronic transport properties at ambient and high pressure, and heat capacity measurements have been performed for temperatures T = 0.55-300 K in a range of magnetic fields up to 14 T and under pressure up to 17.3 GPa. These reveal that NpIr is a moderately heavy fermion Kondo system with strong antiferromagnetic interactions, but there is no evidence of any phase transition down to 0.55 K or at the highest pressure achieved. Experimental results are compared with ab initio calculations of the electronic band structure and lattice heat capacity. An extremely low lattice thermal conductivity is predicted for NpIr at temperatures above 300 K.

1 - 34 of 34
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