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1

Kapellasite: a kagome quantum spin liquid with competing interactions.  

PubMed

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

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

2012-07-20

2

Competing spin pumping effects in magnetic hybrid structures  

SciTech Connect

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., E-mail: aac@df.ufpe.br; Alves Santos, O.; Fonseca Guerra, G. A.; Cunha, R. O.; Rezende, S. M. [Departamento de Física, Universidade Federal de Pernambuco, 50670-901 Recife, PE (Brazil); Rodríguez-Suárez, R. [Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago (Chile)

2014-02-03

3

Competing spin pumping effects in magnetic hybrid structures  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

4

DYNAMIC CHARACTERISTICSOFLIQUID MOTION INPARTIALLYFILLEDTANKS OF SPINNING SPACECRAFT  

E-print Network

DYNAMIC CHARACTERISTICSOFLIQUID MOTION INPARTIALLYFILLEDTANKS OF SPINNING SPACECRAFT BrijN. Agrawal to predict dynamic characteristicsof liquid motion in partially filled tanks of a spinning spacecraft to predict liquid dynamic characteristics in spinning spacecraft. Recently, a finite element model has been

5

Analysis of Switching Dynamics with Competing Support Vector Machines  

E-print Network

1 Analysis of Switching Dynamics with Competing Support Vector Machines Ming-Wei Chang and Chih competing neural networks were used to segment a non-stationary time series, in this article we exploit Annealing, competing experts, expectation maximization, support vector machines, unsupervised time series

Lin, Chih-Jen

6

Spin dynamics in the strong spin-orbit coupling regime  

E-print Network

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... with potential for future applications. The spin-orbit interaction (SOI) is a key tool to electrically manipulate the spin and realize such devices. However, the SOI is a double-edged sword because it will also induce random spin precession through an angle#2...

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

2011-01-01

7

A new type of spin ordering in a random magnet with competing anisotropies  

SciTech Connect

The result of an elastic neutron scattering study of the phase transition in the random magnet with competing anisotropies Fe{sub 0.75}CO{sub 0.25}Br{sub 2} is reported. We found that the ordering of the spin component parallel to the crystalline c axis at the transition from the paramagnetic to antiferromagnetic phase induces an ordering of the spin component perpendicular to it. Thus, there is no boundary separating the higher temperature antiferromagnetic and lower temperature mixed ordering phase. We interpret this new type of spin ordering as arising from a coupling between the orthogonal spin components.

Katsumata, K. [Institute of Physical and Chemical Research, Wako, Saitama (Japan); Shapiro, S.M.; Matsuda, M.; Shirane, G. [Brookhaven National Lab., Upton, NY (United States); Tuchendler, J. [Paris-6 Univ., 75 (France). Lab. de Dispositifs Infrarouge

1992-12-31

8

Competing Spin Phases in Geometrically Frustrated Magnetic Molecules  

Microsoft Academic Search

We identify a class of zero-dimensional classical and quantum Heisenberg spin systems exhibiting anomalous behavior in an external magnetic field B similar to that found for the geometrically frustrated kagome lattice of classical spins. Our calculations for the isotropic Heisenberg model show the emergence of a pronounced minimum in the differential susceptibility dM\\/dB at Bsat\\/3 as the temperature T is

Christian Schröder; Hiroyuki Nojiri; Jürgen Schnack; Peter Hage; Marshall Luban; Paul Kögerler

2005-01-01

9

Coherent spin mixing dynamics in a spin-1 atomic condensate  

SciTech Connect

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

10

Spin-glass dynamics determined from muon spin-relaxation and neutron spin-echo measurements  

SciTech Connect

Muon spin-relaxation (..mu..SR) and neutron spin-echo (NSE) measurements of magnetic-ion correlation times and correlation functions in the spin-glass systems CuMn, AgMn, and AuFe are compared. It is found that the ..mu..SR and NSE measurements are in excellent agreement both above and below the spin-glass freezing temperatures. The experimental results are compared to recent theories of spin-glass dynamics.

Heffner, R.H.; Leon, M.; MacLaughlin, D.E.

1983-01-01

11

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

12

Dynamical Localization in Disordered Quantum Spin Systems  

E-print Network

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

Eman Hamza; Robert Sims; Günter Stolz

2011-08-18

13

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

SciTech Connect

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

14

Ab initio non-relativistic spin dynamics  

NASA Astrophysics Data System (ADS)

Many magnetic materials do not conform to the (anti-)ferromagnetic paradigm where all electronic spins are aligned to a global magnetization axis. Unfortunately, most electronic structure methods cannot describe such materials with noncollinear electron spin on account of formally requiring spin alignment. To overcome this limitation, it is necessary to generalize electronic structure methods and allow each electron spin to rotate freely. Here, we report the development of an ab initio time-dependent non-relativistic two-component spinor (TDN2C), which is a generalization of the time-dependent Hartree-Fock equations. Propagating the TDN2C equations in the time domain allows for the first-principles description of spin dynamics. A numerical tool based on the Hirshfeld partitioning scheme is developed to analyze the time-dependent spin magnetization. In this work, we also introduce the coupling between electron spin and a homogenous magnetic field into the TDN2C framework to simulate the response of the electronic spin degrees of freedom to an external magnetic field. This is illustrated for several model systems, including the spin-frustrated Li3 molecule. Exact agreement is found between numerical and analytic results for Larmor precession of hydrogen and lithium atoms. The TDN2C method paves the way for the ab initio description of molecular spin transport and spintronics in the time domain.

Ding, Feizhi; Goings, Joshua J.; Frisch, Michael J.; Li, Xiaosong

2014-12-01

15

Spin-current-induced dynamics in ferromagnetic nanopillars of lateral spin-valve structures  

E-print Network

Spin-current-induced dynamics in ferromagnetic nanopillars of lateral spin-valve structures J 4 February 2009 Under electrical injection, spin accumulation occurs in lateral spin valves, and the possibility of pure spin-current-induced magnetization reversal. Here, we generate a pure spin current

Otani, Yoshichika

16

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

17

A new spin on protein dynamics.  

PubMed

Site-directed spin labeling is a general method for investigating structure and conformational switching in soluble and membrane proteins. It will also be an important tool for exploring protein backbone dynamics. A semi-empirical analysis of nitroxide sidechain dynamics in spin-labeled proteins reveals contributions from fluctuations in backbone dihedral angles and rigid-body (collective) motions of alpha helices. Quantitative analysis of sidechain dynamics is sometimes possible, and contributions from backbone modes can be expressed in terms of relative order parameters and rates. Dynamic sequences identified by site-directed spin labeling correlate with functional domains, and so nitroxide scanning could provide an efficient strategy for identifying such domains in high-molecular weight proteins, supramolecular complexes and membrane proteins. PMID:12069788

Columbus, Linda; Hubbell, Wayne L

2002-06-01

18

Spinning compact binary dynamics and chameleon orbits  

E-print Network

We analyse the conservative evolution of spinning compact binaries to second post-Newtonian (2PN) order accuracy, with leading order spin-orbit, spin-spin and mass quadrupole-monopole contributions included. As a main result we derive a closed system of first order differential equations in a compact form, for a set of dimensionless variables encompassing both orbital elements and spin angles. These evolutions are constrained by conservation laws holding at 2PN order. As required by the generic theory of constrained dynamical systems we perform a consistency check and prove that the constraints are preserved by the evolution. We apply the formalism to show the existence of chameleon orbits, whose local, orbital parameters evolve from elliptic (in the Newtonian sense) near pericenter, towards hyperbolic at large distances. This behavior is consistent with the picture that General Relativity predicts stronger gravity at short distances than Newtonian theory does.

László Árpád Gergely; Zoltán Keresztes

2014-11-14

19

Spinning compact binary dynamics and chameleon orbits  

NASA Astrophysics Data System (ADS)

We analyze the conservative evolution of spinning compact binaries to second post-Newtonian (2PN) order accuracy, with leading-order spin-orbit, spin-spin and mass quadrupole-monopole contributions included. As a main result we derive a closed system of first-order differential equations in a compact form, for a set of dimensionless variables encompassing both orbital elements and spin angles. These evolutions are constrained by conservation laws holding at 2PN order. As required by the generic theory of constrained dynamical systems we perform a consistency check and prove that the constraints are preserved by the evolution. We apply the formalism to show the existence of chameleon orbits, whose local, orbital parameters evolve from elliptic (in the Newtonian sense) near pericenter, towards hyperbolic at large distances. This behavior is consistent with the picture that general relativity predicts stronger gravity at short distances than Newtonian theory does.

Gergely, László Árpád; Keresztes, Zoltán

2015-01-01

20

Dynamic trajectories of growth and nitrogen capture by competing plants.  

PubMed

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

21

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

22

A System Dynamics simulation analysis of the Influencing Factors of coalmine special operators' competency by training  

Microsoft Academic Search

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

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

2010-01-01

23

Structurally Dynamic Spin Market Networks  

NASA Astrophysics Data System (ADS)

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

Horváth, Denis; Kuscsik, Zoltán

24

Many-body singlets by dynamic spin polarization  

E-print Network

We show that dynamic spin polarization by collective raising and lowering operators can drive a spin ensemble from arbitrary initial state to many-body singlets, the zero-collective-spin states with large scale entanglement. For an ensemble of $N$ arbitrary spins, both the variance of the collective spin and the number of unentangled spins can be reduced to O(1) (versus the typical value of O(N)), and many-body singlets can be occupied with a population of $\\sim 20 %$ independent of the ensemble size. We implement this approach in a mesoscopic ensemble of nuclear spins through dynamic nuclear spin polarization by an electron. The result is of two-fold significance for spin quantum technology: (1) a resource of entanglement for nuclear spin based quantum information processing; (2) a cleaner surrounding and less quantum noise for the electron spin as the environmental spin moments are effectively annihilated.

Wang Yao

2011-01-20

25

Thermostatting the atomic spin dynamics from controlled demons  

NASA Astrophysics Data System (ADS)

Deterministic dynamics in extended phase space of a constant temperature interacting spin system is formulated. The spin temperature is recovered through the constrained equation of motion and is in agreement with Rugh's geometrical approach to temperature for classical Heisenberg spin systems. Detailed comparisons are investigated between state-of-the-art stochastic spin dynamics and deterministic dynamics using a chain of thermostats, for which an accelerated convergence structure is found.

Thibaudeau, Pascal; Beaujouan, David

2012-03-01

26

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

27

Competing valence-bond states of spin-3/2 fermions on a strongly coupled ladder  

NASA Astrophysics Data System (ADS)

We study the possible ground-state configurations of two strongly coupled chains of charge neutral spin-3/2 fermionic atoms interacting via short-range van der Waals interaction. The coupling between the two chains is realized by a relatively large hopping amplitude. Exploiting the fact that such a ladder configuration can be mapped to an effective one-band model, we analyze the emerging ground states of the system. We show that various spatially inhomogeneous states, valence-bond states, and plaquette states compete depending on the filling and the ratio of the interaction strengths in the singlet and quintet scattering channel. We find that a Luttinger liquid state is the ground state of the strongly coupled ladder in an extended region of the parameter space, and we also show that a topologically nontrivial charge Haldane state can emerge in the strongly coupled ladder at quarter and three-quarter fillings.

Szirmai, E.; Nonne, H.

2014-12-01

28

Decoherence and dynamical decoupling control of nitrogen-vacancy center electron spins in nuclear spin baths  

E-print Network

We theoretically study the decoherence and the dynamical decoupling control of nitrogen-vacancy center electron spins in high-purity diamond, where the hyperfine interaction with $^{13}$C nuclear spins is the dominating decoherence mechanism. The decoherence is formulated as the entanglement between the electron spin and the nuclear spins, which is induced by nuclear spin bath evolution conditioned on the electron spin state. The nuclear spin bath evolution is driven by elementary processes such as single spin precession and pairwise flip-flops. The importance of different elementary processes in the decoherence depends on the strength of the external magnetic field.

Zhao, Nan; Liu, Ren-Bao

2011-01-01

29

Decoherence and dynamical decoupling control of nitrogen-vacancy center electron spins in nuclear spin baths  

E-print Network

We theoretically study the decoherence and the dynamical decoupling control of nitrogen-vacancy center electron spins in high-purity diamond, where the hyperfine interaction with $^{13}$C nuclear spins is the dominating decoherence mechanism. The decoherence is formulated as the entanglement between the electron spin and the nuclear spins, which is induced by nuclear spin bath evolution conditioned on the electron spin state. The nuclear spin bath evolution is driven by elementary processes such as single spin precession and pairwise flip-flops. The importance of different elementary processes in the decoherence depends on the strength of the external magnetic field.

Nan Zhao; Sai-Wah Ho; Ren-Bao Liu

2011-08-11

30

EFFECTS OF NUCLEAR SPIN POLARIZATION ON REACTION DYNAMICS IN PHOTOSYNTHETIC  

E-print Network

- cally induced dynamic nuclear polarization [CIDNP]) (Kaptein and Oosterhoff, 1969; Closs, 1969EFFECTS OF NUCLEAR SPIN POLARIZATION ON REACTION DYNAMICS IN PHOTOSYNTHETIC BACTERIAL REACTION-equilibrium distributions of nuclear spin states (nuclear spin polarization). This polarization will persist until the 3PI

Boxer, Steven G.

31

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

32

NMR probe for dynamic-angle spinning  

SciTech Connect

We describe the design of a probe for dynamic-angle spinning (DAS) NMR experiments, comprised of a spinning cylindrical sample holder whose axis may be reoriented rapidly between discrete directions within the bore of a superconducting magnet. This allows the refocusing of nuclear spin magnetization that evolves under anisotropic interactions such as chemical shift anisotropy and quadrupolar coupling, providing high resolution NMR spectra for quadrupolar nuclei in solid materials. The probe includes an axial air delivery system to bearing and drive jets which support and spin a rotor containing the sample. Axis reorientation is accomplished with a pulley attached to the probehead and coupled to a stepping motor outside of the magnet. The choice of motor and gear ratio is based on an analysis of the moments of inertia of the motor and load, the desired angular resolution, and simplicity of design. Control of angular accuracy and precision are discussed, as well as the efficiency of radiofrequency irradiation and detection. High resolution DAS spectra of oxygen-17 and aluminum-27 nuclei in polycrystalline minerals illustrate the experimental capabilities.

Mueller, K.T.; Chingas, G.C.; Pines, A. (Materials Sciences Division, Lawrence Berkeley Laboratory and Department of Chemistry, University of California, Berkeley, California 94720 (USA))

1991-06-01

33

Dynamics of Spin-2 Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

We numerically simulate the dynamics of a spin-2 Bose-Einstein condensate. We find that the initial phase plays an important role in the spin component oscillations. The spin mixing processes can fully cancel out due to quantum interference when taking some initial special phase. In all the spin mixing processes, the total spin is conversed. When the initial population is mainly occupied by a component with the maximal or minimal magnetic quantum number, the oscillations of spin components cannot happen due to the total spin conversation. The presence of quadratic Zeeman energy terms suppresses some spin mixing processes so that the oscillations of spin components are suppressed in some initial spin configuration. However, the linear Zeeman energy terms have no effects on the spin mixing processes.

Hou, Jing-Min

2007-12-01

34

Spin dynamics simulation of electron spin relaxation in Ni2 +(aq)  

NASA Astrophysics Data System (ADS)

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 Ni2 + ion. The spin-lattice (T1) and spin-spin (T2) 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; Mareš, Ji?í; Vaara, Juha

2014-07-01

35

Spin decoherence from Hamiltonian dynamics in quantum dots  

SciTech Connect

The dynamics of a spin-1/2 particle coupled to a nuclear spin bath through an isotropic Heisenberg interaction is studied as a model for the spin decoherence in quantum dots. The time-dependent polarization of the central spin is calculated as a function of the bath-spin distribution and the polarizations of the initial bath state. For short times, the polarization of the central spin shows a Gaussian decay, and at later times it is revived displaying nonmonotonic time dependence. The decoherence time scale depends on moments of the bath-spin distribution, and also on the polarization strengths in various bath-spin channels. The bath polarizations have a tendency to increase the decoherence time scale. The effective dynamics of the central spin polarization is shown to be described by a master equation with non-Markovian features.

Bhaktavatsala Rao, D. D.; Ravishankar, V.; Subrahmanyam, V. [Department of Physics, Indian Institute of Technology, Kanpur-208016 (India)

2006-08-15

36

Simulating electron spin resonance spectra of nitroxide spin labels from molecular dynamics and stochastic trajectories  

PubMed Central

Simulating electron spin resonance spectra of nitroxide spin labels from motional models is necessary for the quantitative analysis of experimental spectra. We present a framework for modeling the spin label dynamics by using trajectories such as those from molecular dynamics (MD) simulations combined with stochastic treatment of the global protein tumbling. This is achieved in the time domain after two efficient numerical integrators are developed: One for the quantal dynamics of the spins and the other for the classical rotational diffusion. For the quantal dynamics, we propagate the relevant part of the spin density matrix in Hilbert space. For the diffusional tumbling, we work with quaternions, which enables the treatment of anisotropic diffusion in a potential expanded as a sum of spherical harmonics. Time-averaging arguments are invoked to bridge the gap between the smaller time step of the MD trajectories and the larger time steps appropriate for the rotational diffusion and?or quantal spin dynamics. PMID:18447510

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

2008-01-01

37

Neutron Spin Echo Studies of Protein Dynamics  

NASA Astrophysics Data System (ADS)

Neutron spin-echo (NSE) spectroscopy was used to study structural fluctuations that occur in hemoglobin (Hb) and myglobin (Mb) in solution. Using NSE in conjunction with Wide Angle X-ray Scattering (WAXS) to very high momentum transfer, q (up to 0.62 inverse Angstroms), the internal dynamics of these proteins were characterized at the level of the dynamical pair correlation function and self-correlation function in the time range of several picoseconds to a few nanoseconds. Comparison of data from the two homologous proteins collected at different temperatures and protein concentrations was used to assess the contributions to the data made by translational and rotational diffusion and internal modes of motion.

Lal, Jyotsana; Fouquet, Peter; Maccarini, Marco; Makowski, Lee

2010-03-01

38

Spin and dynamics in relativistic quantum W. N. Polyzou,  

E-print Network

Spin and dynamics in relativistic quantum theories W. N. Polyzou, Department of Physics in defining the spin and orbital angular momentum content of hadronic systems is discussed. 1 Introduction There is a great deal of interest in the distribution of spin and orbital angular momentum in hadronic systems

Polyzou, Wayne

39

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

40

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

SciTech Connect

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

41

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

ERIC Educational Resources Information Center

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

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

2001-01-01

42

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

43

NMR multiple quantum coherences in quasi-one-dimensional spin systems: Comparison with ideal spin-chain dynamics  

E-print Network

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

44

Electron-spin dynamics in elliptically polarized light waves  

NASA Astrophysics Data System (ADS)

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

Bauke, Heiko; Ahrens, Sven; Grobe, Rainer

2014-11-01

45

Analytical study of spinning solid upper stage dynamics  

NASA Astrophysics Data System (ADS)

Analytical solutions for the spinning vehicle dynamics during the burning phase in vacuum were derived. These solutions explicity incorporate the effects of thrust misalignment, gravity gradient torques, jet damping, dynamic unbalance and spin rate variations. These expressions are useful in preliminary design studies of spinning upper stages of launch vehicles. The main advantages of this approach lies in the fact that the time required to carry out detailed parametric studies is one order lower than regular 6 DOF simulations. The application of this approach for a typical Shuttle Launched Spinning Solid Upper Stage (SSUS) mission incorporating AS-05-A payload is illustrated.

Menon, K. A. P.; Sundararajan, N.

1980-11-01

46

Electron Spin Dynamics in Semiconductor Quantum Dots  

SciTech Connect

An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.

Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T. [Universite de Toulouse, LPCNO, INSA-CNRS-UPS, 135 avenue de Rangueil, 31077 Toulouse (France); Krebs, O.; Lemaitre, A.; Voisin, P. [Laboratoire de Photonique et Nanostructures, route de Nozay, 91460 Marcoussis (France)

2011-07-15

47

Dynamics of two competing species in the presence of Lévy noise sources.  

PubMed

We consider a Lotka-Volterra system of two competing species subject to multiplicative ?-stable Lévy noise. The interaction parameter between the species is a random process which obeys a stochastic differential equation with a generalized bistable potential in the presence both of a periodic driving term and an additive ?-stable Lévy noise. We study the species dynamics, which is characterized by two different regimes, exclusion of one species and coexistence of both. We find quasiperiodic oscillations and stochastic resonance phenomenon in the dynamics of the competing species, analyzing the role of the Lévy noise sources. PMID:20866579

La Cognata, A; Valenti, D; Dubkov, A A; Spagnolo, B

2010-07-01

48

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

NASA Astrophysics Data System (ADS)

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

Mosshammer, Klemens; Brandes, Tobias

2014-10-01

49

Carrier and spin dynamics in charged quantum dots  

Microsoft Academic Search

Carrier and spin dynamics are measured in meutral, positively and negatively charged quantum dots using polarization-sensitive time-resolved photoluminescence. Carrier capture rates are observed to be strongly enhanced in charged quantum dots, suggesting that electron-hole scattering dominates this process. For positive quantum dots, the enhanced spin-polarized electron capture rate eliminates loss of electron spin information in the GaAs barriers prior to

Kimberley C. Hall; Kenan Gundogdu; Thomas F. Boggess; Oleg B. Shchekin; Dennis G. Deppe

2004-01-01

50

Dynamics of test bodies with spin in de Sitter spacetime  

SciTech Connect

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

51

Dynamics of Spin(1)\\/(2) Quantum Plasmas  

Microsoft Academic Search

The fully nonlinear governing equations for spin-(1)\\/(2) quantum plasmas are presented. Starting from the Pauli equation, the relevant plasma equations are derived, and it is shown that nontrivial quantum spin couplings arise, enabling studies of the combined collective and spin dynamics. The linear response of the quantum plasma in an electron-ion system is obtained and analyzed. Applications of the theory

Mattias Marklund; Gert Brodin

2007-01-01

52

Dynamics of spin 1/2 quantum plasmas  

E-print Network

The fully nonlinear governing equations for spin 1/2 quantum plasmas are presented. Starting from the Pauli equation, the relevant plasma equations are derived, and it is shown that nontrivial quantum spin couplings arise, enabling studies of the combined collective and spin dynamics. The linear response of the quantum plasma in an electron--ion system is obtained and analyzed. Applications of the theory to solid state and astrophysical systems as well as dusty plasmas are pointed out.

M. Marklund; G. Brodin

2006-12-06

53

Magnetization dynamics with a spin-transfer torque  

NASA Astrophysics Data System (ADS)

The magnetization reversal and dynamics of a spin valve pillar, whose lateral size is 64×64 nm2, are studied by using micromagnetic simulation in the presence of spin-transfer torque. Spin torques display both characteristics of magnetic damping (or antidamping) and of an effective magnetic field. For a steady-state current, both M-I and M-H hysteresis loops show unique features, including multiple jumps, unusual plateaus, and precessional states. These states originate from the competition between the energy dissipation due to Gilbert damping and the energy accumulation due to the spin torque supplied by the spin current. The magnetic energy oscillates as a function of time even for a steady-state current. For a pulsed current, the minimum width and amplitude of the spin torque for achieving current-driven magnetization reversal are quantitatively determined. The spin torque also shows very interesting thermal activation that is fundamentally different from an ordinary damping effect.

Li, Z.; Zhang, S.

2003-07-01

54

Self-consistent calculation of spin transport and magnetization dynamics  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

55

Self-quenching of nuclear spin dynamics in the central spin problem  

NASA Astrophysics Data System (ADS)

We consider, in the framework of the central spin s =1/2 model, driven dynamics of two electrons in a double quantum dot subject to hyperfine interaction with nuclear spins and spin-orbit coupling. The nuclear subsystem dynamically evolves in response to Landau-Zener singlet-triplet transitions of the electronic subsystem controlled by external gate voltages. Without noise and spin-orbit coupling, subsequent Landau-Zener transitions die out after about 104 sweeps, the system self-quenches, and nuclear spins reach one of the numerous glassy dark states. We present an analytical model that captures this phenomenon. We also account for the multi-nuclear-specie content of the dots and numerically determine the evolution of around 107 nuclear spins in up to 2×105 Landau-Zener transitions. Without spin-orbit coupling, self-quenching is robust and sets in for arbitrary ratios of the nuclear spin precession times and the waiting time between Landau-Zener sweeps as well as under moderate noise. In the presence of spin-orbit coupling of a moderate magnitude, and when the waiting time is in resonance with the precession time of one of the nuclear species, the dynamical evolution of nuclear polarization results in stroboscopic screening of spin-orbit coupling. However, small deviations from the resonance or strong spin-orbit coupling destroy this screening. We suggest that the success of the feedback loop technique for building nuclear gradients is based on the effect of spin-orbit coupling.

Brataas, Arne; Rashba, Emmanuel I.

2014-01-01

56

Global attractors and extinction dynamics of cyclically competing species.  

PubMed

Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species' concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species' global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases. PMID:23767569

Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin

2013-05-01

57

Domain-wall spin dynamics in kagome antiferromagnets.  

PubMed

We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets. PMID:22243109

Lhotel, E; Simonet, V; Ortloff, J; Canals, B; Paulsen, C; Suard, E; Hansen, T; Price, D J; Wood, P T; Powell, A K; Ballou, R

2011-12-16

58

Domain-Wall Spin Dynamics in Kagome Antiferromagnets  

NASA Astrophysics Data System (ADS)

We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.

Lhotel, E.; Simonet, V.; Ortloff, J.; Canals, B.; Paulsen, C.; Suard, E.; Hansen, T.; Price, D. J.; Wood, P. T.; Powell, A. K.; Ballou, R.

2011-12-01

59

Optimized dynamical control of state transfer through noisy spin chains  

E-print Network

We propose a method of optimally controlling the tradeoff of speed and fidelity of state transfer through a noisy quantum channel (spin-chain). This process is treated as qubit state-transfer through a fermionic bath. We show that dynamical modulation of the boundary-qubits levels can ensure state transfer with the best tradeoff of speed and fidelity. This is achievable by dynamically optimizing the transmission spectrum of the channel. The resulting optimal control is robust against both static and fluctuating noise in the channel's spin-spin couplings. It may also facilitate transfer in the presence of diagonal disorder (on site energy noise) in the channel.

Analia Zwick; Gonzalo A. Alvarez; Guy Bensky; Gershon Kurizki

2015-01-09

60

Dynamic control of spin wave spectra using spin-polarized currents  

SciTech Connect

We describe a method of controlling the spin wave spectra dynamically in a uniform nanostripe waveguide through spin-polarized currents. A stable periodic magnetization structure is observed when the current flows vertically through the center of nanostripe waveguide. After being excited, the spin wave is transmitted at the sides of the waveguide. Numerical simulations of spin-wave transmission and dispersion curves reveal a single, pronounced band gap. Moreover, the periodic magnetization structure can be turned on and off by the spin-polarized current. The switching process from full rejection to full transmission takes place within less than 3?ns. Thus, this type magnonic waveguide can be utilized for low-dissipation spin wave based filters.

Wang, Qi; Zhang, Huaiwu, E-mail: hwzhang@uestc.edu.cn; Tang, Xiaoli; Bai, Feiming; Zhong, Zhiyong, E-mail: zzy@uestc.edu.cn [State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054 (China); Fangohr, Hans [Faculty of Engineering and the Environment, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2014-09-15

61

Spin-liquid phase due to competing classical orders in the semiclassical theory of the Heisenberg model with ring exchange on an anisotropic triangular lattice  

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

62

Coherent spin dynamics in spin-imbalanced ferromagnetic spinor condensates plink  

NASA Astrophysics Data System (ADS)

We study the coherent spin dynamics of a ferromagnetic spinor Bose–Einstein condensate (BEC) in its domain formation process with an arbitrary spin configuration. Through a simplified schematic view of the domain structure, a semiclassical theory that captures the essential dynamics of the system is presented, and the coherent spin mixing dynamics can be understood in terms of oscillation in the phase space diagram. Using the phase diagram analysis method, we identify new phases, including the ? phase oscillation and the running phase for the spin-imbalanced ferromagnetic spinor BEC. Project supported by the National Natural Science Foundation of China (Grant No. 11104217), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2014JQ1022), and the Youth Foundation of XUPT, China (Grant No. ZL2013-36).

Qiu, Hai-Bo; Wu, Li-Wei

2015-01-01

63

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

PubMed

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

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

2014-09-01

64

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

65

NMR with generalized dynamics of spin and spatial coordinates  

SciTech Connect

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

66

Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition  

SciTech Connect

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

67

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

68

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

69

Molecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle Fibers  

E-print Network

Molecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle ABSTRACT We have developed a computational molecular dynamics technique to simulate the motions of spin determined molecular dynamics simulation conditions necessary for obtaining a convergent orientational

Thomas, David D.

70

Effect of cosmic string on spin dynamics  

E-print Network

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

Chowdhury, Debashree

2014-01-01

71

Effect of cosmic string on spin dynamics  

E-print Network

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

72

Computation and analysis of spin dynamics  

NASA Astrophysics Data System (ADS)

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

Balandin, Vladimir; Berz, Martin; Golubeva, Nina

1997-02-01

73

Dynamics of self-organized driven particles with competing range interaction  

NASA Astrophysics Data System (ADS)

Nonequilibrium self-organized patterns formed by particles interacting through competing range interaction are driven over a substrate by an external force. We show that, with increasing driving force, the preexisted static patterns evolve into dynamic patterns either via disordered phase or depinned patterns or via the formation of nonequilibrium stripes. Strikingly, the stripes are formed either in the direction of the driving force or in the transverse direction, depending on the pinning strength. The revealed dynamical patterns are summarized in a dynamical phase diagram.

Zhao, H. J.; Misko, V. R.; Peeters, F. M.

2013-08-01

74

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

75

Ultrafast Spin Dynamics Including Spin-Orbit Interaction in Semiconductors Michael Krau,* Martin Aeschlimann, and Hans Christian Schneider  

E-print Network

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

76

Number Fluctuation Dynamics of Atomic Spin Mixing inside a Condensate  

SciTech Connect

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

77

Dynamics of the two-dimensional gonihedric spin model  

Microsoft Academic Search

In this paper, we study dynamical aspects of the two-dimensional (2D) gonihedric spin model using both numerical and analytical methods. This spin model has vanishing microscopic surface tension and it actually describes an ensemble of loops living on a 2D surface. The self-avoidance of loops is parametrized by a parameter kappa . The kappa=0 model can be mapped to one

D. Espriu; A. Prats

2004-01-01

78

Enhancement of spin coherence in a spin-1 Bose-Einstein condensate by dynamical decoupling approaches  

SciTech Connect

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

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

2011-07-15

79

Collective Dynamics in Spin-Textured Electronic Systems  

NASA Astrophysics Data System (ADS)

In chapter I and II, we develop the hydrodynamic theory of collinear spin currents coupled to magnetization dynamics in metallic ferromagnets. The collective spin density couples to the spin current through a U(1) Berry-phase gauge field determined by the local texture and dynamics of the magnetization. We determine phenomenologically the dissipative corrections to the equation of motion for the electronic current, which consist of a dissipative spin-motive force generated by magnetization dynamics and a magnetic texture-dependent resistivity tensor. The reciprocal dissipative, adiabatic spin torque on the magnetic texture follows from the Onsager principle. By applying general thermodynamic relations, we determine a lower bound on the magnetic-texture resistivity. We investigate the effects of thermal fluctuations and find that electronic dynamics contribute to a nonlocal Gilbert damping tensor in the Landau-Lifshitz-Gilbert equation for the magnetization. In chapter III, we apply our general theory to soliton dynamics in spin-textured metals. We find it necessary to modify the Landau-Lifshitz-Gilbert equation and the corresponding solitonic equations of motion to include higher-order texture effects stemming hydrodynamic backaction. As an example, we consider the gyration of a vortex in a point-contact spin valve, and discuss modifications of orbit radius, frequency, and dissipation power. In chapter IV, we generalize our hydrodynamic theory to a kinetic equation, which we derive in a semiclassical expansion of the density-matrix equation of motion up to the first order in quantum mechanical corrections for a general two-band Hamiltonian. We find, in addition to corrections to the single-particle equation of motion due to Berry curvatures, a modification to the phase-space density of states, and interband terms associated with transport through a general curved phase space. We apply our kinetic equation to the case of inhomogeneities stemming from gauge potentials such as electromagnetic perturbations, and specifically to the electromagnetic response of massive 2D Dirac fermions.

Wong, Clement H.

2010-06-01

80

Tunable nonequilibrium dynamics of field quenches in spin ice.  

PubMed

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

81

Tunable nonequilibrium dynamics of field quenches in spin ice  

PubMed Central

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

82

Spin-orbital dynamics in a system of polar molecules.  

PubMed

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

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

2014-01-01

83

Quantum Computation and Quantum Spin Dynamics  

Microsoft Academic Search

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

84

Soliton dynamics in a spin nematic  

SciTech Connect

One-dimensional localized waves, which can be considered as soliton elementary excitations, exist in a magnet with a unit spin and comparable bilinear and biquadratic spin-spin interactions, with which the state of spin nematic is realized. These excitations are characterized by a certain momentum P and a certain energy E. The structure of these solitons has been found, and the E = E(P) dependence, which plays the role of the dispersion law of these soliton elementary excitations, has been constructed. The energy of a soliton with a certain momentum is shown to be lower than that of the quasiparticles of a linear theory. At small momenta, these E = E(P) dependences of the soliton and quasiparticles coincide asymptotically. The dependence of the soliton energy on the soliton momentum is a periodic function with a period P{sub 0} = {pi}{Dirac_h}/a, whose value does not depend on exchange integrals and depends only on a single crystal parameter, namely, the interatomic distance a. These soliton excitations have common features with the so-called Lieb states, which are well known in many condensed matter models.

Ivanov, B. A. [National Academy of Sciences of Ukraine, Institute of Magnetism (Ukraine)], E-mail: bivanov@i.com.ua; Khymyn, R. S. [Taras Shevchenko University (Ukraine)

2007-04-15

85

Destination state screening of active spaces in spin dynamics simulations.  

PubMed

We propose a novel avenue for state space reduction in time domain Liouville space spin dynamics simulations, using detectability as a selection criterion--only those states that evolve into or affect other detectable states are kept in the simulation. This basis reduction procedure (referred to as destination state screening) is formally exact and can be applied on top of the existing state space restriction techniques. As demonstrated below, in many cases this results in further reduction of matrix dimension, leading to considerable acceleration of many spin dynamics simulation types. Destination state screening is implemented in the latest version of the Spinach library (http://spindynamics.org). PMID:21498096

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

2011-06-01

86

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

87

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

88

STAR results on longitudinal spin dynamics  

E-print Network

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

89

Controlling the quantum dynamics of a mesoscopic spin bath in diamond  

PubMed Central

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

90

Spin dynamics in storage rings and linear accelerators  

SciTech Connect

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

Irwin, J.

1994-04-01

91

Record dynamics in spin glassses, superconductors and  

E-print Network

Model of co-evolving biological species Restricted Occupancy Model of vortex dynamics in type II extinction rate for species of such sparse numbers thus reducing the diversity. This is one reason proposed

Jensen, Henrik Jeldtoft

92

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

PubMed Central

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

Maryasov, Alexander G.

2012-01-01

93

Electrical injection of spin-polarized electrons and electrical detection of dynamic nuclear polarization using a Heusler alloy spin source  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

94

Dynamics of the two-dimensional gonihedric spin model  

E-print Network

In this paper we study dynamical aspects of the two-dimensional gonihedric spin model using both numerical and analytical methods. This spin model has vanishing microscopic surface tension and it actually describes an ensemble of loops living on a 2D surface. The self-avoidance of loops is parametrized by a parameter $\\kappa$. The $\\kappa=0$ model can be mapped to one of the six-vertex models discussed by Baxter and it does not have critical behavior. We have found that $\\kappa\

D. Espriu; A. Prats

2005-11-15

95

Covariant hamiltonian spin dynamics in curved space-time  

E-print Network

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; van Holten, J W

2015-01-01

96

Spin Transport and Dynamics in Antiferromagnetic Metals and Magnetic Insulators  

NASA Astrophysics Data System (ADS)

It is demonstrated that in an antiferromagnetic metal a steady-state transport current generates a current-induced out-of-plane spin density, resulting in torques on the magnetization. This spin density is parameterized by a velocity that is proportional to the current. The generalization of the non-linear sigma model equation of motion for antiferromagnetic magnetization dynamics in an antiferromagnetic metal in the presence of a transport current is presented. From this equation of motion a current-induced shift of the spin-wave dispersion is found, as well as current-induced torques that lead to current-driven antiferromagnetic domain wall motion. A key finding is that the form of the current-induced spin density, expressed in terms of the Néèl vector is similar to the current-induced spin density in ferromagnets with the Néèl vector replaced by the magnetization direction. The velocity that characterizes the efficiency of the coupling between current and magnetization is calculated, using linear-response theory in the Boltzmann transport regime. In the absence of dissipation, current-driven antiferromagnetic domain walls are found to move with this characteristic velocity. When magnetization damping is included, the domain wall moves a finite amount and then stops, similar to the intrinsic pinning of current-driven ferromagnetic domain walls. Like in the latter case, including dissipative coupling or non-adiabatic effects between current and magnetization removes this intrinsic pinning. In magnetic insulators there is no transport of electronic charge. Still, there can be transport of spin in the form of spin waves, or, in their quantized form, magnons. Spin transport, carried by quasi-equilibrium magnons, in a magnetic insulator within a Boltzmann transport framework is considered. The spin resistivity of quasi-equilibrium magnons is found to be strongly reduced in comparison with equilibrium magnons, a property that may be useful in designing magnon spintronics applications. The contribution of magnon interactions to their resistivity has been studied for the reason that these dominate in the materials that are experimentally relevant, such as yttrium-iron-garnet (YIG). Firstly, the spin resistivity of a magnon gas using the simplest model, the Heisenberg model, is used. The investigation of material-specific models, in particular for YIG, is then presented. Despite the simplified model, the main qualitative result, the reduction of spin resistivity as a result of enhancing the magnon number by pumping, remains valid. This is because it only depends on the bosonic nature of the magnon excitations that leads to enhanced scattering into states that are already occupied

Swaving, A. C.

2012-03-01

97

Far-from-equilibrium monopole dynamics in spin ice  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

98

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

99

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

PubMed

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

100

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

SciTech Connect

Recent research indicates that the leading edge of lamellipodia of myogenic cells (myoblasts and myotubes) contains presumptive fusion sites, yet the mechanisms that render the plasma membrane fusion-competent remain largely unknown. Here we show that dynamic clustering and dispersion of lipid rafts contribute to both cell adhesion and plasma membrane union during myogenic cell fusion. Adhesion-complex proteins including M-cadherin, {beta}-catenin, and p120-catenin accumulated at the leading edge of lamellipodia, which contains the presumptive fusion sites of the plasma membrane, in a lipid raft-dependent fashion prior to cell contact. In addition, disruption of lipid rafts by cholesterol depletion directly prevented the membrane union of myogenic cell fusion. Time-lapse recording showed that lipid rafts were laterally dispersed from the center of the lamellipodia prior to membrane fusion. Adhesion proteins that had accumulated at lipid rafts were also removed from the presumptive fusion sites when lipid rafts were laterally dispersed. The resultant lipid raft- and adhesion complex-free area at the leading edge fused with the opposing plasma membrane. These results demonstrate a key role for dynamic clustering/dispersion of lipid rafts in establishing fusion-competent sites of the myogenic cell membrane, providing a novel mechanistic insight into the regulation of myogenic cell fusion.

Mukai, Atsushi [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)] [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan); Kurisaki, Tomohiro [Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan)] [Department of Growth Regulation, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan); Sato, Satoshi B. [Research Center for Low Temperature and Material Sciences, Kyoto University, Yoshida-honmachi, Kyoto 606-8501 (Japan)] [Research Center for Low Temperature and Material Sciences, Kyoto University, Yoshida-honmachi, Kyoto 606-8501 (Japan); Kobayashi, Toshihide [Lipid Biology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198 (Japan)] [Lipid Biology Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198 (Japan); Kondoh, Gen [Laboratory of Animal Experiments for Regeneration, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan)] [Laboratory of Animal Experiments for Regeneration, Institute for Frontier Medical Sciences, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507 (Japan); Hashimoto, Naohiro, E-mail: nao@nils.go.jp [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)] [Department of Regenerative Medicine, National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, 36-3 Gengo, Morioka, Oobu, Aichi 474-8522 (Japan)

2009-10-15

101

Spin transport and magnetization dynamics in various magnetic systems  

NASA Astrophysics Data System (ADS)

The general theme of the thesis is the interplay between magnetization dynamics and spin transport. The main presentation is divided into three parts. The first part is devoted to deepening our understanding on magnetic damping of ferromagnetic metals, which is one of the long-standing issues in conventional spintronics that has not been completely understood. For a nonuniformly-magnetized ferromagnetic metal, we find that the damping is nonlocal and is enhanced as compared to that in the uniform case. It is therefore necessary to generalize the conventional Landau-Lifshitz-Gilbert equation to include the additional damping. In a different vein, the decay mechanism of the uniform precession mode has been investigated. We point out the important role of spin-conserving electron-magnon interaction in the relaxation process by quantitatively examining its contribution to the ferromagnetic resonance linewidth. In the second part, a transport theory is developed for magnons which, in addition to conduction electrons, can also carry and propagate spin angular momentum via the magnon current. We demonstrate that the mutual conversion of magnon current and spin current may take place at magnetic interfaces. We also predict a novel magnon-mediated electric drag effect in a metal/magnetic-insulator/metal trilayer structure. This study may pave the way to the new area of insulator-based spintronics. In the third part of thesis, particular attention is paid to the influence the spin orbit coupling on both charge and spin transport. We theoretically investigate magnetotransport anisotropy and the conversion relations of spin and charge currents in various magnetic systems, and apply our results to interpret recent experiments.

Zhang, Shulei

102

Dynamics, crystallization and structures in colloid spin coating  

E-print Network

Spin coating is an out-of-equilibrium technique for producing polymer films and colloidal crystals quickly and reproducibly. In this review, we present an overview of theoretical and experimental studies of the spin coating of colloidal suspensions. The dynamics of the spin coating process is discussed first, and we present insights from both theory and experiment. A key difference between spin coating with polymer solutions and with monodisperse colloidal suspensions is the emergence of long range (centimeter scale) orientational correlations in the latter. We discuss experiments in different physical regimes that shed light on the many unusual partially-ordered structures that have long-range orientational order, but no long-range translational order. The nature of these structures can be tailored by adding electric or magnetic fields during the spin coating procedure. These partially-ordered structures can be considered as model systems for studying the fundamentals of poorly crystalline and defect-rich solids, and they can also serve as templates for patterned and/or porous optical and magnetic materials.

Moorthi Pichumani; Payam Bagheri; Kristin M. Poduska; Wenceslao Gonzalez-Vinas; Anand Yethiraj

2013-01-10

103

The spin glass-like dynamics of gelatin gels  

E-print Network

We show that there are several striking parallels between the dynamics of gelatin gels and spin glasses. In general, glassy systems retain a memory of their past history. A key characteristic differentiating spin glasses from most other glassy systems is that on cooling they appear to "forget" what happened just below the glass transition temperature, but the memory is recovered on heating. We show that gelatin gels also behave in this way. Both systems show critical scaling of the kinetics with temperature and undergo physical aging, that is they never reach equilibrium, but continue to harden indefinitely at a rate which is linear in log(time). The parallels between the dynamics of these two completely different kinds of condensed matter strongly suggest that they share an underlying theory.

Alan Parker; Valery Normand

2003-06-03

104

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

E-print Network

simultaneously1,2,3,4,5 . The name spin ice comes from the fact that lowest energy states obey the ice ruleDynamics and hysteresis in square lattice artificial spin ice G. M. Wysin Department of Physics spin ice on a square lattice in two dimensions. Each island of the spin ice has a three

Wysin, Gary

105

Enhanced spin-precession dynamics in a spin-metamaterial coupled resonator observed in terahertz time-domain measurements  

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

106

Spin-Torque driven magnetization dynamics in spinvalve nanopillars  

NASA Astrophysics Data System (ADS)

Magnetization dynamics due to spin torque in 50 nm x 100 nm hexagon shaped, current-perpendicular-to-plane spinvalve pillar structures are experimentally investigated. Currents, with densities exceeding 10^7 A/cm^2 and having the proper polarity produce significant changes in the free layer magnetization orientation of the spinvalve via spin torque. Measurements reveal three distinct current-induced behaviors whose appearance depends on the current and the applied field. In fields less than the fixed layer switching field, hysteretic free layer reversal is observed. Second, in larger fields, a current induced dynamical response is detected as harmonically related peaks in the device voltage power spectrum. Peaks are seen in the range of 1.5 GHz to 14 GHz, with linewidths ranging from 150 MHz to 2 GHz. The spectral power indicates magnetization excursions in excess of 20^o. The precession frequency decreases with increasing current. This trend is reproduced by numerical simulations that include a spin torque contribution to magnetization dynamics. The third effect is a broadband 1/f type response that is produced by rapid two state switching. The broadband instability and precession behavior are both present in spectra for some values of field and current. However, at higher fields, the 1/f spectra persist whereas the precession is not detected.

Kaka, Shehzaad; Pufall, Matthew; Rippard, William; Silva, Thomas; Russek, Stephen; Katine, Jordan; Carey, Matthew

2004-03-01

107

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

E-print Network

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

Flatte, Michael E.

108

"Dynamical" non-minimal higher-spin interaction and gyromagnetic ratio g=2  

E-print Network

The field-dependent invariant representation (the "dynamical" representation) of the Poincar\\'e algebra is considered as a dynamical principle in order to get the corresponding "dynamical" electromagnetic coupling for higher spins ($s\\geq 1$). If in lower-spin ($s=0,1/2$) cases the "dynamical" coupling is taken to coincide with the minimal electromagnetic coupling the higher-spin coupling is inevitably non-minimal, containing a term linear in the field strength tensor $F_{\\mu\

I. Ots; R. Saar; R. -K. Loide; H. Liivat

2001-06-15

109

Dynamical Quantum Phase Transitions in Random Spin Chains  

NASA Astrophysics Data System (ADS)

Using a renormalization group approach, we solve the time evolution of random Ising spin chains with generic interactions starting from initial states of arbitrary energy. As a function of the Hamiltonian parameters, the system is tuned through a dynamical transition, similar to the ground-state critical point, at which the local spin correlations establish true long-range temporal order. In the state with a dominant transverse field, a spin that starts in an up state loses its orientation with time, while in the "ordered" state it never does. As in ground-state quantum phase transitions, the dynamical transition has unique signatures in the entanglement properties of the system. When the system is initialized in a product state, the entanglement entropy grows as log(t) in the two "phases," while at the critical point it grows as log?(t), with ? a universal number. This universal entanglement growth requires generic ("integrability breaking") interactions to be added to the pure transverse field Ising model.

Vosk, Ronen; Altman, Ehud

2014-05-01

110

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

SciTech Connect

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

111

The dynamic behaviour of liquids in spinning spacecraft  

NASA Astrophysics Data System (ADS)

This paper presents the boundary layer model for analyzing the dynamic behavior of liquids in partially filled tanks of spinning spacecraft. The solution for the model is obtained by solving three boundary value problems: inviscid, the boundary layer, and viscous correction. The boundary layer equations are solved analytically, and the inviscid solution and viscous corrections are obtained by using finite element methods. The computer programs developed for this model have been used to determine the liquid natural frequencies and mode shapes of Intelsat VI for different mission phases. The numerical results show that the first azimuth and elevation slosh modes exist in the spinning tanks. The lower modes are basically inertial modes and the higher modes are a combination of slosh and inertial modes. Since the pendulum models can represent only pure slosh motion, these numerical results indicate that only first elevation and azimuth modes can be represented by them.

Agrawal, Brij N.

112

Autonomous and driven dynamics of spin torque nano-oscillators  

NASA Astrophysics Data System (ADS)

Understanding the dynamical properties of autonomous spin torque nano-oscillators (STNO) and their response to external perturbations is important for their applications as nanoscale microwave sources. We used spectroscopic measurements to study the dynamical characteristics of nanopillar- and point contact-based STNOs incorporating a microstrip in close proximity to the active magnetic layer. By applying microwave current at frequency fext to the microstrip, we were able to generate large microwave fields of more than 30 Oe rms at the location of STNO. We demonstrate that for a wide range of fext, STNO exhibits multiple synchronization regimes with integer and non-integer rational ratios between fext and the oscillation frequency f. We show that the synchronization ranges are determined by the symmetry of the oscillation orbit and the orientation of the driving field relative to the symmetry axis of the orbit. We observe synchronization hysteresis, i.e. a dependence of the synchronization limits on the dynamical history caused by the nonlinearity of STNO. We also show that the oscillation can be parametrically excited in the subcritical regime of STNO by a microwave field at twice the frequency of the oscillation. By measuring the threshold and the frequency range of parametric excitation, we determine damping, spin-polarization efficiency, and coupling to the microwave signal. In addition, by measuring the frequency range of parametric synchronization in the auto-oscillation regime, we determine the dynamic nonlinearity of the nanomagnet. Thus, analysis of the driven oscillations provides complete information about the dynamical characteristics of STNO. Finally, we discuss several unusual dynamical behaviors of STNO caused by their strong nonlinearity.

Urazhdin, Sergei

2012-02-01

113

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

PubMed

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

114

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

115

Probing the dynamics of a nuclear spin bath in diamond through time-resolved central spin magnetometry.  

PubMed

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. PMID:25302916

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

2014-09-26

116

Spin Dynamics in the Presence of Spin-orbit Interactions: from the Weak to the Strong Spin-orbit Coupling Regime  

E-print Network

Dresselhaus SOIs based on these modes and optical grating experiments. We discuss the physical interpretation of each of these modes in the context of Rabi oscillation. In the finite temperature, We study the spin dynamics in the presence of impurity...

Liu, Xin

2012-10-19

117

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

PubMed

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

118

Spin Systems far from Equilibrium: Aging and Dynamic Phase Transition  

NASA Astrophysics Data System (ADS)

Among the many non-equilibrium processes encountered in nature we deal with two different but related aspects. One is the non-equilibrium relaxation process that is at the origin of 'aging phenomena', and the other one is a non-equilibrium phase transition, called 'dynamic phase transition'. One of the main purposes of our research is to explore more realistic situations than studied previously. Indeed, in the study of aging phenomena certain kinds of disorder effects are considered, and we introduce the 'surface' as a spatial boundary to the system undergoing the dynamic phase transition. In order to observe these processes as clearly as possible, we study in both cases simple spin systems. Using Monte Carlo simulations we first investigate aging in three-dimensional Ising spin glasses as well as in two-dimensional Ising models with disorder quenched to low temperatures. The time-dependent dynamical correlation length L(t) is determined numerically and the scaling behavior of various two-time quantities as a function of L( t)/L(s) is discussed where t and s are two different times. For disordered Ising models deviations of L(t from algebraic growth law show up. The generalized scaling forms as a function of L(t/ L(s) reveal a generic simple aging scenario for Ising spin glasses as well as for disordered Ising ferromagnets. We also study the local critical phenomena at a dynamic phase transition by means of numerical simulations of kinetic Ising models with surfaces subjected to a periodic oscillating field. We examine layer-dependent quantities, such as the period-averaged magnetization per layer Q( z) and the layer susceptibility chi(z), and determine local critical exponents through finite size scaling. Both for two and three dimensions, we find that the values of the surface exponents differ from those of the equilibrium critical surface. It is revealed that the surface phase diagram of the non-equilibrium system is not identical to that of the equilibrium system in three dimensions. The study of aging in disordered systems is supported by the U.S. Department of Energy (DOE) through Grant No. DE-FG02-09ER46613. The study of dynamic phase transitions is supported by the U.S. National Science Foundation (NSF) through Grants No. DMR- 0904999 and No. DMR-1205309.

Park, Hyunhang

119

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

E-print Network

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

120

A spinning thermometer to monitor microwave heating and glass transitions in dynamic  

E-print Network

A spinning thermometer to monitor microwave heating and glass transitions in dynamic nuclear in potassium bromide (KBr) allows one to deter- mine the temperature of a spinning sample. We propose to adapt the original design by using a compact KBr tablet placed at the bottom of the magic angle spinning rotor

121

Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer  

Microsoft Academic Search

We study numerically the process of nuclear spin measurement in a solid-state quantum computer of the type proposed by Kane by modeling the quantum dynamics of two coupled nuclear spins on $^{31}$P donors implanted in silicon. We estimate the minimum measurement time necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic subsystem. We

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

122

Electron-nuclear spin dynamics in a mesoscopic solid-state quantum computer  

Microsoft Academic Search

We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins on 31P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic subsystem. We also calculate the

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

123

High-dynamic-range magnetometry with a single nuclear spin in diamond  

E-print Network

High-dynamic-range magnetometry with a single nuclear spin in diamond G. Waldherr1 *, J. Beck1 , P, we implement a quantum phase estimation algorithm6­8 on a single nuclear spin in diamond to combine coherence times4 , even at ambient conditions, and coherent coupling to nearby nuclear spins11,12 . Its

Pfeifer, Holger

124

Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study  

SciTech Connect

Combining an atomistic many-body potential with a classical spin Hamiltonian parameterized by first principles calculations, molecular-spin dynamics computer simulations were performed to investigate phonon-magnon interactions in body centered cubic iron. Results obtained for spin-spin and density-density dynamic structure factors show that noticeable softening and damping of magnon modes occur due to the presence of lattice vibrations. Furthermore, as a result of the phonon-magnon coupling, additional longitudinal spin wave excitations are observed, with the same frequencies as the longitudinal phonon modes.

Perera, Dilina, E-mail: dilinanp@physast.uga.edu; Landau, David P. [Center for Simulational Physics, The University of Georgia, Georgia 30602 (United States); Nicholson, Don M.; Malcolm Stocks, G.; Eisenbach, Markus; Yin, Junqi [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Brown, Gregory [Florida State University, Tallahassee, Florida 32306 (United States)

2014-05-07

125

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

SciTech Connect

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

126

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

127

Spin dynamics of Mn impurities and their bound acceptors in GaAs  

NASA Astrophysics Data System (ADS)

We present results of tight-binding spin-dynamics simulations of individual and pairs of substitutional Mn impurities in GaAs. Our approach is based on the mixed quantum-classical scheme for spin dynamics, with coupled equations of motions for the quantum subsystem, representing the host, and the localized spins of magnetic dopants, which are treated classically. In the case of a single Mn impurity, we calculate explicitly the time evolution of the Mn spin and the spins of nearest-neighbor As atoms, where the acceptor (hole) state introduced by the Mn dopant resides. We relate the characteristic frequencies in the dynamical spectra to the two dominant energy scales of the system, namely, the spin-orbit interaction strength and the value of the p -d exchange coupling between the impurity spin and the host carriers. For a pair of Mn impurities, we find signatures of the indirect (carrier-mediated) exchange interaction in the time evolution of the impurity spins. Finally, we examine temporal correlations between the two Mn spins and their dependence on the exchange coupling and spin-orbit interaction strength, as well as on the initial spin-configuration and separation between the impurities. Our results provide insight into the dynamic interaction between localized magnetic impurities in a nanoscaled magnetic-semiconductor sample, in the extremely-dilute (solotronics) regime.

Mahani, M. R.; Pertsova, A.; Canali, C. M.

2014-12-01

128

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

E-print Network

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.

129

Spin-tunnel investigation of a 1/25-scale model of the General Dynamics F-16XL airplane  

NASA Technical Reports Server (NTRS)

A spin-tunnel investigation of the spin and recovery characteristics of a 1/25-scale model to the General Dynamics F-16XL aircraft was conducted in the Langley Spin Tunnel. Tests included erect and inverted spins at various symmetric and asymmetric loading conditions. The required size of an emergency spin-recovery parachute was determined.

Whipple, R. D.; White, W. L.

1984-01-01

130

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

131

Non-Markovian reduced dynamics and entanglement evolution of two coupled spins in a quantum spin environment  

NASA Astrophysics Data System (ADS)

The exact quantum dynamics of the reduced density matrix of two coupled spin qubits in a quantum Heisenberg XY spin star environment in the thermodynamic limit at arbitrarily finite temperatures is obtained using an operator technique. In this approach, the transformed Hamiltonian becomes effectively Jaynes-Cumming-like and thus the analysis is also relevant to cavity quantum electrodynamics. This special operator technique is mathematically simple and physically clear, and allows us to treat systems and environments that could all be strongly coupled mutually and internally. To study their entanglement evolution, the concurrence of the reduced density matrix of the two coupled central spins is also obtained exactly. It is shown that the dynamics of the entanglement depends on the initial state of the system and the coupling strength between the two coupled central spins, the thermal temperature of the spin environment, and the interaction between the constituents of the spin environment. We also investigate the effect of detuning, which in our model can be controlled by the strength of a locally applied external magnetic field. It is found that the detuning has a significant effect on the entanglement generation between the two-spin qubits.

Yuan, Xiao-Zhong; Goan, Hsi-Sheng; Zhu, Ka-Di

2007-01-01

132

Effective ergodicity in single-spin-flip dynamics.  

PubMed

A quantitative measure of convergence to effective ergodicity, the Thirumalai-Mountain (TM) metric, is applied to Metropolis and Glauber single-spin-flip dynamics. In computing this measure, finite lattice ensemble averages are obtained using the exact solution for a one dimensional Ising model, whereas the time averages are computed with Monte Carlo simulations. The time evolution of the effective ergodic convergence of Ising magnetization is monitored. By this approach, diffusion regimes of the effective ergodic convergence of magnetization are identified for different lattice sizes, nonzero temperature, and nonzero external field values. Results show that caution should be taken when using the TM metric at system parameters that give rise to strong correlations. PMID:25314429

Süzen, Mehmet

2014-09-01

133

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

134

Spin dynamics in a diluted magnetic semiconductor quantum well studied by pump-probe absorption spectroscopy: Magnetic-field-induced suppression of electron-spin relaxation  

Microsoft Academic Search

Exciton spin dynamics is studied in a diluted magnetic semiconductor quantum well of Cd0.95Mn0.05Te by pump-probe absorption spectroscopy under magnetic fields. The time dependences of the saturated absorbance for the higher- and lower-energy spin states of heavy-hole (hh) excitons clarify the following exciton-spin relaxation process in magnetic fields: ultrafast hh-spin relaxation with the formation of dark excitons and subsequent electron-spin

A. Murayama; K. Seo; K. Nishibayashi; I. Souma; Y. Oka

2006-01-01

135

Interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in semiconductor quantum dots  

NASA Astrophysics Data System (ADS)

We theoretically study the interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in two-electron semiconductor double quantum dots near the singlet-triplet (S -T+ ) anticrossing. The goal of the scheme under study is to extend the singlet-triplet (S -T0 ) qubit decoherence time T2* by dynamically transferring the polarization from the electron spins to the nuclear spins. This polarization transfer is achieved by cycling the electron spins over the S -T+ anticrossing. Here, we investigate, both quantitatively and qualitatively, how this hyperfine-mediated dynamical polarization transfer is influenced by the Rashba and Dresselhaus spin-orbit interaction. In addition to T2*, we determine the singlet return probability Ps, a quantity that can be measured in experiments. Our results suggest that the spin-orbit interaction establishes a mechanism that can polarize the nuclear spins in the direction opposite to that of hyperfine-mediated nuclear spin polarization. In materials with relatively strong spin-orbit coupling, this interplay of spin-orbit and hyperfine-mediated nuclear spin polarizations prevents any notable increase in the S -T0 qubit decoherence time T2*.

Ran?i?, Marko J.; Burkard, Guido

2014-12-01

136

Proton spin dynamics in polymer melts: new perspectives for experimental investigations of polymer dynamics  

E-print Network

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

137

Spin-flow vibrational spectroscopy of molecules with flexible spin density: electrochemistry, ESR, cluster and spin dynamics, and bonding in TiSc2N@C80.  

PubMed

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

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

2010-08-24

138

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

PubMed

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

139

Competing quantum effects in the dynamics of a flexible water model  

E-print Network

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

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

2010-11-04

140

Dynamics of three types of annual plants competing for water and light  

NASA Astrophysics Data System (ADS)

We present and discuss a Monte Carlo model describing the dynamics of three types of annual plants which have different tolerances to shade and drought. External conditions (water and light) fluctuate around some values which are our control parameters and which decide how many resources the system receives. The plants compete with their nearest neighbours for the resources, however not in the same way. We show that for certain ranges of the control parameters a coexistence of the three species is observed. We discuss how the characteristics of the the plants - their number, germination, biomass or the number of nearest neighbours, depend on the two control parameters characterising external conditions. We show that elimination is done at the level of adult plants, not seedlings. We find also cooperative behaviour of plants in difficult conditions, as observed in field studies and we propose an explanation for this fact. Apart from plants tolerating shade but requiring more water and those tolerating drought but needing more light, which are common in nature, we introduce a third species with intermediary demands. We investigate under what conditions this new species could dominate and whether the total number of plants, regardless of their type, is larger with or without the intermediate plant. We show that in our model, like in nature, systems with two kinds of plants with opposite characteristics are, in general, as effective as a system with an additional third type of plants. We show that two contradictory hypotheses made by biologists, concerning the demands of plants in drought and shade, could be both true, however in different regimes.

P?kalski, Andrzej; Szwabi?ski, Janusz

2013-02-01

141

Quasiclassical magnetic order and its loss in a spin-1/2 Heisenberg antiferromagnet on a triangular lattice with competing bonds  

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

142

Free vibration and dynamic response analysis of spinning structures  

NASA Technical Reports Server (NTRS)

The proposed effort involved development of numerical procedures for efficient solution of free vibration problems of spinning structures. An eigenproblem solution procedure, based on a Lanczos method employing complex arithmetic, was successfully developed. This task involved formulation of the numerical procedure, FORTRAN coding of the algorithm, checking and debugging of software, and implementation of the routine in the STARS program. A graphics package for the E/S PS 300 as well as for the Tektronix terminals was successfully generated and consists of the following special capabilities: (1) a dynamic response plot for the stresses and displacements as functions of time; and (2) a menu driven command module enabling input of data on an interactive basis. Finally, the STARS analysis capability was further improved by implementing the dynamic response analysis package that provides information on nodal deformations and element stresses as a function of time. A number of test cases were run utilizing the currently developed algorithm implemented in the STARS program and such results indicate that the newly generated solution technique is significantly more efficient than other existing similar procedures.

1986-01-01

143

Pattern recognition in neural networks with competing dynamics: coexistence of fixed-point and cyclic attractors.  

PubMed

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

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

2012-01-01

144

Pattern Recognition in Neural Networks with Competing Dynamics: Coexistence of Fixed-Point and Cyclic Attractors  

PubMed Central

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

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

2012-01-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

146

Two-Dimensional Monopole Dynamics in the Dipolar Spin Ice Dy2Ti2O7  

NASA Astrophysics Data System (ADS)

The spin dynamics of the dipolar spin-ice Dy2Ti2O7 under a dc magnetic field (Bdc) along the [111] direction has been investigated using ac susceptibility (?ac), which enables us to study two-dimensional monopole motion in an ac magnetic field perpendicular to Bdc. We have observed the slowing down of monopole dynamics in the kagomé spin-ice regime (Bdc˜ 0.4 T) and the extreme speeding up under Bdc close to the critical point (Bdc˜ 0.93 T). An analysis using a Monte Carlo simulation suggests that the dynamics changes from a random walk of monopoles to a collective motion as Bdc increases.

Takatsu, Hiroshi; Goto, Kazuki; Otsuka, Hiromi; Higashinaka, Ryuji; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Kadowaki, Hiroaki

2013-07-01

147

Enhancement of faba bean competitive ability by arbuscular mycorrhizal fungi is highly correlated with dynamic nutrient acquisition by competing wheat  

PubMed Central

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

148

Enhancement of faba bean competitive ability by arbuscular mycorrhizal fungi is highly correlated with dynamic nutrient acquisition by competing wheat.  

PubMed

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

149

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

150

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

NASA Astrophysics Data System (ADS)

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

Berezovsky, Jesse

2008-03-01

151

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

NASA Astrophysics Data System (ADS)

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; Melnik, Roderick; Bonilla, Luis L.; Raynolds, James E.

2013-12-01

152

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

SciTech Connect

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

153

Dynamics of the Measurement of Nuclear Spins in a Solid-State Quantum Computer  

Microsoft Academic Search

We study numerically the process of nuclear spin measurement in a solid-state\\u000aquantum computer of the type proposed by Kane by modeling the quantum dynamics\\u000aof two coupled nuclear spins on $^{31}$P donors implanted in silicon. We\\u000aestimate the minimum measurement time necessary for the reliable transfer of\\u000aquantum information from the nuclear spin subsystem to the electronic\\u000asubsystem. We

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

1999-01-01

154

Electron-Nuclear Spin Dynamics in a Mesoscopic Solid-State Quantum Computer  

SciTech Connect

We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins located on {sup 31}P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic one and the probability of error for typical values of external noise.

Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Nagaev, K.E.

1998-12-07

155

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

E-print Network

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

156

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

E-print Network

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

157

Optimal control of coupled spin dynamics in the presence of relaxation  

Microsoft Academic Search

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

158

Dynamic Nuclear Polarization with Single Electron Spins J. R. Petta,1,2  

E-print Network

polarization driven by scattering between spin-polarized edge states induced hys- teresis in conductanceDynamic Nuclear Polarization with Single Electron Spins J. R. Petta,1,2 J. M. Taylor,1,3 A. C Barbara, California 93106, USA (Received 6 September 2007; published 11 February 2008) We polarize nuclear

Petta, Jason

159

Dynamics of nuclear spin measurement in a mesoscopic solid-state quantum computer  

Microsoft Academic Search

We study numerically the process of nuclear spin measurement in a solid-state quantum computer of the type proposed by Kane, by calculating the quantum dynamics of two coupled nuclear spins on 31 P donors implanted in 28 Si. We estimate the time of the `quantum swap operation' - the minimum measurement time required for the reliable transfer of quantum information

Gennady P. Berman; David K. Campbell; Gary D. Doolen; Kirill E. Nagaev

2000-01-01

160

The excitation operator method in the spin dynamics of the one-dimensional XXZ model  

E-print Network

We develop the excitation operator method, which is designed to solve the Heisenberg equation of motion by constructing the excitation operators. We use it to study the spin dynamics in the one-dimensional XXZ model. We find the diffusive spin transport in the gapped phase at the high temperature limit.

Pei Wang

2012-07-12

161

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

E-print Network

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.

162

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

163

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

164

Helium3 spin-echo: Principles and application to dynamics at surfaces  

Microsoft Academic Search

In this review we give a detailed description of the recently developed helium-3 spin-echo technique and its application to several classes of surface dynamic measurements. We review existing surface dynamical probes briefly and illustrate the need for new experimental tools that measure on nanoscale distances and over picosecond timescales. We then describe the helium-3 spin-echo method, which is one such

A. P. Jardine; H. Hedgeland; G. Alexandrowicz; W. Allison; J. Ellis

2009-01-01

165

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

SciTech Connect

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

166

Neutron scattering study of spin dynamics in superconducting (Tl,Rb)2Fe4Se5  

NASA Astrophysics Data System (ADS)

We observed in superconducting (Tl,Rb)2Fe4Se5 spin-wave branches that span an energy range from 6.5 to 209 meV. Spin dynamics are successfully described by a Heisenberg localized spin model whose dominant in-plane interactions include only the nearest (J1 and J1') and next nearest neighbor (J2 and J2') exchange terms within and between the tetramer spin blocks, respectively. These experimentally determined exchange constants would crucially constrain the theoretical viewpoints on magnetism and superconductivity in the Fe-based materials.

Chi, Songxue; Ye, Feng; Bao, Wei; Fang, Minghu; Wang, H. D.; Dong, C. H.; Savici, A. T.; Granroth, G. E.; Stone, M. B.; Fishman, R. S.

2013-03-01

167

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

NASA Astrophysics Data System (ADS)

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.

2012-05-01

168

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

SciTech Connect

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

169

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

NASA Astrophysics Data System (ADS)

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

Häussler, Wolfgang; Kredler, Lukas

2014-05-01

170

Effective one body approach to the dynamics of two spinning black holes with next-to-leading order spin-orbit coupling  

E-print Network

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

171

SU(3) semi-classical representation of quantum dynamics of interacting spins  

E-print Network

We present a formalism for simulating quantum dynamics of lattice spin-one systems 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 SU(3) variables. Three of them represent usual spin components and five others are hidden variables representing local spin-spin correlations. We argue that this method becomes asymptotically exact in high dimensions. This method allows for access to both non-equal time and spatial 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. We argue that these ideas can be extended to other interacting systems.

Shainen M Davidson; Anatoli Polkovnikov

2014-06-04

172

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

173

Spin ordering and dynamics in the frustrated antiferromagnet YBaCo4O7.1  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

174

Three-level spin system under decoherence-minimizing driving fields: Application to nitrogen-vacancy spin dynamics  

E-print Network

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

175

Brownian motion and quantum dynamics of magnetic monopoles in spin ice  

PubMed Central

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

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

2013-01-01

176

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

177

Evolution of cooperating and competing individuals in a dynamic fitness environment  

NASA Astrophysics Data System (ADS)

Evolving a single individual does not provide a solution when a set of individuals is needed to address different aspects of the problem. Genetic algorithms, however, are typically used to evolve a single individual. We have generalized previous work on modeling the immune system and developed a fitness method that allows a single run of a genetic algorithm to evolve a suite of individuals that compete with each other for fitness and yet cooperate to solve a problem. The method is a form of tournament fitness where individuals compete for fitness with other members of the population. The competitions vary throughout the run, resulting in a changing fitness environment. Experimental results and a preliminary model are described that verify the validity of the approach. We also present explanations for unexpected results from our previous work.

Parsons, Rebecca J.

1999-03-01

178

Competence exploration and exploitation in new product development : The moderating effects of environmental dynamism and competitiveness  

Microsoft Academic Search

Purpose – This paper aims to extend research on exploration and exploitation by investigating the effects of competence exploration and exploitation on new product development outcomes in China. Premised from the perspective of environment-performance relationship and the fit-as-moderation view, the authors argue that exploration and exploitation have curvilinear effects on new product development performance due to external environmental factors. Design\\/methodology\\/approach

Tsau-Tang Yang; Ci-Rong Li

2011-01-01

179

Modulating spin transfer torque switching dynamics with two orthogonal spin-polarizers by varying the cell aspect ratio  

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

180

Formulation of numerical procedures for dynamic analysis of spinning structures  

NASA Technical Reports Server (NTRS)

The paper presents the descriptions of recently developed numerical algorithms that prove to be useful for the solution of the free vibration problem of spinning structures. First, a generalized procedure for the computation of nodal centrifugal forces in a finite element owing to any specified spin rate is derived in detail. This is followed by a description of an improved eigenproblem solution procedure that proves to be economical for the free vibration analysis of spinning structures. Numerical results are also presented which indicate the efficacy of the currently developed procedures.

Gupta, K. K.

1986-01-01

181

Entanglement dynamics of spin systems in pure states  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

182

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

SciTech Connect

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

183

Dynamics of a driven spin coupled to an antiferromagnetic spin bath  

NASA Astrophysics Data System (ADS)

We study the behavior of the Rabi oscillations of a driven central spin (qubit) coupled to an antiferromagnetic spin bath (environment). It is found that the decoherence behavior of the central spin depends on the detuning, driving strength, qubit-bath coupling and an important factor ?, associated with the number of coupled atoms, the detailed lattice structure and the temperature of the environment. If detuning exists, Rabi oscillations may show the behavior of collapses and revivals; however, if detuning is absent, such a behavior will not appear. We investigate the weighted frequency distribution of the time evolution of the central spin inversion and give a reasonable explanation of this phenomenon of collapses and revivals. We also discuss the decoherence and pointer states of the qubit from the perspective of von Neumann entropy. We found that the eigenstates of the qubit self-Hamiltonian emerge as pointer states in the weak system-environment coupling limit.

Yuan, Xiao-Zhong; Goan, Hsi-Sheng; Zhu, Ka-Di

2011-02-01

184

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

185

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

186

Atom-diatom scattering dynamics of spinning molecules.  

PubMed

We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H2 and F+H2 collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules. PMID:25591357

Eyles, C J; Floß, J; Averbukh, I Sh; Leibscher, M

2015-01-14

187

Entanglement dynamics via geometric phases in quantum spin chains  

SciTech Connect

We introduce a connection between entanglement induced by interaction and geometric phases acquired by a composite quantum spin system. We begin by analyzing the evaluation of cyclic (Aharonov-Anandan) and noncyclic (Mukunda-Simon) geometric phases for general spin chains evolving in the presence of time-independent magnetic fields. Then, by considering Heisenberg chains, we show that the interaction geometric phase, namely, the total geometric phase with subtraction of free spin contributions, is directly related to the global (Meyer-Wallach) entanglement exhibited by an initially separable state during its evolution in Hilbert space. This is analytically shown for N=2 spins and numerically illustrated for larger chains. This relationship promotes the interaction geometric phase to an indicator of global entanglement in the system, which may constitute a useful tool for quantum tasks based on entanglement as a resource to their performance.

Castro, C. S.; Sarandy, M. S. [Instituto de Fisica, Universidade Federal Fluminense, Avenida Gal. Milton Tavares de Souza s/n, Gragoata, 24210-346, Niteroi, Rio de Janeiro (Brazil)

2011-04-15

188

Dynamics of an all-optical atomic spin gyroscope.  

PubMed

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

Fang, Jiancheng; Wan, Shuangai; Yuan, Heng

2013-10-20

189

Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics  

SciTech Connect

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

190

Magneto-mechanical investigation of spin dynamics in magnetic multilayers  

NASA Astrophysics Data System (ADS)

The Einstein-de Haas effect is used to study experimentally the interfacial spin transport in a bilayer metallic system. Specifically, mechanical torque on a permalloy film interfaced with a non-magnetic metallic film (platinum or copper), deposited on a microcantilever, is measured. The torque is generated by the transfer of the spin angular momentum from the permalloy film to the mechanical angular momentum of the cantilever. Measurement of the cantilever deflection shows that the presence of a thin non-magnetic metallic layer with strong spin-orbit interaction (platinum) changes the interfacial spin transport and causes a dramatic reduction of the mechanical torque. The observed behavior of the cantilever is attributed to the increased effective damping of the domain wall motion in the permalloy layer.

Lim, Sang-Hyun; Imtiaz, Atif; Wallis, T. Mitch; Russek, Stephen; Kabos, Pavel; Cai, Liufei; Chudnovsky, Eugene M.

2014-02-01

191

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

192

Spin  

Microsoft Academic Search

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

193

Discovery of metastable states in a finite-size classical one-dimensional planar spin chain with competing nearest- and next-nearest-neighbor exchange couplings  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

195

Ultrafast optical control of orbital and spin dynamics in a solid-state defect.  

PubMed

Atom-scale defects in semiconductors are promising building blocks for quantum devices, but our understanding of their material-dependent electronic structure, optical interactions, and dissipation mechanisms is lacking. Using picosecond resonant pulses of light, we study the coherent orbital and spin dynamics of a single nitrogen-vacancy center in diamond over time scales spanning six orders of magnitude. We develop a time-domain quantum tomography technique to precisely map the defect's excited-state Hamiltonian and exploit the excited-state dynamics to control its ground-state spin with optical pulses alone. These techniques generalize to other optically addressable nanoscale spin systems and serve as powerful tools to characterize and control spin qubits for future applications in quantum technology. PMID:25123482

Bassett, Lee C; Heremans, F Joseph; Christle, David J; Yale, Christopher G; Burkard, Guido; Buckley, Bob B; Awschalom, David D

2014-09-12

196

From quantum-mechanical to classical dynamics in the central-spin model  

NASA Astrophysics Data System (ADS)

We discuss the semiclassical and classical character of the dynamics of a single spin 1/2 coupled to a bath of noninteracting spins 1/2. On the semiclassical level, we extend our previous approach presented in D. Stanek, C. Raas, and G. S. Uhrig, Phys. Rev. B 88, 155305 (2013), 10.1103/PhysRevB.88.155305 by the explicit consideration of the conservation of the total spin. On the classical level, we compare the results of the classical equations of motions in absence and presence of an external field to the full quantum result obtained by density-matrix renormalization (DMRG). We show that for large bath sizes and not too low magnetic field the classical dynamics, averaged over Gaussian distributed initial spin vectors, agrees quantitatively with the quantum-mechanical one. This observation paves the way for an efficient approach for certain parameter regimes.

Stanek, Daniel; Raas, Carsten; Uhrig, Götz S.

2014-08-01

197

Direct dynamical evidence for the spin glass lower critical dimension 2  

PubMed

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)spin glass dynamics, and are consistent with a lower critical dimension for spin glasses, d?, between 2

Guchhait, Samaresh; Orbach, Raymond

2014-03-28

198

Dynamical topological quantum computation using spin pulse control in the Heisenberg model  

E-print Network

Hamiltonian engineering is an important approach for quantum information processing, when appropriate materials do not exist in nature or are unstable. So far there is no stable material for the Kitaev spin Hamiltonian with anisotropic interactions on a honeycomb lattice (A. Kitaev, Annals of Physics vol 321, 2 (2006)), which plays a crucial role in the realization of both Abelian and non-Abelian anyons. Here, we show how to dynamically realize the Kitaev spin Hamiltonian from the conventional Heisenberg spin Hamiltonian using a pulse-control technique. By repeating the same pulse sequence, the quantum state is dynamically preserved. The effects of the spin-orbit interaction and the hyperfine interaction are also investigated.

Tetsufumi Tanamoto; Keiji Ono; Yu-xi Liu; Franco Nori

2014-06-30

199

Spin wave dynamics and the determination of intrinsic damping in locally excited Permalloy thin films.  

PubMed

Time-resolved scanning Kerr effect microscopy has been used to study magnetization dynamics in Permalloy thin films excited by transient magnetic pulses generated by a micrometer-scale transmission line structure. The results are consistent with magnetostatic spin wave theory and are supported by micromagnetic simulations. Magnetostatic volume and surface spin waves are measured for the same specimen using different bias field orientations and can be accurately calculated by k-space integrations over all excited plane wave components. A single damping constant of Gilbert form is sufficient to describe both scenarios. The nonuniform pulsed field plays a key role in the spin wave dynamics, with its Fourier transform serving as a weighting function for the participating modes. The intrinsic Gilbert damping parameter alpha is most conveniently measured when the spin waves are effectively stationary. PMID:17359122

Liu, Zhigang; Giesen, Fabian; Zhu, Xiaobin; Sydora, Richard D; Freeman, Mark R

2007-02-23

200

Extending the electron spin coherence time of atomic hydrogen by dynamical decoupling.  

PubMed

We study the electron spin decoherence of encapsulated atomic hydrogen in octasilsesquioxane cages induced by the (1)H and (29)Si nuclear spin bath. By applying the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence we significantly suppress the low-frequency noise due to nuclear spin flip-flops up to the point where a maximum T2 = 56 ?s is observed. Moreover, dynamical decoupling with the CPMG sequence reveals the existence of two other sources of decoherence: first, a classical magnetic field noise imposed by the (1)H nuclear spins of the cage organic substituents, which can be described by a virtual fluctuating magnetic field with the proton Larmor frequency, and second, decoherence due to anisotropic hyperfine coupling between the electron and the inner (29)Si spins of the cage. PMID:24352700

Mitrikas, George; Efthimiadou, Eleni K; Kordas, George

2014-02-14

201

Comparison of spin dynamics in the cylindrical and Frenet-Serret coordinate systems  

NASA Astrophysics Data System (ADS)

A comparative analysis of a description of spin dynamics in the cylindrical and Frenet-Serret coordinate systems is carried out. It is shown that these two systems are equivalent. Because of the cylindrical-system reference axes, which do not move relative to stationary detectors, it becomes possible to efficiently use this frame to calculate spin evolution for particles and nuclei in accelerators and storage rings.

Silenko, A. J.

2015-01-01

202

Generalized dynamical spin chain and 4-loop integrability in N = 6 superconformal Chern–Simons theory  

Microsoft Academic Search

We revisit unitary representation of centrally extended psu(2|2) excitation superalgebra. We find most generally that ‘pseudo-momentum’, not lattice momentum, diagonalizes spin chain Hamiltonian and leads to generalized dynamic spin chain. All known results point to lattice momentum diagonalization for N=4 super-Yang–Mills theory. Having different interacting structure, we ask if N=6 superconformal Chern–Simons theory provides an example of pseudo-momentum diagonalization. For

Dongsu Bak; Hyunsoo Min; Soo-Jong Rey

2010-01-01

203

Coherent spin dynamics in nanopatterned ferromagnet-semiconductor hybrids at room-temperature  

SciTech Connect

We used time-resolved Kerr rotation to study the coherent spin dynamics of electrons in Py-GaAs hybrid structures up to room temperature. The geometry of the nanopatterned Py wires was varied in a wide range to modify the fringe field from the ferromagnets and thus the Larmor frequency of the precessing electron spins compared to a reference. At room temperature, the observed fringe field effect is in good agreement with theory while at low temperatures additional strain effects occur.

Hohage, P. E.; Nannen, J.; Bacher, G. [Werkstoffe der Elektrotechnik and CeNIDE, Universitaet Duisburg-Essen, Bismarckstrasse 81, D-47057 Duisburg (Germany); Wahle, M.; Fischer, S. F.; Kunze, U. [Lehrstuhl fuer Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44780 Bochum (Germany); Reuter, D.; Wieck, A. D. [Lehrstuhl fuer Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44780 Bochum (Germany)

2010-01-04

204

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

205

Quantum dynamics and entanglement of spins on a square lattice  

PubMed Central

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

206

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

PubMed Central

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

207

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

SciTech Connect

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

208

Impurity and boundary effects on magnetic monopole dynamics in spin ice  

NASA Astrophysics Data System (ADS)

Using a SQUID magnetometer, we measure the time-dependent magnetic relaxation in Dy2Ti2O7 and find 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 find that surface effects and a very low level of stuffed spins (0.30%) - magnetic Dy ions substituted for non-magnetic Ti ions - can explain these signatures in the relaxation. We find that the additional spins trap the magnetic monopole excitations and provide the first example of how defects in a spin-ice material can obstruct the flow of monopoles.

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

2013-03-01

209

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

PubMed

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

210

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

SciTech Connect

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

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

2012-01-15

211

Topological excitations and the dynamic structure factor of spin liquids on the kagome lattice  

NASA Astrophysics Data System (ADS)

Recent neutron scattering experiments on the spin-1/2 kagome lattice antiferromagnet ZnCu3(OH)6Cl2 (Herbertsmithite) provide the first evidence of fractionalized excitations in a quantum spin liquid state in two spatial dimensions. In contrast to existing theoretical models of both gapped and gapless spin liquids, which give rise to sharp dispersing features in the dynamic structure factor, the measured dynamic structure factor reveals an excitation continuum that is remarkably flat as a function of frequency. Here we show that many experimentally observed features can be explained by the presence of topological vison excitations in a Z2 spin liquid. These visons form flat bands on the kagome lattice, and thus act as a momentum sink for spin-carrying excitations that are probed by neutron scattering. We compute the dynamic structure factor for two different Z2 spin liquids and find that our results for one of them are in qualitative agreement with the neutron scattering experiments above a very low energy cutoff, below which the structure factor is probably dominated by impurities.

Punk, Matthias; Chowdhury, Debanjan; Sachdev, Subir

2014-04-01

212

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

E-print Network

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

Ning Wu; Arun Nanduri; Herschel Rabitz

2014-05-19

213

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

214

Ultrafast optical studies of coherent spin dynamics in magnetic quantum structures  

NASA Astrophysics Data System (ADS)

Using femtosecond lasers and ultrafast optical techniques, we have investigated the time-evolution of the spins of electrons, holes, and excitons which are optically injected into magnetic semiconductor quantum wells. Here, the spins of the mobile electronic carriers can directly couple to the spins of the local magnetic moments (Mn2+) present in the quantum structure, leading to new channels for spin relaxation, decoherence, and angular momentum transfer. Timescales, strengths, and physical manifestations of these dynamic spin-spin interactions are measured in real-time with femtosecond resolution using a method of ultrafast Faraday rotation. Model systems in which to study the interaction of electronic spins with embedded local moments are realized in a new class of 'digital' magnetic heterostructures: II-VI ZnSe/ZnCdSe single quantum wells containing discrete mono- and submonolayer planes of MnSe. Strong coupling between excitons and local moments is observed, resulting in large effective exciton g-factors (g ~ 500) and enhanced Faraday rotation. The fractional planes of magnetic material can be considered nearly ideal 2-D spin distributions, and the statistics of Mn spin clustering in the 2D planes is studied through photoluminescence Zeeman shifts in high magnetic fields (30T). In longitudinal applied magnetic fields (Faraday geometry), the monotonic exciton spin relaxation is rapid (<5ps) and found to depend solely on the magnitude of the exciton Zeeman splitting, regardless of the particular digital magnetic environment. No longlived spin-dependent imprint on the magnetic sublattice is measured. By contrast, in transverse magnetic fields the electron spins are found to precess at THz frequencies, enabling measurement of the electron spin decoherence time separate from the spin relaxation of the holes. Furthermore, the data indicate that the embedded Mn2+ sublattice undergoes an ultrafast coherent rotation about the transient exchange field of the spin polarized holes. The perturbed Mn2+ spin ensemble subsequently undergoes a measurable free-induction decay, permitting all-optical time-domain electron paramagnetic resonance studies of fractional-monolayer magnetic planes.

Crooker, Scott A.

215

Evidence for excited spin-orbit state reaction dynamics in F+H2: Theory and experiment  

E-print Network

Evidence for excited spin-orbit state reaction dynamics in F+H2: Theory and experiment François exoergicity of the reaction. In addition, the spin-orbit, Coriolis, and electrostatic couplings between/2 spin-orbit state. As the collision energy increases, the Born­ Oppenheimer allowed reaction of F in its

Nizkorodov, Sergey

216

Ultrafast spin dynamics in GaAsGaSbInAs heterostructures probed by second harmonic generation  

E-print Network

Ultrafast spin dynamics in GaAsÃ?GaSbÃ?InAs heterostructures probed by second harmonic generation Yu spin-sensitive spectroscopy provides unique in- formation about spin relaxation in semiconductor hetero time-resolved techniques, such as polarized photoluminescence spectroscopy,3,4 pump- probe transmission

Tolk, Norman H.

217

Optimal Controller Tested for a Magnetically Suspended Five-Axis Dynamic Spin Rig  

NASA Technical Reports Server (NTRS)

NASA Glenn Research Center's Structural Mechanics and Dynamics Branch has developed a fully suspended magnetic bearing system for their Dynamic Spin Rig, which performs 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 Dynamic Spin Rig to provide magnetic excitation as well as noncontact magnetic suspension of the 35-lb vertical rotor with blades to induce turbomachinery blade vibration (ref. 1). The new system can provide longer run times at higher speeds and larger vibration amplitudes for rotating blades. Also, it was proven that bearing mechanical life was substantially extended and flexibility was increased in the excitation orientation (direction and phasing).

Choi, Benjamin B.

2003-01-01

218

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

219

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

220

Spin dynamics in oriented lithium phthalocyanine thin films investigated by pulsed electron spin resonance  

NASA Astrophysics Data System (ADS)

Thin films of monolithium phthalocyanine (PcLi) were prepared by vacuum deposition on cleaved mica. The highly anisotropic spin diffusion in these films was studied by electron spin resonance (ESR). Using averaging techniques, we succeeded in the detection of films as thin as 100 nm using pulsed ESR and 2 nm with cw ESR. The electronic relaxation is shown to depend on the substrate temperatures Ts during film deposition which determine the morphology of the films. We find relaxation rates of films which are faster by a factor of 20 (T1e-1) to 30 (T2e-1) than those of single crystals. At ambient temperature, a low-dimensional spin exchange mechanism is proposed for the single crystal. At low temperatures, in single crystals the electronic relaxation rates T1e-1 and T2e-1 hint at a reduced exchange with increased dimensionality d?1. This holds for the films at all temperatures and is explained by different crystal structures of single crystals and films. A generally applicable relaxation model is developed which describes the transition from one-dimensional to three-dimensional spin propagation.

Wachtel, H.; André, J.-J.; Bietsch, W.; von Schütz, J. U.

1995-03-01

221

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

SciTech Connect

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

222

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

PubMed

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

223

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

PubMed Central

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

224

Solvent composition dictates emergence in dynamic molecular networks containing competing replicators.  

PubMed

In Darwinian evolution, species that are better adapted to their environment win the competition for common resources from less well-adapted competitors. Thus, in such scenarios the nature of the environment may dictate the outcome of the competition. We investigated to what degree these biological principles acting at the level of species extend to the molecular level into systems based on fully synthetic self-replicating molecules. We now report two systems in which two replicators compete for a common building block and where the environment dictates which of the two replicators wins. We observed that subtle changes in the environment can lead to dramatic differences in the outcome of the competition. PMID:25584629

Leonetti, Giulia; Otto, Sijbren

2015-02-11

225

Quantum Entangled States and Quasiclassical Dynamics in Macroscopic Spin Systems  

Microsoft Academic Search

When dealing with macroscopic objects one usually observes quasiclassical phenomena, which can be described in terms of quasiclassical (or classical) equa- tions of motion. Recent development of the theory of quantum computation is based on implementation of the entangled states which do not have a classical analogy. Using a simple example of a paramagnetic spin system we show that the

Gennady P. Berman; Gary D. Doolen; Gustavo V. Lopez; Vladimir I. Tsifrinovich

226

Quantum Entangled States and Quasiclassical Dynamics in Macroscopic Spin Systems  

Microsoft Academic Search

When dealing with macroscopic objects one usually observes quasiclassical phenomena, which can be described in terms of quasiclassical (or classical) equations of motion. Recent development of the theory of quantum computation is based on implementation of the entangled states which do not have a classical analogy. Using a simple example of a paramagnetic spin system we show that the entangled

Gennady P. Berman; Gary D. Doolen; Gustavo V. Lopez; Vladimir I. Tsifrinovich

1998-01-01

227

Topological defects in systems with two competing order parameters: Application to superconductors with charge- and spin-density waves  

NASA Astrophysics Data System (ADS)

On the basis of coupled Ginzburg-Landau equations we study nonhomogeneous states in systems with two order parameters (OPs). Superconductors with a superconducting OP ? and a charge- or spin-density wave with amplitude W are examples of such systems. When one OP, say ? , has a form of a topological defect, like, e.g., a vortex or domain wall between the domains with the phases 0 and ? , the other OP W is determined by the Gross-Pitaevskii equation and is localized at the center of the defect. We consider in detail the domain-wall defect for ? and show that the shape of the associated solution for W depends on temperature and doping (or on the curvature of the Fermi surface) ? . It turns out that, provided the temperature or doping level is close to some discrete values Tn and ?n, the spatial dependence of the function W (x ) is determined by the form of the eigenfunctions of the linearized Gross-Pitaevskii equation. The spatial dependence of W0 corresponding to the ground state has the form of a soliton, while other possible solutions Wn(x ) have nodes. The inverse situation when W (x ) has the form of a topological defect and ? (x ) is localized at the center of this defect is also possible. In particular, we predict a surface or interfacial superconductivity in a system where a superconductor is in contact with a material that suppresses W . This superconductivity should have rather unusual temperature dependence existing only in certain intervals of temperature. Possible experimental realizations of such nonhomogeneous states of OPs are discussed.

Moor, Andreas; Volkov, Anatoly F.; Efetov, Konstantin B.

2014-12-01

228

Correlations between the dynamics of parallel tempering and the free-energy landscape in spin glasses.  

PubMed

We present the results of a large-scale numerical study of the equilibrium three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder. Using parallel tempering (replica exchange) Monte Carlo 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. 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 is examined. Our results show that autocorrelation times are directly correlated with the roughness of the free-energy landscape. PMID:23410280

Yucesoy, Burcu; Machta, Jonathan; Katzgraber, Helmut G

2013-01-01

229

Spin-dynamics of the classical easy-plane Heisenberg chain  

NASA Astrophysics Data System (ADS)

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

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

1992-02-01

230

Geometric phases and quantum correlations dynamics in spin-boson model  

SciTech Connect

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

231

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

232

RosettaEPR: Rotamer Library for Spin Label Structure and Dynamics  

PubMed Central

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

233

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

E-print Network

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

234

Laser control of ultrafast spin dynamics on homodinuclear iron- and nickel-oxide clusters  

NASA Astrophysics Data System (ADS)

We present a fully ab initio theory for coherent laser-induced ultrafast spin manipulation on the homodinuclear magnetic clusters FeOFe, FeOOFe, NiONi, and NiOONi. With the oxygen atom(s) bridging the magnetically active centers, the clusters tend to adopt asymmetric geometries due to the Jahn-Teller effect. Therefore they have well-defined spin localization which is required for local spin manipulation. We find that both spin-flip and spin-transfer scenarios can be achieved on the clusters FeOFe and FeOOFe while only spin flip is realized on NiONi and NiOONi, based on which we predict that the Fe-containing clusters are quite promising for logic operations. The different dynamical behavior on these systems is analyzed in detail from the viewpoint of their distinct electronic structures and related spectra. In striving for better magnetization dynamics control, the results obtained on these prototypic systems strongly indicate their great potential in spintronic device design and future practical applications.

Jin, Wei; Li, Chun; Lefkidis, Georgios; Hübner, Wolfgang

2014-01-01

235

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

236

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

237

Flight dynamics of a spinning projectile descending on a parachute  

SciTech Connect

During the past twenty years Sandia National Laboratories and the US Army have vertically gun launched numerous 155mm and eight-inch diameter flight test projectiles. These projectiles are subsequently recovered using an on-board parachute recovery system which is attached to the forward case structure of the projectile. There have been at least five attempts to describe, through analytical and numerical simulations, the translational and rotational motions of a spinning projectile descending on a parachute. However, none of these investigations have correctly described the large nutational motion of the projectile since all of them overlooked the fundamental mechanism which causes these angular motions. Numerical simulations as well as a closed form analytical solution show conclusively that the Magnus moment is responsible for the large nutational motion of the projectile. That is, when the center of pressure for the Magnus force is aft of the center of mass for the projectile, the Magnus moment causes an unstable (or large) nutational motion which always tends to turn the spinning projectile upside down while it is descending on the parachute. Conversely, when the center of mass for the projectile is aft of the center of pressure for the Magnus force, the Magnus moment stabilizes the nutational motion tending to always point the base of the spinning projectile down. The results of this work are utilized to render projectile parachute recovery systems more reliable and to explain what initially may appear to be strange gyrodynamic behavior of a spinning projectile descending on a parachute. 14 refs., 20 figs.

Benedetti, G.A.

1989-02-01

238

Quantum Entangled States and Quasiclassical Dynamics in Macroscopic Spin Systems  

E-print Network

When dealing with macroscopic objects one usually observes quasiclassical phenomena, which can be described in terms of quasiclassical (or classical) equations of motion. Recent development of the theory of quantum computation is based on implementation of the entangled states which do not have a classical analogy. Using a simple example of a paramagnetic spin system we show that the entangled states can be detected in standard macroscopic experiments as a sharp deviation from quasiclassical motion.

Berman, G P; López, G V; Tsifrinovich, V I; Berman, Gennady P.; Doolen, Gary D.; Lopez, Gustavo V.; Tsifrinovich, Vladimir I.

1998-01-01

239

Quantum Entangled States and Quasiclassical Dynamics in Macroscopic Spin Systems  

E-print Network

When dealing with macroscopic objects one usually observes quasiclassical phenomena, which can be described in terms of quasiclassical (or classical) equations of motion. Recent development of the theory of quantum computation is based on implementation of the entangled states which do not have a classical analogy. Using a simple example of a paramagnetic spin system we show that the entangled states can be detected in standard macroscopic experiments as a sharp deviation from quasiclassical motion.

Gennady P. Berman; Gary D. Doolen; Gustavo V. Lopez; Vladimir I. Tsifrinovich

1998-02-05

240

Quantum Entangled States and Quasiclassical Dynamics in Macroscopic Spin Systems  

Microsoft Academic Search

When dealing with macroscopic objects one usually observes quasiclassical\\u000aphenomena, which can be described in terms of quasiclassical (or classical)\\u000aequations of motion. Recent development of the theory of quantum computation is\\u000abased on implementation of the entangled states which do not have a classical\\u000aanalogy. Using a simple example of a paramagnetic spin system we show that the\\u000aentangled

Gennady P. Berman; Gary D. Doolen; Gustavo V. Lopez; Vladimir I. Tsifrinovich

1998-01-01

241

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

242

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

E-print Network

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

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

2014-09-01

243

Spin dynamics and horizon sensor performance for the Solar Mesosphere Explorer  

NASA Technical Reports Server (NTRS)

Numerical techniques for obtaining the trigger altitude of the Solar Mesosphere Explorer (SME) are detailed. The SME has a pair of fixed horizon sensors for attitude determination and initiation of the data acquisition procedures for measuring ozone concentrations at the limb. The spacecraft spin rate is calculated as each of the horizon sensors marks the limb with a pulse telemetered to the ground. A best fit spin dynamics model that takes into account the history of the satellite spin angle and all disturbances to the spin is described. Analyses show that the trigger altitude is calculated to an accuracy of 1.5-2.0 km. A significant indicator of the limb altitude is the stratospheric temperature at the 5 mb pressure level.

Lawrence, G. M.; Cowley, J. R., Jr.

1984-01-01

244

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

PubMed

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

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

2013-12-27

245

Spin Dynamics in Semiconductors, Chapter 4 of Semiconductor Spintron-ics and Quantum Computation edited by D. D. Awschalom, D. Loss, and  

E-print Network

Spin Dynamics in Semiconductors, Chapter 4 of Semiconductor Spintron- ics and Quantum Computation Dynamics in Semiconductors Michael E. Flatt´e, Jeff M. Byers, Wayne H. Lau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4.2 Fundamentals of Semiconductor Spin Coherence . . . . . . . . . . . . . . . . . 108 4

Flatte, Michael E.

246

Low-Frequency Spin Dynamics in the CeMIn5 Materials  

NASA Astrophysics Data System (ADS)

We measure the spin lattice relaxation of the planar In(1) nuclei in the CeMIn5 materials, extract quantitative information about the low energy spin dynamics of the lattice of Ce moments in both CeRhIn5 and CeCoIn5, and identify a crossover in the normal state. Above a temperature T* the Ce lattice exhibits “Kondo gas” behavior characterized by local fluctuations of independently screened moments; below T* both systems exhibit a “Kondo liquid” regime in which interactions between the local moments contribute to the spin dynamics. Both the antiferromagnetic and superconducting ground states in these systems emerge from the Kondo liquid regime. Our analysis provides strong evidence for quantum criticality in CeCoIn5.

Curro, N. J.; Sarrao, J. L.; Thompson, J. D.; Pagliuso, P. G.; Kos, Š.; Abanov, Ar.; Pines, D.

2003-06-01

247

Absorption Effects due to Spin in the Worldline Approach to Black Hole Dynamics  

E-print Network

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

Rafael A. Porto

2007-10-26

248

Real-time dynamics of spin-dependent transport through a double-quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction  

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

249

Real-time dynamics of spin-dependent transport through a double-quantum-dot Aharonov-Bohm interferometer with spin-orbit interaction  

E-print Network

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

250

Feasibility of measuring surface electron spin dynamics by inelastic scattering of metastable helium atoms  

E-print Network

Feasibility of measuring surface electron spin dynamics by inelastic scattering of metastable helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University January 1998 The application of inelastic scattering of monoenergetic beams of metastable 23 S helium

Kais, Sabre

251

Spin dynamics of polaritons in II-VI microcavities: detuning dependence  

E-print Network

Spin dynamics of polaritons in II-VI microcavities: detuning dependence G. Aichmayr1 , M.D. Martín1 studied the polarization of the light emitted by a semiconductor microcavity as a function of the detuning on the cavity-exciton detuning ( = EC - EX): it is positive for > 0 and negative for

Viña, Luis

252

Lattice-Site-Specific Spin Dynamics in Double Perovskite Sr2CoOsO6  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

253

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

SciTech Connect

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

254

Spin dynamics in a frustrated magnet J. van Lierop and D.H. Ryan  

E-print Network

Spin dynamics in a frustrated magnet J. van Lierop and D.H. Ryan Physics Department and Centre in terms of the static and basic dy- namic magnetic behaviour of frustrated magnets, the de- tailed nature-characterized, metallurgically stable, partially frustrated Heisenberg magnet

Ryan, Dominic

255

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

PubMed

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

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

2014-04-11

256

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

E-print Network

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

257

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

E-print Network

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

258

Laser-induced ultrafast spin dynamics in di-, tri- and tetranuclear nickel clusters, and the M process  

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

259

Dynamical Spin Squeezing via Higher Order Trotter-Suzuki Approximation  

E-print Network

Here we provide a scheme of transforming the one-axis twisting Hamiltonian into the two-axis twisting one based on high order Trotter-Suzuki Approximation. Compared with the paper [Y. C. Liu et al., Phys. Rev. Lett. 107, 013601 (2011)], our method can reduce the number of controlling cycles from $1000$ to $50$. Moreover, it is also spin number independent and takes shorter optimal evolution time contrast with the method in the work [C. Shen et al., Phys. Rev. A 87, 051801 (2013)]. The corresponding error analysis is also provided.

Ji-Ying Zhang; Xiang-Fa Zhou; Guang-Can Guo; Zheng-Wei Zhou

2014-07-16

260

Dynamics of a spinning spacecraft during extension of flexible appendages  

NASA Astrophysics Data System (ADS)

This paper addresses the problem of analyzing the deployment of flexible appendages from a central rigid hub of a spinning spacecraft. The rigorous mathematical modeling of mass flow and changing structural configuration of the spacecraft during deployment, while the vehicle experiences small elastic deflection and small angular rate, is presented. The equations of motion are obtained in terms of integro-partial differential equations. An approximate solution for the equations of motion is obtained by using a Raleigh-Ritz method and numerical results are presented for several deployment strategies. For every instantaneous physical configuration of the spacecraft, that extension rate which will lead to unstable behavior is also determined.

Turner, J.; Keat, J.; Messac, A.

1984-05-01

261

Dynamics of polymer film formation during spin coating  

SciTech Connect

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

262

Dynamical magnetic and nuclear polarization in complex spin systems: semi-magnetic II-VI quantum dots  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

263

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics  

PubMed Central

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

264

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

265

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics.  

PubMed

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

266

Coherent spin-transfer dynamics in diluted magnetic semiconductor quantum wells even after optical excitation with zero net angular momentum  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

267

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

NASA Astrophysics Data System (ADS)

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

Nifle, M.; Hilhorst, H. J.

1991-01-01

268

Dynamical phases in quenched spin–orbit-coupled degenerate Fermi gas  

NASA Astrophysics Data System (ADS)

The spin–orbit-coupled degenerate Fermi gas provides a new platform for realizing topological superfluids and related topological excitations. However, previous studies have been mainly focused on the topological properties of the stationary ground state. Here, we investigate the quench dynamics of a spin–orbit-coupled two-dimensional Fermi gas in which the Zeeman field serves as the major quench parameter. Three post-quench dynamical phases are identified according to the asymptotic behaviour of the order parameter. In the undamped phase, a persistent oscillation of the order parameter may support a topological Floquet state with multiple edge states. In the damped phase, the magnitude of the order parameter approaches a constant via a power-law decay, which may support a dynamical topological phase with one edge state at the boundary. In the overdamped phase, the order parameter decays to zero exponentially although the condensate fraction remains finite. These predictions can be observed in the strong-coupling regime.

Dong, Ying; Dong, Lin; Gong, Ming; Pu, Han

2015-01-01

269

Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices.  

PubMed

Thermodynamic properties of a spin ice model on a Kagomé lattice are obtained from dynamic simulations and compared with properties in square lattice spin ice. The model assumes three-component Heisenberg-like dipoles of an array of planar magnetic islands situated on a Kagomé lattice. Ising variables are avoided. The island dipoles interact via long-range dipolar interactions and are restricted in their motion due to local shape anisotropies. We define various order parameters and obtain them and thermodynamic properties from the dynamics of the system via a Langevin equation, solved by the Heun algorithm. Generally, a slow cooling from high to low temperature does not lead to a particular state of order, even for a set of coupling parameters that gives well thermalized states and dynamics. At very low temperature, however, square ice is more likely to reach states near the ground state than Kagomé ice, for the same island coupling parameters. PMID:25640326

Wysin, G M; Pereira, A R; Moura-Melo, W A; de Araujo, C I L

2015-02-25

270

Dynamics During Thrust Maneuvers of Flexible Spinning Satellites with Axial and Radial Booms  

NASA Technical Reports Server (NTRS)

The dynamic response to operational maneuvers of spinning symmetric spacecraft with radial and axial booms was analyzed as part of the prelaunch dynamic analysis of the ISEE-3 spacecraft placed in a halo orbit around an Earth-Sun libration point, and later renamed ICE when it was directed to fly-by comet Giacobini-Zinner. The results presented use simple spacecraft models, and frequently give predictions that are good and easily obtained when the results from using a general purpose multibody dynamics program were very time consuming to obtain. Deployment of radial booms, spin-up after partial deployment, stationkeeping, and trajectory changes are analyzed. The latter two can involve both axial thrusting and pulsed radial thrusting once per revolution.

Longman, R. W.; Fedor, J. V.

1986-01-01

271

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

PubMed

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

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

2014-03-01

272

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

273

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

PubMed

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

Moussaoui, Ali; Auger, Pierre; Roche, Benjamin

2014-09-01

274

Spin-system dynamics and fault detection in threshold networks  

SciTech Connect

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

275

Using synthetic model systems to understand charge separation and spin dynamics in photosynthetic reaction centers.  

SciTech Connect

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

276

In-plane magnetization dynamics driven by spin-polarized currents in magnetic nanostructures  

NASA Astrophysics Data System (ADS)

We have theoretically studied the magnetization behavior in the magnetic trilayer nanostructures under the influence of spin-transfer torque using the Landau-Lifshitz-Gilbert equation. The focus is the large angle dynamic precession mode of the magnetization in the film plane that can be induced and sustained by the spin current under certain circumstance although the Gilbert damping is present. Based on the study, the recent experimental observations of microwave oscillation and its characteristics can be well explained and its origin, which is in controversy, can be understood.

Xi, Haiwen; Lin, Zhi

2004-09-01

277

Spin-wave quantization and dynamic coupling in micron-size circular magnetic dots  

NASA Astrophysics Data System (ADS)

We report on the observation of spin-wave quantization in square arrays of micron-size circular magnetic Ni80Fe20 dots by means of Brillouin light-scattering spectroscopy. For a large wave-vector interval several discrete, dispersionless modes with a frequency splitting of up to 2.5 GHz were observed. The modes are identified as magnetostatic surface spin waves laterally quantized due to in-plane confinement in each single dot. The frequencies of the lowest observed modes decrease with increasing distance between the dots, thus indicating an essential dynamic magnetic dipole interaction between the dots at small interdot distances.

Jorzick, J.; Demokritov, S. O.; Hillebrands, B.; Bartenlian, B.; Chappert, C.; Decanini, D.; Rousseaux, F.; Cambril, E.

1999-12-01

278

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

SciTech Connect

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

279

Transverse susceptibility and the T3/2 law in the dynamic spin-fluctuation theory  

NASA Astrophysics Data System (ADS)

We obtain explicit expressions for elements of the magnetic susceptibility tensor in the dynamic spin-fluctuation theory. Using an analytic continuation of the Green's functions, we show that the transverse susceptibility has spin-wave poles at low temperatures, yielding the asymptotic T3/2 law for magnetization. We derive an explicit expression for the coefficient in the T3/2 law based on the multiband Hubbard Hamiltonian and real band structure. We demonstrate the correct low-temperature behavior of magnetization in the example of iron.

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

2014-11-01

280

Effect of the speed of a single-channel dynamic range compressor on intelligibility in a competing speech task  

NASA Astrophysics Data System (ADS)

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

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

2003-08-01

281

Spatio-temporal dynamics induced by competing instabilities in two asymmetrically coupled nonlinear evolution equations  

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

282

Non-Markovian dynamics of a single-mode cavity strongly coupled to an inhomogeneously broadened spin ensemble  

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

283

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

E-print Network

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

2014-08-14

284

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

NASA Astrophysics Data System (ADS)

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.

Veshtort, Mikhail; Griffin, Robert G.

2011-10-01

285

Emotional Intelligence and Cross-Cultural Communication Competence: An Analysis of Group Dynamics and Interpersonal Relationships in a Diverse Classroom  

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

286

Spin-glass dynamics in Feââ\\/sub x\\/Ti\\/sub 1+\\/\\/sub x\\/Oâ  

Microsoft Academic Search

Zero-field muon-spin-relaxation (..mu..SR) and X-band ESR have been used to study the spin-freezing dynamics in single crystals of the Ising spin glass Feââ\\/sub x\\/ Ti\\/sub 1+\\/\\/sub x\\/ Oâ . Parameters obtained for the power-law and Vogel--Fulcher descriptions of the critical slowing are consistent with other methods for x = 0 and indicate significantly slower freezing in Ti-rich samples. Interpretation of

R. L. Lichti; S. Kumar; C. Boekema

1988-01-01

287

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

288

Borehole temperature response for competing models of Laurentide ice sheet dynamics  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

289

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

E-print Network

We investigate the one-body dissipation dynamics in heavy-ion collisions of $^{16}{\\rm O}$+$^{16}{\\rm O}$ using a fully three-dimensional time-dependent Hartree-Fock (TDHF) theory with the modern Skyrme energy functional and without any symmetry restrictions. The energy dissipation is revealed to decrease in deep-inelastic collisions of the light systems as the bombarding energy increases owing to the competition between collective motion and single-particle degrees of freedom. The role of spin-orbit force is given particular emphasis in deep-inelastic collisions. The spin-orbit force causes a significant enhancement of the dissipation. The time-even coupling of spin-orbit force plays a dominant role at low energies, while the influence of time-odd terms is notable at high energies. About 40-65\\% of the total dissipation depending on the different parameter sets is predicted to arise from the spin-orbit force. The theoretical fusion cross section has a reasonably good agreement with the experimental data, considering that no free parameters are adjusted to reaction dynamics in the TDHF approach.

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

2014-10-21

290

Distinguishing the ultrafast dynamics of orbital and spin magnetic moments in solids  

NASA Astrophysics Data System (ADS)

Ultrafast magnetization dynamics is an important issue for both fundamental science and for applications in order to optimize spin manipulation on a microscopic level. Since the first observation of laser induced spin dynamics,ootnotetextBeaurepaire, E., Merle, J.C., Daunois, A., and Bigot, J.-Y. Phys. Rev. Lett. 76, 4250 (1996). the mechanisms of angular momentum dissipation at picosecond timescales have been widely debated. In order to progress in the understanding of such microscopic ultrafast mechanisms, it is now possible to probe absolute values of magnetization with a high temporal resolution (100 fs). In this context, we have used ultrashort optical laser pulses (60 fs duration) to induce changes of the magnetization in a ferromagnetic CoPd alloy film with perpendicular anisotropy. The dynamics was probed with ultrashort circularly polarized femtosecond X-ray pulses, measuring the X-ray magnetic circular dichroism (XMCD) at Co L2,3 edges.ootnotetextStamm, C. Kachel, T., Pontius, N., Mitnzer, R., Quast, T., Holldack, Khan, S., Lupulescu, C., Aziz, E. F., Wietstruk, M., D"urr, H. A., and Eberhardt, W. Nature Mater. 6, 740-743 (2007).^,ootnotetextC. Boeglin, E. Beaurepaire, V. Halt'e, V. Lopez-Flores, C. Stamm, N. Pontius, H. D"urr, J. -Y. Bigot "Observing how fast the spin-orbit interaction branches spin and orbital moments in solids" Nature 465, 458 (2010). We observe that the two components of the magnetic moments (L and S) show different ultrafast dynamics and that the spin-orbit coupling related to the magneto-crystalline anisotropy in solids is strongly affected by fs laser pulses in the ultrashort time scales. These dynamics can be compared to the purely electronic effect at the CoL3 edge. Electronic excitations and their response to the laser pump pulse will be discussed and related to the modifications in the spin-orbit coupling. We will compare our results with time resolved MOKE experiments recently performed on CoPd alloys.

Boeglin, Christine

2011-03-01

291

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

SciTech Connect

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

292

Valley and spin dynamics in MoSe2 two-dimensional crystals  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

293

Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron  

SciTech Connect

Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD) simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

Chui, C. P. [Department of Electronic and Information Engineering, the Hong Kong Polytechnic University (Hong Kong)] [Department of Electronic and Information Engineering, the Hong Kong Polytechnic University (Hong Kong); Zhou, Yan, E-mail: yanzhou@hku.hk [Department of Physics, the University of Hong Kong (Hong Kong)] [Department of Physics, the University of Hong Kong (Hong Kong)

2014-03-15

294

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

SciTech Connect

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

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

2011-07-01

295

Dynamic spin correlations in the frustrated cubic phase of MnV2O4  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

296

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

297

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

PubMed

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

298

Journal of Low Temperature Physics, VoL 89, Nos. 3/4, 1992 BOUNDARY EFFECTS IN TRANSVERSE SPIN DYNAMICS OF  

E-print Network

implications for helium and hydrogen systems are discussed, including the signs of surface spin modes. SpinJournal of Low Temperature Physics, VoL 89, Nos. 3/4, 1992 BOUNDARY EFFECTS IN TRANSVERSE SPIN DYNAMICS OF SPIN-POLARIZED QUANTUM GASES S. Stepaniants, A. E. Meyerovich Department of Physics, University

Meyerovich, Alex

299

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

SciTech Connect

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

300

Triplet exciton dynamics and spin-lattice relaxation in MTPA(TCNQ)2  

Microsoft Academic Search

A model for the effects of triplet exciton dynamics on the nuclear spin-lattice relaxation is presented. Excitons are considered as random-walking particles on a finite, one-dimensional lattice and as interacting with the nuclear magnetic moments through both dipole-dipole and Fermi contact mechanisms. The model is specifically applied to the phi 3CH3As salt of tetracyanoquinodimethane for which the orientation and temperature

S. R. Bondeson

1978-01-01

301

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

Microsoft Academic Search

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

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

2005-01-01

302

Transient photoluminescence spectroscopy of spin injection dynamics in double quantum wells of diluted magnetic semiconductors  

Microsoft Academic Search

Dynamics of spin injection has been studied in double quantum wells (DQWs) composed of diluted magnetic and non-magnetic semiconductors. Picosecond-transient photoluminescence (PL) of excitons in the DQWs has been measured in magnetic field. In the Cd1?xMnxTe-based DQWs, the PL intensity of the magnetic well (MW) excitons decays faster with decreasing barrier width from 12 to 2nm. This provides the evidence

K. Kayanuma; K. Seo; K. Nishibayashi; A. Murayama; Y. Oka; I. A. Buyanova; W. M. Chen

2006-01-01

303

Dynamic magnetic properties of the mixed spin-1 and spin-3/2 Ising system on a two-layer square lattice  

NASA Astrophysics Data System (ADS)

In this study, the dynamic critical behavior of the mixed spin-1 and spin-3/2 Ising system on a bilayer square lattice is studied by using the Glauber-type stochastic dynamics for both ferromagnetic/ferromagnetic (FM/FM) and antiferromagnetic/ferromagnetic (AFM/FM) interactions in the presence of a time-varying external magnetic field. The dynamic equations describing the time-dependencies of the average magnetizations are derived from the Master equation. The phases in the system are obtained by solving these dynamic equations. The temperature dependence of the dynamic magnetizations is investigated in order to characterize the nature (first- or second-order) of the dynamic phase transitions and to obtain the dynamic phase transition temperatures. The dynamic phase diagrams are constructed in seven different planes for both FM/FM and AFM/FM interactions and the effects of the related interaction parameters on the dynamic phase diagrams are examined. It is found that the dynamic phase diagrams display many dynamic critical points, such as tricritical point, triple point (TP), quadruple point (QP), double critical end point (B), multicritical point (A) and tetracritical point (M). Moreover, the reentrant behavior is observed for AFM/FM interaction in the system.

Temizer, Ümüt

2014-12-01

304

Spin-labeled psoralen probes for the study of DNA dynamics  

SciTech Connect

Six nitroxide spin-labeled psoralen derivatives have been synthesized and evaluated as probes for structural and dynamic studies. Sequence specific photoaddition of these derivatives to DNA oligonucleotides resulted in site-specifically cross-linked and spin-labeled oligomers. Comparison of the general line shape features of the observed electron paramagnetic resonance (EPR) spectra of several duplexes ranging in size from 8 to 46 base pairs with simulated EPR spectra indicate that the nitroxide spin-labeled probe reports the global tumbling motion of the oligomers. While there is no apparent large amplitude motion of the psoralen other than the overall tumbling of DNA on the time scales investigated, there are no indications of bending and other residual motions. The (A)BC excinuclease DNA repair system detects structural or dynamic features of the DNA that distinguish between damaged and undamaged DNA and are independent of the intrinsic structure of the lesion. NMR studies have shown that psoralen-cross-linked DNA has altered backbone dynamics and conformational populations in the immediate vicinity of the adduct. We suggested that the signal for recognition of a lesion to be repaired is in the sugar-phosphate backbone and not in the damaged base(s). 71 refs., 11 figs., 1 tab.

Spielmann, H.P.; Chi, D.Y.; Hunt, N.G. [Lawrence Berkeley Lab., CA (United States)] [and others

1995-11-14

305

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

E-print Network

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

306

Dynamics of tripartite geometric quantifiers of correlations in a quantum spin system  

NASA Astrophysics Data System (ADS)

We derive an exact formula of geometric measure of quantum discord (GMQD) for an arbitrary 3-qubit state. The dynamics of GMQD in a quantum spin system coupled to a thermal bath is studied by simulation and analytical approximation. It is found that tripartite quantum discord has distinct time behaviors within two different eigenspaces. Further, we extend the square norm distance to define tripartite geometric quantifiers of total and classical correlations. We obtain their explicit expressions and discuss the possibility of having a closed additive relation among various kinds of correlations during the dynamical evolution.

Zhou, Jiang; Guo, Hong

2013-06-01

307

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

308

Dynamic interplay between spin-crossover and host-guest function in a nanoporous metal-organic framework material.  

SciTech Connect

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

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

2009-01-01

309

Who is in control? Competing influences of geology, land use and topography on soil moisture and soil temperature dynamics  

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

310

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

SciTech Connect

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

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

2009-01-01

311

COMPETENCIES DICTIONARY Contents Page  

E-print Network

COMPETENCIES DICTIONARY Contents Page Core Competencies Results Orientation/Project Management Functional Competencies Flexibility and Development .....................................................................11-12 Leadership Competencies

Bieber, Michael

312

First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules  

SciTech Connect

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

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

2013-08-21

313

Dynamic Phase Transitions In The Spin-2 Ising System Under An Oscillating Magnetic Field Within The Effective-Field Theory  

SciTech Connect

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

314

Dynamics of the Spin Liquid Phase of Cs2CuCl4  

NASA Astrophysics Data System (ADS)

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

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

2008-03-01

315

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

316

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

E-print Network

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

317

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

SciTech Connect

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

318

Optical analogue of quantum spin and dynamic localization in optical waveguides arrays  

NASA Astrophysics Data System (ADS)

We have discovered an optical analogue of quantum spin in optical waveguides arrays. Quantum-optical analogy is recently a hot topic. By using special configuration of optical devices, some optical analogues of quantum systems can be realized. Stefano Longhi and coworkers proposed some classical realization of quantum phenomena like the two-site Fermi-Hubbard system [1] and Rabi oscillation [2]. In this work, we propose an optical waveguides arrays system with evanescent couplings according a symmetrized Kac matrix. The system can mimic the quantum spin under different operators like the rotation operator. Also by adding a suitable time-dependent applied potential to the system, dynamic localization of optical signal can be realized along the signal propagation. The system can be extended to mimic any arbitrary angular momentum by increasing the number of optical waveguides arrays. The occurrences of spin under rotation operator and dynamic localization are simulated by a field-evolution analysis using an input Gaussian beam.[4pt] [1] S. Longhi, G. Della Valle, V. Foglietti, arXiv:1111.3460 (November 2011)[0pt] [2] Ivan L. Garanovich, Stefano Longhi, Andrey A. Sukhorukov, Yuri S. Kivshar, Physics Reports, Volume 518, Issues 1-2, September 2012, Pages 1-7

Yeung, Kin Chung Au; Yu, Kin Wah

2013-03-01

319

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

SciTech Connect

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

Chembrolu, V.

2010-02-24

320

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

PubMed

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

321

Quantum dynamics of a spin chain in the presence of engineered collective noise  

NASA Astrophysics Data System (ADS)

We experimentally and theoretically investigate the effect of engineered collective noise on the quantum dynamics of a spin chain evolving under the double-quantum Hamiltonian. This Hamiltonian is related by a similarity transformation to the isotropic XX Hamiltonian, and is experimentally accessible in solid-state NMR using coherent averaging techniques. In the absence of noise, a localized magnetic moment is observed to move down the chain at a constant velocity. We show that this transport is disrupted by the presence of collective z-noise, and that the magnetic moment becomes localized at the initial site as the strength of the noise increases. The relevance to quantum information transport in spin chains is also discussed.

Zeitler, Christopher; Anderson, Laurel E.; Viola, Lorenza; Ramanathan, Chandrasekhar

2013-03-01

322

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

PubMed

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

Rózsa, L; Udvardi, L; Szunyogh, L

2014-05-28

323

Measurement-induced dynamics for spin-chain quantum communication and its application for optical lattices  

NASA Astrophysics Data System (ADS)

We present a protocol for quantum state transfer and remote state preparation across spin chains which operate in their antiferromagnetic mode. The proposed mechanism harnesses the inherent entanglement of the ground state of the strongly correlated many-body systems which naturally exists for free. The uniform Hamiltonian of the system does not need any engineering and, during the whole process, remains intact while a single-qubit measurement followed by a single-qubit rotation are employed for both encoding and inducing dynamics in the system. This, in fact, has been inspired by recent progress in observing spin waves in optical lattice experiments, in which manipulation of the Hamiltonian is hard and instead local rotations and measurements have become viable. The attainable average fidelity stays above the classical threshold for chains up to length 50 and the system shows very good robustness against various sources of imperfection.

Pouyandeh, Sima; Shahbazi, Farhad; Bayat, Abolfazl

2014-07-01

324

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

325

Spin dynamics of antiferromagnets under action of femtosecond laser pulses (Review Article)  

NASA Astrophysics Data System (ADS)

Investigations of excitation of spin dynamics in transparent antiferromagnets (AFM) under the action of femtosecond laser pulses are reviewed. A variety of observed effects is considered in the context of a unified approach. The analysis is based on the nonlinear sigma model for the antiferromagnetism vector L with taking into account effective fields induced in a magnetic material due to the interaction between light and the spin system of the magnetic material. The contributions of various magneto-optical effects (both standard Faraday or Cotton-Mouton (Voigt) effects and specific L-dependent effects for AFM) are considered as characteristic contributions to the effective field within the sigma model. The most typical experimental data for real AFM are discussed.

Ivanov, B. A.

2014-02-01

326

Rotating frame spin dynamics of a nitrogen-vacancy center in a diamond nanocrystal  

NASA Astrophysics Data System (ADS)

We investigate the spin dynamics of a nitrogen-vacancy (NV) center contained in an individual diamond nanocrystal in the presence of continuous microwave excitation. Upon periodic reversal of the microwave phase, we observe a train of “Solomon echoes” that effectively extends the system coherence lifetime to reach several tens of microseconds, depending on the microwave power and phase inversion rate. Starting from a model where the NV center interacts with a bath of paramagnetic defects on the nanocrystal surface, we use average Hamiltonian theory to compute the signal envelope from its amplitude at the echo maxima. A comparison between the effective Rabi and Solomon propagators shows that the observed response can be understood as a form of higher-order decoupling from the spin bath.

Laraoui, Abdelghani; Meriles, Carlos A.

2011-10-01

327

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

PubMed

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

328

DYNAMICAL SPIN SUSCEPTIBILITY IN THE TD-LDA AND QSGW APPROXIMATIONS  

SciTech Connect

Abstract. This project was aimed at building the transverse dynamical spin susceptibility with the TD-LDA and the recently-developed Quasparticle Self-Consisent Approximations, which determines an optimum quasiparticle picture in a self-consistent manner within the GW approximation. Our main results were published into two papers, (J. Phys. Cond. Matt. 20, 95214 (2008), and Phys. Rev. B83, 060404(R) (2011). In the first paper we present spin wave dispersions for MnO, NiO, and #11;-MnAs based on quasiparticle self-consistent GW approximation (QSGW). For MnO and NiO, QSGW results are in rather good agreement with experiments, in contrast to the LDA and LDA+U descriptions. For #11;-MnAs, we find a collinear ferromagnetic ground state in QSGW, while this phase is unstable in the LDA. In the second, we apply TD-LDA to the CaFeAs2 â�� the first attempt the first ab initio calculation of dynamical susceptibililty in a system with complex electronic structure Magnetic excitations in the striped phase of CaFe2As2 are studied as a function of local moment amplitude. We find a new kind of excitation: sharp resonances of Stoner-like (itinerant) excitations at energies comparable to the N�´eel temperature, originating largely from a narrow band of Fe d states near the Fermi level, and coexisting with more conventional (localized) spin waves. Both kinds of excitations can show multiple branches, highlighting the inadequacy of a description based on a localized spin model.

SCHILFGAARDE, MARK VAN; KOTANI, TAKAO

2012-10-15

329

Field dependent spin dynamics in Dysprosium2Titanium2Oxygen7  

NASA Astrophysics Data System (ADS)

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

Matthews, Maria Jane

330

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

SciTech Connect

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

331

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

SciTech Connect

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

332

Dynamical phases in quenched spin-orbit-coupled degenerate Fermi gas.  

PubMed

The spin-orbit-coupled degenerate Fermi gas provides a new platform for realizing topological superfluids and related topological excitations. However, previous studies have been mainly focused on the topological properties of the stationary ground state. Here, we investigate the quench dynamics of a spin-orbit-coupled two-dimensional Fermi gas in which the Zeeman field serves as the major quench parameter. Three post-quench dynamical phases are identified according to the asymptotic behaviour of the order parameter. In the undamped phase, a persistent oscillation of the order parameter may support a topological Floquet state with multiple edge states. In the damped phase, the magnitude of the order parameter approaches a constant via a power-law decay, which may support a dynamical topological phase with one edge state at the boundary. In the overdamped phase, the order parameter decays to zero exponentially although the condensate fraction remains finite. These predictions can be observed in the strong-coupling regime. PMID:25600665

Dong, Ying; Dong, Lin; Gong, Ming; Pu, Han

2015-01-01

333

Signal interferences from turbulent spin dynamics in solution nuclear magnetic resonance spectroscopy  

NASA Astrophysics Data System (ADS)

Artifacts arising from aperiodic turbulent spin dynamics in gradient-based nuclear magnetic resonance (NMR) applications are comprehensively surveyed and numerically simulated by a nonlinear Bloch equation. The unexpected dynamics, triggered by the joint action of radiation damping and the distant dipolar field, markedly deteriorate the performance of certain pulse sequences incorporating weak pulsed-field gradients and long evolution times. The effects are demonstrated in three general classes of gradient NMR applications: solvent signal suppression, diffusion measurements, and coherence pathway selection. Gradient-modulated solvent transverse magnetization can be partially rephased in a series of self-refocusing gradient echoes that blank out solute resonances in the CHESS (chemical-shift-selective spectroscopy) and WATERGATE (gradient-tailored water suppression) solvent suppression schemes. In addition, the discovered dynamics contribute to erratic echo attenuation in pulsed gradient spin echo (PGSE) and PGSE stimulated echo diffusion measurements and produce coherence leakage in gradient-selected DQFCOSY and HMQC experiments. Specific remedies for minimizing unwanted effects are presented.

Huang, Susie Y.; Lin, Yung-Ya; Lisitza, Natalia; Warren, Warren S.

2002-06-01

334

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

335

Magnetization and spin dynamics of the spin S=(1)/(2) hourglass nanomagnet Cu5(OH)2(NIPA)4·10H2O  

NASA Astrophysics Data System (ADS)

We report a combined experimental and theoretical study of the spin S=(1)/(2) nanomagnet Cu5(OH)2(NIPA)4·10H2O (Cu5-NIPA). Using thermodynamic, electron spin resonance, and 1H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations, and a strong-coupling theory on the other, we derive a microscopic magnetic model of Cu5-NIPA and characterize the spin dynamics of this system. The elementary fivefold Cu2+ unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S=(1)/(2) doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramers' theorem), and a very large excitation gap of ??68 K. Thus, Cu5-NIPA is a good candidate for achieving long electronic spin relaxation (T1) and coherence (T2) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu2+ spins. This is a purely quantum-mechanical effect since, despite the nonfrustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu5-NIPA is a rare example of a S=(1)/(2) nanomagnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at intermediate temperatures.

Nath, R.; Tsirlin, A. A.; Khuntia, P.; Janson, O.; Förster, T.; Padmanabhan, M.; Li, J.; Skourski, Yu.; Baenitz, M.; Rosner, H.; Rousochatzakis, I.

2013-06-01

336

Spin dynamics of radical pairs with restricted geometries and strong exchange coupling: the role of hyperfine coupling.  

PubMed

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

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

2014-06-19

337

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

338

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

SciTech Connect

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

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

2011-12-23

339

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

SciTech Connect

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

340

Dynamics and Scaling in a Quantum Spin Chain Material with Bond Randomness  

SciTech Connect

Single crystal inelastic neutron scattering is used to study dynamic spin correlations in the quasi-one-dimensional quantum antiferromagnet BaCu{sub 2}(Si{sub 0.5}Ge{sub 0.5}){sub 2}O{sub 7}, where the exchange constant fluctuates due to a random distribution of Si and Ge atoms. The measured low-energy spectrum is dominated by localized excitations and can be understood in the framework of the random singlet model. The observed scaling relations for the frequency dependencies of the correlation length and structure factor are in excellent agreement with recent theoretical predictions for the renormalization group fixed point.

Masuda, Takatsugu [ORNL; Zheludev, Andrey I [ORNL; Uchinokura, K. [RIKEN, Japan; Chung, J.-H. [National Institute of Standards and Technology (NIST); Park, S. [National Institute of Standards and Technology (NIST)

2004-01-01

341

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

SciTech Connect

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

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

1999-12-13

342

BUSINESS SCHOOL At the Lee Business School, we prepare people to compete in today's dynamic marketplace through skill  

E-print Network

for Business and Economic Research for reliable indicators and insightful analysis. The center tracks keyLEE BUSINESS SCHOOL HigHligHts At the Lee Business School, we prepare people to compete in today the extras that come with the Lee Business School ­ nationally recognized, endowed faculty and the Lee

Hemmers, Oliver

343

BUSINESS SCHOOL At the Lee Business School, we prepare people to compete in today's dynamic marketplace through skill  

E-print Network

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

Hemmers, Oliver

344

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

345

Structure and dynamics of ionic aggregates in ethylene ionomer membranes: recent electron spin resonance (ESR) studies  

NASA Astrophysics Data System (ADS)

In this review we present recent advances in the understanding of self-assembling, structure, and dynamics in poly(ethylene- co-methacrylic acid) (EMAA) ionomers as membranes and water dispersions, with focus on the information obtained by electron spin resonance (ESR) studies of amphiphilic and hydrophobic nitroxide spin probes. The probes selected for this study were doxylstearic acids and esters, with the doxyl group attached to carbon atoms at different positions relative to the head group, and a nitroxide group attached to a nonadecane backbone. Application of this approach to the study of EMAA ionomers has demonstrated that, by a judicious choice of the polarity, size, and chemical structure of the probe, it is possible to explore specific regions of the microphase-separated system; an important advantage of the 'position-selectivity' method is the ability to bypass the often difficult synthetic step of spin labeling. Information on the local environment of the probes and on chain mobility in, and in the vicinity of, the ionic aggregates in the EMAA ionomers will be discussed, and compared with results obtained by other techniques.

Kutsumizu, Shoichi; Schlick, Shulamith

2005-04-01

346

Random variable approach to dissipative spin dynamics and Landau-Zener transitions  

NASA Astrophysics Data System (ADS)

We present a random variable approach to solve for the dynamics of a dissipative two-state system. Based on an exact functional integral description, our method reformulates the problem as that of non-unitary time evolution of a quantum state vector under a Hamiltonian containing random noise fields. This non-perturbative formalism goes beyond the frequently used Non-Interacting Blip Approximation (NIBA) and is particularly well suited to treat an explicitly time-dependent Hamiltonian. As an example, we consider the renowned Landau-Zener problem in the presence of an Ohmic bath with a large bath cutoff frequency ?c. We identify an intermediate time regime where the energy separation of the two spin states is much larger than their tunneling coupling ?, but still smaller than ?c such that bath mediated spin transitions still occur. Such a situation can for example be realized with a cold atomic quantum dot setup. We also derive an approximate analytical expression for the decay of the upper spin state population in this regime, which agrees well with our numerical results.

Orth, Peter P.; Le Hur, Karyn; Imambekov, Adilet

2010-03-01

347

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

NASA Astrophysics Data System (ADS)

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

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

2007-03-01

348

Dynamical Monte Carlo investigation of spin reversal and nonequilibrium magnetization of single-molecule magnets  

NASA Astrophysics Data System (ADS)

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 (MDIs). 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 systems with various temperatures and sweeping 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 3 K and the thermal-assisted tunnelings play important roles at intermediate temperature. These are consistent with corresponding experimental results on good Mn12 samples (with less disorders) in the presence of little misalignments between the easy axis and applied magnetic fields, and therefore our magnetization curves are satisfactory. Furthermore, our DMC results show that the MDI, with the thermal effects, have important effects on the LZ tunneling processes, but both the MDI and the LZ tunneling give place to the thermal-activated barrier hurdling effect in determining the magnetization curves when the temperature is near 3 K. This DMC approach can be applicable to other SMM systems and could be used to study other properties of SMM systems.

Liu, Gui-Bin; Liu, Bang-Gui

2010-10-01

349

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

NASA Astrophysics Data System (ADS)

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

Laraoui, Abdelghani; Meriles, Carlos

2012-02-01

350

Molecular dynamics in rod-like liquid crystals probed by muon spin resonance spectroscopy.  

PubMed

Muoniated spin probes were produced by the addition of muonium (Mu) to two rod-like liquid crystals: N-(4-methoxybenzylidene)-4'-n-butylaniline (MBBA) and cholesteryl nonanoate (CN). Avoided level crossing muon spin resonance spectroscopy was used to characterize the muoniated spin probes and to probe dynamics at the molecular level. In MBBA Mu adds predominantly to the carbon of the bridging imine group and the muon and methylene proton hyperfine coupling constants (hfccs) of the resulting radical shift in the nematic phase due to the dipolar hyperfine coupling, the ordering of the molecules along the applied magnetic field and fluctuations about the local director. The amplitude of these fluctuations in in the nematic phase of MBBA is determined from the temperature dependence of the methylene proton hfcc. Mu adds to the double bond of the steroidal ring system of CN and the temperature dependence of the ?(1) line width provides information about the amplitude of the fluctuations about the local director in the chiral nematic phase and the slow isotropic reorientation in the isotropic phase. PMID:21749057

McKenzie, Iain; Scheuermann, Robert; Sedlak, Kamil; Stoykov, Alexey

2011-08-01

351

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

352

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

353

Quantum Dynamics of a Particle with a Spin-dependent Velocity  

E-print Network

We study the dynamics of a particle in continuous time and space, the displacement of which is governed by an internal degree of freedom (spin). In one definite limit, the so-called quantum random walk is recovered but, although quite simple, the model possesses a rich variety of dynamics and goes far beyond this problem. Generally speaking, our framework can describe the motion of an electron in a magnetic sea near the Fermi level when linearisation of the dispersion law is possible, coupled to a transverse magnetic field. Quite unexpected behaviours are obtained. In particular, we find that when the initial wave packet is fully localized in space, the $J_{z}$ angular momentum component is frozen; this is an interesting example of an observable which, although it is not a constant of motion, has a constant expectation value. For a non-completely localized wave packet, the effect still occurs although less pronounced, and the spin keeps for ever memory of its initial state. Generally speaking, as time goes on, the spatial density profile looks rather complex, as a consequence of the competition between drift and precession, and displays various shapes according to the ratio between the Larmor period and the characteristic time of flight. The density profile gradually changes from a multimodal quickly moving distribution when the scatttering rate is small, to a unimodal standing but flattening distribution in the opposite cas case.

Claude Aslangul

2004-06-09

354

Studying Spin-Orbit Dynamics using Measurements of the Proton's Polarized Gluon Asymmetry  

E-print Network

Measurements involving the gluon spin density, Delta G=G++ - G+-, can play an important role in the quantitative understanding of proton structure. To demonstrate this, we show that the shape of the gluon asymmetry, A(x,t)=Delta G(x,t)/G(x,t), contains significant dynamical information about non-perturbative spin-orbit effects. It is instructive to use a separation A(x,t)=A_0^epsilon(x)+epsilon(x,t), where A_0^epsilon(x) is an approximately scale-invariant form that can be calculated within a given factorization prescription from the measured distributions Delta q(x,t), q(x,t) and G(x,t). Applying this separation with the J_z=1/2 sum rule provides a convenient way to determine the total amount of orbital angular momentum generated by mechanisms associated with confinement and chiral dynamics. The results are consistent with alternate non-perturbative approaches to the determination of orbital angular momentum in the proton. Our studies help to specify the accuracy that future measurements should achieve to constrain theoretical models for nucleon structure.

Yevgeny Binder; Gordon P. Ramsey; Dennis Sivers

2011-07-26

355

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

NASA Astrophysics Data System (ADS)

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

Rivas, Angel; Martin-Delgado, Miguel A.

2013-03-01

356

Protein-induced changes in DNA structure and dynamics observed with noncovalent site-directed spin labeling and PELDOR  

PubMed Central

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

357

Recent NASA Research on Aerodynamic Modeling of Post-Stall and Spin Dynamics of Large Transport Airplanes  

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

358

Spin as Primordial Self-Referential Process Driving Quantum Mechanics, Spacetime Dynamics and Consciousness  

Microsoft Academic Search

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

Huping Hu; Maoxin Wu

359

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

360

Dynamical spin-orbital correlation in the frustrated magnet Ba3CuSb2O9.  

PubMed

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

361

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

SciTech Connect

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

362

Using Bio-Functionalized Magnetic Nanoparticles and Dynamic Nuclear Magnetic Resonance to Characterize the Time-Dependent Spin-Spin Relaxation Time for Sensitive Bio-Detection  

PubMed Central

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

363

Dynamics of the sub-Ohmic spin-boson model: a comparison of three numerical approaches.  

PubMed

Dynamics of the sub-Ohmic spin-boson model is examined using three numerical approaches, namely the Dirac-Frenkel time-dependent variation with the Davydov D(1) ansatz, the adaptive time-dependent density matrix renormalization group method within the representation of orthogonal polynomials, and a perturbative approach based on a unitary transformation. In order to probe the validity regimes of the three approaches, we study the dynamics of a qubit coupled to a bosonic bath with and without a local field. Comparison of the up-state population evolution shows that the three approaches are in agreement in the weak-coupling regime but exhibit marked differences when the coupling strength is large. The Davydov D(1) ansatz and the time-dependent density matrix renormalization group can both be reliably employed in the weak-coupling regime, while the former is also valid in the strong-coupling regime as judged by how faithfully the trial state follows the Schrödinger equation. We further explore the bipartite entanglement dynamics between two qubits coupled with individual bosonic baths which reveals entanglement sudden death and revival. PMID:24032962

Yao, Yao; Duan, Liwei; Lü, Zhiguo; Wu, Chang-Qin; Zhao, Yang

2013-08-01

364

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

PubMed

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

365

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

366

Conservation laws protect dynamic spin correlations from decay: Limited role of integrability in the central spin model  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

367

Influence of composition and particle size on spin dynamics and thermodynamic properties of magnetoresistive perovskites.  

PubMed

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

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

2008-02-01

368

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

369

Surface dynamics and friction of K\\/Cu(001) characterized by helium-3 spin-echo and density functional theory  

Microsoft Academic Search

Helium-3 spin-echo measurements of K\\/Cu(001) are presented, the diffusional surface dynamics of the system at low coverages and on picosecond time scales. Langevin molecular-dynamics simulations are used, together with a potential-energy surface derived from density functional theory calculations, to provide further understanding of the experimental data. An anisotropic potential with a corrugation of 35-64 meV and a friction parameter of

H. Hedgeland; P. R. Kole; H. R. Davies; A. P. Jardine; G. Alexandrowicz; W. Allison; J. Ellis; G. Fratesi; G. P. Brivio

2009-01-01

370

Dynamics of Reassembled Thioredoxin Studied by Magic Angle Spinning NMR: Snapshots from Different Timescales  

PubMed Central

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

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

2014-01-01

371

The dynamics in polyethyleneoxide-alkali iodide complexes investigated by neutron spin-echo spectroscopy and molecular dynamics simulations  

NASA Astrophysics Data System (ADS)

We determined the self part of the intermediate scattering function in liquid polyethyleneoxide (PEO) and PEO-alkali iodide complexes by means of neutron spin-echo spectroscopy and molecular dynamics (MD) computer simulations. We present the first accurate quantitative results on the segmental dynamics in the time range up to 1 ns and the wave-vector range from a few nm-1 to approximately 20 nm-1. We investigate the influence of polymer chain length, salt concentration, and cation type. We find that the neutron data and MD data for pure PEO agree very well. A relatively small concentration of dissolved salt (1 metal ion per 15 monomers) leads to a slowing down of the segmental motions by an order of magnitude. Here, the MD simulations agree qualitatively. Increasing the chain length from 23 to 182 monomers has no significant effect except at the highest salt concentration. Similarly, changing the cation from Li to Na hardly makes any difference. The Rouse model does not adequately describe our data.

Mos, B.; Verkerk, P.; Pouget, S.; van Zon, A.; Bel, G.-J.; de Leeuw, S. W.; Eisenbach, C. D.

2000-07-01

372

Micromagnetic simulations of spin-wave normal modes and the spin-transfer-torque driven magnetization dynamics of a ferromagnetic cross  

NASA Astrophysics Data System (ADS)

We studied spin-transfer-torque (STT) switching of a cross-shaped magnetic tunnel junction in a recent report [Roy et al., J. Appl. Phys. 113, 223904 (2013)]. In that structure, the free layer is designed to have four stable energy states using the shape anisotropy of a cross. STT switching showed different regions with increasing current density. Here, we employ the micromagnetic spectral mapping technique in an attempt to understand how the asymmetry of cross dimensions and spin polarization direction of the injected current affect the magnetization dynamics. We compute spatially averaged frequency-domain spectrum of the time-domain magnetization dynamics in the presence of the current-induced STT term. At low currents, the asymmetry of polarization direction and that of the arms are observed to cause a splitting of the excited frequency modes. Higher harmonics are also observed, presumably due to spin-wave wells caused by the regions of spatially non-uniform effective magnetic field. The results could be used towards designing a multi-bit-per-cell STT-based random access memory with an improved storage density.

Pramanik, Tanmoy; Roy, Urmimala; Tsoi, Maxim; Register, Leonard F.; Banerjee, Sanjay K.

2014-05-01

373

Micromagnetic simulations of spin-wave normal modes and the spin-transfer-torque driven magnetization dynamics of a ferromagnetic cross  

SciTech Connect

We studied spin-transfer-torque (STT) switching of a cross-shaped magnetic tunnel junction in a recent report [Roy et al., J. Appl. Phys. 113, 223904 (2013)]. In that structure, the free layer is designed to have four stable energy states using the shape anisotropy of a cross. STT switching showed different regions with increasing current density. Here, we employ the micromagnetic spectral mapping technique in an attempt to understand how the asymmetry of cross dimensions and spin polarization direction of the injected current affect the magnetization dynamics. We compute spatially averaged frequency-domain spectrum of the time-domain magnetization dynamics in the presence of the current-induced STT term. At low currents, the asymmetry of polarization direction and that of the arms are observed to cause a splitting of the excited frequency modes. Higher harmonics are also observed, presumably due to spin-wave wells caused by the regions of spatially non-uniform effective magnetic field. The results could be used towards designing a multi-bit-per-cell STT-based random access memory with an improved storage density.

Pramanik, Tanmoy, E-mail: pramanik.tanmoy@utexas.edu; Roy, Urmimala; Register, Leonard F.; Banerjee, Sanjay K. [Microelectronics Research Center, University of Texas at Austin, Texas 78758 (United States); Tsoi, Maxim [Physics Department, University of Texas at Austin, Texas 78712 (United States)

2014-05-07

374

The self-propelled Brownian spinning top: dynamics of a biaxial swimmer at low Reynolds numbers  

E-print Network

Recently, the Brownian dynamics of self-propelled (active) rod-like particles was explored to model the motion of colloidal microswimmers, catalytically-driven nanorods, and bacteria. Here, we generalize this description to biaxial particles with arbitrary shape and derive the corresponding Langevin equation for a self-propelled Brownian spinning top. The biaxial swimmer is exposed to a hydrodynamic Stokes friction force at low Reynolds numbers, to fluctuating random forces and torques as well as to an external and an internal (effective) force and torque. The latter quantities control its self-propulsion. Due to biaxiality and hydrodynamic translational-rotational coupling, the Langevin equation can only be solved numerically. In the special case of an orthotropic particle in the absence of external forces and torques, the noise-free (zero-temperature) trajectory is analytically found to be a circular helix. This trajectory is confirmed numerically to be more complex in the general case involving a transient...

Wittkowski, Raphael

2011-01-01

375

Tunable magnetization dynamics in disordered FePdPt ternary alloys: Effects of spin orbit coupling  

NASA Astrophysics Data System (ADS)

The magnetization dynamics of disordered Fe0.5(Pd1-xPtx)0.5 alloy films was studied by time-resolved magneto-optical Kerr effect and ferromagnetic resonance. The intrinsic Gilbert damping parameter ?0 and the resonance linewidth change linearly with the Pt atomic concentration. In particular, the induced in-plane uniaxial anisotropy constant KU also increases for x increasing from 0 to 1. All these results can be attributed to the tuning effect of the spin orbit coupling. For the disordered ternary alloys, an approach is proposed to control the induced in-plane uniaxial anisotropy, different from conventional thermal treat methods, which is helpful to design and fabrications of spintronic devices.

Ma, L.; Li, S. F.; He, P.; Fan, W. J.; Xu, X. G.; Jiang, Y.; Lai, T. S.; Chen, F. L.; Zhou, S. M.

2014-09-01

376

Equilibrium and nonequilibrium dynamics of the sub-Ohmic spin-boson model.  

PubMed

Employing the nonperturbative numerical renormalization group method, we study the dynamics of the spin-boson model, which describes a two-level system coupled to a bosonic bath with a spectral density J(omega) proportional to omega(s). We show that, in contrast with the case of Ohmic damping, the delocalized phase of the sub-Ohmic model cannot be characterized by a single energy scale only, due to the presence of a nontrivial quantum phase transition. In the strongly sub-Ohmic regime, s<1, weakly damped coherent oscillations on short time scales are possible even in the localized phase--this is of crucial relevance, e.g., for qubits subject to electromagnetic noise. PMID:17677752

Anders, Frithjof B; Bulla, Ralf; Vojta, Matthias

2007-05-25

377

Competing Technologies  

Microsoft Academic Search

\\u000a In general it can be assumed that there exists a potential market for TPV systems anywhere that an electrical power source\\u000a is required. Hence, in order to identify suitable TPV applications, this chapter reviews other deployed and emerging electricity\\u000a generating technologies.\\u000a \\u000a \\u000a In TPV literature, competing technologies discussed have included internal heat engine generators , solar PV systems, electro-chemical\\u000a cells and

Thomas Bauer

378

Quantum optimal control of isomerization dynamics of a one-dimensional reaction-path model dominated by a competing dissociation channel  

SciTech Connect

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

Kurosaki, Yuzuru [Kansai Photon Science Institute, Japan Atomic Energy Agency, Kizugawa, Kyoto 619-0215 (Japan); Artamonov, Maxim; Ho, Tak-San; Rabitz, Herschel [Department of Chemistry, Princeton University, Princeton, New Jersey 08544 (United States)

2009-07-28

379

Neutron Spin-Echo Investigation of Slow Spin Dynamics in Kagome-Bilayer Frustrated Magnets as Evidence for Phonon Assisted Relaxation in SrCr9xGa129xO19  

E-print Network

Neutron Spin-Echo Investigation of Slow Spin Dynamics in Kagome´-Bilayer Frustrated Magnets Magnetic systems with geometrical frustration provide an interesting field of investigation of complex such as in the pyrochlore lattice. A general feature of frustrated magnets is the existence of short-range correlations

Paris-Sud 11, Université de

380

Magnetic susceptibility and spin dynamics of a polyoxovanadate cluster: A proton NMR study of a model spin tetramer  

NASA Astrophysics Data System (ADS)

We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate compound with formula (NHEt)3[VIV8VV4As8O40(H2O)]?H2O?{V12}. The magnetic properties can be described by considering only the central square of localized V4+ ions and treated by an isotropic Heisenberg Hamiltonian of four intrinsic spins 1/2 coupled by nearest-neighbor antiferromagnetic interaction with J˜17.6 K. In this simplified description the ground state is nonmagnetic with ST=0. The 1H NMR linewidth (full width at half maximum) data depend on both the magnetic field and temperature, and are explained by the dipolar interaction between proton nuclei and V4+ ion spins. The behavior of the nuclear spin-lattice relaxation rate T-11 in the temperature range (4.2 300 K) is similar to that of ?T vs T and it does not show any peak at low temperatures contrary to previous observations in antiferromagnetic rings with larger intrinsic spins. The results are explained by using the general features of the Moriya formula and by introducing a single T-independent broadening parameter for the electronic spin system. From the exponential T dependence of T-11 at low T (2.5 K

Procissi, D.; Shastri, A.; Rousochatzakis, I.; Al Rifai, M.; Kögerler, P.; Luban, M.; Suh, B. J.; Borsa, F.

2004-03-01

381

Materials optimization and ghz spin dynamics of metallic ferromagnetic thin film heterostructures  

NASA Astrophysics Data System (ADS)

Metallic ferromagnetic (FM) thin film heterostructures play an important role in emerging magnetoelectronic devices, which introduce the spin degree of freedom of electrons into conventional charge-based electronic devices. As the majority of magnetoelectronic devices operate in the GHz frequency range, it is critical to understand the high-frequency magnetization dynamics in these structures. In this thesis, we start with the static magnetic properties of FM thin films and their optimization via the field-sputtering process incorporating a specially designed in-situ electromagnet. We focus on the origins of anisotropy and hysteresis/coercivity in soft magnetic thin films, which are most relevant to magentic susceptibility and power dissipation in applications in the sub-GHz frequency regime, such as magnetic-core integrated inductors. Next we explore GHz magnetization dynamics in thin-film heterostructures, both in semi-infinite samples and confined geometries. All investigations are rooted in the Landau-Lifshitz-Gilbert (LLG) equation, the equation of motion for magnetization. The phenomenological Gilbert damping parameter in the LLG equation has been interpreted, since the 1970's, in terms of the electrical resistivity. We present the first interpretation of the size effect in Gilbert damping in single metallic FM films based on this electron theory of damping. The LLG equation is intrinsically nonlinear, which provides possibilities for rf signal processing. We analyze the frequency doubling effect at small-angle magnetization precession from the first-order expansion of the LLG equation, and demonstrate second harmonic generation from Ni81 Fe19 (Permalloy) thin film under ferromagnetic resonance (FMR), three orders of magnitude more efficient than in ferrites traditionally used in rf devices. Though the efficiency is less than in semiconductor devices, we provide field- and frequency-selectivity in the second harmonic generation. To address further the relationship between the rf excitation and the magnetization dynamics in systems with higher complexity, such as multilayered thin films consisting of nonmagnetic (NM) and FM layers, we employ the powerful time-resolved x-ray magnetic circular dichroism (TR-XMCD) spectroscopy. Soft x-rays have element-specific absorption, leading to layer-specific magnetization detection provided the FM layers have distinctive compositions. We discovered that in contrast to what has been routinely assumed, for layer thicknesses well below the skin depth of the EM wave, a significant phase difference exists between the rf magnetic fields H rf in different FM layers separated by a Cu spacer layer. We propose an analysis based on the distribution of the EM waves in the film stack and substrate to interpret this striking observation. For confined geometries with lateral dimensions in the sub-micron regime, there has been a critical absence of experimental techniques which can image small-amplitude dynamics of these structures. We extend the TR-XMCD technique to scanning transmission x-ray microscopy (STXM), to observe directly the local magnetization dynamics in nanoscale FM thin-film elements, demonstrated at picosecond temporal, 40 nm spatial and < 6° angular resolution. The experimental data are compared with our micromagnetic simulations based on the finite element analysis of the time-dependent LLG equation. We resolve standing spin wave modes in nanoscale Ni81 Fe19 thin film ellipses (1000 nm x 500 nm x 20 nm) with clear phase information to distinguish between degenerate eigenmodes with different symmetries for the first time. With the element-specific imaging capability of soft x-rays, spatial resolution up to 15 nm with improved optics, we see great potential for this technique to investigate functional devices with multiple FM layers, and provide insight into the studies of spin injection, manipulation and detection.

Cheng, Cheng

382

Competent Psychopharmacology  

PubMed Central

There is little doubt that undergraduate and post-graduate training of physicians, pharmacists, and nurses is insufficient to prepare them to use psychotropics safely and effectively, especially in the context of their expanded off-label uses. Therefore, the development of competencies in psychotropic prescribing needs to be approached as a long-term, practice-based learning commitment. Proposed are the abilities and knowledge components necessary for safe and effective use of psychotropics. Typical challenges in prescribing for chronic and recurrent illnesses include highly variable responses and tolerability, drug interactions, and adverse effects that can be serious, irreversible, and even fatal. Prescribing psychotropics is further complicated by negative public and professional reports and growing patient concerns about the quality of care, and questions about the efficacy, safety, and addictive risks of psychotropics. Increased efforts are needed to enhance clinical training and knowledge in psychopharmacology among trainees and practising clinicians, with more comprehensive and sustained attention to the assessment of individual patients, and greater reliance on patient education and collaboration. Improved competence in psychotropic prescribing should lead to more informed, thoughtful, and better-targeted applications as one component of more comprehensive clinical care. PMID:25161064

Gardner, David M

2014-01-01

383

Resonant and non-resonant microwave absorption as a probe of the magnetic dynamics and switching in spin valves  

NASA Astrophysics Data System (ADS)

We use the resonant and non-resonant microwave absorption to probe the dynamic and static magnetic parameters of weakly coupled spin valves. The sample series include spin valve structures with varying thickness of the non-magnetic metallic spacer and reference samples comprised only a free or fixed magnetic layer. Beside the common resonance absorption peaks, the observed microwave spectra present step-like features with hysteretic behavior. The latter effect is a direct manifestation of the interlayer coupling between the ferromagnetic layers and provides two static magnetic parameters, the switching field and coercivity of the fixed layer. The analysis of the microwave absorption spectra under in-plane rotation of the applied magnetic field at different spacer thicknesses permits a deeper insight in the magnetic interactions in this system as compared to the conventional magnetometry. We combine the standard Smit-Beljers formalism for the angular dependence of the resonance fields with a Landau-Lifshitz-Gilbert dynamics extended to describe in detail the intensity of microwave absorption in the spin valves. In this way, we extract a set of parameters for each layer including the effective magnetization and anisotropy, exchange bias and interlayer coupling, as well as Gilbert damping. The model reproduces well the experimental findings, both qualitatively and quantitatively, and the estimated parameters are in a reasonable agreement with the values known from the literature. The proposed theoretical treatment can be adopted for other multilayered dynamic systems as, e.g., spin-torque oscillators.

Timopheev, A. A.; Sobolev, N. A.; Pogorelov, Y. G.; Talalaevskij, A. V.; Teixeira, J. M.; Cardoso, S.; Freitas, P. P.; Kakazei, G. N.

2013-07-01

384

Use of rotary echoes in 2H magic-angle spinning NMR for the quantitative study of molecular dynamics  

NASA Astrophysics Data System (ADS)

The interaction of sample spinning and chemical dynamics is analysed in the context of 2H magic-angle spinning NMR. We develop previous analyses and show that a metric based on the intensity of rotational echoes allows kinetic information to be derived without the need for full modelling of the NMR response. This approach is illustrated on the conformational exchange of 1,4-dioxane included in the channel solvate hydrate formed with finasteride. An activation barrier in excellent agreement with previous experimental and theoretical estimates is obtained, without the need for modelling which would be very challenging due to the anisotropic tumbling of the solvent molecules.

Hogg, Naomi H. M.; Boulton, Paul J. T.; Zorin, Vadim E.; Harris, Robin K.; Hodgkinson, Paul

2009-06-01

385

Microwave field distribution in a magic angle spinning dynamic nuclear polarization NMR probe.  

PubMed

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

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

2011-05-01

386

Neutron scattering studies of the ferroelectric distortion and spin dynamics in the type-1 multiferroic perovskite Sr0.56Ba0.44MnO3  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

387

Low temperature spin dynamics in Cr{sub 7}Ni-Cu-Cr{sub 7}Ni coupled molecular rings  

SciTech Connect

Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50?mK) to determine the effect of coupling two Cr{sub 7}Ni molecular rings via a Cu{sup 2+} ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5?K. At lower temperature, the {sup 1}H-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 Cr{sub 7}Ni ring (140?mK)

Bordonali, L., E-mail: lorenzo.bordonali@unipv.it [INSTM and Department of Physics, Università di Pavia, I-27100 Pavia (Italy); Ames Laboratory, and Department of Physics and Astronomy, Iowa State University, Iowa 50011 (United States); Department of Physics “E. Amaldi,” Università Uniroma TRE, Roma (Italy); Furukawa, Y. [Ames Laboratory, and Department of Physics and Astronomy, Iowa State University, Iowa 50011 (United States); Mariani, M.; Sabareesh, K. P. V. [INSTM and Department of Physics, Università di Pavia, I-27100 Pavia (Italy); Garlatti, E. [INSTM and Department of Physics, Università degli Studi di Milano, via Celoria 16, I-20133 Milano (Italy); Dipartimento di Fisica, Università di Parma, Viale Usberti 7/A, I-43100 Parma (Italy); Carretta, S. [Dipartimento di Fisica, Università di Parma, Viale Usberti 7/A, I-43100 Parma (Italy); S3-CNR, Institute of Nanosciences, via Campi 213/A, I-41125 Modena (Italy); Lascialfari, A. [INSTM and Department of Physics, Università degli Studi di Milano, via Celoria 16, I-20133 Milano (Italy); INSTM and Department of Physics, Università di Pavia, I-27100 Pavia (Italy); S3-CNR, Institute of Nanosciences, via Campi 213/A, I-41125 Modena (Italy); Timco, G.; Winpenny, R. E. P. [The Lewis Magnetism Laboratory, The University of Manchester, M13 9PL Manchester (United Kingdom); Borsa, F. [INSTM and Department of Physics, Università di Pavia, I-27100 Pavia (Italy); Ames Laboratory, and Department of Physics and Astronomy, Iowa State University, Iowa 50011 (United States)

2014-05-07

388

Topological phase transition in the quench dynamics of a one-dimensional Fermi gas with spin–orbit coupling  

NASA Astrophysics Data System (ADS)

We study the quench dynamics of a one-dimensional ultracold Fermi gas with synthetic spin-orbit coupling. At equilibrium, the ground state of the system can undergo a topological phase transition and become a topological superfluid with Majorana edge states. As the interaction is quenched near the topological phase boundary, we identify an interesting dynamical phase transition of the quenched state in the long-time limit, characterized by an abrupt change of the pairing gap at a critical quenched interaction strength. We further demonstrate the topological nature of this dynamical phase transition from edge-state analysis of the quenched states. Our findings provide interesting clues for the understanding of topological phase transitions in dynamical processes, and can be useful for the dynamical detection of Majorana edge states in corresponding systems.

Wang, Pei; Yi, Wei; Xianlong, Gao

2015-01-01

389

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

SciTech Connect

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

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

2011-01-01

390

Interplay of quadrupolar order, Ce 4f spin dynamics and RKKY induced conduction electron spin polarization in CeAg  

NASA Astrophysics Data System (ADS)

We report on measurements of the Knight shift K and spin-lattice relaxation rate lgr of positive muons (mgr+) implanted in cubic CeAg, a compound which is known to possess ferromagnetic (T_{\\mathrm {c}} \\simeq 5.5 K) and ferroquadrupolar (TQ = 15-16 K) order. The zero field (ZF) lgr implies randomly and isotropically fluctuating Ce 4f moments above TQ which show a trend to a, perhaps critical, slowing down on approaching TQ. Below TQ the fluctuations are restricted to the now tetragonally distorted axis of CeAg. In a longitudinal field the generally isotropic fluctuations show a tendency towards freezing near Tc, not TQ. The Knight shift results reveal an anisotropic contact hyperfine coupling parameter Ac, which displays abrupt changes at Tc. ZF measurements below Tc reveal the presence of discrete spontaneous internal fields. The results on lgr and Ac are interpreted as arising from quadrupolar effects, concerning in particular the induced spin polarization of the conduction electron system.

Schenck, A.; Gygax, F. N.; Andreica, D.; Onuki, Y.

2003-12-01

391

Exciton dissociation at donor-acceptor heterojunctions: Dynamics using the collective effective mode representation of the spin-boson model  

SciTech Connect

Following the recent quantum dynamics investigation of the charge transfer at an oligothiophene-fullerene heterojunction by the multi-configuration time dependent Hartree method [H. Tamura, R. Martinazzo, M. Ruckenbauer and I. Burghardt, J. Chem. Phys. 137, 22A540 (2012)], we revisit the transfer process by a perturbative non-Markovian master equation treated by the time local auxiliary density matrix approach. We compare the efficiency of the spin-boson model calibrated by quantum chemistry with the effective mode representation. A collective mode is extracted from the spin-boson spectral density. It is weakly coupled to a residual bath of vibrational modes, allowing second-order dynamics. The electron transfer is analyzed for a sampling of inter-fragment distances showing the fine interplay of the electronic coupling and energy gap on the relaxation. The electronic coherence, expected to play a role in the process, is preserved during about 200 fs.

Chenel, Aurélie; Mangaud, Etienne [Laboratoire de Chimie Physique, Bât 349, Université Paris-Sud, UMR 8000, F-91405 Orsay (France) [Laboratoire de Chimie Physique, Bât 349, Université Paris-Sud, UMR 8000, F-91405 Orsay (France); Laboratoire Collisions, Agrégats, Réactivité, UMR 5589, IRSAMC, Université Paul Sabatier, F-31062 Toulouse (France); Burghardt, Irene, E-mail: michele.desouter-lecomte@u-psud.fr, E-mail: chris@irsamc.ups-tlse.fr, E-mail: burghardt@chemie.uni-frankfurt.de [Institut für Physikalische und Theoretische Chemie, Goethe Universität Frankfurt, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main (Germany)] [Institut für Physikalische und Theoretische Chemie, Goethe Universität Frankfurt, Max-von-Laue-Str. 7, D-60438 Frankfurt am Main (Germany); Meier, Christoph, E-mail: michele.desouter-lecomte@u-psud.fr, E-mail: chris@irsamc.ups-tlse.fr, E-mail: burghardt@chemie.uni-frankfurt.de [Laboratoire Collisions, Agrégats, Réactivité, UMR 5589, IRSAMC, Université Paul Sabatier, F-31062 Toulouse (France)] [Laboratoire Collisions, Agrégats, Réactivité, UMR 5589, IRSAMC, Université Paul Sabatier, F-31062 Toulouse (France); Desouter-Lecomte, Michèle, E-mail: michele.desouter-lecomte@u-psud.fr, E-mail: chris@irsamc.ups-tlse.fr, E-mail: burghardt@chemie.uni-frankfurt.de [Laboratoire de Chimie Physique, Bât 349, Université Paris-Sud, UMR 8000, F-91405 Orsay (France) [Laboratoire de Chimie Physique, Bât 349, Université Paris-Sud, UMR 8000, F-91405 Orsay (France); Département de Chimie, Université de Liège, Sart Tilman, B6, B-4000 Liège (Belgium)

2014-01-28

392

Effects of several factors on theoretical predictions of airplane spin characteristics. [dynamic models  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

393

Theoretical Study on the Geometric and Dynamic Performance of Ring Spinning Triangle with Finite Element Method  

NASA Astrophysics Data System (ADS)

Spun yarns are used worldwide for making a wide range of textiles and apparel. The spun yarn is formed by twisting an assembly of short fibers in order to obtain sufficient strength for the downstream processing. In spinning triangle, the fibers will be finally twisted into yarn. Thus the properties of yarn were greatly influenced by the shape and the fiber stress distribution of the spinning triangle. In this study, the theoretical issue of ring spinning triangle was examined by using the finite element method. In order to address more complicated condition of the spinning triangle, some important factors ignored previously, including the yarn spinning torque, the inclined spinning tension and fiber torsional strains, were considered. With the input of different spinning parameters, such as yarn count (yarn linear density), yarn twist, spinning tension and torque, some essential parameters of the spinning triangle, including the fiber tension distribution, fiber torsion distribution and the height of the spinning triangle, were numerically obtained and their quantitative relationships were discussed in detail.

Yan Li, Sheng; Gang Xu, Bin; Ming Tao, Xiao

2010-05-01

394

Spin-Density-Wave Order and Slow Dynamics in Ca3Co2O6  

NASA Astrophysics Data System (ADS)

We study a frustrated quantum Ising model relevant for Ca3Co2O{6 }that comprises a triangular lattice of weakly coupled ferromagnetic chains{ }[Y. Kamiya and C. D. Batista, PRL {109}, 067204 (2012)]. Our quantum Monte Carlo simulation shows that the chains become ferromagnetic and form a three-sublattice ``up-up-down'' structure in the lowest temperature regime T? TCI due to a quantum effect. In contrast, long-wavelength spin-density-wave (SDW) modulations along the chains are stabilized for TCI < T < Tc in agreement with recent experiments. We also discuss a simple mean-field theory revealing quasi-continuous change of the modulation periodicity as a function of T and implying the existence of metastable states in the SDW phase, which explains the slow low-temperature dynamics that has been observed in Ca3Co2O6. The closely related multiferroic materials Ca3CoMnO6 and Lu2CoMnO{6 }will also be discussed.

Batista, Cristian; Kamiya, Yoshitomo

2013-03-01

395

Dynamical and transport properties of a spin-fermion model for Diluted Magnetic Semiconductors  

NASA Astrophysics Data System (ADS)

In a recent paper(G. Alvarez, et. al.), to be appear in Phys. Rev. Lett. and also M. Mayr et. al., Phys. Rev. B 65, 241202 (2002). we studied static properties of a spin-fermion model for DMS, using Monte Carlo techniques and exact diagonalization of the fermionic sector. There the phase diagram for the model was reported. It was observed that TC actually decreases for large enough coupling, and it was reported the appearance of a ``clustered" state just above T_C. In this talk the focus will be on dynamical and transport properties of the model. The D.O.S., the optical conductivity, the appearance of an ``impurity band'', and its relation to the optimal T_ C will be discussed and compared to experimental(Katsumoto et al.) Mater. Sci. and Eng. B 84 88 (2001). and theoretical(J. Sinova et al.), Phys. Rev. B 66 041202 (2002). E. H. Hwang, et. al., Phys. Rev. B 65, 233206 (2002). results. Moreover, the temperature and carrier dependence of the optical conductivity and conductance will be presented. Results for all observables support the view that the relevant regime is that of intermediate coupling, with FM clusters above T_C. In this regime, a metal-insulator transition occurs near TC in agreement with experiments(H. Ohno and F. Matsukura, Solid State Commun. 117), 179, (2001). S. J. Potashnik et al., Appl. Phys. Lett. 79, 1495, (2001)..

Alvarez, Gonzalo; Dagotto, Elbio

2003-03-01

396

Structure and spin dynamics of multiferroic BiFeO3.  

PubMed

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

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

2014-10-29

397

Structure and spin dynamics of multiferroic BiFeO3  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

398

Theory of magnetoresistance based on variable-range hopping in the presence of Hubbard interaction and spin-dynamics  

E-print Network

We develop a theory of magnetoresistance based on variable-range hopping. An exponentially large, low-field and necessarily positive magnetoresistance effect is predicted in the presence of Hubbard interaction and spin-dynamics under certain conditions. The theory was developed with the recently discovered organic magnetoresistance in mind. To account for the experimental observation that the organic magnetoresistance effect can also be negative, we tentatively amend the theory with a mechanism of bipolaron formation.

M. Wohlgenannt

2006-09-22

399

Spin liquids in frustrated magnets  

Microsoft Academic Search

Frustrated magnets are materials in which localized magnetic moments, or spins, interact through competing exchange interactions that cannot be simultaneously satisfied, giving rise to a large degeneracy of the system ground state. Under certain conditions, this can lead to the formation of fluid-like states of matter, so-called spin liquids, in which the constituent spins are highly correlated but still fluctuate

Leon Balents

2010-01-01

400

Effects of spin on the dynamics of the 2D Dirac oscillator in the magnetic cosmic string background  

NASA Astrophysics Data System (ADS)

In this work the dynamics of a 2D Dirac oscillator in the spacetime of a magnetic cosmic string is considered. It is shown that earlier approaches to this problem have neglected a function contribution to the full Hamiltonian, which comes from the Zeeman interaction. The inclusion of spin effects leads to results which confirm a modified dynamics. Based on the self-adjoint extension method, we determined the most relevant physical quantities, such as energy spectrum, wave functions and the self-adjoint extension parameter by applying boundary conditions allowed by the system.

Andrade, Fabiano M.; Silva, Edilberto O.

2014-12-01

401

Effects of spin on the dynamics of the 2D Dirac oscillator in the magnetic cosmic string background  

E-print Network

In this work the dynamics of a 2D Dirac oscillator in the spacetime of a magnetic cosmic string is considered. It is shown that earlier approaches to this problem have neglected a $\\delta$ function contribution to the full Hamiltonian, which comes from the Zeeman interaction. The inclusion of spin effects leads to results which confirm a modified dynamics. Based on the self-adjoint extension method, we determined the most relevant physical quantities, such as energy spectrum, wave functions and the self-adjoint extension parameter by applying boundary conditions allowed by the system.

Fabiano M. Andrade; Edilberto O. Silva

2014-03-17

402

Effects of spin on the dynamics of the 2D Dirac oscillator in the magnetic cosmic string background  

E-print Network

In this work the dynamics of a 2D Dirac oscillator in the spacetime of a magnetic cosmic string is considered. It is shown that earlier approaches to this problem have neglected a $\\delta$ function contribution to the full Hamiltonian, which comes from the Zeeman interaction. The inclusion of spin effects leads to results which confirm a modified dynamics. Based on the self-adjoint extension method, we determined the most relevant physical quantities, such as energy spectrum, wave functions and the self-adjoint extension parameter by applying boundary conditions allowed by the system.

Andrade, Fabiano M

2014-01-01

403

Coherent dynamics of coupled electron and nuclear spin qubits in diamond.  

PubMed

Understanding and controlling the complex environment of solid-state quantum bits is a central challenge in spintronics and quantum information science. Coherent manipulation of an individual electron spin associated with a nitrogen-vacancy center in diamond was used to gain insight into its local environment. We show that this environment is effectively separated into a set of individual proximal 13C nuclear spins, which are coupled coherently to the electron spin, and the remainder of the 13C nuclear spins, which cause the loss of coherence. The proximal nuclear spins can be addressed and coupled individually because of quantum back-action from the electron, which modifies their energy levels and magnetic moments, effectively distinguishing them from the rest of the nuclei. These results open the door to coherent manipulation of individual isolated nuclear spins in a solid-state environment even at room temperature. PMID:16973839

Childress, L; Gurudev Dutt, M V; Taylor, J M; Zibrov, A S; Jelezko, F; Wrachtrup, J; Hemmer, P R; Lukin, M D

2006-10-13

404

Extensive backbone dynamics in the GCAA RNA tetraloop analyzed using 13C NMR spin relaxation and specific isotope labeling  

PubMed Central

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

Johnson, James E.; Hoogstraten, Charles G.

2009-01-01

405

Variational Description of Gibbs-Non-Gibbs Dynamical Transitions for Spin-Flip Systems with a Kac-Type Interaction  

NASA Astrophysics Data System (ADS)

We continue our study of Gibbs-non-Gibbs dynamical transitions. In the present paper we consider a system of Ising spins on a large discrete torus with a Kac-type interaction subject to an independent spin-flip dynamics (infinite-temperature Glauber dynamics). We show that, in accordance with the program outlined in van Enter et al. (Moscow Math. J. 10:687-711, 2010), in the thermodynamic limit Gibbs-non-Gibbs dynamical transitions are equivalent to bifurcations in the set of global minima of the large-deviation rate function for the trajectories of the empirical density conditional on their endpoint. More precisely, the time-evolved measure is non-Gibbs if and only if this set is not a singleton for some value of the endpoint. A partial description of the possible scenarios of bifurcation is given, leading to a characterization of passages from Gibbs to non-Gibbs and vice versa, with sharp transition times. Our analysis provides a conceptual step-up from our earlier work on Gibbs-non-Gibbs dynamical transitions for the Curie-Weiss model, where the mean-field interaction allowed us to focus on trajectories of the empirical magnetization rather than the empirical density.

Fernández, R.; den Hollander, F.; Martínez, J.

2014-07-01

406

Theory of a two-mode spin torque nanooscillator  

NASA Astrophysics Data System (ADS)

A theoretical model for the dynamics in a ferromagnetic thin metal film in the presence of a high-density spin-polarized direct current is presented. By considering the excitation of two spin-wave modes, it is numerically shown that the behavior of the microwave nanooscillator is in perfect analogy to that of two species competing for the same food supply, as described by the Lotka-Volterra model, or to that of a two-mode laser, as described by Lamb’s theory: Only one mode will survive in the steady state.

de Aguiar, F. M.; Azevedo, A.; Rezende, S. M.

2007-04-01

407

EUROPEAN CONFERENCE FOR AEROSPACE SCIENCES Study on the eddy current damping of the spin dynamics of  

E-print Network

4TH EUROPEAN CONFERENCE FOR AEROSPACE SCIENCES Study on the eddy current damping of the spin consideration in this article, are impacted by torques generated by eddy currents as the conducting non, the permanent magnetic field from the magnetosphere generates eddy current in the spinning, conducting body

Paris-Sud XI, Université de

408

Collective oblate rotation at high spins in neutron-rich {sup 180}Hf.  

SciTech Connect

We report on experimental evidence for collective oblate rotation becoming favored at high spins in a rigid, well-deformed, axially symmetric nucleus. Excited states established up to spin 20{h_bar} in {sup 180}Hf are consistent with predictions that nucleon alignments would favor oblate over prolate shapes at high spins in neutron-rich Hf isotopes. The results highlight the influence of valence orbitals on the interplay between nucleon alignments and nuclear shapes and provide a rare example of independent particle dynamics in competing potential wells.

Tandel, U. S.; Tandel, S. K.; Chowdhury, P.; Cline, D.; Wu, C. Y.; Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Zhu, S.; Physics; Univ. of Massachusetts; Univ. of Rochester

2008-01-01

409

Collective Oblate Rotation at High Spins in Neutron-Rich {sup 180}Hf  

SciTech Connect

We report on experimental evidence for collective oblate rotation becoming favored at high spins in a rigid, well-deformed, axially symmetric nucleus. Excited states established up to spin 20({Dirac_h}/2{pi}) in {sup 180}Hf are consistent with predictions that nucleon alignments would favor oblate over prolate shapes at high spins in neutron-rich Hf isotopes. The results highlight the influence of valence orbitals on the interplay between nucleon alignments and nuclear shapes and provide a rare example of independent particle dynamics in competing potential wells.

Tandel, U. S.; Tandel, S. K.; Chowdhury, P. [Department of Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854 (United States); Cline, D.; Wu, C. Y. [Nuclear Structure Research Laboratory, University of Rochester, Rochester, New York 14627 (United States); Carpenter, M. P.; Janssens, R. V. F.; Khoo, T. L.; Lauritsen, T.; Lister, C. J.; Seweryniak, D.; Zhu, S. [Physics Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

2008-10-31

410

Monte Carlo simulations of phase transitions and lattice dynamics in an atom-phonon model for spin transition compounds  

NASA Astrophysics Data System (ADS)

We apply here the Monte Carlo Metropolis method to a known atom-phonon coupling model for 1D spin transition compounds (STC). These inorganic molecular systems can switch under thermal or optical excitation, between two states in thermodynamical competition, i.e. high spin (HS) and low spin (LS). In the model, the ST units (molecules) are linked by springs, whose elastic constants depend on the spin states of the neighboring atoms, and can only have three possible values. Several previous analytical papers considered a unique average value for the elastic constants (mean-field approximation) and obtained phase diagrams and thermal hysteresis loops. Recently, Monte Carlo simulation papers, taking into account all three values of the elastic constants, obtained thermal hysteresis loops, but no phase diagrams. Employing Monte Carlo simulation, in this work we obtain the phase diagram at T=0 K, which is fully consistent with earlier analytical work; however it is more complex. The main difference is the existence of two supplementary critical curves that mark a hysteresis zone in the phase diagram. This explains the pressure hysteresis curves at low temperature observed experimentally and predicts a “chemical” hysteresis in STC at very low temperatures. The formation and the dynamics of the domains are also discussed.

Apetrei, Alin Marian; Enachescu, Cristian; Tanasa, Radu; Stoleriu, Laurentiu; Stancu, Alexandru

2010-09-01

411

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

412

Propagation of dynamic nuclear polarization across the xenon cluster boundaries: elucidation of the spin-diffusion bottleneck.  

PubMed

Earlier Dynamic Nuclear Polarization (DNP) experiments with frozen xenon/1-propanol/trityl mixtures have demonstrated spontaneous formation of pure xenon clusters above 120 K, enabling spectrally-resolved real-time measurements of (129)Xe nuclear magnetization in the clusters and in the surrounding radical-rich matrix. A spin-diffusion bottleneck was postulated to explain the peculiar time evolution of (129)Xe signals in the clusters as well as the apparent discontinuity of (129)Xe polarization across the cluster boundaries. A self-contained ab initio model of nuclear spin diffusion in heterogeneous systems is developed here, incorporating the intrinsic T1 relaxation towards the temperature-dependent equilibrium polarization and the spin-diffusion coefficients based on the measured NMR line widths and the known atomic densities in each compartment. This simple model provides the physical basis for the observed spin-diffusion bottleneck and is in a good quantitative agreement with the earlier measurements. A simultaneous fit of the model to the time-dependent NMR data at two different DNP frequencies provides excellent estimates of the cluster size, the intrinsic sample temperature, and (129)Xe T1 constants. The model was also applied to the NMR data acquired during relaxation towards the thermal equilibrium after the microwaves were turned off, to estimate T1 relaxation time constants inside and outside the clusters. Fitting the model to the data during and after DNP provides consistent estimates of the cluster size. PMID:23981341

Pourfathi, M; Kuzma, N N; Kara, H; Ghosh, R K; Shaghaghi, H; Kadlecek, S J; Rizi, R R

2013-10-01

413

Dynamics of the radiative envelope of rapidly rotating stars: Effects of spin-down driven by mass loss  

NASA Astrophysics Data System (ADS)

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

Rieutord, M.; Beth, A.

2014-10-01

414

Direct versus measurement-assisted bipartite entanglement in multiqubit systems and their dynamical generation in spin systems  

NASA Astrophysics Data System (ADS)

We consider multiqubit systems and relate quantitatively the problems of generating cluster states with high values of concurrence of assistance, and of generating states with maximal bipartite entanglement. We prove an upper bound for the concurrence of assistance. We consider dynamics of spin- 1/2 systems that model qubits, with different couplings and possible presence of magnetic field, to investigate the appearance of the discussed entanglement properties. We find that states with maximal bipartite entanglement can be generated by an isotropic XY Hamiltonian, and their generation can be controlled by the initial state of one of the spins. The same Hamiltonian is capable of creating states with high concurrence of assistance from a suitably chosen initial state. We show that the production of graph states using the Ising Hamiltonian is controllable via a single-qubit rotation of one spin- 1/2 subsystem in the initial multiqubit state. We show that the property of Ising dynamics to convert a product-state basis into a special maximally entangled basis is temporally enhanced by the application of a suitable magnetic field. Similar basis transformations are found to be feasible in the case of isotropic XY couplings with a magnetic field.

Koniorczyk, Mátyás; Rap?an, Peter; Bužek, Vladimír

2005-08-01

415

Water Sector Competency Model  

NSDL National Science Digital Library

The Advanced Technology Environmental and Energy Center (ATEEC) provides this framework of competencies required for workers in the water sector, and includes details on required competencies for field staff and operators. Personal effectiveness, academic competencies, workplace competencies and industry-wide technical competencies are included. Users must download this resource for viewing, which requires a free log-in. There is no cost to download the item. The document is available in PDF file format.

2012-11-07

416

Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: A two-state one-dimensional model  

NASA Astrophysics Data System (ADS)

We construct a two-state one-dimensional reaction-path model for ozone open ? cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O2 + O asymptote on the ground-state 1A' potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

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

2014-02-01

417

Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: A two-state one-dimensional model  

SciTech Connect

We construct a two-state one-dimensional reaction-path model for ozone open ? cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O{sub 2} + O asymptote on the ground-state {sup 1}A{sup ?} potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

Kurosaki, Yuzuru, E-mail: kurosaki.yuzuru@jaea.go.jp [Quantum Beam Science Directorate, Tokai Research and Development Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)] [Quantum Beam Science Directorate, Tokai Research and Development Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan); Ho, Tak-San, E-mail: tsho@Princeton.EDU; Rabitz, Herschel, E-mail: hrabitz@Princeton.EDU [Department of Chemistry, Princeton University, Princeton, New Jersy 08544 (United States)] [Department of Chemistry, Princeton University, Princeton, New Jersy 08544 (United States)

2014-02-28

418

Decomposition-aggregation stability analysis. [for large scale dynamic systems with application to spinning Skylab control system  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

419

Investigating the magnetovolume effect in isotropic body-centered-cubic iron using spin-lattice dynamics simulations  

SciTech Connect

The understanding of the magnetovolume effect lacks explicit consideration of spin-lattice coupling at the atomic level, despite abundant theoretical and experimental studies throughout the years. This research gap is filled by the recently developed spin-lattice dynamics technique implemented in this study, which investigates the magnetovolume effect of isotropic body-centered-cubic (BCC) iron, a topic that has previously been subject to macroscopic analysis only. This approach demonstrates the magnetic anomaly followed by the volumetric changes associated with the effect, each characterized by the corresponding field-induced inflection temperature. The temperature of the heat capacity peaks is useful in determining the temperature for retarding the atomic volume increase. Moreover, this work shows the correlation between the effects of temperature and field strength in determining the equilibrium atomic volume of a ferromagnetic material under a magnetic field.

Chui, C. P. [Department of Electronic and Information Engineering, the Hong Kong Polytechnic University (Hong Kong); Zhou, Yan, E-mail: yanzhou@hku.hk [Department of Physics, the University of Hong Kong (Hong Kong)

2014-08-15

420

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

SciTech Connect

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

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

2010-01-01

421

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

SciTech Connect

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

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

2011-01-01

422

Spin-polarized dynamic transport in tubular two-dimensional electron gases  

NASA Astrophysics Data System (ADS)

The ac conductance of a finite tubular two-dimensional electron gas is studied in the presence of the Rashba spin-orbit interaction. When the tube is coupled to two reservoirs, that interaction splits the steps in the dc current, introducing energy ranges with spin-polarized currents. For this setup, we calculate the current-current correlations (the noise spectrum) and show that the existence of these dc spin-polarized currents can be deduced from the shot noise. We also find that the Wigner-Smith time delay is almost unaffected by the spin-orbit interaction. When the tube is coupled to a single reservoir, we calculate the quantum capacitance and the charge-relaxation resistance, and find that they exhibit singularities near the openings of new channels.

Rothstein, E. A.; Horovitz, B.; Entin-Wohlman, O.; Aharony, A.

2014-12-01

423

Algorithms for the treatment and analysis of spin dynamics in SU(2) and SO(3)  

NASA Astrophysics Data System (ADS)

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

Balandin, Vladimir; Berz, Martin; Golubeva, Nina

1997-04-01

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