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Last update: November 12, 2013.

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

Kapellasite: a kagome quantum spin liquid with competing interactions.

Magnetic susceptibility, NMR, muon spin relaxation, and inelastic neutron scattering measurements show that kapellasite, Cu3Zn(OH)6Cl2, a geometrically frustrated spin-1/2 kagome antiferromagnet polymorphic with herbertsmithite, is a gapless spin liquid showing unusual dynamic short-range correlations of noncoplanar cuboc2 type which persist down to 20 mK. The Hamiltonian is determined from a fit of a high-temperature series expansion to bulk susceptibility data and possesses competing exchange interactions. The magnetic specific heat calculated from these exchange couplings is in good agreement with experiment. The temperature dependence of the magnetic structure factor and the muon relaxation rate are calculated in a Schwinger-boson approach and compared to experimental results. PMID:22861895

Fåk, B; Kermarrec, E; Messio, L; Bernu, B; Lhuillier, C; Bert, F; Mendels, P; Koteswararao, B; Bouquet, F; Ollivier, J; Hillier, A D; Amato, A; Colman, R H; Wills, A S

2012-07-20

3

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

4

Dynamical theory of spin relaxation

NASA Astrophysics Data System (ADS)

The dynamics of a spin system is usually calculated using the density matrix. However, the usual formulation in terms of the density matrix predicts that the signal will decay to zero, and does not address the issue of individual spin dynamics. Using stochastic calculus, we develop a dynamical theory of spin relaxation, the origins of which lie in the component spin fluctuations. This entails consideration of random pure states for individual protons, and how these pure states are correctly combined when the density matrix is formulated. Both the lattice and the spins are treated quantum mechanically. Such treatment incorporates both the processes of spin-spin and (finite temperature) spin-lattice relaxation. Our results reveal the intimate connections between spin noise and conventional spin relaxation.

Field, Timothy R.; Bain, Alex D.

2013-02-01

5

Spin Dynamics from Majorana Fermions

NASA Astrophysics Data System (ADS)

Using the Majorana fermion representation of spin-1/2 local moments, we show how the dynamic spin correlation and susceptibility are obtained directly from the one-particle Majorana propagator. We illustrate our method by applying it to the spin dynamics of a nonequilibrium quantum dot, computing the voltage-dependent spin relaxation rate and showing that, at weak coupling, the fluctuation-dissipation relation for the spin of a quantum dot is voltage dependent. We confirm the voltage-dependent Curie susceptibility recently found by Parcollet and Hooley [

Mao, W.; Coleman, P.; Hooley, C.; Langreth, D.

2003-11-01

6

Thermodynamics of quantum spin chains with competing interactions

NASA Astrophysics Data System (ADS)

We consider integrable quantum spin chains with competing interactions. We apply the quantum transfer matrix approach to these spin chains. This allows us to derive a set of nonlinear integral equations for the thermodynamics of these spin chains. We provide numerical solutions of these integral equations for the entropy as a function of magnetic field, temperature and the coupling constant. In addition we describe, at low but finite temperature, the possible scenarios for the ground state diagram for high-spin chain and longer range interchain interactions.

Tavares, T. S.; Ribeiro, G. A. P.

2013-09-01

7

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

8

Temperature for a dynamic spin ensemble

NASA Astrophysics Data System (ADS)

In molecular dynamics simulations, temperature is evaluated, via the equipartition principle, by computing the mean kinetic energy of atoms. There is no similar recipe yet for evaluating temperature of a dynamic system of interacting spins. By solving semiclassical Langevin spin-dynamics equations, and applying the fluctuation-dissipation theorem, we derive an equation for the temperature of a spin ensemble, expressed in terms of dynamic spin variables. The fact that definitions for the kinetic and spin temperatures are fully consistent is illustrated using large-scale spin dynamics and spin-lattice dynamics simulations.

Ma, Pui-Wai; Dudarev, S. L.; Semenov, A. A.; Woo, C. H.

2010-09-01

9

Dynamics of random spin systems

We present inelastic neutron scattering experiments on three prototypical random magnets. For the dilute, insulating antiferromagnet Rb/sub 2/Co/sub c/Mg/sub 1-c/F/sub 4/, the randomness has purely geometrical consequences, and the anomalous dynamical behavior which we observe for c close to the magnetic percolation threshold is due to the fractal nature of percolating networks. Comparison of inelastic and quasielastic scattering data demonstrate the dynamical nature of the spin glass transition in amorphous, metallic MnSi. Finally, we show the coexistence of spin waves and static spin fluctuations near the crossover from ferromagnetic to spin glass behaviors in amorphous (Fe/sub x/Mn/sub 1-x/)/sub 75/P/sub 16/B/sub 6/Al/sub 3/.

Aeppli, G.

1985-01-01

10

Spin rectification induced by dynamical Hanle effect

NASA Astrophysics Data System (ADS)

Dynamic response of spin accumulation to a time-dependent magnetic field has been investigated in a ferromagnetic/nonmagnetic bilayer under ferromagnetic resonance. In this system, magnetization precession driven by a microwave generates direct-current (dc) and alternate-current (ac) spin accumulation in the nonmagnetic layer by the spin pumping. The ac spin accumulation is coupled with the microwave magnetic field through a dynamical Hanle spin precession, giving rise to rectified spin accumulation comparable with the dc spin accumulation directly generated by the spin pumping.

Sakimura, Hiroto; Matsumoto, Takahiko; Ando, Kazuya

2013-09-01

11

Dynamical model for competing opinions

NASA Astrophysics Data System (ADS)

We propose an opinion model based on agents located at the vertices of a regular lattice. Each agent has an independent opinion (among an arbitrary, but fixed, number of choices) and its own degree of conviction. The latter changes every time two agents which have different opinions interact with each other. The dynamics leads to size distributions of clusters (made up of agents which have the same opinion and are located at contiguous spatial positions) which follow a power law, as long as the range of the interaction between the agents is not too short; i.e., the system self-organizes into a critical state. Short range interactions lead to an exponential cutoff in the size distribution and to spatial correlations which cause agents which have the same opinion to be closely grouped. When the diversity of opinions is restricted to two, a nonconsensus dynamic is observed, with unequal population fractions, whereas consensus is reached if the agents are also allowed to interact with those located far from them. The individual agents' convictions, the preestablished interaction range, and the locality of the interaction between a pair of agents (their neighborhood has no effect on the interaction) are the main characteristics which distinguish our model from previous ones.

Souza, S. R.; Gonçalves, S.

2012-05-01

12

The Dynamics of Competing Cardiac Pacemakers

NASA Astrophysics Data System (ADS)

The modern theory of the dynamics of interacting oscillators has been applied to the analysis of heartbeat interval sequences in order to understand and predict the patterns of occurrence and timing of cardiac rhythm disturbances. The principal new contributions resulting from this research include: (1) The derivation of the symbolic dynamics of uncoupled cardiac pacemakers. (2) The geometric formulation of the interaction of coupled cardiac pacemakers as trajectories on the torus. (3) The derivation of a geometrical transformation of the heart beat interval sequence to the coupling function linking the activity of competing cardiac pacemakers. (4) The development of a transformation of the sequence of heart beat intervals which discriminates cardiac arrhythmias which result from anomalous pathways in the conduction system from those which result from competing pacemakers. (5) The formulation and testing through clinical case studies of a mathematical model which relates changes in heart rate to changes in the frequency of the occurrence of cardiac arrhythmias.

de Paola, Robert

13

Spin dynamics in a spin-orbit-coupled Fermi gas

NASA Astrophysics Data System (ADS)

We study the dynamics of a nondegenerate, harmonically trapped Fermi gas following a sudden ramp of the spin-orbit coupling strength using a Boltzmann equation approach. In the absence of interactions and a Zeeman field, we solve the spin-orbit-coupled Boltzmann equation analytically and derive expressions for the phase-space and temporal dynamics of an arbitrary initial spin state. For a fully spin-polarized initial state, the total magnetization exhibits collapse and revival dynamics in time with a period set by the trapping potential. In real space, this corresponds to oscillations between a fully polarized state and a spin helix. To make predictions relevant to current experiments on spin-orbit-coupled Fermi gases, we then numerically study the dynamics in the presence of an additional momentum-independent Zeeman field. We find that the spin helix is robust for weak magnetic fields but disappears for stronger field strengths. Finally, we explore the spin dynamics in the presence of interactions and find that weak interactions enhance the amplitude of the spin helix.

Natu, Stefan S.; Das Sarma, S.

2013-09-01

14

Spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites.

Correlation-induced spin-charge and spin-orbital coupling effects on spin dynamics in ferromagnetic manganites are calculated with realistic parameters in order to provide a quantitative comparison with experimental results for spin stiffness, magnon dispersion, magnon damping, anomalous zone-boundary magnon softening and Curie temperature. The role of orbital degeneracy, orbital ordering and orbital correlations on spin dynamics in different doping regimes is highlighted. PMID:21403233

Singh, Dheeraj Kumar; Kamble, Bhaskar; Singh, Avinash

2010-09-14

15

NASA Astrophysics Data System (ADS)

The last couple of years have witnessed intense interest in spin ice materials due to the unique nature of its low energy excitations, which take the form of emergent magnetic monopoles. Through combined theoretical and experimental work, it has become increasingly apparent that an effective description of these excitations in terms of free, Coulomb interacting point-like quasiparticles is essential to develop an understanding of the thermodynamic properties of these materials beyond numerical simulations. On the other hand, we are only just beginning to unravel the repercussions of such exotic excitations on the dynamics of spin ice, in relation for instance to how the system relaxes when driven out of equilibrium, or in relation to thermal transport experiments. In this talk we review some of the latest theoretical and experimental results on the out of equilibrium properties of spin ice materials, ranging from thermal and field quenches [Castelnovo, Moessner, & Sondhi, PRL 104, 107201 (2010) and ongoing work] to thermal runaways in response to a varying magnetic field [Slobinsky et al., arXiv:1010.4143v1]. In particular, we discuss how these phenomena can be understood as consequences of the specific nature of the low energy excitations.

Castelnovo, Claudio

2011-03-01

16

Coherent spin mixing dynamics in a spin-1 atomic condensate

We study the coherent off-equilibrium spin mixing inside an atomic condensate. Using mean-field theory and adopting the single-spatial-mode approximation, the condensate spin dynamics is found to be well described by that of a nonrigid pendulum and displays a variety of periodic oscillations in an external magnetic field. Our results illuminate several recent experimental observations and provide critical insights into the observation of coherent interaction-driven oscillations in a spin-1 condensate.

Zhang Wenxian; Chang, M.-S.; Chapman, M.S. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States); Zhou, D.L.; You, L. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100080 (China)

2005-07-15

17

Spinning compact binary : Independent variables and dynamically preserved spin configurations

We establish the set of independent variables suitable to monitor the complicated evolution of the spinning compact binary during the inspiral. Our approach is valid up to the second post-Newtonian order, including leading order spin-orbit, spin-spin and mass quadrupole-mass monopole effects, for generic (noncircular, nonspherical) orbits. Then, we analyze the conservative spin dynamics in terms of these variables. We prove that the only binary black hole configuration allowing for spin precessions with equal angular velocities about a common instantaneous axis roughly aligned to the normal of the osculating orbit, is the equal mass and parallel (aligned or antialigned) spin configuration. This analytic result puts limitations on what particular configurations can be selected in numerical investigations of compact binary evolutions, even in those including only the last orbits of the inspiral.

Gergely, Laszlo Arpad [Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary) and Department of Experimental Physics, University of Szeged, Dom ter 9, Szeged 6720 (Hungary)

2010-04-15

18

Advanced computational methods for nonlinear spin dynamics

We survey methods for the accurate computation of the dynamics of spin in general nonlinear accelerator lattices. Specifically, we show how it is possible to compute high-order nonlinear spin transfer maps in SO(3) or SU(2) representations in parallel with the corresponding orbit transfer maps. Specifically, using suitable invariant subspaces of the coupled spin-orbit dynamics, it is possible to develop a

Martin Berz; Kyoko Makino

2011-01-01

19

NASA Astrophysics Data System (ADS)

A one-dimensional quantum spin model with the competing two-spin and three-spin interactions is investigated in the context of a tensor network algorithm based on the infinite matrix product state representation. The algorithm is an adaptation of Vidal's infinite time-evolving block decimation algorithm to a translation-invariant one-dimensional lattice spin system involving three-spin interactions. The ground-state fidelity per lattice site is computed, and its bifurcation is unveiled, for a few selected values of the coupling constants. We succeed in identifying critical points and deriving local order parameters to characterize different phases in the conventional Ginzburg-Landau-Wilson paradigm.

Wang, Hong-Lei; Dai, Yan-Wei; Hu, Bing-Quan; Zhou, Huan-Qiang

2011-10-01

20

Quantum spin nanotubes--frustration, competing orders and criticalities.

Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the S = 1/2 three-leg spin tube. In contrast to the three-leg spin ladder, the tube has a spin gap in the case of the regular-triangle unit cell when the rung interaction is sufficiently large. The effective theory based on the Hubbard Hamiltonian indicates a quantum phase transition to a gapless spin liquid due to the lattice distortion to an isosceles triangle. This is also supported by the numerical diagonalization and the density matrix renormalization group analyses. Furthermore, combining analytical and numerical approaches, we reveal several novel magnetic-field-induced phenomena: Néel, dimer, chiral and/or inhomogeneous orders, a new mechanism for the magnetization plateau formation, and others. The recently synthesized spin tube materials are also briefly introduced. PMID:21386560

Sakai, Tôru; Sato, Masahiro; Okamoto, Kiyomi; Okunishi, Kouichi; Itoi, Chigak

2010-09-14

21

Advanced computational methods for nonlinear spin dynamics

NASA Astrophysics Data System (ADS)

We survey methods for the accurate computation of the dynamics of spin in general nonlinear accelerator lattices. Specifically, we show how it is possible to compute high-order nonlinear spin transfer maps in SO(3) or SU(2) representations in parallel with the corresponding orbit transfer maps. Specifically, using suitable invariant subspaces of the coupled spin-orbit dynamics, it is possible to develop a differential algebraic flow operator in a similar way as in the symplectic case of the orbit dynamics. The resulting high-order maps can be utilized for a variety of applications, including long-term spin-orbit tracking under preservation of the symplectic-orthonormal structure and the associated determination of depolarization rates. Using normal form methods, it is also possible to determine spin-orbit invariants of the motion, in particular the nonlinear invariant axis as well as the associated spin-orbit tune shifts. The methods are implemented in the code COSY INFINITY [1] and available for spin-orbit computations for general accelerator lattices, including conventional particle optical elements including their fringe fields, as well as user specified field arrangements.

Berz, Martin; Makino, Kyoko

2011-05-01

22

Coherent Collisional Spin Dynamics in Optical Lattices

We report on the observation of coherent, purely collisionally driven spin dynamics of neutral atoms in an optical lattice. For high lattice depths, atom pairs confined to the same lattice site show weakly damped Rabi-type oscillations between two-particle Zeeman states of equal magnetization, induced by spin-changing collisions. Moreover, measurement of the oscillation frequency allows for precise determination of the spin-changing collisional coupling strengths, which are directly related to fundamental scattering lengths describing interatomic collisions at ultracold temperatures.

Widera, Artur; Gerbier, Fabrice; Foelling, Simon; Gericke, Tatjana; Mandel, Olaf; Bloch, Immanuel [Johannes Gutenberg-Universitaet, Staudingerweg 7, 55099 Mainz (Germany)

2005-11-04

23

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

2013-08-01

24

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

25

RNA Dynamics: Perspectives from Spin Labels

Dynamics are an important and indispensible physical attribute that plays essential roles in RNA function. RNA dynamics are complex, spanning vast timescales and encompassing large number of physical modes. The technique of site-directed spin labeling (SDSL), which derives information on local structural and dynamic features of a macromolecule by monitoring a chemically stable nitroxide radical using electron paramagnetic resonance (EPR) spectroscopy, has been applied to monitor intrinsic dynamics at defined structural states as well as to probe conformational transition dynamics of RNAs. Current state of SDSL studies of RNA dynamics is summarized here. Further SDSL developments promise to open up many more opportunities for probing RNA dynamics and connecting dynamics to structure and function.

Nguyen, Phuong

2011-01-01

26

Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate

We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein condensate by a temporal modulation of spin exchange interaction, which is tunable with optical Feshbach resonance. Adopting techniques from coherent control, we demonstrate the localization and freezing of spin mixing dynamics, and the suppression of the intrinsic dynamic instability and spontaneous spin domain formation in a ferromagnetically interacting condensate of {sup 87}Rb atoms. This work points to a promising scheme for investigating the weak magnetic spin dipole interaction, which is usually masked by the more dominant spin exchange interaction.

Zhang Wenxian [Key Laboratory for Advanced Materials and Devices, Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); Sun Bo [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States); Chapman, M. S.; You, L. [School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0430 (United States)

2010-03-15

27

Spin Dynamics of Piperazinium Hexachlorodicuprate

NASA Astrophysics Data System (ADS)

Piperazinium Hexachlorodicuprate (PHCC) has previously been characterized as an antiferromagnetic S=1/2 alternating chain with J=2.1 meV and ?? 0.6. We present the results of zero field inelastic neutron scattering as well as susceptibility and specific heat as a function of applied magnetic field. At 1.4 K, the magnetic excitation spectrum is dominated by a single propagating mode with a gap, ? = 1meV, and bandwidth of ? 2 meV for wavevectors in the (h 0 l) plane. The mode has no dispersion perpendicular to this plane. The heat capacity shows a reduction of the gap as a function of applied field in agreement with a singlet-triplet excitation spectrum. A field induced ordered phase is found above a field H_c1? 7.5 Tesla. In light of these results, we propose an isotropic spin Hamiltonian describing a two-dimensional system of interacting dimers.

Stone, M. B.; Zaliznyak, I.; Reich, D. H.; Broholm, C.

2000-03-01

28

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

29

Spin dynamics of cold fermions with synthetic spin-orbit coupling

NASA Astrophysics Data System (ADS)

We consider spin-relaxation dynamics in cold Fermi gases with a pure-gauge spin-orbit coupling corresponding to recent experiments. We show that such experiments can give direct access to the collisional spin drag rate, and establish conditions for the observation of spin drag effects. In recent experiments the dynamics is found to be mainly ballistic leading to new regimes of reversible spin-relaxation-like processes.

Tokatly, I. V.; Sherman, E. Ya.

2013-04-01

30

Dynamics of Random Spin Systems.

National Technical Information Service (NTIS)

We present inelastic neutron scattering experiments on three prototypical random magnets. For the dilute, insulating antiferromagnet Rb sub 2 Co/sub c/Mg/sub 1-c/F sub 4 , the randomness has purely geometrical consequences, and the anomalous dynamical beh...

G. Aeppli

1985-01-01

31

Spin dynamics in two-dimensional electron and hole systems revealed by resonant spin amplification

NASA Astrophysics Data System (ADS)

Understanding and controlling the spin dynamics in semiconductor heterostructures is a key requirement for the design of future spintronics devices. In GaAs-based heterostructures, electrons and holes have very different spin dynamics. Some control over the spin-orbit fields, which drive the electron spin dynamics, is possible by choosing the crystallographic growth axis. Here, (110)-grown structures are interesting, as the Dresselhaus spinorbit fields are oriented along the growth axis and therefore, the typically dominant Dyakonov-Perel mechanism is suppressed for spins oriented along this axis, leading to long spin depasing times. By contrast, hole spin dephasing is typically very rapid due to the strong spin-orbit interaction of the p-like valence band states. For localized holes, however, most spin dephasing mechanisms are suppressed, and long spin dephasing times may be observed. Here, we present a study of electron and hole spin dynamics in GaAs-AlGaAs-based quantum wells. We apply the resonant spin amplification (RSA) technique, which allows us to extract all relevant spin dynamics parameters, such as g factors and dephasing times with high accuracy. A comparison of the measured RSA traces with the developed theory reveals the anisotropy of the spin dephasing in the (110)-grown two-dimensional electron systems, as well as the complex interplay between electron and hole spin and carrier dynamics in the two-dimensional hole systems.

Korn, T.; Griesbeck, M.; Kugler, M.; Furthmeier, S.; Gradl, C.; Hirmer, M.; Schuh, D.; Wegscheider, W.; Korzekwa, K.; Machnikowski, P.; Kuhn, T.; Glazov, M. M.; Sherman, E. Ya.; Schüller, C.

2012-10-01

32

Dynamic-angle spinning of quadrupolar nuclei

NASA Astrophysics Data System (ADS)

In dynamic-angle spinning (DAS), a sample spins around an axis inclined at an angle ?(t) with respect to the magnetic field such that the averages of Pn(cos?) are zero. The simplest case is where ?(t) assumes two discrete values ?1 and ?2 (complementary DAS angles) such that the averages of P2(cos?) and P4(cos?) are zero, thereby removing second-order quadrupolar (and dipolar) broadening. Examples of DAS complementary angles are ?1=37.38° and ?2=79.18°. Experimental details for DAS experiments are provided and applications to sodium-23 and oxygen-17 NMR illustrate the enhanced resolution achieved by removing the second-order broadening inherent in magic-angle spinning.

Mueller, K. T.; Sun, B. Q.; Chingas, G. C.; Zwanziger, J. W.; Terao, T.; Pines, A.

2011-12-01

33

Dynamic spin response for Heisenberg ladders

We employ the recently proposed plaquette basis to investigate static and dynamic properties of isotropic two-leg Heisenberg spin ladders. Simple noninteracting multiplaquette states provide a remarkably accurate picture of the energy/site and dynamic spin response of these systems. Insights afforded by this simple picture suggest a very efficient truncation scheme for more precise calculations. When the small truncation errors are accounted for using recently developed contractor renormalization techniques, very accurate results requiring a small fraction of the computational effort of exact calculations are obtained. These methods allow us to determine the energy/site, gap, and spin response of 2{times}16 ladders. The former two values are in good agreement with density-matrix renormalization-group results. The spin-response calculations show that nearly all the strength is concentrated in the lowest triplet level and that coherent many-body effects enhance the response/site by nearly a factor of 1.6 over that found for 2{times}2 systems. {copyright} {ital 1998} {ital The American Physical Society}

Piekarewicz, J. [Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida32306 (United States); Shepard, J.R. [Department of Physics, University of Colorado, Boulder, Colorado80309 (United States)

1998-05-01

34

Simple approach to relativistic spin dynamics

NASA Astrophysics Data System (ADS)

Spin dynamics is considered from the point of view of relativistic classical mechanics. It is shown that the assumptions of the Bargmann-Michel-Telegdi theory may be used to obtain an intuitive and convenient equation of motion. The advantage of this approach is that the presence of Thomas precession is automatically and manifestly demonstrated. An easy and unambiguous way to achieve the original Bargmann-Michel-Telegdi equation is also proposed.

ReBilas, Krzysztof

2011-10-01

35

Simulating electron spin resonance spectra of nitroxide spin labels from motional models is necessary for the quantitative analysis of experimental spectra. We present a framework for modeling the spin label dynamics by using trajectories such as those from molecular dynamics (MD) simulations combined with stochastic treatment of the global protein tumbling. This is achieved in the time domain after two

Deniz Sezer; Jack H. Freed

2008-01-01

36

Coherent spin-mixing and wave packets dynamics of spin-1 condensates in optical lattices

NASA Astrophysics Data System (ADS)

The dynamics of wave packets and spin-mixing of spin-1 condensates with repulsive spin-independent and either ferromagnetic or antiferromagnetic spin-dependent interactions in one-dimensional (1D) periodic optical lattices are discussed both analytically and numerically. In the tight-binding limit, the localized states, i.e., self-trapping, moving soliton and breather, in spin-1 condensates are obtained. The moving soliton and breather states show complex characters: if initially the condensates are prepared in spin stationary configuration, normal stable moving soliton and breather exist; however, if initially the condensates are prepared in spin non-stationary state, because of the spin-exchange process, the wave packets experience both local soliton/breather motion and larger scale periodic oscillation (with the spin-exchange period). Interestingly, we find the spin-mixing dynamics are coupled with wave packets dynamics: when the wave packets are self-trapped, the spin-mixing oscillations are also arrested to the stationary configuration; during diffusion of the wave packets, however, the spin-mixing dynamics are inhibited; a robust quasi-periodic spin-mixing oscillation maintains in moving soliton and breather states. These interesting results open up the possibility for controlled manipulation of the spin dynamics by the optical lattices.

Li, Zhi; Zhang, Ai-Xia; Ma, Juan; Xue, Ju-Kui

2010-03-01

37

Spin dynamics in magnetic vortex structures

NASA Astrophysics Data System (ADS)

This dissertation addresses spin dynamics in magnetic vortex structures, which have been experimentally investigated using time-resolved Kerr microscopy. This technique has been successfully implemented as a local spectroscopic probe to observe spin dynamics in geometrically confined magnetic structures with picosecond time resolution and spatial resolution on the order of a few hundred nanometers. Using electron-beam lithography, well-defined permalloy Ni81Fe19 disks with diameters in the range between 500 nm and 5 mum were fabricated. In the remnant state, permalloy disks form a flux-closure structure with a magnetic vortex core at the center of disk. The magnetization inside the core points out-of or into the disk plane. As the applied field decreases from a saturated state, the disks exhibit a distinct magnetization reversal process associated with the nucleation and subsequent annihilation of a magnetic vortex. The motion of a magnetic vortex, a gyrotropic mode, is directly observed in real time and space. The observed eigenfrequencies of the vortex mode as a function of disk size are in a good agreement with micromagnetic simulations. They also fall close to the predictions of a theory in which the magnetization of the displaced vortex is assumed to deform so that there are no magnetostatic charges at the edge of the disk. It is also observed that the vortex-mode eigenfrequency is nearly independent of the in-plane applied field. Azimuthal spin-wave modes, standing waves along the azimuthal direction in the vortex state, are investigated by exciting the spin system using an in-plane magnetic field pulse. Due to the cylindrical symmetry of the vortex state in remanence, two azimuthal modes propagating along opposite directions with the same number of azimuthal nodes are expected to be degenerate. However, our experimental results clearly demonstrate that the relative phase of the two azimuthal modes is determined by the polarity of the vortex core, and the magnitude of the splitting is of the same order as the vortex gyrotropic frequency. The broken degeneracy of the azimuthal spin-wave modes reveals how low-frequency excitations associated with domain structure influence spin-wave dynamics.

Park, Jooho

38

Quantum Spin Dynamics in Single-Molecule Magnets

This thesis contains a thorough investigation of the quantum spin dynamics in Mn12-ac and Mn6 Single-molecule magnets. In particular, we have investigated the interplay between quantum tunneling of magnetization and nuclear spin dynamics in Mn12-ac by ultra-low temperature NMR experiments. We discuss the effect of quantum tunneling on the nuclear spin-lattice relaxation, the nuclear spin diffusion, the thermalization of the

Andrea Morello

2004-01-01

39

Microscopic theory of spin torque induced by spin dynamics in magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

We studied the charge and spin currents in magnetic tunnel junctions in the presence of spin dynamics on the basis of a tight-binding scheme; the spin dynamics is assumed to be present only in one of the two ferromagnetic electrodes. The charge current is pumped by the dynamical spins having the form m?1.m2, where m? (?=1, 2) denotes the direction of magnetization in the electrodes and m1 represents the dynamic spin. In addition, three types of spin currents are induced by the dynamical spins. One of these spin currents has the form m?1×m2, whose coefficient is proportional to the product of the spin polarizations of both the electrodes. This term can possibly prevent magnetization switching, which is an effect that differs from both the Gilbert damping and spin transfer torque effects. Even in the absence of spin dynamics, the spin current exists in the form m1×m2. We have confirmed that the coefficient of this static term is equal to the effective exchange interaction between the two ferromagnetic electrodes.

Miura, Daisuke; Sakuma, Akimasa

2011-04-01

40

Interfacial spin glass state and exchange bias in manganite bilayers with competing magnetic orders

NASA Astrophysics Data System (ADS)

The magnetic properties of manganite bilayers composed of G-type antiferromagnetic (AFM) SrMnO3 and double-exchange ferromagnetic (FM) La0.7Sr0.3MnO3 are studied. A spin-glass state is observed as a result of competing magnetic orders and spin frustration at the La0.7Sr0.3MnO3/SrMnO3 interface. The dependence of the irreversible temperature on the cooling magnetic field follows the Almeida-Thouless line. Although an ideal G-type AFM SrMnO3 is featured with a compensated spin configuration, the bilayers exhibit exchange bias below the spin glass freezing temperature, which is much lower than the Néel temperature of SMO, indicating that the exchange bias is strongly correlated with the spin glass state. The results indicate that the spin frustration that originates from the competition between the AFM super-exchange and the FM double-exchange interactions can induce a strong magnetic anisotropy at the La0.7Sr0.3MnO3/SrMnO3 interface.

Ding, J. F.; Lebedev, O. I.; Turner, S.; Tian, Y. F.; Hu, W. J.; Seo, J. W.; Panagopoulos, C.; Prellier, W.; Van Tendeloo, G.; Wu, T.

2013-02-01

41

Spin Dynamics in Magnetic Vortex Structures

NASA Astrophysics Data System (ADS)

We have studied the spin dynamics of individual permalloy disks with thicknesses of 50 nm and diameters from 200 nm to 2 ? m using time-resolved Kerr microscopy. Magnetic fields up to 800 ˜ Oe are applied in the plane of the disks, for which the micromagnetic configuration in small fields is a vortex. We observe three distinct spin-wave modes in the vortex state: a gyrotropic mode at low frequency (< 1 GHz) that is due to the translational degree of freedom of the vortex core, as well as two spin-wave modes of predominantly magnetostatic character at higher frequencies (> 4 GHz). The frequency of the gyrotropic mode increases with decreasing disk diameter as predicted from the vortex equation of motion as well as micromagnetic simulations. The gyrotropic frequency is independent of the applied field, or, equivalently, of the position of the vortex core inside the disk. Of the upper pair of modes, the lower frequency excitation has an effective wave vector parallel to the edges of the disk and a line of nodes along the diameter. In the saturated state, an ordinary FMR mode is observed in disks with diameters larger than 1 ? m , and this splits into several modes as the diameter decreases. This work was supported by NSF DMR 99-83777, the University of Minnesota MRSEC (NSF DMR-0212032), and the Minnesota Supercomputing Institute.

Park, J. P.; Eames, P.; Crowell, P. A.

2004-03-01

42

Simulating electron spin resonance spectra of nitroxide spin labels from motional models is necessary for the quantitative analysis of experimental spectra. We present a framework for modeling the spin label dynamics by using trajectories such as those from molecular dynamics (MD) simulations combined with stochastic treatment of the global protein tumbling. This is achieved in the time domain after two efficient numerical integrators are developed: One for the quantal dynamics of the spins and the other for the classical rotational diffusion. For the quantal dynamics, we propagate the relevant part of the spin density matrix in Hilbert space. For the diffusional tumbling, we work with quaternions, which enables the treatment of anisotropic diffusion in a potential expanded as a sum of spherical harmonics. Time-averaging arguments are invoked to bridge the gap between the smaller time step of the MD trajectories and the larger time steps appropriate for the rotational diffusion and?or quantal spin dynamics.

Sezer, Deniz; Freed, Jack H.; Roux, Benoit

2008-01-01

43

Using ensemble Monte Carlo simulation, we have studied hot carrier spin dynamics and spin noise in a multi-subband GaAs quantum wire in the presence of a randomly varying Rashba spin-orbit interaction. The random variation reduces the carrier ensemble's spin dephasing time due to the D'yakonov-Perel' mechanism, but otherwise makes no qualitative difference to the temporal spin relaxation characteristics. However, it makes a qualitative difference to the spatial spin relaxation characteristics which change from monotonic and smooth to non-monotonic and chaotic because of a complex interplay between carriers in different subbands. As far as spin fluctuation and spin noise are concerned, the random variation has no major effect except that the low-frequency noise power spectral density increases slightly when the magnitude of the Rashba spin-orbit interaction field is varied randomly while holding the direction constant. PMID:22543262

Agnihotri, Pratik; Bandyopadhyay, Supriyo

2012-04-27

44

Secular spin dynamics of inner main-belt asteroids

Understanding the evolution of asteroid spin states is challenging work, in part because asteroids have a variety of orbits, shapes, spin states, and collisional histories but also because they are strongly influenced by gravitational and non-gravitational (YORP) torques. Using efficient numerical models designed to investigate asteroid orbit and spin dynamics, we study here how several individual asteroids have had their

D. Vokrouhlický; D. Nesvorný; W. F. Bottke

2006-01-01

45

Dynamic spin injection into chemical vapor deposited graphene

NASA Astrophysics Data System (ADS)

We demonstrate dynamic spin injection into chemical vapor deposition (CVD) grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic resonance measurements at room temperature reveal a strong enhancement of the Gilbert damping at the Py/graphene interface, indeed exceeding that observed in Py/platinum interfaces. Similar results are also shown on Co/graphene layers. This enhancement in the Gilbert damping is understood as the consequence of spin pumping at the interface driven by magnetization dynamics. Our observations suggest a strong enhancement of spin-orbit coupling in CVD graphene, in agreement with earlier spin valve measurements.

Patra, A. K.; Singh, S.; Barin, B.; Lee, Y.; Ahn, J.-H.; del Barco, E.; Mucciolo, E. R.; Özyilmaz, B.

2012-10-01

46

Dynamic Stabilization of a Quantum Many-Body Spin System

NASA Astrophysics Data System (ADS)

We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis.

Hoang, T. M.; Gerving, C. S.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

2013-08-01

47

Resident electron spin dynamics of II-VI quantum dots

NASA Astrophysics Data System (ADS)

The spin dynamics of single electrons resident to charged CdSe/ZnSe quantum dots is studied. The spin-orbit mediated spin lifetime is uncovered. It follows a magnetic-field dependence of ?so=190 ms T4/B4. Below about B=2 T, the electron-nuclear hyperfine coupling takes over and the electron spin lifetime shortens. We analyze the temperature dependence of the spin transfer via hyperfine interaction and find that the efficiency for the formation of a nuclear dynamical polarization increases up to 100 K.

Gapon, V.; Puls, J.; Henneberger, F.

2009-05-01

48

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

49

Nonlinear dynamics of spin waves (invited)

For a yttrium-iron-garnet sphere at room temperature, an experimental study is made of the first-order Suhl spin-wave instability using perpendicular pumping at 9.2 GHz with the dc field parallel to the (111) crystal axis. The dynamical behavior of the magnetization is observed with high resolution by varying two control parameters, dc field (580

Jeffries, C.D.; Bryant, P.H.; Nakamura, K.

1988-11-15

50

Spin dynamics in atomically assembled antiferromagnets

NASA Astrophysics Data System (ADS)

Antiferromagnetic materials possess ordered magnetic states that have vanishing magnetization. We used a low-temperature scanning tunneling microscope to construct few-atom antiferromagnets. Even-numbered arrays of antiferromagnetically coupled atoms were found to have no net spin. Their shapes can be defined precisely by atom manipulation avoiding uncompensated magnetic moments at the nanoparticle's edge. We use such spin-compensated atomic arrays to study the intrinsic dynamics of nanoscale antiferromagnets [1]. For chains of more than four atoms we observe two Neel-ordered ground states and frequent switching between them. The spontaneous switching rates depend strongly on the number of coupled atoms and we observed magnetic tunneling of the Neel vector for the smallest structures. In arrays with ten or more atoms the residence time in each state can exceed many hours but current-induced switching proceeds at nanosecond speed. These properties enable a model demonstration of dense magnetic data storage that uses antiferromagnets as memory elements. [1] S. Loth, S. Baumann, C. P. Lutz, D. M. Eigler and A. J. Heinrich, Science 335, 196 (2012).

Loth, Sebastian

2013-03-01

51

Epoch Lifetimes in the Dynamics of a Competing Population

NASA Astrophysics Data System (ADS)

We propose a dynamical model of a competing population whose agents have a tendency to balance their decisions in time. The model is applicable to financial markets in which the agents trade with finite capital, or other multiagent systems such as routers in communication networks attempting to transmit multiclass traffic in a fair way. We find an oscillatory behavior due to the segregation of agents into two groups. Each group remains winning over epochs. The aggregation of smart agents is able to explain the lifetime distribution of epochs to 8 decades of probability. The existence of the super agents further refines the lifetime distribution of short epochs.

Yeung, C. H.; Ma, Y. P.; Wong, K. Y. Michael

52

NASA Astrophysics Data System (ADS)

Spins in semiconductor structures may allow for the realization of scalable quantum bit arrays, an essential component for quantum computation schemes. Specifically, hole spins may be more suited for this purpose than electron spins, due to their strongly reduced interaction with lattice nuclei, which limits spin coherence for electrons in quantum dots. Here, we present resonant spin amplification (RSA) measurements, performed on a p-modulation doped GaAs-based quantum well at temperatures below 500 mK. The RSA traces have a peculiar, butterfly-like shape, which stems from the initialization of a resident hole spin polarization by optical orientation. The combined dynamics of the optically oriented electron and hole spins are well-described by a rate equation model, and by comparison of experiment and model, hole spin dephasing times of more than 70 ns are extracted from the measured data.

Korn, T.; Kugler, M.; Hirmer, M.; Schuh, D.; Wegscheider, W.; Schüller, C.

2011-12-01

53

Competing ^1H Spin Relaxation Mechanisms in Low-Dimensional Per2Pt[mnt]2

NASA Astrophysics Data System (ADS)

Per2[Pt(mnt)2] is a low-dimensional organic conductor consisting of parallel conducting (perylene) and magnetic chains (Pt[mnt]2) which undergo a charge density wave (CDW) and spin-Peierls (SP)-transition, respectively. The conducting chain has been studied extensively, however fundamental questions about the spin-dynamics of the magnetic chain in the SP-state remained. By using ^1H NMR, we discovered the low temperature nuclear relaxation rates (T1-1) display an anomalous upturn at the SP-transition which differs from classical SP-systems. This ``bump'' is suppressed by magnetic field and coincides with the Curie tail, seen in susceptibility measurements. The field-dependent activation energies, extracted from NMR and susceptibility, reveal two distinct behaviors evidencing coexisting spin systems. At low fields, the spin relaxation mechanism derived from a paramagnetic contribution, possibly unpaired Pt spins, is dominant, but is suppressed above 10T. Hence, the intrinsic SP behavior is recovered for high fields. Furthermore, spectra in the field induced (FICDW) state, up to 33T, reveal an increase in the electronic spin polarization. DMR-NSF-1005293

Green, Elizabeth; Brooks, J. S.; Kuhns, P. L.; Reyes, A. P.; Wright, J. A.; Brown, S. E.; Almeida, M.; Matos, M. J.; Henriques, R. T.

2012-02-01

54

Nuclear spin selective laser control of rotational and torsional dynamics.

We explore the possibility of controlling rotational-torsional dynamics of non-rigid molecules with strong, non-resonant laser pulses and demonstrate that transient, laser-induced torsional alignment depends on the nuclear spin of the molecule. Consequently, nuclear spin isomers can be manipulated selectively by a sequence of time-delayed laser pulses. We show that two pulses with different polarization directions can induce either overall rotation or internal torsion, depending on the nuclear spin. Nuclear spin selective control of the angular momentum distribution may open new ways to separate and explore nuclear spin isomers of polyatomic molecules. PMID:22380044

Floss, J; Grohmann, T; Leibscher, M; Seideman, T

2012-02-28

55

NASA Astrophysics Data System (ADS)

The generation of spin currents by thermal gradients is a central issue of spin caloritronics. In addition to the recently observed spin Seebeck effect, a transverse thermoelectric effect has been proposed. This is the generation of a spin Hall current by a temperature gradient in a two-dimensional electron gas (2DEG) with Rashba spin-orbit interaction (SOI). We calculate the spin Seebeck coefficient and the thermo-spin Hall conductivity tensor of the spin current response induced by a frequency dependent temperature gradient in a 2DEG with Rashba and Dresselhaus SOI. We consider quantum wells grown in the main crystallographic directions. The spin splitting caused by SOI opens the possibility of resonant effects due to transitions between the spin-split subbands in response to alternating thermoelectric fields and temperature gradients in the THz regime. The spin current response shows characteristic spectral features in notable contrast to the pure Rashba coupling case. Such behavior is caused by the reduced symmetry of the momentum space available for transitions and the presence of critical points. This anisotropic dynamic response could be useful for spin manipulation via thermal means.

Maytorena, Jesus; Iglesias, Priscilla

2013-03-01

56

Spin-lattice-electron dynamics simulations of magnetic materials

NASA Astrophysics Data System (ADS)

We develop a dynamic spin-lattice-electron model for simulating the time-dependent evolution of coupled spin, atomic, and electronic degrees of freedom in a magnetic material. Using the model, we relate the dissipative parameters entering the Langevin equations for the lattice and spin degrees of freedom to the heat transfer coefficients of a phenomenological spin-lattice-electron three-temperature model. We apply spin-lattice-electron dynamics simulations to the interpretation of experiments on laser-induced demagnetization of iron thin films, and estimate the rates of heat transfer between the spins and electrons, and between atoms and electrons. To model the dynamics of energy dissipation in a magnetic material undergoing plastic deformation, we develop an algorithm that separates the local collective modes of motion of atoms from their random thermal motion. Using this approach, we simulate the propagation of compressive shock waves through magnetic iron. We also explore the microscopic dynamics of dissipative coupling between the spin and lattice subsystems, and show that the rate of spin-lattice heat transfer is proportional to the integral of the four-spin time-dependent correlation function.

Ma, Pui-Wai; Dudarev, S. L.; Woo, C. H.

2012-05-01

57

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

58

Nonlinear dynamics of spin and charge in spin-Calogero model

The fully nonlinear dynamics of spin and charge in spin-Calogero model is studied. The latter is an integrable one-dimensional model of quantum spin-1/2 particles interacting through inverse-square interaction and exchange. Classical hydrodynamic equations of motion are written for this model in the regime where gradient corrections to the exact hydrodynamic formulation of the theory may be neglected. In this approximation variables separate in terms of dressed Fermi momenta of the model. Hydrodynamic equations reduce to a set of decoupled Riemann-Hopf (or inviscid Burgers') equations for the dressed Fermi momenta. We study the dynamics of some nonequilibrium spin-charge configurations for times smaller than the time scale of the gradient catastrophe. We find an interesting interplay between spin and charge degrees of freedom. In the limit of large coupling constant the hydrodynamics reduces to the spin hydrodynamics of the Haldane-Shastry model.

Kulkarni, Manas [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800 (United States); Department of Condensed Matter Physics and Materials Science, Brookhaven National Laboratory, Upton, New York 11973 (United States); Franchini, Fabio [Abdus Salam ICTP, Strada Costiera 11, Trieste 34100 (Italy); Abanov, Alexander G. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800 (United States)

2009-10-15

59

Spin dynamics under local gauge fields in chiral spin-orbit coupling systems

Research Highlights: > We derive a modified LLG equation in magnetic systems with spin-orbit coupling (SOC). > Our results are applied to magnetic multilayers, and DMS and magnetic Rashba systems. > SOC mediated magnetization switching is predicted in rare earth metals (large SOC). > The magnetization trajectory and frequency can be modulated by applied voltage. > This facilitates potential application as tunable microwave oscillators. - Abstract: We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) x U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.

Tan, S.G., E-mail: TAN_Seng_Ghee@dsi.a-star.edu.sg [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Jalil, M.B.A. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Fujita, T. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liu, X.J. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore)

2011-02-15

60

Electron and Nuclear Spin Dynamics in Antiferromagnetic Molecular Rings

We study theoretically the spin dynamics of antiferromagnetic molecular rings, such as the ferric wheel Fe{sub 10} . For a single nuclear or impurity spin coupled to one of the electron spins of the ring, we calculate nuclear and electronic spin correlation functions and show that nuclear magnetic resonance (NMR) and electron spin resonance (ESR) techniques can be used to detect coherent tunneling of the Neel vector in these rings. The location of the NMR/ESR resonances gives the tunnel splitting and its linewidth an upper bound on the decoherence rate of the electron spin dynamics. We illustrate the experimental feasibility of our proposal with estimates for Fe{sub 10} molecules.

Meier, Florian; Loss, Daniel

2001-06-04

61

Spin dynamics of the itinerant helimagnet MnSi studied by positive muon spin relaxation

The local magnetic fields and spin dynamics of the itinerant helimagnet MnSi (Tc~=29.5 K) have been studied experimentally using positive muon spin rotation and relaxation (mu+SR) methods. In the ordered phase (T

R. Kadono; T. Matsuzaki; T. Yamazaki; S. R. Kreitzman; J. H. Brewer

1990-01-01

62

Spin dynamics of the itinerant helimagnet MnSi studied by positive muon spin relaxation.

National Technical Information Service (NTIS)

The local magnetic fields and spin dynamics of the itinerant helimagnet MnSi(T(sub c) (approx equal) 29.5 K) have been studied experimentally using positive muon spin rotation/relaxation ((mu)(sup +)SR) methods. In the ordered phase (T < T(sub c)), zero-f...

R. Kadono T. Matsuzaki T. Yamazaki S. R. Kreitzman J. H. Brewer

1990-01-01

63

Self-consistent calculation of spin transport and magnetization dynamics

NASA Astrophysics Data System (ADS)

A spin-polarized current transfers its spin-angular momentum to a local magnetization, exciting various types of current-induced magnetization dynamics. So far, most studies in this field have focused on the direct effect of spin transport on magnetization dynamics, but ignored the feedback from the magnetization dynamics to the spin transport and back to the magnetization dynamics. Although the feedback is usually weak, there are situations when it can play an important role in the dynamics. In such situations, simultaneous, self-consistent calculations of the magnetization dynamics and the spin transport can accurately describe the feedback. This review describes in detail the feedback mechanisms, and presents recent progress in self-consistent calculations of the coupled dynamics. We pay special attention to three representative examples, where the feedback generates non-local effective interactions for the magnetization after the spin accumulation has been integrated out. Possibly the most dramatic feedback example is the dynamic instability in magnetic nanopillars with a single magnetic layer. This instability does not occur without non-local feedback. We demonstrate that full self-consistent calculations generate simulation results in much better agreement with experiments than previous calculations that addressed the feedback effect approximately. The next example is for more typical spin valve nanopillars. Although the effect of feedback is less dramatic because even without feedback the current can make stationary states unstable and induce magnetization oscillation, the feedback can still have important consequences. For instance, we show that the feedback can reduce the linewidth of oscillations, in agreement with experimental observations. A key aspect of this reduction is the suppression of the excitation of short wavelength spin waves by the non-local feedback. Finally, we consider nonadiabatic electron transport in narrow domain walls. The non-local feedback in these systems leads to a significant renormalization of the effective nonadiabatic spin transfer torque. These examples show that the self-consistent treatment of spin transport and magnetization dynamics is important for understanding the physics of the coupled dynamics and for providing a bridge between the ongoing research fields of current-induced magnetization dynamics and the newly emerging fields of magnetization-dynamics-induced generation of charge and spin currents.

Lee, Kyung-Jin; Stiles, M. D.; Lee, Hyun-Woo; Moon, Jung-Hwan; Kim, Kyoung-Whan; Lee, Seo-Won

2013-10-01

64

Dynamics of a light aircraft in spin

This paper focuses mainly on the experimental and in-flight spin investigations for an executive light airplane, named I-23 and built in the Institute of Aviation (Warsaw, Poland). It is a single-engine, all composite, straight wing, retractable undercarriage, conventional configuration and flight control system airplane. In-flight spin tests confirmed good rudder and elevator effectiveness for spin recovery in a wide range

Zdobys?aw Goraj; Alfred Baron; Jan Kacprzyk

2002-01-01

65

Non-equlibrium energy dynamics in spin chains and ladders

We investigate the real-time dynamics of the energy density in spin-1\\/2 chains and ladders, starting from initial states with an inhomogeneous profile of bond energies, extending our previous work on the dynamics of spin-density wave packets [1]. These simulations are carried out using the adaptive time-dependent density matrix renormalization group algorithm. We analyze the time-dependence of the spatial variance of

Fabian Heidrich-Meisner; Stephan Langer; Markus Heyl; Ian McCulloch

2011-01-01

66

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

67

Lattice Instability and Competing Spin Structures in the Double Perovskite Insulator Sr2FeOsO6

NASA Astrophysics Data System (ADS)

The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, Fe57 Mössbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom.

Paul, Avijit Kumar; Reehuis, Manfred; Ksenofontov, Vadim; Yan, Binghai; Hoser, Andreas; Többens, Daniel M.; Abdala, Paula M.; Adler, Peter; Jansen, Martin; Felser, Claudia

2013-10-01

68

Spin dynamics characterization in magnetic dots

The spin structure in a magnetic dot is studied as a function of the exchange coupling strength and dot size within the semiclassical approximation on a discrete lattice. As the exchange coupling is decreased or the size is increased, the ground state undergoes a phase change from a homogeneous single-domain ferromagnet (HSDF) to a spin vortex. The line separating these

Mohammad-Reza Mozaffari; Keivan Esfarjani

2007-01-01

69

Based on the System Dynamics theory and the causality of the factors influencing competency of mine special operators, this paper established a dynamic simulation model of Training function on the Influencing Factors of mine special operators' Competency. The studies showed, under the same training inputs, coping capacity, sense of security responsibility, and self-management skills have more visible role. Besides, the

Deng Hong-bin; Gao Tao-li; Deng Xiao-li

2010-01-01

70

Non-equilibrium dynamics in spin glasses

NASA Astrophysics Data System (ADS)

A spin glass that is quenched or slowly cooled from a paramagnetic equilibrium state at a temperature above the spin glass temperature (Tg) is at all temperatures below Tg subjected to a spontaneous spin reconfiguration process that at each moment and temperature affects the spin system on one specific length scale. This length scale is set by the cooling rate and for finite cooling rates it decreases in size as the temperature is lowered. Experimentally and from simulations of different spin glass models, the non-equilibrium processes that occur once the system is kept at a constant temperature (isothermal aging) have been found to show a universal behaviour and to have very specific influence on the relaxation function as observed from the time dependence of the correlation function (simulations) or the relaxation of the magnetization as response to the application of a weak enough magnetic field. The response depends on the wait time at constant temperature and the relaxation rate has a maximum at an observation time corresponding to the wait time before the system is probed. This behavior can be interpreted to reflect a continuous and unrestricted growth of the size of equilibrium spin glass domains at constant temperature as predicted in droplet scaling pictures of the spin glass state. Also supportive of these models and in accord with the prediction of a chaotic nature of the equilibrium spin glass state with temperature is an interrupted growth and rejuvenation of the system once the temperature is allowed to be shifted away from the stop temperature. A subsequent memory and recovery of memory of the original spin structure (domain size) once the stop temperature is recovered after a thermal sequence to lower temperatures will be discussed in terms of the ghost domain picture developed by H.Yoshino et al. in Eur. Phys. J. B 20, 367 (2001).

Nordblad, Per

2004-03-01

71

Computation and analysis of spin dynamics

NASA Astrophysics Data System (ADS)

A method is described that allows the computation and analysis of high-order spin maps for general non-autonomous optical systems. It is shown how the equations of motion in curvilinear coordinates resulting from the Thomas-BMT equation can be solved within a differential algebraic framework in SU(2) and SO(3) representations. The resulting maps are subjected to a spin-orbit normal form transformation, and the nonlinear orbit dependencies of the invariant polarization axis as well as the orbit dependent spin tune can be obtained. For the case of electron machines, the resulting invariant polarization can be used to determine the radiative equilibrium polarization via the Derbenev-Kondratenko approach. Both the computation of the spin map as well as the algorithm for the computation of the invariant axis have been implemented in the code COSY INFINITY [2] [3] [4].

Balandin, Vladimir; Berz, Martin; Golubeva, Nina

1997-02-01

72

Computation and analysis of spin dynamics

A method is described that allows the {bold computation and analysis of high-order spin maps for general non-autonomous optical systems.} It is shown how the equations of motion in curvilinear coordinates resulting from the Thomas-BMT equation can be solved within a differential algebraic framework in SU(2) and SO(3) representations. The resulting maps are subjected to a spin-orbit normal form transformation, and the {bold nonlinear orbit dependencies of the invariant polarization axis as well as the orbit dependent spin tune can be obtained}. For the case of electron machines, the resulting invariant polarization can be used to determine the radiative equilibrium polarization via the Derbenev-Kondratenko approach. Both the computation of the spin map as well as the algorithm for the computation of the invariant axis have been implemented in the code {bold COSY INFINITY} [2] [3] [4]. {copyright} {ital 1997 American Institute of Physics.}

Balandin, V. [Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States)]|[Institute for Nuclear Research of RAS, 60th October Anniversary Pr., 7a Moscow (Russia); Berz, M. [Department of Physics and Astronomy and National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824 (United States); Golubeva, N. [Institute for Nuclear Research of RAS, 60th October Anniversary Pr., 7a Moscow (Russia)

1997-02-01

73

Strain and spin dynamics in gallium arsenide

The effect of uniaxial tensile strain on spin coherence in n-type GaAs epilayers is probed using time-resolved Kerr rotation, photoluminescence, and optically-detected nuclear magnetic resonance spectroscopies. The bandgap, electron spin lifetime, electron g-factor, and nuclear quadrupolar splitting are simultaneously imaged over millimeter-scale areas of the epilayers for continuously varying values of strain. All-optical nuclear magnetic resonance techniques allow access to

Hadrian Knotz

2008-01-01

74

Computation and analysis of spin dynamics

A method is described that allows the computation and analysis of high-order spin maps for general non-autonomous optical systems. It is shown how the equations of motion in curvilinear coordinates resulting from the Thomas-BMT equation can be solved within a differential algebraic framework in SU(2) and SO(3) representations. The resulting maps are subjected to a spin-orbit normal form transformation, and

Vladimir Balandin; Martin Berz; Nina Golubeva

1997-01-01

75

Spin dynamics of atoms and magnetic nanostructures on surfaces

NASA Astrophysics Data System (ADS)

Scanning tunneling microscopy is a powerful tool for studying the electronic and magnetic properties of magnetic nanostructures on surfaces. Over the last decade, inelastic tunneling spectroscopy has been used to probe discrete energy levels of quantum spin systems. These states can often be described as solutions of simple spin Hamiltonians. In spin excitation spectroscopy, a spin system is kicked from the ground into excited spin states at discrete energy increments. In this talk we will focus on the dynamics of quantum spin systems on surfaces. STM can measure tunnel currents in the range of pico amps with millisecond time resolution. This time resolution is well matched to observing transition between spin states of artificial magnetic nanostructures on surfaces that can be built and measured with STM. We will highlight an example of extended, artificial antiferromagnets on a Cu2N surface (Science 2012). Smaller magnetic clusters relax much faster but their dynamics can be measured with pump probe techniques. A pump voltage pulse drives the spin system into excited states and a subsequent probe pulse measures the resulting population of spin states. An exponential decay back to the ground state is observed when averaging over many pump-probe cycles (Science 2010). We will show results down to nanosecond time resolution with an ultimate limit set by modern electronics at about 100 pico seconds. Individual atoms on Cu2N relax their spin states even faster. Hence, another technique is employed to determine spin relaxation times: small tunnel currents always leave the spin system in the ground state while high currents can create non-equilibrium distributions of spin states. This approach relies on some modeling but allows time domain measurements down to about 1 pico second (Nature Physics 2010). Transition metal atoms on metal surfaces relax even faster, on time scales of about 100 femtoseconds. This fast relaxation manifests itself as a measurable lifetime broadening of spin excitation spectra. Combining these approaches allows measurements of spin relaxation times over about 16 orders of magnitude for spins on surfaces -- while maintaining the atomic scale spatial resolution of STM!

Heinrich, Andreas

2013-03-01

76

Strain and spin dynamics in gallium arsenide

NASA Astrophysics Data System (ADS)

The effect of uniaxial tensile strain on spin coherence in n-type GaAs epilayers is probed using time-resolved Kerr rotation, photoluminescence, and optically-detected nuclear magnetic resonance spectroscopies. The bandgap, electron spin lifetime, electron g-factor, and nuclear quadrupolar splitting are simultaneously imaged over millimeter-scale areas of the epilayers for continuously varying values of strain. All-optical nuclear magnetic resonance techniques allow access to the strain induced nuclear quadrupolar resonance splitting in field regimes not easily addressable using conventional optically-detected nuclear magnetic resonance. Additionally, time-resolved Kerr rotation spectroscopy as a function of pump-probe distance, voltage and magnetic field is used to measure the momentum-dependent spin splitting energies in GaAs and InGaAs epilayers. The magnitude of the spin splitting is found to increase linearly with applied tension and voltage. The strain of the samples can be reproducibly controlled in the cryostat using three- and four-point bending applied with a mechanical vise. This allows us to mechanically adjust the spin-strain coupling in the material. A strain-drift-diffusion model is used to determine the value of the spin-strain coupling coefficient for a strained GaAs epilayer. Finally, a series of in-plane GaAs field emitter devices were fabricated to the aim of transporting coherent spin information across a vacuum gap. Field emitter fabrication and design are presented along with preliminary emission data. Initial results are promising but several challenges remain before the goal can be realized.

Knotz, Hadrian

77

Hole dynamics in spin and orbital ordered vanadium perovskites.

A theory of doped perovskite vanadates with spin and orbital orders is presented. Mobile holes are strongly renormalized by spin excitations (magnons) in the spin G-type and orbital C-type (SG-OC) order, and orbital excitations (orbitons) in the spin C-type and orbital G-type (SC-OG) one. Hole dynamics in a staggered t(2g) orbital array is distinguished from that in the antiferromagnetic order and the e(g) orbital one. The fragile character of the (SG-OC) order in Y1-xCaxVO3 is attributed to the orbiton softening induced by a reduction of the spin order parameter. PMID:15904170

Ishihara, Sumio

2005-04-22

78

Edge Dynamics in a Quantum Spin Hall State: Effects from Rashba Spin-Orbit Interaction

We analyze the dynamics of the helical edge modes of a quantum spin Hall state in the presence of a spatially nonuniform Rashba spin-orbit (SO) interaction. A randomly fluctuating Rashba SO coupling is found to open a scattering channel which causes localization of the edge modes for a weakly screened electron-electron (e-e) interaction. A periodic modulation of the SO coupling,

Anders Ström; Henrik Johannesson; G. I. Japaridze

2010-01-01

79

We study the enhancement of spin coherence with periodic, concatenated, or Uhrig dynamical decoupling N-pulse sequences in a spin-1 Bose-Einstein condensate, where the intrinsic dynamical instability in such a ferromagnetically interacting condensate causes spin decoherence and eventually leads to a multiple spatial-domain structure or a spin texture. Our results show that all three sequences successfully enhance the spin coherence by pushing the wave vector of the most unstable mode in the condensate to a larger value. Among the three sequences with the same number of pulses, the concatenated one shows the best performance in preserving the spin coherence. More interestingly, we find that all three sequences exactly follow the same enhancement law, k{sub -}T{sup 1/2}=c, with k{sub -} the wave vector of the most unstable mode, T the sequence period, and c a sequence-dependent constant. Such a law between k{sub -} and T is also derived analytically for an attractive scalar Bose-Einstein condensate subjected to a periodic dynamical decoupling sequence.

Ning Boyuan; Zhuang Jun; Zhang Wenxian [Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Department of Optical Science and Engineering, Fudan University, Shanghai 200433 (China); You, J. Q. [Department of Physics, Fudan University, Shanghai 200433 (China)

2011-07-15

80

Number Fluctuation Dynamics of Atomic Spin Mixing inside a Condensate

We investigate the quantum dynamics of number fluctuations inside an atomic condensate during coherent spin mixing among internal states of the ground state hyperfine manifold, by quantizing the semiclassical nonrigid pendulum model in terms of the conjugate variable pair: the relative phase and the atom number. Our result provides a theoretical basis that resolves the resolution limit, or the effective ''shot-noise'' level, for counting atoms that is needed to clearly detect quantum correlation effects in spin mixing.

Chang, Lee; Zhai, Q.; Lu Rong [Center for Advanced Study, Tsinghua University, Beijing 100084 (China); You, L. [Center for Advanced Study, Tsinghua University, Beijing 100084 (China); School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332 (United States)

2007-08-24

81

Engineering correlation and entanglement dynamics in spin systems.

We show that correlation and entanglement dynamics of spin systems can be precisely controlled and engineered using only a small number of external physical control parameters. We first point out that the correlation dynamics of such systems can be understood in terms of spin-wave propagation, giving a simple physical explanation of the behavior seen in a number of recent works. We then extend this picture to more realistic translationally invariant systems prepared in product states. Since spin waves propagate according to a system's dispersion relation which typically depends on external physical parameters, this insight provides a convenient way to understand how dynamics can be controlled. We demonstrate these ideas in a simple example system, showing that correlations can be made to propagate in well-defined packets whose speed can be engineered in advance, controlled during the evolution, or even stopped altogether. PMID:18518356

Cubitt, T S; Cirac, J I

2008-05-08

82

Dynamic orientation of spin I nuclei. II.

The Jeffries-Abragam effect in an electron-nuclear coupled spin system (S = (1/2), I = 1) is studied in detail. From a population-distribution analysis of the system, the nuclear orientation parameters are computed and their temperature dependence discussed. Conditions for obtaining stimulated emission are examined in detail. The results are compared with those of an earlier paper. PMID:20049014

Bhatia, K L; Narchal, M L

1966-06-01

83

Spin and Charge Dynamics of High Transition Temperature Cuprates

NASA Astrophysics Data System (ADS)

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 the normal as well as super -conducting states. In the normal state, we review the spin dynamics of the cuprates with special emphasis on neutron scattering experiments in both rm YBa_{2}Cu_{3}O_ {6+x} and rm La_ {2-x}Sr_{x}CuO_4 systems. When realistic models of the Fermi surface shapes are incorporated, along with a moderate degree of spin fluctuation softening, we find good semiquantitative agreement with neutron scattering experiments, as well as Cu-site NMR data for both cuprates. Building on the success of this Fermi-liquid-based scheme, we explore the implications for unconventional d-wave pairing from magnetic data. In our studies of the charge dynamics, we review a gauge-invariant formalism for calculating the electromagnetic response of a superconductor, with special emphasis on the coupling between collective modes and impurity scattering. We address recent experiments on the cuprates which demonstrate a coupling of the c-axis plasma excitation to the superconducting order parameter and explore the consequences for different gap symmetry.

Zha, Yuyao

84

Checkerboards, stripes, and corner energies in spin models with competing interactions

NASA Astrophysics Data System (ADS)

We study the zero-temperature phase diagram of Ising spin systems in two dimensions in the presence of competing interactions: long-range antiferromagnetic and nearest-neighbor ferromagnetic of strength J. We first introduce the notion of a “corner energy,” which shows, when the antiferromagnetic interaction decays faster than the fourth power of the distance, that a striped state is favored with respect to a checkerboard state when J is close to Jc, the transition to the ferromagnetic state, i.e., when the length scales of the uniformly magnetized domains become large. Next, we perform detailed analytic computations on the energies of the striped and checkerboard states in the cases of antiferromagnetic interactions with exponential decay and with power-law decay r-p, p>2, which depend on the Manhattan distance instead of the Euclidean distance. We prove that the striped phase is always favored compared to the checkerboard phase when the scale of the ground-state structure is very large. This happens for J?Jc if p>3, and for J sufficiently large if 2

Giuliani, Alessandro; Lebowitz, Joel L.; Lieb, Elliott H.

2011-08-01

85

Theory of quantum control of spin-photon dynamics and spin decoherence in semiconductors

NASA Astrophysics Data System (ADS)

Single electron spin in a semiconductor quantum dot (QD) and single photon wavepacket propagating in an optical waveguide are investigated as carriers of quantum bit (qubit) for information processing. Cavity quantum electrodynamics of the coupled system composed of charged QD, microcavity and waveguide provides a quantum interface for the interplay of stationary spin qubits and flying photon qubits via cavity assisted optical control. This interface forms the basis for a wide range of essential functions of a quantum network, including transferring, swapping, and entangling qubits at distributed quantum nodes as well as a deterministic source and an efficient detector of a single photon wavepacket with arbitrarily specified shape. The cavity assisted optical process also made possible ultrafast initialization and QND readout of the spin qubit in QD. In addition, the strong optical nonlinearity of dot-cavity-waveguide coupled system enables phase gate and entanglement operation for flying single photon qubits in waveguides. The coherence of the electron spin is the wellspring of these quantum applications being investigated. At low temperature and strong magnetic field, the dominant cause of electron spin decoherence is the coupling with the interacting lattice nuclear spins. We present a quantum solution to the coupled dynamics of the electron with the nuclear spin bath. The decoherence is treated in terms of quantum entanglement of the electron with the nuclear pair-flip excitations driven by the various nuclear interactions. A novel nuclear interaction, mediated by virtue spin-flips of the single electron, plays an important role in single spin free-induction decay (FID). The spin echo not only refocuses the dephasing by inhomogeneous broadening in ensemble dynamics but also eliminates the decoherence by electron-mediated nuclear interaction. Thus, the decoherence times for single spin FID and ensemble spin echo are significantly different. The quantum theory of decoherence also leads to a method of coherence recovery of the electron by disentanglement, realized through maneuvering the nuclear bath evolution by control of the electron spin-flip. The studies form the basis to outline the construction of a solid-state quantum network for scalable and distributed processing of quantum information.

Yao, Wang

86

Destination state screening of active spaces in spin dynamics simulations

NASA Astrophysics Data System (ADS)

We propose a novel avenue for state space reduction in time domain Liouville space spin dynamics simulations, using detectability as a selection criterion - only those states that evolve into or affect other detectable states are kept in the simulation. This basis reduction procedure (referred to as destination state screening) is formally exact and can be applied on top of the existing state space restriction techniques. As demonstrated below, in many cases this results in further reduction of matrix dimension, leading to considerable acceleration of many spin dynamics simulation types. Destination state screening is implemented in the latest version of the Spinach library (http://spindynamics.org).

Krzystyniak, M.; Edwards, Luke J.; Kuprov, Ilya

2011-06-01

87

Modeling Quantum Spin Dynamics in an Ultracold Gas

NASA Astrophysics Data System (ADS)

A recent experiment in our lab focuses on investigating spin dynamics in the quantum regime, where mean field approaches fail. Previous theoretical models for the quantum dynamical evolution of a spin-1 Bose-Einstein condensate do not include the effects of atomic loss that is unavoidable in experiment. Here, we present results of different loss models including a fully quantum calculation of this complicated many body system using a Monte-Carlo approach. We compare the results of these methods to recent experimental measurements and obtain good agreement.

Land, B. J.; Hamley, C. D.; Gerving, C. S.; Hoang, T. M.; Anquez, M. L. B.; Chapman, M. S.

2012-06-01

88

Low frequency spin dynamics in a quantum Hall canted antiferromagnet

NASA Astrophysics Data System (ADS)

In quantum Hall (QH) systems, Coulomb interactions combined with the macroscopic degeneracy of Landau levels (LLs) drive the electron system into strongly correlated phases as illustrated by the series of fractional QH effects and may also lead to various forms of broken symmetry dictated by the LL filing factor ?. When two layers of such electron systems are closely separated by a thin tunnel barrier, the addition of interlayer interactions and the layer degree of freedom brings about even richer electronic phases, opening up possibilities for different classes of symmetry breaking. In particular, at total filling factor ?T = 2, where the two of the four lowest LLs split by the Zeeman and interlayer tunnel couplings are occupied, the competing degrees of freedom due to the layer and spin are predicted to lead to rich magnetic phases. Here we present results of resistively detected nuclear spin relaxation measurements in closely separated electron systems that reveal strong low-frequency spin fluctuations in the QH regime at ?T = 2 [1]. As the temperature is decreased, the spin fluctuations, manifested by a sharp enhancement of the nuclear spin-lattice relaxation rate 1/T1, continue to grow down to the lowest temperature of 66 mK. The observed divergent behavior of 1/T1 signals a gapless spin excitation mode (i.e., a Goldstone mode) and is a hallmark of the theoretically predicted canted antiferromagnetic order. Our data demonstrate the realization of a two-dimensional system with broken planar spin rotational symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit. [1] N. Kumada, K. Muraki, and Y. Hirayama, Science 313, 329 (2006).

Muraki, Koji

2007-03-01

89

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

2009-06-12

90

Coarse graining of spin net models: dynamics of intertwiners

NASA Astrophysics Data System (ADS)

Spin foams are models of quantum gravity and therefore quantum space time. A key open issue is to determine the possible continuum phases of these models. Progress on this issue has been prohibited by the complexity of the full four-dimensional models. We consider here simplified analogue models, so called spin nets, that retain the main dynamical ingredient of spin foams, the simplicity constraints. For a certain class of these spin net models we determine the phase diagram and therefore the continuum phases via a coarse graining procedure based on tensor network renormalization. This procedure will also reveal an unexpected fixed point, which turns out to define a new triangulation invariant vertex model.

Dittrich, Bianca; Martín-Benito, Mercedes; Schnetter, Erik

2013-10-01

91

Non-equlibrium energy dynamics in spin chains and ladders

NASA Astrophysics Data System (ADS)

We investigate the real-time dynamics of the energy density in spin-1/2 chains and ladders, starting from initial states with an inhomogeneous profile of bond energies, extending our previous work on the dynamics of spin-density wave packets [1]. These simulations are carried out using the adaptive time-dependent density matrix renormalization group algorithm. We analyze the time-dependence of the spatial variance of the bond energies which yields necessary criteria for ballistic or diffusive energy dynamics. In the case of the XXZ chain, our results are consistent with ballistic behavior, both in the massless and the massive phase. For the massless regime, we compare our numerical results to predictions from bosonization for, e.g., the velocity that the initial perturbation spreads with. In the case of ladders, we find an involved dynamics whose qualitative interpretation is still under scrutiny. [4pt] [1] Langer et al. Phys. Rev. B 79, 214409 (2009)

Heidrich-Meisner, Fabian; Langer, Stephan; Heyl, Markus; McCulloch, Ian

2011-03-01

92

Response: Spinning the Pinwheel, Together: More Thoughts on Affective Social Competence.

ERIC Educational Resources Information Center

|Addresses the variations, reactions, and additions to the affective social competence model presented earlier. Specifically addresses the issue of whether sending, receiving, and experiencing are equal components to affective social competence; the time course of affective social competence; the cognitive representations of self and world;…

Halberstadt, Amy G.; Dunsmore, Julie C.; Denham, Susanne A.

2001-01-01

93

Introducing spin in Schrodinger dynamics of particle motion

A non-perturbative relativistic atomic theory is presented. Spin is successfully introduced in Schrodinger dynamics of particle motion and the resulting energy levels of Hydrogen atom are shown to be exactly same as that of Dirac's theory. The separation of new radial and angular wave equations in spherical polar coordinates is as simple as that of the Schrodinger theory. The solutions

Vikram H. Zaveri

2007-01-01

94

Dynamics of carrions in the spin-fermion model.

National Technical Information Service (NTIS)

The spectrum of hole quasiparticles (carrions) and the role of magnetic correlations has been considered in the framework of spin-fermion (Kondo-Heisenberg) model by means of the equation-of-motion method. The hole quasiparticle dynamics has been discusse...

A. L. Kuzemskij D. Marvakov

1996-01-01

95

Spin dynamics in storage rings and linear accelerators

The purpose of these lectures is to survey the subject of spin dynamics in accelerators: to give a sense of the underlying physics, the typical analytic and numeric methods used, and an overview of results achieved. Consideration will be limited to electrons and protons. Examples of experimental and theoretical results in both linear and circular machines are included.

Irwin, J.

1994-04-01

96

Dynamical Blume-Capel Model: Competing Metastable States at Infinite Volume

NASA Astrophysics Data System (ADS)

This paper concerns the microscopic dynamical description of competing metastable states. We study, at infinite volume and very low temperature, metastability and nucleation for kinetic Blume-Capel model: a ferromagnetic lattice model with spins taking three possible values: -1, 0, 1. In a previous paper ([MO]) we considered a simplified, irreversible, nucleation-growth model; in the present paper we analyze the full Blume-Capel model. We choose a region U of the thermodynamic parameters such that, everywhere in U: -b{1} (all minuses) corresponds to the highest (in energy) metastable state, b{0} (all zeroes) corresponds to an intermediate metastable state and +b{1} (all pluses) corresponds to the stable state. We start from -b{1} and look at a local observable. Like in [MO], we find that, when crossing a special line in U, there is a change in the mechanism of transition towards the stable state +b{1}. We pass from a situation: 1. where the intermediate phase b{0} is really observable before the final transition, with a permanence in b{0} typically much longer than the first hitting time to b{0}; to the situation: 2. where b{0} is not observable since the typical permanence in b{0} is much shorter than the first hitting time to b{0} and, moreover, large growing 0-droplets are almost full of +1 in their interior so that there are only relatively thin layers of zeroes between +1 and -1.

Manzo, F.; Olivieri, E.

2001-09-01

97

NASA Astrophysics Data System (ADS)

The quasi-one-dimensional cuprates (La,Y,Sr,Ca)14Cu24O41, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a charge-density wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of Sr14-xCaCu24O41, however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y)y(S,Ca)14-yCu24O41 and fully doped Sr14-xCaCu24O41. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated low-dimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d-wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of Sr14-xCaCu24O41 which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system.

Vuleti?, T.; Korin-Hamzi?, B.; Ivek, T.; Tomi?, S.; Gorshunov, B.; Dressel, M.; Akimitsu, J.

2006-05-01

98

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.

Maryasov, Alexander G.

2012-01-01

99

Nonequilibrium dynamics of a fast oscillator coupled to Glauber spins

NASA Astrophysics Data System (ADS)

A fast harmonic oscillator is linearly coupled with a system of Ising spins that are in contact with a thermal bath, and evolve under a slow Glauber dynamics at dimensionless temperature ?. The spins have a coupling constant proportional to the oscillator position. The oscillator-spin interaction produces a second order phase transition at ? = 1 with the oscillator position as its order parameter: the equilibrium position is zero for ? > 1 and nonzero for ? < 1. For ? < 1, the dynamics of this system is quite different from relaxation to equilibrium. For most initial conditions, the oscillator position performs modulated oscillations about one of the stable equilibrium positions with a long relaxation time. For random initial conditions and a sufficiently large spin system, the unstable zero position of the oscillator is stabilized after a relaxation time proportional to ?. If the spin system is smaller, the situation is the same until the oscillator position is close to zero, then it crosses over to a neighborhood of a stable equilibrium position about which it keeps oscillating for an exponentially long relaxation time. These results of stochastic simulations are predicted by modulation equations obtained from a multiple scale analysis of macroscopic equations.

Bonilla, L. L.; Prados, A.; Carpio, A.

2010-09-01

100

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable 1H polarization is determined by the ratio of the buildup rate and the spin–lattice relaxation rate, in turn depend on the 1H spin density. It is shown that the final 1H polarization can be enhanced by diluting the 1H spins with

Akinori Kagawa; Yu Murokawa; Kazuyuki Takeda; Masahiro Kitagawa

2009-01-01

101

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

102

SPIN DYNAMICS IN AGS AND RHIC.

A fundamental aspect of particle physics is the spin of the particles. With polarized beams, the internal structure of the proton may be probed in ways that are unattainable with unpolarized beams. The Relativistic Heavy Ion Collider (RHIC) has the unique capability of colliding protons with both transverse and longitudinal polarization at center-of-mass energies up to 500 GeV. In this paper we examine the methods used to accelerate and manipulate polarized proton beams in RHIC and its injectors. Special techniques include the use of a partial Siberian snake and an ac dipole in the AGS. In RHIC we use four superconducting helical Siberian snakes (two per ring) for acceleration, and eight superconducting helical rotators for independent control of polarization directions at two interaction regions.

Mackay, W W; Bai, M; Courant, E D; Brown, K; Glenn, W; Huang, H; Luccio, A; Ptitsyn, V; Roser, T; Satogata, T; Ltepikian, S; Tsoupas, N

2003-05-12

103

NASA Astrophysics Data System (ADS)

We demonstrated electrical spin injection from a half-metallic Heusler alloy Co2MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co2MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 spin source, suggesting that the spin polarization of Co2MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel.

Akiho, Takafumi; Shan, Jinhai; Liu, Hong-xi; Matsuda, Ken-ichi; Yamamoto, Masafumi; Uemura, Tetsuya

2013-06-01

104

Chaotic dynamics in a periodically driven spin-1 condensate

We use periodically modulated magnetic fields to drive spin-1 Bose-Einstein condensates (BECs) and study the corresponding spin-mixing dynamics. Due to the time-dependent driving, this system permits chaotic dynamics depending on the drive parameters, which could not occur in previous studies. From the investigation of the Poincare sections, we find there exist complex trajectories in the phase space, leading to very complicated structures of the phase space with mixed regular and chaotic regions. By calculating the quasienergy levels of the corresponding Floquet operators, the signatures of quantum chaos are also found in this system. The level spacing distribution is very close to the Poisson distribution or Wigner distribution when the corresponding classical dynamics is regular or chaotic.

Cheng Jing [Department of Physics, South China University of Technology, Guangzhou 510640 (China); Kavli Institute for Theoretical Physics China, CAS, Beijing 100190 (China)

2010-02-15

105

Atomistic spin dynamics of low-dimensional magnets

NASA Astrophysics Data System (ADS)

We investigate the magnetic properties of a range of low-dimensional ferromagnets using a combination of first-principles calculations and atomistic spin dynamics simulations. This approach allows us to evaluate the ground state and finite temperature properties of experimentally well characterized systems such as Co/Cu(111), Co/Cu(001), Fe/Cu(001) and Fe/W(110), for different thicknesses of the magnetic layer. We compare our calculated spin wave spectra with experimental data available in the literature, and find a good quantitative agreement. We also predict magnon spectra for systems for which no experimental data exist at the moment, and estimate the role of temperature effects.

Bergqvist, Lars; Taroni, Andrea; Bergman, Anders; Etz, Corina; Eriksson, Olle

2013-04-01

106

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

107

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

108

Development of Competence in Dynamic Learning Environments. No. 79.

ERIC Educational Resources Information Center

|Perspective Text Analysis is a way to measure competence by measuring the strategy of synthesizing, which intelligence tests or questionnaires cannot measure. This paper proposes the use of Perspective Text Analysis in the study of instructional materials. Perspective Text Analysis has been applied in various learning environments, and the…

Bierschenk, Inger

109

Universal Dynamical Decoupling of a Single Solid-State Spin from a Spin Bath

NASA Astrophysics Data System (ADS)

Controlling the interaction of a single quantum system with its environment is a fundamental challenge in quantum science and technology. We strongly suppressed the coupling of a single spin in diamond with the surrounding spin bath by using double-axis dynamical decoupling. The coherence was preserved for arbitrary quantum states, as verified by quantum process tomography. The resulting coherence time enhancement followed a general scaling with the number of decoupling pulses. No limit was observed for the decoupling action up to 136 pulses, for which the coherence time was enhanced more than 25 times compared to that obtained with spin echo. These results uncover a new regime for experimental quantum science and allow us to overcome a major hurdle for implementing quantum information protocols.

de Lange, G.; Wang, Z. H.; Ristè, D.; Dobrovitski, V. V.; Hanson, R.

2010-10-01

110

Dynamics of spinning compact binaries in general relativity

NASA Astrophysics Data System (ADS)

This thesis investigates the dynamics of binary systems composed of spinning compact objects in the context of general relativity. Compact binaries are promising sources of gravitational radiation for both ground- and space-based gravitational-wave detectors. If the dynamics of these systems were chaotic, the number of waveform templates needed to match a given gravitational-wave signal would grow exponentially with increasing detection sensitivity, rendering the preferred matched filter detection method computationally impractical. It is therefore urgent to understand whether the binary dynamics can be chaotic, and, if so, how prevalent this chaos is. We first consider the dynamics of a spinning compact object orbiting a much more massive rotating black hole, as modeled by the Papapetrou equations in Kerr spacetime. We find that many initial conditions lead to positive Lyapunov exponents, indicating chaotic dynamics. Despite the formal existence of chaotic solutions, we find that chaos occurs only for physically unrealistic values of the small body's spin. As a result, chaos will not affect theoretical templates in the extreme mass-ratio limit for which the Papapetrou equations are valid. We next consider the dynamics of spinning black-hole binaries, as modeled by the post-Newtonian (PN) equations, which are valid for orbital velocities much smaller than the speed of light. We study thoroughly the special case of quasi-circular orbits with comparable mass ratios. Our survey shows that chaos occurs in a negligible fraction of possible configurations, and only for such small radii that the PN approximation is likely to be invalid. As a result, at least in the case of comparable mass black-hole binaries, theoretical templates will not be significantly affected by chaos. In a final, self-contained chapter, we discuss various methods for the calculation of Lyapunov exponents in systems of ordinary differential equations. We introduce several new techniques applicable to constrained dynamical systems, developed in the course of studying the dynamics of spinning compact binaries. Considering the Papapetrou and post-Newtonian systems together, our most important general conclusion is that we find no chaos in any relativistic binary system for orbits that clearly satisfy the approximations required for the equations of motion to be physically valid.

Hartl, Michael David

111

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

112

Non-equilibrium dynamics of spin facilitated glass models

NASA Astrophysics Data System (ADS)

We consider the dynamics of spin facilitated models of glasses in the non-equilibrium ageing regime following a sudden quench from high to low temperatures. We briefly review known results obtained for the broad class of kinetically constrained models, and then present new results for the behaviour of the one-spin facilitated Fredrickson Andersen and East models in various spatial dimensions. The time evolution of one-time quantities, such as the energy density, and the detailed properties of two-time correlation and response functions are studied using a combination of theoretical approaches, including exact mappings of master operators and reductions to integrable quantum spin chains, field theory and renormalization group, and independent interval and timescale separation methods. The resulting analytical predictions are confirmed by means of detailed numerical simulations. The models we consider are characterized by trivial static properties, with no finite temperature singularities, but they nevertheless display a surprising variety of dynamic behaviour during ageing, which can be directly related to the existence and growth in time of dynamic lengthscales. Well-behaved fluctuation dissipation ratios can be defined for these models, and we study their properties in detail. We confirm in particular the existence of negative fluctuation dissipation ratios for a large number of observables. Our results suggest that well-defined violations of fluctuation dissipation relations, of a purely dynamic origin and unrelated to the thermodynamic concept of effective temperatures, could in general be present in non-equilibrium glassy materials.

Léonard, Sébastien; Mayer, Peter; Sollich, Peter; Berthier, Ludovic; Garrahan, Juan P.

2007-07-01

113

Spin dynamics in CeB6 studied by muon spin relaxation

NASA Astrophysics Data System (ADS)

The dynamics of magnetic fluctuations in the paramagnetic and antiferroquadrupolarly (AFQ) ordered phases of single crystal CeB6 was investigated by means of muon spin relaxation experiments. Applied magnetic fields up to 2.5 T were used. Since in the AFQ phase the contact hyperfine coupling that contributes to the fluctuating field amplitudes at the three d -type interstitial muon sites strongly depends on the temperature and the applied field, as shown by the corresponding Knight-shift results, this feature was taken into account in determining the magnetic fluctuation rates. The extracted correlation time ?c of the magnetic fluctuations depends only weakly on the applied field, its temperature dependence demonstrates an accelerated slowing down of the spin dynamics in parallel with the development of the AFQ order.

Gygax, F. N.; Schenck, A.; Solt, G.; Zaharko, O.

2010-03-01

114

Spin current driven by magnetization dynamics in Rashba systems

NASA Astrophysics Data System (ADS)

Spin currents induced by the spin pumping effect in the presence of Rashba spin-orbit interaction are studied theoretically. Results indicate that the spin-orbit interaction induces an effective field which enables us to handle spin currents.

Takeuchi, Akihito; Tatara, Gen

2011-12-01

115

Anisotropies and spin dynamics in ultrathin magnetic multilayer structures

NASA Astrophysics Data System (ADS)

High quality magnetic films were prepared by Molecular Beam Epitaxy (MBE) using Thermal Deposition (TD) and Pulse Laser Deposition (PLD) techniques. Ferromagnetic Resonance (FMR) and Mossbauer studies have shown that the Fe films prepared by PLD exhibited a more intermixed interface lattice structure than those prepared by TD. Dramatic decrease of the in-plane interface uniaxial anisotropy for the PLD films compared to those prepared by TD has shown that the in-plane uniaxial anisotropy is caused by magnetoelasticity driven by the Fe/GaAs(001) interface lattice shear. Magnetization dynamics of the ultrathin Fe/Au,Ag/Fe films was studied using Time-Resolved Magneto-Optical Kerr Effect (TRMOKE) and FMR in the frequency range from 1 to 73 GHz. The Gilbert damping was studied in the Au/Fe/GaAs(001) structures as a function of the Fe and Au layer thickness, respectively. The observed increase in magnetic damping in the Fe film covered with thick Au capping layers was explained by spin pumping at the Fe/Au interface accompanied by spin relaxation and diffusion of the accumulated spin density in the Au layer. The spin diffusion length in Au was found to be 34 nm at room temperature. Significant increase of the Gilbert damping was observed in the Au/Fe/GaAs structures with decreasing Fe film thickness. Its origin lies in the additional damping at the Fe/GaAs interface. Direct detection of the spin current propagating across the Ag spacer in Fe/Ag,Au/Fe/GaAs(001) structures was carried out with stroboscopic TRMOKE measurements. The Fe layer grown on GaAs served as a spin pumping source and the Fe layer grown on the Au,Ag spacer was used as a probe for detection of the spin current propagating across the Au and Ag spacers. The experimental results were interpreted using selfconsistent solution of the Landau Lifshitz Gilbert (LLG) equations of motion with the spin diffusion equation for the accumulated spin density in the Au and Ag spacers. The spin diffusion length in Ag was found to be 150 nm.

Kardasz, Bartlomiej

116

TOPICAL REVIEW: Quantum spin nanotubes—frustration, competing orders and criticalities

NASA Astrophysics Data System (ADS)

Recent developments of theoretical studies on spin nanotubes are reviewed, especially focusing on the S = 1/2 three-leg spin tube. In contrast to the three-leg spin ladder, the tube has a spin gap in the case of the regular-triangle unit cell when the rung interaction is sufficiently large. The effective theory based on the Hubbard Hamiltonian indicates a quantum phase transition to a gapless spin liquid due to the lattice distortion to an isosceles triangle. This is also supported by the numerical diagonalization and the density matrix renormalization group analyses. Furthermore, combining analytical and numerical approaches, we reveal several novel magnetic-field-induced phenomena: Néel, dimer, chiral and/or inhomogeneous orders, a new mechanism for the magnetization plateau formation, and others. The recently synthesized spin tube materials are also briefly introduced.

Sakai, Tôru; Sato, Masahiro; Okamoto, Kiyomi; Okunishi, Kouichi; Itoi, Chigak

2010-10-01

117

We report on micromagnetic simulation results of radiation of strong spin waves from the cores of magnetic vortices driven by their dynamics motion or the annihilation of a vortex-antivortex pair in a rectangular shaped magnetic thin film. Such strong spin-waves are distinguished from spin wave modes typically excited in patterned magnetic elements. The spin wave excitation with relatively low frequencies

Ki-Suk Lee; Sangkook Choi; Sang-Koog Kim

2005-01-01

118

Study of Spin Dynamics by Means of On-Chip SQUIDs

We developed an on-chip SQUID (Superconducting Quantum Interference Device) measurement technique to study spin dynamics in Single Molecular Magnets (SMMs) and other spin systems. SMMs systems are thought as potential qubit candidates, due to their quantum nature and the possibility to construct superposition of molecular spin states. If spins are enough diluted to minimize dipolar interactions and therefore increase decoherence

Lei Chen

2010-01-01

119

Spin Dynamics in the Time and Frequency Domain

NASA Astrophysics Data System (ADS)

The current status of experimental approaches to analyze the spin wave dynamics in ferromagnetic nanoscale structures is reviewed. Recent developments in frequency- and field swept spectroscopy to determine the resonant response of nanoscale ferromagnets are described together with time-resolved measurements in the GHz frequency and pico second time domain, respectively. Examples for the analysis and manipulation of different mechanisms for the relaxation of the magnetization after microwave excitation into its ground state are presented.

Farle, Michael; Silva, Tom; Woltersdorf, Georg

120

Introducing spin in Schrodinger dynamics of particle motion

A non-perturbative relativistic atomic theory is presented. Spin is\\u000asuccessfully introduced in Schrodinger dynamics of particle motion and the\\u000aresulting energy levels of Hydrogen atom are shown to be exactly same as that\\u000aof Dirac's theory. The separation of new radial and angular wave equations in\\u000aspherical polar coordinates is as simple as that of the Schrodinger theory. The\\u000asolutions

Vikram H. Zaveri

2007-01-01

121

Optimal control of stochastic magnetization dynamics by spin current

NASA Astrophysics Data System (ADS)

Fluctuation-induced stochastic magnetization dynamics plays an important role in spintronics devices. Here we propose that it can be optimally controlled by spin currents to minimize or maximize the Freidlin-Wentzell action functional of the system hence to increase or decrease the probability of the large fluctuations. We apply this method to study the thermally activated magnetization switching problem and to demonstrate the merits of the optimal control strategy.

Wang, Yong; Zhang, Fu-Chun

2013-05-01

122

Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets

We develop the hydrodynamic theory of collinear spin currents coupled to magnetization dynamics in metallic ferromagnets. The collective spin density couples to the spin current through a U(1) Berry-phase gauge field determined by the local texture and dynamics of the magnetization. We determine phenomenologically the dissipative corrections to the equation of motion for the electronic current, which consist of a

Clement H. Wong; Yaroslav Tserkovnyak

2009-01-01

123

Spin Dynamics in InAs Quantum Dots

NASA Astrophysics Data System (ADS)

Spin coherence in InAs Self-Assemble Quantum Dots (SAQD's) could be useful for optical delay lines and quantum information technology. Very uniform dots and a very accurate measurement of dephasing processes are required to realize these possibilities. To this effect we report decoherence times in InAs SAQD. Here we describe measurements of spin dynamics from a 17 layered nominally undoped wafer of InAs SAQDs with a varying dot-size. We used Time Resolved Kerr Rotation (TRKR) for a wavelength resonant with the 3D InAs Stranski-Krastanow strain mediated quantum dots. Response is observed from 0 to 5 T that corresponds to a freely precessing spin with g = 0.45, a 1.2 ns lifetime at B=0 that decreases with B, and a sine-like phase. We attribute this spin to an electron from either the ground state of a negative trion or the excited state of a positive trion. The dots are dots unintentionally doped from background doping in the MBE chamber. Work supported in part by ONR, NSA/ARO, and DARPA/QUIST. JW is an NRC/NRL Postdoctoral Research Associate.

Whitaker, Janica; Bracker, Allan; Gammon, Daniel; Kennedy, Thomas

2006-03-01

124

Protein structural dynamics revealed by site-directed spin labeling and multifrequency EPR

Multifrequency electron paramagnetic resonance (EPR), combined with site-directed spin labeling, is a powerful spectroscopic tool to characterize protein dynamics. The lineshape of an EPR spectrum reflects combined rotational dynamics of the spin probe’s local motion within a protein, reorientations of protein domains, and overall protein tumbling. All these motions can be restricted and anisotropic, and separation of these motions is important for thorough characterization of protein dynamics. Multifrequency EPR distinguishes between different motions of a spin-labeled protein, due to the frequency dependence of EPR resolution to fast and slow motion of a spin probe. This gives multifrequency EPR its unique capability to characterize protein dynamics in great detail. In this review, we analyze what makes multifrequency EPR sensitive to different rates of spin probe motion and discuss several examples of its usage to separate spin probe dynamics and overall protein dynamics, to characterize protein backbone dynamics, and to resolve protein conformational states.

Thomas, David D.

2011-01-01

125

Spin dynamics and manipulation in GaMnAs alloys

NASA Astrophysics Data System (ADS)

We review recent experiments on spin excitation and manipulation in the ferromagnetic semiconductor GaMnAs. Spin dynamics in GaMnAs have been studied by two complementary approaches - by frequency-domain techniques, such as Brillouin light scattering (BLS) and ferromagnetic resonance (FMR); and by optical real-time techniques, such as ultrafast pump-probe magneto-optical spectroscopy. Using BLS and FMR, magnon frequencies (or resonance fields), were investigated as a function of Mn concentration, temperature and direction of magnetization, leading to information on magnetic anisotropy. Time-resolved magneto-optical Kerr effect, on the other hand, was used to study photo-induced femtosecond magnetization rotation, ultrafast optical demagnetization, and collective magnetization precession. Optically-induced transient changes in magnetization of GaMnAs produced by femtosecond laser pulses are analyzed and discussed in terms of the Landau-Lifshitz-Gilbert model. Finally, for completeness, we also discuss carrier-mediated nonthermal and thermal (lattice-heating) contributions to spin dynamics.

Liu, X.; Zhou, Y. Y.; Harley, E.; McNeil, L. E.; Wang, J.; Qi, J.; Xu, Y.; Steigerwald, A.; Tolk, N.; Zahn, J. P.; Gamouras, A.; March, S.; Hall, K. C.; Furdyna, J. K.

2010-02-01

126

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

127

Competing Orders: Superfluidity and Spin Coherence in a Dilute Fermi Gas

The quest to achieve superfluidity in a two-component atomic Fermi gas is one of the most active research areas in ultra cold gases. Experimentally the possibility exists to prepare each atom in a superposition of two hyperfine states. In this case the system can be thought of as a spin-1\\/2 system, with longitudinal and transverse spin degrees of freedom. In

Jamie E. Williams; Nicolai N. Nygaard; Charles W. Clark

2003-01-01

128

Visualization of spin dynamics in single nanosized magnetic elements.

The design of future spintronic devices requires a quantitative understanding of the microscopic linear and nonlinear spin relaxation processes governing the magnetization reversal in nanometer-scale ferromagnetic systems. Ferromagnetic resonance is the method of choice for a quantitative analysis of relaxation rates, magnetic anisotropy and susceptibility in a single experiment. The approach offers the possibility of coherent control and manipulation of nanoscaled structures by microwave irradiation. Here, we analyze the different excitation modes in a single nanometer-sized ferromagnetic stripe. Measurements are performed using a microresonator set-up which offers a sensitivity to quantitatively analyze the dynamic and static magnetic properties of single nanomagnets with volumes of (100 nm)(3). Uniform as well as non-uniform volume modes of the spin wave excitation spectrum are identified and found to be in excellent agreement with the results of micromagnetic simulations which allow the visualization of the spatial distribution of these modes in the nanostructures. PMID:21693797

Banholzer, A; Narkowicz, R; Hassel, C; Meckenstock, R; Stienen, S; Posth, O; Suter, D; Farle, M; Lindner, J

2011-06-21

129

Review on System-Spin Environment Dynamics of Quantum Discord

NASA Astrophysics Data System (ADS)

Recent work has relatively comprehensively studied the quantum discord, which is supposed to account for all the nonclassical correlations present in a bipartite state (including entanglement), and provide computational speedup and quantum enhancement even in separable states. Firstly, we introduce several different indicators of nonclassical correlations, including their definitions and interpretations, mathematical properties, and the relationship between them. Secondly, we review two major topics of quantum discord. One is the remarkable behavior at quantum phase transitions. The pairwise quantum discord for nearest neighbors as well as distant spin pairs can perfectly signal the critical behavior of many physical models, even at finite temperatures. The other is quantum discord dynamics in open systems, especially for "system-spin environment" models. Quantum discord is more robust than entanglement against external perturbations. It can be created, greatly amplified or protected under certain conditions, and presents promising applications in quantum technologies such as quantum computers.

Liu, Ben-Qiong; Shao, Bin; Li, Jun-Gang; Zou, Jian

2013-01-01

130

Dynamic switching of the spin circulation in tapered magnetic nanodisks

NASA Astrophysics Data System (ADS)

Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. With each having two possible states, there are four possible stable magnetization configurations that can be utilized for a multibit memory cell. Dynamic control of vortex core polarity has been demonstrated using both alternating and pulsed magnetic fields and currents. Here, we show controlled dynamic switching of spin circulation in vortices using nanosecond field pulses by imaging the process with full-field soft X-ray transmission microscopy. The dynamic reversal process is controlled by far-from-equilibrium gyrotropic precession of the vortex core, and the reversal is achieved at significantly reduced field amplitudes when compared with static switching. We further show that both the field pulse amplitude and duration required for efficient circulation reversal can be controlled by appropriate selection of the disk geometry.

Uhlí?, V.; Urbánek, M.; Hladík, L.; Spousta, J.; Im, M.-Y.; Fischer, P.; Eibagi, N.; Kan, J. J.; Fullerton, E. E.; Šikola, T.

2013-05-01

131

Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light.

We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics. PMID:22274257

Quinteiro, G F; Tamborenea, P I; Berakdar, J

2011-12-19

132

Nonequilibrium dynamical phase transition of 3D kinetic Ising\\/Heisenberg spin system

We have studied the nonequilibrium dynamic phase transitions of both three-dimensional (3D) kinetic Ising and Heisenberg spin systems in the presence of a perturbative magnetic field by Monte Carlo simulation. The feature of the phase transition is characterized by studying the distribution of the dynamical order parameter. In the case of anisotropic Ising spin system (ISS), the dynamic transition is

Yuan-Zhi Shao; J. K. L. Lai; C. H. Shek; Guang-Ming Lin; Tu Lan

2004-01-01

133

Constrained dynamics of universally coupled massive spin 2-spin 0 gravities

NASA Astrophysics Data System (ADS)

The 2-parameter family of massive variants of Einsteins gravity (on a Minkowski background) found by Ogievetsky and Polubarinov by excluding lower spins can also be derived using universal coupling. A Dirac-Bergmann constrained dynamics analysis seems not to have been presented for these theories, the Freund-Maheshwari-Schonberg special case, or any other massive gravity beyond the linear level treated by Marzban, Whiting and van Dam. Here the Dirac-Bergmann apparatus is applied to these theories. A few remarks are made on the question of positive energy. Being bimetric, massive gravities have a causality puzzle, but it appears soluble by the introduction and judicious use of gauge freedom.

Pitts, J. Brian

2006-03-01

134

Group dynamics for the acquisition of competences in Project Management

NASA Astrophysics Data System (ADS)

The Bologna Process promotes European citizens' employability from teaching fields in the University which implies the design of activities addressed to the development of skills for the labor market and engagement of employers. This work has been conceived for improving the formation of Engineering Project Management through group dynamics focused on: 1) the use of the creativity for solving problems; 2) promoting leadership capacities and social skills in multidisciplinary/multicultural work groups; 3) the ethical, social and environmental compromise; 4) the continuous learning. Different types of activities were designed: short activities of 15-30 minutes where fragments of books or songs are presented and discussed and long activities (2 h) where groups of students take different roles for solving common problems and situations within the Engineering Projects context. An electronic book with the content of the dynamics and the material for the students has been carried out. A sample of 20 students of Electronic Engineering degree which had participated at least in two dynamics, evaluated the utility for improving their formation in Engineering Project Management with a mark of 8.2 (scale 0-10, standard deviation equal to 0.9). On the other hand, the teachers observed how this type of work, promotes the interdisciplinary training and the acquisition of social skills, usually not-included in the objectives of the subjects.

Taguas, E. V.; Aguilar, M. C.; Castillo, C.; Polo, M. J.; Pérez, R.

2012-04-01

135

Magnetic vortex dynamics induced by spin-transfer torque

NASA Astrophysics Data System (ADS)

We theoretically study the dynamics of a magnetic vortex under spin-polarized electric current in ferromagnets. The equation of motion of the vortex in terms of collective coordinates is derived. We compare our theory with recent experiments for current-induced vortex displacement and resonance motion in a ferromagnetic nanodot. Our estimate for the displacement and the resonance frequency shows a good agreement with the experiment. We also study the current-induced motion of a vortex wall in a ferromagnetic thin wire.

Shibata, J.; Nakatani, Y.; Tatara, G.; Kohno, H.; Otani, Y.

2007-03-01

136

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

137

Phase and spin dynamics in a superconductor/ferromagnet/superconductor junction

NASA Astrophysics Data System (ADS)

We study a phase dynamics induced by a spin dynamics in a ferromagnetic Josephson junction, in which two superconductors (SC's) are separated by a ferromagnetic layer. A new phenomenological model for the phase variable is proposed by including the spin dynamics excited by the ferromagnetic resonance (FMR) in the gauge invariant phase of s-wave SC's. We found that the current-voltage characteristics show step structures by tuning the microwave frequency to FMR. The result originats from the coupling between the spin and the phase dynamics, and provides a new route to observe the spin wave excitation by using the Josephson effect.

Hikino, S.; Mori, M.; Takahashi, S.; Maekawa, S.

2009-03-01

138

Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling

We introduce and solve a semiclassical random walk (RW) model that describes the dynamics of spin polarization waves in zinc-blende semiconductor quantum wells. We derive the dispersion relations for these waves, including the Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the effects of an electric field applied parallel to the spin polarization wave vector. In agreement with calculations based on quantum kinetic theory [P. Kleinert and V. V. Bryksin, Phys. Rev. B 76, 205326 (2007)], the RW approach predicts that spin waves acquire a phase velocity in the presence of the field that crosses zero at a nonzero wave vector, q{sub 0}. In addition, we show that the spin-wave decay rate is independent of field at q{sub 0} but increases as (q-q{sub 0}){sup 2} for q {ne} q{sub 0}. These predictions can be tested experimentally by suitable transient spin grating experiments.

Yang, Luyi; Orenstein, J.; Lee, Dung-Hai

2010-09-27

139

Experimental test of the Chao matrix formalism for spin dynamics.

NASA Astrophysics Data System (ADS)

We recently started testing Chao's proposed new matrix formalism for describing the spin dynamics due to a single spin resonance in a stored polarized beam. This formalism seems to be the first generalization of the Froissart-Stora equation since it was published in 1960. It allows one to calculate analytically the polarization's behavior inside a resonance, which is not possible using the Froissart-Stora equation. We recently tested some Chao formalism predictions using a 1.85 GeV/c polarized deuteron beam stored in COSY. We swept an rf dipole's frequency through 200 Hz, at different sweep rates, while varying the distance from the sweep's end frequency to an rf-induced spin resonance's central frequency. We compared our experimental data with the predictions of the Chao formalism and the prediction of a phenomenological Froissart-Stora-based two-fluid model. The Froissart-Stora formula itself can make no prediction inside the resonance. The data seem to support the validity of the Chao formalism. (Supported by the German BMBF Science Ministry.)

Morozov, V. S.; Chao, A. W.; Krisch, A. D.; Leonova, M. A.; Raymond, R. S.; Sivers, D. W.; Wong, V. K.; Gebel, R.; Lehrach, A.; Lorentz, B.; Maier, R.; Prasuhn, D.; Schnase, A.; Stockhorst, H.; Hinterberger, F.; Ulbrich, K.

2007-04-01

140

Experimental investigation of the dynamics of spinning tethered bodies

NASA Astrophysics Data System (ADS)

Ground based experiments are conducted as a part of the OEDIPUS-C sounding rocket mission, scheduled for launch in the winter of 1995. Here OEDIPUS stands for Observation of Electrified Distribution in Ionospheric Plasma—a Unique Strategy. The OEDIPUS-C configuration consists of two spinning bodies connected by a 1 km long tether (the spin axis is nominally along the tether line). The objective is to assess dynamic behaviour of the tether and the payload. The test configuration consists of an end-body supported by a tether. The test procedure involves slow spin-up of the system and identifying the speeds corresponding to onset of the tether modes or the large amplitude end-body coning. This is referred to as the critical speed and corresponds to the stability boundary of the system. Experimental results are obtained for four different bodies to study the system stability over a wide range of mass and geometric parameters. Effect of offset of the tether attachment from the end-body centre of mass is also investigated. The observed critical speeds are compared with those given by the linear theory. The test results are generally in very good agreement with the theory, however several transient phenomena observed during the test suggest that system nonlinearities cannot be ignored when modelling such a complex system.

Modi, V. J.; Pradhan, S.; Chu, M.; Tyc, G.; Misra, A. K.

1996-10-01

141

Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition

Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)! , i.e., much larger than that of most traditional network structures. We show that a small winnerless competition network composed of FitzHugh-Nagumo spiking neurons efficiently transforms input information into a spatiotemporal output.

Rabinovich, M.; Volkovskii, A.; Lecanda, P.; Huerta, R.; Abarbanel, H. D. I.; Laurent, G.

2001-08-06

142

Competing Jahn-Teller and spin Jahn-Teller ordering in ACr2O4 spinels

NASA Astrophysics Data System (ADS)

Magnetic ordering is strongly linked to structural distortions in the frustrated antiferromagnets ZnCr2O4 and MgCr2O4. These systems undergo spin Jahn-Teller distortions at the onset of magnetic order. The addition of magnetic A site cations in ACr2O4 spinels can relieve frustration. High-resolution variable-temperature synchrotron powder X-ray diffraction, detailed magnetic studies, and heat capacity measurements show that dilute amounts of Jahn-Teller active Cu^2+ or Co^2+ on the A sites of these spinels have different effects on structure but similar effects on magnetism. Partial replacement of A by Cu^2+ generates Jahn-Teller distortions at temperatures above the endmember Neel temperatures, yet spin interactions remain frustrated to ˜ 12 K. This contrasts with Co^2+ substitution which also maintains frustration, but results in a suppression of spin Jahn-Teller ordering in ZnCr2O4. We report decoupled Jahn-Teller and spin Jahn-Teller ordering in the canonical frustrated systems ZnCr2O4 and MgCr2O4 that is tunable by varying the identity of the magnetic A site substituent.

Kemei, Moureen; Moffitt, Stephanie; Suchomel, Matthew; Shoemaker, Daniel; Seshadri, Ram

2013-03-01

143

Competing antiferromagnetic and spin-glass phases in a hollandite structure

NASA Astrophysics Data System (ADS)

We introduce a simple lattice model with Ising spins as a zeroth-order approximation of the hollandite-type magnetic compounds. We argue that geometrical frustration of the lattice in combination with nearest-neighbor antiferromagnetic (AFM) interactions are responsible for the appearance of a spin-glass phase in presence of disorder. We investigate this system numerically using parallel tempering. The model reproduces magnetic transitions present in some oxides with hollandite structure and displays a rich phenomenology: in the absence of disorder we have identified five different ground states, depending on the relative strength and sign of the interactions: one ferromagnetically ordered, three antiferromagnetically ordered, and one disordered, macroscopically degenerate ground state. Remarkably, for the sets of AFM couplings having an AFM ground state in the clean system, there exists a critical value of the disorder above which the ground state becomes a spin glass while maintaining all the couplings antiferromagnetically. This model presents this kind of transition with nearest-neighbor frustrated AFM interactions. We argue that this model is useful for understanding the relation between AFM coupling, disorder, and appearance of spin-glass phases.

Crespo, Y.; Andreanov, A.; Seriani, N.

2013-07-01

144

Spin dynamics of a magnetic antivortex: Micromagnetic simulations

NASA Astrophysics Data System (ADS)

We report on a study of the dynamics of a magnetic antivortex in a submicrometer, asteroid-shaped, permalloy ferromagnet using micromagnetic simulations. As with vortex states in disk and square geometries, a gyrotropic mode was found in which a shifted antivortex core orbits about the center of the asteroid. Pulsed magnetic fields were used to generate azimuthal or radial spin wave modes, depending on the field orientation. The degeneracy of low-frequency azimuthal mode frequencies is lifted by gyrotropic motion of the antivortex core, and restored by inserting a hole in the center of the particle to suppress this motion. We briefly compare the dynamics of the vortex state of the asteroid to the antivortex. The size dependence of the antivortex modes is reported.

Wang, Hao; Campbell, C. E.

2007-12-01

145

Ground-state spin dynamics of ErCo2

NASA Astrophysics Data System (ADS)

We have studied the ground-state magnetic excitation spectrum of ErCo2 at 4.2 K using neutron inelastic scattering. Four modes were observed, two which are nondispersive and two which are weakly dispersive. Each of the weakly dispersive modes is degenerate with one of the nondispersive modes at the zone boundary, but falls lower in energy at the zone center. From the dynamic structure factor of the excitations we conclude that the nondispersive modes correspond to out-of-phase precession of the two rare-earth spins in the primitive cell, while the weakly dispersive modes correspond to in-phase precession. The results are described very well by a Green's-function random-phase-approximation theory using standard basis operators to account for the crystalline electric fields, which we find to be comparable in strength to the exchange interactions. The observed excitation modes are associated with transitions from the Er3+ ground state to the second and fourth excited states. By fitting the energies and intensities of the modes we determine JEr-Er=0+/-0.01 meV, JEr-Co=-0.153 meV, A04=4.3 meV/a40, and A06=-0.142 meV/a60. We did not observe a predominantly Co spin-wave mode predicted by the theory, which may indicate a breakdown of the Heisenberg model when applied to the Co spins. Calculations for the observed modes, however, are nearly independent of the dynamics assumed for the Co sublattice.

Koon, N. C.; Rhyne, J. J.

1981-01-01

146

Muonium chemistry and spin dynamics in sulphur, modelling interstitial hydrogen

NASA Astrophysics Data System (ADS)

The nature of the elusive muonium centre in sulphur is re-examined in the light of new data on its level-crossing resonance and spin-lattice relaxation. The aim is to provide a model for the solid-state chemistry of interstitial hydrogen in this element, which is as yet unknown, as well as to solve one of the longest standing puzzles in ?SR spectroscopy, namely the surprisingly strong depolarization of muons mimicking ion-implanted protons in this innocuous non-magnetic material. The paramagnetic muonium (and by inference hydrogen) centre is confirmed to have the character of a molecular radical, but with huge anisotropy at cryogenic temperatures and a striking shift of the resonance at ordinary temperatures, the hyperfine parameters appearing to collapse and vanish towards the melting point. New density-functional supercell calculations identify a number of possible structures for the defect centre, including a novel form of bond-centred muonium in a closed-ring S8Mu complex. Simulations of the spin dynamics and fits to the spectra suggest a dynamical equilibrium or chemical exchange between several configurations, with occupancy of the bond-centre site falling from unity at low cryogenic temperatures to zero near the melting point.

Cox, S. F. J.; Lord, J. S.; McKenzie, I.; Adjizian, J.-J.; Heggie, M. I.; Jayasooriya, U. A.; Grinter, R.; Reid, I. D.

2011-08-01

147

High Dynamic Range Magnetometry with a Single Spin in Diamond

NASA Astrophysics Data System (ADS)

Detection of the weak magnetic fields associated with nanometer sized volumes of spins could allow for non-invasive, element-specific probing of a variety of important physical and biological systems. Averaging out random noise which is the commonly used standard measurement strategy (SM) in most nano-sensors, will at best lead to a field variance that is inversely proportional to the total averaging time. Further, there exists a trade-off between the field sensitivity and the dynamic range in the SM. In this work, we demonstrate an alternative approach for accurate magnetic sensing, using novel phase estimation algorithms (PEA), implemented on a single electronic spin associated with the nitrogen-vacancy (NV) defect center in diamond. The field variance in our approach scales down faster than the SM. The trade-off between the field sensitivity and the dynamic range no longer exists in this approach. Our results show an improvement of ˜6.25 dB in the field sensitivity compared to the SM, over a large field sensing range ( ˜±0.3 mT). Besides their direct impact on applications in demonstrated nanoscale magnetic sensing and imaging, this may also open the way for application of other quantum feedback and control techniques to magnetometry.

Nusran, N. M.; Ummal Momeen, M.; Gurudev Dutt, M. V.

2012-02-01

148

Influence of adaptation on the nonlinear dynamics of a system of competing populations

NASA Astrophysics Data System (ADS)

We investigate the nonlinear dynamics of a system of populations competing for the same limited resource assuming that they can adapt their growth rates and competition coefficients with respect to the number of individuals of each population. The adaptation leads to an enrichment of the nonlinear dynamics of the system which is demonstrated by a discussion of new orbits in the phase space of the system, completely dependent on the adaptation parameters, as well as by an investigation of the influence of the adaptation parameters on the dynamics of a strange attractor of the model system of ODEs.

Dimitrova, Z. I.; Vitanov, N. K.

2000-08-01

149

Dynamical exchange interaction from time-dependent spin density functional theory

NASA Astrophysics Data System (ADS)

We report on ab initio time-dependent spin-dynamics simulations for a two-center magnetic molecular complex within the framework of the time-dependent noncollinear spin-density functional theory. In particular, we discuss how the dynamical behavior of the ab initio spin-density in the time domain can be mapped onto a model Hamiltonian based on the classical Heisenberg spin-spin interaction JS1·S2. By analyzing individual localized-spin trajectories, extracted from the spin-density evolution, we demonstrate a practical method for evaluating the effective Heisenberg exchange coupling constant J from first-principles simulations. We find that J, extracted in such a dynamical way, agrees quantitatively with that calculated by the standard density functional theory broken-symmetry scheme.

Stamenova, Maria; Sanvito, Stefano

2013-09-01

150

National Technical Information Service (NTIS)

Methods used in two computer programs for dynamic simulation of a particular deformable satellite, GEOS 4, are presented. General considerations are given on dynamics of spinning deformable systems. A multibody approach is adopted to determine the various...

P. Y. Willems P. Boland D. A. Johnson J. C. Samin

1976-01-01

151

Energy-Dependent Electron-Electron Scattering and Spin Dynamics in a Two Dimensional Electron Gas

Measurements of spin dynamics of electrons in a degenerate two dimensional electron gas, where the Dyakonov-Perel mechanism is dominant, have been used to investigate the electron scattering time (tp*) as a function of energy near the Fermi energy. Close to the Fermi energy the spin evolution is oscillatory, indicating a quasi-collision-free regime of spin dynamics. As the energy is increased

W. J. H. Leylanda; R. T. Harley; M. Henini; A. J. Shields; I. Farrer; D. A. Ritchie

2008-01-01

152

NASA Astrophysics Data System (ADS)

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable 1H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the 1H spin density. It is shown that the final 1H polarization can be enhanced by diluting the 1H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various 1H abundances. It is also shown that the 1H spin diffusion coefficient can be determined by examining the initial buildup rate of 1H polarization for various repetition rates of the DNP sequence.

Kagawa, Akinori; Murokawa, Yu; Takeda, Kazuyuki; Kitagawa, Masahiro

2009-03-01

153

In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable (1)H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the (1)H spin density. It is shown that the final (1)H polarization can be enhanced by diluting the (1)H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various (1)H abundances. It is also shown that the (1)H spin diffusion coefficient can be determined by examining the initial buildup rate of (1)H polarization for various repetition rates of the DNP sequence. PMID:19091611

Kagawa, Akinori; Murokawa, Yu; Takeda, Kazuyuki; Kitagawa, Masahiro

2008-11-27

154

Spin probe ESR studies of dynamics of single walled carbon nanotubes

The highly sensitive technique of spin-probe Electron Spin Resonance (ESR) has been used to study dynamics of carbon nanotubes. The ESR signals were recorded for the nitroxide free radical TEMPO in carbon nanotubes from 5 to 300K. The onset of the fast dynamics of the probe molecule was indicated by appearance of a narrow triplet at 230K. The ESR measurements

A. K. Dhami; Shrivalli Bhat; Ajay Sharma; S. V. Bhat

2008-01-01

155

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.

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

2012-01-01

156

A molecular dynamics (MD) approach which determines automatically the complex magnetic structures in itinerant electron systems is applied to FexCr100?x alloys with use of 250 atoms in a MD unit cell. Various complex magnetic structures due to competing interactions are obtained: the ferromagnetism (F) of Fe with a noncollinear structure of Cr in the range 50?x?75, the coexistence of the

N. Kimura; Y. Kakehashi

2001-01-01

157

Molecular dynamics simulation of spinning detonation in energetic AB material

NASA Astrophysics Data System (ADS)

Spinning detonation-wave structure is observed in molecular dynamics simulation of a solid energetic material (EM) confined in the round tube with smooth walls. The EM is represented by a modified AB model with adjustable barrier height for exothermic reaction AB+B -> A+BB, which allows us to study the evolution of detonation-wave structure produced by instabilities of the planar detonation front as a function of physico-chemical properties of the EM material, including its thermochemistry and reactive equation of state. The planar detonation wave in a tube of relatively small radius evlolves into an unstable pulsating detonation through the development of longitudinal perturbations, which can later lead to a collapse of the detonation wave. However, as the tube radius is increased, the detonation wave structure is stabilized by a development of a single-headed spinning detonation having an unusual four-wave configuration. Further increase of the tube radius results in a multi-headed detonation structure with turbulent-like distributions of pressure and other physical variables at the front, similar to that observed in gases.

Zhakhovsky, Vasily; Budzevich, Mikalai; Landerville, Aaron; Oleynik, Ivan; White, Carter

2013-03-01

158

Electron Correlation and Spin Dynamics in Iron Pnictides and Chalcogenides

NASA Astrophysics Data System (ADS)

Superconductivity in the iron pnictides and chalcogenides is closely connected to a bad-metal normal state and a nearby antiferromagnetic order. Therefore, considerable attention has been focused on the role of electron correlations and spin dynamics. In this article, we summarize some key experiments that quite directly imply strong electron correlations in these materials, and discuss aspects of the recent theoretical studies on these issues. In particular, we outline a w-expansion, which treats the correlation effects using the Mott transition as the reference point. For the parent systems, it gives rise to an effective J1-J2 model that is coupled to the itinerant electrons in the vicinity of the Fermi energy; this model yields an isoelectronically-tuned quantum critical point, and allows a study of the distribution of the spin spectral weight in the energy and momentum space in the paramagnetic phase. Within the same framework, we demonstrate the Mott insulating phase in the iron oxychalcogenides as well as the alkaline iron selenides; for the latter system, we also consider the role of an orbital-selective Mott phase. Finally, we discuss the singlet superconducting pairing driven by the short-range J1-J2 interactions. Our considerations highlight the iron pnictides and chalcogenides as exemplifying strongly-correlated electron systems at the boundary of electronic localization and itinerancy.

Yu, Rong; Si, Qimiao; Goswami, Pallab; Abrahams, Elihu

2013-07-01

159

Spin-wave dynamics in a ferrimagnetic sphere

An experimental study is made of the interactions between spin-wave modes excited in a sphere of yttrium iron garnet by pumping the Suhl subsidiary absorption at 9.2 GHz with the dc field parallel to (111). The dynamical behavior of the magnetization is observed under high resolution by varying two control parameters, dc field (580 Oe

Bryant, P.H.; Jeffries, C.D.; Nakamura, K.

1988-10-15

160

Using Markov models to simulate electron spin resonance spectra from molecular dynamics trajectories

Simulating electron spin resonance (ESR) spectra directly from molecular dynamics simulations of a spin labeled protein necessitates a large number (hundreds or thousands) of relatively long (hundreds of ns) trajectories. To meet this challenge, we explore the possibility of constructing accurate stochastic models of the spin label dynamics from atomistic trajectories. A systematic, two-step procedure, based on the probabilistic framework of hidden Markov models, is developed to build a discrete-time Markov chain process that faithfully captures the internal spin label dynamics on time scales longer than about 150 ps. The constructed Markov model is used both to gain insight into the long-lived conformations of the spin label and to generate the stochastic trajectories required for the simulation of ESR spectra. The methodology is illustrated with an application to the case of a spin labeled poly-alanine alpha helix in explicit solvent.

Sezer, Deniz; Freed, Jack H.; Roux, Benoit

2008-01-01

161

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

162

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

163

Surface hopping trajectory simulations with spin-orbit and dynamical couplings

NASA Astrophysics Data System (ADS)

In this paper we consider the inclusion of the spin-orbit interaction in surface hopping molecular dynamics simulations to take into account spin forbidden transitions. Two alternative approaches are examined. The spin-diabatic one makes use of eigenstates of the spin-free electronic Hamiltonian and of ?2 and is commonly applied when the spin-orbit coupling is weak. We point out some inconsistencies of this approach, especially important when more than two spin multiplets are coupled. The spin-adiabatic approach is based on the eigenstates of the total electronic Hamiltonian including the spin-orbit coupling. Advantages and drawbacks of both strategies are discussed and illustrated with the help of two model systems.

Granucci, Giovanni; Persico, Maurizio; Spighi, Gloria

2012-12-01

164

Self-consistent magnetization dynamics of a ferromagnetic quantum dot driven by a spin bias

NASA Astrophysics Data System (ADS)

We present an iterative scheme which combines the non-equilibrium Green's function (NEGF) for evaluating the quantum spin transport in a ferromagnetic quantum dot device and the Landau-Lifshitz (LL) equation for modeling the magnetization dynamics of the dot. For a given initial magnetization, the spin polarization of current and the resulting spin torque in the dot are calculated using the NEGF formalism. The torque acts on the magnetic moment of the dot, and the resultant magnetization dynamics is obtained from the LL equation. The new value of the dot's magnetization is then used as an input for the next round of NEGF calculation, and the whole process is repeated iteratively. The spin torque is thus calculated self-consistently with the dynamics of the magnetic moment of the dot. We apply this self-consistent iterative scheme to study the magnetization dynamics in an exemplary quantum dot system with an induced spin bias in the leads under varying damping conditions.

Siu, Z. B.; Jalil, M. B. A.; Tan, S. G.

2012-04-01

165

Hydrodynamic theory of coupled current and magnetization dynamics in spin-textured ferromagnets

NASA Astrophysics Data System (ADS)

We develop the hydrodynamic theory of collinear spin currents coupled to magnetization dynamics in metallic ferromagnets. The collective spin density couples to the spin current through a U(1) Berry-phase gauge field determined by the local texture and dynamics of the magnetization. We determine phenomenologically the dissipative corrections to the equation of motion for the electronic current, which consist of a dissipative spin-motive force generated by magnetization dynamics and a magnetic texture-dependent resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the magnetic texture follows from the Onsager principle. We investigate the effects of thermal fluctuations and find that electronic dynamics contribute to a nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the magnetization. Several simple examples, including magnetic vortices, helices, and spirals, are analyzed in detail to demonstrate general principles.

Wong, Clement H.; Tserkovnyak, Yaroslav

2009-11-01

166

Signature of magnetization dynamics in spin-transfer-driven nanopillars with tilted easy axis

NASA Astrophysics Data System (ADS)

Special spin-transfer-driven magnetic behaviors can take place in a spin valve nanopillar with perpendicular anisotropy due to reduced symmetry of easy axis. Micromagnetic simulation demonstrates a dip in the average magnetization curve, which corresponds to the experimentally observed undulation of dc resistance. The dip is a signature of spin-transfer-driven reversable magnetic process with slightly tilted easy axis in the free layer. This featured magnetization dynamics includes non-uniform magnetization precession and multi-mode propagating spin waves, which are attributed to the competition among tilted magnetic anisotropy, magnetic field, and spin transfer torque.

Zhang, Hong; Lin, Weiwei; Mangin, Stéphane; Zhang, Zongzhi; Liu, Yaowen

2013-01-01

167

Electric detection ofmagnetization dynamics through inverse spin Hall effects

NASA Astrophysics Data System (ADS)

Spin currents, flows of spin angular momentum, are essential in spintronics. To explore the physics of spin currents, effective methods for detecting and generating spin currents should be established. Here we report the observation of the inverse/direct spin-Hall effects in metallic films. These effects enable electric generation and detection of spin currents. We have applied these effects to the observation of the spin-Seebeck effect. The inverse spin-Hall effect (ISHE) is the generation of a charge current from a spin current via the spin-orbit interaction. We have observed ISHE in metallic films at room temperature. The sample used in the present study is a bilayer film comprising a 10-nm-thick ferromagnetic NiFe layer and a 7- nm-thick nonmagnetic metallic (NM=Pt, Pd, Cu, Nb, and Au) layer. In our sample system, a pure spin current is injected from the NiFe layer into the NM layer using the spin-pumping effect operated by ferromagnetic resonance (FMR). ISHE in the NM layer converts the spin current into an electric current, which causes charge accumulation at the edges of the NM layer, or a difference of electric potential between the edges. By measuring this potential difference, this method allows us to detect ISHE in the films. We also demonstrated that the reverse effect of this spin- pumping induced ISHE allows the electric manipulation of magnetization relaxation even in a large-area film. This result can be argued in terms of the combination of the spin-torque effect and the direct spin-Hall effect. A model calculation reproduces the experimental data. This effect can be applied to a quantitative measurement of spin currents without assuming microscopic parameters. We have applied ISHE to the observation of the spin-Seebeck effect. By means of ISHE, we measured spin voltage generated from a temperature gradient in NiFe. This thermally induced spin voltage persists even at distances far from the sample ends and its sign is reversed between the ends of the sample along the temperature gradient. These behaviors are consistent with a phenomenological two-band model for the spin-Seebeck effect. The spin-Seebeck effect can be applied directly to constructing thermal spin generators for driving spintronics devices, thereby opening the door to thermo-spintronics.

Saitoh, Eiji

2010-03-01

168

Low-energy-state dynamics of entanglement for spin systems

We develop the ideas of the quantum renormalization group and quantum information by exploring the low-energy-state dynamics of entanglement resources of a system close to its quantum critical point. We demonstrate that low-energy-state dynamical quantities of one-dimensional magnetic systems can show a quantum phase transition point and show scaling behavior in the vicinity of the transition point. To present our idea, we study the evolution of two spin entanglements in the one-dimensional Ising model in the transverse field. The system is initialized as the so-called thermal ground state of the pure Ising model. We investigate the evolution of the generation of entanglement with increasing magnetic field. We obtain that the derivative of the time at which the entanglement reaches its maximum with respect to the transverse field diverges at the critical point and its scaling behaviors versus the size of the system are the same as the static ground-state entanglement of the system.

Jafari, R. [Department of Physics, Institute for Advanced Studies in Basic Sciences, Zanjan 45137-66731 (Iran, Islamic Republic of)

2010-11-15

169

Spinach - A software library for simulation of spin dynamics in large spin systems

NASA Astrophysics Data System (ADS)

A large number of states in systems with over 20 spins never contribute to the system trajectory and may be dropped from the basis. This makes the simulation complexity scaling polynomial in the number of spins. Display OmittedResearch highlightsOpen-source function library written in Matlab. Provides efficient simulation algorithms for large spin systems. Most liquid-state NMR experiments on 40+ spin systems can be simulated on a workstation.

Hogben, H. J.; Krzystyniak, M.; Charnock, G. T. P.; Hore, P. J.; Kuprov, Ilya

2011-02-01

170

Simulating the Dynamics and Orientations of Spin Labeled Side Chains in a Protein-DNA Complex

Site-directed spin labeling, wherein a nitroxide side chain is introduced into a protein at a selected mutant site, is increasingly employed to investigate biological systems by electron spin resonance (ESR) spectroscopy. An understanding of the packing and dynamics of the spin label is needed to extract the biologically relevant information about the macromolecule from ESR measurements. In this work, molecular dynamics (MD) simulations were performed on the spin labeled restriction endonuclease, EcoRI in complex with DNA. Mutants of this homodimeric enzyme were previously constructed and distance measurements were performed using the Double Electron Electron Resonance experiment. These correlated distance constraints have been leveraged with MD simulations to learn about side chain packing and preferred conformers of the spin label on sites in an ?-helix and a ?-strand. We found three dihedral angles of the spin label side chain to be most sensitive to the secondary structure where the spin label was located. Conformers sampled by the spin label differed between secondary structures as well. C?-C? distance distributions were constructed and used to extract details about the protein backbone mobility at the two spin labeled sites. These simulation studies enhance our understanding of the behavior of spin labels in proteins and thus expand the ability of ESR spectroscopy to contribute to knowledge of protein structure and dynamics.

Sarver, Jessica L.; Townsend, Jacqueline E.; Rajapakse, Gayathri; Jen-Jacobson, Linda; Saxena, Sunil

2012-01-01

171

Dynamics of the collective modes of an inhomogeneous spin ensemble in a cavity

We study the excitation dynamics of an inhomogeneously broadened spin ensemble coupled to a single cavity mode. The collective excitations of the spin ensemble can be described in terms of generalized spin waves, and, in the absence of the cavity, the free evolution of the spin ensemble can be described as a drift in the wavenumber without dispersion. In this article we show that the dynamics in the presence of coupling to the cavity mode can be described solely by a modified time evolution of the wavenumbers. In particular, we show that collective excitations with a well-defined wavenumber pass without dispersion from negative to positive-valued wavenumbers without populating the zero wavenumber spin wave mode. The results are relevant for multimode collective quantum memories where qubits are encoded in different spin waves.

Wesenberg, Janus H. [Centre for Quantum Technologies, National University of Singapore, Singapore 117543 (Singapore); Kurucz, Zoltan; Moelmer, Klaus [Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark)

2011-02-15

172

Spin dynamics of a Mn atom in a semiconductor quantum dot under resonant optical excitation

NASA Astrophysics Data System (ADS)

We analyze the spin dynamics of an individual magnetic atom (Mn) inserted in a II-VI semiconductor quantum dot under resonant optical excitation. In addition to standard optical pumping expected for a resonant excitation, we show that for particular conditions of laser detuning and excitation intensity, the Mn spin population can be trapped in the state which is resonantly excited. This effect is modeled considering the coherent spin dynamics of the coupled electronic and nuclear spin of the Mn atom optically dressed by a resonant laser field. This “spin population trapping” mechanism is controlled by the combined effect of the coupling with the laser field and the coherent interaction between the different Mn spin states induced by an anisotropy of the strain in the plane of the quantum dot.

Jamet, S.; Boukari, H.; Besombes, L.

2013-06-01

173

Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate

We observe coherent spin oscillations in an antiferromagnetic spin-1 Bose-Einstein condensate of sodium. The variation of the spin oscillations with magnetic field shows a clear signature of nonlinearity, in agreement with theory, which also predicts anharmonic oscillations near a critical magnetic field. Measurements of the magnetic phase diagram agree with predictions made in the approximation of a single spatial mode. The oscillation period yields the best measurement to date of the sodium spin-dependent interaction coefficient, determining that the difference between the sodium spin-dependent s-wave scattering lengths a{sub f=2}-a{sub f=0} is 2.47{+-}0.27 Bohr radii.

Black, A. T.; Gomez, E.; Turner, L. D.; Jung, S.; Lett, P. D. [Joint Quantum Institute, University of Maryland and National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2007-08-17

174

NASA Astrophysics Data System (ADS)

Aiming at the optimization of the spin-diffusion length in (001) GaAs quantum wells, we explore the effect of the anisotropy of the spin-orbit coupling on the competition between the Rashba and the Dresselhaus spin-orbit couplings by solving the kinetic spin Bloch equations with the electron-phonon and the electron-electron scattering explicitly included. For identical strengths of the Rashba and the Dresselhaus spin-orbit couplings, the spin-diffusion length shows strong anisotropy not only for the spin-polarization direction but also for the spin-diffusion direction. Two special directions are used seeking for the large diffusion length: (1¯10) and (110). Without the cubic term of the Dresselhaus spin-orbit coupling and with the identical Dresselhaus and Rashba strengths, infinite diffusion lengths can be obtained either for the spin-diffusion/injection direction along (1¯10) , regardless of the direction of spin polarization, or for the spin polarization along (110), regardless of the direction of the spin diffusion/injection. However, the cubic Dresselhaus term cannot be neglected, resulting in a finite spin-diffusion length which decreases with the temperature and the electron density. The anisotropy for the spin-diffusion direction and spin-polarization direction is maintained. For the spin-diffusion/injection direction along (1¯10) , the spin-diffusion length increases first with the increase of the Rashba strength (from 0) which can be tuned by the external gate voltage; when the Rashba strength is slightly smaller than (instead of equal to) the Dresselhaus strength, the diffusion length reaches its maximum, followed by a decrease with further increase of the Rashba strength.

Cheng, J. L.; Wu, M. W.; da Cunha Lima, I. C.

2007-05-01

175

Dynamic heterogeneities in the out-of-equilibrium dynamics of simple spherical spin models

NASA Astrophysics Data System (ADS)

The response of spherical two-spin interaction models, the spherical ferromagnet (s-FM) and the spherical Sherrington-Kirkpatrick (s-SK) model, is calculated for the protocol of the so-called nonresonant hole burning (NHB) experiment for temperatures below the respective critical temperatures. It is shown that it is possible to select dynamic features in the out-of-equilibrium dynamics of both models, one of the hallmarks of dynamic heterogeneities. The behavior of the s-SK model and the s-FM model in three dimensions is very similar, showing dynamic heterogeneities in the long-time behavior, i.e., in the aging regime. The appearance of dynamic heterogeneities in the s-SK model explicitly demonstrates that these are not necessarily related to spatial heterogeneities. For the s-FM model, it is shown that the nature of the dynamic heterogeneities changes as a function of dimensionality. With the increasing dimension, the frequency selectivity of the NHB diminishes and the dynamics in the mean-field limit of the s-FM model becomes homogeneous.

Diezemann, Gregor

2003-08-01

176

Numerical and analytical approach to the quantum dynamics of two coupled spins in bosonic baths

The quantum dynamics of a spin chain interacting with multiple bosonic baths is described in a mixed Wigner-Heisenberg representation. The formalism is illustrated by simulating the time evolution of the reduced density matrix of two coupled spins, where each spin is also coupled to its own bath of harmonic oscillators. In order to prove the validity of the approach, an analytical solution in the Born-Markov approximation is found. The agreement between the two methods is shown.

Sergi, Alessandro; Sinayskiy, Ilya; Petruccione, Francesco [School of Physics, University of KwaZulu-Natal, Pietermaritzburg, Private Bag X01 Scottsville, 3209 Pietermaritzburg (South Africa); Quantum Research Group, School of Physics, University of KwaZulu-Natal, Durban 4001 (South Africa); Quantum Research Group, School of Physics and National Institute for Theoretical Physics, University of KwaZulu-Natal, Durban 4001 (South Africa)

2009-07-15

177

Spin dynamics and four-photon mixing in InSb

NASA Astrophysics Data System (ADS)

The spin flip Raman interaction can be used to excite coherent spin precession in semiconductors. Resonant, four-photon mixing is shown to be equivalent to Raman scattering from this coherent state. Studies of the four-photon intensity give information concerning spin dynamics (T1 and T2) in n-InSb. Research sponsored by the U.S. Air Force Office of Scientific Research Air Force Systems Command under Contract/Grant AFOSR-71-2010.

Nguyen, V. T.; Burkhardt, E. G.; Wolff, P. A.

1976-01-01

178

Time-domain measurement of current-induced spin wave dynamics.

The performance of spintronic devices critically depends on three material parameters, namely, the spin polarization in the current (P), the intrinsic Gilbert damping (?), and the coefficient of the nonadiabatic spin transfer torque (?). However, there has been no method to determine these crucial material parameters in a self-contained manner. Here we show that P, ?, and ? can be simultaneously determined by performing a single series of time-domain measurements of current-induced spin wave dynamics in a ferromagnetic film. PMID:22304283

Sekiguchi, Koji; Yamada, Keisuke; Seo, Soo-Man; Lee, Kyung-Jin; Chiba, Daichi; Kobayashi, Kensuke; Ono, Teruo

2012-01-05

179

Anisotropic exchange and spin dynamics in the type-II antiferromagnetic cerium monochalcogenide CeSe

The anisotropic magnetic interactions and the spin dynamics of the fcc type-II antiferromagnetic cerium monochalcogenide CeSe have been studied by neutron scattering. The spin waves split with an energy gap of 0.34 meV into two transverse modes due to exchange anisotropy. Within the random-phase approximation a self-consistent effective spin 1\\/2 Hamiltonian with highly anisotropic nearest-neighbour coupling and isotropic next-nearest coupling

A. Dönni; A. Furrer; P. Fischer; F. Hulliger; S. M. Hayden

1992-01-01

180

Detection and Measurement of Spin-Dependent Dynamics in Random Telegraph Signals

NASA Astrophysics Data System (ADS)

A quantum point contact was used to observe single-electron fluctuations of a quantum dot in a GaAs heterostructure. The resulting random telegraph signals (RTS) contain statistical information about the electron spin state if the tunneling dynamics are spin dependent. We develop a statistical method to extract information about spin-dependent dynamics from RTS and use it to demonstrate that these dynamics can be studied in the thermal energy regime. The tunneling rates of each spin state are independently measured in a finite external magnetic field. We confirm previous findings of a decrease in overall tunneling rates for the spin excited state compared to the ground state as an external magnetic field is increased.

House, M. G.; Xiao, Ming; Guo, GuoPing; Li, HaiOu; Cao, Gang; Rosenthal, M. M.; Jiang, HongWen

2013-09-01

181

Detection and measurement of spin-dependent dynamics in random telegraph signals.

A quantum point contact was used to observe single-electron fluctuations of a quantum dot in a GaAs heterostructure. The resulting random telegraph signals (RTS) contain statistical information about the electron spin state if the tunneling dynamics are spin dependent. We develop a statistical method to extract information about spin-dependent dynamics from RTS and use it to demonstrate that these dynamics can be studied in the thermal energy regime. The tunneling rates of each spin state are independently measured in a finite external magnetic field. We confirm previous findings of a decrease in overall tunneling rates for the spin excited state compared to the ground state as an external magnetic field is increased. PMID:24093289

House, M G; Xiao, Ming; Guo, Guoping; Li, Haiou; Cao, Gang; Rosenthal, M M; Jiang, Hongwen

2013-09-18

182

NASA Astrophysics Data System (ADS)

The colossal magnetoresistive (CMR) manganites are archetypal systems in which to study the effects of a strong interplay between spin, charge and lattice degrees of freedom. The existence of magnetoelastic polarons, clusters of ferromagnetically aligned spins surrounding a local lattice distortion, have been inferred from transport (M. Jaime et al./), Phys. Rev. B 60, (1999), in press. and local structure (D. Louca et al./), Phys. Rev. B 56, R8475 (1997); C. H. Booth et al./, Phys. Rev. Lett. 80, 853 (1998). measurements, but there have been comparatively fewer definitive spin probe (J. W. Lynn et al./) Phys. Rev. Lett. 76, 4046 (1996); G. Allodi et al./, Phys. Rev. B57, 1024 (1998). measurements. In this talk muon spin relaxation (?SR) measurements (R. H. Heffner et al./), Phys. Rev. Lett. 77, 1869 (1996); R. H. Heffner et al./, Phys. Rev. Lett. 81, 1706 (1998). in the system La_1-xCa_xMnO_3, x = 0.0, 0.07, 0.18, 0.33, 0.65 and 1.00 are discussed. These materials span the range from insulating and/or charge-ordered antiferromagnetic to conducting ferromagnetic (FM) ground states. Particular emphasis is given to the FM transitions, in which a combination of ?SR and neutron spin echo measurements reveals two characteristic time scales in the spin fluctuation spectrum. The temperature dependence, momentum dependence and relative fluctuation rates of these separate dynamical components strongly suggest the existence of small (? 10 Åspatially separated regions with very different spin and, most likely, charge and lattice dynamics. The data are discussed in terms of the growth of small polarons into overlapping regions of correlated spins below T_C, resulting in a microscopically inhomogeneous FM transition.

Heffner, Robert

2000-03-01

183

We analyze both theoretically and by means of numerical simulations the phenomena of filamentation and dynamical formation of self-guided nonlinear waves in media featuring competing cubic and quintic nonlinearities. We provide a theoretical description of recent experiments in terms of a linear stability analysis supported with simulations, showing the possibility of the observation of modulational instability suppression of intense light pulses traveling across such nonlinear media. We also show a mechanism of indirect excitation of light condensates by means of coalescence processes of nonlinear coherent structures produced by managed filamentation of high-power laser beams.

Novoa, David; Michinel, Humberto; Tommasini, Daniele; Carpentier, Alicia V. [Departamento de Fisica Aplicada, Facultade de Ciencias de Ourense, Universidade de Vigo, As Lagoas s/n, ES-32004 Ourense (Spain)

2010-04-15

184

Spin Dynamics and Quantum Tunneling in Fe8 Nanomagnet and in AFM rings by NMR.

National Technical Information Service (NTIS)

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 antiferrom...

S. Baek

2004-01-01

185

Reading Charge Transport from the Spin Dynamics on the Surface of a Topological Insulator

NASA Astrophysics Data System (ADS)

Resolving the conductance of the topological surface states (TSSs) from the bulk contribution has been a great challenge for studying the transport properties of topological insulators. By developing a nonperturbative diffusion equation that describes fully the spin-charge dynamics in the strong spin-orbit coupling regime, we present a proposal to read the charge transport information of TSSs from its spin dynamics which can be isolated from the bulk contribution by the time-resolved second harmonic generation pump-probe measurement. We demonstrate the qualitatively different Dyaknov-Perel spin relaxation behavior between the TSSs and the two-dimensional spin-orbit coupling electron gas. The decay time of both in-plane and out-of-plane spin polarization is naturally proved to be identical to the charge transport time. The out-of-plane spin dynamics is shown to be in the experimentally reachable regime of the femtosecond pump-probe spectroscopy and thereby we suggest experiments to detect the charge transport properties of the TSSs from their unique spin dynamics.

Liu, Xin; Sinova, Jairo

2013-10-01

186

Ergodicity properties of energy conserving single spin flip dynamics in the XY model

A single spin flip stochastic energy conserving dynamics for the XY model is considered. We study the ergodicity properties of the dynamics. It is shown that phase space trajectories densely fill the geometrically connected parts of the energy surface. We also show that while the dynamics is discrete and the phase point jumps around, it cannot make transitions between closed

Abhishek Dhar

1998-01-01

187

National Technical Information Service (NTIS)

A simplified dynamic modelling for the attitude motion of spin stabilized artificial satellites is proposed. Torques due to induced magnetic fields on the satellite, eddy currents, and gravity gradient are considered. The corresponding Euler equations are...

H. K. Kuga W. C. C. Silva U. T. V. Guedes

1987-01-01

188

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

NASA Astrophysics Data System (ADS)

The spin dynamics and microstructure properties of a sputtered 12 nm Ni81Fe19 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-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 Ni81Fe19 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 Ni81Fe19 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

2013-02-01

189

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., E-mail: zenchuk@itp.ac.ru [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)

2011-09-15

190

Modifications to SOLA-VOF for Flow Dynamics in Spinning Cylinders.

National Technical Information Service (NTIS)

Fluid dynamic processes within spinning containers involve many complex phenomena. Boundary layer effects and free surface motions can be strongly coupled with angular momentum effects to produce highly complex flow structures. This situation exists in fl...

C. W. Hirt J. R. Campbell

1985-01-01

191

Multi-teraflops Spin Dynamics Studies of the Magnetic Structure of FeMn/Co Interfaces.

National Technical Information Service (NTIS)

The authors have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese/Cobalt (FeMn/Co) interfaces. These large scale quantum mechanical simulations, involving...

A. Canning B. Ujfalussy T. C. Schulthess X. G. Zhang W. A. Shelton

2004-01-01

192

Dynamic spin correlations in 'stuffed' spin ice Ho(2+x)Ti(2-x)O(7-d)

The magnetic correlations in 'stuffed' spin ice Ho{sub 2+x}Ti{sub 2-x}O{sub 7-{delta}} 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 Ho{sub 2+x}Ti{sub 2-x}O{sub 7}, one can identify, above the freezing temperature, a quantum relaxation regime which is enhanced as it persists to even higher temperatures, T{approx}30-40K , than in the parent compound.

Ehlers, Georg [ORNL

2008-01-01

193

Dynamical stabilization of spin systems in time-dependent magnetic fields

NASA Astrophysics Data System (ADS)

The quantum dynamics of a spin system subjected to a Rabi magnetic field configuration modified by a weak oscillating field along the Z-axis is investigated. We show that when the Rabi frequency is appropriately matched with the frequency of the perturbative field, the spin system exhibits a dynamical stabilization phenomenon defined as the tendency to occupy a fixed quantum superposition during a finite period of time.

Bezvershenko, Yu V.; Holod, P. I.; Messina, A.

2011-02-01

194

Femtosecond dynamics of spin-dependent SHG response from NiO?(001)

. Based on a parameterized electronic many-body theory we calculate the spectrum of optical second-harmonic generation (SHG)\\u000a on an antiferromagnetic (AF) surface: NiO?(001). The occurrence of AF spectral lines is further exploited for the calculation\\u000a of ultra-fast spin dynamics. This spin dynamics is observable in SHG. It is characterized by both a sharp drop of the AF signal\\u000a within a

O. Ney; M. Trzeciecki; W. Hübner

2002-01-01

195

NASA Astrophysics Data System (ADS)

We have investigated the effect of an external magnetic field on the electron spin lifetime in narrow gap semiconductors (NGS). In zero field, we show that the D'yakonov-Perel process dominates even at low temperatures. In the Faraday configuration it is suppressed and the spin lifetime increases with field, whereas in Voigt configuration, the additional Margulis-Margulis process, which is particularly effective in NGS, shortens the spin lifetime considerably. The spin dynamics are found to be very sensitive to both the magnitude and direction of the magnetic field.

Litvinenko, K. L.; Leontiadou, M. A.; Li, Juerong; Bowyer, E. T.; Clowes, S. K.; Pidgeon, C. R.; Murdin, B. N.

2011-12-01

196

Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the 'effective' Hamiltonian and the 'real' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pade-resummed coefficients) which depends on the choice of some basic 'effective spin vector' S{sub eff}, and which is deformed by comparable-mass effects; and (iv) an additional effective spin-orbit interaction term involving another spin vector {sigma}. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter a{sub LSO}{identical_to}cJ{sub LSO}/(G(H{sub LSO}/c{sup 2}){sup 2}). We find that the inclusion of NLO spin-orbit terms has a significant 'moderating' effect on the dynamical characteristics of the circular orbits for large and parallel spins.

Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard [Institut des Hautes Etudes Scientifiques, 91440 Bures-sur-Yvette (France); Faculty of Physics, University of Bialystok, Lipowa 41, 15-424 Bialystok (Poland); Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet, Max-Wien-Pl. 1, 07743 Jena (Germany)

2008-07-15

197

Next-to-leading order gravitational spin(1)-spin(2) dynamics in Hamiltonian form

Based on recent developments by the authors a next-to-leading order spin(1)-spin(2) Hamiltonian is derived for the first time. The result is obtained within the canonical formalism of Arnowitt, Deser, and Misner (ADM) utilizing their generalized isotropic coordinates. A comparison with other methods is given.

Steinhoff, Jan; Hergt, Steven; Schaefer, Gerhard [Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet, Max-Wien-Pl. 1, 07743 Jena (Germany)

2008-04-15

198

Noninvasive electrical detection of electron spin dynamics at the N atom in N@C60.

Endohedral N@C(60) contains an electron spin of S = 3/2 at the central N atom, which, shielded by the C(60) cage, has an extremely long spin relaxation time. The ?-conjugated C(60) cage, when connected to electrodes, provides a highly conductive path for electron transport and enables a noninvasive electrical detection of dynamics of the central spin. Here we use the Keldysh non-equilibrium Green's function and establish a microscopic description of how spin dynamics, including resonance and relaxation, can manifest itself in the device conductance. We predict that magnetic electrodes can enhance the detectivity by orders of magnitude compared with nonmagnetic electrodes. It is shown that this electrical detection is more sensitive to the longitudinal spin component than the transverse one. Hence the transient spin nutation is particularly useful in determining spin decoherence time T(2) in such transport device structures. This theory can be used to describe recent experiments of electrically detected spin dynamics in C(60) and other systems. PMID:21399301

Yu, Z G

2010-07-02

199

Probing dynamics of a spin ensemble of P1 centers in diamond using a superconducting resonator

NASA Astrophysics Data System (ADS)

Solid-state spin ensembles are promising candidates for realizing a quantum memory for superconducting circuits. Understanding the dynamics of such ensembles is a necessary step towards achieving this goal. Here, we investigate the dynamics of an ensemble of nitrogen impurities (P1 centers) in diamond using magnetic-field controlled coupling to the first two modes of a superconducting (NbTiN) coplanar waveguide resonator. Three hyperfine-split spin sub-ensembles are clearly resolved in the 0.25-1.2 K temperature range, with a collective coupling strength extrapolating to 23 MHz at full polarization. The coupling to multiple modes allows us to distinguish the contributions of dipolar broadening and magnetic field inhomogeneity to the spin linewidth. We find the spin polarization recovery rate to be temperature independent below 1 K and conclude that spin out-diffusion across the resonator mode volume provides the mechanism for spin relaxation of the ensemble. Furthermore, by pumping spins in one sub-ensemble and probing the spins in the other sub-ensembles, we observe fast steady-state cross-relaxation (compared to spin repolarization) across the hyperfine transitions. These observations have important implications for using the three sub-ensembles as independent quantum memories.

de Lange, Gijs; Ranjan, Vishal; Schutjens, Ron; Debelhoir, Thibault; Groen, Joost; Szombati, Daniel; Thoen, David; Klapwijk, Teun; Hanson, Ronald; Dicarlo, Leonardo

2013-03-01

200

Protein Structural Dynamics Revealed by Site-Directed Spin Labeling and Multifrequency EPR.

Multifrequency electron paramagnetic resonance (EPR) of spin-labeled protein is a powerful spectroscopic technique to study protein dynamics on the rotational correlation time scale from 100 ps to 100 ns. Nitroxide spin probe, attached to cysteine residue, reports on local topology within the labeling site, dynamics of protein domains reorientation, and protein global tumbling in solution. Due to spin probe's magnetic tensors anisotropy, its mobility is directly reflected by the EPR lineshape. The multifrequency approach significantly decreases ambiguity of EPR spectra interpretation. The approach, described in this chapter, provides a practical guideline that can be followed to carry out the experiments and data analysis. PMID:24061916

Nesmelov, Yuri E

2014-01-01

201

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

202

Dynamics of laser-induced spin reorientation in Co/SmFeO3 heterostructure

NASA Astrophysics Data System (ADS)

Ultrafast control of a ferromagnet (FM) via exchange coupling with an antiferromagnet (AFM) is demonstrated in a Co/SmFeO3 heterostructure. Employing time-resolved photoemission electron microscopy combined with x-ray magnetic circular dichroism, a sub-100-ps change of the Co spins orientation by up to 10? driven by the ultrafast heating of the SmFeO3 orthoferrite substrate through its spin reorientation phase transition is revealed. Numerical modeling of the ultrafast-laser-induced heat profile in the heterostructure, and the subsequent coupled spins dynamics and equilibration of the spin systems suggest that the localized laser-induced spin reorientation is hindered compared with the static case. Moreover, numerical simulations show that a relatively small Co/SmFeO3 exchange interaction could be sufficient to induce a complete and fast spin reorientation transition (SRT).

Le Guyader, L.; Kleibert, A.; Nolting, F.; Joly, L.; Derlet, P. M.; Pisarev, R. V.; Kirilyuk, A.; Rasing, Th.; Kimel, A. V.

2013-02-01

203

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.

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

2013-01-01

204

Dynamical Jahn-Teller effect in a spin-orbital coupled system

NASA Astrophysics Data System (ADS)

Dynamical Jahn-Teller (DJT) effect in a spin-orbital coupled system on a honeycomb lattice is examined, motivated from recently observed spin-liquid behavior in Ba3CuSb2O9. An effective vibronic Hamiltonian, where the superexchange interaction and the DJT effect are taken into account, is derived. We find that the DJT effect induces a spin-orbital resonant state where local spin-singlet states and parallel orbital configurations are entangled with each other. This spin-orbital resonant state is realized in between an orbital-ordered state, where spin-singlet pairs are localized, and an antiferromagnetic ordered state. Based on the theoretical results, a possible scenario for Ba3CuSb2O9 is proposed.

Nasu, Joji; Ishihara, Sumio

2013-09-01

205

Brownian motion and quantum dynamics of magnetic monopoles in spin ice

NASA Astrophysics Data System (ADS)

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.

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

2013-02-01

206

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 Dy(2)Ti(2)O(7) 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

207

Electrical current and coupled electron-nuclear spin dynamics in double quantum dots

NASA Astrophysics Data System (ADS)

We examine electronic transport in a spin-blockaded double quantum dot. We show that by tuning the strength of the spin-orbit interaction the current flowing through the double dot exhibits a dip at zero magnetic field or a peak at a magnetic field for which the two-electron energy levels anticross. This behavior is due to the dependence of the singlet-triplet mixing on the field and spin-orbit amplitude. We derive approximate expressions for the current as a function of the amplitudes of the states involved in the transport. We also consider an alternative model that takes into account a finite number of nuclear spins and study the resulting coupled dynamics between electron and nuclear spins. We show that if the spin ensemble is in a thermal state there are regular oscillations in the transient current followed by quasichaotic revivals akin to those seen in a thermal Jaynes-Cummings model.

Giavaras, G.; Lambert, Neill; Nori, Franco

2013-03-01

208

NASA Astrophysics Data System (ADS)

The spin dynamics of Sr-doped cobaltite La1-xSrxCoO3 (x=0.14 and x=0.4) has been investigated in both zero magnetic field and high field by NMR. The results are consistent with microscopically phase-separated regions of ferromagnetic and nonferromagnetic materials. Nuclear spin-lattice and spin-spin relaxation in the ferromagnetic regions is attributed to fluctuating hyperfine fields produced by double exchange between Co ions. The linear temperature dependence of the correlation time, obtained from the data analysis, suggests that lattice excitations modify the double-exchange process as the temperature is raised. In the nonferromagnetic regions, a distribution of nuclear spin-lattice relaxation times is found. It is likely that low-frequency fluctuating localized moments, such as small spin clusters, in spin-glass regions provide the relaxation mechanism for both the spin-glass and low-spin (S=0) regions. A simple model involving these ideas can account for the stretched exponential nuclear magnetization recovery in the nonferromagnetic regions, and permits an estimate to be made of the mean size of low-spin regions.

Hoch, M. J.; Kuhns, P. L.; Moulton, W. G.; Reyes, A. P.; Wu, J.; Leighton, C.

2004-01-01

209

NASA Astrophysics Data System (ADS)

Using time-resolved x-ray resonant magnetic scattering we report on the precessional dynamics of spin valve systems with parallel (P) and antiparallel (AP) orientation of the ferromagnetic layers separated by a nonmagnetic spacer layers. Previously we observed in Co/Cu/Ni81Fe19(Py) spin valve systems an increase of the magnetic damping parameter in Py with changing magnetization direction of Py and Co layers from P to AP orientation [Salikhov , Appl. Phys. Lett.APPLAB0003-695110.1063/1.3633115 99, 092509 (2011)]. We attributed this finding to the configurational dependence of the spin pumping effect [Kim and Chappert, J. Magn. Magn. Mater.JMMMDC0304-885310.1016/j.jmmm.2004.09.036 286, 56 (2005)]. Here we extend our earlier findings by investigating the temperature dependence of the spin pumping effect and possible other causes for the configurational dependence of the damping parameter, such as domain wall induced coupling or magnetic dipole coupling. The main focus is on Co/Cu/Py trilayers and on Co2MnGe/V/Py trilayers with spin valve properties.

Salikhov, R.; Abrudan, R.; Brüssing, F.; Gross, K.; Luo, C.; Westerholt, K.; Zabel, H.; Radu, F.; Garifullin, I. A.

2012-10-01

210

Low Temperature Dynamics of - and Spin-Density Wave States

NASA Astrophysics Data System (ADS)

The dynamics of charge-and spin-density wave states (CDW and SDW) at low temperatures are investigated by studying field and frequency dependencies of electrical transport properties in quasi-one-dimensional model compounds--K _{0.3}MoO_3 for CDW and (TMTSF)_2PF _6 for SDW. In K_{0.3}MoO _3 the relaxation of metastable states establishes frozen CDW internal deformation dynamics into a time scale slower than experiments at T = 4.2K. A frequency independent dielectric constant of 7 times 10^5 and a linear increase of serial conductivity from 10^{-3 } to 10^9 Hz indicate underdamped CDW dynamics with sigma_ {rm max}>2 times 10^5 (Omegacm) ^{-1}. The connection between dc nonlinearity and the frequency dependence of ac conductivity can be made with an assumption of rigid CDW motion. The rigidity of CDW can be depinned and pinned within a time scale less than 50nSec. The impurity dependence of CDW in K_{0.3}Mo _{rm 1-x}W_ {rm x}O_3 shows strong pinning behaviors for dielectric constant and threshold field at T = 4.2K in contrast with weak pinning characteristics for high temperature response indicating a modification of the phase-correlation length by Coulomb interaction in the absence of screening normal electrons. In (TMTSF)_2PF _6 at T = 2K a stretched exponential form of SDW relaxation is observed with a static dielectric constant of 2 times 10^9 and tau_0 ~1mSec. The dielectric constant at 1.3 GHz indicates a strong reduction of spectral weight of the pinned mode at mm-wave frequency. The sharp threshold (E_{T} = 3mV/cm) is rather temperature independent from 5 down to 1.5K and SDW conductivity is scaled with single particles conductivity. All of this indicate a similar SDW dynamics to CDW at high temperatures. Below 1K a temperature independent nonlinear conduction becomes prominent, and its field dependence can be well described by a tunneling form of sigma (E) = sigma_0 exp{-(E_0/E) } and with sigma_0 comparable to normal state conductivity and E _0 = 2.5V/cm orders of magnitudes smaller than the single particle tunneling across the gap. The magnetoresistance of this nonlinearity indicates involvement of single particles. The disorder, which has shown to cause a weak pinning of SDW at high temperatures by others, resulting in a strong pinning Like behavior, E _0~sqrt{E_{T} }. The collapse of SDW order parameter at pinning sites by electric fields may be responsible for the low temperature SDW nonlinearity.

Kim, Yong Min

211

Spin dynamics of trimers on a distorted kagome lattice

NASA Astrophysics Data System (ADS)

We treat the ground state, elementary excitations, and neutron scattering cross section for a system of trimers consisting of three tightly bound spins (1)/(2) on a distorted kagome lattice, subject to isotropic nearest-neighbor (usually antiferromagnetic) Heisenberg interactions. The interactions between trimers are assumed to be weak compared to the intratrimer interactions. We compare the spin-wave excitation spectrum of trimers with that obtained from standard spin-wave theory and attribute the differences at low energy to the fact that the trimer formulation includes exactly the effects of intratrimer zero-point motion.

Harris, A. B.; Yildirim, T.

2013-07-01

212

Finite temperature spin-dynamics and phase transitions in spin-orbital models

We study finite temperature properties of a generic spin-orbital model relevant to transition metal compounds, having coupled quantum Heisenberg-spin and Ising-orbital degrees of freedom. The model system undergoes a phase transition, consistent with that of a 2D Ising model, to an orbitally ordered state at a temperature set by short-range magnetic order. At low temperatures the orbital degrees of freedom freeze-out and the model maps onto a quantum Heisenberg model. The onset of orbital excitations causes a rapid scrambling of the spin spectral weight away from coherent spin-waves, which leads to a sharp increase in uniform magnetic susceptibility just below the phase transition, reminiscent of the observed behavior in the Fe-pnictide materials.

Chen, C.-C.

2010-04-29

213

Dynamical spin localization of spinor condensate driven by external magnetic fields

We study the dynamical response of a spinor Bose condensate under the influence of external magnetic fields which have both a random and a time varying systematic component. We find that the external noise may eventually destroy the Rabi oscillation and dynamical spin localization. The destruction of the Rabi oscillation due to the noise is much easier than that of

Ping Zhang; Ai-Zhen Zhang; Duan Suqing; Xian-Geng Zhao

2001-01-01

214

Nucleation and dynamics of magnetic vortices under spin-polarized current

Spin-polarized current in a ferromagnet is known to lead to the instability of the uniformly magnetized state. In this paper, it is demonstrated by micromagnetic simulations that, in films or wide wires, the above instability is followed by the formation of magnetic vortices. Subsequent magnetization dynamics is also studied in terms of vortices, which includes pair dynamics and pair annihilation.

Yoshinobu Nakatani; Junya Shibata; Gen Tatara; Hiroshi Kohno; André Thiaville; Jacques Miltat

2008-01-01

215

When a fluid flows inside a tube, the deformations of the tube can interact with the fluid flowing within it and these dynamic interactions can result in significant lateral motions of the tube and the flowing fluid. The purpose of this report is to examine the dynamic stability of a spinning tube through which an incompressible frictionless fluid is flowing.

G. A. Benedetti

1990-01-01

216

Dynamics of the modified Kibble-?urek mechanism in antiferromagnetic spin-1 condensates

NASA Astrophysics Data System (ADS)

We investigate the dynamics and outcome of a quantum phase transition from an antiferromagnetic to a phase-separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms. We explicitly demonstrate double universality in the dynamics within experiments with various quench times. Furthermore, we show that spin domains created in the nonequilibrium transition constitute a set of mutually incoherent quasicondensates. The quasicondensates appear to be positioned in a semiregular fashion, which is a result of the conservation of local magnetization during the postselection dynamics.

Witkowska, Emilia; Dziarmaga, Jacek; ?wis?ocki, Tomasz; Matuszewski, Micha?

2013-08-01

217

We have developed a computational molecular dynamics technique to simulate the motions of spin labels bound to the regulatory domain of scallop myosin. These calculations were then directly compared with site-directed spin labeling experimental results obtained by preparing seven single-cysteine mutants of the smooth muscle (chicken gizzard) myosin regulatory light chain and performing electron paramagnetic resonance experiments on these spin-labeled regulatory light chains in functional scallop muscle fibers. We determined molecular dynamics simulation conditions necessary for obtaining a convergent orientational trajectory of the spin label, and from these trajectories we then calculated correlation times, orientational distributions, and order parameters. Simulated order parameters closely match those determined experimentally, validating our molecular dynamics modeling technique, and demonstrating our ability to predict preferred sites for labeling by computer simulation. In several cases, more than one rotational mode was observed within the 14-ns trajectory, suggesting that the spin label samples several local energy minima. This study uses molecular dynamics simulations of an experimental system to explore and enhance the site-directed spin labeling technique.

LaConte, Leslie E W; Voelz, Vincent; Nelson, Wendy; Enz, Michael; Thomas, David D

2002-01-01

218

Growth direction dependence of the electron spin dynamics in {111} GaAs quantum wells

NASA Astrophysics Data System (ADS)

The electron spin dynamics is studied by time-resolved Kerr rotation in GaAs/AlGaAs quantum wells embedded in NIP structures grown on (111)A or (111)B-oriented substrates. In both cases the spin lifetimes are significantly increased by applying an external electric field, but this field has to point along the growth direction for structures grown on (111)A and opposite to it for the ones grown on (111)B. This extended electron spin lifetime is the result of the suppression of the D'yakonov-Perel spin relaxation mechanism [Sov. Phys. Solid State 13, 3023 (1972)] due to the cancellation effect of the internal Dresselhaus term [Phys. Rev. 100, 580 (1955)] with the external electric field induced Rashba one [J. Phys. C 17, 6039 (1984)], both governing the conduction band spin-orbit splitting. These results demonstrate the key role played by the growth direction in the design of spintronic devices.

Ye, H. Q.; Wang, G.; Liu, B. L.; Shi, Z. W.; Wang, W. X.; Fontaine, C.; Balocchi, A.; Amand, T.; Lagarde, D.; Renucci, P.; Marie, X.

2012-07-01

219

Coherent spin dynamics of donor bound electrons in GaAs

NASA Astrophysics Data System (ADS)

We report experimental studies of coherent spin dynamics of donor-bound electrons in high-purity GaAs by using transient differential transmission. The donor-bound exciton transitions, which are not visible in the linear absorption spectrum, are spectrally resolved in the nonlinear differential transmission spectra. The spin beats in the transient differential transmission response, arising from electron spin precession in an external magnetic field, are investigated with the pump and probe coupling to various donor-bound exciton transitions. The spectral dependence of the spin beats provides important information on the polarization selection rule for the underlying donor-bound exciton transitions. The polarization selection rules deduced from these experiments indicate that contributions from higher-energy donor-bound exciton transitions can severely limit the effectiveness of optical spin control using mechanisms such as polarization-dependent optical Stark shifts.

Phelps, Carey; O'Leary, Shannon; Prineas, John; Wang, Hailin

2011-08-01

220

Polynomially scaling spin dynamics simulation algorithm based on adaptive state-space restriction.

We report progress with an old problem in magnetic resonance -- that of the exponential scaling of simulation complexity with the number of spins. It is demonstrated below that a polynomially scaling algorithm can be obtained (and accurate simulations performed for over 200 coupled spins) if the dimension of the Liouville state space is reduced by excluding unimportant and unpopulated spin states. We found the class of such states to be surprisingly wide. It actually appears that a majority of states in large spin systems are not essential in magnetic resonance simulations and can safely be dropped from the state space. In restricted state spaces the spin dynamics simulations scale polynomially. In cases of favourable interaction topologies (sparse graphs, e.g. in protein NMR) the asymptotic scaling is linear, opening the way to direct fitting of molecular structures to experimental spectra. PMID:17936658

Kuprov, Ilya; Wagner-Rundell, Nicola; Hore, P J

2007-09-21

221

Constrained spin-density dynamics of an iron-sulfur complex: Ferredoxin cofactor

NASA Astrophysics Data System (ADS)

The computation of antiferromagnetic exchange coupling constants J by means of efficient density-based approaches requires in practice to take care of both spin projection to approximate the low spin ground state and proper localization of the magnetic orbitals at the transition metal centers. This is demonstrated here by a combined approach where the extended broken-symmetry (EBS) technique is employed to include the former aspect, while spin density constraints are applied to ensure the latter. This constrained EBS (CEBS) approach allows us to carry out ab initio molecular dynamics on a spin-projected low spin potential energy surface that is generated on-the-fly by propagating two coupled determinants and thereby accessing the antiferromagnetic coupling along the trajectory. When applied to the prototypical model of the oxidized [2Fe-2S] cofactor in Ferredoxins, [Fe2S2(SH)4]2-, at room temperature, CEBS leads to remarkably good results for geometrical structures and coupling constants J.

Ali, Md. Ehesan; Nair, Nisanth N.; Staemmler, Volker; Marx, Dominik

2012-06-01

222

Spin dynamics in triangular-lattice antiferromagnets CuCr1-xMgxO2

NASA Astrophysics Data System (ADS)

The electron spin resonance (ESR) spectroscopy was employed to investigate the spin dynamics in triangular-lattice antiferromagnets CuCr1-xMgxO2 with x=0 and 0.02. All spectra can be well fitted by a single Lorentzian lineshape. The analysis of the g-factor, the linewidth ?H, and the ESR intensity I as a function of temperature suggests the development of significant antiferromagnetic (AFM) spin fluctuations at temperature well above TN in both samples. However, the evolution of the AFM spin fluctuations is different for each sample. For the undoped sample the ESR intensity I is almost temperature independent between ~100 K and 50 K and then drops rapidly below 50 K. But for x=0.02, the I monotonously increases with cooling and reduces rapidly only below TN. These results indicate that the AFM spin fluctuations are extremely strong in the undoped sample and appear to be suppressed upon Mg doping.

Li, Renwen; Qu, Zhe; Tong, Wei; Zhang, Yuheng

2011-02-01

223

NASA Astrophysics Data System (ADS)

In a test of principle a neutron spin filter has been built, which is based on dynamic nuclear polarization (DNP) using photo-excited triplet states. This DNP method has advantages over classical concepts as the requirements for cryogenic equipment and magnets are much relaxed: the spin filter is operated in a field of 0.3 T at a temperature of about 100 K and has performed reliably over periods of several weeks.The neutron beam was also used to analyze the polarization of the target employed as a spin filter. We obtained an independent measurement of the proton spin polarization of ?0.13 in good agreement with the value determined with NMR. Moreover, the neutron beam was used to measure the proton spin polarization as a function of position in the naphthalene sample. The polarization was found to be homogeneous, even at low laser power, in contradiction to existing models describing the photo-excitation process.

Haag, M.; van den Brandt, B.; Eichhorn, T. R.; Hautle, P.; Wenckebach, W. Th.

2012-06-01

224

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

225

Mean-field dynamics of spin-orbit coupled Bose-Einstein condensates.

Spin-orbit coupling (SOC), the interaction between the spin and momentum of a quantum particle, is crucial for many important condensed matter phenomena. The recent experimental realization of SOC in neutral bosonic cold atoms provides a new and ideal platform for investigating spin-orbit coupled quantum many-body physics. In this Letter, we derive a generic Gross-Pitaevskii equation as the starting point for the study of many-body dynamics in spin-orbit coupled Bose-Einstein condensates. We show that different laser setups for realizing the same SOC may lead to different mean-field dynamics. Various ground state phases (stripe, phase separation, etc.) of the condensate are found in different parameter regions. A new oscillation period induced by the SOC, similar to the Zitterbewegung oscillation, is found in the center-of-mass motion of the condensate. PMID:22400756

Zhang, Yongping; Mao, Li; Zhang, Chuanwei

2012-01-19

226

The problem of how single central spins interact with a nuclear spin bath is essential for understanding decoherence and relaxation in many quantum systems, yet is highly nontrivial owing to the many-body couplings involved. Different models yield widely varying time scales and dynamical responses (exponential, power-law, gaussian, etc.). Here we detect the small random fluctuations of central spins in thermal equilibrium [holes in singly charged (In,Ga)As quantum dots] to reveal the time scales and functional form of bath-induced spin relaxation. This spin noise indicates long (400 ns) spin correlation times at a zero magnetic field that increase to ?5???s as dominant hole-nuclear relaxation channels are suppressed with small (100 G) applied fields. Concomitantly, the noise line shape evolves from Lorentzian to power law, indicating a crossover from exponential to slow [?1/log(t)] dynamics. PMID:22681099

Li, Yan; Sinitsyn, N; Smith, D L; Reuter, D; Wieck, A D; Yakovlev, D R; Bayer, M; Crooker, S A

2012-05-03

227

Dimensionality crossover and frustrated spin dynamics on a triangular lattice

NASA Astrophysics Data System (ADS)

Investigations of the magnetic behavior of the layered oxide, LiNi0.65Co0.25Mn0.10O2 , through ac and time-dependent susceptibility, dc linear and nonlinear susceptibility as well as neutron-diffraction measurements are presented. A ferrimagneticlike spin ordering appears at 119 K with a spontaneous magnetization coexisting with spin frustration in two dimensions (2D). At lower temperature, a cluster-glass transition is found at 17.4 K indicating a transformation to a completely frustrated state in three dimensions (3D). A dimensionality crossover with temperature, from 2D to 3D, in a magnetically frustrated system has been demonstrated. The observed magnetic behavior is believed to originate from a percolating system of spin clusters defined by disordered and frustrated exchange interactions and the findings conform well with predictions of the percolation cluster model.

Wikberg, J. M.; Dahbi, M.; Saadoune, I.; Gustafsson, T.; Edström, K.; Svedlindh, P.

2010-06-01

228

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

We experimentally studied the spin-dependent collision dynamics of 87 Rb spin-2 Bose-Einstein condensates confined in an optical trap. The condensed atoms were initially populated in the | F=2, mF =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

T. Kuwamoto; K. Araki; T. Eno; T. Hirano

2004-01-01

229

Chemically induced dynamic spin polarization in two dimensional systems: Theoretical predictions

Theoretical predictions for chemically induced dynamic spin polarization [CIDN(E)P] and Heisenberg spin exchange in two dimensional fluid systems are developed. An idealized model, which yields simple limiting results is first discussed in order to illustrate the importance of the geometrical aspects of this problem upon the CIDN(E)P observables. Pedersen–Freed theory, which employs numerical solutions of the stochastic-Liouville equation is then

Gary P. Zientara; Jack H. Freed

1979-01-01

230

Chemically induced dynamic spin polarization in two dimensional systems: Theoretical predictions

Theoretical predictions for chemically induced dynamic spin polarization [CIDN(E)P] and Heisenberg spin exchange in two dimensional fluid systems are developed. An idealized model, which yields simple limiting results is first discussed in order to illustrate the importance of the geometrical aspects of this problem upon the CIDN(E)P observables. Pedersen-Freed theory, which employs numerical solutions of the stochastic-Liouville equation is then

Gary P. Zientara; Jack H. Freed

1979-01-01

231

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

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

Suguru Araki

1988-01-01

232

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

233

Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments

We study the Rabi oscillations decay of a spin decohered by a spin bath whose internal dynamics is caused by dipolar coupling between the bath spins. The form and rate of decay as a function of the intrabath coupling is obtained analytically, and confirmed numerically. The complex form of decay smoothly varies from power law to exponential, and the rate changes nonmonotonically with the intrabath coupling, decreasing for both slow and fast baths. The form and rate of Rabi oscillations decay can be used to experimentally determine the intrabath coupling strength for a broad class of solid-state systems.

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

2009-06-09

234

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

235

State transfer in static and dynamic spin chains with disorder

We examine the speed and fidelity of several protocols for state or single excitation transfer in finite spin chains subject to diagonal and off-diagonal disorder. We find that, for a given chain length and maximal achievable interspin exchange (XY) coupling strength, the optimal static spin-coupling protocol, implementing the fastest state transfer between the two ends of the chain, is more susceptible to off-diagonal (XY coupling) disorder, as compared to a much slower but robust adiabatic transfer protocol with time-dependent coupling strengths.

Petrosyan, David; Nikolopoulos, Georgios M.; Lambropoulos, P. [Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas, GR-71110 Heraklion, Crete (Greece)

2010-04-15

236

Comparison of Quantum and Classical Relaxation in Spin Dynamics

NASA Astrophysics Data System (ADS)

The classical Landau-Lifshitz equation with a damping term has been derived from the time evolution of a quantum mechanical wave function under the assumption of a non-Hermitian Hamilton operator. Further, the trajectory of a classical spin (S) has been compared with the expectation value of the spin operator (S^). A good agreement between classical and quantum mechanical trajectories can be found for Hamiltonians linear in S^ or S, respectively. Quadratic or higher order terms in the Hamiltonian result in a disagreement.

Wieser, R.

2013-04-01

237

Dynamical nuclear spin polarization induced by electronic current through double quantum dots

NASA Astrophysics Data System (ADS)

We analyse electron-spin relaxation in electronic transport through coherently coupled double quantum dots (DQDs) in the spin blockade regime. In particular, we focus on hyperfine (HF) interaction as the spin-relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different HF coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all HF-mediated spin-relaxation processes coming from different opposite spin level approaches. We find that the current as a function of the external magnetic field shows a peak or a dip and that the transition from a current dip to a current peak behaviour is obtained by decreasing the HF coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the DQD and the spin-flip processes due to the nuclear environment.

López-Monís, Carlos; Iñarrea, Jesús; Platero, Gloria

2011-05-01

238

NASA Astrophysics Data System (ADS)

We present magnetic susceptibility, H1 nuclear magnetic resonance (NMR) spectra, spin-spin- and spin-lattice-relaxation rates data, collected in the temperature range 1.65

Amiri, H.; Mariani, M.; Lascialfari, A.; Borsa, F.; Timco, G. A.; Tuna, F.; Winpenny, R. E. P.

2010-03-01

239

Collective mode spectra and dynamical response functions of weakly coupled random spin chains

NASA Astrophysics Data System (ADS)

We study the dynamics of weakly coupled random antiferromagnetic spin chains at low temperature. We use the celebrated real-space renormalization group technique to tackle the intrachain couplings, and treat the interchain couplings within the Mean-Field/Random Phase Approximation (RPA) framework. Earlier work based on mean-field treatment of the inter chain couplings[joshi] indicated the existence of disorder-induced Neel ordering in such systems and clarified their phase diagrams. In the present work we apply the RPA formalism to calculate the dynamical response functions in the low temperature ordered phase. We obtain the dynamical susceptibility, structure factor, and the spin-wave spectra. Comparisons will be made with inelastic neutron scattering experiment for quasi-one-dimensional spin systems such as CuGeO3. References [joshi] Anuvrat Joshi and Kun Yang, Phys. Rev. B 67, 174403 (2003)

Yusuf, Eddy

2005-03-01

240

NASA Astrophysics Data System (ADS)

To exploit the quantum coherence of electron spins in solids in future technologies such as quantum manipulating, it's first vital to overcome the problem of spin decoherence due to their coupling the noisy environment. Dynamical decoupling is a particularly promising strategy for combating decoherence. I will briefly introduce the roadmap for dynamical decoupling and show our experimental research on the field in detail. We first applied the optimal dynamical decoupling scheme [1] on electron spins of ensemble sample [2]. Based on the technology, the dynamical decoupling sequence was used to observe the anomalous coherence effect and of single electron spin based on nitrogen-vacancy defect center in diamond [3]. For application, combined the dynamical decoupling together with quantum metrology protocol, the phase estimation was enhanced [4]. Instead of pulsed model, continuous dynamical decoupling was realized in our experiment and applied to protect quantum gate [5]. The next step, we will apply multi flip pulses to enhance the magnetic field sensitivity of NV center towards to the micro-scale magnetic resonance and single molecular imaging. [1] G. S. Uhrig, Phys. Rev. Lett. 98, 100504 (2007) [2] J. Du, et al., Nature 461, 1265 (2009) [3] P. Huang, et al., Nature Communications, 2, 570 (2011) [4] X. Rong, et al., Europhys. Lett. 95, 60005 (2011) [5] X. Xu, et al., Phys. Rev. Lett. 109, 070502 (2012)

Du, Jiangfeng

2013-03-01

241

Dynamical magnetic anisotropy in spin--1 molecular systems

NASA Astrophysics Data System (ADS)

We study electronic transport through a deformable spin-1 molecular system in a break junction setup, under the influence of a local vibrational mode. Our study shows that the magnetic anisotropy, which arises due to stretching along the transport axis[Science 328 1370 (2010)], is renormalized by the interactions with vibrations. The coupling induces additional spin--asymmetric hybridizations that contribute to the net molecular anisotropy. We show that the low temperature physics of such device can be described by an anisotropic Kondo model (J> J), with a magnetic anisotropy term, ANetSz^2, negative at zero stretching. A quantum phase transition (QPT) is explored by stretching the molecule, driving ANet into positive values, and changing the character of the device from a non--Fermi--liquid (NFL) to a Fermi liquid (FL) ground state. This transition can be directly observed through the zero--bias conductance, which we find to be finite for negative anisotropy, zero for positive anisotropy, and to reach the unitary limit at ANet 0. At that point, an underscreened spin-1 Kondo ground state appears due to the restitution of the spin-1 triplet degeneracy.

Ruiz-Tijerina, David; Cornaglia, Pablo; Balseiro, Carlos; Ulloa, Sergio

2012-02-01

242

Relativistic Spin-Flavor States in Light Front Dynamics

NASA Astrophysics Data System (ADS)

Orthonormal spin-flavor wave functions of Lorentz covariant quark models of the Bakamjian- Thomas type are constructed for nucleon resonances. Three different bases are presented. The manifestly Lorentz covariant Dirac-Melosh basis is related to the Pauli-Melosh basis and the symmetrized Bargmann-Wigner basis that are manifestly orthogonal.

Beyer, M.; Kuhrts, C.; Weber, H. J.

1998-11-01

243

Nanosecond Scanning Tunneling Microscopy: resolving spin dynamics at the atomic scale

NASA Astrophysics Data System (ADS)

With the advent of nanoelectronics, functional electronic elements advance towards atomic dimensions and analysis techniques need to keep pace. Scanning tunneling microscopes (STM) have evolved into standard tools to measure the static electronic properties of nanostructures, molecules and atoms. Here we show how the STM can be used to access the equally important dynamical properties on time scales ranging from pico- to nanoseconds. We combine inelastic electron tunneling spectroscopy (IETS) with an all-electronic pump-probe measurement scheme and record the dynamical evolution of magnetic atoms on surfaces in the time domain [1]. We focus on the dynamics of electron spin relaxation in transition metal atoms placed onto a copper nitride decoupling layer on Cu(100). On this surface Fe atoms experience large magneto-crystalline anisotropy [2] that enables long spin lifetimes. At the same time the quantum mechanical nature of the discrete spin states allows for an additional path of spin relaxation: quantum tunneling of magnetization. We probe the dynamic behavior associated with this process and find that placing a Cu atom close to a Fe atom boosts the uniaxial anisotropy energy and creates a long-lived spin state with relaxation times in excess of 200 ns. The ability to probe individual nanostructures with atomic spatial and nanosecond temporal resolution opens a new avenue to explore spin dynamics and other dynamical phenomena on the intrinsic length scale of the underlying interactions. [4pt] [1] S. Loth, M. Etzkorn, C. P. Lutz, D. M. Eigler, A. J. Heinrich, Science 329 1628 (2010). [0pt] [2] C.F. Hirjibehedin, et al., Science 317, 1199 (2007).

Loth, Sebastian

2011-03-01

244

Quantum wave-packet dynamics in spin-coupled vibronic states.

Extending the Shin-Metiu two-electron Hamiltonian, we construct a new Hamiltonian with effective singlet-triplet couplings. The Born-Oppenheimer electronic potentials and couplings are obtained for different parameters, and the laser-free dynamics is calculated with the full Hamiltonian and in the adiabatic limit. We compare the dynamics of the system using nuclear wave packets for different numbers of Born-Oppenheimer potentials and vibronic wave packets on a full 3-dimensional (two electron coordinates plus one nuclear coordinate) grid. Using strong fields, we show that it is possible to dynamically lock the spin state of the system by decoupling the singlet-triplet transition via a nonresonant dynamic Stark effect in the adiabatic limit. Although a similar spin-locking mechanism is observed in the dynamics of vibronic wave packets, multiphoton ionization cannot be neglected leading to the breakdown of the control scheme. PMID:22946899

Falge, Mirjam; Engel, Volker; Lein, Manfred; Vindel-Zandbergen, Patricia; Chang, Bo Y; Sola, Ignacio R

2012-09-20

245

When a fluid flows inside a tube, the deformations of the tube can interact with the fluid flowing within it and these dynamic interactions can result in significant lateral motions of the tube and the flowing fluid. The purpose of this report is to examine the dynamic stability of a spinning tube through which an incompressible frictionless fluid is flowing. The tube can be considered as either a hollow beam or a hollow cable. The analytical results can be applied to spinning or stationary tubes through which fluids are transferred; e.g., liquid coolants, fuels and lubricants, slurry solutions, and high explosives in paste form. The coupled partial differential equations are determined for the lateral motion of a spinning Bernoulli-Euler beam or a spinning cable carrying an incompressible flowing fluid. The beam, which spins about an axis parallel to its longitudinal axis and which can also be loaded by a constant axial force, is straight, uniform, simply supported, and rests on a massless, uniform elastic foundation that spins with the beam. Damping for the beam and foundation is considered by using a combined uniform viscous damping coefficient. The fluid, in addition to being incompressible, is frictionless, has a constant density, and flows at a constant speed relative to the longitudinal beam axis. The Galerkin method is used to reduce the coupled partial differential equations for the lateral motion of the spinning beam to a coupled set of 2N, second order, ordinary differential equations for the generalized beam coordinates. By simplifying these equations and examining the roots of the characteristic equation, an analytical solution is obtained for the lateral dynamic instability of the beam (or cable). The analytical solutions determined the minimum critical fluid speed and the critical spin speeds, for a specified fluid speed, in terms of the physical parameters of the system.

Benedetti, G.A.

1990-11-01

246

NASA Astrophysics Data System (ADS)

Electron spins form a two-level quantum system in which the remarkable properties of quantum mechanics can be probed and utilized for many applications. By learning to manipulate these spins, it may be possible to construct a completely new form of technology based on the electron spin degree of freedom, known as spintronics. The most ambitious goal of spintronics is the development of quantum computing, in which electron spins are utilized as quantum bits, or qubits, with properties that are not possible with classical bits. Before these ideas can become reality, a system must be found in which spin lifetimes are long enough and in which spins can be completely controlled. Semiconductors are an excellent candidate for electron spin control since they can be integrated into on-chip devices and produced on a scalable level. The focus of this dissertation is on electron spin control in two different semiconductor systems, namely a two-dimensional electron gas in a modulation-doped quantum well and donor-bound electrons in bulk semiconductors. Both systems have been studied extensively for a variety of purposes. However, the ability to manipulate spins has been elusive. In this dissertation, the first experimentally successful demonstration of electron spin control in a two-dimensional electron gas is presented, in which ultrafast optical pulses induce spin rotations via the optical Stark effect. Donor-bound electron spin manipulation in bulk semiconductors is also investigated in this dissertation. Important information was obtained on the limiting factors that serve to prohibit spin control in this system. By taking these new factors into account, it is our hope that full electron spin control can eventually be accomplished in this system. Finally, through the course of investigating electron spin dynamics, a strange nonlinear optical behavior was observed in a bilayer system, which was determined to result from a coupling of optical interactions with tunneling rates between layers. The data suggest that there is a strong interplay between interlayer and intralayer correlations in this system. Investigations into the nature of this interaction were undertaken and are presented in the last part of this dissertation. This dissertation includes previously published and unpublished co-authored material.

Phelps, Carey E.

247

Spin dynamics and spin freezing in the triangular lattice antiferromagnets FeGa2S4 and NiGa2S4

NASA Astrophysics Data System (ADS)

Magnetic susceptibility and muon spin relaxation (?SR) experiments have been carried out on the quasi-2D triangular-lattice spin S=2 antiferromagnet FeGa2S4. The ?SR data indicate a sharp onset of a frozen or nearly frozen spin state at T*=31(2) K, twice the spin-glass-like freezing temperature Tf=16(1) K. The susceptibility becomes field dependent below T*, but no sharp anomaly is observed in any bulk property. A similar transition is observed in ?SR data from the spin-1 isomorph NiGa2S4. In both compounds the dynamic muon spin relaxation rate ?d(T) above T* agrees well with a calculation of spin-lattice relaxation by Chubukov, Sachdev, and Senthil in the renormalized classical regime of a 2D frustrated quantum antiferromagnet. There is no firm evidence for other mechanisms. At low temperatures, ?d(T) becomes temperature independent in both compounds, indicating persistence of spin dynamics. Scaling of ?d(T) between the two compounds is observed from ˜Tf to ˜1.5T*. Although the ?SR data by themselves cannot exclude a truly static spin component below T*, together with the susceptibility data they are consistent with a slowly fluctuating “spin gel” regime between Tf and T*. Such a regime and the absence of a divergence in ?d(T) at T* are features of two unconventional mechanisms: (1) binding/unbinding of Z2 vortex excitations, and (2) impurity spins in a nonmagnetic spin-nematic ground state. The absence of a sharp anomaly or history dependence at T* in the susceptibility of FeGa2S4, and the weakness of such phenomena in NiGa2S4, strongly suggest transitions to low-temperature phases with unconventional dynamics.

Zhao, Songrui; Dalmas de Réotier, P.; Yaouanc, A.; MacLaughlin, D. E.; Mackie, J. M.; Bernal, O. O.; Nambu, Y.; Higo, T.; Nakatsuji, S.

2012-08-01

248

NASA Astrophysics Data System (ADS)

Two experiments are carried out to investigate the dynamic behavior of the liquid partially filled in spherical tanks of a spinning satellite. One is the simulation test at the spin up phase of the rocket. The other is the sloshing test to analyze the propellant sloshing effects on the satellite attitude control. These experiments are specially set for the Engineering Test Satellite V which has two spherical tanks 37 percent filled with hydrazine, but the results obtained can be applicable to the other problems of the liquid dynamics in spherical tanks.

Komatsu, Keiji; Ono, Syuji; Shimizu, Junichiro; Nagashima, Ryuichi

249

Femtosecond electron and spin dynamics of the Gd(0001) surface are investigated by time-resolved photoemission and second harmonic generation. Upon optical excitation the spin polarization of the surface state is reduced by half while its exchange splitting remains nearly unchanged. Electron-magnon interaction is proposed to facilitate electron-spin-flip scattering among spin-mixed surface and bulk states, which provides a mechanism for ultrafast demagnetization. PMID:16197177

Lisowski, M; Loukakos, P A; Melnikov, A; Radu, I; Ungureanu, L; Wolf, M; Bovensiepen, U

2005-09-22

250

A method of creating pseudopure spin states in large clusters of coupled spins is described. It is based on filtering multiple-quantum coherence of the highest order, followed by a time-reversal period and partial saturation. Experimental demonstration is presented for a cluster of six dipolar-coupled proton spins of a benzene molecule in a liquid crystalline matrix, and the details of spin dynamics are studied numerically.

Lee, Jae-Seung; Khitrin, A.K. [Department of Chemistry, Kent State University, Kent, Ohio 44242-0001 (United States)

2004-08-01

251

Spin dynamics and relaxation in graphene nanoribbons: electron spin resonance probing.

Here we report the results of a multifrequency (~9, 20, 34, 239.2, and 336 GHz) variable-temperature continuous wave (cw) and X-band (~9 GHz) pulse electron spin resonance (ESR) measurement performed at cryogenic temperatures on potassium split graphene nanoribbons (GNRs). Important experimental findings include the following: (a) The multifrequency cw ESR data infer the presence of only carbon-related paramagnetic nonbonding states, at any measured temperature, with the g value independent of microwave frequency and temperature. (b) A linear broadening of the ESR signal as a function of microwave frequency is noticed. The observed linear frequency dependence of ESR signal width points to a distribution of g factors causing the non-Lorentzian line shape, and the g broadening contribution is found to be very small. (c) The ESR process is found to be characterized by slow and fast components, whose temperature dependences could be well described by a tunneling level state model. This work not only could help in advancing the present fundamental understanding on the edge spin (or magnetic)-based properties of GNRs but also pave the way to GNR-based spin devices. PMID:22901098

Rao, Singamaneni S; Stesmans, Andre; van Tol, Johan; Kosynkin, Dmitry V; Higginbotham-Duque, A; Lu, Wei; Sinitskii, Alexander; Tour, James M

2012-08-28

252

RosettaEPR: Rotamer Library for Spin Label Structure and Dynamics.

An increasingly used parameter in structural biology is the measurement of distances between spin labels bound to a protein. One limitation to these measurements is the unknown position of the spin label relative to the protein backbone. To overcome this drawback, we introduce a rotamer library of the methanethiosulfonate spin label (MTSSL) into the protein modeling program Rosetta. Spin label rotamers were derived from conformations observed in crystal structures of spin labeled T4 lysozyme and previously published molecular dynamics simulations. Rosetta's ability to accurately recover spin label conformations and EPR measured distance distributions was evaluated against 19 experimentally determined MTSSL labeled structures of T4 lysozyme and the membrane protein LeuT and 73 distance distributions from T4 lysozyme and the membrane protein MsbA. For a site in the core of T4 lysozyme, the correct spin label conformation (?1 and ?2) is recovered in 99.8% of trials. In surface positions 53% of the trajectories agree with crystallized conformations in ?1 and ?2. This level of recovery is on par with Rosetta performance for the 20 natural amino acids. In addition, Rosetta predicts the distance between two spin labels with a mean error of 4.4 Å. The width of the experimental distance distribution, which reflects the flexibility of the two spin labels, is predicted with a mean error of 1.3 Å. RosettaEPR makes full-atom spin label modeling available to a wide scientific community in conjunction with the powerful suite of modeling methods within Rosetta. PMID:24039810

Alexander, Nathan S; Stein, Richard A; Koteiche, Hanane A; Kaufmann, Kristian W; McHaourab, Hassane S; Meiler, Jens

2013-09-05

253

Spin-dynamical theory of the wave-corpuscular duality

The assumption that translations of the electron are accompanied by spin precession enables a deterministic description of electron diffraction and quantization of atomic systems. It is shown that the electromagnetic field of the processing electron is responsible for modulation of the beam intensity of an electron scattered from a system of charges and for mechanical stability of the orbital motion of electrons in bound states.

Gryzinski, M.

1987-10-01

254

Energy-dependent electron-electron scattering and spin dynamics in a two-dimensional electron gas

Measurements of spin dynamics of electrons in a degenerate two dimensional\\u000aelectron gas, where the Dyakonov-Perel mechanism is dominant, have been used to\\u000ainvestigate the electron scattering time (tp*) as a function of energy near the\\u000aFermi energy. Close to the Fermi energy the spin evolution is oscillatory,\\u000aindicating a quasi-collision-free regime of spin dynamics. As the energy is\\u000aincreased

W. J. H. Leyland; R. T. Harley; M. Henini; A. J. Shields; D. A. Ritchie

2008-01-01

255

Energy-dependent electron-electron scattering and spin dynamics in a two-dimensional electron gas

The measurement of spin dynamics of electrons in a degenerate two-dimensional electron gas, wherein the Dyakonov-Perel mechanism is dominant, has been used to investigate the electron scattering time (taup*) as a function of energy near the Fermi energy. Close to the Fermi energy, the spin evolution is oscillatory, which indicates a quasicollision-free regime of spin dynamics. As the energy is

W. J. H. Leyland; R. T. Harley; M. Henini; A. J. Shields; I. Farrer; D. A. Ritchie

2008-01-01

256

Relaxational dynamics of the Edwards-Anderson model and the mean-field theory of spin-glasses

Langevin equations for the relaxation of spin fluctuations in a soft-spin version of the Edwards-Anderson model are used as a starting point for the study of the dynamic and static properties of spin-glasses. An exact uniform Lagrangian for the average dynamic correlation and response functions is derived for arbitrary range of random exchange, using a functional-integral method proposed by De

H. Sompolinsky; Annette Zippelius

1982-01-01

257

NASA Astrophysics Data System (ADS)

Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series Pr(Os1-xRux)4Sb12 and Pr1-yLayOs4Sb12 to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate ? associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations x and y in a manner consistent with the “hyperfine enhancement” of Pr141 nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic Pr3+ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between Pr141 and muon spins and within the Pr141 spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.

Shu, Lei; Maclaughlin, D. E.; Aoki, Y.; Tunashima, Y.; Yonezawa, Y.; Sanada, S.; Kikuchi, D.; Sato, H.; Heffner, R. H.; Higemoto, W.; Ohishi, K.; Ito, T. U.; Bernal, O. O.; Hillier, A. D.; Kadono, R.; Koda, A.; Ishida, K.; Sugawara, H.; Frederick, N. A.; Yuhasz, W. M.; Sayles, T. A.; Yanagisawa, T.; Maple, M. B.

2007-07-01

258

The nitroxide spin label 1-oxyl-2,2,5,5-tetramethylpyrroline-3-methyl-methanethiosulfonate (MTSSL), commonly used in site-directed spin labeling of proteins, is studied with molecular dynamics (MD) simulations. After developing force field parameters for the nitroxide moiety and the spin label linker, we simulate MTSSL attached to a poly-alanine alpha helix in explicit solvent to elucidate the factors affecting its conformational dynamics. Electron spin resonance spectra at 9 and 250 GHz are simulated in the time domain using the MD trajectories and including global rotational diffusion appropriate for the tumbling of T4 Lysozyme in solution. Analysis of the MD simulations reveals the presence of significant hydrophobic interactions of the spin label with the alanine side chains.

Sezer, Deniz; Freed, Jack H.; Roux, Benoit

2009-01-01

259

We investigate the interaction between dipalmitoylphosphatidylcholine (DPPC) and a nitroxide spin label in order to understand its influences on lipid structure and dynamics using molecular dynamics simulations. The system was modified by covalently attaching nitroxide spin labels to the headgroups of two DPPC molecules. (S-(2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl)methyl methanesulfonothioate) (MTSL) was used as the spin label. The label position and dynamics were analyzed as was the impact of the modified DPPC on the structure of the surrounding lipids. The modified DPPC molecules locate closer to the center of the membrane than unmodified DPPC molecules. The rotation of the spin label is unrestricted, but there are favored orientations. MTSL depresses the deuterium order parameters of the carbon atoms close to the headgroup in surrounding DPPC molecules. The spin label has no impact on order parameters of carbon atoms at the end of the lipid tails. The lateral diffusion constant of the modified DPPC is indistinguishable from unmodified DPPC molecules. These novel computational results suggest an experimental validation. PMID:23948659

Kemmerer, Sabrina; Voss, John C; Faller, Roland

2013-08-13

260

Dynamic nuclear polarization is a method which allows for a dramatic increase of the NMR signals due to polarization transfer between electrons and their neighboring nuclei, via microwave irradiation. These experiments have become popular in recent years due to the ability to create hyper-polarized chemically and biologically relevant molecules, in frozen glass forming mixtures containing free radicals. Three mechanisms have been proposed for the polarization transfer between electrons and their surrounding nuclei in such non-conducting samples: the solid effect and cross effect mechanisms, which are based on quantum mechanics and relaxation on small spin systems, and thermal mixing, which originates from the thermodynamic macroscopic notion of spin temperature. We have recently introduced a spin model, which is based on the density matrix formalism and includes relaxation, and applied it to study the solid effect and cross effect mechanisms on small spin systems. In this publication we use the same model to describe the thermal mixing mechanism, and the creation of spin temperature. This is obtained without relying on the spin temperature formalism. Simulations of small model systems are used on systems with homogeneously and inhomogeneously broadened EPR lines. For the case of a homogeneously broadened line we show that the nuclear enhancement results from the thermal mixing and solid effect mechanisms, and that spin temperatures are created in the system. In the inhomogeneous case the enhancements are attributed to the solid effect and cross effect mechanisms, but not thermal mixing. PMID:23160533

Hovav, Yonatan; Feintuch, Akiva; Vega, Shimon

2012-11-16

261

Electron spin dynamics and g-factor in GaAsBi

NASA Astrophysics Data System (ADS)

Electron spin dynamics in elastically strained bulk GaAsBi epilayer with 2.2% Bi concentration has been measured by time resolved photoluminescence spectroscopy. Under external transverse magnetic field, the measurement of the photoluminescence polarization oscillations resulting from the Larmor precession of electron spins yields an accurate determination of the Landé g-factor. We find that the value of g increases from -0.81 to -0.68 when the temperature rises from T = 100 K to T = 300 K. This is typically double the value of GaAs, in agreement with the larger spin-orbit interaction in GaAsBi. In this temperature range, the electron spin lifetime decreases from 370 to 100 ps.

Mazzucato, S.; Zhang, T. T.; Carrère, H.; Lagarde, D.; Boonpeng, P.; Arnoult, A.; Lacoste, G.; Balocchi, A.; Amand, T.; Fontaine, C.; Marie, X.

2013-06-01

262

Muon spin relaxation study of spin dynamics in a polysaccharide iron complex

Polysaccharide iron complex, a ferritin analog, has been examined with zero-field muon spin-relaxation at temperatures from 2 to 40 K. Spectra exhibit a clear separation of static moments and collective excitations at low temperatures. At intermediate temperatures, superparamagnetic relaxation is observed and a blocking temperature of T{sub B}=10{+-}2.5K is measured, in agreement with transmission Mossbauer spectra and frequency dependent {chi}{sub ac} data. Superparamagnetic relaxation rates of 20{endash}150 MHz are in agreement with those extrapolated from Mossbauer spectra using a multilevel magnetic relaxation model. {copyright} 2001 American Institute of Physics.

van Lierop, J.; Ryan, D. H.; Pumarol, M. E.; Roseman, M.

2001-06-01

263

Simulation of the dynamics of many-body quantum spin systems using phase-space techniques

NASA Astrophysics Data System (ADS)

We reformulate the full quantum dynamics of spin systems using a phase-space representation based on SU(2) coherent states which generates an exact mapping of the dynamics of any spin system onto a set of stochastic differential equations. This representation is superior in practice to an earlier phase-space approach based on Schwinger bosons, with the numerical effort scaling only linearly with system size. By also implementing extrapolation techniques from quasiclassical equations to the full quantum limit, we are able to extend useful simulation times severalfold. This approach is applicable in any dimension including cases where frustration is present in the spin system. The method is demonstrated by simulating quenches in the transverse-field Ising model in one and two dimensions.

Ng, Ray; Sørensen, Erik S.; Deuar, Piotr

2013-10-01

264

Absorption effects due to spin in the worldline approach to black hole dynamics

We generalize the effective point particle approach to black hole dynamics to include spin. In this approach, dissipative effects are captured by degrees of freedom localized on the worldline. The absorptive properties of the black hole are determined by correlation functions which can be matched with the graviton absorption cross section in the long wavelength approximation. For rotating black holes, superradiance is responsible for the leading contribution. The effective theory is then used to predict the power loss due to spin in the dynamics of nonrelativistic binary systems. An enhancement of three powers of the relative velocity is found with respect to the nonrotating case. Then we generalize the results to other types of constituents in the binary system, such as rotating neutron stars. Finally, we compute the power loss absorbed by a test spinning black hole in a given spacetime background.

Porto, Rafael A. [Department of Physics, University of California, Santa Barbara, California 93106 (United States)

2008-03-15

265

Dynamics revealed by correlations of time-distributed weak measurements of a single spin

NASA Astrophysics Data System (ADS)

We show that the correlations in stochastic outputs of time-distributed weak measurements can be used to study the dynamics of an individual quantum object, with a proof-of-principle setup based on small Faraday rotation caused by a single spin in a quantum dot. In particular, the third-order correlation can reveal the 'true' spin decoherence, which would otherwise be concealed by the inhomogeneous broadening effect in the second-order correlations. The viability of such approaches lies in the fact that (i) in weak measurement the state collapse that would disturb the system dynamics occurs at a very low probability and (ii) a shot of measurement projecting the quantum object to a known basis state serves as a starter or stopper of the evolution without pumping or coherently controlling the system as otherwise required in conventional spin echo.

Liu, R.-B.; Fung, S.-H.; Fung, H.-K.; Korotkov, A. N.; Sham, L. J.

2010-01-01

266

Morphologic Parameters of Normal Swallowing Events Using Single-Shot Fast Spin Echo Dynamic MRI

This study was designed to determine visible and measurable morphological parameters in normal swallowing using dynamic MRI with single-shot fast spin echo (SSFSE), as a preliminary study in view of noninvasive MRI swallowing evaluation in patients with dysphagia. Seven healthy volunteers aged 24–40 underwent dynamic MRI with SSFSE, with a 1.5-T unit, using a head and neck antenna. Patients repeated

Dana M. Hartl; Marcella Albiter; Frédéric Kolb; Bernard Luboinski; Robert Sigal

2003-01-01

267

We report on neutron spin-echo (NSE) measurements on deuterated styrene-protonated butadiene diblock copolymer micelles in deuterated n-decane to investigate the dynamics of butadiene blocks in the corona. Before the NSE measurements, we performed small-angle neutron-scattering (SANS) measurements on the micelles to evaluate the structure to give a basis for the discussion of the dynamics. In the SANS study, we have

T. Kanaya; M. Monkenbusch; H. Watanabe; M. Nagao; D. Richter

2005-01-01

268

Theory of the dynamic spin response function near the Kosterlitz-Thouless transition

The pioneering work of Ambegaokar, Halperin, Nelson, and Siggia on dynamical phenomena in superfluid films near the Kosterlitz-Thouless transition is formulated in a more systematic way in the context of the classical two-dimensional (2D) XY model. Specifically, we extend the discussion of Nelson and Fisher on spin dynamics to include the effect of the vortices. The coupled equations of motion

René Cté; Allan Griffin

1986-01-01

269

Kinetic theories for spin models for cooperative relaxation dynamics

NASA Astrophysics Data System (ADS)

The facilitated kinetic Ising models with asymmetric spin flip constraints introduced by Jackle and co-workers [J. Jackle, S. Eisinger, Z. Phys. B 84, 115 (1991); J. Reiter, F. Mauch, J. Jackle, Physica A 184, 458 (1992)] exhibit complex relaxation behavior in their associated spin density time correlation functions. This includes the growth of relaxation times over many orders of magnitude when the thermodynamic control parameter is varied, and, in some cases, ergodic-nonergodic transitions. Relaxation equations for the time dependence of the spin density autocorrelation function for a set of these models are developed that relate this autocorrelation function to the irreducible memory function of Kawasaki [K. Kawasaki, Physica A 215, 61 (1995)] using a novel diagrammatic series approach. It is shown that the irreducible memory function in a theory of the relaxation of an autocorrelation function in a Markov model with detailed balance plays the same role as the part of the memory function approximated by a polynomial function of the autocorrelation function with positive coefficients in schematic simple mode coupling theories for supercooled liquids [W. Gotze, in Liquids, Freezing and the Glass Transition, D. Levesque, J. P. Hansen, J. Zinn-Justin eds., 287 (North Holland, New York, 1991)]. Sets of diagrams in the series for the irreducible memory function are summed which lead to approximations of this type. The behavior of these approximations is compared with known results from previous analytical calculations and from numerical simulations. For the simplest one dimensional model, relaxation equations that are closely related to schematic extended mode coupling theories [W. Gotze, ibid] are also derived using the diagrammatic series. Comparison of the results of these approximate theories with simulation data shows that these theories improve significantly on the results of the theories of the simple schematic mode coupling theory type. The potential implications for the further elaboration of mode coupling theories for supercooled liquids is discussed.

Pitts, Steven Jerome

270

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

271

Scale-independent spin effects in D-brane dynamics

We study spin interactions between two moving D-branes using the Green-Schwarz formalism of boundary states. We focus our attention on the leading terms for small velocities ?, of the form ?4?n\\/r7?p+n (?2?n\\/r3?p+n) for p?p (p?p + 4) systems, with 16 (8) supercharges. In analogy with standard GS computations of massless four-point one-loop amplitudes in Type I theory, the above terms

Jose F. Morales; Claudio A. Scrucca; Marco Serone

1998-01-01

272

On the theory of nonlinear spin wave dynamics in ferromagnetic films (abstract)

The aim of this work is to develop a theory of nonlinear spin waves (SW) in ferromagnetic films (FF) appropriate for description of rich nonlinear SW dynamics observed in Refs. 1 and 2. We use classical Hamiltonian formalism developed in Ref. 3 for unbounded ferromagnets in combination with the theory of dipole-exchange SW spectrum for FF.4 The main distinctions in

A. N. Slavin

1991-01-01

273

We analyze the recently developed folding algorithm (Bañuls et al 2009 Phys. Rev. Lett.102 240603) for simulating the dynamics of infinite quantum spin chains and we relate its performance to the kind of entanglement produced under the evolution of product states. We benchmark the accomplishments of this technique with respect to alternative strategies using Ising Hamiltonians with transverse and parallel

Alexander Müller-Hermes; J Ignacio Cirac; Mari Carmen Bañuls

2012-01-01

274

Dynamics of the spin-2 Bose condensate driven by external magnetic fields

Dynamic response of the F=2 spinor Bose-Einstein condensate (BEC) under the influence of external magnetic fields is studied. A general formula is given for the oscillation period to describe population transfer from the initial polar state to other spin states. We show that when the frequency and the reduced amplitude of the longitudinal magnetic field are related in a specific

Ping Zhang; C. K. Chan; Xiang-Gui Li; Qi-Kun Xue; Xian-Geng Zhao

2002-01-01

275

Dynamic spin-glass behavior in a disorder-free, two-component model of quantum frustrated magnets

NASA Astrophysics Data System (ADS)

Motivated by the observation of a spin-glass transition in almost disorder-free Kagome antiferromagnets, and by the specific form of the effective low-energy model of the S = 1/2, trimerized Kagome antiferromagnet, we investigate the possibility to obtain a spin-glass behavior in two-component, disorder-free models. We concentrate on a toy-model, a modified Ashkin-Teller model in a magnetic field that couples only to one species of spins, for which we prove that a dynamic spin-glass behavior occurs. The dynamics of the magnetization is closely related to that of the underlying Ising model in zero field in which spins and pseudo-spins are intimately coupled. The spin-glass like history dependence of the magnetization is a consequence of the ageing of the underlying Ising model.

Mila, F.; Dean, D.

2002-04-01

276

Two approaches to the description of spin dynamics of electron-nuclear system in quantum dots are compared: the quantum-mechanical one is based on direct diagonalization of the model Hamiltonian and semiclassical one is based on coupled equations for precession of mean electron spin and mean spin of nuclear spin fluctuations. The comparison was done for a model problem describing periodic excitation of electron-nuclear system by optical excitation. The computation results show that scattering of parameters related to fluctuation of the nuclear spin system leads to appearance of an ordered state in the system caused by periodic excitation and to the effect of electron-spin mode locking in an external magnetic field. It is concluded that both models can qualitatively describe the mode-locking effect, however give significantly different quantitative results. This may indicate the limited applicability of the precession model for describing the spin dynamics in quantum dots in the presence of optical pumping.

Petrov, M. Yu., E-mail: m.petrov@spbu.ru; Yakovlev, S. V. [Saint Petersburg State University (Russian Federation)

2012-08-15

277

Ultrafast spin dynamics and critical behavior in half-metallic ferromagnet: Sr2FeMoO6

Ultrafast spin dynamics in ferromagnetic half-metallic compound Sr2FeMoO6 is investigated by pump-probe measurements of the magneto-optical Kerr effect. The half-metallic nature of this material gives rise to anomalous thermal insulation between spins and electrons and allows us to pursue the spin dynamics from a few to several hundred picoseconds after the optical excitation. The optically detected magnetization dynamics clearly shows the crossover from microscopic photoinduced demagnetization to macroscopic critical behavior with universal power law divergence of relaxation time for a wide dynamical critical region. PMID:10970664

Kise; Ogasawara; Ashida; Tomioka; Tokura; Kuwata-Gonokami

2000-08-28

278

We show that spin-density separation in a Bose gas is not restricted to 1D but also occurs in higher dimensions. The ratio ({alpha}) of the intraspecies atom-atom interaction strength to the interspecies interaction strength strongly influences the dynamics of spin-density separation and the elementary excitations. The density wave is phononlike for all values of {alpha}. For {alpha}<1, the spin wave is also phononlike. The spin waves have a quadratic dispersion in the {alpha}=1 coupling regime, while in the phase separated regime ({alpha}>1) the spin waves are found to be damped. The dynamical structure factor reveals two distinct peaks corresponding to the density and spin waves for {alpha}{<=}1. For {alpha}>1 there is only one dynamical structure factor peak corresponding to the density wave.

Chung, M.-C.; Bhattacherjee, A. B. [Max-Planck-Institut fuer Physik komplexer Systeme, 01187 Dresden (Germany)

2008-08-15

279

Particle Spin Dynamics as the Grassmann Variant of Classical Mechanics.

National Technical Information Service (NTIS)

A generalization of the classical mechanics is presented. The dynamical variables are assumed to be elements of an algebra with anticommuting generators (The Grassmann algebra). The action functional and the Poisson brackets are defined. The equations of ...

F. A. Berezin M. S. Marinov

1976-01-01

280

NASA Astrophysics Data System (ADS)

Dynamical magnetic and nuclear polarization in complex spin systems is discussed on the example of transfer of spin from exciton to the central spin of magnetic impurity in a quantum dot in the presence of a finite number of nuclear spins. The exciton is described in terms of electron and heavy-hole spins interacting via exchange interaction with magnetic impurity, via hyperfine interaction with a finite number of nuclear spins and via dipole interaction with photons. The time evolution of the exciton, magnetic impurity and nuclear spins is calculated exactly between quantum jumps corresponding to exciton radiative recombination. The collapse of the wavefunction and the refilling of the quantum dot with a new spin-polarized exciton is shown to lead to the build up of magnetization of the magnetic impurity as well as nuclear spin polarization. The competition between electron spin transfer to magnetic impurity and to nuclear spins simultaneous with the creation of dark excitons is elucidated. The technique presented here opens up the possibility of studying optically induced dynamical magnetic and nuclear polarization in complex spin systems.

Abolfath, Ramin M.; Trojnar, Anna; Roostaei, Bahman; Brabec, Thomas; Hawrylak, Pawel

2013-06-01

281

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.

Herrera-Aguilar, Jose L.; Larralde, Hernan; Aldana, Maximino

2012-01-01

282

Spin-wave gap and spin dynamics of {gamma}-Mn alloys

The magnetic phase diagram of {gamma}-Mn alloys contains both collinear and noncollinear magnetic phases in fct and fcc crystal structures. Using a two-band model which incorporates the magnetoelastic coupling, we find that the gap {Delta}{sub sw}(T) in the spin-wave dispersion is proportional to the 3/2 power of the sublattice magnetization M(T), in agreement with experiments on both the collinear and noncollinear magnetic phases. For the noncollinear magnetic phases observed in MnNi and FeMn alloys, high-frequency excitations are predicted with {omega}({rvec q}=0){approximately}{Delta}, where 2{Delta} is the energy gap in the quasiparticle spectrum. {copyright} {ital 1998} {ital The American Physical Society}

Fishman, R.S. [Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831-6032 (United States); Liu, S.H. [Physics Department, University of California, San Diego, California 92093 (United States)

1998-09-01

283

NASA Astrophysics Data System (ADS)

The description of the tunneling of a macroscopic variable in the presence of a bath of localized spins is a subject of great fundamental and practical interest, and is relevant for many solid-state qubit designs. Most of the attention is usually given to the dynamics of the “central spin” (i.e., the qubit), while little is known about the spin bath itself. Here, we present a detailed study of the dynamics of the nuclear spin bath in the Mn12-ac single-molecule magnet, probed by NMR experiments down to very low temperatures (T?20mK) . The results are critically analyzed in the framework of the Prokof’ev-Stamp theory of nuclear-spin-mediated quantum tunneling. We find that the longitudinal relaxation rate of the Mn55 nuclei in Mn12-ac becomes roughly T independent below T?0.8K and can be strongly suppressed with a longitudinal magnetic field. This is consistent with the nuclear relaxation being caused by quantum tunneling of the molecular spin, and we attribute the tunneling fluctuations to the minority of fast-relaxing molecules present in the sample. The transverse nuclear relaxation is also T independent for T<0.8K , and can be explained qualitatively and quantitatively by the dipolar coupling between like nuclei in neighboring molecules. This intercluster nuclear spin diffusion mechanism is an essential ingredient for the global relaxation of the nuclear spin bath. We also show that the isotopic substitution of H1 by H2 leads to a slower nuclear longitudinal relaxation, consistent with the decreased tunneling probability of the molecular spin. Finally, we demonstrate that even at the lowest temperatures—where only T -independent quantum tunneling fluctuations are present—the nuclear spins remain in thermal equilibrium with the lattice phonons, and we investigate the time scale for their thermal equilibration. After a review of the theory of macroscopic spin tunneling in the presence of a spin bath, we argue that most of our experimental results are consistent with that theory, but the thermalization of the nuclear spins is not. This calls for an extension of the spin-bath theory to include the effect of spin-phonon couplings in the nuclear-spin-mediated tunneling process.

Morello, Andrea; de Jongh, L. J.

2007-11-01

284

NASA Astrophysics Data System (ADS)

A quantum kinetic study of correlated spin transfer between optically excited electrons and Mn atoms in a ZnMnSe quantum well is presented. The simulations predict genuine signatures of non-Markovian spin dynamics which are particularly pronounced for special two-color laser excitations with a zero net angular momentum where a Markovian theory predicts an almost zero total electron spin for all times. In contrast, in the quantum kinetic simulations a sizable total electron spin builds up. Subsequently, a coherent oscillatory exchange of spin between the electron and Mn subsystems is observed.

Thurn, C.; Cygorek, M.; Axt, V. M.; Kuhn, T.

2013-10-01

285

Spin-system dynamics and fault detection in threshold networks

We consider an agent on a fixed but arbitrary node of a known threshold network, with the task of detecting an unknown missing link. We obtain analytic formulas for the probability of success when the agent's tool is the free evolution of a single excitation on an XX spin system paired with the network. We completely characterize the parameters, which allows us to obtain an advantageous solution. From the results emerges an optimal (deterministic) algorithm for quantum search, from which a quadratic speedup with respect to the optimal classical analog and in line with well-known results in quantum computation is gained. When attempting to detect a faulty node, the chosen setting appears to be very fragile and the probability of success too small to be of any direct use.

Kirkland, Steve; Severini, Simone [Hamilton Institute, National University of Ireland, Maynooth County Kildare (Ireland); Department of Physics and Astronomy, University College London, WC1E 6BT London (United Kingdom)

2011-01-15

286

Memory effects in the dynamic response of a random two-spin Ising system

NASA Astrophysics Data System (ADS)

Motivated by magnetic memory effects observable in spin glasses we study an extremely simplified model system. It consists of two Ising spins with Glauber dynamics, whose equilibrium correlation is a rapidly and randomly changing function of the external field. As in spin glasses, a nonliear dynamic response appears even in the regime of linear static properties. We calculate (i) the linear and nonlinear ac susceptibility in zero field and (ii) the linear ac susceptibility as a function of the rate change of a slowly varying background field. Mathematically the problem is to deal with a stochastic differential equation with long-ranged correlations in time. For an oscillating field of sufficiently large amplitude H0 (but still in the statically linear regime) these correlations lead to nonanalytic correction terms sim H0^{-1} log H0 in the dynamic susceptibility. Motivé par des effets de mémoire observables dans les verres de spin l'on étudie un système modèle extrêmement simplifié. Ils se compose de deux spins d'Ising à dynamique de Glauber, dont la fonction de corrélation à l'équilibre varie rapidement et aléatoirement en fonction du champ extérieur. Comme dans les verres de spin, une réponse dynamique non linéaire apparaît déjà dans le régime linéaire des propriétés statiques. On calcule (i) les susceptibilités alternatives linéaire et non linéaire en champ zéro et (ii) la susceptibilité alternative linéaire en fonction du taux de variation d'un champ primaire à variation lente. Le problème mathématique consiste en une équation différentielle stochastique avec des corrélations temporelles de longue portée. Pour un champ oscillant d'amplitude H0 suffisamment grande (mais toujours dans le régime statiquement linéaire) ces corrélations conduisent à des termes correctifs non analytiques sim H0^{-1} log H0 dans la susceptibilité dynamique.

Nifle, M.; Hilhorst, H. J.

1991-01-01

287

NASA Astrophysics Data System (ADS)

The so-called 'spin ices' form when exchange interactions, crystal fields, and dipolar interactions are in a delicate balance. This gives rise to a ground state which has a considerable amount of residual spin entropy, much like the proton entropy in water ice through the freezing transition. Recently, 'stuffed' spin ices have provided a means to probe how delicate a balance is needed to stabilize the disordered ground state. Surprisingly, it is found that an increase of the density of spins results in very little change in the residual entropy, which leads to the interesting idea that residual entropy states might be more common than once believed for magnetism. In this communication, we detail the crystal growth of stuffed spin ice Ho2.3Ti1.7O7-?, and we complete neutron scattering experiments to observe how the spins order at low temperatures. It is found that even with this large perturbation, the system still has some key signatures of the spin ice state, but the spin dynamics is significantly altered. With this new data, an explanation emerges for the zero-point entropy in the stuffed spin ices.

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

2007-08-01

288

Nonequilibrium dynamical phase transition of 3D kinetic Ising/Heisenberg spin system

NASA Astrophysics Data System (ADS)

We have studied the nonequilibrium dynamic phase transitions of both three-dimensional (3D) kinetic Ising and Heisenberg spin systems in the presence of a perturbative magnetic field by Monte Carlo simulation. The feature of the phase transition is characterized by studying the distribution of the dynamical order parameter. In the case of anisotropic Ising spin system (ISS), the dynamic transition is discontinuous and continuous under low and high temperatures respectively, which indicates the existence of a tri-critical point (TCP) on the phase \\linebreak boundary separating low-temperature order phase and high-temperature disorder phase. The TCP shifts towards the higher temperature region with the decrease of frequency, i.e. TTCP=1.33×exp(-omega/30.7). In the case of the isotropic Heisenberg spin system (HSS), however, the situation on dynamic phase transition of HSS is quite different from that of ISS in that no stable dynamical phase transition was observed in kinetic HSS after a threshold time. The evolution of magnetization in the HSS driven by a symmetrical external field after a certain duration always tends asymptotically to a disorder state no matter what an initial state the system starts with. The threshold time tau depends upon the amplitude H0, reduced temperature T/TC and the frequency omega as tau = C.omegaalpha.H0-beta.(T/TC)-gamma.

Shao, Yuan-Zhi; Lai, J. K. L.; Shek, C. H.; Lin, Guang-Ming; Lan, Tu

2004-02-01

289

Dynamic observation of pulmonary perfusion using continuous arterial spin-labeling in a pig model.

The continuous arterial spin-labeling (CASL) method of perfusion MRI is used to observe pulmonary perfusion dynamically in an animal model. Specifically, a respiratory-triggered implementation of the CASL method is used with approximate spatial resolution of 0.9 x 1.8 x 5.0 mm (0.008 cc) and 2-minute temporal resolution. Perfusion MRI is performed dynamically during repeated balloon occlusion of a segmental pulmonary artery, as well as during pharmacological stimulation. A total of three Yorkshire pigs were studied. The results demonstrate the ability of the endogenous spin-labeling method to characterize the dynamic changes in pulmonary perfusion that occur during important physiological alterations. PMID:11477677

Roberts, D A; Rizi, R R; Lipson, D A; Ferrante, M A; Bearn, L; Rolf, L; Baumgardner, J; Yamomoto, A; Hatabu, H; Hansen-Flaschen, J; Gefter, W B; Schnall, M D

2001-08-01

290

Spin-torque-induced rotational dynamics of a magnetic vortex dipole

NASA Astrophysics Data System (ADS)

We study, both experimentally and by numerical modeling, the magnetic dynamics that can be excited in a magnetic thin-film nanopillar device using the spin torque from a spatially localized current injected via a tens-of-nanometer-diameter aperture. The current-driven magnetic dynamics can produce large-amplitude microwave emission at zero magnetic field, with a frequency well below that of the uniform ferromagnetic resonance mode. Micromagnetic simulations indicate that the physical origin of this efficient microwave nano-oscillator is the nucleation and subsequent steady-state rotational dynamics of a magnetic vortex dipole driven by the localized spin torque. The results show that this implementation of a spintronic nano-oscillator is a promising candidate for microwave technology applications.

Finocchio, G.; Ozatay, O.; Torres, L.; Buhrman, R. A.; Ralph, D. C.; Azzerboni, B.

2008-11-01

291

NASA Astrophysics Data System (ADS)

Antiferromagnetic (AFM) materials with zero or vanishingly small macroscopic magnetization are nowadays the constituent elements of spintronic devices. However, the possibility to use them as active elements that show nontrivial and controllable magnetic dynamics is still discussible. In the present paper we extend the phenomenologic theory [Andreev and Marchenko, Sov. Phys. Usp.SOPUAP0038-567010.1070/PU1980v023n01ABEH004859 23, 21 (1980)] of macroscopic dynamics in AFM materials for the cases typical for spin-valve devices. In particular, we consider the solidlike magnetic dynamics of AFM materials with strong exchange coupling in the presence of a spin-polarized current and give the general expression for the current-induced Rayleigh dissipation function in terms of the rotation vector for different types of AFMs. Based on the analysis of linearized equations of motion we predict the current-induced spin reorientation and AFM resonance, and find the values of critical currents in terms of AFMR frequencies and damping constants. The possibility of a current-induced spin-diode effect and second-harmonic generation in the AFM layer is also shown.

Gomonay, Helen V.; Kunitsyn, Roman V.; Loktev, Vadim M.

2012-04-01

292

Problem of temperature dependence in the dynamic spin-fluctuation theory for strong ferromagnets

NASA Astrophysics Data System (ADS)

Temperature dependence of the magnetic characteristics of Fe and Fe-Ni Invar is considered in the dynamic nonlocal approximation of the spin-fluctuation theory. Calculations by several numerical methods show that the magnetic characteristics can have a discontinuous jump at high temperatures, well below the Curie temperature. Using the methods of catastrophe theory, we investigate the effect of small changes in the initial data on the results of the calculation. It is demonstrated that the discontinuous jump can only be smoothed but cannot be eliminated entirely without a significant change in the system of equations of the spin-fluctuation theory. Possible variants of such changes are discussed.

Reser, B. I.; Melnikov, N. B.

2008-07-01

293

Polarized-neutron study of spin dynamics in the Kondo insulator YbB12.

Inelastic neutron scattering experiments have been performed on the archetype compound YbB(12), using neutron polarization analysis to separate the magnetic signal from the phonon background. With decreasing temperature, components characteristic for a single-site spin-fluctuation dynamics are suppressed, giving place to specific, strongly Q-dependent, low-energy excitations near the spin-gap edge. This crossover is discussed in terms of a simple crystal-field description of the incoherent high-temperature state and a predominantly local mechanism for the formation of the low-temperature singlet ground state. PMID:17930630

Nemkovski, K S; Mignot, J-M; Alekseev, P A; Ivanov, A S; Nefeodova, E V; Rybina, A V; Regnault, L-P; Iga, F; Takabatake, T

2007-09-26

294

The spin-1/2 kagome lattice antiferromagnet herbertsmithite, ZnCu(3)(OH)(6)Cl(2), is a candidate material for a quantum spin liquid ground state. We show that the magnetic response of this material displays an unusual scaling relation in both the bulk ac susceptibility and the low energy dynamic susceptibility as measured by inelastic neutron scattering. The quantity chiT(alpha) with alpha approximately 0.66 can be expressed as a universal function of H/T or omega/T. This scaling is discussed in relation to similar behavior seen in systems influenced by disorder or by the proximity to a quantum critical point. PMID:20481955

Helton, J S; Matan, K; Shores, M P; Nytko, E A; Bartlett, B M; Qiu, Y; Nocera, D G; Lee, Y S

2010-04-06

295

Nucleation and dynamics of magnetic vortices under spin-polarized current

NASA Astrophysics Data System (ADS)

Spin-polarized current in a ferromagnet is known to lead to the instability of the uniformly magnetized state. In this paper, it is demonstrated by micromagnetic simulations that, in films or wide wires, the above instability is followed by the formation of magnetic vortices. Subsequent magnetization dynamics is also studied in terms of vortices, which includes pair dynamics and pair annihilation. Using a simple analytical model that considers the vortices as points, the dynamics of two interacting vortices under the current is classified according to their vorticity and polarity. This explains well the essential features of the simulation results.

Nakatani, Yoshinobu; Shibata, Junya; Tatara, Gen; Kohno, Hiroshi; Thiaville, André; Miltat, Jacques

2008-01-01

296

Static versus Dynamic Heterogeneities in the D=3 Edwards-Anderson-Ising Spin Glass

NASA Astrophysics Data System (ADS)

We numerically study the aging properties of the dynamical heterogeneities in the Ising spin glass. We find that a phase transition takes place during the aging process. Statics-dynamics correspondence implies that systems of finite size in equilibrium have static heterogeneities that obey finite-size scaling, thus signaling an analogous phase transition in the thermodynamical limit. We compute the critical exponents and the transition point in the equilibrium setting, and use them to show that aging in dynamic heterogeneities can be described by a finite-time scaling ansatz, with potential implications for experimental work.

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

2010-10-01

297

The kinetic spin-1 Blume-Capel model with Glauber dynamic

NASA Astrophysics Data System (ADS)

We study the dynamic phase transitions (DPT), within a mean-field approach, in the kinetic spin-1 Blume-Capel model by using the Glauber-type stochastic dynamics. The nature of the transition is characterized by investigating the behavior of the thermal variation of the dynamic order parameter and the Lyapunov exponent. The phase diagram is constructed in the temperatures ( T) and single-ion anisotropy amplitude ( D) plane. Our results predict first-order transitions at low temperature and large anisotropy strengths, which correspond in the phase diagram to the existence of a nonequilibrium tricritical point (TCP). We compare our results with the equilibrium phase diagram.

Costabile, E.; Salmon, O. R.; de Sousa, J. R.

2012-04-01

298

Dynamics in One-Dimensional Spin Systems - Density Matrix Renormalization Group Study

NASA Astrophysics Data System (ADS)

We study the one-dimensional S = 1/2 Heisenberg model with an uniform and a staggered magnetic fields, using the dynamical density-matrix renormalization group (DDMRG) technique. The DDMRG enables us to investigate the dynamical properties of chain with lengths up to a few hundreds, and the results are numerically exact in the same sense as 'exact diagonalization' results are. Thus, we can analyze the low-energy spectrum almost in the thermodynamic limit. In this work, we calculate the dynamical spin structure factor and demonstrate the performance of the DDMRG method applying the open-end boundary conditions as well as the periodic boundary conditions.

Nishimoto, S.; Arikawa, M.

299

Dynamics in One-Dimensional Spin Systems - Density Matrix Renormalization Group Study

NASA Astrophysics Data System (ADS)

We study the one-dimensional S = 1/2 Heisenberg model with an uniform and a staggered magnetic fields, using the dynamical density-matrix renormalization group (DDMRG) technique. The DDMRG enables us to investigate the dynamical properties of chain with lengths up to a few hundreds, and the results are numerically exact in the same sense as `exact diagonalization' results are. Thus, we can analyze the low-energy spectrum almost in the thermodynamic limit. In this work, we calculate the dynamical spin structure factor and demonstrate the performance of the DDMRG method applying the open-end boundary conditions as well as the periodic boundary conditions.

Nishimoto, S.; Arikawa, M.

2007-09-01

300

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

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 [Dipartimento di Fisica, Universita della Calabria, I-87036 Arcavacata di Rende (Italy); INFN - Gruppo collegato di Cosenza, I-87036 Arcavacata di Rende, Cosenza (Italy); Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen's University, Belfast BT7 1NN (United Kingdom); Plastina, Francesco [Dipartimento di Fisica, Universita della Calabria, I-87036 Arcavacata di Rende (Italy); INFN - Gruppo collegato di Cosenza, I-87036 Arcavacata di Rende, Cosenza (Italy); Paternostro, Mauro [Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen's University, Belfast BT7 1NN (United Kingdom)

2011-09-15

301

Systematic perturbation approach for a dynamical scaling law in a kinetically constrained spin model

NASA Astrophysics Data System (ADS)

The dynamical behaviours of a kinetically constrained spin model (Fredrickson-Andersen model) on a Bethe lattice are investigated by a perturbation analysis that provides exact final states above the nonergodic transition point. It is observed that the time-dependent solutions of the derived dynamical systems obtained by the perturbation analysis become systematically closer to the results obtained by Monte Carlo simulations as the order of the perturbation series is increased. This systematic perturbation analysis also clarifies the existence of a dynamical scaling law, which provides an implication for a universal relation between a size scale and a timescale near the nonergodic transition.

Ohta, Hiroki

2011-01-01

302

The main contribution of this paper is to identify the need for a quantitative management-tool to manage organisational competencies in International Supply Chains in order to ensure the long-term survival of an International Supply Networks though complex and dynamic environments. Additionally contributions and limitations of existing tools in strategic controlling in respect to managing organisational competencies in International Supply Networks

Michael Hülsmann; Linda Austerschulte; Jörn Grapp

303

Alamethicin F50/5 is a hydrophobic peptide that is devoid of charged residues and that induces voltage-dependent ion channels in lipid membranes. The peptide backbone is likely to be involved in the ion conduction pathway. Electron spin-echo spectroscopy of alamethicin F50/5 analogs in which a selected Aib residue (at position n = 1, 8, or 16) is replaced by the TOAC amino-acid spin label was used to study torsional dynamics of the peptide backbone in association with phosphatidylcholine bilayer membranes. Rapid librational motions of limited angular amplitude were observed at each of the three TOAC sites by recording echo-detected spectra as a function of echo delay time, 2?. Simulation of the time-resolved spectra, combined with conventional EPR measurements of the librational amplitude, shows that torsional fluctuations of the peptide backbone take place on the subnanosecond to nanosecond timescale, with little temperature dependence. Associated fluctuations in polar fields from the peptide could facilitate ion permeation.

Bartucci, Rosa; Guzzi, Rita; De Zotti, Marta; Toniolo, Claudio; Sportelli, Luigi; Marsh, Derek

2008-01-01

304

Simulation of spin dynamics: a tool in MRI system development

NASA Astrophysics Data System (ADS)

Magnetic Resonance Imaging (MRI) is a routine diagnostic tool in the clinics and the method of choice in soft-tissue contrast medical imaging. It is an important tool in neuroscience to investigate structure and function of the living brain on a systemic level. The latter is one of the driving forces to further develop MRI technology, as neuroscience especially demands higher spatiotemporal resolution which is to be achieved through increasing the static main magnetic field, B0. Although standard MRI is a mature technology, ultra high field (UHF) systems, at B0 >= 7 T, offer space for new technical inventions as the physical conditions dramatically change. This work shows that the development strongly benefits from computer simulations of the measurement process on the basis of a semi-classical, nuclear spin-1/2 treatment given by the Bloch equations. Possible applications of such simulations are outlined, suggesting new solutions to the UHF-specific inhomogeneity problems of the static main field as well as the high-frequency transmit field.

Stöcker, Tony; Vahedipour, Kaveh; Shah, N. Jon

2011-05-01

305

The model used to describe the spin dynamics in quantum dots after optical excitation is considered. Problems of the electron-spin polarization decay and the dependence of the steady-state polarization on magnetic field are solved on the basis of exact diagonalization of the model Hamiltonian. An important role of the nuclear state is shown and methods of its calculation for different regimes of optical excitation are proposed. The effect of spin echo generation after application of a {pi} pulse of a magnetic field is predicted for the system under consideration.

Kozlov, G. G. [St. Petersburg State University, Institute of Physics (Russian Federation)], E-mail: gkozlov@photonics.phys.spbu.ru

2007-10-15

306

The technological concept of 'digital alloying' offered by molecular-beam epitaxy is demonstrated to be a very effective tool for tailoring static and dynamic magnetic properties of diluted magnetic semiconductors. Compared to common 'disordered alloys' with the same Mn concentration, the spin-lattice relaxation dynamics of magnetic Mn ions has been accelerated by an order of magnitude in (Cd,Mn)Te digital alloys, without any noticeable change in the giant Zeeman spin splitting of excitonic states, i.e., without effect on the static magnetization. The strong sensitivity of the magnetization dynamics to clustering of the Mn ions opens a degree of freedom for spin engineering.

Kneip, M.K.; Yakovlev, D.R.; Bayer, M.; Karczewski, G.; Wojtowicz, T.; Kossut, J. [Experimentelle Physik II, Universitaet Dortmund, D-44221 Dortmund (Germany); Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw (Poland)

2006-04-10

307

Competing orders and spin-density-wave instability in La(O1-xFx)FeAs

The interplay between different ordered phases, such as superconducting, charge or spin ordered phases, is of central interest in condensed-matter physics. The very recent discovery of superconductivity with a remarkable Tc=26 K in Fe-based oxypnictide La(O1-xFx)FeAs (see Kamihara Y. et al., J. Am. Chem. Soc., 130 (2008) 3296) is a surprise to the scientific community and has generated tremendous interest.

J. Dong; H. J. Zhang; G. Xu; Z. Li; G. Li; W. Z. Hu; D. Wu; G. F. Chen; X. Dai; Z. Fang; N. L. Wang

2008-01-01

308

Dynamical decoupling of a single-electron spin at room temperature

NASA Astrophysics Data System (ADS)

Here we report the increase of the coherence time T2 of a single-electron spin at room temperature by using dynamical decoupling. We show that the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can prolong the T2 of a single nitrogen-vacancy center in diamond up to 2.44 ms compared to the Hahn echo measurement where T2=400?s. Moreover, by performing spin-locking experiments we demonstrate that with CPMG the maximum possible T2 is reached. On the other hand, we do not observe a strong increase of the coherence time in nanodiamonds, possibly due to the short spin-lattice relaxation time T1=100?s (compared to T1=5.93 ms in bulk). An application for detecting low magnetic fields is demonstrated, where we show that the sensitivity using the CPMG method is improved by about a factor of 2 compared to the Hahn echo method.

Naydenov, Boris; Dolde, Florian; Hall, Liam T.; Shin, Chang; Fedder, Helmut; Hollenberg, Lloyd C. L.; Jelezko, Fedor; Wrachtrup, Jörg

2011-02-01

309

Dynamics of the spin Hall effect in topological insulators and graphene

NASA Astrophysics Data System (ADS)

A single two-dimensional Dirac cone with a mass gap produces a quantized (spin) Hall step in the absence of magnetic field. What happens in strong electric fields? This question is investigated by analyzing time evolution and dynamics of the spin Hall effect. After switching on a longitudinal electric field, a stationary Hall current is reached through damped oscillations. The Hall conductivity remains quantized as long as the electric field (E) is too weak to induce Landau-Zener transitions, but quantization breaks down for strong fields and the conductivity decreases as 1/E. These apply to the spin-Hall conductivity of graphene and the Hall and magnetoelectric response of topological insulators.

Dóra, Balázs; Moessner, Roderich

2011-02-01

310

Spin dynamics of the triangular lattice antiferromagnet ?-SrCr2O4

NASA Astrophysics Data System (ADS)

We study the spin dynamics of the layered S=3/2 triangular lattice antiferromagnet ?-SrCr2O4 by means of inelastic neutron scattering on powder and single-crystal specimen. While the incommensurate long-range order observed below TN=43K resembles the usual 120^o-structure predicted for the perfect triangular lattice antiferromagnet, a spin-wave theory fit to the entire single-crystal dataset reveals strongly distorted exchange interactions. The extreme sensitivity of direct-exchange interactions to the small static Cr^3+-Cr^3+ distance variations reported by neutron diffraction, is quantitatively confirmed by ab-initio calculations that corroborate the spin-wave theory results.

Mourigal, M.; Wen, J.-J.; Wan, Y.; Koohpayeh, S.; Valdés Aguilar, R.; Armitage, N. P.; Tchernyshov, O.; Broholm, C. L.; Dutton, S.; Cava, R. J.; Birol, T.; Das, H.; Fennie, C. J.; Lin, L.; Liu, J.-M.; Stone, M. B.; Tian, W.

2013-03-01

311

Experimental test of the new analytic matrix formalism for spin dynamics

NASA Astrophysics Data System (ADS)

We recently started testing Chao’s proposed new matrix formalism for describing the spin dynamics due to a single spin resonance. The Chao formalism is probably the first fundamental improvement of the Froissart-Stora equation in that it allows analytic calculations of the beam polarization’s behavior inside a resonance. We tested the Chao formalism using a 1.85GeV/c polarized deuteron beam stored in COSY, by sweeping an rf dipole’s frequency through 200 Hz, while varying the distance from the sweep’s end frequency to an rf-induced spin resonance’s central frequency. Since the Froissart-Stora equation itself can make no prediction inside a resonance, we compared our experimental data with the predictions of the Chao formalism and those of an empirical two-fluid model based on the Froissart-Stora equation. The data strongly favor the Chao formalism.

Morozov, V. S.; Chao, A. W.; Krisch, A. D.; Leonova, M. A.; Raymond, R. S.; Sivers, D. W.; Wong, V. K.; Gebel, R.; Lehrach, A.; Lorentz, B.; Maier, R.; Prasuhn, D.; Stockhorst, H.; Hinterberger, F.; Ulbrich, K.; Schnase, A.

2007-04-01

312

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

313

Dynamic nuclear spin polarization in the resonant laser excitation of an InGaAs quantum dot.

Resonant optical excitation of lowest-energy excitonic transitions in self-assembled quantum dots leads to nuclear spin polarization that is qualitatively different from the well-known optical orientation phenomena. By carrying out a comprehensive set of experiments, we demonstrate that nuclear spin polarization manifests itself in quantum dots subjected to finite external magnetic field as locking of the higher energy Zeeman transition to the driving laser field, as well as the avoidance of the resonance condition for the lower energy Zeeman branch. We interpret our findings on the basis of dynamic nuclear spin polarization originating from noncollinear hyperfine interaction and find excellent agreement between experiment and theory. Our results provide evidence for the significance of noncollinear hyperfine processes not only for nuclear spin diffusion and decay, but also for buildup dynamics of nuclear spin polarization in a coupled electron-nuclear spin system. PMID:23003088

Högele, A; Kroner, M; Latta, C; Claassen, M; Carusotto, I; Bulutay, C; Imamoglu, A

2012-05-09

314

A general approach for the prediction of EPR spectra directly and completely from single dynamical trajectories generated from Molecular Dynamics (MD) simulations is described. The approach is applicable to an arbitrary system of electron and nuclear spins described by a general form of the spin-Hamiltonian for the entire motional range. It is shown that for a reliable simulation of motional EPR spectra only a single truncated dynamical trajectory generated until the point when correlation functions of rotational dynamics are completely relaxed is required. The simulation algorithm is based on a combination of the propagation of the spin density matrix in the Liouville space for this initial time interval and the use of well defined parameters calculated entirely from the dynamical trajectory for prediction of the evolution of the spin density matrix at longer times. A new approach is illustrated with the application to a nitroxide spin label MTSL attached to the protein sperm whale myoglobin. It is shown that simulation of the EPR spectrum, which is in excellent agreement with experiment, can be achieved from a single MD trajectory. Calculations reveal the complex nature of the dynamics of a spin label which is a superposition of the fast librational motions within dihedral states, of slow rotameric dynamics among different conformational states of the nitroxide tether and of the slow rotational diffusion of the protein itself. The significance of the slow rotameric dynamics of the nitroxide tether on the overall shape of the EPR spectrum is analysed and discussed. PMID:21279205

Oganesyan, Vasily S

2011-01-31

315

Trapping membrane proteins in the confines of a crystal lattice obscures dynamic modes essential for interconversion between multiple conformations in the functional cycle. Moreover, lattice forces could conspire with detergent solubilization to stabilize a minor conformer in an ensemble thus confounding mechanistic interpretation. Spin labeling in conjunction with electron paramagnetic resonance (EPR) spectroscopy offers an exquisite window into membrane protein dynamics in the native–like environment of a lipid bilayer. Systematic application of spin labeling and EPR identifies sequence-specific secondary structures, defines their topology and their packing in the tertiary fold. Long range distance measurements (60-80Å) between pairs of spin labels enable quantitative analysis of equilibrium dynamics and triggered conformational changes. This review highlights the contribution of spin labeling to bridging structure and mechanism. Efforts to develop methods for determining structures from EPR restraints and to increase sensitivity and throughput promise to expand spin labeling applications in membrane protein structural biology.

Mchaourab, Hassane S.; Steed, P. Ryan; Kazmier, Kelli

2011-01-01

316

NASA Astrophysics Data System (ADS)

A pendulum prepared perfectly inverted and motionless is a prototype of unstable equilibrium and corresponds to an unstable hyperbolic fixed point in the dynamical phase space. Here, we measure the non-equilibrium dynamics of a spin-1 Bose-Einstein condensate initialized as a minimum uncertainty spin-nematic state to a hyperbolic fixed point of the phase space. Quantum fluctuations lead to non-linear spin evolution along a separatrix and non-Gaussian probability distributions that are measured to be in good agreement with exact quantum calculations up to 0.25s. At longer times, atomic loss due to the finite lifetime of the condensate leads to larger spin oscillation amplitudes, as orbits depart from the separatrix. This demonstrates how decoherence of a many-body system can result in apparent coherent behaviour. This experiment provides new avenues for studying macroscopic spin systems in the quantum limit and for investigations of important topics in non-equilibrium quantum dynamics.

Gerving, C. S.; Hoang, T. M.; Land, B. J.; Anquez, M.; Hamley, C. D.; Chapman, M. S.

2012-11-01

317

NASA Astrophysics Data System (ADS)

Stochastic dynamical reduction for the case of spin- z measurement of a spin-1/2 particle describes a random walk on the spin- z axis. The measurement's result depends on which of the two points: spin- z=± ?/2 is reached first. Born's rule is recovered as long as the expected step size in spin- z is independent of proximity to endpoints. Here, we address the questions raised by this description: (1) When is collapse triggered, and what triggers it? (2) Why is the expected step size in spin- z (as opposed to polar angle) independent of proximity to endpoints? (3) Why does spin "lock" in the vertical directions? The difficulties associated with (1) are rooted, as is Bell's theorem, in the time-asymmetric assumption that the present distribution over hidden variables is independent of future settings. We believe, a priori of any of the experiments of modern physics, that such a time-asymmetric assumption is dubious when probing the microscopic scale. As for (2) and (3), they are simultaneously resolved by abandoning the fundamental distinction drawn between spin and spatial angular momentum, and by appealing to very tiny (in both magnitude and spatial extent) but numerous patches of magnetic noise in the Stern-Gerlach's field.

Halabi, T.

2013-10-01

318

Coherent spin oscillations and non-linear dynamics in two quantum magnets

NASA Astrophysics Data System (ADS)

I present experimental studies of the low-temperature linear and nonlinear AC magnetic behavior of two insulating magnetic materials: the dilute Ising magnet Lithium Yttrium Holmium Tetraflouride (LiHo0.045Y0.955 F4); and the frustrated Heisenberg magnet Neodymium Gadolinium Gallium Garnet (NdxGd3-xGa5O12 for x={0.01, 0.05, 0.1}). We find that under certain thermodynamic limits, LiHo 0.045Y0.955F4 can be continuously tuned between competing low-temperature states by cooling the sample in an external, DC magnetic field. Furthermore, we demonstrate the magnetic pump/probe technique as a powerful tool to quantify the stability of the magnetic state in the presence of disorder, and to probe the coupling between the spin states and the incoherent nuclear spin bath. In addition, I present susceptibility data for the three different concentrations of NdxGd3-x Ga5O12, which show that the doped samples possess the same coherent spin degrees of freedom as is seen in the pure sample. We find that even in the lightest-doped sample (0.1%), the presence of disorder suppresses the onset of Antiferromagnetic order by a factor of two, and that any transition in the other samples (0.5% and 1%) must be below 50 mK.

Schmidt, Michael Andrew

319

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

320

Spin-orbital entanglement due to dynamical Jahn-Teller effect

NASA Astrophysics Data System (ADS)

Quantum spin liquid (QSL) state is one of the fascinating themes in correlated electron systems. Recently, a new candidate of the QSL state is experimentally reported in a layered copper oxide Ba3CuSb2O9. In this material, a Cu^2+ has the eg orbital degree of freedom and the dynamical Jahn-Teller effect (DJTE) is suggested to play a key role for the emergence of the QSL state. Motivated from the recent experiments in Ba3CuSb2O9, we study the DJTE in the spin-orbital coupled system and examine a possibility of the QSL state in a spin-orbital system with lattice vibrations. In particular, we focus on the competitive or cooperative phenomena between the superexchange (SE) interaction and the DJTE. A SE interaction Hamiltonian is derived from the d-p type Hamiltonian and the DJTE Hamiltonian for the low-lying vibronic states is represented by the orbital pseudo-spin and the lattice vibration. We analyze the model, where these two interactions are taken into account on a honeycomb lattice, by using the cluster mean-field approximation with the exact diagonalization (ED) method and the combined method of the quantum Monte-Carlo method and ED method. We find that magnetic orders are unstable in a wide parameter region and a spin-singlet dimer state associated with an orbital order is realized. With increasing the DJTE, the orbital order is strongly suppressed and a resonance state of the spin-orbital dimers appears. We confirm that the spin and orbital degrees of freedom are strongly entangled with each other in this resonance state.

Nasu, Joji; Ishihara, Sumio

2013-03-01

321

Optimal control of coupled spin dynamics in the presence of relaxation

NASA Astrophysics Data System (ADS)

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 approach these bounds and maximize the sensitivity of the experiments. The two systems examined in detail in this thesis, arising in the context of protein NMR spectroscopy, are a coupled heteronuclear spin pair and an Ising spin chain. New schemes for coherence and polarization transfer are found, which yield substantial gains in transfer efficiency, compared to the traditionally used pulse sequences. From the standpoint of mathematical control theory, the problems arising in connection with optimal manipulation of dissipative quantum dynamics, motivate the study of a class of dissipative bilinear control systems and the computation of their reachable sets. For these systems we show that the optimal solution, corresponding to the maximization of transfer efficiency, and the reachable set can be found by solving a semidefinite program.

Stefanatos, Dionisis

322

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

323

Dynamic spin correlations in the frustrated cubic phase of MnV2O4

NASA Astrophysics Data System (ADS)

The ferrimagnetic spinel MnV2O4 undergoes an orbital-induced cubic-to-tetragonal distortion at TYK=58 K, below which noncollinear commensurate ferrimagnetic ordering occurs. Using inelastic neutron scattering, we investigated low-energy dynamics in its cubic phase above TYK. We observed two types of coexisting short-range magnetic excitations: the dispersive spin waves centered around the Brillouin-zone centers, k0 = (0, 0, 0), and quasielastic spin fluctuations centered at incommensurate wave vectors, kincom = (?, ?, 0). The coexistence of the two distinct features can be understood as a dynamic realization of the conical spiral order observed in cubic spinels such as CoCr2O4.

Chung, Jae-Ho; Song, Young-Sang; Kim, J.-H.; Suzuki, T.; Katsufuji, T.; Matsuda, M.; Lee, S.-H.

2013-09-01

324

NASA Astrophysics Data System (ADS)

The magnetic properties of the mixed spin-1 and spin-5/2 Ising system with a crystal-field interaction in the presence of a time-varying oscillating external magnetic field on a hexagonal lattice are studied using the Glauber-type stochastic dynamics. The lattice is formed by alternate layers of spins ?=1 and S=5/2. The set of mean-field dynamic equations is obtained by employing the Master equation. These equations are solved and firstly, the time variations of the average sublattice magnetizations are investigated in order to find the phases in the system. Then, the thermal behaviors of the dynamic sublattice magnetizations and the dynamic total magnetization are also investigated to obtain the dynamic phase transition points and the dynamic compensation temperatures. From this investigation, the nature (continuous and discontinuous) of the phase transitions and the type of the compensation behavior are determined. The dynamic phase diagrams are presented for both the presence and absence of the dynamic compensation temperatures in the nine different planes. It was found that the system exhibits five fundamental phases, nine different mixed phases which are composed of binary and ternary combinations of fundamental phases and the compensation temperature or the N-type behavior in the Néel classification nomenclature.

Özk?l?ç, Ay?egül; Temizer, Ümüt

2013-03-01

325

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

326

Magnetic soft x-ray microscopy-imaging fast spin dynamics inmagnetic nanostructures

Magnetic soft X-ray microscopy combines 15nm spatial resolution with 70ps time resolution and elemental sensitivity. Fresnel zone plates are used as X-ray optics and X-ray magnetic circular dichroism serves as magnetic contrast mechanism. Thus scientifically interesting and technologically relevant low dimensional nanomagnetic systems can be imaged at fundamental length and ultrafast time scales in a unique way. Studies include magnetization reversal in magnetic multilayers, nanopatterned systems, vortex dynamics in nanoelements and spin current induced phenomena.

Fischer, Peter; Kim, Dong-Hyun; Mesler, Brooke L.; Chao, Weilun; Sakdinawat, Anne E.; Anderson, Erik H.

2007-06-01

327

Critical dynamics near the glass transition as explored with muon spin relaxation

The dynamics of two molecular glass formers are monitored at microsecond scales via muon spin relaxation. Measurements in transverse magnetic fields display unambiguous signatures of critical behavior at temperatures somewhat above those signaling the thermodynamic glass transition, namely at the onset of stochastic molecular motions. The temperature dependence of transverse relaxation rates and amplitudes is found to provide accurate and unbiased estimates for a critical temperature T{sub c} as predicted by kinetic theories of the glass transition.

Bermejo, F.J.; Bustinduy, I. [C.S.I.C. - Department of Electricity and Electronics, Universidad Basque Country, P.O. Box 644 Bilbao 48080 (Spain); Consejo Superior de Investigaciones Cientificas, Serrano 123, E-28006 Madrid (Spain); Gonzalez, M.A. [Institut Laue Langevin, Boite Postale 156x, F-38042 Grenoble Cedex 9 (France); Chong, S.H. [Laboratoire de Physique Mathematique et Theorique, Universite Montpellier II, 34095 Montpellier (France); Cabrillo, C. [Instituto de Estructura de la Materia, Consejo Superior de Investigaciones Cientificas, Serrano 123, E-28006 Madrid (Spain); Cox, S.F.J. [ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX (United Kingdom); Condensed Matter and Materials Physics Group, University College London, WC1E 6BT (United Kingdom)

2004-12-01

328

Exact Edge Singularities and Dynamical Correlations in Spin1\\/2 Chains

Exact formulas for the singularities of the dynamical structure factor, Szz(q,omega), of the S=1\\/2 xxz spin chain at all q and any anisotropy and magnetic field in the critical regime are derived, expressing the exponents in terms of the phase shifts which are known exactly from the Bethe ansatz solution. We also study the long-time asymptotics of the self-correlation function

Rodrigo G. Pereira; Steven R. White; Ian Affleck

2008-01-01

329

Exact Edge Singularities and Dynamical Correlations in Spin1\\/2 Chains

Exact formulas for the singularities of the dynamical structure factor,\\u000aS^{zz}(q,omega), of the S=1\\/2 xxz spin chain at all q and any anisotropy and\\u000amagnetic field in the critical regime are derived, expressing the exponents in\\u000aterms of the phase shifts which are known exactly from the Bethe ansatz\\u000asolution. We also study the long time asymptotics of the self-correlation

Rodrigo G. Pereira; Steven R. White; Ian Affleck

2008-01-01

330

Solid-State Nuclear Spin-Flip Maser Pumped by Dynamic Nuclear Polarization

We report the observation of a coherent, maser-type rf radiation of the 27Al nuclear-spin system in Al2O3: Cr3+ pumped by dynamic nuclear polarization to negative temperature. A theoretical description is presented for the sharp, superradiant bursts which follow the fast tuning of a resonant LC circuit to a selected NMR line of 27Al. Experimental results are discussed which demonstrate the

P. Bösiger; E. Brun; D. Meier

1977-01-01

331

Photochemically Induced Dynamic Nuclear Polarization (Photo-CIDNP) Magic-Angle Spinning NMR

Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed\\u000a by NMR spectroscopy as enhanced absorptive (positive) or emissive (negative) signals. In solids, photo-CIDNP has been observed\\u000a since its discovery in 1994 in various photosynthetic reaction centers (RCs) by magic angle spinning (MAS) solid-state NMR.\\u000a The photo-CIDNP effect in solids can be explained by a combination

Eugenio Daviso; Gunnar Jeschke; Jörg Matysik

332

NASA Astrophysics Data System (ADS)

We analyze the recently developed folding algorithm (Bañuls et al 2009 Phys. Rev. Lett. 102 240603) for simulating the dynamics of infinite quantum spin chains and we relate its performance to the kind of entanglement produced under the evolution of product states. We benchmark the accomplishments of this technique with respect to alternative strategies using Ising Hamiltonians with transverse and parallel fields, as well as XY models. Also, we evaluate its capability of finding ground and thermal equilibrium states.

Müller-Hermes, Alexander; Cirac, J. Ignacio; Bañuls, Mari Carmen

2012-07-01

333

Spin Dynamics of Strongly-Doped La_1-xSr_xMnO_3

Cold neutron triple-axis measurements have been used to investigate the nature of the long-wavelength spin dynamics in strongly-doped La_1-xSr_xMnO3 single crystals with x=0.2 and 0.3. Bragg scattering indicates that the magnetization near TC exhibits power law behavior, with beta ~= 0.30 for both systems, as expected for a three-dimensional ferromagnet. Both systems behave like isotropic ferromagnets at low T, with

L. Vasiliu-Doloc; J. W. Lynn; Y. M. Mukovskii; A. A. Arsenov; D. A. Shulyatev

1998-01-01

334

A Multifrequency Electron Spin Resonance Study of T4 Lysozyme Dynamics

Electron spin resonance (ESR) spectroscopy at 250GHz and 9GHz is utilized to study the dynamics and local structural ordering of a nitroxide-labeled enzyme, T4 lysozyme (EC 3.2.1.17), in aqueous solution from 10°C to 35°C. Two separate derivatives, labeled at sites 44 and 69, were analyzed. The 250-GHz ESR spectra are well described by a microscopic ordering with macroscopic disordering (MOMD)

Jeff P. Barnes; Zhichun Liang; Hassane S. Mchaourab; Jack H. Freed; Wayne L. Hubbell

1999-01-01

335

Dynamics of entanglement in one-dimensional spin systems

We study the dynamics of quantum correlations in a class of exactly solvable Ising-type models. We analyze in particular the time evolution of initial Bell states created in a fully polarized background and on the ground state. We find that the pairwise entanglement propagates with a velocity proportional to the reduced interaction for all the four Bell states. Singletlike states are favored during the propagation, in the sense that tripletlike states change their character during the propagation under certain circumstances. Characteristic for the anisotropic models is the instantaneous creation of pairwise entanglement from a fully polarized state; furthermore, the propagation of pairwise entanglement is suppressed in favor of a creation of different types of entanglement. The 'entanglement wave' evolving from a Bell state on the ground state turns out to be very localized in space time. Our findings agree with a recently formulated conjecture on entanglement sharing; some results are interpreted in terms of this conjecture.

Amico, Luigi; Osterloh, Andreas; Plastina, Francesco; Fazio, Rosario; Massimo Palma, G. [MATIS-INFM and Dipartimento di Metodologie Fisiche e Chimiche (DMFCI), Viale A. Doria 6, 95125 Catania (Italy); NEST-INFM and Scuola Normale Superiore, I-56127 Pisa (Italy); NEST-INFM and Dipartimento di Tecnologie dell'Informazione, Universita degli Studi di Milano, Via Bramante 65, I-26013 Crema, CR (Italy)

2004-02-01

336

Quantum memory assisted probing of dynamical spin correlations.

We propose a method to probe time-dependent correlations of nontrivial observables in many-body ultracold lattice gases. The scheme uses a quantum nondemolition matter-light interface, first to map the observable of interest on the many-body system into the light and then to store coherently such information into an external system acting as a quantum memory. Correlations of the observable at two (or more) instances of time are retrieved with a single final measurement that includes the readout of the quantum memory. Such a method brings to reach the study of dynamics of many-body systems in and out of equilibrium by means of quantum memories in the field of quantum simulators. PMID:22401082

Romero-Isart, O; Rizzi, M; Muschik, C A; Polzik, E S; Lewenstein, M; Sanpera, A

2012-02-10

337

Dynamic shape effect in {sup 126}Ba at low spin

Lifetimes of excited states in {sup 126}Ba have been measured with high precision by means of the GASP spectrometer using the coincidence recoil distance technique. The reaction {sup 100}Mo({sup 30}Si,4{ital n}) {sup 126}Ba at a beam energy of 130 MeV was used. The data were analyzed with the differential decay-curve method (DDCM). The obtained transition quadrupole moments disagree with the predictions of the asymmetric rotor model (ARM), the interacting boson model (IBM), and the general collective model (GCM). They give evidence for a sudden dynamic shape change in {sup 126}Ba between the 4{sup +} and 10{sup +} levels of the ground-state band. {copyright} {ital 1996 The American Physical Society.}

Dewald, A.; Weil, D.; Kruecken, R.; Kuehn, R.; Peusquens, R.; Tiesler, H.; Vogel, O.; Zell, K.O.; von Brentano, P.; Bazzacco, D.; Rossi-Alvarez, C.; Pavan, P.; DeAcuna, D.; De Angelis, G.; De Poli, M. [Institut fuer Kernphysik der Universitaet zu Koeln, D-50937 Koeln (Germany)]|[Dipartimento di Fisica dell` Universita and INFN Sezione Padova, I-35131 Padova (Italy)]|[INFN, Laboratori Nazionali di Legnaro, I-35020 Legnaro (Italy)

1996-11-01

338

The nanoporous metal-organic framework [Fe(pz)Ni(CN){sub 4}], 1 (where pz is pyrazine), exhibits hysteretic spin-crossover at ambient conditions and is robust to the adsorption and desorption of a wide range of small molecular guests, both gases (N{sub 2}, O{sub 2}, CO{sub 2}) and vapors (methanol, ethanol, acetone, acetonitrile, and toluene). Through the comprehensive analysis of structure, host-guest properties, and spin-crossover behaviors, it is found that this pillared Hofmann system uniquely displays both guest-exchange-induced changes to spin-crossover and spin-crossover-induced changes to host-guest properties, with direct dynamic interplay between these two phenomena. Guest desorption and adsorption cause pronounced changes to the spin-crossover behavior according to a systematic trend in which larger guests stabilize the high-spin state and therefore depress the spin-crossover temperature of the host lattice. When stabilizing the alternate spin state of the host at any given temperature, these processes directly stimulate the spin-crossover process, providing a chemisensing function. Exploitation of the bistability of the host allows the modification of adsorption properties at a fixed temperature through control of the host spin state, with each state shown to display differing chemical affinities to guest sorption. Guest desorption then adsorption, and vice versa, can be used to switch between spin states in the bistable temperature region, adding a guest-dependent memory effect to this system.

Southon, P. D.; Liu, L.; Fellows, E. A.; Price, D. J.; Halder, G. J.; Chapman, K. W.; Moubaraki, B.; Murray, K. S.; Letard, J.F.; Kepert, C. J.; Univ. Sydney; Monash Univ.; Universite Bordeaux

2009-01-01

339

Imaging fast spin dynamics at the nanoscale with soft x-ray microscopy

NASA Astrophysics Data System (ADS)

Nanoscale and multicomponent magnetic systems are attracting both fundamental interest and are widely used in technological applications such as high density magnetic storage and sensor devices. The challenge to modern magnetic microscopies is to image magnetic microstructures in such specimens with high spatial and time resolution and elemental specificity. Magnetic soft X-ray microscopy is a novel technique combining a spatial resolution down to currently 15nm, elemental sensitivity due to X-ray magnetic circular dichroism used as huge magnetic contrast mechanism and a sub-ns time resolution limited by the current time structure of the synchrotron radiation used as source for circularly polarized soft X-rays. We report on recent results and achievements in magnetic soft X-ray microscopy obtained at the full-field soft X-ray microscopy beamline 6.1.2 (XM-1) located at the Advanced Light Source in Berkeley CA. Magnetization reversal processes at the grain level in a nanogranular CoCrPt system were studied with 15nm spatial resolution to obtain insight into spin fluctuations on a fundamental length scale. The inherent elemental sensitivity of XMCD contrast allows e.g. in (coupled) multilayered magnetic systems to explore their microscopic magnetization reversal process with layer resolution. Spin dynamics in magnetic nanostructures can be addressed by a stroboscopic pump and probe scheme utilizing the inherent time structure of synchrotron radiation, where the pump is a fast electronic pulse launched into a waveguide structure to excite the spin dynamics of a magnetic nanoelement. Varying the delay time between the pump and the probing x-ray flash one can follow the time development of e.g local spin and vortex dynamics and relaxation phenomena, but also spin-torque driven domain wall displacements with sub-ns time resolution. Current developments of X-ray optics aim to achieve better than 10nm spatial resolution. At upcoming high brillant ultrast X-ray sources snapshots of spin dynamics with fs time resolution recorded with magnetic soft X-ray microscopy can be foreseen. Many thanks to D.-H. Kim, B. Mesler, W. Chao, R. Oort, E. Anderson, G. Meier, R. Eiselt, M. Bolte, M.-Y. Im, S.-C. Shin, S. Mangin, E. Fullerton.

Fischer, Peter

2007-03-01

340

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

341

Dynamical phase transitions and temperature-induced quantum correlations in an infinite spin chain

We study the dynamics of entanglement in the infinite asymmetric XY spin chain, in an applied transverse field. The system is prepared in a thermal equilibrium state (ground state at zero temperature) at the initial instant, and it starts evolving after the transverse field is completely turned off. We investigate the evolved state of the chain at a given fixed time, and show that the nearest-neighbor entanglement in the chain exhibits a critical behavior (which we call a dynamical phase transition), controlled by the initial value of the transverse field. The character of the dynamical phase transition is qualitatively different for short and long evolution times. We also find a nonmonotonic behavior of entanglement with respect to the temperature of the initial equilibrium state. Interestingly, the region of the initial field for which we obtain a nonmonotonicity of entanglement (with respect to temperature) is directly related to the position and character of the dynamical phase transition in the model.

Sen, Aditi; Sen, Ujjwal; Lewenstein, Maciej [ICFO-Institut de Ciencies Fotoniques, Jordi Girona 29, Edifici Nexus II, E-08034 Barcelona (Spain) and Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany)

2005-11-15

342

Dynamics of quasi-species models with a complex spin coherent state representation

NASA Astrophysics Data System (ADS)

We investigate the dynamics of the parallel mutation-selection quasi-species model of biological evolution for various fitness landscapes. By using the semiclassical propagator for spin coherent states, for the linear fitness landscape, we find the expression for the transition rate from an arbitrary initial state to an arbitrary final state and expressions for the mean fitness and the surplus. For the sharp-peak fitness landscape, we find the solutions to the dynamics equation in two time regions and the crossover time which separates these two regions. Finally, we present a semiclassical method to derive analytic expressions for the dynamics of the mean fitness and the surplus for general symmetric fitness landscapes, and in case of the quadratic fitness landscape, we obtain the dynamics of the mean fitness consistent with previous results.

Ancliff, Mark; Park, Jeong-Man

2012-12-01

343

NASA Astrophysics Data System (ADS)

In the study of trapped two-component Bose gases, a widely used dynamical protocol is to start from the ground state of a one-component condensate and then switch half the atoms into another hyperfine state. The slightly different intra-component and inter-component interactions can then lead to highly non-trivial dynamics, especially in the density mismatch between the two components, commonly referred to as ‘spin’ density. We study and classify the possible subsequent dynamics, over a wide variety of parameters spanned by the trap strength and by the inter- to intra-component interaction ratio. A stability analysis suited to the trapped situation provides us with a framework to explain the various types of dynamics in different regimes.

Vidanovi?, Ivana; van Druten, N. J.; Haque, Masudul

2013-03-01

344

NASA Astrophysics Data System (ADS)

We show that facilitated spin models of cooperative dynamics introduced by Fredrickson and Andersen display on Bethe lattices a glassy behaviour similar to the one predicted by the mode-coupling theory of supercooled liquids and the dynamical theory of mean-field disordered systems. At low temperature such cooperative models show a two-step relaxation and their equilibration time diverges at a finite temperature according to a power law. The geometric nature of the dynamical arrest corresponds to a bootstrap percolation process which leads to a phase space organization similar to the one of mean-field disordered systems. The relaxation dynamics after a subcritical quench exhibits aging and converges asymptotically to the threshold states that appear at the bootstrap percolation transition.

Sellitto, M.; Biroli, G.; Toninelli, C.

2005-02-01

345

We present time-resolved studies of the spin polarization dynamics during and after initialization through pulsed electrical spin injection into InGaAs quantum dots embedded in a p-i-n-type spin-injection light-emitting diode. Experiments are performed with pulse widths in the nanosecond range and a time-resolved single photon counting setup is used to detect the subsequent electroluminescence. We find evidence that the achieved spin polarization shows an unexpected temporal behavior, attributed mainly to many-carrier and non-equilibrium effects in the device.

Asshoff, P.; Loeffler, W.; Fluegge, H.; Zimmer, J.; Mueller, J.; Westenfelder, B.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M. [Institut fuer Angewandte Physik and DFG Center for Functional Nanostructures (CFN), Universitaet Karlsruhe, 76131 Karlsruhe (Germany)

2010-01-04

346

Coherent dynamics of locally interacting spins in self-assembled Cd1-xMnxSe/ZnSe quantum dots

NASA Astrophysics Data System (ADS)

The coherent dynamics of locally interacting spins of carriers and magnetic atoms in the crystal matrix of self-assembled CdMnSe/ZnSe quantum dots was analyzed by means of time resolved Kerr rotation. We demonstrate that even in such a system of tightly interacting spins a coherent transfer of spin between the different subsystems is possible. Strong evidence for an enhancement of the spin coherence time of both the carrier and the manganese system with respect to higher dimensional structures is found.

Scheibner, M.; Kennedy, T. A.; Worschech, L.; Forchel, A.; Bacher, G.; Slobodskyy, T.; Schmidt, G.; Molenkamp, L. W.

2006-02-01

347

Spin-dynamics of the spin-correlated radical pair (SCRP) P{sub 700}{sup +}A{sub 1A}{sup -} in the photosystem I (PSI) reaction center protein have been investigated with high-frequency (HF), time-resolved EPR spectroscopy. The superior spectral resolution of HF EPR enables spin-dynamics for both the donor and acceptor radicals in the pair to be monitored independently. Decay constants of each spin were measured as a function of temperature and compared to data obtained at X-band EPR. Relaxation times, T{sub 1}, and decay rates, k{sub S}, are the same at both X- and D-band magnetic fields. The spin-dynamics within the radical pair were determined from theoretical simulation of experimental time-resolved HF EPR spectra. At low temperatures, T < 60 K, the decay of the SCRP from the singlet state, k{sub S}, is the predominant process, while at high temperatures, T > 130 K, the T{sub 1} relaxation is much faster than k{sub S}. The recombination rate k{sub S} was observed to decrease as the temperature is increased. These EPR spectral results are in agreement with previously reported optical measurements of P{sub 700}{sup +}A{sub 1}{sup -} radical pair recombination.

Poluektov, O. G.; Paschenko, S. V.; Utschig, L. M.; Chemical Sciences and Engineering Division

2009-01-01

348

NASA Astrophysics Data System (ADS)

The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen)2(NCS)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{[Me2Pyrz]3BH}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.; Miyamachi, T.; Da Costa, V.; Boukari, S.; Scheurer, F.; Joly, L.; Ohresser, P.; Otero, E.; Choueikani, F.; Gaspar, A. B.; Real, J. A.; Wulfhekel, W.; Bowen, M.; Beaurepaire, E.

2013-08-01

349

Spin-dynamics of the spin-correlated radical pair (SCRP) P(700)(+)A(1A)(-) in the photosystem I (PSI) reaction center protein have been investigated with high-frequency (HF), time-resolved EPR spectroscopy. The superior spectral resolution of HF EPR enables spin-dynamics for both the donor and acceptor radicals in the pair to be monitored independently. Decay constants of each spin were measured as a function of temperature and compared to data obtained at X-band EPR. Relaxation times, T(1), and decay rates, k(S), are the same at both X- and D-band magnetic fields. The spin-dynamics within the radical pair were determined from theoretical simulation of experimental time-resolved HF EPR spectra. At low temperatures, T < 60 K, the decay of the SCRP from the singlet state, k(S), is the predominant process, while at high temperatures, T > 130 K, the T(1) relaxation is much faster than k(S). The recombination rate k(S) was observed to decrease as the temperature is increased. These EPR spectral results are in agreement with previously reported optical measurements of P(700)(+)A(1)(-) radical pair recombination. PMID:19639149

Poluektov, O G; Paschenko, S V; Utschig, L M

2009-06-23

350

NASA Astrophysics Data System (ADS)

We study the dynamics of spin-1 atoms in a periodic optical-lattice potential and an external magnetic field in a quantum quench scenario where we start from a superfluid ground state in a shallow lattice potential and suddenly raise the lattice depth. The time evolution of the nonequilibrium state shows collective collapse-and-revival oscillations of matter-wave coherence as well as oscillations in the spin populations. We show that the complex pattern of these two types of oscillations reveals details about the superfluid and magnetic properties of the initial many-body ground state. Furthermore, we show that the strengths of the spin-dependent and spin-independent atom-atom interactions can be deduced from the observations. The Hamiltonian that describes the physics of the final deep lattice not only contains two-body interactions but also effective multibody interactions, which arise due to virtual excitations to higher bands. We derive these effective spin-dependent three-body interaction parameters for spin-1 atoms and describe how spin mixing is affected. Spinor atoms are unique in the sense that multibody interactions are directly evident in the in situ number densities in addition to the momentum distributions. We treat both antiferromagnetic (e.g., 23Na) and ferromagnetic (e.g., 87Rb and 41K) condensates.

Mahmud, K. W.; Tiesinga, E.

2013-08-01

351

Within the wider context of water behavior in soils, and with a particular emphasis on clays surrounding underground radioactive waste packages, we present here the translational dynamics of water in clays in low hydrated states as studied by coupling molecular dynamics (MD) simulations and quasielastic neutron scattering experiments by neutron spin echo (NSE). A natural montmorillonite clay of interest is modeled by a synthetic clay which allows us to understand the determining parameters from MD simulations by comparison with the experimental values. We focus on temperatures between 300 and 350 K, i.e., the range relevant to the highlighted application. The activation energy Ea experimentally determined is 6.6 kJ/mol higher than that for bulk water. Simulations are in good agreement with experiments for the relevant set of conditions, and they give more insight into the origin of the observed dynamics. PMID:21381672

Marry, Virginie; Dubois, Emmanuelle; Malikova, Natalie; Durand-Vidal, Serge; Longeville, Stéphane; Breu, Josef

2011-03-07

352

We introduce a new class of plasmonic crystals possessing graphene-like internal symmetries and Dirac-type spectrum in k-space. We study dynamics of surface plasmon polaritons supported in the plasmonic crystals by employing the formalism of Dirac dynamics for relativistic quantum particles. Through an analogy with graphene, we introduce a concept of pseudo-spin and chirality to indicate built-in symmetry of the plasmonic crystals near Dirac point. The surface plasmon polaritons with different pseudo-spin states are shown to split in the crystals into two beams, analogous to spin Hall effect. PMID:21164881

Nam, Sung Hyun; Zhou, Jiangfeng; Taylor, Antoinette J; Efimov, Anatoly

2010-11-22

353

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

354

Academic Freedom, the First Amendment and Competing Stakeholders: The Dynamics of a Changing Balance

ERIC Educational Resources Information Center

The Supreme Court first affirmed the importance of academic freedom in 1957. Yet in subsequent cases, First Amendment precedent has displaced the concept of academic freedom to resolve disputes among competing interests on public campuses, primarily in favor of institutions. This paper draws on the concepts of path dependence and policy space to…

Jorgensen, James D.; Helms, Lelia B.

2008-01-01

355

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

356

Dynamics of the Spin Liquid Phase of Cs2CuCl4

NASA Astrophysics Data System (ADS)

The dynamics of a spin-liquid phase of an antiferromagnet on the anisotropic triangular lattice and in a magnetic field are studied with a combination of Gutzwiller-projected wavefunctions and mean-field theory. Candidate ground states that support fermionic gapless spinon excitations include four different U(1) spin liquidsootnotetextY. Zhou, X. G. Wen, cond-mat/0210662 (2003).. The lattice and the states interpolate between limiting cases of 1D decoupled chains (J/J^' = 0) and the isotropic 2D square lattice (J/J^'= ?). Parameters of the mean field theory are chosen to minimize the ground state energy of the corresponding Gutzwiller-projected wavefunction. The spin-lattice relaxation rate 1/T1, calculated within the mean-field approximation, is compared to NMR measurementsootnotetextM. A. Vachon, O. Ma, J. B. Marston, V. F. Mitrovi'c, unpublished (2007). in the spin liquid phase of Cs2CuCl4ootnotetextY. Tokiwa, T. Radu, R. Coldea, H. Wilhelm, Z. Tylczynski, F. Steglich, PRB 73, 134414 (2006)..

Ma, Ookie; Vachon, Marc-Andre; Mitrovi{?}, Vesna F.; Marston, Brad

2008-03-01

357

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

358

Universal quantum control of two-electron spin quantum bits using dynamic nuclear polarization

NASA Astrophysics Data System (ADS)

One fundamental requirement for quantum computation is to carry out universal manipulations of quantum bits at rates much faster than the qubit's rate of decoherence. Recently, fast gate operations have been demonstrated in logical spin qubits composed of two electron spins where the rapid exchange of the two electrons permits electrically controllable rotations around one axis of the qubit. However, universal control of the qubit requires arbitrary rotations around at least two axes. Here, we show that by subjecting each electron spin to a magnetic field of different magnitude, we achieve full quantum control of the two-electron logical spin qubit with nanosecond operation times. Using a single device, a magnetic-field gradient of several hundred millitesla is generated and sustained using dynamic nuclear polarization of the underlying Ga and As nuclei. Universal control of the two-electron qubit is then demonstrated using quantum state tomography. The presented technique provides the basis for single- and potentially multiple-qubit operations with gate times that approach the threshold required for quantum error correction.

Foletti, Sandra; Bluhm, Hendrik; Mahalu, Diana; Umansky, Vladimir; Yacoby, Amir

2009-12-01

359

Ultrafast electron dynamics in a metallic quantum well nanofilm with spin splitting

NASA Astrophysics Data System (ADS)

Using time- and angle-resolved two-photon photoemission spectroscopy, we investigate the energy- and momentum-dependent ultrafast electron dynamics in the Rashba spin-split quantum-well nanofilm Bi/Cu(111). We find an expected increase of electron lifetimes towards the band bottom due to a competition of intra- and interband scattering processes. In addition, we find an unexpected peculiar decrease of the lifetimes around the intersection of the split bands. We compare the experimental results with calculated lifetimes due to electron-electron scattering in a model system of a 2D electron gas including a Rashba interaction term and an effective statically screened Coulomb interaction. Although the Rashba model reproduces the increase of lifetimes towards the band bottom well, there is no indication of the experimentally observed decrease around the intersection point in this simple model system. To investigate spin-orbit coupling effects, beyond those contained in a pure Rashba model, we introduce a phenomenological k-dependent spin mixing that leads to a “spin hot spot.” It is shown that such a mixing would strongly increase the electron-electron scattering rate around the band intersection and thus improves the agreement with experiment.

Ruffing, A.; Vollmar, S.; Jakobs, S.; Kaltenborn, S.; Baral, A.; Cinchetti, M.; Mathias, S.; Schneider, H. C.; Aeschlimann, M.

2013-08-01

360

The dynamic phase transitions are studied in the spin-2 Ising model under a time-dependent oscillating magnetic field by using the effective-field theory with correlations. The effective-field dynamic equation is derived by employing the Glauber transition rates and the phases in the system are obtained by solving this dynamic equation. The nature (first- or second-order) of the dynamic phase transition is characterized by investigating the thermal behavior of the dynamic order parameter and the dynamic phase transition temperatures are obtained. The dynamic phase diagrams are presented in (T/zJ, h/zJ) plane.

Ertas, Mehmet; Keskin, Mustafa [Department of Physics, Erciyes University, 38039 Kayseri (Turkey); Deviren, Bayram [Department of Physics, Nevsehir University, 50300 Nevsehir (Turkey)

2010-12-23

361

NASA Astrophysics Data System (ADS)

We provide an extensive study of the subohmic spin-boson model with power-law density of states J(?)??s (with 0~~dynamics of the three possible spin components, from very weak dissipation to the quantum critical regime. Two complementary methods, the bosonic numerical renormalization group and Majorana diagrammatics, are used to explore the physical properties in a wide range of parameters. We show that the bosonic self-energy is the crucial ingredient for the description of critical fluctuations, but that many-body vertex corrections need to be incorporated as well in order to obtain quantitative agreement of the diagrammatics with the numerical simulations. Our results suggest that the out-of-equilibrium dynamics in dissipative models beyond the Bloch-Redfield regime should be reconsidered in the long-time limit. Regarding also the spin-boson Hamiltonian as a toy model of quantum criticality, some of the insights gained here may be relevant for field theories of electrons coupled to bosons in higher dimensions.~~

Florens, S.; Freyn, A.; Venturelli, D.; Narayanan, R.

2011-10-01

362

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

363

Dynamic generation of spin-squeezed states in bosonic Josephson junctions

NASA Astrophysics Data System (ADS)

We analyze the formation of squeezed states in a condensate of ultracold bosonic atoms confined by a double-well potential. The emphasis is set on the dynamical formation of such states from initially coherent many-body quantum states. Two cases are described: the squeezing formation in the evolution of the system around the stable point, and in the short-time evolution in the vicinity of an unstable point. The latter is shown to produce highly squeezed states on very short times. On the basis of a semiclassical approximation to the Bose-Hubbard Hamiltonian, we are able to predict the amount of squeezing, its scaling with N, and the speed of coherent spin formation with simple analytical formulas which successfully describe the numerical Bose-Hubbard results. This method of producing highly squeezed spin states in systems of ultracold atoms is compared to other standard methods in the literature.

Juliá-Díaz, B.; Zibold, T.; Oberthaler, M. K.; Melé-Messeguer, M.; Martorell, J.; Polls, A.

2012-08-01

364

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

365

Breakdown of the field-induced superconductivity by dynamical spin reversal

NASA Astrophysics Data System (ADS)

The quasi-two-dimensional molecular conductor ?-(BETS)2FeCl4, where BETS is bis(ethylenedithio)tetraselenafulvalene, shows a superconductivity in the high magnetic field environment. This is due to the compensation effect between the external field and the internal field created by the Fe3+ magnetic moment. Here, we report the simultaneous transport and electron spin resonance (ESR) measurements in the field-induced superconducting state down to 1.65 K. We find that the field-induced superconductivity is partially destroyed by ESR transitions, namely, by dynamical spin reversals of Fe3+. Moreover, it is found from our ESR results that the field-induced superconducting state is inhomogeneous, coexisting with the residual paramagnetic metal state.

Oshima, Yugo; Nojiri, Hiroyuki; Uji, Shinya; Brooks, James S.; Tokumoto, Takahisa; Cui, Heng-Bo; Kato, Reizo; Kobayashi, Akiko; Kobayashi, Hayao

2012-07-01

366

Dynamical structure factor of spin 1/2 Heisenberg antiferromagnet on Kagome lattice

NASA Astrophysics Data System (ADS)

The ground state of spin 1/2 anti-ferromagnet on kagome lattice can be viewed as a collection of small and heavy bound pairs of fermionic spinons [1]. Magnetic excitations of the model correspond to breaking such pairs into their constituents. In the current work, the dynamical structure factor is calcualted for low energy magnetic excitations just above the spin gap. It is observed that the structure factor is similar to the one of an isolated dimer due to the tightness of the bound state. The result is consistent with experiments done in Helton etal [2] and M.A. de Vries etal [3]. [4pt] [1] Zhihao Hao and Oleg Tchernyshyov, Phys. Rev. Lett. 103, 187203.[0pt] [2] J. S. Helton etal, Phys. Rev. Lett. 98, 107204.[0pt] [3] M. A. de Vries etal, arXiv:0902.3194.

Hao, Zhihao; Mellado, Paula; Tchernyshyov, Oleg

2010-03-01

367

Low-energy spin dynamics of the s = 1/2 kagome system herbertsmithite

NASA Astrophysics Data System (ADS)

The low-energy (? = ?? < 1 meV), low-temperature (T = 0.05 K) spin dynamics of the s = 1/2 kagome candidate herbertsmithite are probed in the presence of magnetic fields up to 2.5 T. The zero-field spectra reveal a very weak continuum of scattering at T = 10 K and a broad inelastic peak centred at ?max = 0.2 meV at lower temperatures, T < 1 K. The broad peak is found to be strongly damped, with a liquid-like structure factor implying correlations at length scales up to r = 6 Å. The field dependence of the peak appears to follow the Zeeman splitting of s = 1/2 excitations, consistent with the weakly split ‘doublets’ observed in low-temperature specific heat. A possible explanation of these observations is a short-range correlated state involving defect spins between the kagome planes and moments in the kagome layers.

Nilsen, G. J.; de Vries, M. A.; Stewart, J. R.; Harrison, A.; Rønnow, H. M.

2013-03-01

368

Thrive, not just survive: enhance dynamic capabilities of SMEs through IS competence

Purpose – Small and mid-sized enterprises (SMEs) are facing challenges in an increasingly fierce environment. This paper aims to explore the promise of information systems (IS) in enhancing the survival and competitiveness of SMEs in a dynamic environment. To address this issue, the paper draws upon the dynamic capability theory and develops a research model of IS-enabled dynamic capabilities to

Yi Wang; Xinping Shi

2011-01-01

369

This paper argues that the management of product-systems calls for a new logic for vertical integration, outsourcing, and R&D strategies. The particular characteristics of product-systems, in fact, requires a thorough understanding of the core, linkage, and peripheral underlying technologies, suggesting, therefore, that simple notions of core competencies that recommend the outsourcing of production, and even worse the development, of component

Andrea Prencipe

1997-01-01

370

NASA Astrophysics Data System (ADS)

The characteristics of localized excitations in quasi-one-dimensional systems are rather sensitive to the interplay between the electron-phonon (e-ph) and electron-electron (e-e) interactions giving rise to competition and possible coexistence of various symmetry-broken ground states such as the bond-order wave (BOW), the charge-density wave (CDW), and the spin-density wave (SDW). Such effects are observable in halogen-bridged mixed-valence transition-metal complexes, and can be elucidated within the Bogoliubov-de Gennes formalism using an extended Peierls-Hubbard model. The coexistence of local BOW, CDW, and SDW distortions is demonstrated in this paper for polarons and self-trapped excitons (STE) in different symmetry-broken ground states. An extensive study of localized excitations over a wide range of the on-site e-ph coupling ?2 and the Hubbard interaction U leads to the following observations. (a) As ?2 increases at fixed U, the number of bound states inside the gap changes from two to four for the STE case and from two to three for the polaron case. (b) Upon its further increase, one type of STE with a certain pattern of SDW distortion and charge transfer is transforming into another type of STE with a different pattern. (c) A nonmonotonic dependence of the lattice relaxation energy on ?2 is predicted within the lattice relaxation approach developed by Su and Yu earlier, and is attributed to a crossover from the weak-coupling to strong-coupling behavior showing up as the emergence of new bound states inside the gap. Moreover, the nonradiative transition rate of STE is also calculated and is used to tentatively interpret the very short lifetime of STE in PtCl complexes. Such nonmonotonic dependence of the relaxation rate on the coupling constant may also be observed in other quasi-one-dimensional systems as well.

Wang, Chui-Lin; Wang, Wen-Zheng; Gu, Guo-Liang; Su, Zhao-Bin; Yu, Lu

1993-10-01

371

Regular arrays of soft magnetic dots in the vortex state are being considered as a potentially new high-density nonvolatile recording media characterized by two binary properties: chirality and polarity of magnetic vortex core. Here we unambiguously demonstrate the existence of two distinct dynamic vortex (stable and metastable) regimes with qualitatively different spin wave eigenmodes. We find that dynamic response in

Farkhad Aliev; Juan Francisco Sierra; Ahmad Awad; Gleb Kakazei; Dong-Soo Han; Sang-Koong Kim; Konstantin Guslienko; Bojan Ilic; Vitali Metlushko

2009-01-01

372

NASA Astrophysics Data System (ADS)

We show that the dynamics of disordered charge density waves (CDWs) and spin density waves (SDWs) is a collective phenomenon. The very low temperature specific heat relaxation experiments are characterized by: (i) ``interrupted'' ageing (meaning that there is a maximal relaxation time); and (ii) a broad power-law spectrum of relaxation times which is the signature of a collective phenomenon. We propose a random energy model that can reproduce these two observations and from which it is possible to obtain an estimate of the glass cross-over temperature (typically Tg = 100-200 mK). The broad relaxation time spectrum can also be obtained from the solutions of two microscopic models involving randomly distributed solitons. The collective behavior is similar to domain growth dynamics in the presence of disorder and can be described by the dynamical renormalization group that was proposed recently for the one dimensional random field Ising model [D.S. Fisher, P. Le Doussal, C. Monthus, Phys. Rev. Lett. 80, 3539 (1998)]. The typical relaxation time scales like ?exp(Tg/T). The glass cross-over temperature Tg related to correlations among solitons is equal to the average energy barrier and scales like Tg 2x??. x is the concentration of defects, ? the correlation length of the CDW or SDW and ? the charge or spin gap.

Mélin, R.; Biljakovi?, K.; Lasjaunias, J. C.; Monceau, P.

2002-04-01

373

Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath

NASA Astrophysics Data System (ADS)

Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses [the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence [the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are C13 nuclear spins and the environment consists of a H1 nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.

Ajoy, Ashok; Álvarez, Gonzalo A.; Suter, Dieter

2011-03-01

374

Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath

Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses [the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence [the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are {sup 13}C nuclear spins and the environment consists of a {sup 1}H nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.

Ajoy, Ashok [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Birla Institute of Technology and Science, Pilani, Zuarinagar, Goa 403726 (India); NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India); Alvarez, Gonzalo A.; Suter, Dieter [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany)

2011-03-15

375

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

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 (B{sub 0}) and dynamic (B{sub 1}) fields into the formation. Both B{sub 0} and B{sub 1} 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 B{sub 1} and B{sub 0} 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. [Schlumberger Oilfield Services, Sugar Land, TX 77478 (United States)

2008-12-05

376

Dynamical simulation of a two-electron spin qubit based on hyperfine interaction

NASA Astrophysics Data System (ADS)

The interaction with the nuclear field is one of the main sources of decoherence in solid state quantum bits. However, recently it has been shown that hyperfine interaction can also be used to manipulate the spin state of electrons in double quantum dots. In this work, we simulate numerically the dynamics of a spin-based quantum bit consisting of two electrons confined in a double quantum dot, including the interaction with a random nuclear field. The two electron wavefunction is built using an antisymmetric function expansion and the total hamiltonian is discretized spatially using finite differences. For the dynamic simulation, an exponential approximation of the time propagator is used. In order to model the hyperfine interaction, a normally-distributed random magnetic field is assigned to each simulation grid point. The dynamics of the system is calculated by averaging over an ensemble of quantum dots. It is shown how the hyperfine field can be used to drive transitions between singlet and triplet states, an effect that has already been found experimentally. Particularly, it is shown how these transitions can be controlled using an applied electric field, thus allowing for the realization of a two-electron quantum gate.

Rodriguez-Moreno, Miguel Angel; Meza-Montes, Lilia; Hernandez de La Luz, David

2012-02-01

377

Spin-glass dynamics of La0.95Sr0.05CoO3

NASA Astrophysics Data System (ADS)

Experimental studies of dynamic magnetic properties of a highly homogeneous sample of La0.95Sr0.05CoO3 perovskite evidence the existence of a low-temperature spin-glass phase. A dynamic scaling analysis of ac susceptibility data according to conventional critical slowing down implies a finite spin-glass phase-transition temperature Tg~14.6 K and a dynamic exponent z?~10.3. Low-field magnetic relaxation experiments show essentially logarithmic magnetic relaxation and aging effects at all temperatures below Tg and that temperature perturbations affect the relaxation function in a way that is characteristic for a low-temperature spin-glass phase. Finally, it is also shown that ``simple'' remanent magnetization vs temperature curves, measured after specific cooling protocols, can yield information on dynamic properties such as aging and memory phenomena.

Nam, D. N. H.; Mathieu, R.; Nordblad, P.; Khiem, N. V.; Phuc, N. X.

2000-10-01

378

Spin dynamics in the negatively charged terbium (III) bis-phthalocyaninato complex.

The experimental and theoretical study of the electron spin dynamics in the anionic form of a single-ion molecule magnet (SIMM), the bis-phthalocyaninato terbium (III) molecule [Pc(2)Tb](-)[TBA](+), has been addressed by means of solid state (1)H NMR spectroscopy. The magnetic properties of the caged Tb(3+) metal center were investigated in a series of diamagnetically diluted preparations, where the excess of tetrabutylamonium bromide ([TBA]Br)(n) salt was used as diamagnetic matrix complement. We found that a high temperature activated spin dynamics characterizes the systems, which involved phonon-assisted transitions among the crystal field levels in qualitative agreements with literature results. However, the activation barriers in these processes range from 641 cm(-1) for the diamagnetically diluted samples to 584 cm(-1) for those undiluted; thus, they exhibit barriers 2-3 times larger than witnessed in earlier (230 cm(-1)) reports (e.g., Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694-8695). At cryogenic temperatures, fluctuations are driven by tunneling processes between the m = +6 and -6 low-energy levels. We found that the barrier Delta and the tunneling rates change from sample to sample and especially the diamagnetically diluted [Pc(2)Tb](-) molecules appear affected by the sample's magneto/thermal history. These observations emphasize that matrix arrangements around [Pc(2)Tb](-) can appreciably alter the splitting of the crystal field levels, its symmetry, and hence, the spin dynamics. Therefore, understanding how small differences in molecular surroundings (as for instance occurring by depositing on surfaces) can trigger substantial modifications in the SIMM property is of utmost importance for the effective operation of such molecules for single-molecule data storage, for example. PMID:19275145

Branzoli, Francesca; Carretta, Pietro; Filibian, Marta; Zoppellaro, Giorgio; Graf, Michael J; Galan-Mascaros, Jose R; Fuhr, Olaf; Brink, Susan; Ruben, Mario

2009-04-01

379

High Speed Linear and Nonlinear Optical Measurements of Spin Dynamics in Ferromagnetic Thin Films

NASA Astrophysics Data System (ADS)

We have developed vectorial magnetodynamic measurements using ultrafast laser technology with a time resolution of 10 ps(T. M. Crawford, T. J. Silva, C. W. Teplin, and C. T. Rogers, Appl. Phys. Lett. 74, 3386 (1999).)(P. Kabos, A. B. Kos, and T. J. Silva, J. Appl. Phys. 87, 5980 (2000).). We use both conventional magneto-optics (MOKE) and the novel second-harmonic magneto-optic Kerr effect (SHMOKE)(W. Huebner and K.-H. Bennemann, Phys. Rev. B, 5973 (1989).)(J. Reif, J. C. Zink, C.-H. Schneider, and J. Kirschner, Phys. Rev. Lett, 2878 (1991).)(B. Koopmans, M. G. Koerkamp, Th. Rasing, H. van den Berg, Phys. Rev. Lett, 3692 (1995).). Special effort has been made to measure the dynamic properties of commercially viable magnetic thin films for data storage applications. We have demonstrated the coherent control of precessional dynamics using pulse-shaping of the excitation. Using this method, we have found that magnetization can be rotated in an under-damped film by as much as 40 degrees without any commensurate precessional oscillations(T. M. Crawford, P. Kabos, and T. J. Silva, Appl. Phys. Lett. 76, 2113 (2000).). We have made simultaneous vector-resolved measurements with both linear and nonlinear magneto-optics, without observing any significant differences between the surface (SHMOKE) and bulk (MOKE) spin dynamics, even for metallic films as thick as 250 nm. We have measured the flux propagation velocity for a half-micron thick film and found it to be in agreement with magnetostatic spin wave theory. Finally, we have observed the transient magnetization reduction for large excitations in a transverse-biased sample due to spin wave formation.

Thomas, Silva

2001-03-01

380

Dynamics of thermal effects in the spin-wave theory of quantum antiferromagnets

NASA Astrophysics Data System (ADS)

We derive a master equation that allows us to study non-equilibrium dynamics of a quantum antiferromagnet. By resorting to spin-wave theory, we obtain a closed analytic form for the magnon decay rates. These turn out to be closely related to form factors, which are experimentally accessible by means of neutron and Raman scattering. Furthermore, we compute the time evolution of the staggered magnetization showing that, for moderate temperatures, the magnetic order is not spoiled even if the coupling is fully isotropic.

Rivas, Ángel; Martin-Delgado, Miguel A.

2013-04-01

381

Dynamics and control of a quasi-one-dimensional spin system

NASA Astrophysics Data System (ADS)

We study experimentally a system comprised of linear chains of spin-1/2 nuclei that provides a test bed for multibody dynamics and quantum-information processing. This system is a paradigm for a class of quantum-information processing 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.

Cappellaro, P.; Ramanathan, C.; Cory, D. G.

2007-09-01

382

Spin Dynamics in Two-Dimensional Arrays of Quantum Dots with Local Ordering of Nanoclusters

Electron paramagnetic resonance (EPR) is used to probe the spin dynamics in two-dimensional (2D) quantum dot (QD) arrays with local ordering of nanoclusters. A careful examination of EPR line shape, width and g-factor values allow us to attribute this signal to the electrons localized in the strain-induced potential wells in Si in the vicinity of the Ge dots. The strong orientation dependence of EPR line width is defined by changing localization degree of electrons at different magnetic field directions. The theoretical approximation of orientation dependence of EPR line width allows estimating the effective radius of electron localization, as {approx}80 nm.

Zinovieva, A. F.; Dvurechenskii, A. V.; Stepina, N. P.; Nikiforov, A. I.; Lyubin, A. S. [Institute of Semiconductor Physics, 630090 Novosibirsk, pr. Lavrentieva 13 (Russian Federation); Sobolev, N.; Carmo, M. C. [Departamento de Fisica e I3N, Universidade de Aveiro, Aveiro (Portugal)

2011-12-23

383

Does the Heisenberg Model Describe the Multimagnon Spin Dynamics in Antiferromagnetic CuO Layers?

We compute the absorption spectrum for multimagnon excitations assisted by phonons in insulating layered cuprates using exact diagonalization in clusters of up to 32 sites. The resulting line shape is very sensitive to the underlying magnetic Hamiltonian describing the spin dynamics. For the usual Heisenberg description of undoped Cu-O planes we find, in accordance with experiment, a two-magnon peak followed by high energy sidebands. However the relative weight of the sidebands is too small to reproduce the experiment. An extended Heisenberg model including a sizable four-site cyclic exchange term is shown to be consistent with the experimental data. (c) 1999 The American Physical Society.

Lorenzana, J. [Istituto Nazionale di Fisica della Materia-Dipartimento di Fisica, Universita di Roma ''La Sapienza'', Piazzale A. Moro 2, I-00185 Roma (Italy); Centro Atomico Bariloche and Instituto Balseiro, 8400 San Carlos de Bariloche (Argentina); Eroles, J. [Centro Atomico Bariloche and Instituto Balseiro, 8400 San Carlos de Bariloche, (Argentina); Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Sorella, S. [Istituto Nazionale di Fisica della Materia, SISSA, Via Beirut 4, 34014 Trieste, (Italy)

1999-12-13

384

Precessional dynamics and damping in Co/Cu/Py spin valves

NASA Astrophysics Data System (ADS)

We have studied the precessional dynamics of Co/Cu/Py (where Py = Ni81Fe19) trilayers by time-resolved x-ray resonant magnetic scattering at the synchrotron radiation facility BESSY II. We have found that the magnetic precessional decay time of Fe magnetic moments in Py layers decreases when changing the mutual orientation of the magnetization direction of Py and Co layers from parallel to antiparallel. The observed changes of the decay time can be associated with the spin pumping induced damping effect.

Salikhov, R.; Abrudan, R.; Brüssing, F.; Buschhorn, St.; Ewerlin, M.; Mishra, D.; Radu, F.; Garifullin, I. A.; Zabel, H.

2011-08-01

385

Broadband spin dynamics of the magnetic vortex state: Effect of the pulsed field direction

NASA Astrophysics Data System (ADS)

The dynamic spin modes observed in magnetic vortex structures are shown to depend strongly on the nature of the initial excitation by a transient pulse field. In submicrometer-sized Permalloy disks, when a uniform perpendicular transient field is used to perturb the magnetization, radial standing-wave modes are excited; whereas if an in-plane transient field is used, angular or azimuthal modes are formed. The existence of the vortex core is responsible for a frequency splitting of the azimuthal modes, as demonstrated through comparison to micromagnetic simulations of a ring geometry.

Zhu, Xiaobin; Liu, Zhigang; Metlushko, Vitali; Grütter, Peter; Freeman, Mark R.

2005-05-01

386

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 counterpropagating coherent states is ejected from the center 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. From this we can analyze the entanglement production and interpret the ejected coherent states as a manifestation of the so-called "accelerator modes" of a classically chaotic system. PMID:16712391

Boness, T; Bose, S; Monteiro, T S

2006-05-09

387

The quasi-one-dimensional cuprates (La,Y,Sr,Ca)14Cu24O41, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a charge-density wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in

T. Vuletic; B. Korin-Hamzic; T. Ivek; S. Tomic; B. Gorshunov; M. Dressel; J. Akimitsu

2006-01-01

388

Compositional Patterning in Systems Driven by Competing Dynamics Of Different Length Scale

We study an alloy system where short-ranged, thermally driven diffusion competes with externally imposed, finite-ranged, athermal atomic exchanges, as is the case in alloys under irradiation. Using a Cahn-Hilliard-type approach, we show that when the range of these exchanges exceeds a critical value labyrinthine concentration patterns at a mesoscopic scale can be stabilized. Furthermore, these steady-state patterns appear only for a window of the frequency of forced exchanges. Our results suggest that ion beams may provide a novel route to stabilize and tune the size of nanoscale structural features in materials. (c) 2000 The American Physical Society.

Enrique, Raul A.; Bellon, Pascal

2000-03-27

389

NASA Astrophysics Data System (ADS)

The transient spin polarization dynamics in bulk cadmium telluride (CdTe) at 70 K is investigated by the circularly polarized pump-probe reflection technique. A general expression is derived from the rate equations of a two-level system with small signal approximation to describe the light-helicity-dependent reflection spectrum. The initial degree of electron spin polarization in the excited state and the electron spin relaxation time in bulk CdTe at low temperature with different carrier density are analyzed according to this model. Our experimental results reveal that the D'yakonov–Perel' mechanism based on a fully microscopic kinetic spin Bloch equation (microscopic KSBE) approach dominates in the electron spin relaxation process in bulk CdTe crystal.

Ma, Hong; Leng, Jiancai

2013-10-01

390

NASA Astrophysics Data System (ADS)

We calculated the real-time non-equilibrium dynamics of quantum spin systems at finite temperatures. The mathematical framework originates from the C*-approach to quantum statistical mechanics and was applied to the samples investigated by means of spin-polarized scanning tunneling microscopy. Quantum fluctuations around thermal equilibrium were analyzed and calculated. The time-averaged expectation values agree with the time-averaged experimental data for magnetization curves. The method was used to investigate the dynamics of a sample for shorter times than the resolution time of the experimental setup. Furthermore, predictions of the relaxation times of single spins on metallic and semiconductor surfaces are made. To check the validity of our model, we compared our results with experimental data obtained from Fe adatoms on InSb and from Co adatoms on Pt(111) and found good agreement. Approximated thermalization was found numerically for the expectation values of the spin operators.

Them, K.; Stapelfeldt, T.; Vedmedenko, E. Y.; Wiesendanger, R.

2013-01-01

391

NASA Astrophysics Data System (ADS)

We report a general approach for the simulation of the electron paramagnetic resonance (EPR) spectra of spin labels attached to peptides and proteins directly from replica-exchange molecular dynamics (REMD) trajectories. Conventional MD trajectories are generally inadequate for the prediction of EPR line shapes since the label can become trapped in one or more of a set of rotameric states, thus preventing both conformational sampling and accurate estimates of the exchange rates between different rotamers. The advantage of using REMD is its ability to provide both efficient conformational sampling and kinetic information for spin-label dynamics. Our approach is illustrated with spin-labeled peptide. This approach to REMD-EPR simulation paves the way for the wider application of MD modeling to the simulation and interpretation of EPR spectra of spin-labeled molecules.

Tyrrell, S.; Oganesyan, V. S.

2013-10-01

392

Ultrafast dynamics of photoexcited charge and spin currents in semiconductor nanostructures

NASA Astrophysics Data System (ADS)

Employing the quantum interference among one- and two-photon excitations induced by ultrashort two-color laser pulses it is possible to generate charge and spin currents in semiconductors and semiconductor nanostructures on femtosecond time scales. Here, it is reviewed how the excitation process and the dynamics of such photocurrents can be described on the basis of a microscopic many-body theory. Numerical solutions of the semiconductor Bloch equations (SBE) provide a detailed description of the time-dependent material excitations. Applied to the case of photocurrents, numerical solutions of the SBE for a two-band model including many-body correlations on the second-Born Markov level predict an enhanced damping of the spin current relative to that of the charge current. Interesting effects are obtained when the scattering processes are computed beyond the Markovian limit. Whereas the overall decay of the currents is basically correctly described already within the Markov approximation, quantum-kinetic calculations show that memory effects may lead to additional oscillatory signatures in the current transients. When transitions to coupled heavy- and light-hole valence bands are incorporated into the SBE, additional charge and spin currents, which are not described by the two-band model, appear.

Meier, Torsten; Pasenow, Bernhard; Duc, Huynh Thanh; Vu, Quang Tuyen; Haug, Hartmut; Koch, Stephan W.

2007-02-01

393

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

394

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 in order to position 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 carbons 5-, 8-, 10-, 12- and 16- of stearic acid. The EPR-determined affinity for the enzyme increases as the length of the alkyl end of the probe increases, with ??G 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 on carbon 5 has highest affinity for the lipoxygenase and it is a competitive inhibitor, with Ki 9 ?M. 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.

Wu, Fayi; Gaffney, Betty J.

2008-01-01

395

Avoiding the loss of coherence of quantum mechanical states is an important prerequisite for quantum information processing. Dynamical decoupling (DD) is one of the most effective experimental methods for maintaining coherence, especially when one can access only the qubit system and not its environment (bath). It involves the application of pulses to the system whose net effect is a reversal of the system-environment interaction. In any real system, however, the environment is not static, and therefore the reversal of the system-environment interaction becomes imperfect if the spacing between refocusing pulses becomes comparable to or longer than the correlation time of the environment. The efficiency of the refocusing improves therefore if the spacing between the pulses is reduced. Here, we quantify the efficiency of different DD sequences in preserving different quantum states. We use {sup 13}C nuclear spins as qubits and an environment of {sup 1}H nuclear spins as the environment, which couples to the qubit via magnetic dipole-dipole couplings. Strong dipole-dipole couplings between the proton spins result in a rapidly fluctuating environment with a correlation time of the order of 100 {mu}s. Our experimental results show that short delays between the pulses yield better performance if they are compared with the bath correlation time. However, as the pulse spacing becomes shorter than the bath correlation time, an optimum is reached. For even shorter delays, the pulse imperfections dominate over the decoherence losses and cause the quantum state to decay.

Alvarez, Gonzalo A.; Suter, Dieter [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Ajoy, Ashok [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Birla Institute of Technology and Science, Pilani, Zuarinagar, Goa 403726 (India); NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India); Peng Xinhua [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Hefei National Laboratory for Physical Sciences at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)

2010-10-15

396

Rotating Frame Spin dynamics of a Single Nitrogen Vacancy Center in Diamond Nanocrystal

NASA Astrophysics Data System (ADS)

We investigate the spin dynamics of a nitrogen-vacancy (NV) center contained in individual diamond nanocrystals with an average diameter of 70 ± 20 nm in the presence of continuous microwave excitation. Upon periodic reversal of the microwave phase, we observe a train of rotary (Solomon) echoes that effectively extends the system coherence lifetime to reach several tens of microseconds, depending on the microwave power and phase inversion rate [1]. Starting from a model where the NV center interacts with a bath of paramagnetic defects on the nanocrystal surface, we use average Hamiltonian theory to compute the signal envelope from its amplitude at the echo maxima. A comparison between the effective Rabi and Solomon propagators shows that the observed response can be understood as a form of higher-order decoupling from the spin bath. The observed rotary echoes can be thought of as the rotating frame analog of Hahn's spin echoes, implying that the present scheme may find use for nanodiamond-based magnetic sensing. [1] A. Laraoui, C. A. Meriles, Phys. Rev. B 84, 161403(R) (2011).

Laraoui, Abdelghani; Meriles, Carlos

2012-02-01

397

System dynamics is progressively taught in different levels of education systems, and there are challenges as for integrating it into the curricula of different professions and at the same time striving to grow it into a profession on its own. This paper starts recognizing that no representation of what is learned in system dynamics has been published in a way

Martin Schaffernicht; Patricio Madariaga

398

?-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

2012-09-18

399

We have used saturation transfer electron paramagnetic resonance (ST-EPR) to study the rotational dynamics of spin-labeled regulatory light chain (RLC) in scallop ( Placopecten magellanicus) muscle fibers. The single cysteine (Cys 51) in isolated clam (Mercenaria) RLC was labeled with an indanedione spin label (InVSL). RLC was completely and specifically extracted from scallop striated muscle fibers, eliminating the Ca sensitivity

Osha Roopnarine; Andrew G. Szent-Györgyi; David D. Thomas

1998-01-01

400

NMR study of the spin dynamics in Tl2Ba2CuOy (Tc=85 K)

In order to understand the spin dynamics in the over-doped region of the high-Tc oxides, the temperature (T) dependence of the Knight shift and the spin-lattice relaxation time (T1) at the Cu and the O sites of the CuO2 plane were measured in the normal state of Tl2Ba2CuOy with maximum Tc (Tc=85 K). The T dependence of the Knight shift

Shinsaku Kambe; Hiroshi Yasuoka; Akihiko Hayashi; Yutaka Ueda

1993-01-01

401

Evidence for correlation between spin and charge dynamics in La2Cu1-xLixO4

NASA Astrophysics Data System (ADS)

From ac magnetic susceptibility measurements on Li-doped La2CuO4, with Hac parallel and perpendicular to the CuO plane, we find frequency-dependent behavior below a spin-glass temperature (TSG). TSG obtained from magnetic susceptibility is higher than the charge-glass temperature TCG obtained from dielectric constant measurements, indicating that spin freezes first and drives charge freezing at a lower temperature. Similar frequency dependence of the two characteristic freezing temperatures underlines that charge and spin dynamics are strongly correlated in this cuprate compound.

Park, Eunsung; Park, Tuson; Sarrao, J. L.; Thompson, J. D.

2009-04-01

402

Dynamics of the sub-Ohmic spin-boson model: a time-dependent variational study.

The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D1 ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength ? ? 0.1 for s = 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schro?dinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s ? 1). PMID:23464144

Wu, Ning; Duan, Liwei; Li, Xin; Zhao, Yang

2013-02-28

403

Crossover in the specific heat of dilute magnets induced by critical spin-wave dynamics

NASA Astrophysics Data System (ADS)

The dynamics of spin waves in dilute Heisenberg magnets becomes critical at concentrations p near the percolation threshold pc where, by virtue of the divergence of the percolation correlation length ?, the systems become self-similar. The resulting crossover in dispersion relation and density of states from hydrodynamic to critical behavior affects static thermal properties influenced by excitation of spin waves. In a previous work we showed that, in fact, the crossover in dynamics induces a crossover in the magnetization behavior. In this work we investigate the effects of the dynamic crossover on another thermal property, the specific heat. The study of the specific heat involves new aspects since it includes the contribution of the excitations on the whole distribution of finite clusters, besides the contribution of the excitations on the infinite cluster, while the magnetization involves only the excitations on the infinite cluster. It is shown that for low temperatures T and small ?p=(p-pc) the specific heat of a dilute ferromagnet at concentrations p>pc is C(p,T)=?p?dg(?p?zJ/kBT), where ? is the percolation-correlation-length exponent, z the dynamic critical exponent, d the Euclidean dimensionality, and J the exchange constant. At concentrations p

Pimentel, I. R.; Stinchcombe, R. B.

1994-09-01

404

Spin dynamics in the extended kagom'e YBaCo4O7

NASA Astrophysics Data System (ADS)

The extended kagom'e systemYBaCo4O7 consists of antiferromagnetically coupled Co^2+ and Co^3+ ions arranged in stacks with alternating kagom'e and triangular layers in ab planes in the orthorhombic lattice. The oxygen-stoichiometric material orders below 110 K. The system exhibits interesting exchange topology with both trigonal bipyramids and triangular kagom'e clusters of Co ions. Model calculations and neutron scattering experiments, made by other workers, have provided considerable information on the magnetic structure. Ordered chains are found for the apical ions along the c-axis with neighbor chains having oppositely directed polarizations perpendicular to c in an antiferromagnetic configuration. Only short range order is present in the kagom'e planes at temperatures as low as 2 K. The present pulsed NMR measurements, made on a single crystal, both in zero magnetic field and in low applied fields, distinguish the Co ion sites and provide information on the evolution of the spin dynamics for the plane and chain sites as a function of temperature in the range 1.7 - 50 K above which signal wipe-out occurs. A dramatic change in the spin dynamics is found below 5 K.

Hoch, Michael; Kuhns, Philip; Besara, Tiglet; Reyes, Arneil; Mitchell, John

2012-02-01

405

?SR study of spin dynamics in LiY1-xHoxF4

NASA Astrophysics Data System (ADS)

We present zero-field positive muon spin relaxation (?SR) measurements for LiY1-xHoxF4 samples with x = 0.0017, 0.0085, 0.0406, and 0.0855. We characterize the dynamics associated with the formation of the (F-?-F)- complex by comparing our data with Monte Carlo simulations to determine the concentration range over which the spin dynamics are determined primarily by the Ho3+-? interaction rather than by the F-? interaction. Simulations show that F-?-F oscillations should evolve into a Lorentzian Kubo--Toyabe decay for an increasing static magnetic field distribution ? (i.e., increasing x), but the data do not show this behavior, consistent with the recently reported existence of strong magnetic fluctuations in this system at low temperatures. Anisotropy in the field distribution is shown to cause small errors of the order of 10% from behavior predicted for an isotropic distribution. Finally, numerical calculations show that values of ? calculated in the single-ion limit greatly exceed the values extracted from curve fits, suggesting that strong correlations play an important role in this system.

Johnson, R. C.; Chen, K. H.; Giblin, S. R.; Lord, J. S.; Amato, A.; Baines, C.; Barbara, B.; Malkin, B. Z.; Graf, M. J.

2011-05-01

406

Dynamics of Thermal Effects in the Spin-Wave Theory of Quantum Antiferromagnets

NASA Astrophysics Data System (ADS)

The main propose of this work [1] is to study the dynamics of quantum antiferromagnets due to the interaction with a thermal environment. To this end we resort to the spin wave theory which has become by now an standard and reference tool in order to have a good approximate description of quantum antiferromagnetic systems in appropriate dimensions. We derive a master equation that allows us to study non-equilibrium dynamics due to the thermal bosons in the environment, and give closed analytic form for the magnon decay rates. Moreover, we show that these ones turn out to be closely related to form factors, which are experimentally accessible by means of neutron and Raman scattering. Furthermore, we compute the time-evolution of the staggered magnetization showing that, for moderate temperatures, the magnetic order is not spoilt even if the coupling is fully isotropic. As far as we know, this is a fundamental aspect of spin wave theory that has remained unexplored. We expect this presentation may be interesting for a broad audience as it is at the crossroads of strongly correlated systems and the physics of quantum open systems, that is so much rooted in quantum information theory.[4pt] [1] A. Rivas and M.A. Martin-Delgado, Ann. Phys. (N.Y.) (in press), and arXiv:1112.315.

Rivas, Angel; Martin-Delgado, Miguel A.

2013-03-01

407

NASA Astrophysics Data System (ADS)

The longitudinal-field muon relaxation experiments have been carried out in the Pr,La)Os4Sb12 and Pr(Os,Ru)4Sb12 alloy systems. At low temperatures, the dynamic fluctuations are involved in muon relaxation in addition to the contribution from a distributions of static muon local fields. The temperature and concentration dependencies of the muon damping rate ? indicate that this dynamic contribution is due to ^141Pr nuclear magnetism, which is enhanced by hyperfine coupling to the Pr^3+ Van Vleck susceptibility. Further evidence comes from the field dependence of ?, which is in reasonable agreement with the modified model for muon spin relaxation by dipole-coupled nuclear spins.

Shu, Lei; Maclaughlin, D. E.; Higemoto, W.; Heffner, R. H.; Ohishi, K.; Ito, T. U.; Aoki, Y.; Tunashima, Y.; Yonezawa, Y.; Sanada, S.; Kikuchi, D.; Sato, H.; Ishida, K.; Kadono, R.; Koda, A.; Bernal, O. O.; Sugawara, H.; Frederick, N. A.; Yuhasz, W. M.; Sayles, T. A.; Yanagisawa, T.; Maple, M. B.

2007-03-01

408

Site-directed spin labeling and pulsed electron–electron double resonance (PELDOR or DEER) have previously been applied successfully to study the structure and dynamics of nucleic acids. Spin labeling nucleic acids at specific sites requires the covalent attachment of spin labels, which involves rather complicated and laborious chemical synthesis. Here, we use a noncovalent label strategy that bypasses the covalent labeling chemistry and show that the binding specificity and efficiency are large enough to enable PELDOR or DEER measurements in DNA duplexes and a DNA duplex bound to the Lac repressor protein. In addition, the rigidity of the label not only allows resolution of the structure and dynamics of oligonucleotides but also the determination of label orientation and protein-induced conformational changes. The results prove that this labeling strategy in combination with PELDOR has a great potential for studying both structure and dynamics of oligonucleotides and their complexes with various ligands.

Reginsson, Gunnar W.; Shelke, Sandip A.; Rouillon, Christophe; White, Malcolm F.; Sigurdsson, Snorri Th.; Schiemann, Olav

2013-01-01

409

NASA Astrophysics Data System (ADS)

Diblock copolymers in the melt exhibit order-disorder phase transitions (ODT), which are accompanied by strong concentration fluctuations. These transitions are generally described in terms of the random phase approximation (RPA) of Leibler and Fredrickson, which is able to explain small angle scattering results in the neighborhood of the ODT, in particular around the correlation peak at q*. The RPA theory has been extended to include dynamical phenomena, predicting the short time relaxation of the dynamic structure factor in polymeric multicomponent systems. We report small angle neutron scattering and neutron spin echo experiments on polyethylene-block-polyethylethylene (PE-PEE) and poly(ethylene-propylene)-block-polyethylethylene (PEP-PEE) copolymers with molecular weights of 16.500 and 68.000 g/mol, which explore the structure and dynamics of these block copolymers. Studying melts with different hydrogen/deuterium labeling it was possible to observe experimentally the different relaxation modes of such systems separately. In particular the collective relaxation behavior as well as the single chain motion were accessed. The experimental results were quantitatively compared with the RPA predictions, which were based solely on the dynamical properties of the corresponding homopolymers and the static structure factors. The collective dynamics exhibits an unanticipated fast relaxation mode. This mode is most visible at low wave numbers (q>=q*) but extends to length scales considerably shorter than the radius of gyration. Furthermore, the dynamical RPA yields expressions for the mobilities of chain segments in the block copolymer melt. These combination rules are at variance with the experimental findings for the single chain dynamics, while they hold for the collective response.

Montes, H.; Monkenbusch, M.; Willner, L.; Rathgeber, S.; Fetters, L.; Richter, D.

1999-05-01

410

We have recently theorized that consciousness is intrinsically connected to quantum mechanical spin since said spin is embedded in the microscopic structure of spacetime and is more fundamental than spacetime itself, that is, spin is the \\

Huping Hu; Maoxin Wu

411

NASA Astrophysics Data System (ADS)

The structural and dynamical properties of high-spin Ru2+ in aqueous solution have been theoretically studied using molecular dynamics (MD) simulations. The conventional MD simulation based on pair potentials gives the overestimated average first shell coordination number of 9, whereas the value of 5.9 was observed when the three-body corrected function was included. A combined ab initio quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulation has been performed to take into account the many-body effects on the hydration shell structure of Ru2+. The most important region, the first hydration shell, was treated by ab initio quantum mechanics at UHF level using the SBKJC VDZ ECP basis set for Ru2+ and the 6-31G? basis sets for water. An exact coordination number of 6 for the first hydration shell was obtained from the QM/MM simulation. The QM/MM simulation predicts the average Ru2+ O distance of 2.42 Å for the first hydration shell, whereas the values of 2.34 and 2.46 Å are resulted from the pair potentials without and with the three-body corrected simulations, respectively. Several other structural properties representing position and orientation of the solvate molecules were evaluated for describing the hydration shell structure of the Ru2+ ion in dilute aqueous solution. A mean residence time of 7.1 ps was obtained for water ligands residing in the second hydration shell.

Kritayakornupong, Chinapong; Hannongbua, Supot

2007-01-01

412

A dynamic global vegetation model (DGVM) coupled with a land surface model (LSM) is generally initialized using a spin-up\\u000a process to derive a physically-consistent initial condition. Spin-up forcing, which is the atmospheric forcing used to drive\\u000a the coupled model to equilibrium solutions in the spin-up process, varies across earlier studies. In the present study, the\\u000a impact of the spin-up forcing

Fang Li; Xiaodong Zeng; Xiang Song; Dongxiao Tian; Pu Shao; Dongling Zhang

2011-01-01

413

Dynamic magnetization switching and spin wave excitations by voltage-induced torque

NASA Astrophysics Data System (ADS)

The effect of electric fields on ultrathin ferromagnetic metal layer is one of the promising approaches for manipulating the spin direction with low-energy consumption, localization, and coherent behavior. Several experimental approaches to realize it have been investigated using ferromagnetic semiconductors [1], magnetostriction together with piezo-electric materials [2], multiferroic materials [3], and ultrathin ferromagnetic layer [4-9]. In this talk, we will present a dynamic control of spins by voltage-induced torque. We used the magnetic tunnel junctions with ultrathin ferromagnetic layer, which shows voltage-induced perpendicular magnetic anisotropy change. By applying the voltage to the junction, the magnetic easy-axis in the ultrathin ferromagnetic layer changes from in-plane to out-of-plane, which causes a precession of the spins. This precession resulted in a two-way toggle switching by determining an appropriate pulse length [8]. On the other hand, an application of rf-voltage causes an excitation of a uniform spin-wave [9]. Since the precession of spin associates with an oscillation in the resistance of the junction, the applied rf-signal is rectified and produces a dc-voltage. From the spectrum of the dc-voltage as a function of frequency, we could estimate the voltage-induced torque.[4pt] [1] H. Ohno, et al., Nature 408, 944-946 (2000), D. Chiba, et al, Science 301, 943-945 (2003). [2] V. Novosad, et al., J. Appl. Phys. 87, 6400-6402 (2000), J. --W. Lee, et al., Appl. Phys. Lett. 82, 2458-2460 (2003). [3] W. Eerenstein, et al., Nature 442, 759-765 (2006), Y. --H. Chu, et al., Nature Materials 7, 478-482 (2008). [4] M. Weisheit, et al., Science 315, 349-351 (2007). [5] T. Maruyama, et al., Nature Nanotechnology 4, 158-161 (2009). [6] M. Endo, et al., Appl. Phys. Lett. 96, 212503 (2010). [7] D. Chiba, et al., Nature Materials 10, 853 (2011). [8]Y. Shiota, et al., Nature Materials 11, 39 (2012) [9]T. Nozaki, et al., Nat. Phys. 8, 491 (2012)

Shiota, Yoichi

2013-03-01

414

A simulation study of magnetic vortex structures and spin dynamic modes in permalloy materials

NASA Astrophysics Data System (ADS)

Transverse spin wave modes of a long thin-film permalloy stripe have been studied using micromagnetic simulations and a semi-analytical theory. Lower frequency modes were found localized near the edge of the stripe and higher frequency modes exhibited a crossover property. These features result from the inhomogeneous distribution of the equilibrium magnetization and internal field across the stripe, which is adjusted by an applied field across the width of the stripe. Mode frequencies and wave profiles show distinct characteristics under different applied fields. Mode softening happens at two critical fields corresponding to a symmetry transition of the magnetic system. Spin dynamic modes of a magnetic antivortex in asteroid-shaped permalloy samples were systematically explored using micromagnetic simulations. A gyrotropic mode was found due to the shift of the antivortex from its equilibrium position. Azimuthal and radial spin wave modes have been excited by a pulsed magnetic field in different directions. Coupling between gyrotropic and azimuthal modes splits the degeneracy of paired azimuthal modes. Frequencies of the spin wave modes decrease with asteroid size and thickness while the frequency of the gyrotropic mode increases with asteroid thickness but decreases with asteroid size. The vortex dynamics of a magnetic vortex-antivortex-vortex structure in elliptical permalloy samples was studied using a theoretical model and micromagnetic simulations. Three gyrotropic modes were found to exist and each of them can be excited by a special initial configuration of core displacements. The polarizations of three cores play an important role on the mode frequencies and relative core movements in each mode. The annihilation process of a magnetic vortex pair confined in stadium-shaped permalloy samples was investigated using micromagnetic simulations. With the strength of an applied magnetic field across the width of stadia increasing, the equilibrium magnetization of the system exhibits three different states, which we attribute to the competition mainly between the Zeeman energy and the magnetostatic energy. The geometry dependence of the critical transition field and the linear response of the equilibrium vortex separation to the field were qualitatively explained through a dimensional analysis model.

Wang, Hao

415

An Improved Picture of Methyl Dynamics in Proteins from SRLS Analysis of 2H Spin Relaxation

Protein dynamics is intimately related to biological function. Core dynamics is usually studied with 2H spin relaxation of the 13CDH2 group, analyzed traditionally with the model-free (MF) approach. We showed recently that MF is oversimplified in several respects. This includes the assumption that the local motion of the dynamic probe and the global motion of the protein are decoupled, the local geometry is simple, and the local ordering has axial symmetry. Because of these simplifications MF has yielded a puzzling picture where the methyl rotation axis is moving rapidly with amplitudes ranging from nearly complete disorder to nearly complete order in tightly packed protein cores. Our conclusions emerged from applying to methyl dynamics in proteins the slowly relaxing local structure (SRLS) approach of Polimeno and Freed (J. Phys. Chem. 1995, 99, 1099), which can be considered the generalization of MF, with all the simplifications mentioned above removed. The SRLS picture derived here for the B1 immunoglobulin binding domain of peptostreptococcal protein L, studied over the temperature range of 15 ? 45 °C, is fundamentally different from the MF picture. Thus, methyl dynamics is characterized structurally by rhombic local potentials with varying symmetries, and dynamically by tenfold slower rates of local motion. On average potential rhombicity decreases, mode-coupling increases and the rate of local motion increases with increasing temperature. The average activation energy for local motion is 2.0 ± 0.2 kcal/mol. Mode-coupling affects the analysis even at 15 oC. The accuracy of the results is improved by including in the experimental data set relaxation rates associated with rank 2 coherences.

Meirovitch, Eva; Shapiro, Yury E.; Polimeno, Antonino; Freed, Jack H.

2010-01-01

416

NASA Astrophysics Data System (ADS)

We investigate the effect of static electron-phonon coupling on real-time dynamics of spin and charge transport in ?-conjugated polyene chains. The polyene chain is modeled by the Pariser-Parr-Pople Hamiltonian with dimerized nearest-neighbor parameter t0(1+?) for short bonds and t0(1-?) for long bonds, and long-range electron-electron interactions. We follow the time evolution of the spin and charge using time-dependent density matrix renormalization group technique when a hole is injected at one end of the chain in its ground state. We find that spin and charge dynamics followed through spin and charge velocities depend both on chain length and extent of dimerization ?. Analysis of the results requires focusing on physical quantities such as average spin and charge polarizations, particularly in the large dimerization limit. In the dimerization range 0.0 ? ? ? 0.15, spin-charge dynamics is found to have a well-defined behavior, with spin-charge separation (measured as the ratio of charge velocity to spin velocity) as well as the total amount of charge and spin transported in a given time along the chain decreasing as dimerization increases. However, in the range 0.3 ? ? ? 0.5, it is observed that the dynamics of spin and charge transport becomes complicated. It is observed that, for large ? values, spin-charge separation is suppressed and the injected hole fails to travel the entire length of the chain.

Dutta, Tirthankar; Ramasesha, S.

2011-12-01

417

Recent agenda?setting exercises in the national innovation systems and industrial dynamics literatures have highlighted the unresolved methodological challenges faced by those seeking to explore the innovation process in a co?evolutionary perspective. The paper seeks to contribute to this debate by drawing upon the research methods and presentational conventions of business historians. The empirical study concerns the emergence of radical innovations

Richard Blundel

2006-01-01

418

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

419

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

420

DYNAMIC CAPABILITIES AND COMPETENCE OBSOLESCENCE: EMPIRICAL DATA FROM RESEARCH-INTENSIVE FIMRS

The dynamic capabilities approach focuses on a firm's ability to develop its resource base in order to meet environmental expectations. Therefore, it is closely interrelated to issues of balancing exploration and exploitation in organizational learning. Scholars argue that organizations can combine both learning modes by adapting ambidextrous organizational designs. Yet, owing to strategic contradictions, ambidextrous organizations are faced with perpetual

WOLFGANG H. GÜTTEL; STEFAN W. KONLECHNER

2007-01-01

421

A pendulum prepared perfectly inverted and motionless is a prototype of unstable equilibrium and corresponds to an unstable hyperbolic fixed point in the dynamical phase space. Here, we measure the non-equilibrium dynamics of a spin-1 Bose-Einstein condensate initialized as a minimum uncertainty spin-nematic state to a hyperbolic fixed point of the phase space. Quantum fluctuations lead to non-linear spin evolution along a separatrix and non-Gaussian probability distributions that are measured to be in good agreement with exact quantum calculations up to 0.25?s. At longer times, atomic loss due to the finite lifetime of the condensate leads to larger spin oscillation amplitudes, as orbits depart from the separatrix. This demonstrates how decoherence of a many-body system can result in apparent coherent behaviour. This experiment provides new avenues for studying macroscopic spin systems in the quantum limit and for investigations of important topics in non-equilibrium quantum dynamics. PMID:23132019

Gerving, C S; Hoang, T M; Land, B J; Anquez, M; Hamley, C D; Chapman, M S

2012-01-01

422

Dynamical spin–orbital correlation in the frustrated magnet Ba3CuSb2O9

NASA Astrophysics Data System (ADS)

At low temperatures, atomic magnetic moments usually exhibit some order, for example ferromagnetic order. An exception is frustrated magnets, in which the symmetry impedes the minimization of energy by pairwise magnetic interactions. In such frustrated magnets, new quantum phases, such as spin liquids, are expected. Theoretically, a quantum liquid based on the orbital degree of freedom has also been considered possible when spin and orbital degrees of freedom are entangled. However, to date, experimental observation of such a dynamic spin–orbital state has been a challenge. Here we report an X-ray scattering study of a dynamic spin–orbital state in the frustrated magnet Ba3CuSb2O9. Orbital dynamical motion and increasing short-range orbital correlation with cooling are observed. The most significant feature is that the temperature variation of the orbital correlation is clearly affected by the magnetic interaction. This finding strongly supports a new quantum state in which spins and orbitals are entangled.

Ishiguro, Yuki; Kimura, Kenta; Nakatsuji, Satoru; Tsutsui, Satoshi; Baron, Alfred Q. R.; Kimura, Tsuyoshi; Wakabayashi, Yusuke

2013-06-01