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1

COMPETING SPIN WAVES AND SUPERCONDUCTING

(j - i) is the transfer matrix element and U is the onÂsite Coulomb repulsion, which is kept in the zero for the renormal- ized electron propagators of the coexisting phases of SDW antiferro- magnetism into account the full Green's functions as well as the dynamical structure of the correlations, is used

Entel, P.

2

Competing spin pumping effects in magnetic hybrid structures

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

3

Magnetically Tuned Spin Dynamics Resonance

We present the experimental observation of a magnetically tuned resonance phenomenon in the spin mixing dynamics of ultracold atomic gases. In particular, we study the magnetic field dependence of spin conversion in F=2 {sup 87}Rb spinor condensates in the crossover from interaction dominated to quadratic Zeeman dominated dynamics. We discuss the observations in the framework of spin dynamics as well as matter wave four wave mixing. Furthermore, we show that the validity range of the single mode approximation for spin dynamics is significantly extended at high magnetic field.

Kronjaeger, J.; Becker, C.; Bongs, K.; Sengstock, K. [Institut fuer Laserphysik, Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); Navez, P. [Labo Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); additional address: Universitaet Duisburg-Essen, Universitaetsstrasse 5, 45117 Essen (Germany)

2006-09-15

4

Magnetically tuned spin dynamics resonance.

We present the experimental observation of a magnetically tuned resonance phenomenon in the spin mixing dynamics of ultracold atomic gases. In particular, we study the magnetic field dependence of spin conversion in F=2 (87)Rb spinor condensates in the crossover from interaction dominated to quadratic Zeeman dominated dynamics. We discuss the observations in the framework of spin dynamics as well as matter wave four wave mixing. Furthermore, we show that the validity range of the single mode approximation for spin dynamics is significantly extended at high magnetic field. PMID:17025866

Kronjäger, J; Becker, C; Navez, P; Bongs, K; Sengstock, K

2006-09-15

5

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

6

Coherent spin dynamics in semiconductor quantum dots

NASA Astrophysics Data System (ADS)

We briefly review recent achievements in experimental and theoretical studies of the spin dynamics of electrons and trions under optical pulse-train excitation. The microscopic origin of spin coherence generation, control and detection by means of light is uncovered. The specific features of spin-Faraday, Kerr, and ellipticity signals are analyzed. We show that these effects provide complementary information about spin dynamics. The equilibrium spin dynamics probed by the spin noise spectroscopy is also discussed.

Glazov, M. M.

2013-04-01

7

Dynamic prediction by landmarking in competing risks.

We propose an extension of the landmark model for ordinary survival data as a new approach to the problem of dynamic prediction in competing risks with time-dependent covariates. We fix a set of landmark time points tLM within the follow-up interval. For each of these landmark time points tLM , we create a landmark data set by selecting individuals at risk at tLM ; we fix the value of the time-dependent covariate in each landmark data set at tLM . We assume Cox proportional hazard models for the cause-specific hazards and consider smoothing the (possibly) time-dependent effect of the covariate for the different landmark data sets. Fitting this model is possible within the standard statistical software. We illustrate the features of the landmark modelling on a real data set on bone marrow transplantation. PMID:23086627

Nicolaie, M A; van Houwelingen, J C; de Witte, T M; Putter, H

2013-05-30

8

Electron spin decoherence in nuclear spin baths and dynamical decoupling

We introduce the quantum theory of the electron spin decoherence in a nuclear spin bath and the dynamical decoupling approach for protecting the electron spin coherence. These theories are applied to various solid-state systems, such as radical spins in molecular crystals and NV centers in diamond.

Zhao, N.; Yang, W.; Ho, S. W.; Hu, J. L.; Wan, J. T. K.; Liu, R. B. [Department of Physics, Chinese University of Hong Kong, Shatin, New Territories (Hong Kong)

2011-12-23

9

Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture

We report the observation of coherent heteronuclear spin dynamics driven by inter-species spin-spin interaction in an ultracold spinor mixture, which manifests as periodical and well correlated spin oscillations between two atomic species. In particular, we investigate the magnetic field dependence of the oscillations and find a resonance behavior which depends on {\\em both} the linear and quadratic Zeeman effects and the spin-dependent interaction. We also demonstrate a unique knob for controlling the spin dynamics in the spinor mixture with species-dependent vector light shifts. Our finds are in agreement with theoretical simulations without any fitting parameters.

Li, Xiaoke; He, Xiaodong; Wang, Fudong; Guo, Mingyang; Xu, Zhi-Fang; Zhang, Shizhong; Wang, Dajun

2015-01-01

10

Exact dynamics of XX central spin models

The dynamical behavior of a star network of spins, wherein each of N decoupled spins interact with a central spin through non uniform Heisenberg XX interaction is exactly studied. The time-dependent Schrodinger equation of the spin system model is solved starting from an arbitrary initial state. The resulting solution is analyzed and briefly discussed.

M. A. Jivulescu; E. Ferraro; A. Napoli; A. Messina

2009-04-04

11

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

12

Quantum Dynamics of Spin Wave Propagation Through

in a continuous medium. Such structure can be created or annihilated by some external action [1]. The manipulation pictures (a,b,c,d): Spin configurations at time t/ = 0; Right pictures (e,f,g): Dynamically stable spin picture (h): Spin configuration at time t/ = 100 for the Heisenberg model ( = 1), illustrating

13

Set-valued dynamic treatment regimes for competing outcomes

Summary Dynamic treatment regimes operationalize the clinical decision process as a sequence of functions, one for each clinical decision, where each function maps up-to-date patient information to a single recommended treatment. Current methods for estimating optimal dynamic treatment regimes, for example Q-learning, require the specification of a single outcome by which the ‘goodness’ of competing dynamic treatment regimes is measured. However, this is an over-simplification of the goal of clinical decision making, which aims to balance several potentially competing outcomes, e.g., symptom relief and side-effect burden. When there are competing outcomes and patients do not know or cannot communicate their preferences, formation of a single composite outcome that correctly balances the competing outcomes is not possible. This problem also occurs when patient preferences evolve over time. We propose a method for constructing dynamic treatment regimes that accommodates competing outcomes by recommending sets of treatments at each decision point. Formally, we construct a sequence of set-valued functions that take as input up-to-date patient information and give as output a recommended subset of the possible treatments. For a given patient history, the recommended set of treatments contains all treatments that produce non-inferior outcome vectors. Constructing these set-valued functions requires solving a non-trivial enumeration problem. We offer an exact enumeration algorithm by recasting the problem as a linear mixed integer program. The proposed methods are illustrated using data from the CATIE schizophrenia study. PMID:24400912

Laber, Eric B.; Lizotte, Daniel J.; Ferguson, Bradley

2014-01-01

14

Electrically driven spin dynamics of paramagnetic impurities.

The spin dynamics of dilute paramagnetic impurities embedded in a semiconductor GaAs channel of a conventional lateral spin valve has been investigated. It is observed that the electron spin of paramagnetic Mn atoms can be polarized electrically when driven by a spin valve in the antiparallel configuration. The transient current through the MnAs/GaAs/MnAs spin valve bears the signature of the underlying spin dynamics driven by the exchange interaction between the conduction band electrons in GaAs and the localized Mn electron spins. The time constant for this interaction is observed to be dependent on temperature and is estimated to be 80 ns at 15 K. PMID:18518470

Saha, D; Siddiqui, L; Bhattacharya, P; Datta, S; Basu, D; Holub, M

2008-05-16

15

Seeing spin dynamics in atomic gases

The dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.

Dan M. Stamper-Kurn

2014-12-31

16

Dynamics of antiferromagnets driven by spin current

NASA Astrophysics Data System (ADS)

When a spin-polarized current flows through a ferromagnetic (FM) metal, angular momentum is transferred to the background magnetization via spin-transfer torques. In antiferromagnetic (AFM) materials, however, the corresponding problem is unsolved. We derive microscopically the dynamics of an AFM system driven by spin current generated by an attached FM polarizer, and find that the spin current exerts a driving force on the local staggered order parameter. The mechanism does not rely on the conservation of spin angular momentum, nor does it depend on the induced FM moments on top the AFM background. Two examples are studied: (i) A domain wall is accelerated to a terminal velocity by purely adiabatic effect where the Walker's breakdown is avoided. (ii) Spin injection modifies the AFM resonance frequency, and spin current injection triggers spin wave instability of local moments above a threshold.

Cheng, Ran; Niu, Qian

2014-02-01

17

Dynamics of Antiferromagnets Driven by Spin Current

When a spin-polarized current flows through a ferromagnetic (FM) metal, angular momentum is transferred to the background magnetization via spin-transfer torques. In antiferromagnetic (AFM) materials, however, the corresponding problem is unsolved. We derive microscopically the dynamics of an AFM system driven by spin current generated by an attached FM polarizer, and find that the spin current exerts a driving force on the local staggered order parameter. The mechanism does not rely on the conservation of spin angular momentum, nor does it depend on the induced FM moments on top the AFM background. Two examples are studied: (i) A domain wall is accelerated to a terminal velocity by purely adiabatic effect where the Walker's break-down is avoided; and (ii) Spin injection modifies the AFM resonance frequency, and spin current injection triggers spin wave instability of local moments above a threshold.

Ran Cheng; Qian Niu

2014-02-11

18

Dynamical behavior of two predators competing over a single prey.

Dynamical behavior of a food web comprising two predators competing over a single prey has been investigated. The analysis of the food web model shows that the persistence is not possible for two competing predators sharing a single prey species in the cases when any one of the boundary prey-predator planes has a stable equilibrium point. The principle of competitive exclusion holds in such cases. However, numerical simulations exhibit persistence in the presence of periodic solutions in the boundary planes. The system exhibits quasi-periodic behavior in the positive octant. The co-existence in the form of a limit cycle is also possible in some cases. PMID:17574733

Gakkhar, Sunita; Singh, Brahampal; Naji, Raid Kamel

2007-01-01

19

Relativistic dynamical spin excitations of magnetic adatoms

NASA Astrophysics Data System (ADS)

We present a first-principles theory of dynamical spin excitations in the presence of spin-orbit coupling. The broken global spin rotational invariance leads to a new sum rule. We explore the competition between the magnetic anisotropy energy and the external magnetic field, as well as the role of electron-hole excitations, through calculations for 3 d -metal adatoms on the Cu(111) surface. The spin excitation resonance energy and lifetime display nontrivial behavior, establishing the strong impact of relativistic effects. We legitimate the use of the Landau-Lifshitz-Gilbert equation down to the atomic limit, but with parameters that differ from a stationary theory.

dos Santos Dias, M.; Schweflinghaus, B.; Blügel, S.; Lounis, S.

2015-02-01

20

Dynamics of the dual spin turn

NASA Astrophysics Data System (ADS)

In the initial attitude acquisition of a GEO satellite, the axis around which a bias-momentum satellite spins can be transferred directly by means of the run-up of a momentum wheel. This technique is called the dual-spin turn. In this paper, the dynamics of the dual-spin turn is formulated, and stability conditions are obtained. Numerical examples show that a nutation occurs as the wheel runs up, and that the nutation angle depends on dynamics parameters. Generally, the larger the spacecraft momentum is and the lower the wheel run-up rate is, the smaller the nutation angle becomes.

Nagano, Hiroshi

21

Competing effective interactions of Dirac electrons in the Spin–Fermion system

Recently discovered advanced materials, such as heavy fermions, frequently exhibit a rich phase diagram suggesting the presence of different competing interactions. A unified description of the origin of these multiple interactions, albeit very important for the comprehension of such materials is, in general not available. It would be therefore very useful to have a simple model where the common source of different interactions could be possibly traced back. In this work we consider a system consisting in a set of localized spins on a square lattice with antiferromagnetic nearest neighbors interactions and itinerant electrons, which are assumed to be Dirac-like and interact with the localized spins through a Kondo magnetic interaction. This system is conveniently described by the Spin–Fermion model, which we use in order to determine the effective interactions among the itinerant electrons. By integrating out the localized degrees of freedom we obtain a set of different interactions, which includes: a BCS-like superconducting term, a Nambu–Jona-Lasinio-like, excitonic term and a spin–spin magnetic term. The resulting phase diagram is investigated by evaluation of the mean-field free-energy as a function of the relevant order parameters. This shows the competition of the above interactions, depending on the temperature, chemical potential and coupling constants. -- Highlights: •Antiferromagnetic Heisenberg–Kondo lattice model with itinerant Dirac fermions. •Integrating out the spins generates competing interactions: BCS-like, excitonic and magnetic. •Novel mechanism of superconductivity from magnetic interactions between the spins and electrons. •Dome-shaped dependence of the temperature on the chemical potential in agreement with pnictides.

Marino, E.C., E-mail: marino@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ, 21941-972 (Brazil); Nunes, Lizardo H.C.M., E-mail: lizardonunes@ufsj.edu.br [Departamento de Ciências Naturais, Universidade Federal de São João del Rei, 36301-000 São João del Rei, MG (Brazil)

2014-01-15

22

Parallel algorithm for spin and spin-lattice dynamics simulations

NASA Astrophysics Data System (ADS)

To control numerical errors accumulated over tens of millions of time steps during the integration of a set of highly coupled equations of motion is not a trivial task. In this paper, we propose a parallel algorithm for spin dynamics and the newly developed spin-lattice dynamics simulation [P. W. Ma , Phys. Rev. B 78, 024434 (2008)]. The algorithm is successfully tested in both types of dynamic calculations involving a million spins. It shows good stability and numerical accuracy over millions of time steps (˜1ns) . The scheme is based on the second-order Suzuki-Trotter decomposition (STD). The usage can avoid numerical energy dissipation despite the trajectory and machine errors. The mathematical base of the symplecticity, for properly decomposed evolution operators, is presented. Due to the noncommutative nature of the spin in the present STD scheme, a unique parallel algorithm is needed. The efficiency and stability are tested. It can attain six to seven times speed up when eight threads are used. The run time per time step is linearly proportional to the system size.

Ma, Pui-Wai; Woo, C. H.

2009-04-01

23

Spin dynamics in the strong spin-orbit coupling regime

PHYSICAL REVIEW B 84, 035318 (2011) Spin dynamics in the strong spin-orbit coupling regime Xin Liu,1 Xiong-Jun Liu,1 and Jairo Sinova1,2 1Department of Physics, Texas A&M University, College Station, Texas 77843-4242, USA 2Institute of Physics... frequency #2;so take the form: H so = (?1 ? 2?3 cos 2? )kx?y + (?2 + 2?3 cos 2? )ky?x, (5) where ?1 = ? + ?1 and ?2 = ?1 ? ?. 035318-11098-0121/2011/84(3)/035318(8) 2011 American Physical Society XIN LIU, XIONG-JUN LIU, AND JAIRO SINOVA PHYSICAL REVIEW B...

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

2011-01-01

24

Magnetic Suspension for Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

NASA Lewis Research Center's Dynamic Spin Rig, located in Building 5, Test Cell CW-18, is used to test turbomachinery blades and components by rotating them in a vacuum chamber. A team from Lewis' Machine Dynamics Branch successfully integrated a magnetic bearing and control system into the Dynamic Spin Rig. The magnetic bearing worked very well both to support and shake the shaft. It was demonstrated that the magnetic bearing can transmit more vibrational energy into the shaft and excite some blade modes to larger amplitudes than the existing electromagnetic shakers can.

Johnson, Dexter

1998-01-01

25

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

26

Spin Hall phenomenology of magnetic dynamics

NASA Astrophysics Data System (ADS)

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

Tserkovnyak, Yaroslav; Bender, Scott A.

2014-07-01

27

Spin dynamics simulation studies of classical spin models

NASA Astrophysics Data System (ADS)

A general spin dynamics program has been developed which can determine the dynamic structure factor S(q, ?), and the intermediate function S(q, t), in the [100], [110], and [111] directions, for a number of classical magnetic models at any temperature desired. The dynamics in both the critical and hydrodynamic regimes of a variety of classical Heisenberg models have been investigated. Our simulation results are compared to the results of experiments as well as other theoretical techniques since large spin magnetic crystals exist where these models are appropriate, including the SC isotropic antiferromagnet RbMnF3, the BCC anisotropic antiferromagnets MnF2 and FeF2 and the FCC isotropic ferromagnets EuO and EuS. For the isotropic antiferromagnet a dynamic critical exponent of z = 1.5 was found, in agreement with both the experimental results and analytical theory. In disagreement with the findings of other theoretical techniques, but in agreement with the experimental results, a diffusive central peak was found to exist at the critical temperature in S(q, ?). For the anisotropic antiferromagnet, in agreement with experiment and theory, the dynamic structure factor S(q, ?), was found to have a diffusive longitudinal component and a suppressed propagative transverse component. We found the dynamic critical exponent to be z~2 but were unable to differentiate between two conflicting theoretical predictions of z = 2 and z = 2.175. Both the SC and BCC isotropic Heisenberg model, with both ferromagnetic and antiferromagnetic interactions, as well as the anisotropic Heisenberg antiferromagnet were studied in the hydrodynamic regime. The spin-wave stiffness coefficient D(T) was determined as a function of temperature. For all these models the propagative excitations in the longitudinal component of the dynamic structure factor were found to result from two-spin-waves. This results in a prediction that the longitudinal component of the dynamic structure factor contains two peaks separated by twice the energy gap frequency for the anisotropic antiferromagnet. The diffusive central peak was found to persist well into the hydrodynamic regime for the antiferromagnetic case but not the ferromagnetic case in agreement with experimental results. Initial results for the biquadratic and double exchange Hamiltonians in the hydrodynamic regime have also been obtained.

Bunker, Alex Edwin

1998-10-01

28

Investigation of triple spin correlations and spin dynamics in ferromagnets

Data on the experimental detection and use of three-particle (chiral) spin dynamic correlations in ferromagnets are presented. The oblique-geometry method for investigating polarized neutron small-angle scattering is described, which gives the dependence that the scattering asymmetry has on the polarization P signs and the scattering angle {theta}. The following results of the dynamics investigation in the critical and ferromagnetic phases in the magnetic field are presented: the temperature dependence of the critical field H{sub c}, the factorization of the momentum transfer dependence of three-particle vertices, the corroboration of the 'hard' version of the dipole critical dynamics, and the dynamics of amorphous magnets and invars.

Okorokov, A. I., E-mail: okorokov@pnpi.spb.ru [Russian Academy of Sciences, Konstantinov Institute of Nuclear Physics, St. Petersburg (Russian Federation)

2011-12-15

29

Competing Effects of Interactions and Spin-Orbit Coupling in a Quantum Wire

NASA Astrophysics Data System (ADS)

We study the interplay of electron-electron interactions and Rashba spin-orbit coupling in one-dimensional ballistic wires. Using the renormalization group approach we construct the phase diagram in terms of Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength. We identify the parameter regimes with a dynamically generated spin gap and show where the Luttinger liquid prevails. We also discuss the consequences for the operation of the Datta-Das transistor.

Gritsev, V.; Japaridze, G.; Pletyukhov, M.; Baeriswyl, D.

2005-04-01

30

Competing effects of interactions and spin-orbit coupling in a quantum wire.

We study the interplay of electron-electron interactions and Rashba spin-orbit coupling in one-dimensional ballistic wires. Using the renormalization group approach we construct the phase diagram in terms of Rashba coupling, Tomonaga-Luttinger stiffness and backward scattering strength. We identify the parameter regimes with a dynamically generated spin gap and show where the Luttinger liquid prevails. We also discuss the consequences for the operation of the Datta-Das transistor. PMID:15904028

Gritsev, V; Japaridze, G; Pletyukhov, M; Baeriswyl, D

2005-04-01

31

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. PMID:21882345

Nguyen, Phuong

2011-01-01

32

Temperature dependent dynamical spin simulations

NASA Astrophysics Data System (ADS)

We have calculated the thermodynamic properties of a classical system of spins interacting with a thermo-bath described by a spin version of the Nose-Hoover thermostat. Different model Hamiltonians have been considered and the sensitivity of the final results on the parameters characterizing the thermo-bath has been tested. The parameters for some of the Hamiltonians are obtained from first principle calculations within density functional framework. We have studied various correlation functions and the degree of ergodicity; and we report such observables as susceptibility, energy, and moment distributions for typical 3d systems. ^* Work was patially carried out at the Ames Laboratory, which is operated for the U.S.Department of Energy by Iowa State University under Contract No. W-7405-82. Work was supported by the Director for Energy Research, Office of Basic Energy Sciences of the U.S.Department of Energy.

Zhang, Yuanhan; Antropov, V. P.; Harmon, B. N.; van Schilfgaarde, M.

1996-03-01

33

Dynamic trajectories of growth and nitrogen capture by competing plants.

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

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

2012-03-01

34

Low-temperature Glauber dynamics under weak competing interactions

NASA Astrophysics Data System (ADS)

We consider the low but nonzero-temperature regimes of the Glauber dynamics in a chain of Ising spins with first- and second-neighbor interactions J1,J2 . For 0 <-J2/|J1| <1 it is known that at T =0 the dynamics is both metastable and noncoarsening, while being always ergodic and coarsening in the limit of T ?0+ . Based on finite-size scaling analyses of relaxation times, here we argue that in that latter situation the asymptotic kinetics of small or weakly frustrated -J2/|J1| ratios is characterized by an almost ballistic dynamic exponent z ?1.03 (2 ) and arbitrarily slow velocities of growth. By contrast, for noncompeting interactions the coarsening length scales are estimated to be almost diffusive.

Grynberg, M. D.

2015-03-01

35

Dynamics of spin charge carriers in polyaniline

NASA Astrophysics Data System (ADS)

The review summarizes the results of the study of emeraldine forms of polyaniline by multifrequency (9.7-140 GHz, 3-cm and 2-mm) wavebands Electron Paramagnetic Resonance (EPR) spectroscopy combined with the spin label and probe, steady-state saturation of spin-packets, and saturation transfer methods. Spin excitations formed in emeraldine form of polyaniline govern structure, magnetic resonance, and electronic properties of the polymer. Conductivity in neutral or weakly doped samples is defined mainly by interchain charge tunneling in the frames of the Kivelson theory. As the doping level increases, this process is replaced by a charge thermal activation transport by molecular-lattice polarons. In heavily doped polyaniline, the dominating is the Mott charge hopping between well-conducting crystalline ravels embedded into amorphous polymer matrix. The main properties of polyaniline are described in the first part. The theoretical background of the magnetic, relaxation, and dynamics study of nonlinear spin carriers transferring a charge in polyaniline is briefly explicated in the second part. An original data obtained in the EPR study of the nature, relaxation, and dynamics of polarons as well as the mechanism of their transfer in polyaniline chemically modified by sulfuric, hydrochloric, camphorsulfonic, 2-acrylamido-2-methyl-1-propanesulfonic, and para-toluenesulfonic acids up to different doping levels are analyzed in the third part. Some examples of utilization of polyaniline in molecular electronics and spintronics are described.

Krinichnyi, V. I.

2014-06-01

36

Combined molecular dynamics-spin dynamics simulations of bcc iron

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

37

Combined molecular dynamics-spin dynamics simulations of bcc iron

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

Perera, Meewanage Dilina N [ORNL] [ORNL; Yin, Junqi [ORNL] [ORNL; Landau, David P [University of Georgia, Athens, GA] [University of Georgia, Athens, GA; Nicholson, Don M [ORNL] [ORNL; Stocks, George Malcolm [ORNL] [ORNL; Eisenbach, Markus [ORNL] [ORNL; Brown, Greg [ORNL] [ORNL

2014-01-01

38

Competing orders and spin density wave instabilities in FeAs-based systems

NASA Astrophysics Data System (ADS)

The discovery of superconductivity with Tc up to 55 K in layered FeAs-based compounds has generated tremendous interest in the scientific community. Except for relatively high Tc, the Fe pnictides display many interesting properties. Among others, the presence of competing orders is one of the most intriguing phenomena. In the early stage of our study on the compounds, we identified a spin-density-wave (SDW) ordered state for the parent compound with a stripe (or collinear) type spin structure based on the transport, specific heat, optical spectroscopy measurements and the first- principle calculations. The proposed spin structure from a nesting of the Fermi surfaces is confirmed by subsequent neutron experiments. However, it could also be explained by a local superexchange picture. In this talk I shall focus on our recent optical data on single crystal samples, trying to address the debating issue about itinerant or localized approaches to the SDW order. We found that the undoped compounds are quite metallic with relatively high plasma frequencies above TSDW. Upon entering the SDW ordered state, a large part of the Drude component is removed by the gapping of Fermi surfaces. Meanwhile, the carrier scattering rate is even more dramatically reduced. Those observations favor an itinerant description for the driving mechanism of SDW instability. Nevertheless, our experiments also indicate that Fe pnictides are not simple metals. A high energy gap-like feature is present even above TSDW, which seems to be linked with the antiferromagnetic spin fluctuations. For the superconducting samples, a superconducting pairing energy gap is clearly observed in the far-infrared reflectance measurement. The Ferrell-Glover- Tinkham sum rule is satisfied at a low energy scale. Work done in collaboration with: G. F. Chen, J. L. Luo, Z. Fang, X. Dai, W. Z. Hu, J. Dong, G. Li, Z. Li, P. Dai, J. Lynn, H. Q. Yuang, J. Singleton.

Wang, Nan Lin

2009-03-01

39

Entropy-vanishing transition and glassy dynamics in frustrated spins.

In an effort to understand the glass transition, the dynamics of a nonrandomly frustrated spin model has been analyzed. The phenomenology of the spin model is similar to that of a supercooled liquid undergoing the glass transition. The slow dynamics can be associated with the presence of extended stringlike structures which demarcate regions of fast spin flips. An entropy-vanishing transition, with the string density as the order parameter, is related to the observed glass transition in the spin model. PMID:11289854

Yin, H; Chakraborty, B

2001-03-01

40

Spin glass dynamics at the mesoscale

NASA Astrophysics Data System (ADS)

The mesoscale allows a new probe of spin glass dynamics. Because the spin glass lower critical dimension dl>2 , the growth of the correlation length ? (t ,T ) can change the nature of the spin glass state at a crossover time tco when ? (tco,T )=? , a minimum characteristic sample length (e.g., film thickness for thin films and crystallite size for bulk samples). For thin films, and times t

Guchhait, Samaresh; Kenning, Gregory G.; Orbach, Raymond L.; Rodriguez, Gilberto F.

2015-01-01

41

Decoherence of coupled electron spins via nuclear spin dynamics in quantum dots

NASA Astrophysics Data System (ADS)

In double quantum dots, the exchange interaction between two electron spins renormalizes the excitation energy of pair flips in the nuclear spin bath, which in turn modifies the non-Markovian bath dynamics. As the energy renormalization varies with the static Overhauser field mismatch between the quantum dots, the electron singlet-triplet decoherence resulting from the bath dynamics depends on sampling of nuclear spin states from an ensemble, leading to the transition from superexponential decoherence in single-sample dynamics to power-law decay under ensemble averaging. In contrast, the decoherence of a single electron spin in one dot is essentially the same for different choices of the nuclear spin configuration.

Yang, W.; Liu, R. B.

2008-02-01

42

Quantum heat bath for spin-lattice dynamics

NASA Astrophysics Data System (ADS)

Quantization of spin-wave excitations necessitates the reconsideration of the classical fluctuation-dissipation relation (FDR) used for temperature control in spin-lattice dynamics simulations of ferromagnetic metals. In this paper, Bose-Einstein statistics is used to reinterpret the Langevin dynamics of both lattice and spins, allowing quantum statistics to be mimicked in canonical molecular dynamics simulations. The resulting quantum heat baths are tested by calculating the specific heats and magnetization over a wide temperature range, from 0 K to above the Curie temperature, with molecular dynamics (MD), spin dynamics (SD), and spin-lattice dynamics (SLD) simulations. The results are verified with experimental data and available theoretical analysis. Comparison with classical results also shows the importance of quantization effects for spin excitations in all the ferromagnetically ordered configurations.

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

2015-03-01

43

Momentum and spin in entropic quantum dynamics

NASA Astrophysics Data System (ADS)

We study quantum theory as an example of entropic inference. Our goal is to remove conceptual difficulties that arise in quantum mechanics. Since probability is a common feature of quantum theory and of any inference problem, we briefly introduce probability theory and the entropic methods to update probabilities when new information becomes available. Nelson's stochastic mechanics and Caticha's derivation of quantum theory are discussed in the subsequent chapters. Our first goal is to understand momentum and angular momentum within an entropic dynamics framework and to derive the corresponding uncertainty relations. In this framework momentum is an epistemic concept -- it is not an attribute of the particle but of the probability distributions. We also show that the Heisenberg's uncertainty relation is an osmotic effect. Next we explore the entropic analog of angular momentum. Just like linear momentum, angular momentum is also expressed in purely informational terms. We then extend entropic dynamics to curved spaces. An important new feature is that the displacement of a particle does not transform like a vector. It involves second order terms that account for the effects of curvature . This leads to a modified Schrodinger equation for curved spaces that also take into account the curvature effects. We also derive Schrodinger equation for a charged particle interacting with external electromagnetic field on general Riemannian manifolds. Finally we develop the entropic dynamics of a particle of spin 1/2. The particle is modeled as a rigid point rotator interacting with an external EM field. The configuration space of such a rotator is R 3 x S3 (S 3 is the 3-sphere). The model describes the regular representation of SU(2) which includes all the irreducible representations (spin 0, 1/2, 1, 3/2,...) including spin 1/2.

Nawaz, Shahid

44

Dynamically generated pure spin current in single-layer graphene

NASA Astrophysics Data System (ADS)

The conductance mismatch problem limits the spin-injection efficiency significantly, and spin injection into graphene usually requires high-quality tunnel barriers to circumvent the conductance mismatch. We introduce an approach which enables the generation of pure spin current into single-layer graphene (SLG) that is free from electrical conductance mismatch by using dynamical spin injection. An experimental demonstration of spin-pumping-induced spin current generation and spin transport in SLG at room temperature was successfully achieved, and the spin coherence length was estimated to be 1.36 ?m by using a conventional theoretical model based on the Landau-Lifshitz-Gilbert equation. The spin coherence length is proportional to the quality of SLG, which indicates that spin relaxation in SLG is governed by the Elliot-Yafet mechanism, as was reported.

Tang, Zhenyao; Shikoh, Eiji; Ago, Hiroki; Kawahara, Kenji; Ando, Yuichiro; Shinjo, Teruya; Shiraishi, Masashi

2013-04-01

45

Spin-Lattice Dynamics Simulations of Ferromagnetic Iron

NASA Astrophysics Data System (ADS)

We develop a Spin-Lattice Dynamics (SLD) simulation model for ferromagnetic iron where atoms are treated as classical particles with spins. The atoms interact via many-body forces as well as via spin-orientation-dependent forces of the Heisenberg form. The coupling between the lattice and the spin degrees of freedom is described by a coordinate-dependent exchange function. An algorithm for integrating the spin-lattice dynamics equations of motion is based on the 2nd order Suzuki-Trotter decomposition for the non-commuting Liouville evolution operators for atomic coordinates and spins. The notions of the spin thermostat and the spin temperature are introduced through a combined application of the Langevin spin dynamics and the fiuctuation-dissipation theorem. Several applications of the new method described in the paper illustrate the significant effect of the spin degrees of freedom on the dynamics of atomic motion in iron and iron-based alloys, and confirm that the Spin-Lattice Dynamics approach provides a viable framework for performing realistic large-scale simulations of magnetic materials.

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

2008-04-01

46

Action competency is defined as the ability of an individual to self-evaluate their own performance capabilities. The current experiment demonstrated that physical and observational training with a motor skill alters action competency ratings in a similar manner. Using a pre-test and post-test protocol, the results revealed that action competency is constrained prior to training by the intrinsic dynamics of relative phase (?), with in-phase (? = 0°) and anti-phase (? = 180°) patterns receiving higher competency ratings than other relative phase patterns. After 2 days of training, action competency ratings for two trained relative phase patterns, +60° and +120°, increased following physical practice or observational practice. A transfer test revealed that both physical performance ability and action competency ability transferred to the symmetry partners (-60° and -120°) of the two trained relative phase patterns following physical or observational training. The findings also revealed that relative motion direction acts as categorical information that helps to organize action production and facilitate action competency. The results are interpreted based on the coordination dynamics theory of perception-action coupling, and extend this theory by showing that visual perception, action production, and action competency are all constrained in a consistent manner by the dynamics of the order parameter relative phase. As a whole, the findings revealed that relative motion, relative phase, and possibly relative amplitude information are all distinct sources of information that contribute to the emergence of a kinematic understanding of action in the nervous system. PMID:25618008

Buchanan, John J; Ramos, Jorge; Robson, Nina

2015-04-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

48

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

49

Aging dynamics of the Heisenberg spin glass L. Berthier*

Aging dynamics of the Heisenberg spin glass L. Berthier* Theoretical Physics, 1 Keble Road, Oxford vectorial character. Finally, the present dynamical study offers perspectives into the possibility of spin a vectorial character, so that a more natural Hamiltonian to consider is H i,j JijSi·Sj , 2 where the Si

Berthier, Ludovic

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

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

NASA Astrophysics Data System (ADS)

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

Yue, Han

2013-06-01

52

Mechanical analogues of spin Hamiltonians and dynamics

NASA Astrophysics Data System (ADS)

Bloch et al. mapped the precession of the spin-half in a magnetic field of variable magnitude and direction to the rotations of a rigid sphere rolling on a curved surface utilizing SU(2)-SO(3) isomorphism. This formalism is extended to study the behaviour of spin-orbit interactions and the mechanical analogy for Rashba-Dresselhauss spin-orbit interaction in two dimensions is presented by making its spin states isomorphic to the rotations of a rigid sphere rolling on a ring. The change in phase of spin is represented by the angle of rotation of sphere after a complete revolution. In order to develop the mechanical analogy for the spin filter, we find that perfect spin filtration of down spin makes the sphere to rotate at some unique angles and the perfect spin filtration of up spin causes the rotations with certain discrete frequencies.

Kaur, Harjeet; Jain, Sudhir R.; Malik, Sham S.

2014-01-01

53

Molecular dynamics, spin dynamics study of phonon-magnon interactions in BCC iron

NASA Astrophysics Data System (ADS)

By combining an atomistic many-body potential (Finnis-Sinclair) with a classical Heisenberg-like spin Hamiltonian, we perform combined molecular and spin dynamics simulations to investigate phonon-magnon interactions in BCC iron. The coupling between atomic and spin degrees of freedom is established via a distance dependent exchange interaction derived from first principles electronic structure calculations. Coupled equations of motion are integrated using a second order Suzuki-Trotter decomposition of the exponential time evolution operator. To investigate the effect of lattice vibrations on spin wave spectrum, we calculate spin-spin and density-density dynamic structure factors S(q, ?), and compare that to the results obtained from pure spin dynamics simulations performed on a rigid lattice. In the presence of lattice vibrations, we observe an additional peak in the longitudinal spin-spin dynamic structure factor which coincides with the peak position in density-density dynanmic structure factor.

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

2013-03-01

54

The [superscript 19]F spins in a crystal of fluorapatite have often been used to experimentally approximate a one-dimensional spin system. Under suitable multipulse control, the nuclear-spin dynamics may be modeled to first ...

Zhang, Wenxian

55

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 results…

Bierschenk, Inger

56

NASA Astrophysics Data System (ADS)

A physically transparent and mathematically simple semiclassical model is employed to examine dynamics in the central-spin problem. The results reproduce previous findings obtained by various quantum approaches and, at the same time, provide information on the electron spin dynamics and Berry's phase effects over a wider range of experimentally relevant parameters than available previously. This development is relevant to dynamics of bound magnetic polarons and spin dephasing of an electron trapped by an impurity or a quantum dot, and coupled by a contact interaction to neighboring localized magnetic impurities or nuclear spins. Furthermore, it substantiates the applicability of semiclassical models to simulate dynamic properties of spintronic nanostructures with a mesoscopic number of spins.

Dietl, Tomasz

2015-03-01

57

Quantum approach of mesoscopic magnet dynamics with spin transfer torque

NASA Astrophysics Data System (ADS)

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

Wang, Yong; Sham, L. J.

2013-05-01

58

Quench dynamics in spin crossover induced by high pressure

In this paper we have studied analytically and numerically dynamics of spin crossover induced by time-dependent pressure. We show that quasi static pressure, with a slow dependence on time, yields a spin crossover leading to transition from the state of quantum system with high spin (HS) to the low spin (LS). However, a quench dynamics under shock-wave load is more complicated. The final state of the system depends on the amplitude and pulse velocity, resulting in the mixture of the HS and LS states.

Alexander I. Nesterov; Sergey G. Ovchinnikov

2012-09-20

59

. In this Letter, we investigate spin-exchange effects between K vapor and 3 He gas in a very low magnetic fieldDynamics of Two Overlapping Spin Ensembles Interacting by Spin Exchange T.W. Kornack and M interacting by spin exchange. The interactions are dominated by the imaginary part of the spin-exchange cross

Romalis, Mike

60

for the seminal proposal of Datta and Das of a ballistic spin-field-effect tran- sistor DD-SFET .5 HoweverPhysical limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics; published 5 August 2005 We investigate the spin dynamics and relaxation in remotely doped two dimensional

Sipe,J. E.

61

Dynamic Advertising Strategies of Competing Durable Good Producers

This work develops a diffusion model which incorporates word-of-mouth and advertising effects for two firms introducing competing brands of a new durable product. The competition between the two firms is formulated as a two-player, nonzero sum Markovian game. The firms are assumed to behave noncooperatively in choosing their advertising strategies and the solution concept is a Nash noncooperative equilibrium. Optimal

Dan Horsky; Karl Mate

1988-01-01

62

This study compared levels of social competence and language development in 74 young children with hearing loss and 38 hearing peers aged 2.5-5.3 years. This study was the first to examine the relationship between oral language and social competence using a dynamic systems framework in children with and without hearing loss. We hypothesized that, due to deficits in oral language, children who were deaf would display lower levels of social competence than their hearing peers. Furthermore, language age would predict social competence scores. Social competence was measured with a general and deaf-specific measure. Results showed that children with hearing loss performed significantly worse than hearing peers on the general measure but better than the norms on the deaf-specific measure. Controlling for maternal education and income, regression analyses indicated that hearing status and language age predicted social competence in both groups. Among children with hearing loss, correlations were also found between age at diagnosis, age at amplification, and two of the general social competence measures. Results supported our hypothesis that deficits in language would have cascading negative effects on the development of social competence in young deaf children. Development of early intervention programs that target both language and social skills are needed for this population. PMID:25583707

Hoffman, Michael F; Quittner, Alexandra L; Cejas, Ivette

2015-04-01

63

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

64

Dynamics of test bodies with spin in de Sitter spacetime

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

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

2011-02-15

65

Preparation of two-particle total-hyperfine-spin-singlet states via spin-changing dynamics

NASA Astrophysics Data System (ADS)

We present our proposals for generating a total-hyperfine-spin-zero state for two f=1 or two f=2 particles, starting from initial unentangled states. We show that our goal can be achieved by exploiting spin-changing dynamics and quadratic Zeeman shifts with realistic choices of external magnetic fields and evolution time intervals.

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

2012-07-01

66

Spin-glass order induced by dynamic frustration

LETTERS Spin-glass order induced by dynamic frustration E. A. GOREMYCHKIN1,2 , R. OSBORN1 *, B. D . It is generally accepted that both frustration and disorder are essential ingredients in all spin glasses, so fluctuations of the crystal-field levels that destabilize the induced moments and frustrate the development

Chandra, Premi

67

Spin dynamics simulation of electron spin relaxation in Ni{sup 2+}(aq)

The ability to quantitatively predict and analyze the rate of electron spin relaxation of open-shell systems is important for electron paramagnetic resonance and paramagnetic nuclear magnetic resonance spectroscopies. We present a combined molecular dynamics (MD), quantum chemistry (QC), and spin dynamics simulation method for calculating such spin relaxation rates. The method is based on the sampling of a MD trajectory by QC calculations, to produce instantaneous parameters of the spin Hamiltonian used, in turn, to numerically solve the Liouville-von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by simulating the relaxation of electron spin in an aqueous solution of Ni{sup 2+} ion. The spin-lattice (T{sub 1}) and spin-spin (T{sub 2}) relaxation rates are extracted directly from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available, indirectly obtained experimental data is obtained by our method.

Rantaharju, Jyrki, E-mail: jjrantaharju@gmail.com; Mareš, Ji?í, E-mail: jiri.mares@oulu.fi; Vaara, Juha, E-mail: juha.vaara@iki.fi [NMR Research Group, Department of Physics, University of Oulu, P.O. Box 3000, Oulu, FIN-90014 (Finland)

2014-07-07

68

Nonadiabatic multichannel dynamics of a spin-orbit coupled condensate

We systematically investigate the nonadiabatic dynamics of a driven spin-orbit coupled Bose-Einstein condensate, and find that the standard Landau-Zener (LZ) tunneling fails in the regime of weak driven force and/or strong spin-orbital coupling. We show both analytically and numerically that the full nonadiabatic dynamics requires a new mechanism through multichannel quantum interference, which is beyond semi-classical approach and provides an oscillating power-law decay in the long time limit. Furthermore, the condensate density profile is found to be dynamically fragmented by the multichannel effects and enhanced by interaction effects. Experimental indication of these nonadiabatic dynamics is discussed.

Bo Xiong; Jun-hui Zheng; Daw-wei Wang

2014-10-30

69

Dynamics, synchronization, and quantum phase transitions of two dissipative spins

We analyze the static and dynamic properties of two Ising-coupled quantum spins embedded in a common bosonic bath as an archetype of dissipative quantum mechanics. First, we elucidate the ground-state phase diagram for an Ohmic and a sub-Ohmic bath using a combination of bosonic numerical renormalization group (NRG), analytical techniques, and intuitive arguments. Second, by employing the time-dependent NRG we investigate the system's rich dynamical behavior arising from the complex interplay between spin-spin and spin-bath interactions. Interestingly, spin oscillations can synchronize due to the proximity of the common non-Markovian bath and the system displays highly entangled steady states for certain nonequilibrium initial preparations. We complement our nonperturbative numerical results by exact analytical solutions when available and provide quantitative limits on the applicability of the perturbative Bloch-Redfield approach at weak coupling.

Orth, Peter P.; Le Hur, Karyn [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Roosen, David; Hofstetter, Walter [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, 60438 Frankfurt/Main (Germany)

2010-10-01

70

NMR with generalized dynamics of spin and spatial coordinates

This work is concerned with theoretical and experimental aspects of the generalized dynamics of nuclear spin and spatial coordinates under magnetic-field pulses and mechanical motions. The main text begins with an introduction to the concept of ''fictitious'' interactions. A systematic method for constructing fictitious spin-1/2 operators is given. The interaction of spins with a quantized-field is described. The concept of the fictitious interactions under the irradiation of multiple pulses is utilized to design sequences for selectively averaging linear and bilinear operators. Relations between the low-field sequences and high-field iterative schemes are clarified. These relations and the transformation properties of the spin operators are exploited to develop schemes for heteronuclear decoupling of multi-level systems. The resulting schemes are evaluated for heteronuclear decoupling of a dilute spin-1/2 from a spin-1 in liquid crystal samples and from a homonuclear spin-1/2 pair in liquids. A relation between the spin and the spatial variables is discussed. The transformation properties of the spin operators are applied to spatial coordinates and utilized to develop methods for removing the orientational dependence responsible for line broadening in a powder sample. Elimination of the second order quadrupole effects, as well as the first order anisotropies is discussed. It is shown that various sources of line broadening can effectively be eliminated by spinning and/or hopping the sample about judiciously chosen axes along with appropriate radio-frequency pulse sequences.

Lee, Chang Jae

1987-11-01

71

We investigate the spin dynamics and relaxation in remotely doped two dimensional electron systems where the dopants lead to random fluctuations of the Rashba spin-orbit coupling. Due to the resulting random-spin precession, the spin-relaxation time...

Sherman, EY; Sinova, Jairo.

2005-01-01

72

Dynamic Lattice Supersymmetry in Spin Chains

NASA Astrophysics Data System (ADS)

Supersymmetry operators that change a spin chain's length have appeared in numerous contexts, ranging from the AdS/CFT correspondence to statistical mechanics models. In this article, we present, via an analysis of the Bethe equations, all homogeneous, rational and trigonometric, integrable spin chains for which length-changing supersymmetry can be present. Furthermore, we write down the supercharges explicitly for the simplest new models, namely the spin chains with the -fold antisymmetric tensor product of the fundamental representation at each site and check their compatibility with integrability.

Meidinger, David; Mitev, Vladimir

2014-09-01

73

NASA Astrophysics Data System (ADS)

We investigate the effect of ring exchange on the ground-state properties and magnetic excitations of the S =1/2 Heisenberg model on the anisotropic triangular lattice with ring exchange at T =0 using linear spin-wave theory. Classically, we find stable Néel, spiral and collinear magnetically ordered phases. Upon including quantum fluctuations to the model, linear spin-wave theory shows that ring exchange induces a large quantum disordered region in the phase diagram, completely wiping out the classically stable collinear phase. Analysis of the spin-wave spectra for each of these three models demonstrates that the large spin-liquid phase observed in the full model is a direct manifestation of competing classical orders. To understand the origin of these competing phases, we introduce models where either the four spin contributions from ring exchange, or the renormalization of the Heisenberg terms due to ring exchange are neglected. We find that these two terms favor rather different physics.

Holt, Michael; Powell, Ben J.; Merino, Jaime

2014-05-01

74

The Dynamics of Competing Cascades in Social Media: Applications to Agenda Setting

effective tools to set the public agenda [18]. The plethora of information present in social media clearlyThe Dynamics of Competing Cascades in Social Media: Applications to Agenda Setting Siddharth@cs.vt.edu ABSTRACT Agenda setting in online social media is today an inten- sively competitive space with multiple

Ramakrishnan, Naren

75

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

NASA Astrophysics Data System (ADS)

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

Kulagina, Iryna; Linder, Jacob

2014-08-01

76

Effect of cosmic string on spin dynamics

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

Debashree Chowdhury; B. Basu

2014-11-07

77

Coherent Spin Dynamics in Semiconductor Nanostructures

NASA Astrophysics Data System (ADS)

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

Flatté, Michael E.

2004-03-01

78

The spin-temperature theory of dynamic nuclear polarization and nuclear spin-lattice relaxation

NASA Technical Reports Server (NTRS)

A detailed derivation of the equations governing dynamic nuclear polarization (DNP) and nuclear spin lattice relaxation by use of the spin temperature theory has been carried to second order in a perturbation expansion of the density matrix. Nuclear spin diffusion in the rapid diffusion limit and the effects of the coupling of the electron dipole-dipole reservoir (EDDR) with the nuclear spins are incorporated. The complete expression for the dynamic nuclear polarization has been derived and then examined in detail for the limit of well resolved solid effect transitions. Exactly at the solid effect transition peaks, the conventional solid-effect DNP results are obtained, but with EDDR effects on the nuclear relaxation and DNP leakage factor included. Explicit EDDR contributions to DNP are discussed, and a new DNP effect is predicted.

Byvik, C. E.; Wollan, D. S.

1974-01-01

79

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

80

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

Aeschlimann, Martin

81

Preserving electron spin coherence in solids by optimal dynamical decoupling

NASA Astrophysics Data System (ADS)

To exploit the quantum coherence of electron spins in solids in future technologies such as quantum computing, it is first vital to overcome the problem of spin decoherence due to their coupling to the noisy environment. Dynamical decoupling, which uses stroboscopic spin flips to give an average coupling to the environment that is effectively zero, is a particularly promising strategy for combating decoherence because it can be naturally integrated with other desired functionalities, such as quantum gates. Errors are inevitably introduced in each spin flip, so it is desirable to minimize the number of control pulses used to realize dynamical decoupling having a given level of precision. Such optimal dynamical decoupling sequences have recently been explored. The experimental realization of optimal dynamical decoupling in solid-state systems, however, remains elusive. Here we use pulsed electron paramagnetic resonance to demonstrate experimentally optimal dynamical decoupling for preserving electron spin coherence in irradiated malonic acid crystals at temperatures from 50K to room temperature [1]. Using a seven-pulse optimal dynamical decoupling sequence, we prolonged the spin coherence time to about 30 ms; it would otherwise be about 0.04 ms without control or 6.2 ms under one-pulse control. By comparing experiments with microscopic theories, we have identified the relevant electron spin decoherence mechanisms in the solid. Recently, we demonstrate experimentally that dynamical decoupling can preserve bipartite pseudo-entanglement in phosphorous donors in a silicon system [2]. In particular, the lifetime of pseudo entangled states is extended from 0.4 us in the absence of decoherence control to 30 us in the presence of a two-flip dynamical decoupling sequence. [4pt] [1]. Jiangfeng Du, Xing Rong, Nan Zhao, Ya Wang, Jiahui Yang and R. B. Liu, Preserving electron spin coherence in solids by optimal dynamical decoupling, Nature 461, 1265-1268 (2009). [0pt] [2] Ya Wang, Xing Rong, Pengbo Feng, Wanjie Xu, Bo Chong, Ji-Hu Su, Jiangbin Gong, and Jiangfeng Du, Preservation of bipartite pseudo-entanglement in solids using dynamical decoupling, submitted to Phys. Rev. Lett.

Du, Jiangfeng

2011-03-01

82

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

83

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

84

Spin–orbital dynamics in a system of polar molecules

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

85

Storing entanglement of nuclear spins via Uhrig dynamical decoupling

Stroboscopic spin flips have already been shown to prolong the coherence times of quantum systems under noisy environments. Uhrig's dynamical decoupling scheme provides an optimal sequence for a quantum system interacting with a dephasing bath. Several experimental demonstrations have already verified the efficiency of such dynamical decoupling schemes in preserving single-qubit coherences. In this work we describe the experimental study of Uhrig's dynamical decoupling in preserving two-qubit entangled states using an ensemble of spin-1/2 nuclear pairs in solution state. We find that the performance of odd-order Uhrig sequences in preserving entanglement is superior to both even-order Uhrig sequences and periodic spin-flip sequences. We also find that there exists an optimal order of the Uhrig sequence in which a singlet state can be stored at high correlation for about 30 seconds.

Roy, Soumya Singha; Mahesh, T. S. [Indian Institute of Science Education and Research, Pune 411008 (India); Agarwal, G. S. [Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078 (United States)

2011-06-15

86

Storing entanglement of nuclear spins via Uhrig Dynamical Decoupling

Stroboscopic spin flips have already been shown to prolong the coherence times of quantum systems under noisy environments. Uhrig's dynamical decoupling scheme provides an optimal sequence for a quantum system interacting with a dephasing bath. Several experimental demonstrations have already verified the efficiency of such dynamical decoupling schemes in preserving single qubit coherences. In this work we describe the experimental study of Uhrig's dynamical decoupling in preserving two-qubit entangled states using an ensemble of spin-1/2 nuclear pairs in solution state. We find that the performance of odd-order Uhrig sequences in preserving entanglement is superior to both even-order Uhrig sequences and periodic spin-flip sequences. We also find that there exists an optimal length of the Uhrig sequence at which the decoherence time gets boosted from a few seconds to about 30 seconds.

Soumya Singha Roy; T. S. Mahesh; G. S. Agarwal

2011-10-07

87

Tunable nonequilibrium dynamics of field quenches in spin ice

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

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

2014-01-01

88

Tunable nonequilibrium dynamics of field quenches in spin ice.

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

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

2014-01-14

89

Quantum Computation and Quantum Spin Dynamics

We analyze the stability of quantum computations on physically realizable quantum computers by simulating quantum spin models representing quantum computer hardware. Examples of logically identical implementations of the controlled-NOT operation are used to demonstrate that the results of a quantum computation are unstable with respect to the physical realization of the quantum computer. We discuss the origin of these instabilities

Hans de Raedt; Kristel Michielsen; Anthony Hams; Seiji Miyashita; Keiji Saito

2001-01-01

90

Dynamics of magnetization in ferromagnet with spin-transfer torque

NASA Astrophysics Data System (ADS)

We review our recent works on dynamics of magnetization in ferromagnet with spin-transfer torque. Driven by constant spin-polarized current, the spin-transfer torque counteracts both the precession driven by the effective field and the Gilbert damping term different from the common understanding. When the spin current exceeds the critical value, the conjunctive action of Gilbert damping and spin-transfer torque leads naturally the novel screw-pitch effect characterized by the temporal oscillation of domain wall velocity and width. Driven by space- and time-dependent spin-polarized current and magnetic field, we expatiate the formation of domain wall velocity in ferromagnetic nanowire. We discuss the properties of dynamic magnetic soliton in uniaxial anisotropic ferromagnetic nanowire driven by spin-transfer torque, and analyze the modulation instability and dark soliton on the spin wave background, which shows the characteristic breather behavior of the soliton as it propagates along the ferromagnetic nanowire. With stronger breather character, we get the novel magnetic rogue wave and clarify its formation mechanism. The generation of magnetic rogue wave mainly arises from the accumulation of energy and magnons toward to its central part. We also observe that the spin-polarized current can control the exchange rate of magnons between the envelope soliton and the background, and the critical current condition is obtained analytically. At last, we have theoretically investigated the current-excited and frequency-adjusted ferromagnetic resonance in magnetic trilayers. A particular case of the perpendicular analyzer reveals that the ferromagnetic resonance curves, including the resonant location and the resonant linewidth, can be adjusted by changing the pinned magnetization direction and the direct current. Under the control of the current and external magnetic field, several magnetic states, such as quasi-parallel and quasi-antiparallel stable states, out-of-plane precession, and bistable states can be realized. The precession frequency can be expressed as a function of the current and external magnetic field.

Li, Zai-Dong; He, Peng-Bin; Liu, Wu-Ming

2014-11-01

91

Competing mechanism for generating high spin excitations in ?-soft nuclei: the 136Nd case

NASA Astrophysics Data System (ADS)

High-spin structures in 136Nd have been investigated via the 110Pd( 30Si,4n) reaction at 125 MeV using the GASP array. Several bands consisting of stretched quadrupole transitions were identified. Two of them reach spins comparable to those of the highly-deformed (HD) band in 136Nd, which is based on a neutron i {13}/{2}- {h {9}/{2}}/{f {7}/{2}} configuration. Total routhian surface (TRS) calculations indicate that regular high-spin excitations in this ?-soft nucleus, can be also generated through successive pairs of h {11}/{2} protons and neutrons coupled to a stable small-deformation triaxial core. The previously reported ?-ray transitions of an excited HD band, identical to the yrast HD band, are not confirmed by our data.

Petrache, C. M.; Bazzacco, D.; Lunardi, S.; Rossi Alvarez, C.; Venturelli, R.; Bucurescu, D.; Ur, C. A.; De Acuña, D.; Maron, G.; Napoli, D. R.; Medina, N. H.; Oliveira, J. R. B.; Wyss, R.

1996-02-01

92

Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin

NASA Astrophysics Data System (ADS)

The ability to discriminate between simultaneously occurring noise sources in the local environment of semiconductor InGaAs quantum dots, such as electric and magnetic field fluctuations, is key to understanding their respective dynamics and their effect on quantum dot coherence properties. We present a discriminatory approach to all-optical sensing based on two-color resonance fluorescence of a quantum dot charged with a single electron. Our measurements show that local magnetic field fluctuations due to nuclear spins in the absence of an external magnetic field are described by two correlation times, both in the microsecond regime. The nuclear spin bath dynamics show a strong dependence on the strength of resonant probing, with correlation times increasing by a factor of 4 as the optical transition is saturated. We interpret the behavior as motional averaging of both the Knight field of the resident electron spin and the hyperfine-mediated nuclear spin-spin interaction due to optically induced electron spin flips.

Stanley, M. J.; Matthiesen, C.; Hansom, J.; Le Gall, C.; Schulte, C. H. H.; Clarke, E.; Atatüre, M.

2014-11-01

93

Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin

The ability to discriminate between simultaneously occurring noise sources in the local environment of semiconductor InGaAs quantum dots, such as electric and magnetic field fluctuations, is key to understanding their respective dynamics and their effect on quantum dot coherence properties. We present a discriminatory approach to all-optical sensing based on two-color resonance fluorescence of a quantum dot charged with a single electron. Our measurements show that local magnetic field fluctuations due to nuclear spins in the absence of an external magnetic field are described by two correlation times, both in the microsecond regime. The nuclear spin bath dynamics show a strong dependence on the strength of resonant probing, with correlation times increasing by a factor of four as the optical transition is saturated. We interpret the behavior as motional averaging of both the Knight field of the resident electron spin and the hyperfine-mediated nuclear spin-spin interaction due to optically-induced electron spin flips.

Megan J. Stanley; Clemens Matthiesen; Jack Hansom; Claire Le Gall; Carsten H. H. Schulte; Edmund Clarke; Mete Atatüre

2014-11-17

94

STAR results on longitudinal spin dynamics

We present preliminary results on the double longitudinal spin asymmetries A_LL in inclusive jet production and the longitudinal spin transfer asymmetries D_LL in inclusive Lambda and anti-Lambda hyperon production. The data amount to about 0.5 pb-1 collected at RHIC in 2003 and 2004 with beam polarizations up to 45 %. The jet A_LL asymmetries, measured over 5 < pT < 17 GeV/c, are consistent with evaluations based on deep-inelastic scattering parametrizations for the gluon polarization in the nucleon, and disfavor large positive values of gluon polarization in the nucleon. The Lambda and anti-Lambda D_LL, measured at midrapidity and at low average transverse momentum of 1.5 GeV/c, are consistent with zero within their dominant statistical uncertainties.

Joanna Kiryluk; for the STAR Collaboration

2006-08-08

95

Controlling the quantum dynamics of a mesoscopic spin bath in diamond

Understanding and mitigating decoherence is a key challenge for quantum science and technology. The main source of decoherence for solid-state spin systems is the uncontrolled spin bath environment. Here, we demonstrate quantum control of a mesoscopic spin bath in diamond at room temperature that is composed of electron spins of substitutional nitrogen impurities. The resulting spin bath dynamics are probed using a single nitrogen-vacancy (NV) centre electron spin as a magnetic field sensor. We exploit the spin bath control to dynamically suppress dephasing of the NV spin by the spin bath. Furthermore, by combining spin bath control with dynamical decoupling, we directly measure the coherence and temporal correlations of different groups of bath spins. These results uncover a new arena for fundamental studies on decoherence and enable novel avenues for spin-based magnetometry and quantum information processing. PMID:22536480

de Lange, Gijs; van der Sar, Toeno; Blok, Machiel; Wang, Zhi-Hui; Dobrovitski, Viatcheslav; Hanson, Ronald

2012-01-01

96

Spin dynamics simulations for a nanoscale Heisenberg antiferromagnet

NASA Astrophysics Data System (ADS)

Thermoinduced magnetization(TiM) is a novel response which was predicted to occur in nanoscale antiferromagnetic materials. Extensive Monte Carlo simulations footnotetextG. Brown, A. Janotti, M. Eisenbach, and G. M. Stocks, Phys.Rev.B 72, 140405(2005) have shown that TiM is an intrinsic property of the antiferromagnetic classical Heisenberg model below the Neel temperature. To obtain a fundamental understanding of TiM, spin dynamics(SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an antiferromagnetic nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with free boundary conditions are used. We employed the fast spin dynamics algorithms with fourth-order Suzuki-Trotter decompositions of the exponential operator. Additional small excitation peaks due to surface effects are found in transverse S(q,w).

Hou, Zhuofei; Landau, D. P.; Brown, G.; Stocks, G. M.

2010-03-01

97

Dynamics of nanospheres: Spin waves and collective plasmons

This work investigates the dynamic response of nanospheres. We explore two seemingly different, but nonetheless conceptually related areas. Our first studies were directed toward the microwave response of nanoscale ferromagnetic spheres and arrays of such spheres, where spin excitations are of interest. Then we turn our attention to the collective plasmons of nanoscale metallic structures, and their influence on important

Ping Chu

2007-01-01

98

Spin transport and current induced magnetization dynamics in magnetic nanostructures

NASA Astrophysics Data System (ADS)

The study of the interaction between conducting electrons and magnetization in a ferromagnet has stimulated much interest following the discovery of the giant magnetoresistive effect two decades ago. With the advance of fabrication techniques at the nanometer length scale, a variety of new magnetic nanostructures have emerged. These structures are interesting from both a scientific and technological perspective. Some of them have successfully led to applications in information storage industry. This thesis theoretically studies some of these structures and focuses on two aspects: (1) the effect of surface roughness in magnetoresistive devices, (2) spin transfer torque induced magnetization dynamics. Surface roughness is known to be an important source of scattering in small structures. We employ Landauer's formalism to study spin dependent electron transport in structures like spin valve, magnetic tunnel junction and nanowires. An efficient algorithm is developed to solve the scattering problem numerically. It is found that the resistivity and magnetoresistance are strongly influenced by the surface roughness scattering. The coupling between spin polarized current and local magnetic moment results in a torque on the magnetization. This induces dynamic effects such as magnetization reversal and switching. We propose an exchange coupled composite structure to study current induced reversal and show that this structure can significantly reduce the critical current. The spin torque can cancel the damping torque and induce steady precession. This type of spin torque oscillator is attractive as a microwave device at the nanoscale. Several of these oscillators can couple together and oscillate in a phase coherent manner. The mechanism for the coupling is studied analytically and using micromagnetic simulation. It is found that the coupling exhibits an oscillatory behavior through a spin wave mediated interaction.

Chen, Xi

99

Dynamical heterogeneities in irreversible gels: analogy with spin glasses

NASA Astrophysics Data System (ADS)

We describe the sol-gel transition by introducing an order parameter, defined as the average of local variables, and its fluctuations. It can be shown that these quantities are related to percolation quantities, but in principle they can be measured without resorting to connectivity properties. In this framework it appears that the dynamical transition associated with gelation is a real thermodynamic transition, as happens in spin glasses. The strong analogies between the sol-gel transition and the spin glass transition are also discussed.

Fierro, A.; Abete, T.; de Candia, A.; Del Gado, E.; Coniglio, A.

2009-12-01

100

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

101

Covariant hamiltonian spin dynamics in curved space-time

NASA Astrophysics Data System (ADS)

The dynamics of spinning particles in curved space-time is discussed, emphasizing the hamiltonian formulation. Different choices of hamiltonians allow for the description of different gravitating systems. We give full results for the simplest case with minimal hamiltonian, constructing constants of motion including spin. The analysis is illustrated by the example of motion in Schwarzschild space-time. We also discuss a non-minimal extension of the hamiltonian giving rise to a gravitational equivalent of the Stern-Gerlach force. We show that this extension respects a large class of known constants of motion for the minimal case.

d'Ambrosi, G.; Satish Kumar, S.; van Holten, J. W.

2015-04-01

102

Dynamics and inertia of skyrmionic spin structures

NASA Astrophysics Data System (ADS)

Skyrmions are topologically protected winding vector fields characterized by a spherical topology. Magnetic skyrmions can arise as the result of the interplay of various interactions, including exchange, dipolar and anisotropy energy in the case of magnetic bubbles and an additional Dzyaloshinskii-Moriya interaction in the case of chiral skyrmions. Whereas the static and low-frequency dynamics of skyrmions are already well under control, their gigahertz dynamical behaviour has not been directly observed in real space. Here, we image the gigahertz gyrotropic eigenmode dynamics of a single magnetic bubble and use its trajectory to experimentally confirm its skyrmion topology. The particular trajectory points to the presence of strong inertia, with a mass much larger than predicted by existing theories. This mass is endowed by the topological confinement of the skyrmion and the energy associated with its size change. It is thereby expected to be found in all skyrmionic structures in magnetic systems and beyond. Our experiments demonstrate that the mass term plays a key role in describing skyrmion dynamics.

Büttner, Felix; Moutafis, C.; Schneider, M.; Krüger, B.; Günther, C. M.; Geilhufe, J.; Schmising, C. V. Korff; Mohanty, J.; Pfau, B.; Schaffert, S.; Bisig, A.; Foerster, M.; Schulz, T.; Vaz, C. A. F.; Franken, J. H.; Swagten, H. J. M.; Kläui, M.; Eisebitt, S.

2015-03-01

103

Universal dynamical decoupling of a single solid-state spin from a spin bath

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

de Lange, G; Ristè, D; Dobrovitski, V V; Hanson, R

2010-01-01

104

Universal dynamical decoupling of a single solid-state spin from a spin bath

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

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

2010-10-21

105

Spin dynamics in highly frustrated pyrochlore magnets

NASA Astrophysics Data System (ADS)

This paper aims at showing the complementarity between time-of-flight and triple-axis neutron scattering experiments, on the basis of two topical examples in the field of geometrical magnetic frustration. Rare earth pyrochlore magnets R2Ti2O7 (R is a rare earth) play a prominent role in this field, as they form model systems showing a rich variety of ground states, depending on the balance between dipolar, exchange interactions and crystal field. We first review the case of the XY antiferromagnet Er2 Ti2 O7. Here a transition towards a Néel state is observed, possibly induced by an order-by-disorder mechanism. Effective exchange parameters can be extracted from S(Q,?). We then examine the case of the spin liquid Tb2 Ti2 O7. Recent experiments reveal a complex ground state characterized by "pinch points" and supporting a low energy excitation. These studies demonstrate the existence of a coupling between crystal field transitions and a transverse acoustic phonon mode.

Petit, Sylvain; Guitteny, Solène; Robert, Julien; Bonville, Pierre; Decorse, Claudia; Ollivier, Jacques; Mutka, Hannu; Mirebeau, Isabelle

2015-01-01

106

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

107

Dynamical competition between quantum Hall and quantum spin Hall effects

NASA Astrophysics Data System (ADS)

In this paper, we investigate the occurrence of quantum phase transitions in topological systems out of equilibrium. More specifically, we consider graphene with a sizable spin-orbit coupling, irradiated by circularly polarized light. In the absence of light, the spin-orbit coupling drives a quantum spin Hall phase where edge currents with opposite spins counterpropagate. On the other hand, the light generates a time-dependent vector potential, which leads to a hopping parameter with staggered time-dependent phases around the benzene ring. The model is a dynamical version of the Haldane model, which considers a static staggered flux with zero total flux through each plaquette. Since the light breaks time-reversal symmetry, a quantum Hall (QH) phase protected by an integer topological invariant arises. An important difference with the static QH phase is the existence of counterpropagating edge states at different momenta, which are made possible by zero- and two-photon resonances. By numerically solving the complete problem, with spin-orbit coupling and light, and investigating different values of the driving frequency ? , we show that the spectrum exhibits nontrivial gaps not only at zero energy but also at ? /2 . This additional gap is created by photon resonances between the valence and conduction band of graphene, and the symmetry of the spectrum forces it to lie at ? /2 . By increasing the intensity of the irradiation, the topological state in the zero energy gap undergoes a dynamical phase transition from a quantum spin Hall to a quantum Hall phase, whereas the gap around ? /2 remains in the quantum Hall regime.

Quelle, A.; Morais Smith, C.

2014-11-01

108

Ultrafast terahertz spin dynamics: from phonon-induced spin order to coherent magnon control

NASA Astrophysics Data System (ADS)

Ultrashort pulses in the terahertz (THz) spectral range allow us to study and control spin dynamics on time scales faster than a single oscillation cycle of light. In a first set of experiments, we harness an optically triggered coherent lattice vibration to induce a transient spin-density wave in BaFe2As2, the parent compound of pnictide superconductors. The time-dependent multi-THz response of the non-equilibrium phases shows that the ordering quasi-adiabatically follows a coherent lattice oscillation at a frequency as high as 5.5 THz. The results suggest important implications for unconventional superconductivity. In a second step, we utilize the magnetic field component of intense THz transients to directly switch on and off coherent spin waves in the antiferromagnetic nickel oxide NiO. A femtosecond optical probe traces the magnetic dynamics in the time domain and verifies that the THz field addresses spins selectively via Zeeman interaction. This concept provides a universal ultrafast handle on magnetic excitations in the electronic ground state.

Kim, K. W.; Porer, M.; Bernhard, C.; Demsar, J.; Pashkin, A.; Kampfrath, T.; Sell, A.; Wolf, M.; Leitenstorfer, A.; Huber, R.

2013-02-01

109

Dynamic-angle spinning and double rotation of quadrupolar nuclei

Nuclear magnetic resonance (NMR) spectroscopy of quadrupolar nuclei is complicated by the coupling of the electric quadrupole moment of the nucleus to local variations in the electric field. The quadrupolar interaction is a useful source of information about local molecular structure in solids, but it tends to broaden resonance lines causing crowding and overlap in NMR spectra. Magic- angle spinning, which is routinely used to produce high resolution spectra of spin-{1/2} nuclei like carbon-13 and silicon-29, is incapable of fully narrowing resonances from quadrupolar nuclei when anisotropic second-order quadrupolar interactions are present. Two new sample-spinning techniques are introduced here that completely average the second-order quadrupolar coupling. Narrow resonance lines are obtained and individual resonances from distinct nuclear sites are identified. In dynamic-angle spinning (DAS) a rotor containing a powdered sample is reoriented between discrete angles with respect to high magnetic field. Evolution under anisotropic interactions at the different angles cancels, leaving only the isotropic evolution of the spin system. In the second technique, double rotation (DOR), a small rotor spins within a larger rotor so that the sample traces out a complicated trajectory in space. The relative orientation of the rotors and the orientation of the larger rotor within the magnetic field are selected to average both first- and second-order anisotropic broadening. The theory of quadrupolar interactions, coherent averaging theory, and motional narrowing by sample reorientation are reviewed with emphasis on the chemical shift anisotropy and second-order quadrupolar interactions experienced by half-odd integer spin quadrupolar nuclei. The DAS and DOR techniques are introduced and illustrated with application to common quadrupolar systems such as sodium-23 and oxygen-17 nuclei in solids.

Mueller, K.T. (Lawrence Berkeley Lab., CA (United States) California Univ., Berkeley, CA (United States). Dept. of Chemistry)

1991-07-01

110

Dynamic magnetism of an iron(II)-chlorido spin chain and its hexametallic segment.

An air-stable iron(ii) chain compound [Fe(phen)(Cl)2]n (, phen = 1,10-phenanthroline) was prepared and exhibits intrachain ferromagnetic interactions as well as competing interchain antiferromagnetic interactions that are mediated by ?-? stacking of the phen ligands, resulting in metamagnetic behaviour. The interchain interactions can be altered by changing the external magnetic field, and disparate magnetic dynamics was thus observed from zero to the critical field of 1500 Oe. Zero-field cooled (ZFC) and field-cooled (FC) magnetization and heat capacity measurements indicate that long-range antiferromagnetic ordering occurs at lower fields, and this ordering disappears when the external field is larger than 1500 Oe. The low-frequency ac susceptibility data are consistent with the exponential increase of the temperature-dependent dc data, indicating a Glauber-type dynamics under the field of 1500 Oe. Thus, is considered as a metamagnetic single-chain magnet. For further analysis, a discrete hexametallic segment of the chain, [Fe6(phen)6(Cl)12] (), was also isolated and was shown to possess a high-spin ground state and display slow magnetic relaxations like single-molecule magnets. Magnetic analysis using CONDON suggests weak ferromagnetic interactions between the metal centres. The polymeric compound can be viewed as being constructed using the hexametallic unit which is of a low energy barrier, suggesting the significance of intrachain ferromagnetic interactions in enhancing the spin-reversal energy barrier of the short chains. PMID:25428779

Qin, Lei; Zhang, Zhong; Zheng, Zhiping; Speldrich, Manfred; Kögerler, Paul; Xue, Wei; Wang, Bao-Ying; Chen, Xiao-Ming; Zheng, Yan-Zhen

2015-01-21

111

Spin dynamics simulations for a nanoscale Heisenberg antiferromagnetic film

NASA Astrophysics Data System (ADS)

Thermoinduced magnetization(TiM) is a novel response predicted to occur in nanoscale antiferromagnetic (AF) materials. Extensive Monte Carlo simulationsootnotetextG. Brown, A. Janotti, M. Eisenbach, and G. M. Stocks, Phys.Rev.B 72, 140405(2005) have shown that TiM is an intrinsic property of the AF classical Heisenberg model. To obtain a fundamental understanding of TiM, spin dynamics (SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an AF nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with two free-surfaces and periodic boundaries parallel to the surfaces are used. We applied fast SD algorithms with 4th-order Suzuki-Trotter decompositions of the exponential operator. Discrete spin wave modes due to spin wave confinementootnotetextSpin Wave Confinement, edited by S. O Demokritov (Pan Stanford Publishing, Singapore, 2008) are found in transverse S(q,,?) in the perpendicular direction to free surfaces.

Hou, Zhuofei; Landau, David; Stocks, G. Malcolm

2011-03-01

112

Dynamics of spin-1 bosons in an optical lattice

NASA Astrophysics Data System (ADS)

We study spin-mixing and collapse and revival dynamics of spin-1 atoms in an optical lattice. Starting with the ferromagnetic or anti-ferromagnetic superfluid ground state - a sudden raising of the lattice depth creates a non-equilibrium state. Analysis of the oscillations in atom numbers in different spin states and the collapse and revivals in visibility reveals details about the system parameters and the initial superfluid state. For example, in situ number oscillations reveal the spin-dependent interactions, and visibility oscillations reveal the ratio of on-site and spin-dependent interactions, and thus the various scattering lengths in different channels can be determined. To study the interplay of superlfuidity and magnetism, we also examine the oscillations in various observables in the presence of an external magnetic field in the form of quadratic Zeeman energy. The frequency spectrum of the oscillations reveals the discrete energy levels and relative importance of different Fock states in the initial superfluid and magnetic states.

Mahmud, Khan W.; Tiesinga, Eite

2013-03-01

113

Introducing spin in Schrodinger dynamics of particle motion

A non-perturbative relativistic atomic theory is presented in which Dirac's theory and Schrodinger theory are shown to originate from a common wave equation. 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 of the angular part of the wave equation are exactly same as that of the Schrodinger theory. The new theory accounts for the energy due to spin-orbit interaction as well as for the additional potential energy due to spin and spin-orbit coupling. Spin angular momentum operator is as neatly integrated into the equation of motion as the orbital angular momentum operator. This requires modification to classical Laplacian operator. Consequently the Dirac matrices and the k operator of Dirac's theory are dispensed with. The theory also p...

Zaveri, Vikram H

2007-01-01

114

Coherent spin-rotational dynamics of oxygen superrotors

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

115

Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig

NASA Technical Reports Server (NTRS)

The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig is an apparatus for vibration testing of turbomachine blades in a vacuum at rotational speeds from 0 to 40,000 rpm. This rig includes (1) a vertically oriented shaft on which is mounted an assembly comprising a rotor holding the blades to be tested, (2) two actively controlled heteropolar radial magnetic bearings at opposite ends of the shaft, and (3) an actively controlled magnetic thrust bearing at the upper end of the shaft. This rig is a more capable successor to a prior apparatus, denoted the Dynamic Spin Rig (DSR), that included a vertically oriented shaft with a mechanical thrust bearing at the upper end and a single actively controlled heteropolar radial magnetic bearing at the lower end.

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

2005-01-01

116

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

117

Dynamic nuclear polarization from current-induced electron spin polarization

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

118

Magnetization dynamics and spin diffusion in semiconductors and metals

NASA Astrophysics Data System (ADS)

Spintronics is an emerging field of research focused on introducing the electron spin degree of freedom into electronics. Its aims include devising new means of magnetization manipulation in ferromagnets and creating systems in which the electrical expression of spin-related phenomena is possible. In this dissertation we present theoretical work important for both of these goals. In a process of ultrafast light-induced demagnetization the magnetization of a ferromagnet decreases on a sub-picosecond time-scale following an excitation by a strong laser pulse. We present a theory of this phenomenon which is applicable to ferromagnetic (III,Mn)V semiconductors. Using it we qualitatively explain the experimental results obtained recently in these materials. We also give a theory of ultrafast demagnetization in transition metals, in which we put previously proposed approaches on a sound conceptual basis, and analyze a new mechanism of demagnetization due to emission of spin waves by hot carriers. Recent progress in growth of metal-semiconductor interfaces has enabled efficient spin-polarized transport between metallic ferromagnets and semiconductors such as GaAs. We present a theory of diffusive spin transport in such metal-semiconductor structures. In contrast to popular one-dimensional approach, we take into account realistic two-dimensional lateral geometry of these systems. We also focus on room temperature regime. Our analysis of spin accumulation achievable in systems of sub-micron dimensions leads to a proposal of a new family of spintronic devices with multiple ferromagnetic terminals in contact with a semiconductor channel. We show that in a three-terminal "spin transistor" digital electric expression of spin accumulation is possible. We also calculate the time-dependent spin transport induced by rotation of one of the magnets in this system, and we show that electrical sensing of magnetization dynamics is realistic in metal-semiconductor structures. An analogous five terminal system can work as a reprogrammable logic gate, with the logic inputs and the gate functionality encoded in the directions of the ferromagnetic terminals. A system capable of electrical detection of circular polarization of light is also modeled. All these proposals will hopefully set new directions in applied spintronics research and stimulate new experiments.

Cywinski, Lukasz

2007-12-01

119

Dynamic scaling in Cd1-xMnxTe spin glasses: A probe of the spin autocorrelation function

The dynamic scaling relations for the frequency-dependent magnetic susceptibility are derived, using the spin autocorrelation function q(t)~t-a exp[-(t\\/tau)b], which successfully describes results from Monte Carlo simulations on a three-dimensional Ising spin-glass model. This functional form accounts very well for the observed frequency and temperature dependences of the imaginary component of the ac magnetic susceptibility in Cd1-xMnxTe, above the spin-glass transition

Bénédicte Leclercq; Claudette Rigaux

1993-01-01

120

Influence of the particle number on the spin dynamics of ultracold atoms

NASA Astrophysics Data System (ADS)

We study the dependency of the quantum spin dynamics on the particle number in a system of ultracold spin-1 atoms within the single-spatial-mode approximation. We find, for all strengths of the spin-dependent interaction, convergence toward the mean-field dynamics in the thermodynamic limit. The convergence is, however, particularly slow when the spin-changing collisional energy and the quadratic Zeeman energy are equal; that is, deviations between quantum and mean-field spin dynamics may be extremely large under these conditions. Our estimates show that quantum corrections to the mean-field dynamics may play a relevant role in experiments with spinor Bose-Einstein condensates. This is especially the case in the regime of few atoms, which may be accessible in optical lattices. Here, spin dynamics is modulated by a beat note at large magnetic fields due to the significant influence of correlated many-body spin states.

Heinze, Jannes; Deuretzbacher, Frank; Pfannkuche, Daniela

2010-08-01

121

Influence of the particle number on the spin dynamics of ultracold atoms

We study the dependency of the quantum spin dynamics on the particle number in a system of ultracold spin-1 atoms within the single-spatial-mode approximation. We find, for all strengths of the spin-dependent interaction, convergence toward the mean-field dynamics in the thermodynamic limit. The convergence is, however, particularly slow when the spin-changing collisional energy and the quadratic Zeeman energy are equal; that is, deviations between quantum and mean-field spin dynamics may be extremely large under these conditions. Our estimates show that quantum corrections to the mean-field dynamics may play a relevant role in experiments with spinor Bose-Einstein condensates. This is especially the case in the regime of few atoms, which may be accessible in optical lattices. Here, spin dynamics is modulated by a beat note at large magnetic fields due to the significant influence of correlated many-body spin states.

Heinze, Jannes; Pfannkuche, Daniela [I. Institut fuer Theoretische Physik, Universitaet Hamburg, Jungiusstrasse 9, D-20355 Hamburg (Germany); Deuretzbacher, Frank [Institut fuer Theoretische Physik, Leibniz Universitaet Hannover, Appelstrasse 2, D-30167, Hannover (Germany)

2010-08-15

122

Dynamics of entanglement of two electron spins interacting with nuclear spin baths in quantum dots

We study the dynamics of entanglement of two electron spins in two quantum dots, in which each electron is interacting with its nuclear spin environment. Focusing on the case of uncoupled dots, and starting from either Bell or Werner states of two qubits, we calculate the decay of entanglement due to hyperfine interaction with the nuclei. We mostly focus on the regime of magnetic fields in which the bath-induced electron spin flips play a role, for example their presence leads to appearance of entanglement sudden death at finite time for two qubits initialized in a Bell state. For these fields the intra-bath dipolar interactions and inhomogeneity of hyperfine couplings are irrelevant on timescales of coherence (and entanglement) decay, and most of the presented calculations are performed using the uniform-coupling approximation to the exact hyperfine Hamiltonian. We provide a comprehensive overview of entanglement decay in this regime, considering both free evolution of the qubits, and an echo protocol with simultaneous application of $\\pi$ pulses to the two spins. All the currently experimentally relevant bath states are considered: the thermal state, narrowed states (characterized by diminished uncertainty of one of the components of the Overhauser field) for two uncorrelated baths, and a correlated narrowed state with well-defined value of the $z$ component of the Overhauser field interdot gradient. While we mostly use concurrence to quantify the amount of entanglement in a mixed state of the two electron spins, we also discuss the predicted behavior of currently experimentally relevant entanglement witnesses, and in particular we give results for quantum teleportation fidelity using a partially disentangled state as a resource.

Igor Bragar; ?ukasz Cywi?ski

2014-11-23

123

Nonlinear equations of dynamics for spinning paraboloidal antennas

NASA Technical Reports Server (NTRS)

The nonlinear strain-displacement and velocity-displacement relations of spinning imperfect rotational paraboloidal thin shell antennas are derived for nonaxisymmetrical deformations. Using these relations with the admissible trial functions in the principle functional of dynamics, the nonlinear equations of stress inducing motion are expressed in the form of a set of quasi-linear ordinary differential equations of the undetermined functions by means of the Rayleigh-Ritz procedure. These equations include all nonlinear terms up to and including the third degree. Explicit expressions are given for the coefficient matrices appearing in these equations. Both translational and rotational off-sets of the axis of revolution (and also the apex point of the paraboloid) with respect to the spin axis are considered. Although the material of the antenna is assumed linearly elastic, it can be anisotropic.

Utku, S.; Shoemaker, W. L.; Salama, M.

1983-01-01

124

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

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

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

2014-09-21

125

Large-scale simulation of the spin-lattice dynamics in ferromagnetic iron

NASA Astrophysics Data System (ADS)

We develop a dynamical simulation model for magnetic iron where atoms are treated as classical particles with intrinsic spins. The atoms interact via scalar many-body forces as well as via spin orientation dependent forces of the Heisenberg form. The coupling between the lattice and spin degrees of freedom is described by a coordinate-dependent exchange function where the spin orientation dependent forces are proportional to the gradient of this function. The spin-lattice dynamics simulation approach extends the existing magnetic potential treatment to the case where the energy of interaction between the atoms depends on the relative noncollinear orientations of spins. An algorithm for integrating the linked spin-coordinate equations of motion is based on the second-order Suzuki-Trotter decomposition for noncommuting operators of evolution for coordinate and spin variables. The notions of the spin thermostat and the spin temperature are introduced through the combined application of the Langevin spin dynamics and the fluctuation-dissipation theorem. We investigate several applications of the method, performing microcanonical ensemble simulations of adiabatic spin-lattice relaxation of periodic arrays of 180° domain walls, and isothermal-isobaric ensemble dynamical simulations of thermally equilibrated homogeneous systems at various temperatures. The predicted isothermal magnetization curve agrees well with the experimental data for a broad range of temperatures. The equilibrium as well as time-correlation functions of spin orientations exhibit the presence of short-range magnetic order above the Curie temperature. Furthermore, short-range order spin fluctuations are shown to contribute to the thermal expansion of the material. Our analysis illustrates the significant part played by the spin degrees of freedom in the dynamics of motion of atoms in magnetic iron and iron-based alloys. It also shows that the spin-lattice dynamics algorithm developed in this paper offers a viable way of performing large-scale dynamical atomistic simulations of magnetic materials.

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

2008-07-01

126

The effect of iron spin transition on convective dynamics, slab dynamics and the geoid

NASA Astrophysics Data System (ADS)

Iron bearing minerals in the Earths lower mantle show a transition from high-spin to low-spin in the iron constituent. This has been observed in particular for ferropericlase both experimentally (Fei et al, 2007, Lin et al. 2005) and in first principles calculations (Wu et al, 2009). The situation is less unambiguous for perovskite. Umemoto et al (2010) showed that the effect on volume is small compared to experimental uncertainty. Therefore we only considered the spin effects in ferropericlase in our models. The spin transition is characterized by a high valued positive Clapeyron slope ? = 19MPa-K while the smoothness of the transition increases with temperature. Fei et al. (2007) showed that at room temperature the spin transition pressure for iron richer composition occurs at higher values, e.g 40 GPa at 20 mol% FeO, 60 GPa at 40 mol% FeO. In order to get a full thermodynamic description of mantle material that includes the effects of spin transitions in ferropericlase we developed a model based on the multi-Einstein vibrational model approach of Jacobs et al. (2013). This model represents volume-pressure data of Lin et al. (2005), spin fraction data predicted by Wu et al. (2009) and it also includes the observed composition dependence of the spin transition pressure. Our new model further includes the thermodynamic description of Jacobs and de Jong (2007) that has been extended to describe thermodynamic properties of iron bearing (Mg,Fe)SiO3 perovskite. Because the spin transition pressure is composition dependent, the spin transition results in the formation of miscibility gap regions separating compositions enriched in high spin and compositions enriched in low-spin state. The spin transition affects thermodynamic properties, density, thermal expansivity, bulk modulus and heat capacity which in turn impact the convection dynamics of the Earth mantle. For instance, due to the high positive Clapeyron-slope of the transition convective mixing becomes more vigorous as observed in Boussinesq type modelling results of Bower et al, 2009, Shanas et al, 2011. Negative buoyancy of lithospheric slabs in the deep mantle is enhanced by the increase of thermal expansivity induced by the spin transition. Therefore the sinking rate of slabs are affected by the presence of the spin transition. Therefore the effects of the transition must be included in mantle convection modelling, done in order to bracket mantle viscosity values (Cizkova et al., 2012). Here we investigate the impact of the iron spin transition on the convective dynamics of the mantle and the distribution of material properties. As the spin transition related variations of material properties (e.g. thermal expansivity) are significant especially at lower temperatures, we concentrate mainly on the consequences for slab dynamics. To this end we use a compressible convection model based on a self consistent formulation of the thermo-physical material properties density, thermal expansivity and specific heat at constant pressure as described in (Jacobs and van den Berg, 2011). Finally, we evaluate the consequences of spin induced density contrasts in cold downwellings for the interpretation of the geoid. Bower et al. (2009) Geophys Res Lett, 36, L10306 Cizkova et al. (2012) Phys Earth Planet Inter 200, 56-62 Fei et al. (2007) Geophy res Lett, 34, L17307, 1-5 Jacobs and de Jong (2007) Geochim Cosmochim Acta, 71, 3630-3655 Jacobs and van den Berg (2011) Phys Earth Planet Inter, 186, 36-48 Jacobs et al. (2013) Phys Chem Minerals, in press Lin et al. (2005) Nature 436, 377-380 Shahnas et al (2011) J Geophys Res 116, B08205, 1-16 Umemoto et al (2010) Phys Earth Planet Int, 180, 209-214 Wu et al (2009) Phys Rev B 80, 014409, 1-8

Jacobs, Michael; van den Berg, Arie; Spakman, Wim; Cadek, Ondrej; Cizkova, Hana; Matyska, Ctirad

2013-04-01

127

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

128

S U (3 ) Semiclassical Representation of Quantum Dynamics of Interacting Spins

NASA Astrophysics Data System (ADS)

We present a formalism for simulating quantum dynamics of lattice spin-1 systems by first introducing local hidden variables and then doing semiclassical (truncated Wigner) approximation in the extended phase space. In this way, we exactly take into account the local on-site Hamiltonian and approximately treat spin-spin interactions. In particular, we represent each spin with eight classical S U (3 ) variables. Three of them represent the usual spin components and five others are hidden variables representing local spin-spin correlations. We compare our formalism with exact quantum dynamics of fully connected spin systems and find very good agreement. As an application, we discuss quench dynamics of a Bose-Hubbard model near the superfluid-insulator transition for a 3D lattice system consisting of 1000 sites.

Davidson, Shainen M.; Polkovnikov, Anatoli

2015-01-01

129

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

130

Spin dynamics of the anisotropic spin-1 antiferromagnetic chain at finite magnetic fields

NASA Astrophysics Data System (ADS)

We present results of a study of the antiferromagnetic spin-1 chain, subject to the simultaneous presence of single-ion anisotropy and external magnetic fields. Using a quantum Monte Carlo calculation based on the stochastic series expansion method, we first uncover a rich quantum phase diagram comprising Néel, Haldane, Luttinger-liquid, and large-anisotropy phases. Second, we scan across this phase diagram over a wide range of parameters, evaluating the transverse dynamic structure factor, which we show to exhibit sharp massive modes as well as multiparticle continua. For vanishing anisotropy and fields, comparison with existing results from other analytic and numerical approaches shows convincing consistency.

Rahnavard, Yousef; Brenig, Wolfram

2015-02-01

131

Dynamics and Control of a Quasi-1D Spin System

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

Paola Cappellaro; Chandrasekhar Ramanathan; David G. Cory

2007-06-04

132

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

133

Spin-down Dynamics of Magnetized Solar-type Stars

NASA Astrophysics Data System (ADS)

It has long been known that solar-type stars undergo significant spin-down, via magnetic braking, during their main-sequence lifetimes. However, magnetic braking only operates on the surface layers; it is not yet completely understood how angular momentum is transported within the star and how rapidly the spin-down information is communicated to the deep interior. In this work, we use insight from recent progress in understanding internal solar dynamics to model the interior of other solar-type stars. We assume, following Gough & McIntyre, that the bulk of the radiation zone of these stars is held in uniform rotation by the presence of an embedded large-scale primordial field, confined below a stably stratified, magnetic-free tachocline by large-scale meridional flows downwelling from the convection zone. We derive simple equations to describe the response of this model interior to spin-down of the surface layers, which are identical to the two-zone model of MacGregor & Brenner, with a coupling timescale proportional to the local Eddington-Sweet timescale across the tachocline. This timescale depends both on the rotation rate of the star and on the thickness of the tachocline, and it can vary from a few hundred thousand years to a few Gyr, depending on stellar properties. Qualitative predictions of the model appear to be consistent with observations, although they depend sensitively on the assumed functional dependence of the tachocline thickness on the stellar rotation rate.

Oglethorpe, R. L. F.; Garaud, P.

2013-12-01

134

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

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

135

Spin soliton dynamics and magnetic susceptibility of (DMe-DCNQI)2Li by ESR under pressure$

Spin soliton dynamics and magnetic susceptibility of (DMe-DCNQI)2Li by ESR under pressure$ M-0198, Japan Abstract At ambient pressure, a 1/4 filled spin-Peierls system (DMe-DCNQI)2Li shows spin; Antiferromagnetic order 1. Introduction We have studied the electronic states of one-dimensional (1D) system of (DMe

Mizoguchi, Kenji

136

ContinuousWeak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble Greg A. Smith,1

that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement Faraday effect to probe the spins in an ensemble of laser cooled Cs atoms.[4Â6] Our setup employs a probe spins is domi- nated by a nonlinear term in the light shift generated by the Faraday probe, which leads

Jessen, Poul S.

137

Dynamical spin structure factor of one-dimensional interacting fermions

NASA Astrophysics Data System (ADS)

We revisit the dynamic spin susceptibility ? (q ,? ) of one-dimensional interacting fermions. To second order in the interaction, backscattering results in a logarithmic correction to ? (q ,? ) at q ?kF , even if the single-particle spectrum is linearized near the Fermi points. Consequently, the dynamic spin structure factor Im ? (q ,? ) is nonzero at frequencies above the single-particle continuum. In the boson language, this effect results from the marginally irrelevant backscattering operator of the sine-Gordon model. Away from the threshold, the high-frequency tail of Im ? (q ,? ) due to backscattering is larger than that due to finite mass by a factor of kF/q . We derive the renormalization group equations for the coupling constants of the g -ology model at finite ? and q and find the corresponding expression for ? (q ,? ) , valid to all orders in the interaction but not in the immediate vicinity of the continuum boundary, where the finite-mass effects become dominant.

Zyuzin, Vladimir A.; Maslov, Dmitrii L.

2015-02-01

138

Dynamical spin injection at a quasi-one-dimensional ferromagnet-graphene interface

NASA Astrophysics Data System (ADS)

We present a study of dynamical spin injection from a three-dimensional ferromagnet into two-dimensional single-layer graphene. Comparative ferromagnetic resonance (FMR) studies of ferromagnet/graphene strips buried underneath the central line of a coplanar waveguide show that the FMR linewidth broadening is the largest when the graphene layer protrudes laterally away from the ferromagnetic strip, indicating that the spin current is injected into the graphene areas away from the area directly underneath the ferromagnet being excited. Our results confirm that the observed damping is indeed a signature of dynamical spin injection, wherein a pure spin current is pumped into the single-layer graphene from the precessing magnetization of the ferromagnet. The observed spin pumping efficiency is difficult to reconcile with the expected backflow of spins according to the standard spin pumping theory and the characteristics of graphene, and constitutes an enigma for spin pumping in two-dimensional structures.

Singh, S.; Ahmadi, A.; Cherian, C. T.; Mucciolo, E. R.; del Barco, E.; Özyilmaz, B.

2015-01-01

139

Lattice dynamics in spin-crossover nanoparticles through nuclear inelastic scattering

NASA Astrophysics Data System (ADS)

We used nuclear inelastic scattering (NIS) to investigate the lattice dynamics in [Fe(pyrazine)(Ni(CN)4)] spin crossover nanoparticles. The vibrational density of states of iron was extracted from the NIS data, which allowed to determine characteristic thermodynamical and lattice dynamical parameters as well as their spin-state dependence. The optical part of the NIS spectra compares well with the Raman scattering data reflecting the expansion/contraction of the coordination octahedron during the spin transition. From the acoustic part, we extracted the sound velocity in the low-spin (vLS=2073 ±31 m s-1) and high-spin (vHS=1942 ±23 m s-1) states of the particles. The spin-state dependence of this parameter is of primary interest to rationalize the spin-transition behavior in solids as well as its dynamics and finite size effects.

Félix, Gautier; Mikolasek, Mirko; Peng, Haonan; Nicolazzi, William; Molnár, Gábor; Chumakov, Aleksandr I.; Salmon, Lionel; Bousseksou, Azzedine

2015-01-01

140

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

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

Weber, C.P.

2010-04-28

141

Universal dynamics of quantum spin decoherence in a nuclear spin bath Yi-Ya Tian, Pochung Chen, and Daw-Wei Wang Physics Department, National Tsing-Hua University, Hsinchu, Taiwan 30013, Republic systematically investigate the universal spin decoherence dynamics of a localized electron in an arbitrary

Wang, Daw-Wei

142

Rényi information flow in the Ising model with single-spin dynamics

NASA Astrophysics Data System (ADS)

The n -index Rényi mutual information and transfer entropies for the two-dimensional kinetic Ising model with arbitrary single-spin dynamics in the thermodynamic limit are derived as functions of ensemble averages of observables and spin-flip probabilities. Cluster Monte Carlo algorithms with different dynamics from the single-spin dynamics are thus applicable to estimate the transfer entropies. By means of Monte Carlo simulations with the Wolff algorithm, we calculate the information flows in the Ising model with the Metropolis dynamics and the Glauber dynamics, respectively. We find that not only the global Rényi transfer entropy, but also the pairwise Rényi transfer entropy, peaks in the disorder phase.

Deng, Zehui; Wu, Jinshan; Guo, Wenan

2014-12-01

143

Engineering nuclear spin dynamics with optically pumped nitrogen-vacancy center

We present a general theory for using an optically pumped diamond nitrogen-vacancy center as a tunable, non-equilibrium bath to control a variety of nuclear spin dynamics (such as dephasing, relaxation, squeezing, polarization, etc.) and the nuclear spin noise. It opens a new avenue towards engineering the dissipative and collective nuclear spin evolution and solves an open problem brought up by the $^{13}$C nuclear spin noise suppression experiment [E. Togan \\textit{et al}., Nature 478, 497 (2011)].

Ping Wang; Jiangfeng Du; Wen Yang

2015-03-01

144

Strain dependent electron spin dynamics in bulk cubic GaN

NASA Astrophysics Data System (ADS)

The electron spin dynamics under variable uniaxial strain is investigated in bulk cubic GaN by time-resolved magneto-optical Kerr-rotation spectroscopy. Spin relaxation is found to be approximately independent of the applied strain, in complete agreement with estimates for Dyakonov-Perel spin relaxation. Our findings clearly exclude strain-induced relaxation as an effective mechanism for spin relaxation in cubic GaN.

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

2015-03-01

145

Many-Body Quantum Spin Dynamics with Monte Carlo Trajectories on a Discrete Phase Space

NASA Astrophysics Data System (ADS)

Interacting spin systems are of fundamental relevance in different areas of physics, as well as in quantum information science and biology. These spin models represent the simplest, yet not fully understood, manifestation of quantum many-body systems. An important outstanding problem is the efficient numerical computation of dynamics in large spin systems. Here, we propose a new semiclassical method to study many-body spin dynamics in generic spin lattice models. The method is based on a discrete Monte Carlo sampling in phase space in the framework of the so-called truncated Wigner approximation. Comparisons with analytical and numerically exact calculations demonstrate the power of the technique. They show that it correctly reproduces the dynamics of one- and two-point correlations and spin squeezing at short times, thus capturing entanglement. Our results open the possibility to study the quantum dynamics accessible to recent experiments in regimes where other numerical methods are inapplicable.

Schachenmayer, J.; Pikovski, A.; Rey, A. M.

2015-01-01

146

Competing 1??* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.

Deactivation of excited electronic states through coupling to dissociative (1)??* states in heteroaromatic systems has received considerable attention in recent years, particularly as a mechanism that contributes to the ultraviolet (UV) photostability of numerous aromatic biomolecules and their chromophores. Recent studies have expanded upon this work to look at more complex species, which involves understanding competing dynamics on two different (1)??* potential energy surfaces (PESs) localized on different heteroatom hydride coordinates (O-H and N-H bonds) within the same molecule. In a similar spirit, the work presented here utilizes ultrafast time-resolved velocity map ion imaging to study competing dissociation pathways along (1)??* PESs in mequinol (p-methoxyphenol), localized at O-H and O-CH(3) bonds yielding H atoms or CH(3) radicals, respectively, over an excitation wavelength range of 298-238 nm and at 200 nm. H atom elimination is found to be operative via either tunneling under a conical intersection (CI) (298 ? ? ? 280 nm) or ultrafast internal conversion through appropriate CIs (? ? 245 nm), both of which provide mechanisms for coupling onto the dissociative state associated with the O-H bond. In the intermediate wavelength range of 280 ? ? ? 245 nm, mediated H atom elimination is not observed. In contrast, we find that state driven CH(3) radical elimination is only observed in the excitation range 264 ? ? ? 238 nm. Interpretation of these experimental results is guided by: (i) high level complete active space with second order perturbation theory (CASPT2) calculations, which provide 1-D potential energy cuts of the ground and low lying singlet excited electronic states along the O-H and O-CH(3) bond coordinates; and (ii) calculated excitation energies using CASPT2 and the equation-of-motion coupled cluster with singles and doubles excitations (EOM-CCSD) formalism. From these comprehensive studies, we find that the dynamics along the O-H coordinate generally mimic H atom elimination previously observed in phenol, whereas O-CH(3) bond fission in mequinol appears to present notably different behavior to the CH(3) elimination dynamics previously observed in anisole (methoxybenzene). PMID:22948565

Hadden, David J; Roberts, Gareth M; Karsili, Tolga N V; Ashfold, Michael N R; Stavros, Vasilios G

2012-10-14

147

Spin probe dynamics of n-hexadecane in confined geometry

NASA Astrophysics Data System (ADS)

A combined study of the rotational dynamics of the stable free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the phase behavior of n-hexadecane (n-HXD) in the bulk and the confined states in a series of silica gels (SG) by means of ESR and DSC is presented. A slow to fast motion transition of the spin probe TEMPO in the bulk n-HXD occurs at T50 G,bulk ? Tm,bulk, i.e., well below the melting temperature due to its trapping and localized mobility in the interlamellar gap of the crystallites [J. Bartoš, H. Švajdlenková, M. Zaleski, M. Edelmann, M. Lukešová, Physica B 430, 99 (2013)]. On the other hand, the dynamics of the TEMPO in the confined systems is strongly slowing down with T50 G (Dpore) >Tm(Dpore) and slightly increases with the pore size Dpore = 60, 100 and 300 Å of the SG's. At the same time, both the corresponding melting temperature, Tm (Dpore), and melting enthalpy, ?Hm (Dpore), decrease with Dpore together with the mutual anti-correlation between T50 G and Tm as a function of the inverse of pore diameter, 1/Dpore. Moreover, the dynamic heterogeneity of the TEMPO in the confined state below T50 G (Dpore) is closely related to the phase transformation. The strong slowing down of the spin probe motion likely results from its preferential localization at the interface layer of the matrix pore due to specific interaction of TEMPO molecules with the polar silanol groups of the SG matrix. This is supported by special study on a series of the variously filled n-HXD/SG systems, other similar experimental findings as well as by theoretical spectral argument.

Lukešová, Miroslava; Švajdlenková, Helena; Sippel, Pit; Macová, Eva; Berek, Dušan; Loidl, Alois; Bartoš, Josef

2015-02-01

148

Arterial spin labeling and dynamic susceptibility contrast CBF MRI in postischemic hyperperfusion,

Arterial spin labeling and dynamic susceptibility contrast CBF MRI in postischemic hyperperfusion Texas Veterans Health Care System, San Antonio, Texas, USA Arterial spin labeling (ASL) and dynamic.76±0.14 seconds in normal pixels to 1.93±0.17 seconds in hyperperfusion pixels. Arterial transit time decreased

Duong, Timothy Q.

149

We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically-defined double quantum dot (DQD) in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.

Martin J. A. Schuetz; Eric M. Kessler; Lieven M. K. Vandersypen; J. Ignacio Cirac; Geza Giedke

2014-05-30

150

Solid effect in magic angle spinning dynamic nuclear polarization

NASA Astrophysics Data System (ADS)

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 ? _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, Björn; Smith, Albert A.; Griffin, Robert G.

2012-08-01

151

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 ?(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 (1)H 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 (1)H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect. PMID:22894339

Corzilius, Björn; Smith, Albert A; Griffin, Robert G

2012-08-01

152

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

Buß, J. H.; Schaefer, A.; Hägele, D.; Rudolph, J. [Arbeitsgruppe Spektroskopie der kondensierten Materie, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum (Germany); Schupp, T.; As, D. J. [Department of Physics, University of Paderborn, Warburger Str. 100, D-33095 Paderborn (Germany)

2014-11-03

153

Imaging intracellular protein dynamics by spinning disk confocal microscopy

The palette of fluorescent proteins has grown exponentially over the last decade, and as a result live imaging of cells expressing fluorescently tagged proteins is becoming more and more main stream. Spinning disk confocal microscopy (SDC) is a high speed optical sectioning technique, and a method of choice to observe and analyze intracellular fluorescent protein dynamics at high spatial and temporal resolution. In an SDC system, a rapidly rotating pinhole disk generates thousands of points of light that scan the specimen simultaneously, which allows direct capture of the confocal image with low noise scientific grade cooled charged-coupled device (CCD) cameras, and can achieve frame rates of up 1000 frames per second. In this chapter we describe important components of a state-of-the-art spinning disk system optimized for live cell microscopy, and provide a rationale for specific design choices. We also give guidelines how other imaging techniques such as total internal reflection (TIRF) microscopy or spatially controlled photoactivation can be coupled with SDC imaging, and provide a short protocol on how to generate cell lines stably expressing fluorescently tagged proteins by lentivirus-mediated transduction. PMID:22264541

Stehbens, Samantha; Pemble, Hayley; Murrow, Lindsay; Wittmann, Torsten

2012-01-01

154

A key role for unusual spin dynamics in ferropnictides

NASA Astrophysics Data System (ADS)

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

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

2009-02-01

155

NASA Astrophysics Data System (ADS)

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

Meriles, Carlos A.; Doherty, Marcus W.

2014-07-01

156

NASA Astrophysics Data System (ADS)

We consider a system of two strongly coupled electron spins in zero magnetic field, each of which is interacting with an individual bath of nuclear spins via the hyperfine interaction. Applying the long-spin approximation that we introduced in a previous paper [Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/95/47009 95, 47009 (2011)] (here each bath is replaced by a single long spin), we numerically study the electron spin and entanglement dynamics. We demonstrate that the decoherence time is scaling with the bath size according to a power law. As expected, the decaying part of the dynamics decreases with increasing bath polarization. However, surprisingly it turns out that, under certain circumstances, combining quantum dots of different geometry to the double dot setup has a very similar effect on the magnitude of the spin decay. Finally, we show that even for a comparatively weak exchange coupling the electron spins can be fully entangled.

Erbe, B.; Schliemann, J.

2012-04-01

157

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

Meriles, Carlos A. [Department of Physics, CUNY-City College of New York, New York, New York 10031 (United States); Doherty, Marcus W. [Laser Physics Centre, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

2014-07-14

158

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. PMID:18698714

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

2008-01-01

159

Electric field control of spin dynamics in a magnetically active tunnel junction

NASA Astrophysics Data System (ADS)

The dynamics of a single spin embedded in a tunnelling junction is studied. Within a nonequilibrium Keldysh Green's function technique, we derive a quantum Langevin equation describing the spin dynamics. In the high temperature limit, it reduces to a Bloch equation, for which the spin relaxation rate, as determined by the temporal fluctuation, is linearly proportional to the temperature. In the opposite limit, the relaxation rate depends on the applied voltage, in contrast to the case of a spin in an equilibrium environment. We also show that spin-flip transition processes during electron tunnelling convert the applied electric field (i.e. voltage bias) into an effective magnetic field. Consequently, the dynamics of the spin, otherwise precessing along the static magnetic field, will have either a frequency shift proportional to the dc bias or a magnetic resonance driven indirectly by an ac electric field at the Larmor frequency ?L. An experiment to measure this effect is also proposed.

Zhu, Jian-Xin; Fransson, Jonas

2006-11-01

160

Quench dynamics and statistics of measurements for a line of quantum spins in two dimensions

NASA Astrophysics Data System (ADS)

Motivated by recent experiments, we investigate the dynamics of a line of spin-down spins embedded in the ferromagnetic spin-up ground state of a two-dimensional XXZ model close to the Ising limit. In a situation where the couplings in the x and y directions are different, the quench dynamics of this system is governed by the interplay of one-dimensional excitations (kinks and holes) moving along the line and single-spin excitations evaporating into the two-dimensional background. A semiclassical approximation can be used to calculate the dynamics of this complex quantum system. Recently, it became possible to perform projective quantum measurements on such spin systems, allowing us to determine, e.g., the z component of each individual spin. We predict the statistical properties of such measurements which contain much more information than correlation functions.

Lux, Jonathan; Rosch, Achim

2015-02-01

161

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

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

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

2009-12-22

162

Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements.

Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties. PMID:25493776

Field, Timothy R

2014-11-01

163

Dynamical theory of spin noise and relaxation: Prospects for real-time NMR measurements

NASA Astrophysics Data System (ADS)

Recent developments in theoretical aspects of spin noise and relaxation and their interrelationship reveal a modified spin density, distinct from the density matrix, as the necessary object to describe fluctuations in spin systems. These fluctuations are to be viewed as an intrinsic quantum mechanical property of such systems immersed in random magnetic environments and are observed as "spin noise" in the absence of any radio frequency excitation. With the prospect of ultrafast digitization, the role of spin noise in real-time parameter extraction for (NMR) spin systems, and the advantage over standard techniques, is of essential importance, especially for systems containing a small number of spins. In this article we outline prospects for harnessing the recent dynamical theory in terms of spin-noise measurement, with attention to real-time properties.

Field, Timothy R.

2014-11-01

164

Significant progress was made in recent years in the understanding of the proton spin kinetics in polymer melts. Generally, the proton spin kinetics is determined by intramolecular and intermolecular magnetic dipole-dipole contributions of proton spins. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. It appears that this postulate is far from reality. The relative weights of intra- and intermolecular contributions are time dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics the influence of the intermolecular magnetic dipole-dipole interactions increases faster with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. The intermolecular contribution in the proton relaxation of polymer melts can experimentally be isolated using the isotope dilution technique and this opens a new perspective for experimental investigations of polymer dynamics by proton NMR.

N. Fatkullin; S. Stapf; M. Hofmann; R. Meierc; E. A. Roessler

2014-05-25

165

NASA Astrophysics Data System (ADS)

Significant progress was made in recent years in the understanding of the proton spin kinetics in polymer melts. Generally, the proton spin kinetics is determined by intramolecular and intermolecular magnetic dipole-dipole contributions of proton spins. During many decades it was postulated that the main contribution is a result of intramolecular magnetic dipole-dipole interactions of protons belonging to the same polymer segment. It appears that this postulate is far from reality. The relative weights of intra- and intermolecular contributions are time dependent and sensitive to details of polymer chain dynamics. It is shown that for isotropic models of polymer dynamics the influence of the intermolecular magnetic dipole-dipole interactions increases faster with increasing evolution time (i.e. decreasing frequency) than the corresponding influence of the intramolecular counterpart. On the other hand, an inverted situation is predicted by the tube-reptation model: here the influence of the intramolecular magnetic dipole-dipole interactions increases faster with time than the contribution from intermolecular interactions. The intermolecular contribution in the proton relaxation of polymer melts can experimentally be isolated using the isotope dilution technique and this opens a new perspective for experimental investigations of polymer dynamics by proton NMR.

Fatkullin, N.; Stapf, S.; Hofmann, M.; Meier, R.; Rössler, E. A.

2015-01-01

166

Tracking excited-state charge and spin dynamics in iron coordination complexes.

Crucial to many light-driven processes in transition metal complexes is the absorption and dissipation of energy by 3d electrons. But a detailed understanding of such non-equilibrium excited-state dynamics and their interplay with structural changes is challenging: a multitude of excited states and possible transitions result in phenomena too complex to unravel when faced with the indirect sensitivity of optical spectroscopy to spin dynamics and the flux limitations of ultrafast X-ray sources. Such a situation exists for archetypal polypyridyl iron complexes, such as [Fe(2,2'-bipyridine)3](2+), where the excited-state charge and spin dynamics involved in the transition from a low- to a high-spin state (spin crossover) have long been a source of interest and controversy. Here we demonstrate that femtosecond resolution X-ray fluorescence spectroscopy, with its sensitivity to spin state, can elucidate the spin crossover dynamics of [Fe(2,2'-bipyridine)3](2+) on photoinduced metal-to-ligand charge transfer excitation. We are able to track the charge and spin dynamics, and establish the critical role of intermediate spin states in the crossover mechanism. We anticipate that these capabilities will make our method a valuable tool for mapping in unprecedented detail the fundamental electronic excited-state dynamics that underpin many useful light-triggered molecular phenomena involving 3d transition metal complexes. PMID:24805234

Zhang, Wenkai; Alonso-Mori, Roberto; Bergmann, Uwe; Bressler, Christian; Chollet, Matthieu; Galler, Andreas; Gawelda, Wojciech; Hadt, Ryan G; Hartsock, Robert W; Kroll, Thomas; Kjær, Kasper S; Kubi?ek, Katharina; Lemke, Henrik T; Liang, Huiyang W; Meyer, Drew A; Nielsen, Martin M; Purser, Carola; Robinson, Joseph S; Solomon, Edward I; Sun, Zheng; Sokaras, Dimosthenis; van Driel, Tim B; Vankó, György; Weng, Tsu-Chien; Zhu, Diling; Gaffney, Kelly J

2014-05-15

167

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

168

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. PMID:22404310

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

2012-01-01

169

Magnetization dynamics and spin diffusion in semiconductors and metals

Datta and Das [16] it was noted that the gate voltage could also in?uence the spinDatta and Das [16] in 1990, in which the electric ?eld of the gate together with spin-spin-transistors. A di?usive version of a Datta-Das system

Cywi?ski, ?ukasz

2007-01-01

170

NASA Astrophysics Data System (ADS)

We use the coupled cluster method (CCM) to study the zero-temperature ground-state (GS) properties of a spin-1/2 J1-J2 Heisenberg antiferromagnet on a triangular lattice with competing nearest-neighbor and next-nearest-neighbor exchange couplings J1>0 and J2?? J1>0 , respectively, in the window 0 ?? <1 . The classical version of the model has a single GS phase transition at ?cl=1/8 in this window from a phase with 3-sublattice antiferromagnetic (AFM) 120? Néel order for ? ?cl . This classical accidental degeneracy is lifted by quantum fluctuations, which favor a 2-sublattice AFM striped phase. For the quantum model we work directly in the thermodynamic limit of an infinite number of spins, with no consequent need for any finite-size scaling analysis of our results. We perform high-order CCM calculations within a well-controlled hierarchy of approximations, which we show how to extrapolate to the exact limit. In this way we find results for the case ? =0 of the spin-1/2 model for the GS energy per spin, E /N =-0.5521 (2 ) J1 , and the GS magnetic order parameter, M =0.198 (5 ) (in units where the classical value is Mcl=1/2), which are among the best available. For the spin-1/2 J1-J2 model we find that the classical transition at ? =?cl is split into two quantum phase transitions at ?1c=0.060 (10 ) and ?2c=0.165 (5 ) . The two quasiclassical AFM states (viz., the 120? Néel state and the striped state) are found to be the stable GS phases in the regime ? ?2c , respectively, while in the intermediate regimes ?1c

Li, P. H. Y.; Bishop, R. F.; Campbell, C. E.

2015-01-01

171

Membrane Protein Structure and Dynamics Studied by Site-Directed SpinLabeling ESR

ESR spectroscopy of site-directed spin-labeled biomolecules (Site-Directed Spin Labeling, SDSL) has emerged as a powerful\\u000a method for studying the structure and conformational dynamics of proteins and nucleic acids under conditions relevant to function\\u000a (for reviews see, e.g., Feix and Klug 1998; Hubbell et al. 1996; Hubbell et al. 1998, 2002). In this technique a spin-label side chain is introduced at

Enrica Bordignon; Heinz-Jürgen Steinhoff

172

Spin echo dynamics under an applied drift field in graphene nanoribbon superlattices

We investigate the evolution of spin dynamics in graphene nanoribbon superlattices (GNSLs) with armchair and zigzag edges in the presence of a drift field. We determine the exact evolution operator and show that it exhibits spin echo phenomena due to rapid oscillations of the quantum states along the ribbon. The evolution of the spin polarization is accompanied by strong beating patterns. We also provide detailed analysis of the band structure of GNSLs with armchair and zigzag edges.

Prabhakar, Sanjay, E-mail: sprabhakar@wlu.ca [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada)] [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada); Melnik, Roderick [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada) [M 2NeT Laboratory, Wilfrid Laurier University, 75 University Avenue West, Waterloo, Ontario N2L 3C5 (Canada); Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Bonilla, Luis L. [Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain)] [Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes (Spain); Raynolds, James E. [Drinker Biddle and Reath LLP, Washington, DC 20005 (United States)] [Drinker Biddle and Reath LLP, Washington, DC 20005 (United States)

2013-12-02

173

Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond

We investigate spin-dependent decay and intersystem crossing in the optical cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We use spin control and pulsed optical excitation to extract both the spin-resolved lifetimes of the excited states and the degree of optically-induced spin polarization. By optically exciting the centre with a series of picosecond pulses, we determine the spin-flip probabilities per optical cycle, as well as the spin-dependent probability for intersystem crossing. This information, together with the indepedently measured decay rate of singlet population provides a full description of spin dynamics in the optical cycle of NV centres. The temperature dependence of the singlet population decay rate provides information on the number of singlet states involved in the optical cycle.

Lucio Robledo; Hannes Bernien; Toeno van der Sar; Ronald Hanson

2010-10-06

174

Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond

We investigate spin-dependent decay and intersystem crossing in the optical cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We use spin control and pulsed optical excitation to extract both the spin-resolved lifetimes of the excited states and the degree of optically-induced spin polarization. By optically exciting the centre with a series of picosecond pulses, we determine the spin-flip probabilities per optical cycle, as well as the spin-dependent probability for intersystem crossing. This information, together with the indepedently measured decay rate of singlet population provides a full description of spin dynamics in the optical cycle of NV centres. The temperature dependence of the singlet population decay rate provides information on the number of singlet states involved in the optical cycle.

Robledo, Lucio; van der Sar, Toeno; Hanson, Ronald

2010-01-01

175

Binary dynamics from spin1-spin2 coupling at fourth post-Newtonian order

We calculate via the effective field theory (EFT) approach the next-to-next-to-leading order (NNLO) spin1-spin2 conservative potential for a binary. Hereby, we first demonstrate the ability of the EFT approach to go at NNLO in post-Newtonian (PN) corrections from spin effects. The NNLO spin1-spin2 interaction is evaluated at fourth PN order for a binary of maximally rotating compact objects. This sector includes contributions from diagrams, which are not pure spin1-spin2 diagrams, as they contribute through the leading-order spin accelerations and precessions, that should be first taken into account here. The fact that the spin is derivative-coupled adds significantly to the complexity of computations. In particular, for the irreducible two-loop diagrams, which are the most complicated to evaluate in this sector, irreducible two-loop tensor integrals up to order 4 are required. The EFT calculation is carried out in terms of the nonrelativistic gravitational (NRG) fields. However, not all of the benefits of the NRG fields apply to spin interactions, as all possible diagram topologies are realized at each order of $G$ included. Still, the NRG fields remain advantageous, and thus there was no use of automated computations in this work. Our final result can be reduced, and a corresponding Hamiltonian may be derived.

Michele Levi

2014-06-25

176

Statics and dynamics of the two-spin-facilitated kinetic Ising model

NASA Astrophysics Data System (ADS)

The two-spin-facilitated kinetic Ising model, or Fredrickson-Andersen model, in two dimensions is investigated, where down-spins are energetically favored over up-spins due to a suitably oriented magnetic field and the only interaction between spins is a dynamic constraint which allows any spin to flip only if it has at least two nearest up-spin neighbors. From Monte Carlo simulations it is known that the model exhibits glasslike behavior where the autocorrelation time of a spin as a function of temperature is well described by the Adam-Gibbs expression. Due to the dynamic constraint, the state space is divided into nonconnected partitions the most important of which is the high temperature partition which includes the all-spins-up state. A proof given earlier by Fredrickson and Andersen is completed, which states that for infinitly large lattices and for a temperature larger than zero, the probability that a randomly picked state is part of the high temperature partition approaches unity. It is also shown that the system is ergodic, i.e., that no glass transition may occur at a temperature larger than zero. These results hold also for the model in higher dimensions than two and for the three-spin-facilitated kinetic Ising model in three dimensions. It is suggested that the model equilibrates by cooperative diffusion of a critical droplet of up-spins.

Reiter, Johannes

1991-07-01

177

Optimal control of coupled spin dynamics in the presence of relaxation

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

Dionisis Stefanatos

2005-01-01

178

The competitive dynamics between tumor cells, a replication-competent virus and an immune response

Replication-competent viruses have been used as an alternative therapeutic approach for cancer treatment. However, new clinical data revealed an innate immune response to virus that may mitigate the effects of treatment. Recently, Wein, Wu and Kirn have established a model which describes the interaction between tumor cells, a replication-competent virus and an immune response (Cancer Research 63 (2003):1317–1324). The purpose

Youshan Tao; Qian Guo

2005-01-01

179

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

NASA Astrophysics Data System (ADS)

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

Temizer, Ümüt; Tülek, Mesimi; Yarar, Semih

2014-12-01

180

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

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

Barnes, Alexander B.

181

Nonlinear analysis of magnetization dynamics excited by spin Hall effect

NASA Astrophysics Data System (ADS)

We investigate the possibility of exciting self-oscillation in a perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation state, the energy supplied by the spin torque during a precession on a constant energy curve should equal the dissipation due to damping. Also, the current to balance the spin torque and the damping torque in the self-oscillation state should be larger than the critical current to destabilize the initial state. We find that these conditions in the spin Hall system are not satisfied by deriving analytical solutions of the energy supplied by the spin transfer effect and the dissipation due to the damping from the nonlinear LLG equation. This indicates that the self-oscillation of a perpendicular ferromagnet cannot be excited solely by the spin Hall torque.

Taniguchi, Tomohiro

2015-03-01

182

Photo-Induced Spin Dynamics in Nanoelectronic Devices

NASA Astrophysics Data System (ADS)

The present research is devoted to the investigation of electron spin transmission through a nanoelectronic device. This device is modeled as nonmagnetic semiconductor quantum dot coupled to two diluted magnetic semiconductor leads. The spin transport characteristics through such a device are investigated under the effect of an ac-field of a wide range of frequencies. The present result shows a periodic oscillation of the conductance for both the cases of parallel and antiparallel spin alignment. These oscillations are due to Fano-resonance. Results for spin polarization and giant magneto-resistance show the coherency property. The present research might be useful for developing single spin-based quantum bits (qubits) required for quantum information processing and quantum spin-telecommunication.

Mina, D. Asham; Walid, A. Zein; Adel, H. Phillips

2012-10-01

183

The mechanistic understanding of the dynamic processes linking nutrient acquisition and biomass production of competing individuals can be instructive in optimizing intercropping systems. Here, we examine the effect of inoculation with Funneliformis mosseae on competitive dynamics between wheat and faba bean. Wheat is less responsive to mycorrhizal inoculation. Both inoculated and uninoculated wheat attained the maximum instantaneous N and P capture approximately five days before it attained the maximum instantaneous biomass production, indicating that wheat detected the competitor and responded physiologically to resource limitation prior to the biomass response. By contrast, the instantaneous N and P capture by uninoculated faba bean remained low throughout the growth period, and plant growth was not significantly affected by competing wheat. However, inoculation substantially enhanced biomass production and N and P acquisition of faba bean. The exudation of citrate and malate acids and acid phosphatase activity were greater in mycorrhizal than in uninoculated faba bean, and rhizosphere pH tended to decrease. We conclude that under N and P limiting conditions, temporal separation of N and P acquisition by competing plant species and enhancement of complementary resource use in the presence of AMF might be attributable to the competitive co-existence of faba bean and wheat. PMID:25631933

Qiao, Xu; Bei, Shuikuan; Li, Chunjie; Dong, Yan; Li, Haigang; Christie, Peter; Zhang, Fusuo; Zhang, Junling

2015-01-01

184

The mechanistic understanding of the dynamic processes linking nutrient acquisition and biomass production of competing individuals can be instructive in optimizing intercropping systems. Here, we examine the effect of inoculation with Funneliformis mosseae on competitive dynamics between wheat and faba bean. Wheat is less responsive to mycorrhizal inoculation. Both inoculated and uninoculated wheat attained the maximum instantaneous N and P capture approximately five days before it attained the maximum instantaneous biomass production, indicating that wheat detected the competitor and responded physiologically to resource limitation prior to the biomass response. By contrast, the instantaneous N and P capture by uninoculated faba bean remained low throughout the growth period, and plant growth was not significantly affected by competing wheat. However, inoculation substantially enhanced biomass production and N and P acquisition of faba bean. The exudation of citrate and malate acids and acid phosphatase activity were greater in mycorrhizal than in uninoculated faba bean, and rhizosphere pH tended to decrease. We conclude that under N and P limiting conditions, temporal separation of N and P acquisition by competing plant species and enhancement of complementary resource use in the presence of AMF might be attributable to the competitive co-existence of faba bean and wheat. PMID:25631933

Qiao, Xu; Bei, Shuikuan; Li, Chunjie; Dong, Yan; Li, Haigang; Christie, Peter; Zhang, Fusuo; Zhang, Junling

2015-01-01

185

Charge and Spin Dynamics of the Hubbard Chains

NASA Technical Reports Server (NTRS)

We calculate the local correlation functions of charge and spin for the one-chain and two-chain Hubbard model using density matrix renormalization group method and the recursion technique. Keeping only finite number of states we get good accuracy for the low energy excitations. We study the charge and spin gaps, bandwidths and weights of the spectra for various values of the on-site Coulomb interaction U and the electron filling. In the low energy part, the local correlation functions are different for the charge and spin. The bandwidths are proportional to t for the charge and J for the spin respectively.

Park, Youngho; Liang, Shoudan

1999-01-01

186

Role of orbital dynamics in spin relaxation and weak antilocalization in quantum dots.

We develop a semiclassical theory for spin-dependent quantum transport to describe weak (anti)localization in quantum dots with spin-orbit coupling. This allows us to distinguish different types of spin relaxation in systems with chaotic, regular, and diffusive orbital classical dynamics. We find, in particular, that for typical Rashba spin-orbit coupling strengths, integrable ballistic systems can exhibit weak localization, while corresponding chaotic systems show weak antilocalization. We further calculate the magnetoconductance and analyze how the weak antilocalization is suppressed with decreasing quantum dot size and increasing additional in-plane magnetic field. PMID:15698215

Zaitsev, Oleg; Frustaglia, Diego; Richter, Klaus

2005-01-21

187

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

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

Häussler, Wolfgang [Heinz Maier-Leibnitz Zentrum, Technische Universität München, D-85748 Garching, Germany and Physik-Department E21, Technische Universität München, D-85748 Garching (Germany); Kredler, Lukas [Physik-Department E21, Technische Universität München, D-85748 Garching (Germany)

2014-05-15

188

1H-NMR study of the spin dynamics of fine superparamagnetic nanoparticles

We report a broadband 1H-NMR study of the temperature spin dynamics of nearly monodisperse dextran-coated ?-Fe2O3 magnetic nanoparticles. We observed a maximum in T1?1(T) that decreases in amplitude and shifts toward higher temperatures with increasing field. We suggest that this is related to the progressive superparamagnetic spin blocking of the ferrite core. The data can be explained by assuming a single electronic spin-spin correlation time and introducing a field-dependent distribution of anisotropy energy barriers.

Bordonali, L.; Furukawa, Y.; Kraken, M.; Litterst, F.J.; Sangregorio, C.; Casula, M.F.; Lascialfari, A.

2012-05-25

189

Spin-exchange dynamical structure factor of the S=1/2 Heisenberg chain.

We determine the spin-exchange dynamical structure factor of the Heisenberg spin chain, as is measured by indirect resonant inelastic x-ray scattering (RIXS). We find that two-spin RIXS excitations nearly entirely fractionalize into two-spinon states. These share the same continuum lower bound as single-spin neutron scattering excitations, even if the relevant final states belong to orthogonal symmetry sectors. The RIXS spectral weight is mainly carried by higher-energy excitations, and is beyond the reach of the low-energy effective theories of Luttinger liquid type. PMID:21568610

Klauser, Antoine; Mossel, Jorn; Caux, Jean-Sébastien; van den Brink, Jeroen

2011-04-15

190

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

191

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 Pad\\'e-resummed coefficients) which depends on the choice of some basic ``effective spin vector'' $\\bf{S}_{\\rm eff}$, and which is deformed by comparable-mass effects, and (iv) an additional effective spin-orbit interaction term involving another spin vector $\\bsigma$. 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 $\\hat{a}_{\\rm LSO}\\equiv c J_{\\rm LSO}/\\boldsymbol(G(H_{\\rm LSO}/c^2)^2\\boldsymbol)$. 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.

Thibault Damour; Piotr Jaranowski; Gerhard Schäfer

2008-03-06

192

X-ray and Neutron Scattering Studies of Magnetic Domain Dynamics and Spin Structures

NASA Astrophysics Data System (ADS)

The study of magnetic spin structures at nanometer length scales and their dynamics is of both fundamental and technological importance. X-rays and neutrons are penetrating probes that are suitable for studying these in the bulk and the interfaces of the materials. In this thesis, the magnetic domain dynamics are studied by resonant soft x-ray scattering together with x-ray photon correlation spectroscopy. The domain fluctuations reveal when the temperature is close to the phase transition temperature. We find the domain wall dynamics in an antiferromagnet corresponds to a collective motion of spins and exhibit some universal features associated with the jamming behavior in many jammed soft condensed matter systems. We also discuss about the utilization of polarized neutron reflectometry to study the interfacial spin structure in an exchange biased bilayer. The magnetization profiles are obtained which show that some spins are not completely reversible when the magnetic field is reversed. These spins include pinned uncompensated spins in the antiferromagnet and the interfacial spins exchange coupled to those spins. A previously established model was found to reproduce the magnetization profile observed. Finally, we carried out a grazing incidence small angle neutron scattering experiment on an optical grating as a way to test the Distorted Wave Born Approximation (DWBA). DWBA is briefly reviewed and we used it to calculate the scattering intensity of the system.

Chen, San-Wen

193

NASA Astrophysics Data System (ADS)

We analytically derive deterministic equations of order parameters such as spontaneous magnetization in infinite-range quantum spin systems obeying quantum Monte Carlo dynamics. By means of the Trotter decomposition, we consider the transition probability of Glauber-type dynamics of microscopic states for the corresponding classical system. Under the static approximation, differential equations with respect to macroscopic order parameters are explicitly obtained from the master equation that describes the microscopic-law. We discuss several possible applications of our approach to disordered spin systems for statistical-mechanical informatics. Especially, we argue the ground state searching for infinite-range random spin systems via quantum adiabatic evolution.

Inoue, Jun-Ichi

2011-03-01

194

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

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

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

2011-12-15

195

Dynamical spin response in cuprate superconductors from low-energy to high-energy

NASA Astrophysics Data System (ADS)

Within the framework of the kinetic energy driven superconducting mechanism, the dynamical spin response of cuprate superconductors is studied from low-energy to high-energy. The spin self-energy is evaluated explicitly in terms of the collective charge carrier modes in the particle-hole and particle-particle channels, and employed to calculate the dynamical spin structure factor. Our results show the existence of damped but well-defined dispersive spin excitations in the whole doping phase diagram. In particular, the low-energy spin excitations in the superconducting-state have an hour-glass-shaped dispersion, with commensurate resonance that appears in the superconducting-state only, while the low-energy incommensurate spin fluctuations can persist into the normal-state. The high-energy spin excitations in the superconducting-state on the other hand retain roughly constant energy as a function of doping, with spectral weights and dispersion relations comparable to those in the corresponding normal-state. The theory also shows that the unusual magnetic correlations in cuprate superconductors can be ascribed purely to the spin self-energy effects which arise directly from the charge carrier-spin interaction in the kinetic energy of the system.

Kuang, Lülin; Lan, Yu; Feng, Shiping

2015-01-01

196

Unified dynamics of electrons and photons via Zitterbewegung and spin-orbit interaction

NASA Astrophysics Data System (ADS)

We show that when an electron or photon propagates in a cylindrically symmetric waveguide, it experiences both a Zitterbewegung effect and a spin-orbit interaction leading to identical propagation dynamics for both particles. Applying a unified perturbative approach to both particles simultaneously, we find that to first order in perturbation theory, their Hamiltonians each contain identical Darwin (Zitterbewegung) and spin-orbit terms, resulting in the unification of their dynamics. The presence of the Zitterbewegung effect may be interpreted physically as the delocalization of the electron on the scale of its Compton wavelength, or the delocalization of the photon on the scale of its wavelength in the waveguide. The presence of the spin-orbit interaction leads to the prediction of several rotational effects: the spatial or time evolution of either particle's spin or polarization vector is controlled by the sign of its orbital angular momentum quantum number or, conversely, its spatial wave function is controlled by its spin angular momentum.

Leary, C. C.; Smith, Karl H.

2014-02-01

197

Relaxation Dynamics of an Isolated Large-Spin Fermi Gas Far from Equilibrium

NASA Astrophysics Data System (ADS)

A fundamental question in many-body physics is how closed quantum systems reach equilibrium. We address this question experimentally and theoretically in an ultracold large-spin Fermi gas where we find a complex interplay between internal and motional degrees of freedom. The fermions are initially prepared far from equilibrium with only a few spin states occupied. The subsequent dynamics leading to redistribution among all spin states is observed experimentally and simulated theoretically using a kinetic Boltzmann equation with full spin coherence. The latter is derived microscopically and provides good agreement with experimental data without any free parameters. We identify several collisional processes that occur on different time scales. By varying density and magnetic field, we control the relaxation dynamics and are able to continuously tune the character of a subset of spin states from an open to a closed system.

Ebling, Ulrich; Krauser, Jasper Simon; Fläschner, Nick; Sengstock, Klaus; Becker, Christoph; Lewenstein, Maciej; Eckardt, André

2014-04-01

198

Spin dynamics of low-dimensional excitons due to acoustic phonons

NASA Astrophysics Data System (ADS)

We investigate the spin dynamics of excitons interacting with acoustic phonons in quantum wells, quantum wires and quantum discs by employing a multiband model based on the 4 × 4 Luttinger Hamiltonian. We also use the Bir-Pikus Hamiltonian to model the coupling of excitons to both longitudinal acoustic phonons and transverse acoustic phonons, thereby providing us with a realistic framework in which to determine details of the spin dynamics of excitons. We use a fractional dimensional formulation to model the excitonic wavefunctions and we demonstrate explicitly the decrease of spin relaxation time with dimensionality. Our numerical results are consistent with experimental results of spin relaxation times for various configurations of the GaAs/Al0.3Ga0.7As material system. We find that longitudinal and transverse acoustic phonons are equally significant in processes of exciton spin relaxations involving acoustic phonons.

Thilagam, A.; Lohe, M. A.

2006-03-01

199

Within the framework of a general three-level problem, the dynamics of the nitrogen-vacancy (NV) spin is studied for the case of a special type of external driving consisting of a set of continuous fields with decreasing intensities. Such a set has been proposed for minimizing coherence losses. Each new driving field with smaller intensity is designed to protect against the fluctuations induced by the driving field at the preceding step with larger intensity. We show that indeed this particular type of external driving minimizes the loss of coherence, using purity and entropy as quantifiers for this purpose. As an illustration, we study the coherence loss of an NV spin due to a surrounding spin bath of $^{13}$C nuclei.

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

2014-09-06

200

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

201

Quantum and classical correlations in high temperature dynamics of two coupled large spins

NASA Astrophysics Data System (ADS)

We study dynamical correlations of two coupled large spins depending on the time and on the spin quantum numbers. In the high-temperature approximation, we obtain analytical expressions for the mutual informations, quantum and classical parts of correlations. The latter was obtained performing the non-orthogonal projective (POVM) measurements onto the spin coherent states of two spins or one spin, as well as by means of the orthogonal projective measurement of von Neumann. Contribution from quantum correlations is much less than that from classical ones and decreasing with the increase in spin quantum numbers at short times. However, it is not so in a time equal to half of the quantum period.

Zobov, V. E.

2013-01-01

202

Long timescale dynamics of spin textures in a degenerate F=1 $^{87}$ Rb spinor Bose gas

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

Guzman, J; Wenz, A N; Murch, K W; Thomas, C K; Stamper-Kurn, D M

2011-01-01

203

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

204

NASA Astrophysics Data System (ADS)

We study in-plane magnetic tunnel junctions with additional perpendicular polarizer for subnanosecond-current-induced switching memories. The spin-transfer-torque switching dynamics was studied as a function of the cell aspect ratio both experimentally and by numerical simulations using the macrospin model. We show that the anisotropy field plays a significant role in the dynamics, along with the relative amplitude of the two spin-torque contributions. This was confirmed by micromagnetic simulations. Real-time measurements of the reversal were performed with samples of low and high aspect ratio. For low aspect ratios, a precessional motion of the magnetization was observed and the effect of temperature on the precession coherence was studied. For high aspect ratios, we observed magnetization reversals in less than 1 ns for high enough current densities, the final state being controlled by the current direction in the magnetic tunnel junction cell.

Lacoste, B.; de Castro, M. Marins; Devolder, T.; Sousa, R. C.; Buda-Prejbeanu, L. D.; Auffret, S.; Ebels, U.; Ducruet, C.; Prejbeanu, I. L.; Vila, L.; Rodmacq, B.; Dieny, B.

2014-12-01

205

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 inter-spin 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.

David Petrosyan; Georgios M. Nikolopoulos; P. Lambropoulos

2010-01-14

206

According to quantum mechanics, spin—the intrinsic angular momentum of an electron, nucleus, or elementary particle at rest—is\\u000a a decidedly nonclassical concept. The ? spin statistics theorem of ? quantum statistics distinguishes bosons and fermions\\u000a obeying ? Bose-Einstein statistics or ? Fermi-Dirac statistics, respectively, depending on whether the particle's spin is\\u000a an even or odd multiple of h\\/2, with h =

Klaus Hentschel

207

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

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 analyze the jurisprudence of academic freedom, evaluate

James D. Jorgensen; Lelia B. Helms

2008-01-01

208

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

209

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

210

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

211

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

NASA Astrophysics Data System (ADS)

Secular Kozai oscillation, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planet’s orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as 10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincare surfaces of section to demonstrate the chaotic behavior. As the system parameters (such as planet mass) vary, “periodic islands” can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.

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

2014-05-01

212

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

NASA Astrophysics Data System (ADS)

Secular Kozai oscillations, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planet's orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as $10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincar\\'{e} surfaces of section to demonstrate thechaotic behavior. As the system parameters (such as planet mass) vary, ``periodic islands'' can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.

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

2014-05-01

213

Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics

NASA Astrophysics Data System (ADS)

An introduction giving elementary properties of cavity exciton-polariton will be given. The condition of occurrence of the polariton lasing effect and of the polariton Bose Eintein condensation will be discussed. The impact of the structural disorder on the superfluid behavior of polariton condensates will be analysed. The spin properties of polariton condensates will be discussed. I will show how the anisotropy of the polariton-polariton interaction leads to the suppression of zeeman splitting for polariton condensates (spin Meissner effects). I will show how the combined impact of disorder and spin Meissner effect can lead to the formation of a new condense phase. I will show how these phenomena can allow for the realization of a polaritonic Datta Das spin transistor.

Malpuech, Guillaume; Solnyshkov, Dmitry; Shelykh, Ivan

2009-10-01

214

Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics

An introduction giving elementary properties of cavity exciton-polariton will be given. The condition of occurrence of the polariton lasing effect and of the polariton Bose Eintein condensation will be discussed. The impact of the structural disorder on the superfluid behavior of polariton condensates will be analysed. The spin properties of polariton condensates will be discussed. I will show how the anisotropy of the polariton-polariton interaction leads to the suppression of zeeman splitting for polariton condensates (spin Meissner effects). I will show how the combined impact of disorder and spin Meissner effect can lead to the formation of a new condense phase. I will show how these phenomena can allow for the realization of a polaritonic Datta Das spin transistor.

Malpuech, Guillaume; Solnyshkov, Dmitry [LASMEA, CNRS and University Blaise Pascal Clermont Ferrand (France); Shelykh, Ivan [Science Institute University of Reykjavik, Reykjavik (Iceland); St. Petersburg State Polytechnical University, St. Petersburg (Russian Federation)

2009-10-07

215

Molecular dynamics simulations and 31P-NMR spin-lattice (R1) relaxation rates from 0.022 to 21.1 T of fluid phase dipalmitoylphosphatidylcholine bilayers are compared. Agreement between experiment and direct prediction from simulation indicates that the dominant slow relaxation (correlation) times of the dipolar and chemical shift anisotropy spin-lattice relaxation are ?10ns and 3ns, respectively. Overall reorientation of the lipid body, consisting of the

Jeffery B. Klauda; Mary F. Roberts; Alfred G. Redfield; Bernard R. Brooks; Richard W. Pastor

2008-01-01

216

Nuclear magnetometry studies of spin dynamics in quantum Hall systems

NASA Astrophysics Data System (ADS)

We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of ?tot=2 . We found not only a rapid nuclear relaxation but also a sudden change in the nuclear-spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear-spin ensemble triggered by hyperfine interaction in quantum Hall system.

Fauzi, M. H.; Watanabe, S.; Hirayama, Y.

2014-12-01

217

Analysis of thermally induced magnetization dynamics in spin-transfer nano-oscillators

NASA Astrophysics Data System (ADS)

The thermally induced magnetization dynamics in the presence of spin-polarized currents injected into a spin-valve-like structure used as microwave spin-transfer nano-oscillator (STNO) is considered. Magnetization dynamics is described by the stochastic Landau-Lifshitz-Slonczewski (LLS) equation. First, it is shown that, in the presence of thermal fluctuations, the spectrum of the output signal of the STNO exhibits multiple peaks at low and high frequencies. This circumstance is associated with the occurrence of thermally induced transitions between stationary states and magnetization self-oscillations. Then, a theoretical approach based on the separation of time-scales is developed to obtain a stochastic dynamics only in the slow state variable, namely the energy. The stationary distribution of the energy and the aforementioned transition rates are analytically computed and compared with the results of direct integration of the LLS dynamics, showing very good agreement.

d'Aquino, M.; Serpico, C.; Bertotti, G.; Bonin, R.; Mayergoyz, I. D.

2012-05-01

218

Effect of surfactant and solvent on spin-lattice relaxation dynamics of magnetic nanocrystals.

The effect of varying the surfactant and solvent medium on the dynamics of spin-lattice relaxation in photoexcited Fe3O4 nanocrystals has been investigated by measuring the time-dependent magnetization employing pump-probe transient Faraday rotation technique. The variation of the surfactants having surface-binding functional groups modified not only the static magnetization but also the dynamics of the recovery of the magnetization occurring via spin-lattice relaxation in the photoexcited Fe3O4 nanocrystals. The variation of the polarity and size of the solvent molecules can also influence the spin-lattice relaxation dynamics. However, the effect is limited to the nanocrystals having sufficiently permeable surfactant layer, where the small solvent molecules (e.g., water) can access the surface and dynamically modify the ligand field on the surface. PMID:23003213

Maiti, Sourav; Chen, Hsiang-Yun; Chen, Tai-Yen; Hsia, Chih-Hao; Son, Dong Hee

2013-04-25

219

Spin-sensitive intersubband dynamics of optically generated carriers in semiconductor quantum wells

NASA Astrophysics Data System (ADS)

A theoretical analysis of the intersubband dynamics in undoped quantum wells is presented where spin-oriented carriers are initially generated by circularly polarized interband excitations. Subsequent resonant intersubband excitations induce Rabi rotations between the subbands resulting in a fast periodic modulation of the spin orientation in each subband. It is investigated whether pure spin modulations can be performed where the charge density of the subbands is kept constant when initially equal occupations of the two lowest conduction subbands with opposite spin orientations have been prepared. While this is the expected behavior for a three-band model of noninteracting particles it turns out that when the Coulomb interaction is taken into account the spin modulations are typically accompanied by corresponding modulations of the subband occupations. It is demonstrated that under realistic conditions it should nevertheless be feasible to realize a pure spin rotation in a given subband provided the intersubband excitations are sufficiently short or the carrier density is sufficiently low. Successive spin rotations are shown to decrease the degree of spin polarization even when spin-relaxation processes are neglected.

Vogel, M.; Vagov, A.; Axt, V. M.; Seilmeier, A.; Kuhn, T.

2009-10-01

220

Spin correlations and reentrant spin-glass behavior in amorphous Fe-Mn alloys. II. Dynamics

Inelastic-neutron-scattering measurements have been performed on amorphous (Fe/sub 1-x/Mn/sub x/)/sub 75/P/sub 16/B/sub 6/Al/sub 3/ alloys for several concentrations x bracketing the spin-glass--ferromagnetic multicritical point found from magnetization measurements. For x = 0.35, the alloy is nonferromagnetic, and the inelastic spectra are dominated at all temperatures by a resolution-limited quasielastic peak. We find no evidence for propagating modes of any kind. In a 10-kG applied field, the central peak is substantially reduced, and dispersionless sidebands, centered at the Larmor precession frequency, appear. Three samples (x = 0.30, 0.25, and 0.20) on the ferromagnetic side of the phase diagram have also been studied. Spectra were collected for one of these (x = 0.25) above its Curie point. These data are consistent with ordinary spin diffusion. For all three samples, resolvable spin-wave peaks exist at temperatures below the Curie points but above the spin-glass transitions established in bulk measurements. As the temperature is reduced, the spin-wave stiffness first increases, as in normal ferromagnets, and then decreases. At the lowest temperatures, resolvable spin-wave peaks are absent, and the spectra are dominated by a resolution-limited (<30 ..mu..eV full width at half maximum) quasielastic peak. For the most iron-rich material (x = 0.20), true inelastic scattering coexists with the central peak, even at 5 K. This inelastic scattering broadens and decreases in intensity with increasing momentum transfer Q, in a manner consistent with simple spin-wave theory. The central-peak intensity decays according to a power law Q/sup -alpha/, with ..cap alpha..> or approx. =2.

Aeppli, G.; Shapiro, S.M.; Birgeneau, R.J.; Chen, H.S.

1984-03-01

221

Direct Dynamical Evidence for the Spin Glass Lower Critical Dimension 2

NASA Astrophysics Data System (ADS)

A dynamical method is introduced to study the effect of dimensionality on phase transitions. Direct experimental measurements for the lower critical dimension for spin glasses is provided as an example. The method makes use of the spin glass correlation length ?(t,T). Once nucleated, it can become comparable to sample dimensions in convenient time and temperature ranges. Thin films of amorphous Ge:Mn alloys were prepared with thickness L ?15.5 nm. Conventional behavior is observed as long as ?(t,T)

Guchhait, Samaresh; Orbach, Raymond

2014-03-01

222

We show that intramolecular exchange disorder recently found in the geometrically frustrated magnetic molecules {Mo(72)Fe(30)} and {Mo(72)Cr(30)} leads, in a classical Heisenberg model description, to spin freezing and slow magnetization dynamics reminiscent of spin glass behaviour. Also we suggest that our low temperature and low magnetic field nuclear magnetic resonance (NMR) measurements on {Mo(72)Fe(30)}, showing rapid and strong broadening of the proton line width on cooling below 600 mK, are evidence for a crossover from paramagnetic behaviour to a frozen spin configuration. Similar broadening is observed in {Mo(72)Cr(30)}. This observed effect is consistent with our theory of spin freezing and slow magnetization dynamics in these systems due to exchange disorder. PMID:21393733

Schröder, C; Fang, X; Furukawa, Y; Luban, M; Prozorov, R; Borsa, F; Kumagai, K

2010-06-01

223

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

224

NASA Astrophysics Data System (ADS)

Polarized Raman-scattering spectra of superconducting, single-crystalline FeSe evidence pronounced phonon anomalies with temperature reduction. A large (˜6.5%) hardening of the B1g(Fe) phonon mode is attributed to the suppression of local fluctuations of the iron spin state with a gradual decrease of the iron paramagnetic moment. Ab initio lattice dynamic calculations support this conclusion. The enhancement of the low-frequency spectral weight above the structural phase transition temperature Ts and its change below Ts is discussed in relation with the opening of an energy gap between low (S=0) and higher spin states which prevents magnetic order in FeSe. The very narrow phonon linewidths compared to observations in FeTe suggest the absence of intermediate spin states in the fluctuating spin state manifold in FeSe. In the tetragonal phase under approaching Ts we observe the development of a quasielastic Raman response that is typical for the presence of nematic fluctuations.

Gnezdilov, Vladimir; Pashkevich, Yurii G.; Lemmens, Peter; Wulferding, Dirk; Shevtsova, Tatiana; Gusev, Alexander; Chareev, Dmitry; Vasiliev, Alexander

2013-04-01

225

Dynamics of Polymer Blend Film Formation During Spin Coating

NASA Astrophysics Data System (ADS)

Spin casting is a process broadly used to obtain a uniform film on a flat substrate. A homogeneous film results from the balance between centrifugal and viscous forces. Here we revisit the Meyerhofer model of the spin casting process by taking in account the centrifugal forces, a uniform time dependent evaporation rate, and account for the changes in viscosity using the Huggins intrinsic viscosity. Time resolved light reflectometry is used to monitor the thickness changes of a polystyrene-poly(methyl methacrylate)(which we denote as PS and PMMA) film initially dissolved in toluene and spin cast for ten seconds at 1000 rpm. The experimental data are in good agreement with the model. We also investigate how the volume fraction of PS and PMMA influences the thinning of the film during spin casting. A distinct change in the temporal evolution of thickness as a function of time delimits the first phase of the spin casting process where centrifugal forces are dominant from a second phase dominated by the solvent evaporation. This hypothesis is supported by in-situ off specular scattering data. The time at which this change from centrifugal to evaporation-dominated behaviour is delayed as the volume fraction of PMMA increases.

Mouhamad, Youmna; Clarke, Nigel; Jones, Richard A. L.; Geoghegan, Mark

2012-02-01

226

Hyperfine interaction and its effects on spin dynamics in organic solids

NASA Astrophysics Data System (ADS)

Hyperfine interaction (HFI) and spin-orbit coupling are two major sources that affect electron spin dynamics. Here we present a systematic study of the HFI and its role in organic spintronic applications. For electron spin dynamics in disordered ?-conjugated organics, the HFI can be characterized by an effective magnetic field whose modular square is a weighted sum of contact and dipolar contributions. We determine the effective HFI fields of some common ?-conjugated organics studied in the literature via first-principles calculations. Most of them are found to be less than 2 mT. While the H atoms are the major source of the HFI in organics containing only the C and H atoms, many organics contain other nuclear spins, such as Al and N in tris-(8-hydroxyquinoline) aluminum, that contribute to the total HFI. Consequently, the deuteration effect on the HFI in the latter may be much weaker than in the former. The HFI gives rise to multiple resonance peaks in electron spin resonance. In disordered organic solids, these individual resonances are unresolved, leading to a broad peak whose width is proportional to the effective HFI field. As electrons hop among adjacent organic molecules, they experience a randomly varying local HFI field, inducing electron spin relaxation and diffusion. This is analyzed rigorously based on master equations. Electron spin relaxation undergoes a crossover along the ratio between the electron hopping rate ?¯ and the Larmor frequency ? of the HFI field. The spin relaxation rate increases (decreases) with ?¯ when ?¯?? (?¯??). A coherent beating of electron spin at ? is possible when the external field is small compared to the HFI. In this regime, the magnetic field is found to enhance the spin relaxation.

Yu, Z. G.; Ding, Feizhi; Wang, Haobin

2013-05-01

227

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

(DMe-DCNQI)2M (M=Li, Ag) is a 14-filled spin-Peierls system. We study the spin\\/charge dynamics in the insulating state by EPR. The linewidth shows exponential dependence at T?Tsp. Further, pressure enhances mainly prefactor of the exponential dependences. These results are successfully understood in terms of the relaxation accompanied with the intercolumn hopping caused by the spin–orbit interaction both for the Li and

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

2004-01-01

228

Quantum dynamics and entanglement of spins on a square lattice

Bulk magnetism in solids is fundamentally quantum mechanical in nature. Yet in many situations, including our everyday encounters with magnetic materials, quantum effects are masked, and it often suffices to think of magnetism in terms of the interaction between classical dipole moments. Whereas this intuition generally holds for ferromagnets, even as the size of the magnetic moment is reduced to that of a single electron spin (the quantum limit), it breaks down spectacularly for antiferromagnets, particularly in low dimensions. Considerable theoretical and experimental progress has been made in understanding quantum effects in one-dimensional quantum antiferromagnets, but a complete experimental description of even simple two-dimensional antiferromagnets is lacking. Here we describe a comprehensive set of neutron scattering measurements that reveal a non-spin-wave continuum and strong quantum effects, suggesting entanglement of spins at short distances in the simplest of all two-dimensional quantum antiferromagnets, the square lattice Heisenberg system. PMID:17884986

Christensen, N. B.; Rønnow, H. M.; McMorrow, D. F.; Harrison, A.; Perring, T. G.; Enderle, M.; Coldea, R.; Regnault, L. P.; Aeppli, G.

2007-01-01

229

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

We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed. PMID:25147490

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

2014-01-01

230

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

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

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

2014-03-21

231

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

Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50?mK) to determine the effect of coupling two Cr7 Ni molecular rings via a Cu 2+ ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5?K. At lower temperature, the 1H-NMR line broadens dramatically indicating spin freezing. From the plot of the line width vs. magnetization, it is found that the freezing temperature is higher (260?mK) in the coupled ring with respect to the single Cr7 Ni ring (140?mK).

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

2014-05-07

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

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

We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed. PMID:25147490

2014-01-01

234

Spin and charge dynamics of a quasi-one-dimensional antiferromagnetic metal

NASA Astrophysics Data System (ADS)

We use quantum Monte Carlo simulations to study a finite-temperature dimensional-crossover-driven evolution of spin and charge dynamics in an anisotropic two-dimensional system of weakly coupled Hubbard chains with a half-filled band. The low-temperature behavior of the charge gap indicates a crossover between two distinct energy scales: a high-energy one-dimensional (1D) Mott gap due to the umklapp process and a low-energy gap which stems from long-range antiferromagnetic (AF) spin fluctuations. Away from the 1D regime and at temperature scales above the charge gap, the emergence of a zero-frequency Drude-like feature in the interchain optical conductivity ??(? ) implies the onset of a higher-dimensional metal. In this metallic phase, enhanced quasiparticle scattering off finite-range AF spin fluctuations results in incoherent single-particle dynamics. The coupling between spin and charge fluctuations is also seen in the spin dynamical structure factor S (q ,? ) displaying damped spin excitations (paramagnons) close to the AF wave vector q =(? ,? ) and particle-hole continua near 1D momentum transfers spanning quasiparticles at the Fermi surface. We relate our results to the charge deconfinement in quasi-1D organic Bechgaard-Fabre salts.

Raczkowski, Marcin; Assaad, Fakher F.; Pollet, Lode

2015-01-01

235

Spin Crossover in Ferropericlase from First-Principles Molecular Dynamics

NASA Astrophysics Data System (ADS)

Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of Earth's lower mantle. With increasing pressure, the Fe ions in the material begin to collapse from a magnetic to nonmagnetic spin state. We present a finite-temperature first-principles phase diagram of this spin crossover, finding a broad pressure range with coexisting magnetic and nonmagnetic ions due to favorable enthalpy of mixing of the two. Furthermore, we find the electrical conductivity of the mineral to reach semimetallic values inside Earth.

Holmström, E.; Stixrude, L.

2015-03-01

236

Electrical control of spin dynamics in spin-orbit coupled ferromagnets

in the lattice could be used, 22 Chapter 2: Theoretical background introducing larger lattice electric potentials. (Ga,Mn)Sb substitutes the Arsenide ions for Antimony, increasing the spin-orbit energy splitting by ?2.5 times.121 (Ga,Mn)Sb has been grown by MBE...

Skinner, Timothy

2015-01-06

237

Quantum dynamics of double-qubits in a spin star lattice with an XY interaction

The dynamics of two coupled spins-1/2 interacting with a spin-bath via the quantum Heisenberg XY coupling is studied. The pair of central spins served as a quantum open subsystem are initially prepared in two types of states: the product states and the Bell states. The bath, which consists of $N$ (in the thermodynamic limit $N\\to\\infty$) mutually coupled spins-1/2, is in a thermal state at the beginning. By the Holstein-Primakoff transformation, the model can be treated effectively as two spin qubits embedded in a single mode cavity. The time-evolution of the purity, z-component summation and the concurrence of the central spins can be determined by a Laguerre polynomial scheme. It is found that (i) at a low temperature, the uncoupled subsystem in a product state can be entangled due to the interaction with bath, which is tested by the Peres-Horodecki separability; however, at a high temperature, the bath produces a stronger destroy effect on the purity and entanglement of the subsystem; (ii) when the coupling strength between the two central spins is large, they are protected strongly against the bath; (iii) when the interaction between the subsystem and the bath is strong, the collapse of the two spin qubits from their initial entangled state is fast.

Jun Jing; Zhi-Guo Lü

2007-10-09

238

Two-level system in spin baths: Non-adiabatic dynamics and heat transport

We study the non-adiabatic dynamics of a two-state subsystem in a bath of independent spins using the non-interacting blip approximation, and derive an exact analytic expression for the relevant memory kernel. We show that in the thermodynamic limit, when the subsystem-bath coupling is diluted (uniformly) over many (infinite) degrees of freedom, our expression reduces to known results, corresponding to the harmonic bath with an effective, temperature-dependent, spectral density function. We then proceed and study the heat current characteristics in the out-of-equilibrium spin-spin-bath model, with a two-state subsystem bridging two thermal spin-baths of different temperatures. We compare the behavior of this model to the case of a spin connecting boson baths, and demonstrate pronounced qualitative differences between the two models. Specifically, we focus on the development of the thermal diode effect, and show that the spin-spin-bath model cannot support it at weak (subsystem-bath) coupling, while in the intermediate-strong coupling regime its rectifying performance outplays the spin-boson model.

Segal, Dvira [Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S 3H6 (Canada)] [Chemical Physics Theory Group, Department of Chemistry, University of Toronto, 80 Saint George St., Toronto, Ontario M5S 3H6 (Canada)

2014-04-28

239

Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator

The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen-vacancy center spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen-vacancy spin-strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen-vacancy center. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen-vacancy ground state spin. The nitrogen-vacancy center is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 10^(-6) strain Hz^(-1/2). Finally, we show how this spin-resonator system could enable coherent spin-phonon interactions in the quantum regime.

Preeti Ovartchaiyapong; Kenneth W. Lee; Bryan A. Myers; Ania C. Bleszynski Jayich

2014-06-10

240

Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator

The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high-quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen–vacancy centre spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen–vacancy spin–strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen–vacancy centre. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen–vacancy ground-state spin. The nitrogen–vacancy centre is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 × 10?6 strain Hz?1/2. Finally, we show how this spin-resonator system could enable coherent spin–phonon interactions in the quantum regime. PMID:25034828

Ovartchaiyapong, Preeti; Lee, Kenneth W.; Myers, Bryan A.; Jayich, Ania C. Bleszynski

2014-01-01

241

Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator.

The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high-quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen-vacancy centre spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen-vacancy spin-strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen-vacancy centre. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen-vacancy ground-state spin. The nitrogen-vacancy centre is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 × 10(-6) strain Hz(-1/2). Finally, we show how this spin-resonator system could enable coherent spin-phonon interactions in the quantum regime. PMID:25034828

Ovartchaiyapong, Preeti; Lee, Kenneth W; Myers, Bryan A; Jayich, Ania C Bleszynski

2014-01-01

242

Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator

NASA Astrophysics Data System (ADS)

The development of hybrid quantum systems is central to the advancement of emerging quantum technologies, including quantum information science and quantum-assisted sensing. The recent demonstration of high-quality single-crystal diamond resonators has led to significant interest in a hybrid system consisting of nitrogen-vacancy centre spins that interact with the resonant phonon modes of a macroscopic mechanical resonator through crystal strain. However, the nitrogen-vacancy spin-strain interaction has not been well characterized. Here, we demonstrate dynamic, strain-mediated coupling of the mechanical motion of a diamond cantilever to the spin of an embedded nitrogen-vacancy centre. Via quantum control of the spin, we quantitatively characterize the axial and transverse strain sensitivities of the nitrogen-vacancy ground-state spin. The nitrogen-vacancy centre is an atomic scale sensor and we demonstrate spin-based strain imaging with a strain sensitivity of 3 × 10-6 strain Hz-1/2. Finally, we show how this spin-resonator system could enable coherent spin-phonon interactions in the quantum regime.

Ovartchaiyapong, Preeti; Lee, Kenneth W.; Myers, Bryan A.; Jayich, Ania C. Bleszynski

2014-07-01

243

The dynamics of a doped hole in a cuprate is not controlled by spin fluctuations

NASA Astrophysics Data System (ADS)

Understanding what controls the dynamics of the quasiparticle that results when a hole is doped into an antiferromagnetically ordered CuO2 layer is the first necessary step in the quest for a theory of the high-temperature superconductivity in cuprates. Here we show that the long-held belief that the quantum spin fluctuations of the antiferromagnetic background play a key role in determining this dynamics is wrong. Indeed, we demonstrate that the correct, experimentally observed quasiparticle dispersion is generically obtained for a three-band model describing the hole moving on the oxygen sublattice and coupled to a Néel lattice of spins without spin fluctuations. We argue that results from one-band model studies actually support this conclusion, and that this significant conceptual change in our understanding of this phenomenology opens the way to studying few-hole dynamics, to accurately gauge the strength of the `magnetic glue’ and its contribution to superconductivity.

Ebrahimnejad, Hadi; Sawatzky, George A.; Berciu, Mona

2014-12-01

244

Spin dynamics with non-abelian Berry gauge fields as a semiclassical constrained hamiltonian system

The dynamics of observables which are matrices depending on \\hbar and taking values in classical phase space is defined retaining the terms up to the first order in \\hbar of the Moyal bracket. Within this semiclassical approach a first order lagrangian involving gauge fields is studied as a constrained hamiltonian system. This provides a systematic study of spin dynamics in the presence of non-abelian Berry gauge fields. We applied the method to various types of dynamical spin systems and clarified some persisting discussions. In particular employing the Berry gauge field which generates the Thomas precession, we calculated the force exerted on an electron in the external electric and magnetic fields. Moreover, a simple semiclassical formulation of the spin Hall effect is accomplished.

Omer F. Dayi

2008-07-08

245

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

246

Effect of modularity on the Glauber dynamics of the dilute spin glass model

NASA Astrophysics Data System (ADS)

We study the Glauber dynamics of the dilute, infinite-ranged spin glass model, the so-called dilute Sherrington-Kirkpatrick (dSK) model. The dSK model has sparse couplings and can be classified by the modularity ( M) of the coupling matrix. We investigate the effect of the modularity on the relaxation dynamics starting from a random initial state. By using the Glauber dynamics and the replica method, we derive the relaxation dynamics equations for the magnetization ( m) and the energy per spin ( r), in addition to the equation for the spin glass order parameter ( q ?? ). In the replica symmetric (RS) analysis, we find that there are two solutions for the RS spin glass order parameter ( q): q = 0which is stable for r < 1/2 and q = (-1+4 r 2)/(32 r 4) which is stable for r > 1/2 in the non-modular system and q = 0 which is stable for r < 1/ and q = (-1+8 r 2)/(128 r 4) which is stable for r > 1/ in the completely modular system. By substituting the proper q values into the equations for r, we find that the relaxation dynamics of r depends on the modularity, M. These results suggest that, in the context of evolutionary theory, the modularity may emerge spontaneously in the point-mutation-only framework (Glauber dynamics) under a changing environment.

Park, Jeong-Man

2014-11-01

247

DYNAMICS OF THE LUNAR SPIN AXIS Jack Wisdom

with low obliquity, with prograde synchronous spin. The Moon evolved outward due to tidal friction the rate of tidal heating that results from the forced Cassini obliquity. At each epoch, the lunar orbit taken from the lunar tidal evolution model of Goldreich (1966). The picture that was developed

Wisdom, Jack

248

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

2012-11-26

249

NASA Astrophysics Data System (ADS)

Using an effective Hamiltonian including the Zeeman and internal interactions, we describe the quantum theory of magnetization dynamics when the spin system evolves nonadiabatically and out of equilibrium. The Lewis-Riesenfeld dynamical invariant method is employed along with the Liouville-von Neumann equation for the density matrix. We derive a dynamical equation for magnetization defined with respect to the density operator with a general form of damping that involves the nonequilibrium contribution in addition to the Landau-Lifshitz-Gilbert equation. Two special cases of the radiation-spin interaction and the spin-spin exchange interaction are considered. For the radiation-spin interaction, the damping term is shown to be of the Gilbert type, while in the spin-spin exchange interaction case, the results depend on a coupled chain of correlation functions.

Saradzhev, F. M.; Khanna, F. C.; Kim, Sang Pyo; de Montigny, M.

2007-01-01

250

Geometric phases and quantum correlations dynamics in spin-boson model

We explore the dynamics of spin-boson model for the Ohmic bath by employing the master equation approach and obtain an explicit expression of reduced density matrix. We also calculate the geometric phases of the spin-boson model by making use of the analytical results and discuss how the dissipative bosonic environment affects geometric phases. Furthermore, we investigate the dynamics of quantum discord and entanglement of two qubits each locally interacting with its own independent bosonic environments. It is found that the decay properties of quantum discord and entanglement are sensitive to the choice of initial state's parameter and coupling strength between system and bath.

Wu, Wei; Xu, Jing-Bo, E-mail: xujb@zju.edu.cn [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)

2014-01-28

251

A spin-wave logic gate based on a width-modulated dynamic magnonic crystal

NASA Astrophysics Data System (ADS)

An electric current controlled spin-wave logic gate based on a width-modulated dynamic magnonic crystal is realized. The device utilizes a spin-wave waveguide fabricated from a single-crystal Yttrium Iron Garnet film and two conducting wires attached to the film surface. Application of electric currents to the wires provides a means for dynamic control of the effective geometry of waveguide and results in a suppression of the magnonic band gap. The performance of the magnonic crystal as an AND logic gate is demonstrated.

Nikitin, Andrey A.; Ustinov, Alexey B.; Semenov, Alexander A.; Chumak, Andrii V.; Serga, Alexander A.; Vasyuchka, Vitaliy I.; Lähderanta, Erkki; Kalinikos, Boris A.; Hillebrands, Burkard

2015-03-01

252

Dynamics and decoherence in the central spin model using exact methods

The dynamics and decoherence of an electronic spin-1/2 qubit coupled to a bath of nuclear spins via hyperfine interactions in a quantum dot is studied. We show how exact results from the integrable solution can be used to understand the dynamic behavior of the qubit. It is possible to predict the main frequency contributions and their broadening for relatively general initial states analytically, leading to an estimate of the corresponding decay times. Furthermore, for a small bath polarization, a new low-frequency time scale is observed.

Michael Bortz; Sebastian Eggert; Christian Schneider; Robert Stubner; Joachim Stolze

2010-10-21

253

Spin and lattice dynamics in thin films: From femtoseconds to nanoseconds

NASA Astrophysics Data System (ADS)

In this dissertation we set out to quantitatively investigate the dynamics of magnetic thin films. Specifically, we studied the spin dynamics in epitaxial metallic ferromagnets and the coupling to other degrees of freedom, such as electron and phonon excitations. Key aspects of the spin dynamics were found to occur across a wide range of temporal scales, from femtoseconds to nanoseconds. Accordingly, new instrumental and experimental tools were developed in order to address the complex behavior of the magnetization under strongly non-equilibrium conditions. A new pump-probe fiberlaser-based magnetometer was built and used to access the time-dependence of the magnetic behavior during spin wave excitation and relaxation. The performance of this instrument offers significant advantages over existing methods, including: an unusually large temporal dynamic range (150 fs-10 ns), high frequency bandwidth (~5 THz), high detection sensitivity that corresponds to a signal to noise ratio of better than 107, and fast data acquisition at kilohertz scanning rates. These instrumental capabilities allowed us to perform unprecedented studies of coherent spin waves propagating through epitaxial Fe films. The femtosecond laser pulse induces coherent magnetization dynamics indirectly via thermal excitation, resulting in magnon-electron and magneto-elastic coupling. The spin wave propagation speeds and attenuation lengths were determined during spin wave propagation and reflection at the film boundaries. Coherent spin waves with frequency less than 24 GHz, propagate at velocities < 1.3 km/s, consistent with their dispersion relation. A not well understood behavior occurs for spin waves with wavevector k~0, which are transmitted super-sonically through films of about one classical skin depth thick (1.5 mum). A major step in this work was to establish all-optical techniques for manipulation and coherent control of the magnetization vector. An optically-induced spin reorientation transition of first-order is observed for the first time, which provides a new route to ultrafast coherent magnetization switching. The switching is found to be a three-step temporal process: a coherent reorientation (~ 100 ps) is followed by a spin precession in a newly created metastable state (~ 300 ps), which evolves into a dual domain state that undergoes relaxation within ~ 2 - 4 ns.

Stoica, Vladimir Alexandru

254

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

2013-01-01

255

Dynamical instabilities in a fluid spin-up and in an open flow system

NASA Astrophysics Data System (ADS)

The dynamics of two different fluid flow systems are studied. First, an open system is modulated flow through a sudden symmetric expansion. Here, there are 3 control parameters: the mean flow rate, the amplitude, and frequency of modulation. A rich variety of finite dimensional behavior is observed as the amplitude of modulation, measured as a percentage of the mean flow rate, is increased from 0 to 10 percent. The behavior consists of frequency locking to 1/2 of the driving frequency, quasi-periodicity, hysteresis, homoclinicity with an associated irregular mode and period doubling. These dynamics exist in the flow modulation experiment whereas no indication of finite dimensional behavior is found in the steady flow case. The spin-up from rest of a fluid filled torus was studied both experimentally and numerically. The dynamics of the transient phenomenon in an unstable spin-up configuration are examined in this closed system. The spin-up process is found to progress through a sequence of states as the final rotational rate is increased. These states are viscous diffusion, establishment of a significant secondary flow, appearance of fronts, breaking of axisymmetry and nonuniqueness, and also an inner wall phenomenon. As the final rotational rate is changed, the fractional spin-up time behaves anomalously near transitions between these states but it does not give any other indication of the fluid's dynamical condition. A technique is described which allows the phase portraits of many equivalent experimental runs to be constructed together. The results produced are a useful device for comparing flow paths in the spin-up process. The time dependent Navier-Stokes equations are solved numerically for axisymmetric spin-up flows. The quantitative and qualitative agreement with experimental results is excellent for values of the dynamical control parameter less than 500.

Madden, Francis

1991-02-01

256

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

NASA Astrophysics Data System (ADS)

We apply the time-dependent analytical R-matrix theory to develop a movie of hole motion in a Kr atom upon ionization by strong circularly polarized field. We find rich hole dynamics, ranging from rotation to swinging motion. The motion of the hole depends on the final energy and the spin of the photoelectron and can be controlled by the laser frequency and intensity. Crucially, hole rotation is a purely non-adiabatic effect, completely missing in the framework of quasistatic (adiabatic) tunneling theories. We explore the possibility to use hole rotation as a clock for measuring ionization time. Analyzing the relationship between the relative phases in different ionization channels we show that in the case of short-range electron-core interaction the hole is always initially aligned along the instantaneous direction of the laser field, signifying zero delays in ionization. Finally, we show that strong-field ionization in circular fields creates spin currents (i.e. different flow of spin-up and spin-down density in space) in the ions. This phenomenon is intimately related to the production of spin-polarized electrons in strong laser fields Barth and Smirnova (2013 Phys. Rev. A 88 013401). We demonstrate that rich spin dynamics of electrons and holes produced during strong field ionization can occur in typical experimental conditions and does not require relativistic intensities or strong magnetic fields.

Barth, Ingo; Smirnova, Olga

2014-10-01

257

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

Spin-Lattice Dynamics Simulation of Magnon-Phonon-Electron Heat Transfer on the Million Atom Scale explicitly solves equations of motion for the atoms and spins, and includes interaction with electron between magnetic and atomic degrees of freedom is necessary for understanding the dynamics of energy

258

Attitude dynamic of spin-stabilized satellites with flexible appendages

NASA Technical Reports Server (NTRS)

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

Renard, M. L.

1973-01-01

259

Spin glasses and fragile glasses: Statics, dynamics, and complexity

In this paper I will briefly review some theoretical results that have been obtained in recent years for spin glasses and fragile glasses. I will concentrate my attention on the predictions coming from the so called broken replica symmetry approach and on their experimental verifications. I will also mention the relevance or these results for other fields, and in general for complex systems. PMID:16690744

Parisi, Giorgio

2006-01-01

260

Spin-labeled heparins as polarizing agents for dynamic nuclear polarization.

A potentially biocompatible class of spin-labeled macromolecules, spin-labeled (SL) heparins, and their use as nuclear magnetic resonance (NMR) signal enhancers are introduced. The signal enhancement is achieved through Overhauser-type dynamic nuclear polarization (DNP). All presented SL-heparins show high (1)H DNP enhancement factors up to E=-110, which validates that effectively more than one hyperfine line can be saturated even for spin-labeled polarizing agents. The parameters for the Overhauser-type DNP are determined and discussed. A striking result is that for spin-labeled heparins, the off-resonant electron paramagnetic resonance (EPR) hyperfine lines contribute a non-negligible part to the total saturation, even in the absence of Heisenberg spin exchange (HSE) and electron spin-nuclear spin relaxation (T(1ne)). As a result, we conclude that one can optimize the use of, for example, biomacromolecules for DNP, for which only small sample amounts are available, by using heterogeneously distributed radicals attached to the molecule. PMID:20960494

Dollmann, Björn C; Kleschyov, Andrei L; Sen, Vasily; Golubev, Valery; Schreiber, Laura M; Spiess, Hans W; Münnemann, Kerstin; Hinderberger, Dariush

2010-12-01

261

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

Many exoplanetary systems containing hot Jupiters are observed to have highly misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov oscillations of orbital eccentricity and inclination induced by a binary companion, in conjunction with tidal dissipation, constitute a major channel for the production of hot Jupiters. We demonstrate that gravitational interaction between the planet and its oblate host star can lead to chaotic evolution of the stellar spin axis during Kozai cycles. As parameters such as the planet mass and stellar rotation period are varied, periodic islands can appear in an ocean of chaos, in a manner reminiscent of other dynamical systems. In the presence of tidal dissipation, the complex spin evolution can leave an imprint on the final spin-orbit misalignment angles. PMID:25214623

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

2014-09-12

262

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

NASA Astrophysics Data System (ADS)

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

Pigeon, S.; Xuereb, A.; Lesanovsky, I.; Garrahan, J. P.; De Chiara, G.; Paternostro, M.

2015-01-01

263

Exact quantum dynamics of spin systems using the positive-P representation

NASA Astrophysics Data System (ADS)

We discuss a scheme for simulating the exact real time quantum dynamics of interacting quantum spin systems within the positive-P formalism. As model systems we study the transverse field Ising model as well as the Heisenberg model undergoing a quench away from the classical ferromagnetic ordered state. In using the positive-P representation (PPR), the dynamics of the interacting quantum spin system is mapped onto a set of stochastic differential equations (SDEs). The number of which scales linearly with the number of spins, N, compared to an exact solution through diagonalization that in the case of the Heisenberg model would require matrices exponentially large in N. This mapping is exact and can in principle be extended to higher dimensional interacting systems as well as to systems with an explicit coupling to the environment. We compare the results from using a PPR approach based on both the optical coherent states as well as SU(2) Radcliff coherent states.

Ng, Ray; Sorensen, Erik

2011-03-01

264

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

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

2014-10-02

265

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

266

Optimal dynamic dispatch owing to spinning-reserve and power-rate limits

This paper deals with the formulation and solution of the optimal dynamic dispatch problem owing to spinning-reserve and power-rate limits. The power production of a thermal unit is considered as a dynamic system, which limits the maximum increase and decrease of power. The solution is obtained with a special projection method having conjugate search directions that quickly and accurately solves the associated non-linear programming problem with up to 2400 variables and up to 9600 constraints.

Van den Bosh, P.P.J.

1985-12-01

267

Many organisms have a complex life-cycle in which dispersal occurs at the propagule stage. For marine environments, there is growing evidence that high levels of recruitment back to the natal population (self-recruitment) are common in many marine organisms. For fish, swimming behavior is frequently invoked as a key mechanism allowing high self-recruitment. For organisms with weak-swimming larvae, such as many marine invertebrates, the mechanisms behind self-recruitment are less clear. Here, we assessed whether the combination of passive retention of larvae due to re-circulation processes near reefs, and the dynamics of settlement competence, can produce the high levels of self-recruitment previously estimated by population genetic studies for reef-building corals. Additionally, we investigated whether time to motility, which is more readily measurable than competence parameters, can explain the between-species variation in self-recruitment. We measured the larval competence dynamics of broadcast-spawning and brooding corals and incorporated these in a model of larval retention around reefs to estimate the potential for self-recruitment and assess its variation among species and reefs. Our results suggest that the larvae of many corals, even those with an obligate planktonic phase, develop with sufficient rapidity to allow high levels of self-recruitment, particularly for reefs with long water retention times. Time to motility explained 77-86% of the between-species variation in potential self-recruitment in scenarios with a realistic range of retention times. Among broadcast spawners, time to motility was strongly and positively correlated with egg size, i.e., broadcast spawner species with small eggs developed more rapidly and exhibited greater potential for self-recruitment. These findings suggest that, along with water retention estimates, easy-to-measure species traits, such as egg size and time to motility, may be good predictors of potential self-recruitment, and therefore may be used to characterize the spectrum of self-recruitment in corals. PMID:23687891

Figueiredo, Joana; Baird, Andrew H; Connolly, Sean R

2013-03-01

268

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

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

269

CLNS 98/1588 Spin and Beam Dynamics in the Muon g2 Storage Ring --

CLNS 98/1588 Spin and Beam Dynamics in the Muon gÂ2 Storage Ring -- Systematic Errors Yuri F. Orlov. Orlov c , C. Pai b , C. Polly g , J. Pretz l , R. Prigl b , G. zu Putlitz e , S.I. Redin l , O. Rind

270

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

Dörte Hansen

2007-11-28

271

PHYSICAL REVIEW A 83, 062312 (2011) Dynamics of entanglement in a two-dimensional spin system

disturbance to the system, creating rapid oscillations, the system shows great controllability under of the applied field even with the same frequency for periodic fields. This follow-up trend breaks downPHYSICAL REVIEW A 83, 062312 (2011) Dynamics of entanglement in a two-dimensional spin system Qing

Kais, Sabre

2011-01-01

272

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

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

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

2013-02-07

273

helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron a metastable He atom and the surface electron spins are determined by a configuration interaction calculation

Kais, Sabre

274

Charged domain-wall dynamics in doped antiferromagnets and spin fluctuations in cuprate in this regime in terms of holes bound to domain walls, separating antiferromagnetic regions -- see Fig. 1 is characterized by many- hole correlations of the charged magnetic domain-wall type. Here we focus on the strong

van Saarloos, Wim

275

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

276

NASA Astrophysics Data System (ADS)

In this manuscript we present an ab initio picture of ultrafast magneto-optical dynamics in clusters containing 2, 3, and 4 Ni atoms. The presence of the magnetic centers in the clusters renders our systems of choice highly interesting for studying ultrafast spin dynamics. Here we systematically study functional cooperativity by increasing both the number of active centers and the spin multiplicities included in our Hilbert space (singlets ? triplets ? quintets), and deriving several ultrafast, laser-driven, spin-manipulation scenarios. Our results indicate various cooperative effects like spin flip by the M process, and simultaneous spin flip and spin transfer, as well as reversible and irreversible demagnetization scenarios. As it turns out the functional cooperativity of the clusters strongly benefits from the delicate interplay of the spin multiplicity and the number of active centers.

Chaudhuri, D.; Xiang, H. P.; Lefkidis, G.; Hübner, W.

2014-12-01

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

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 ...

Smith, Albert A.

279

Dynamics of polymer film formation during spin coating

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

280

Dynamics of polymer film formation during spin coating

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

Mouhamad, Y.; Clarke, N.; Jones, R. A. L.; Geoghegan, M., E-mail: geoghegan@sheffield.ac.uk [Department of Physics and Astronomy, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH (United Kingdom); Mokarian-Tabari, P. [Materials Research Group, Department of Chemistry and the Tyndall National Institute, University College Cork, Cork (Ireland)

2014-09-28

281

Relaxation dynamics in a transient network fluid with competing gel and glass phases

We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics.

Pinaki Chaudhuri; Pablo I. Hurtado; Ludovic Berthier; Walter Kob

2015-02-01

282

Advances and applications of dynamic-angle spinning nuclear magnetic resonance

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

Baltisberger, J.H.

1993-06-01

283

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

284

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics

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

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

2014-01-01

285

Experimental investigation of excitonic spin relaxation dynamics in GaN

NASA Astrophysics Data System (ADS)

By performing nondegenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized A and B excitons in wurtzite epitaxial GaN. By analyzing the differential reflectivity spectra (?R/R) of the two circularly polarized probe components, we are able to identify each spin relaxation channel (electron, light- and heavy-hole spin flips) separately and to extract characteristic times of the different spin relaxation processes. In addition, spectral oscillatory features are observed for negative delays. They show a rapid rise determined by the fast dephasing time T2 of the excitonic transitions. We show that the high density of dislocations increases the spin relaxation of electrons and holes through the Elliot-Yafet mechanism and makes the exciton dephasing time very short. The measured heavy-hole relaxation time, which is not extremely short compared to the electron relaxation time, can be related to the band structure, in which the degeneracy between different spin valence bands is partially lifted.

Brimont, Christelle; Gallart, Mathieu; Crégut, Olivier; Hönerlage, Bernd; Gilliot, Pierre

2008-03-01

286

Dynamics and performance optimization of spin-torque switching in magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

In this thesis I present a theoretical description for spin-torque switching using AC and DC spin-currents. This description builds from the standard Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque. By exploiting a separation in time-scales between the fast precessional motion of the free layer magnetization about the effective field and the slow drift of the free layer towards higher or lower energies that results from ST and damping, I reduce the free layer switching dynamics to that of a one dimensional system. Using this description I characterize certain current and frequency values important to switching, such as the DC critical current and the AC upper bifurcation frequency. Finally, using this description I show how to optimize the efficiency of AC, DC, and combination AC/DC spin-current strategies to minimize the Joule heat loss associated with switching. This leads to a well-defined range of spin-current polarization and free layer anisotropy values where each spin-current strategy is optimal.

Dunn, Thomas Edward

287

Universality and extremal aging for dynamics of spin glasses on sub-exponential time scales

We consider Random Hopping Time (RHT) dynamics of the Sherrington - Kirkpatrick (SK) model and p-spin models of spin glasses. For any of these models and for any inverse temperature we prove that, on time scales that are sub-exponential in the dimension, the properly scaled clock process (time-change process) of the dynamics converges to an extremal process. Moreover, on these time scales, the system exhibits aging like behavior which we called extremal aging. In other words, the dynamics of these models ages as the random energy model (REM) does. Hence, by extension, this confirms Bouchaud's REM-like trap model as a universal aging mechanism for a wide range of systems which, for the first time, includes the SK model.

G. Ben Arous; O. Gun

2010-10-25

288

Deployment dynamics of a simplified spinning IKAROS solar sail via absolute coordinate based method

NASA Astrophysics Data System (ADS)

The spinning solar sail of large scale has been well developed in recent years. Such a solar sail can be considered as a rigid-flexible multibody system mainly composed of a spinning central rigid hub, a number of flexible thin tethers, sail membranes, and tip masses. A simplified interplanetary kite-craft accelerated by radiation of the Sun (IKAROS) model is established in this study by using the absolute-coordinate-based (ACB) method that combines the natural coordinate formulation (NCF) describing the central rigid hub and the absolute nodal coordinate formulation (ANCF) describing flexible parts. The initial configuration of the system in the second-stage deployment is determined through both dynamic and static analyses. The huge set of stiff equations of system dynamics is solved by using the generalized-alpha method, and thus the deployment dynamics of the system can be well understood.

Zhao, Jiang; Tian, Qiang; Hu, Hai-Yan

2013-02-01

289

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

290

"Light-cone" dynamics after quantum quenches in spin chains.

Signal propagation in the nonequilibrium evolution after quantum quenches has recently attracted much experimental and theoretical interest. A key question arising in this context is what principles, and which of the properties of the quench, determine the characteristic propagation velocity. Here we investigate such issues for a class of quench protocols in one of the central paradigms of interacting many-particle quantum systems, the spin-1/2 Heisenberg XXZ chain. We consider quenches from a variety of initial thermal density matrices to the same final Hamiltonian using matrix product state methods. The spreading velocities are observed to vary substantially with the initial density matrix. However, we achieve a striking data collapse when the spreading velocity is considered to be a function of the excess energy. Using the fact that the XXZ chain is integrable, we present an explanation of the observed velocities in terms of "excitations" in an appropriately defined generalized Gibbs ensemble. PMID:25396393

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

2014-10-31

291

Spin-system dynamics and fault detection in threshold networks

NASA Astrophysics Data System (ADS)

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

2011-01-01

292

Prethermalization and dynamical transition in an isolated trapped ion spin chain

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

Zhe-Xuan Gong; L. -M. Duan

2013-05-05

293

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

294

Our current work in modeling reaction center dynamics has resulted in the observation of each major spin-dependent photochemical pathway that is observed in reaction centers. The development of new, simpler model systems has permitted us to probe deeply into the mechanistic issues that drive these dynamics. Based on these results we have returned to biomimetic chlorophyll-based electron donors to mimic these dynamics. Future studies will focus on the details of electronic structure and energetic of both the donor-acceptor molecules and their surrounding environment that dictate the mechanistic pathways and result in efficient photosynthetic charge separation.

Wasielewski, M. R.

1998-08-27

295

Spin distribution as a probe to investigate the dynamical effects in fusion reactions

NASA Astrophysics Data System (ADS)

The spin distributions are measured for the compound nucleus 80Sr populated in the reactions 16O+64Zn and 32S+48Ti. The comparison of the experimental results for both the systems shows that the mean ?-ray multiplicity values for the system 32S+48Ti are lower than those for 16O+64Zn. The spin distribution of the compound nucleus populated through the symmetric channel is also found to be lower than the asymmetric channel. Present investigation directly shows the effect of entrance channel mass asymmetry on the reaction dynamics.

Kaur, Maninder; Behera, B. R.; Singh, Gulzar; Singh, Varinderjit; Madhavan, N.; Muralithar, S.; Nath, S.; Gehlot, J.; Mohanto, G.; Mukul, Ish; Siwal, Davinder; Thakur, Meenu; Kapoor, Kushal; Sharma, Priya; Jhingan, Akhil; Varughese, T.; Bala, Indu; Chatterjee, M. B.; Nayak, B. K.; Saxena, A.

2015-01-01

296

Homoclinic solutions and motion chaotization in attitude dynamics of a multi-spin spacecraft

NASA Astrophysics Data System (ADS)

The attitude dynamics of the multi-spin spacecraft (MSSC) and the torque-free angular motion of the multi-rotor system are considered. Some types of homoclinic and general solutions are obtained in hyperbolic and elliptic functions. The local homoclinic chaos in the MSSC angular motion is investigated under the influence of polyharmonic perturbations. Some possible applications of the multi-rotor system are indicated, including gyrostat-satellites, dual-spin spacecraft, roll-walking robots, and also the inertialess method of the spacecraft attitude (angular) reorientation/control.

Doroshin, Anton V.

2014-07-01

297

Wigner formalism for a particle on an infinite lattice: dynamics and spin

The recently proposed Wigner function for a particle in an infinite lattice [NJP 14, 103009 (2012)] is extended here to include an internal degree of freedom, as spin. The formalism is developed to account for dynamical processes, with or without decoherence. We show explicit solutions for the case of Hamiltonian evolution under a position-dependent potential, and for evolution governed by a master equation under some simple models of decoherence. Discrete processes are also discussed. Finally we discuss the possibility of introducing a negativity concept for the Wigner function in the case in which the spin degree of freedom is included.

M. Hinarejos; M. C. Bañuls; A. Pérez

2015-01-23

298

Dynamical properties of three terminal magnetic tunnel junctions: Spintronics meets spin-orbitronics

This Letter introduces a micromagnetic model able to characterize the magnetization dynamics in three terminal magnetic tunnel junctions, where the effects of spin-transfer torque and spin-orbit torque are taken into account. Our results predict that the possibility to separate electrically those two torque sources is very promising from a technological point of view for both next generation of nanoscale spintronic oscillators and microwave detectors. A scalable synchronization scheme based on the parallel connection of those three terminal devices is also proposed.

Tomasello, R. [Department of Computer Science, Modeling, Electronics and System Science, University of Calabria, Rende (CS) (Italy)] [Department of Computer Science, Modeling, Electronics and System Science, University of Calabria, Rende (CS) (Italy); Carpentieri, M., E-mail: m.carpentieri@poliba.it [Department of Electrical and Information Engineering, Politecnico of Bari, via E. Orabona 4, I-70125 Bari (Italy); Finocchio, G. [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy)] [Department of Electronic Engineering, Industrial Chemistry and Engineering, University of Messina, C.da di Dio, I-98166 Messina (Italy)

2013-12-16

299

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

300

Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

NASA Astrophysics Data System (ADS)

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

Cao, Rong

301

1loop contribution to the dynamical exponents in spin glasses

in MF theory are the averÂ aged response and correlation functions, defined respectively: G(t \\Gamma t 0, by considering the 1Âloop correction to the mean field (MF) theory in a renormalization group calculation is the coordination number). Purely relaxation dynamics is introduced by the Langevin equation: \\Gamma \\Gamma1 0 @s i

Roma "La Sapienza", UniversitÃ di

302

Overall and internal dynamics of DNA as monitored by five-atom-tethered spin labels.

Electron paramagnetic resonance (EPR) spectra of the two-atom-tethered six-membered ring thymidylate spin label (DUMTA) incorporated into duplexes of different sizes were found to display a helix length dependence and a local-order parameter S = 0.32 +/- 0.01 for B-DNA based on the dynamic cylinder model (Keyes, R. S., and A. M. Bobst. 1995. Detection of internal and overall dynamics of a two-atom-tethered spin-labeled DNA. Biochemistry. 34:9265-9276). This sensitivity to size, which reflects global tumbling, is now reported for the more flexible five-atom-tethered five-membered ring thymidylate spin label (DUAP) that can be readily incorporated enzymatically and sequence specifically into nucleic acids of different sizes. The DUAPs containing B-DNA systems were simulated with the same dynamic cylinder model, giving S = 0.20 +/- 0.01 for the more flexibly tethered spin label. This shows that S is dependent on tether length but not on global motion. An analysis with the same motional model of the B-Z transition in a (dG-dC)n polymer containing the five-atom-tethered six-membered ring cytidylate spin label (DCAT) (Strobel, O. K., R. S. Keyes, and A. M. Bobst. 1990b. Base dynamics of local Z-DNA conformations as detected by electron paramagnetic resonance with spin-labeled deoxycytidine analogues. Biochemistry. 29:8522-8528) revealed an increase in S from 0.15 +/- 0.01 to 0.26 +/- 0.01 in response to the B- to Z-DNA transition. This indicates that S is not only sensitive to tether length, but also to conformational changes in DNA. Both the DUAP- and the DCAT-labeled systems were also simulated with a base disk model. From the DUAP spectral series, the perpendicular component of the correlation time tau perpendicular describing the spin-labeled base diffusion was found to be sensitive to global tumbling, confirming earlier results obtained with DUMTA. The DCAT polymer results demonstrated that tau perpendicular monitors a conformational change from B- to Z-DNA, indicating that tau perpendicular is also sensitive to local base dynamics. These results confirm that the dynamics of five-atom-tethered nitroxides are coupled to the nucleic acid dynamics and, as with two-atom-tethered spin labels, can be characterized by S and tau perpendicular. The analyses of both spin-labeled systems provide good evidence for spin-labeled base motions within double-stranded DNA occurring on the nanosecond time scale, and establish that both labels can be used to monitor changes in global tumbling and local order parameter due to variations in DNA conformation and protein-DNA interactions. PMID:8994613

Keyes, R S; Bobst, E V; Cao, Y Y; Bobst, A M

1997-01-01

303

Evidence for spin solitons and their dynamics in a spin-Peierls system ,,DMe-DCNQI...2Li Maki-Peierls system (DMe-DCNQI)2Li has been studied with electron paramagnetic resonance EPR under hydrostatic-dicyanoquinone-diimine (DMe-DCNQI)2Li is a one-dimensional 1D -band sys- tem composed of 1D stacks of DMe-DCNQI molecules

Mizoguchi, Kenji

304

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

305

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

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

2014-10-02

306

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

307

Generalized Number Theoretic Spin Chain-Connections to Dynamical Systems and Expectation Values

We generalize the number theoretic spin chain, a one-dimensional statistical model based on the Farey fractions, by introducing a new parameter x>=0. This allows us to write recursion relations in the length of the chain. These relations are closely related to the Lewis three-term equation, which is useful in the study of the Selberg \\zeta-function. We then make use of these relations and spin orientation transformations. We find a simple connection with the transfer operator of a model of intermittency in dynamical systems. In addition, we are able to calculate certain spin expectation values explicitly in terms of the free energy or correlation length. Some of these expectation values appear to be directly connected with the mechanism of the phase transition.

Jan Fiala; Peter Kleban

2005-03-12

308

Engineering the dynamics of effective spin-chain models for strongly interacting atomic gases

NASA Astrophysics Data System (ADS)

We consider a one-dimensional gas of cold atoms with strong contact interactions and construct an effective spin-chain Hamiltonian for a two-component system. The resulting Heisenberg spin model can be engineered by manipulating the shape of the external confining potential of the atomic gas. We find that bosonic atoms offer more flexibility for independently tuning the parameters of the spin Hamiltonian through interatomic (intraspecies) interaction, which is absent for fermions due to the Pauli exclusion principle. Our formalism can have important implications for control and manipulation of the dynamics of few- and many-body quantum systems; as an illustrative example relevant to quantum computation and communication, we consider state transfer in the simplest nontrivial system of four particles representing exchange-coupled qubits.

Volosniev, A. G.; Petrosyan, D.; Valiente, M.; Fedorov, D. V.; Jensen, A. S.; Zinner, N. T.

2015-02-01

309

In this paper, we combine thermal effects with Landau-Zener (LZ) quantum tunneling effects in a dynamical Monte Carlo (DMC) framework to produce satisfactory magnetization curves of single-molecule magnet (SMM) systems. We use the giant spin approximation for SMM spins and consider regular lattices of SMMs with magnetic dipolar interactions (MDI). We calculate spin reversal probabilities from thermal-activated barrier hurdling, direct LZ tunneling, and thermal-assisted LZ tunnelings in the presence of sweeping magnetic fields. We do systematical DMC simulations for Mn12 -ac systems with various temperatures and sweeping field rates. Our simulations produce clear step structures in low-temperature magnetization curves, and our results show that the thermally activated barrier hurdling becomes dominating at high temperature near 3K and the thermal-assisted tunnelings play important roles at intermediate temperature. Our magnetization curves are satisfactory compared to experimental results, considering possible...

Liu, Gui-Bin

2010-01-01

310

Engineering the Dynamics of Effective Spin-Chain Models for Strongly Interacting Atomic Gases

We consider a one-dimensional gas of cold atoms with strong contact interactions and construct an effective spin-chain Hamiltonian for a two-component system. The resulting Heisenberg spin model can be engineered by manipulating the shape of the external confining potential of the atomic gas. We find that bosonic atoms offer more flexibility for tuning independently the parameters of the spin Hamiltonian through interatomic (intra-species) interaction which is absent for fermions due to the Pauli exclusion principle. Our formalism can have important implications for control and manipulation of the dynamics of few- and many-body quantum systems; as an illustrative example relevant to quantum computation and communication, we consider state transfer in the simplest non-trivial system of four particles representing exchange-coupled qubits.

A. G. Volosniev; D. Petrosyan; M. Valiente; D. V. Fedorov; A. S. Jensen; N. T. Zinner

2015-02-21

311

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

312

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

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

Veshtort, Mikhail; Griffin, Robert G.

2011-01-01

313

Replica exchange Monte Carlo simulations of the ising spin glass: Static and dynamic properties

NASA Astrophysics Data System (ADS)

Spin glasses have been the subject of intense study and considerable controversy for decades, and the low-temperature phase of short-range spin glasses is still poorly understood. Our main goal is to improve our understanding in this area and find an answer to the following question: Are there only a single pair or a countable infinity of pure states in the low temperature phase of the EA spin glass? To that aim we first start by introducing spin glasses and provide a brief history of their research, then proceed to describe our method of simulation, the parallel tempering Monte Carlo algorithm. Next, we present the results of a large-scale numerical study of the equilibrium three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder. In order to understand how the parallel tempering algorithm works, we measure various static, as well as dynamical quantities, such as the autocorrelation times and round-trip times for the parallel tempering Monte Carlo method. We examine the correlation between static and dynamic observables for ˜ 5000 disorder realizations and up to 1000 spins down to temperatures at 20% of the critical temperature, and our results show that autocorrelation times are directly correlated with the roughness of the free-energy landscape. In the following chapters, the three- and four-dimensional Edwards-Anderson and mean-field Sherrington-Kirkpatrick Ising spin glasses are studied again via large scale Monte Carlo simulations at low temperatures, deep within the spin glass phase. Performing a careful statistical analysis of several thousand independent disorder realizations and using an observable that detects peaks in the overlap distribution, we show that the Sherrington-Kirkpatrick and Edwards-Anderson models have a distinctly different low-temperature behavior. We arrive to the following conclusion: The structure of the spin-glass overlap distribution for the Edwards-Anderson model suggests that its low-temperature phase has only a single pair of pure states. Finally we present results for several new observables, along with a few preliminary studies and suggestions for future research.

Yucesoy, Burcu

314

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

NASA Technical Reports Server (NTRS)

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

1962-01-01

315

Dynamics of entanglement in a two-dimensional spin system

NASA Astrophysics Data System (ADS)

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; Sadiek, Gehad; Kais, Sabre

2011-06-01

316

Spin dynamics of the cerium and uranium monopnictides studied by neutron scattering (invited)

NASA Astrophysics Data System (ADS)

The spin dynamics of the cerium and uranium monopnictides studied by diffuse and inelastic neutron scattering is reviewed. The diffuse scattering above the antiferromagnetic ordering temperature largely corresponds to longitudinal spin fluctuations which are highly anisotropic. For CeAs, CeSb, and UAs multicritical behavior has been found, i.e., the symmetry of the critical scattering above TN differs from the actual type of magnetic ordering below TN. In the ordered state the magnetic excitation spectrum of UN and UAs exhibits only a broad response, whereas well defined spin-wave branches have been observed for USb and the cerium monopnictides. A very detailed study of the magnetic excitations has been performed for CeAs, where the spin-wave dispersion is split into two modes of transverse polarization due to the exchange anisotropy. One of these modes exhibits nearly zero energy gap and quadratic dispersion which has not previously been observed in antiferromangets. A generalized random-phase-approximation calculation taking into account anisotropic exchange interactions consistently describes the transverse magnetic excitations for T

Hälg, B.; Furrer, A.

1984-03-01

317

The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In{sub 0.5}Ga{sub 0.5}As was studied by increasing the sheet density of the dots from 2?×?10{sup 10} to 7?×?10{sup 10}?cm{sup ?2} and reducing their size through a decrease in growth temperature from 500 to 470?°C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro, E-mail: murayama@ist.hokudai.ac.jp [Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814 (Japan)

2014-09-07

318

Fingerprints for Spin-Selection Rules in the Interaction Dynamics of O2 at Al(111) Christian are spin singlets. Intriguingly, the dissociative adsorption of oxygen at metal surfaces represents exactly from the surface where other mechanisms such as charge transfer from the metal are still quite weak

319

Spin Dynamics of a Single Mn Ion in a CdTe/(Cd, Mg, Zn)Te Quantum Dot

The spin dynamics of a single Mn ion confined in a CdTe/(Cd, Mg, Zn)Te quantum dot is determined by measurements of photon correlation of photoluminescence. The characteristic time of spin flip is a few nanoseconds and strongly depends on the excitation power.

Goryca, Mateusz; Kossacki, Piotr; Golnik, Andrzej; Kazimierczuk, Tomasz; Nawrocki, Michal [Institute of Experimental Physics, University of Warsaw, Hoza 69, 00-681 Warszawa (Poland); Wojnar, Piotr [Institute of Physics, Polish Academy of Sciences, al. Lotnikow 32/46, 02-668 Warszawa (Poland)

2010-01-04

320

1H nuclear spin relaxation of liquid water from molecular dynamics simulations.

We have investigated the nuclear spin relaxation properties of (1)H in liquid water with the help of molecular dynamics simulations. We have computed the (1)H nuclear spin relaxation times T1 and T2 and determined the contribution of the different interactions to the relaxation at different temperatures and for different classical water models (SPC/E, TIP3P, TIP4P, and TIP4P/2005). Among the water models considered, the TIP4P/2005 model exhibits the best agreement with the experiment. The same analysis was performed with Car-Parrinello ab initio molecular dynamics simulations of bulk water at T = 330 K, which provided results close to the experimental values at room temperature. To complete the study, we have successfully accounted for the temperature-dependence of T1 and T2 in terms of a simplified model, which considers the reorientation in finite angle jumps and the diffusive translation of water molecules. PMID:25584483

Calero, C; Martí, J; Guàrdia, E

2015-02-01

321

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

Alexander J. Silenko

2007-10-02

322

Dissipative quantum dynamics of fermions in optical lattices: A slave-spin approach

NASA Astrophysics Data System (ADS)

We investigate the influence of a Markovian environment on the dynamics of interacting spinful fermionic atoms in a lattice. To explore the physical phenomena occurring at short times, we develop a method based on a slave-spin representation of fermions that is amenable to the investigation of the dynamics of dissipative systems. We apply this approach to two different dissipative couplings that can occur in current experiments: a coupling via the local density and a coupling via the local double occupancy. We complement our study based on this method, with results obtained using the adiabatic elimination technique and with an exact study of a two-site model. We uncover that the decoherence is slowed down by increasing either the interaction strength or the dissipative coupling (the Zeno effect). We also find, for the coupling to the local double occupancy, that the final steady state can sustain single-particle coherence.

Bernier, Jean-Sébastien; Poletti, Dario; Kollath, Corinna

2014-11-01

323

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

NASA Technical Reports Server (NTRS)

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

Bainum, P. M.

1976-01-01

324

Non-Markovian dynamics of a qubit coupled to an Ising spin bath

We study the analytically solvable Ising model of a single qubit system coupled to a spin bath. The purpose of this study is to analyze and elucidate the performance of Markovian and non-Markovian master equations describing the dynamics of the system qubit, in comparison to the exact solution. We find that the time-convolutionless master equation performs particularly well up to fourth order in the system-bath coupling constant, in comparison to the Nakajima-Zwanzig master equation. Markovian approaches fare poorly due to the infinite bath correlation time in this model. A recently proposed post-Markovian master equation performs comparably to the time-convolutionless master equation for a properly chosen memory kernel, and outperforms all the approximation methods considered here at long times. Our findings shed light on the applicability of master equations to the description of reduced system dynamics in the presence of spin baths.

Krovi, Hari [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Oreshkov, Ognyan [Department of Physics, University of Southern California, Los Angeles 90089 (United States); Ryazanov, Mikhail [Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States); Lidar, Daniel A. [Department of Electrical Engineering, University of Southern California, Los Angeles, California 90089 (United States); Department of Physics, University of Southern California, Los Angeles 90089 (United States); Department of Chemistry, University of Southern California, Los Angeles, California 90089 (United States)

2007-11-15

325

Nonequilibrium Spin-Glass Dynamics from Picoseconds to a Tenth of a Second

NASA Astrophysics Data System (ADS)

We study numerically the nonequilibrium dynamics of the Ising spin glass, for a time spanning 11 orders of magnitude, thus approaching the experimentally relevant scale (i.e., seconds). We introduce novel analysis techniques to compute the coherence length in a model-independent way. We present strong evidence for a replicon correlator and for overlap equivalence. The emerging picture is compatible with noncoarsening behavior.

Belletti, F.; Cotallo, M.; Cruz, A.; Fernandez, L. A.; Gordillo-Guerrero, A.; Guidetti, M.; Maiorano, A.; Mantovani, F.; Marinari, E.; Martin-Mayor, V.; Sudupe, A. Muñoz; Navarro, D.; Parisi, G.; Perez-Gaviro, S.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Sciretti, D.; Tarancon, A.; Tripiccione, R.; Velasco, J. L.; Yllanes, D.

2008-10-01

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

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

the sample, analogous to the Faraday effect for transmitted light. For a probe laser energy E, the KR angle dynamics provide a sensitive probe of the local nuclear spin environment. The magneto-optical Kerr effect.5 ns Ti:sapphire II Pump 0 4 8 12 Ti:sapphire I EOM Sample Probe Pump Pol. BS x z y PL(a.u.) XX XÂ Â20

Loss, Daniel

328

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

Obaid, Rana [Institut für Theoretische Chemie, Universität Wien, Währinger Str. 17, 1090 Wien (Austria); Faculty of Pharmacy, Al-Quds University, Abu Dis, Palestine (Country Unknown); Kinzel, Daniel; Oppel, Markus, E-mail: markus.oppel@univie.ac.at; González, Leticia [Institut für Theoretische Chemie, Universität Wien, Währinger Str. 17, 1090 Wien (Austria)

2014-10-28

329

The ferromagnetic semiconductor (Ga,Mn)As has been a focus of much research prompted by its potential applications in semiconductor spintronics. In this thesis, studies of the defect configuration and spin dynamics in this material are reported. The technique of resonant Raman scattering was used to study the defect configuration. Insulating nano-islands consisting of substitutional Mn Ga acceptors and interstitial MnI donors

Daimian Wang

2007-01-01

330

Dynamics of the nitroxide side-chain in spin labeled proteins

The dynamics of the tether linking methanethiosulfonate (MTSSL) spin probes to ?-helices has been investigated, with the purpose of rationalizing its effects on ESR lineshapes. Torsional profiles for the chain bonds have been calculated ab initio, and steric interactions with the ?-helix and the neighboring residues have been introduced at the excluded-volume level. As a consequence of the restrictions deriving from chain geometry and local constraints, a limited number of allowed conformers has been identified, which undergo torsional oscillations and conformational jumps. Torsional fluctuations are described as damped oscillations, while transition rates between conformers are calculated according to the Langer multidimensional extension of the Kramers theory. The time-scale and amplitude of the different motions are compared; the major role played by rotations of the outermost bonds of the side-chain emerges, along with the effects of substituents in the pyrroline ring on the conformer distribution and dynamics. The extent and symmetry of magnetic tensor averaging produced by the side-chain motions are estimated, the implications for the ESR spectra of spin labeled proteins are discussed, and suggestions for the introduction of realistic features of the spin probe dynamics into the lineshape simulation are presented. PMID:17181283

Tombolato, Fabio; Ferrarini, Alberta; Freed, Jack H.

2010-01-01

331

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

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

2014-08-01

332

NASA Astrophysics Data System (ADS)

Pattern formation often occurs in spatially extended physical, biological, and chemical systems due to an instability of the homogeneous steady state. The type of the instability usually prescribes the resulting spatio-temporal patterns and their characteristic length scales. However, patterns resulting from the simultaneous occurrence of instabilities cannot be expected to be simple superposition of the patterns associated with the considered instabilities. To address this issue, we design two simple models composed by two asymmetrically coupled equations of non-conserved (Swift-Hohenberg equations) or conserved (Cahn-Hilliard equations) order parameters with different characteristic wave lengths. The patterns arising in these systems range from coexisting static patterns of different wavelengths to traveling waves. A linear stability analysis allows to derive a two parameter phase diagram for the studied models, in particular, revealing for the Swift-Hohenberg equations, a co-dimension two bifurcation point of Turing and wave instability and a region of coexistence of stationary and traveling patterns. The nonlinear dynamics of the coupled evolution equations is investigated by performing accurate numerical simulations. These reveal more complex patterns, ranging from traveling waves with embedded Turing patterns domains to spatio-temporal chaos, and a wide hysteretic region, where waves or Turing patterns coexist. For the coupled Cahn-Hilliard equations the presence of a weak coupling is sufficient to arrest the coarsening process and to lead to the emergence of purely periodic patterns. The final states are characterized by domains with a characteristic length, which diverges logarithmically with the coupling amplitude.

Schüler, D.; Alonso, S.; Torcini, A.; Bär, M.

2014-12-01

333

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

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

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

2009-09-22

334

New Dynamic Spin Rig Capabilities Used to Determine Rotating Blade Dynamics

NASA Technical Reports Server (NTRS)

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

Provenza, Andrew J.

2004-01-01

335

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

336

ERIC Educational Resources Information Center

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

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

2013-01-01

337

Pattern formation often occurs in spatially extended physical, biological, and chemical systems due to an instability of the homogeneous steady state. The type of the instability usually prescribes the resulting spatio-temporal patterns and their characteristic length scales. However, patterns resulting from the simultaneous occurrence of instabilities cannot be expected to be simple superposition of the patterns associated with the considered instabilities. To address this issue, we design two simple models composed by two asymmetrically coupled equations of non-conserved (Swift-Hohenberg equations) or conserved (Cahn-Hilliard equations) order parameters with different characteristic wave lengths. The patterns arising in these systems range from coexisting static patterns of different wavelengths to traveling waves. A linear stability analysis allows to derive a two parameter phase diagram for the studied models, in particular, revealing for the Swift-Hohenberg equations, a co-dimension two bifurcation point of Turing and wave instability and a region of coexistence of stationary and traveling patterns. The nonlinear dynamics of the coupled evolution equations is investigated by performing accurate numerical simulations. These reveal more complex patterns, ranging from traveling waves with embedded Turing patterns domains to spatio-temporal chaos, and a wide hysteretic region, where waves or Turing patterns coexist. For the coupled Cahn-Hilliard equations the presence of a weak coupling is sufficient to arrest the coarsening process and to lead to the emergence of purely periodic patterns. The final states are characterized by domains with a characteristic length, which diverges logarithmically with the coupling amplitude. PMID:25554062

Schüler, D; Alonso, S; Torcini, A; Bär, M

2014-12-01

338

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

Kyrychenko, Alexander; Ladokhin, Alexey S

2013-05-16

339

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

A spin-Peierls system (DMe-DCNQI)2Li has been studied with electron paramagnetic resonance (EPR) under hydrostatic pressure. A definite frequency dependence of the EPR linewidth is observed for the Curie spins that appear below TSP, demonstrating a clear one-dimensional diffusive character similar to t-(CH)x. This is strong evidence for Curie spins to arise from spin solitons as domain walls caused by structural

Maki Hiraoka; Hirokazu Sakamoto; Kenji Mizoguchi; Reizo Kato

2002-01-01

340

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

341

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

NASA Technical Reports Server (NTRS)

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

1963-01-01

342

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

343

Bioengineering Spin-Offs from Dynamical Systems Theory

NASA Astrophysics Data System (ADS)

Recently, there has been considerable interest in applying concepts and techniques from dynamical systems and statistical physics to physiological systems. In this talk, we present work dealing which two active topics in this area: stochastic resonance and (2) chaos control. Stochastic resonance is a phenomenon wherein the response of nonlinear system to a weak input signal is optimally enhanced by the presence of a particular level of noise. Here we demonstrate that noise-based techniques can be used to lower sensory detection thresholds in humans. We discuss how from a bioengineering and clinical standpoint, these developments may be particularly relevant for individuals with elevated sensory thresholds, such as older adults and patients with peripheral neuropathy. Chaos control techniques have been applied to a wide range of experimental systems, including biological preparations. The application of chaos control to biological systems has led to speculations that these methods may be clinically useful. Here we demonstrate that the principles of chaos control can be utilized to stabilize underlying unstable periodic orbits in non-chaotic biological systems. We discuss how from a bioengineering and clinical standpoint, these developments may be important for suppressing or eliminating certain types of cardiac arrhythmias.

Collins, J. J.

1997-03-01

344

NASA Astrophysics Data System (ADS)

We study the spin dynamics in the presence of impurity and electron-electron (e-e) scattering in a III-V semiconductor quantum well with arbitrary spin-orbit coupling (SOC) strength and symmetry at finite temperature. In the regime where the strength of the Rashba and linear Dresselhaus SOC match, known as the SU(2) symmetry point, experiments have observed the spin-helix mode with a large spin-lifetime whose unexplained nonmonotonic temperature dependence peaks at around 75 K. As a key test of our theory, we are able to naturally explain quantitatively this nonmonotonic dependence and show that it arises as a competition between the Dyakonov-Perel mechanism, suppressed at the SU(2) point, and the Elliott-Yafet mechanism. In the strong SOC regime, we show that our theory directly reproduces the previous known analytical result at the SU(2) symmetry point in the ballistic regime.

Liu, Xin; Jairo, Sinova

2013-03-01

345

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

2011-04-01

346

In this comment we explain the discrepancy found between the results in arXiv:0712.1716v1 for the 3PN spin-spin potential and those previously derived in gr-qc/0604099. We point out that to compare one must include sub-leading lower order spin-orbit effects which contribute to the spin-spin potential once one transforms to the PN frame. When these effects are included the results in arXiv:0712.1716v1 do indeed reproduce those found in gr-qc/0604099.

Rafael A. Porto; Ira Z. Rothstein

2007-12-12

347

NASA Astrophysics Data System (ADS)

An intriguing aspect of unconventional superconductivity is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In the iron pnictides, these competing phases are marked by a tetragonal-to-orthorhombic structural transition and a collinear spin-density wave (SDW) transition. There has been macroscopic evidence for competition between these phases and superconductivity as the magnitude of both the orthorhombicity and magnetic moment are suppressed in the superconducting state. Here, using angle-resolved photoemission spectroscopy on detwinned underdoped Ba1-xKxFe2As2, we observe a coexistence of both the SDW gap and superconducting gap in the same electronic structure. Furthermore, our data reveal that following the onset of superconductivity, the SDW gap decreases in magnitude and shifts in a direction consistent with a reduction of the orbital anisotropy. This observation provides direct spectroscopic evidence for the dynamic competition between superconductivity and both SDW and electronic nematic orders in these materials.

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

2014-04-01

348

Thanks to the growing interest in personalized medicine, joint modeling of longitudinal marker and time-to-event data has recently started to be used to derive dynamic individual risk predictions. Individual predictions are called dynamic because they are updated when information on the subject's health profile grows with time. We focus in this work on statistical methods for quantifying and comparing dynamic predictive accuracy of this kind of prognostic models, accounting for right censoring and possibly competing events. Dynamic area under the ROC curve (AUC) and Brier Score (BS) are used to quantify predictive accuracy. Nonparametric inverse probability of censoring weighting is used to estimate dynamic curves of AUC and BS as functions of the time at which predictions are made. Asymptotic results are established and both pointwise confidence intervals and simultaneous confidence bands are derived. Tests are also proposed to compare the dynamic prediction accuracy curves of two prognostic models. The finite sample behavior of the inference procedures is assessed via simulations. We apply the proposed methodology to compare various prediction models using repeated measures of two psychometric tests to predict dementia in the elderly, accounting for the competing risk of death. Models are estimated on the French Paquid cohort and predictive accuracies are evaluated and compared on the French Three-City cohort. PMID:25311240

Blanche, Paul; Proust-Lima, Cécile; Loubère, Lucie; Berr, Claudine; Dartigues, Jean-François; Jacqmin-Gadda, Hélène

2014-10-13

349

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

350

Purpose of review Although the basic standards of adjudicative competence were specified by the U.S. Supreme Court in 1960, there remain a number of complex conceptual and practical issues in interpreting and applying these standards. In this report we provide a brief overview regarding the general concept of adjudicative competence and its assessment, as well as some highlights of recent empirical studies on this topic. Findings Most adjudicative competence assessments are conducted by psychiatrists or psychologists. There are no universal certification requirements, but some states are moving toward required certification of forensic expertise for those conducting such assessments. Recent data indicate inconsistencies in application of the existing standards even among forensic experts, but the recent publication of consensus guidelines may foster improvements in this arena. There are also ongoing efforts to develop and validate structured instruments to aid competency evaluations. Telemedicine-based competency interviews may facilitate evaluation by those with specific expertise for evaluation of complex cases. There is also interest in empirical development of educational methods to enhance adjudicative competence. Summary Adjudicative competence may be difficult to measure accurately, but the assessments and tools available are advancing. More research is needed on methods of enhancing decisional capacity among those with impaired competence. PMID:18650693

Dawes, Sharron E.; Palmer, Barton W.; Jeste, Dilip V.

2008-01-01

351

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

352

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

NASA Astrophysics Data System (ADS)

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

Zhong, S. Y.

2012-03-01

353

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

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

Weizhu Bao; Yongyong Cai

2014-07-22

354

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

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

355

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

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

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

2011-12-15

356

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

NASA Astrophysics Data System (ADS)

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

Guzman, J.; Jo, G.-B.; Wenz, A. N.; Murch, K. W.; Thomas, C. K.; Stamper-Kurn, D. M.

2011-12-01

357

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

Facilitated spin models were introduced some decades ago to mimic systems characterized by a glass transition. Recent developments have shown that a class of facilitated spin models is also able to reproduce characteristic signatures of the structural relaxation properties of glass-forming liquids. While the equilibrium phase diagram of these models can be calculated analytically, the dynamics are usually investigated numerically. Here we propose a network-based approach, called approximate master equation (AME), to the dynamics of the Fredrickson-Andersen model. The approach correctly predicts the critical temperature at which the glass transition occurs. We also find excellent agreement between the theory and the numerical simulations for the transient regime, except in close proximity of the liquid-glass transition. Finally, we analytically characterize the critical clusters of the model and show that the departures between our AME approach and the Monte Carlo can be related to the large interface between blocked and unblocked spins at temperatures close to the glass transition. PMID:25314497

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

2014-09-01

358

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

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

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

2014-12-01

359

NASA Astrophysics Data System (ADS)

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

Blume, Theresa; Hassler, Sibylle; Weiler, Markus

2014-05-01

360

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

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

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

2014-05-20

361

Spin dynamics and implications for superconductivity: Some problems with the d-wave scenario

We review the spin dynamics of the normal state of the cuprates with special emphasis on neutron data in both the YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} and La{sub 2-x}Sr{sub x}CuO{sub 4} systems. When realistic models of the Fermi surface shapes are incorporated, along with a moderate degree of spin fluctuations, we find good semi-quantiative agreement with experiment for both cuprates. Building on the success of this Fermi-liquid-based scheme, we explore the implications for d-wave pairing from a number of vantage points. We conclude that our present experimental and theoretical understanding is inadequate to confirm or refute the d-wave scenario.

Levin, K.; Zha, Y.; Radtke, R.J. [Chicago Univ., IL (United States). Dept. of Physics; Si, Q. [Rutgers Univ., Piscataway, NJ (United States). Serin Physics Lab.; Norman, M.R. [Argonne National Lab., IL (United States); Schuttler, H.B. [Georgia Univ., Athens, GA (United States). Dept. of Physics and Astronomy

1993-09-01

362

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

363

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

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

364

Multidimensional instability and dynamics of spin avalanches in crystals of nanomagnets.

We obtain a fundamental instability of the magnetization-switching fronts in superparamagnetic and ferromagnetic materials such as crystals of nanomagnets, ferromagnetic nanowires, and systems of quantum dots with large spin. We develop the instability theory for both linear and nonlinear stages. By using numerical simulations we investigate the instability properties focusing on spin avalanches in crystals of nanomagnets. The instability distorts spontaneously the fronts and leads to a complex multidimensional front dynamics. We show that the instability has a universal physical nature, with a deep relationship to a wide variety of physical systems, such as the Darrieus-Landau instability of deflagration fronts in combustion, inertial confinement fusion, and thermonuclear supernovae, and the instability of doping fronts in organic semiconductors. PMID:25479521

Jukimenko, O; Dion, C M; Marklund, M; Bychkov, V

2014-11-21

365

Spin diffusion and the dynamic structure of a protein. Streptomyces subtilisin inhibitor

NASA Astrophysics Data System (ADS)

The method of cross saturation in the 1H NMR spectrum is examined in detail at 360 to 400 MHz in a medium-sized globular protein, Streptomyces subtilisin inhibitor (SSI) (MW 23,000) in neutral aqueous (D 2O) solution for the purpose of clarifying the relationship between the phenomenon of spin diffusion and the dynamic structure of a protein. Continuous irradiation of a portion of the spectrum with a weak radiofrequency field of ?H2/2 ? = 50- to 70-Hz order results in saturation extending over the entire spectral range, showing a similar hot spin temperature for a large group of protons which, according to X-ray and NMR results, exist in a rigid core region of SSI. However, there are a number of resonances that receive saturation at distinctively slower rates. Some of these lines are identified with side-chain protons of amino acids in the exposed segments of SSI. Transverse relaxation measurements show that in solution most of these side chains undergo rapid internal motions. Differential efficiency of cross saturation between the core and the exposed segments observed above is discussed in terms of the overall cross-relaxation rate ( TIS-1) between irradiated (S) and observed (I) protons, which represents the spin-diffusion efficiency. The time constant TIS is particularly sensitive to the interresidue geometry as well as to local motion. It is proposed that the method of cross saturation in 1H NMR may be used for studying the gross dynamic structure, in particular for the detection of exposed and/or mobile segments, in proteins of a wide range of molecular weight, i.e., above 10,000 daltons for which the conventional 1H spin-lattice relaxation measurement is no longer useful.

Akasaka, Kazuyuki

366

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

367

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

368

In dynamic nuclear polarization (DNP) experiments applied to organic solids for creating nonequilibrium, high (1)H spin polarization, an efficient buildup of (1)H polarization is attained by partially deuterating the material of interest with an appropriate (1)H concentration. In such a dilute (1)H spin system, it is shown that the (1)H spin diffusion rate and thereby the buildup efficiency of (1)H polarization can further be enhanced by continually applying radiofrequency irradiation for deuterium decoupling during the DNP process. As experimentally confirmed in this work, the electron spin polarization of the photoexcited triplet state is mainly transferred only to those (1)H spins, which are in the vicinity of the electron spins, and (1)H spin diffusion transports the localized (1)H polarization over the whole sample volume. The (1)H spin diffusion coefficients are estimated from DNP repetition interval dependence of the initial buildup rate of (1)H polarization, and the result indicates that the spin diffusion coefficient is enhanced by a factor of 2 compared to that without (2)H decoupling. PMID:20969400

Negoro, M; Nakayama, K; Tateishi, K; Kagawa, A; Takeda, K; Kitagawa, M

2010-10-21

369

Flight Control Design using Nonlinear Inverse Dynamics

Aircraft in extreme flight conditions such as stalls and spins experience nonlinear forces and moments generated from high angles of attack and high angular rates. Flight control systems based upon nonlinear inverse dynamics offer the potential for providing improved levels of safety and performance in these flight conditions over the competing designs developed using linearizing assumptions. Inverse dynamics are generated

Robert F. Stengel

1986-01-01

370

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

371

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

372

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

373

Current induced domain wall dynamics in the presence of spin orbit torques

Current induced domain wall (DW) motion in perpendicularly magnetized nanostripes in the presence of spin orbit torques is studied. We show using micromagnetic simulations that the direction of the current induced DW motion and the associated DW velocity depend on the relative values of the field like torque (FLT) and the Slonczewski like torques (SLT). The results are well explained by a collective coordinate model which is used to draw a phase diagram of the DW dynamics as a function of the FLT and the SLT. We show that a large increase in the DW velocity can be reached by a proper tuning of both torques.

Boulle, O., E-mail: Olivier.boulle@cea.fr; Buda-Prejbeanu, L. D.; Jué, E.; Miron, I. M.; Gaudin, G. [SPINTEC, CEA/CNRS/UJF/INPG, INAC, 38054 Grenoble Cedex 9 (France)

2014-05-07

374

NASA Astrophysics Data System (ADS)

We numerically simulate the creation process of two-dimensional skyrmionic excitations in antiferromagnetic spin-1 Bose-Einstein condensates by solving the full three-dimensional dynamics of the system from the Gross-Pitaevskii equation. Our simulations reproduce quantitatively the experimental results of Choi et al. [Phys. Rev. Lett. 108, 035301 (2012), 10.1103/PhysRevLett.108.035301] without any fitting parameters. Furthermore, we examine the stability of the skyrmion by computing the temporal evolution of the condensate in a harmonic potential. The presence of both the quadratic Zeeman effect and dissipation in the simulations is vital for reproducing the experimentally observed decay time.

Ollikainen, T.; Ruokokoski, E.; Möttönen, M.

2014-03-01

375

Cyclotron dynamics of a Kondo singlet in a spin-orbit-coupled alkaline-earth-metal atomic gas

NASA Astrophysics Data System (ADS)

We propose a scheme to investigate the interplay between the Kondo-exchange interaction and the quantum spin Hall effect with ultracold fermionic alkaline-earth-metal atoms trapped in two-dimensional optical lattices using ultracold collision and laser-assisted tunneling. In the strong Kondo-coupling regime, although the loop trajectory of the mobile atom disappears, collective dynamics of an atom pair in two clock states can exhibit an unexpected spin-dependent cyclotron orbit in a plaquette, realizing the quantum spin Hall effect of the Kondo singlet. We demonstrate that the collective cyclotron dynamics of the spin-zero Kondo singlet is governed by an effective Harper-Hofstadter model in addition to second-order diagonal tunneling.

Jiang, Bo-Nan; Lv, Hao; Wang, Wen-Li; Du, Juan; Qian, Jun; Wang, Yu-Zhu

2014-11-01

376

From all-electron fixed-spin-moment calculations [1], we showed that the ferromagnetic and checkerboard antiferromagnetic ordering in LaOFeAs were not stable and the stripe Fe-spin configuration (i.e. SDW) was the only stable ground state. The main exchange interaction between Fe ions are large, antiferromagnetic, and frustrated. The magnetic stripe SDW phase breaks the tetragonal symmetry, removes the frustration, and causes a structural

Taner Yildirim

2009-01-01

377

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

378

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

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

Seung-Ho-Baek

2004-12-19

379

Dynamical decoupling of qubits in a spin bath under periodic quantum control

We investigate the feasibility for the preservation of coherence and entanglement of one- and two-spin qubits coupled to an interacting quantum spin-1/2 chain within the dynamical decoupling (DD) scheme. The performance is examined by counting the number of computing pulses that can be applied periodically with periods of T before qubits become decoherent, while an identical decoupling pulse sequence is applied within each cycle. By considering pulses with mixed directions and finite width controlled by magnetic fields, it is shown that pulse-width accumulation degrades the performance of sequences with larger numbers of pulses and that feasible magnetic fields in practice restrict consideration to sequences with few than 10 decoupling pulses within each cycle. Furthermore, within each cycle T, exact nontrivial pulse sequences are found to suppress the qubit-bath coupling to O(T{sup N+1}) progressively with the minimum number of pulses being 4, 7, and 12 for N=1,2,3. These sequences, when applied to all qubits, are shown to preserve both the entanglement and coherence. Based on time-dependent density matrix renormalization, our numerical results show that for modest magnetic fields (10-40 T) available in laboratories, the overall performance is optimized when the number of pulses in each cycle is 4 or 7 with pulse directions alternating between x and z. Our results provide useful guides for the preservation of coherence and entanglement of spin qubits in the solid state.

Kao, Jun-Ting; Hung, Jo-Tzu; Chen, Pochung [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China); Mou, Chung-Yu [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China); Institute of Physics, Academia Sinica, Nankang, Taiwan (China); Physics Division, National Center for Theoretical Sciences, P.O. Box 2-131, Hsinchu, Taiwan (China)

2010-12-15

380

An investigation of the relativistic dynamics of N+1 spin-12 particles placed in an external, homogeneous magnetic field is carried out. The system can represent an atom with a fermion nucleus and N electrons. Quantum electrodynamical interactions, namely, projected Briet and magnetic interactions, are chosen to formulate the relativistic Hamiltonian. The quasi-free-particle picture is retained here. The total pseudomomentum is conserved, and its components are distinct when the total charge is zero. Therefore, the center-of-mass motion can be separated from the Hamiltonian for a neutral (N+1)-fermion system, leaving behind a unitarily transformed, effective Hamiltonian H(0) at zero total pseudomomentum. The latter operator represents the complete relativistic dynamics in relative coordinates while interaction is chosen through order alpha4mc2. Each one-particle part in the effective Hamiltonian can be brought to a separable form for positive- and negative-energy states by replacing the odd operator in it through two successive unitary transformations, one due to Tsai [Phys. Rev. D 7, 1945 (1973)] and the other due to Weaver [J. Math. Phys. 18, 306 (1977)]. Consequently, the projector changes and the interaction that involves the concerned particle also becomes free from the corresponding odd operators. When this maneuver is applied only to the nucleus, and the non-Hermitian part of the transformed interaction is removed by another unitary transformation, a familiar form of the atomic relativistic Hamiltonian H(atom) emerges. This operator is equivalent to H(0). A good Hamiltonian for relativistic quantum chemical calculations, H(Qchem), is obtained by expanding the nuclear part of the atomic Hamiltonian through order alpha4mc2 for positive-energy states. The operator H(Qchem) is obviously an approximation to H(atom). When the same technique is used for all particles, and subsequently the non-Hermitian terms are removed by suitable unitary transformations, one obtains a Hamiltonian H(T) that is equivalent to H(atom) but is in a completely separable form. As the semidiscrete eigenvalues and eigenfunctions of the one-particle parts are known, the completely separable Hamiltonian can be used in computation. A little more effort leads to the derivation of the correct atomic Hamiltonian in the nonrelativistic limit, H(nonrel). The operator H(nonrel) is an approximation to H(T). It not only retains the relativistic and radiative effects, but also directly exhibits the phenomena of electron paramagnetic resonance and nuclear magnetic resonance. PMID:16122294

Misra, Anirban; Datta, Sambhu N

2005-08-01

381

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

E. Demler; A. Maltsev; A. Prokofiev

2012-01-30

382

NASA Astrophysics Data System (ADS)

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

Marsat, Sylvain

2015-04-01

383

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

NASA Technical Reports Server (NTRS)

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

Spain, C. V.

1987-01-01

384

Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E? symmetry.

A spectrum exhibiting E? symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E? description for CoNb?O?. PMID:25541800

Wu, Jianda; Kormos, Márton; Si, Qimiao

2014-12-12

385

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 D{sub 1} 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 {alpha} Almost-Equal-To 0.1 for s= 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schroedinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s Much-Less-Than 1).

Wu Ning; Duan Liwei; Zhao Yang [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Li Xin [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Institute of High Energy Physics, Theoretical Physics Center for Science Facilities, Chinese Academy of Sciences, 100049 Beijing (China)

2013-02-28

386

Real-time dynamics of open quantum spin systems driven by dissipative processes

We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY-model towards a disordered phase at late times. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.

Florian Hebenstreit; Debasish Banerjee; Manes Hornung; Fu-Jiun Jiang; Franziska Schranz; Uwe-Jens Wiese

2015-02-10

387

Real-time dynamics of open quantum spin systems driven by dissipative processes

We study the real-time evolution of large open quantum spin systems in two spatial dimensions, whose dynamics is entirely driven by a dissipative coupling to the environment. We consider different dissipative processes and investigate the real-time evolution from an ordered phase of the Heisenberg or XY-model towards a disordered phase at late times. The corresponding Kossakowski-Lindblad equation is solved via an efficient cluster algorithm. We find that the symmetry of the dissipative process determines the time scales which govern the approach towards a new equilibrium phase at late times. Most notably, we find a slow equilibration if the dissipative process conserves any of the magnetization Fourier modes. In these cases, the dynamics can be interpreted as a diffusion process of the conserved quantity.

Hebenstreit, Florian; Hornung, Manes; Jiang, Fu-Jiun; Schranz, Franziska; Wiese, Uwe-Jens

2015-01-01

388

Mercury's spin-orbit model and signature of its dynamical parameters

The 3:2 spin-orbit resonance between the rotational and orbital motions of Mercury results from a functional dependance on a tidal friction adding to a non-zero eccentricity with a permanent asymmetry in the equatorial plane of the planet. The upcoming space missions, MESSENGER and BepiColombo with onboard instrumentation capable of measuring the Mercury's rotational parameters, stimulate the objective to attempt to an accurate theory of the planet's rotation. We have used our BJV relativistic model of solar system integration including the spin-orbit motion of the Moon. This model had been previously built in accordance with the requirements of the Lunar Laser Ranging observational accuracy. We extended this model to the spin-orbit couplings of the terrestrial planets including Mercury; the updated model is called SONYR (acronym of Spin-Orbit N-BodY Relativistic model). An accurate rotation of Mercury has been then obtained. Moreover, the conception of the SONYR model is suitable for analyzing the different families of hermean rotational librations. We accurately identify the non-linear relations between the rotation of Mercury and its dynamical figure (\\cmr2, $C_{20}$, and $C_{22}$). Notably, for a variation of 1% on the \\cmr2 value, signatures in the $\\phi$ hermean libration in longitude as well as in the $\\eta$ obliquity of the planet are respectively 0.45 arcseconds (as) and 2.4 milliarcseconds (mas). These determinations provide new constraints on the internal structure of Mercury to be discussed with the expected accuracy forecasted in the BepiColombo mission (respectively 3.2 and 3.7 as according to Milani et al 2001).

Nicolas Rambaux; Eric Bois

2003-07-17

389

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

NASA Astrophysics Data System (ADS)

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

Horváth, Denis; Kuscsik, Zoltán; Gmitra, Martin

2006-09-01

390

?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

391

Theme: Coping with Competencies.

ERIC Educational Resources Information Center

Consists of five articles on the topic of competencies in vocational agriculture. Topics covered include (1) competency-based instruction, (2) competencies for agricultural recordkeeping, (3) competencies in hydroponics, and (4) competencies in agribusiness. (CH)

Brown, Daniel; And Others

1989-01-01

392

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. PMID:22941643

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

2013-01-01

393

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. PMID:22941643

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

2013-01-01

394

ERIC Educational Resources Information Center

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

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

2012-01-01

395

accredited in business and accounting by AACSB International the Association to Advance Collegiate Schools on the educational, social, economic, and physical well-being of Nevada's children and seeks to improve their livesLEE BUSINESS SCHOOL HIGHLIGHTS At the Lee Business School, we prepare people to compete in today

Hemmers, Oliver

396

NASA Technical Reports Server (NTRS)

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

Murch, Austin M.; Foster, John V.

2007-01-01

397

The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.

Gonzalo A. Alvarez

2007-05-15

398

NASA Astrophysics Data System (ADS)

The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.

Alvarez, Gonzalo A.

2007-05-01

399

The Impact of Superplasticity and the Iron Spin Transition on Mantle Dynamics

NASA Astrophysics Data System (ADS)

Our understanding of mantle dynamical processes depends critically upon knowledge of the physical properties of mantle minerals at high pressure and temperature. The Earth's lower mantle is believed to consist mainly of iron bearing aluminous silicate perovskite [Al-(Mg,Fe)SiO3] and ferropericlase [(Mg,Fe)O] together with a small amount of calcium silicate perovskite (CaSiO3) and Al2O3 (eg. Ringwood, 1982). In light of recent experimental measurements it is now generally accepted that the dominant mineral of the lowermost mantle is a "post-perovskite phase" (Murakami, 2004). The exothermic perovskite-post-perovskite (pv-ppv) phase transition may accommodate a higher rate of heat extraction from the core. On the other hand the electronic spin and valence states of iron-bearing minerals may also strongly influence the properties of mantle material and in turn the dynamics of Earth's interior. Most recent experimental results suggest that the electronic iron spin transition is associated with significant changes in density, compressibility, sound velocities, radiative thermal conductivity and electrical conductivity in ferropericlase (Lin et al., 2008). These studies also show that both perovskite and post- perovskite accommodate the same intermediate-spin Fe2+ state and that their opacity and absorption behavior at infrared wavelengths are very similar in high P-T experiments. Therefore corresponding changes in the radiative thermal conductivity, electrical conductivity and iron partitioning would occur due to the crystal structural transition, rather than due to the electronic spin transition, from perovskite to post-perovskite (Lin et al., 2008). Furthermore, dislocation creep which is believed to be the dominant deformation mechanism in the post-perovskite phase would be associated with lower viscosity than in the viscosity of perovskite at the same P-T conditions (Cizkova et al., 2008). These results may have significant implications for the dynamics of Earth's lower mantle and for the extent to which the convective circulation is layered, an issue that remains outstanding. In the work to be reported in this paper we have studied the impact of the iron spin transition on the style of convective mixing. Although the density increase with depth may slightly lower the mantle mean temperature, the higher thermal conductivity due to the increase of the radiative contribution below the D" layer enhances the influence of the lower viscosity by increasing the mean mantle temperature. A further issue that we address in this paper concerns the extent to which superplastic behavior associated with the endothermic phase transition at 660 km depth may influence mantle layering. During a solid-solid phase transition a polycrystalline material may deform superplastically due to the reduction in grain size that occurs when material changes phase (e.g. Sammis & Dein, 1974; Paterson, 1983; Ranalli, 1991). Our numerical models show that the inclusion of such a superplastic layer at the level of the 660 km transition enhances the degree of mantle layering and the regularity of the avalanches of material that episodically occur across this important interface that separates the upper mantle from the lower mantle. Keywords: layered mantle convection, iron spin transition, perovskite-post perovskite phase transition, superplasticity

Shahnas, H.; Peltier, W.

2009-05-01

400

Critical spin dynamics in Nd1-xSrxMnO3 with x~0.5

NASA Astrophysics Data System (ADS)

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

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

2000-02-01

401

Spin-polarized Molecular Dynamics simulations of liquid iron silicate at high pressures.

NASA Astrophysics Data System (ADS)

Liquid iron silicate (Fe2SiO4) is an important component of natural silicate liquids appearing in Earth's interior. The effect of iron in the properties of these melts is a crucial issue, as it displays a high-spin to low-spin transition at high pressures which is accompanied by volume reduction and changes in the optical absorption spectrum. This phenomenon has a major influence on properties like the buoyancy or the thermal conductivity of the melt, and ultimately on the chemical and thermal evolution of our planet. Computer simulations using ab initio methods have proven to be a powerful approach to the study of liquid silicate systems[1,2], although not yet including Fe. In this paper, we report ab initio molecular dynamics studies of liquid iron silicate at high pressure (up to 400 GPa) and high temperatures (from 3000K to 6000K) that allow us to predict different properties of the system. We use the spin-polarized formalism and the GGA+U density functional for a better treatment of the iron magnetic moments in the system. Previous studies in the solid phase have shown that GGA predicts fayalite as a metal, while the introduction of U leads to a correct description of the band gap and the magnetic ordering of the system. We extend this analysis to the liquid phase. By means of these simulations we predict the liquid structure and thermodynamic properties of the liquid. We compute the theoretical Hugoniot for the system and find good agreement with values obtained from shock experiments [3]. Our calculations show large differences in the magnitude and orientation of the magnetic moments depending on the choice of functional; the GGA+U functional consistently provides larger values of the individual moments (about 1 unit larger) and of the total magnetization of the system. The high-spin to low-spin transition is predicted to take place at pressures from around 260GPa at 3000K to around 280GPa at 6000K in this iron-rich system. [1] N. P. de Koker, L. Stixrude, B. B. Karki, Geochim Cosmochim Acta 2008, 72, 1427. [2] B. B. Karki, D. Bhattarai, L. Stixrude, Phys. Rev. B 2007, 76, 104205. [3] G. Q. Chen, T. J. Ahrens, E. M. Stolper, Phys. Earth Planet. Inter. 2002, 134, 35.

Munoz Ramo, David; Stixrude, Lars

2010-05-01

402

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

403

NASA Astrophysics Data System (ADS)

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi2Se3. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin-resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin-polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.

Cacho, C.; Crepaldi, A.; Battiato, M.; Braun, J.; Cilento, F.; Zacchigna, M.; Richter, M. C.; Heckmann, O.; Springate, E.; Liu, Y.; Dhesi, S. S.; Berger, H.; Bugnon, Ph.; Held, K.; Grioni, M.; Ebert, H.; Hricovini, K.; Minár, J.; Parmigiani, F.

2015-03-01

404

The prospect of optically inducing and controlling a spin-polarized current in spintronic devices has generated wide interest in the out-of-equilibrium electronic and spin structure of topological insulators. In this Letter we show that only measuring the spin intensity signal over several orders of magnitude by spin-, time-, and angle-resolved photoemission spectroscopy can provide a comprehensive description of the optically excited electronic states in Bi_{2}Se_{3}. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin-resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin-polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds. PMID:25793848

Cacho, C; Crepaldi, A; Battiato, M; Braun, J; Cilento, F; Zacchigna, M; Richter, M C; Heckmann, O; Springate, E; Liu, Y; Dhesi, S S; Berger, H; Bugnon, Ph; Held, K; Grioni, M; Ebert, H; Hricovini, K; Minár, J; Parmigiani, F

2015-03-01

405

Spin-vibronic quantum dynamics for ultrafast excited-state processes.

Ultrafast intersystem crossing (ISC) processes coupled to nuclear relaxation and solvation dynamics play a central role in the photophysics and photochemistry of a wide range of transition metal complexes. These phenomena occurring within a few hundred femtoseconds are investigated experimentally by ultrafast picosecond and femtosecond transient absorption or luminescence spectroscopies, and optical laser pump-X-ray probe techniques using picosecond and femtosecond X-ray pulses. The interpretation of ultrafast structural changes, time-resolved spectra, quantum yields, and time scales of elementary processes or transient lifetimes needs robust theoretical tools combining state-of-the-art quantum chemistry and developments in quantum dynamics for solving the electronic and nuclear problems. Multimode molecular dynamics beyond the Born-Oppenheimer approximation has been successfully applied to many small polyatomic systems. Its application to large molecules containing a transition metal atom is still a challenge because of the nuclear dimensionality of the problem, the high density of electronic excited states, and the spin-orbit coupling effects. Rhenium(I) ?-diimine carbonyl complexes, [Re(L)(CO)3(N,N)](n+) are thermally and photochemically robust and highly flexible synthetically. Structural variations of the N,N and L ligands affect the spectroscopy, the photophysics, and the photochemistry of these chromophores easily incorporated into a complex environment. Visible light absorption opens the route to a wide range of applications such as sensors, probes, or emissive labels for imaging biomolecules. Halide complexes [Re(X)(CO)3(bpy)] (X = Cl, Br, or I; bpy = 2,2'-bipyridine) exhibit complex electronic structure and large spin-orbit effects that do not correlate with the heavy atom effects. Indeed, the (1)MLCT ? (3)MLCT intersystem crossing (ISC) kinetics is slower than in [Ru(bpy)3](2+) or [Fe(bpy)3](2+) despite the presence of a third-row transition metal. Counterintuitively, singlet excited-state lifetime increases on going from Cl (85 fs) to Br (128 fs) and to I (152 fs). Moreover, correlation between the Re-X stretching mode and the rate of ISC is observed. In this Account, we emphasize on the role of spin-vibronic coupling on the mechanism of ultrafast ISC put in evidence in [Re(Br)(CO)3(bpy)]. For this purpose, we have developed a model Hamiltonian for solving an 11 electronic excited states multimode problem including vibronic and SO coupling within the linear vibronic coupling (LVC) approximation and the assumption of harmonic potentials. The presence of a central metal atom coupled to rigid ligands, such as ?-diimine, ensures nuclear motion of small amplitudes and a priori justifies the use of the LVC model. The simulation of the ultrafast dynamics by wavepacket propagations using the multiconfiguration time-dependent Hartree (MCTDH) method is based on density functional theory (DFT), and its time-dependent extension to excited states (TD-DFT) electronic structure data. We believe that the interplay between time-resolved experiments and these pioneering simulations covering the first picoseconds and including spin-vibronic coupling will promote a number of quantum dynamical studies that will contribute to a better understanding of ultrafast processes in a wide range of organic and inorganic chromophores easily incorporated in biosystems or supramolecular devices for specific functions. PMID:25647179

Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal

2015-03-17

406

Dynamical spin-orbital correlation in the frustrated magnet Ba3CuSb2O9.

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. PMID:23771213

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

2013-01-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

408

NASA Astrophysics Data System (ADS)

We report a neutron diffraction and muon spin relaxation ?SR study of static and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional spin-chain system. A proposed model for the antiferromagnetic structure includes: a propagation vector k?AF=(0,0,1), independent of external magnetic fields for fields below a critical value Hc(T). The ordered moments of 2.18 ?B per Co ion are aligned along the crystallographic c axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged ferromagnetically (forming zigzag paths) along one of the axes and antiferromagnetically along the other. The temperature dependence of the sublattice magnetization is consistent with the expectations of the three-dimensional (3D) Ising model. A similar behavior is observed for the internal static fields at different muon stopping sites. Muon time spectra measured at weak longitudinal fields and temperatures much higher than TN can be well described using a single muon site with an exponential muon spin relaxation that gradually changes into an stretched exponential on approaching TN. The temperature-induced changes of the relaxation suggest that the Co fluctuations dramatically slow down and the system becomes less homogeneous as it approaches the antiferromagnetic state.

Kawasaki, Yu; Gavilano, Jorge L.; Keller, Lukas; Schefer, Jürg; Christensen, Niels Bech; Amato, Alex; Ohno, Takashi; Kishimoto, Yutaka; He, Zhangzhen; Ueda, Yutaka; Itoh, Mitsuru

2011-02-01

409

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

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

2014-01-01

410

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

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

2014-01-01

411

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

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

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

2010-02-15

412

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

Kostylev, M. [School of Physics, M013, University of Western Australia, Crawley, Perth 6009, Western Australia (Australia)

2014-06-21

413

Dynamical generation of dark solitons in spin-orbit-coupled Bose–Einstein condensates

NASA Astrophysics Data System (ADS)

We numerically investigate the ground state, the Raman-driving dynamics and the nonlinear excitations of a realized spin-orbit-coupled Bose-Einstein condensate in a one-dimensional harmonic trap. Depending on the Raman coupling and the interatomic interactions, three ground-state phases are identified: stripe, plane wave and zero-momentum phases. A narrow parameter regime with coexistence of stripe and zero-momentum or plane wave phases in real space is found. Several sweep progresses across different phases by driving the Raman coupling linearly in time is simulated and the non-equilibrium dynamics of the system in these sweeps are studied. We find kinds of nonlinear excitations, with the particular dark solitons excited in the sweep from the stripe phase to the plane wave or zero-momentum phase within the trap. Moreover, the number and the stability of the dark solitons can be controlled in the driving, which provide a direct and easy way to generate dark solitons and study their dynamics and interaction properties.

Cao, Shuai; Shan, Chuan-Jia; Zhang, Dan-Wei; Qin, Xizhou; Xu, Jun

2015-02-01

414

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 dry swallow, water swallow, marshmallow swallow, cake swallow, and cookie chewing for a total of five series, with 15 acquisitions per series at a rate of 700 ms per acquisition. A checklist of swallowing events and anatomic landmarks was used to determine which anatomic landmarks are always visible, which phases or swallowing movements are always visible, and which landmarks can be used to measure oral and pharyngeal motion in swallowing. The oral preparatory, oral, and oropharyngeal phases of deglutition were visible in all cases. No aspiration, reflux, or abnormal residue was observed. Spatial resolution allowed for anatomical measurements of laryngeal elevation, oropharyngeal diameter, and tongue base and velum displacement in all cases. SSFSE dynamic MRI is pertinent for evaluation of the anatomical and physiological characteristics of swallow. The temporal parameters, however, cannot be studied using this technique. Motion artifacts preclude its use in the study of mastication. It remains complementary to videofluoroscopy and other techniques in swallow evaluation. PMID:14571329

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

2003-01-01

415

Dynamical Model of the Molten Metal Puddle in Planar Flow Spin Casting

NASA Astrophysics Data System (ADS)

Planar flow spin casting is a single stage rapid manufacturing technique for producing thin metal sheets or ribbons. Liquid metal is forced through a nozzle into a narrow planar gap where a puddle, constrained by surface tension, is formed. Upon contacting a rotating wheel substrate, the metal freezes and a ribbon is spun off. The process is modeled using control volumes to account for unsteady balances that relate puddle dynamics to the macroscopic processing conditions. The puddle meniscus is a flexible boundary for the control volume and motions of the meniscus corresponds to unsteady behavior. Contact line dynamics are incorporated into the system. Periodic cross-stream oscillation defects in the ribbon have been correlated with high-frequency vibrations of the puddle menisci ( ˜1000Hz). In order to determine the source of the puddle vibrations, a dynamical model is formulated and processing conditions for which disturbances to the puddle result in an oscillatory response are sought. Both linear and nonlinear stability analyses of the ODE model system are performed.

Theisen, Eric; Byrne, Cormac; Steen, Paul H.; Weinstein, Steven

2004-11-01

416

Nonadiabatic ab initio molecular dynamics including spin-orbit coupling and laser fields.

Nonadiabatic ab initio molecular dynamics (MD) including spin-orbit coupling (SOC) and laser fields is investigated as a general tool for studies of excited-state processes. Up to now, SOCs are not included in standard ab initio MD packages. Therefore, transitions to triplet states cannot be treated in a straightforward way. Nevertheless, triplet states play an important role in a large variety of systems and can now be treated within the given framework. The laser interaction is treated on a non-perturbative level that allows nonlinear effects like strong Stark shifts to be considered. As MD allows for the handling of many atoms, the interplay between triplet and singlet states of large molecular systems will be accessible. In order to test the method, IBr is taken as a model system, where SOC plays a crucial role for the shape of the potential curves and thus the dynamics. Moreover, the influence of the nonresonant dynamic Stark effect is considered. The latter is capable of controlling reaction barriers by electric fields in time-reversible conditions, and thus a control laser using this effect acts like a photonic catalyst. In the IBr molecule, the branching ratio at an avoided crossing, which arises from SOC, can be influenced. PMID:22452086

Marquetand, Philipp; Richter, Martin; González-Vázquez, Jesús; Sola, Ignacio; González, Leticia

2011-01-01

417

Spin dynamics in the BEC phase of the S=1/2 quantum spin system TlCuCl 3

NASA Astrophysics Data System (ADS)

The copper salt S=1/2 TlCuCl 3 is a three-dimensional quantum spin system with a singlet ground-state of dimer origin. A spin energy gap ??0.7 meV separates the ground-state from the triplet waves, which propagate along all directions in reciprocal space. Across the quantum critical point at Hc= ?/ g?B Bose-Einstein condensation of the triplet quasi-particles has been observed. The inelastic neutron scattering spectra at H> Hc proof the coexistence of a gapless Goldstone mode, which has a linear dispersion, with renormalized quadratic Zeeman modes.

Rüegg, Ch.; Cavadini, N.; Furrer, A.; Krämer, K.; Güdel, H.-U.; Vorderwisch, P.; Habicht, K.; Mutka, H.; Wildes, A.

2004-05-01

418

Spin dynamics in the BEC phase of the S=1\\/2 quantum spin system TlCuCl 3

The copper salt S=1\\/2 TlCuCl3 is a three-dimensional quantum spin system with a singlet ground-state of dimer origin. A spin energy gap ??0.7meV separates the ground-state from the triplet waves, which propagate along all directions in reciprocal space. Across the quantum critical point at Hc=?\\/g?B Bose–Einstein condensation of the triplet quasi-particles has been observed. The inelastic neutron scattering spectra at

Ch. Rüegg; N. Cavadini; A. Furrer; K. Krämer; H.-U Güdel; P. Vorderwisch; K. Habicht; H. Mutka; A. Wildes

2004-01-01

419

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

420

Vortex dynamics in spin-orbit-coupled Bose-Einstein condensates

NASA Astrophysics Data System (ADS)

I use a time-dependent Lagrangian formalism and a variational trial function to study the dynamics of a two-component vortex in a spin-orbit-coupled Bose-Einstein condensate (BEC). For a single-component BEC, various experiments have validated this theoretical approach, for example a thermal quench that yields a quantized vortex in roughly 25% of trials [Freilich et al., Science 329, 1182 (2010), 10.1126/science.1191224]. To be definite, I assume the specific spin-orbit form used by Lin and coworkers [Nature (London) 462, 628 (2009), 10.1038/nature08609; Nature (London) 471, 83 (2011), 10.1038/nature09887] in recent NIST experiments, which introduces a spatial asymmetry because of the external Raman laser beams. I here generalize this formalism to include a two-component order parameter that has quantized circulation in each component but not necessarily with the same circulation. For example, a singly quantized vortex in just one component yields a BEC analog of the half-quantized vortex familiar in 3He-A and in p-wave chiral superconductors. This and other unusual two-component vortices have both periodic trajectories and unbounded trajectories that leave the condensate, depending on the initial conditions. The optimized phase of the order parameter induces a term in the particle current that cancels the contribution from the vector potential, leaving pure circulating current around the vortex.

Fetter, Alexander L.

2014-02-01