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1

Kapellasite: a kagome quantum spin liquid with competing interactions

NASA Astrophysics Data System (ADS)

In recent years, the search for an experimental quantum spin liquid in two dimensions has attracted much interest in the community. Magnetic frustration and quantum fluctuations are believed to be key ingredients to stabilize such a spin liquid ground state in 2D. The S=12 kagome lattice combines these two ingredients. Among the materials available with this geometry, herbertsmithite has proven to be a very promising candidate. There, the antiferromagnetic nearest neighbor coupling J1 is dominant. In this talk, I will explore the effect of frustration generated by competing interactions on the quantum kagome lattice, based on experiments performed on kapellasite Cu3Zn(OH)6Cl2, a polymorph to herbertsmithite. The system Hamiltonian, determined from a fit of a high-temperature series expansion to magnetic susceptibility and specific heat data, points to competing interactions with a ferromagnetic nearest neighbor exchange J1 and an ``across-hexagon'' antiferromagnetic one Jd, with a ratio |Jd/ J1|˜0.85. Local probes (?SR, ^35Cl-NMR) and inelastic neutron scattering (INS) experiments evidence a gapless spin-liquid state down to 20 mK, showing unusual dynamic short-range correlations characteristic of a 12 spin sublattices antiferromagnetic state called Cuboc2. We further investigate the spin dynamics at different timescales by NMR, ?SR and INS measurements and discuss our results within the context of theoretical calculations using the Schwinger-Boson mean field approach.

Kermarrec, Edwin

2013-03-01

2

Spin dynamics in the multiferroic materials (invited)

NASA Astrophysics Data System (ADS)

We report high resolution inelastic neutron scattering measurements and spin dynamics calculations in two multiferroic materials: the geometrically frustrated triangular lattice CuFeO2 and mineral Hübnerite MnWO4. In un-doped CuFeO2 a low-T collinear spin structure is stabilized by long range magnetic interactions. When doped with a few percent of gallium, the spin order evolves into a complex noncollinear configuration and the system becomes multiferroic. Similarly, the ground state collinear spin order in pure MnWO4 results from delicate balance between competing magnetic interactions up to 11th nearest neighbors and can be tuned by substitution of Mn ions with magnetic or nonmagnetic impurities. The comprehensive investigation of spin dynamics in both systems help to understand the fundamental physical process and the interactions leading to the close interplay of magnetism and ferroelectricity in this type of materials.

Ye, Feng; Fishman, Randy S.; Haraldsen, Jason; Lorenz, Bernd; Chu, C. W.; Kimura, Tsuyoshi

2012-04-01

3

Competing spin pumping effects in magnetic hybrid structures

NASA Astrophysics Data System (ADS)

Pure spin current can be detected by its conversion into charge current in nanometer thick nonmagnetic metal layer with large spin-orbit coupling by means of the inverse spin Hall effect (ISHE). Recently, it has been shown that the metallic ferromagnet Permalloy (Py) can also be used as spin current detector in experiments in which an ISHE voltage is created in a Py layer in contact with the insulating ferromagnet yttrium iron garnet (YIG) under a thermal gradient in the longitudinal spin Seebeck configuration. Here, we report experiments with microwave driven spin pumping in heterostructures made with single crystal YIG film and a nanometer thick Py or Pt layer that show that Py behaves differently than nonmagnetic metals as a spin current detector. The results are attributed to the competition between the spin currents generated by the dynamics of the magnetizations in YIG and in Py, which are exchange coupled at the interface.

Azevedo, A.; Alves Santos, O.; Fonseca Guerra, G. A.; Cunha, R. O.; Rodríguez-Suárez, R.; Rezende, S. M.

2014-02-01

4

Spin dynamics in the multiferroic materials (invited)

We report high resolution inelastic neutron scattering measurements and spin dynamics calculations in two multiferroic materials: the geometrically frustrated triangular lattice CuFeO2 and mineral Hu bnerite MnWO4. In un-doped CuFeO2 a low-T collinear spin structure is stabilized by long range magnetic interactions. When doped with a few percent of gallium, the spin order evolves into a complex noncollinear configuration and the system becomes multiferroic. Similarly, the ground state collinear spin order in pure MnWO4 results from delicate balance between competing magnetic interactions up to 11th nearest neighbors and can be tuned by substitution of Mn ions with magnetic or nonmagnetic impurities. The comprehensive investigation of spin dynamics in both systems help to understand the fundamental physical process and the interactions leading to the close interplay of magnetism and ferroelectricity in this type of materials. VC2012 American Institute of Physics. [doi:10.1063/1.3677863

Ye, Feng [ORNL; Fishman, Randy Scott [ORNL; Haraldsen, Jason T [ORNL; Lorenz, Bernd [University of Houston, Houston; Chu, C. W. [University of Houston, Houston; Kimura, K. [Osaka University

2012-01-01

5

NASA Astrophysics Data System (ADS)

We describe a regime for low-field magnetoresistance in organic semiconductors, in which the spin-relaxing effects of localized nuclear spins and electronic spins interfere. The regime is studied by the controlled addition of localized electronic spins to a material that exhibits substantial room-temperature magnetoresistance (˜20%). Although initially the magnetoresistance is suppressed by the doping, at intermediate doping there is a regime where the magnetoresistance is insensitive to the doping level. For much greater doping concentrations the magnetoresistance is fully suppressed. The behavior is described within a theoretical model describing the effect of carrier spin dynamics on the current.

Wang, Y.; Harmon, N. J.; Sahin-Tiras, K.; Wohlgenannt, M.; Flatté, M. E.

2014-08-01

6

Dynamic wetting with two competing adsorbates

NASA Astrophysics Data System (ADS)

We study the dynamic properties of a model for wetting with two competing adsorbates on a planar substrate. The two species of particles have identical properties and repel each other. Starting with a flat interface one observes the formation of homogeneous droplets of the respective type separated by nonwet regions where the interface remains pinned. The wet phase is characterized by slow coarsening of competing droplets. Moreover, in 2+1 dimensions an additional line of continuous phase transition emerges in the bound phase, which separates an unordered phase from an ordered one. The symmetry under interchange of the particle types is spontaneously broken in this region and finite systems exhibit two metastable states, each dominated by one of the species. The critical properties of this transition are analyzed by numeric simulations.

Gogolin, Christian; Meltzer, Christian; Willers, Marvin; Hinrichsen, Haye

2009-04-01

7

Polarized hyperons probe dynamics of quark spin

Researchers at Jefferson Laboratory demonstrate how two analyses of the same data provide two plausible models of spin transfer in exclusive hyperon production, yielding quite different pictures of quark spin dynamics and challenging existing theories.

Daniel S. Carman; T. S. Harry Lee; Mac Mestayer; Reinhard Schumacher

2007-08-01

8

Dynamic core competences through meta-learning and strategic context

Traditional approaches to studying competitive advantage, while valuable, are not adequate to explain how firms can operate effectively in turbulent and often chaotic environments. A resource or skill-based view focusing on development and application of core competences is offered to supplement the traditional approaches. We present a model of the development and outcomes of dynamic core competences based on organizational

Richard Bettis; M. A. Hitt

1996-01-01

9

Electron-spin dynamics induced by photon spins

NASA Astrophysics Data System (ADS)

Strong rotating magnetic fields may cause a precession of the electron?s spin around the rotation axis of the magnetic field. The superposition of two counterpropagating laser beams with circular polarization and opposite helicity features such a rotating magnetic field component but also carries spin. The laser?s spin density, which can be expressed in terms of the laser?s electromagnetic fields and potentials, couples to the electron?s spin via a relativistic correction to the Pauli equation. We show that the quantum mechanical interaction of the electron?s spin with the laser?s rotating magnetic field and with the laser?s spin density counteract each other in such a way that a net spin rotation remains with a precession frequency that is much smaller than the frequency one would expect from the rotating magnetic field alone. In particular, the frequency scales differently with the laser?s electric field strength depending on whether relativistic corrections are taken into account or not. Thus, the relativistic coupling of the electron?s spin to the laser?s spin density changes the dynamics not only quantitatively but also qualitatively as compared to the nonrelativistic theory. The electron?s spin dynamics are a genuine quantum mechanical relativistic effect.

Bauke, Heiko; Ahrens, Sven; Keitel, Christoph H.; Grobe, Rainer

2014-10-01

10

Exploring the quantum frontier of spin dynamics

NASA Astrophysics Data System (ADS)

Our familiar classical concept of a spin is that of a system characterized by the direction in which the spin is pointing. In this picture, we may think of the dynamics of a spin as the motion of a classical gyroscope, wich we can aptly describe the spin dynamics as the motion of a point on a sphere. This classical description of the spin dynamics, formalized in the Landau-Lifshits-Gilbert equation, has proved extremely successful in the field micro- and nanomagnetism. However, as the size of the system is further decreased (e.g., when considering molecular magnets such as the Fe8 or Mn12 systems, which have a spin S=10), quantum effects such as tunneling, interference, entanglement, coherence, etc., play an essential role, and one must adopt a fully quantum mechanical description of the spin system. The landscape in which the system evolves is then no longer a mere sphere, but rather it is the projective Hilbert space (wich is the projective complex space <=P^2S for a spin S), as space of considerably greater richness and complexity than the sphere of classical spin dynamics. A very appealing tool to describe a quantum spin system is Majorana's stellar representation, which is the extension for a spin S of the Bloch sphere description of a spin .5ex1 -.1em/ -.15em.25ex2 . I shall discuss how this representation can help us in improving our understanding of fundamental quantum processes and concept such as Landau-Zener transitions, Rabi oscillations, Berry phase, diabolical points and illustrate this on the example of spin dynamics of molecular magnets.

Bruno, Patrick

2011-03-01

11

Competing orders in a magnetic field:spin and charge density waves in the cuprate superconductors

We describe two-dimensional quantum spin fluctuations in a superconducting Abrikosov flux lattice induced by a magnetic field applied to a doped Mott insulator. Complete numerical solutions of a self-consistent large N theory provide detailed information on the phase diagram and on the spatial structure of the dynamic spin spectrum. Our results apply to phases with and without longrange spin density

Ying Zhang; Eugene Demler; Subir Sachdev

2002-01-01

12

Dynamical Localization in Disordered Quantum Spin Systems

NASA Astrophysics Data System (ADS)

We say that a quantum spin system is dynamically localized if the time-evolution of local observables satisfies a zero-velocity Lieb-Robinson bound. In terms of this definition we have the following main results: First, for general systems with short range interactions, dynamical localization implies exponential decay of ground state correlations, up to an explicit correction. Second, the dynamical localization of random xy spin chains can be reduced to dynamical localization of an effective one-particle Hamiltonian. In particular, the isotropic xy chain in random exterior magnetic field is dynamically localized.

Hamza, Eman; Sims, Robert; Stolz, Günter

2012-10-01

13

Coherent Electron Spin Dynamics in Quantum Dots

NASA Astrophysics Data System (ADS)

The coherent spin dynamics of electrons in confined in quantum dots is discussed. A new measurement technique, mode-locking of electron spin precession by and with a pulsed excitation laser is used to address the coherence, which otherwise would be masked in ensemble studies by dephasing. The background of nuclei leads to a refocusing such that all optically excited electron spins become synchronized with the laser. With this tool spin coherence times in the microseconds range are demonstrated at cryogenic temperatures. The mode locking can be tailored by the laser excitation protocol such that strong signals at arbitrary times can be generated in Faraday rotation experiments.

Bayer, Manfred; Greilich, Alex; Yakovlev, Dmitri R.

14

Spin-glass dynamics with conserved magnetization

The dynamical response of a spin-glass is studied at the mean-field level for models in which the total magnetization is conserved. The first model considered is totally dissipative, like the conventional relaxational ones, but the Langevin equation is diffusive. In the k-->0 limit, the diffusion constant is unaffected by the proximity of the spin-glass transition, but the region of k

J. A. Hertz; R. A. Klemm

1983-01-01

15

Dynamics of spin effects of compact binaries

NASA Astrophysics Data System (ADS)

For a 10-dimensional post-Newtonian canonical conservative Hamiltonian system of spinning compact binaries, where the orbital part is accurate to the third-order post-Newtonian expansion and the spin-orbit contributions are up to the next-to-next-to-leading order, its dynamics is integrable and not at all chaotic due to the presence of five independent isolating integrals, including the total energy, three components of the total angular momentum vector and the length of the orbital angular momentum. As the spin-spin effects of the two spinning bodies are further included, only the length of the orbital angular momentum is no longer conserved, so that the dynamics becomes typically non-integrable. Numerical simulations support the onset of chaos. Above all, many chaotic orbits whose initial radii are larger than 10M and whose Lyapunov times are less than the corresponding inspiral decay times are found. In addition, a threshold value of the maximum ratio of the spin-spin Hamiltonian to the whole Hamiltonian for distinguishing between the ordered and chaotic cases is also given.

Mei, Lijie; Ju, Mingjie; Wu, Xin; Liu, Sanqiu

2013-11-01

16

Spin Hall phenomenology of magnetic dynamics

NASA Astrophysics Data System (ADS)

We study the role of spin-orbit interactions in the coupled magnetoelectric dynamics of a ferromagnetic film coated with an electrical conductor. While the main thrust of this work is phenomenological, several popular simple models are considered microscopically in some detail, including Rashba and Dirac two-dimensional electron gases coupled to a magnetic insulator, as well as a diffusive spin Hall system. We focus on the long-wavelength magnetic dynamics that experiences current-induced torques and produces fictitious electromotive forces. Our phenomenology provides a suitable framework for analyzing experiments on current-induced magnetic dynamics and reciprocal charge pumping, including the effects of magnetoresistance and Gilbert-damping anisotropies, without a need to resort to any microscopic considerations or modeling. Finally, some remarks are made regarding the interplay of spin-orbit interactions and magnetic textures.

Tserkovnyak, Yaroslav; Bender, Scott A.

2014-07-01

17

Quantum Spin Dynamics in Molecular Magnets

The detailed theoretical understanding of quantum spin dynamics in various molecular magnets is an important step on the roadway to technological applications of these systems. Quantum effects in both ferromagnetic and antiferromagnetic molecular clusters are, by now, theoretically well understood. Ferromagnetic molecular clusters allow one to study the interplay of incoherent quantum tunneling and thermally activated transitions between states with

Michael N. Leuenberger; Florian Meier; Daniel Loss

2002-01-01

18

Structurally Dynamic Spin Market Networks

NASA Astrophysics Data System (ADS)

The agent-based model of stock price dynamics on a directed evolving complex network is suggested and studied by direct simulation. The stationary regime is maintained as a result of the balance between the extremal dynamics, adaptivity of strategic variables and reconnection rules. The inherent structure of node agent "brain" is modeled by a recursive neural network with local and global inputs and feedback connections. For specific parametric combination the complex network displays small-world phenomenon combined with scale-free behavior. The identification of a local leader (network hub, agent whose strategies are frequently adapted by its neighbors) is carried out by repeated random walk process through network. The simulations show empirically relevant dynamics of price returns and volatility clustering. The additional emerging aspects of stylized market statistics are Zipfian distributions of fitness.

Horváth, Denis; Kuscsik, Zoltán

19

Magnetic monopole dynamics in spin ice.

One of the most remarkable examples of emergent quasi-particles is that of the 'fractionalization' of magnetic dipoles in the low energy configurations of materials known as 'spin ice' into free and unconfined magnetic monopoles interacting via Coulomb's 1/r law (Castelnovo et al 2008 Nature 451 42-5). Recent experiments have shown that a Coulomb gas of magnetic charges really does exist at low temperature in these materials and this discovery provides a new perspective on otherwise largely inaccessible phenomenology. In this paper, after a review of the different spin ice models, we present detailed results describing the diffusive dynamics of monopole particles starting both from the dipolar spin ice model and directly from a Coulomb gas within the grand canonical ensemble. The diffusive quasi-particle dynamics of real spin ice materials within the 'quantum tunnelling' regime is modelled with Metropolis dynamics, with the particles constrained to move along an underlying network of oriented paths, which are classical analogues of the Dirac strings connecting pairs of Dirac monopoles. PMID:21471628

Jaubert, L D C; Holdsworth, P C W

2011-04-27

20

Dynamics of competing ideas in complex social systems

NASA Astrophysics Data System (ADS)

Individuals accepting an idea may intentionally or unintentionally impose influences in a certain neighborhood area, making it less likely or even impossible for other individuals within the area to accept competing ideas. Depending on whether such influences strictly prohibit neighborhood individuals from accepting other ideas or not, we classify them into exclusive and non-exclusive influences, respectively. Our study reveals, for the first time, the rich and complex dynamics of two competing ideas with neighborhood influences in scale-free social networks: depending on whether they have exclusive or non-exclusive influences, the final state varies from multiple co-existence to founder control to exclusion, with different sizes of population accepting each of the ideas, respectively. Such results provide helpful insights for better understanding of the spread (and the control of the spread) of ideas in human society.

Wang, Yubo; Xiao, Gaoxi; Liu, Jian

2012-01-01

21

Communication: Quantum dynamics in classical spin baths

NASA Astrophysics Data System (ADS)

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability.

Sergi, Alessandro

2013-07-01

22

Quantum Dynamics in Classical Spin Baths

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability.

Alessandro Sergi

2013-06-14

23

Communication: quantum dynamics in classical spin baths.

A formalism for studying the dynamics of quantum systems embedded in classical spin baths is introduced. The theory is based on generalized antisymmetric brackets and predicts the presence of open-path off-diagonal geometric phases in the evolution of the density matrix. The weak coupling limit of the equation can be integrated by standard algorithms and provides a non-Markovian approach to the computer simulation of quantum systems in classical spin environments. It is expected that the theory and numerical schemes presented here have a wide applicability. PMID:23883002

Sergi, Alessandro

2013-07-21

24

Equilibrium dynamics of spin-glass systems

We present a critical analysis of the Sompolinsky theory of equilibrium dynamics. By using the spherical 2+p spin-glass model we test the asymptotic static limit of the Sompolinsky solution showing that it fails to yield a thermodynamically stable solution. We then present an alternative formulation, based on the Crisanti, Hoerner, and Sommers [Z. Phys. B: Condens. Matter 92, 257 (1993)] dynamical solution of the spherical p-spin spin-glass model, reproducing a stable static limit that coincides, in the case of a one step replica symmetry breaking ansatz, with the solution at the dynamic free energy threshold at which the relaxing system gets stuck off equilibrium. We formally extend our analysis to any number of replica symmetry breakings R. In the limit R{yields}{infinity}, both formulations lead to the Parisi antiparabolic differential equation. This is the special case, though, where no dynamic blocking threshold occurs. The formulation does not contain the additional order parameter {delta} of the Sompolinsky theory.

Crisanti, A.; Leuzzi, L. [Dipartimento di Fisica, Universita di Roma 'La Sapienza', Istituto Nazionale Fisica della Materia, Unita di Roma, Rome (Italy); SMC, P.le Aldo Moro 2, I-00185 Rome (Italy); Istituto Studi della Complessita (ISC), CNR, Via dei Taurini 19, I-00185 Rome (Italy)

2007-04-01

25

Decoherence dynamics of a single spin versus spin ensemble

We study decoherence of central spins by a spin bath, focusing on the difference between measurement of a single central spin and measurement of a large number of central spins (as found in typical spin-resonance experiments). For a dilute spin bath, the single spin demonstrates Gaussian free-induction decay, in contrast to exponential decay characteristic of spin ensembles. A strong difference between a single spin and a spin ensemble also exists for the Rabi oscillation decay: for a repeated Rabi oscillation experiment, suppression of decoherence happens for a single spin while acceleration takes place for a spin ensemble. The mathematical origin of such behavior is similar to quantum Zeno/anti-Zeno effects.

Dobrovitski, V. V.; Feiguin, A. E.; Awschalom, D. D.; Hanson, R.

2008-06-26

26

Quantum Spin Dynamics in Molecular Magnets

Summary. ?The detailed theoretical understanding of quantum spin dynamics in various molecular magnets is an important step on the\\u000a roadway to technological applications of these systems. Quantum effects in both ferromagnetic and antiferromagnetic molecular\\u000a clusters are, by now, theoretically well understood. Ferromagnetic molecular clusters allow one to study the interplay of\\u000a incoherent quantum tunneling and thermally activated transitions between states with

Michael N. Leuenberger; Florian Meier; Daniel Loss

2003-01-01

27

Combined molecular dynamics-spin dynamics simulations of bcc iron

NASA Astrophysics Data System (ADS)

Using a classical model that treats translational and spin degrees of freedom on an equal footing, we study phonon-magnon interactions in BCC iron with combined molecular and spin dynamics methods. The atomic interactions are modeled via an empirical many-body potential while spin dependent interactions are established through a Hamiltonian of the Heisenberg form with a distance dependent magnetic exchange interaction obtained from first principles electronic structure calculations. The temporal evolution of translational and spin degrees of freedom was determined by numerically solving the coupled equations of motion, using an algorithm based on the second order Suzuki-Trotter decomposition of the exponential operators. By calculating Fourier transforms of space- and time-displaced correlation functions, we demonstrate that the the presence of lattice vibrations leads to noticeable softening and damping of spin wave modes. As a result of the interplay between lattice and spin subsystems, we also observe additional longitudinal spin wave excitations, with frequencies which coincide with that of the longitudinal lattice vibrations.

Perera, Dilina; Landau, David P.; Nicholson, Don M.; Stocks, G. Malcolm; Eisenbach, Markus; Yin, Junqi; Brown, Gregory

2014-03-01

28

Entanglement Dynamics of Two Coupled Spins in a Spin Star Environment

NASA Astrophysics Data System (ADS)

We theoretically study the entanglement dynamics of two coupled spins in a spin star environment, whose elements are coupled to local bosonic baths. It is shown that the dynamics of the entanglement depends on the initial state of the system and the coupling strength between the two coupled central spins, the interactions between the central system and the environment, as well as interactions between the bath spin and the reservoir. We also investigate the effect of non-Markovian dynamics in contrast with the Markovian case. It is found that the non-Markovian dynamics has a significant effect on the disentanglement between the two central spins.

Nie, Jing; Yang, Xiuyi; Yu, Qing-Xu; Li, Chong

2014-04-01

29

Spin and Charge Dynamics of High Transition Temperature Cuprates

Understanding the spin and charge dynamics of the cuprates may lead to some of the most important advancements in our understanding of these materials. In this thesis, we investigate these properties for both normal and superconducting states. In our studies of the spin dynamics, we discuss the implications of magnetic data for the nature of the low-lying spin excitations in

Yuyao Zha

1994-01-01

30

Dynamic trajectories of growth and nitrogen capture by competing plants.

Although dynamic, plant competition is usually estimated as biomass differences at a single, arbitrary time; resource capture is rarely measured. This restricted approach perpetuates uncertainty. To address this problem, we characterized the competitive dynamics of Dactylis glomerata and Plantago lanceolata as continuous trajectories of biomass production and nitrogen (N) capture. Plants were grown together or in isolation. Biomass and N content were measured at 17 harvests up to 76 d after sowing. Data were fitted to logistic models to derive instantaneous growth and N capture rates. Plantago lanceolata was initially more competitive in terms of cumulative growth and N capture, but D. glomerata was eventually superior. Neighbours reduced maximum biomass, but influenced both maximum N capture and its rate constant. Timings of maximal instantaneous growth and N capture rates were similar between species when they were isolated, but separated by 16 d when they were competing, corresponding to a temporal convergence in maximum growth and N capture rates in each species. Plants processed N and produced biomass differently when they competed. Biomass and N capture trajectories demonstrated that competitive outcomes depend crucially on when and how 'competition' is measured. This potentially compromises the interpretation of conventional competition experiments. PMID:22236094

Trinder, Clare; Brooker, Rob; Davidson, Hazel; Robinson, David

2012-03-01

31

Dynamic Assessment and Its Potential for the Assessment of Reading Competence

ERIC Educational Resources Information Center

This article describes the approach of dynamic assessment, focusing on general approaches as well as specific constraints for the assessment of reading competence. Starting with an overview of the literature on dynamic assessments within educational research, the framework of dynamic assessment in which the current level of competence and…

Dorfler, Tobias; Golke, Stefanie; Artelt, Cordula

2009-01-01

32

Nonlinear dynamics of spinning spacecraft appendages

The paper considers dynamics of appendages connected to a spinning spacecraft with an offset from the spacecraft center of mass. It is observed that if the second and higher order terms involving the small elastic deformations are neglected, the system is stable for negative offset, but unstable for positive offset. However, if these higher order terms are retained, the system is stable for both types of offset. (The nonlinearities in rotational motion are retained in both cases). The cause of this anomaly is explained in the paper.

Misra, A.K. [McGill Univ., Montreal (Canada)

1994-12-31

33

Dynamic Nuclear Spin Resonance in n-GaAs

NASA Astrophysics Data System (ADS)

The dynamics of optically detected nuclear magnetic resonance is studied in n-GaAs via time-resolved Kerr rotation using an on-chip microcoil for rf field generation. Both optically allowed and optically forbidden NMR are observed with a dynamics controlled by the interplay between dynamic nuclear polarization via hyperfine interaction with optically generated spin-polarized electrons and nuclear spin depolarization due to magnetic resonance absorption. Comparing the characteristic nuclear spin relaxation rate obtained in experiment with master equation simulations, the underlying nuclear spin depolarization mechanism for each resonance is extracted.

Chen, Y. S.; Reuter, D.; Wieck, A. D.; Bacher, G.

2011-10-01

34

Dynamic nuclear spin resonance in n-GaAs.

The dynamics of optically detected nuclear magnetic resonance is studied in n-GaAs via time-resolved Kerr rotation using an on-chip microcoil for rf field generation. Both optically allowed and optically forbidden NMR are observed with a dynamics controlled by the interplay between dynamic nuclear polarization via hyperfine interaction with optically generated spin-polarized electrons and nuclear spin depolarization due to magnetic resonance absorption. Comparing the characteristic nuclear spin relaxation rate obtained in experiment with master equation simulations, the underlying nuclear spin depolarization mechanism for each resonance is extracted. PMID:22107431

Chen, Y S; Reuter, D; Wieck, A D; Bacher, G

2011-10-14

35

Spin dynamics and disorder effects in the S =1/2 kagome Heisenberg spin-liquid phase of kapellasite

NASA Astrophysics Data System (ADS)

We report 35Cl NMR, ESR, ? SR , and specific-heat measurements on the S =1/2 frustrated kagome magnet kapellasite ? -Cu3Zn(OH)6Cl2, where a gapless spin-liquid phase is stabilized by a set of competing exchange interactions. Our measurements confirm the ferromagnetic character of the nearest-neighbor exchange interaction J1 and give an energy scale for the competing interactions |J |˜10 K. The study of the temperature-dependent ESR line shift reveals a moderate symmetric exchange anisotropy term D , with |D /J |˜3 %. These findings validate a posteriori the use of the J1-J2-Jd Heisenberg model to describe the magnetic properties of kapellasite [Bernu et al., Phys. Rev. B 87, 155107 (2013), 10.1103/PhysRevB.87.155107]. We further confirm that the main deviation from this model is the severe random depletion of the magnetic kagome lattice by 27%, due to Cu/Zn site mixing, and specifically address the effect of this disorder by 35Cl NMR, performed on an oriented polycrystalline sample. Surprisingly, while being very sensitive to local structural deformations, our NMR measurements demonstrate that the system remains homogeneous with a unique spin susceptibility at high temperature, despite a variety of magnetic environments. Unconventional spin dynamics is further revealed by NMR and ? SR in the low-T , correlated, spin-liquid regime, where a broad distribution of spin-lattice relaxation times is observed. We ascribe this to the presence of local low-energy modes.

Kermarrec, E.; Zorko, A.; Bert, F.; Colman, R. H.; Koteswararao, B.; Bouquet, F.; Bonville, P.; Hillier, A.; Amato, A.; van Tol, J.; Ozarowski, A.; Wills, A. S.; Mendels, P.

2014-11-01

36

Domain wall dynamics in a spin-reorientation transition system Au/Co/Au

We report measurements of domain wall dynamics in an ultrathin Au/Co/Au system that exhibits a spin reorientation phase transition as a function of temperature.The domain walls exhibit cooperative motion throughout the temperature range of 150 - 300 K. The decay times were found to exhibit a maximum at the transition temperature. The slowdown has been explained as due to formation of a double well in the energy landscape by the different competing interactions. Our results show that the complex, slow dynamics can provide a more fundamental understanding of magnetic phase transitions.

Roy, Sujoy; Seu, Keoki; Turner, Joshua J.; Park, Sungkyun; Kevan, Steve; Falco, Charles M.

2009-05-14

37

ULTRAFAST ELECTRON SPIN DYNAMICS OF AS-GROWN Ga1-xMnxAs WITH APPROPRIATE Mn DOPING

NASA Astrophysics Data System (ADS)

The electron spin dynamics in the as-grown Ga1-xMnxAs films with appropriate Mn doping of x 2-5% is studied using time-resolved magneto-optical Kerr effect measurements. Due to the existence of Mn interstitials, the s-d exchange scattering is found to play an important role for the as-grown Ga1-xMnxAs, and compete with p-d exchange coupling to dominate the electron spin relaxation process. The contribution of electron-electron Coulomb scattering to the electron spin dynamics for the as-grown Ga1-x MnxAs appears to be as important as that of the annealed ones. Our findings are fundamentally important for better understanding the electron spin dynamics in Ga1-xMnxAs for its future spintronic applications.

Yue, Han

2013-06-01

38

Electron-spin dynamics in elliptically polarized light waves

NASA Astrophysics Data System (ADS)

We investigate the coupling of the spin angular momentum of light beams with elliptical polarization to the spin degree of freedom of free electrons. It is shown that this coupling, which is of similar origin as the well-known spin-orbit coupling, can lead to spin precession. The spin-precession frequency is proportional to the product of the laser field's intensity and its spin density. The electron-spin dynamics is analyzed by employing exact numerical methods as well as time-dependent perturbation theory based on the fully relativistic Dirac equation and on the nonrelativistic Pauli equation that is amended by a relativistic correction that accounts for the light's spin density.

Bauke, Heiko; Ahrens, Sven; Grobe, Rainer

2014-11-01

39

Quantum approach of mesoscopic magnet dynamics with spin transfer torque

NASA Astrophysics Data System (ADS)

We present a theory of magnetization dynamics driven by spin-polarized current in terms of the quantum master equation. In the spin coherent state representation, the master equation becomes a Fokker-Planck equation, which naturally includes the spin transfer and quantum fluctuation. The current electron scattering state is correlated to the magnet quantum states, giving rise to quantum correction to the electron transport properties in the usual semiclassical theory. In the large-spin limit, the magnetization dynamics is shown to obey the Hamilton-Jacobi equation or the Hamiltonian canonical equations.

Wang, Yong; Sham, L. J.

2013-05-01

40

Spin dynamics in the strong spin-orbit coupling regime

) The nonzero normalized oscillatory frequency, Im(i#2;? ), appears when #2;so? > 12 . 035318-3 XIN LIU, XIONG-JUN LIU, AND JAIRO SINOVA PHYSICAL REVIEW B 84, 035318 (2011) For the uniform spin polarization, the decay rate of the spin satisfies i#2;? = 1... regime when the system only has bulk inversion asymmetry. (a) The normalized exponential decay rate, Re(i#2;? ), increases with increasing q and approaches 1 at large q. (b) The nonzero normalized oscillatory frequency, Im(i#2;? ), increases linearly...

Liu, Xin; Liu, Xiong-Jun; Sinova, Jairo.

2011-01-01

41

Semiclassical spin-spin dynamics and feedback control in transport through a quantum dot

NASA Astrophysics Data System (ADS)

We present a theory of magnetotransport through an electronic orbital, where the electron spin interacts with a (sufficiently) large external spin via an exchange interaction. Using a semiclassical approximation, we derive a set of equations of motions for the electron density matrix and the mean value of the external spin that turns out to be highly nonlinear. The dissipation via the electronic leads is implemented in terms of a quantum master equation that is combined with the nonlinear terms of the spin-spin interaction. With an anisotropic exchange coupling a variety of dynamics is generated, such as self-sustained oscillations with parametric resonances or even chaotic behavior. Within our theory we can integrate a Maxwell-demon-like closed-loop feedback scheme that is capable of transporting particles against an applied bias voltage and that can be used to implement a spin filter to generate spin-dependent oscillating currents of opposite directions.

Mosshammer, Klemens; Brandes, Tobias

2014-10-01

42

Dynamics of test bodies with spin in de Sitter spacetime

We study the motion of spinning test bodies in the de Sitter spacetime of constant positive curvature. With the help of the 10 Killing vectors, we derive the 4-momentum and the tensor of spin explicitly in terms of the spacetime coordinates. However, in order to find the actual trajectories, one needs to impose the so-called supplementary condition. We discuss the dynamics of spinning test bodies for the cases of the Frenkel and Tulczyjew conditions.

Obukhov, Yuri N.; Puetzfeld, Dirk [Department of Mathematics and Institute of Origins, University College London, Gower Street, London, WC1E 6BT (United Kingdom); Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Muehlenberg 1, 14476 Golm (Germany)

2011-02-15

43

Dynamics of test bodies with spin in de Sitter spacetime

We study the motion of spinning test bodies in the de Sitter spacetime of constant positive curvature. With the help of the 10 Killing vectors, we derive the 4-momentum and the tensor of spin explicitly in terms of the spacetime coordinates. However, in order to find the actual trajectories, one needs to impose the so-called supplementary condition. We discuss the dynamics of spinning test bodies for the cases of the Frenkel and Tulczyjew conditions.

Yuri N. Obukhov; Dirk Puetzfeld

2010-10-07

44

Towards real spin glasses: Ground states and dynamics

NASA Astrophysics Data System (ADS)

Spin glasses are paradigmatic examples of systems with quenched disorder. They fall out of equilibrium at sufficiently low temperatures, at which point their dynamics becomes extremely history-dependent. Despite thirty years of study, the nature of the possible spin glass phase remains controversial as does its relation to the way in which spatial structures and correlations evolve over time in an out-of-equilibrium spin glass. This thesis frames a set of broad underlying questions about spin-glass ground states and spin-glass dynamics and provides answers to some among them. First, the basic form of the spin-glass phase diagram is considered. A new scaling approach to experimental magnetic susceptibility data is introduced to investigate the controversial question of whether three-dimensional spin glasses undergo a phase transition in a field. Next, the nature of the spin glass phase is considered. A possible phase in short-range spin glasses exhibiting infinitely many equilibrium states is proposed and characterized in real space. Some models with correlations in their exchange interactions are argued to exhibit this phase and their potential relation to infinite-range models is discussed. The relation of out-of-equilibrium dynamics to underlying ground state structure is then explored. As time passes, a length scale over which the system is locally equilibrated must grow as must a length scale associated with regions of infinite system order. The relation between these two length scales is examined. Equilibration dynamics is considered for particular examples of spin-glass-like systems both with two ground states and with many ground states. Experiments with scanning probes in equilibrating systems are proposed. Identifying experimental signatures associated with different ground state structures are discussed and experimental ways to quantify the history-dependence of dynamics are suggested.

White, Olivia Lawrence

45

Dynamics of spin vortices in two-dimensional planar magnets

We investigate the dynamics of a dilute gas of free spin vortices in a two-dimensional planar magnet. An equation of motion for the spin vortex is presented and compared with the corresponding equation for a vortex in a superfluid film. Exploiting a similar analogy with the dynamics of a two-dimensional plasma in a perpendicular magnetic field we calculate the mean-square

D. L. Huber

1982-01-01

46

Arbitrary spin in a spin bath: Exact dynamics and approximation techniques

A model of an arbitrary spin coupled to a bath of spins 1/2 in a star configuration is considered. The exact reduced dynamics of the central spin is found for the case of non-correlated initial conditions of the system and the bath. The exact solution is used to test two approximation techniques, namely, the Nakajima-Zwanzig projection operator technique and the time-convolutionless projection operator technique corresponding to the second order of the coupling constant. Two types of projection operators are used for deriving the master equations and the results are compared with the exact solution for a central spin equal to one. It is shown that the approximate master equations reproduce the exact dynamics on time-scales $1/(A\\sqrt{N})$, where A is the coupling constant and N is the number of spins in the bath.

V. Semin; I. Sinayskiy; F. Petruccione

2014-01-29

47

QND Measurement of Large-Spin Ensembles by Dynamical Decoupling

Quantum non-demolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the build-up of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise.

M. Koschorreck; M. Napolitano; B. Dubost; M. W. Mitchell

2010-05-17

48

QND Measurement of Large-Spin Ensembles by Dynamical Decoupling

Quantum non-demolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the build-up of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise.

Koschorreck, M; Dubost, B; Mitchell, M W

2010-01-01

49

Dynamical heterogeneity in the Ising spin glass

We investigate the relationship between bulk and local relaxation in the Ising spin glass ~in two and three dimensions! for temperatures above but approaching the glass transition temperature, using Monte Carlo computer simulations. We find that the stretched exponential form of the bulk spin autocorrelation function results from a spatial average over a broad range of behavior, from strongly nonexponential

Sharon C. Glotzer; Naeem Jan; Turab Lookman; Allan B. MacIsaac; Peter H. Poole

1998-01-01

50

Protection of centre spin coherence by dynamic nuclear spin polarization in diamond.

We experimentally investigate the protection of electron spin coherence of a nitrogen-vacancy (NV) centre in diamond by dynamic nuclear spin polarization (DNP). The electron spin decoherence of an NV centre is caused by the magnetic field fluctuation of the (13)C nuclear spin bath, which contributes large thermal fluctuation to the centre electron spin when it is in an equilibrium state at room temperature. To address this issue, we continuously transfer the angular momentum from electron spin to nuclear spins, and pump the nuclear spin bath to a polarized state under the Hartmann-Hahn condition. The bath polarization effect is verified by the observation of prolongation of the electron spin coherence time (T). Optimal conditions for the DNP process, including the pumping pulse duration and repeat numbers, are proposed by numerical simulation and confirmed by experiment. We also studied the depolarization effect of laser pulses. Our results provide a new route for quantum information processing and quantum simulation using the polarized nuclear spin bath. PMID:25042514

Liu, Gang-Qin; Jiang, Qian-Qing; Chang, Yan-Chun; Liu, Dong-Qi; Li, Wu-Xia; Gu, Chang-Zhi; Po, Hoi Chun; Zhang, Wen-Xian; Zhao, Nan; Pan, Xin-Yu

2014-09-01

51

Spin-dynamics study of the classical ferromagnetic XY chain

NASA Astrophysics Data System (ADS)

The time-dependent behavior of the classical, ferromagnetic xy chain in a symmetry-breaking magnetic field was studied using a very fast, vectorized spin-dynamics method. The equations of motion were integrated using starting configurations determined by Monte Carlo simulations. By calculating spin-spin correlation functions and taking space-time Fourier transforms, we determined S(q,?) for a wide range of fields and temperatures. We identify and measure the characteristics of single spin-wave peaks and two spin-wave sum peaks, as well as central peaks due to both soliton and two spin-wave difference processes. These results are discussed in light of existing theory and experiments.

Gerling, R. W.; Landau, D. P.

1990-04-01

52

Spin supercurrent, magnetization dynamics, and ?-state in spin-textured Josephson junctions

NASA Astrophysics Data System (ADS)

The prospect of combining the dissipationless nature of superconducting currents with the spin polarization of magnetic materials is interesting with respect to exploring superconducting analogs of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: (i) a superconductor?ferromagnet?superconductor (S?F?S) junction with spin-active interfaces, (ii) a S?F1?F2?F3?S Josephson junction with a ferromagnetic trilayer, and (iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase dependence of the charge supercurrent and the magnetization dynamics caused by the spin polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference ? in the ground state. Such a ?-junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is controlled by the chirality of the magnetization configuration.

Kulagina, Iryna; Linder, Jacob

2014-08-01

53

Effect of cosmic string on spin dynamics

In the present paper, we have investigated the role of cosmic string on spin current and Hall electric field. Due to the background cosmic string, the modified electric field of the system generates renormalized spin orbit coupling, which induces a modified non-Abelian gauge field. The defect causes a change in the AB and AC phases appearing due to the modified electromagnetic field. In addition, for a time varying electric field we perform explicit analytic calculations to derive the exact form of spin electric field and spin current, which is defect parameter dependent and of oscillating type. Furthermore, in an asymmetric crystal within the Drude model approach we investigate the dependence of the cosmic string parameters on cosmic string induced Hall electric field.

Debashree Chowdhury; B. Basu

2014-11-07

54

Effect of cosmic string on spin dynamics

In the present paper, we have investigated the role of cosmic string on spin current and Hall electric field. Due to the background cosmic string, the modified electric field of the system generates renormalized spin orbit coupling, which induces a modified non-Abelian gauge field. The defect causes a change in the AB and AC phases appearing due to the modified electromagnetic field. In addition, for a time varying electric field we perform explicit analytic calculations to derive the exact form of spin electric field and spin current, which is defect parameter dependent and of oscillating type. Furthermore, in an asymmetric crystal within the Drude model approach we investigate the dependence of the cosmic string parameters on cosmic string induced Hall electric field.

Chowdhury, Debashree

2014-01-01

55

Coherent Spin Dynamics in Semiconductor Nanostructures

NASA Astrophysics Data System (ADS)

Manipulation of coherent spins in semiconductors without laboratory AC (or in some cases DC) magnetic fields can be driven with the electronic spin-orbit interaction. This relativistic effect produces ``pseudomagnetic'' fields surpassing plausible laboratory magnetic fields by orders of magnitude. The theory of two principal examples will be described here: the coupling between light fields and electron spin in quantum dots, and the use of DC electric fields to manipulate spin coherence times in quantum wells. We find that intense coherent optical illumination of quantum dots can generate ultrafast ˜ 1000 Tesla pseudomagnetic fields suitable for electron spin rotation. These effective fields are roughly spherically symmetric for colloidal quantum dots, but for structurally aspherical quantum dots (such as self-assembled dots during molecular beam epitaxy growth) these pseudomagnetic fields are highly anisotropic - large parallel to the growth direction and often a factor of five or ten smaller along perpendicular directions. The structural anisotropy also leads to very anisotropic selection rules for light emission in quantum dot spin-light-emitting-diodes. For the second principal example, manipulation of spin coherence times in quantum wells, the zero-field spin coherence times and the tuning ranges depend strongly on the crystalline orientation of the growth axis. Near room temperature in (110)-grown structures for applied electric fields of 10-100 kV/cm, the tuning range can exceed several orders of magnitude. This work was done in collaboration with W. H. Lau and C. E. Pryor and was supported by DARPA/ARO and an ARO MURI.

Flatté, Michael E.

2004-03-01

56

Ultrafast Spin Dynamics Including Spin-Orbit Interaction in Semiconductors Michael KrauÃ?,* Martin quantities accessible by time-resolved 2-photon photoemission [18], Faraday effect [19], and differential

Aeschlimann, Martin

57

Multiple quantum NMR dynamics in dipolar ordered spin systems

NASA Astrophysics Data System (ADS)

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by the dipole-dipole interactions in the case of the dipolar ordered initial state. We suggest two different methods of MQ NMR. One of them is based on the measurement of the dipolar temperature in the quasiequilibrium state which is established after the time of order ?loc-1 ( ?loc is the dipolar local field) after the MQ NMR experiment. The other method uses an additional resonance (?/4)y pulse after the preparation period of the standard MQ NMR experiment in solids. Many-spin clusters and correlations are created faster in such experiments than in the usual MQ NMR experiments and can be used for the investigation of many-spin dynamics of nuclear spins in solids.

Doronin, S. I.; Fel'Dman, E. B.; Kuznetsova, E. I.; Furman, G. B.; Goren, S. D.

2007-10-01

58

Excitation of complex spin dynamics patterns in a quantum-dot electron spin ensemble

NASA Astrophysics Data System (ADS)

We exploit the flexibility offered by an (In,Ga)As/GaAs quantum dot spin ensemble to demonstrate that complex dynamic evolutions can be excited in the ensemble magnetization and accessed by tailored pulsed laser protocols. The modes for spin precession about a magnetic field are adapted to the periodic excitation protocol such that at specific times the magnetization can effectively be decomposed in two, three, or four equal components with angles of ?,2?/3, or ? /2 between them. Optical orientation of these components by an additional laser pulse leads to the generation of higher harmonics in the spin precession, as evidenced by time-resolved ellipticity measurements.

Varwig, S.; Yugova, I. A.; René, A.; Kazimierczuk, T.; Greilich, A.; Yakovlev, D. R.; Reuter, D.; Wieck, A. D.; Bayer, M.

2014-09-01

59

LETTER TO THE EDITOR: Dynamical crossover in 'hot' spin ice

The magnetic dynamics of the spin ice material Ho2Ti2O7 in its paramagnetic ('hot') phase have been investigated by a combination of neutron spin echo and ac-susceptibility techniques. Relaxation at high temperatures (T > 15 K) is proved to occur by a thermally activated single-ion process that is distinct from the process that dominates at lower temperatures (1 K < T

G. Ehlers; A. L. Cornelius; M. Orendác; M. Kajnaková; T. Fennell; S. T. Bramwell; J. S. Gardner

2003-01-01

60

Incomplete fusion dynamics by spin distribution measurements

Spin distributions for various evaporation residues populated via complete and incomplete fusion of {sup 16}O with {sup 124}Sn at 6.3 MeV/nucleon have been measured, using charged particles (Z=1,2)-{gamma} coincidence technique. Experimentally measured spin distributions of the residues produced as incomplete fusion products associated with 'fast'{alpha}- and 2{alpha}-emission channels observed in the 'forward cone' are found to be distinctly different from those of the residues produced as complete fusion products. Moreover, 'fast'{alpha}-particles that arise from larger angular momentum in the entrance channel are populated at relatively higher driving input angular momentum than those produced through complete fusion. The incomplete fusion residues are populated in a limited, higher-angular-momentum range, in contrast to the complete fusion products, which are populated over a broad spin range.

Singh, D.; Ali, R.; Ansari, M. Afzal; Singh, Pushpendra P.; Sharma, M. K.; Singh, B. P. [Department of Physics, Aligarh Muslim University, Aligarh 202 002 (India); Babu, K. Surendra [Department of Physics, G. B. Pant University, Pantnagar 263 145 (India); Sinha, Rishi K. [Department of Physics, Banaras Hindu University, Varanasi 221 005 (India); Kumar, R.; Muralithar, S.; Singh, R. P.; Bhowmik, R. K. [Inter-University Accelerator Centre, New Delhi 110 067 (India)

2010-02-15

61

Computer Simulation of Quantum Dynamics in a Classical Spin Environment

In this paper a formalism for studying the dynamics of quantum systems coupled to classical spin environments is reviewed. The theory is based on generalized antisymmetric brackets and naturally predicts open-path off-diagonal geometric phases in the evolution of the density matrix. It is shown that such geometric phases must also be considered in the quantum-classical Liouville equation for a classical bath with canonical phase space coordinates; this occurs whenever the adiabatics basis is complex (as in the case of a magnetic field coupled to the quantum subsystem). When the quantum subsystem is weakly coupled to the spin environment, non-adiabatic transitions can be neglected and one can construct an effective non-Markovian computer simulation scheme for open quantum system dynamics in classical spin environments. In order to tackle this case, integration algorithms based on the symmetric Trotter factorization of the classical-like spin propagator are derived. Such algorithms are applied to a model comprising a quantum two-level system coupled to a single classical spin in an external magnetic field. Starting from an excited state, the population difference and the coherences of this two-state model are simulated in time while the dynamics of the classical spin is monitored in detail. It is the author's opinion that the numerical evidence provided in this paper is a first step toward developing the simulation of quantum dynamics in classical spin environments into an effective tool. In turn, the ability to simulate such a dynamics can have a positive impact on various fields, among which, for example, nano-science.

Alessandro Sergi

2014-04-24

62

Dynamic spin-Hall effect and driven spin helix for linear spin-orbit interactions

NASA Astrophysics Data System (ADS)

We derive boundary conditions for the electrically induced spin accumulation in a finite, disordered two-dimensional semiconductor channel. While for dc electric fields these boundary conditions select spatially constant spin profiles equivalent to a vanishing spin-Hall effect, we show that an in-plane ac electric field results in a nonzero ac spin-Hall effect, i.e., it generates a spatially nonuniform out-of-plane polarization even for linear intrinsic spin-orbit interactions. Analyzing different geometries in [001]- and [110]-grown quantum wells, we find that although this out-of-plane polarization is typically confined to within a few spin-orbit lengths from the channel edges, it is also possible to generate spatially oscillating spin profiles which extend over the whole channel. The latter is due to the excitation of a driven spin-helix mode in the transverse direction of the channel. We show that while finite frequencies suppress this mode, it can be amplified by a magnetic field tuned to resonance with the frequency of the electric field. In this case, finite-size effects at equal strengths of Rashba and Dresselhaus SOI lead to an enhancement of the magnitude of this helix mode. We comment on the relation between spin currents and boundary conditions.

Duckheim, Mathias; Maslov, Dmitrii L.; Loss, Daniel

2009-12-01

63

Spin-orbital dynamics in a system of polar molecules.

Spin-orbit coupling in solids normally originates from the electron motion in the electric field of the crystal. It is key to understanding a variety of spin-transport and topological phenomena, such as Majorana fermions and recently discovered topological insulators. Implementing and controlling spin-orbit coupling is thus highly desirable and could open untapped opportunities for the exploration of unique quantum physics. Here we show that dipole-dipole interactions can produce an effective spin-orbit coupling in two-dimensional ultracold polar molecule gases. This spin-orbit coupling generates chiral excitations with a non-trivial Berry phase 2?. These excitations, which we call chirons, resemble low-energy quasiparticles in bilayer graphene and emerge regardless of the quantum statistics and for arbitrary ratios of kinetic to interaction energies. Chirons manifest themselves in the dynamics of the spin density profile, spin currents and spin coherences, even for molecules pinned in a deep optical lattice and should be observable in current experiments. PMID:25377238

Syzranov, Sergey V; Wall, Michael L; Gurarie, Victor; Rey, Ana Maria

2014-01-01

64

Tunable nonequilibrium dynamics of field quenches in spin ice.

We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state--a "Coulomb phase"--whose excitations are point-like defects--magnetic monopoles--in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties--including even the effective dimensionality of the system--can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics. PMID:24379372

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L

2014-01-14

65

Tunable nonequilibrium dynamics of field quenches in spin ice

We present nonequilibrium physics in spin ice as a unique setting that combines kinematic constraints, emergent topological defects, and magnetic long-range Coulomb interactions. In spin ice, magnetic frustration leads to highly degenerate yet locally constrained ground states. Together, they form a highly unusual magnetic state—a “Coulomb phase”—whose excitations are point-like defects—magnetic monopoles—in the absence of which effectively no dynamics is possible. Hence, when they are sparse at low temperature, dynamics becomes very sluggish. When quenching the system from a monopole-rich to a monopole-poor state, a wealth of dynamical phenomena occur, the exposition of which is the subject of this article. Most notably, we find reaction diffusion behavior, slow dynamics owing to kinematic constraints, as well as a regime corresponding to the deposition of interacting dimers on a honeycomb lattice. We also identify potential avenues for detecting the magnetic monopoles in a regime of slow-moving monopoles. The interest in this model system is further enhanced by its large degree of tunability and the ease of probing it in experiment: With varying magnetic fields at different temperatures, geometric properties—including even the effective dimensionality of the system—can be varied. By monitoring magnetization, spin correlations or zero-field NMR, the dynamical properties of the system can be extracted in considerable detail. This establishes spin ice as a laboratory of choice for the study of tunable, slow dynamics. PMID:24379372

Mostame, Sarah; Castelnovo, Claudio; Moessner, Roderich; Sondhi, Shivaji L.

2014-01-01

66

Quantum Spin Dynamics and Quantum Computation

We describe a simulation method for a quantum spin model of a generic, general purpose quantum computer. The use of this quantum computer simulator is illustrated through several implementations of Grover's database search algorithm. Some preliminary results on the stability of quantum algorithms are presented.

H. De Raedt; A. H. Hams; K. Michielsen; S. Miyashita; K. Saito

1999-11-09

67

Quantum dynamics of two-spin-qubit systems.

The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks. PMID:21828484

Nguyen, Van Hieu

2009-07-01

68

TOPICAL REVIEW: Quantum dynamics of two-spin-qubit systems

NASA Astrophysics Data System (ADS)

The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks.

Nguyen, Van Hieu

2009-07-01

69

Dynamic Behavior of Spin Glass Systems on Quenched OE 3 Graphs

Dynamic Behavior of Spin Glass Systems on Quenched OE 3 Graphs C. Baillie (a) , D. A. Johnston (b study the dynamical outÂofÂequilibrium behavior of a J = \\Sigma1 Ising spin glass on quenched OE 3 field spin glasses. condÂmat/9606194 1 #12; Spin models on quenched OE 3 graphs have been considered

Roma "La Sapienza", UniversitÃ di

70

Spin-dynamics study of the classical anisotropic XY chain

NASA Astrophysics Data System (ADS)

We have investigated the time-dependent behavior of the classical XY chain in a symmetry-breaking anisotropy field using an ultrafast spin-dynamics method in which we integrate the equation of motion with equilibrium spin configurations determined by Monte Carlo simulations. All three polarizations of the scattering function S(q,?) were determined for temperature kBT=0.2J and fields varying from 0.1J to 0.6J. Substantial differences are found as compared with the isotropic ferromagnetic chain in a transverse magnetic field. The soliton contribution, single-spin-wave peaks, and both the sum and difference two-spin-wave contributions are separated. Half-widths and integrated intensities are extracted and compared with theoretical predictions based on mapping onto the sine-Gordon model.

Kim, D. Y.; Gerling, R. W.; Landau, D. P.

1990-07-01

71

LETTER TO THE EDITOR: Dynamical crossover in 'hot' spin ice

NASA Astrophysics Data System (ADS)

The magnetic dynamics of the spin ice material Ho2Ti2O7 in its paramagnetic ('hot') phase have been investigated by a combination of neutron spin echo and ac-susceptibility techniques. Relaxation at high temperatures (T > 15 K) is proved to occur by a thermally activated single-ion process that is distinct from the process that dominates at lower temperatures (1 K < T < 15 K). It is argued that the low-temperature process must involve quantum mechanical spin tunnelling, as quasi-classical channels of relaxation are exhausted in this temperature range. Our results resolve a mystery in the physics of spin ice: why has a 15 K ac-susceptibility peak been observed in Dy2Ti2O7 but not in Ho2Ti2O7 or Ho2Sn2O7?

Ehlers, G.; Cornelius, A. L.; Orendác, M.; Kajnaková, M.; Fennell, T.; Bramwell, S. T.; Gardner, J. S.

2003-01-01

72

Dynamic polarization of Mn spins coupled to vertical optical cavities

NASA Astrophysics Data System (ADS)

Single magnetic spins in semiconductors can exhibit long lifetimes and are electrically controllable due to coupling of their spin states with those of the host semiconductor. In particular, Mn ions doped into GaAs quantum wells have spin lifetimes ˜10 nanoseconds and can be optically manipulated in zero magnetic fieldootnotetextR. C. Myers, M. H. Mikkelsen, J.-M. Tang, A. C. Gossard, M. E. Flatt'e, and D. D. Awschalom, Nature Materials 7, 203 (2008).. To study this system in the low density limit, we incorporate a distributed Bragg reflector optical cavity around the Mn containing wells, which enhances Mn luminescence and allows spatial isolation of a small number of Mn ions imaged using scanning micro-photoluminescence. In such structures, we observe unusually long Mn T2^*> 60 ns. We discuss the effect of cavity coupling on spin dynamics Mn ions in the single ion limit.

Calusine, G.; Myers, R. C.; Awschalom, D. D.

2009-03-01

73

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Here, we demonstrate quantum control of a mesoscopic spin bath in diamond at room temperature that is composed of electron spins of substitutional nitrogen impurities. The resulting spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre electron spin as a magnetic field sensor. We exploit the spin bath control to dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by combining spin bath control with dynamical decoupling, we directly measure the coherence and temporal correlations of different groups of bath spins. These results uncover a new arena for fundamental studies on decoherence and enable novel avenues for spin-based magnetometry and quantum information processing.

G. de Lange; T. van der Sar; M. S. Blok; Z. H. Wang; V. V. Dobrovitski; R. Hanson

2011-04-24

74

Global attractors and extinction dynamics of cyclically competing species

NASA Astrophysics Data System (ADS)

Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species’ concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species’ global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases.

Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin

2013-05-01

75

Physical limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics for the seminal proposal of Datta and Das of a ballistic spin-field-effect tran- sistor DD-SFET .5 However-SFET to the ballistic re- gime. Schliemann et al.7 have recently suggested a way to de- sign a SFET in 001 -plane

Sipe,J. E.

76

Spin-glass order induced by dynamic frustration

of long-range magnetic correlations. This novel mechanism for producing a frustrated ground state could with increasing separation. Except for specific classes of geometrically frustrated lattices, well-ordered crystalLETTERS Spin-glass order induced by dynamic frustration E. A. GOREMYCHKIN1,2 , R. OSBORN1 *, B. D

Chandra, Premi

77

Lectures on Glauber Dynamics for Discrete Spin Models

These notes have been the subject of a course I gave in the summer 1997 for the school in probability theory in Saint-Flour. I review in a self-contained way the state of the art, sometimes providing new and simpler proofs of the most relevant results, of the theory of Glauber dynamics for classical lattice spin models of statistical mechanics. The

Fabio Martinelli

78

Spin Dynamics Simulations A Powerful Method for the Study of Critical Dynamics

(ReceivedOctober 31, 1999) Spin-dynamics techniques can now be used to study the deterministic time-dependent behavior of magnetic systems containing over 105 spins with quite goodaccuracy. This approach will be introduced, including the theoretical foundations of the methods of analy- sis. Then newly developed, improved techniques based upon Suzuki-Trotter decomposition methods will be described. The current \\

D. P. Landau; Alex Bunker; Hans Gerd Evertz; M. Krech; Shan-Ho Tsai

79

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2.

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant. PMID:22743542

Maryasov, Alexander G; Bowman, Michael K

2012-08-01

80

Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of ½

The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or ‘powder’ sample when g tensor anisotropy is significant. PMID:22743542

Maryasov, Alexander G.

2012-01-01

81

Ultrafast coherent control of Spin- and magnetization dynamics

NASA Astrophysics Data System (ADS)

The manipulating of the electron spin is not only relevant for magnetic storage but may also lead to the development of novel electronic devices with new characteristics (so-called spintronics). Therefore, the investigations of the physical mechanisms underlying the manipulation of electron spin in ferromagnets, semiconductors and hybrid ferromagnet/semiconductor structures constitute at present an exciting area of research. Due to the fact that in antiferromagnets no angular momentum is associated with the order parameter, spin dynamics in these materials is intrinsically much faster than in ferromagnets, expanding the area of spin-dynamics even more ^[1]. Femto-second laser excitation opens the way to excite magnetic systems on a time scale much shorter than fundamental time scales such as spin-lattice relaxation or precession times. This has already lead to surprising and exciting results like changes in magnetization on a sub-picoscond time scale ^[2]. Fs laser pulses can also be used to generate short magnetic field pulses, that allow coherent control of the magnetization dynamics ^[3] . Recent progress in this area will be discussed, demonstrating in particular the use of time resolved magneto-optical methods to investigate the static and dynamic properties of magnetically ordered structures and the possibility of direct spin manipulation with optical fields^[4,5]. [1] A. V. Kimel, A. Kirilyuk, A. Tsvetkov, R. V. Pisarev, and Th. Rasing, Nature 429 850 (2004). [2] Spin Dynamics in Confined Magnetic Structures I-II, edited by B. Hillebrands and K. Ounadjela (Springer-Verlag, Berlin, 2002-2003). [3] Th. Gerrits, H. A. M. van den Berg, J. Hohlfeld, L. Bär, and Th. Rasing, Nature 418, 509 (2002). [4] A. Kimel, A. Kirilyuk, P.A. Usachev, R.V. Pisarev, A.M. Balbashov and Th. Rasing, Nature 435, 655 (2005) [5] F. Hansteen, A.V. Kimel, A. Kirilyuk and Th. Rasing, PRL 95, 047402-1 (2005). Acknowledgements This work was partially supported by the European IST network SPINOSA, the RTN network DYNAMICS, the Russian Foundation for Basic Research (RFBR), Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) as well as Stichting voor Fundamenteel Onderzoek der Materie (FOM).

Rasing, Theo

2006-03-01

82

Conservative effects in spin-transfer-driven magnetization dynamics

NASA Astrophysics Data System (ADS)

It is shown that under certain conditions spin transfer results in conservative magnetization dynamics. This dynamics occurs along closed precessional-type trajectories, and it admits a special integral of motion which is reduced to the usual magnetic energy when the spin current is reduced to zero. The existence of this conservative dynamics is due to the symmetry properties of the magnetization dynamics equation with respect to simultaneous inversions of magnetization and time. When an external dc magnetic field is applied parallel to the spin polarization, the conservative magnetization dynamics is transformed into relaxations. It is demonstrated that there exists such a state function (Lyapunov function) that monotonically either increases or decreases during these relaxations, depending on the directions of the injected current and applied dc magnetic field. These results hold in the absence of intrinsic (thermal) damping. When the intrinsic damping is included in the description, mutual compensation between field-induced and damping-induced nonconservative effects may occur, which may eventually lead to the appearance of limit cycles, that is, of magnetization self-oscillations.

Bertotti, G.; Serpico, C.; Mayergoyz, I. D.

2014-09-01

83

Correlation dynamics of three spin under a classical dephasing environment

By starting from the stochastic Hamiltonian of the three correlated spins and modeling their frequency fluctuations as caused by dephasing noisy environments described by Ornstein-Uhlenbeck processes, we study the dynamics of quantum correlations, including entanglement and quantum discord. We prepared initially our open system with Greenberger-Horne-Zeilinger or W state and present the exact solutions for evolution dynamics of entanglement and quantum discord between three spins under both Markovian and non-Markovian regime of this classical noise. By comparison the dynamics of entanglement with that of quantum discord we find that entanglement can be more robust than quantum discord against this noise. It is shown that by considering non-Markovian extensions the survival time of correlations prolong.

Mahdian, M; Salimi, S

2012-01-01

84

Correlation dynamics of three spin under a classical dephasing environment

By starting from the stochastic Hamiltonian of the three correlated spins and modeling their frequency fluctuations as caused by dephasing noisy environments described by Ornstein-Uhlenbeck processes, we study the dynamics of quantum correlations, including entanglement and quantum discord. We prepared initially our open system with Greenberger-Horne-Zeilinger or W state and present the exact solutions for evolution dynamics of entanglement and quantum discord between three spins under both Markovian and non-Markovian regime of this classical noise. By comparison the dynamics of entanglement with that of quantum discord we find that entanglement can be more robust than quantum discord against this noise. It is shown that by considering non-Markovian extensions the survival time of correlations prolong.

M. Mahdian; R. Yousefjani; S. Salimi

2012-04-18

85

On the Spin-axis Dynamics of a Moonless Earth

The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, the Earth's obliquity is stabilized by the Moon, and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically-forced climate change is the rate of chaotic diffusion. Accordingly, here we reexamine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in the Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structu...

Li, Gongjie

2014-01-01

86

Computer studies of multiple-quantum spin dynamics

The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.

Murdoch, J.B.

1982-11-01

87

Thermally assisted spin-transfer torque dynamics in energy space

NASA Astrophysics Data System (ADS)

We consider the general Landau-Lifshitz-Gilbert theory underlying the magnetization dynamics of a macrospin magnet subject to spin-torque effects and thermal fluctuations. Thermally activated dynamical properties are analyzed by averaging the full magnetization equations over constant-energy orbits. After averaging, all the relevant dynamical scenarios are a function of the ratio between hard and easy axis anisotropies. We derive analytically the range of currents for which limit cycles exist and discuss the regimes in which the constant energy orbit averaging technique is applicable.

Pinna, D.; Kent, A. D.; Stein, D. L.

2013-09-01

88

We investigate the anisotropic integrable spin chain consisting of spins $s={1/2}$ and $s=1$ by means of thermodynamic Bethe ansatz for the anisotropy $\\gamma>\\pi/3$, where the analysis of the Takahashi conditions leads to a more complicated string picture. We give the phase diagram with respect to the two real coupling constants $\\bar{c}$ and $\\tilde{c}$, which contains a new region where the ground state is formed by strings with infinite Fermi zones. In this region the velocities of sound for the two physical excitations have been calculated from the dressed energies. This leads to an additional line of conformal invariance not known before.

B. -D. Doerfel; St. Meissner

1997-08-20

89

Far-from-equilibrium monopole dynamics in spin ice

NASA Astrophysics Data System (ADS)

Condensed matter in the low-temperature limit reveals exotic physics associated with unusual orders and excitations, with examples ranging from helium superfluidity to magnetic monopoles in spin ice. The far-from-equilibrium physics of such low-temperature states may be even more exotic, yet to access it in the laboratory remains a challenge. Here we demonstrate a simple and robust technique--the `magnetothermal avalanche quench'--and its use in the controlled creation of non-equilibrium populations of magnetic monopoles in spin ice at millikelvin temperatures. These populations are found to exhibit spontaneous dynamical effects that typify far-from-equilibrium systems and yet are captured by simple models. Our method thus opens new directions in the study of far-from-equilibrium states in spin ice and other exotic magnets.

Paulsen, C.; Jackson, M. J.; Lhotel, E.; Canals, B.; Prabhakaran, D.; Matsuhira, K.; Giblin, S. R.; Bramwell, S. T.

2014-02-01

90

Matrix Formalism for Spin Dynamics Near a Single Depolarization Resonance

A matrix formalism is developed to describe the spin dynamics in a synchrotron near a single depolarization resonance as the particle energy (and therefore its spin precession frequency) is varied in a prescribed pattern as a function of time such as during acceleration. This formalism is first applied to the case of crossing the resonance with a constant crossing speed and a finite total step size, and then applied also to other more involved cases when the single resonance is crossed repeatedly in a prescribed manner consisting of linear ramping segments or sudden jumps. How repeated crossings produce an interference behavior is discussed using the results obtained. For a polarized beam with finite energy spread, a spin echo experiment is suggested to explore this interference effect.

Chao, Alexander W.; /SLAC

2005-10-26

91

Competing spin waves and superconducting fluctuations in strongly correlated electron systems

A special diagram technique recently proposed for strongly correlated electron systems is used to study the peculiarities of a spin-density wave (SDW) in competition with superconductivity. This method allows formulation of the Dyson equations for the renormalized electron propagators of the co-existing phases of SDW antiferromagnetism and superconductivity. We find the surprising result that triplet superconductivity appears provided that we

V. A. Moskalenko; P. Entel; D. F. Digor; L. A. Dohotaru

2005-01-01

92

The impact of competing zealots on opinion dynamics

NASA Astrophysics Data System (ADS)

An individual’s opinion on an issue is greatly impacted by others in his or her social network. Most people are open-minded and ready to change their opinion when presented evidence; however, some are zealots or inflexibles, that is, individuals who refuse to change their opinion while staunchly advocating an opinion in hopes of convincing others. Zealotry is present in opinions of significant personal investment, such as political, religious or corporate affiliation; it tends to be less commonplace in opinions involving rumors or fashion trends. In this paper, we examine the effect that zealots have in a population whose opinion dynamics obey the naming game model. We present numerical and analytical results about the number and nature of steady state solutions, demonstrating the existence of a bifurcation in the space of zealot fractions. Our analysis indicates conditions under which a minority zealot opinion ultimately prevails, and conditions under which neither opinion attains a majority. We also present numerical and simulation analysis of finite populations and on networks with partial connectivity.

Verma, Gunjan; Swami, Ananthram; Chan, Kevin

2014-02-01

93

NASA Astrophysics Data System (ADS)

The stationary states of the kinetic mixed spin-2 and spin-5/2 Ising ferrimagnetic system with repulsive biquadratic coupling are examined within a mean-field approach under the presence of a time varying (sinusoidal) magnetic field. We employ Glauber-type stochastic dynamics to construct a set of coupled mean-field dynamic equations, and we solve these equations to find the phases in the system. We also investigate the thermal behavior of the dynamic order parameters to characterize the nature (continuous or discontinuous) of the dynamic phase transitions (DPTs) and obtain the DPT points. The phase diagrams are presented in the reduced magnetic field amplitude and reduced temperature plane, and a comparison is made with the results of other kinetic mixed spin systems. We also study the behavior of the dynamic magnetic hysteresis and investigate the effects of the frequency on hysteresis properties, and we find the results are in good agreement with some previous theoretical and experimental works.

Erta?, Mehmet; Keskin, Mustafa; Deviren, Bayram

2012-03-01

94

Coherent spin–rotational dynamics of oxygen superrotors

NASA Astrophysics Data System (ADS)

We use state- and time-resolved coherent Raman spectroscopy to study the rotational dynamics of oxygen molecules in ultra-high rotational states. While it is possible to reach rotational quantum numbers up to N? 50 by increasing the gas temperature to 1500 K, low population levels and gas densities result in correspondingly weak optical response. By spinning {{O}2} molecules with an optical centrifuge, we efficiently excite extreme rotational states with N?slant 109 in high-density room temperature ensembles. Fast molecular rotation results in the enhanced robustness of the created rotational wave packets against collisions, enabling us to observe the effects of weak spin–rotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spin–rotational coherence due to collisions is measured as a function of the molecular angular momentum and its dependence on the collisional adiabaticity parameter is discussed. We find that at high values of N, the rotational decoherence of oxygen is much faster than that of the previously studied non-magnetic nitrogen molecules, pointing at the effects of spin relaxation in paramagnetic gases.

Milner, Alexander A.; Korobenko, Aleksey; Milner, Valery

2014-09-01

95

NASA Astrophysics Data System (ADS)

We demonstrate enhancement of the spin precession of orthoferrite ErFeO3 using the magnetic near-field produced by a split-ring resonator (SRR), using the terahertz pump-optical Faraday probe measurement. The precession amplitude was enhanced by ˜8 times when the resonance frequency of spin precession was close to the magnetic resonance of SRR. The time evolution of spin precession was successfully reproduced by a coupled spin- and SRR-resonance model mediated by the magnetic near-field. It is suggested that optimization of the metamaterial structure would further increase the enhancement factor, leading to the nonlinear control of spin dynamics using terahertz radiation.

Kurihara, T.; Nakamura, K.; Yamaguchi, K.; Sekine, Y.; Saito, Y.; Nakajima, M.; Oto, K.; Watanabe, H.; Suemoto, T.

2014-10-01

96

NASA Astrophysics Data System (ADS)

We investigate the anisotropic integrable spin chain consisting of spins 0305-4470/31/1/011/img1 and s = 1 by means of thermodynamic Bethe ansatz for the anisotropy 0305-4470/31/1/011/img2, where the analysis of the Takahashi conditions leads to a more complicated string picture. We give the phase diagram with respect to the two real coupling constants 0305-4470/31/1/011/img3 and 0305-4470/31/1/011/img4, which contain a new region where the ground state is formed by strings with infinite Fermi zones. In this region the velocities of sound for the two physical excitations have been calculated from the dressed energies. This leads to an additional line of conformal invariance not known before.

Dörfel, B.-D.; Meißner, St.

1998-01-01

97

Dynamic clustering and dispersion of lipid rafts contribute to fusion competence of myogenic cells

Recent research indicates that the leading edge of lamellipodia of myogenic cells (myoblasts and myotubes) contains presumptive fusion sites, yet the mechanisms that render the plasma membrane fusion-competent remain largely unknown. Here we show that dynamic clustering and dispersion of lipid rafts contribute to both cell adhesion and plasma membrane union during myogenic cell fusion. Adhesion-complex proteins including M-cadherin, ?-catenin,

Atsushi Mukai; Tomohiro Kurisaki; Satoshi B. Sato; Toshihide Kobayashi; Gen Kondoh; Naohiro Hashimoto

2009-01-01

98

Dynamic nuclear polarization from current-induced electron spin polarization

NASA Astrophysics Data System (ADS)

Current-induced electron spin polarization is shown to produce nuclear hyperpolarization through dynamic nuclear polarization. Saturated fields of several millitesla are generated upon the application of an electric field over a time scale of 100 s in InGaAs epilayers and measured using optical Larmor magnetometry. We show that, in contrast to previous demonstrations of current-induced dynamic nuclear polarization, the direction of the current relative to the crystal axis and external magnetic field may be used to control the magnitude and direction of the saturation nuclear field.

Trowbridge, C. J.; Norman, B. M.; Kato, Y. K.; Awschalom, D. D.; Sih, V.

2014-08-01

99

Efficient Lie-Poisson Integrator for Secular Spin Dynamics of Rigid Bodies Slawomir Breiter

Efficient Lie-Poisson Integrator for Secular Spin Dynamics of Rigid Bodies Slawomir Breiter is presented for the problem of the secular evolution of the spin axis. Under the assumption that a celestial), but on the other hand Earth and Mars remain the distinguished cases where secular spin dynamics (type 2) applies

Nesvorny, David

100

Nuclear spin dynamics in parabolic quantum wells Ionel Tifrea* and Michael E. Flatte

Nuclear spin dynamics in parabolic quantum wells Ionel TÂ¸ifrea* and Michael E. FlatteÂ´ Department March 2004 We present a detailed analytical and numerical analysis of the nuclear spin dynamics of the electronic wave function in small electric fields. The nuclear spin relaxation via the hyperfine interaction

Flatte, Michael E.

101

Dynamics of polyrotaxane investigated by neutron spin echo

NASA Astrophysics Data System (ADS)

The dynamics of a molecular necklace known as polyrotaxane (PR), in which ?-cyclodextrins (CDs) are threaded into a poly (ethylene glycol) (PEG) chain, was investigated by means of neutron spin echo (NSE) measurements. We observed that threading CDs into PEG slowed down the local dynamics and changed its Q-dependence. A solution of PEG in DMSO-d 6 showed a dynamical crossover from collective diffusion dynamics to the Zimm mode, just as in conventional polymer solutions; however, the motion of PR in DMSO-d 6 was diffusive for the whole Q range. This may be because the persistence length lp of PR was much larger than that of PEG and was similar to the mesh size of PR. The diffusive mode in a high Q regime, corresponding to a length scale of less than the lp value of PR, contained the mode of the sliding of CDs along a rod-like PEG segment in one dimension.

Mayumi, Koichi; Nagao, Michihiro; Endo, Hitoshi; Osaka, Noboru; Shibayama, Mitsuhiro; Ito, Kohzo

2009-09-01

102

Spin Dynamics Simulations ---A Powerful Method for the Study of Critical Dynamics

Spin-dynamics techniques can now be used to study the deterministic time-dependent behavior of magnetic systems containing over 105 spins with quite good accuracy. This approach will be introduced, including the theoretical foundations of the methods of analysis. Then newly developed, improved techniques based upon Suzuki-Trotter decomposition methods will be described. The current ``state-of-the-art'' will be evaluated with specific examples drawn

D. P. Landau; Alex Bunker; H. G. Evertz; M. Krech; Shan-Ho Tsai

2000-01-01

103

Dynamical Spin Injection into p-Type Germanium at Room Temperature

NASA Astrophysics Data System (ADS)

We demonstrate dynamical spin injection into p-type germanium (Ge) at room temperature (RT) using spin pumping. The generated pure spin current is converted to a charge current by the inverse spin-Hall effect (ISHE) arising in the p-type Ge sample. A clear electromotive force due to the ISHE is detected at RT. The spin-Hall angle for p-type Ge is roughly estimated to be ?SHE = 9.6×10-4 at RT.

Koike, Mariko; Shikoh, Eiji; Ando, Yuichiro; Shinjo, Teruya; Yamada, Shinya; Hamaya, Kohei; Shiraishi, Masashi

2013-02-01

104

NASA Astrophysics Data System (ADS)

In the search for topological phases in correlated electron systems, materials with 5d transition-metal ions, in particular the iridium-based pyrochlores A2Ir2O7, provide fertile grounds. Several topological states have been predicted but the actual realization of such states is believed to critically depend on the strength of local potentials arising from distortions of the IrO6 cages. We test this hypothesis by measuring with resonant inelastic x-ray scattering the electronic level splittings in the A =Y, Eu systems, which we show to agree very well with ab initio quantum chemistry electronic-structure calculations for the series of materials with A =Sm, Eu, Lu, and Y. We find, however, that the primary source for quenching the spin-orbit interaction is not a distortion of the IrO6 octahedra but longer-range lattice anisotropies which inevitably break the local cubic symmetry.

Hozoi, L.; Gretarsson, H.; Clancy, J. P.; Jeon, B.-G.; Lee, B.; Kim, K. H.; Yushankhai, V.; Fulde, Peter; Casa, D.; Gog, T.; Kim, Jungho; Said, A. H.; Upton, M. H.; Kim, Young-June; van den Brink, Jeroen

2014-03-01

105

First-principles approach to noncollinear magnetism: towards spin dynamics.

A description of noncollinear magnetism in the framework of spin-density functional theory is presented for the exact exchange energy functional which depends explicitly on two-component spinor orbitals. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within the optimized effective potential (OEP) framework. With the example of a magnetically frustrated Cr monolayer it is shown that the resulting magnetization density exhibits much more noncollinear structure than standard calculations. Furthermore, a time-dependent generalization of the noncollinear OEP method is well suited for an ab initio description of spin dynamics. We also show that the magnetic moments of solids Fe, Co, and Ni are well reproduced. PMID:17677641

Sharma, S; Dewhurst, J K; Ambrosch-Draxl, C; Kurth, S; Helbig, N; Pittalis, S; Shallcross, S; Nordström, L; Gross, E K U

2007-05-11

106

Effect of electron spin dynamics on solid-state dynamic nuclear polarization performance.

For the broadest dissemination of solid-state dynamic nuclear polarization (ssDNP) enhanced NMR as a material characterization tool, the ability to employ generic mono-nitroxide radicals as spin probes is critical. A better understanding of the factors contributing to ssDNP efficiency is needed to rationally optimize the experimental condition for the practically accessible spin probes at hand. This study seeks to advance the mechanistic understanding of ssDNP by examining the effect of electron spin dynamics on ssDNP performance at liquid helium temperatures (4-40 K). The key observation is that bi-radicals and mono-radicals can generate comparable nuclear spin polarization at 4 K and 7 T, which is in contrast to the observation for ssDNP at liquid nitrogen temperatures (80-150 K) that finds bi-radicals to clearly outperform mono-radicals. To rationalize this observation, we analyze the change in the DNP-induced nuclear spin polarization (Pn) and the characteristic ssDNP signal buildup time as a function of electron spin relaxation rates that are modulated by the mono- and bi-radical spin concentration. Changes in Pn are consistent with a systematic variation in the product of the electron spin-lattice relaxation time and the electron spin flip-flop rate that constitutes an integral saturation factor of an inhomogeneously broadened EPR spectrum. We show that the comparable Pn achieved with both radical species can be reconciled with a comparable integral EPR saturation factor. Surprisingly, the largest Pn is observed at an intermediate spin concentration for both mono- and bi-radicals. At the highest radical concentration, the stronger inter-electron spin dipolar coupling favors ssDNP, while oversaturation diminishes Pn, as experimentally verified by the observation of a maximum Pn at an intermediate, not the maximum, microwave (?w) power. At the maximum ?w power, oversaturation reduces the electron spin population differential that must be upheld between electron spins that span a frequency difference matching the (1)H NMR frequency-characteristic of the cross effect DNP. This new mechanistic insight allows us to rationalize experimental conditions where generic mono-nitroxide probes can offer competitive ssDNP performance to that of custom designed bi-radicals, and thus helps to vastly expand the application scope of ssDNP for the study of functional materials and solids. PMID:24968276

Siaw, Ting Ann; Fehr, Matthias; Lund, Alicia; Latimer, Allegra; Walker, Shamon A; Edwards, Devin T; Han, Song-I

2014-09-21

107

NASA Astrophysics Data System (ADS)

Using fast electron spin resonance spectroscopy of a single nitrogen-vacancy defect in diamond, we demonstrate real-time readout of the Overhauser field produced by its nuclear spin environment under ambient conditions. These measurements enable narrowing the Overhauser field distribution by postselection, corresponding to a conditional preparation of the nuclear spin bath. Correlations of the Overhauser field fluctuations are quantitatively inferred by analyzing the Allan deviation over consecutive measurements. This method allows us to extract the dynamics of weakly coupled nuclear spins of the reservoir.

Dréau, A.; Jamonneau, P.; Gazzano, O.; Kosen, S.; Roch, J.-F.; Maze, J. R.; Jacques, V.

2014-09-01

108

Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors

NASA Astrophysics Data System (ADS)

The symmetry of the wavefunction describing the Cooper pairs is one of the most fundamental quantities in a superconductor, but for iron-based superconductors it has proved to be problematic to determine, owing to their complex multi-band nature. Here we use a first-principles many-body method, including the two-particle vertex function, to study the spin dynamics and the superconducting pairing symmetry of a large number of iron-based compounds. Our results show that these high-temperature superconductors have both dispersive high-energy and strong low-energy commensurate or nearly commensurate spin excitations, which play a dominant role in Cooper pairing. We find three closely competing types of pairing symmetries, which take a very simple form in the space of active iron 3d orbitals, and differ only in the relative quantum mechanical phase of the xz, yz and xy orbital components of the Cooper pair wavefunction. The extensively discussed s+- symmetry appears when contributions from all orbitals have equal sign, whereas a novel orbital-antiphase s+- symmetry emerges when the xy orbital has an opposite sign to the xz and yz orbitals. This orbital-antiphase pairing symmetry agrees well with the angular variation of the superconducting gaps in LiFeAs (refs , ).

Yin, Z. P.; Haule, K.; Kotliar, G.

2014-11-01

109

We report on the linear response density functional study of the magnetization dynamics in Co(100) film driven by a nonuniform magnetic field. At resonant frequencies in the terahertz range, the magnetic field excites standing spin waves of the system and the induced magnetization penetrates the whole volume of the film. The pattern of magnetization precession is strongly influenced by the spin-flip excitations of single electrons which lead to the Landau damping of the spin-wave modes. Our results pave the way for the precise control of terahertz magnetization dynamics in itinerant magnets. PMID:20868192

Buczek, Pawe?; Ernst, Arthur; Sandratskii, Leonid M

2010-08-27

110

Dynamics and Control of a Quasi-1D Spin System

We study experimentally a system comprised of linear chains of spin-1/2 nuclei that provides a test-bed for multi-body dynamics and quantum information processing. This system is a paradigm for a new class of quantum information devices that can perform particular tasks even without universal control of the whole quantum system. We investigate the extent of control achievable on the system with current experimental apparatus and methods to gain information on the system state, when full tomography is not possible and in any case highly inefficient.

Paola Cappellaro; Chandrasekhar Ramanathan; David G. Cory

2007-06-04

111

Proton spin-lattice relaxation and spin dynamics in magnetic molecular clusters

NASA Astrophysics Data System (ADS)

We present data of proton spin-lattice relaxation rate (NSLR) in the temperature range 4-300K and as a function of external magnetic field from 0.1 to 9.1 Tesla in magnetic molecular clusters : (i) almost coplanar rings of respectively six(Fe6) and ten(Fe10) iron(III) ions with spin S=5/2 ; (ii) the dodecanuclear manganese cluster Mn12; (iii) the core of biological molecule ferritin in solid state. It is shown that the ^1H NSLR is an effective probe of spin dynamics of the magnetic ions. The NSLR data in the different samples are compared among themselves and are contrasted to the data in infinite linear magnetic chains. A theoretical model which extends to the rings the calculation of the autocorrelation function for 3-dimensional paramagnets and which incorporates the effects of temperature reproduces many of the observed features. * Operated by Iowa State University for USDOE under Contract No. W-7405-Eng-82

Borsa, F.; Jang, Z.; Shastri, A.; Luban, M.; Lascialfari, A.; Gatteschi, D.; Luscombe, J. H.

1997-03-01

112

Emergent magnetic monopoles and their dynamics in artificial spin ice

NASA Astrophysics Data System (ADS)

Electrically charged particles such as electrons are common in our world. In contrast, no elementary particles with a net magnetic charge have ever been observed. After a recent discovery that magnetic monopoles can emerge in a system of magnetic dipoles [1], much attention has been paid to the behavior of magnetic monopoles in artificial spin ice, arrays of nano-scale magnetic islands or wires that mimic the behavior of geometrically frustrated materials [2]. We have developed a theoretical model of magnetization dynamics in artificial spin ice under the action of an external magnetic field [3]. Magnetization reversal is mediated by the creation, propagation and absorption of domain walls carrying two units of magnetic. Domain walls are emitted from lattice junctions when the local field becomes large enough to overcome the Coulomb attraction between the magnetic charges of the domain wall and the junction. This interaction is also responsible for a positive feedback that triggers magnetic avalanches observed experimentally in artificial spin ice. [4pt] [1] C. Castelnovo, R. Moessner, and S. L. Sondhi, Nature 451, 42 (2008). [0pt] [2] O. Tchernyshyov, Nat. Phys. 6, 323 (2010). [0pt] [3] P. Mellado, O. Petrova, Y. Shen, and O. Tchernyshyov, Phys. Rev. Lett. 105, 187206 (2010).

Shen, Yichen; Petrova, Olga; Mellado, Paula; Tchernyshyov, Oleg

2011-03-01

113

Quantum Computation and Quantum Spin Dynamics Hans De Raedt, Kristel Michielsen, and Anthony Hams

quantum computers by simulating quantum spin models representing quantum computer hardware. ExamplesQuantum Computation and Quantum Spin Dynamics Hans De Raedt, Kristel Michielsen, and Anthony Hams@yuragi.t.u-tokyo.ac.jp, saitoh@spin.t.u-tokyo.ac.jp We analyze the stability of quantum computations on physically realiz- able

114

Relationship between energy landscape and low-temperature dynamics of J spin glasses

1 Relationship between energy landscape and low-temperature dynamics of Â±J spin glasses S. Kobea-Zellerfeld, Germany Clusters and valleys in the exact low-energy landscape of finite Edwards-Anderson Â±J spin glasses of the spin cor- relation function reflects a walk through the landscape at a given temperature and shows

Kobe, Sigismund

115

Non-diffusive spin dynamics in a two-dimensional electrongas

We describe measurements of spin dynamics in thetwo-dimensional electron gas in GaAs/GaAlAs quantum wells. Opticaltechniques, including transient spin-grating spectroscopy, are used toprobe the relaxation rates of spin polarization waves in the wavevectorrange from zero to 6E4 cm-1. We find that the spin polarization lifetimeis maximal at nonzero wavevector, in contrast with expectation based onordinary spin diffusion, but in quantitative agreement with recenttheories that treat diffusion in the presence of spin-orbitcoupling.

Weber, Christopher P.; Orenstein, Joseph; Bernevig, B. Andrei; Zhang, Shou-Cheng; Stephens, Jason; Awschalom, David D.

2006-12-12

116

Non-diffusive spin dynamics in a two-dimensional electron gas

We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wavevector range from zero to 6 x 10{sup 4} cm{sup -1}. We find that the spin polarization lifetime is maximal at nonzero wavevector, in contrast with expectation based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.

Weber, C.P.

2010-04-28

117

Spin-Entry Characteristics of a Large Supersonic Bomber as Determined by Dynamic Model Tests

NASA Technical Reports Server (NTRS)

An investigation has been conducted in the Langley spin tunnel and at a catapult launch facility of a 1/60-scale dynamic model to determine the spin-entry characteristics of a large supersonic bomber. Catapult tests indicated that spin-entry motions were obtainable for a center-of-gravity location of 0.21 mean aerodynamic chord but were not obtainable at a center-of-gravity location of 0.25 mean aerodynamic chord. Deflected ailerons were effective in promoting or preventing the spin- entry motion and this effect was qualitatively the same as it was for the fully developed spin. Varying the configuration had little significant effect on the spin-entry characteristics. Brief tests conducted with the model in the Langley spin tunnel indicated that fully developed spins were obtainable at the forward center-of-gravity location and that spins were highly unlikely at the rearward center-of-location.

Bowman, James S.

1965-01-01

118

Dynamical effects of phonons on soliton binding in quasi-one-dimensional spin-Peierls systems

NASA Astrophysics Data System (ADS)

The role of dynamical magneto-elastic coupling in spin-Peierls chains is investigated by various numerical techniques. We show that, generically, a Heisenberg spin chain coupled to dynamical optical phonons exhibits a transition towards a spontaneously dimerized state. The low energy excitations are characterized as topological solitons. No binding between solitons occurs in the isolated spin-phonon chain. However, elastic interchain coupling can lead to the formation of bound states.

Augier, D.; Poilblanc, D.; Sørensen, E.; Affleck, I.

1999-01-01

119

Optically detected coherent spin dynamics of a single electron in a quantum dot

LETTERS Optically detected coherent spin dynamics of a single electron in a quantum dot M. H dynamics provide a sensitive probe of the local nuclear spin environment. The magneto-optical Kerr effect, Schematic diagram of the experimental set-up (EOM, electro-optic modulator; Pol. BS, polarizing beam

Loss, Daniel

120

Solid effect in magic angle spinning dynamic nuclear polarization

For over five decades, the solid effect (SE) has been heavily utilized as a mechanism for performing dynamic nuclear polarization (DNP). Nevertheless, it has not found widespread application in contemporary, high magnetic field DNP experiments because SE enhancements display an \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{upgreek} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}\\omega _0 ^{ - 2}\\end{equation*} \\end{document}?0?2 field dependence. In particular, for nominally forbidden zero and double quantum SE transitions to be partially allowed, it is necessary for mixing of adjacent nuclear spin states to occur, and this leads to the observed field dependence. However, recently we have improved our instrumentation and report here an enhancement of ? = 91 obtained with the organic radical trityl (OX063) in magic angle spinning experiments performed at 5 T and 80 K. This is a factor of 6-7 higher than previous values in the literature under similar conditions. Because the solid effect depends strongly on the microwave field strength, we attribute this large enhancement to larger microwave field strengths inside the sample volume, achieved with more efficient coupling of the gyrotron to the sample chamber. In addition, we develop a theoretical model to explain the dependence of the buildup rate of enhanced nuclear polarization and the steady-state enhancement on the microwave power. Buildup times and enhancements were measured as a function of 1H concentration for both trityl and Gd-DOTA. Comparison of the results indicates that for trityl the initial polarization step is the slower, rate-determining step. However, for Gd-DOTA the spread of nuclear polarization via homonuclear 1H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect. PMID:22894339

Corzilius, Bjorn; Smith, Albert A.; Griffin, Robert G.

2012-01-01

121

NASA Astrophysics Data System (ADS)

The electron spin dynamics in n-doped bulk cubic GaN is investigated for very high temperatures from 293 K up to 500 K by time-resolved Kerr-rotation spectroscopy. We find extraordinarily long spin lifetimes exceeding 1 ns at 500 K. The temperature dependence of the spin relaxation time is in qualitative agreement with predictions of Dyakonov-Perel theory, while the absolute experimental times are an order of magnitude shorter than predicted. Possible reasons for this discrepancy are discussed, including the role of phase mixtures of hexagonal and cubic GaN as well as the impact of localized carriers.

Buß, J. H.; Schaefer, A.; Schupp, T.; As, D. J.; Hägele, D.; Rudolph, J.

2014-11-01

122

A key role for unusual spin dynamics in ferropnictides

NASA Astrophysics Data System (ADS)

The discovery of high-Tc ferropnictides introduced a new family of superconductors, and has already revealed a complicated and often contradictory picture of the structural and magnetic properties. An almost unprecedented sensitivity of the calculated magnetism and Fermi surface to structural details prevents correspondence to experiment. Experimental probes of the order parameter are in surprisingly strong disagreement, even considering the relative immaturity of the field. We outline various and seemingly contradictory evidence, both theoretical and experimental, and show it can be rectified by assuming a large-moment spin density wave, well defined but with magnetic twin and antiphase boundaries, dynamic on the experimental timescale. Under this assumption, calculations can accurately reproduce even very fine details of the structure, and a natural explanation for the temperature separation of structural and magnetic transitions is provided. Thus, our theory restores agreement between experiment and theory in crucial areas, making further cooperative progress possible on both fronts.

Mazin, I. I.; Johannes, M. D.

2009-02-01

123

Effective ergodicity in single-spin-flip dynamics

NASA Astrophysics Data System (ADS)

A quantitative measure of convergence to effective ergodicity, the Thirumalai-Mountain (TM) metric, is applied to Metropolis and Glauber single-spin-flip dynamics. In computing this measure, finite lattice ensemble averages are obtained using the exact solution for a one dimensional Ising model, whereas the time averages are computed with Monte Carlo simulations. The time evolution of the effective ergodic convergence of Ising magnetization is monitored. By this approach, diffusion regimes of the effective ergodic convergence of magnetization are identified for different lattice sizes, nonzero temperature, and nonzero external field values. Results show that caution should be taken when using the TM metric at system parameters that give rise to strong correlations.

Süzen, Mehmet

2014-09-01

124

Entanglement entropy dynamics of disordered quantum spin chains

By means of free fermionic techniques we study the time evolution of the entanglement entropy, S(t), of a block of spins in the random transverse-field Ising chain after a sudden change of the parameters of the Hamiltonian. We consider global quenches, when the parameters are modified uniformly in space, as well as local quenches, when two disconnected blocks are suddenly joined together. For a non-critical final state, the dynamical entanglement entropy is found to approach a finite limiting value for both types of quenches. If the quench is performed to the critical state, the entropy grows for an infinite block as S(t) \\sim ln ln t. This type of ultraslow increase is explained through the strong disorder renormalization group method.

Ferenc Igloi; Zsolt Szatmari; Yu-Cheng Lin

2012-01-18

125

Diffusive spin dynamics in lanthanomanganites with colossal magnetoresistance behaviour

NASA Astrophysics Data System (ADS)

Neutron scattering has been used to study the magnetic correlations and the spin dynamics in the ferromagnetic lanthanum-manganite La 0.75Ca 0.25MnO 3 above and below the Curie temperature. This material is known to exhibit colossal magnetoresistence behaviour, and its origin is strictly correlated to electron-lattice coupling. Quasielastic neutron scattering measurements show the presence of a diffusive central peak in the low- Q region (up to about 0.5 Å -1) that persists above TC. The correlation length deduced from this contribution is about 8 Å, the diffusion coefficient derived from the Q-dependence of the quasielastic broadening agrees with that expected for electron diffusion ‘assisted’ by lattice distortions.

Bergenti, I.; Deriu, A.; Licci, F.; Turilli, G.; Cicognani, G.

2001-07-01

126

NASA Astrophysics Data System (ADS)

Key to future spintronics and spin-based information processing technologies is the generation, manipulation, and detection of spin polarization in a solid state platform. Here, we theoretically explore an alternative route to spin injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in diamond. We focus on the geometry where carriers and NV centers are confined to proximate, parallel layers and use a "trap-and-release" model to calculate the spin cross-relaxation probabilities between the charge carriers and neighboring NV centers. We identify near-unity regimes of carrier polarization depending on the NV spin state, applied magnetic field, and carrier g-factor. In particular, we find that unlike holes, electron spins are distinctively robust against spin-lattice relaxation by other, unpolarized paramagnetic centers. Further, the polarization process is only weakly dependent on the carrier hopping dynamics, which makes this approach potentially applicable over a broad range of temperatures.

Meriles, Carlos A.; Doherty, Marcus W.

2014-07-01

127

A quantum jump description for the non-Markovian dynamics of the spin-boson model

NASA Astrophysics Data System (ADS)

We derive a time-convolutionless master equation for the spin-boson model in the weak coupling limit. The temporarily negative decay rates in the master equation indicate short time memory effects in the dynamics, which are explicitly revealed when the dynamics is studied using the non-Markovian jump description. The approach gives new insights into the memory effects influencing the spin dynamics and demonstrates how for the spin-boson model the co-operative action of different channels complicates the detection of memory effects in the dynamics.

Laine, E.-M.

2010-09-01

128

A quantum jump description for the non-Markovian dynamics of the spin-boson model

We derive a time-convolutionless master equation for the spin-boson model in the weak coupling limit. The temporarily negative decay rates in the master equation indicate short time memory effects in the dynamics which is explicitly revealed when the dynamics is studied using the non-Markovian jump description. The approach gives new insight into the memory effects influencing the spin dynamics and demonstrates, how for the spin-boson model the the co-operative action of different channels complicates the detection of memory effects in the dynamics.

E. -M. Laine

2009-09-30

129

A quantum jump description for the non-Markovian dynamics of the spin-boson model

We derive a time-convolutionless master equation for the spin-boson model in the weak coupling limit. The temporarily negative decay rates in the master equation indicate short time memory effects in the dynamics which is explicitly revealed when the dynamics is studied using the non-Markovian jump description. The approach gives new insight into the memory effects influencing the spin dynamics and demonstrates, how for the spin-boson model the the co-operative action of different channels complicates the detection of memory effects in the dynamics.

Laine, E -M

2009-01-01

130

The recently isolated TiSc(2)N@C(80) was used to study the spin state of a Ti(3+) ion in a mixed metal nitride cluster in a fullerene cage. The electronic state of the new clusterfullerene is characterized starting with the redox behavior of this structure. It differs markedly from that of homometallic nitride clusterfullerenes in giving reversible one-electron transfers even on the cathodic scale. Both oxidation and reduction of TiSc(2)N@C(80) occur at the endohedral cluster changing the valence state of Ti from Ti(II) in anion to Ti(IV) in cation. The unpaired electron in TiSc(2)N@C(80) is largely fixed at the Ti ion as shown by low temperature ESR measurements. Isotropic g-factor 1.9454 points to the significant spin-orbit coupling with an unquenched orbital momentum of the 3d electron localized on Ti. Measurements with the frozen solution also point to the strong anisotropy of the g-tensor. DFT computations show that the cluster can adopt several nearly isoenergetic configurations. DFT-based Born-Oppenheimer molecular dynamics (BOMD) simulations reveal that, unlike in Sc(3)N@C(80), the cluster dynamics in TiSc(2)N@C(80) cannot be described as a 3D rotation. The cluster rotates around the Ti-N axis, while the Ti atom oscillates in one position around the pentagon/hexagon edge. Evolution of the spin populations along the BOMD trajectory has shown that the spin distribution in the cluster is very flexible, and both an intracluster and cluster-cage spin flows take place. Fourier transformation of the time dependencies of the spin populations results in the spin-flow vibrational spectra, which reveal the major spin-flow channels. It is shown that the cluster-cage spin flow is selectively coupled to one vibrational mode, thus, pointing to the utility of the clusterfullerene for the molecular spin transport. Spin-flow vibrational spectroscopy is thus shown to be a useful method for characterization of the spin dynamics in radicals with flexible spin density distribution. PMID:20731461

Popov, Alexey A; Chen, Chuanbao; Yang, Shangfeng; Lipps, Ferdinand; Dunsch, Lothar

2010-08-24

131

Measurement backaction on the quantum spin-mixing dynamics of a spin-1 Bose-Einstein condensate

We consider a small F=1 spinor condensate inside an optical cavity driven by an optical probe field, and subject the output of the probe to a homodyne detection, with the goal of investigating the effect of measurement backaction on the spin dynamics of the condensate. Using the stochastic master equation approach, we show that the effect of backaction is sensitive to not only the measurement strength but also the quantum fluctuation of the spinor condensate. The same method is also used to estimate the atom numbers below which the effect of backaction becomes so prominent that extracting spin dynamics from this cavity-based detection scheme is no longer practical.

Zhang Keye; Zhou Lu; Zhang Weiping [Quantum Institute for Light and Atoms, Department of Physics, East China Normal University, Shanghai 200062 (China); Ling, Hong Y. [Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey 08028-1700 (United States); Pu Han [Department of Physics and Astronomy, and Rice Quantum Institute, Rice University, Houston, Texas 77251-1892 (United States)

2011-06-15

132

Dynamics of Overhauser Field under nuclear spin diffusion in a quantum dot

The coherence of electron spin can be significantly enhanced by locking the Overhauser field from nuclear spins using the nuclear spin preparation. We propose a theoretical model to calculate the long time dynamics of the Overhauser field under intrinsic nuclear spin diffusion in a quantum dot. We obtain a simplified diffusion equation that can be numerically solved and show quantitatively how the Knight shift and the electron-mediated nuclear spin flip-flop affect the nuclear spin diffusion. The results explain several recent experimental observations, where the decay time of Overhauser field is measured under different configurations, including variation of the external magnetic field, the electron spin configuration in a double dot, and the initial nuclear spin polarization rate.

Zhe-Xuan Gong; Zhang-qi Yin; L. -M. Duan

2009-12-22

133

Spinning Black Hole Pairs: Dynamics and Gravitational Waves

NASA Astrophysics Data System (ADS)

Black hole binaries will be an important source of gravitational radiation for both ground-based and future space-based gravitational wave detectors. The study of such systems will offer a unique opportunity to test the dynamical predictions of general relativity when gravity is very strong. To date, most investigations of black hole binary dynamics have focused attention on restricted scenarios in which the black holes do not spin (and thus are confined to move in a plane) and/or in which they stay on quasi-circular orbits. However, spinning black hole pairs in eccentric orbits are now understood to be astrophysically equally important. These spinning binaries exhibit a range of complicated dynamical behaviors, even in the absence of radiation reaction. Their conservative dynamics is complicated by extreme perihelion precession compounded by spin-induced precession. Although the motion seems to defy simple decoding, we are able to quantitatively define and describe the fully three-dimensional motion of arbitrary mass-ratio binaries with at least one black hole spinning and expose an underlying simplicity. To do so, we untangle the dynamics by constructing an instantaneous orbital plane and showing that the motion captured in that plane obeys elegant topological rules. In this thesis, we apply the above prescription to two formal systems used to model black hole binaries. The first is defined by the conservative 3PN Hamiltonian plus spin-orbit coupling and is particularly suitable to comparable-mass binaries. The second is defined by geodesics of the Kerr metric and is used exclusively for extreme mass-ratio binaries. In both systems, we define a complete taxonomy for fully three-dimensional orbits. More than just a naming system, the taxonomy provides unambiguous and quantitative descriptions of the orbits, including a determination of the zoom-whirliness of any given orbit. Through a correspondence with the rational numbers, we are able to show that all of the qualitative features of the well-studied equatorial geodesic motion around Schwarzschild and Kerr black holes are also present in more general black hole binary systems. This includes so-called zoom-whirl behavior, which turns out to be unexpectedly prevalent in comparable-mass binaries in the strong-field regime just as it is for extreme mass-ratio binaries. In each case we begin by thoroughly cataloging the constant radius orbits which generally lie on the surface of a sphere and have acquired the name "spherical orbits". The spherical orbits are significant as they energetically frame the distribution of all orbits. In addition, each unstable spherical orbit is asymptotically approached by an orbit that whirls an infinite number of times, known as a homoclinic orbit. We further catalog the homoclinic trajectories, each of which is the infinite whirl limit of some part of the zoom-whirl spectrum and has a further significance as the separatrix between inspiral and plunge for eccentric orbits. We then show that there exists a discrete set of orbits that are geometrically closed n-leaf clovers in a precessing orbital plane. When viewed in the full three dimensions, these orbits do not close, but they are nonetheless periodic when projected into the orbital plane. Each n-leaf clover is associated with a rational number, q, that measures the degree of perihelion precession in the precessing orbital plane. The rational number q varies monotonically with the orbital energy and with the orbital eccentricity. Since any bound orbit can be approximated as near one of these periodic n-leaf clovers, this special set offers a skeleton that illuminates the structure of all bound orbits in both systems, in or out of the equatorial plane. A first significant conclusion that can be drawn from this analysis is that all generic orbits in the final stages of inspiral under gravitational radiation losses are characterized by precessing clovers with few leaves, and that no orbit will behave like the tightly precessing ellipse of Mercury. We close with a practical applicati

Grossman, Rebecca

134

Dynamical Self-Quenching of Spin Pumping into Double Quantum Dots

NASA Astrophysics Data System (ADS)

Nuclear spin polarization can be pumped into spin-blockaded quantum dots by multiple Landau-Zener passages through singlet-triplet anticrossings. By numerical simulations of realistic systems with 107 nuclear spins during 105 sweeps, we uncover a mechanism of dynamical self-quenching which results in a fast saturation of the nuclear polarization under stationary pumping. This is caused by screening the random field of the nuclear spins. For moderate spin-orbit coupling, self-quenching persists but its patterns are modified. Our finding explains low polarization levels achieved experimentally and calls for developing new protocols that break the self-quenching limitations.

Brataas, Arne; Rashba, Emmanuel I.

2012-12-01

135

Dynamical decoupling design for identifying weakly coupled nuclear spins in a bath

NASA Astrophysics Data System (ADS)

Identifying weakly coupled nuclear spins around single electron spins is a key step toward implementing quantum information processing using coupled electron-nuclei spin systems or sensing like single-spin nuclear magnetic resonance detection using diamond defect spins. Dynamical decoupling control of the center electron spin with periodic pulse sequences [e.g., the Carre-Purcell-Meiboom-Gill (CPMG) sequence] has been successfully used to identify single nuclear spins and to resolve structure of nuclear spin clusters. Here, we design a type of pulse sequence by replacing the repetition unit (a single ? pulse) of the CPMG sequence with a group of nonuniformly spaced ? pulses. Using the nitrogen-vacancy center system in diamond, we theoretically demonstrate that the designed pulse sequence improves the resolution of nuclear spin noise spectroscopy, and more information about the surrounding nuclear spins is extracted. The principle of dynamical decoupling design proposed in this paper is useful in many systems (e.g., defect spin qubit in solids, trapped ion, and superconducting qubit) for high-resolution noise spectroscopy.

Zhao, Nan; Wrachtrup, Jörg; Liu, Ren-Bao

2014-09-01

136

Dynamical spin chirality and spin anisotropy in Sr14Cu24O41 : A neutron polarization analysis study

NASA Astrophysics Data System (ADS)

Low-dimensional quantum spin systems constitute an ideal built-in laboratory to study fundamental aspects of solid-state physics. By engineering suitable compounds, fundamental theories have been tested during the past decades and many studies are still underway. Quantum phase transitions, possible coupling mechanisms to explain high- TC superconductivity, ring exchange and orbital and spin currents, and the occurrence of Luttinger liquids and Bose-Einstein condensation are among the matters studied in this fascinating area of quantum systems. Here we add two values to this extensive list, which are the study of the spin anisotropy in spin-singlet ground-state compounds and the study of magnetic chirality, as measured by inelastic polarized neutron scattering techniques. To this end we have used the paramagnetic spin-singlet ground-state compound Sr14Cu24O41 and discussed in detail the scattering properties of the first excited state of the chain sublattice, a spin triplet. In-plane and out-of-plane magnetic fluctuations are measured to be anisotropic and further discussed in the light of the current hypothesis of spin-orbit coupling. We show that under appropriate conditions of magnetic field and neutron polarization, the trivial magnetic chirality selects only one of the Zeeman-split triplet states for scattering and erases the other one that possesses opposite helicity. Our analysis pertains to previous studies of dynamical magnetic chirality and chiral critical exponents, where the ground state is chiral itself, the so-called nontrivial dynamical magnetic chirality. As it turns out, both trivial and nontrivial dynamical magnetic chiralities have identical selection rules for inelastic polarized neutron scattering experiments and it is not at all evident that they can be distinguished in a paramagnetic compound.

Lorenzo, J. E.; Boullier, C.; Regnault, L. P.; Ammerahl, U.; Revcolevschi, A.

2007-02-01

137

Controlling coherent and incoherent spin dynamics by steering the photoinduced energy flow

NASA Astrophysics Data System (ADS)

We present a femtosecond spectroscopic magneto-optical investigation of the coherent and incoherent spin dynamics in the antiferromagnetic dielectric KNiF3. The pathways of the photoinduced energy flow to spins were controlled by tuning the pump photon energy. In particular, we demonstrate that laser pulses, with photon energy tuned to a nearly-zero-absorption region, excite the spin system without any signatures of heating of electrons or phonons. In this regime the ultrafast excitation of coherent spin waves is followed by a gradual increase of the spin temperature solely due to decoherence of the laser-generated magnons, as revealed by our simultaneous measurement of both the transversal and the longitudinal component of the spin dynamics.

Bossini, D.; Kalashnikova, A. M.; Pisarev, R. V.; Rasing, Th.; Kimel, A. V.

2014-02-01

138

Nondestructive optical probe of coherent single spin dynamics in a quantum dot

NASA Astrophysics Data System (ADS)

Understanding the coherent dynamics of a single electron spin in a quantum dot (QD) is important for potential applications in solid-state, spin-based quantum information processing. Here, results will be presented focusing on optical detection of a single spin and observation of the temporal evolution of the spin state. First, we demonstrate the detection of a single electron spin in a QD using a continuously averaged magneto-optical Kerr rotation (KR) measurement ootnotetextJ. Berezovsky, M. H. Mikkelsen, et al., Science 314, 1916 (2006).. In contrast to many other single spin detection schemes, the KR measurement minimally disturbs the system, making it potentially useful for exploring quantum measurementphenomena or spin-photon entanglement. This continuous single QD KR technique is then extended into the time domain using pulsed pump and probe lasers, allowing the observation of the coherent evolution of an electron spin state with nanosecond temporal resolution ootnotetextM. H. Mikkelsen, J. Berezovsky, et al., Nature Physics 3, 770 (2007).. This provides a direct measurement of the electron g-factor and spin lifetime, and additionally serves as a sensitive probe of the local nuclear spin environment. Finally, we perform ultrafast coherent optical manipulation of the electron spin state in the QD using the optical Stark effect ootnotetextJ. Berezovsky, M. H. Mikkelsen, et al., submitted (2007)., where an off-resonant optical pulse induces rotations of the spin state through angles up to ? radians on picosecond timescales.

Berezovsky, Jesse

2008-03-01

139

Spin dynamics and diffusion in GaMnAs

NASA Astrophysics Data System (ADS)

We use an ultrafast transient spin grating to measure the lifetime and diffusion coefficient of optically oriented spins in (Ga,Mn)As. We measure films with nominal doping of 5%, 6%, and 7% Mn. Both below and above the Curie temperature we observe a spin lifetime of about 8 ps. The spins diffuse at nearly the same rate as do electrons (about 70 cm^2/s), allowing us to identify our signal as the spins of mobile, photoexcited electrons. The rapidity of the spin diffusion indicates that spin Coulomb drag (SCD), due to electron-electron collisions, is weak. We attribute this weakness to screening of the Coulomb interaction by holes. SCD appears to have comparable strength in both the ferromagnetic and normal states.

Weber, Chris; Mattia, Kassandra; Kittlaus, Eric; Liu, Xinyu; Furdyna, Jacek

2013-03-01

140

Dynamical effects of phonons on soliton binding in low-dimensional spin-Peierls systems

NASA Astrophysics Data System (ADS)

The role of dynamical magneto-elastic coupling in spin-Peierls chains is investigated by various numerical techniques. We show that a Heisenberg spin chain coupled to dynamical optical phonons exhibits a transition towards a spontaneously dimerized state in a wide range of parameters space. The low energy excitations are fully characterized as topological solitons. No binding between solitons is observed in the isolated spin-phonon chain and the dynamical spin structure factor shows only a broad magnon dispersion. However, elastic interchain coupling leads to a narrowing of the magnon resonances. These results are discussed in the context of the new inorganic spin-Peierls compound NaV_2O_5.

Augier, David; Poilblanc, Didier; Sørensen, Erik; Affleck, Ian

1998-03-01

141

Dynamics of systems with isotropic competing interactions in an external field: a Langevin approach

NASA Astrophysics Data System (ADS)

We study the Langevin dynamics of a ferromagnetic Ginzburg-Landau Hamiltonian with a competing long-range repulsive term in the presence of an external magnetic field. The model is analytically solved within the self consistent Hartree approximation for two different initial conditions: disordered or zero field cooled (ZFC), and fully magnetized or field cooled (FC). To test the predictions of the approximation we develop a suitable numerical scheme to ensure the isotropic nature of the interactions. Both the analytical approach and the numerical simulations of two-dimensional finite systems confirm a simple aging scenario at zero temperature and zero field. At zero temperature a critical field h c is found below which the initial conditions are relevant for the long time dynamics of the system. For h < h c a logarithmic growth of modulated domains is found in the numerical simulations but this behavior is not captured by the analytical approach which predicts a t 1/2 growth law at T = 0.

Díaz-Méndez, R.; Mendoza-Coto, A.; Mulet, R.; Nicolao, L.; Stariolo, D. A.

2011-06-01

142

PHYSICAL REVIEW B 85, 184301 (2012) Spin-lattice-electron dynamics simulations of magnetic materials

PHYSICAL REVIEW B 85, 184301 (2012) Spin-lattice-electron dynamics simulations of magnetic Kong Polytechnic University, Hong Kong SAR, China (Received 16 January 2012; revised manuscript for simulating the time-dependent evolution of coupled spin, atomic, and electronic degrees of freedom

143

Pinning of dynamic spin density wave fluctuations in the cuprate superconductors

preserve spin-rotation invariance, such as impurities or vortex cores. The pinning leads to static spatial by scanning tunnelling microscopy to the dynamic spin structure factor measured by inelastic neutron scattering. Many studies of the cuprates assume that high temper- ature superconductivity is best understood

144

Optimal control of coupled spin dynamics in the presence of relaxation

In this thesis, we study methods for optimal manipulation of coupled spin dynamics in the presence of relaxation. We use these methods to compute analytical upper bounds for the efficiency of coherence and polarization transfer between coupled nuclear spins in multidimensional nuclear magnetic resonance (NMR) experiments, under the presence of relaxation. We derive relaxation optimized pulse sequences which achieve or

Dionisis Stefanatos

2005-01-01

145

Higher-order spin effects in the dynamics of compact binaries II. Radiation field

Higher-order spin effects in the dynamics of compact binaries II. Radiation field Luc Blancheta by binary black holes, we investigate the gravitational radiation field of point particles with spins within of rapidly rotating Kerr-type black-hole binaries with the ground- based detectors LIGO, Virgo, GEO 600

146

Ground states, energy landscape and low-temperature dynamics of J spin glasses

Ground states, energy landscape and low-temperature dynamics of Â±J spin glasses S. Kobe1 and J glass, and use the branch-and-bound method from combinatorial opti- mization to analyze its energy landscape. The spin glass model is a prototype that combines questions of computational complexity from

Kobe, Sigismund

147

Dynamic phase diagrams of the mixed Ising bilayer system consisting of spin-3/2 and spin-2

NASA Astrophysics Data System (ADS)

The nonequilibrium behavior of the mixed spin-3/2 and spin-2 Ising system on the bilayer square lattice under a time-varying magnetic field is studied by using the Glauber-type stochastic dynamics. The dynamic equations describing the behavior of the system are derived by utilizing the Master equation and Glauber transition rates. The time variations of average magnetizations and the thermal variations of the dynamic magnetizations are investigated to obtain the dynamic phase diagrams. The dynamic phase diagrams are constructed in four different planes for the ferromagnetic/ferromagnetic (FM/FM), antiferromagnetic/ferromagnetic (AFM/FM) and antiferromagnetic/antiferromagnetic (AFM/AFM) interactions and the effects of the Hamiltonian parameters on the dynamic critical behavior of the system are studied. It is observed that the system exhibits seven fundamental phases and twenty five mixed phases which are composed of binary, ternary and tetrad combinations of fundamental phases. It is also found that the dynamic phase diagrams contain both first- and second-order phase transitions besides dynamic tricritical point, triple point (TP), quadruple point (QP), double critical end point (B), zero temperature critical point (Z), multicritical point (A) and tetracritical point (M). The reentrant behavior occurs for the FM/FM interaction.

Temizer, Ümüt; Tülek, Mesimi; Yarar, Semih

2014-12-01

148

Muon-spin-relaxation investigation of the spin dynamics of geometrically frustrated chromium spinels

dc magnetic susceptibility (chi) and muon-spin-relaxation measurements (muSR) on the geometrically frustrated systems MgCr2O4 and CdCr2O4 indicate a transition from a paramagnetic state to a quasistatic spin state at 12.5 K and 7.8 K, respectively. Comparison of low-temperature field strength measured by muSR to that predicted by a dipole model suggests that only about 15% of the spin is static

M. T. Rovers; P. P. Kyriakou; H. A. Dabkowska; G. M. Luke; M. I. Larkin; A. T. Savici

2002-01-01

149

Cryogenic sample exchange NMR probe for magic angle spinning dynamic nuclear polarization

We describe a cryogenic sample exchange system that dramatically improves the efficiency of magic angle spinning (MAS) dynamic nuclear polarization (DNP) experiments by reducing the time required to change samples and by ...

Barnes, Alexander B.

150

NASA Astrophysics Data System (ADS)

The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with the dipolar ordered initial state is considered. The high symmetry of the Hamiltonian responsible for the MQ NMR dynamics (the MQ Hamiltonian) is used to develop analytic and numerical methods for the investigation of the MQ NMR dynamics in systems consisting of hundreds of spins from the "first principles." We obtain the dependence of the intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR coherences) for systems of 200-600 spins. It is shown that these profiles may be well approximated by exponential distribution functions. We also compare the MQ NMR dynamics in the systems of equivalent spins having two different initial states, the dipolar ordered state and the thermal equilibrium state in a strong external magnetic field.

Doronin, S. I.; Fel'dman, E. B.; Zenchuk, A. I.

2011-09-01

151

Dynamics of a Mn spin coupled to a single hole confined in a quantum dot

NASA Astrophysics Data System (ADS)

Using the emission of the positively charged exciton as a probe, we analyze the dynamics of the optical pumping and the dynamics of the relaxation of a Mn spin exchange coupled with a confined hole spin in a II-VI semiconductor quantum dot. The hole-Mn spin can be efficiently initialized in a few tens of ns under optical injection of spin-polarized carriers. We show that this optical pumping process and its dynamics are controlled by electron-Mn flip-flops within the positively charged exciton-Mn complex. The pumping mechanism and its magnetic field dependence are theoretically described by a model including the dynamics of the electron-Mn complex in the excited state and the dynamics of the hole-Mn complex in the ground state of the positively charged quantum dot. We measure at zero magnetic field a spin-relaxation time of the hole-Mn spin in the ?s range or shorter. This hole-Mn spin relaxation is induced by the presence of valence-band mixing in self-assembled quantum dots.

Varghese, B.; Boukari, H.; Besombes, L.

2014-09-01

152

Dynamic spin correlations in stuffed spin ice Ho2+xTi2-xO7-?

NASA Astrophysics Data System (ADS)

The magnetic correlations in “stuffed” spin ice Ho2+xTi2-xO7-? have been characterized using quasielastic neutron scattering. At temperatures above 1K , these correlations are short ranged in nature and dynamic on a picosecond to nanosecond time scale. As for the case of pure spin ice Ho2Ti2O7 , one can identify, above the freezing temperature, a quantum relaxation regime which is enhanced as it persists to even higher temperatures, Ttilde 30-40K , than in the parent compound.

Ehlers, G.; Gardner, J. S.; Qiu, Y.; Fouquet, P.; Wiebe, C. R.; Balicas, L.; Zhou, H. D.

2008-02-01

153

Uncovering the features of spin dynamics in hadronic physics

NASA Astrophysics Data System (ADS)

We summarize the program pursued by Michael J. Moravcsik and the authors on spin amplitude analyses and interpretation. We present the recent observations that “phase histograms” reveal striking peaks corresponding to spin amplitudes that tend to have definite simple phase relations. An interpretation is proposed in which the spin amplitudes receive a coherent and an incoherent contribution over large ranges of energies and angles. Continuing research directions are reported.

Goldstein, G. R.; Arash, F.

1990-06-01

154

Multistage dynamics of the spin-lattice polaron formation

NASA Astrophysics Data System (ADS)

We follow the formation of a spin-lattice polaron after a quantum quench that simulates absorption of the pump pulse in the time-resolved experiments. We discover a two-stage relaxation where spin and lattice degrees of freedom represent an integral part of the relaxation mechanism. In the first stage, the kinetic energy of the spin-lattice polaron relaxes towards its ground-state value. In the second, typically much longer stage, a subsequent energy transfer between lattice and spin degrees of freedom via the charge carrier emerges. The multistage relaxation is generic and occurs even when carriers couple to different subsystems with comparable strengths.

Kogoj, Jan; Lenar?i?, Zala; Golež, Denis; Mierzejewski, Marcin; Prelovšek, Peter; Bon?a, Janez

2014-09-01

155

Manipulation of nuclear spin dynamics in n-GaAs using an on-chip microcoil

NASA Astrophysics Data System (ADS)

We present an approach for electrically manipulating nuclear spins in n-GaAs using an on-chip microcoil. Optically injected spin-polarized electrons are used to generate a dynamic nuclear polarization via electron-nucleus hyperfine interaction with a characteristic time constant of ˜10 min. The saturated Overhauser field amplitude is on the order of several 10 mT and proportional to the spin polarization degree of the injected electrons. Applying an rf field resonant for the A75s nuclei, complete depolarization of A75s nuclear spins is observed.

Chen, Y. S.; Huang, J.; Ludwig, A.; Reuter, D.; Wieck, A. D.; Bacher, G.

2011-01-01

156

Dynamic neutron scattering on incoherent systems using efficient resonance spin flip techniques

NASA Astrophysics Data System (ADS)

We have performed numerical ray-tracing Monte-Carlo-simulations of incoherent dynamic neutron scattering experiments. We intend to optimize the efficiency of incoherent measurements depending on the fraction of neutrons scattered without and with spin flip at the sample. In addition to conventional spin echo, we have numerically and experimentally studied oscillating intensity techniques. The results point out the advantages of these different spin echo variants and are an important prerequisite for neutron resonance spin echo instruments like RESEDA (FRM II, Munich), to choose the most efficient technique depending on the scattering vector range and the properties of the sample system under study.

Häussler, Wolfgang; Kredler, Lukas

2014-05-01

157

Chaotic spin-dependent electron dynamics in a field-driven double dot potential

NASA Astrophysics Data System (ADS)

We study the nonlinear classical dynamics of an electron confined in a double-well potential and subjected to a spin-orbit coupling as well as a constant external magnetic field. It is shown that due to the spin-orbit coupling the energy can be transferred from the spin to the orbital degree of freedom. It is shown that depending on the strength of the spin-orbit coupling and the energy of the system, the electronic orbital motion undergoes a transition from the regular to the chaotic regime.

Chotorlishvili, L.; Toklikishvili, Z.; Komnik, A.; Berakdar, J.

2012-12-01

158

NASA Astrophysics Data System (ADS)

Within the framework of a general three-level problem, the dynamics of the nitrogen-vacancy (NV) spin is studied for the case of a special type of external driving consisting of a set of continuous fields with decreasing intensities. Such a set has been proposed for minimizing coherence losses. Each new driving field with smaller intensity is designed to protect against the fluctuations induced by the driving field at the preceding step with larger intensity. We show that indeed this particular type of external driving minimizes the loss of coherence, using purity and entropy as quantifiers for this purpose. As an illustration, we study the coherence loss of an NV spin due to a surrounding spin bath of C13 nuclei.

Mishra, S. K.; Chotorlishvili, L.; Rau, A. R. P.; Berakdar, J.

2014-09-01

159

Spin ordering and dynamics in the frustrated antiferromagnet YBaCo4O7.1

NASA Astrophysics Data System (ADS)

The stoichiometric 114-layered material YBaCo4O7 exhibits long-range antiferromagnetic order below a Néel temperature of 106 K. Nonstoichiometric YBaCo4O7.1, which contains a relatively small amount (1.4%) of interstitial oxygen, has recently been shown to have drastically modified magnetic properties compared to the parent compound. The present experiments have used magnetization, ac susceptibility, and zero applied field NMR to study the spin configuration and spin dynamics in a single crystal of YBaCo4O7.1 as a function of temperature below 100 K. Evidence has been obtained for a magnetic transition at 80 K corresponding to some form of spin freeze-out. Based on previous results for the stoichiometric material, it is likely that the freezing process involves spins in the triangular layers in this frustrated antiferromagnet. At lower temperatures, dynamic effects persist and below 50 K a fraction of the spins, located primarily in the kagome layers, constitute what may be termed a viscous spin liquid component. For T < 10 K, a disordered or glasslike spin structure, with a large distribution of spin correlation times, emerges as the low-temperature state of the spin system.

Yuan, S.; Hu, X.; Kuhns, P. L.; Reyes, A. P.; Brooks, J. S.; Besara, T.; Siegrist, T.; Zheng, H.; Mitchell, J. F.; Hoch, M. J. R.

2014-03-01

160

Dipolar temperature and multiple-quantum NMR dynamics in dipolar ordered-spin systems

NASA Astrophysics Data System (ADS)

We investigate analytically and numerically the multiple-quantum (MQ) NMR dynamics in systems of nuclear spins 1/2 coupled by dipole-dipole interactions in the case of the dipolar-ordered initial state. We suggest a new method of MQ NMR based on the measurement of the dipolar temperature in the quasi-equilibrium state, which establishes after the time of order ?{loc/-1} (?loc is the dipolar local field) after the MQ NMR experiment. Manyspin clusters and correlations are created faster in such an experiment than in usual MQ NMR experiments and can be used for the investigation of the many-spin dynamics of nuclear spins in solids.

Doronin, S. I.; Fel'Dman, E. B.; Kuznetsova, E. I.; Furman, G. B.; Goren, S. D.

2007-09-01

161

Spin segregation via dynamically induced long-range interactions in a system of ultracold fermions

We investigate theoretically the time evolution of a one-dimensional system of spin-1/2 fermions in a harmonic trap after, initially, a spiral spin configuration far from equilibrium is created. We predict a spin segregation building up in time already for weak interaction under realistic experimental conditions. The effect relies on the interplay between exchange interaction and the harmonic trap, and it is found for a wide range of parameters. It can be understood as a consequence of an effective, dynamically induced long-range interaction that is derived by integrating out the rapid oscillatory dynamics in the trap.

Ebling, Ulrich [ICFO-Institut de Ciencies Fotoniques, Avenida Carl Friedrich Gauss, 3, 08860 Castelldefels, Barcelona (Spain); Eckardt, Andre [ICFO-Institut de Ciencies Fotoniques, Avenida Carl Friedrich Gauss, 3, 08860 Castelldefels, Barcelona (Spain); Max-Planck-Institut fuer Physik komplexer Systeme, Noethnitzer Strasse 38, D-01187 Dresden (Germany); Lewenstein, Maciej [ICFO-Institut de Ciencies Fotoniques, Avenida Carl Friedrich Gauss, 3, 08860 Castelldefels, Barcelona (Spain); Institucio Catalana de Recerca i Estudis Avancats, Lluis Companys 23, E-08010 Barcelona (Spain)

2011-12-15

162

Computation of dynamical correlation functions of the spin-1 Babujan-Takhtajan chain

NASA Astrophysics Data System (ADS)

The dynamical structure factor of the Babujan-Takhtajan antiferromagnetic spin-1 chain is computed numerically at zero temperature and zero magnetic field, using the higher spin generalization of an algebraic Bethe ansatz-based method previously used for spin-1/2 integrable chains. This method, which consists in the explicit construction of eigenstates and the summation of the Lehmann representation of the correlator, is particularly challenging to implement here in view of the presence of strongly deviated string solutions to the Bethe equations. We show that a careful treatment of these deviations makes it possible to obtain perfect saturation of sum rules for small system sizes, and extremely good saturation for large system sizes where the dynamical structure factor is computed by including all two-spinon and four-spinon contributions. The real-space spin-spin correlation, obtained by Fourier transforming our results, displays asymptotics fitting predictions from conformal field theory.

Vlijm, Rogier; Caux, Jean-Sébastien

2014-05-01

163

Spin-Echo Dynamics of a Heavy Hole in a Quantum Dot

NASA Astrophysics Data System (ADS)

We develop a theory for the spin-echo dynamics of a heavy hole in a quantum dot, accounting for both hyperfine- and electric-field-induced fluctuations. We show that a moderate applied magnetic field can drive this system to a motional-averaging regime, making the hyperfine interaction ineffective as a decoherence source. Furthermore, we show that decay of the spin-echo envelope is highly sensitive to the geometry. In particular, we find a specific choice of initialization and ?-pulse axes which can be used to study intrinsic hyperfine-induced hole-spin dynamics, even in systems with substantial electric-field-induced dephasing. These results point the way to designed hole-spin qubits as a robust and long-lived alternative to electron spins.

Wang, Xiaoya Judy; Chesi, Stefano; Coish, W. A.

2012-12-01

164

Using action dynamics to assess competing stimulus control during stimulus equivalence testing.

Previous studies have identified potential sources of competing stimulus control in tests for stimulus equivalence. The present experiment employed the Nintendo Wii remote (Wiimote®) to investigate whether such competition would affect suboperant action dynamics (e.g., topographies of equivalence responses). Following one-to-many training on conditional discriminations sufficient to establish three 3-member equivalence classes, participants were presented with a test for equivalence responding that included five different trial types. These included "traditional" equivalence trials, on which the incorrect stimulus had previously been presented as a correct comparison stimulus during training, trials on which a novel unrelated word was provided as the incorrect comparison, and trials on which the incorrect stimulus varied in orthographical and phonological similarity to the sample stimulus. The presence of phonological and orthographic distractor stimuli significantly reduced the probability of equivalence-consistent responding, relative to neutral distractors, but this effect was almost exclusively seen in participants who failed to demonstrate equivalence on traditional equivalence trials. Analyses of correct response trajectories suggested that the prior history of reinforcement for choosing the incorrect stimulus on the traditional equivalence trial gave rise to greater competition than did phonological or orthographic similarity between the sample and incorrect comparisons. PMID:23378287

O'Hora, Denis P; Tyndall, Ian T; McMorrow, Mairéad; Dale, Rick A C

2013-09-01

165

Brownian motion and quantum dynamics of magnetic monopoles in spin ice

Spin ice illustrates many unusual magnetic properties, including zero point entropy, emergent monopoles and a quasi liquid–gas transition. To reveal the quantum spin dynamics that underpin these phenomena is an experimental challenge. Here we show how crucial information is contained in the frequency dependence of the magnetic susceptibility and in its high frequency or adiabatic limit. The typical response of Dy2Ti2O7 spin ice indicates that monopole diffusion is Brownian but is underpinned by spin tunnelling and is influenced by collective monopole interactions. The adiabatic response reveals evidence of driven monopole plasma oscillations in weak applied field, and unconventional critical behaviour in strong applied field. Our results clarify the origin of the relatively high frequency response in spin ice. They disclose unexpected physics and establish adiabatic susceptibility as a revealing characteristic of exotic spin systems. PMID:23443563

Bovo, L.; Bloxsom, J.A.; Prabhakaran, D.; Aeppli, G.; Bramwell, S.T.

2013-01-01

166

NASA Astrophysics Data System (ADS)

The spin relaxation processes within the pyrochlore Ho2Ru2O7 have been investigated by neutron scattering and bulk property techniques. A single-ion process, that is thermally activated, dominates the spin-spin relaxation spectrum above 2 K. Assuming Arrhenius behaviour, we found an activation energy ? = (329 ± 6) K and characteristic relaxation time ?0 = (5.2 ± 0.3) × 10-12 s in the paramagnetic state, akin to those found in the spin ice, Ho2Ti2O7. Atlow temperature (T<95 K) the activation energy lowers and below 20 K the entropy and ac susceptibility are similar to that observed in other spin ice compounds within a 10 kOe field.

Gardner, J. S.; Cornelius, A. L.; Chang, L. J.; Prager, M.; Brückel, Th; Ehlers, G.

2005-11-01

167

Perfusion measurements using dynamic susceptibility contrast imaging provide additional information about the mean vessel size of microvasculature when supplemented with a dual gradient echo (GE) - spin echo (SE) contrast. Dynamic increase in the corresponding transverse relaxation rate constant changes, ?R2GE and ?R2SE , forms a loop on the (? R2SE3/2, ?R2GE ) plane, rather than a reversible line. The shape of the loop and the direction of its passage differentiate between healthy brain and pathological tissue, such as tumour and ischemic tissue. By considering a tree model of microvasculature, the direction of the loop is found to be influenced mainly by the relative arterial and venous blood volume, as well as the tracer bolus dispersion. A parameter ? is proposed to characterize the direction and shape of the loop, which might be considered as a novel imaging marker for describing the pathology of cerebrovascular network. PMID:22611004

Xu, Chao; Kiselev, Valerij G; Möller, Harald E; Fiebach, Jochen B

2013-04-01

168

Entanglement dynamics of spin systems in pure states

NASA Astrophysics Data System (ADS)

We investigate numerically the appearance and evolution of entanglement in spin systems prepared initially in a pure state. We consider the dipolar coupling spin systems of different molecular structures: benzene C6H6 , cyclopentane C5H10 , sodium butyrate CH3(CH2)2CO2Na , and calcium hydroxyapatite Ca5(OH)(PO4)3 . Numerical simulations show that the close relationship exists between the intensity of second order (2Q) coherences and concurrences of nearest spins in a cyclopentane molecule.

Furman, G. B.; Meerovich, V. M.; Sokolovsky, V. L.

2009-09-01

169

Spin soliton dynamics and pressure effects in the spin-Peierls system (DMe-DCNQI) 2M (M=Li, Ag)

NASA Astrophysics Data System (ADS)

(DMe-DCNQI) 2M (M=Li, Ag) is a {1}/{4}-filled spin-Peierls system. We study the spin/charge dynamics in the insulating state by EPR. The linewidth shows exponential dependence at T? Tsp. Further, pressure enhances mainly prefactor of the exponential dependences. These results are successfully understood in terms of the relaxation accompanied with the intercolumn hopping caused by the spin-orbit interaction both for the Li and Ag salts. This is consistent with the scenario that the hole and spin solitons help the intercolumn charge and spin transports.

Hiraoka, M.; Sakamoto, H.; Mizoguchi, K.; Kato, T.; Furukawa, K.; Kato, R.; Hiraki, K.; Takahashi, T.

2004-05-01

170

Spin dynamics in the frozen state of the dipolar spin ice material Dy2Ti2O7

NASA Astrophysics Data System (ADS)

Low temperature magnetic ac susceptibility measurements of single crystal dipolar spin ice Dy2Ti2O7 are presented. The measured dynamics qualitatively agree with simulations based on current magnetic monopole theory, but not with thermal relaxation measurements, whose dynamics freeze out at a slower rate. The relaxation is found to exhibit thermally activated Arrhenius behavior with an activation energy of 9.79,. A comparison between the measurement results of Ho2Ti2O7 and Dy2Ti2O7 will also be made.

Revell, H. M.; Yaraskavitch, L. R.; Meng, S.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Kycia, J. B.

2012-02-01

171

Dynamics of an all-optical atomic spin gyroscope.

We present the transfer function of an all-optical atomic spin gyroscope through a series of differential equations and validate the transfer function by experimental test. A transfer function is the basis for further control system design. We build the differential equations based on a complete set of Bloch equations describing the all-optical atomic spin gyroscope, and obtain the transfer function through application of the Laplace transformation to these differential equations. Moreover, we experimentally validate the transfer function in an all-optical Cs-Xe129 atomic spin gyroscope through a series of step responses. This transfer function is convenient for analysis of the form of control system required. Furthermore, it is available for the design of the control system specifically to improve the performance of all-optical atomic spin gyroscopes. PMID:24216575

Fang, Jiancheng; Wan, Shuangai; Yuan, Heng

2013-10-20

172

We study the properties of the dynamical phase transition occurring in neural network models in which a competition between associative memory and sequential pattern recognition exists. This competition occurs through a weighted mixture of the symmetric and asymmetric parts of the synaptic matrix. Through a generating functional formalism, we determine the structure of the parameter space at non-zero temperature and near saturation (i.e., when the number of stored patterns scales with the size of the network), identifying the regions of high and weak pattern correlations, the spin-glass solutions, and the order-disorder transition between these regions. This analysis reveals that, when associative memory is dominant, smooth transitions appear between high correlated regions and spurious states. In contrast when sequential pattern recognition is stronger than associative memory, the transitions are always discontinuous. Additionally, when the symmetric and asymmetric parts of the synaptic matrix are defined in terms of the same set of patterns, there is a discontinuous transition between associative memory and sequential pattern recognition. In contrast, when the symmetric and asymmetric parts of the synaptic matrix are defined in terms of independent sets of patterns, the network is able to perform both associative memory and sequential pattern recognition for a wide range of parameter values. PMID:22900014

Herrera-Aguilar, José L; Larralde, Hernán; Aldana, Maximino

2012-01-01

173

Spin dynamics and magnetoelectric properties of the coupled-spin tetrahedral compound Cu2Te2O5Cl2

NASA Astrophysics Data System (ADS)

We report on the spin dynamics and discovery of magnetoelectricity in the coupled-spin tetrahedral compound Cu2Te2O5Cl2. Te125 NMR measurements show an anomalous resonance frequency shift and a signal wipe-out phenomenon around the Néel temperature TN = 18.2 K, which could be attributed to the anomalous critical slowing down of the Cu spin fluctuations on the NMR time scale (˜10-100 MHz). The critical exponent of (T1T)-1?(T-TN)-? is 0.40 ± 0.03, as compared to 0.5 for a three-dimensional mean-field model. This is in contrast to the Br compound [S.-H. Baek et al., Phys. Rev. B 86, 180405 (2012), 10.1103/PhysRevB.86.180405], which exhibits pronounced singlet dynamics with a large spin gap. Electric polarization (Pc) is observed along the c axis for temperatures below TN under finite magnetic field but not sensitive to the electric poling. Pc increases sharply over zero to 2 T and then reaches saturation. Below TN, Pc changes its sign depending on the applied magnetic field direction, positive for the H?c axis and negative for H ? c axis. We discuss possible explanations for the observed magnetoelectric (ME) behavior in terms of linear ME effect, spin-driven multiferroicity, and an exchange striction of intertetrahedral exchange paths involving the Te4+ lone-pair ions. Our results suggest that Cu2Te2O5Cl2 is a type of ME material whose properties are tuned by intertetrahedral exchange interactions involving polarizable Te4+ ions.

Besara, T.; Choi, E. S.; Choi, K.-Y.; Kuhns, P. L.; Reyes, A. P.; Lemmens, P.; Berger, H.; Dalal, N. S.

2014-08-01

174

Zero-temperature spin dynamics of a random two-dimensional [ital XY] model

We study the zero-temperature spin dynamics of a random-exchange two-dimensional [ital XY] model using both exact numerical methods and an approach based upon the coherent potential approximation (CPA). The model, which presents a mixed-phase to spin-glass phase transition, consists of a ferromagnetic host with nearest-neighbor bonds [ital J] to which one substitutes impurity bonds of strength [minus][lambda][ital J] at concentration [ital x]. In both phases, the long-wavelength magnetic excitations of this system are spin waves with a linear spectrum. The [ital x] and [lambda] dependence of the spin-wave velocity is determined numerically by calculating the stiffness constant of the system with a new transfer-matrix algorithm. The stiffness constant and the spin-wave velocity decrease rapidly with increasing [ital x]. The two quantities are smooth across the phase boundary, and they saturate in the spin-glass phase. At shorter wavelengths, the [ital q] dependence of the energies and lifetimes of the spin waves in the ferromagnetic and spin-glass states differs qualitatively, reflecting the morphological differences that exist between the spin configurations characteristic of the two phases. Line shapes and linewidths depend strongly on the polarization of the excitations. Whereas out-of-plane modes stay propagative at all concentrations, in-plane ones are inhomogeneously broadened and are overdamped at long wavelengths. There is good overall agreement between the exact numerical results and those obtained using the CPA.

Gawiec, P.; Grempel, D.R. (Laboratoire de Magnetisme et Diffraction Neutronique, DRFMC/SPSMS, Centre d'Etudes Nucleaires de Grenoble, 85X, F-38041 Grenoble Cedex (France))

1993-09-01

175

Competing quantum effects in the dynamics of a flexible water model

Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O--H stretches are described by Morse-type functions. We have parameterized this model to give the correct liquid structure, diffusion coefficient, and infra-red absorption frequencies in quantum (path integral-based) simulations. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of simple empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infra-red absorption spectrum.

Scott Habershon; Thomas E. Markland; David E. Manolopoulos

2010-11-04

176

Dynamic Business Share Allocation in a Supply Chain with Competing Suppliers

This paper studies a repeated game between a manufacturer and two competing suppliers with imperfect monitoring. We present a principal-agent model for managing long-term supplier relationships using a unique form of ...

Li, Hongmin

177

1 Effects of competing orders and quantum criticality on the quasiparticle tunneling spectroscopy, and the characteristic field correlates well with the quasiparticle tunneling spectra, showing increasing spectral cuprates are examined by comparing theory with experimental data, and the physics implications

Yeh, Nai-Chang

178

Low energy spin dynamics in the spin ice, Ho2Sn2O7

The magnetic properties of Ho{sub 2}Sn{sub 2}O{sub 7} have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho{sub 2}Ti{sub 2}O{sub 7} spin ice, no significant changes were observed in the high temperature properties, T {approx}> 20 K. As the temperature is lowered and correlations develop, Ho{sub 2}Sn{sub 2}O{sub 7} enters its quantum phase at a slightly higher temperature than Ho{sub 2}Ti{sub 2}O{sub 7} and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be {approx}700 T.

Ehlers, Georg [ORNL; Huq, Ashfia [ORNL; Diallo, Souleymane Omar [Oak Ridge National Laboratory (ORNL); Adriano, Cris [ORNL; Rule, K [Helmholtz-Zentrum Berlin; Cornelius, A. L. [University of Nevada, Las Vegas; Fouquet, Peter [Institut Laue-Langevin (ILL); Pagliuso, P G [Instituto de Fisica Gleb Wataghin, Unicamp, Brazil; Gardner, Jason [Indiana University

2012-01-01

179

Low energy spin dynamics in the spin ice Ho2Sn2O7

NASA Astrophysics Data System (ADS)

The magnetic properties of Ho2Sn2O7 have been investigated and compared to other spin ice compounds. Although the lattice has expanded by 3% relative to the better studied Ho2Ti2O7 spin ice, no significant changes were observed in the high temperature properties, T ? 20 K. As the temperature is lowered and correlations develop, Ho2Sn2O7 enters its quantum phase at a slightly higher temperature than Ho2Ti2O7 and is more antiferromagnetic in character. Below 80 K a weak inelastic mode associated with the holmium nuclear spin system has been measured. The hyperfine field at the holmium nucleus was found to be ?700 T.

Ehlers, G.; Huq, A.; Diallo, S. O.; Adriano, C.; Rule, K. C.; Cornelius, A. L.; Fouquet, P.; Pagliuso, P. G.; Gardner, J. S.

2012-02-01

180

Multiple quantum NMR dynamics of spin-12 carrying molecules of a gas in nanopores

NASA Astrophysics Data System (ADS)

We consider the multiple quantum (MQ) NMR dynamics of a gas of spin carrying molecules in nanocavities. MQ NMR dynamics is determined by the residual dipole-dipole interactions, which are not averaged completely due to the molecular diffusion in nanopores. Since the averaged nonsecular Hamiltonian describing MQ NMR dynamics depends on only one coupling constant, this Hamiltonian commutes with the square of the total spin angular momentum Î2. We use the basis of common eigenstates of Î2 and the projection of I on the external magnetic field for investigation of MQ NMR dynamics. This approach allows us to study MQ NMR dynamics in systems consisting of several hundreds of spins. The analytical approximation of the stationary profile of MQ coherences is obtained. The analytical expressions for MQ NMR coherence intensities of the five-spin system in a nanopore are found. Numerical investigations allow us to find the dependencies of intensities of MQ coherences on their orders (the profiles of MQ coherences) in systems consisting of 600 spins and even more. It is shown that the stationary MQ coherence profile in the considered system is an exponential one.

Doronin, S. I.; Fedorova, A. V.; Fel'Dman, E. B.; Zenchuk, A. I.

2009-09-01

181

Spin dynamics in the geometrically frustrated multiferroic CuCrO2

The spin dynamics of the geometrically frustrated triangular antiferromagnet multiferroic CuCrO2 have been mapped out using inelastic neutron scattering. The relevant spin Hamiltonian parameters modeling the incommensurate modulated helicoid have been determined, and correspond to antiferromagnetic nearest- and next-nearest-neighbor interactions in the ab plane with a strong planar anisotropy. The weakly dispersive excitation along c reflects the essentially two-dimensional character

M. Poienar; F. Damay; C. Martin; J. Robert; S. Petit

2010-01-01

182

Electromagnon by chiral spin dynamics in the triangular lattice antiferromagnet

NASA Astrophysics Data System (ADS)

From high field electron spin resonance measurements in illuminating polarized light, we have revealed the existence of electromagnon, i.e., magnon excitation by oscillatory electric fields of light, in the field-induced 1/5-plateau phase of the triangular lattice antiferromagnet CuFeO2. We indicate that peculiar magnon modes, which generate uniform fluctuation of the vector spin chirality at wave vector k =0, appear in the magnetic ordered phase with a collinear spin structure on triangular lattice. Our experimental results demonstrate that such magnon modes couple with an electric component of light, leading to the emergence of the electromagnon. Moreover, the measurements in circularly polarized light exhibit an anomalous behavior that circular dichroism, which is usually found in magnetic resonance, is absent in the resonance signal of the electromagnon. The microscopic mechanism of the electromagnon in CuFeO2 is also discussed.

Kimura, S.; Fujita, T.; Hagiwara, M.; Yamaguchi, H.; Kashiwagi, T.; Terada, N.; Sawada, Y.; Watanabe, K.

2014-08-01

183

Spin-dynamics study of the classical ferromagnetic XY chain in a random field

NASA Astrophysics Data System (ADS)

The classical one-dimensional XY model in a symmetry-breaking Gaussian-distributed random magnetic field was studied using an ultrafast, vectorized spin-dynamics program on a Cray Y-MP. We calculated the time- and space-displaced spin-spin correlation functions, which was then Fourier-transformed to get the neutron-scattering law S(q,?). We see a clear change of the different contributions when the random field is switched on. At low temperatures the random field induces significant increases in the soliton density.

Gerling, R. W.; Landau, D. P.

1993-02-01

184

Doping induced spin state transition in LaCoO3: dynamical mean-field study.

Hole and electron doped LaCoO3 is studied using dynamical mean-field theory. The one-particle spectra are analyzed and compared to the available experimental data, in particular the x-ray absorption spectra. Analyzing the temporal spin-spin correlation functions we find the atomic intermediate spin state is not important for the observed Curie-Weiss susceptibility. Contrary to the commonly held view about the roles played by the t2g and eg electrons we find narrow quasiparticle bands of t2g character crossing the Fermi level accompanied by strongly damped eg excitations. PMID:23848917

Augustinský, P; K?ápek, V; Kuneš, J

2013-06-28

185

Nonlinear magnetic vortex dynamics in a circular nanodot excited by spin-polarized current

NASA Astrophysics Data System (ADS)

We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed.

Guslienko, Konstantin Y.; Sukhostavets, Oksana V.; Berkov, Dmitry V.

2014-08-01

186

The dynamics of particle disks. II - Effects of spin degrees of freedom

NASA Technical Reports Server (NTRS)

The present treatment of the thermal equilibria of differentially-rotating, axisymmetric disks consisting of identical, spin-possessing as well as translational DOF-possessing hard sphere particles characterizes these disks' dynamics by means of two novel parameters: (1) the tangential restitution coefficient, and (2) the dimensionless moment of inertia. It is established that rings composed of spinning particles can generally be thermally balanced within more restricted ranges of the optical depth, as well as at higher values of the normal restitution coefficient, than spinless rings. Mean spin is indefinite in the present framework of neglected finite particle-size effects.

Araki, Suguru

1988-01-01

187

Neutron Scattering Study on spin dynamics in superconducting (TlRb)2Fe4Se5

Spin dynamics in superconducting (Tl,Rb)2Fe4Se5 was investigated using the inelastic neutron scattering technique. Spin wave branches that span an energy range from 6.5 to 209 meV are success- fully described by a Heisenberg model whose dominant interactions include only the in-plane nearest (J1 and J0 1) and next nearest neighbor (J2 and J0 2) exchange terms within and between the tetramer spin blocks, respectively. These exchange constants, experimentally determined in this work, would crucially constrain the diverse theoretical viewpoints on magnetism and superconductivity in the Fe-based materials.

Chi, Songxue [ORNL; Ye, Feng [ORNL; Bao, Wei [Renmin University of China; Fang, Dr. Minghu [Zhejiang University; Wang, H.D. [Zhejiang University; Dong, C.H. [Zhejiang University; Savici, Andrei T [ORNL; Granroth, Garrett E [ORNL; Stone, Matthew B [ORNL; Fishman, Randy Scott [ORNL

2013-01-01

188

Low temperature spin dynamics in Cr7Ni-Cu-Cr7Ni coupled molecular rings

NASA Astrophysics Data System (ADS)

Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50 mK) to determine the effect of coupling two Cr7Ni molecular rings via a Cu2+ ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5 K. At lower temperature, the 1H-NMR line broadens dramatically indicating spin freezing. From the plot of the line width vs. magnetization, it is found that the freezing temperature is higher (260 mK) in the coupled ring with respect to the single Cr7Ni ring (140 mK).

Bordonali, L.; Furukawa, Y.; Mariani, M.; Sabareesh, K. P. V.; Garlatti, E.; Carretta, S.; Lascialfari, A.; Timco, G.; Winpenny, R. E. P.; Borsa, F.

2014-05-01

189

Spin dynamics and domain formation of a spinor Bose-Einstein condensate in an optical cavity

We consider a ferromagnetic spin-1 Bose-Einstein condensate (BEC) dispersively coupled to a unidirectional ring cavity. We show that the ability of the cavity to modify, in a highly nonlinear fashion, matter-wave phase shifts adds an additional dimension to the study of spinor condensates. In addition to demonstrating strong matter-wave bistability as in our earlier publication [L. Zhou et al., Phys. Rev. Lett. 103, 160403 (2009)], we show that the interplay between atomic and cavity fields can greatly enrich both the physics of critical slowing down in spin-mixing dynamics and the physics of spin-domain formation in spinor condensates.

Zhou Lu; Zhang Keye; Zhang Weiping [State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, Shanghai 200062 (China); Pu Han [Department of Physics and Astronomy, and Rice Quantum Institute, Rice University, Houston, Texas 77251-1892 (United States); Ling, Hong Y. [Department of Physics and Astronomy, Rowan University, Glassboro, New Jersey 08028-1700 (United States)

2010-06-15

190

Large-amplitude spin dynamics driven by a THz pulse in resonance with an electromagnon.

Multiferroics have attracted strong interest for potential applications where electric fields control magnetic order. The ultimate speed of control via magnetoelectric coupling, however, remains largely unexplored. Here, we report an experiment in which we drove spin dynamics in multiferroic TbMnO3 with an intense few-cycle terahertz (THz) light pulse tuned to resonance with an electromagnon, an electric-dipole active spin excitation. We observed the resulting spin motion using time-resolved resonant soft x-ray diffraction. Our results show that it is possible to directly manipulate atomic-scale magnetic structures with the electric field of light on a sub-picosecond time scale. PMID:24603154

Kubacka, T; Johnson, J A; Hoffmann, M C; Vicario, C; de Jong, S; Beaud, P; Grübel, S; Huang, S-W; Huber, L; Patthey, L; Chuang, Y-D; Turner, J J; Dakovski, G L; Lee, W-S; Minitti, M P; Schlotter, W; Moore, R G; Hauri, C P; Koohpayeh, S M; Scagnoli, V; Ingold, G; Johnson, S L; Staub, U

2014-03-21

191

Direct observation of dynamics of single spinning dust grains in weakly magnetized complex plasma

The rotational dynamics of single dust grains in a weak magnetic field is investigated on a kinetic level. Experiments reveal spin-up of spherical dust grains and alignment of their magnetic moments parallel to the magnetic induction vector. The angular velocity of spinning prolate grains varies as magnetic induction increases to 250 G. Spinning dust grains are found to flip over only when the magnetic field magnitude is changing. The results demonstrate that dusty plasma has paramagnetic properties. Qualitative interpretations are proposed to explain newly discovered phenomena.

Dzlieva, E. S.; Karasev, V. Yu., E-mail: plasmadust@yandex.ru [St. Petersburg State University, Institute of Physics (Russian Federation); Petrov, O. F. [Russian Academy of Sciences, Institute for High Energy Densities, Joint Institute for High Temperatures (Russian Federation)

2012-01-15

192

We investigate cubic-in-spin effects for inspiralling compact objects binaries, both in the dynamics and the energy flux emitted in gravitational waves, at the leading post-Newtonian order. We use a Lagrangian formalism to implement finite-size effects, and extend it at cubic order in the spins, which corresponds to the octupolar order in a multipolar decomposition. This formalism allows us to derive the equation of motion, equations of precession for the spin, and stress-energy tensor of each body in covariant form, and admits a formal generalization to any multipolar order. For spin-induced multipoles, i.e. in the case where the rotation of the compact object is sole responsible for the additional multipole moments, we find a unique structure for the octupolar moment representing cubic-in-spin effects. We apply these results to compute the associated effects in the dynamics of compact binary systems, and deduce the corresponding terms in the energy loss rate due to gravitational waves. These effects enter at the third-and-a-half post-Newtonian order, and can be important for binaries involving rapidly spinning black holes. We provide simplified results for spin-aligned, circular orbits, and discuss the quantitative importance of the new contributions.

Sylvain Marsat

2014-11-15

193

Laser-induced ultrafast spin dynamics in ErFeO3

NASA Astrophysics Data System (ADS)

Using 100-fs optical laser pulses, we have been able to excite and probe spin dynamics in the rare-earth orthoferrite ErFeO3. The investigation was performed in a broad temperature range with the focus on the vicinities of the compensation point Tcomp?47K and the spin reorientation transition region in the interval 86K?T?99K. Spin precession excited by the laser pulse was present in a large part of the investigated temperature range, but was especially strong near the spin reorientation region. In this region the laser pulse also caused an ultrafast spin reorientation. By changing the laser pulse fluence, we could vary both the reorientation amplitude and the reorientation speed. We show that the laser-induced spin dynamics in ErFeO3 is caused in part by heating and in part by the inverse Faraday effect. Comparing to the results of similar experiments in other rare-earth orthoferrites, we found the speed of the laser-induced spin reorientation to be significantly lower. We attribute this finding to the weaker electron-phonon coupling of the Er3+ 4f electrons with the lattice.

de Jong, J. A.; Kimel, A. V.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.

2011-09-01

194

Dynamic response of a spin-1/2 Kondo singlet

NASA Astrophysics Data System (ADS)

We present a study of spin-1/2 Kondo singlets in single electron transistors under a microwave frequency bias excitation. We compare time-averaged conductance G to predicted universal response with respect to microwave frequency, oscillation amplitude, and the Kondo temperature and find a nonadiabatic response when the microwave photon energy hf is comparable to the Kondo temperature kBTK. We show that our measurements are qualitatively consistent with the predictions for the radiation-induced decoherence rate of the Kondo spin.

Hemingway, Bryan; Herbert, Stephen; Melloch, Michael; Kogan, Andrei

2014-09-01

195

Rabi oscillations, decoherence, and disentanglement in a qubit-spin-bath system: exact dynamics

We examine the influence of environmental interactions on simple quantum systems by obtaining the exact reduced dynamics of a qubit coupled to a one-dimensional spin bath. In contrast to previous studies, both the qubit-bath coupling and the nearest neighbor intrabath couplings are taken as the spin-flip XX-type. We first study the Rabi oscillations of a single qubit with the spin bath prepared in a spin coherent state, finding that nonresonance and finite intrabath interactions have significant effects on the qubit dynamics. Next, we discuss the bath-induced decoherence of the qubit when the bath is initially in the ground state, and show that the decoherence properties depend on the internal phases of the spin bath. By considering two independent copies of the qubit-bath system, we finally probe the disentanglement dynamics of two noninteracting entangled qubits. We find that entanglement sudden death appears when the spin bath is in its critical phase. We show that the single-qubit decoherence factor is an upper bound for the two-qubit concurrence.

Ning Wu; Arun Nanduri; Herschel Rabitz

2014-03-19

196

Coherent spinor dynamics in a spin-1 Bose condensate

ÂEinstein condensation typically focus on non-interacting (ideal) particles, elastic collisions are essential in order states, a condensate in the third spin state is coherently and reversibly created by atomic collisions temperature. A hallmark of BoseÂEinstein condensation is the coherence between particles--every particle

Loss, Daniel

197

Competing Orders in Strongly Correlated Systems

NASA Astrophysics Data System (ADS)

Systems with competing orders are of great interest in condensed matter physics. When two phases have comparable energies, novel interplay effects such can be induced by tuning an appropriate parameter. In this thesis, we study two problems of competing orders - (i) ultracold atom gases with competing superfluidity and Charge Density Wave (CDW) orders, and (ii) low dimensional antiferromagnets with Neel order competing against various disordered ground states. In the first part of the thesis, we study the attractive Hubbard model which could soon be realized in ultracold atom experiments. Close to half-filling, the superfluid ground state competes with a low-lying CDW phase. We study the collective excitations of the superfluid using the Generalized Random Phase Approximation (GRPA) and strong-coupling spin wave analysis. The competing CDW phase manifests as a roton-like excitation. We characterize the collective mode spectrum, setting benchmarks for experiments. We drive competition between orders by imposing superfluid flow. Superflow leads to various instabilities: in particular, we find a dynamical instability associated with CDW order. We also find a novel dynamical incommensurate instability analogous to exciton condensation in semiconductors. In the second part, inspired by experiments on Bi3Mn 4O12(NO3)(BMNO), we first study the interlayer dimer state in spin-S bilayer antiferromagnets. At a critical bilayer coupling strength, condensation of triplet excitations leads to Neel order. In describing this transition, bond operator mean field theory suffers from systematic deviations. We bridge these deviations by taking into account corrections arising from higher spin excitations. The interlayer dimer state shows a field induced Neel transition, as seen in BMNO. Our results are relevant to the quantitative modelling of spin-S dimerized systems. We then study the J1 - J2 model on the honeycomb lattice with frustrating next-nearest neighbour exchange. For J2 >J1/6, quantum and thermal fluctuations lead to lattice nematic states. For S=1/2, this lattice nematic takes the form of a valence bond solid. With J2

Ramachandran, Ganesh

198

Spin dynamics and tunneling of the Néel vector in the Fe10 magnetic wheel

NASA Astrophysics Data System (ADS)

The spin dynamics of a ring-shaped molecule comprising 10 iron(III) ions (s=5/2) is studied by inelastic neutron scattering. Exchange integrals and single-ion anisotropy parameters are determined by studying several intermultiplet excitations. Difficulties associated with the dimension of the Hilbert space are overcome by exploiting both the irreducible tensor operator technique and the Lanczos algorithm. By calculating the time correlation function of the Néel vector we show that the low-temperature spin dynamics of Fe10 is only approximately described by the semiclassical picture of tunneling of the Néel vector.

Santini, P.; Carretta, S.; Amoretti, G.; Guidi, T.; Caciuffo, R.; Caneschi, A.; Rovai, D.; Qiu, Y.; Copley, J. R. D.

2005-05-01

199

Spin-dynamics of the classical easy-plane Heisenberg chain

NASA Astrophysics Data System (ADS)

Dynamics of the ferromagnetic easy-plane Heisenberg chain has been simulated by a standard Monte Carlo algorithm and the accurate numerical integration of the equations of motion for the spin variables. The dynamic structure factors S( q, ?) have been calculated for a wide range of field and temperatures and interpreted in terms of spin-wave and soliton effects. A comparison with known neutron scattering experiments for CsNiF 3 is presented and deviations from the sine-Gordon theory are revealed.

Grille, H.; Kamieniarz, G.; Gerling, R. W.

1992-02-01

200

We propose an experiment to probe ferromagnetic phenomena in an ultracold Fermi gas, while alleviating the sensitivity to three-body loss and competing many-body instabilities. The system is initialized in a small pitch spin spiral, which becomes unstable in the presence of repulsive interactions. To linear order the exponentially growing collective modes exhibit critical slowing down close to the Stoner transition point. Also, to this order, the dynamics are identical on the paramagnetic and ferromagnetic sides of the transition. However, we show that scattering off the exponentially growing modes qualitatively alters the collective mode structure. The critical slowing down is eliminated and in its place a new unstable branch develops at large wave vectors. Furthermore, long-wavelength instabilities are quenched on the paramagnetic side of the transition. We study the experimental observation of the instabilities, specifically addressing the trapping geometry and how phase-contrast imaging will reveal the emerging domain structure. These probes of the dynamical phenomena could allow experiments to detect the transition point and distinguish between the paramagnetic and ferromagnetic regimes.

Conduit, G. J. [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 76100 (Israel); Physics Department, Ben Gurion University, Beer Sheva, 84105 (Israel); Altman, E. [Department of Condensed Matter Physics, Weizmann Institute of Science, Rehovot, 76100 (Israel)

2010-10-15

201

Spin dynamics in the frozen state of the dipolar spin ice material Dy2Ti2O7

NASA Astrophysics Data System (ADS)

Low-temperature magnetic ac susceptibility measurements of single-crystal dipolar spin ice Dy2Ti2O7 are presented. The relaxation is found to exhibit thermally activated Arrhenius behavior with an activation energy of 9.79 K (˜9Jeff), which is not consistent with a simple scaling of 6Jeff, as previously found for Ho2Ti2O7. There are distinct quantifiable differences between Dy2Ti2O7 and Ho2Ti2O7 absorption spectra. The measured dynamics does not agree with simulations based on current magnetic monopole theory nor thermal relaxation measurements, but instead freezes out at a faster rate.

Yaraskavitch, L. R.; Revell, H. M.; Meng, S.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Kycia, J. B.

2012-01-01

202

Dynamical phase transitions in 3-dimensional spin glasses

We study the time evolution of the distance between two configurations submitted to the same thermal noise for the 3d k J Ising spin glass. We observe three temperature regimes: a high-temperature regime where the distances vanishes in the long-time limit. An intermediate-temperature regime where the distance has a nomm limit independent of the initial distance. A low-temperature regime where

B. Derrida; G. Weisbuch

1987-01-01

203

Direct observation of coherent interorbital spin-exchange dynamics.

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold ^{173}Yb fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of ^{173}Yb atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism. PMID:25279608

Cappellini, G; Mancini, M; Pagano, G; Lombardi, P; Livi, L; Siciliani de Cumis, M; Cancio, P; Pizzocaro, M; Calonico, D; Levi, F; Sias, C; Catani, J; Inguscio, M; Fallani, L

2014-09-19

204

Attitude dynamic of spin-stabilized satellites with flexible appendages

NASA Technical Reports Server (NTRS)

Equations of motion and computer programs have been developed for analyzing the motion of a spin-stabilized spacecraft having long, flexible appendages. Stability charts were derived, or can be redrawn with the desired accuracy for any particular set of design parameters. Simulation graphs of variables of interest are readily obtainable on line using program FLEXAT. Finally, applications to actual satellites, such as UK-4 and IMP-1 have been considered.

Renard, M. L.

1973-01-01

205

Direct Observation of Coherent Interorbital Spin-Exchange Dynamics

NASA Astrophysics Data System (ADS)

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold Yb173 fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of Yb173 atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism.

Cappellini, G.; Mancini, M.; Pagano, G.; Lombardi, P.; Livi, L.; Siciliani de Cumis, M.; Cancio, P.; Pizzocaro, M.; Calonico, D.; Levi, F.; Sias, C.; Catani, J.; Inguscio, M.; Fallani, L.

2014-09-01

206

Spin-Lattice Dynamics Simulation of Magnon-Phonon-Electron Heat Transfer on the Million Atom Scale

Spin-Lattice Dynamics Simulation of Magnon-Phonon-Electron Heat Transfer on the Million Atom Scale Engineering, The Hong Kong Polytechnic University, Hong Kong SAR, China (Dated: 31 August 2011) We develop an atomistic spin-lattice-dynamics model for simulating energy relaxation in magnetic materials. The model

207

Feature Ba sed Modelling uses attribute value machine learning techniques to model an agent's competency. This is achieved by creating a model describing the relationships between the features of the agent's actions and of the contexts in which those actions are performed. This paper describes techniques that have been developed for creating these models and for extracting key information therefrom.

Geoffrey I. Webb; Mark Kuzmycz

1995-01-01

208

Feature Based Modelling uses attribute value machine learning techniques to model an agent's competency. This is achieved by creating a model describing the relationships between the features of the agent's actions and of the contexts in which those actions are performed. This paper describes techniques that have been developed for creating these models and for extracting key information therefrom. An

Geoffrey I. Webb; Mark Kuzmycz

1995-01-01

209

The resource-based perspective has done much to identify idiosyncratic firm attributes that may be a principal source of competitive advantages. Unfortunately, there has been little systematic industry evidence to support the strategic importance of core competence, nor has there been much work on the temporal or cumulative nature of core capabilities within an industrial setting. Further, little or no research

Steven T. Walsh; Robert L. Boylan; Chris McDermott; Al Paulson

2005-01-01

210

Testing dynamic relations between perceived competence and fear of failure in young athletes

Conceptually, achievement motives are stable phenomena; however, recent evidence suggests that fear of failure (FF) levels decrease slightly as participants gain experience with an activity. One plausible explanation for this decrease in FF is that practice (and consequential reinforcement and approval from coaches) leads to increased perceptions of competence and concomitant reductions in the perceived likelihood and aversiveness of failing.

David E. Conroy; J Douglas Coatsworth; Angela M. Fifer

2005-01-01

211

ERIC Educational Resources Information Center

Cultural sensitivity and cultural competence in the selection of culturally sensitive treatments is a requisite for effective counseling practice in working with diverse clients and their families, particularly when clients present with health issues or medical problems. Described here is a strategy for selecting culturally sensitive treatments…

Sperry, Len

2010-01-01

212

Chaotic dynamics of stellar spin in binaries and the production of misaligned hot Jupiters

NASA Astrophysics Data System (ADS)

Many exoplanetary systems containing hot Jupiters are observed to have highly misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov oscillations of orbital eccentricity and inclination induced by a binary companion, in conjunction with tidal dissipation, constitute a major channel for the production of hot Jupiters. We demonstrate that gravitational interaction between the planet and its oblate host star can lead to chaotic evolution of the stellar spin axis during Kozai cycles. As parameters such as the planet mass and stellar rotation period are varied, periodic islands can appear in an ocean of chaos, in a manner reminiscent of other dynamical systems. In the presence of tidal dissipation, the complex spin evolution can leave an imprint on the final spin-orbit misalignment angles.

Storch, Natalia I.; Anderson, Kassandra R.; Lai, Dong

2014-09-01

213

Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters

Many exoplanetary systems containing hot Jupiters are observed to have highly misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov oscillations of orbital eccentricity/inclination induced by a binary companion, in conjunction with tidal dissipation, is a major channel for the production of hot Jupiters. We demonstrate that gravitational interaction between the planet and its oblate host star can lead to chaotic evolution of the stellar spin axis during Kozai cycles. As parameters such as the planet mass and stellar rotation period vary, periodic islands can appear in an ocean of chaos, in a manner reminiscent of other dynamical systems. In the presence of tidal dissipation, the complex spin evolution can leave an imprint on the final spin-orbit misalignment angles.

Storch, Natalia I; Lai, Dong

2014-01-01

214

We derive Keplerian-type parametrization for the solution of post-Newtonian (PN) accurate conservative dynamics of spinning compact binaries moving in eccentric orbits. The PN accurate dynamics that we consider consists of the third post-Newtonian accurate conservative orbital dynamics influenced by the leading order spin effects, namely the leading order spin-orbit interactions. The orbital elements of the representation are explicitly given in terms of the conserved orbital energy, angular momentum and a quantity that characterizes the leading order spin-orbit interactions in Arnowitt, Deser, and Misner-type coordinates. Our parametric solution is applicable in the following two distinct cases: (i) the binary consists of equal mass compact objects, having two arbitrary spins, and (ii) the binary consists of compact objects of arbitrary mass, where only one of them is spinning with an arbitrary spin. As an application of our parametrization, we present gravitational wave polarizations, whose amplitudes are restricted to the leading quadrupolar order, suitable to describe gravitational radiation from spinning compact binaries moving in eccentric orbits. The present parametrization will be required to construct `ready to use' reference templates for gravitational waves from spinning compact binaries in inspiralling eccentric orbits. Our parametric solution for the post-Newtonian accurate conservative dynamics of spinning compact binaries clearly indicates, for the cases considered, the absence of chaos in these systems. Finally, we note that our parametrization provides the first step in deriving a fully second post-Newtonian accurate `timing formula', that may be useful for the radio observations of relativistic binary pulsars like J0737-3039.

Christian Koenigsdoerffer; Achamveedu Gopakumar

2005-01-05

215

Dynamical symmetries and crossovers in a three-spin system with collective dissipation

We consider the non-equilibrium dynamics of a simple system consisting of interacting spin-$1/2$ particles subjected to a collective damping. The model is close to situations that can be engineered in hybrid electro/opto-mechanical settings. Making use of large-deviation theory, we find a Gallavotti-Cohen symmetry in the dynamics of the system as well as evidence for the coexistence of two dynamical phases with different activity levels. We show that additional damping processes smoothen out this behavior. Our analytical results are backed up by Monte Carlo simulations that reveal the nature of the trajectories contributing to the different dynamical phases.

Simon Pigeon; André Xuereb; Igor Lesanovsky; Juan P. Garrahan; Gabriele De Chiara; Mauro Paternostro

2014-09-01

216

NASA Astrophysics Data System (ADS)

A theoretical method recently developed is used to find all possible equilibrium magnetic states of a finite-size classical one-dimensional planar spin chain with competing nearest-neighbor (nn) and next-nearest-neighbor (nnn) exchange interactions. The energy of a classical planar model with N spins is a function of N absolute orientational angles or equivalently, due to the absence of in-plane anisotropy, of (N -1 ) relative orientational angles. The lowest energy stable state (ground state) corresponds to a global minimum of the energy in the (N -1 ) -dimensional space, while metastable states correspond to local minima. For a given value of the ratio, ? , between nnn and nn exchange couplings, all the equilibrium configurations of the model were calculated with great accuracy for N ?16 , and a stability analysis was subsequently performed. For any value of N , the ground state was found to be "symmetric" with respect to the middle of the chain in the relative angles representation. For the chosen value of ? , the ground state consists of a helix whose chirality is constant in sign along the chain (i.e., all the spins turn clockwise, or all anticlockwise), but whose pitch varies owing to finite-size effects; e.g., for positive chirality we found that the chiral order parameter ? (N )>0 increases monotonically with increasing N , approaching the value (? =1 ) pertinent to the ground state in the limit N ?? . For finite but not too small values of N , we found metastable states characterized by one reversal of chirality, either localized just in the middle of the chain ["antisymmetric" state, with chiral order parameter ? (N )=0 ], or shifted away from the middle of the chain, to the right or to the left [pairs of "ugly" states, with equal and opposite values of ? (N )?0 ; the attribute "ugly" refers to the absence of a definite symmetry in the relative angles representation]. Concerning the stability of these states with one reversal of chirality, two main results were found. First, the "antisymmetric" state is metastable for even N and unstable for odd N . Second, an additional pair of "ugly" states is found whenever the number of spins in the chain is increased by 1; the states in each additional pair are unstable for even N and metastable for odd N . Analysis of stable and metastable configurations in the framework of a discrete nonlinear mapping approach provides further support for the above results.

Popov, Alexander P.; Rettori, Angelo; Pini, Maria Gloria

2014-10-01

217

NASA Astrophysics Data System (ADS)

The spin-resolved nonequilibrium real-time electron transport through a double-quantum-dot (DQD) Aharonov-Bohm (AB) interferometer with spin-orbit interaction (SOI) is explored. The SOI and AB interference in the real-time dynamics of spin transport is expressed by effective magnetic fluxes. Analytical formulas for the time-dependent currents, for initially unpolarized spins, are presented. In many cases, there appear spin currents in the electrodes, for which the spins in each electrode are polarized along characteristic directions, predetermined by the SOI parameters and by the geometry of the system. Special choices of the system parameters yield steady-state currents in which the spins are fully polarized along these characteristic directions. The time required to reach this steady state depends on the couplings of the DQD to the leads. The magnitudes of the currents depend strongly on the SOI-induced effective fluxes. Without the magnetic flux, the spin-polarized current cannot be sustained to the steady states, due to the phase rigidity for this system. For a nondegenerate DQD, transient spin transport can be produced by the sole effects of SOI. We also show that one can extract the spin-resolved currents from measurements of the total charge current.

Tu, Matisse Wei-Yuan; Aharony, Amnon; Zhang, Wei-Min; Entin-Wohlman, Ora

2014-10-01

218

SU(2s+1) symmetry and nonlinear dynamic equations of spin s magnets

The article is devoted to the description of dynamics of magnets with arbitrary spin on the basis of the Hamiltonian formalism. The relationship between the magnetic ordering and Poisson bracket subalgebras of the magnetic degrees of freedom for spin s=1/2; 1; 3/2 has been established. We have been obtained non-linear dynamic equations without damping for normal and degenerate non-equilibrium states of high-spin magnets with the properties of the SO(3), SU(4), SU(2)$\\times$SU(2), SU(3), SO(4), SO(5) symmetry of exchange interaction. The connection between models of the magnetic exchange energy and the Casimir invariants has been discussed.

M. Y. Kovalevsky; A. V. Glushchenko

2013-12-20

219

Dynamic Dipole and Quadrupole Phase Transitions in the Kinetic Spin3\\/2 Model

The dynamic phase transition has been studied, within a mean-field approach, in the kinetic spin-3\\/2 Ising model Hamiltonian\\u000a with arbitrary bilinear and biquadratic pair interactions in the presence of a time dependent oscillating magnetic field by\\u000a using the Glauber-type stochastic dynamics. The nature (first- or second-order) of the transition is characterized by investigating\\u000a the behavior of the thermal variation of

Mustafa Keskin; Osman Canko; Muharrem Kirak

2007-01-01

220

Spin-dependent scattering and absorption of thermal neutrons on dynamically polarized nuclei

field where the sum is over the different nuclei, of number density Ni. The pseudo-magnetic moments y* are related to the scattering lengths by where gn = - 1.913 is the neutron magnetic moment in units of nuclear957 Spin-dependent scattering and absorption of thermal neutrons on dynamically polarized nuclei H

Paris-Sud XI, UniversitÃ© de

221

Lattice-site-specific spin dynamics in double perovskite Sr2CoOsO6.

Magnetic properties and spin dynamics have been studied for the structurally ordered double perovskite Sr2CoOsO6. Neutron diffraction, muon-spin relaxation, and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature TN1=108??K, cobalt (3d7, S=3/2) and osmium (5d2, S=1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase below TN2=67??K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at T?5??K. Ab initio calculations indicate that the effective exchange coupling between cobalt and osmium sites is rather weak, so that cobalt and osmium sublattices exhibit different ground states and spin dynamics, making Sr2CoOsO6 distinct from previously reported double-perovskite compounds. PMID:24766007

Yan, Binghai; Paul, Avijit Kumar; Kanungo, Sudipta; Reehuis, Manfred; Hoser, Andreas; Többens, Daniel M; Schnelle, Walter; Williams, Robert C; Lancaster, Tom; Xiao, Fan; Möller, Johannes S; Blundell, Stephen J; Hayes, William; Felser, Claudia; Jansen, Martin

2014-04-11

222

Effects of ruthenium seed layer on the microstructure and spin dynamics of thin permalloy films

The spin dynamics and microstructure properties of a sputtered 12 nm Ni{sub 81}Fe{sub 19} thin film have been enhanced by the use of a ruthenium seed layer. Both the ferromagnetic resonance field and linewidth are enhanced dramatically as the thickness of ruthenium seed layer is increased. The surface anisotropy energy constant can also be largely tailored from 0.06 to 0.96 erg/cm{sup -2} by changing the seed layer thickness. The changes to the dynamics magnetization properties are caused by both ruthenium seed layer induced changes in the Ni{sub 81}Fe{sub 19} structure properties and surface topography properties. Roughness induced inhomogeneous linewidth broadening is also seen. The damping constant is highly tunable via the ruthenium thickness. This approach can be used to tailor both the structure and spin dynamic properties of thin Ni{sub 81}Fe{sub 19} films over a wide range. And it may benefit the applications of spin dynamics and spin current based devices.

Jin Lichuan; Zhang Huaiwu; Tang Xiaoli; Bai Feiming; Zhong Zhiyong [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China)

2013-02-07

223

Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

In this work, I have investigated the high frequency magnetic properties of a variety of novel materials by using the microwave techniques. The work consists of two parts: (1) spin dynamics study in magnetic multilayer thin films, (2) fabrication and characterization of novel magnetic materials. In the first part, we have observed nonlinear behaviors of the normal Gilbert damping G0

Rong Cao

2009-01-01

224

Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments V. V. Dobrovitski,1

Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments V. V. Dobrovitski,1 A. E, California 93106, USA (Received 1 April 2009; published 9 June 2009) We study the Rabi oscillations decay and rate of Rabi oscillations decay can be used to experimentally determine the intrabath coupling strength

225

-spin systems is consid- ered. The study is based on a calculation of the differential inelastic reflection to experimental studies. In this paper we examine the possibility of extending the applicability of He* atom atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron

Kais, Sabre

226

Compact binary systems with spinning components are considered. Finite size effects due to rotational deformation are taken into account. The dynamical evolution and next to leading order gravitational wave forms are calculated, taking into account the orbital motion up to the first post-Newtonian approximation.

Dörte Hansen

2007-10-01

227

Dynamics of Artificial Kagome `Spin Ice' In Geometrically Frustrated Permalloy Nano Structures

Thin films of ferro-magnetic material with lithographically designed geometries can be used as an analog for the study of spin ice or frustrated systems. Here we study the magnetic structure and magnetization dynamics of permalloy thin films in a frustrated, hexagonal geometry using Transmission Lorentz Microscopy. The permalloy films are evaporated through patterns defined by conventional electron beam lithography to

Yi Qi; Todd Brintlinger; John Cumings

2007-01-01

228

Lattice-Site-Specific Spin Dynamics in Double Perovskite Sr2CoOsO6

NASA Astrophysics Data System (ADS)

Magnetic properties and spin dynamics have been studied for the structurally ordered double perovskite Sr2CoOsO6. Neutron diffraction, muon-spin relaxation, and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature TN1=108 K, cobalt (3d7, S =3/2) and osmium (5d2, S =1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase below TN2=67 K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at T ?5 K. Ab initio calculations indicate that the effective exchange coupling between cobalt and osmium sites is rather weak, so that cobalt and osmium sublattices exhibit different ground states and spin dynamics, making Sr2CoOsO6 distinct from previously reported double-perovskite compounds.

Yan, Binghai; Paul, Avijit Kumar; Kanungo, Sudipta; Reehuis, Manfred; Hoser, Andreas; Többens, Daniel M.; Schnelle, Walter; Williams, Robert C.; Lancaster, Tom; Xiao, Fan; Möller, Johannes S.; Blundell, Stephen J.; Hayes, William; Felser, Claudia; Jansen, Martin

2014-04-01

229

Polarization dynamics in spin-polarized vertical-cavity surface-emitting lasers

NASA Astrophysics Data System (ADS)

Spin-polarized lasers and especially spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) are at- tractive novel spintronic devices providing functionalities and characteristics superior to their conventional purely charge-based counterparts. This applies in particular to ultrafast dynamics, modulation capability and chirp control of directly modulated lasers. Here we demonstrate that ultrafast oscillations of the circular polarization degree can be generated in VCSELs by pulsed spin injection which have the potential to reach frequencies beyond 100 GHz. These oscillations are due to the coupling of the carrier-spin-photon system via the optical birefringence for the linearly polarized laser modes in the micro-cavity and are principally decoupled from conventional relaxation oscillations of the carrier-photon system. Utilizing these polarization oscillations is a very promising path to ultrafast directly modulated spin-VCSELs in the near future as long as an effective concept can be developed to modulate or switch these polarization oscillations. After briefly reviewing the state of research in the emerging field of spin-VCSELs, we present a novel concept for controlled switching of polarization oscillations by use of multiple optical spin injection pulses. Depending on the amplitude and phase conditions of the excitation pulses, constructive or destructive interference of polarization oscillations leads to an excitation, stabilization or switch-off of these oscillations. Furthermore even short single polarization bursts can be generated with pulse widths only limited by the resonance frequency of the polarization oscillation. Consequently, this concept is an important building block for using spin controlled polarization oscillations for future communication applications.

Gerhardt, Nils C.; Höpfner, Henning; Lindemann, Markus; Hofmann, Martin R.

2014-08-01

230

NASA Astrophysics Data System (ADS)

Ultrasound velocity measurements of the magnesium chromite spinel MgCr2O4 reveal elastic anomalies in the paramagnetic phase that are characterized as due to geometrical frustration. The temperature dependence of the tetragonal shear modulus (C11-C12)/2 exhibits huge Curie-type softening, which should be the precursor to spin Jahn-Teller distortion in the antiferromagnetic phase. The trigonal shear modulus C44 exhibits nonmonotonic temperature dependence with a characteristic minimum at ˜50 K, indicating a coupling of the lattice to a dynamical molecular-spin state. These results strongly suggest the coexistence of the dynamical spin Jahn-Teller effect and a dynamical molecular-spin state in the paramagnetic phase, which is compatible with the coexistence of magnetostructural order and a dynamical molecular-spin state in the antiferromagnetic phase.

Watanabe, Tadataka; Ishikawa, Shin-Ichi; Suzuki, Haruki; Kousaka, Yusuke; Tomiyasu, Keisuke

2012-10-01

231

Dynamics of polymer film formation during spin coating

NASA Astrophysics Data System (ADS)

Standard models explaining the spin coating of polymer solutions generally fail to describe the early stages of film formation, when hydrodynamic forces control the solution behavior. Using in situ light scattering alongside theoretical and semi-empirical models, it is shown that inertial forces (which initially cause a vertical gradient in the radial solvent velocity within the film) play a significant role in the rate of thinning of the solution. The development of thickness as a function of time of a solute-free liquid (toluene) and a blend of polystyrene and poly(methyl methacrylate) cast from toluene were fitted to different models as a function of toluene partial pressure. In the case of the formation of the polymer blend film, a concentration-dependent (Huggins) viscosity formula was used to account for changes in viscosity during spin coating. A semi-empirical model is introduced, which permits calculation of the solvent evaporation rate and the temporal evolution of the solute volume fraction and solution viscosity.

Mouhamad, Y.; Mokarian-Tabari, P.; Clarke, N.; Jones, R. A. L.; Geoghegan, M.

2014-09-01

232

Advances and applications of dynamic-angle spinning nuclear magnetic resonance

This dissertation describes nuclear magnetic resonance experiments and theory which have been developed to study quadrupolar nuclei (those nuclei with spin greater than one-half) in the solid state. Primarily, the technique of dynamic-angle spinning (DAS) is extensively reviewed and expanded upon in this thesis. Specifically, the improvement in both the resolution (two-dimensional pure-absorptive phase methods and DAS angle choice) and sensitivity (pulse-sequence development), along with effective spinning speed enhancement (again through choice of DAS conditions or alternative multiple pulse schemes) of dynamic-angle spinning experiment was realized with both theory and experimental examples. The application of DAS to new types of nuclei (specifically the {sup 87}Rb and {sup 85}Rb nuclear spins) and materials (specifically amorphous solids) has also greatly expanded the possibilities of the use of DAS to study a larger range of materials. This dissertation is meant to demonstrate both recent advances and applications of the DAS technique, and by no means represents a comprehensive study of any particular chemical problem.

Baltisberger, J.H.

1993-06-01

233

Chaos-driven dynamics in spin-orbit coupled atomic gases

The dynamics, appearing after a quantum quench, of a trapped, spin-orbit coupled, dilute atomic gas is studied. The characteristics of the evolution is greatly influenced by the symmetries of the system, and we especially compare evolution for an isotropic Rashba coupling and for an anisotropic spin-orbit coupling. As we make the spin-orbit coupling anisotropic, we break the rotational symmetry and the underlying classical model becomes chaotic; the quantum dynamics is affected accordingly. Within experimentally relevant time-scales and parameters, the system thermalizes in a quantum sense. The corresponding equilibration time is found to agree with the Ehrenfest time, i.e. we numerically verify a ~log(1/h) scaling. Upon thermalization, we find the equilibrated distributions show examples of quantum scars distinguished by accumulation of atomic density for certain energies. At shorter time-scales we discuss non-adiabatic effects deriving from the spin-orbit coupled induced Dirac point. In the vicinity of the Dirac point, spin fluctuations are large and, even at short times, a semi-classical analysis fails.

Jonas Larson; Brandon Anderson; Alexander Altland

2012-08-14

234

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal. PMID:24496221

Mendil, J.; Nieves, P.; Chubykalo-Fesenko, O.; Walowski, J.; Santos, T.; Pisana, S.; Munzenberg, M.

2014-01-01

235

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

NASA Astrophysics Data System (ADS)

Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal.

Mendil, J.; Nieves, P.; Chubykalo-Fesenko, O.; Walowski, J.; Santos, T.; Pisana, S.; Münzenberg, M.

2014-02-01

236

Nonequilibrium structure factor for conserved spin dynamics: Abrupt temperature increase

NASA Astrophysics Data System (ADS)

We consider the nonequilibrium, elastic-scattering structure factor S(q,t) (q denotes the wave vector, t the time), for the Kawasaki spin-conserving kinetic Ising model of a one-dimensional system with nearest-neighbor interactions, initially in equilibrium at temperature TI, that is suddenly placed in contact with a heat bath at temperature TF, with TF>>TI. We present detailed results for the case of TF=?, for which we have succeeded in calculating the exact form of S(q,t). For finite TF, we present an approximation scheme for the higher-order nonequilibrium correlation functions that leads to closure of the hierarchy of equations of motion. The merits of this approximation are that (i) S(q,t) is guaranteed to satisfy an exact sum rule over the Brillouin zone (BZ) of wave vectors q, and (ii) S(q,t) evolves to the correct value in the long-time limit. For antiferromagnetic coupling, the structure factor, initially dominated by the Bragg peak associated with TI at the edge of the BZ, decays exponentially with time, e-t/?q while approximately preserving its shape in q space, since the lifetime ?q is nearly independent of q. Except near the center of the BZ, after the Bragg peak has decayed sufficiently, the dependence of S(q,t) on q can be characterized as though the spins rapidly quasiequilibrate to the equilibrium structure factor associated with TF, ?(q,TF), in that S(q,t)/?(q,TF) is independent of q, but is time dependent, slowly approaching unity as t-1/2 for large t. For q~=0 the initial form of S remains in effect until the value of t is of order q-2. For ferromagnetic coupling, the initial Bragg peak for q~=0 does not preserve its shape while decaying exponentially, since the lifetime ?q strongly depends on the wave-vector q, diverging as q-2 for q-->0, and, in particular, it is as though the spins for q~=0 remain ``frozen'' at TI. Analogous to the behavior for antiferromagnetic interactions, away from the center of the BZ, we find that S(q,t)/?(q,TF) is independent of q and is a function of t/tw, very slowly approaching unity. The characteristic ``waiting time'' tw is anomalously long, proportional to ?2, where ? is the equilibrium correlation length at temperature TI. This behavior of tw can be related to the random walk of domain boundaries.

Luscombe, James H.; Luban, Marshall

1996-09-01

237

"Light-Cone" Dynamics After Quantum Quenches in Spin Chains

NASA Astrophysics Data System (ADS)

Signal propagation in the nonequilibrium evolution after quantum quenches has recently attracted much experimental and theoretical interest. A key question arising in this context is what principles, and which of the properties of the quench, determine the characteristic propagation velocity. Here we investigate such issues for a class of quench protocols in one of the central paradigms of interacting many-particle quantum systems, the spin-1 /2 Heisenberg X X Z chain. We consider quenches from a variety of initial thermal density matrices to the same final Hamiltonian using matrix product state methods. The spreading velocities are observed to vary substantially with the initial density matrix. However, we achieve a striking data collapse when the spreading velocity is considered to be a function of the excess energy. Using the fact that the X X Z chain is integrable, we present an explanation of the observed velocities in terms of "excitations" in an appropriately defined generalized Gibbs ensemble.

Bonnes, Lars; Essler, Fabian H. L.; Läuchli, Andreas M.

2014-10-01

238

Stochastic Differential Equations for Quantum Dynamics of Spin-Boson Networks

The quantum dynamics of open many-body systems poses a challenge for computational approaches. Here we develop a stochastic scheme based on the positive P phase-space representation to study the nonequilibrium dynamics of coupled spin-boson networks that are driven and dissipative. Such problems are at the forefront of experimental research in cavity and solid state realizations of quantum optics, as well as cold atom physics, trapped ions and superconducting circuits. We demonstrate and test our method on a driven, dissipative two-site system, each site involving a spin coupled to a photonic mode, with photons hopping between the sites, where we find good agreement with Monte Carlo Wavefunction simulations. In addition to numerically reproducing features recently observed in an experiment [Phys. Rev. X 4, 031043 (2014)], we also predict a novel steady state quantum dynamical phase transition for an asymmetric configuration of drive and dissipation.

Stephan Mandt; Darius Sadri; Andrew A. Houck; Hakan E. Türeci

2014-10-12

239

Dynamical transition in the D=3 Edwards-Anderson spin glass in an external magnetic field.

We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses. PMID:24730822

Baity-Jesi, M; Baños, R A; Cruz, A; Fernandez, L A; Gil-Narvion, J M; Gordillo-Guerrero, A; Iñiguez, D; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Muñoz Sudupe, A; Navarro, D; Parisi, G; Perez-Gaviro, S; Pivanti, M; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J; Schifano, S F; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D

2014-03-01

240

Spin dynamics of the LAGEOS satellite in support of a measurement of the Earth's gravitomagnetism

NASA Astrophysics Data System (ADS)

LAGEOS is an accurately tracked, dense spherical satellite covered with 426 retroreflectors. Ciufolini has suggested the launch of an additional satellite (LAGEOS-3) into an orbit supplementary to that of the 1976-launched LAGEOS-1. In addition to providing a more accurate real-time measurement of the Earth's length of day and polar wobble, this paired-satellite experiment would provide the first direct measurement of the general relativistic frame-dragging effect. Of the five dominant error sources in this experiment, the largest one involves surface forces on the satellite, and their consequent impact on the orbital nodal precession. The surface forces are a function of the spin dynamics of the satellite. Consequently, we undertake here a theoretical effort to model the spin dynamics of LAGEOS. In this paper we derive, and solve numerically, a set of Euler equations that evolve the angular momentum vector for a slightly oblate spheroid of brass orbiting an Earth-like mass, idealized as being a perfect sphere and having a perfect polar-oriented dipole magnetic field. We have identified three phases of the rotational dynamics-a fast spin phase, a spin-orbit resonance phase, and an asymptotic (tidally locked) phase. From our numerical runs we give analytic expressions for this tidally locked phase.

Habib, Salman; Holz, Daniel E.; Kheyfets, Arkady; Matzner, Richard A.; Miller, Warner A.; Tolman, Brian W.

1994-11-01

241

Transport through single-level systems: Spin dynamics in the nonadiabatic regime

NASA Astrophysics Data System (ADS)

We investigate the Fano-Anderson model coupled to a large ensemble of spins under the influence of an external magnetic field. The interaction between the two spin systems is treated within a mean-field approach, and we assume an anisotropic coupling between these two systems. By using a nonadiabatic approach, we make no further approximations in the theoretical description of our system, apart from the semiclassical treatment. Therewith, we can include the short-time dynamics as well as the broadening of the energy levels arising due to the coupling to the external electronic reservoirs. We study the spin dynamics in the regime of low and high bias. For the infinite bias case, we compare our results to those obtained from a simpler rate equation approach, where higher-order transitions are neglected. We show that these higher-order terms are important in the range of low magnetic field. Additionally, we analyze extensively the finite bias regime with methods from nonlinear dynamics, and we discuss the possibility of switching of the large spin.

Metelmann, A.; Brandes, T.

2012-12-01

242

Approach to solving spin-boson dynamics via non-Markovian quantum trajectories

NASA Astrophysics Data System (ADS)

We develop a systematic and efficient approach for numerically solving the non-Markovian quantum state diffusion equation for an open quantum system that can be strongly coupled to an environment. As an important application, we consider a real-time simulation of a spin-boson model in a strong-coupling regime that is difficult to deal with using conventional methods. We show that the non-Markovian stochastic Schrödinger equation can be efficiently implemented as a real-time simulation for this model, so as to give an accurate description of spin-boson dynamics beyond the rotating-wave approximation.

Li, Zeng-Zhao; Yip, Cho-Tung; Deng, Hai-Yao; Chen, Mi; Yu, Ting; You, J. Q.; Lam, Chi-Hang

2014-08-01

243

Prethermalization and dynamical transition in an isolated trapped ion spin chain

We propose an experimental scheme to observe prethermalization and dynamical transition in one-dimensional XY spin chain with long range interaction and inhomogeneous lattice spacing, which can be readily implemented with the recently developed trapped-ion quantum simulator. Local physical observables are found to relax to prethermal values at intermediate time scale, followed by complete relaxation to thermal values at much longer time. The physical origin of prethermalization is explained by spotting a non-trivial structure in lower half of the energy spectrum. The dynamical behavior of the system is shown to cross difference phases when the interaction range is continuously tuned, indicating the existence of dynamical phase transition.

Zhe-Xuan Gong; L. -M. Duan

2013-05-05

244

Role of environmental correlations in the non-Markovian dynamics of a spin system

NASA Astrophysics Data System (ADS)

We study the dynamics of a chain of interacting quantum particles affected by an individual or collective environment(s), focusing on the role played by the environmental quantum correlations over the evolution of the chain. The presence of entanglement in the state of the environment magnifies the non-Markovian nature of the chain’s dynamics, giving rise to structures in figures of merit such as spin entanglement and purity that are not observed under a separable environmental state. Our analysis can be relevant to problems tackling the open-system dynamics of biological complexes of strong current interest.

Lorenzo, Salvatore; Plastina, Francesco; Paternostro, Mauro

2011-09-01

245

Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

NASA Astrophysics Data System (ADS)

In this work, I have investigated the high frequency magnetic properties of a variety of novel materials by using the microwave techniques. The work consists of two parts: (1) spin dynamics study in magnetic multilayer thin films, (2) fabrication and characterization of novel magnetic materials. In the first part, we have observed nonlinear behaviors of the normal Gilbert damping G0 and the effective spin-mixing conductance g?? in Pt/NiFe/Pt thin films when the incident microwave power is above a critical ac field hrf of 1.6 Oe. Both G0 and g?? are affected by the coupling between spin coherent precession and spin wave modes. Our work is the first experimental demonstration of nonlinear behavior of the effective spin-mixing conductance g?? . It suggests the nonlinear spin wave modes excited at high incident microwave power is detrimental to the spin pumping effect and should be avoided in future spin battery design. We have also studied the magnetization dynamic in IrMn/FeCo/Cu/NiFe/Cu spin valve through the Gilbert damping. Our results show that the Gilbert damping constant of NiFe is enhanced in antiparallel configuration when the magnetizations of both FM layers are precessing. This enhancement is induced by the dynamic exchange between the magnetizations of NiFe and FeCo layers. We have observed the dc voltage generation across the tunneling barrier while the spin precession is excited in the ferromagnetic free layer by the microwave field. The magnitude of the dc voltage peak is around few muVs with AlOx tunneling barrier. Our results directly indicate that spin current can be pumped through the tunneling barrier thus generates the dc voltage across the barrier. The results raise an important question about the role of the F/I barrier interface in spin pumping mechanism. More detailed experiment and theory studies are certainly needed, especially in MgO barrier based MTJ that could become a good candidate for realizing spin battery device. In the second part, we have experimentally observed, in addition to conventional PBG from Bragger scattering, two groups of magnetically tunable PBGs in 2D magnetic photonic crystals due to magnetic surface plasmon and spin-wave resonance bands, respectively. The former is particularly interesting because of its analogy to surface plasmon in metals. Simulations on transmission coefficients are in a good agreement with experimental results. Our results thus provide a first demonstation of the concept of the magnetic SP bands and illustrate the fundamental mechanism for EM propogation at subwavelength confinement via surface plasmons. We have also experimentally studied the high frequency properties of the novel metamaterials, including NiFex/Polymer 100-x nanocomposites and magnetic left-handed materials (m-LHMs). In the nanocomposites study, we found the microwave transmission in NiFe x/Polymer100-x nanocomposites can be improved in the presence of an external magnetic field. It provides us a potential method to make a controllable microwave absorber for wave transmission at microwave frequency, which has various applications in microwave devices and communication. In m-LHM study, we have theoretically investigated the possibility of realizing LHM in metallic magnetic system. We have found that these thin magnetic films consist of metallic entities that may exhibit left-handed behaviors near the vicinity of the ferromagnetic resonant frequency o0. Experimentally, we observed the thickness dependent peak shifts in both multilayer [NiFe(10nm)/SiO2(2nm)]N thin films and granular Fe 30(SiO2)70 thin films. This suggests a negative refraction index.

Cao, Rong

246

NASA Astrophysics Data System (ADS)

We study the dynamics of a spin ensemble strongly coupled to a single-mode resonator driven by external pulses. When the mean frequency of the spin ensemble is in resonance with the cavity mode, damped Rabi oscillations are found between the spin ensemble and the cavity mode which we describe very accurately, including the dephasing effect of the inhomogeneous spin broadening. We demonstrate that a precise knowledge of this broadening is crucial both for a qualitative and a quantitative understanding of the temporal spin-cavity dynamics. On this basis we show that coherent oscillations between the spin ensemble and the cavity can be enhanced by a few orders of magnitude, when driving the system with pulses that match special resonance conditions. Our theoretical approach is tested successfully with an experiment based on an ensemble of negatively charged nitrogen-vacancy centers in diamond strongly coupled to a superconducting coplanar single-mode waveguide resonator.

Krimer, Dmitry O.; Putz, Stefan; Majer, Johannes; Rotter, Stefan

2014-10-01

247

We study the dynamics of a spin ensemble strongly coupled to a single-mode resonator driven by external pulses. When the mean frequency of the spin ensemble is in resonance with the cavity mode, damped Rabi oscillations are found between the spin ensemble and the cavity mode which we describe very accurately, including the dephasing effect of the inhomogeneous spin broadening. We demonstrate that a precise knowledge of this broadening is crucial both for a qualitative and a quantitative understanding of the temporal spin-cavity dynamics. On this basis we show that coherent oscillations between the spin ensemble and the cavity can be enhanced by a few orders of magnitude, when driving the system with pulses that match special resonance conditions. Our theoretical approach is tested successfully with an experiment based on an ensemble of negatively charged nitrogen-vacancy (NV) centers in diamond strongly coupled to a superconducting coplanar single-mode waveguide resonator.

Krimer, Dmitry O; Majer, Johannes; Rotter, Stefan

2014-01-01

248

We study the dynamics of a spin ensemble strongly coupled to a single-mode resonator driven by external pulses. When the mean frequency of the spin ensemble is in resonance with the cavity mode, damped Rabi oscillations are found between the spin ensemble and the cavity mode which we describe very accurately, including the dephasing effect of the inhomogeneous spin broadening. We demonstrate that a precise knowledge of this broadening is crucial both for a qualitative and a quantitative understanding of the temporal spin-cavity dynamics. On this basis we show that coherent oscillations between the spin ensemble and the cavity can be enhanced by a few orders of magnitude, when driving the system with pulses that match special resonance conditions. Our theoretical approach is tested successfully with an experiment based on an ensemble of negatively charged nitrogen-vacancy (NV) centers in diamond strongly coupled to a superconducting coplanar single-mode waveguide resonator.

Dmitry O. Krimer; Stefan Putz; Johannes Majer; Stefan Rotter

2014-10-02

249

Spin Dynamics of the Magnetoresistive Pyrochlore Tl2Mn2O7

NASA Astrophysics Data System (ADS)

Neutron scattering has been used to study the magnetic order and spin dynamics of the colossal magnetoresistive pyrochlore Tl2Mn2O7. On cooling from the paramagnetic state, magnetic correlations develop and appear to diverge at Tc (123 K). In the ferromagnetic phase well defined spin waves are observed, with a gapless ( ?<0.04 meV) dispersion relation E = Dq2 as expected for an ideal isotropic ferromagnet. As T-->Tc from low T, the spin waves renormalize, but no significant central diffusive component to the fluctuation spectrum is observed in stark contrast to the La1-x\\(Ca,Ba,Sr\\)xMnO3 system. These results argue strongly that the mechanism responsible for the magnetoresistive effect has a different origin in these two classes of materials.

Lynn, J. W.; Vasiliu-Doloc, L.; Subramanian, M. A.

1998-05-01

250

Spin dynamics and domain formation of a spinor Bose-Einstein condensate in an optical cavity

NASA Astrophysics Data System (ADS)

We consider a ferromagnetic spin-1 Bose-Einstein condensate (BEC) dispersively coupled to a unidirectional ring cavity. We show that the ability of the cavity to modify, in a highly nonlinear fashion, matter-wave phase shifts adds an additional dimension to the study of spinor condensates. In addition to demonstrating strong matter-wave bistability as in our earlier publication [L. Zhou , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.160403 103, 160403 (2009)], we show that the interplay between atomic and cavity fields can greatly enrich both the physics of critical slowing down in spin-mixing dynamics and the physics of spin-domain formation in spinor condensates.

Zhou, Lu; Pu, Han; Ling, Hong Y.; Zhang, Keye; Zhang, Weiping

2010-06-01

251

Magnetic field dependence of the dynamics of {sup 87}Rb spin-2 Bose-Einstein condensates

We experimentally studied the spin-dependent collision dynamics of {sup 87}Rb spin-2 Bose-Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the |F=2,m{sub F}=0> state, and their time evolutions in the trap were measured in the presence of external magnetic field strengths ranging from 0.1 to 3.0 G. The atom loss rate due to inelastic two-body collisions was found to be 1.4(2)x10{sup -13} cm{sup 3} s{sup -1}. Spin mixing in the F=2 manifold developed dramatically for the first few tens of milliseconds, and the oscillations in the population distribution between different magnetic components were observed over a limited range of magnetic field strengths. The antiferromagnetic property of this system was deduced from the magnetic field dependence on the evolution of relative populations for each m{sub F} component.

Kuwamoto, T.; Araki, K.; Eno, T.; Hirano, T. [Department of Physics, Gakushuin University, 1-5-1 Mejiro, Toshima-ku, Tokyo 171-8588 (Japan)

2004-06-01

252

Proton-driven spin diffusion in rotating solids via reversible and irreversible quantum dynamics

Proton-driven spin diffusion (PDSD) experiments in rotating solids have received a great deal of attention as a potential source of distance constraints in large biomolecules. However, the quantitative relationship between the molecular structure and observed spin diffusion has remained obscure due to the lack of an accurate theoretical description of the spin dynamics in these experiments. We start with presenting a detailed relaxation theory of PDSD in rotating solids that provides such a description. The theory applies to both conventional and radio-frequency-assisted PDSD experiments and extends to the non-Markovian regime to include such phenomena as rotational resonance (R2). The basic kinetic equation of the theory in the non-Markovian regime has the form of a memory function equation, with the role of the memory function played by the correlation function. The key assumption used in the derivation of this equation expresses the intuitive notion of the irreversible dissipation of coherences in macroscopic systems. Accurate expressions for the correlation functions and for the spin diffusion constants are given. The theory predicts that the spin diffusion constants governing the multi-site PDSD can be approximated by the constants observed in the two-site diffusion. Direct numerical simulations of PDSD dynamics via reversible Liouville-von Neumann equation are presented to support and compliment the theory. Remarkably, an exponential decay of the difference magnetization can be observed in such simulations in systems consisting of only 12 spins. This is a unique example of a real physical system whose typically macroscopic and apparently irreversible behavior can be traced via reversible microscopic dynamics. An accurate value for the spin diffusion constant can be usually obtained through direct simulations of PDSD in systems consisting of two 13C nuclei and about ten 1H nuclei from their nearest environment. Spin diffusion constants computed by this method are in excellent agreement with the spin diffusion constants obtained through equations given by the relaxation theory of PDSD. The constants resulting from these two approaches were also in excellent agreement with the results of 2D rotary resonance recoupling proton-driven spin diffusion (R3-PDSD) experiments performed in three model compounds, where magnetization exchange occurred over distances up to 4.9 Å. With the methodology presented, highly accurate internuclear distances can be extracted from such data. Relayed transfer of magnetization between distant nuclei appears to be the main (and apparently resolvable) source of uncertainty in such measurements. The non-Markovian kinetic equation was applied to the analysis of the R2 spin dynamics. The conventional semi-phenomenological treatment of relxation in R2 has been shown to be equivalent to the assumption of the Lorentzian spectral density function in the relaxatoin theory of PDSD. As this assumption is a poor approximation in real physical systems, the conventional R2 treatment is likely to carry a significant model error that has not been recognized previously. The relaxation theory of PDSD appears to provide an accurate, parameter-free alternative. Predictions of this theory agreed well with the full quantum mechanical simulations of the R2 dynamics in the few simple model systems we considered. PMID:21992326

Veshtort, Mikhail; Griffin, Robert G.

2011-01-01

253

Tests of Dynamic Scale Model of Gemini Capsule in the Langley 20-Foot Free-Spinning Tunnel

NASA Technical Reports Server (NTRS)

Tests of Dynamic Scale Model of Gemini Capsule in the Langley 20-Foot Free-Spinning Tunnel. The film shows three spin tunnel tests of a 1/20 scale model of the Gemini capsule. In the first test, the capsule spins freely. In tests 2 and 3, a drogue parachute is attached to the capsule. [Entire movie available on DVD from CASI as Doc ID 20070030989. Contact help@sti.nasa.gov

1962-01-01

254

Finite Temperature Dynamics of the Spin-1/2 Heisenberg Chain.

NASA Astrophysics Data System (ADS)

We report on our recent studies of the finite temperature (T) dynamics of the isotropic antiferromagnetic S=1/2 Heisenberg chain for all values of the ratio T/J (J is the nearest-neighbor exchange). (A) Dynamics in the low-T region (T/J << 1) is studied via a simple ansatz taking into account marginally irrelevant operator which describes Umklapp scattering between right- and left-moving spinons (O. A. Starykh, R. R. P. Singh, A. W. Sandvik, Phys. Rev. Lett.) 78, 539 (1997). This operator is found to produce (i) logarithmic T-dependent corrections to the scaling dimension of the spin operator, and (ii) multiple logarithmic corrections to the spin correlation function, in agreement with previous renormalization group and thermal Bethe-ansatz studies. As a result, the staggered spin susceptibility \\chi(q,?) shows deviations from the quantum-critical scaling behavior expected for the model with critical correlations in the ground state. Our quantum Monte Carlo (QMC) and high-temperature expansions (HTE) studies provide striking quantitative confirmation of this behavior. We also demonstrate that these logarithmic corrections are essential for the quantitative comparison with the measured spin-lattice (1/T_1) and Gaussian spin-echo (1/T_2G) NMR decay rates of Sr_2CuO3 (M. Takigawa, O. A. Starykh. A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 56, 13681 (1997). (B) Spin dynamics in the intermediate and high-T regions (T/J >= 0.5) is studied by combining HTE with the recursion method, and QMC with the maximum entropy method. We find that the spectral weight of the dynamic structure factor S(k,?) gradually transfers from a diffusive long-wavelenght modes (k ~ 0) at T >> J to a propagating antiferromagnetic ones (k ~ ?) at intermediate temperatures (T ~ J). We extract the NMR 1/T1 rate from the ? arrow 0 limit of S(k,?), and also discuss temperature scaling of the structure factor and staggered spin susceptibility ( O. A. Starykh, A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 55, 14953 (1997).

Starykh, Oleg A.

1998-03-01

255

We study semiclassical dynamics of anisotropic Heisenberg models in two and three dimensions. Such models describe lattice spin systems and hard core bosons in optical lattices. We solve numerically Landau-Lifshitz type equations on a lattice and show that in the phase diagram of magnetization and interaction anisotropy, one can identify several distinct regimes of dynamics. These regions can be distinguished based on the character of one dimensional solitonic excitations, and stability of such solitons to transverse modulation. Small amplitude and long wavelength perturbations can be analyzed analytically using mapping of non-linear hydrodynamic equations to KdV type equations. Numerically we find that properties of solitons and dynamics in general remain similar to our analytical results even for large amplitude and short distance inhomogeneities, which allows us to obtain a universal dynamical phase diagram. As a concrete example we study dynamical evolution of the system starting from a state with magneti...

Demler, E; Prokofiev, A

2012-01-01

256

Dynamics of entanglement in a two-dimensional spin system

We consider the time evolution of entanglement in a finite two-dimensional transverse Ising model. The model consists of a set of seven localized spin-(1/2) particles in a two-dimensional triangular lattice coupled through nearest-neighbor exchange interaction in the presence of an external time-dependent magnetic field. The magnetic field is applied in different function forms: step, exponential, hyperbolic, and periodic. We found that the time evolution of the entanglement shows an ergodic behavior under the effect of the time-dependent magnetic fields. Also, we found that while the step magnetic field causes great disturbance to the system, creating rapid oscillations, the system shows great controllability under the effects of the other magnetic fields where the entanglement profile follows closely the shape of the applied field even with the same frequency for periodic fields. This follow-up trend breaks down as the strength of the field, the transition constant for the exponential and hyperbolic forms, or the frequency for periodic field increase leading to rapid oscillations. We observed that the entanglement is very sensitive to the initial value of the applied periodic field: the smaller the initial value is, the less distorted the entanglement profile is. Furthermore, the effect of thermal fluctuations is very devastating to the entanglement, which decays very rapidly as the temperature increases. Interestingly, although a large value of the magnetic field strength may yield a small entanglement, the magnetic field strength was found to be more persistent against thermal fluctuations than the small field strengths.

Xu Qing [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Sadiek, Gehad [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Physics, Ain Shams University, Cairo 11566 (Egypt); Kais, Sabre [Department of Physics, King Saud University, Riyadh 11451 (Saudi Arabia); Department of Chemistry and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States)

2011-06-15

257

Dissipation dynamics and spin-orbit force in time-dependent Hartree-Fock theory

NASA Astrophysics Data System (ADS)

We investigate the one-body dissipation dynamics in heavy-ion collisions of O16+O16 using a fully three-dimensional time-dependent Hartree-Fock (TDHF) theory with the modern Skyrme energy functional and without any symmetry restrictions. The energy dissipation is revealed to decrease in deep-inelastic collisions of the light systems as the bombarding energy increases owing to the competition between collective motion and single-particle degrees of freedom. The role of spin-orbit force is given particular emphasis in deep-inelastic collisions. The spin-orbit force causes a significant enhancement of the dissipation. The time-even coupling of spin-orbit force plays a dominant role at low energies, while the influence of time-odd terms is notable at high energies. About 40-65% of the total dissipation depending on the different parameter sets is predicted to arise from the spin-orbit force. The theoretical fusion cross section has a reasonably good agreement with the experimental data, considering that no free parameters are adjusted to reaction dynamics in the TDHF approach.

Dai, Gao-Feng; Guo, Lu; Zhao, En-Guang; Zhou, Shan-Gui

2014-10-01

258

NASA Astrophysics Data System (ADS)

The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In0.5Ga0.5As was studied by increasing the sheet density of the dots from 2 × 1010 to 7 × 1010 cm-2 and reducing their size through a decrease in growth temperature from 500 to 470 °C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro

2014-09-01

259

A buildup of the vertical polarization in the resonant electric dipole moment (EDM) experiment [Y. F. Orlov, W. M. Morse, and Y. K. Semertzidis, Phys. Rev. Lett. 96, 214802 (2006)] is affected by a horizontal electric field in the particle rest frame oscillating at a resonant frequency. This field is defined by the Lorentz transformation of an oscillating longitudinal electric field and a uniform vertical magnetic one. The effect of a longitudinal electric field is significant, while the contribution from a magnetic field caused by forced coherent longitudinal oscillations of particles is dominant. The effect of electric field on the spin dynamics was not taken into account in previous calculations. This effect is considerable and leads to decreasing the EDM effect for the deuteron and increasing it for the proton. The formula for resonance strengths in the EDM experiment has been derived. The spin dynamics has been calculated.

Alexander J. Silenko

2006-04-11

260

Valley and spin dynamics in MoSe2 two-dimensional crystals.

We study valley and spin dynamics in monolayer molybdenum diselenide by polarization-resolved femtosecond transient absorption spectroscopy. Valley- and spin-polarized excitons are injected by a circularly polarized laser pulse, with an excess energy of 120 meV. Relaxation of the valley polarization is time-resolved by measuring dynamical circular dichroism of a linearly polarized probe pulse tuned to 790 nm, the peak of the exciton resonance of monolayer MoSe2. We obtain a valley relaxation time of 9 ± 3 ps at room temperature, which is at least one order of magnitude shorter than the simultaneously measured exciton lifetime. The results illustrate potential applications of MoSe2 in room-temperature valleytronic and spintronic devices. PMID:25212540

Kumar, Nardeep; He, Jiaqi; He, Dawei; Wang, Yongsheng; Zhao, Hui

2014-10-01

261

The dynamics of spin stabilized spacecraft with movable appendages, part 2

NASA Technical Reports Server (NTRS)

The dynamics and stability of a spin stabilized spacecraft with a hinged appendage system are treated analytically and numerically. The hinged system consists of a central hub with masses attached to (assumed) massless booms of fixed length whose orientation relative to the main part can change. The general three dimensional deployment dynamics of such a hinged system is considered without any restriction on the location of the hinge points. The equations of motion for the hinged system, with viscous damping at both hinge points, are linearized about the nominal equilibrium position where the booms are orthogonal to the nominal spin axis for the case of two dimensional and three dimensional motion. Analytic stability criteria are obtained from the necessary condition on the sign of all the coefficients in the system characteristic equation.

Bainum, P. M.

1976-01-01

262

An efficient numerical method for computing dynamics of spin F = 2 Bose-Einstein condensates

In this paper, we extend the efficient time-splitting Fourier pseudospectral method to solve the generalized Gross-Pitaevskii (GP) equations, which model the dynamics of spin F = 2 Bose-Einstein condensates at extremely low temperature. Using the time-splitting technique, we split the generalized GP equations into one linear part and two nonlinear parts: the linear part is solved with the Fourier pseudospectral method; one of nonlinear parts is solved analytically while the other one is reformulated into a matrix formulation and solved by diagonalization. We show that the method keeps well the conservation laws related to generalized GP equations in 1D and 2D. We also show that the method is of second-order in time and spectrally accurate in space through a one-dimensional numerical test. We apply the method to investigate the dynamics of spin F = 2 Bose-Einstein condensates confined in a uniform/nonuniform magnetic field.

Wang Hanquan, E-mail: hanquan.wang@gmail.com [School of Statistics and Mathematics, Yunnan University of Finance and Economics, Kunming, Yunnan Province 650221 (China); Department of Mathematics, National University of Singapore, Singapore 117543 (Singapore)

2011-07-01

263

Effective spin-glass Hamiltonian for the anomalous dynamics of the HMF model

We discuss an effective spin-glass Hamiltonian which can be used to study the glassy-like dynamics observed in the metastable states of the Hamiltonian mean field (HMF) model. By means of the Replica formalism, we were able to find a self-consistent equation for the glassy order parameter which reproduces, in a restricted energy region below the phase transition, the microcanonical simulations

Alessandro Pluchino; Vito Latora; Andrea Rapisarda

2006-01-01

264

Multiple quantum NMR dynamics in a gas of spin-carrying molecules in fluctuating nanopores

NASA Astrophysics Data System (ADS)

The effect of Gaussian fluctuations of nanopores filled with a gas of spin-carrying molecules ( s = 1/2) on the multiple quantum (MQ) NMR dynamics is investigated at different variances and correlation times of the fluctuations. We show that the fluctuations smooth out the evolution of MQ NMR coherence intensities which rapidly oscillate as functions of time in the absence of fluctuations. The growth and decay of the MQ coherence clusters in the fluctuating nanopore are also investigated.

Fel'dman, E. B.; Zenchuk, A. I.

2011-11-01

265

NUCLEAR RELAXATION AND SPIN DYNAMICS IN NMP TCNQ F. DEVREUX (*), M. GUGLIELMI and M. NECHTSCHEIN (*)

541 NUCLEAR RELAXATION AND SPIN DYNAMICS IN NMP TCNQ F. DEVREUX (*), M. GUGLIELMI and M Ã©tÃ© effectuÃ©es en fonction de la frÃ©quence dans des echantillons de NMP TCNQ sÃ©lectivement deutÃ©riÃ©s Ã©lectroniques localisÃ©s sur les chaines de NMP et associÃ©s Ã un transfert de charge incomplet. AprÃ¨s

Paris-Sud XI, UniversitÃ© de

266

Fully suspended, five-axis, three-magnetic-bearing dynamic spin rig with forced excitation

A significant advancement in the dynamic spin rig (DSR), i.e., the five-axis, three-magnetic-bearing DSR, is used to perform\\u000a vibration tests of turbomachinery blades and components under rotating and non-rotating conditions in a vacuum. The rig has\\u000a three magnetic bearings as its critical components: two heteropolar radial active magnetic bearings and a magnetic thrust\\u000a bearing. The bearing configuration allows full vertical

C. R. Morrison; A. Provenza; A. Kurkov; G. Montague; K. Duffy; O. Mehmed; D. Johnson; R. Jansen

2005-01-01

267

Limiting dynamics for spherical models of spin glasses at high temperature

We analyze the coupled non-linear integro-differential equations whose solutions is the thermodynamical limit of the empirical correlation and response functions in the Langevin dynamics for spherical p-spin disordered mean-field models. We provide a mathematically rigorous derivation of their FDT solution (for the high temperature regime) and of certain key properties of this solution, which are in agreement with earlier derivations based on physical grounds.

Amir Dembo; Alice Guionnet; Christian Mazza

2006-09-20

268

Quantum jumps and spin dynamics of interacting atoms in a strongly coupled atom-cavity system

We experimentally investigate the spin dynamics of one and two neutral atoms strongly coupled to a high finesse optical cavity. We observe quantum jumps between hyperfine ground states of a single atom. The interaction-induced normal mode splitting of the atom-cavity system is measured via the atomic excitation. Moreover, we observe evidence for conditional dynamics of two atoms simultaneously coupled to the cavity mode. Our results point towards the realization of measurement-induced entanglement schemes for neutral atoms in optical cavities.

M. Khudaverdyan; W. Alt; T. Kampschulte; S. Reick; A. Thobe; A. Widera; D. Meschede

2009-01-23

269

The dynamics of diluted Ho spin ice Ho2-xYxTi2O7 studied byneutron spin echo spectroscopy

We have studied the spin relaxation in diluted spin ice Ho{sub 2-x} Y{sub x} Ti{sub 2}O{sub 7} by means of neutron spin echo spectroscopy. Remarkably, the geometrical frustration is not relieved by doping with non-magnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x {approx_equal} 1.6. At higher doping with non-magnetic Y (x {ge} 1.6) a new relaxation process at relatively high temperature (up to at least T {approx_equal} 55 K) appears which is more than 10 times faster than the thermally activated main relaxation process. We find evidence that over the whole range of composition all Ho spins participate in the dynamics. These results are compared to a.c. susceptibility measurements of the diluted Ho and Dy spin ice systems. X-ray absorption fine structure (EXAFS) spectra and x-ray diffraction show that the samples are structurally well ordered.

Ehlers, G.; Gardner, J.S.; Booth, C.H.; Daniel, M.; Kam, K.C.; Cheetham, A.K.; Antonio, D.; Brooks, H.E.; Cornelius, A.L.; Bramwell,S.T.; Lago, J.; Haussler, W.; Rosov, N.

2006-02-27

270

New Dynamic Spin Rig Capabilities Used to Determine Rotating Blade Dynamics

NASA Technical Reports Server (NTRS)

The Dynamic Spin Rig Facility at the NASA Glenn Research Center is used to determine the structural response of rotating engine components without the effects of aerodynamic loading. Recently, this rig's capabilities were enhanced through the replacement of grease-lubricated ball bearings with magnetic bearings. Magnetic bearings offer a number of advantages--the most important here being that they not only fully support the rotor system, but excite it as well. Three magnetic bearings support the rotor and provide five axes of controlled motion: an x- and y-axis translation at each of two radial bearings and a z-axis translation in the vertical or axial direction. Sinusoidal excitation (most commonly used) can be imparted on the rotor through the radial magnetic bearings in either a fixed or rotating frame of reference. This excitation is added directly to the magnetic bearing control output. Since the rotor is fully levitated, large translations and rotations of the rotor system can be achieved. Some of the capabilities of this excitation system were determined and reported. The accelerations obtained at the tip of a titanium flat plate test article versus the swept sine excitation sent to both radial bearings in phase and perpendicular to the plane containing the two blades are shown. Recent tests required the excitation of fundamental bending and torsional blade resonances at rotor speeds up to 10,000 rpm. Successful fixed synchronous rotation of the excitation signal provided the best detectable blade resonant vibrations at excitation frequencies up to 1100 Hz for the particular blades of interest. A noncontacting laser measurement system was used to collect blade-tip motions. From these data, the amplitude and frequency of the motion could be determined as well as the blade damping properties. Damping could be determined using two methods: (1) free decay and (2) curve fitting the vibration amplitude as a function of frequency in and around the resonance of interest and using the half-power method. The free decay of a composite blade vibrating at its first bending resonance while rotating at 3000 rp is shown. This new system is currently being used to support the Efficient Low-Noise Fan project at Glenn. The damping properties of prototype hollow composite blades specially designed to reduce fan noise are currently being determined.

Provenza, Andrew J.

2004-01-01

271

Spin-labeled lipids are commonly used as fluorescence quenchers in studies of membrane penetration of dye-labeled proteins and peptides using depth-dependent quenching. Accurate calculations of depth of the fluorophore rely on the use of several spin labels placed in the membrane at various positions. The depth of the quenchers (spin probes) has to be determined independently, however; experimental determination of transverse distributions of spin probe depths is difficult. In this article, we use molecular dynamics (MD) simulations to study the membrane behavior and depth distributions of spin–labeled phospholipids in a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayer. To probe different depths within the bilayer, a series containing five Doxyl-labeled lipids (n-Doxyl PC) has been studied, in which a spin moiety was covalently attached to n–th carbon atoms (where n=5, 7, 10, 12 and 14) of the sn-2 stearoyl chain of the host phospholipid. Our results demonstrate that the chain–attached spin labels are broadly distributed across the model membrane and their environment is characterized by a high degree of mobility and structural heterogeneity. Despite the high thermal disorder, the depth distributions of the Doxyl labels were found to correlate well with their attachment positions, indicating that the distribution of the spin label within the model membrane is dictated by the depth of the n–th lipid carbon atom and not by intrinsic properties of the label. In contrast, a much broader and heterogeneous distribution was observed for a headgroup–attached Tempo spin label of Tempo–PC lipids. MD simulations reveal that, due to the hydrophobic nature, a Tempo moiety favors partitioning from the headgroup region deeper into the membrane. Depending on the concentration of Tempo-PC lipids, the probable depth of the Tempo moiety could span a range from 14.4 Å to 18.2 Å from the membrane center. Comparison of the MD–estimated immersion depths of Tempo and n-Doxyl labels with their suggested experimental depth positions allows us to review critically the possible sources of error in depth-dependent fluorescence quenching studies. PMID:23614631

Kyrychenko, Alexander; Ladokhin, Alexey S.

2013-01-01

272

NASA Astrophysics Data System (ADS)

Segmental dynamic heterogeneity of short-chain grafted poly(dimethylsiloxane) (PDMS) on pyrogenic silica was investigated using 1H NMR spin-diffusion. A double-quantum dipolar filter was employed for selection of the interface (rigid) region. One-dimensional spin-diffusion equations were solved numerically for a space distribution of spin diffusivity D( x) of the mobile PDMS chains. The degree of heterogeneity can be quantified by the parameters of Gaussian and exponential diffusivity distribution functions which yield similar diffusivities. The rigid and mobile domain sizes and spin diffusivities were correlated with the PDMS chain length, the temperature, and 1H residual dipolar couplings.

Bertmer, Marko; Demco, Dan E.; Wang, Mingfei; Melian, Claudiu; Marcean-Chelcea, Ramona I.; Fechete, Radu; Baias, Maria; Blümich, Bernhard

2006-11-01

273

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen){sub 2}(NCS){sub 2} (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe([Me{sub 2}Pyrz]{sub 3}BH){sub 2} (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen.

Davesne, V.; Gruber, M. [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France) [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France); Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany); Miyamachi, T. [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwashi, Chiba 277-8581 (Japan)] [Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwashi, Chiba 277-8581 (Japan); Da Costa, V.; Boukari, S.; Scheurer, F.; Joly, L.; Bowen, M.; Beaurepaire, E. [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France)] [Institut de Physique et de Chimie des Matériaux de Strasbourg, Université de Strasbourg, CNRS UMR 7504 23 rue du Loess, 67034 Strasbourg (France); Ohresser, P.; Otero, E.; Choueikani, F. [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France)] [Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France); Gaspar, A. B.; Real, J. A. [Institut of Molecular Science, Universitat de València, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 València (Spain)] [Institut of Molecular Science, Universitat de València, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 València (Spain); Wulfhekel, W. [Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)] [Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe (Germany)

2013-08-21

274

Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics inIron Arsenide Compounds

Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.

Christianson, Andrew D [ORNL; Osborn, R. [Argonne National Laboratory (ANL); Rosenkranz, Stephen [Argonne National Laboratory (ANL); Goremychkin, E. A. [ISIS Facility, Rutherford Appleton Laboratory

2009-01-01

275

Dynamic Model Investigation of a 1/20 Scale Gemini Spacecraft in the Langley Spin Tunnel

NASA Technical Reports Server (NTRS)

Dynamic Model Investigation of a 1/20 Scale Gemini Spacecraft in the Langley Spin Tunnel. The investigation was conducted in the Langley spin tunnel. The tunnel is an atmospheric wind tunnel with a vertically rising airstream in the test section and a maximum airspeed of approximately 90 feet per second. For this investigation, the model was hand launched into the vertically rising airstream. At times the model, both with and without a drogue parachute, was launched gently with as little disturbance as possible to determine what motions of the spacecraft were self-excited. At other times, the spacecraft with pre-deployed drogue parachute was launched into various spinning motions to determine the effectiveness of the drogue parachute in terminating these spinning motions. During drogue-parachute deployment tests, the spacecraft was launched into various spinning and tumbling motions and the drogue parachute was deployed. The motions of the model were photographed with a motion-picture camera, and some of the film records were read to obtain typical time histories of the model motion. The angles of attack indicated in the time histories presented are believed to be accurate within +/-1 degree. The mass and dimensional characteristics of the dynamic model are believed to be measured to an accuracy of: +/-1 percent for the weight, +/-1 percent for z(sub cg)/d, +/-15 percent for x (sub cg), and +/-5 percent for the moments of inertia. The towline and bridle-line lengths were simulated to an accuracy of +/-1 foot full scale. [Entire movie available on DVD from CASI as Doc ID 20070030985. Contact help@sti.nasa.gov

1963-01-01

276

Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.

Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.

Osborn, R.; Rosenkranz, S.; Goremychkin, E. A.; Christianson, A. D. (Materials Science Division); (ORNL)

2009-03-20

277

Spin Dynamics in Permalloy Disks with Vortex Structure

NASA Astrophysics Data System (ADS)

Micron sized ferromagnetic permalloy disks exhibiting a ferromagnetic vortex structure are excited by a magnetic field pulse. The fast rise time pulse field is generated by an optically triggered electrical pulse in a lithographically fabricated microcoil. Experiments were performed for a series of different sample dimensions. The excitation is imaged using time resolved magneto-optic polar Kerr microscopy in a stroboscopic experiment. We present the spatially resolved magnetic maps at different delay times, stitched together to form a magnetic movie. The dynamical excitations are composed of symmetric and non-sysmmetric parts which can not be separated at first glance. However, in a detailed analysis up to five Eigen-modes can be extracted from the data and can be visualized in the Fourier transform of the magnetic movie. The symmetric excitations can be accounted for in a simple model based purely on dipolar interactions. The model is supported by micromagnetic simulations and shows good quantitative agreement in the resonance frequencies for different modes. Furthermore, insight can be gained into the energy dissipation of the system from the same data.

Buess, Matthias; Höllinger, Rainer; Haug, Thomas; Perzlmaier, Korbinian; Back, Christian H.; Pescia, Danilo; Scheinfein, Micheal R.

2004-03-01

278

Competing thermodynamic and dynamic factors select molecular assemblies on a gold surface.

Controlling the self-assembly of surface-adsorbed molecules into nanostructures requires understanding physical mechanisms that act across multiple length and time scales. By combining scanning tunneling microscopy with hierarchical ab initio and statistical mechanical modeling of 1,4-substituted benzenediamine (BDA) molecules adsorbed on a gold (111) surface, we demonstrate that apparently simple nanostructures are selected by a subtle competition of thermodynamics and dynamics. Of the collection of possible BDA nanostructures mechanically stabilized by hydrogen bonding, the interplay of intermolecular forces, surface modulation, and assembly dynamics select at low temperature a particular subset: low free energy oriented linear chains of monomers and high free energy branched chains. PMID:24483804

Haxton, Thomas K; Zhou, Hui; Tamblyn, Isaac; Eom, Daejin; Hu, Zonghai; Neaton, Jeffrey B; Heinz, Tony F; Whitelam, Stephen

2013-12-27

279

Evidence for spin solitons and their dynamics in a spin-Peierls system (DMe-DCNQI)2Li

NASA Astrophysics Data System (ADS)

A spin-Peierls system (DMe-DCNQI)2Li has been studied with electron paramagnetic resonance (EPR) under hydrostatic pressure. A definite frequency dependence of the EPR linewidth is observed for the Curie spins that appear below TSP, demonstrating a clear one-dimensional diffusive character similar to t-(CH)x. This is strong evidence for Curie spins to arise from spin solitons as domain walls caused by structural defects. The estimated extent of the spin soliton is less than several molecular units. A relation with the antiferromagnetic ordering provoked by impurities as found in CuGeO3 is discussed.

Hiraoka, Maki; Sakamoto, Hirokazu; Mizoguchi, Kenji; Kato, Reizo

2002-05-01

280

Analysis of Work: Describing Competences through a Dynamic Approach to Jobs.

ERIC Educational Resources Information Center

Human resources management personnel have been encouraged to develop a job analysis approach capable of grasping work situations that are more complex, less defined, and in a state of flux. In France, this perspective has given rise to Emploi Type Etudie dans sa Dynamique (ETED) or "typical job studied in its dynamic," an approach that reflects…

Mandon, Nicole; Sulzer, Emmanuel

1998-01-01

281

The Study of Competence-Anxiety Relations within Social Interaction: A Dynamic Systems Approach.

ERIC Educational Resources Information Center

This study presents a dynamic systems model that suggests that social behavior emerges from the self-organization of cognition-emotion relationships and becomes stable through a process of positive feedback and coupling of components over time. Five 10- to 12-year-old children identified as anxious in evaluative situations by their teacher were…

Phillips, Sian

282

Learning to Compete in Dynamic Food Systems: Elements for Successful Supply Chains in CAFTA-DR

Shifts in the agrifood system are felt globally from rural communities to urban consumers. These changes are transmitted along integrated supply chains managed by increasingly powerful food retailers. The survival of individual farmers and farmer associations lies in their capacity to participate in these dynamic systems. While the rate and depth of change varies across continents and nations, some key

Mark Lundy; Thomas Reardon

283

Hole dynamics and spin currents after ionization in strong circularly polarized laser fields

We apply the time-dependent analytical R-matrix theory to develop a movie of hole motion in a Kr atom upon ionization by strong circularly polarized field. We find rich hole dynamics, ranging from rotation to swinging motion. The motion of the hole depends on the final energy and the spin of the photoelectron and can be controlled by the laser frequency and intensity. Crucially, hole rotation is a purely non-adiabatic effect, completely missing in the framework of quasistatic (adiabatic) tunneling theories. We explore the possibility to use hole rotation as a clock for measuring ionization time. Analysing the relationship between the relative phases in different ionization channels we show that in the case of short-range electron-core interaction the hole is always initially aligned along the instantaneous direction of the laser field, signifying zero delays in ionization. Finally, we show that strong-field ionization in circular fields creates spin currents (i.e. different flow of spin-up and spin-down densi...

Barth, Ingo

2014-01-01

284

Evidence of impurity and boundary effects on magnetic monopole dynamics in spin ice

NASA Astrophysics Data System (ADS)

Electrical resistance is a crucial and well-understood property of systems ranging from computer microchips to nerve impulse propagation in the human body. Here we study the motion of magnetic charges in spin ice and find that extra spins inserted in Dy2Ti2O7 trap magnetic monopole excitations and provide the first example of how defects in a spin-ice material obstruct the flow of monopoles--a magnetic version of residual resistance. We measure the time-dependent magnetic relaxation in Dy2Ti2O7 and show that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we show that surface effects and a very low level of stuffed spins (0.30%)--magnetic Dy ions substituted for non-magnetic Ti ions--cause these signatures in the relaxation. In addition, we find evidence that the rapidly diverging experimental timescale is due to a temperature-dependent attempt rate proportional to the monopole density.

Revell, H. M.; Yaraskavitch, L. R.; Mason, J. D.; Ross, K. A.; Noad, H. M. L.; Dabkowska, H. A.; Gaulin, B. D.; Henelius, P.; Kycia, J. B.

2013-01-01

285

Numerical Investigations of Post-Newtonian Hamiltonian Dynamics for Spinning Compact Binaries

NASA Astrophysics Data System (ADS)

Spinning compact binaries, consisting of neutron stars or black holes, not only have rich dynamic phenomena of resonance and chaos, but also are the most promising source for detecting gravitational waves. There should be a certain relation between the dynamics of the gravitational bodies and the gravitational waveforms. Based on the least-squares correction, several manifold correction schemes like the single-scaling method and the dual-scaling method are designed to suppress numerical errors from 6 integrals of motion in a conservative post-Newtonian (PN) Hamiltonian of spinning compact binaries. Taking a fifth order Runge-Kutta algorithm as a basic integrator, we wonder whether the PN contributions, the spin effects, and the classification of orbits exert some influences on these correction schemes and the Nacozy's approach. It is found that they are almost the same in correcting the integrals for the pure Kepler problem. Once the third-order PN contributions are added to the pure orbital part, there are explicit differences of correction effectiveness among these methods. As an interesting case, the efficiency of correction is better for chaotic eccentric orbits than for quasicircular regular ones. In all cases tested, the new momentum-position dual-scaling scheme does always have the optimal performance. It costs a little but not much expensive additional computational cost when the spin effects exist, and several time-saving techniques are used. The corrected numerical results are more accurate than the uncorrected ones, so that chaos from the numerical errors can be avoided. See Phys. Rev. D 81, 104037 (2010) for more details. Lubich et al. (Phys. Rev. D 81, 104025 (2010)) presented a noncanonically symplectic integrator for the PN Hamiltonian of a spinning compact binary. However, the Euler mixed integrator is problematic because of its bad numerical stability.We improved the work by constructing the second-order and the fourth-order fixed symplectic integrators, where the second-order symplectic implicit midpoint rule and its symmetric compositions are together used to integrate a PN Hamiltonian with the canonical spin variables of Wu and Xie (Phys. Rev. D 81, 084045 (2010)). Many numerical tests show that the mixed leapfrog integrator is always superior to the midpoint rule in the accuracy, while both of them are almost equivalent in the computational efficiency. Particularly, the optimized fourth-order algorithm compared with the mixed leapfrog scheme provides a good precision and needs no expensive additional computational time. The chaoticity of the system can lead to fast iterative convergence and improve the computational efficiency. Because symplectic integrators have no secular change in the energy errors, can give more reliable dynamical information from gravitational waves. See Phys. Rev. D 82, 124040 (2010) for more information. In sum, we have confirmed that the dynamics of the spinning compact binaries can not be determined uniquely by the dynamical parameters, initial conditions, and initial spin angles. Instead, a combination of them is a sourse for causing chaos. These support the results of Wu and Xie (Phys. Rev. D 77, 103012 (2008)).Finally, the gravitational waveforms from chaotic orbits are proved to be stochastic.

Zhong, S. Y.

2012-03-01

286

Dynamic susceptibility evidence of surface spin freezing in ultrafine NiFe2O4 nanoparticles.

We investigated the dynamic behavior of ultrafine NiFe2O4 nanoparticles (average size D = 3.5 nm) that exhibit anomalous low temperature magnetic properties such as low saturation magnetization and high-field irreversibility in both M(H) and ZFC-FC processes. Besides the expected blocking of the superspin, observed at T1 approximately 45 K, the system undergoes a magnetic transition at T2 approximately 6 K. For the latter, frequency- and temperature-resolved dynamic susceptibility data reveal characteristics that are unambiguously related to collective spin freezing: the relative variation (per frequency decade) of the in-phase susceptibility peak temperature is approximately 0.025, critical dynamics analysis yields an exponent znu = 9.6 and a zero-field freezing temperature T(F) = 5.8 K, and, in a magnetic field, T(F)(H) is excellently described by the de Almeida-Thouless line delta T(F) = 1 - T(F)(H)/T(F) alpha H(2/3). Moreover, out-of-phase susceptibility versus temperature datasets collected at different frequencies collapse on a universal dynamic scaling curve. All these observations indicate the existence of a spin-glass-like surface layer that surrounds the superparamagnetic core and undergoes a transition to a frozen state upon cooling below 5.8 K. PMID:19809109

Tackett, Ronald J; Bhuiya, Abdul W; Botez, Cristian E

2009-11-01

287

On the key role of a dynamical estimate of the Solar spin and gravitational multipole moments

NASA Astrophysics Data System (ADS)

We review the question of the solar quadrupole moment (J2) which is at the crossroad of solar physics, astrometry and celestial mechanics. The order of magnitude of J2 is known to be 10-7. Precise estimates, however, strongly depend on the method used: stellar equations combined with a differential rotation model, the Theory of Figures of the Sun, or inversion techniques applied to helioseismology. A variability of J2 with the solar cycle is even considered. Nevertheless, a precise value of J2 is useful to compute dynamical effects like light deflection in the vicinity of the Sun, or in planetary ephemeris. Conversely, a precise dynamical estimate of J2 might be crucial to constrain solar density and rotation models. The future space missions GAIA and BepiColombo should lead to a dynamical estimate of J2, decorrelated from the Post-Newtonian parameter ?. A dynamical relativistic Post-Newtonian modeling of planetary motions, including not only the solar quadrupole moment but also its spin, might lead to interesting constraints on those two key solar parameters, via analysis of spin-orbit couplings and of the stability of the Solar System modelled.

Pireaux, S.; Rozelot, J.-P.

2005-12-01

288

Ground states and dynamics of spin-orbit-coupled Bose-Einstein condensates

We study analytically and asymptotically as well as numerically ground states and dynamics of two-component spin-orbit-coupled Bose-Einstein condensates (BECs) modeled by the coupled Gross-Pitaevskii equations (CGPEs). In fact, due to the appearance of the spin-orbit (SO) coupling in the two-component BEC with a Raman coupling, the ground state structures and dynamical properties become very rich and complicated. For the ground states, we establish the existence and non-existence results under different parameter regimes, and obtain their limiting behaviors and/or structures with different combinations of the SO and Raman coupling strengths. For the dynamics, we show that the motion of the center-of-mass is either non-periodic or with different frequency to the trapping frequency when the external trapping potential is taken as harmonic and the initial data is chosen as a stationary state (e.g. ground state) with a shift, which is completely different from the case of a two-component BEC without the SO coupling, and obtain the semiclassical limit of the CGPEs in the linear case via the Wigner transform method. Efficient and accurate numerical methods are proposed for computing the ground states and dynamics, especially for the case of box potentials. Numerical results are reported to demonstrate the efficiency and accuracy of the numerical methods and show the rich phenomenon in the SO-coupled BECs.

Weizhu Bao; Yongyong Cai

2014-07-22

289

Long-time-scale dynamics of spin textures in a degenerate F=1 {sup 87}Rb spinor Bose gas

We investigate the long-term dynamics of spin textures prepared by cooling unmagnetized spinor gases of F=1 {sup 87}Rb to quantum degeneracy, observing domain coarsening and a strong dependence of the equilibration dynamics on the quadratic Zeeman shift q. For small values of |q|, the textures arrive at a configuration independent of the initial spin-state composition, characterized by large length-scale spin domains and the establishment of easy-axis (negative q) or easy-plane (positive q) magnetic anisotropy. For larger |q|, equilibration is delayed as the spin-state composition of the degenerate spinor gas remains close to its initial value. These observations support the mean-field equilibrium phase diagram predicted for a ferromagnetic spinor Bose-Einstein condensate and also illustrate that equilibration is achieved under a narrow range of experimental settings, making the F=1 {sup 87}Rb gas more suitable for studies of nonequilibrium quantum dynamics.

Guzman, J.; Jo, G.-B.; Murch, K. W.; Thomas, C. K. [Department of Physics, University of California, Berkeley, California 94720 (United States); Wenz, A. N. [Department of Physics, University of California, Berkeley, California 94720 (United States); Physikalisches Institut, Ruprecht-Karls-Universitaet Heidelberg, D-69120 Heidelberg (Germany); Stamper-Kurn, D. M. [Department of Physics, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2011-12-15

290

Time-resolved x-ray imaging of magnetization dynamics in spin-transfer torque devices

Time-resolved x-ray imaging techniques have recently demonstrated the capability to probe the magnetic switching of nanoscale devices. This technique has enabled, for example, the direct observation of the nonuniform intermediate states assumed by the magnetic free layer during reversal by a spin-polarized current. These experiments have shown an interesting size-dependent behavior associated with the motion of vortices to mediate the magnetization reversal which cannot be explained by the macrospin picture of spin-torque switching. In this paper we present both experimental and analytical results which show the origin of the complex switching behavior. We use time-resolved x-ray microscopy to further study the switching behavior of samples with 45{sup o} angle between the free and polarizing magnetic layers. A model is developed in terms of a linearized Landau-Lifshitz-Gilbert equation showing that the initial dynamics is dominated by the balance between the Oersted field and thermal fluctuations. The spin torque amplifies this dynamics, leading to a strong sensitivity to sample size, angle, and temperature. The model is in good agreement with current and previous experimental observations.

Chembrolu, V.

2010-02-24

291

Tracking protein dynamics with photoconvertible Dendra2 on spinning disk confocal systems.

Understanding the dynamic properties of cellular proteins in live cells and in real time is essential to delineate their function. In this context, we introduce the Fluorescence Recovery After Photobleaching-Photoactivation unit (Andor) combined with the Nikon Eclipse Ti E Spinning Disk (Andor) confocal microscope as an advantageous and robust platform to exploit the properties of the Dendra2 photoconvertible fluorescent protein (Evrogen) and analyse protein subcellular trafficking in living cells. A major advantage of the spinning disk confocal is the rapid acquisition speed, enabling high temporal resolution of cellular processes. Furthermore, photoconversion and imaging are less invasive on the spinning disk confocal as the cell exposition to illumination power is reduced, thereby minimizing photobleaching and increasing cell viability. We have tested this commercially available platform using experimental settings adapted to track the migration of fast trafficking proteins such as UBC9, Fibrillarin and have successfully characterized their differential motion between subnuclear structures. We describe here step-by-step procedures, with emphasis on cellular imaging parameters, to successfully perform the dynamic imaging and photoconversion of Dendra2-fused proteins at high spatial and temporal resolutions necessary to characterize the trafficking pathways of proteins. PMID:25186063

Woods, Elena; Courtney, Jane; Scholz, Dimitri; Hall, William W; Gautier, Virginie W

2014-12-01

292

Analytical approach to the dynamics of facilitated spin models on random networks

NASA Astrophysics Data System (ADS)

Facilitated spin models were introduced some decades ago to mimic systems characterized by a glass transition. Recent developments have shown that a class of facilitated spin models is also able to reproduce characteristic signatures of the structural relaxation properties of glass-forming liquids. While the equilibrium phase diagram of these models can be calculated analytically, the dynamics are usually investigated numerically. Here we propose a network-based approach, called approximate master equation (AME), to the dynamics of the Fredrickson-Andersen model. The approach correctly predicts the critical temperature at which the glass transition occurs. We also find excellent agreement between the theory and the numerical simulations for the transient regime, except in close proximity of the liquid-glass transition. Finally, we analytically characterize the critical clusters of the model and show that the departures between our AME approach and the Monte Carlo can be related to the large interface between blocked and unblocked spins at temperatures close to the glass transition.

Fennell, Peter G.; Gleeson, James P.; Cellai, Davide

2014-09-01

293

COMPETING SPIN WAVES AND SUPERCONDUCTING

Duisburg, Germany c Institute of Applied Physics, Moldova Academy of Sciences, Chisinau 2028, Moldova d Technical University, Chisinau 2004, Moldova (Received ...) Abstract A special diagram technique recently

Entel, P.

294

An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba(1-x)K(x)Fe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials. PMID:24762657

Yi, M; Zhang, Y; Liu, Z-K; Ding, X; Chu, J-H; Kemper, A F; Plonka, N; Moritz, B; Hashimoto, M; Mo, S-K; Hussain, Z; Devereaux, T P; Fisher, I R; Wen, H H; Shen, Z-X; Lu, D H

2014-01-01

295

Ultrafast infrared studies of the role of spin states in organometallic reaction dynamics.

The importance of spin state changes in organometallic reactions is a topic of significant interest, as an increasing number of reaction mechanisms involving changes of spin state are consistently being uncovered. The potential influence of spin state changes on reaction rates can be difficult to predict, and thus this class of reactions remains among the least well understood in organometallic chemistry. Ultrafast time-resolved infrared (TRIR) spectroscopy provides a powerful tool for probing the dynamics of spin state changes in organometallic catalysis, as such processes often occur on the picosecond to nanosecond time scale and can readily be monitored in the infrared via the absorptions of carbonyl reporter ligands. In this Account, we summarize recent work from our group directed toward identifying trends in reactivity that can be used to offer predictive insight into the dynamics of coordinatively unsaturated organometallic reaction intermediates. In general, coordinatively unsaturated 16-electron (16e) singlets are able to coordinate to solvent molecules as token ligands to partially stabilize the coordinatively unsaturated metal center, whereas 16e triplets and 17-electron (17e) doublets are not, allowing them to diffuse more rapidly through solution than their singlet counterparts. Triplet complexes typically (but not always) undergo spin crossover prior to solvent coordination, whereas 17e doublets do not coordinate solvent molecules as token ligands and cannot relax to a lower spin state to do so. 16e triplets are typically able to undergo facile spin crossover to yield a 16e singlet where an associative, exothermic reaction pathway exists. The combination of facile spin crossover with faster diffusion through solution for triplets can actually lead to faster catalytic reactivity than for singlets, despite the forbidden nature of these reactions. We summarize studies on odd-electron complexes in which 17e doublets were found to display varying behavior with regard to their tendency to react with 2-electron donor ligands to form 19-electron (19e) adducts. The ability of 19e adducts to serve as reducing agents in disproportionation reactions depends on whether the excess electron density localized at the metal center or at a ligand site. The reactivity of both 16e and 17e complexes toward a widely used organic nitroxyl radical (TEMPO) are reviewed, and both classes of complexes generally react similarly via an associative mechanism with a low barrier to these reactions. We also describe recent work targeted at unraveling the photoisomerization mechanism of a thermal-solar energy storage complex in which spin state changes were found to play a crucial role. Although a key triplet intermediate was found to be required for this photoisomerization mechanism to proceed, the details of why this triplet is formed in some complexes (those based on ruthenium) and not others (those based on iron, molybdenum, or tungsten) remains uncertain, and further exploration in this area may lead to a better understanding of the factors that influence intramolecular and excited state spin state changes. PMID:24819619

Lomont, Justin P; Nguyen, Son C; Harris, Charles B

2014-05-20

296

A Comparison Study of Magnetic Bearing Controllers for a Fully Suspended Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

NASA Glenn Research Center (GRC) has developed a fully suspended magnetic bearing system for the Dynamic Spin Rig (DSR) that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust bearing and the associated control system were integrated into the DSR to provide noncontact magnetic suspension and mechanical excitation of the 35 lb vertical rotor with blades to induce turbomachinery blade vibration. A simple proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked very well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, and energy savings for the system. The test results of a variety of controllers we demonstrated up to the rig's maximum allowable speed of 10,000 rpm are shown.

Choi, Benjamin; Johnson, Dexter; Morrison, Carlos; Mehmed, Oral; Huff, Dennis (Technical Monitor)

2002-01-01

297

Langevin spin dynamics based on ab initio calculations: numerical schemes and applications.

A method is proposed to study the finite-temperature behaviour of small magnetic clusters based on solving the stochastic Landau-Lifshitz-Gilbert equations, where the effective magnetic field is calculated directly during the solution of the dynamical equations from first principles instead of relying on an effective spin Hamiltonian. Different numerical solvers are discussed in the case of a one-dimensional Heisenberg chain with nearest-neighbour interactions. We performed detailed investigations for a monatomic chain of ten Co atoms on top of a Au(0?0?1) surface. We found a spiral-like ground state of the spins due to Dzyaloshinsky-Moriya interactions, while the finite-temperature magnetic behaviour of the system was well described by a nearest-neighbour Heisenberg model including easy-axis anisotropy. PMID:24806308

Rózsa, L; Udvardi, L; Szunyogh, L

2014-05-28

298

Correlated projection operator approach to non-Markovian dynamics in spin baths

The dynamics of an open quantum system is usually studied by performing a weak-coupling and weak-correlation expansion in the system-bath interaction. For systems exhibiting strong couplings and highly non-Markovian behavior this approach is not justified. We apply a recently proposed correlated projection superoperator technique to the model of a central spin coupled to a spin bath via full Heisenberg interaction. Analytical solutions to both the Nakajima-Zwanzig and the time-convolutionless master equation are determined and compared with the results of the exact solution. The correlated projection operator technique significantly improves the standard methods and can be applied to many physical problems such as the hyperfine interaction in a quantum dot.

Fischer, Jan [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany); Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel (Switzerland); Breuer, Heinz-Peter [Physikalisches Institut, Universitaet Freiburg, Hermann-Herder-Strasse 3, D-79104 Freiburg (Germany)

2007-11-15

299

Dynamical splayed ferromagnetic ground state in the quantum spin ice Yb(2)Sn(2)O(7).

From magnetic, specific heat, (170)Yb Mössbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb(2)Sn(2)O(7), we show that below the first order transition at 0.15 K all of the Yb(3+) ions are long-range magnetically ordered and each has a moment of 1.1 ?(B) which lies at ? 10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [Phys. Rev. Lett. 108, 037202 (2012)] for a pyrochlore lattice of Kramers 1/2 effective spins. PMID:25166842

Yaouanc, A; Dalmas de Réotier, P; Bonville, P; Hodges, J A; Glazkov, V; Keller, L; Sikolenko, V; Bartkowiak, M; Amato, A; Baines, C; King, P J C; Gubbens, P C M; Forget, A

2013-03-22

300

Spin dynamics in the geometrically frustrated multiferroic CuCrO2

NASA Astrophysics Data System (ADS)

The spin dynamics of the geometrically frustrated triangular antiferromagnet multiferroic CuCrO2 have been mapped out using inelastic neutron scattering. The relevant spin Hamiltonian parameters modeling the incommensurate modulated helicoid have been determined, and correspond to antiferromagnetic nearest- and next-nearest-neighbor interactions in the ab plane with a strong planar anisotropy. The weakly dispersive excitation along c reflects the essentially two-dimensional character of the magnetic interactions. Classical energy calculations clearly point out the relevance of the balance between the adjacent planes coupling, the in-plane nearest-neighbor interactions anisotropy, and a weakly antiferromagnetic next-nearest-neighbor interaction, in stabilizing the three-dimensional magnetic order in CuCrO2 .

Poienar, M.; Damay, F.; Martin, C.; Robert, J.; Petit, S.

2010-03-01

301

Dynamics of chiral oscillations - A comparative analysis with spin-flipping

Chiral oscillation as well as spin flipping effects correspond to quantum phenomena of fundamental importance in the context of particle physics and, in particular, of neutrino physics. From the point of view of first quantized theories, we are specifically interested in appointing the differences between chirality and helicity by obtaining their dynamic equations for a fermionic Dirac-type particle (neutrino). We also identify both effects when the non-minimal coupling with an external (electro)magnetic field in the neutrino interacting Lagrangian is taken into account. We demonstrate that, however, there is no constraint between chiral oscillations, when it takes place in vacuum, and the process of spin flipping related to the helicity quantum number, which does not take place in vacuum. To conclude, we show that the origin of chiral oscillations (in vacuum) can be interpreted as position very rapid oscillation projections onto the longitudinal direction of momentum.

Alex E. Bernardini

2005-11-18

302

NASA Astrophysics Data System (ADS)

A spin version of dynamical mean-field theory is extended for magnetically ordered states in the Heisenberg model. The self-consistency equations are solved with high numerical accuracy by means of the continuous-time quantum Monte Carlo with bosonic baths coupled to the spin. The resultant solution is critically tested by known physical properties. In contrast with the mean-field theory, soft paramagnons appear near the transition temperature. Moreover, the Nambu-Goldstone mode (magnon) in the ferromagnetic phase is reproduced reasonably well. However, antiferromagnetic magnons have an energy gap in contradiction to the Nambu-Goldstone theorem. The origin of this failure is discussed in connection with the artificial first-order nature of the transition.

Otsuki, Junya; Kuramoto, Yoshio

2013-07-01

303

Field dependent spin dynamics in Dysprosium2Titanium2Oxygen7

NASA Astrophysics Data System (ADS)

We have studied the field dependent magnetic properties of three crystalline directions of the spin ice material Dy2Ti 2O7---the [100], [110], and [111] directions. Comprehensive magnetization and ac susceptibility data were taken in the temperature range 1.8 K < T < 7 K at fields of up to H = 4 T in the frequency range from dc to f = 10 kHz. We found that crystalline anisotropy plays an important role in determining the spin dynamics in this temperature and magnetic field regime, as well as surprising features presenting in the kHz frequency range where the ac measurement is performed faster than the characteristic relaxation time of the system. In particular, the [110] direction showed a distinct region of freezing into the "spin-chain" state and the [111] direction showed a distinct "kagome-ice" region, as well as an unexpected peak at higher frequencies---remnant of the first-order phase transition at lower temperatures. The [110] and [111] crystalline directions were determined to be of enough interest to extend to lower temperature using a much more difficult dilution refrigerator experiment. Two large crystals were provided by groups at Universidad Nacional de La Plata -CONICET, Argentina, and University of Oxford, United Kingdom, respectively, for the additional purpose of probing the spatial variation inside the crystal (as opposed to measuring the whole crystal as is traditionally done in ac susceptibility experiments). Differences between the end and the center of the crystals were observed in an applied field and approaching the higher frequency measurement limit. Additionally, two more projects are presented on the related materials Tb2Ti2O7 and Tb2Ti2-xSn xO7. The former was lead by Sean Giblin and Peter Baker from ISIS, and the latter by Maria Dahlberg from the Pennsylvania State University. A search for the magnetization plateau associated with the quantum spin ice state was the motivation behind the Tb2Ti2O7 study; however, only unusual dynamics in a regime that coincided with muon results were found. Thus, the set of materials Tb2Ti2-xSn xO7 provided an excellent way to probe the interactions that determine the nature of the low-temperature phase (soft spin ice or spin liquid, in this case), and several intermediate states of interest were found.

Matthews, Maria Jane

304

Effect of hawk-dove game on the dynamics of two competing species.

Outcomes of interspecific competition, and especially the possibility of coexistence, have been extensively studied in theoretical ecology because of their implications in community assemblages. During the last decades, the influence of different time scales through the local/regional dynamics of animal communities has received an increasing attention. Nevertheless, different time scales involved in interspecific competition can result form other processes than spatial dynamics. Here, we envision and analyze a new theoretical framework that couples a game theory approach for competition with a demographic model. We take advantage of these two time scales to derive a reduced model governing the total densities of the two populations and we study how these two time scales interfere and influence outcomes of species competition. We find that a competition process occurring on a faster time scale than demography yields a "priority effect" where the first species introduced outcompetes the other one. We then confirm previous findings stipulating that species coexistence is favored by large difference in time scales because the extinction/recolonization process. Our results then highlight that an integration of demographic and competition time scales at both local and regional levels is mandatory to explain communities assemblages and should become a research priority. PMID:24908380

Moussaoui, Ali; Auger, Pierre; Roche, Benjamin

2014-09-01

305

Spin-orbit effects on the full dynamics of double quantum dot qubit states

NASA Astrophysics Data System (ADS)

We study spin-obit interaction (SOI) and relaxation effects on the measurement of the extended singlet state return probability P(S) in a double quantum dot (DQD) system with two electrons, in the presence of hyperfine interaction (HFI) and weak external magnetic fields. Using appropriate pulse cycles to change the detuning between the two quantum dots, we describe the full dynamical behavior of the system taking into account the complete set of states. We find that the mixing of the ms=1;(T+) triplet with the (0,2) local singlet, induced by SOI via non-spin-conserving tunneling transitions, has an important effect on the measurement of P(S), and a clear experimental signature. The numerical results are also analyzed in terms of a Feshbach projection to the effective low-energy dynamics, which explain the role of SOI on the relaxation and overall dynamics relevant in experiments. We also explore the case of the Landau-Zener-St"uckelberg interferometry realized via voltage sweeps through the S-T+anticrossing generated by HFI in the DQD energy spectrum [1]. We focus on studying the effects of SOI and relaxation on the interferometric properties of the system in this regime. [1] J.R. Petta, H. Lu and A.C. Gossard, Science 327, 669 (2010).

Cota, Ernesto; Rolon, Juan E.; Platero, Gloria; Ulloa, Sergio E.

2012-02-01

306

Spin Dynamics Simulations of Multiple Echo Spacing Pulse Sequences in Grossly Inhomogeneous Fields

NASA Astrophysics Data System (ADS)

Pulse sequences with multiple lengths of echo spacings are used in oilfield NMR logging for diffusion-based NMR applications such as rock and fluid characterization. One specific implementation is the so-called diffusion editing sequence comprising two long echo spacings followed by a standard CPMG at a shorter echo spacing. The echoes in the CPMG portion contain signal from both the direct and stimulated echoes. Modern oilfield NMR logging tools are designed for continuous depth logging of earth formations by projecting both the static (B0) and dynamic (B1) fields into the formation. Both B0 and B1 profiles are grossly inhomogeneous which results in non-steady-state behavior in the early echoes. The spin dynamics effects present a challenge for processing the echo amplitudes to measure porosity (amplitude extrapolated to zero time) and attenuations for fluid or pore size characterization. In this work we describe a calculation of the spin dynamics of the diffusion editing sequence with two long echo spacings. The calculation takes into account full B1 and B0 field maps, and comparisons will be made for sensors and parameters typical of oilfield logging tools and environments.

Heidler, R.; Bachman, H. N.; Johansen, Y.

2008-12-01

307

Do Bitcoins make the world go round? On the dynamics of competing crypto-currencies

Bitcoins have emerged as a possible competitor to usual currencies, but other crypto-currencies have likewise appeared as competitors to the Bitcoin currency. The expanding market of crypto-currencies now involves capital equivalent to $10^{10}$ US Dollars, providing academia with an unusual opportunity to study the emergence of value. Here we show that the Bitcoin currency in itself is not special, but may rather be understood as the contemporary dominating crypto-currency that may well be replaced by other currencies. We suggest that perception of value in a social system is generated by a voter-like dynamics, where fashions form and disperse even in the case where information is only exchanged on a pairwise basis between agents.

Bornholdt, Stefan

2014-01-01

308

Subnanosecond radical pair (RP) formation by electron transfer from an excited singlet state or by bond breaking produces two correlated spins coupled by their spin-spin exchange (J) and magnetic dipole (D) interactions. In the high magnetic field limit, the two-spin system can be described by a singlet state (S) and three triplet states (T?, T(+1), T(-1)). When J is small relative to the electron Zeeman interaction, |T?? is the only triplet state that is populated by coherent spin mixing with the |S? state because the |T(+1)? and |T(-1)? states are well-separated from |S? by a large energy gap. Herein, we describe the spin dynamics for RPs having restricted geometries in which J is similar in magnitude to the electron Zeeman interaction and does not fluctuate significantly. Under these circumstances, depending on the sign of J, the energies of |T(+1)? or |T(-1)? are close to that of |S? so that weak isotropic electron-nuclear hyperfine coupling leads to population of |T(+1)? or |T(-1)?. An approximate relationship for the triplet quantum yield is developed for a RP in the large J regime, where one or both electrons interact with nearby spin-1/2 nuclei. This relationship also yields the net spin polarization transfer to the nuclear spins. PMID:24870373

Zarea, Mehdi; Carmieli, Raanan; Ratner, Mark A; Wasielewski, Michael R

2014-06-19

309

Despite the concept of nuclear spin isomers (NSIs) exists since the early days of quantum mechanics, only few approaches have been suggested to separate different NSIs. Here, a method is proposed to discriminate different NSIs of a quinodimethane derivative using its electronic excited state dynamics. After electronic excitation by a laser field with femtosecond time duration, a difference in the behavior of several quantum mechanical operators can be observed. A pump-probe experimental approach for separating these different NSIs is then proposed. PMID:25362315

Obaid, Rana; Kinzel, Daniel; Oppel, Markus; González, Leticia

2014-10-28

310

Calibration of the spin-scan ozone imager aboard the dynamics Explorer 1 satellite

NASA Technical Reports Server (NTRS)

The calibration technique, which contains the calibrated backscattered radiance values necessary for performing the calibrations, is presented. The calibration constants for September to October 1981 to determine total columnar ozone from the Spin-Scan Ozone Imager (SOI), which is a part of the auroral imaging instrumentation aboard the Dynamics Explorer 1 Satellite, are provided. The precision of the SOI-derived total columnar ozone is estimated to be better than 2.4 percent. Linear regression analysis was used to calculate correlation coefficients between total columnar ozone obtained from Dobson ground stations and SOI which indicate that the SOI total columnar ozone determination is equally accurate for clear or cloudy weather conditions.

Bressette, Walter E.; Keating, Gerald M.; Young, David F.

1987-01-01

311

Entanglement and dynamics of spin-chains in periodically-pulsed magnetic fields: accelerator modes

We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counter-propagating coherent states are ejected from the centre of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the Quantum Kicked Rotor (QKR). From this we can analyse the entanglement production and interpret the ejected coherent states as a manifestation of so-called `accelerator modes' of a classically chaotic system.

T. Boness; S. Bose; T. S. Monteiro

2006-02-13

312

NASA Astrophysics Data System (ADS)

Using a ``noise-vocoder'' cochlear implant simulator [Shannon et al., Science 270, 303-304 (1995)], the effect of the speed of dynamic range compression on speech intelligibility was assessed, using normal-hearing subjects. The target speech had a level 5 dB above that of the competing speech. Initially, baseline performance was measured with no compression active, using between 4 and 16 processing channels. Then, performance was measured using a fast-acting compressor and a slow-acting compressor, each operating prior to the vocoder simulation. The fast system produced significant gain variation over syllabic timescales. The slow system produced significant gain variation only over the timescale of sentences. With no compression active, about six channels were necessary to achieve 50% correct identification of words in sentences. Sixteen channels produced near-maximum performance. Slow-acting compression produced no significant degradation relative to the baseline. However, fast-acting compression consistently reduced performance relative to that for the baseline, over a wide range of performance levels. It is suggested that fast-acting compression degrades performance for two reasons: (1) because it introduces correlated fluctuations in amplitude in different frequency bands, which tends to produce perceptual fusion of the target and background sounds and (2) because it reduces amplitude modulation depth and intensity contrasts.

Stone, Michael A.; Moore, Brian C. J.

2003-08-01

313

We present computations of certain finite-size scaling functions and universal amplitude ratios in the large-N limit of the CP{sup N-1} field theory. We pay particular attention to the uniform susceptibility, the spin stiffness, and the specific heat. Field theoretic arguments have shown that the long-wavelength description of the phase transition between the Neel and valence-bond solid states in square lattice S=1/2 antiferromagnets is expected to be the noncompact CP{sup 1} field theory. We provide a detailed comparison between our field theoretic calculations and quantum Monte Carlo data close to the Neel-VBS transition on a S=1/2 square-lattice model with competing four-spin interactions (the JQ model)

Kaul, Ribhu K. [Department of Physics, Harvard University, Cambridge, Massachusetts 02138 (United States); Melko, Roger G. [Department of Physics and Astronomy, University of Waterloo, Ontario, N2L 3G1 (Canada)

2008-07-01

314

The purpose of this study was to develop, deliver, and assess relevant interprofessional (IP) simulation experiences for prelicensure students from multiple disciplines in certificate, diploma, and degree programs. Seventy-eight students from four post-secondary institutions participated in either a high-fidelity mannequin postoperative simulation experience (dynamic simulation) or a standardized patient homecare simulation experience (routine simulation). The University of West England Questionnaire was used pre- and post-simulation experience to determine the change in communication and teamwork. Overall, students' perceptions of their communication and teamwork skills increased after completing either simulation. Students from certificate, diploma, and degree programs participating in the same simulations demonstrated improvements on self-report measures of communication and teamwork. The key was creating a simulation learning experience that reflected the realities of practice, rather than the participants' credentials. Placing students in teams that are relevant for practice, rather than grouping them by academic credentials, is necessary and can provide positive learning experiences for all participants, as demonstrated by these results. PMID:25194064

King, Sharla; Carbonaro, Michael; Greidanus, Elaine; Ansell, Dawn; Foisy-Doll, Colette; Magus, Sam

2014-01-01

315

NASA Astrophysics Data System (ADS)

Earlier, using the slave-boson representation of the t-J Hamiltonian which properly introduces the coupling of both the charge and spin degrees of freedom, we were able to successfully predict the "arch" shaped bose condensation line in the phase diagram of high Tc superconductivity, in agreement with observations [1]. Encouraged from this study, we examine both the charge and spin dynamics, that is, the optical conductivity and spin susceptability of high Tc cuprates as a function of hole doping rate and temperature. It is shown that in both cases the computed results are consistent with observations. In the present study we will discuss the physics of involving both the charge and spin degrees of freedom for the explanation of the observed optical conductivity and spin susceptability. 1.Sung-Sik Lee abd Sung-Ho Suck Salk, Physica C, in press: (cond-mat/0001218); (cond-mat/9905268); (cond-mat/9907226)

Salk, Sung-Ho Suck; Lee, Sung-Sik; Eom, Jae-Hyun; Kim, Ki-Seok

2001-03-01

316

Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM Rings by NMR

In this thesis, our main interest has been to investigate the spin dynamics and quantum tunneling in single molecule magnets (SMMs), For this we have selected two different classes of SMMs: a ferrimagnetic total high spin S = 10 cluster Fe8 and antiferromagnetic (AFM) ring-type clusters. For Fe8, our efforts have been devoted to the investigation of the quantum tunneling of magnetization in the very low temperature region. The most remarkable experimental finding in Fe8 is that the nuclear spin-lattice relaxation rate (1/T{sub l}) at low temperatures takes place via strong collision mechanism, and thus it allows to measure directly the tunneling rate vs T and H for the first time. For AFM rings, we have shown that 1/T{sub l} probes the thermal fluctuations of the magnetization in the intermediate temperature range. We find that the fluctuations are dominated by a single characteristic frequency which has a power law T-dependence indicative of fluctuations due to electron-acoustic phonon interactions.

Seung-Ho-Baek

2004-12-19

317

Silicon spin chains at finite temperature: Dynamics of Si(553)-Au

NASA Astrophysics Data System (ADS)

When gold is deposited on Si(553), the surface self-assembles to form a periodic array of steps with nearly perfect structural order. In scanning tunneling microscopy these steps resemble quasi-one-dimensional atomic chains. At temperatures below ˜50 K the chains develop a tripled periodicity. We recently predicted, on the basis of density-functional theory calculations at T=0, that this tripled periodicity arises from the complete polarization of the electron spin on every third silicon atom along the step; in the ground state these linear chains of silicon spins are antiferromagnetically ordered. Here we explore, using ab initio molecular dynamics and kinetic Monte Carlo simulations, the behavior of silicon spin chains on Si(553)-Au at finite temperature. Thermodynamic phase transitions at T>0 in one-dimensional systems are prohibited by the Mermin-Wagner theorem. Nevertheless we find that a surprisingly sharp onset occurs upon cooling—at about 30 K for perfect surfaces and at higher temperature for surfaces with defects—to a well-ordered phase with tripled periodicity, in good agreement with experiment.

Erwin, Steven C.; Snijders, Paul C.

2013-06-01

318

Kerr rotation studies of single electron spin dynamics in a quantum dot

NASA Astrophysics Data System (ADS)

Kerr rotation measurements are used to directly and non-destructively probe the dynamics of a single electron spin in a charge-tunable quantum dot. The dot is formed by interface fluctuations of a GaAs quantum well and embedded in a vertical optical cavity. Using Hanle techniques, we perform single electron Kerr rotation measurements at T=10K in order to monitor the depolarization of an optically pumped electron spin within an applied transverse magnetic field. This reveals information about the time averaged transverse spin lifetime, T2^*. At gate voltages for which the charging rate of the dot is relatively low, the results yield a T2^* in agreement with values expected from the hyperfine interaction in these materials. In contrast, at larger charging rates, we find that T2^* is strongly reduced, indicating the importance of additional decoherence mechanisms in that regime. J. Berezovsky, M. H. Mikkelsen, O. Gywat, N. G. Stoltz, L. A. Coldren, and D. D. Awschalom,Science Express, 9 November 2006, (10.1126/science.1133862).

Mikkelsen, M. H.; Berezovsky, J.; Gywat, O.; Stoltz, N. G.; Coldren, L. A.; Awschalom, D. D.

2007-03-01

319

ERIC Educational Resources Information Center

This study discusses the significance of emotional intelligence and intercultural communication competence in globally diverse classroom settings. Specifically, the research shows a correlation between degrees of emotional intelligence and human communication competence (age, gender, and culture). The dataset consists of 364 participants. Nearly…

Washington, Melvin C.; Okoro, Ephraim A.; Okoro, Sussie U.

2013-01-01

320

?-Lactoglobulin (?-LG) is a member of the lipocalin protein family involved in the transport of fatty acids and other small hydrophobic molecules. The main binding site is at a central cavity, referred to as "calyx", formed by the protein ?-barrel sandwich. Continuous-wave and pulsed Fourier transform electron spin resonance (cw- and FT-EPR) spectroscopy and molecular dynamics (MD) simulation were combined to investigate the interaction of fatty acids with bovine ?-LG. Stearic acid bearing the nitroxide label at different positions, n, along the acyl chain (n-SASL, n = 5, 7, 10, 12, 16) were used. The EPR data show that the protein affinity for SASL decreases on going from n = 5 to 16. This behavior is due to the accommodation of the SASL in the protein calyx, which is hampered by steric hindrance of the doxyl ring for n ? 10, as evidenced by MD data. Conformation and dynamics of 5-SASL are similar to those of the unlabeled stearate molecule. 5-SASL in the protein binding site undergoes librational motion of small amplitude on the nanosecond time scale at cryogenic temperature and rotational dynamics with correlation time of 4.2 ns at physiological temperature. The results highlight the dynamical features of fatty acids/?-LG interaction. PMID:22950964

Guzzi, Rita; Rizzuti, Bruno; Bartucci, Rosa

2012-09-27

321

We study semiclassical dynamics of anisotropic Heisenberg models in two and three dimensions. Such models describe lattice spin systems and hard core bosons in optical lattices. We solve numerically Landau-Lifshitz type equations on a lattice and show that in the phase diagram of magnetization and interaction anisotropy, one can identify several distinct regimes of dynamics. These regions can be distinguished based on the character of one dimensional solitonic excitations, and stability of such solitons to transverse modulation. Small amplitude and long wavelength perturbations can be analyzed analytically using mapping of non-linear hydrodynamic equations to KdV type equations. Numerically we find that properties of solitons and dynamics in general remain similar to our analytical results even for large amplitude and short distance inhomogeneities, which allows us to obtain a universal dynamical phase diagram. As a concrete example we study dynamical evolution of the system starting from a state with magnetization step and show that formation of oscillatory regions and their stability to transverse modulation can be understood from the properties of solitons. In regimes unstable to transverse modulation we observe formation of lump type solutions with modulation in all directions. We discuss implications of our results for experiments with ultracold atoms.

E. Demler; A. Maltsev; A. Prokofiev

2012-01-30

322

Borehole temperature response for competing models of Laurentide ice sheet dynamics

NASA Astrophysics Data System (ADS)

Borehole temperature profiles (BTP) are not only the source for estimates of the background geothermal heat flow, but also allow the reconstruction of past surface temperature changes. Though shallow boreholes (e. g. less than 500 m) are abundant in most continental areas, their use is inhibited by the necessity of extracting the paleoclimatic signal present in the borehole temperature at any depth. However, assuming a long-term ground surface temperature history (GSTH), a generalized reduced temperature may be used for the interpretation of the shallow observations. To derive or test the required assumptions, very deep boreholes (say, > 2000 m) are highly important also for the investigation of shallow measurements. In areas which were influenced by the Last Glacial Period (LGP), the existence of the large scale ice sheets (e.g. the Laurentide or Weichselian), the spatial distribution of basal conditions, and the timing of their retreat have a major influence on the subsurface temperature regime. Though for parts of its history no longer directly related to atmospheric temperature, deep BTPs carry information on basal conditions, oceanic transgressions, and retreat histories, and can thus contribute to the confirmation/rejection, or even calibration of ice sheet models. From this it follows that a meaningful interpretation of the paleoclimatic signal can only proceed with a reasonable understanding of the regional ice sheet behavior, and, in order to quantify the effects, a calibrated numerical ice sheet model. From such a model, synthetic long term GSTHs may be generated, which can subsequently be used to derive the generalized reduced temperatures for the shallow BTPs. This approach is challenging in several aspects: (1) high-resolution, high-order/hybrid ice sheet models are only now emerging, and the physics at the base (e.g. ice streams) needs improvement; (2) a calibration in the sense of a Bayesian inverse problem are rare, and (3) appropriate sets of borehole data (including the corresponding metadata) still have to be collected and need to undergo strict quality control before being used. In addition, a methodological concept fora regional interpretation is missing. In this contribution we will compare the borehole temperature response for two ice sheet models of the Laurentide glaciation, differing in their dynamics. Both were realized by running the hybrid SIA/SSA code GRISLI in different modes. The subsurface temperature anomalies thus generated are significant. Unfortunately the existing deep boreholes in the area are not placed in areas of high sensitivity (e.g., Northern Quebec, Canadian Archipelago). Notwithstanding these difficulties, we will present results for some of these available boreholes in central and northern Canada and Alaska.

Rath, Volker; Alvarez-Solas, Jorge; Robinson, Alex; Montoya-Redondo, Marisa

2013-04-01

323

Application of a system modification technique to dynamic tuning of a spinning rotor blade

NASA Technical Reports Server (NTRS)

An important consideration in the development of modern helicopters is the vibratory response of the main rotor blade. One way to minimize vibration levels is to ensure that natural frequencies of the spinning main rotor blade are well removed from integer multiples of the rotor speed. A technique for dynamically tuning a finite-element model of a rotor blade to accomplish that end is demonstrated. A brief overview is given of the general purpose finite element system known as Engineering Analysis Language (EAL) which was used in this work. A description of the EAL System Modification (SM) processor is then given along with an explanation of special algorithms developed to be used in conjunction with SM. Finally, this technique is demonstrated by dynamically tuning a model of an advanced composite rotor blade.

Spain, C. V.

1987-01-01

324

Dynamical sectors for a spinning particle in AdS3

NASA Astrophysics Data System (ADS)

We consider the dynamics of a particle of mass M and spin J in AdS3. The study reveals the presence of different dynamical sectors depending on the relative values of M, J and the AdS3 radius R. For the subcritical M2R2-J2>0 and supercritical M2R2-J2<0 cases, it is seen that the equations of motion give the geodesics of AdS3. For the critical case M2R2=J2 there exist extra gauge transformations which further reduce the physical degrees of freedom, and the motion corresponds to the geodesics of AdS2. This result should be useful in the holographic interpretation of the entanglement entropy for two-dimensional conformal field theories with gravitational anomalies.

Batlle, Carles; Gomis, Joaquim; Kamimura, Kiyoshi; Zanelli, Jorge

2014-09-01

325

the spin glass freezing temperature, in order to gain some insight into the process of freezing of spins EXPERIMENTAL STUDIES OF DYNAMICS OF SPIN GLASSES A.P. Murani Institut Lme-Langeuin, B.P. 156X, 38042 Grenob de spectre de temps de relaxation evoluant continuellement avec la temperature et s'dtendant de temps

Boyer, Edmond

326

The co-evolutionary dynamics of directed network of spin market agents

NASA Astrophysics Data System (ADS)

The spin market model [S. Bornholdt, Int. J. Mod. Phys. C 12 (2001) 667] is generalized by employing co-evolutionary principles, where strategies of the interacting and competitive traders are represented by local and global couplings between the nodes of dynamic directed stochastic network. The co-evolutionary principles are applied in the frame of Bak-Sneppen self-organized dynamics [P. Bak, K. Sneppen, Phys. Rev. Lett. 71 (1993) 4083] that includes the processes of selection and extinction actuated by the local (node) fitness. The local fitness is related to orientation of spin agent with respect to the instant magnetization. The stationary regime is formed due to the interplay of self-organization and adaptivity effects. The fat tailed distributions of log-price returns are identified numerically. The non-trivial model consequence is the evidence of the long time market memory indicated by the power-law range of the autocorrelation function of volatility with exponent smaller than one. The simulations yield network topology with broad-scale node degree distribution characterized by the range of exponents 1.3

Horváth, Denis; Kuscsik, Zoltán; Gmitra, Martin

2006-09-01

327

An investigation of the relativistic dynamics of N+1 spin-12 particles placed in an external, homogeneous magnetic field is carried out. The system can represent an atom with a fermion nucleus and N electrons. Quantum electrodynamical interactions, namely, projected Briet and magnetic interactions, are chosen to formulate the relativistic Hamiltonian. The quasi-free-particle picture is retained here. The total pseudomomentum is conserved,

Anirban Misra; Sambhu N. Datta

2005-01-01

328

NASA Technical Reports Server (NTRS)

A simulation study was conducted to investigate aerodynamic modeling methods for prediction of post-stall flight dynamics of large transport airplanes. The research approach involved integrating dynamic wind tunnel data from rotary balance and forced oscillation testing with static wind tunnel data to predict aerodynamic forces and moments during highly dynamic departure and spin motions. Several state-of-the-art aerodynamic modeling methods were evaluated and predicted flight dynamics using these various approaches were compared. Results showed the different modeling methods had varying effects on the predicted flight dynamics and the differences were most significant during uncoordinated maneuvers. Preliminary wind tunnel validation data indicated the potential of the various methods for predicting steady spin motions.

Murch, Austin M.; Foster, John V.

2007-01-01

329

Magnetic order, magnetic correlations, and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7

NASA Astrophysics Data System (ADS)

Er2Ti2O7 is believed to be a realization of an XY antiferromagnet on a frustrated lattice of corner-sharing regular tetrahedra. It is presented as an example of the order-by-disorder mechanism in which fluctuations lift the degeneracy of the ground state, leading to an ordered state. Here we report detailed measurements of the low-temperature magnetic properties of Er2Ti2O7, which displays a second-order phase transition at TN?1.2 K with coexisting short- and long-range orders. Magnetic susceptibility studies show that there is no spin-glass-like irreversible effect. Heat capacity measurements reveal that the paramagnetic critical exponent is typical of a 3-dimensional XY magnet while the low-temperature specific heat sets an upper limit on the possible spin-gap value and provides an estimate for the spin-wave velocity. Muon spin relaxation measurements show the presence of spin dynamics in the nanosecond time scale down to 21 mK. This time range is intermediate between the shorter time characterizing the spin dynamics in Tb2Sn2O7, which also displays long- and short-range magnetic order, and the time scale typical of conventional magnets. Hence the ground state is characterized by exotic spin dynamics. We determine the parameters of a symmetry-dictated Hamiltonian restricted to the spins in a tetrahedron, by fitting the paramagnetic diffuse neutron scattering intensity for two reciprocal lattice planes. These data are recorded in a temperature region where the assumption that the correlations are limited to nearest neighbors is fair.

Dalmas de Réotier, P.; Yaouanc, A.; Chapuis, Y.; Curnoe, S. H.; Grenier, B.; Ressouche, E.; Marin, C.; Lago, J.; Baines, C.; Giblin, S. R.

2012-09-01

330

Critical spin dynamics in Nd1-xSrxMnO3 with x~0.5

NASA Astrophysics Data System (ADS)

Magnetic ion spin dynamics has been investigated in the perovskite manganite Nd1-xSrxMnO3 single crystals at the hole concentrations x of 0.5 and 0.55 by muon spin relaxation (?+SR) spectroscopy. We have observed the critical slowing down of Mn ion spin fluctuations on approaching the ferromagnetic ordering at ~251 K in Nd0.5Sr0.5MnO3. The critical paramagnetic spin fluctuations, measured by the muon spin relaxation rate ?1, exhibit a crossover behavior from exchange critical regime to dipolar critical regime. This crossover is explained by considering the suppression of longitudinal and transverse components of spin susceptibility by dipolar interactions closer to TC and the dipolar vector qD is found to be 0.020(2) Å -1. The dynamic critical exponent z=2.00(12), deduced from muon spin relaxation rates away from TC (nonasymptotic regime), agrees with the experimental and the theoretical results of 3d dipolar ferromagnets. Critical slowing down is not observed in the x=0.55 crystal at the onset of antiferromagnetic ordering at ~220 K. Muon spin relaxation in the x=0.5 crystal (above TN~160 K) and in the x=0.55 crystal (both above and below TN) is root exponential and indicates nondiffusive relaxation mechanism as is in a magnetic glass. The growth of a glasslike relaxation component concomitant with the magnetic ordering has been observed in both the crystals. We suggest that this glassy component originates from those Mn ions located in local regions containing small and differently sized spin clusters.

Krishnamurthy, V. V.; Watanabe, I.; Nagamine, K.; Kuwahara, H.; Tokura, Y.

2000-02-01

331

NASA Astrophysics Data System (ADS)

Can we identify distinct signatures of landscape elements in the event response of soil moisture and soil temperature? Moisture and temperature dynamics in soils are largely controlled by the climatic boundary conditions of rainfall, evapotranspiration and radiation. However, certain landscape features also leave characteristic finger prints on soil moisture and soil temperature time series. The extent of these influences and their time variable relative importance are important in a number of contexts, such as landscape scale prediction of soil moisture patterns or runoff generation, process predictions in ungauged basins or the improvement of hydrological model structures for the mesoscale. The competing influences of geology, land use and topography on temperature and moisture characteristics in the vadose zone are explored at the CAOS hydrological observatory in Luxemburg (http://www.caos-project.de/) with a unique experimental setup of 45 sensor clusters. These sensor clusters cover three different geologies (schist, sandstone, marls), two land use classes (forest and grassland), five different landscape positions (plateau, top-, mid- and lower hillslope as well as near stream/floodplain locations), and contrasting expositions. At each of these sensor clusters three soil moisture profiles with sensors at depths from 10 to 70 cm, four soil temperature profiles as well as air temperature, relative humidity, global radiation, rainfall/throughfall, sapflow and shallow groundwater and stream water levels were measured continuously. Time series of up to 2 years for the schist region and up to 6 months for the complete set of sites allow for a first intercomparison of characteristic event response behavior.

Blume, Theresa; Hassler, Sibylle; Weiler, Markus

2014-05-01

332

Influence of Charge Density Waves and Spin Density Waves on Optical Absorption and Lattice Dynamics.

NASA Astrophysics Data System (ADS)

An incommensurate charge density wave (CDW) arises from, and causes, an extra periodic potential acting on the conduction electrons. The presence of this potential in the one-electron Schrodinger equation results in energy gaps in the energy spectrum E(vec{rm k}) which, for jellium, would have been merely hbar^2k^2/2m. New optical transitions from filled states (below the Fermi level) to empty states (above) lead to a uniaxial absorption (the CDW optical conductivity). This new optical absorption, which has explained the Mayer-El Naby anomaly in metallic potassium, can also explain the anomaly (similar to the Mayer-El Naby) found in bulk metallic sodium. A generalized treatment of the ellipsometric method which recognizes the anisotropy of the CDW absorption in evaporated films can explain the excess absorption just below the Wilson -Butcher threshold for Na films. Spin density waves (SDWs) have built-in charge modulations, equal in magnitude but opposite in sign, for the two spin states. A small shift in the relative phase of the spin-up and spin-down modulations creates an additional charge response, and causes a peak in the response function Q(vec{rm q}) for vec{rm q} near +/-vec{rm Q}, where vec{rm Q} is the SDW wave vector. When this spin-split-phase contribution to Q(vec{rm q}) is incorporated into the theory for phonon spectra of metals, the anomalous depression of the two lower modes near (1/3,1/3,0) for zinc and cadmium can be understood. The dynamic pseudopotential theory for phonons in metals involving the shell model, which divides each ion into an inner core and an outermost filled electron shell, is applied to calculate the phonon spectra of the divalent hexagonal-close-packed (hcp) metals Mg, Zn, and Cd. The outermost filled L shell of sodium, set into oscillation by the electric field of a photon, leads to an extra term in the interband matrix element. This term interferes with the vec{rm A} cdotvec{rm p} term in the Wilson-Butcher tail, and explains the extra optical absorption peak in the ultra-violet.

Xuan, Yashu

333

The purpose of this study was to evaluate the appropriateness of two competing hypotheses concerning reflective and impulsive behavior: anxiety-over-errors or anxiety-over-competence. Eighty-five 8- to 10-year-old children were classified as reflective or impulsive on the basis of their performance on one form of the Matching Familiar Figures Test (MFFT). Half of each cognitive style group was randomly assigned to a

Johnny N. K. Yap; R. De V. Peters

1985-01-01

334

Dynamical decoupling (DD) is an efficient tool for preserving quantum coherence in solid-state spin systems. However, the imperfections of real pulses can ruin the performance of long DD sequences. We investigate the accumulation of pulse errors in DD using the electron spins of phosphorus donors in silicon as a test system. We study periodic DD sequences (PDD) based on spin rotations about two perpendicular axes, and their concatenated and symmetrized versions. We show that pulse errors may quickly destroy some spin components, but maintain other components with high fidelity over long times. Thus, preservation of a single spin component does not always imply efficient DD. Pulse sequences based on spin rotations about $x$ and $y$ axes outperform those based on $x$ and $z$ axes due to the accumulation of pulse errors. Concatenation provides an efficient way to suppress the impact of pulse errors, and can maintain high fidelity for all spin components: pulse errors do not accumulate (to first order) as the con...

Wang, Zhi-Hui; Tyryshkin, A M; Lyon, S A; Ager, J W; Haller, E E; Dobrovitski, V V

2010-01-01

335

Incommensurability and spin dynamics in the low-temperature phases of Ni3V2O8

NASA Astrophysics Data System (ADS)

Magnetic order and low-energy spin dynamics in the zero field ground state of Ni3V2O8 are revealed in elastic and inelastic neutron scattering experiments. Neutron diffraction shows that below T=2.3 K the Ni2+ moments (spin S=1) order in a cycloid pattern with incommensurate wave vector kICM=(0,1,?), where ?=0.4030±0.0004, which is superimposed on a commensurate antiferromagnetic spin arrangement with kCM=(0,0,0). Three spin wave modes are discerned below E˜3 meV in inelastic measurements and qualitatively described by a model Hamiltonian that involves near neighbor exchange, local anisotropy, and a small biquadratic coupling between the spine and cross-tie sites. Results from both elastic and inelastic scattering experiments suggest that the two sublattices on spine and cross-tie sites are largely decoupled.

Ehlers, G.; Podlesnyak, A. A.; Hahn, S. E.; Fishman, R. S.; Zaharko, O.; Frontzek, M.; Kenzelmann, M.; Pushkarev, A. V.; Shiryaev, S. V.; Barilo, S.

2013-06-01

336

NASA Astrophysics Data System (ADS)

Mazur's inequality renders statements about persistent correlations possible. We generalize it in a convenient form applicable to any set of linearly independent constants of motion. This approach is used to show rigorously that a fraction of the initial spin correlations persists indefinitely in the isotropic central spin model unless the average coupling vanishes. The central spin model describes a major mechanism of decoherence in a large class of potential realizations of quantum bits. Thus the derived results contribute significantly to the understanding of the preservation of coherence. We will show that persisting quantum correlations are not linked to the integrability of the model but are caused by a finite operator overlap with a finite set of constants of motion.

Uhrig, Götz S.; Hackmann, Johannes; Stanek, Daniel; Stolze, Joachim; Anders, Frithjof B.

2014-08-01

337

Dynamic behavior of fatty acid spin labels within a binding site of soybean lipoxygenase-1.

The putative substrate-binding site in lipoxygenases is long and internal. There is little direct evidence about how the unsaturated fatty acid substrates enter and move within the cavity to position themselves correctly for electron transfer reactions with the catalytic non-heme iron. An EPR spectroscopy approach, with spin-labeled fatty acids, is taken here to investigate dynamic behavior of fatty acids bound to soybean lipoxygenase-1. The probes are labeled on C5, C8, C10, C12, and C16 of stearic acid. The EPR-determined affinity for the enzyme increases as the length of the alkyl end of the probe increases, with a DeltaDeltaG of -190 cal/methylene. The probes in the series exhibit similar enhanced paramagnetic relaxation by the iron center. These results indicate that the members of the series have a common binding site. All of the bound probes undergo considerable local mobility. The stearate spin-labeled at C5 has the highest affinity for the lipoxygenase, and it is a competitive inhibitor, with a K(i) of 9 muM. Surprisingly, this stearate labeled near the carboxyl end undergoes more local motion than those labeled in the middle of the chain, when it is bound. This shows that the carboxyl end of the fatty-acid spin label is not rigidly docked on the protein. During catalysis, repositioning of the substrate carboxyl on the protein surface may be coupled to motion of portions of the chain undergoing reaction. PMID:17029406

Wu, Fayi; Gaffney, Betty J

2006-10-17

338

In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs) and dynamic magnetic resonance (DMR) to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP) while the BMNs are the anti-CRP bound onto dextran-coated Fe3O4 particles labeled as Fe3O4-antiCRP. It was found the time-dependent spin-spin relaxation time, T2, of protons decreases as time evolves. Additionally, the ?T2 of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 ?g/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL). The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins. PMID:25397920

Liao, Shu-Hsien; Chen, Kuen-Lin; Wang, Chun-Min; Chieh, Jen-Jie; Horng, Herng-Er; Wang, Li-Min; Wu, C H; Yang, Hong-Chang

2014-01-01

339

NASA Astrophysics Data System (ADS)

High-field magnetization and high-frequency electron spin resonance (ESR) are employed to differentiate magnetism between an orthorhombic and a hexagonal majority phase of Ba3CuSb2O9. For the orthorhombic sample, an ESR signal changes its temperature dependence at TS˜200 K, suggesting a static Jahn-Teller (JT) ordering. A magnetization curve follows a power-law behavior M ˜H?m with the exponent ?m=0.72±0.06 for 8

Do, S.-H.; van Tol, J.; Zhou, H. D.; Choi, K.-Y.

2014-09-01

340

Dynamics and hysteresis in square lattice artificial spin-ice G. M. Wysin

-dimensional spin ice materials that exhibit geometrical frustration effects: not all the pair- wise spin-range dipolar forces, which leads to geometrical frustration. Each island is assumed to possess a three, spin-ice, frustration, magnetic hysteresis, susceptibility. I. INTRODUCTION: SQUARE SPIN ICE

Wysin, Gary

341

Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential

We study the exact dynamics of a one-dimensional spin-polarized gas of fermions in a double-well potential at zero and finite temperature. Despite the system being made of noninteracting fermions, its dynamics can be quite complex, showing strongly aperiodic spatio-temporal patterns during the tunneling. The extension of these results to the case of mixtures of spin-polarized fermions interacting with self-trapped Bose-Einstein condensates (BECs) at zero temperature is considered as well. In this case we show that the fermionic dynamics remains qualitatively similar to that observed in the absence of BEC but with the Rabi frequencies of fermionic excited states explicitly depending on the number of bosons and on the boson-fermion interaction strength. From this, the possibility of controlling quantum fermionic dynamics by means of Feshbach resonances is suggested.

Salasnich, L.; Mazzarella, G.; Toigo, F. [Dipartimento di Fisica 'Galileo Galilei' and CNISM, Universita di Padova, Via Marzolo 8, I-35122 Padua (Italy); Salerno, M. [Dipartimento di Fisica 'E.R. Caianiello', CNISM and INFN-Gruppo Collegato di Salerno, Universita di Salerno, Via Ponte don Melillo, I-84084 Fisciano(Italy)

2010-02-15

342

Control Study for Five-axis Dynamic Spin Rig Using Magnetic Bearings

NASA Technical Reports Server (NTRS)

The NASA Glenn Research Center (GRC) has developed a magnetic bearing system for the Dynamic Spin Rig (DSR) with a fully suspended shaft that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust magnetic bearing and the associated control system were integrated into the DSR to provide magnetic excitation as well as non-contact mag- netic suspension of a 15.88 kg (35 lb) vertical rotor with blades to induce turbomachinery blade vibration. For rotor levitation, a proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, more blade vibration amplitude, and energy savings for the system. The test results of a variety of controllers that were demonstrated up to 10.000 rpm are shown. Furthermore, rotor excitation operation and conceptual study of active blade vibration control are addressed.

Choi, Benjamin; Johnson, Dexter; Provenza, Andrew; Morrison, Carlos; Montague, Gerald

2003-01-01

343

The thermodynamic behavior and spin dynamics of the colossal magnetoresistive (CMR) perovskites of general formula La(1-x)(A)xMn(1-y)(B)yO3 (where A is an alkaline earth, and B = Al, In) have been studied in order to evidence the effect of composition and the influence of nanocrystallinity on the thermodynamic and magnetic characteristics. By using electron paramagnetic resonance (EPR) spectroscopy, the behavior of the exchange coupling integral (J) between Mn spins and the polaron activation energy (Ea) have been investigated. The thermodynamic properties represented by the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the equilibrium partial pressures of oxygen have been obtained by using solid electrolyte electrochemical cells method. The influence of the oxygen stoichiometry change on the thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with measurements of the electromotive force (EMF). The results were correlated with the average Mn valence values as determined by redox titration. The properties of the rare-earth manganites are strongly affected by the A- and B-site substitution and by the oxygen nonstoichiometry. New features related to the modifications in properties connected with the nanocrystalline state were evidenced. The correlation existing between the magnetic and thermodynamic characteristics were discussed in relation to significant changes in the overall concentration of defects. PMID:18464427

Tanasescu, Speranta; Maxim, Florentina; Teodorescu, Florina; Giurgiu, Liviu

2008-02-01

344

Control Study for Five-Axis Dynamic Spin Rig Using Magnetic Bearings

NASA Technical Reports Server (NTRS)

The NASA Glenn Research Center (GRC) has developed a magnetic bearing system for the Dynamic Spin Rig (DSR) with a fully suspended shaft that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust magnetic bearing and the associated control system were integrated into the DSR to provide magnetic excitation as well as non-contact mag- netic suspension of a 15.88 kg (35 lb) vertical rotor with blades to induce turbomachinery blade vibration. For rotor levitation, a proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, more blade vibration amplitude, and energy savings for the system. The test results of a variety of controllers that were demonstrated up to 10.000 rpm are shown. Furthermore, rotor excitation operation and conceptual study of active blade vibration control are addressed.

Choi, Benjamin; Johnson, Dexter; Provenza, Andrew; Morrison, Carlos; Montague, Gerald

2003-01-01

345

NASA Astrophysics Data System (ADS)

We report simulation of EPR spectra directly and entirely from trajectories generated from molecular dynamics simulations. Results are reported for a model 3?-DOXYL-5?-cholestane spin probe in a coarse-grained solvent representing a 5CB nematic host. The results are in excellent agreement with the experimental spectra. The calculated order parameters associated with the paramagnetic probe show strong correlation with the order parameter of 5CB mesogens and are in agreement with those reported in the literature. Simulation of EPR spectra entirely from molecular dynamics of real structures provides direct correlation between molecular motions and the features observed in the spectra, allowing unambiguous interpretation of the spectra. This method opens the possibility for “computer engineering” of spin-labeled materials with the desired properties, such as spin-labeled proteins, prior to experiment.

Oganesyan, V. S.; Kuprusevicius, E.; Gopee, H.; Cammidge, A. N.; Wilson, M. R.

2009-01-01

346

NASA Astrophysics Data System (ADS)

In this work, we derive the interface exchange boundary conditions for the classical linear dynamics of magnetization in ferromagnetic layers with the interface Dzyaloshinskii-Moriya interaction (IDMI). We show that IDMI leads to pinning of dynamic magnetization at the interface. An unusual peculiarity of the IDMI-based pinning is that its scales as the spin-wave wave number. We incorporate these boundary conditions into an existing numerical model for the dynamics of the Damon-Eshbach spin wave in ferromagnetic films. IDMI affects the dispersion and the frequency non-reciprocity of the travelling Damon-Eshbach spin wave. For a broad range of film thicknesses L and wave numbers, the results of the numerical simulations of the spin wave dispersion are in a good agreement with a simple analytical expression, which shows that the contribution of IDMI to the dispersion scales as 1/L, similarly to the effect of other types of interfacial anisotropy. Suggestions to experimentalists how to detect the presence of IDMI in a spin wave experiment are given.

Kostylev, M.

2014-06-01

347

Dynamic and static fluctuations in polymer gels studied by neutron spin-echo

NASA Astrophysics Data System (ADS)

We report neutron spin-echo measurements on three types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40, the second is PVA gel in an aqueous borax solution and the third is chemically cross-linked PVA gel. The observed normalized intermediate scattering functions I( Q, t)/ I( Q,0) were very different among them. The I( Q, t)/ I( Q,0) of the first and third gels showed a non-decaying component in addition to a decaying component, but the second one did not have the non-decaying one. This clearly indicates that the fluctuations in the first and third PVA gels consist of static and dynamic fluctuations whereas the second PVA gel does include only the dynamic fluctuations. The dynamic and static fluctuations of the PVA gels were analyzed in terms of a restricted motion in the gel network and the Zimm motion, respectively.

Kanaya, T.; Takahashi, N.; Nishida, K.; Seto, H.; Nagao, M.; Takeba, Y.

2006-11-01

348

NASA Astrophysics Data System (ADS)

We use R-matrix theory with time dependence (RMT) to investigate multiphoton ionization of ground-state atomic carbon with initial orbital magnetic quantum number ML=0 and ML=1 at a laser wavelength of 390 nm and peak intensity of 1014W/cm2. Significant differences in ionization yield and ejected-electron momentum distribution are observed between the two values for ML. We use our theoretical results to model how the spin-orbit interaction affects electron emission along the laser polarization axis. Under the assumption that an initial C atom is prepared at zero time delay with ML=0, the dynamics with respect to time delay of an ionizing probe pulse modeled by using RMT theory is found to be in good agreement with available experimental data.

Rey, H. F.; van der Hart, H. W.

2014-09-01

349

Imaging sub-ns spin dynamics in magnetic nanostructures with Magnetic Transmission X-ray microscopy

NASA Astrophysics Data System (ADS)

Magnetic transmission soft X-ray microscopy combining a 20nm lateral resolution with element-specific magnetic contrast was used in a stroboscopic pump-and-probe scheme to study spin dynamics in magnetic nanostructures. The pump is a short (rise time <100psec) field pulse up to 100Oe to the sample generated by an electronic pulse into a microcoil and the probe is the flash of the circularly polarized X-ray beam at the ALS with a pulse width of about 70psec, which was delayed up to 2000psec (after the pump). Results obtained at the Fe L3 edge with 4×4?m2 squared and 50nm thin permalloy elements indicate local variations of the time varying domain pattern indicatint different local precessional frequencies. The experimental findings are consistent with micromagnetic simulations and time dependent Kerr microscopy results.

Fischer, P.; Stoll, H.; Puzic, A.; Van Waeyenberge, B.; Raabe, J.; Haug, T.; Denbeaux, G.; Pearson, A.; Höllinger, R.; Back, C. H.; Weiss, D.; Schütz, G.

2004-05-01

350

Electron dynamics in the carbon atom induced by spin-orbit interaction

We use R-Matrix theory with Time dependence (RMT) to investigate multiphoton ionization of ground-state atomic carbon with initial orbital magnetic quantum number $M_L$=0 and $M_L$=1 at a laser wavelength of 390 nm and peak intensity of 10$^{14}$ W cm$^{-2}$. Significant differences in ionization yield and ejected-electron momentum distribution are observed between the two values for $M_L$. We use our theoretical results to model how the spin-orbit interaction affects electron emission along the laser polarization axis. Under the assumption that an initial C atom is prepared at zero time delay with $M_L=0$, the dynamics with respect to time delay of an ionizing probe pulse modelled using RMT theory is found to be in good agreement with available experimental data.

Rey, H F

2014-01-01

351

Solid-state NMR spectroscopy can be used to probe internal protein dynamics in the absence of the overall molecular tumbling. In this study, we report 15N backbone dynamics in differentially enriched 1-73(U-13C, 15N)/74-108(U-15N) reassembled thioredoxin on multiple timescales using a series of 2D and 3D MAS NMR experiments probing the backbone amide 15N longitudinal relaxation, 1H-15N dipolar order parameters, 15N chemical shift anisotropy (CSA), and signal intensities in the temperature-dependent and 1H T2? -filtered NCA experiments. The spin-lattice relaxation rates R1(R1 = 1/T1) were observed in the range from 0.012 to 0.64 s-1 indicating large site-to-site variations in dynamics on pico- to nanosecond time scales. The 1H-15N dipolar order parameters, ~~, and 15N CSA anisotropies, ?? reveal the backbone mobilities in reassembled thioredoxin, as reflected in the average ~~~~= 0.89 ± 0.06 and ?? = 92.3 ± 5.2 ppm, respectively. From the aggregate of experimental data from different dynamics methods, some degree of correlation between the motions on the different time scales has been suggested. Analysis of the dynamics parameters derived from these solid-state NMR experiments indicates higher mobilities for the residues constituting irregular secondary structure elements than for those located in the ?-helices and ?-sheets, with no apparent systematic differences in dynamics between the ?-helical and ?-sheet residues. Remarkably, the dipolar order parameters derived from the solid-state NMR measurements and the corresponding solution NMR generalized order parameters display similar qualitative trends as a function of the residue number. The comparison of the solid-state dynamics parameters to the crystallographic B-factors has identified the contribution of static disorder to the B-factors. The combination of longitudinal relaxation, dipolar order parameter, and CSA line shape analyses employed in this study provides snapshots of dynamics and a new insight on the correlation of these motions on multiple time scales. PMID:19736935~~

Yang, Jun; Tasayco, Maria Luisa; Polenova, Tatyana

2014-01-01

352

The dynamics of spin-polarized wavepackets driven by periodic electric field is considered for the electrons is in a mesoscopic quantum dot formed at the edge of two-dimensional HgTe/CdTe topological insulator representing a new class of materials with Weyl massless energy spectra, where the motion of carriers is less sensitive to disorder and impurity potentials. It is found that the interplay of strongly coupled spin and charge degrees of freedom creates the regimes of both regular and irregular dynamics with certain universal properties manifested for both free and driven evolution, in the clean limit and in the presence of the moderate disorder. The weak disorder influence is predicted to be overcome by periodic driving while the moderate disorder induces the in-plane spin relaxation, leading to possibility of establishing novel types of driven evolution in nanostructures formed in the topological insulators. The dynamical properties of regular and chaotic behavior of charge and spin in these structures may be of interest for future progress in both quantum nonlinear dynamics on the nanoscale and in the applied nanoscience such as spintronics and nanoelectronics.

D. V. Khomitsky; A. A. Chubanov; A. A. Konakov

2014-08-07

353

glass (ISG) model, at and above the critical temperature Tg. The data show a long time stretchedPHYSICAL REVIEW B 84, 054442 (2011) Dynamics in the Sherrington-Kirkpatrick Ising spin glass glass (ISG) model has been intensively studied for almost 40 years. Introduced1,2 as a starting point

Boyer, Edmond

354

Fully Suspended, Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig With Forced Excitation

NASA Technical Reports Server (NTRS)

The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig, a significant advancement in the Dynamic Spin Rig (DSR), is used to perform vibration tests of turbomachinery blades and components under rotating and nonrotating conditions in a vacuum. The rig has as its critical components three magnetic bearings: two heteropolar radial active magnetic bearings and a magnetic thrust bearing. The bearing configuration allows full vertical rotor magnetic suspension along with a feed-forward control feature, which will enable the excitation of various natural blade modes in bladed disk test articles. The theoretical, mechanical, electrical, and electronic aspects of the rig are discussed. Also presented are the forced-excitation results of a fully levitated, rotating and nonrotating, unbladed rotor and a fully levitated, rotating and nonrotating, bladed rotor in which a pair of blades was arranged 180 degrees apart from each other. These tests include the bounce mode excitation of the rotor in which the rotor was excited at the blade natural frequency of 144 Hz. The rotor natural mode frequency of 355 Hz was discerned from the plot of acceleration versus frequency. For nonrotating blades, a blade-tip excitation amplitude of approximately 100 g/A was achieved at the first-bending critical (approximately 144 Hz) and at the first-torsional and second-bending blade modes. A blade-tip displacement of 70 mils was achieved at the first-bending critical by exciting the blades at a forced-excitation phase angle of 908 relative to the vertical plane containing the blades while simultaneously rotating the shaft at 3000 rpm.

Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Montague, Gerald; Duffy, Kirsten; Mehmed, Oral; Johnson, Dexter; Jansen, Ralph

2004-01-01

355

Probing Structure and Dynamics of Protein Assemblies by Magic Angle Spinning NMR Spectroscopy

CONSPECTUS In living organisms, biological molecules often organize into multi-component complexes. Such assemblies consist of various proteins and carry out essential functions, ranging from cell division, transport, and energy transduction to catalysis, signaling, and viral infectivity. To understand the biological functions of these assemblies, in both healthy and disease states, researchers need to study their three-dimensional architecture and molecular dynamics. To date, the large size, the lack of inherent long-range order, and insolubility have made atomic-resolution studies of many protein assemblies challenging or impractical using traditional structural biology methods such as X-ray diffraction and solution NMR spectroscopy. In the past ten years, we have focused our work on the development and application of magic angle spinning solid-state NMR (MAS NMR) methods to characterize large protein assemblies at atomic-level resolution. In this Account, we discuss the rapid progress in the field of MAS NMR spectroscopy, citing work from our laboratory and others on methodological developments that have facilitated the in-depth analysis of biologically important protein assemblies. We emphasize techniques that yield enhanced sensitivity and resolution, such as fast MAS (spinning frequencies of 40 kHz and above) and non-uniform sampling protocols for data acquisition and processing. We also discuss the experiments for gaining distance restraints and for recoupling anisotropic tensorial interactions under fast MAS conditions. We give an overview of sample preparation approaches when working with protein assemblies. Following the overview of contemporary MAS NMR methods, we present case studies into the structure and dynamics of two classes of biological systems under investigation in our laboratory. We will first turn our attention to cytoskeletal microtubule motor proteins including mammalian dynactin and dynein light chain 8. We will then discuss protein assemblies from the HIV-1 retrovirus. PMID:23402263

Yan, Si; Suiter, Christopher L.; Hou, Guangjin; Zhang, Huilan; Polenova, Tatyana

2013-01-01

356

Spin dynamics of qqq wave function on light front in high momentum limit of QCD: Role of qqq force

NASA Astrophysics Data System (ADS)

The contribution of a spin-rich qqq force (in conjunction with pairwise qq forces) to the analytical structure of the qqq wave function is worked out in the high momentum regime of QCD where the confining interaction may be ignored, so that the dominant effect is Coulombic. A distinctive feature of this study is that the spin-rich qqq force is generated by a ggg vertex (a genuine part of the QCD Lagrangian) wherein the 3 radiating gluon lines end on as many quark lines, giving rise to a (Mercedes-Benz type) Y-shaped diagram. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. With these ingredients, the differential equation for the 3D wave function ? receives well-defined contributions from the qq and qqq forces. In particular a negative eigenvalue of the spin operator i ?1 · ?2 × ?3 which is an integral part of the qqq force, causes a characteristic singularity in the differential equation, signalling the dynamical effect of a spin-rich qqq force not yet considered in the literature. The potentially crucial role of this interesting effect vis-a-vis the so-called 'spin anomaly' of the proton, is a subject of considerable physical interest.

Mitra, A. N.

2008-04-01

357

Dynamical decoupling (DD) is an efficient tool for preserving quantum coherence in solid-state spin systems. However, the imperfections of real pulses can ruin the performance of long DD sequences. We investigate the accumulation and compensation of different pulse errors in DD using the electron spins of phosphorus donors in silicon as a test system. We study periodic DD sequences (PDD) based on spin rotations about two perpendicular axes, and their concatenated and symmetrized versions. We show that pulse errors may quickly destroy some spin states, but maintain other states with high fidelity over long times. Pulse sequences based on spin rotations about $x$ and $y$ axes outperform those based on $x$ and $z$ axes due to the accumulation of pulse errors. Concatenation provides an efficient way to suppress the impact of pulse errors, and can maintain high fidelity for all spin components: pulse errors do not accumulate (to first order) as the concatenation level increases, despite the exponential increase in the number of pulses. Our theoretical model gives a clear qualitative picture of the error accumulation, and produces results in quantitative agreement with the experiments.

Zhi-Hui Wang; Wenxian Zhang; A. M. Tyryshkin; S. A. Lyon; J. W. Ager; E. E. Haller; V. V. Dobrovitski

2010-11-29

358

Spin-lattice coupling induced weak dynamical magnetism in EuTiO3 at high temperatures

NASA Astrophysics Data System (ADS)

EuTiO3, which is a G-type antiferromagnet below TN=5.5 K, has some fascinating properties at high temperatures, suggesting that macroscopically hidden dynamically fluctuating weak magnetism exists at high temperatures. This conjecture is substantiated by magnetic field dependent magnetization measurements, which exhibit pronounced anomalies below 200 K becoming more distinctive with increasing magnetic field strength. Additional results from muon spin rotation experiments provide evidence for weak fluctuating bulk magnetism induced by spin-lattice coupling which is strongly supported in increasing magnetic field.

Guguchia, Z.; Keller, H.; Kremer, R. K.; Köhler, J.; Luetkens, H.; Goko, T.; Amato, A.; Bussmann-Holder, A.

2014-08-01

359

In response to the global economic crisis, organizations are cutting costs and focusing on core competencies. One natural corollary of this situation has been an increased interest in the outsourcing of IT services. Such sourcing relationships are established and maintained via formally negotiated IT service level agreements (SLAs), the goal of which is to generate utility for both parties. Understanding

Haluk Demirkan; Michael Goul; Daniel S. Soper

2009-01-01

360

ERIC Educational Resources Information Center

Observation competence plays a fundamental role in outdoor scientific investigation. The computerized concept mapping technique as a Mindtool has shown the potential for enhancing meaningful learning in science education. The purposes of the present study are to develop a concept map integrated mobile learning design for ecology observation and to…

Hung, Pi-Hsia; Hwang, Gwo-Jen; Su, I-Hsiang; Lin, I-Hua

2012-01-01

361

LEE BUSINESS SCHOOL HigHligHts At the Lee Business School, we prepare people to compete in today the extras that come with the Lee Business School Â nationally recognized, endowed faculty and the Lee and the local business community. Points of Pride Â·The Lee Business School is one of only 178 schools worldwide

Hemmers, Oliver

362

LEE BUSINESS SCHOOL HIGHLIGHTS At the Lee Business School, we prepare people to compete in today the extras that come with the Lee Business School Â nationally recognized, endowed faculty and the Lee and the local business community. POINTS OF PRIDE Â·The Lee Business School is one of only 178 schools worldwide

Hemmers, Oliver

363

Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction

In a ferromagnetic metal layer, the coupled charge and spin diffusion equations are obtained in the presence of both Rashba spin-orbit interaction and magnetism. The mis-alignment between the magnetization and the non-equilibrium spin density induced by the Rashba field gives rise to Rashba spin torque acting on the ferromagnetic order parameter. In a general form, we find that the Rashba

Xuhui Wang; Aurelien Manchon

2011-01-01

364

Microwave Field Distribution in a Magic Angle Spinning Dynamic Nuclear Polarization NMR Probe

We present a calculation of the microwave field distribution in a magic angle spinning (MAS) probe utilized in dynamic nuclear polarization (DNP) experiments. The microwave magnetic field (B1S) profile was obtained from simulations performed with the High Frequency Structure Simulator (HFSS) software suite, using a model that includes the launching antenna, the outer Kel-F stator housing coated with Ag, the RF coil, and the 4 mm diameter sapphire rotor containing the sample. The predicted average B1S field is 13µT/W1/2, where S denotes the electron spin. For a routinely achievable input power of 5 W the corresponding value is ? SB1S = 0.84 MHz. The calculations provide insights into the coupling of the microwave power to the sample, including reflections from the RF coil and diffraction of the power transmitted through the coil. The variation of enhancement with rotor wall thickness was also successfully simulated. A second, simplified calculation was performed using a single pass model based on Gaussian beam propagation and Fresnel diffraction. This model provided additional physical insight and was in good agreement with the full HFSS simulation. These calculations indicate approaches to increasing the coupling of the microwave power to the sample, including the use of a converging lens and fine adjustment of the spacing of the windings of the RF coil. The present results should prove useful in optimizing the coupling of microwave power to the sample in future DNP experiments. Finally, the results of the simulation were used to predict the cross effect DNP enhancement (?) vs. ?1S/(2?) for a sample of 13C-urea dissolved in a 60:40 glycerol/water mixture containing the polarizing agent TOTAPOL; very good agreement was obtained between theory and experiment. PMID:21382733

Nanni, Emilio A.; Barnes, Alexander B.; Matsuki, Yoh; Woskov, Paul P.; Corzilius, Bjorn; Griffin, Robert G.; Temkin, Richard J.

2011-01-01

365

NASA Astrophysics Data System (ADS)

The magnetic order, spin dynamics, and crystal structure of the multiferroic Sr0.56Ba0.44MnO3 have been investigated using neutron and x-ray scattering. Ferroelectricity develops at TC=305 K with a polarization of 4.2 µC /cm2 associated with the displacements of the Mn ions, while the Mn4+ spins order below TN?200 K into a simple G-type commensurate magnetic structure. Below TN the ferroelectric order decreases dramatically, demonstrating that the two order parameters are strongly coupled. The ground state spin dynamics is characterized by a spin gap of 4.6(5) meV and the magnon density of states peaking at 43 meV. Detailed spin wave simulations with a gap and isotropic exchange of J =4.8(2) meV describe the excitation spectrum well. Above TN strong spin correlations coexist with robust ferroelectric order.

Pratt, Daniel K.; Lynn, Jeffrey W.; Mais, James; Chmaissem, Omar; Brown, Dennis E.; Kolesnik, Stanislaw; Dabrowski, Bogdan

2014-10-01

366

We present theoretical calculations of dynamic nuclear polarization (DNP) due to the cross effect in nuclear magnetic resonance under magic-angle spinning (MAS). Using a three-spin model (two electrons and one nucleus), cross effect DNP with MAS for electron spins with a large g-anisotropy can be seen as a series of spin transitions at avoided crossings of the energy levels, with varying degrees of adiabaticity. If the electron spin-lattice relaxation time T1e is large relative to the MAS rotation period, the cross effect can happen as two separate events: (i) partial saturation of one electron spin by the applied microwaves as one electron spin resonance (ESR) frequency crosses the microwave frequency and (ii) flip of all three spins, when the difference of the two ESR frequencies crosses the nuclear frequency, which transfers polarization to the nuclear spin if the two electron spins have different polarizations. In addition, adiabatic level crossings at which the two ESR frequencies become equal serve to maintain non-uniform saturation across the ESR line. We present analytical results based on the Landau-Zener theory of adiabatic transitions, as well as numerical quantum mechanical calculations for the evolution of the time-dependent three-spin system. These calculations provide insight into the dependence of cross effect DNP on various experimental parameters, including MAS frequency, microwave field strength, spin relaxation rates, hyperfine and electron-electron dipole coupling strengths, and the nature of the biradical dopants. PMID:22938251

Thurber, Kent R.; Tycko, Robert

2012-01-01

367

Spin dynamics, short range order and spin freezing in Y0.5Ca0.5BaCo4O7

Y0.5Ca0.5BaCo4O7 was recently introduced as a possible candidate for capturing some of the predicted classical spin kagome ground-state features. Stimulated by this conjecture, we have taken up a more complete study of the spin correlations in this compound with neutron scattering methods on a powder sample characterized with high-resolution neutron diffraction and the temperature dependence of magnetic susceptibility and specific heat. We have found that the frustrated near-neighbor magnetic correlations involve not only the kagome planes but concern the full Co sublattice, as evidenced by the analysis of the wave-vector dependence of the short-range order. We conclude from our results that the magnetic moments are located on the Co sublattice as a whole and that correlations extend beyond the two-dimensional kagome planes. We identify intriguing dynamical properties, observing high-frequency fluctuations with a Lorentzian linewidth G?20 meV at ambient temperature. On cooling a low-frequency ({approx}1 meV) dynamical component develops alongside the high-frequency fluctuations, which eventually becomes static at temperatures below T {approx} 50 K. The high-frequency response with an overall linewidth of {approx}10 meV prevails at T?2 K, coincident with a fully elastic short-range-ordered contribution.

Stewart, John Ross [ISIS Facility, Rutherford Appleton Laboratory; Ehlers, Georg [ORNL; Fouquet, Peter [Institut Laue-Langevin (ILL); Mutka, Hannu [Institut Laue-Langevin (ILL); Payen, Christophe [Institut des Materiaux Jean Rouxel (IMN), Universite de Nantes-CNRS; Lortz, Rolf [University of Geneva

2011-01-01

368

NASA Astrophysics Data System (ADS)

We employ a combination of pulsed- and continuous-wave polarized terahertz spectroscopy techniques to probe temperature-dependent spin waves in the antiferromagnet NdFeO3. Our optical data span 1.6-467 K and reveal a conspicuous spin reorientation between 110 and 170 K, during which the lower-energy mode softens completely. Complementary inelastic neutron scattering reveals that the frequencies of the optically excited spin waves are consistent with a temperature-variable spin gap in the low-energy spin-wave dispersion of NdFeO3. The result links the temperature dependence of the spin waves to a dynamic in-plane anisotropy. The magnetic anisotropy is calculated based on the results of the optical measurements. The change observed in the anisotropy energy along the a and c crystal axes suggests that the spin reorientation evident in NdFeO3 is driven by temperature-dependent in-plane anisotropy.

Constable, Evan; Cortie, D. L.; Horvat, Joseph; Lewis, R. A.; Cheng, Zhenxiang; Deng, Guochu; Cao, Shixun; Yuan, Shujuan; Ma, Guohong

2014-08-01

369

In today's turbulent environment, customers are playing a more important role in competition, which can be reflected by customers as co-producer, value co-producer, or co-developer of knowledge and competencies, etc. Accordingly, business priority should be given to what customers really value. Unlike previous studies, which emphasize market performance mainly from the internal or firm's perspective, this paper proposes that firms

Yonggui Wang; Hing-Po Lo

2003-01-01

370

Revisiting static and dynamic spin-ice correlations in Ho2Ti2O7 with neutron scattering

NASA Astrophysics Data System (ADS)

Elastic and inelastic neutron-scattering studies have been carried out on the pyrochlore magnet Ho2Ti2O7 . Measurements in zero applied magnetic field show that the disordered spin-ice ground state of Ho2Ti2O7 is characterized by a pattern of rectangular diffuse elastic scattering within the [HHL] plane of reciprocal space, which closely resembles the zone-boundary scattering seen in its sister compound Dy2Ti2O7 . Well-defined peaks in the zone-boundary scattering develop only within the spin-ice ground state below ˜2K . In contrast, the overall diffuse-scattering pattern evolves on a much higher-temperature scale of ˜17K . The diffuse scattering at small wave vectors below [001] is found to vanish on going to Q=0 , an explicit signature of expectations for dipolar spin ice. Very high energy-resolution inelastic measurements reveal that the spin-ice ground state below ˜2K is also characterized by a transition from dynamic to static spin correlations on the time scale of 10-9s . Measurements in a magnetic field applied along the [11¯0] direction in zero-field-cooled conditions show that the system can be broken up into orthogonal sets of polarized ? chains along [11¯0] and quasi-one-dimensional ? chains along [110]. Three-dimensional correlations between ? chains are shown to be very sensitive to the precise alignment of the [11¯0] externally applied magnetic field.

Clancy, J. P.; Ruff, J. P. C.; Dunsiger, S. R.; Zhao, Y.; Dabkowska, H. A.; Gardner, J. S.; Qiu, Y.; Copley, J. R. D.; Jenkins, T.; Gaulin, B. D.

2009-01-01

371

NASA Technical Reports Server (NTRS)

The influence of different mathematical and aerodynamic models on computed spin motion was investigated along with the importance of some of the aerodynamic and nonaerodynamic quantities defined in these models. An analytical technique was used which included the aerodynamic forces and moments acting on a spinning aircraft due to steady rotational flow and the contribution of the rotary derivatives to the oscillatory component of the total angular rates. It was shown that (1) during experimental-analytical correlation studies, the flight-recorded control time histories must be faithfully duplicated since the spinning motion can be sensitive to a small change in the application of the spin entry controls; (2) an error in the assumed inertias, yawing moments at high angle of attack, and initial spin entry bank angle do not influence the developed spin significantly; (3) damping in pitch derivatives and the center of gravity location play a role in the spinning motion; and (4) the experimental spin investigations conducted in a constant atmospheric density environment duplicate the Froude number only at the initial full-scale spin altitude (since the full-scale airplane at high altitudes experiences large density changes during the spin.)

Bihrle, W., Jr.; Barnhart, B.

1974-01-01

372

Structure and spin dynamics of multiferroic BiFeO3

NASA Astrophysics Data System (ADS)

Multiferroic materials have attracted much interest due to the unusual coexistence of ferroelectric and (anti-)ferromagnetic ground states in a single compound. They offer an exciting platform for new physics and potentially novel devices. BiFeO3 is one of the most celebrated multiferroic materials and has highly desirable properties. It is the only known room-temperature multiferroic with TC ? 1100 K and TN ? 650 K, and exhibits one of the largest spontaneous electric polarisations, P ? 80 µC cm?2. At the same time, it has a magnetic cycloid structure with an extremely long period of 620 Å, which arises from competition between the usual symmetric exchange interaction and the antisymmetric Dzyaloshinskii–Moriya (DM) interaction. There is also an intriguing interplay between the DM interaction and single ion anisotropy K. In this review, we have attempted to paint a complete picture of bulk BiFeO3 by summarising the structural and dynamic properties of both the spin and lattice parts and their magneto-electric coupling.

Park, Je-Geun; Le, Manh Duc; Jeong, Jaehong; Lee, Sanghyun

2014-10-01

373

Structure and spin dynamics of multiferroic BiFeO3.

Multiferroic materials have attracted much interest due to the unusual coexistence of ferroelectric and (anti-)ferromagnetic ground states in a single compound. They offer an exciting platform for new physics and potentially novel devices. BiFeO3 is one of the most celebrated multiferroic materials and has highly desirable properties. It is the only known room-temperature multiferroic with TC ? 1100 K and TN ? 650 K, and exhibits one of the largest spontaneous electric polarisations, P ? 80 µC cm(-2). At the same time, it has a magnetic cycloid structure with an extremely long period of 620 ?, which arises from competition between the usual symmetric exchange interaction and the antisymmetric Dzyaloshinskii-Moriya (DM) interaction. There is also an intriguing interplay between the DM interaction and single ion anisotropy K. In this review, we have attempted to paint a complete picture of bulk BiFeO3 by summarising the structural and dynamic properties of both the spin and lattice parts and their magneto-electric coupling. PMID:25299241

Park, Je-Geun; Le, Manh Duc; Jeong, Jaehong; Lee, Sanghyun

2014-10-29

374

Self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers.

Recently the Brownian dynamics of self-propelled (active) rodlike particles was explored to model the motion of colloidal microswimmers, catalytically driven nanorods, and bacteria. Here we generalize this description to biaxial particles with arbitrary shape and derive the corresponding Langevin equation for a self-propelled Brownian spinning top. The biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low Reynolds numbers, to fluctuating random forces and torques as well as to an external and an internal (effective) force and torque. The latter quantities control its self-propulsion. Due to biaxiality and hydrodynamic translational-rotational coupling, the Langevin equation can only be solved numerically. In the special case of an orthotropic particle in the absence of external forces and torques, the noise-free (zero-temperature) trajectory is analytically found to be a circular helix. This trajectory is confirmed numerically to be more complex in the general case of an arbitrarily shaped particle under the influence of arbitrary forces and torques involving a transient irregular motion before ending up in a simple periodic motion. By contrast, if the external force vanishes, no transient regime is found, and the particle moves on a superhelical trajectory. For orthotropic particles, the noise-averaged trajectory is a generalized concho-spiral. We furthermore study the reduction of the model to two spatial dimensions and classify the noise-free trajectories completely finding circles, straight lines with and without transients, as well as cycloids and arbitrary periodic trajectories. PMID:22463211

Wittkowski, Raphael; Löwen, Hartmut

2012-02-01

375

Order and dynamics inside H-PDLC nanodroplets: an ESR spin probe study.

We have performed a detailed study of the order and dynamics of the commercially available BL038 liquid crystal (LC) inside nanosized (50-300 nm) droplets of a reflection-mode holographic-polymer dispersed liquid crystal (H-PDLC) device where LC nanodroplet layers and polymer layers are alternately arranged, forming a diffraction grating. We have determined the configuration of the LC local director and derived a model of the nanodroplet organization inside the layers. To achieve this, we have taken advantage of the high sensitivity of the ESR spin probe technique to study a series of temperatures ranging from the nematic to the isotropic phase of the LC. Using also additional information on the nanodroplet size and shape distribution provided by SEM images of the H-PDLC cross section, the observed director configuration has been modeled as a bidimensional distribution of elongated nanodroplets whose long axis is, on the average, parallel to the layers and whose internal director configuration is a uniaxial quasi-monodomain aligned along the nanodroplet long axis. Interestingly, at room temperature the molecules tend to keep their average orientation even when the layers are perpendicular to the magnetic field, suggesting that the molecular organization is dictated mainly by the confinement. This result might explain, at least in part, (i) the need for switching voltages significantly higher and (ii) the observed faster turn-off times in H-PDLCs compared to standard PDLC devices. PMID:19331398

Bacchiocchi, Corrado; Miglioli, Isabella; Arcioni, Alberto; Vecchi, Ilaria; Rai, Kashma; Fontecchio, Adam; Zannoni, Claudio

2009-04-23

376

We report for the first time that the dynamic magnetic intermediate state (DMI) was observed at a speed of several ns during spin transfer switching for MgO-based magnetic tunnel junctions (MTJs). The DMI was observed as slow resistance oscillation at the center of the parallel to anti-parallel state by single shot time domain measurements. The DMI is observable at certain

Tatsuya Aoki; Yasuo Ando; Mikihiko Oogane; Hiroshi Naganuma

2010-01-01

377

NASA Astrophysics Data System (ADS)

Motivated by the recent experiment of Choi [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.108.035301 108, 035301 (2012)], we simulate, within the Gross-Pitaevskii equation, the process of creating a skyrmion in an antiferromagnetic spin-1 Bose-Einstein condensate via the magnetic-field rotation method. Complex skymion structures are found and the factors influencing them are discussed. The dynamics of the system is mainly quasiperiodic. When the center of the skyrmion is displaced from the trap center, half vortices can be found at an intermediate stage of the dynamical evolution, but they do not necessarily lead to the destruction of the skyrmions.

Huang, Chao-Chun; Yip, S.-K.

2013-07-01

378

Cooling a magnetic resonance force microscope via the dynamical back action of nuclear spins

NASA Astrophysics Data System (ADS)

We analyze the back-action influence of nuclear spins on the motion of the cantilever of a magnetic force resonance microscope. We calculate the contribution of nuclear spins to the damping and frequency shift of the cantilever. We show that, at the Rabi frequency, the energy exchange between the cantilever and the spin system cools or heats the cantilever depending on the sign of the high-frequency detuning. We also show that the spin noise leads to a significant damping of the cantilever motion.

Greenberg, Ya. S.; Il'Ichev, E.; Nori, Franco

2009-12-01

379

Conformational dynamics play a key role in the properties and functions of proteins and nucleic acids. Heteronuclear NMR spin relaxation is a uniquely powerful site-specific probe of dynamics in proteins and has found increasing applications to nucleotide base side chains and anomeric sites in RNA. Applications to the nucleic acid ribose backbone, however, have been hampered by strong magnetic coupling among ring carbons in uniformly 13C-labeled samples. In this work, we apply a recently-developed, metabolically-directed isotope labeling scheme that places 13C with high efficiency and specificity at the nucleotide ribose C2’ and C4’ sites. We take advantage of this scheme to explore backbone dynamics in the well-studied GCAA RNA tetraloop. Using a combination of CPMG (Carr-Purcell-Meiboom-Gill) and R1? relaxation dispersion spectroscopy to explore exchange processes on the microsecond to millisecond timescale, we find an extensive pattern of dynamic transitions connecting a set of relatively well-defined conformations. In many cases, the observed transitions appear to be linked to C3’-endo/C2’-endo sugar pucker transitions of the corresponding nucleotides, and may also be correlated across multiple nucleotides within the tetraloop. These results demonstrate the power of NMR spin relaxation based on alternate-site isotope labeling to open a new window into the dynamic properties of ribose backbone groups in RNA. PMID:19049467

Johnson, James E.; Hoogstraten, Charles G.

2009-01-01

380

Spin-distribution measurement: A sensitive probe for incomplete fusion dynamics

Spin distributions of various reaction products populated via complete and/or incomplete fusion of {sup 16}O with {sup 169}Tm have been measured at projectile energy {approx_equal}5.6 MeV/nucleon. Particle (Z=1,2) {gamma}-coincidences have been employed to achieve the information about involved reaction modes on the basis of their entry state spin populations. The experimentally measured spin distributions for incomplete fusion products have been found to be distinctly different than those observed for complete fusion products. The driving input angular momenta associated with incomplete fusion products have been found to be relatively higher than complete fusion products, and increases with direct {alpha}-multiplicity. It has also been observed that incomplete fusion products are less fed and/or the population of lower spin states are strongly hindered, while complete fusion products indicating strong feeding over a broad spin range.

Singh, Pushpendra P.; Singh, B. P.; Sharma, Manoj Kumar; Unnati,; Singh, D.; Ansari, M. A.; Prasad, R. [Department of Physics, A. M. University, Aligarh (UP) 202002 (India); Kumar, R.; Golda, K. S.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K. [NP-Group, Inter-University Accelerator Center, P.O. Box No. 10502, New Delhi 110067 (India)

2008-07-15

381

Quantum wave packet optimal control simulations with intense laser pulses have been carried out for studying molecular isomerization dynamics of a one-dimensional (1D) reaction-path model involving a dominant competing dissociation channel. The 1D intrinsic reaction coordinate model mimics the ozone open --> cyclic ring isomerization along the minimum energy path that successively connects the ozone cyclic ring minimum, the transition state (TS), the open (global) minimum, and the dissociative O(2) + O asymptote on the O(3) ground-state (1)A(') potential energy surface. Energetically, the cyclic ring isomer, the TS barrier, and the O(2) + O dissociation channel lie at approximately 0.05, approximately 0.086, and approximately 0.037 hartree above the open isomer, respectively. The molecular orientation of the modeled ozone is held constant with respect to the laser-field polarization and several optimal fields are found that all produce nearly perfect isomerization. The optimal control fields are characterized by distinctive high temporal peaks as well as low frequency components, thereby enabling abrupt transfer of the time-dependent wave packet over the TS from the open minimum to the targeted ring minimum. The quick transition of the ozone wave packet avoids detrimental leakage into the competing O(2) + O channel. It is possible to obtain weaker optimal laser fields, resulting in slower transfer of the wave packets over the TS, when a reduced level of isomerization is satisfactory. PMID:19655866

Kurosaki, Yuzuru; Artamonov, Maxim; Ho, Tak-San; Rabitz, Herschel

2009-07-28

382

Ultrafast optical control of electron spins in quantum wells and quantum dots

NASA Astrophysics Data System (ADS)

Using two-color time-resolved Faraday rotation and ellipticity, we demonstrate ultrafast optical control of electron spins in GaAs quantum wells and InAs quantum dots. In quantum wells, a magnetic-field induced electron spin polarization is manipulated by off-resonant pulses. By measuring the amplitude and phase of the spin polarization as a function of pulse detuning, we observe the two competing optical processes: real excitation, which generates a spin polarization through excitation of electron-hole pairs; and virtual excitation, which can manipulate a spin polarization through a stimulated Raman process without exciting electron-hole pairs. In InAs quantum dots, the spin coherence time is much longer, so that the effect of many repetitions of the pump pulses is important. Through real excitation, the pulse train efficiently polarizes electron spins that precess at multiples of the laser repetition frequency, leading to a "mode-locking" phenomenon. Through virtual excitation, the spins can be partially rotated toward the magnetic field direction, leading to a sensitive dependence of the spin orientation on the precession frequency and detuning. The electron spin dynamics strongly influence the nuclear spin dynamics as well, leading to directional control of the nuclear polarization distribution.

Carter, Samuel G.; Economou, Sophia E.; Shabaev, Andrew; Kennedy, Thomas A.; Bracker, Allan S.; Reinecke, Thomas L.; Chen, Zhigang; Cundiff, Steven T.

2010-02-01

383

NASA Astrophysics Data System (ADS)

First principles calculations using ab initio density functional theory using the ultrasoft pseudopotential method and generalized gradient approximations (GGA) have been carried out for heavy metal iron-pernitride (FeN2). We have performed both non-spin and spin polarized calculations and found that the spin polarized ground state is energetically more favourable with a magnetic moment of 1.86 ? B. The calculated electronic band structure, density of states and contour plot suggest that natural iron-pernitride is metallic. The high bulk modulus of FeN2 confirms that the FeN2 has lower compressibility and high hardness. The present values of the bulk modulus, N-N bond length, magnetic moment and optimized structure parameters agree with the previous studies. A detailed analysis of the phonon dispersion curves allows us to conclude that the spin polarized phonon dispersion curves contain positive frequencies throughout the Brillouin zone and hence confirms the dynamical stability. The eigen displacements of Raman and infrared active phonon modes at the zone centre for FeN2 are discussed in detail. The total and partial phonon density of states are also reported along with lattice specific heat and Debye temperature.

Gupta, Sanjay D.; Gupta, Sanjeev K.; Jha, Prafulla K.

2013-01-01

384

NASA Astrophysics Data System (ADS)

We study two anisotropically interacting spins coupled to optical phonons; we restrict our analysis to the regime of strong coupling to the environment, to the antiadiabatic region, and to the subspace with zero value for STz (the z component of the total spin). In the case where each spin is coupled to a different phonon bath, we assume that the system and the environment are initially uncorrelated (and form a simply separable state) in the polaronic frame of reference. By analyzing the polaron dynamics through a non-Markovian quantum master equation, we find that the system manifests a small amount of decoherence that decreases both with increasing nonadiabaticity and with enhancing strength of coupling; whereas, under the Markovian approximation, the polaronic system exhibits a decoherence-free behavior. For the situation where both spins are coupled to the same phonon bath, we also show that the system is decoherence-free in the subspace where STz is fixed. To suppress decoherence through quantum control, we employ a train of ? pulses and demonstrate that unitary evolution of the system can be retained. We propose realization of a weakly decohering charge qubit from an electron in an oxide-based (tunnel-coupled) double-quantum-dot system.

Dey, Amit; Yarlagadda, Sudhakar

2014-02-01

385

Dynamics of the iron spins in superconducting YBa2(Cu(1-x)Fe(x))O7

NASA Technical Reports Server (NTRS)

The dynamics of the iron spins in YBa2(Cu(1-x)Fe(x))3O7 alloys (0 = to or less than 0.12) was studied by the means of inelastic neutron scattering. Measurements were performed using the time of flight technique with an excellent resolution of 50 micro eV, in a temperature range of 1.8 to 300 K. The doped samples show an elastic and a quasielastic intensity strongly varying with temperature. A spin glass like freezing is revealed at low temperature by a sudden decrease of the quasielastic intensity, an increase of the elastic or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature corresponds to the one already determinated by a magnetic splitting in Mossbauer experiments. Above freezing, the occurrence of superconductivity slightly modifies the characteristics of the spin relaxation in the paramagnetic state, as shown by measurements in two x = 0.06 samples. In the whole temperature range of measurement, the dependence of the quasielastic intensity with the scattering vector q, mainly reflects the variation of the Iron form factor, which shows that the spins are almost uncorrelated.

Mirebeau, I.; Hennion, M.; Moorjani, K.

1990-01-01

386

NASA Astrophysics Data System (ADS)

Aims: This paper aims at deciphering the dynamics of the envelope of a rotating star when some angular momentum loss due to mass loss is present. We especially wish to know when the spin-down flow forced by the mass loss supersedes the baroclinic flows that pervade the radiative envelope of rotating stars. Methods: We consider a Boussinesq fluid enclosed in a rigid sphere whose flows are forced both by the baroclinic torque, the spin-down of an outer layer, and an outward mass flux. The spin-down forcing is idealized in two ways: either by a rigid layer that imposes its spinning down velocity at some interface or by a turbulent layer that imposes a stress at this same interface to the interior of the star. Results: In the case where the layer is rigid and imposes its velocity, we find that, as the mass-loss rate increases, the flow inside the star shows two transitions: the meridional circulation associated with baroclinic flows is first replaced by its spin-down counterpart, while at much stronger mass-loss rates the baroclinic differential rotation is superseded by the spin-down differential rotation. When boundary conditions specify the stress instead of the velocity, we find just one transition as the mass-loss rate increases. Besides the two foregoing transitions, we find a third transition that separates an angular momentum flux dominated by stresses from an angular momentum flux dominated by advection. Thus, with this very simplified two-dimensional stellar model, we find three wind regimes: weak (or no wind), moderate, and strong. In the weak wind case, the flow in the radiative envelope is of baroclinic origin. In the moderate case, the circulation results from the spin-down while the differential rotation may either be of baroclinic or of spin-down origin, depending on the boundary conditions or more generally on the coupling between mass and angular momentum losses. For fast rotating stars, our model says that the moderate wind regime starts when mass loss is higher than ~ 10-11 M?/yr. In the strong wind case, the flow in the radiative envelope is mainly driven by angular momentum advection. This latter transition mass-loss rate depends on the mass and the rotation rate of the star, being around 10-8 M?/yr for a 3 M? ZAMS star rotating at 200 km s-1 according to our model.

Rieutord, M.; Beth, A.

2014-10-01

387

NASA Astrophysics Data System (ADS)

Semiconductor quantum dots provide a platform for studying and exploiting individual electron spins as they interact with a complex solid state environment. Colloidal nanocrystal quantum dots are of particular interest for potential applications, because they can achieve sufficient confinement to operate at room temperature with relatively robust electron spin coherence. The strong confinement in these nanostructures leads to significant effects caused by mixing of valence subbands and variation in particle size and shape. These effects influence the processes of carrier spin initialization and detection. We have performed ensemble time-resolved Faraday rotation experiments as well as single-dot photoluminescence excitation measurements to study how the strong quantum confinement affects the spin physics in these systems. Single dot PLE measurements reveal mechanisms of transition broadening that are relevant at room temperature, including thermal broadening and spectral diffusion due to mobile charges in the surrounding environment. We find that the mixing of valence subbands in the confined hole states largely determines the efficiency of optical spin pumping and Faraday-rotation-based spin detection. By studying these effects, we take a step towards controlling and exploiting spin coherence in this flexible room temperature platform.

Berezovsky, Jesse; Fumani, Ahmad K.; Wolf, Michael

2014-08-01

388

Religious competence as cultural competence

Definitions of cultural competence often refer to the need to be aware and attentive to the religious and spiritual needs and orientations of patients. However, the institution of psychiatry maintains an ambivalent attitude to the incorporation of religion and spirituality into psychiatric practice. This is despite the fact that many patients, especially those from underserved and underprivileged minority backgrounds, are devotedly religious and find much solace and support in their religiosity. I use the case of mental health of African Americans as an extended example to support the argument that psychiatric services must become more closely attuned to religious matters. I suggest ways in which this can be achieved. Attention to religion can aid in the development of culturally competent and accessible services, which in turn, may increase engagement and service satisfaction among religious populations. PMID:22421686

2012-01-01

389

Collision dynamics between stretched states of spin-2 87 Rb Bose–Einstein condensates

We experimentally observed the time dependence of the spin populations of spin-2 87Rb Bose–Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the stretched states\\u000a |F=2,m\\u000a \\u000a F\\u000a =+2? and |F=2,m\\u000a \\u000a F\\u000a =?2? with several varieties of population imbalances. No spin-exchange collisions were observed in a weak magnetic field of\\u000a 45 mG. The atom loss rate

S. Tojo; A. Tomiyama; M. Iwata; T. Kuwamoto; T. Hirano

2008-01-01

390

Doping dependence of spin dynamics in electron-doped Ba(Fe1-xCox)2As2

The spin dynamics in single crystal, electron-doped Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} has been investigated by inelastic neutron scattering over the full range from undoped to the overdoped regime. We observe damped magnetic fluctuations in the normal state of the optimally doped compound (x=0.06) that share a remarkable similarity with those in the paramagnetic state of the parent compound (x=0). In the overdoped superconducting compound (x=0.14), magnetic excitations show a gaplike behavior, possibly related to a topological change in the hole Fermi surface (Lifshitz transition) while the imaginary part of the spin susceptibility {chi}' prominently resembles that of the overdoped cuprates. For the heavily overdoped, nonsuperconducting compound (x=0.24) the magnetic scattering disappears, which could be attributed to the absence of a hole Fermi-surface pocket observed by photoemission.

Matan, K. [Univ. of Tokyo and JST, TRIP/Tokyo; Ibuka, S. [Univ. of Tokyo and JST, TRIP/Tokyo; Morinaga, R. [Univ. of Tokyo and JST, TRIP/Tokyo; Chi, Songxue [NIST and Univ. of MD; Lynn, J W [NIST Center for Neutron Research (NCRN), Gaithersburg, MD; Christianson, Andrew D [ORNL; Lumsden, Mark D [ORNL; Sato, T. J. [Univ. of Tokyo and JST, TRIP/Tokyo

2010-01-01

391

How anatomy shapes dynamics: a semi-analytical study of the brain at rest by a simple spin model

Resting state networks (RSNs) show a surprisingly coherent and robust spatiotemporal organization. Previous theoretical studies demonstrated that these patterns can be understood as emergent on the basis of the underlying neuroanatomical connectivity skeleton. Integrating the biologically realistic DTI/DSI-(Diffusion Tensor Imaging/Diffusion Spectrum Imaging)based neuroanatomical connectivity into a brain model of Ising spin dynamics, we found a system with multiple attractors, which can be studied analytically. The multistable attractor landscape thus defines a functionally meaningful dynamic repertoire of the brain network that is inherently present in the neuroanatomical connectivity. We demonstrate that the more entropy of attractors exists, the richer is the dynamical repertoire and consequently the brain network displays more capabilities of computation. We hypothesize therefore that human brain connectivity developed a scale free type of architecture in order to be able to store a large number of different and flexibly accessible brain functions. PMID:23024632

Deco, Gustavo; Senden, Mario; Jirsa, Viktor

2012-01-01

392

NASA Astrophysics Data System (ADS)

We report neutron spin-echo measurements on two types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40 , and the second is PVA gel in an aqueous borax solution. The observed normalized intermediate scattering functions I(Q,t)/I(Q,0) are very different between them. The former I(Q,t)/I(Q,0) shows a nondecaying component in addition to a fast decay, but the latter does not have the nondecaying one. This clearly indicates that the fluctuations in the former PVA gel consist of static and dynamic fluctuations whereas the latter PVA gel does include only the dynamic fluctuations. The dynamic fluctuations of the former and latter gels have been analyzed in terms of a restricted motion in the network and Zimm motion, respectively, and the origins of these motions will be discussed.

Kanaya, T.; Takahashi, N.; Nishida, K.; Seto, H.; Nagao, M.; Takeda, T.

2005-01-01

393

NASA Technical Reports Server (NTRS)

This report presents the development and description of the decomposition aggregation approach to stability investigations of high dimension mathematical models of dynamic systems. The high dimension vector differential equation describing a large dynamic system is decomposed into a number of lower dimension vector differential equations which represent interconnected subsystems. Then a method is described by which the stability properties of each subsystem are aggregated into a single vector Liapunov function, representing the aggregate system model, consisting of subsystem Liapunov functions as components. A linear vector differential inequality is then formed in terms of the vector Liapunov function. The matrix of the model, which reflects the stability properties of the subsystems and the nature of their interconnections, is analyzed to conclude over-all system stability characteristics. The technique is applied in detail to investigate the stability characteristics of a dynamic model of a hypothetical spinning Skylab.

Siljak, D. D.; Weissenberger, S.; Cuk, S. M.

1973-01-01

394

Size-dependent magnetic ordering and spin-dynamics in DyPO4 and GdPO4 nanoparticles

Low-temperature magnetic susceptibility and heat capacity measurements on nanoparticles (d 2.6 nm) of the antiferromagnetic compounds DyPO4 (TN = 3:4 K) and GdPO4 (TN = 0:77 K) provide clear demonstrations of finite-size effects, which limit the divergence of the magnetic correlation lengths, thereby suppressing the bulk long-range magnetic ordering transitions. Instead, the incomplete antiferromagnetic order inside the particles leads to the formation of net magnetic moments on the particles. For the nanoparticles of Ising-type DyPO4 superparamagnetic blocking is found in the ac-susceptibility at 1 K, those of the XY-type GdPO4 analogue show a dipolar spin-glass transition at 0:2 K. Monte Carlo simulations for the magnetic heat capacities of both bulk and nanoparticle samples are in agreement with the experimental data. Strong size effects are also apparent in the Dy3+ and Gd3+ spin-dynamics, which were studied by zero-field SR relaxation and high-field 31P-NMR nuclear relaxation measurements. The freezing transitions observed in the ac-susceptibility of the nanoparticles also appear as peaks in the temperature dependence of the zero-field SR rates, but at slightly higher temperatures - as to be expected from the higher frequency of the muon probe. For both bulk and nanoparticles of GdPO4, the muon and 31P-NMR rates are for T 5 K dominated by exchange-narrowed hyperfine broadening arising from the electron spin-spin interactions inside the particles. The dipolar hyperfine interactions acting on the muons and the 31P are, however, much reduced in the nanoparticles. For the DyPO4 analogues the high-temperature rates appear to be fully determined by electron spin-lattice relaxation processes.

Evangelisti, Marco [Instituto de Ciencia de Materiales de Aragon (ICMA), Spain; Sorop, Tibi G [Leiden University; Bakharev, Oleg N [Leiden University; Visser, Dirk [ISIS Facility, Rutherford Appleton Laboratory; Hillier, Adrian D. [ISIS Facility, Rutherford Appleton Laboratory; Alonso, Juan [Universidad de Malaga, Spain; Haase, Markus [University of Osnabruck, Barbarastr Germany; Boatner, Lynn A [ORNL; De Jongh, L. Jos [Leiden University

2011-01-01

395

NASA Astrophysics Data System (ADS)

Spin dynamics in a dissipative environment are treated via the evolution (master) equation for the quasiprobability density function of spin orientations in the phase space of the polar and azimuthal angles in the weak spin-bath coupling and high-temperature limits. The explicit solution is written for an arbitrary spin Hamiltonian as a finite series of spherical harmonics analogous to the (infinite) Fourier series representation of the classical case governed by the Fokker-Planck equation. Therefore, the expansion coefficients, i.e., the statistical averages of the spherical harmonics, may be determined as before from a differential-recurrence relation, yielding the stochastic spin dynamics for arbitrary spin number S. For large S the differential-recurrence relations reduce to those generated by the Fokker-Planck equation. Thus, the spin dynamics may be treated in a manner transparently linking to the classical representations, thereby providing quantum corrections to classical averages. The method is illustrated via the magnetization relaxation of a uniaxial paramagnet with a dc field H0 applied at an arbitrary angle to the easy axis, which is the quantum version of the most basic model in classical superparamagnetism.

Kalmykov, Yuri P.; Titov, Serguey V.; Coffey, William T.

2012-09-01

396

PHYSICAL REVIEW B 86, 054416 (2012) Longitudinal magnetic fluctuations in Langevin spin dynamics

, by introducing stochastic and dissipation terms in the spin equations of motion.1 These two terms, steering,26,28Â30 There are several computational methods that include the treatment of longitudinal and transverse magnetic degrees

397

Proton-driven spin diffusion in rotating solids via reversible and irreversible quantum dynamics

Proton-driven spin diffusion (PDSD) experiments in rotating solids have received a great deal of attention as a potential source of distance constraints in large biomolecules. However, the quantitative relationship between ...

Veshtort, Mikhail

398

Physica E 34 (2006) 355358 Dynamics of nuclear spins appearing in transport measurements of an

nonlinear transport between spin polarized edge channels is studied. The observed hysteresis of the I2V be calculated using the LandauerÂBuÂ¨ ttiker multichannel formulae [5]. Assum- ing the absence of backscattering

Hohls, Frank

399

An introduction to the spectrum, symmetries, and dynamics of spin-1/2 Heisenberg chains

NASA Astrophysics Data System (ADS)

Quantum spin chains are prototype quantum many-body systems that are employed in the description of various complex physical phenomena. We provide an introduction to this subject by focusing on the time evolution of a Heisenberg spin-1/2 chain and interpreting the results based on the analysis of the eigenvalues, eigenstates, and symmetries of the system. We make available online all computer codes used to obtain our data.

Joel, Kira; Kollmar, Davida; Santos, Lea F.

2013-06-01

400

Spin Dynamics: A Paradigm for Time Optimal Control on Compact Lie Groups

The development of efficient time optimal control strategies for coupled spin systems plays a fundamental role in nuclear\\u000a magnetic resonance (NMR) spectroscopy. In particular, one of the major challenges lies in steering a given spin system to\\u000a a maximum of its so-called transfer function. In this paper we study in detail these questions for a system of two weakly\\u000a coupled

G. Dirr; U. helmke; K. Hüper; M. Kleinsteuber; Y. Liu

2006-01-01

401

NASA Astrophysics Data System (ADS)

Pauling's model of hydrogen disorder in water ice represents the prototype of a frustrated system. Over the years it has spawned several analogous models, including Anderson's model antiferromagnet and the statistical "vertex" models. Spin Ice is a sixteen vertex model of "ferromagnetic frustration" that is approximated by real materials, most notably the rare earth pyrochlores Ho2Ti2O7, Dy2Ti2O7 and Ho2Sn2O7. These "spin ice materials" have the Pauling zero point entropy and in all respects represent almost ideal realisations of Pauling's model. They provide experimentalists with unprecedented access to a wide variety of novel magnetic states and phase transitions that are located in different regions of the field-temperature phase diagram. They afford theoreticians the opportunity to explore many new features of the magnetic interactions and statistical mechanics of frustrated systems. This chapter is a comprehensive review of the physics -- both experimental and theoretical -- of spin ice. It starts with a discussion of the historic problem of water ice and its relation to spin ice and other frustrated magnets. The properties of spin ice are then discussed in three sections that deal with the zero field spin ice state, the numerous field-induced states (including the recently identified "kagomé ice") and the magnetic dynamics. Some materials related to spin ice are briefly described and the chapter is concluded with a short summary of spin ice physics.

Bramwell, Steven T.; Gingras, Michel J. P.; Holdsworth, Peter C. W.

2013-03-01

402

NASA Astrophysics Data System (ADS)

Using a cochlear implant simulator, Stone and Moore [J. Acoust. Soc. Am. 114, 1023-1034 (2003)] reported that wideband fast-acting compression led to poorer intelligibility than slow-acting compression in a competing speech task. Compression speed was varied by using different pairs of attack and release times. In the first experiment reported here, it is shown that attack times less than about 2 ms in a wideband compressor are deleterious to intelligibility. In experiment 2, fast wideband compression was applied to the target and background either before or after mixing. The former reduced the modulation depth of each signal but maintained the independence between the two signals, while the latter introduced ``comodulation.'' Using simulations with 6 and 11 channels, intelligibility was higher when compression was applied before mixing. In experiment 3, wideband compression was compared with multichannel compression; the latter led to reduced comodulation effects. For 6 channels, the position of the compressor, either wideband or within each channel, had no effect on intelligibility. For 11 channels, channel compression severely degraded intelligibility compared to wideband compression, presumably because of the greater reduction of across-channel contrasts. Overall, caution appears necessary in the use of fast-acting compression in cochlear implants, so as to preserve intelligibility. .

Stone, Michael A.; Moore, Brian C. J.

2004-10-01

403

NASA Astrophysics Data System (ADS)

Polyelectrolyte spin assembly (PSA) of multilayers is a sequential process featuring adsorption of oppositely charged polyelectrolytes from dilute solutions undergoing spin-coating flow. We investigated the dependence of multilayer film build-up of poly(sodium-4-styrene sulfonate) and poly(allylamine hydrochloride) on solution ionic strength and spin rate. We observed that at fixed spin rate the PSA growth rate shows a non-monotonic dependence on salt concentration. It first increases and then decreases with increasing the solution ionic strength. This observation is a manifestation of two competing mechanisms driven by electrostatic interactions and shear flow, which control film build up. This non-monotonic behavior is explained in the framework of a Flory-like theory of multilayer formation from polyelectrolyte solution under shear flow. We performed molecular dynamics simulations to further elucidate the factors controlling the film structure.

Lefaux, Christophe; Dobrynin, Andrey; Mather, Patrick

2005-03-01

404

Spin dynamics of the intermediate-valence compound EuCu{sub 2}Si{sub 2}

The dynamic magnetic response of the intermediate-valence compound EuCu{sub 2}Si{sub 2} has been studied using inelastic neutron scattering. At low temperatures, strong renormalization of the {sup 7}F{sub 0} {sup {yields}} {sup 7}F{sub 1} spin-orbit transition energy is detected; it is likely to be related to partial delocalization of the f electrons of Eu. An increase in the temperature increases the valence instability of europium and results in further changes in the magnetic excitation spectrum parameters and the appearance of an intense quasi-elastic component.

Alekseev, P. A. [Russian Research Centre 'Kurchatov Institute' (Russian Federation); Mignot, J.-M. [CEA/Saclay, Laboratoire Leon Brillouin (France); Nemkovski, K. S.; Lazukov, V. N., E-mail: lvn@isssph.kiae.ru; Nefeodova, E. V. [Russian Research Centre 'Kurchatov Institute' (Russian Federation); Menushenkov, A. P., E-mail: menushen@htsc.mephi.ru; Kuznetsov, A. V. [Moscow Engineering Physics Institute (State University) (Russian Federation); Bewley, R. I. [ISIS, Rutherford Appleton Laboratory (United Kingdom); Gribanov, A. V. [Moscow State University (Russian Federation)

2007-07-15

405

NASA Astrophysics Data System (ADS)

For the forward going proton and ? meson, the coherent ? meson production in the (p,p?) reaction on the spin-isospin saturated nucleus occurs only due to the ? meson exchange interaction between the beam proton and nucleus. In this process, the nucleon in the nucleus can be excited to resonances N* and the ? meson in the final state can arise due to N*?N?. We investigate the dynamics of resonances, including nucleon Born terms, and their interferences in the coherently added cross section of this reaction. We discuss the importance of N(1520) resonance and show the sensitivity of the cross section to the hadron-nucleus interaction.

Das, Swapan

2014-10-01

406

NASA Astrophysics Data System (ADS)

We report for the first time that the dynamic magnetic intermediate state (DMI) was observed at a speed of several ns during spin transfer switching for MgO-based magnetic tunnel junctions (MTJs). The DMI was observed as slow resistance oscillation at the center of the parallel to anti-parallel state by single shot time domain measurements. The DMI is observable at certain current amplitudes. The outbreak probability decreases with further current increase. We concluded that the DMI originates from inhomogeneous magnetization behavior. On the other hand, previous single shot time domain measurements have shown only for single-domain-like magnetization behavior.

Aoki, Tatsuya; Ando, Yasuo; Oogane, Mikihiko; Naganuma, Hiroshi

2010-05-01

407

Ultrafast dynamics of the Mn3+ d-d transition and spin-lattice interaction in YMnO3 film

NASA Astrophysics Data System (ADS)

We investigate the photo-induced carrier dynamics and spin-lattice interaction in hexagonal YMnO3 film by the temperature-dependent femtosecond pump-probe spectroscopy. The spin-lattice interaction is identified from the slow component of the transient transmittance change with the excitation energies tuned to 1.7 eV and 2.0 eV, which are close to Mn3+ ions d(xz),(yz)?d(z2) and d(x2-y2),(xy)?d(z2) transition, respectively. Temperature dependences of the spin-lattice relaxation parameters demonstrate that the spin-lattice interaction is strongly connected with the d-d transition within Mn3+ ions and enhanced by spin ordering.

Jin, Zuanming; Ma, Hong; Li, Gaofang; Xu, Yue; Ma, Guohong; Cheng, Zhenxiang

2012-01-01

408

Spin-orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

NASA Astrophysics Data System (ADS)

Spin-orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin-orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin-orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious "magnetic field" in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz-Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.

Samokhin, K. V.

2009-11-01

409

Variation of the lattice and spin dynamics in Bi1-xDyxFeO3 nanoparticles

NASA Astrophysics Data System (ADS)

Infrared and Raman-scattering spectroscopies were employed to explore the lattice and spin dynamics of Bi1-xDyxFeO3 nanoparticles. With increasing substitution of Bi by Dy in the range of 0.00 ? x ? 0.40, we observe (1) evidence for an increase of local lattice distortion of the FeO6 octahedra, and significant changes of phonon parameters in the x = 0.15 sample, corresponding to the structural transformation from rhombohedral to orthorhombic, (2) the chemically substituted enhanced dielectric constant of 43.4 in the x = 0.20 sample, (3) the development of two-magnon excitations in Dy substituted samples, which sensitively gauges the modification of magnetic structures from a cycloidal spin to a homogeneous magnetized state, and (4) Dy substitution disrupts the lattice-spin interactions at high temperatures. These findings extend our understanding of tailoring the structural and magnetic properties of chemically substituted multiferroic nanoparticles and advance the technologically important development of these materials.

Liu, H. L.; Su, Y. C.; Tang, Y. H.; Lin, J. G.

2014-04-01

410

NASA Astrophysics Data System (ADS)

We study the universal low-energy dynamics associated with the spontaneous breaking of Lorentz invariance down to spatial rotations. The effective lagrangian for the associated Goldstone field can be uniquely determined by the non-linear realization of a broken time diffeomorphism symmetry, up to some overall mass scales. It has previously been shown that this symmetry breaking pattern gives rise to a Higgs phase of gravity, in which gravity is modified in the infrared. In this paper, we study the effects of direct couplings between the Goldstone boson and standard model fermions, which necessarily accompany Lorentz-violating terms in the theory. The leading interaction is the coupling to the axial vector current, which reduces to spin in the non-relativistic limit. A spin moving relative to the ``ether" rest frame will emit Goldstone Cerenkov radiation. The Goldstone also induces a long-range inverse-square law force between spin sources with a striking angular dependence, reflecting the underlying Goldstone shockwaves and providing a smoking gun for this theory. We discuss the regime of validity of the effective theory describing these phenomena, and the possibility of probing Lorentz violations through Goldstone boson signals in a way that is complementary to direct tests in some regions of parameter space.

Arkani-Hamed, Nima; Cheng, Hsin-Chia; Luty, Markus; Thaler, Jesse

2005-07-01

411

NASA Astrophysics Data System (ADS)

Microscopic structural instabilities of EuTiO3 single crystals were investigated by synchrotron x-ray diffraction. Antiferrodistortive (AFD) oxygen octahedron rotational order was observed alongside Ti derived antiferroelectric distortions. The competition between the two instabilities is reconciled through a cooperatively modulated structure allowing both to coexist. The combination of electric and magnetic fields increases the population of the modulated AFD order, illustrating how the origin of the large magnetoelectric coupling derives from the dynamic equilibrium between AFD and polar instabilities.

Kim, Jong-Woo; Thompson, Paul; Brown, Simon; Normile, Peter S.; Schlueter, John A.; Shkabko, Andrey; Weidenkaff, Anke; Ryan, Philip J.

2013-01-01

412

Students' dynamic geometric reasoning about quantum spin-1/2 states

NSDL National Science Digital Library

Quantum states are traditionally cognitively managed exclusively with algebra rather than geometry. One reason for emphasizing algebra is the high dimensionality of quantum mathematical systems; even spin-1/2 systems require a 2-d complex number space for describing their quantum states, which can be hard to visualize. Using "nested phasor diagrams," which use nesting to increase the dimensionality of graphic space, we taught undergraduate students to represent spin-1/2 states graphically as well as algebraically. In oral exams, students were asked to identify which spin-1/2 states, expressed arithmetically, would generate the same set of probabilities as each other (i.e., they are the same except for a different overall phase factor). Video records of oral exams (N=13) show that no student performed this task successfully using an algebraic method; instead, all successful students solved the problem graphically. Furthermore, most students who were successful used a certain gesture to solve the problem.

Close, Hunter G.; Schiber, Catherine C.; Close, Eleanor W.; Donnelly, David

2014-01-30

413

Using 13C spin relaxation NMR in combination with molecular dynamic (MD) simulations, we characterized internal motions within double-stranded DNA on the pico- to nano-second time scale. We found that the C–H vectors in all cytosine ribose moieties within the Dickerson–Drew dodecamer (5?-CGCGAATTCGCG-3?) are subject to high amplitude motions, while the other nucleotides are essentially rigid. MD simulations showed that repuckering is a likely motional model for the cytosine ribose moiety. Repuckering occurs with a time constant of around 100 ps. Knowledge of DNA dynamics will contribute to our understanding of the recognition specificity of DNA-binding proteins such as cytosine methyltransferase. PMID:18579564

Duchardt, Elke; Nilsson, Lennart

2008-01-01

414

NASA Astrophysics Data System (ADS)

We report re`sults of different time-frequency analyses (Wavelet and Hilbert-Huang Transform (HHT)) of voltage measurements related to a spin-torque oscillator working in a regime of non-stationary dynamics. Our results indicate that the Wavelet analysis identifies the non-stationary magnetization dynamics revealing the existence of intermittent and independent excited modes while the HHT is able to accurately extract the time domain traces of each independent mode. Overall performance indicates a route for a complete characterization of time-frequency domain data of a STO, pointing out that the combined Wavelet-HHT methodology developed is general and can be also used for a variety of other different scenarios.

Siracusano, Giulio; Corte, Aurelio La

2014-02-01

415

Spectrum, symmetries, and dynamics of Heisenberg spin-1/2 chains

NASA Astrophysics Data System (ADS)

Quantum spin chains are prototype quantum many-body systems. They are employed in the description of various complex physical phenomena. Here we provide an introduction to the subject by focusing on the time evolution of Heisenberg spin-1/2 chains with couplings between nearest-neighbor sites only. We study how the anisotropy parameter and the symmetries of the model affect its time evolution. Our predictions are based on the analysis of the eigenvalues and eigenstates of the system and then confirmed with actual numerical results.

Joel, Kira; Kollmar, Davida; Santos, Lea

2013-03-01

416

NASA Astrophysics Data System (ADS)

The lowest-energy singlet (1 1A') and two lowest-energy triplet (1 3A' and 1 3A'') electronic states of CO2 are characterized using dynamically weighted multireference configuration interaction (dw-MRCI+Q) electronic structure theory calculations extrapolated to the complete basis set (CBS) limit. Global analytic representations of the dw-MRCI+Q/CBS singlet and triplet surfaces and of their CASSCF/aug-cc-pVQZ spin-orbit coupling surfaces are obtained via the interpolated moving least squares (IMLS) semiautomated surface fitting method. The spin-forbidden kinetics of the title reaction is calculated using the coupled IMLS surfaces and coherent switches with decay of mixing non-Born-Oppenheimer molecular dynamics. The calculated spin-forbidden association rate coefficient (corresponding to the high pressure limit of the rate coefficient) is 7-35 times larger at 1000-5000 K than the rate coefficient used in many detailed chemical models of combustion. A dynamical analysis of the multistate trajectories is presented. The trajectory calculations reveal direct (nonstatistical) and indirect (statistical) spin-forbidden reaction mechanisms and may be used to test the suitability of transition-state-theory-like statistical methods for spin-forbidden kinetics. Specifically, we consider the appropriateness of the ``double passage'' approximation, of assuming statistical distributions of seam crossings, and of applications of the unified statistical model for spin-forbidden reactions.

Jasper, Ahren W.; Dawes, Richard

2013-10-01

417

The electron spin resonance (ESR) technique has been applied to study the spin dynamics in broad temperature range for rare earth doped Mn(0.5)Zn(0.5)Fe(1.9)Gd(0.1)O(4) (MZG5) magnetic fluid. Zero field cooled (ZFC) ESR spectra of MZG5 fluid exhibit an isotropic shift in the resonance field below 40 K, while the field cooled (FC) ESR spectra show a deviation from sin(2)? behavior and an angle dependent hysteresis, this unambiguously points to the dominating unidirectional freezing of surface spins below 40 K. Above 60 K, the resonance field exhibits sin(2)? behavior, indicating the uniaxial anisotropy contribution of core spin. This indicates that surface spin freezing temperature is around 40 K. The presence of surface spin freezing and the coupling between core and surface spins are further supported by cycle dependent FC ESR spectra measured at 20 K, which show the systematic increase in resonance field (H(res)) and intensity. The double peak behavior of blocking temperature distribution retrieved from ZFC-FC magnetization measurement is an additional corroboration of the existence of surface spin glass like layer. PMID:23123769

Parekh, Kinnari; Upadhyay, R V

2012-12-01

418

Microscopic structural instabilities of EuTiO3 single crystals were investigated by synchrotron x-ray diffraction. Antiferrodistortive (AFD) oxygen octahedron rotational order was observed alongside Ti derived antiferroelectric distortions. The competition between the two instabilities is reconciled through a cooperatively modulated structure allowing both to coexist. The combination of electric and magnetic fields increases the population of the modulated AFD order, illustrating how the origin of the large magnetoelectric coupling derives from the dynamic equilibrium between AFD and polar instabilities. PMID:23383935

Kim, Jong-Woo; Thompson, Paul; Brown, Simon; Normile, Peter S; Schlueter, John A; Shkabko, Andrey; Weidenkaff, Anke; Ryan, Philip J

2013-01-11

419

NASA Astrophysics Data System (ADS)

In a recent inelastic neutron scattering experiment in the pseudogap state of the high-temperature superconductor YBa2Cu3O6.6, an unusual “vertical” dispersion of the spin excitations with a large in-plane anisotropy was observed. In this paper, we discuss in detail the spin susceptibility of the singlet d-density wave, the triplet d-density wave as well as the more common spin density wave orders with hopping anisotropies. From numerical calculations within the framework of random phase approximation, we find nearly vertical dispersion relations for spin excitations with anisotropic incommensurability at low energy ??90meV, which are reminiscent of the experiments. At very high energy ??165meV, we also find energy-dependent incommensurability. Although there are some important differences between the three cases, unpolarized neutron measurements cannot discriminate between these alternate possibilities; the vertical dispersion, however, is a distinct feature of all three density wave states in contrast to the superconducting state, which shows an hour-glass shape dispersion.

Hsu, Chen-Hsuan; Wang, Zhiqiang; Chakravarty, Sudip

2012-12-01

420

Diffusive spin dynamics in ferromagnetic thin films with a Rashba interaction

In a ferromagnetic metal layer, the coupled charge and spin diffusion equations are obtained in the presence of both Rashba spin-orbit interaction and magnetism. The mis-alignment between the magnetization and the non-equilibrium spin density induced by the Rashba field gives rise to Rashba spin torque acting on the ferromagnetic order parameter. In a general form, we find that the Rashba torque consists of both in-plane and out-of-plane components, ie $\\bm{T}=T_{\\bot}\\hat{\\bm{y}}\\times{\\hat{\\bm m}}+T_{\\parallel}{\\hat{\\bm m}}\\times({\\hat{\\bm y}}\\times{\\hat{\\bm m}})$. Numerical simulations on a two dimensional nano-wire discuss the impact of diffusion on the Rashba torque, which reveals a large enhancement to the ratio $T_{\\parallel}/T_{\\bot}$ for thin wires. Our theory provides an explanation to the mechanism that drives the magnetization switching in a single ferromagnet as observed in the recent experiments.

Wang, Xuhui

2011-01-01

421

A New Spin Probe of Protein Dynamics: Nitrogen Relaxation in 15N-2H Amide Groups

to set up, and, in general, straight- forward to interpret. 15N spin relaxation studies in the past have tumbling. Combining several data sets permits evaluation of the spectral density J(D + N) for each amide site. This spectral density samples a uniquely low frequency (26 MHz at a 500 MHz field) and, therefore

Skrynnikov, Nikolai

422

Slowly rotating black holes in dynamical Chern-Simons gravity: Deformation quadratic in the spin

NASA Astrophysics Data System (ADS)

We derive a stationary and axisymmetric black hole solution to quadratic order in the spin angular momentum. The previously found, linear-in-spin terms modify the odd-parity sector of the metric, while the new corrections appear in the even-parity sector. These corrections modify the quadrupole moment, as well as the (coordinate-dependent) location of the event horizon and the ergoregion. Although the linear-in-spin metric is of Petrov type D, the quadratic-order terms render it of type I. The metric does not possess a second-order Killing tensor or a Carter-like constant. The new metric does not possess closed timelike curves or spacetime regions that violate causality outside of the event horizon. The new, even-parity modifications to the Kerr metric decay less rapidly at spatial infinity than the leading order in spin, odd-parity ones, and thus, the former are more important when considering black holes that are rotating moderately fast. We calculate the modifications to the Hamiltonian, binding energy and Kepler’s third law. These modifications are crucial for the construction of gravitational wave templates for black hole binaries, which will enter at second post-Newtonian order, just like dissipative modifications found previously.

Yagi, Kent; Yunes, Nicolás; Tanaka, Takahiro

2012-08-01

423

Dynamical ac study of the critical behavior in Heisenberg spin glasses Marco Picco1

and determine an apparent finite temperature transition which is compatible with the chiral-glass temperature . Although our data indicate that the spin-glass transition occurs at the same temperature as the chiral undergoes a chiral-glass phase tran- sition at a finite temperature6,7 while it was for long time believed

Ritort, Felix

424

Coupling between Current and Dynamic Magnetization : from Domain Walls to Spin Waves

NASA Astrophysics Data System (ADS)

So far, we have derived some general expressions for domain-wall motion and the spin motive force. We have seen that the ? parameter plays a large role in both subjects. In all chapters of this thesis, there is an emphasis on the determination of this parameter. We also know how to incorporate thermal fluctuations for rigid domain walls, as shown above. In Chapter 2, we study a different kind of fluctuations: shot noise. This noise is caused by the fact that an electric current consists of electrons, and therefore has fluctuations. In the process, we also compute transmission and reflection coefficients for a rigid domain wall, and from them the linear momentum transfer. More work on fluctuations is done in Chapter 3. Here, we consider a (extrinsically pinned) rigid domain wall under the influence of thermal fluctuations that induces a current via spin motive force. We compute how the resulting noise in the current is related to the ? parameter. In Chapter 4 we look into in more detail into the spin motive forces from field driven domain walls. Using micro magnetic simulations, we compute the spin motive force due to vortex domain walls explicitly. As mentioned before, this gives qualitatively different results than for a rigid domain wall. The final subject in Chapter 5 is the application of the general expression for spin motive forces to magnons. Although this might seem to be unrelated to domain-wall motion, this calculation allows us to relate the ? parameter to macroscopic transport coefficients. This work was supported by Stichting voor Fundamenteel Onderzoek der Materie (FOM), the Netherlands Organization for Scientific Research (NWO), and by the European Research Council (ERC) under the Seventh Framework Program (FP7).

Lucassen, M. E.

2012-05-01

425

NASA Astrophysics Data System (ADS)

A large class of symmetry-protected topological phases (SPT) in boson/spin systems have been recently predicted by the group cohomology theory. In this work, we consider bosonic SPT states at least with charge symmetry [U(1) or ZN] or spin-Sz rotation symmetry [U(1) or ZN] in two (2D) and three dimensions (3D) and the surface of 3D. If both are U(1), we apply external electromagnetic field/“spin gauge field” to study the charge/spin response. For the SPT examples we consider {i.e., Uc(1)?Z2T, Us(1)×Z2T, Uc(1)×[Us(1)?Z2]; subscripts c and s are short for charge and spin; Z2T and Z2 are time-reversal symmetry and ? rotation about Sy, respectively}, many variants of Witten effect in the 3D SPT bulk and various versions of anomalous surface quantum Hall effect are defined and systematically investigated. If charge or spin symmetry reduces to ZN by considering charge-N or spin-N condensate, instead of the linear response approach, we gauge the charge/spin symmetry, leading to a dynamical gauge theory with some remaining global symmetry. The 3D dynamical gauge theory describes a symmetry-enriched topological phase (SET), i.e., a topologically ordered state with global symmetry which admits nontrivial ground-state degeneracy depending on spatial manifold topology. For the SPT examples we consider, the corresponding SET states are described by dynamical topological gauge theory with topological BF term and axionic ? term in 3D bulk. In addition, the surface of SET is described by the chiral boson theory with quantum anomaly.

Ye, Peng; Wang, Juven

2013-12-01

426

In this study, the center-of-mass diffusion and shape fluctuations of large unilamellar 1-palmitoyl-2-oleyl-sn-glycero-phosphatidylcholine vesicles prepared by extrusion are studied by means of neutron spin echo in combination with dynamic light scattering. The intermediate scattering functions were measured for several different values of the momentum transfer, q, and for different cholesterol contents in the membrane. The combined analysis of neutron spin echo and dynamic light scattering data allows calculation of the bending elastic constant, ?, of the vesicle bilayer. A stiffening effect monitored as an increase of ? with increasing cholesterol molar ratio is demonstrated by these measurements. PMID:19413968

Arriaga, Laura R.; Lopez-Montero, Ivan; Monroy, Francisco; Orts-Gil, Guillermo; Farago, Bela; Hellweg, Thomas

2009-01-01

427

LK?14 is a 14 amino acid peptide with a periodic sequence of leucine and lysine residues consistent with an amphipathic ?-helix. This “hydrophobic periodicity” has been found to result in an ?-helical secondary structure at air-water interfaces and on both polar and non-polar solid polymer surfaces. In this paper the dynamics of LK?14 peptides, selectively deuterated at a single leucine and adsorbed onto polystyrene and carboxylated polystyrene beads, are studied using 2H Magic Angle Spinning (MAS) solid state NMR over a 100 degree temperature range. We first demonstrate the sensitivity enhancement possible with 2H MAS techniques, which in turn enables us to obtain high quality 2H NMR spectra for selectively deuterated peptides adsorbed onto solid polymer surfaces. An extensive literature shows that the dynamics of leucine side chains are sensitive to the local structural environment of the protein. Therefore the degree to which the dynamics of leucine side chains and the backbone of the peptide LK?14 are influenced by surface proximity and surface chemistry is studied as a function of temperature with 2H MAS NMR. It is found that the dynamics of the leucine side chains in LK?14 depend strongly upon the orientation of the polymer on the surface, which in turn depends on whether the LK?14 peptide adsorbs onto a polar or non-polar surface. 2H MAS line shapes therefore permit probes of surface orientation over a wide temperature range. PMID:21650191

Breen, Nicholas F.; Li, Kun; Olsen, Gregory L.; Drobny, Gary P.

2011-01-01

428

COMPETENCIES DICTIONARY Contents Page

COMPETENCIES DICTIONARY Contents Page Core Competencies Results Orientation/Project Management ......................................................................................................7-8 Conflict Resolution Verbal and Written Communication .......................................................10

Bieber, Michael

429

Computation of mutual fitness by competing bacteria

Competing populations in shared spaces with nonrenewable resources do not necessarily wage a battle for dominance at the cost of extinction of the less-fit strain if there are fitness advantages to the presence of the other strain. We report on the use of nanofabricated habitat landscapes to study the population dynamics of competing wild type and a growth advantage in

Juan E. Keymer; Peter Galajda; Guillaume Lambert; David Liao; Robert H. Austin

2008-01-01

430

Interatomic Exchange Interactions for Finite-Temperature Magnetism and Nonequilibrium Spin Dynamics

NASA Astrophysics Data System (ADS)

We derive ab inito exchange parameters for general noncollinear magnetic configurations, in terms of a multiple scattering formalism. We show that the general exchange formula has an anisotropiclike term even in the absence of spin-orbit coupling, and that this term is large, for instance, for collinear configuration in bcc Fe, whereas for fcc Ni it is quite small. We demonstrate that keeping this term leads to what one should consider a biquadratic effective spin Hamiltonian even in the case of collinear arrangement. In noncollinear systems this term results in new tensor elements that are important for exchange interactions at finite temperatures, but they have less importance at low temperature. To illustrate our results in practice, we calculate for bcc Fe magnon spectra obtained from configuration-dependent exchange parameters, where the configurations are determined by finite-temperature effects. Our theory results in the same quantitative results as the finite-temperature neutron scattering experiments.

Szilva, A.; Costa, M.; Bergman, A.; Szunyogh, L.; Nordström, L.; Eriksson, O.

2013-09-01

431

Spin dynamics in nonsequential two-photon double ionization of helium in an intense laser field

Nonsequential two-photon double ionization of a two-electron system (He and He-like ions) in a circularly polarized intense laser field is developed in a relativistic field theoretic way. Antisymmetry is maintained in the correlated wave functions of He in the initial state after modification to include Dirac spinor, and in the Volkov wave functions of the two electrons in the final free state. The present theory endeavors to provide an estimate of the helicity-dependent angular asymmetry in spin-current generation in nonsequential two-photon double ionization. Angular dependence of circular dichroism obtained in this paper, in coplanar and orthogonal geometries, is compared with the only existing nonrelativistic result obtained using lowest-order perturbation theory. Present result for dichroism underestimates the nonrelativistic result. Entanglement in the spins of the ejected electrons is concluded.

Bhattacharyya, S.; Mazumder, Mina; Chakrabarti, J. [Indian Association for Cultivation of Science, Jadavpur, Kolkata (India); Faisal, F. H. M. [Fakultaet fuer Physik, Universitaet Bielefeld, Postfach D-100131 (Germany)

2011-04-15

432

Control of crisis-induced intermittency in the dynamics of a kicked, damped spin

NASA Astrophysics Data System (ADS)

A method of controlling the intermittent behavior induced by a crisis is applied to a model of a periodically kicked, damped spin. Using small, occasional changes of a parameter, one can make the system remain on a former attractor, enlarged or destroyed by a crisis. The amplitude of the changes grows linearly with the distance from the crisis point, and the frequency of interventions scales as the inverse of the characteristic time of the intermittency.

Kacperski, Krzysztof; Ho?yst, Janusz A.

1997-05-01

433

Chiral spin states, hole dynamics, and superconductivity in strongly correlated electronic systems

Relation between strongly correlated electronic systems and anyonlike systems is established. A U(1) gauge theory is developed for the frustrated Hubbard model in the limit of infinite on-site Coulomb repulsion. An effective Chern-Simons theory, which describes chiral spin liquids is obtained. The fermions (holes) are coupled to the gauge fields creating thus an anyonlike system. I show that under some

N. I. Karchev

1991-01-01

434

Higher spin contributions to holographic fluid dynamics in AdS5/CFT4

NASA Astrophysics Data System (ADS)

We calculate the graviton's ? function in the AdS string-theoretic sigma model, perturbed by vertex operators for Vasiliev's higher spin gauge fields in AdS5. The result is given by ?mn=Rmn+4Tmn(g ,u) (with the AdS radius set to 1 and the graviton polarized along the AdS5 boundary), with the matter stress-energy tensor given by that of conformal holographic fluid in d =4, evaluated at the temperature given by T =1/?. The stress-energy tensor is given by Tmn=gmn+4umun+?NTmn(N) where u is the vector excitation satisfying u2=-1 and N is the order of the gradient expansion in the dissipative part of the tensor. We calculate the contributions up to N =2. The higher spin excitations contribute to the ? function, ensuring the overall Weyl covariance of the matter stress tensor. We conjecture that the structure of gradient expansion in d =4 conformal hydrodynamics at higher orders is controlled by the higher spin operator algebra in AdS5.

Lee, Seungjin; Polyakov, Dimitri

2014-08-01

435

Dynamic Duality and the Phase Structure of Some Non-Abelian Spin Systems.

NASA Astrophysics Data System (ADS)

Lattice systems with discrete Z(,N) (CRTIMES) S(,N) and S(,N) (CRTIMES) S(,N) global symmetry admit a complete set of locally commuting disorder variables. Any kink state can be created by finite products of these operators acting on the classical vacuum. Exact dual forms of the partition functions are constructed and dual order parameters are defined. The Z(,N) (CRTIMES) S(,N) spin systems in two dimensions with an appropriate choice of action are vulnerable to a variety of analytic methods and are exactly dual to a vortex-charge plasma. They are shown to have an intermediate spin wave dominated phase between the conventional ordered and disordered phases for N > 16. A renormalization group analysis of the plasma indicates that, unlike that of the Z(,N) models, the spin wave phase is massive, the mass being the reciprocal of a dual correlation length. This length becomes infinite in the limit of large N with (beta)/N fixed. In any number of dimensions the large N limit is infinitely stable against magnetization, though long range order can occur for dimensionality greater than two.

Orland, Peter Oliver

1982-05-01

436

NASA Astrophysics Data System (ADS)

We construct a two-state one-dimensional reaction-path model for ozone open ? cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O2 + O asymptote on the ground-state 1A' potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] u