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  • 1.
    Akansel, Serkan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Behera, Nilamani
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Husain, Sajid
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Chaudhary, Sujeet
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Thickness dependent enhancement of damping in Co2FeAl/β-Ta thin films2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 13, article id 134421Article in journal (Refereed)
    Abstract [en]

    In the present work Co2FeAl (CFA) thin films were deposited by ion beam sputtering on Si (100) substrates at the optimized deposition temperature of 300°C. A series of CFA films with different thickness (tCFA ); 8, 10, 12, 14, 16, 18 and 20 nm were prepared and all samples were capped with a 5 nm thick b-Ta layer. The thickness dependent static and dynamic properties of the films were studied by SQUID magnetometry, in-plane as well as out-of-plane broadband VNA-FMR measurements and angle dependent cavity FMR measurements. The saturation magnetization and the coercive field were found to be weakly thickness dependent and lie in the range 900 – 950 kA/m and 0.53 – 0.87 kA/m, respectively. The effective damping parameter ( αeff) extracted from in-plane and out-of-plane FMR results reveal a 1/tCFA dependence, the values for the in-plane αeff being larger due to two-magnon scattering (TMS). The origin of the αeff thickness dependence is spin pumping into the non-magnetic b-Ta layer and in case of the in-plane  αeff also a thickness dependent TMS contribution. From the out-of-plane FMR results, it was possible to disentangle the different contributions to αeff   and to the extract values for the intrinsic Gilbert damping (αG ) and the effective spin-mixing conductance (g_eff^↑↓ ) of the CFA/ b-Ta interface, yielding αG=1.1X10-3 and g_eff^↑↓=2.90x1019 m-2.

  • 2.
    Albaalbaky, Ahmed
    et al.
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ledue, Denis
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Patte, Renaud
    Normandie Univ, UNIROUEN, CNRS, INSA Rouen,GPM, St Etienne Du Rouvray, France..
    Fresard, Raymond
    Normandie Univ, UNICAEN, ENSICAEN, CNRS,CRISMAT, F-14050 Caen, France..
    Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 6, article id 064431Article in journal (Refereed)
    Abstract [en]

    Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO2 below its Neel temperature T-N, we investigate its magnetic and ferroelectric properties using ab initio calculations and Monte Carlo simulations. Exchange interactions up to the third nearest neighbors in the ab plane, interlayer interaction, and single ion anisotropy constants in CuCrO2 are estimated by a series of density functional theory calculations. In particular, our results evidence a hard axis along the [110] direction due to the lattice distortion that takes place along this direction below T-N. Our Monte Carlo simulations indicate that the system possesses a Neel temperature T-N approximate to 27 K very close to the ones reported experimentally (T-N = 24-26 K). Also we show that the ground state is a proper-screw magnetic configuration with an incommensurate propagation vector pointing along the [110] direction. Moreover, our work reports the emergence of spin helicity below T-N which leads to ferroelectricity in the extended inverse Dzyaloshinskii-Moriya model. We confirm the electric control of spin helicity by simulating P-E hysteresis loops at various temperatures.

  • 3.
    Andersson, Mikael Svante
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Mathieu, Roland
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Normile, Peter S.
    Univ Castilla La Mancha, Spain.
    Lee, Su Seong
    Inst Bioengn & Nanotechnol, Singapore.
    Singh, Gurvinder
    Norwegian Univ Sci & Technol NTNU, Dept Mat Sci & Engn, Norway.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    De Toro, José A.
    Univ Castilla La Mancha, Spain.
    Magnetic properties of nanoparticle compacts with controlled broadening of the particle size distribution2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 18, article id 184431Article in journal (Refereed)
    Abstract [en]

    Binary random compacts with different proportions of small (volume V) and large (volume 2V) essentially bare maghemite nanoparticles are used to investigate the effect of controllably broadening the particle size distribution on the magnetic properties of magnetic nanoparticle assemblies with strong dipolar interaction. A series of eight random mixtures of highly uniform 9.0- and 11.5-nm-diameter maghemite particles prepared by thermal decomposition is studied. In spite of the severely broadened size distributions in the mixed samples, well-defined superspin glass transition temperatures are observed across the series, their values increasing linearly with the weight fraction of large particles.

  • 4.
    Awoga, Oladunjoye A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bouhon, Adrien
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Domain walls in a chiral d-wave superconductor on the honeycomb lattice2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 1, article id 014521Article in journal (Refereed)
    Abstract [en]

    We perform a fully self-consistent study of domain walls between different chiral domains in chiral d(x2-y2) +/- id(xy) -wave superconductors with an underlying honeycomb lattice structure. We investigate domain walls along all possible armchair and zigzag directions and with a finite global phase shift across the domain wall, in addition to the change of chirality. For armchair domain walls we find the lowest domain wall energy at zero global phase shift, while the most favorable zigzag domain wall has a finite global phase shift dependent on the doping level. Belowthe van Hove singularity the armchair domain wall is most favorable, while at even higher doping the zigzag domain wall has the lowest energy. The domain wall causes a local suppression of the superconducting order parameter, with the superconducting recovery length following a universal curve for all domain walls. Moreover, we always find four subgap states crossing zero energy and well localized to the domain wall. However, the details of their energy spectrum vary notably, especially with the global phase shift across the domain wall.

  • 5.
    Awoga, Oladunjoye
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Björnson, Kristofer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Disorder robustness and protection of Majorana bound states in ferromagnetic chains on conventional superconductors2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 18, article id 184511Article in journal (Refereed)
    Abstract [en]

    Majorana bound states (MBSs) are well established in the clean limit in chains of ferromagnetically aligned impurities deposited on conventional superconductors with finite spin-orbit coupling. Here we show that these MBSs are very robust against disorder. By performing self-consistent calculations we find that the MBSs are protected as long as the surrounding superconductor show no large signs of inhomogeneity. We also find that longer chains offer more stability against disorder for the MBSs, albeit the minigap decreases, as do increasing strengths of spin-orbit coupling and superconductivity.

  • 6.
    Awoga, Oladunjoye
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Probing unconventional superconductivity in proximitized graphene by impurity scattering2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 21, article id 214515Article in journal (Refereed)
    Abstract [en]

    We demonstrate how potential impurities are a very powerful tool for determining the pairing symmetry in graphene, proximity coupled to a spin-singlet superconductor. All d-wave states are characterized by subgap resonances, with spatial patterns clearly distinguishing between nodal and chiral d-wave symmetry, while s-wave states have no subgap resonances. We also find strong supergap impurity resonances associated with the normal state Dirac point. Subgap and supergap resonances only interact at very low doping levels, then causing suppression of the supergap resonances.

  • 7.
    Barthel, J.
    et al.
    Rhein Westfal TH Aachen, Cent Facil Electron Microscopy, D-52074 Aachen, Germany.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Mayer, J.
    Rhein Westfal TH Aachen, Cent Facil Electron Microscopy, D-52074 Aachen, Germany.;Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ho, P. -L
    Beijing National Center for Electron Microscopy, Laboratory of Advanced Materials, The State Key Laboratory of New Ceramics and Fine Processing, and School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China.; Central Facility for Electron Microscopy, RWTH Aachen University, 52074 Aachen, Germany.
    Zhong, X. Y.
    Tsinghua Univ, State Key Lab New Ceram & Fine Proc, Lab Adv Mat, Beijing Natl Ctr Electron Microscopy, Beijing 100084, Peoples R China.;Tsinghua Univ, Sch Mat Sci & Engn, Beijing 100084, Peoples R China..
    Lentzen, M.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Dunin-Borkowski, R. E.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Urban, K. W.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany..
    Brown, H. G.
    Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia..
    Findlay, S. D.
    Monash Univ, Sch Phys & Astron, Clayton, Vic 3800, Australia..
    Allen, L. J.
    Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany.;Univ Melbourne, Sch Phys, Parkville, Vic 3010, Australia..
    Understanding electron magnetic circular dichroism in a transition potential approach2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 14, article id 144103Article in journal (Refereed)
    Abstract [en]

    This paper introduces an approach based on transition potentials for inelastic scattering to understand the underlying physics of electron magnetic circular dichroism (EMCD). The transition potentials are sufficiently localized to permit atomic-scale EMCD. Two-beam and three-beam systematic row cases are discussed in detail in terms of transition potentials for conventional transmission electron microscopy, and the basic symmetries which arise in the three-beam case are confirmed experimentally. Atomic-scale EMCD in scanning transmission electron microscopy (STEM), using both a standard STEM probe and vortex beams, is discussed.

  • 8.
    Bekaert, J.
    et al.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Partoens, B.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Milosevic, M. V.
    Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
    Advanced first-principles theory of superconductivity including both lattice vibrations and spin fluctuations: The case of FeB42018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 1, article id 014503Article in journal (Refereed)
    Abstract [en]

    We present an advanced method to study spin fluctuations in superconductors quantitatively and entirely fromfirst principles. This method can be generally applied to materials where electron-phonon coupling and spinfluctuations coexist. We employ it here to examine the recently synthesized superconductor iron tetraboride(FeB4) with experimentalTc∼2.4K[H.Gouet al.,Phys.Rev.Lett.111,157002(2013)]. We prove thatFeB4is particularly prone to ferromagnetic spin fluctuations due to the presence of iron, resulting in a largeStoner interaction strength,I=1.5 eV, as calculated from first principles. The other important factor is itsFermi surface that consists of three separate sheets, among which two are nested ellipsoids. The resultingsusceptibility has a ferromagnetic peak aroundq=0, from which we calculated the repulsive interaction betweenCooper pair electrons using the random phase approximation. Subsequently, we combined the electron-phononinteraction calculated from first principles with the spin fluctuation interaction in fully anisotropic Eliashbergtheory calculations. We show that the resulting superconducting gap spectrum is conventional, yet very stronglydepleted due to coupling to the spin fluctuations. The critical temperature decreases from Tc=41 K, if they arenot taken into account, toTc=1.7 K, in good agreement with the experimental value.

  • 9. Bekaert, J.
    et al.
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Partoens, B.
    Oppeneer, Peter M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Milošević, M. V.
    Evolution of multigap superconductivity in the atomically thin limit: Strain-enhanced three-gap superconductivity in monolayer MgB22017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, article id 094510Article in journal (Refereed)
  • 10.
    Bekaert, J.
    et al.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Vercauteren, S.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Aperis, Alex
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Komendova, Lucia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Prozorov, R.
    Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA.;Iowa State Univ, Ames Lab, Ames, IA 50011 USA..
    Partoens, B.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Milosevic, M. V.
    Univ Antwerp, Dept Phys, Condensed Matter Theory Grp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium..
    Anisotropic type-I superconductivity and anomalous superfluid density in OsB22016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 14, article id 144506Article in journal (Refereed)
    Abstract [en]

    We present a microscopic study of superconductivity in OsB2, and discuss the origin and characteristic length scales of the superconducting state. From first-principles we show that OsB2 is characterized by three different Fermi sheets, and we prove that this fermiology complies with recent quantum-oscillation experiments. Using the found microscopic properties, and experimental data from the literature, we employ Ginzburg-Landau relations to reveal that OsB2 is a distinctly type-I superconductor with a very low Ginzburg-Landau parameter kappa-a rare property among compound materials. We show that the found coherence length and penetration depth corroborate the measured thermodynamic critical field. Moreover, our calculation of the superconducting gap structure using anisotropic Eliashberg theory and ab initio calculated electron-phonon interaction as input reveals a single but anisotropic gap. The calculated gap spectrum is shown to give an excellent account for the unconventional behavior of the superfluid density of OsB2 measured in experiments as a function of temperature. This reveals that gap anisotropy can explain such behavior, observed in several compounds, which was previously attributed solely to a two-gap nature of superconductivity.

  • 11.
    Berger, Andrew J.
    et al.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Edwards, Eric R. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Nembach, Hans T.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Karis, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Weiler, Mathias
    Tech Univ Munich, Phys Dept, D-85748 Garching, Germany;Bayerische Akad Wissensch, Walther Meissner Inst, D-85748 Garching, Germany.
    Silva, T. J.
    NIST, Quantum Electromagnet Div, Boulder, CO 80305 USA.
    Determination of the spin Hall effect and the spin diffusion length of Pt from self-consistent fitting of damping enhancement and inverse spin-orbit torque measurements2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 2, article id 024402Article in journal (Refereed)
    Abstract [en]

    Understanding the evolution of spin-orbit torque (SOT) with increasing heavy-metal thickness in ferromagnet/normal metal (FM/NM) bilayers is critical for the development of magnetic memory based on SOT. However, several experiments have revealed an apparent discrepancy between damping enhancement and dampinglike SOT regarding their dependence on NM thickness. Here, using linewidth and phase-resolved amplitude analysis of vector network analyzer ferromagnetic resonance (VNA-FMR) measurements, we simultaneously extract damping enhancement and both fieldlike and dampinglike inverse SOT in Ni80Fe20/Pt bilayers as a function of Pt thickness. By enforcing an interpretation of the data which satisfies Onsager reciprocity, we find that both the damping enhancement and dampinglike inverse SOT can be described by a single spin diffusion length (approximate to 4nm), and that we can separate the spin pumping and spin-memory loss contributions to the total damping. This analysis indicates that less than 40% of the angular momentum pumped by FMR through the Ni80Fe20/Pt interface is transported as spin current into the Pt. On account of the spin-memory loss and corresponding reduction in total spin current available for spin-charge transduction in the Pt, we determine the Pt spin Hall conductivity [sigma(SH) = (2.36 +/- 0.04) x 10(6) omega(-1) m(-1)] and bulk spin Hall angle (theta(SH) = 0.387 +/- 0.008) to be larger than commonly cited values. These results suggest that Pt can be an extremely useful source of SOT if the FM/NM interface can be engineered to minimize spin loss. Lastly, we find that self-consistent fitting of the damping and SOT data is best achieved by a model with Elliott-Yafet spin relaxation and extrinsic inverse spin Hall effect, such that both the spin diffusion length and spin Hall conductivity are proportional to the Pt charge conductivity.

  • 12.
    Björnson, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Balatsky, Alexander V.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Superconducting order parameter π-phase shift in magnetic impurity wires2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 10, article id 104521Article in journal (Refereed)
    Abstract [en]

    It has previously been found that a magnetic impurity in a conventional s-wave superconductor can give rise to a local π-phase shift of the superconducting order parameter. By studying a finite wire of ferromagnetic impurities, we are able to trace the origin of the π-phase shift to a resonance condition for the Bogoliubov-de Gennes quasiparticle states. When non-resonating states localized at the impurity sites are pulled into the condensate for increasing magnetic strength, the superconducting order parameter is reduced in discrete steps, eventually resulting in a π-phase shift. We also show that for a finite spin-orbit coupling, the π-phase shift is preserved and occurs in a large portion of the topologically non-trivial phase.

  • 13.
    Björnson, Kristofer
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Univ Copenhagen, Niels Bohr Inst, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark..
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Probing chiral edge states in topological superconductors through spin-polarized local density of state measurements2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 14, article id 140504Article in journal (Refereed)
    Abstract [en]

    We show that spin-polarized local density of states (LDOS) measurements can uniquely determine the chiral nature of topologically protected edge states surrounding a ferromagnetic island embedded in a conventional superconductor with spin-orbit coupling. The spin-polarized LDOS show a strong spin polarization directly tied to the normal direction of the edge with opposite polarizations on opposite sides of the island and with a distinct oscillatory pattern in energy.

  • 14.
    Bondarenko, N.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Y.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chico, J.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Bergman, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Eriksson, O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Skorodumova, N. V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 220401Article in journal (Refereed)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 15.
    Borla, Umberto
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Tech Univ Munich, Dept Phys, D-85748 Garching, Germany..
    Kuzmanovski, Dushko
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Tuning Majorana zero modes with temperature in pi-phase Josephson junctions2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 1, article id 014507Article in journal (Refereed)
    Abstract [en]

    We study a superconductor-normal-state-superconductor Josephson junction along the edge of a quantum spin Hall insulator with a superconducting pi phase across the junction. We solve self-consistently for the superconducting order parameter and find both real junctions, where the order parameter is fully real throughout the system, and junctions where the order parameter has a complex phase winding. Real junctions host two Majorana zero modes (MZMs), while phase-winding junctions have no subgap states close to zero energy. At zero temperature we find that the phase-winding solution always has the lowest free energy, which we establish as being due to a strong proximity effect into the N region. With increasing temperature this proximity effect is dramatically decreased and we find a phase transition into a real junction with two MZMs.

  • 16.
    Borlenghi, Simone
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mahani, M. R.
    Royal Inst Technol, Dept Mat & Nanophys, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden..
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat & Nanophys, Sch Informat & Commun Technol, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, Swedish E Sci Res Ctr SeRC, SE-10044 Stockholm, Sweden..
    Fransson, Jonas
    Nanoscale control of heat and spin conduction in artificial spin chains2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 13, article id 134419Article in journal (Refereed)
    Abstract [en]

    We describe a mechanism to control the energy and magnetization currents in an artificial spin chain, consisting of an array of permalloy nanodisks coupled through a magnetodipolar interaction. The chain is kept out of equilibrium by two thermal baths with different temperatures connected to its ends, which control the current propagation. Transport is enhanced by applying a uniform radio-frequency pump field resonating with some of the spin-wave modes of the chain. Moreover, the two currents can be controlled independently by tuning the static field applied on the chain. Thus we describe two effective means for the independent control of coupled currents and the enhancement of thermal and spin-wave conductivity in a realistic magnonics device, suggesting that similar effects could be observed in a large class of nonlinear oscillating systems.

  • 17.
    Borlenghi, Simone
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mahani, M. R.
    KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden..
    Fangohr, Hans
    Univ Southampton, Dept Engn & Environm, Southampton SO17 1BJ, Hants, England.;European XFEL GmbH, Holzkoppel 4, D-22869 Schenefeld, Germany..
    Franchin, M.
    Univ Southampton, Dept Engn & Environm, Southampton SO17 1BJ, Hants, England..
    Delin, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Sch Engn Sci, Dept Appl Phys, Electrum 229, SE-16440 Kista, Sweden.;KTH Royal Inst Technol, Swedish E Sci Res Ctr SeRC, SE-10044 Stockholm, Sweden..
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Micromagnetic simulations of spin-torque driven magnetization dynamics with spatially resolved spin transport and magnetization texture2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094428Article in journal (Refereed)
    Abstract [en]

    We present a simple and fast method to simulate spin-torque driven magnetization dynamics in nanopillar spin-valve structures. The approach is based on the coupling between a spin transport code based on random matrix theory and a micromagnetics finite-elements software. In this way the spatial dependence of both spin transport and magnetization dynamics is properly taken into account. Our results are compared with experiments. The excitation of the spin-wave modes, including the threshold current for steady-state magnetization precession and the nonlinear frequency shift of the modes are reproduced correctly. The giant magneto resistance effect and the magnetization switching also agree with experiment. The similarities with recently described spin-caloritronics devices are also discussed.

  • 18.
    Bouhon, Adrien
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Global band topology of simple and double Dirac-point semimetals2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 24, article id 241101Article in journal (Refereed)
    Abstract [en]

    We combine space group representation theory together with the scanning of closed subdomains of the Brillouin zone with Wilson loops to algebraically determine the global band-structure topology. Considering space group No. 19 as a case study, we show that the energy ordering of the irreducible representations at the high-symmetry points {Gamma, S, T, U} fully determines the global band topology, with all topological classes characterized through their simple and double Dirac points.

  • 19.
    Bouhon, Adrien
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schmidt, Johann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Topological nodal superconducting phases and topological phase transition in the hyperhoneycomb lattice2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104508Article in journal (Refereed)
    Abstract [en]

    We establish the topology of the spin-singlet superconducting states in the bare hyperhoneycomb lattice, and we derive analytically the full phase diagram using only symmetry and topology in combination with simple energy arguments. The phase diagram is dominated by two states preserving time-reversal symmetry. We find a line-nodal state dominating at low doping levels that is topologically nontrivial and exhibits surface Majorana flatbands, which we show perfectly match the bulk-boundary correspondence using the Berry phase approach. At higher doping levels, we find a fully gapped state with trivial topology. By analytically calculating the topological invariant of the nodal lines, we derive the critical point between the line-nodal and fully gapped states as a function of both pairing parameters and doping. We find that the line-nodal state is favored not only at lower doping levels but also if symmetry-allowed deformations of the lattice are present. Adding simple energy arguments, we establish that a fully gapped state with broken time-reversal symmetry likely appears covering the actual phase transition. We find this fully gapped state to be topologically trivial, while we find an additional point-nodal state at very low doing levels that also break time-reversal symmetry and has nontrivial topology with associated Fermi surface arcs. We eventually address the robustness of the phase diagram to generalized models also including adiabatic spin-orbit coupling, and we show how all but the point-nodal state are reasonably stable.

  • 20.
    Cayao, Jorge
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Odd-frequency superconducting pairing and subgap density of states at the edge of a two-dimensional topological insulator without magnetism2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 15, article id 155426Article in journal (Refereed)
    Abstract [en]

    We investigate the emergence and consequences of odd-frequency spin-triplet s-wave pairing in superconducting hybrid junctions at the edge of a two-dimensional topological insulator without any magnetism. More specifically, we consider several different normal-superconductor hybrid systems at the topological insulator edge, where spin-singlet s-wave superconducting pairing is proximity induced from an external conventional superconductor. We perform fully analytical calculations and show that odd-frequency mixed spin-triplet s-wave pairing arises due to the unique spin-momentum locking in the topological insulator edge state and the naturally nonconstant pairing potential profile in hybrid systems. Importantly, we establish a one-to-one correspondence between the local density of states (LDOS) at low energies and the odd-frequency spin-triplet pairing in NS, NSN, and SNS junctions along the topological insulator edge; at interfaces the enhancement in the LDOS can directly be attributed to the contribution of odd-frequency pairing. Furthermore, in SNS junctions we show that the emergence of the zero-energy LDOS peak at the superconducting phase phi = pi is associated purely with odd-frequency pairing in the middle of the junction.

  • 21.
    Cayao, Jorge
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Odd-frequency superconducting pairing in junctions with Rashba spin-orbit coupling2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 7, article id 075425Article in journal (Refereed)
    Abstract [en]

    We consider normal-superconductor (NS) and superconductor-normal-superconductor (SNS) junctions based on one-dimensional nanowires with Rashba spin-orbit coupling and proximity-induced s-wave spin-singlet superconductivity and analytically demonstrate how both even- and odd-frequency and spin-singlet and -triplet superconducting pair correlations are always present. In particular, by using a fully quantum mechanical scattering approach, we show that Andreev reflection induces mixing of spatial parities at interfaces, thus being the unique process which generates odd-frequency pairing; on the other hand, both Andreev and normal reflections contribute to even-frequency pairing. We further find that locally neither odd-frequency nor spin-triplet correlations are induced, but only even-frequency spin-singlet pairing. In the superconducting regions of NS junctions, the interface-induced amplitudes decay into the bulk, with the odd-frequency components being generally much larger than the even-frequency components at low frequencies. The odd-frequency pairing also develops short- and long-period oscillations due to the chemical potential and spin-orbit coupling, respectively, leading to a visible beating feature in their magnitudes. Moreover, we find that in short SNS junctions at pi-phase difference and strong spin-orbit coupling, the odd-frequency spin-singlet and -triplet correlations strongly dominate with an alternating spatial pattern for a large range of subgap frequencies.

  • 22.
    Cayao, Jorge
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    San-Jose, Pablo
    CSIC, ICMM, Cantoblanco, Madrid 28049, Spain..
    Black-Schaffer, Annica M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Aguado, Ramon
    CSIC, ICMM, Cantoblanco, Madrid 28049, Spain..
    Prada, Elsa
    Univ Autonoma Madrid, Dept Fis Mat Condensada, Condensed Matter Phys Ctr IFIMAC, E-28049 Madrid, Spain.;Univ Autonoma Madrid, Inst Nicolas Cabrera, E-28049 Madrid, Spain..
    Majorana splitting from critical currents in Josephson junctions2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 20, article id 205425Article in journal (Refereed)
    Abstract [en]

    A semiconducting nanowire with strong Rashba spin-orbit coupling and coupled to a superconductor can be tuned by an external Zeeman field into a topological phase with Majorana zero modes. Here we theoretically investigate how this exotic topological superconductor phase manifests in Josephson junctions based on such proximitized nanowires. In particular, we focus on critical currents in the short junction limit (L-N << xi, where L-N is the junction length and xi is the superconducting coherence length) and show that they contain important information about nontrivial topology and Majoranas. This includes signatures of the gap inversion at the topological transition and a unique oscillatory pattern that originates from Majorana interference. Interestingly, this pattern can be modified by tuning the transmission across the junction, thus providing complementary evidence of Majoranas and their energy splittings beyond standard tunnel spectroscopy experiments, while offering further tunability by virtue of the Josephson effect.

  • 23.
    Chernysheva, Ekaterina
    et al.
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France;Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Srour, Waked
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Philippe, Bertrand
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Baris, Bulent
    Sorbonne Univ, CNRS, Ecole Super Phys & Chim Ind, Lab Phys & Etud Mat,UMR 8213, 10 Rue Vauquelin, F-75005 Paris, France.
    Chenot, Stephane
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Felix Duarte, Roberto
    Helmholtz Zentrum Berlin Mat & Energie GmbH, D-12489 Berlin, Germany.
    Gorgoi, Mihaela
    Helmholtz Zentrum Berlin Mat & Energie GmbH, D-12489 Berlin, Germany.
    Cruguel, Herve
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Montigaud, Herve
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France.
    Jupille, Jacques
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Cabailh, Gregory
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Grachev, Sergey
    UMR 125 CNRS St Gobain Rech, SVI, 39 Quai Lucien Lefranc, F-93303 Aubervilliers, France.
    Lazzari, Remi
    Sorbonne Univ, CNRS, Inst NanoSci Paris, UMR 7588, 4 Pl Jussieu, F-75005 Paris, France.
    Band alignment at Ag/ZnO(0001) interfaces: A combined soft and hard x-ray photoemission study2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 23, article id 235430Article in journal (Refereed)
    Abstract [en]

    Band alignment at the interface between evaporated silver films and Zn- or O-terminated polar orientations of ZnO is explored by combining soft and hard x-ray photoemissions on native and hydrogenated surfaces. Ultraviolet photoemission spectroscopy (UPS) is used to track variations of work function, band bending, ionization energy, and Schottky barrier during silver deposition. The absolute values of band bending and the bulk position of the Fermi level are determined on continuous silver films by hard x-ray photoemission spectroscopy (HAXPES) through a dedicated modeling of core levels. Hydrogenation leads to the formation of similar to 0.3 monolayer of donorlike hydroxyl groups on both ZnO-O and ZnO-Zn surfaces and to the release of metallic zinc on ZnO-Zn. However, no transition to an accumulation layer is observed. On bare surfaces, silver adsorption is cationic on ZnO(000 (1) over bar)-O [anionic on ZnO(0001)-Zn] at the earliest stages of growth as expected from polarity healing before adsorbing as a neutral species. UPS and HAXPES data appear quite consistent. The two surfaces undergo rather similar band bendings for all types of preparation. The downward band bending of V-bb,(ZnO-O) = -0.4 eV and V-bb,(ZnO-Zn) = -0.6 eV found for the bare surfaces is reinforced upon hydrogenation (V-bb,(ZnO-O+H) = -1.1 eV, V-bb,(ZnO-Zn+H) = -1.2 eV). At the interface with Ag, a unique value of band bending of -0.75 eV is observed. While exposure to atomic hydrogen modulates strongly the energetic positions of the surface levels, a similar Schottky barrier of 0.5-0.7 eV is found for thick silver films on the two surfaces.

  • 24.
    Conradson, Steven D.
    et al.
    Inst Josef Stefan, Ljubljana 1000, Slovenia.;Washington State Univ, Pullman, WA 99164 USA..
    Andersson, David A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Boland, Kevin S.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bradley, Joseph A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Univ Washington, Seattle, WA 98195 USA..
    Byler, Darrin D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Durakiewicz, Tomasz
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Marie Curie Sklodowska Univ, PL-20031 Lublin, Poland..
    Gilbertson, Steven M.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Kozimor, Stosh A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Kvashnina, Kristina O.
    European Synchrotron ESRF, CS40220, F-38043 Grenoble 9, France.;Helmholtz Zentrum Dresden Rossendorf, Inst Resource Ecol, D-01314 Dresden, Germany..
    Nordlund, Dennis
    SLAC Natl Accelerator Lab, Menlo Pk, CA 94025 USA..
    Rodriguez, George
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Seidler, Gerald T.
    Univ Washington, Seattle, WA 98195 USA..
    Bagus, Paul S.
    Univ North Texas, Denton, TX 76203 USA..
    Butorin, Sergei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Conradson, Dylan R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Espinosa-Faller, Francisco J.
    Univ Marista Merida, Merida 97300, Yucatan, Mexico..
    Hess, Nancy J.
    Pacific Northwest Natl Lab, Richland, WA 99352 USA..
    Kas, Joshua J.
    Univ Washington, Seattle, WA 98195 USA..
    Lezama-Pacheco, Juan S.
    Stanford Univ, Stanford, CA 94305 USA..
    Martin, Philippe
    CEA, Nucl Energy Div, Res Dept Min & Fuel Recycling Proc, SFMA,LCC, F-30207 Bagnols Sur Ceze, France..
    Martucci, Mary B.
    Univ New Mexico, Los Alamos, NM 87544 USA..
    Rehr, John J.
    Univ Washington, Seattle, WA 98195 USA..
    Valdez, James A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bishop, Alan R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Baldinozzi, Gianguido
    Ecole Cent Paris, CNRS, F-99290 Chatenay Malabry, France..
    Clark, David L.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Tayal, Akhil
    Synchrotron Soleil, F-91192 Gif Sur Yvette, France..
    Closure of the Mott gap and formation of a superthermal metal in the Frohlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 12, article id 125114Article in journal (Refereed)
    Abstract [en]

    Mixed valence O-doped UO2+x. and photoexcited UO2 containing transitory U3+ and U5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Frohlich-type, nonequilibrium, phononcoupled Bose-Einstein condensate whose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO2, U4O9, and U3O7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f states of the valence band by similar to 0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2-2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied U5f states of UO2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO2 therefore fulfills the criteria for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5-10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are: (1) the direct formation of both of these long lived (> 3-10 ps) excited states without the short lived nonthermal intermediate; (2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and (3) the absence of hot electrons accompanying the insulating UO2 excited state. This heterogeneous, nonequilibrium, Frohlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.

  • 25.
    Dankert, Andre
    et al.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Bhaskar, Priyamvada
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Khokhriakov, Dmitrii
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Rodrigues, Isabel H.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Karpiak, Bogdan
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Kamalakar, M. Venkata
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden.
    Charpentier, Sophie
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Garate, Ion
    Univ Sherbrooke, Inst Quant & Regrp Quebecois Mat Pointe, Dept Phys, Sherbrooke, PQ J1K 2R1, Canada..
    Dash, Saroj P.
    Chalmers Univ Technol, Quantum Device Lab, Dept Microtechnol & Nanosci, S-41296 Gothenburg, Sweden..
    Origin and evolution of surface spin current in topological insulators2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125414Article in journal (Refereed)
    Abstract [en]

    The Dirac surface states of topological insulators offer a unique possibility for creating spin polarized charge currents due to the spin-momentum locking. Here we demonstrate that the control over the bulk and surface contribution is crucial to maximize the charge-to-spin conversion efficiency. We observe an enhancement of the spin signal due to surface-dominated spin polarization while freezing out the bulk conductivity in semiconducting Bi1.5Sb0.5Te1.7Se1.3 below 100 K. Detailed measurements up to room temperature exhibit a strong reduction of the magnetoresistance signal between 2 and 100 K, which we attribute to the thermal excitation of bulk carriers and to the electron-phonon coupling in the surface states. The presence and dominance of this effect up to room temperature is promising for spintronic science and technology.

  • 26.
    Di Marco, Igor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Held, Andreas
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Keshavarz, Samara
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kvashnin, Yaroslav O
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chioncel, Liviu
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany..
    Half-metallicity and magnetism in the Co2MnAl/CoMnVAl heterostructure2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 3, article id 035105Article in journal (Refereed)
    Abstract [en]

    We present a study of the electronic structure and magnetism of Co2MnAl, CoMnVAl, and their heterostructure. We employ a combination of density-functional theory and dynamical mean-field theory (DFT+DMFT). We find that Co2MnAl is a half-metallic ferromagnet, whose electronic and magnetic properties are not drastically changed by strong electronic correlations, static or dynamic. Nonquasiparticle states are shown to appear in the minority spin gap without affecting the spin polarization at the Fermi level predicted by standard DFT. We find that CoMnVAl is a semiconductor or a semimetal, depending on the employed computational approach. We then focus on the electronic and magnetic properties of the Co2MnAl/CoMnVAl heterostructure, predicted by previous first-principle calculations as a possible candidate for spin-injecting devices. We find that two interfaces, Co-Co/V-Al and Co-Mn/Mn-Al, preserve the half-metallic character, with and without including electronic correlations. We also analyze the magnetic exchange interactions in the bulk and at the interfaces. At the Co-Mn/Mn-Al interface, competing magnetic interactions are likely to favor the formation of a noncollinear magnetic order, which is detrimental for the spin polarization.

  • 27.
    Dong, Zhihua
    et al.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Li, Wei
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Schonecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Long, Mujun
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Longitudinal spin fluctuation contribution to thermal lattice expansion of paramagnetic Fe2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 5, article id 054426Article in journal (Refereed)
    Abstract [en]

    Using an efficient first-principles computational scheme for paramagnetic body-centered cubic (bcc) and face-centered cubic (fcc) Fe, we investigate the impact of thermal longitudinal spin fluctuations (LSFs) on the thermal lattice expansion. The equilibrium physical parameters are derived from the self-consistent Helmholtz free energy, in which the LSFs are considered within the adiabatic approximation and the anharmonic lattice vibration effect is included using the Debye-Gruneisen model taking into account the interplay between thermal, magnetic, and elastic degrees of freedom. Thermal LSFs are energetically more favorable in the fcc phase than in the bcc one giving a sizable contribution to the linear thermal expansion of gamma-Fe. The present scheme leads to accurate temperature-dependent equilibriumWigner-Seitz radius, bulk modulus, and Debye temperature within the stability fields of the two phases and demonstrates the importance of thermal spin fluctuations in paramagnetic Fe.

  • 28.
    Dong, Zhihua
    et al.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Schonecker, Stephan
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Chen, Dengfu
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Li, Wei
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Long, Mujun
    Chongqing Univ, Coll Mat Sci & Engn, Chongqing 400030, Peoples R China..
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Elastic properties of paramagnetic austenitic steel at finite temperature: Longitudinal spin fluctuations in multicomponent alloys2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 17, article id 174415Article in journal (Refereed)
    Abstract [en]

    We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c(44) by similar to 6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.

  • 29.
    Edström, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. ETH, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland..
    Magnetocrystalline anisotropy of Laves phase Fe2Ta1-xWx from first principles: Effect of 3d-5d hybridization2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 6, article id 064422Article in journal (Refereed)
    Abstract [en]

    ThemaThe magnetic properties of Fe2Ta and Fe2W in the hexagonal Laves phase are computed using density functional theory in the generalized gradient approximation, with the full potential linearized augmented plane-wave method. The alloy Fe2Ta1−xWx is studied using the virtual crystal approximation to treat disorder, with some comparisons to supercell calculations. Fe2Ta is found to be ferromagnetic with a saturation magnetization of μ0Ms=0.66T while, in contrast to earlier computational work, Fe2W is found to be ferrimagnetic with μ0Ms=0.35T. The transition from the ferri- to the ferromagnetic state occurs for x≤0.1. The magnetocrystalline anisotropy energy (MAE) is calculated to 1.25MJ/m3 for Fe2Ta and 0.87MJ/m3 for Fe2W. The MAE is found to be smaller for all values x in Fe2Ta1−xWx than for the end compounds and it is negative (in-plane anisotropy) for 0.1≤x≤0.9. The MAE is carefully analyzed in terms of the electronic structure. Even though there are weak 5d contributions to the density of states at the Fermi energy in both end compounds, a reciprocal space analysis, using the magnetic force theorem, reveals that the MAE originates mainly from regions of the Brillouin zone with strong 3d−5d hybridization near the Fermi energy. Perturbation theory and its applicability in relation to the MAE is discussed.

  • 30.
    Ertan, Emelie
    et al.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden..
    Kimberg, Victor
    Royal Inst Technol, Theoret Chem & Biol, S-10691 Stockholm, Sweden.;Siberian Fed Univ, Inst Nanotechnol Spect & Quantum Chem, Krasnoyarsk 660041, Russia..
    Gel'mukhanov, Faris
    Royal Inst Technol, Theoret Chem & Biol, S-10691 Stockholm, Sweden.;Siberian Fed Univ, Inst Nanotechnol Spect & Quantum Chem, Krasnoyarsk 660041, Russia..
    Hennies, Franz
    Lund Univ, MAX Lab 4, S-22100 Lund, Sweden..
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Schmitt, Thorsten
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Strocov, Vladimir N.
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland..
    Zhou, Kejin
    Paul Scherrer Inst, Swiss Light Source, CH-5232 Villigen, Switzerland.;Diamond Light Source Ltd, Diamond House,Harwell Sci & Innovat Campus, Didcot OX11 0DE, Oxon, England..
    Iannuzzi, Marcella
    Univ Zurich, Inst Phys Chem, CH-8057 Zurich, Switzerland..
    Foehlisch, Alexander
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Odelius, Michael
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, S-10691 Stockholm, Sweden..
    Pietzsch, Annette
    Helmholtz Zentrum Berlin Mat & Energie GmbH, Albert Einstein Str 15, D-12489 Berlin, Germany..
    Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 14, article id 144301Article in journal (Refereed)
    Abstract [en]

    Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.

  • 31.
    Etter, Sarah B.
    et al.
    Swiss Fed Inst Technol, Inst Theoret Phys, CH-8093 Zurich, Switzerland..
    Bouhon, Adrien
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Sigrist, Manfred
    Swiss Fed Inst Technol, Inst Theoret Phys, CH-8093 Zurich, Switzerland..
    Spontaneous surface flux pattern in chiral p-wave superconductors2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 6, article id 064510Article in journal (Refereed)
    Abstract [en]

    In chiral p-wave superconductors, magnetic flux patterns may appear spontaneously when translational symmetry is broken such as at surfaces, domain walls, or impurities. However, in the candidate material Sr2RuO4 no direct signs of such magnetic fields have been detected experimentally. In this paper, the flux pattern at the edge of a disk-shaped sample is examined using the phenomenological Ginzburg-Landau approach. The detailed shape of the flux pattern, including self-screening, is computed numerically for different surface types by systematically scanning a range of boundary conditions. Moreover, specific features of the electronic structure are included qualitatively through the coefficients in the Ginzburg-Landau functional. Both the shape and the magnitude of the flux pattern are found to be highly sensitive to all considered parameters. In conclusion, such spontaneous magnetic flux patterns are not a universal feature of chiral p-wave superconductors.

  • 32.
    Flovik, Vegard
    et al.
    Norwegian Univ Sci & Technol, Dept Phys, Ctr Quantum Spintron, NO-7491 Trondheim, Norway..
    Qaiumzadeh, Alireza
    Norwegian Univ Sci & Technol, Dept Phys, Ctr Quantum Spintron, NO-7491 Trondheim, Norway..
    Nandy, Ashis K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52425 Julich, Germany.;JARA, D-52425 Julich, Germany.
    Heo, Changhoon
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands..
    Rasing, Theo
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands..
    Generation of single skyrmions by picosecond magnetic field pulses2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 14, article id 140411Article in journal (Refereed)
    Abstract [en]

    We numerically demonstrate an ultrafastmethod to create single skyrmions in a collinear ferromagnetic sample by applying a picosecond (effective) magnetic field pulse in the presence of Dzyaloshinskii-Moriya interaction. For small samples the applied magnetic field pulse could be either spatially uniform or nonuniform while for large samples a nonuniform and localized field is more effective. We examine the phase diagram of pulse width and amplitude for the nucleation. Our finding could ultimately be used to design future skyrmion-based devices.

  • 33.
    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.

  • 34.
    Geilhufe, R. Matthias
    et al.
    KTH Royal Inst Technol, Ctr Quantum Mat, Nordita, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Bouhon, Adrien
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Borysov, Stanislav S.
    KTH Royal Inst Technol, Ctr Quantum Mat, Nordita, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Balatsky, Alexander V.
    KTH Royal Inst Technol, Ctr Quantum Mat, Nordita, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Three-dimensional organic Dirac-line materials due to nonsymmorphic symmetry: A data mining approach2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 4, article id 041103Article in journal (Refereed)
    Abstract [en]

    A datamining study of electronic Kohn-Sham band structures was performed to identify Dirac materials within the Organic Materials Database. Out of that, the three-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-1H-1,3-diazepine was found to host different Dirac-line nodes within the band structure. From a group theoretical analysis, it is possible to distinguish between Dirac-line nodes occurring due to twofold degenerate energy levels protected by the monoclinic crystalline symmetry and twofold degenerate accidental crossings protected by the topology of the electronic band structure. The obtained results can be generalized to all materials having the space group P2(1)/c (No. 14, C-2h(5)) by introducing three distinct topological classes.

  • 35.
    Gray, A. X.
    et al.
    Temple Univ, Dept Phys, Philadelphia, PA 19122 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Hoffmann, M. C.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Jeong, J.
    IBM Almaden Res Ctr, San Jose, CA 95120 USA.
    Aetukuri, N. P.
    IBM Almaden Res Ctr, San Jose, CA 95120 USA.
    Zhu, D.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Hwang, H. Y.
    MIT, Dept Chem, Cambridge, MA 02139 USA.
    Brandt, N. C.
    MIT, Dept Chem, Cambridge, MA 02139 USA.
    Wen, H.
    Argonne Natl Lab, Adv Photon Source, Argonne, IL 60439 USA.
    Sternbach, A. J.
    Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA;Boston Univ, Dept Phys, 590 Commonwealth Ave, Boston, MA 02215 USA.
    Bonetti, S.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Reid, A. H.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Kukreja, R.
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Graves, C.
    Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Wang, T.
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Granitzka, P.
    Univ Amsterdam, Van der Waals Zeeman Inst, NL-1018 XE Amsterdam, Netherlands;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Chen, Z.
    Stanford Univ, Dept Phys, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Higley, D. J.
    Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Chase, T.
    Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Jal, E.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Abreu, E.
    Swiss Fed Inst Technol, Inst Quantum Elect, CH-8006 Zurich, Switzerland;Boston Univ, Dept Phys, 590 Commonwealth Ave, Boston, MA 02215 USA.
    Liu, M. K.
    Boston Univ, Dept Phys, 590 Commonwealth Ave, Boston, MA 02215 USA;SUNY Stony Brook, Dept Phys & Astron, Stony Brook, NY 11794 USA.
    Weng, T-C
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lightsource, Menlo Pk, CA 94025 USA.
    Sokaras, D.
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lightsource, Menlo Pk, CA 94025 USA.
    Nordlund, D.
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lightsource, Menlo Pk, CA 94025 USA.
    Chollet, M.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Alonso-Mori, R.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Lemke, H.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Glownia, J. M.
    SLAC Natl Accelerator Lab, Linac Coherent Light Source, Menlo Pk, CA 94025 USA.
    Trigo, M.
    SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Zhu, Y.
    Argonne Natl Lab, Adv Photon Source, Argonne, IL 60439 USA.
    Ohldag, H.
    SLAC Natl Accelerator Lab, Stanford Synchrotron Radiat Lightsource, Menlo Pk, CA 94025 USA.
    Freeland, J. W.
    Argonne Natl Lab, Adv Photon Source, Argonne, IL 60439 USA.
    Samant, M. G.
    IBM Almaden Res Ctr, San Jose, CA 95120 USA.
    Berakdar, J.
    Martin Luther Univ Halle Wittenberg, Inst Phys, D-06099 Halle, Germany.
    Averitt, R. D.
    Univ Calif San Diego, Dept Phys, La Jolla, CA 92093 USA;Boston Univ, Dept Phys, 590 Commonwealth Ave, Boston, MA 02215 USA.
    Nelson, K. A.
    MIT, Dept Chem, Cambridge, MA 02139 USA.
    Parkin, S. S. P.
    IBM Almaden Res Ctr, San Jose, CA 95120 USA.
    Dürr, Hermann
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, FREIA. SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, Menlo Pk, CA 94025 USA.
    Ultrafast terahertz field control of electronic and structural interactions in vanadium dioxide2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 4, article id 045104Article in journal (Refereed)
    Abstract [en]

    Vanadium dioxide (VO2), an archetypal correlated-electron material, undergoes an insulator-metal transition near room temperature that exhibits electron-correlation-driven and structurally driven physics. Using ultrafast temperature- and fluence-dependent optical spectroscopy and x-ray scattering, we show that multiple interrelated electronic and structural processes in the nonequilibrium dynamics in VO2 can be disentangled in the time domain. Specifically, following intense subpicosecond terahertz (THz) electric-field excitation, a partial collapse of the insulating gap occurs within the first picosecond. At temperatures sufficiently close to the transition temperature and for THz peak fields above a threshold of approximately 1 MV/cm, this electronic reconfiguration initiates a change in lattice symmetry taking place on a slower timescale. We identify the kinetic energy increase of electrons tunneling in the strong electric field as the driving force, illustrating a promising method to control electronic and structural interactions in correlated materials on an ultrafast timescale.

  • 36.
    Hammar, Henning
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Time-dependent spin and transport properties of a single-molecule magnet in a tunnel junction2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 5, article id 054311Article in journal (Refereed)
    Abstract [en]

    In single-molecule magnets, the exchange between a localized spin moment and the electronic background provides a suitable laboratory for studies of dynamical aspects of both local spin and transport properties. Here we address the time evolution of a localized spin moment coupled to an electronic level in a molecular quantum dot embedded in a tunnel junction between metallic leads. The interactions between the localized spin moment and the electronic level generate an effective interaction between the spin moment at different instances in time. Therefore, we show that, despite being a single-spin system, there are effective contributions of isotropic Heisenberg and anisotropic Ising and Dzyaloshinski-Moriya character acting on the spin moment. The interactions can be controlled by gate voltage, voltage bias, the spin polarization in the leads, in addition to external magnetic fields. Signatures of the spin dynamics are found in the transport properties of the tunneling system, and we demonstrate that measurements of the spin current may be used for readout of the local spin moment orientation.

  • 37.
    Hammar, Henning
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Fransson, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Transient spin dynamics in a single-molecule magnet2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 21, article id 214401Article in journal (Refereed)
    Abstract [en]

    We explore the limitations and validity of semiclassically formulated spin equations of motion. Using a single-molecule magnet as a test model, we employ three qualitatively different approximation schemes. From a microscopic model, we derive a generalized spin equation of motion in which the parameters have a nonlocal time dependence. This dynamical equation is simplified to the Landau-Lifshitz-Gilbert equation with (i) time-dependent and (ii) time-independent parameters. We show that transient dynamics is essentially nonexisting in the latter approximation, while the former breaks down in the regime of strong coupling between the spin and the itinerant electrons.

  • 38.
    Hasan, Mehedi
    et al.
    ITMO Univ, St Petersburg 197101, Russia.;Nanyang Technol Univ, Div Phys & Appl Phys, Singapore 637371, Singapore..
    Yudin, Dmitry
    ITMO Univ, St Petersburg 197101, Russia..
    Iorsh, Ivan
    ITMO Univ, St Petersburg 197101, Russia.;Nanyang Technol Univ, Div Phys & Appl Phys, Singapore 637371, Singapore..
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Shelykh, Ivan
    ITMO Univ, St Petersburg 197101, Russia.;Univ Iceland, Sci Inst, IS-107 Reykjavik, Iceland..
    Topological edge-state engineering with high-frequency electromagnetic radiation2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 20, article id 205127Article in journal (Refereed)
    Abstract [en]

    We outline here how strong light-matter interaction can be used to induce quantum phase transition between normal and topological phases in two-dimensional topological insulators. We consider the case of a HgTe quantum well, in which band inversion occurs above a critical value of the well thickness, and demonstrate that coupling between electron states and the E field from an off-resonant linearly polarized laser provides a powerful tool to control topological transitions, even for a thickness of the quantum well that is below the critical value. We also show that topological phase properties of the edge states, including their group velocity, can be tuned in a controllable way by changing the intensity of the laser field. These findings open up the possibility for new experimental means with which to investigate topological insulators and shed new light on topological-insulator-based technologies that are under active discussion.

  • 39.
    Hedlund, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Cedervall, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Edström, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Materials Theory, ETH Zürich.
    Werwinski, Miroslaw
    Polish Academy of Sciences.
    Kontos, Sofia
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Örebro University.
    Rusz, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Sahlberg, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Magnetic properties of the Fe5SiB2−Fe5PB2 system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 9, article id 094433Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of the compound Fe5Si1−xPxB2 have been studied, with a focus on the Curie temperature TC, saturation magnetization MS, and magnetocrystalline anisotropy. Field and temperature dependent magnetization measurements were used to determine TC(x) and MS(x). The saturation magnetization at 10 K (300 K) is found to monotonically decrease from 1.11MA/m (1.03MA/m) to 0.97MA/m (0.87MA/m), as x increases from 0 to 1. The Curie temperature is determined to be 810 and 615 K in Fe5SiB2 and Fe5PB2, respectively. The highest TC is observed for x=0.1, while it decreases monotonically for larger x. The Curie temperatures have also been theoretically determined to be 700 and 660 K for Fe5SiB2 and Fe5PB2, respectively, using a combination of density functional theory and Monte Carlo simulations. The magnitude of the effective magnetocrystalline anisotropy was extracted using the law of approach to saturation, revealing an increase with increasing phosphorus concentration. Low-field magnetization vs temperature results for x=0,0.1,0.2 indicate that there is a transition from easy-axis to easy-plane anisotropy with decreasing temperature.

  • 40.
    Herper, Heike C.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ni-based Heusler compounds: How to tune the magnetocrystalline anisotropy2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 1, article id 014411Article in journal (Refereed)
    Abstract [en]

    Tailoring and controlling magnetic properties is an important factor for materials design. Here, we present a case study for Ni-based Heusler compounds of the type Ni(2)YZ with Y = Mn, Fe, Co and Z = B, Al, Ga, In, Si, Ge, Sn based on first-principles electronic structure calculations. These compounds are interesting since the materials properties can be quite easily tuned by composition and many of them possess a noncubic ground state being a prerequisite for a finite magnetocrystalline anisotropy (MAE). We discuss systematically the influence of doping at the Y and Z sublattices as well as the effect of lattice deformation on the MAE. We show that in case of Ni(2)CoZ the phase stability and the MAE can be improved using quaternary systems with elements from main group III and IV on the Z sublattice whereas changing the Y sublattice occupation by adding Fe does not lead to an increase of the MAE. Furthermore, we studied the influence of the lattice ratio on the MAE. Showing that small deviations can lead to a doubling of the MAE as in case of Ni2FeGe. Even though we demonstrate this for a limited set of systems, the findings may carry over to other related systems.

  • 41.
    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.

  • 42.
    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.

  • 43.
    Hou, Ling
    et al.
    Shanxi University, Institute of Theoretical Physics; Shanxi University, Department of Physics; Chinese Academy of Sciences (CAS), Institute of High Energy Physics; Dongguan Neutron Science Center.
    Li, Wei-Dong
    Shanxi University, Institute of Theoretical Physics; Shanxi University, Department of Physics.
    Wang, Fangwei
    Dongguan Neutron Science Center; Chinese Academy of Sciences, Institute of Physics, Beijing National Laboratory for Condensed Matter Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, Bao-Tian
    Chinese Academy of Sciences (CAS), Institute of High Energy Physics; Dongguan Neutron Science Center.
    Structural, electronic, and thermodynamic properties of curium dioxide: Density functional theory calculations2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 23, article id 235137Article in journal (Refereed)
    Abstract [en]

    We present a systematic investigation of the structural, magnetic, electronic, mechanical, and thermodynamic properties of CmO2 with the local density approximation (LDA)+U and the generalized gradient approximation (GGA)+U approaches. The strong Coulomb repulsion and the spin-orbit coupling (SOC) effects on the lattice structures, electronic density of states, and band gaps are carefully studied, and compared with other AO2 (A=U, Np, Pu, and Am). The ferromagnetic configuration with half-metallic character is predicted to be energetically stable while a charge-transfer semiconductor is predicted for the antiferromagnetic configuration. The elastic constants and phonon spectra show that the fluorite structure is mechanically and dynamically stable. Based on the first-principles phonon density of states, the lattice vibrational energy is calculated using the quasiharmonic approximation. Then, the Gibbs free energy, thermal expansion coefficient, specific heat, and entropy are obtained and compared with experimental data. The mode Grüneisen parameters are presented to analyze the anharmonic properties. The Slack relation is applied to obtain the lattice thermal conductivity in temperature range of 300–1600 K. The phonon group velocities are also calculated to investigate the heat transfer. For all these properties, if available, we compare the results of CmO2 with other AO2.

  • 44.
    Husain, Sajid
    et al.
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Kumar, Ankit
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Barwal, Vineet
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Behera, Nilamani
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Akansel, Serkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Chaudhary, Sujeet
    Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016, India.
    Spin pumping in ion-beam sputtered Co2FeAl/Mo bilayers: Interfacial Gilbert damping2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 6, article id 064420Article in journal (Refereed)
    Abstract [en]

    The spin-pumping mechanism and associated interfacial Gilbert damping are demonstrated in ion-beam sputtered Co2FeAl (CFA)/Mo bilayer thin films employing ferromagnetic resonance spectroscopy. The dependence of the net spin-current transportation on Mo layer thickness, 0 to 10 nm, and the enhancement of the net effective Gilbert damping are reported. The experimental data have been analyzed using spin-pumping theory in terms of spin current pumped through the ferromagnet/nonmagnetic metal interface to deduce the real spin-mixing conductance and the spin-diffusion length, which are estimated to be 1.56(±0.30)×1019m−2 and 2.61(±0.15)nm, respectively. The damping constant is found to be 8.8(±0.2)×10−3 in the Mo(3.5 nm)-capped CFA(8 nm) sample corresponding to an ∼69% enhancement of the original Gilbert damping 5.2(±0.6)×10−3 in the Al-capped CFA thin film. This is further confirmed by inserting the Cu dusting layer which reduces the spin transport across the CFA/Mo interface. The Mo layer thickness-dependent net spin-current density is found to lie in the range of 1−4MAm−2, which also provides additional quantitative evidence of spin pumping in this bilayer thin-film system.

  • 45.
    Johnson, R. D.
    et al.
    Rutherford Appleton Lab STFC, ISIS Facil, Didcot OX11 0QX, Oxon, England.;Univ Oxford, Dept Phys, Clarendon Lab, Oxford OX1 3PU, England..
    McClarty, P. A.
    Rutherford Appleton Lab STFC, ISIS Facil, Didcot OX11 0QX, Oxon, England..
    Khalyavin, D. D.
    Rutherford Appleton Lab STFC, ISIS Facil, Didcot OX11 0QX, Oxon, England..
    Manuel, P.
    Rutherford Appleton Lab STFC, ISIS Facil, Didcot OX11 0QX, Oxon, England..
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Knee, C. S.
    Chalmers, Dept Chem & Biol Engn, SE-41296 Gothenburg, Sweden.;ESAB AB, Lindholmsalln 9, SE-40277 Gothenburg, Sweden..
    Temperature-induced phase transition from cycloidal to collinear antiferromagnetism in multiferroic Bi0.9Sm0.1FeO3 driven by f-d induced magnetic anisotropy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 5, article id 054420Article in journal (Refereed)
    Abstract [en]

    In multiferroic BiFeO3 a cycloidal antiferromagnetic structure is coupled to a large electric polarization at room temperature, giving rise to magnetoelectric functionality that may be exploited in novel multiferroic-based devices. In this paper, we demonstrate that substituting samarium for 10% of the bismuth ions increases the periodicity of the room-temperature cycloid, and upon cooling to below similar to 15 K the magnetic structure tends towards a simple G-type antiferromagnet, which is fully established at 1.5 K. We show that this transition results from f-d exchange coupling, which induces a local anisotropy on the iron magnetic moments that destroys the cycloidal order-a result of general significance regarding the stability of noncollinear magnetic structures in the presence of multiple magnetic sublattices.

  • 46.
    Keatley, P. S.
    et al.
    Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England..
    Sani, Sohrab R.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. KTH Royal Inst Technol, Sch ICT, Mat & Nano Phys, Electrum 229, S-16440 Kista, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Hrkac, G.
    Univ Exeter, Coll Engn Math & Phys Sci, Exeter EX4 4SB, Devon, England..
    Mohseni, S. M.
    Shahid Beheshti Univ, Dept Phys, GC, Tehran 19839, Iran..
    Durrenfeld, P.
    Univ Gothenburg, Dept Phys, Fysikgrand 3, S-41296 Gothenburg, Sweden..
    Akerman, J.
    KTH Royal Inst Technol, Sch ICT, Mat & Nano Phys, Electrum 229, S-16440 Kista, Sweden.;NanOsc AB, Electrum 205, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, Fysikgrand 3, S-41296 Gothenburg, Sweden..
    Hicken, R. J.
    Univ Exeter, Dept Phys & Astron, Stocker Rd, Exeter EX4 4QL, Devon, England..
    Superharmonic injection locking of nanocontact spin-torque vortex oscillators2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 9, article id 094404Article in journal (Refereed)
    Abstract [en]

    Superharmonic injection locking of single nanocontact (NC) spin-torque vortex oscillators (STVOs) subject to a small microwave current has been explored. Frequency locking was observed up to the fourth harmonic of the STVO fundamental frequency f(0) in microwave magnetoelectronic measurements. The large frequency tunability of the STVO with respect to f(0) allowed the device to be locked to multiple subharmonics of the microwave frequency f(RF), or to the same subharmonic over a wide range of fRF by tuning the dc current. In general, analysis of the locking range, linewidth, and amplitude showed that the locking efficiency decreased as the harmonic number increased, as expected for harmonic synchronization of a nonlinear oscillator. Time-resolved scanning Kerr microscopy (TRSKM) revealed significant differences in the spatial character of the magnetization dynamics of states locked to the fundamental and harmonic frequencies, suggesting significant differences in the vortex core trajectories within the same device. Superharmonic injection locking of a NC-STVO may open up possibilities for devices such as nanoscale frequency dividers, while differences in the core trajectory may allow mutual synchronization to be achieved in multioscillator networks by tuning the spatial character of the dynamics within shared magnetic layers.

  • 47.
    Keqi, A.
    et al.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Gehlmann, M.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA;Forschungszentrum Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany.
    Conti, G.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Nemsak, S.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA;Forschungszentrum Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany.
    Rattanachata, A.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Minar, J.
    Univ West Bohemia, New Technol Res Ctr, Plzen 30614, Czech Republic.
    Plucinski, L.
    Forschungszentrum Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany.
    Rault, J. E.
    Synchrotron SOLEIL, F-91192 St Aubin, France.
    Rueff, J. P.
    Synchrotron SOLEIL, F-91192 St Aubin, France.
    Scarpulla, M.
    Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA;Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA;Univ Utah, Dept Elect & Comp Engn, Salt Lake City, UT 84112 USA.
    Hategan, M.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA.
    Pálsson, Gunnar K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics. Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Conlon, C.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Eiteneer, D.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Saw, A. Y.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Gray, A. X.
    Temple Univ, Dept Phys, Philadelphia, PA 19122 USA.
    Kobayashi, K.
    Japan Atom Energy Agcy, 1-1-1 Kouto, Sayo, Hyogo 6795148, Japan.
    Ueda, S.
    Natl Inst Mat Sci, Synchrotron Xray Stn SPring 8, 1-1-1 Kouto, Sayo, Hyogo 6795148, Japan;NIMS, Res Ctr Adv Measurement & Characterizat, 1-2-1 Sengen, Tsukuba, Ibaraki 3050047, Japan.
    Dubon, O. D.
    Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA;Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA.
    Schneider, C. M.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA;Forschungszentrum Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany.
    Fadley, C. S.
    Univ Calif Davis, Dept Phys, Davis, CA 95616 USA;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.
    Electronic structure of the dilute magnetic semiconductor Ga1-xMnxP from hard x-ray photoelectron spectroscopy and angle-resolved photoemission2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 15, article id 155149Article in journal (Refereed)
    Abstract [en]

    We have investigated the electronic structure of the dilute magnetic semiconductor (DMS) Ga0.98Mn0.02P and compared it to that of an undoped GaP reference sample, using hard x-ray photoelectron spectroscopy (HXPS) and hard x-ray angle-resolved photoemission spectroscopy (HARPES) at energies of about 3 keV. We present experimental data, as well as theoretical calculations, to understand the role of the Mn dopant in the emergence of ferromagnetism in this material. Both core-level spectra and angle-resolved or angle-integrated valence spectra are discussed. In particular, the HARPES experimental data are compared to free-electron final-state model calculations and to more accurate one-step photoemission theory. The experimental results show differences between Ga0.98Mn0.02P and GaP in both angle-resolved and angle-integrated valence spectra. The Ga0.98Mn0.02P bands are broadened due to the presence of Mn impurities that disturb the long-range translational order of the host GaP crystal. Mn-induced changes of the electronic structure are observed over the entire valence band range, including the presence of a distinct impurity band close to the valence-band maximum of the DMS. These experimental results are in good agreement with the one-step photoemission calculations and a prior HARPES study of Ga0.97Mn0.03As and GaAs [Gray et al., Nat. Mater. 11, 957 (2012)], demonstrating the strong similarity between these two materials. The Mn 2p and 3s core-level spectra also reveal an essentially identical state in doping both GaAs and GaP.

  • 48.
    Keshavarz, Samara
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Schött, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Millis, Andrew J.
    Columbia Univ, Dept Phys, New York, NY USA; Flatiron Inst, Ctr Computat Quantum Phys, New York, NY USA.
    Kvashnin, Yaroslav
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic structure, magnetism, and exchange integrals in transition-metal oxides: Role of the spin polarization of the functional in DFT+U calculations2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 18, article id 184404Article in journal (Refereed)
    Abstract [en]

    Density functional theory augmented with Hubbard-U corrections (DFT+U) is currently one of the most widely used methods for first-principles electronic structure modeling of insulating transition-metal oxides (TMOs). Since U is relatively large compared to bandwidths, the magnetic excitations in TMOs are expected to be well described by a Heisenberg model. However, in practice the calculated exchange parameters J(ij) depend on the magnetic configuration from which they are extracted and on the functional used to compute them. In this work we investigate how the spin polarization dependence of the underlying exchange-correlation functional influences the calculated magnetic exchange constants of TMOs. We perform a systematic study of the predictions of calculations based on the local density approximation plus U (LDA+U) and the local spin density approximation plus U (LSDA+U) for the electronic structures, total energies, and magnetic exchange interactions Jij extracted from ferromagnetic (FM) and antiferromagnetic (AFM) configurations of several transition-metal oxide materials. We report that for realistic choices of Hubbard U and Hund's J parameters, LSDA+U and LDA+U calculations result in different values of the magnetic exchange constants and band gap. The dependence of the band gap on the magnetic configuration is stronger in LDA+U than in LSDA+U and we argue that this is the main reason why the configuration dependence of Jij is found to be systematically more pronounced in LDA+U than in LSDA+U calculations. We report a very good correspondence between the computed total energies and the parametrized Heisenberg model for LDA+U calculations, but not for LSDA+U, suggesting that LDA+U is a more appropriate method for estimating exchange interactions.

  • 49.
    Klarbring, Johan
    et al.
    Linköping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Skorodumova, Natalia V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH Royal Inst Technol, Mat Sci & Engn Dept, Stockholm, Sweden..
    Simak, Sergei I.
    Linköping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Finite-temperature lattice dynamics and superionic transition in ceria from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

  • 50.
    Kumar, Ankit
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Akansel, Serkan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stopfel, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
    Fazlali, M.
    Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Åkerman, J.
    Univ Gothenburg, Dept Phys, SE-41296 Gothenburg, Sweden..
    Brucas, Rimantas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Spin transfer torque ferromagnetic resonance induced spin pumping in the Fe/Pd bilayer system2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 6, article id 064406Article in journal (Refereed)
    Abstract [en]

    Inconsistencies in estimates of the spin Hall angle (theta(SH)) and spin diffusion length (lambda(SD)) of nonmagnetic (NM) layers using the spin transfer torque ferromagnetic resonance (ST-FMR) in ferromagnetic FM/NM bilayer structures are attributed to the inverse spin Hall effect (ISHE) and interfacial parameter contributions, interface spin transparency, interfacial anisotropic magnetoresistance, and effective spin-mixing conductance. These contributions in Fe(10 nm)/Pd(2-8 nm) bilayer structures have been probed employing the simultaneous detection of ST-FMR and ISHE in conjunction with in-plane FMR measurements. The interfacial contributions are found to increase with an increase in Pd layer thickness (t(NM)), which can be linked to the spin pumping effect in conjunction with spin backflow. Correcting the t(NM) dependence of the ST-FMR spectra for the interfacial and ISHE contributions prior to estimating theta(SH) and theta(SD) of the Pd layer, the estimated values are found to be 0.10 +/- 0.03 and 5.4 +/- 1.2 nm, respectively.

12 1 - 50 of 95
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