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Sample records for competing spin dynamics

  1. Spin dynamics in the presence of competing ferromagnetic and antiferromagnetic correlations in Yb2Ti2O7

    NASA Astrophysics Data System (ADS)

    Robert, J.; Lhotel, E.; Remenyi, G.; Sahling, S.; Mirebeau, I.; Decorse, C.; Canals, B.; Petit, S.

    2015-08-01

    In this work, we show that the zero-field excitation spectra in the quantum spin ice candidate pyrochlore compound Yb2Ti2O7 is a continuum characterized by a very broad and almost flat dynamical response, which extends up to 1 -1.5 meV, coexisting or not with a quasielastic response depending on the wave vector. The spectra do not evolve between 50 mK and 2 K, indicating that the spin dynamics is only little affected by the temperature in both the short-range correlated and ordered regimes. Although classical spin dynamics simulations qualitatively capture some of the experimental observations, we show that they fail to reproduce this broad continuum. In particular, the simulations predict an energy scale twice smaller than the experimental observations. This analysis is based on a careful determination of the exchange couplings, able to reproduce both the zero-field diffuse scattering and the spin wave spectrum rising in the field polarized state. According to this analysis, Yb2Ti2O7 lies at the border between a ferro- and an antiferromagnetic phase. These results suggest that the unconventional ground state of Yb2Ti2O7 is governed by strong quantum fluctuations arising from the competition between those phases. The observed spectra may correspond to a continuum of deconfined spinons as expected in quantum spin liquids.

  2. Hadron Spin Dynamics

    SciTech Connect

    Brodsky, Stanley J.

    2002-01-09

    Spin effects in exclusive and inclusive reactions provide an essential new dimension for testing QCD and unraveling hadron structure. Remarkable new experiments from SLAC, HERMES (DESY), and Jefferson Lab present many challenges to theory, including measurements at HERMES and SMC of the single spin asymmetries in ep {yields} e{prime}{pi}X where the proton is polarized normal to the scattering plane. This type of single spin asymmetry may be due to the effects of rescattering of the outgoing quark on the spectators of the target proton, an effect usually neglected in conventional QCD analyses. Many aspects of spin, such as single-spin asymmetries and baryon magnetic moments are sensitive to the dynamics of hadrons at the amplitude level, rather than probability distributions. I will illustrate the novel features of spin dynamics for relativistic systems by examining the explicit form of the light-front wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents and providing a transparent basis for understanding the structure of relativistic composite systems and their matrix elements in hadronic physics. I also present a survey of outstanding spin puzzles in QCD, particularly A{sub NN} in elastic pp scattering, the J/{psi} {yields} {rho}{pi} puzzle, and J/{psi} polarization at the Tevatron.

  3. Competing spin pumping effects in magnetic hybrid structures

    SciTech Connect

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

    2014-02-03

    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.

  4. Spin-current emission governed by nonlinear spin dynamics.

    PubMed

    Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

    2015-01-01

    Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712

  5. Spin-current emission governed by nonlinear spin dynamics

    NASA Astrophysics Data System (ADS)

    Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

    2015-10-01

    Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators.

  6. Spin-current emission governed by nonlinear spin dynamics

    PubMed Central

    Tashiro, Takaharu; Matsuura, Saki; Nomura, Akiyo; Watanabe, Shun; Kang, Keehoon; Sirringhaus, Henning; Ando, Kazuya

    2015-01-01

    Coupling between conduction electrons and localized magnetization is responsible for a variety of phenomena in spintronic devices. This coupling enables to generate spin currents from dynamical magnetization. Due to the nonlinearity of magnetization dynamics, the spin-current emission through the dynamical spin-exchange coupling offers a route for nonlinear generation of spin currents. Here, we demonstrate spin-current emission governed by nonlinear magnetization dynamics in a metal/magnetic insulator bilayer. The spin-current emission from the magnetic insulator is probed by the inverse spin Hall effect, which demonstrates nontrivial temperature and excitation power dependences of the voltage generation. The experimental results reveal that nonlinear magnetization dynamics and enhanced spin-current emission due to magnon scatterings are triggered by decreasing temperature. This result illustrates the crucial role of the nonlinear magnon interactions in the spin-current emission driven by dynamical magnetization, or nonequilibrium magnons, from magnetic insulators. PMID:26472712

  7. Electron spin decoherence in nuclear spin baths and dynamical decoupling

    SciTech Connect

    Zhao, N.; Yang, W.; Ho, S. W.; Hu, J. L.; Wan, J. T. K.; Liu, R. B.

    2011-12-23

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

  8. Spin-flop transition driven by competing magnetoelastic anisotropy terms in a spin-spiral antiferromagnet

    NASA Astrophysics Data System (ADS)

    Benito, L.

    2015-06-01

    Holmium, the archetypical system for spin-spiral antiferromagnetism, undergoes an in-plane spin-flop transition earlier attributed to competing symmetry-breaking and fully symmetric magnetoelastic anisotropy terms [Phys. Rev. Lett. 94, 227204 (2005), 10.1103/PhysRevLett.94.227204], which underlines the emergence of sixfold magnetoelastic constants in heavy rare earth metals, as otherwise later studies suggested. A model that encompasses magnetoelastic contributions to the in-plane sixfold magnetic anisotropy is laid out to elucidate the mechanism behind the spin-flop transition. The model, which is tested in a Ho-based superlattice, shows that the interplay between competing fully symmetric ? -magnetoelastic and symmetry-breaking ? -magnetoelastic anisotropy terms triggers the spin reorientation. This also unveils the dominant role played by the sixfold exchange magnetostriction constant, where D?2 66?0.32 GPa against its crystal-field counterpart M?2 66?-0.2 GPa, in contrast to the crystal-field origin of the symmetry-breaking magnetostriction in rare earth metals.

  9. Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture

    E-print Network

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

    2015-01-01

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

  10. Scattering bottleneck for spin dynamics in metallic helical antiferromagnetic dysprosium

    NASA Astrophysics Data System (ADS)

    Langner, M. C.; Roy, S.; Kemper, A. F.; Chuang, Y.-D.; Mishra, S. K.; Versteeg, R. B.; Zhu, Y.; Hertlein, M. P.; Glover, T. E.; Dumesnil, K.; Schoenlein, R. W.

    2015-11-01

    Ultrafast studies of magnetization dynamics have revealed fundamental processes that govern spin dynamics, and the emergence of time-resolved x-ray techniques has extended these studies to long-range spin structures that result from interactions with competing symmetries. By combining time-resolved resonant x-ray scattering and ultrafast magneto-optical Kerr studies, we show that the dynamics of the core spins in the helical magnetic structure occur on much longer time scales than the excitation of conduction electrons in the lanthanide metal Dy. The observed spin behavior differs markedly from that observed in the ferromagnetic phase of other lanthanide metals or transition metals and is strongly dependent on temperature and excitation fluence. This unique behavior results from coupling of the real-space helical spin structure to the shape of the conduction electron Fermi surface in momentum space, which creates a bottleneck in spin scattering events that transfer the valence excitation to the core spins. The dependence of the dynamics on the intersite interactions renders the helical ordering much more robust to perturbations than simple ferromagnetic or antiferromagnetic ordering, where dynamics are driven primarily by on-site interactions.

  11. Spin dynamics simulations at AGS

    SciTech Connect

    Huang, H.; MacKay, W.W.; Meot, F.; Roser, T.

    2010-05-23

    To preserve proton polarization through acceleration, it is important to have a correct model of the process. It has been known that with the insertion of the two helical partial Siberian snakes in the Alternating Gradient Synchrotron (AGS), the MAD model of AGS can not deal with a field map with offset orbit. The stepwise ray-tracing code Zgoubi provides a tool to represent the real electromagnetic fields in the modeling of the optics and spin dynamics for the AGS. Numerical experiments of resonance crossing, including spin dynamics in presence of the snakes and Q-jump, have been performed in AGS lattice models, using Zgoubi. This contribution reports on various results so obtained.

  12. Microscopic studies of nonlocal spin dynamics and spin transport (invited)

    SciTech Connect

    Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

    2015-05-07

    Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

  13. Microscopic studies of nonlocal spin dynamics and spin transport (invited)

    NASA Astrophysics Data System (ADS)

    Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris

    2015-05-01

    Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.

  14. Polarized hyperons probe dynamics of quark spin

    SciTech Connect

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

    2007-08-01

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

  15. Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture

    NASA Astrophysics Data System (ADS)

    Zhu, Bing; Li, Xiaoke; He, Xiaodong; Wang, Fudong; Guo, Mingyang; Xu, Zhifang; Zhang, Shizhong; Wang, Dajun

    2015-05-01

    We report the observation of interspecies spin-spin interaction driven coherent heteronuclear spin dynamics in an ultracold spinor mixture, which manifests itself as periodical and well correlated magnetization transfer between two atomic species. In particular, we investigate the magnetic field dependence and control of the spin dynamics, and find excellent agreement with a many-body theoretical model. Furthermore, we present a unique knob for fine control of spinor mixtures with species dependent vector light shift. This work is supported by Hong Kong Research Grants Council (General Research Fund Projects CUHK 403813 and CUHK 14305214).

  16. Spin dynamics with inertia in metallic ferromagnets

    NASA Astrophysics Data System (ADS)

    Kikuchi, Toru; Tatara, Gen

    2015-11-01

    The nonadiabatic contribution of environmental degrees of freedom yields an effective inertia of spin in the effective spin dynamics. In this paper, we study several aspects of the inertia of spin in metallic ferromagnets: (i) a concrete expression of the spin inertia ms: ms=? Sc/(2 gsd) , where Sc is the spin polarization of conduction electrons and gsd is the s d coupling constant; (ii) a dynamical behavior of spin with inertia, discussed from the viewpoints of a spinning top and of a particle on a sphere; (iii) the behavior of spin waves and domain walls in the presence of inertia and the behavior of spin with inertia under a time-dependent magnetic field.

  17. Coherent spin mixing dynamics in a spin-1 atomic condensate

    SciTech Connect

    Zhang Wenxian; Chang, M.-S.; Chapman, M.S.; Zhou, D.L.; You, L.

    2005-07-15

    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.

  18. Competing decay modes of a high-spin isomer in the proton-unbound nucleus ¹??Ta*

    DOE PAGESBeta

    Carroll, R. J.; Univ. of Liverpool, Liverpool; Page, R. D.; Joss, D. T.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Cederwall, B.; Eeckhaudt, S.; Grahn, T.; et al

    2015-01-01

    An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both ? and ? decay modes. The large spin change required to decay via ?-ray emission incurs a lifetime long enough for ? decay to compete. The ? decay has an energy of 8644(11) keV, which is among the highest observed in the region, a partial half-life of 440(70) ?s and changes the spin by 11?. In this study, additional evidence supporting the assignment of this ? decay to the high-spin isomer in 158Ta will bemore »presented.« less

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

    SciTech Connect

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

    1983-01-01

    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.

  20. Seeing spin dynamics in atomic gases

    E-print Network

    Dan M. Stamper-Kurn

    2014-12-31

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

  1. Spin dynamics in paramagnetic diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Phan, Van-Nham; Tran, Minh-Tien

    2015-10-01

    Microscopic properties of low-energy spin dynamics in diluted magnetic semiconductor are addressed in a framework of the Kondo lattice model including random distribution of magnetic dopants. Based on the fluctuation-dissipation theorem, we derive an explicit dependence of the spin diffusion coefficient on the single-particle Green function which is directly evaluated by dynamical mean-field theory. In the paramagnetic state, the magnetic scattering has been manifested to suppress spin diffusion. In agreement with other ferromagnet systems, we also point out that the spin diffusion in diluted magnetic semiconductors at small carrier concentration displays a monotonic 1 /T -like temperature dependence. By investigating the spin diffusion coefficient on a wide range of the model parameters, the obtained results have provided a significant scenario to understand the spin dynamics in the paramagnetic diluted magnetic semiconductors.

  2. Spin dynamics in driven composite multiferroics

    NASA Astrophysics Data System (ADS)

    Wang, Zidong; Grimson, Malcolm J.

    2015-09-01

    A spin dynamics approach has been used to study the behavior of the magnetic spins and the electric pseudo-spins in a 1-D composite multiferroic chain with a linear magneto-electric coupling at the interface. The response is investigated with either external magnetic or electric fields driving the system. The spin dynamics is based on the Landau-Lifshitz-Gilbert equation. A Gaussian white noise is later added into the dynamic process to include the thermal effects. The interface requires a closer inspection of the magneto-electric effects. Thus, we construct a 2-D ladder model to describe the behavior of the magnetic spins and the electric pseudo-spins with different magneto-electric couplings.

  3. Spin, Isospin and Strong Interaction Dynamics

    E-print Network

    E. Comay

    2011-07-23

    The structure of spin and isospin is analyzed. Although both spin and isospin are related to the same SU(2) group, they represent different dynamical effects. The Wigner-Racah algebra is used for providing a description of bound states of several Dirac particles in general and of the proton state in particular. Isospin states of the four $\\Delta (1232)$ baryons are discussed. The work explains the small contribution of quarks spin to the overall proton spin (the proton spin crisis). It is also proved that the addition of QCD's color is not required for a construction of an antisymmetric state of the $\\Delta ^{++} (1232)$ baryon.

  4. Kinetic Ashkin-Teller model with competing dynamics

    NASA Astrophysics Data System (ADS)

    Bekhechi, S.; Benyoussef, A.; Ettaki, B.; Loulidi, M.; El Kenz, A.; Hontinfinde, F.

    2001-07-01

    We study a two-dimensional nonequilibrium Ashkin-Teller model based on competing dynamics induced by contact with a heat bath at temperature T, and subject to an external source of energy. The dynamics of the system is simulated by two competing stochastic processes: a Glauber dynamics with probability p, which simulates the contact with the heat bath; and a Kawasaki dynamics with probability 1-p, which takes into account the flux of energy into the system. Monte Carlo simulations were employed to determine the phase diagram for the stationary states of the model and the corresponding critical exponents. The phase diagrams of the model exhibit a self-organization phenomenon for certain values of the fourth coupling interaction strength. On the other hand, from exponent calculations, the equilibrium critical behavior is preserved when nonequilibrium conditions are applied.

  5. Unusual spin dynamics in topological insulators.

    PubMed

    Dóra, Balázs; Simon, Ferenc

    2015-01-01

    The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ?(d-1) with d?=?2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d?=?2K?-?1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems. PMID:26439629

  6. Unusual spin dynamics in topological insulators

    PubMed Central

    Dóra, Balázs; Simon, Ferenc

    2015-01-01

    The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ?d?1 with d?=?2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d?=?2K???1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems. PMID:26439629

  7. Unusual spin dynamics in topological insulators

    NASA Astrophysics Data System (ADS)

    Dóra, Balázs; Simon, Ferenc

    2015-10-01

    The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ?d-1 with d?=?2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d?=?2K?-?1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems.

  8. Ab initio non-relativistic spin dynamics

    SciTech Connect

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

    2014-12-07

    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 Li{sub 3} 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.

  9. Numerical Study of Competing Spin-Glass and Ferromagnetic Order

    NASA Astrophysics Data System (ADS)

    Simkin, M. V.

    1997-03-01

    Two and three dimensional random Ising models with a Gaussian distribution of couplings with variance J and non-vanishing mean value J0 are studied using the zero-temperature domain-wall renormalization group (DWRG). The DWRG trajectories in the (J_0,J) plane after rescaling can be collapsed on two curves: one for J_0/J > rc and other for J_0/J < r_c. In the first case the DWRG flows are toward the ferromagnetic fixed point both in two and three dimensions while in the second case flows are towards a paramagnetic fixed point and spin-glass fixed point in two and three dimensions respectively. No evidence for an extra phase is found. Click here for the full text of the paper.

  10. Dynamics of a Slender Spinning Membrane

    NASA Astrophysics Data System (ADS)

    Juang, Jer-Nan; Hung, Chung-Han; Wilkie, William K.

    2015-10-01

    A novel approach is introduced to conduct dynamic analysis of a spinning, high aspect ratio membrane. In this formulation, an inextensible, long, slender membrane is modeled using a discrete set of lumped masses. Lagranges equations are used to derive the highly coupled ordinary differential equations for in-plane, out-of-plane, and twisting motions for the spinning membrane. The generalized and uncoupled linear equations for small motion are used to compute the vibration mode frequencies which are compared to results from an uncoupled analysis of blade motion using rotor dynamics. Linearized behavior is shown to reduce to the linearized solutions for the spinning membrane blade developed by MacNeal. Numerical simulations along with 3-D animations are used to study the linear and nonlinear uncoupled dynamics of the spinning membrane.

  11. Competing decay modes of a high-spin isomer in the proton-unbound nucleus ¹??Ta*

    SciTech Connect

    Carroll, R. J.; Page, R. D.; Joss, D. T.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Cederwall, B.; Eeckhaudt, S.; Grahn, T.; Gray-Jones, C.; Greenlees, P. T.; Hadinia, B.; Jones, P. M.; Julin, R.; Juutinen, S.; Leino, M.; Leppänen, A. -P.; Nyman, M.; O'Donnell, D.; Pakarinen, J.; Rahkila, P.; Sandzelius, M.; Sarén, J.; Scholey, C.; Seweryniak, D.; Simpson, J.

    2015-01-01

    An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both ? and ? decay modes. The large spin change required to decay via ?-ray emission incurs a lifetime long enough for ? decay to compete. The ? decay has an energy of 8644(11) keV, which is among the highest observed in the region, a partial half-life of 440(70) ?s and changes the spin by 11?. In this study, additional evidence supporting the assignment of this ? decay to the high-spin isomer in 158Ta will be presented.

  12. Relaxation and coherent oscillations in the spin dynamics of II-VI diluted magnetic quantum wells

    NASA Astrophysics Data System (ADS)

    Ungar, F.; Cygorek, M.; Tamborenea, P. I.; Axt, V. M.

    2015-10-01

    We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic quantum wells in the presence of spin-orbit interaction. We extend a recent study where it was shown that the spin-orbit interaction and the exchange sd coupling in bulk and quantum wells can compete resulting in qualitatively new dynamics when they act simultaneously. We concentrate on Hg1-x-yMnxCdyTe quantum wells, which have a highly tunable Rashba spin-orbit coupling. Our calculations use a recently developed formalism which incorporates electronic correlations originating from the exchange sd-coupling. We find that the dependence of electronic spin oscillations on the excess energy changes qualitatively depending on whether or not the spin-orbit interaction dominates or is of comparable strength with the sd interaction.

  13. Competing chiral orders in the topological Haldane-Hubbard model of spin-1/2 fermions and bosons

    NASA Astrophysics Data System (ADS)

    Hickey, C.; Rath, P.; Paramekanti, A.

    2015-04-01

    Motivated by experiments on ultracold atoms which have realized the Haldane model for a Chern insulator, we consider its strongly correlated Mott limit with spin-1/2 fermions. We find that slave rotor mean-field theory yields gapped or gapless chiral spin liquid Mott insulators. To study competing magnetic orders, we consider the strong coupling effective spin Hamiltonian which includes chiral three-spin exchange. We obtain its classical phase diagram, uncovering various chiral magnetic orders including tetrahedral, cone, and noncoplanar spiral states which can compete with putative chiral quantum spin liquids. We study the effect of thermal fluctuations on these states, identifying crossovers in the spin chirality, and phase transitions associated with lattice symmetry breaking. We also discuss analogous effective spin Hamiltonians for correlated spin-1/2 bosons. Finally, we point out possible experimental implications of our results for cold atom experiments.

  14. Spin dynamics in the strong spin-orbit coupling regime 

    E-print Network

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

    2011-01-01

    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 ASCR... frequency ?so take the form: H so = (?1 ? 2?3 cos 2? )kx?y + (?2 + 2?3 cos 2? )ky?x, (5) where ?1 = ? + ?1 and ?2 = ?1 ? ?. 035318-11098-0121/2011/84(3)/035318(8) 2011 American Physical Society XIN LIU, XIONG-JUN LIU, AND JAIRO SINOVA PHYSICAL REVIEW B 84...

  15. Magnetic Suspension for Dynamic Spin Rig

    NASA Technical Reports Server (NTRS)

    Johnson, Dexter

    1998-01-01

    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.

  16. Atomistic spin dynamics and surface magnons.

    PubMed

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

    2015-06-24

    Atomistic spin dynamics simulations have evolved to become a powerful and versatile tool for simulating dynamic properties of magnetic materials. It has a wide range of applications, for instance switching of magnetic states in bulk and nano-magnets, dynamics of topological magnets, such as skyrmions and vortices and domain wall motion. In this review, after a brief summary of the existing investigation tools for the study of magnons, we focus on calculations of spin-wave excitations in low-dimensional magnets and the effect of relativistic and temperature effects in such structures. In general, we find a good agreement between our results and the experimental values. For material specific studies, the atomistic spin dynamics is combined with electronic structure calculations within the density functional theory from which the required parameters are calculated, such as magnetic exchange interactions, magnetocrystalline anisotropy, and Dzyaloshinskii-Moriya vectors. PMID:26030259

  17. Spin dynamics and spin freezing at ferromagnetic quantum phase transitions

    NASA Astrophysics Data System (ADS)

    Schmakat, P.; Wagner, M.; Ritz, R.; Bauer, A.; Brando, M.; Deppe, M.; Duncan, W.; Duvinage, C.; Franz, C.; Geibel, C.; Grosche, F. M.; Hirschberger, M.; Hradil, K.; Meven, M.; Neubauer, A.; Schulz, M.; Senyshyn, A.; Süllow, S.; Pedersen, B.; Böni, P.; Pfleiderer, C.

    2015-07-01

    We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1- y Fe2+ y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1- x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.

  18. Spinning compact binary dynamics and chameleon orbits

    NASA Astrophysics Data System (ADS)

    Gergely, László Árpád; Keresztes, Zoltán

    2015-01-01

    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.

  19. Spinning compact binary dynamics and chameleon orbits

    E-print Network

    László Árpád Gergely; Zoltán Keresztes

    2014-12-20

    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.

  20. Coherent Collisional Spin Dynamics in Optical Lattices

    SciTech Connect

    Widera, Artur; Gerbier, Fabrice; Foelling, Simon; Gericke, Tatjana; Mandel, Olaf; Bloch, Immanuel

    2005-11-04

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

  1. Dynamics of competing ideas in complex social systems

    NASA Astrophysics Data System (ADS)

    Wang, Yubo; Xiao, Gaoxi; Liu, Jian

    2012-01-01

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

  2. RNA Dynamics: Perspectives from Spin Labels

    PubMed Central

    Nguyen, Phuong

    2011-01-01

    Dynamics are an important and indispensible physical attribute that plays essential roles in RNA function. RNA dynamics are complex, spanning vast timescales and encompassing large number of physical modes. The technique of site-directed spin labeling (SDSL), which derives information on local structural and dynamic features of a macromolecule by monitoring a chemically stable nitroxide radical using electron paramagnetic resonance (EPR) spectroscopy, has been applied to monitor intrinsic dynamics at defined structural states as well as to probe conformational transition dynamics of RNAs. Current state of SDSL studies of RNA dynamics is summarized here. Further SDSL developments promise to open up many more opportunities for probing RNA dynamics and connecting dynamics to structure and function. PMID:21882345

  3. Dynamics of fractionalization in quantum spin liquids

    NASA Astrophysics Data System (ADS)

    Knolle, J.; Kovrizhin, D. L.; Chalker, J. T.; Moessner, R.

    2015-09-01

    We present the theory of dynamical spin response for the Kitaev honeycomb model, obtaining exact results for the structure factor (SF) in gapped and gapless, Abelian and non-Abelian quantum spin-liquid (QSL) phases. We also describe the advances in methodology necessary to compute these results. The structure factor shows signatures of spin fractionalization into emergent quasiparticles: Majorana fermions and fluxes of Z2 gauge field. In addition to a broad continuum from spin fractionalization, we find sharp (? -function) features in the response. These arise in two distinct ways: from excited states containing only (static) fluxes and no (mobile) fermions, and from excited states in which fermions are bound to fluxes. The SF is markedly different in Abelian and non-Abelian QSLs, and bound fermion-flux composites appear only in the non-Abelian phase.

  4. Chiral Dynamics and Single-Spin Asymmetries

    E-print Network

    Dennis Sivers

    2007-11-20

    Parity-conserving single-spin asymmetries provide a specific measure of coherent spin-orbit dynamics in quantum chromodynamics. The origin of these effects can be traced to the interplay of chiral dynamics and confinement in the theory. The most elegant display of the relevant mechanisms occurs in the Collins functions and the polarizing fragmentation functions and fracture functions for particles with spin. In the nucleon, these same dynamical mechanisms generate virtual quantum structures leading to the Boer-Mulders functions and orbital distributions. Two complementary formalisms for these distributions appear. The familiar gauge-link formalism incorporates oll nonperturbative dynamics into nonlocal correlators. The constructive formalism introduced by the author describes distributions normalized to an intrinsic property of the nucleon, namely, the currents specified in the Bakker-Leader-Trueman sum rule. The connection between these two approaches can be explored in the process dependence of single-spin asymmetries in various hard-scattering processes. The study of the SU(2) Weyl-Dirac equation in spherical coordinates allows typical Wilson operators that determine this process dependence to be evaluated in the coordinate gauge.

  5. Managerial competencies necessary in today's dynamic health care environment.

    PubMed

    Anderson, Peggy; Pulich, Marcia

    2002-12-01

    The traditional functions of management--planning, organizing, leading, and controlling--continue to be the key activities used to enable the organization to accomplish its goals and objectives. Though significant changes have occurred in all organizational structures, processes, and managerial styles, these traditional functions remain a constant. What has undergone significant change, as this article examines, are the skills and competencies within each function, which managers must develop and employ if they are to be successful practitioners in today's dynamic health care organizations. PMID:14959894

  6. Introduction Theory of nonequilibrium dynamics Single spin dynamics Conclusion Introduction Theory of nonequilibrium dynamics Single spin dynamics Conclusion

    E-print Network

    Anders, Frithjof

    Nonequilibrium: two conditions: ^0 and Hf ^(t) = e-iHf t ^0eiHf t Calculation of the trace using an energy of an observable ^O (t) = Tr ^O ^(t) Equilibrium: single condition ^(t) = ^0 = exp(-Hf )/Z Nonequilibrium: twoIntroduction Theory of nonequilibrium dynamics Single spin dynamics Conclusion #12;Introduction

  7. Many-body singlets by dynamic spin polarization

    E-print Network

    Wang Yao

    2011-01-20

    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.

  8. Dynamics of spin charge carriers in polyaniline

    NASA Astrophysics Data System (ADS)

    Krinichnyi, V. I.

    2014-06-01

    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.

  9. Combined molecular dynamics-spin dynamics simulations of bcc iron

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  10. Dynamics of the Lunar Spin Axis

    NASA Technical Reports Server (NTRS)

    Wisdom, Jack

    2006-01-01

    The evolution of the lunar spin axis is studied. Prior work has assumed that the inclination of the lunar orbit is constant and that the node regresses uniformly. This work takes into account the nonconstant inclination and nonuniform regression of the node as determined from averaged models of the motion of the lunar orbit. The resulting dynamics is considerably more rich, exhibiting additional resonances, period doubling and tripling, and chaos.

  11. Spin wave dynamics and magnetization switching in exchange-coupled bilayers

    NASA Astrophysics Data System (ADS)

    Seki, Takeshi

    2014-03-01

    Magnetic moments under the application of electric current or rf magnetic field show uniform or non-uniform dynamical motions, which are keys to develop novel spintronic devices such as nanometer-sized auto-oscillators and logic circuits. Spin waves are representative of spatially non-uniform magnetization dynamics. We demonstrated that spin waves could be utilized also to reduce the switching field in exchange-coupled bilayers consisting of hard magnetic L10-FePt and soft magnetic Permalloy (Py; Ni81Fe19). The switching field of L10-FePt was drastically reduced when the spin waves were excited. This ``spin wave-assisted magnetization switching'' is a route to balance competing goals for high coercive field, which is essential to maintain a good thermal stability of magnetization in a nanometer region, and low switching field, leading to the device operation with low power consumption. Those are important to realize high-performance spintronic and magnetic storage devices.In this talk, the concept and mechanism of spin wave-assisted magnetization switching are introduced. By comparing the experiments and the numerical simulation, it is found that perpendicular standing spin wave modes are mainly excited in Py of the exchange-coupled bilayers and those spin waves affect the dynamics of L10-FePt through the exchange coupling mechanism at the interface. The significant reduction of switching field is achieved by exciting the spin waves with large oscillation amplitude. In addition, the spin wave-assisted magnetization switching shows the characteristic magnetic field angular dependence, which is totally different from that of uniform magnetization dynamics. We also show the spin wave dynamics in perpendicularly magnetized exchange-coupled bilayers.

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

    NASA Astrophysics Data System (ADS)

    Miura, Daisuke; Sakuma, Akimasa

    2011-04-01

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

  13. Semi-Classical Dynamics in Quantum Spin Systems

    E-print Network

    J. Froehlich; A. Knowles; E. Lenzmann

    2007-09-28

    We consider two limiting regimes, the large-spin and the mean-field limit, for the dynamical evolution of quantum spin systems. We prove that, in these limits, the time evolution of a class of quantum spin systems is determined by a corresponding Hamiltonian dynamics of classical spins. This result can be viewed as a Egorov-type theorem. We extend our results to the thermodynamic limit of lattice spin systems and continuum domains of infinite size, and we study the time evolution of coherent spin states in these limiting regimes.

  14. Spin glass dynamics at the mesoscale

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    The mesoscale allows a new probe of spin glass dynamics. Because the spin glass lower critical dimension dl>2 , the growth of the correlation length ? (t ,T ) can change the nature of the spin glass state at a crossover time tco when ? (tco,T )=? , a minimum characteristic sample length (e.g., film thickness for thin films and crystallite size for bulk samples). For thin films, and times t dynamics is observed. When t >tco , a crossover to d =2 behavior takes place. The parallel correlation length, associated with a Tg=0 transition, increases in time from the saturated value of the perpendicular correlation length ? to an equilibrium value of the parallel correlation length proportional to T-?. This results in a pancakelike correlated state, with a thickness ? and a temperature-dependent in-plane radius that increases with decreasing temperature. Activated dynamics is associated with these states. Measurements on Cu:Mn thin films are analyzed quantitatively within this framework. We extract a temperature-dependent activation energy from a fit to the frequency dependence of the dynamic susceptibility. The extrapolated temperature at which the activation energy would become large is close to the extrapolated glass transition temperature from ac susceptibility measurements. All known relevant experimental data are consistent with this approach. For polycrystalline materials, there is a distribution of length scales P (? ) . For sufficiently broad distributions, a logarithmic time dependence is derived for the time decay of the thermoremanent magnetization MTRM(t ,T ) using an approach originally derived by Ma. Properties dependent upon an effective waiting time tweff are derived that are consistent with experiment, and further measurements are suggested.

  15. Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR

    NASA Astrophysics Data System (ADS)

    Wiecki, P.; Roy, B.; Johnston, D. C.; Bud'ko, S. L.; Canfield, P. C.; Furukawa, Y.

    2015-09-01

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe2As2 families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.

  16. Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR.

    PubMed

    Wiecki, P; Roy, B; Johnston, D C; Bud'ko, S L; Canfield, P C; Furukawa, Y

    2015-09-25

    In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic and in-plane ferromagnetic (FM) wave vectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using ^{75}As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole- and electron-doped BaFe_{2}As_{2} families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of T_{c} and the shape of the superconducting dome in these and other iron-pnictide families. PMID:26451577

  17. Current-driven spin dynamics of artificially constructed quantum magnets.

    PubMed

    Khajetoorians, Alexander Ako; Baxevanis, Benjamin; Hübner, Christoph; Schlenk, Tobias; Krause, Stefan; Wehling, Tim Oliver; Lounis, Samir; Lichtenstein, Alexander; Pfannkuche, Daniela; Wiebe, Jens; Wiesendanger, Roland

    2013-01-01

    The future of nanoscale spin-based technologies hinges on a fundamental understanding and dynamic control of atomic-scale magnets. The role of the substrate conduction electrons on the dynamics of supported atomic magnets is still a question of interest lacking experimental insight. We characterized the temperature-dependent dynamical response of artificially constructed magnets, composed of a few exchange-coupled atomic spins adsorbed on a metallic substrate, to spin-polarized currents driven and read out by a magnetic scanning tunneling microscope tip. The dynamics, reflected by two-state spin noise, is quantified by a model that considers the interplay between quantum tunneling and sequential spin transitions driven by electron spin-flip processes and accounts for an observed spin-transfer torque effect. PMID:23288534

  18. Suppression of spin-bath dynamics for improved coherence of multi-spin-qubit systems.

    PubMed

    Bar-Gill, N; Pham, L M; Belthangady, C; Le Sage, D; Cappellaro, P; Maze, J R; Lukin, M D; Yacoby, A; Walsworth, R

    2012-01-01

    Multi-qubit systems are crucial for the advancement and application of quantum science. Such systems require maintaining long coherence times while increasing the number of qubits available for coherent manipulation. For solid-state spin systems, qubit coherence is closely related to fundamental questions of many-body spin dynamics. Here we apply a coherent spectroscopic technique to characterize the dynamics of the composite solid-state spin environment of nitrogen-vacancy colour centres in room temperature diamond. We identify a possible new mechanism in diamond for suppression of electronic spin-bath dynamics in the presence of a nuclear spin bath of sufficient concentration. This suppression enhances the efficacy of dynamical decoupling techniques, resulting in increased coherence times for multi-spin-qubit systems, thus paving the way for applications in quantum information, sensing and metrology. PMID:22617298

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

    E-print Network

    Aeschlimann, Martin

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

  20. Dynamics of artificial spin ice: a continuous honeycomb network

    E-print Network

    Shen, Yichen

    We model the dynamics of magnetization in an artificial analogue of spin ice specializing to the case of a honeycomb network of connected magnetic nanowires. The inherently dissipative dynamics is mediated by the emission ...

  1. Probing quantum dynamics of strongly interacting spin ensembles

    NASA Astrophysics Data System (ADS)

    Kucsko, Georg; Maurer, Peter; Choi, Joonhee; Yao, Norman; Choi, Soonwon; Knap, Michael; Gopalakrishnan, Sarang; Lukin, Mikhail; Harvard Univ Team

    2015-05-01

    Ensembles of strongly interacting spins offer an attractive platform for the study of many-body quantum dynamics. We present detailed study of the electronic spin dynamics within a diamond sample with very high nitrogen vacancy (NV) concentration (?80 ppm). Due to the small distance between neighboring NV centers, the spin-spin interactions dominate over decoherence. Furthermore, by utilizing dynamical decoupling techniques, it is possible to suppress decoherence and study many-body phenomena. In particular, we present investigation of the interplay between interactions and disorder in such a system.

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

    SciTech Connect

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

    2009-05-14

    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.

  3. Comparisons of Social Competence in Young Children with and without Hearing Loss: A Dynamic Systems Framework

    ERIC Educational Resources Information Center

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

    2015-01-01

    This study compared levels of social competence and language development in 74 young children with hearing loss and 38 hearing peers aged 2.5-5.3 years. This study was the first to examine the relationship between oral language and social competence using a dynamic systems framework in children with and without hearing loss. We hypothesized that,…

  4. Dynamics of a macroscopic spin qubit in spin-orbit coupled Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Mardonov, Sh; Modugno, M.; Sherman, E. Ya

    2015-06-01

    We consider a macroscopic spin qubit based on spin-orbit coupled Bose-Einstein condensates, where, in addition to the spin-orbit coupling (SOC), spin dynamics strongly depends on the interaction between particles. The evolution of the spin for freely expanding, trapped, and externally driven condensates is investigated. For condensates oscillating at the frequency corresponding to the Zeeman splitting in the synthetic magnetic field, the spin Rabi frequency does not depend on the interaction between the atoms since it produces only internal forces and does not change the total momentum. However, interactions and SOC bring the system into a mixed spin state, where the total spin is inside rather than on the Bloch sphere. This greatly extends the available spin space making it three-dimensional, but imposes limitations on the reliable spin manipulation of such a macroscopic qubit. The spin dynamics can be modified by introducing suitable spin-dependent initial phases, determined by the SOC, in the spinor wave function.

  5. Spin dynamics of a confined electron interacting with magnetic or nuclear spins: A semiclassical approach

    NASA Astrophysics Data System (ADS)

    Dietl, Tomasz

    2015-03-01

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

  6. Nonequilibrium dynamics of spin-orbit-coupled lattice bosons

    NASA Astrophysics Data System (ADS)

    Ng, H. T.

    2015-10-01

    We study the nonequilibrium dynamics of two-component bosonic atoms in a one-dimensional optical lattice in the presence of spin-orbit coupling. In the Mott-insulating regime, the two-component bosonic system at unity filling can be described by the quantum spin X X Z model. The atoms are initially prepared in their lower spin states. The system becomes out of equilibrium by suddenly introducing spin-orbit coupling to the atoms. The system shows the relaxation and nonstationary dynamics, respectively, in the different interaction regimes. We find that the time average of magnetization is useful to characterize the many-body dynamics. The effects of even and odd numbers of sites are discussed. Our result sheds light on nonequilibrium dynamics due to the interplay between spin-orbit coupling and atomic interactions.

  7. Impact of nuclear spin dynamics on electron transport through donors

    NASA Astrophysics Data System (ADS)

    Gorman, S. K.; Broome, M. A.; Baker, W. J.; Simmons, M. Y.

    2015-09-01

    We present an analysis of electron transport through two weakly coupled precision-placed phosphorus donors in silicon. In particular, we examine the (1,1)?(0,2) charge transition where we predict a type of current blockade driven entirely by the nuclear spin dynamics. Using this nuclear spin blockade mechanism, we devise a protocol to read out the state of single nuclear spins using electron-transport measurements only. We extend our model to include realistic effects such as Stark shifted hyperfine interactions and multidonor clusters. In the case of multidonor clusters we show how nuclear spin blockade can be alleviated, allowing for low magnetic field electron-spin measurements.

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

    ERIC Educational Resources Information Center

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

    2001-01-01

    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;…

  9. Nonlinear dynamics of spin and charge in spin-Calogero model

    SciTech Connect

    Kulkarni, Manas; Franchini, Fabio; Abanov, Alexander G.

    2009-10-15

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

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

    SciTech Connect

    Tan, S.G.; Jalil, M.B.A.; Fujita, T.; Liu, X.J.

    2011-02-15

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

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

    NASA Astrophysics Data System (ADS)

    Mosshammer, Klemens; Brandes, Tobias

    2014-10-01

    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.

  12. Dynamics of test bodies with spin in de Sitter spacetime

    SciTech Connect

    Obukhov, Yuri N.; Puetzfeld, Dirk

    2011-02-15

    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.

  13. Binary Black Holes: Spin Dynamics and Gravitational Recoil

    E-print Network

    Frank Herrmann; Ian Hinder; Deirdre M. Shoemaker; Pablo Laguna; Richard A. Matzner

    2007-09-17

    We present a study of spinning black hole binaries focusing on the spin dynamics of the individual black holes as well as on the gravitational recoil acquired by the black hole produced by the merger. We consider two series of initial spin orientations away from the binary orbital plane. In one of the series, the spins are anti-aligned; for the second series, one of the spins points away from the binary along the line separating the black holes. We find a remarkable agreement between the spin dynamics predicted at 2nd post-Newtonian order and those from numerical relativity. For each configuration, we compute the kick of the final black hole. We use the kick estimates from the series with anti-aligned spins to fit the parameters in the \\KKF{,} and verify that the recoil along the direction of the orbital angular momentum is $\\propto \\sin\\theta$ and on the orbital plane $\\propto \\cos\\theta$, with $\\theta$ the angle between the spin directions and the orbital angular momentum. We also find that the black hole spins can be well estimated by evaluating the isolated horizon spin on spheres of constant coordinate radius.

  14. Binary black holes: Spin dynamics and gravitational recoil

    NASA Astrophysics Data System (ADS)

    Herrmann, Frank; Hinder, Ian; Shoemaker, Deirdre M.; Laguna, Pablo; Matzner, Richard A.

    2007-10-01

    We present a study of spinning black hole binaries focusing on the spin dynamics of the individual black holes as well as on the gravitational recoil acquired by the black hole produced by the merger. We consider two series of initial spin orientations away from the binary orbital plane. In one of the series, the spins are antialigned; for the second series, one of the spins points away from the binary along the line separating the black holes. We find a remarkable agreement between the spin dynamics predicted at 2nd post-Newtonian order and those from numerical relativity. For each configuration, we compute the kick of the final black hole. We use the kick estimates from the series with antialigned spins to fit the parameters in the Kidder kick formula, and verify that the recoil in the direction of the orbital angular momentum is ?sin?? and on the orbital plane ?cos??, with ? the angle between the spin directions and the orbital angular momentum. We also find that the black hole spins can be well estimated by evaluating the isolated horizon spin on spheres of constant coordinate radius.

  15. Phase diagrams of a spin-1 Ising system with competing short- and long-range interactions.

    PubMed

    Salmon, Octavio D Rodriguez; de Sousa, J Ricardo; Neto, Minos A

    2015-09-01

    We have studied the phase diagrams of the one-dimensional spin-1 Blume-Capel model with anisotropy constant D, in which equivalent-neighbor ferromagnetic interactions of strength -J are superimposed on nearest-neighbor antiferromagnetic interactions of strength K. A rich critical behavior is found due to the competing interactions. At zero temperature two ordered phases exist in the D/J-K/J plane, namely the ferromagnetic (F) and the antiferromagnetic one (AF). For lower values of D/J(D/J<0.25) these two ordered phases are separated by the point K_{c}=0.25J. For 0.250.5, only phases AF and F exist and are separated by a line given by D/J=K/J. At finite temperatures, we found that the ferromagnetic region of the phase diagram in the k_{B}T/J-D/J plane is enriched by another ferromagnetic phase F^{^{'}} above a first-order line for 0.195

  16. Phase diagrams of a spin-1 Ising system with competing short- and long-range interactions

    NASA Astrophysics Data System (ADS)

    Salmon, Octavio D. Rodriguez; de Sousa, J. Ricardo; Neto, Minos A.

    2015-09-01

    We have studied the phase diagrams of the one-dimensional spin-1 Blume-Capel model with anisotropy constant D , in which equivalent-neighbor ferromagnetic interactions of strength -J are superimposed on nearest-neighbor antiferromagnetic interactions of strength K . A rich critical behavior is found due to the competing interactions. At zero temperature two ordered phases exist in the D /J -K /J plane, namely the ferromagnetic (F ) and the antiferromagnetic one (AF ). For lower values of D /J (D /J <0.25 ) these two ordered phases are separated by the point Kc=0.25 J . For 0.25 0.5 , only phases AF and F exist and are separated by a line given by D /J =K /J . At finite temperatures, we found that the ferromagnetic region of the phase diagram in the kBT /J -D /J plane is enriched by another ferromagnetic phase F'above a first-order line for 0.195

  17. Polariton Spin Dynamics in IIVI Microcavities M. D. Martin1

    E-print Network

    Viña, Luis

    Polariton Spin Dynamics in II­VI Microcavities M. D. Marti´n1 )*) (a), G. Aichmayr (a), L. Vin~a (a.36.þc; 78.47.þp; 78.66.Hf; S8.13 The spin dynamics of cavity polaritons, in the non-linear regime by the polariton final state stimulated scattering, the emission is counter-polarized with the excita- tion

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

    SciTech Connect

    Rantaharju, Jyrki Mareš, Ji?í Vaara, Juha

    2014-07-07

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

  19. Dynamic control of spin wave spectra using spin-polarized currents

    SciTech Connect

    Wang, Qi; Zhang, Huaiwu Tang, Xiaoli; Bai, Feiming; Zhong, Zhiyong; Fangohr, Hans

    2014-09-15

    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.

  20. Optimized dynamical control of state transfer through noisy spin chains

    E-print Network

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

    2015-01-09

    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.

  1. Optimized dynamical control of state transfer through noisy spin chains

    NASA Astrophysics Data System (ADS)

    Zwick, Analia; Álvarez, Gonzalo A.; Bensky, Guy; Kurizki, Gershon

    2014-06-01

    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.

  2. QND Measurement of Large-Spin Ensembles by Dynamical Decoupling

    E-print Network

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

    2010-01-01

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

  3. QND Measurement of Large-Spin Ensembles by Dynamical Decoupling

    E-print Network

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

    2010-05-17

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

  4. Dynamics of nonequilibrium thermal entanglement for simple spin chains

    NASA Astrophysics Data System (ADS)

    Sinayskiy, I.; Pumulo, N.; Petruccione, F.

    2011-10-01

    The dynamics of simple spin chains of two and three spins coupled at both ends to separate bosonic baths at different temperatures is studied. An exact analytical solution of the master equation in the Born-Markov approximation for the reduced density matrix of the chain is constructed. It is shown that for long times the reduced density matrix converges to the non-equilibrium steady-state. Dynamical and steady state properties of the concurrence between the first and the last spin are studied.

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

    SciTech Connect

    Orth, Peter P.; Le Hur, Karyn; Roosen, David; Hofstetter, Walter

    2010-10-01

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

  6. Electron Shot Noise and Nuclear Spin Dynamics in Spin-Blockaded Quantum Dots

    NASA Astrophysics Data System (ADS)

    Rudner, Mark; Koppens, Frank; Folk, Joshua; Vandersypen, Lieven; Levitov, Leonid

    2010-03-01

    In the spin-blockade regime of double quantum dots [1], electron transport through the system constitutes a purely electrical means of probing and manipulating the dynamics of nuclear spins. Intense interest in this system as a platform to study spin coherence and many-body dynamics has spawned a wide range of experiments [2], which have revealed many complex dynamical phenomena. Here we identify a fundamental process in which nuclear spin dynamics can be driven by electron shot noise; fast electric current fluctuations generate much slower nuclear polarization dynamics, which in turn affect electron dynamics via the Overhauser field. The resulting extremely slow current fluctuations account for a variety of observed phenomena that were not previously understood. We propose a simple model for the coupled dynamics of electron and nuclear spins that captures much of the essential physics behind these experiments and validate the model by comparison with experimental data. [1] K. Ono et al. Science 297, 1313 (2002). [2] R. Hanson et al., Rev. Mod. Phys. 79, 1217 (2007).

  7. NMR with generalized dynamics of spin and spatial coordinates

    SciTech Connect

    Lee, Chang Jae

    1987-11-01

    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.

  8. A Competency Model for Process Dynamics and Control and Its Use for Test Construction at University Level

    ERIC Educational Resources Information Center

    Taskinen, Päivi H.; Steimel, Jochen; Gräfe, Linda; Engell, Sebastian; Frey, Andreas

    2015-01-01

    This study examined students' competencies in engineering education at the university level. First, we developed a competency model in one specific field of engineering: process dynamics and control. Then, the theoretical model was used as a frame to construct test items to measure students' competencies comprehensively. In the empirical…

  9. Aging dynamics of quantum spin glasses of rotors

    NASA Astrophysics Data System (ADS)

    Kennett, Malcolm P.; Chamon, Claudio; Ye, Jinwu

    2001-12-01

    We study the long time dynamics of quantum spin glasses of rotors using the nonequilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin-glass phase, which we approach by looking at the divergence of the spin-relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RPG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out-of-equilibrium fluctuation-dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.

  10. Binary Black Holes: Spin Dynamics and Gravitational Recoil

    E-print Network

    Herrmann, Frank; Shoemaker, Deirdre M; Laguna, Pablo; Matzner, Richard A

    2007-01-01

    We present a study of spinning black hole binaries focusing on the spin dynamics of the individual black holes as well as on the gravitational recoil acquired by the black hole produced by the merger. We consider two series of initial spin orientations away from the binary orbital plane. In one of the series, the spins are anti-aligned; for the second series, one of the spins points away from the binary along the line separating the black holes. We find a remarkable agreement between the spin dynamics predicted at 2nd post-Newtonian order and those from numerical relativity. For each configuration, we compute the kick of the final black hole. We use the kick estimates from the series with anti-aligned spins to fit the parameters in the Kidder kick formula, and verify that the recoil along the direction of the orbital angular momentum is proportional to $\\sin\\theta$ and on the orbital plane to $\\cos\\theta$, with $\\theta$ the angle between the spin directions and the orbital angular momentum.

  11. Simulating spin dynamics in organic solids under heteronuclear decoupling.

    PubMed

    Frantsuzov, Ilya; Ernst, Matthias; Brown, Steven P; Hodgkinson, Paul

    2015-09-01

    Although considerable progress has been made in simulating the dynamics of multiple coupled nuclear spins, predicting the evolution of nuclear magnetisation in the presence of radio-frequency decoupling remains challenging. We use exact numerical simulations of the spin dynamics under simultaneous magic-angle spinning and RF decoupling to determine the extent to which numerical simulations can be used to predict the experimental performance of heteronuclear decoupling for the CW, TPPM and XiX sequences, using the methylene group of glycine as a model system. The signal decay times are shown to be strongly dependent on the largest spin order simulated. Unexpectedly large differences are observed between the dynamics with and without spin echoes. Qualitative trends are well reproduced by modestly sized spin system simulations, and the effects of finite spin-system size can, in favourable cases, be mitigated by extrapolation. Quantitative prediction of the behaviour in complex parameter spaces is found, however, to be very challenging, suggesting that there are significant limits to the role of numerical simulations in RF decoupling problems, even when specialist techniques, such as state-space restriction, are used. PMID:26073419

  12. Spin dynamics of atoms and magnetic nanostructures on surfaces

    NASA Astrophysics Data System (ADS)

    Heinrich, Andreas

    2013-03-01

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

  13. On the dynamics of XY spin chains with impurities

    NASA Astrophysics Data System (ADS)

    Genovese, Giuseppe

    2015-09-01

    We provide a theoretical set up for studying the dynamics in quantum spin chain models with inhomogeneous two-body interaction. We frame in our formalism models that can be mapped into fermion systems with quadratic Hamiltonian, namely XY chains with transverse magnetic field. Local and global existence results of the dynamics are discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  15. Charge dynamics and spin order in doped Hubbard models

    SciTech Connect

    Kampf, A.P.; Brenig, W.

    1994-04-01

    Hole motion in an antiferromagnetic (AF) environment is accompanied by the emission of spin wave excitations. Spin-wave shakeoffs are responsible for incoherent contributions to the dynamics of propagating holes. Using a spin-density-wave polaron scheme the authors calculate the optical conductivity {sigma}({omega}) and show that the incoherent part of the hole spectrum contributes to the low-frequency part of {sigma}({omega}). Separately, the authors discuss the possible formation of spiral spin patterns upon doping of the half-filled one-band Hubbard model. In particular, the authors consider the influence of band structure effects arising from nearest- and next-nearest-neighbor hopping processes on a square lattice. Differences in the ground state spin patterns for hole and electron doping are obtained offering a possible explanation for the persistence of AF order in low electron-doped cuprate superconductors.

  16. Concatenated dynamical decoupling in a solid-state spin bath

    E-print Network

    Witzel, W M

    2007-01-01

    Concatenated dynamical decoupling (CDD) pulse sequences hold much promise as a strategy to mitigate decoherence in quantum information devices. It is important to investigate the actual performance of these dynamical decoupling strategies in real systems that are promising qubit candidates. In this Letter, we compute the echo decay of concatenations of the Hahn echo sequence for a solid-state electronic spin qubit in a nuclear spin bath. We use a cluster expansion technique and find that increasing orders of the expansion must be included with each concatenation of the pulse sequence. The simple pair approximation, previously used to study restoration, through CDD, of coherence lost to a mesoscopic spin bath, fails to accurately compute CDD echo decay of a solid-state spin qubit.

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

    SciTech Connect

    Ning Boyuan; Zhuang Jun; Zhang Wenxian; You, J. Q.

    2011-07-15

    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.

  18. Number Fluctuation Dynamics of Atomic Spin Mixing inside a Condensate

    SciTech Connect

    Chang, Lee; Zhai, Q.; Lu Rong; You, L.

    2007-08-24

    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.

  19. Dynamics of genuine multipartite entanglement in a quantum spin system

    NASA Astrophysics Data System (ADS)

    Zhou, Jiang; Guo, Hong

    2012-11-01

    The time evolution of genuine multipartite entanglement is numerically studied in a model many-spin system decohered by a structured spin bath. It is found that multipartite entanglement can be more persistent than the bipartite entanglement and can even evolve into a specific constant under certain conditions. Besides, multipartite entanglement sudden death and sudden birth are observed. It is shown that the randomness of the coupling strength and connectivity between the spins in the environment will suppress these birth and death phenomena. Furthermore, the initial state of the central system plays a significant role in determining multipartite entanglement dynamics.

  20. Robust Dynamical Decoupling Sequences for Individual Nuclear Spin Addressing

    E-print Network

    J. Casanova; Z. -Y. Wang; J. F. Haase; M. B. Plenio

    2015-10-10

    We propose the use of non-equally spaced decoupling pulses for high-resolution selective addressing of nuclear spins by a quantum sensor. The analytical model of the basic operating principle is supplemented by detailed numerical studies that demonstrate the high degree of selectivity and the robustness against static and dynamic control field errors of this scheme. We exemplify our protocol with an NV center-based sensor to demonstrate that it enables the identification of individual nuclear spins that form part of a large spin ensemble.

  1. Robust dynamical decoupling sequences for individual-nuclear-spin addressing

    NASA Astrophysics Data System (ADS)

    Casanova, J.; Wang, Z.-Y.; Haase, J. F.; Plenio, M. B.

    2015-10-01

    We propose the use of non-equally-spaced decoupling pulses for high-resolution selective addressing of nuclear spins by a quantum sensor. The analytical model of the basic operating principle is supplemented by detailed numerical studies that demonstrate the high degree of selectivity and the robustness against static and dynamic control-field errors of this scheme. We exemplify our protocol with a nitrogen-vacancy-center-based sensor to demonstrate that it enables the identification of individual nuclear spins that form part of a large spin ensemble.

  2. Dynamical nuclear spin polarization in a double quantum dot

    NASA Astrophysics Data System (ADS)

    Ramon, Guy; Deng, Changxue; Hu, Xuedong

    2006-03-01

    The hyperfine interaction between an electron spin confined in a semiconductor quantum dot and the nuclear spins in the surrounding lattice has been identified as one of the main sources for decoherence in low temperature GaAs quantum dots. Recent experiments in gated double dot systems [1] have attempted to utilize the degeneracy point between the two-electron singlet and polarized triplet states to polarize the nuclear spins, thereby reducing their decoherence effects on the electron spins. Here we analyze the dynamics of the system of two electrons and a nuclear spin bath subject to the hyperfine interaction. We consider the effective spin Hamiltonian for the two-electron system, and represent the nuclear spins in the basis of their collective states. The nuclear polarization rates are evaluated for various initial conditions of the nuclear spin system, and optimal conditions for efficient polarization are discussed. [1] J. R. Petta, A. C. Johnson, J. M. Taylor, E. A. Laird, A. Yacoby, M. D. Lukin, C. M. Marcus, M. P. Hanson, A. C. Gossard, Science 309, 2180 (2005).

  3. Tunable nonequilibrium dynamics of field quenches in spin ice.

    PubMed

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

    2014-01-14

    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

  4. Tunable nonequilibrium dynamics of field quenches in spin ice

    PubMed Central

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

    2014-01-01

    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

  5. Dynamical stability of the Holographic System with Two Competing Orders

    E-print Network

    Du, Yiqiang; Tian, Yu; Zhang, Hongbao

    2015-01-01

    We investigate the dynamical stability of the holographic system with two order parameters, which exhibits competition and coexistence of condensations. In the linear regime, we have developed the gauge dependent formalism to calculate the quasi-normal modes by gauge fixing, which turns out be considerably convenient. Furthermore, by giving different Gaussian wave packets as perturbations at the initial time, we numerically evolve the full nonlinear system until it arrives at the final equilibrium state. Our results show that the dynamical stability is consistent with the thermodynamical stability. Interestingly, the dynamical evolution, as well as the quasi-normal modes, shows that the relaxation time of this model is generically much longer than the simplest holographic system. We also find that the late time behavior can be well captured by the lowest lying quasi-normal modes except for the non-vanishing order towards the single ordered phase. To our knowledge, this exception is the first counter example t...

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

    NASA Astrophysics Data System (ADS)

    Yao, Wang

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

  7. Longitudinal spin dynamics in the Heisenberg ferromagnet: Diagrammatic approach

    NASA Astrophysics Data System (ADS)

    Izyumov, Yu. A.; Chaschin, N. I.; Yushankhai, V. Yu.

    2002-06-01

    Based on the diagrammatic technique for spin operators, the ferromagnetic Heisenberg model is studied with an emphasis on the longitudinal spin dynamics. The diagram rules are, to our knowledge, newly formulated by using equations in terms of variational derivatives of a generating functional describing interactions of the spin system with auxiliary fluctuating fields. This approach provides us with an efficient procedure to derive graphical representations for perturbation expansion series for different spin Green functions. Since fluctuations of the longitudinal spin components are generated by processes of virtual creation and annihilation of transverse spin component modes (renormalized spin waves), the infinite series involving all distinct loops built from spin-wave propagators are summed up. This results in an expression for the longitudinal spin susceptibility ?zz(q,?) taking a generalized RPA-type form with a strongly renormalized denominator including all the terms ~1/z (z is the first coordination lattice number). The corresponding longitudinal component of the dynamic structure factor exhibits a three-peak structure with two wide maxima at frequencies ?q~+/-Jq and a sufficiently narrow central peak that grows fast when approaching the Curie temperature. With growing temperature, the intensity of the ?q peaks increases, and they merge with the central peak whereas the width of the entire spectral distribution decreases. At fixed temperature, the distribution width changes linearly with wave vector q. The observed picture is applicable beyond the hydrodynamic regime that is valid at small q and higher temperatures. Study of the evolution of the spectral distribution from a three-peak structure to a single-peaked one, valid beyond the hydrodynamic regime, with increasing temperature can help to explain conflicting results of neutron studies of longitudinal fluctuations in different ferromagnets.

  8. Destination state screening of active spaces in spin dynamics simulations

    NASA Astrophysics Data System (ADS)

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

    2011-06-01

    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).

  9. Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization

    NASA Astrophysics Data System (ADS)

    Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

    2015-09-01

    Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160 K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea -eb - n } during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions.

  10. Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization.

    PubMed

    Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva

    2015-09-01

    Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea-eb-n} during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions. PMID:26232770

  11. Dynamical stability of the Holographic System with Two Competing Orders

    E-print Network

    Yiqiang Du; Shan-Quan Lan; Yu Tian; Hongbao Zhang

    2015-11-23

    We investigate the dynamical stability of the holographic system with two order parameters, which exhibits competition and coexistence of condensations. In the linear regime, we have developed the gauge dependent formalism to calculate the quasi-normal modes by gauge fixing, which turns out be considerably convenient. Furthermore, by giving different Gaussian wave packets as perturbations at the initial time, we numerically evolve the full nonlinear system until it arrives at the final equilibrium state. Our results show that the dynamical stability is consistent with the thermodynamical stability. Interestingly, the dynamical evolution, as well as the quasi-normal modes, shows that the relaxation time of this model is generically much longer than the simplest holographic system. We also find that the late time behavior can be well captured by the lowest lying quasi-normal modes except for the non-vanishing order towards the single ordered phase. To our knowledge, this exception is the first counter example to the general belief that the late time behavior towards a final stable state can be captured by the lowest lying quasi-normal modes. In particular, a double relation is found for this exception in certain cases.

  12. Group dynamics for the acquisition of competences in Project Management

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  13. Spacetime dynamics of spinning particles - exact gravito-electromagnetic analogies

    E-print Network

    L. Filipe O. Costa; José Natário; Miguel Zilhão

    2015-07-29

    We compare the rigorous equations describing the motion of spinning test particles in gravitational and electromagnetic fields, and show that if the Mathisson-Pirani spin condition holds then exact gravito-electromagnetic analogies emerge. These analogies provide a familiar formalism to treat gravitational problems, as well as a means for comparing the two interactions. Fundamental differences are manifest in the symmetries and time projections of the electromagnetic and gravitational tidal tensors. The physical consequences of the symmetries of the tidal tensors are explored comparing the following analogous setups: magnetic dipoles in the field of non-spinning/spinning charges, and gyroscopes in the Schwarzschild, Kerr, and Kerr-de Sitter spacetimes. The implications of the time-projections of the tidal tensors are illustrated by the work done on the particle in various frames; in particular, a reciprocity is found to exist: in a frame comoving with the particle, the electromagnetic (but not the gravitational) field does work on it, causing a variation of its proper mass; conversely, for "static observers", a stationary gravitomagnetic (but not a magnetic) field does work on the particle, and the associated potential energy is seen to embody the Hawking-Wald spin-spin interaction energy. The issue of hidden momentum, and its counterintuitive dynamical implications, is also analyzed. Finally, a number of issues regarding the electromagnetic interaction are clarified, namely the differences in the dynamics of electric and magnetic dipoles, and the physical meaning of Dixon's equations.

  14. STAR results on longitudinal spin dynamics

    E-print Network

    Joanna Kiryluk; for the STAR Collaboration

    2006-08-08

    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.

  15. Antiferromagnetic order and spin dynamics in iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Dai, Pengcheng

    2015-07-01

    High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.

  16. Spin dynamics simulations for a nanoscale Heisenberg antiferromagnetic film

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

    Thermoinduced magnetization(TiM) is a novel response predicted to occur in nanoscale antiferromagnetic (AF) materials. Extensive Monte Carlo simulations have shown that TiM is an intrinsic property of the AF classical Heisenberg model. To obtain a fundamental understanding of TiM, spin dynamics (SD) simulations are performed to study the spin wave behavior, which seems to be the cause of TiM. A classical Heisenberg model with an AF nearest-neighbor exchange interaction and uniaxial single-site anisotropy is studied. Simple-cubic lattices with two free-surfaces and periodic boundaries parallel to the surfaces are used. We applied fast SD algorithms with 4th-order Suzuki-Trotter decompositions of the exponential operator. Discrete spin wave modes due to spin wave confinement are found in transverse S(q, ?) in the perpendicular direction to free surfaces. Research supported by UT-Battelle, and Office of Science, DOE.

  17. Concatenated dynamical decoupling in a solid-state spin bath

    E-print Network

    W. M. Witzel; S. Das Sarma

    2007-12-13

    Concatenated dynamical decoupling (CDD) pulse sequences hold much promise as a strategy to mitigate decoherence in quantum information processing. It is important to investigate the actual performance of these dynamical decoupling strategies in real systems that are promising qubit candidates. In this Rapid Communication, we compute the echo decay of concatenations of the Hahn echo sequence for a solid-state electronic spin qubit in a nuclear spin bath using a cluster expansion technique. We find that each level of concatenation reverses the effect of successive levels of intrabath fluctuations. On the one hand, this advances CDD as a versatile and realistic decoupling strategy. On the other hand, this invalidates, as overly optimistic, results of the simple pair approximation used previously to study restoration, through CDD, of coherence lost to a mesoscopic spin bath.

  18. Investigations of quantum pendulum dynamics in a spin-1 BEC

    NASA Astrophysics Data System (ADS)

    Hoang, Thai; Gerving, Corey; Land, Ben; Anquez, Martin; Hamley, Chris; Chapman, Michael

    2013-05-01

    We investigate the quantum spin dynamics of a spin-1 BEC initialized to an unstable critical point of the dynamical phase space. The subsequent evolution of the collective states of the system is analogous to an inverted simple pendulum in the quantum limit and yields non-classical states with quantum correlations. For short evolution times in the low depletion limit, we observe squeezed states and for longer times beyond the low depletion limit we observe highly non-Gaussian distributions. C.D. Hamley, C.S. Gerving, T.M. Hoang, E.M. Bookjans, and M.S. Chapman, ``Spin-Nematic Squeezed Vacuum in a Quantum Gas,'' Nature Physics 8, 305-308 (2012).

  19. Hexagonal type Ising nanowire with mixed spins: Some dynamic behaviors

    NASA Astrophysics Data System (ADS)

    Kantar, Ersin; Kocakaplan, Yusuf

    2015-11-01

    The dynamic behaviors of a mixed spin (1/2-1) hexagonal Ising nanowire (HIN) with core-shell structure in the presence of a time dependent magnetic field are investigated by using the effective-field theory with correlations based on the Glauber-type stochastic dynamics (DEFT). According to the values of interaction parameters, temperature dependence of the dynamic magnetizations, the hysteresis loop areas and the dynamic correlations are investigated to characterize the nature (first- or second-order) of the dynamic phase transitions (DPTs). Dynamic phase diagrams, including compensation points, are also obtained. Moreover, from the thermal variations of the dynamic total magnetization, the five compensation types can be found under certain conditions, namely the Q-, R-, S-, P-, and N-types.

  20. Odd-parity superconductivity by competing spin-orbit coupling and orbital effect in artificial heterostructures

    NASA Astrophysics Data System (ADS)

    Watanabe, Tatsuya; Yoshida, Tomohiro; Yanase, Youichi

    2015-11-01

    We show that odd-parity superconductivity occurs in multilayer Rashba systems without requiring spin-triplet Cooper pairs. A pairing interaction in the spin-singlet channel stabilizes the odd-parity pair-density-wave (PDW) state in the magnetic field parallel to the two-dimensional conducting plane. It is shown that the layer-dependent Rashba spin-orbit coupling and the orbital effect play essential roles for the PDW state in binary and tricolor heterostructures. We demonstrate that the odd-parity PDW state is a symmetry-protected topological superconducting state characterized by the one-dimensional winding number in the symmetry class BDI. The superconductivity in the artificial heavy-fermion superlattice CeCoIn5/YbCoIn5 and bilayer interface SrTiO3/LaAlO3 is discussed.

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

    NASA Astrophysics Data System (ADS)

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

    1996-02-01

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

  2. Nearest-Neighbor Repulsion and Competing Charge and Spin Order in the Extended Hubbard Model.

    NASA Astrophysics Data System (ADS)

    Bahman, Davoudi; Tremblay, A.-M. S.

    2006-03-01

    We generalize the Two-Particle Self-Consistent (TPSC) approach to study the extended Hubbard model where the nearest-neighbor interaction V is present in addition to the local interaction U. Our results are in good agreement with available Quantum Monte-Carlo results over the whole range of density n up to intermediate coupling. As a function of U, V and n we observe different kinds of charge and spin orders, like commensurate/incommensurate charge and spin density wave, phase separation, and ferromagnetic order. For attractive V superconductivity could exist in the regions where the other types of charge and spin orders do not dominate. Ref.: B. Davoudi and A.-M.S. Tremblay, cond-mat/0509707

  3. Spin dynamics in a Curie-switch.

    PubMed

    Kravets, A F; Tovstolytkin, A I; Dzhezherya, Yu I; Polishchuk, D M; Kozak, I M; Korenivski, V

    2015-11-11

    Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2-magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affect the resonance fields of both F1 and F2 layers. Our theoretical calculations as well as measurements show that the key magnetic parameters of the spacer, which govern the ferromagnetic resonance in F1/f/F2/AF, are the magnetic exchange length ([Formula: see text]), effective saturation magnetization at T??=??0 (m 0) and effective Curie temperature ([Formula: see text]). The values of these key parameters are deduced from the experimental data for multilayers with f??=??Ni x Cu100-x , for the key ranges in the Ni-concentration ([Formula: see text] at. %) and spacer thickness ([Formula: see text] nm). The results obtained provide a deeper insight into thermally-controlled spin precession and switching in magnetic nanostructures, with potential applications in spin-based oscillators and memory devices. PMID:26471166

  4. Spin dynamics in a Curie-switch

    NASA Astrophysics Data System (ADS)

    Kravets, A. F.; Tovstolytkin, A. I.; Dzhezherya, Yu I.; Polishchuk, D. M.; Kozak, I. M.; Korenivski, V.

    2015-11-01

    Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2—magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affect the resonance fields of both F1 and F2 layers. Our theoretical calculations as well as measurements show that the key magnetic parameters of the spacer, which govern the ferromagnetic resonance in F1/f/F2/AF, are the magnetic exchange length (? ), effective saturation magnetization at T??=??0 (m 0) and effective Curie temperature (T\\text{C}\\text{eff} ). The values of these key parameters are deduced from the experimental data for multilayers with f??=??Ni x Cu100?x , for the key ranges in the Ni–concentration (x=54\\div 70 at. %) and spacer thickness (d=3\\div 6 nm). The results obtained provide a deeper insight into thermally-controlled spin precession and switching in magnetic nanostructures, with potential applications in spin-based oscillators and memory devices.

  5. On the spin-axis dynamics of a Moonless Earth

    SciTech Connect

    Li, Gongjie; Batygin, Konstantin

    2014-07-20

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

  6. Computer studies of multiple-quantum spin dynamics

    SciTech Connect

    Murdoch, J.B.

    1982-11-01

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

  7. Covariant hamiltonian spin dynamics in curved space-time

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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.

  8. Covariant hamiltonian spin dynamics in curved space-time

    E-print Network

    d'Ambrosi, G; van Holten, J W

    2015-01-01

    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.

  9. Dynamical supersymmetry on the XXX spin chain

    E-print Network

    Matsui, Chihiro

    2015-01-01

    We show the XXX model has the N = 2 dynamical supersymmetry. Using the supercharges defined by the Jordan-Wigner fermions, it was found that the anti-commutation relation of the supercharges gives the Hamiltonian of the XXX model with magnetic field. In order to compare the length-change supercharges with the conventional ones, we interpreted their actions in the spinon basis. In the last part of this paper, we propose the application of the dynamical supersymmetry to the models with magnetic impurities through the Bethe-ansatz analysis.

  10. Dynamical supersymmetry on the XXX spin chain

    E-print Network

    Chihiro Matsui

    2015-04-30

    We show the XXX model has the N = 2 dynamical supersymmetry. Using the supercharges defined by the Jordan-Wigner fermions, it was found that the anti-commutation relation of the supercharges gives the Hamiltonian of the XXX model with magnetic field. In order to compare the length-change supercharges with the conventional ones, we interpreted their actions in the spinon basis. In the last part of this paper, we propose the application of the dynamical supersymmetry to the models with magnetic impurities through the Bethe-ansatz analysis.

  11. Spin dynamics in highly frustrated pyrochlore magnets

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  12. Spin/Orbital Dynamics in Titanates and Vanadates

    NASA Astrophysics Data System (ADS)

    Ulrich, Clemens

    2004-03-01

    In cubic perovskite systems like the titanates and vanadates, the d-valence electrons exhibit a multitude of competing many-body ground states where quantum fluctuations play an important role. Neutron spectroscopy in the Mott-Hubbard insulator LaTiO3 has revealed a reduced magnetic moment and a nearly isotropic spin wave dispersion [1]. These results are difficult to reconcile with predictions based on the standard Goodenough-Kanamori rules. Due to the small or even absent distortion of the TiO6 octahedra, the t_2g levels are fully degenerate. Theoretical considerations indicate that these orbitals are only weakly ordered or may even form a coherent orbital-liquid ground state [2]. Our investigations of the ferromagnetic Mott insulator YTiO3 have shown, that even in a system with Jahn-Teller distortion, orbital zero-point fluctuations have to be taken into account [3]. YVO3 undergoes a series of temperature induced phase transitions between states with different spin and orbital ordering patterns, i.e. a C-type and a G-type magnetic phase [4]. The C-type magnetic phase has a highly unusual magnetic structure and spin wave spectrum than cannot be understood within a conventional spin wave theory. A good description of the neutron scattering data is obtained by introducing quasi-1D orbital fluctuations [5]. This leads to the tentative identification of this phase with a previously theoretically proposed 'orbital Peierls state'. [1] B. Keimer et al., Phys. Rev. Lett. 85, 3946 (2000). [2] G. Khaliullin and S. Maekawa, Phys. Rev. Lett. 85, 3950 (2000). [3] C. Ulrich et al., Phys. Rev. Lett. 89, 167202 (2002). [4] Y. Ren et al., Nature 396, 441 (1998). [5] C. Ulrich et al., cond.-mat./0211589; accepted for publication in Phys. Rev. Lett.

  13. Dynamic-angle spinning and double rotation of quadrupolar nuclei

    SciTech Connect

    Mueller, K.T. California Univ., Berkeley, CA . Dept. of Chemistry)

    1991-07-01

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

  14. Ultrafast and Distinct Spin Dynamics in Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Radu, I.; Stamm, C.; Eschenlohr, A.; Radu, F.; Abrudan, R.; Vahaplar, K.; Kachel, T.; Pontius, N.; Mitzner, R.; Holldack, K.; Föhlisch, A.; Ostler, T. A.; Mentink, J. H.; Evans, R. F. L.; Chantrell, R. W.; Tsukamoto, A.; Itoh, A.; Kirilyuk, A.; Kimel, A. V.; Rasing, Th.

    2015-08-01

    Controlling magnetic order on ultrashort timescales is crucial for engineering the next-generation magnetic devices that combine ultrafast data processing with ultrahigh-density data storage. An appealing scenario in this context is the use of femtosecond (fs) laser pulses as an ultrafast, external stimulus to fully set the orientation and the magnetization magnitude of a spin ensemble. Achieving such control on ultrashort timescales, e.g., comparable to the excitation event itself, remains however a challenge due to the lack of understanding the dynamical behavior of the key parameters governing magnetism: The elemental magnetic moments and the exchange interaction. Here, we investigate the fs laser-induced spin dynamics in a variety of multi-component alloys and reveal a dissimilar dynamics of the constituent magnetic moments on ultrashort timescales. Moreover, we show that such distinct dynamics is a general phenomenon that can be exploited to engineer new magnetic media with tailor-made, optimized dynamic properties. Using phenomenological considerations, atomistic modeling and time-resolved X-ray magnetic circular dichroism (XMCD), we demonstrate demagnetization of the constituent sub-lattices on significantly different timescales that depend on their magnetic moments and the sign of the exchange interaction. These results can be used as a “recipe” for manipulation and control of magnetization dynamics in a large class of magnetic materials.

  15. Planar Spin-Transfer Device with a Dynamic Polarizer.

    NASA Astrophysics Data System (ADS)

    Bazaliy, Yaroslaw; Olaosebikan, Debo; Jones, Barbara

    2007-03-01

    In planar nano-magnetic devices magnetization direction is kept close to a given plane by the large easy-plane magnetic anisotropy (e.g. by shape anisotropy in a thin film). In conventional micromagnetics it is known that in this case the magnetization motion is effectively in-plane with only one angle required for its description, and can become overdamped even for small values of the Gilbert damping. We extend the equations of the effective in-plane dynamics to include the spin-transfer torques. The simplifications achieved in the overdamped regime allow us to study systems with several dynamic magnetic pieces (``free layers''). A transition from a spin-transfer device with a static polarizer to a device with two equivalent magnets is observed: when the size difference between the magnets is less than critical, the device does not exhibit switching, but goes directly into the ``windmill'' precession state.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  17. The spin glass-like dynamics of gelatin gels

    E-print Network

    Alan Parker; Valery Normand

    2003-06-03

    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.

  18. LETTER TO THE EDITOR: Algebraic Bethe ansatz for a spin-½ quantum linear chain with competing interactions

    NASA Astrophysics Data System (ADS)

    Rego-Monteiro, M. A.

    2000-11-01

    We propose a generalization of the formula that gives an integrable quantum 1D spin Hamiltonian with nearest-neighbour interactions as a logarithmic derivative of a vertex model transfer matrix in order to include in this scheme more realistic integrable models. We compute exactly this generalized formula using the R matrix of the XXX model, obtaining the Majumdar-Ghosh Hamiltonian plus a charge-like interaction term. We diagonalize this Hamiltonian using the quantum inverse scattering method and present the Bethe ansatz equations of the model.

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

    E-print Network

    Flatte, Michael E.

    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

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

    NASA Astrophysics Data System (ADS)

    Bragar, Igor; Cywi?ski, ?ukasz

    2015-04-01

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

  1. Dynamics of hot random quantum spin chains: from anyons to Heisenberg spins

    NASA Astrophysics Data System (ADS)

    Parameswaran, Siddharth; Potter, Andrew; Vasseur, Romain

    2015-03-01

    We argue that the dynamics of the random-bond Heisenberg spin chain are ergodic at infinite temperature, in contrast to the many-body localized behavior seen in its random-field counterpart. First, we show that excited-state real-space renormalization group (RSRG-X) techniques suffer from a fatal breakdown of perturbation theory due to the proliferation of large effective spins that grow without bound. We repair this problem by deforming the SU (2) symmetry of the Heisenberg chain to its `anyonic' version, SU(2)k , where the growth of effective spins is truncated at spin S = k / 2 . This enables us to construct a self-consistent RSRG-X scheme that is particularly simple at infinite temperature. Solving the flow equations, we compute the excited-state entanglement and show that it crosses over from volume-law to logarithmic scaling at a length scale ?k ~e?k3 . This reveals that (a) anyon chains have random-singlet-like excited states for any finite k; and (b) ergodicity is restored in the Heisenberg limit k --> ? . We acknowledge support from the Quantum Materials program of LBNL (RV), the Gordon and Betty Moore Foundation (ACP), and UC Irvine startup funds (SAP).

  2. Dynamics Of Proton Spin : Role Of $qqq$ Force

    E-print Network

    A. N. Mitra

    2007-12-18

    The analytic structure of the $qqq$ wave function, obtained recently in the high momentum regime of QCD, is employed for the formulation of baryonic transition amplitudes via quark loops. A new aspect of this study is the role of a direct ($Y$-shaped, Mercedes-Benz type) $qqq$ force in generating the $qqq$ wave function. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. The dynamics of this 3-body force shows up through a characteristic singularity in the hypergeometric differential equation for the 3D wave function $\\phi$, corresponding to a $negative$ eigenvalue of the spin operator $i \\sigma_1.\\sigma_2\\times \\sigma_3$ which is an integral part of the $qqq$ force. As a first application of this wave function to the problem of the proton spin anomaly, the two-gluon contribution to the anomaly yields an estimate of the right sign, although somewhat smaller in magnitude. Keywords: 3bodyforce; proton-spin; 2gluon anomaly; fractional correction $\\theta$

  3. Filamentation processes and dynamical excitation of light condensates in optical media with competing nonlinearities

    SciTech Connect

    Novoa, David; Michinel, Humberto; Tommasini, Daniele; Carpentier, Alicia V.

    2010-04-15

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

  4. Short-Time Glassy Dynamics in Viscous Protein Solutions with Competing Interactions

    NASA Astrophysics Data System (ADS)

    Godfrin, P. Douglas; Hudson, Steven D.; Hong, Kunlun; Porcar, Lionel; Falus, Peter; Wagner, Norman J.; Liu, Yun

    2015-11-01

    The glass transition of colloidal dispersions interacting with both a short-ranged attraction and long-ranged repulsion is studied using highly purified lysozyme solutions. Newtonian liquid behavior is observed at all conditions while measurements of the dynamics in the short-time limit show features typical of glassy colloidal systems at high protein concentrations. This interesting behavior is due to the competition of the attraction and repulsion that produces a heterogeneous microstructure only at intermediate range length scales. The results demonstrate that theories for the macroscopic properties of systems with competing interactions need to include intermediate range order.

  5. Gibbsianizing nonequilibrium dynamics of artificial spin ice and other spin systems

    NASA Astrophysics Data System (ADS)

    Lammert, Paul E.; Crespi, Vincent H.; Nisoli, Cristiano

    2012-04-01

    Beyond effective temperature for nonequilibrium spin systems is the concept of an effective potential, an ‘as if’ potential with no regard for real energies. But if the former is ad hoc, the latter would surely seem more so. We take up the task of tying a flow of effective interaction in coupling space to specified dynamics, and illustrate what can be done with pencil-and-paper approximations as well as Monte-Carlo integration of the flow equations. This Gibbsianization program is applied to a model of a zero-temperature quench from a completely disordered state as well as a model of artificial spin lattice rotational demagnetization in the disorder-dominated regime. Lessons are drawn regarding the most fruitful effective potentials to use in modelling laboratory systems.

  6. Planar spin-transfer device with dynamical polarizer and analizer

    NASA Astrophysics Data System (ADS)

    Bazaliy, Yaroslaw; Kravchenko, Anton

    2011-03-01

    The behavior of the planar spin-transfer devices with monodomain magnetic layers can be described by the macrospin Landau-Lifshitz-Gilbert (LLG) equation with spin-transfer terms. The LLG description of a device with two layers is simplified after applying the overdamped, large easy-plane anisotropy approximation. A decrease of the magnetic layer thickness asymmetry creates a transition from the conventional polarizer-analizer (``fixed layer -- free layer'') operation regime to the regime of the nearly identical magnets. Here electric current leads to a ``Slonczewski windmill'' dynamic state, rather than producing the magnetic switching. The ``windmill'' precession state of a device with two free layers was investigated by numerical solution of the LLG equation.

  7. Physical limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics in remote-doped structures 

    E-print Network

    Sherman, EY; Sinova, Jairo.

    2005-01-01

    limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics in remote-doped structures E. Ya. Sherman1 and Jairo Sinova2 1Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, Canada M5S 1A7 2...? is the in-plane momentum. The controlled precession of injected spin-polarized carriers around this effective Zeeman field produced by the Rashba coupling in momentum space is the basis for the seminal proposal of Datta and Das of a ballistic spin...

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

    SciTech Connect

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

    2009-10-15

    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.

  9. Dynamics and Control of a Quasi-1D Spin System

    E-print Network

    Paola Cappellaro; Chandrasekhar Ramanathan; David G. Cory

    2007-06-04

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

  10. Spin dynamics and relaxation in the classical-spin Kondo-impurity model beyond the Landau–Lifschitz–Gilbert equation

    NASA Astrophysics Data System (ADS)

    Sayad, Mohammad; Potthoff, Michael

    2015-11-01

    The real-time dynamics of a classical spin in an external magnetic field and local exchange coupled to an extended one-dimensional system of non-interacting conduction electrons is studied numerically. Retardation effects in the coupled electron-spin dynamics are shown to be the source for the relaxation of the spin in the magnetic field. Total energy and spin is conserved in the non-adiabatic process. Approaching the new local ground state is therefore accompanied by the emission of dispersive wave packets of excitations carrying energy and spin and propagating through the lattice with Fermi velocity. While the spin dynamics in the regime of strong exchange coupling J is rather complex and governed by an emergent new time scale, the motion of the spin for weak J is regular and qualitatively well described by the Landau–Lifschitz–Gilbert (LLG) equation. Quantitatively, however, the full quantum–classical hybrid dynamics differs from the LLG approach. This is understood as a breakdown of weak-coupling perturbation theory in J in the course of time. Furthermore, it is shown that the concept of the Gilbert damping parameter is ill-defined for the case of a one-dimensional system.

  11. Skyrmion dynamics in chiral ferromagnets under spin-transfer torque

    NASA Astrophysics Data System (ADS)

    Komineas, Stavros; Papanicolaou, Nikos

    2015-11-01

    We study the dynamics of skyrmions under spin-transfer torque in Dzyaloshinskii-Moriya materials with easy-axis anisotropy. In particular, we study the motion of a topological skyrmion with skyrmion number Q =1 and a nontopological skyrmionium with Q =0 using their linear momentum, virial relations, and numerical simulations. The nontopological Q =0 skyrmionium is accelerated in the direction of the current flow and it either reaches a steady state with constant velocity, or it is elongated to infinity. The steady-state velocity is given by a balance between current and dissipation and has an upper limit. In contrast, the topological Q =1 skyrmion converges to a steady state with constant velocity at an angle to the current flow. When the spin current stops the Q =1 skyrmion is spontaneously pinned, whereas the Q =0 skyrmionium continues propagation. Exact solutions for the propagating skyrmionium are identified as solutions of equations given numerically in a previous work. Further exact results for propagating skyrmions are given in the case of the pure exchange model. The traveling solutions provide arguments that a spin-polarized current will cause rigid motion of a skyrmion or a skyrmionium.

  12. Non-Equilibrium Spin Dynamics in the Subpicosecond Regime

    NASA Astrophysics Data System (ADS)

    Rebei, Adnan

    2007-03-01

    Femto-second laser pulses are becoming an important tool that allows us to explore non-equilibrium spin dynamics at short time (high frequency) scales [1]. It has therefore become apparent [2] that more rigorous treatments are needed to correctly address spin relaxation at these energies. I will show how functional-methods of calculations of correlation energies in electron gas [3] can be successfully adapted to the problem of relaxation in magnetic systems [4]. The study of short time response entails a careful treatment of initial conditions. Our formalism naturally takes care of this and avoids the assumption that the system has been in equilibrium in the infinite past, an assumption common in Boltzmann-type treatments. As an example, we discuss possible non-equilibrium effects due to ultrasonic attenuation on spin relaxation when the magnon sub-system is initially near the Curie point. [1] A. V. Kimmel et al, Nature 435, 655 (2005); L. Guidoni et al., Phys. Rev. Lett. 89, 017401 (2002). [2] A. Rebei and J. Hohlfeld, Phys. Rev. 97, 117601 (2006); A. Rebei and M. Simionato, Phys. Rev. B 71, 174415 (2005). [3] A. Rebei and W. N. G. Hitchon, Int. J. Mod. Phys. B 17, 973 (2003). [4] A. Rebei, W.N.G. Hitchon, and G. J. Parker, Phys. Rev. B 72, 064408 (2005).

  13. Detection of spin torque magnetization dynamics through low frequency noise

    NASA Astrophysics Data System (ADS)

    Cascales, Juan Pedro; Herranz, David; Ebels, Ursula; Katine, Jordan A.; Aliev, Farkhad G.

    2015-08-01

    We present a comparative study of high frequency dynamics and low frequency noise in elliptical magnetic tunnel junctions with lateral dimensions under 100 nm presenting current-switching phenomena. The analysis of the high frequency oscillation modes with respect to the current reveals the onset of a steady-state precession regime for negative bias currents above J = 10 7 A / cm 2 , when the magnetic field is applied along the easy axis of magnetization. By the study of low frequency noise for the same samples, we demonstrate the direct link between changes in the oscillation modes with the applied current and the normalised low frequency (1/f) noise as a function of the bias current. These findings prove that low frequency noise studies could be a simple and powerful technique to investigate spin-torque based magnetization dynamics.

  14. Spin glass model for dynamics of cell reprogramming

    NASA Astrophysics Data System (ADS)

    Pusuluri, Sai Teja; Lang, Alex H.; Mehta, Pankaj; Castillo, Horacio E.

    2015-03-01

    Recent experiments show that differentiated cells can be reprogrammed to become pluripotent stem cells. The possible cell fates can be modeled as attractors in a dynamical system, the ``epigenetic landscape.'' Both cellular differentiation and reprogramming can be described in the landscape picture as motion from one attractor to another attractor. We perform Monte Carlo simulations in a simple model of the landscape. This model is based on spin glass theory and it can be used to construct a simulated epigenetic landscape starting from the experimental genomic data. We re-analyse data from several cell reprogramming experiments and compare with our simulation results. We find that the model can reproduce some of the main features of the dynamics of cell reprogramming.

  15. Quenching of dynamic nuclear polarization by spin–orbit coupling in GaAs quantum dots

    PubMed Central

    Nichol, John M.; Harvey, Shannon P.; Shulman, Michael D.; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I.; Halperin, Bertrand I.; Yacoby, Amir

    2015-01-01

    The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin–orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron–nuclear system, despite weak spin–orbit coupling in GaAs. Using Landau–Zener sweeps to measure static and dynamic properties of the electron spin–flip probability, we observe that the size of the spin–orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin–orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin–orbit coupling in central-spin systems. PMID:26184854

  16. Interplay of spin and motional dynamics in ultracold atoms and molecules

    NASA Astrophysics Data System (ADS)

    Hazzard, Kaden

    2015-05-01

    Several recent ultracold experiments have realized many-body ``spin models'' - systems where interacting spins are frozen in space. One example I will discuss is polar molecules in an optical lattice. By comparing the JILA group's measurements of far-from-equilibrium molecule dynamics with theoretical predictions, we were able to characterize the spin Hamiltonian and benchmark a new numerical algorithm. Even richer possibilities exist beyond spin models, where both spin and motional degrees of freedom evolve dynamically. Such interplay of spin and motion underlies exotic phenomena such as high-temperature superconductivity. I will describe how the unique properties of emerging ultracold systems - nonreactive ultracold molecules, Rydberg atoms, and alkaline earth atoms - make possible the independent control of the spins, their motion, and the spin-motion coupling.

  17. Lattice dynamics in spin-crossover nanoparticles through nuclear inelastic scattering

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  18. Engineering nuclear spin dynamics with optically pumped nitrogen-vacancy center

    E-print Network

    Ping Wang; Jiangfeng Du; Wen Yang

    2015-03-01

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

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

    E-print Network

    Johannes Schachenmayer; Alexander Pikovski; Ana Maria Rey

    2015-02-25

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  1. Electrical Noise Study of Spin Glass Dynamics in Mesoscopic Copper Manganese

    NASA Astrophysics Data System (ADS)

    Israeloff, Nathan Eli

    1991-08-01

    The electrical resistance of the archetypal spin glass _{rm Cu}Mn is surprisingly sensitive to small changes in the spin configuration. This enhanced sensitivity results from long-range electron quantum interference at low temperatures. Due to this effect, substantial resistance noise is produced by spontaneous spin fluctuations below the spin-glass freezing transition. Described here are the results of noise experiments on extremely small 'mesoscopic' samples of _ {rm Cu}Mn. These samples are so small that only a handful of spin fluctuation events are observed during a measurement. Thus we have probed, for the first time, the glassy dynamics with sufficient microscopic detail to uncover the main features of the dynamical pattern. The results are incompatible with the simple 'droplet' picture of spin glasses which is currently in vogue. Noise statistics reveal instead very cooperative dynamics, closely resembling hierarchical dynamics models.

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

    NASA Technical Reports Server (NTRS)

    Bowman, James S.

    1965-01-01

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

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

    E-print Network

    Duong, Timothy Q.

    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

  4. Solid effect in magic angle spinning dynamic nuclear polarization

    PubMed Central

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

    2012-01-01

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

  5. Imaging intracellular protein dynamics by spinning disk confocal microscopy

    PubMed Central

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

    2012-01-01

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

  6. Manipulating magnetic anisotropy and ultrafast spin dynamics of magnetic nanostructures

    NASA Astrophysics Data System (ADS)

    Cheng, Zhao-Hua; He, Wei; Zhang, Xiang-Qun; Sun, Da-Li; Du, Hai-Feng; Wu, Qiong; Ye, Jun; Fang, Ya-Peng; Liu, Hao-Liang

    2015-07-01

    We present our extensive research into magnetic anisotropy. We tuned the terrace width of Si(111) substrate by a novel method: varying the direction of heating current and consequently manipulating the magnetic anisotropy of magnetic structures on the stepped substrate by decorating its atomic steps. Laser-induced ultrafast demagnetization of a CoFeB/MgO/CoFeB magnetic tunneling junction was explored by the time-resolved magneto-optical Kerr effect (TR-MOKE) for both the parallel state (P state) and the antiparallel state (AP state) of the magnetizations between two magnetic layers. It was observed that the demagnetization time is shorter and the magnitude of demagnetization is larger in the AP state than those in the P state. These behaviors are attributed to the ultrafast spin transfer between two CoFeB layers via the tunneling of hot electrons through the MgO barrier. Our observation indicates that ultrafast demagnetization can be engineered by the hot electron tunneling current. This opens the door to manipulate the ultrafast spin current in magnetic tunneling junctions. Furthermore, an all-optical TR-MOKE technique provides the flexibility for exploring the nonlinear magnetization dynamics in ferromagnetic materials, especially with metallic materials. Project supported by the National Basic Research Program of China (Grant Nos. 2015CB921403, 2011CB921801, and 2012CB933101) and the National Natural Science Foundation of China (Grant Nos. 51427801, 11374350, 51201179, and 11274361).

  7. Dynamics of spin stabilized spacecraft during deployment of telescoping appendages

    NASA Technical Reports Server (NTRS)

    Sellappan, R.; Bainum, P. M.

    1976-01-01

    The dynamics of a spin stabilized spacecraft with telescoping appendages are treated both analytically and numerically. Two types of telescoping appendages are considered: (a) where an end mass is mounted at the end of an (assumed) massless boom; and (b) where the appendage is assumed to consist of a uniformly distributed homogeneous mass throughout its length. For the telescoping system Eulerian equations of motion are developed. During all deployment sequences it is assumed that the transverse component of angular momentum is much smaller than the component along the major spin axis. Closed form analytical solutions for the time response of the transverse components of angular velocities are obtained when the spacecraft hub has a nearly spherical mass distribution. For the more general case, a series solution is obtained and this solution is limited by its radius of convergence. The comparison of the different approximate analytical methods with numerical integration results are studied and it is observed that the oscillatory nature of the responses of the transverse angular velocity components reduces rapidly with faster extension rates.

  8. Assessing intracranial vascular compliance using dynamic arterial spin labeling.

    PubMed

    Yan, Lirong; Liu, Collin Y; Smith, Robert X; Jog, Mayank; Langham, Michael; Krasileva, Kate; Chen, Yufen; Ringman, John M; Wang, Danny J J

    2016-01-01

    Vascular compliance (VC) is an important marker for a number of cardiovascular diseases and dementia, which is typically assessed in the central and peripheral arteries indirectly by quantifying pulse wave velocity (PWV), and/or pulse pressure waveform. To date, very few methods are available for the quantification of intracranial VC. In the present study, a novel MRI technique for in-vivo assessment of intracranial VC was introduced, where dynamic arterial spin labeling (ASL) scans were synchronized with the systolic and diastolic phases of the cardiac cycle. VC is defined as the ratio of change in arterial cerebral blood volume (?CBV) and change in arterial pressure (?BP). Intracranial VC was assessed in different vascular components using the proposed dynamic ASL method. Our results show that VC mainly occurs in large arteries, and gradually decreases in small arteries and arterioles. The comparison of intracranial VC between young and elderly subjects shows that aging is accompanied by a reduction of intracranial VC, in good agreement with the literature. Furthermore, a positive association between intracranial VC and cerebral perfusion measured using pseudo-continuous ASL with 3D GRASE MRI was observed independent of aging effects, suggesting loss of VC is associated with a decline in perfusion. Finally, a significant positive correlation between intracranial and central (aortic arch) VC was observed using an ungated phase-contrast 1D projection PWV technique. The proposed dynamic ASL method offers a promising approach for assessing intracranial VC in a range of cardiovascular diseases and dementia. PMID:26364865

  9. Experiences in Evaluating Outcomes in Tool-Based, Competence Building Education in Dynamical Systems Using Symbolic Computer Algebra

    ERIC Educational Resources Information Center

    Perram, John W.; Andersen, Morten; Ellekilde, Lars-Peter; Hjorth, Poul G.

    2004-01-01

    This paper discusses experience with alternative assessment strategies for an introductory course in dynamical systems, where the use of computer algebra and calculus is fully integrated into the learning process, so that the standard written examination would not be appropriate. Instead, students' competence was assessed by grading three large…

  10. Generation of spin-polarized currents via cross-relaxation with dynamically pumped paramagnetic impurities

    SciTech Connect

    Meriles, Carlos A.; Doherty, Marcus W.

    2014-07-14

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

  11. Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates in a Random Potential.

    PubMed

    Mardonov, Sh; Modugno, M; Sherman, E Ya

    2015-10-30

    Disorder plays a crucial role in spin dynamics in solids and condensed matter systems. We demonstrate that for a spin-orbit coupled Bose-Einstein condensate in a random potential two mechanisms of spin evolution that can be characterized as "precessional" and "anomalous" are at work simultaneously. The precessional mechanism, typical for solids, is due to the condensate displacement. The unconventional anomalous mechanism is due to the spin-dependent velocity producing the distribution of the condensate spin polarization. The condensate expansion is accompanied by a random displacement and fragmentation, where it becomes sparse, as clearly revealed in the spin dynamics. Thus, different stages of the evolution can be characterized by looking at the condensate spin. PMID:26565441

  12. Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates in a Random Potential

    NASA Astrophysics Data System (ADS)

    Mardonov, Sh.; Modugno, M.; Sherman, E. Ya.

    2015-10-01

    Disorder plays a crucial role in spin dynamics in solids and condensed matter systems. We demonstrate that for a spin-orbit coupled Bose-Einstein condensate in a random potential two mechanisms of spin evolution that can be characterized as "precessional" and "anomalous" are at work simultaneously. The precessional mechanism, typical for solids, is due to the condensate displacement. The unconventional anomalous mechanism is due to the spin-dependent velocity producing the distribution of the condensate spin polarization. The condensate expansion is accompanied by a random displacement and fragmentation, where it becomes sparse, as clearly revealed in the spin dynamics. Thus, different stages of the evolution can be characterized by looking at the condensate spin.

  13. Spin dynamics in high- T c copper oxides

    NASA Astrophysics Data System (ADS)

    Lavagna, M.; Stemmann, G.; Pépin, C.

    1995-05-01

    We analyze the spectrum of magnetic excitations as observed by neutron diffraction and NMR experiments in Y Ba2Cu3O6+x, in the frame of the single-band t-t'-J model in which the next-nearest-neighbour hopping term has been introduced in order to fit the shape of the Fermi surface revealed in photoemission. Within the slave-boson approach, we have as well examined the d-wave superconducting state, and the singlet-RVB phase appropriate to describe the normal state of heavily-doped systems. Our calculations show a smooth evolution of the spectrum from one phase to the other, with the existence of a spin-gap in the frequency-dependence of ??(?Q,w)-The value of the threshold of excitations EG is found to increase with doping, while the characteristic temperature-scale Tm at which the spin-gap opens, exhibits a regular decrease, reaching Tc only in overdoped regime. This very atypical combined variation of EG and Tm with doping results of strong-correlation effects in presence o realistic band structure. We point out the presence of a resonance in the w-dependence of ??(?Q,w) in good agreement with the neutron diffraction results obtained at x = 0.92 and x = 1.0. This resonance is analyzed as a dynamical Kohn anomaly of the second kind in the Cooper channel. Finally, we examine the ?q-dependence of the dynamical susceptibility allowing to study the magnetic correlation length ? as a function of doping, frequency and temperature.

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

    PubMed

    Field, Timothy R

    2014-11-01

    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

  15. Spin dynamics in relativistic light-matter interaction

    E-print Network

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

    2015-04-14

    Various spin effects are expected to become observable in light-matter interaction at relativistic intensities. Relativistic quantum mechanics equipped with a suitable relativistic spin operator forms the theoretical foundation for describing these effects. Various proposals for relativistic spin operators have been offered by different authors, which are presented in a unified way. As a result of the operators' mathematical properties only the Foldy-Wouthuysen operator and the Pryce operator qualify as possible proper relativistic spin operators. The ground states of highly charged hydrogen-like ions can be utilized to identify a legitimate relativistic spin operator experimentally. Subsequently, the Foldy-Wothuysen spin operator is employed to study electron-spin precession in high-intensity standing light waves with elliptical polarization. For a correct theoretical description of the predicted electron-spin precession relativistic effects due to the spin angular momentum of the electromagnetic wave has to be taken into account even in the limit of low intensities.

  16. Spinning Black Hole Pairs: Dynamics and Gravitational Waves

    NASA Astrophysics Data System (ADS)

    Grossman, Rebecca

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

  17. Enhanced solid-state multi-spin metrology using dynamical decoupling

    E-print Network

    L. M. Pham; N. Bar-Gill; C. Belthangady; D. Le Sage; P. Cappellaro; M. D. Lukin; A. Yacoby; R. L. Walsworth

    2012-01-30

    We use multi-pulse dynamical decoupling to increase the coherence lifetime (T2) of large numbers of nitrogen-vacancy (NV) electronic spins in room temperature diamond, thus enabling scalable applications of multi-spin quantum information processing and metrology. We realize an order-of-magnitude extension of the NV multi-spin T2 for diamond samples with widely differing spin environments. For samples with nitrogen impurity concentration 2 ms, comparable to the longest coherence time reported for single NV centers, and demonstrate a ten-fold enhancement in NV multi-spin sensing of AC magnetic fields.

  18. Resolving remote nuclear spins in a noisy bath by dynamical decoupling design

    NASA Astrophysics Data System (ADS)

    Ma, Wenchao; Shi, Fazhan; Xu, Kebiao; Wang, Pengfei; Xu, Xiangkun; Rong, Xing; Ju, Chenyong; Duan, Chang-Kui; Zhao, Nan; Du, Jiangfeng

    2015-09-01

    We experimentally resolve several weakly coupled nuclear spins in diamond using a series of dynamical decoupling controls. Some nuclear spin signals, hidden by decoherence under ordinary dynamical decoupling controls, are shifted forward in time domain to the coherence time range and thus rescued from the fate of being submerged by the noisy spin bath. In this way, more and remote single nuclear spins are resolved. Additionally, the field of detection can be continuously tuned on subnanoscale. This method extends the capacity of nanoscale magnetometry and may be applicable in other systems for high-resolution noise spectroscopy.

  19. Resolving Remoter Nuclear Spins in a Noisy Bath by Dynamical Decoupling Design

    E-print Network

    Wenchao Ma; Fazhan Shi; Kebiao Xu; Pengfei Wang; Xiangkun Xu; Xing Rong; Chenyong Ju; Chang-Kui Duan; Nan Zhao; Jiangfeng Du

    2015-06-16

    We experimentally resolve several weakly coupled nuclear spins in diamond using a series of novelly designed dynamical decoupling controls. Some nuclear spin signals, hidden by decoherence under ordinary dynamical decoupling controls, are shifted forward in time domain to the coherence time range and thus rescued from the fate of being submerged by the noisy spin bath. In this way, more and remoter single nuclear spins are resolved. Additionally, the field of detection can be continuously tuned on sub-nanoscale. This method extends the capacity of nanoscale magnetometry and may be applicable in other systems for high-resolution noise spectroscopy.

  20. Continuous weak measurement and nonlinear dynamics in a cold spin ensemble.

    PubMed

    Smith, Greg A; Chaudhury, Souma; Silberfarb, Andrew; Deutsch, Ivan H; Jessen, Poul S

    2004-10-15

    A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a nonperturbing measurement on the much longer time scale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation. PMID:15524989

  1. Low-energy-state dynamics of entanglement for spin systems

    SciTech Connect

    Jafari, R.

    2010-11-15

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

  2. Free vibration and dynamic response analysis of spinning structures

    NASA Technical Reports Server (NTRS)

    1986-01-01

    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.

  3. Magnetization dynamics in an artificial spin ice on kagome

    NASA Astrophysics Data System (ADS)

    Petrova, Olga; Mellado, Paula; Tchernyshyov, Oleg

    2010-03-01

    We study magnetization dynamics in an artificial spin ice on kagome realized as a honeycomb network of connected ferromagnetic nanowires studied recently by several experimental groups [1]. The sites of the honeycomb network carry magnetic charge, defined as the source of the magnetic field H, of strength ±1 in suitably chosen units. Magnetization reversal in individual wires under the action of an applied magnetic field is mediated by the emission of a domain wall carrying magnetic charge ±2 at one of the wire's ends, its propagation along the wire and its absorption at the other end. We include the effects of quenched disorder, arising from lattice imperfections, domain wall's inertia, observed recently in permalloy nanowires, and magnetostatic interactions between magnetic charges [2]. The inertia and magnetostatic repulsion between like charges are responsible for avalanches in magnetization reversal observed experimentally [1]. That and an inherently dissipative character of the magnetization dynamics suggest interesting parallels with granular materials [3]. [1] Y. Qi, T. Brintlinger, and J. Cumings, Phys. Rev. B 77, 094418 (2008). [2] E. Saitoh et al., Nature 432, 203 (2004). [3] X. Ke et al., Phys. Rev. Lett. 101, 037205 (2008).

  4. RNA-based regulation: dynamics and response to perturbations of competing RNAs.

    PubMed

    Figliuzzi, Matteo; De Martino, Andrea; Marinari, Enzo

    2014-08-19

    The observation that, through a titration mechanism, microRNAs (miRNAs) can act as mediators of effective interactions among their common targets (competing endogenous RNAs or ceRNAs) has brought forward the idea (i.e., the ceRNA hypothesis) that RNAs can regulate each other in extended cross-talk networks. Such an ability might play a major role in posttranscriptional regulation to shape a cell's protein repertoire. Recent work focusing on the emergent properties of the cross-talk networks has emphasized the high flexibility and selectivity that may be achieved at stationarity. On the other hand, dynamical aspects, possibly crucial on the relevant timescales, are far less clear. We have carried out a dynamical study of the ceRNA hypothesis on a model of posttranscriptional regulation. Sensitivity analysis shows that ceRNA cross-talk is dynamically extended, i.e., it may take place on timescales shorter than those required to achieve stationarity even in cases where no cross-talk occurs in the steady state, and is possibly amplified. In addition, in the case of large, transfection-like perturbations, the system may develop a strongly nonlinear, threshold response. Finally, we show that the ceRNA effect provides a very efficient way for a cell to achieve fast positive shifts in the level of a ceRNA when necessary. These results indicate that competition for miRNAs may indeed provide an elementary mechanism to achieve system-level regulatory effects on the transcriptome over physiologically relevant timescales. PMID:25140437

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

    SciTech Connect

    Wesenberg, Janus H.; Kurucz, Zoltan; Moelmer, Klaus

    2011-02-15

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

  6. Spin relaxation dynamics in highly uniform InAs quantum dots

    NASA Astrophysics Data System (ADS)

    Tackeuchi, A.; Ohtsubo, R.; Yamaguchi, K.; Murayama, M.; Kitamura, T.; Kuroda, T.; Takagahara, T.

    2004-05-01

    We have investigated carrier spin dynamics in highly uniform self-assembled InAs quantum dots. The highly uniform quantum dots allowed us to observe the spin dynamics in the ground state and that in the second state separately, without the disturbance of inhomogeneous broadening. The spin relaxation times in the ground state and the second state were measured to be 1.0 and 0.6 ns, respectively. Our measurements reveal the absence of the carrier density dependence of the spin relaxation time. The measured spin relaxation time decreases rapidly from 1.1 ns at 10 K to 200 ps at 130 K. This large change in the spin relaxation time is well explained in terms of the mechanism of acoustic phonon emission.

  7. Spin Relaxation Dynamics in Highly Uniform InAs Quantum Dots

    NASA Astrophysics Data System (ADS)

    Tackeuchi, A.; Suzuki, Y.; Murayama, M.; Kitamura, T.; Kuroda, T.; Takagahara, T.; Yamaguchi, K.

    2005-06-01

    We have investigated carrier spin dynamics in highly uniform self-assembled InAs quantum dots. The highly uniform quantum dots allowed us to observe the spin dynamics in the ground state and that in the first excited state separately, without the disturbance of inhomogeneous broadening. The spin relaxation times in the ground state and the first excited state were measured to be 1.0 ns and 0.6 ns, respectively. Our measurements reveal the absence of the carrier density dependence of the spin relaxation time. The measured spin relaxation time decreases rapidly from 1.1 ns at 10 K to 200 ps at 130 K. This large change in the spin relaxation time is well explained in terms of the mechanism of acoustic phonon emission.

  8. Control of spin dynamics in a two-dimensional electron gas by electromagnetic dressing

    NASA Astrophysics Data System (ADS)

    Pervishko, A. A.; Kibis, O. V.; Morina, S.; Shelykh, I. A.

    2015-11-01

    We solved the Schrödinger problem for a two-dimensional electron gas (2DEG) with the Rashba spin-orbit interaction in the presence of a strong high-frequency electromagnetic field (dressing field). The found eigenfunctions and eigenenergies of the problem are used to describe the spin dynamics of the dressed 2DEG within the formalism of the density matrix response function. Solving the equations of spin dynamics, we show that the dressing field can switch the spin relaxation in the 2DEG between the cases corresponding to the known Elliott-Yafet and D'yakonov-Perel' regimes. As a result, the spin properties of the 2DEG can be tuned by a high-frequency electromagnetic field. The present effect opens an unexplored way for controlling the spin with light and, therefore, forms the physical prerequisites for creating light-tuned spintronics devices.

  9. Non-Markovian dynamics in a spin star system: Exact solution and approximation techniques

    NASA Astrophysics Data System (ADS)

    Breuer, Heinz-Peter; Burgarth, Daniel; Petruccione, Francesco

    2004-07-01

    The reduced dynamics of a central spin coupled to a bath of N spin- (1)/(2) particles arranged in a spin star configuration is investigated. The exact time evolution of the reduced density operator is derived, and an analytical solution is obtained in the limit N?? of an infinite number of bath spins, where the model shows complete relaxation and partial decoherence. It is demonstrated that the dynamics of the central spin cannot be treated within the Born-Markov approximation. The Nakajima-Zwanzig and the time-convolutionless projection operator technique are applied to the spin star system. The performance of the corresponding perturbation expansions of the non-Markovian equations of motion is examined through a comparison with the exact solution.

  10. Quasi-omnidirectional electrical spectrometer for studying spin dynamics in magnetic tunnel junctions.

    PubMed

    Yamaguchi, Akinobu; Fukushima, Akio; Kubota, Hitoshi; Yuasa, Shinji

    2012-02-01

    We report an omnidirectional electrical spectroscopy setup for studying the spin dynamics in a nanoscale magnet. It has a measureable solid angle range comprising about 50% of the total range and allows the magnetoresistance and spin-torque diode signal to be measured simultaneously at any angle to the magnetization. This setup can provide detailed information about the spin-wave resonance modes excited in a nanoscale magnet. PMID:22380116

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

    SciTech Connect

    Prabhakar, Sanjay; Melnik, Roderick; Gregorio Millan Institute, Universidad Carlos III de Madrid, 28911 Leganes ; Bonilla, Luis L.; Raynolds, James E.

    2013-12-02

    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.

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

    NASA Astrophysics Data System (ADS)

    Sergi, Alessandro; Sinayskiy, Ilya; Petruccione, Francesco

    2009-07-01

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

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

    E-print Network

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

    2010-01-01

    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.

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

    E-print Network

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

    2010-10-06

    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.

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

    PubMed

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

    2013-09-01

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

  16. Combined molecular and spin dynamics study of collective excitations in BCC iron

    NASA Astrophysics Data System (ADS)

    Perera, Dilina; Landau, David P.; Nicholson, Don; Stocks, G. Malcolm

    2014-03-01

    Spin dynamics simulations of classical spin systems have revealed a substantial amount of information regarding the collective excitations in magnetic materials. However, much of the previous work has been restricted to lattice-based spin models that completely disregard the effect of lattice vibrations. Combining an empirical many body potential with a spin Hamiltonian parameterized by first principles calculations, we present a compressible magnetic model for BCC iron, which treats the dynamics of translational degrees of freedom on an equal footing with the magnetic (spin) degrees of freedom. This model provides us with a unified framework for performing combined molecular and spin dynamics simulations and make simultaneous quantitative measurements of the spin wave and vibrational spectrum. Results from our simulations reveal that the presence of lattice vibrations leads to softening and damping of spin waves, as well as evidence for a novel form of longitudinal spin wave excitation coupled with the longitudinal phonon mode of the same frequency. Furthermore, we will also discuss the influence of lattice vibrations at different temperatures and the implications of using different atomistic potentials. Research sponsored by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, ``Center for Defect Physics,'' an Energy Frontier Research Center. Done...processed 13325 records...10:54:51

  17. Quantum control of orbital and spin dynamics in diamond using ultrafast optical pulses

    NASA Astrophysics Data System (ADS)

    Heremans, F. Joseph

    2015-03-01

    Optically addressable spin defects in solid-state materials have shown great potential for applications ranging from metrology to quantum information processing. Many of these experiments require a detailed understanding of the full Hamiltonian dynamics in order to develop precise quantum control. Here we use picosecond resonant optical pulses to investigate the coherent orbital and spin dynamics of the nitrogen-vacancy (NV) center in diamond, over timescales spanning six orders of magnitude. We implement an ultrafast optical pump-probe technique to study the NV center's orbital-doublet, spin-triplet excited state at cryogenic temperatures (T < 20 K), where the excited state becomes stable and optically coherent with the ground state. This technique, coupled with optical polarization selection rules, allows us to probe the coherent orbital dynamics of the NV center's excited state. These experiments reveal dynamics on femtosecond to nanosecond timescales due to the interplay between the ground and excited state orbital levels. This all-optical technique also provides a method to dynamically control the spin state of the NV center by harnessing the excited state structure. Through studying the spin dynamics of the NV center with coherent pulses of light, we are able to rotate the spin state on sub-nanosecond timescales. Furthermore, by tuning the excited-state spin Hamiltonian with an external magnetic field, we demonstrate arbitrary-axis spin rotations through controlled unitary evolution of the spin state. Extending this to the full excited-state manifold, we develop a time-domain quantum tomography technique to precisely map the NV center's excited state Hamiltonian. These techniques generalize to other systems and can be a powerful tool in characterizing and controlling qubits in other optically addressable spin systems. This work is supported by the AFOSR and NSF.

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

    E-print Network

    Pei Wang

    2012-07-12

    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.

  19. LIMITING DYNAMICS FOR SPHERICAL MODELS OF SPIN GLASSES AT HIGH TEMPERATURE

    E-print Network

    Mazza Christian

    are the same). When m = 2, one gets the so-called Sherrington-Kirckpatrick spherical spin glass, which has beenLIMITING DYNAMICS FOR SPHERICAL MODELS OF SPIN GLASSES AT HIGH TEMPERATURE AMIR DEMBO, ALICE whose solution is the thermody- namical limit of the empirical correlation and response functions

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

    E-print Network

    Thomas, David D.

    of the smooth muscle (chicken gizzard) myosin regulatory light chain and performing electron paramagneticMolecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle resonance experiments on these spin-labeled regulatory light chains in functional scallop muscle fibers. We

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

    NASA Astrophysics Data System (ADS)

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

    2011-02-01

    We introduce a software library incorporating our recent research into efficient simulation algorithms for large spin systems. Liouville space simulations (including symmetry, relaxation and chemical kinetics) of most liquid-state NMR experiments on 40+ spin systems can now be performed without effort on a desktop workstation. Much progress has also been made with improving the efficiency of ESR, solid state NMR and Spin Chemistry simulations. Spinach is available for download at http://spindynamics.org.

  2. The multiple quantum NMR dynamics in systems of equivalent spins with a dipolar ordered initial state

    SciTech Connect

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

    2011-09-15

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

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

    E-print Network

    Nanni, Emilio A.

    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[subscript 1S]) profile was ...

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

    E-print Network

    Barnes, Alexander

    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 ...

  5. Charge and Spin Dynamics of the Hubbard Chains

    NASA Technical Reports Server (NTRS)

    Park, Youngho; Liang, Shoudan

    1999-01-01

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

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

    SciTech Connect

    Häussler, Wolfgang; Kredler, Lukas

    2014-05-15

    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.

  7. 1H-NMR study of the spin dynamics of fine superparamagnetic nanoparticles

    SciTech Connect

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

    2012-05-25

    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.

  8. Spin dynamics in gravitational fields of rotating bodies and the equivalence principle

    SciTech Connect

    Obukhov, Yuri N.; Silenko, Alexander J.; Teryaev, Oleg V.

    2009-09-15

    We discuss the quantum and classical dynamics of a particle with spin in the gravitational field of a rotating source. A relativistic equation describing the motion of classical spin in curved spacetimes is obtained. We demonstrate that the precession of the classical spin is in a perfect agreement with the motion of the quantum spin derived from the Foldy-Wouthuysen approach for the Dirac particle in a curved spacetime. We show that the precession effect depends crucially on the choice of a tetrad. The results obtained are compared to the earlier computations for different tetrad gauges.

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

    E-print Network

    Thibault Damour; Piotr Jaranowski; Gerhard Schäfer

    2008-03-06

    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.

  10. High temperature spin dynamics in linear magnetic chains, molecular rings, and segments by nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Adelnia, Fatemeh; Mariani, Manuel; Ammannato, Luca; Caneschi, Andrea; Rovai, Donella; Winpenny, Richard; Timco, Grigore; Corti, Maurizio; Lascialfari, Alessandro; Borsa, Ferdinando

    2015-05-01

    We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac)3NITEt and the magnetically frustrated Gd(hfac)3NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr8 closed ring and in Cr7Cd and Cr8Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.

  11. Quantum nondemolition measurement of large-spin ensembles by dynamical decoupling.

    PubMed

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

    2010-08-27

    Quantum nondemolition (QND) measurement of collective variables by off-resonant optical probing has the ability to create entanglement and squeezing in atomic ensembles. Until now, this technique has been applied to real or effective spin one-half systems. We show theoretically that the buildup of Raman coherence prevents the naive application of this technique to larger spin atoms, but that dynamical decoupling can be used to recover the ideal QND behavior. We experimentally demonstrate dynamical decoupling by using a two-polarization probing technique. The decoupled QND measurement achieves a sensitivity 5.7(6) dB better than the spin projection noise. PMID:20868158

  12. SU(2s+1) symmetry and nonlinear dynamics of high spin magnets

    SciTech Connect

    Kovalevsky, M.Y. Glushchenko, A.V.

    2014-10-15

    The article is devoted to the description of dynamics of magnets with arbitrary spin on the basis of the Hamiltonian formalism. The relationship of quantum states and magnetic degrees of freedom has been considered. Subalgebras of Poisson bracket of magnetic values for spin s=1/2; 1; 3/2 have been established. We have obtained non-linear dynamic equations for the normal and degenerate non-equilibrium states of high-spin magnets with the SO(3), SU(4), SU(2)×SU(2), SU(3), SO(4), SO(5) symmetries of exchange interaction. The connection between models of magnetic exchange energy and the Casimir invariants has been discussed.

  13. Unified Dynamics of Electrons and Photons via Zitterbewegung and Spin-Orbit Interaction

    E-print Network

    C. C. Leary; Karl H. Smith

    2013-10-08

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

  14. Coherent spin dynamics of electrons and excitons in nanostructures (a review)

    NASA Astrophysics Data System (ADS)

    Glazov, M. M.

    2012-01-01

    The studies of spin phenomena in semiconductor low-dimensional systems have grown into the rapidly developing area of the condensed matter physics: spintronics. The most urgent problems in this area, both fundamental and applied, are the creation of charge carrier spin polarization and its detection, as well as electron spin control by nonmagnetic methods. Here, we present a review of recent achievements in the studies of spin dynamics of electrons, holes, and their complexes in the pump-probe method. The microscopic mechanisms of spin orientation of charge carriers and their complexes by short circularly polarized optical pulses and the formation processes of the spin signals of Faraday and Kerr rotation of the probe pulse polarization plane as well as induced ellipticity are discussed. A special attention is paid to the comparison of theoretical concepts with experimental data obtained on the n-type quantum well and quantum dot array samples.

  15. Brownian motion and quantum dynamics of magnetic monopoles in spin ice

    PubMed Central

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

    2013-01-01

    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

  16. Competing quantum effects in the dynamics of a flexible water model

    E-print Network

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

    2010-11-04

    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.

  17. Localization-delocalization transition in the dynamics of dipolar-coupled nuclear spins

    NASA Astrophysics Data System (ADS)

    Álvarez, Gonzalo A.; Suter, Dieter; Kaiser, Robin

    2015-08-01

    Nonequilibrium dynamics of many-body systems are important in many scientific fields. Here, we report the experimental observation of a phase transition of the quantum coherent dynamics of a three-dimensional many-spin system with dipolar interactions. Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we quench the interaction Hamiltonian to drive the evolution of the system. Depending on the quench strength, we then observe either localized or extended dynamics of the system coherence. We extract the critical exponents for the localized cluster size of correlated spins and diffusion coefficient around the phase transition separating the localized from the delocalized dynamical regime. These results show that NMR techniques are well suited to studying the nonequilibrium dynamics of complex many-body systems.

  18. Strain-induced coherent dynamics of coupled carriers and Mn spins in a quantum dot

    NASA Astrophysics Data System (ADS)

    Lafuente-Sampietro, A.; Boukari, H.; Besombes, L.

    2015-08-01

    We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton (X+). We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical ? systems which can be addressed independently. We show that the spin dynamics of the X+-Mn complex is dominated by the electron-Mn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in the time domain. Quantum beats reflecting the coherent transfer of population between electron-Mn spin states, which are mixed by an anisotropic strain in the plane of the quantum dot, are clearly observed. We finally highlight that this strain-induced coherent coupling is tunable with an external magnetic field.

  19. Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems: Semi-magnetic II-VI Quantum Dots

    E-print Network

    Abolfath, Ramin M; Roostaei, Bahman; Brabec, Thomas; Hawrylak, Pawel

    2013-01-01

    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 the electron and heavy hole spins interacting via exchange interaction with magnetic impurity, via hypeprfine 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 new spin polarized exciton is shown to lead to 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 pres...

  20. Dynamics of extended spinning masses in a gravitational field

    SciTech Connect

    Mashhoon, Bahram; Singh, Dinesh

    2006-12-15

    We develop a first-order approximation method for the influence of spin on the motion of extended spinning test masses in a gravitational field. This approach is illustrated for approximately circular equatorial motion in the exterior Kerr spacetime. In this case, the analytic results for the first-order approximation are compared to the numerical integration of the exact system and the limitations of the first-order results are pointed out. Furthermore, we employ our analytic results to illustrate the gravitomagnetic clock effect for spinning particles.

  1. Dynamic Lattice Supersymmetry in gl(n|m) Spin Chains

    E-print Network

    Meidinger, David

    2013-01-01

    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 gl(n|m) spin chains for which length-changing supersymmetry can be present. Furthermore, we write down the supercharges explicitly for the simplest new models, namely the sl(n|1) spin chains with the (n-1)-fold antisymmetric tensor product of the fundamental representation at each site and check their compatibility with integrability.

  2. Modeling two-spin dynamics in a noisy environment

    SciTech Connect

    Testolin, M. J.; Hollenberg, L. C. L.; Cole, J. H.

    2009-10-15

    We describe how the effect of charge noise on a pair of spins coupled via the exchange interaction can be calculated by modeling charge fluctuations as a random telegraph noise process using probability density functions. We develop analytic expressions for the time-dependent superoperator of a pair of spins as a function of fluctuation amplitude and rate. We show that the theory can be extended to include multiple fluctuators, in particular, spectral distributions of fluctuators. These superoperators can be included in time-dependent analyses of the state of spin systems designed for spintronics or quantum information processing to determine the decohering effects of exchange fluctuations.

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

    SciTech Connect

    Chen, C.-C.

    2010-04-29

    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.

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

    PubMed Central

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

    2015-01-01

    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

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

    PubMed

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

    2015-01-01

    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

  6. Polaron spin filtering in an organic ferromagnetic polymer: a dynamics simulation.

    PubMed

    Wang, Hui; Li, Yuan; Li, Dong-Mei; Cui, Bin; Liu, De-Sheng

    2016-01-01

    We present a model study of the dynamic properties of a polaron in an organic ferromagnetic polymer by focusing on the spin correlation between the polymer backbone and the side radicals. The simulations are performed by using a tight-binding description coupled with a nonadiabatic dynamics method. We find that, in the presence of an external electric field, the polarons with both up and down spins can get trapped near the side radicals of the polymer chain unless the electric field is stronger than a critical field. However, the magnitudes of the critical electric field vary quite differently for the spin-up and spin-down polarons as a function of the number of side radicals in the polymer, leading to the exponential change of the range of the electric field within which the spin-filtering takes place. The range of the electric field increases nearly in a linear manner with the strength of the electron-lattice coupling as a result of the increase of the polaron binding energy. The impact of the strength of the spin correlation between the backbone and the side radicals on the polaron spin filtering is also discussed. These findings are expected to be useful for the design of organic-based spin filters. PMID:26616237

  7. Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics

    SciTech Connect

    Malpuech, Guillaume; Solnyshkov, Dmitry; Shelykh, Ivan

    2009-10-07

    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.

  8. Entanglement dynamics via geometric phases in quantum spin chains

    SciTech Connect

    Castro, C. S.; Sarandy, M. S.

    2011-04-15

    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.

  9. Coherent Spin Dynamics in Molecular Cr8Zn Wheels.

    PubMed

    Ghirri, Alberto; Chiesa, Alessandro; Carretta, Stefano; Troiani, Filippo; van Tol, Johan; Hill, Stephen; Vitorica-Yrezabal, Inigo; Timco, Grigore A; Winpenny, Richard E P; Affronte, Marco

    2015-12-17

    Controlling and understanding transitions between molecular spin states allows selection of the most suitable ones for qubit encoding. Here we present a detailed investigation of single crystals of a polynuclear Cr8Zn molecular wheel using 241 GHz electron paramagnetic resonance (EPR) spectroscopy in high magnetic field. Continuous wave spectra are well reproduced by spin Hamiltonian calculations, which evidence that transitions in correspondence to a well-defined anticrossing involve mixed states with different total spin. We studied, by means of spin echo experiments, the temperature dependence of the dephasing time (T2) down to 1.35 K. These results are reproduced by considering both hyperfine and intermolecular dipolar interactions, evidencing that the dipolar contribution is completely suppressed at the lowest temperature. Overall, these results shed light on the effects of the decoherence mechanisms, whose understanding is crucial to exploit chemically engineered molecular states as a resource for quantum information processing. PMID:26633293

  10. Nuclear magnetometry studies of spin dynamics in quantum Hall systems

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  11. Cascaded spin motive force driven by the dynamics of the skyrmion lattice

    SciTech Connect

    Ohe, Jun-ichiro; Shimada, Yuhki

    2013-12-09

    We numerically investigate the spin motive force (SMF) driven by the dynamics of a Skyrmion lattice. The rotating mode of the Skyrmion core excited by the AC magnetic field induces the large spin-dependent electric field near the core. Due to the collective dynamics of Skyrmion lattice, the measurable voltage is enhanced by the cascade effect of the SMF. The amplitude of the AC voltage is estimated to 30??V in a macroscopic sample, where 100 Skyrmions exist between two probes. We also investigate the SMF due to the dynamics of the helical magnetic state, where the enhancement of the SMF does not occur.

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

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

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

  13. Anomalous magnetic structure and spin dynamics in magnetoelectric LiFePO4

    DOE PAGESBeta

    Toft-Petersen, Rasmus; Reehuis, Manfred; Jensen, Thomas B. S.; Andersen, Niels H.; Li, Jiying; Le, Manh Duc; Laver, Mark; Niedermayer, Christof; Klemke, Bastian; Lefmann, Kim; et al

    2015-07-06

    We report significant details of the magnetic structure and spin dynamics of LiFePO4 obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation of the spins away from the principal b axis, and they determine that the rotation is toward the a axis. In addition, we find a significant spin-canting component along c. Furthermore, the possible causes of these components are discussed, and their significance for the magnetoelectric effect is analyzed. Inelastic neutron scattering along the three principal directions reveals a highly anisotropic hard plane consistent with earlier susceptibility measurements. While using a spin Hamiltonian, we showmore »that the spin dimensionality is intermediate between XY- and Ising-like, with an easy b axis and a hard c axis. As a result, it is shown that both next-nearest neighbor exchange couplings in the bc plane are in competition with the strongest nearest neighbor coupling.« less

  14. Dynamics of photoinduced change of magnetoanisotropy parameter in orthoferrites probed with terahertz excited coherent spin precession

    NASA Astrophysics Data System (ADS)

    Yamaguchi, Keita; Kurihara, Takayuki; Watanabe, Hiroshi; Nakajima, Makoto; Suemoto, Tohru

    2015-08-01

    The effects of femtosecond laser excitation on the anisotropy parameter in orthoferrites ErFe O3 and DyFe O3 were probed through Faraday rotation induced by coherent spin precession, which was triggered by a terahertz pulse. Through the delayed frequency shift of the precession, gradual change in the anisotropic energy of the iron spins is evidenced. This is attributed to the slow energy transfer from the F e3 + 3 d electron system to the rare-earth 4 f electron system, which in turn alters the anisotropy parameter of the F e3 + spins. The result presented here reveals the time dependent spin alignment mechanism in cant-type antiferromagnetic orthoferrites and enables deeper understanding of spin orientation dynamics triggered by electronic excitation.

  15. Dissipative dynamics of entangled finite-spin systems with non-competitive external fields

    E-print Network

    Nakagawa, Koichi

    2015-01-01

    We apply a new method based upon thermofield dynamics (TFD) to study entanglement of finite-spin systems with non-competitive external fields for both equilibrium and non-equilibrium cases. For the equilibrium finite-spin systems, the temperature dependence of the extended density matrices is derived using this method, and the effect of non-competitive external field is elucidated. For the non-equilibrium finite-spin systems, the time dependence of the extended density matrices and the extended entanglement entropies is derived in accordance with von Noumann equation, and the dissipative dynamics of the finite-spin systems is argued. Consequently, the applicability of the TFD-based method to describe entanglement is confirmed in both equilibrium and non-equilibrium cases.

  16. Dynamical skyrmion state in a spin current nano-oscillator with perpendicular magnetic anisotropy.

    PubMed

    Liu, R H; Lim, W L; Urazhdin, S

    2015-04-01

    We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films. PMID:25884135

  17. Fingerprints of Interacting Hardcore Bosons on a Lattice: Spin Dynamics in Dimer Spin Systems with Field-Tuned Quantum Criticality.

    NASA Astrophysics Data System (ADS)

    Ruegg, Christian

    2007-03-01

    Spin-dimer based magnetic insulators are model systems for the experimental and theoretical investigation of field-tuned quantum criticality and, in particular, the ground states of strongly interacting hardcore bosons (triplets), for which there are increasing parallels to ultra-cold atoms in optical lattices. We have investigated corresponding quantum phase transitions by inelastic neutron scattering (INS) in spin systems, which cover both the effect of dimensionality and the degree of quasi-particle mobility. These quantities characterize the triplet excitations and definite the magnon-`BEC' phases above the field-induced quantum critical point in these materials. Inorganic compounds like the 3D copper-halide family ACuCl3 (A=K, Tl, NH4), the strongly frustrated Shastry-Sutherland material SrCu2(BO3)2, and quasi-2D BaCuSi2O6 all show distinct spin dynamics associated with the boson system, which they represent. The fascinating quasi-1D limit is accessible in novel organic materials, which promote a characteristic quantum phase -- the Luttinger spin-liquid. Recent INS results, which explore this exciting quantum phase, will be compared to those obtained in higher dimensions and elaborate predictions by theory.

  18. Existence of a dynamic compensation temperature of the mixed spin-1 and spin-3/2 Ising model within the effective-field theory

    NASA Astrophysics Data System (ADS)

    Shi, Xiaoling; Qi, Yang

    2015-07-01

    The effective-field theory with correlations based on Glauber-type stochastic dynamic is used to study the dynamic compensation behavior of the mixed spin-1 and spin-3/2 ferrimagnetic Ising model. The system is a layered honeycomb structure in which two kinds of spins (spin-1 and spin-3/2) occupy sites alternately. This is related to the experimental works of a molecular-based magnetic multilayer film, AMIIFeII(C2O4)3(A = N(n -CnH 2 n + 1) 4 ,MII = Mn,Fe) . The system is in the presence of a sinusoidal oscillating magnetic field and the Glauber dynamic is used to describe the time evolution of the system. The effects of the interlayer coupling and a crystal-field constant of the spin-1 sublattice on the compensation temperature are investigated. Dynamic phase diagrams, including the compensation points are presented. Besides second-order phase transition, lines of first-order phase transition, the dynamic tricritical point, the dynamic zero-temperature critical point and the multicritical point are found. The dynamic tricritical point, the dynamic compensation point and the non-magnetic phase predicted by the mean-field theory are confirmed by the effective-field theory.

  19. Longitudinal and transversal spin dynamics of donor-bound electrons in fluorine-doped ZnSe: spin inertia versus Hanle effect

    E-print Network

    F. Heisterkamp; E. A. Zhukov; A. Greilich; D. R. Yakovlev; V. L. Korenev; A. Pawlis; M. Bayer

    2015-03-26

    The spin dynamics of the strongly localized, donor-bound electrons in fluorine-doped ZnSe epilayers is studied by pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time, $T_1$, in a wide range of magnetic fields, temperatures, and pump densities. The $T_1$ time of the donor-bound electron spin of about 1.6 $\\mu$s remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range $1.8-45$ K. The inhomogeneous spin dephasing time, $T_2^*=8-33$ ns, is measured using the resonant spin amplification and Hanle effects under pulsed and steady-state pumping, respectively. These findings impose severe restrictions on possible spin relaxation mechanisms.

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

    SciTech Connect

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

    2013-01-01

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

  1. Finite-Temperature Entanglement Dynamics in an Anisotropic Two-Qubit Heisenberg Spin Chain

    NASA Astrophysics Data System (ADS)

    Chen, Tao; Shan, Chuanjia; Li, Jinxing; Liu, Tangkun; Huang, Yanxia; Li, Hong

    2010-07-01

    This paper investigates the entanglement dynamics of an anisotropic two-qubit Heisenberg spin chain in the presence of decoherence at finite temperature. The time evolution of the concurrence is studied for different initial Werner states. The influences of initial purity, finite temperature, spontaneous decay and Hamiltonian on the entanglement evolution are analyzed in detail. Our calculations show that the finite temperature restricts the evolution of the entanglement all the time when the Hamiltonian improves it and the spontaneous decay to the reservoirs can produce quantum entanglement with the anisotropy of spin-spin interaction. Finally, the steady-state concurrence which may remain non-zero for low temperature is also given.

  2. Stochastic differential equations for quantum dynamics of spin-boson networks

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    A popular approach in quantum optics is to map a master equation to a stochastic differential equation, where quantum effects manifest themselves through noise terms. We generalize this approach based on the positive-P representation to systems involving spin, in particular networks or lattices of interacting spins and bosons. We test our approach on a driven dimer of spins and photons, compare it to the master equation, and predict a novel dynamic phase transition in this system. Our numerical approach has scaling advantages over existing methods, but typically requires regularization in terms of drive and dissipation.

  3. Cubic order spin effects in the dynamics and gravitational wave energy flux of compact object binaries

    E-print Network

    Sylvain Marsat

    2015-01-23

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

  4. Proving Competence: Integrative Assessment and Web-Based Portfolio System in a Dynamic Curriculum.

    ERIC Educational Resources Information Center

    Wielenga, Douwe

    Since 1997, the Amsterdam Faculty of Education (EFA) has been officially recognized as a center for experimental teacher education. This paper describes the development of an assessment system and a World Wide Web-based portfolio system to help students take responsibility for their learning and their competence at three consecutive integrative…

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

    E-print Network

    Nizkorodov, Sergey

    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

  6. Slow Spin Dynamics in Superconducting Ca0.9Ce0.1Fe2As2

    PubMed Central

    Nadeem, K.; Zhang, W.; Chen, D. Y.; Ren, Z. A.; Qiu, X. G.

    2015-01-01

    Slow spin dynamics has been observed in superconducting under-doped Ca0.9Ce0.1Fe2As2 single crystal. Below 100?K, the system exhibits hysteresis in the cooling and warming protocols of temperature dependent resistivity due to first order tetragonal to orthorhombic structural transition with simultaneous magnetic transition from paramagnetic to spin density wave antiferromagnetic state of the iron (Fe) ions. Zero field cooled/field cooled (ZFC/FC) magnetization curves showed splitting at 32?K followed by a sharp increase of the FC curve and then FC plateau at low temperatures. Slow spin relaxation in both the ZFC and FC protocols was observed which is typical for spin-glass system. The system also showed features analogue to spin-glass behavior such as ZFC peak, FC plateau, ZFC slow spin relaxation, magnetic hysteresis, and ZFC ac memory effect. The spin-glass like behavior was rather weak and vanished at higher fields. The origin of the slow spin dynamics could be the inhomogeneous distribution of the cerium (Ce) spins ordered along the c-axis OR interactions between Fe and Ce spins which lead to magnetic frustration of Ce spins. All these findings support the coexistence of slow spin dynamics of Ce spins and superconductivity in Ca0.9Ce0.1Fe2As2 single crystal. PMID:26024047

  7. Slow Spin Dynamics in Superconducting Ca0.9Ce0.1Fe2As2.

    PubMed

    Nadeem, K; Zhang, W; Chen, D Y; Ren, Z A; Qiu, X G

    2015-01-01

    Slow spin dynamics has been observed in superconducting under-doped Ca0.9Ce0.1Fe2As2 single crystal. Below 100 K, the system exhibits hysteresis in the cooling and warming protocols of temperature dependent resistivity due to first order tetragonal to orthorhombic structural transition with simultaneous magnetic transition from paramagnetic to spin density wave antiferromagnetic state of the iron (Fe) ions. Zero field cooled/field cooled (ZFC/FC) magnetization curves showed splitting at 32 K followed by a sharp increase of the FC curve and then FC plateau at low temperatures. Slow spin relaxation in both the ZFC and FC protocols was observed which is typical for spin-glass system. The system also showed features analogue to spin-glass behavior such as ZFC peak, FC plateau, ZFC slow spin relaxation, magnetic hysteresis, and ZFC ac memory effect. The spin-glass like behavior was rather weak and vanished at higher fields. The origin of the slow spin dynamics could be the inhomogeneous distribution of the cerium (Ce) spins ordered along the c-axis OR interactions between Fe and Ce spins which lead to magnetic frustration of Ce spins. All these findings support the coexistence of slow spin dynamics of Ce spins and superconductivity in Ca0.9Ce0.1Fe2As2 single crystal. PMID:26024047

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

    PubMed Central

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

    2014-01-01

    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

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

    E-print Network

    Jun Jing; Zhi-Guo Lü

    2007-10-09

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

  10. Quantum Spin Dynamics of Mode-Squeezed Luttinger Liquids in Two-Component Atomic Gases

    SciTech Connect

    Widera, Artur; Trotzky, Stefan; Cheinet, Patrick; Foelling, Simon; Gerbier, Fabrice; Bloch, Immanuel; Gritsev, Vladimir; Lukin, Mikhail D.; Demler, Eugene

    2008-04-11

    We report on the observation of many-body spin dynamics of interacting, one-dimensional (1D) ultracold bosonic gases with two spin states. By controlling the nonlinear atomic interactions close to a Feshbach resonance we are able to induce a phase diffusive many-body spin dynamics of the relative phase between the two components. We monitor this dynamical evolution by Ramsey interferometry, supplemented by a novel, many-body echo technique, which unveils the role of quantum fluctuations in 1D. We find that the time evolution of the system is well described by a Luttinger liquid initially prepared in a multimode squeezed state. Our approach allows us to probe the nonequilibrium evolution of one-dimensional many-body quantum systems.

  11. Anomalously slow spin dynamics and short-range correlations in the quantum spin ice systems Yb2Ti2O7 and Yb2Sn2O7

    NASA Astrophysics Data System (ADS)

    Maisuradze, A.; Dalmas de Réotier, P.; Yaouanc, A.; Forget, A.; Baines, C.; King, P. J. C.

    2015-09-01

    We report a positive muon spin relaxation and rotation (? SR ) study of the quantum spin ice materials Yb2Ti2O7 and Yb2Sn2O7 focusing on the low field response. In agreement with earlier reports, data recorded in small longitudinal fields evidence anomalously slow spin dynamics in the microsecond range below the temperature Tc at which the specific heat displays an intense peak, namely Tc=0.24 K and 0.15 K, respectively, for the two systems. We found that slow dynamics extends above Tc up to at least 0.7 K for both compounds. The conventional dynamical Gaussian Kubo-Toyabe model describes the ? SR spectra recorded above Tc. At lower temperatures a published analytical extension of the Gaussian Kubo-Toyabe model provides a good description, consistent with the existence of short-range magnetic correlations. While the physical response of the two systems is qualitatively the same, Yb2Ti2O7 exhibits a much larger local magnetic susceptibility than Yb2Sn2O7 below Tc. Considering previously reported ac susceptibility, neutron scattering, and ? SR results, we suggest the existence of anomalously slow spin dynamics to be a common physical property of pyrochlore magnetic materials. The possibility of molecular spin substructures to be associated to the slow dynamics and therefore the short-range correlations is mentioned. The slow spin dynamics observed under field does not exclude the presence of much faster dynamics detected in extremely low or zero field.

  12. Keeping a spin qubit alive in natural silicon: Comparing optimal working points and dynamical decoupling

    E-print Network

    Setrak J. Balian; Ren-Bao Liu; T. S. Monteiro

    2015-04-22

    There are two distinct techniques of proven effectiveness for extending the coherence lifetime of spin qubits in environments of other spins. One is dynamical decoupling, whereby the qubit is subjected to a carefully timed sequence of control pulses; the other is tuning the qubit towards 'optimal working points' (OWPs), which are sweet-spots for reduced decoherence in magnetic fields. By means of quantum many-body calculations, we investigate the effects of dynamical decoupling pulse sequences far from and near OWPs for a central donor qubit subject to decoherence from a nuclear spin bath. Key to understanding the behavior is to analyse the degree of suppression of the usually dominant contribution from independent pairs of flip-flopping spins within the many-body quantum bath. We find that to simulate recently measured Hahn echo decays at OWPs (lowest-order dynamical decoupling), one must consider clusters of three interacting spins, since independent pairs do not even give finite $T_2$ decay times. We show that while operating near OWPs, dynamical decoupling sequences require hundreds of pulses for a single order of magnitude enhancement of $T_2$, in contrast to regimes far from OWPs, where only about ten pulses are required.

  13. Keeping a spin qubit alive in natural silicon: Comparing optimal working points and dynamical decoupling

    NASA Astrophysics Data System (ADS)

    Balian, S. J.; Liu, Ren-Bao; Monteiro, T. S.

    2015-06-01

    There are two distinct techniques of proven effectiveness for extending the coherence lifetime of spin qubits in environments of other spins. One is dynamical decoupling, whereby the qubit is subjected to a carefully timed sequence of control pulses; the other is tuning the qubit towards "optimal working points" (OWPs), which are sweet spots for reduced decoherence in magnetic fields. By means of quantum many-body calculations, we investigate the effects of dynamical decoupling pulse sequences far from and near OWPs for a central donor qubit subject to decoherence from a nuclear spin bath. Key to understanding the behavior is to analyze the degree of suppression of the usually dominant contribution from independent pairs of flip-flopping spins within the many-body quantum bath. We find that to simulate recently measured Hahn echo decays at OWPs (lowest-order dynamical decoupling), one must consider clusters of three interacting spins since independent pairs do not even give finite-T2 decay times. We show that while operating near OWPs, dynamical decoupling sequences require hundreds of pulses for a single order of magnitude enhancement of T2, in contrast to regimes far from OWPs, where only about 10 pulses are required.

  14. Spin-glass order induced by dynamic frustration

    E-print Network

    Loss, Daniel

    -earth intermetallic compounds, the magnetic moments of the f electrons on each rare-earth site interact of the other degenerate spin configurations. In recent years, two stoichiometric intermetallic compounds have it was surprising that PrAu2Si2, a stoichiometric compound with a well-ordered crystal structure, was reported2

  15. Dynamic stability of a spinning tube conveying a fluid through a symmetrical noncircular cross-section

    SciTech Connect

    Benedetti, G.A.

    1990-11-01

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

  16. Gravitational radiation and angular momentum flux from a spinning dynamical black hole

    E-print Network

    Wang, Chih-Hung

    2013-01-01

    A four-dimensional asymptotic expansion scheme is used to study the next order effects of the nonlinearity near a spinning dynamical black hole. The angular momentum flux and energy flux formula are then obtained by asymptotic expansion and the compatibility of the coupling Newman-Penrose equations. After constructing the reference frame in terms of the compatible constant spinors, the energy-momentum flux is derived and it is related to the black hole area growth. Directly from the flux formula of the spinning dynamical horizon, we find that the physically reasonable condition on the positivity of the gravitational energy flux yields that the shear will monotonically decrease with time.

  17. Geometric phases and quantum correlations dynamics in spin-boson model

    SciTech Connect

    Wu, Wei; Xu, Jing-Bo

    2014-01-28

    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.

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

    SciTech Connect

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

    2015-03-09

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

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

    PubMed

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

    2013-01-01

    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

  20. Effect of thermal fluctuations in spin-torque driven magnetization dynamics

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

    Nanomagnets with uniaxial symmetry driven by an external field and spin-polarized currents are considered. Anisotropy, applied field, and spin polarization are all aligned along the symmetry axis. Thermal fluctuations are described by adding a Gaussian white noise stochastic term to the Landau-Lifshitz-Gilbert equation for the deterministic dynamics. The corresponding Fokker-Planck equation is derived. It is shown that deterministic dynamics, thermal relaxation, and transition rate between stable states are governed by an effective potential including the effect of current injection.

  1. Unified theory of dynamical mean field and self-consistently renormalized spin-fluctuations

    NASA Astrophysics Data System (ADS)

    Kitajima, Toshiyuki; Saso, Tetsuro

    2000-06-01

    A unified theory of the dynamical mean-field and the self-consistently renormalized spin-fluctuations (SCR) for strongly correlated electron systems is proposed. Starting from the iterative perturbation theory, local dynamical magnetic susceptibility ?L( ?) is constructed with inclusion of the vertex corrections, and the effect of spin fluctuations is incorporated in the form similar to the SCR theory. Temperature dependence of specific heat and electrical resistivity are calculated to be proportional to T(1- const. T) and T3/2, respectively, at the quantum critical point and low temperatures.

  2. RosettaEPR: Rotamer Library for Spin Label Structure and Dynamics

    PubMed Central

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

    2013-01-01

    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

  3. Dynamics and control of flexible spinning solar sails under reflectivity modulation

    NASA Astrophysics Data System (ADS)

    Mu, Junshan; Gong, Shengping; Ma, Pengbin; Li, Junfeng

    2015-10-01

    Electrochromic devices have been used for the attitude control of a spinning solar sail in a deep space mission by modulating the reflectivity of the sail membrane. As a flexible spinning solar sail has no rigid structure to support its membrane, the distributed load due to solar radiation will lead to the deformation of the sail membrane, and the control torque generated by reflectivity modulation can introduce oscillatory motion to the membrane. By contrast, the deformation and oscillatory motion of the sail membrane have an impact on the performance of the reflectivity control. This paper investigates the dynamics and control of flexible spinning solar sails under reflectivity modulation. The static deformation of a spinning sail membrane subjected to solar radiation pressure in an equilibrium state is analyzed. The von Karman theory is used to obtain the displacements and the stress distribution in the equilibrium states. A simplified analytical first-order mode is chosen to model the membrane oscillation. The coupled membrane oscillation-attitude-orbit dynamics are considered for a GeoSail formation flying mission. The relative attitude and orbit control of flexible spinning solar sails under reflectivity modulation are numerically tested. The simulations indicate that the membrane deformation and oscillation have a lower impact on the control of the reflectivity modulated sails than the increase of the spinning rate.

  4. Non-local detection of spin dynamics via spin rectification effect in yttrium iron garnet/SiO2/NiFe trilayers near simultaneous ferromagnetic resonance

    NASA Astrophysics Data System (ADS)

    Soh, Wee Tee; Peng, Bin; Ong, C. K.

    2015-08-01

    The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.

  5. Acoustic study of dynamical molecular-spin state without magnetic phase transition in spin-frustrated ZnFe2O4

    NASA Astrophysics Data System (ADS)

    Watanabe, Tadataka; Takita, Shota; Tomiyasu, Keisuke; Kamazawa, Kazuya

    2015-11-01

    Ultrasound velocity measurements were performed on a single crystal of spin-frustrated ferrite spinel ZnFe2O4 from 300 K down to 2 K. In this cubic crystal, all the symmetrically independent elastic moduli exhibit softening with a characteristic minimum with decreasing temperature below ˜100 K. This elastic anomaly suggests a coupling between dynamical lattice deformations and molecular-spin excitations. In contrast, the elastic anomalies, normally driven by the magnetostructural phase transition and its precursor, are absent in ZnFe2O4 , suggesting that the spin-lattice coupling cannot play a role in relieving frustration within this compound. The present study infers that, for ZnFe2O4 , the dynamical molecular-spin state evolves at low temperatures without undergoing precursor spin-lattice fluctuations and spin-lattice ordering. It is expected that ZnFe2O4 provides the unique dynamical spin-lattice liquidlike system, where not only the spin molecules but also the cubic lattice fluctuate spatially and temporally.

  6. Dynamic magnetization states of a spin valve in the presence of dc and ac currents: Synchronization, modification, and chaos

    E-print Network

    Li, Charles

    Dynamic magnetization states of a spin valve in the presence of dc and ac currents: Synchronization and numerical calculations of dynamic magnetization states of a spin valve in the presence of dc and ac currents between the frequency of the original dc current-driven oscillation and the fre- quency of the applied ac

  7. Muon spin relaxation and hyperfine-enhanced Pr141 nuclear spin dynamics in Pr(Os,Ru)4Sb12 and (Pr,La)Os4Sb12

    NASA Astrophysics Data System (ADS)

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

    2007-07-01

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

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

    PubMed

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

    2014-09-12

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

  9. The magnetic field dependence of cross-effect dynamic nuclear polarization under magic angle spinning

    NASA Astrophysics Data System (ADS)

    Mance, Deni; Gast, Peter; Huber, Martina; Baldus, Marc; Ivanov, Konstantin L.

    2015-06-01

    We develop a theoretical description of Dynamic Nuclear Polarization (DNP) in solids under Magic Angle Spinning (MAS) to describe the magnetic field dependence of the DNP effect. The treatment is based on an efficient scheme for numerical solution of the Liouville-von Neumann equation, which explicitly takes into account the variation of magnetic interactions during the sample spinning. The dependence of the cross-effect MAS-DNP on various parameters, such as the hyperfine interaction, electron-electron dipolar interaction, microwave field strength, and electron spin relaxation rates, is analyzed. Electron spin relaxation rates are determined by electron paramagnetic resonance measurements, and calculations are compared to experimental data. Our results suggest that the observed nuclear magnetic resonance signal enhancements provided by MAS-DNP can be explained by discriminating between "bulk" and "core" nuclei and by taking into account the slow DNP build-up rate for the bulk nuclei.

  10. Bethe lattice approach and relaxation dynamics study of spin-crossover materials

    NASA Astrophysics Data System (ADS)

    Oke, Toussaint Djidjoho; Hontinfinde, Félix; Boukheddaden, Kamel

    2015-07-01

    Dynamical properties of Prussian blue analogs and spin-crossover materials are investigated in the framework of a Blume-Emery-Griffiths (BEG) spin-1 model, where states ±1 and 0 represent the high-spin (HS) state and the low-spin state, respectively. The quadrupolar interaction depends on the temperature in the form . Magnetic interactions are controlled by a factor such that for (), magnetic ordering is not expected. The model is exactly solved using the Bethe lattice approach for the equilibrium properties. The results are closer to those calculated by numerical simulations with suitable Arrhenius-type transition rates. The study of relaxation processes of non-equilibrium HS states revealed one-step nonlinear sigmoidal relaxation curves of the HS fraction at low temperatures. We found that increasing the magnetic interactions leads to the appearance of a plateau in the thermal hysteresis as well as in the relaxation curves of the HS fraction at low temperature.

  11. Low field domain wall dynamics in artificial spin-ice basis structure

    NASA Astrophysics Data System (ADS)

    Kwon, J.; Goolaup, S.; Lim, G. J.; Kerk, I. S.; Chang, C. H.; Roy, K.; Lew, W. S.

    2015-10-01

    Artificial magnetic spin-ice nanostructures provide an ideal platform for the observation of magnetic monopoles. The formation of a magnetic monopole is governed by the motion of a magnetic charge carrier via the propagation of domain walls (DWs) in a lattice. To date, most experiments have been on the static visualization of DW propagation in the lattice. In this paper, we report on the low field dynamics of DW in a unit spin-ice structure measured by magnetoresistance changes. Our results show that reversible DW propagation can be initiated within the spin-ice basis. The initial magnetization configuration of the unit structure strongly influences the direction of DW motion in the branches. Single or multiple domain wall nucleation can be induced in the respective branches of the unit spin ice by the direction of the applied field.

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

    E-print Network

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

    2015-01-21

    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.

  13. Insensitivity of spin dynamics to the orbital angular momentum transferred from twisted light to extended semiconductors

    NASA Astrophysics Data System (ADS)

    Cygorek, M.; Tamborenea, P. I.; Axt, V. M.

    2015-09-01

    We study the spin dynamics of carriers due to the Rashba interaction in semiconductor quantum disks and wells after excitation with light with orbital angular momentum. We find that although twisted light transfers orbital angular momentum to the excited carriers and the Rashba interaction conserves their total angular momentum, the resulting electronic spin dynamics is essentially the same for excitation with light with orbital angular momentum l =+|l | and l =-|l | . The differences between cases with different values of |l | are due to the excitation of states with slightly different energies and not to the different angular momenta per se and vanish for samples with large radii where a k -space quasicontinuum limit can be established. These findings apply not only to the Rashba interaction but also to all other envelope-function-approximation spin-orbit Hamiltonians like the Dresselhaus coupling.

  14. Effective magnetization damping for a dynamical spin texture in metallic ferromagnet

    NASA Astrophysics Data System (ADS)

    Sukhostavets, Oksana V.; Gonzalez, Julian M.; Guslienko, Konstantin Y.

    2015-10-01

    An additional magnetization damping for an inhomogeneous spin texture in metallic ferromagnets is calculated on the basis of the s-d exchange model. The effect of conduction electrons on the magnetization dynamics is accounted for the case of slowly varying spin texture within adiabatic approximation by using a coordinate transformation to the local quantization axis. The moving magnetic vortex in a circular nanodot made of permalloy is considered as an example. The dependence of the damping on the dot geometrical sizes is obtained. It is found that the additional damping can reach up to 50% of magnitude of the phenomenological Gilbert damping in the Landau-Lifshitz equation of magnetization motion and should be taken into account for any inhomogeneous spin texture dynamics in ferromagnetic metals.

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

    E-print Network

    M. Y. Kovalevsky; A. V. Glushchenko

    2014-01-11

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

  16. Chaotic dynamics of two 1/2 spin-qubit system in the optical cavity

    E-print Network

    L. Chotorlishvili; Z. Toklikishvili

    2007-09-04

    Spin systems are one of the most promising candidates for quantum computation. At the same time control of a system's quantum state during time evolution is one of the actual problems. It is usually considered that to hold well-known resonance condition in magnetic resonance is sufficient to control spin system. But because of nonlinearity of the system, obstructions of control of system's quantum state may emerge. In particular quantum dynamics of two 1/2 spin-qubit system in the optical cavity is studied in this work. The problem under study is a generalization of paradigmatic model for Cavity Quantum Electrodynamics of James-Cummings model in case of interacting spins. In this work it is shown that dynamics is chaotic when taking into account center-of-mass motion of the qubit and recoil effect. And besides even in case of zero detuning chaotic dynamics emerges in the system. It is also shown in this work that because of the chaotic dynamics the system execute irreversible transition from pure quantum-mechanical state to mixed one. Irreversibility in its turn is an obstacle for controlling state of quantum-mechanical system.

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

    SciTech Connect

    Jin Lichuan; Zhang Huaiwu; Tang Xiaoli; Bai Feiming; Zhong Zhiyong

    2013-02-07

    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.

  18. 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

  19. Temperature for a dynamic spin ensemble Pui-Wai Ma,1,2

    E-print Network

    of the system 1 . In experiment and microscopic molecular dynamics simulations it is probed by monitoring differen- tiating the Hamiltonian makes it the most convenient and most often used recipe for monitoring be readily applied. Having a recipe for monitoring the spin temperature is necessary for analyzing a large

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  1. EPR, charge transport, and spin dynamics in doped polyanilines

    NASA Astrophysics Data System (ADS)

    Kon'kin, A. L.; Shtyrlin, V. G.; Garipov, R. R.; Aganov, A. V.; Zakharov, A. V.; Krinichnyi, V. I.; Adams, P. N.; Monkman, A. P.

    2002-08-01

    Charge transport and magnetic properties of films of polyaniline (PAN) doped with 10-camphorsulfonic acid and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) have been studied by conductivity, magnetic-susceptibility superconducting quantum interference device measurements, and 3-cm and 8-mm electron paramagnetic resonance (EPR) spectroscopy at doping levels (x) from 0.3 to 0.9 over a temperature range from 15 to 300 K. The temperature dependences of conductivities were explained in terms of the advanced multiphase heterogeneous granular metallic (HGM) model with percolation including disordered metallic (DM) and nonmetallic (NM) phases. The anomalous conductivity change in the PAN-AMPSAx system at T>240 K was accounted quantitatively for a solid-phase equilibrium with the occurrence of the disordered anion phase from the metallic islands. A means for analysis of the EPR line shape in conducting media has been developed and, with this, conductivity and microwave dielectric constants were estimated and two EPR signals, R1 and R2, were detected in both systems. It was shown that R1 signal belongs to pinned radicals of isolated polymer chains, whereas R2 is the weight-averaged signal, resulting from three types of paramagnetic centers, localized and mobile spins in the NM and DM phases, which interact via exchange. From the temperature and frequency dependences of the R2 linewidth the spin-diffusion parameters for the NM phase in both systems were determined. It was found that the HGM model allows good explanation of both charge transport and spin diffusion in the doped polyaniline films.

  2. A comment on 'Accurate spin axes and solar system dynamics'

    E-print Network

    Jacques Laskar

    2003-11-19

    In a recent paper, Edvardsson etal (2002) propose a new solution for the spin evolution of the Earth and Mars. Their results differ significantly with respect to previous studies, as they found a large contribution on the precession of the planet axis from the tidal effects of Phobos and Deimos. In fact, this probably results from the omission by the authors of the torques exerted on the satellites orbits by the planet's equatorial bulge, as otherwise the average torque exerted by the satellites on the planet is null.

  3. ANTIOPE, a program for computer experiments on spin dynamics

    NASA Astrophysics Data System (ADS)

    de Bouregas, F. Stickney; Waugh, J. S.

    ANTIOPE is a self-contained program, running on personal computers, for simulating a variety of real and hypothetical NMR experiments. Systems of up to five spins with fixed or anisotropic truncated Hamiltonians can be subjected to time-varying external fields of arbitrary amplitudes, frequencies, and phases and to the effects of random motions and sample rotations. The resulting 1D and 2D data sets can be manipulated and plotted interactively. No conventional programming skills are required: the program interacts with the user in NMR terms and provides extensive prompting, error trapping, warning facilities and context-sensitive help.

  4. Short-time dynamics in dispersions with competing short-range attraction and long-range repulsion.

    PubMed

    Riest, Jonas; Nägele, Gerhard

    2015-12-01

    Dynamic clustering of globular Brownian particles in dispersions exhibiting competing short-range attraction and long-range repulsion (SALR) such as low-salinity protein solutions has gained a lot of interest over the past few years. While the structure of the various cluster phases has been intensely explored, little is known about the dynamics of SALR systems. We present the first systematic theoretical study of short-time diffusion and rheological transport properties of two-Yukawa potential SALR systems in the single-particle dominated dispersed-fluid phase, using semi-analytic methods where the salient hydrodynamic interactions are accounted for. We show that the dynamics has unusual features compared to reference systems with pure repulsion or attraction. Results are discussed for the hydrodynamic function characterizing short-time diffusion that reveals an intermediate-range-order (cluster) peak, self-diffusion and sedimentation coefficients, and high-frequency viscosity. As important applications, we discuss the applicability of two generalized Stokes-Einstein relations, and assess the wavenumber range required for the determination of self-diffusion in a dynamic scattering experiment. PMID:26426932

  5. Dynamical Magnetic and Nuclear Polarization in Complex Spin Systems: Semi-magnetic II-VI Quantum Dots

    E-print Network

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

    2012-05-17

    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 the electron and heavy hole spins interacting via exchange interaction with magnetic impurity, via hypeprfine 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 new spin polarized exciton is shown to lead to 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.

  6. Dynamics of polymer film formation during spin coating

    SciTech Connect

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

    2014-09-28

    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.

  7. Solid effect in magic angle spinning dynamic nuclear polarization

    E-print Network

    Smith, Albert A.

    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 ...

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

    PubMed

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

    2014-01-01

    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

  9. Advances and applications of dynamic-angle spinning nuclear magnetic resonance

    SciTech Connect

    Baltisberger, J.H.

    1993-06-01

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

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

    PubMed Central

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

    2014-01-01

    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

  11. Optimizing a Dynamical Decoupling Protocol for Solid-State Electronic Spin Ensembles in Diamond

    E-print Network

    Demitry Farfurnik; Andrey Jarmola; Linh M. Pham; Zhi-Hui Wang; Viatcheslav V. Dobrovitski; Ronald L. Walsworth; Dmitry Budker; Nir Bar-Gill

    2015-07-14

    We demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to $77$ K suppresses longitudinal spin relaxation $T_1$ effects and DD microwave pulses are used to increase the transverse coherence time $T_2$ from $\\sim 0.7$ ms up to $\\sim 30$ ms. We extend previous work of single-axis (CPMG) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We identify that the optimal control scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of AC magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states.

  12. Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond

    DOE PAGESBeta

    Farfurnik, D.; Jarmola, A.; Pham, L. M.; Wang, Z. H.; Dobrovitski, V. V.; Walsworth, R. L.; Budker, D.; Bar-Gill, N.

    2015-08-24

    In this study, we demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to 77 K suppresses longitudinal spin relaxation T1 effects and DD microwave pulses are used to increase the transverse coherence time T2 from ~0.7ms up to ~30ms. Furthermore, we extend previous work of single-axis (Carr-Purcell-Meiboom-Gill) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We also identify that the optimal controlmore »scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of ac magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states.« less

  13. Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond

    SciTech Connect

    Farfurnik, D.; Jarmola, A.; Pham, L. M.; Wang, Z. H.; Dobrovitski, V. V.; Walsworth, R. L.; Budker, D.; Bar-Gill, N.

    2015-08-24

    In this study, we demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to 77 K suppresses longitudinal spin relaxation T1 effects and DD microwave pulses are used to increase the transverse coherence time T2 from ~0.7ms up to ~30ms. Furthermore, we extend previous work of single-axis (Carr-Purcell-Meiboom-Gill) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We also identify that the optimal control scheme for preserving an arbitrary spin state is a recursive protocol, the concatenated version of the XY8 pulse sequence. The improved spin coherence might have an immediate impact on improvements of the sensitivities of ac magnetometry. Moreover, the protocol can be used on denser diamond samples to increase coherence times up to NV-NV interaction time scales, a major step towards the creation of quantum collective NV spin states.

  14. Quantum spin dynamics at terahertz frequencies in 2D hole gases and improper ferroelectrics

    NASA Astrophysics Data System (ADS)

    Lloyd-Hughes, J.

    2015-08-01

    Terahertz time-domain spectroscopy permits the excitations of novel materials to be examined with exquisite precision. Improper ferroelectric materials such as cupric oxide (CuO) exhibit complex magnetic ground states. CuO is antiferromagnetic below 213K, but has an incommensurate cycloidal magnetic phase between 213K and 230K. Remarkably, the cycloidal magnetic phase drives ferroelectricity, where the material becomes polar. Such improper multiferroics are of great contemporary interest, as a better understanding of the science of magnetoelectric materials may lead to their application in actuators, sensors and solid state memories. Improper multiferroics also have novel quasiparticle excitations: electromagnons form when spin-waves become electric-dipole active. By examining the dynamic response of spins as they interact with THz radiation we gain insights into the underlying physics of multi-ferroics. In contrast to improper ferroelectrics, where magnetism drives structural inversion asymmetry (SIA), two-dimensional electronic systems can exhibit non-degenerate spin states as a consequence of SIA created by strain and/or electric fields. We identify and explore the influence of the Rashba spin-orbit interaction upon cyclotron resonance at terahertz frequencies in high-mobility 2D hole gases in germanium quantum wells. An enhanced Rashba spin-orbit interaction can be linked to the strain of the quantum well, while a time-frequency decomposition method permitted the dynamical formation and decay of spin-split cyclotron resonances to be tracked on picosecond timescales. Long spin-decoherence times concurrent with high hole mobilities highlight the potential of Ge quantum wells in spintronics.

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

    NASA Astrophysics Data System (ADS)

    Nifle, M.; Hilhorst, H. J.

    1991-01-01

    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.

  16. Stationary-phase EPR for exploring protein structure, conformation, and dynamics in spin-labeled proteins.

    PubMed

    López, Carlos J; Fleissner, Mark R; Brooks, Evan K; Hubbell, Wayne L

    2014-11-18

    Proteins tethered to solid supports are of increasing interest in bioanalytical chemistry and protein science in general. However, the extent to which tethering modifies the energy landscape and dynamics of the protein is most often unknown because there are few biophysical methods that can determine secondary and tertiary structures and explore conformational equilibria and dynamics of a tethered protein with site-specific resolution. Site-directed spin labeling (SDSL) combined with electron paramagnetic resonance (EPR) offers a unique opportunity for this purpose. Here, we employ a general strategy using unnatural amino acids that enables efficient and site-specific tethering of a spin-labeled protein to a Sepharose solid support. Remarkably, EPR spectra of spin-labeled T4 lysozyme (T4L) reveal that a single site-specific attachment suppresses rotational motion of the protein sufficiently to allow interpretation of the spectral line shape in terms of protein internal dynamics. Importantly, line shape analysis and distance mapping using double electron-electron resonance reveal that internal dynamics, the tertiary fold, conformational equilibria, and ligand binding of the tethered proteins were similar to those in solution, in contrast to random attachment via native lysine residues. The results of this study set the stage for the development of an EPR-based flow system that will house soluble and membrane proteins immobilized site-specifically, thereby enabling facile screening of structural and dynamical effects of binding partners. PMID:25333901

  17. Spin-system dynamics and fault detection in threshold networks

    SciTech Connect

    Kirkland, Steve; Severini, Simone

    2011-01-15

    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.

  18. Dynamics of a fluid contained in a spinning, coning cylinder

    NASA Astrophysics Data System (ADS)

    Sedney, Raymond; Hall, Philip; Gerber, Nathan

    1988-01-01

    The fluid motion inside a cylinder which simultaneously spins and cones is determined according to linear theory for small coning angles. The Navier-Stokes equations are solved by expansions in spatial eigenfunctions. This form of spectral method gives an efficient solver over a wide range of Reynolds numbers; cases for Re less than or equal to 2,500 have been computed. The results are validated by comparing computed and measured pressure and moment coefficients. Comparisons are also made with results from a nonlinear finite difference method for which the CPU time is about 400 times that of the present method. The CPU time for the spatial eigenvalue method varies from 10 seconds at Re = 10 to 25 minutes at Re = 1,000. The restriction of linear theory is not severe; for coning angle of 20 deg, the moment coefficient from linear and nonlinear computations differ by 2 percent.

  19. Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models

    E-print Network

    Sebastian Steinhaus

    2015-09-17

    The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretisation. However extracting this mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple 2D toy model for Yang--Mills coupled to spin foams, namely an Ising model coupled to so--called intertwiner models defined for $\\text{SU}(2)_k$. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretisation. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions.

  20. Correspondence between spin-dynamic phases and pulse program phases of NMR spectrometers.

    PubMed

    Roehrl, Michael H A; Heffron, Gregory J; Wagner, Gerhard

    2005-06-01

    Spin state selective experiments have become very useful tools in solution NMR spectroscopy, particularly in the context of TROSY line narrowing. However, the practical implementation of such pulse sequences is frequently complicated by unexpected instrument behavior. Furthermore, a literal theoretical analysis of sequences published with specific phase settings can fail to rationalize such experiments and can seemingly contradict experimental findings. In this communication, we develop a practical approach to this ostensible paradox. Spin-dynamic design, rationalization, and simulation of NMR pulse sequences, as well as their confident and reliable implementation across current spectrometer hardware platforms, require precise understanding of the underlying nutation axis conventions. While currently often approached empirically, we demonstrate with a simple but general pulse program how to uncover these correspondences a priori in the general case. From this, we deduce a correspondence table between the spin-dynamic phases used in NMR theory and simulation on the one hand and pulse program phases of current commercial spectrometers on the other. As a practical application of these results, we analyze implementations of the original (1)H-(15)N TROSY experiment and illustrate how steady-state magnetization can be predictably, rather than empirically, added to a desired component. We show why and under which circumstances a literal adoption of phases from published sequences can lead to incorrect results. We suggest that pulse sequences should be consistently given with spin-dynamically correct (physical) phases, rather than in spectrometer-specific (software) syntax. PMID:15862251

  1. Coupled intertwiner dynamics: A toy model for coupling matter to spin foam models

    NASA Astrophysics Data System (ADS)

    Steinhaus, Sebastian

    2015-09-01

    The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretization. However, extracting these mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple two-dimensional toy model for Yang-Mills coupled to spin foams, namely an Ising model coupled to so-called intertwiner models defined for SU (2 )k. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretization. We coarse grain this toy model via tensor network renormalization and uncover an interesting dynamics: the Ising phase transition temperature turns out to be sensitive to the background configurations and conversely, the Ising model can induce phase transitions in the background. Moreover, we observe a strong coupling of both systems if close to both phase transitions.

  2. Exciton fine structure and spin/valley dynamics in nanosystems (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Glazov, Mikhail M.

    2015-09-01

    In my invited talk the fine structure of neutral and charged excitons for GaAs/AlGaAs quantum dots (QDs) grown on (111) plane as well for transition metal dichalcogenides (TMDCs) monolayers will be discussed. These, at first glance, different systems posses similar trigonal symmetry, which makes exciton fine structure and spin dynamics unusual compared with standard low-dimensional semiconductors. The effects of long-range exchange interaction induced mixing of excitons in two valleys of TMDCs and of magneto-induced mixing of bright and dark excitonic states in trigonal QDs are predicted and confirmed experimentally. Manifestations of excitonic spin/valley dynamics in photoluminescence, pump-probe Kerr rotation and spin noise are discussed. The presentation will be based on the following references: [1] G. Sallen, B. Urbaszek, M. M. Glazov, et al., Dark-Bright Mixing of Interband Transitions in Symmetric Semiconductor Quantum Dots, Phys. Rev. Lett. 107, 166604 (2011). [2] L. Bouet, M. Vidal, T. Mano, N. Ha, T. Kuroda, M. V. Durnev, M. M. Glazov, et al., Charge tuning in [111] grown GaAs droplet quantum dots, Appl. Phys. Lett. 105, 082111 (2014). [3] M. M. Glazov, et al., Exciton fine structure and spin decoherence in monolayers of transition metal dichalcogenides Phys. Rev. B 89, 201302(R) (2014). [4] C. R. Zhu, K. Zhang, M. Glazov, et al., Exciton valley dynamics probed by Kerr rotation in WSe2 monolayers, Phys. Rev. B 90, 161302(R) (2014).

  3. Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical Lattice

    E-print Network

    Stefan S. Natu; J. H. Pixley; S. Das Sarma

    2015-02-03

    We study the physics of interacting spin-$1$ bosons in an optical lattice using a variational Gutzwiller technique. We compute the mean-field ground state wave-function and discuss the evolution of the condensate, spin, nematic, and singlet order parameters across the superfluid-Mott transition. We then extend the Gutzwiller method to derive the equations governing the dynamics of low energy excitations in the lattice. Linearizing these equations, we compute the excitation spectra in the superfluid and Mott phases for both ferromagnetic and antiferromagnetic spin-spin interactions. In the superfluid phase, we recover the known excitation spectrum obtained from Bogoliubov theory. In the nematic Mott phase, we obtain gapped, quadratically dispersing particle and hole-like collective modes, whereas in the singlet Mott phase, we obtain a non-dispersive gapped mode, corresponding to the breaking of a singlet pair. For the ferromagnetic Mott insulator, the Gutzwiller mean-field theory only yields particle-hole like modes but no Goldstone mode associated with long range spin order. To overcome this limitation, we supplement the Gutzwiller theory with a Schwinger boson mean-field theory which captures super-exchange driven fluctuations. In addition to the gapped particle-hole-like modes, we obtain a gapless quadratically dispersing ferromagnetic spin-wave Goldstone mode. We discuss the evolution of the singlet gap, particle-hole gap, and the effective mass of the ferromagnetic Goldstone mode as the superfluid-Mott phase boundary is approached from the insulating side. We discuss the relevance and validity of Gutzwiller mean-field theories to spinful systems, and potential extensions of this framework to include more exotic physics which appears in the presence of spin-orbit coupling or artificial gauge fields.

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

    SciTech Connect

    Tomasello, R.; Carpentieri, M.; Finocchio, G.

    2013-12-16

    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.

  5. Statics and Dynamics of Spin and Electric Dipoles in 3-Dimension, 4-Dimension, and Other Dimensions 

    E-print Network

    SASLOW, WM; Fulling, Stephen A.; Hu, Chia-Ren.

    1985-01-01

    VOLUME 31, NUMBER 1 1 JANUARY 1985 Statics and dynamics of spin and electric dipoles in three, four, and other dimensions W. M. Saslow Department of Physics, Texas Ad'cM University, College Station, Texas 77843 S. A. Fulling Department of...Mathematics, Texas Ad'cM University, College Station, Texas 77843 C.-R. HU Department ofPhysics, Texas Ad'cM University, College Station, Texas 77843 (Received 4 May 1984) Properly, spin is an antisymmetric tensor, and therefore in n-dimensional spaces where...

  6. Transient dynamics of spin-polarized injection in helical Luttinger liquids

    NASA Astrophysics Data System (ADS)

    Calzona, A.; Carrega, M.; Dolcetto, G.; Sassetti, M.

    2015-11-01

    We analyze the time evolution of spin-polarized electron wave packets injected into the edge states of a two-dimensional topological insulator. In the presence of electron interactions, the system is described as a helical Luttinger liquid and injected electrons fractionalize. However, because of the presence of metallic detectors, no evidences of fractionalization are encoded in dc measurements, and in this regime the system does not show deviations from its non-interacting behavior. Nevertheless, we show that the helical Luttinger liquid nature emerges in the transient dynamics, where signatures of charge/spin fractionalization can be clearly identified.

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

    SciTech Connect

    Wasielewski, M. R.

    1998-08-27

    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.

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

    SciTech Connect

    Lorenzo, Salvatore; Plastina, Francesco; Paternostro, Mauro

    2011-09-15

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

  9. Nonperturbative spin-boson and spin-spin dynamics and nonlinear Fano interferences: a unified dissipaton theory based study.

    PubMed

    Zhang, Hou-Dao; Xu, Rui-Xue; Zheng, Xiao; Yan, YiJing

    2015-01-14

    We consider the hybrid system-bath dynamics, based on the Yan's dissipaton formalism [Y. J. Yan, J. Chem. Phys. 140, 054105 (2014)]. This theory provides a unified quasi-particle treatment on three distinct classes of quantum bath, coupled nonperturbatively to arbitrary quantum systems. In this work, to study the entangled system and bath polarization and nonlinear Fano interference, we incorporate further the time-dependent light field, which interacts with both the molecular system and the collective bath dipoles directly. Numerical demonstrations are carried out on a two-level system, with comparison between phonon and exciton baths, in both linear and nonlinear Fano interference regimes. PMID:25591343

  10. Nonperturbative spin–boson and spin–spin dynamics and nonlinear Fano interferences: A unified dissipaton theory based study

    SciTech Connect

    Zhang, Hou-Dao; Xu, Rui-Xue Zheng, Xiao; Yan, YiJing

    2015-01-14

    We consider the hybrid system–bath dynamics, based on the Yan’s dissipaton formalism [Y. J. Yan, J. Chem. Phys. 140, 054105 (2014)]. This theory provides a unified quasi-particle treatment on three distinct classes of quantum bath, coupled nonperturbatively to arbitrary quantum systems. In this work, to study the entangled system and bath polarization and nonlinear Fano interference, we incorporate further the time-dependent light field, which interacts with both the molecular system and the collective bath dipoles directly. Numerical demonstrations are carried out on a two-level system, with comparison between phonon and exciton baths, in both linear and nonlinear Fano interference regimes.

  11. Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

    E-print Network

    Jun Xu; Bao-An Li; Wen-Qing Shen; Yin Xia

    2015-08-16

    It is well known that non-central nuclear forces, such as the spin-orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known since only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may carry useful information about the in-medium properties of non-central nuclear interactions, besides earlier studies using the time-dependent Hartree-Fock approach to understand effects of spin-orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore dynamical effects of non-central nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focuses of these studies have been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies while so far there is still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.

  12. Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

    NASA Astrophysics Data System (ADS)

    Xu, Jun; Li, Bao-An; Shen, Wen-Qing; Xia, Yin

    2015-10-01

    It is well known that noncentral nuclear forces, such as the spin-orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known because only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may convey useful information about the in-medium properties of noncentral nuclear interactions, besides earlier studies using the time-dependent Hartree-Fock approach to understand the effects of spin-orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore the dynamical effects of noncentral nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focus of these studies has been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies but so far there are still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.

  13. Time-resolved dynamics of the spin Hall effect

    E-print Network

    Loss, Daniel

    . GOSSARD AND D. D. AWSCHALOM* Center for Spintronics and Quantum Computation, University of California­orbit physics as well as a valuable capability for potential spintronics devices1­4 . One realization in spintronics devices, understanding dynamics on this timescale is critical for both physical and practical

  14. PHYSICAL REVIEW B 83, 134418 (2011) Langevin spin dynamics

    E-print Network

    2011-01-01

    .134418 PACS number(s): 75.10.Hk, 75.40.Mg, 76.60.Es, 76.60.Jx I. INTRODUCTION Langevin dynamics is a subject to constraints limiting their application11,12 or contain mathematical inconsistencies.13,14 Some literature

  15. Critical Dynamics of Longitudinal Component in Ordered Spin System

    NASA Astrophysics Data System (ADS)

    Shirota, R.; Miyake, K.; Ito, M.; Yamada, K.

    1981-08-01

    Dynamical susceptibility of the longitudinal component, ?L(q, ?), in XY-and its generalized system is calculated below the critical point, using the ?-expansion method in the renormalization group theory. In the limit of long-wavelength, ?L(0, ?) has the ?-dependence ?-?(?=4-d), which means the long-time-tail, not exponential decay.

  16. Introducing a static receptor to compete with a dynamic combinatorial library in template binding.

    PubMed

    Ulatowski, Filip; Lichosyt, Dawid; Jurczak, Janusz

    2015-11-14

    We show herein that establishing a competition between a static receptor and components of dynamic combinatorial libraries to bind an appropriately selected template can be used to determine association constants by HPLC analysis after freezing of the equilibrium. PMID:26419756

  17. Spin coherence lifetime extension in Tm$^{3+}$:YAG through dynamical decoupling

    E-print Network

    M. F. Pascual-Winter; R. -C. Tongning; T. Chanelière; J. -L. Le Gouët

    2013-02-20

    We report on spin coherence lifetime extension on Tm$^{3+}$:YAG obtained through dynamically decoupling the thulium spins from their magnetic environment. The coherence lifetime reached with a Carr-Purcell-Meiboom-Gill sequence revealed a 450-fold extension [$\\sim$$(230 \\pm 30)$ ms] with respect to previously measured values. Comparison to a simple theoretical model allowed us to estimate the correlation time of the fluctuations of the ground level transition frequency to $(172 \\pm 30)$ $\\mu$s at 1.7 K. For attaining efficient decoupling sequences, we developed a strategy inspired by the \\emph{zero-first-order Zeeman} effect to minimize the large inhomogeneous broadening of the ground level spin transition.

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

    E-print Network

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

    2015-02-21

    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.

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

    PubMed Central

    Veshtort, Mikhail; Griffin, Robert G.

    2011-01-01

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

  20. Uniqueness regime for Markov dynamics on quantum lattice spin systems

    NASA Astrophysics Data System (ADS)

    Crawford, N.; De Roeck, W.; Schütz, M.

    2015-10-01

    We consider a lattice of weakly interacting quantum Markov processes. Without interaction, the dynamics at each site is relaxing exponentially to a unique stationary state. With interaction, we show that there remains a unique stationary state in the thermodynamic limit, i.e. absence of phase coexistence, and the relaxation towards it is exponentially fast for local observables. We do not assume that the quantum Markov process is reversible (detailed balance) w.r.t. a local Hamiltonian.

  1. Uniqueness regime for Markov dynamics on quantum lattice spin systems

    E-print Network

    Nicholas Crawford; Wojciech De Roeck; Marius Schütz

    2015-10-16

    We consider a lattice of weakly interacting quantum Markov processes. Without interaction, the dynamics at each site is relaxing exponentially to a unique stationary state. With interaction, we show that there remains a unique stationary state in the thermodynamic limit, i.e. absence of phase coexistence, and the relaxation towards it is exponentially fast for local observables. We do not assume that the quantum Markov process is reversible (detailed balance) w.r.t. a local Hamiltonian.

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

    PubMed

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

    2015-05-01

    We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics. PMID:25956109

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  4. Bosonization approach to charge and spin dynamics of one-dimensional spin- (1)/(2) fermions with band curvature in a clean quantum wire

    NASA Astrophysics Data System (ADS)

    Teber, Sofian

    2007-07-01

    We consider one-dimensional spin- (1)/(2) fermions in a clean quantum wire, with forward scattering interactions and a nonlinear single-particle spectrum ?k=v?k?+k2/2m , where v is the Fermi velocity and 1/m is the band curvature. We calculate the dynamical structure factor (DSF) of the model at small wave vector q with the help of the bosonization technique. For spinless fermions, we show that, starting from the single-parametric spectrum ?=u?q? , bosonization emulates the two-parametric excitation spectrum ?=u?q?±q2/2m* , where m* decreases with increasing repulsive interactions. Moreover, away from the excitation cone, i.e., ??u?q? , bosonization yields the two-pair excitation continuum of the DSF. For spinful fermions, we show that the spin-charge coupling (SCC) due to band curvature affects the charge and spin DSFs in an asymmetric way. For the charge DSF, SCC manifests as a two-peak structure: a charge peak at ?=u??q? but also a spin peak at ?=u??q? , as charge fluctuations may decay via chargeless spin-singlet excitations. For the magnetic DSF, SCC manifests as a continuous transfer of magnetic spectral weight to frequencies ?>u??q? , as spin fluctuations decay via pairs of chargeless spin and spinless charge-neutral excitations.

  5. Anisotropic spin relaxation in n -GaAs from strong inhomogeneous hyperfine fields produced by the dynamical polarization of nuclei

    NASA Astrophysics Data System (ADS)

    Harmon, N. J.; Peterson, T. A.; Geppert, C. C.; Patel, S. J.; Palmstrøm, C. J.; Crowell, P. A.; Flatté, M. E.

    2015-10-01

    The hyperfine field from dynamically polarized nuclei in n -GaAs is very spatially inhomogeneous, as the nuclear polarization process is most efficient near the randomly distributed donors. Electrons with polarized spins traversing the bulk semiconductor will experience this inhomogeneous hyperfine field as an effective fluctuating spin precession rate, and thus the spin polarization of an electron ensemble normal to the fluctuating hyperfine fields will relax. A theory of spin relaxation based on the theory of random walks is applied to such an ensemble precessing in an oblique magnetic field, and the precise form of the (unequal) longitudinal and transverse spin relaxation is analytically derived. To investigate this mechanism, electrical three-terminal Hanle measurements were performed on epitaxially grown Co2MnSi /n -GaAs heterostructures fabricated into electrical spin injection devices. The proposed anisotropic spin relaxation mechanism is required to satisfactorily describe the Hanle line shapes when the applied field is oriented at large oblique angles.

  6. Non-equilibrium dynamics of an unstable quantum pendulum explored in a spin-1 Bose-Einstein condensate

    NASA Astrophysics Data System (ADS)

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

    2012-11-01

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

  7. Nonequilibrium dynamics of a mixed spin-1/2 and spin-3/2 Ising ferrimagnetic system with a time dependent oscillating magnetic field source

    NASA Astrophysics Data System (ADS)

    Vatansever, Erol; Polat, Hamza

    2015-10-01

    Nonequilibrium phase transition properties of a mixed Ising ferrimagnetic model consisting of spin-1/2 and spin-3/2 on a square lattice under the existence of a time dependent oscillating magnetic field have been investigated by making use of Monte Carlo simulations with a single-spin flip Metropolis algorithm. A complete picture of dynamic phase boundary and magnetization profiles have been illustrated and the conditions of a dynamic compensation behavior have been discussed in detail. According to our simulation results, the considered system does not point out a dynamic compensation behavior, when it only includes the nearest-neighbor interaction, single-ion anisotropy and an oscillating magnetic field source. As the next-nearest-neighbor interaction between the spins-1/2 takes into account and exceeds a characteristic value which sensitively depends upon values of single-ion anisotropy and only of amplitude of external magnetic field, a dynamic compensation behavior occurs in the system. Finally, it is reported that it has not been found any evidence of dynamically first-order phase transition between dynamically ordered and disordered phases, which conflicts with the recently published molecular field investigation, for a wide range of selected system parameters.

  8. Imaging Spin Dynamics on the Nanoscale using X-Ray Microscopy

    NASA Astrophysics Data System (ADS)

    Stoll, Hermann; Noske, Matthias; Weigand, Markus; Richter, Kornel; Krüger, Benjamin; Reeve, Robert; Hänze, Max; Adolff, Christian; Stein, Falk-Ulrich; Meier, Guido; Kläui, Mathias; Schütz, Gisela

    2015-04-01

    The dynamics of emergent magnetic quasiparticles, such as vortices, domain walls, and bubbles are studied by scanning transmission x-ray microscopy (STXM), combining magnetic (XMCD) contrast with about 25 nm lateral resolution as well as 70 ps time resolution. Essential progress in the understanding of magnetic vortex dynamics is achieved by vortex core reversal observed by sub-GHz excitation of the vortex gyromode, either by ac magnetic fields or spin transfer torque. The basic switching scheme for this vortex core reversal is the generation of a vortex-antivortex pair. Much faster vortex core reversal is obtained by exciting azimuthal spin wave modes with (multi-GHz) rotating magnetic fields or orthogonal monopolar field pulses in x and y direction, down to 45 ps in duration. In that way unidirectional vortex core reversal to the vortex core 'down' or 'up' state only can be achieved with switching times well below 100 ps. Coupled modes of interacting vortices mimic crystal properties. The individual vortex oscillators determine the properties of the ensemble, where the gyrotropic mode represents the fundamental excitation. By self-organized state formation we investigate distinct vortex core polarization configurations and understand these eigenmodes in an extended Thiele model. Analogies with photonic crystals are drawn. Oersted fields and spin-polarized currents are used to excite the dynamics of domain walls and magnetic bubbles. From the measured phase and amplitude of the displacement of domain walls we deduce the size of the non-adiabatic spin-transfer torque. For sensing applications, the displacement of domain walls is studied and a direct correlation between domain wall velocity and spin structure is found. Finally the synchronous displacement of multiple domain walls using perpendicular field pulses is demonstrated as a possible paradigm shift for magnetic memory and logic applications.

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

    SciTech Connect

    Haelg, B.; Furrer, A.

    1984-03-20

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

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

    NASA Astrophysics Data System (ADS)

    Shiota, Yoichi

    2013-03-01

    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, magnetostriction together with piezo-electric materials, multiferroic materials, and ultrathin ferromagnetic layer. 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. On the other hand, an application of rf-voltage causes an excitation of a uniform spin-wave. 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. This research was supported by CREST-JST, G-COE program, and JSPS for the fellowship. Collaborators include T. Nozaki, S. Miwa, F. Bonell, N. Mizuochi, T. Shinjo, and Y. Suzuki.

  11. Rapid 3D dynamic arterial spin labeling with a sparse model-based image reconstruction.

    PubMed

    Zhao, Li; Fielden, Samuel W; Feng, Xue; Wintermark, Max; Mugler, John P; Meyer, Craig H

    2015-11-01

    Dynamic arterial spin labeling (ASL) MRI measures the perfusion bolus at multiple observation times and yields accurate estimates of cerebral blood flow in the presence of variations in arterial transit time. ASL has intrinsically low signal-to-noise ratio (SNR) and is sensitive to motion, so that extensive signal averaging is typically required, leading to long scan times for dynamic ASL. The goal of this study was to develop an accelerated dynamic ASL method with improved SNR and robustness to motion using a model-based image reconstruction that exploits the inherent sparsity of dynamic ASL data. The first component of this method is a single-shot 3D turbo spin echo spiral pulse sequence accelerated using a combination of parallel imaging and compressed sensing. This pulse sequence was then incorporated into a dynamic pseudo continuous ASL acquisition acquired at multiple observation times, and the resulting images were jointly reconstructed enforcing a model of potential perfusion time courses. Performance of the technique was verified using a numerical phantom and it was validated on normal volunteers on a 3-Tesla scanner. In simulation, a spatial sparsity constraint improved SNR and reduced estimation errors. Combined with a model-based sparsity constraint, the proposed method further improved SNR, reduced estimation error and suppressed motion artifacts. Experimentally, the proposed method resulted in significant improvements, with scan times as short as 20s per time point. These results suggest that the model-based image reconstruction enables rapid dynamic ASL with improved accuracy and robustness. PMID:26169322

  12. Dynamic Nuclear Spin Polarization in the Resonant Laser Excitation of an InGaAs Quantum Dot

    E-print Network

    Ludwig-Maximilians-Universität, München

    ] and negatively charged QDs [10­12]. A particularly striking feature of resonant DNSP using the higher energy different energy level diagrams: for both charge states, the locking of the coupled electron- nuclear spinDynamic Nuclear Spin Polarization in the Resonant Laser Excitation of an InGaAs Quantum Dot A. Ho

  13. Electric Field Tunability of Nuclear and Electronic Spin Dynamics due to the Hyperfine Interaction in Semiconductor Nanostructures

    E-print Network

    Flatte, Michael E.

    Electric Field Tunability of Nuclear and Electronic Spin Dynamics due to the Hyperfine Interaction) of the electronic and nuclear spin coherence times to small electric fields is predicted for both uniformly devices are based on precise control of the electronic charge distribution using electric fields, ignoring

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

    SciTech Connect

    Goryca, Mateusz; Kossacki, Piotr; Golnik, Andrzej; Kazimierczuk, Tomasz; Nawrocki, Michal; Wojnar, Piotr

    2010-01-04

    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.

  15. Quantum chaos of a particle in a square well: Competing length scales and dynamical localization

    NASA Astrophysics Data System (ADS)

    Sankaranarayanan, R.; Lakshminarayan, A.; Sheorey, V. B.

    2001-10-01

    The classical and quantum dynamics of a particle trapped in a one-dimensional infinite square well with a time-periodic pulsed field is investigated. This is a two-parameter non-KAM (Kolmogorov-Arnold-Moser) generalization of the kicked rotor, which can be seen as the standard map of particles subjected to both smooth and hard potentials. The virtue of the generalization lies in the introduction of an extra parameter R, which is the ratio of two length scales, namely, the well width and the field wavelength. If R is a noninteger the dynamics is discontinuous and non-KAM. We have explored the role of R in controlling the localization properties of the eigenstates. In particular, the connection between classical diffusion and localization is found to generalize reasonably well. In unbounded chaotic systems such as these, while the nearest neighbor spacing distribution of the eigenvalues is less sensitive to the nature of the classical dynamics, the distribution of participation ratios of the eigenstates proves to be a sensitive measure; in the chaotic regimes the latter is log-normal. We find that the tails of the well converged localized states are exponentially localized despite the discontinuous dynamics while the bulk part shows fluctuations that tend to be closer to random matrix theory predictions. Time evolving states show considerable R dependence, and tuning R to enhance classical diffusion can lead to significantly larger quantum diffusion for the same field strengths, an effect that is potentially observable in present day experiments.

  16. Relativistic quantum dynamics of neutral particle in external electric fields: An approach on effects of spin

    E-print Network

    Azevedo, F S; Castro, Luis B; Filgueiras, Cleverson; Cogollo, D

    2015-01-01

    The planar quantum dynamics of spin-1/2 neutral particle interacting with electrical fields is considered. A set of first order differential equations are obtained directly from the planar Dirac equation with nonminimum coupling. New solutions of this system, in particular, for the Aharonov-Casher effect, are found and discussed in detail. Pauli equation is also obtained by studying the motion of the particle when it describes a circular path of constant radius. We also analyze the planar dynamics in the full space, including the $r=0$ region. The self-adjoint extension method is used to obtain the energy levels and wave functions of the particle for two particular values for the self-adjoint extension parameter. The energy levels obtained are analogous to the Landau levels and explicitly depend on the spin projection parameter.

  17. Relativistic quantum dynamics of neutral particle in external electric fields: An approach on effects of spin

    E-print Network

    F. S. Azevedo; Edilberto O. Silva; Luis B. Castro; Cleverson Filgueiras; D. Cogollo

    2015-06-11

    The planar quantum dynamics of spin-1/2 neutral particle interacting with electrical fields is considered. A set of first order differential equations are obtained directly from the planar Dirac equation with nonminimum coupling. New solutions of this system, in particular, for the Aharonov-Casher effect, are found and discussed in detail. Pauli equation is also obtained by studying the motion of the particle when it describes a circular path of constant radius. We also analyze the planar dynamics in the full space, including the $r=0$ region. The self-adjoint extension method is used to obtain the energy levels and wave functions of the particle for two particular values for the self-adjoint extension parameter. The energy levels obtained are analogous to the Landau levels and explicitly depend on the spin projection parameter.

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

    SciTech Connect

    Wang Hanquan

    2011-07-01

    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.

  19. Why Dynamic Simulations are Needed to Calculate Thermally Averaged Spin Hamiltonians

    NASA Astrophysics Data System (ADS)

    Weitekamp, Daniel P.; Mueller, Leonard J.

    1998-03-01

    The spin Hamiltonian needed to describe nearly all magnetic resonance experiments is an average over rapidly relaxing spatial degrees of freedom. This has previously been taken to be a Boltzmann average of quantities calculable from the time-independent Hamiltonian describing the system. We show why this approach is conceptually flawed and describe the physics of previously unsuspected, intrinsically dynamic, contributions to the spin Hamiltonian for this ubiquitous situation. Numerical estimates indicate that these new terms are required in order to simulate nuclear magnetic resonance spectra at the resolution with which they are routinely measured. An approach is outlined in which ab initio electronic structures may be combined with a tractable semi-classical description of rovibrational relaxation to give the necessary dynamic corrections, which are described by an average Liouvillian born as the result of spatial susceptibility (ALBATROSS).

  20. Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment

    E-print Network

    Ren Yi-Chong; Fan Hong-Yi

    2015-09-03

    We propose a new approach called Ket-Bra Entangled State (KBES) Method for converting master equation into Schr\\"{o}dinger-like equation. With this method, we investigate decoherence process and entanglement dynamics induced by a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the corresponding master equation is solved concisely by KBES method; Furthermore, the effects of anisotropy, temperature, external field and initial state on concurrence dynamics is analyzed in detail for the case that initial state is Extended Wenger-Like(EWL) state. Finally we research the coherence and concurrence of the final state (namely the density operator for time tend to infinite)

  1. Structural and dynamical properties of ionic liquids: Competing influences of molecular properties

    NASA Astrophysics Data System (ADS)

    Spohr, Heidrun V.; Patey, G. N.

    2010-04-01

    Room temperature ionic liquids differ from molten salts in many ways, our work concentrates on two distinguishing features. These are large cation-anion size disparities and at least one ionic species where the center of mass and the center of charge do not coincide. In earlier work, we examined the influences of these features in isolation on simple spherical models. This paper extends this work to ionic liquid models where both features are present, and where the characteristic distance ?+-' determining the strength of the Coulombic attractions is unconstrained. We consider the interplay among these molecular features and elucidate their relative importance to the behavior of ionic liquids. Particular attention is focused on the transport properties. We find that size disparity, charge location, and ?+-' can all have large (often competing) effects. In our models, size disparity and small charge displacements lead to weakly bound, directional ion pairs, and the resulting asymmetric ion-counterion distribution gives rise to increased diffusion coefficients, consequently lower viscosity, and increased conductivity. These observations are analogous to effects reported in the literature, and we see similarities between the directional ion pairs in our models and directional cation-anion pairing through weak hydrogen bonding in room temperature ionic liquids. In our models, large charge displacements lead to strongly bound, long-lived, directional ion pairs, and in this regime the trends noted above are reversed, increased viscosities, and decreased conductivities are observed. Recently, creating more strongly hydrogen bonded, directional ion pairs has been put forward as possible means of achieving larger viscosity reductions. The trend reversal that we observe suggests that this might not work in practice.

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

    SciTech Connect

    Bermejo, F.J.; Bustinduy, I.; Gonzalez, M.A.; Chong, S.H.; Cabrillo, C.; Cox, S.F.J.

    2004-12-01

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

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

    SciTech Connect

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

    2007-06-01

    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.

  4. Discrimination of nuclear spin isomers exploiting the excited state dynamics of a quinodimethane derivative

    SciTech Connect

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

    2014-10-28

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

  5. Spin Dynamics of Kelvin's Pebbles, Jellett's Eggs, and Shiva's Lingam Stones

    NASA Astrophysics Data System (ADS)

    Brecher, Kenneth

    2015-04-01

    Study of the problem of the rise of the center of mass (COM) of spinning objects is said to have begun in the late nineteenth century. These early mathematical treatments aimed to explain the motion of the newly invented and patented ``tippe top.'' This semi-spheroidal top will invert when spun on a smooth surface while raising its COM. Because of the importance of friction in their dynamics, such non-holonomic systems are not readily amenable to analytic treatment, or of intuitive understanding. In notes written in 1844 - before the invention of the tippe top - Lord Kelvin (William Thomson) discussed the problem of the rising COM of spinning objects. He experimented with both oblate and prolate ellipsoidal pebbles, but did not publish a complete theoretical treatment of the problem. J. H. Jellett, in his 1872 book ``Theory of Friction,'' provided a partial account of the related problem of the rise of the COM for an egg-shaped (ovoid) object, making use of a new (adiabatic) invariant of the motion that he devised. Naturally occurring prolate ellipsoidal ``Lingam stones'' from the Narmada River in India exhibit similar counter-intuitive dynamical behavior. When spun around its minor axis in a horizontal plane, a Lingam stone will stand erect and spin around its major axis in a vertical position. This presentation will explore the history and some of the experimental facts and theoretical ideas about the rotational dynamics of such physical objects.

  6. Spin and valley dynamics of excitons in transition metal dichalcogenide monolayers

    NASA Astrophysics Data System (ADS)

    Glazov, M. M.; Ivchenko, E. L.; Wang, G.; Amand, T.; Marie, X.; Urbaszek, B.; Liu, B. L.

    2015-11-01

    Monolayers of transition metal dichalcogenides, namely, molybdenum and tungsten disulfides and diselenides demonstrate unusual optical properties related to the spin-valley locking effect. Particularly, excitation of monolayers by circularly polarized light selectively creates electron-hole pairs or excitons in non-equivalent valleys in momentum space, depending on the light helicity. This allows studying the inter-valley dynamics of charge carriers and Coulomb complexes by means of optical spectroscopy. Here we present a concise review of the neutral exciton fine structure and its spin and valley dynamics in monolayers of transition metal dichalcogenides. It is demonstrated that the long-range exchange interaction between an electron and a hole in the exciton is an efficient mechanism for rapid mixing between bright excitons made of electron-hole pairs in different valleys. We discuss the physical origin of the long-range exchange interaction and outline its derivation in both the electrodynamical and $\\mathbf k \\cdot \\mathbf p$ approaches. We further present a model of bright exciton spin dynamics driven by an interplay between the long-range exchange interaction and scattering. Finally, we discuss the application of the model to describe recent experimental data obtained by time-resolved photoluminescence and Kerr rotation techniques.

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

    E-print Network

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

    2009-09-22

    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.

  8. Quasi-static spin dynamics in the Van-Vleck paramagnet PrNi5

    NASA Astrophysics Data System (ADS)

    Kayzel, F.; Franse, J. J. M.; Gubbens, P. C. M.; Moolenaar, A. A.; Dalmas de Réotier, P.; Yaouanc, A.; Bonville, P.; Imbert, P.; Pari, P.

    1994-12-01

    We have recorded at ISIS zero field and longitudinal ?SR relaxation spectra on a single crystal of the Van- Vleck paramagnet PrNi 5 from room temperature down to 0.09 K. Our data clearly indicate that at low temperature the rare earth spin dynamics is quasi-static, i.e. its correlation time is larger than 10-6 s. From the ?SR methodological point of view, this work provides the first example of a ?SR study of the dynamics of an hyperfine-enhanced nuclear dipole system.

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

    SciTech Connect

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

    2006-02-27

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

  10. Energy Band and Josephson Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Yu, Zi-Fa; Xue, Ju-Kui

    2015-10-01

    We theoretically investigate the energy band structure and Josephson dynamics of a spin-orbit coupled Bose-Einstein condensate in a double-well potential. We study the energy band structure and the corresponding tunneling dynamics of the system by properly adjusting the SO coupling, Raman coupling, Zeeman field and atomic interactions. The coupled effects of SO coupling, Raman coupling, Zeeman field and atomic interactions lead to the appearance of complex energy band structure including the loop structure. Particularly, the emergence of the loop structure in energy band also depends on SO coupling, Raman coupling, Zeeman field and atomic interactions. Correspondingly, the Josephson dynamics of the system are strongly related to the energy band structure. Especially, the emergence of the loop structure results in complex tunneling dynamics, including suppression-revival transitions and self-trapping of atoms transfer between two spin states and two wells. This engineering provides a possible means for studying energy level and corresponding dynamics of two-species SO coupled BECs. Supported by the National Natural Science Foundation of China under Grant Nos. 11274255 and 11305132, by Specialized Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20136203110001, by the Natural Science Foundation of Gansu province under Grant No. 2011GS04358, and by Creation of Science and Technology of Northwest Normal University under Grant Nos. NWNU-KJCXGC-03-48, NWNU-LKQN-12-12

  11. Coupled Charge-Spin Dynamics of the Magnetoresistive Pyrochlore Tl2Mn2O7 Probed Using Ultrafast Midinfrared Spectroscopy

    NASA Astrophysics Data System (ADS)

    Prasankumar, R. P.; Okamura, H.; Imai, H.; Shimakawa, Y.; Kubo, Y.; Trugman, S. A.; Taylor, A. J.; Averitt, R. D.

    2005-12-01

    Optical-pump midinfrared probe spectroscopy is used to investigate coupled charge-spin dynamics in the magnetoresistive pyrochlore Tl2Mn2O7. We find that the temporal persistence of the photoexcited carrier density is strongly influenced by spin disorder above and below the ferromagnetic Curie temperature. Our results are consistent with a picture whereby spin disorder leads to spatial segregation of the initially excited Tl 6s-O 2p electron-hole pairs, effectively reducing the probability for recombination. This further implies that colossal magnetoresistance in these materials may be driven primarily by Mn t2g spin disorder.

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

    SciTech Connect

    Davesne, V.; Gruber, M.; Physikalisches Institut, Karlsruhe Institut of Technology, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe ; Miyamachi, T.; Da Costa, V.; Boukari, S.; Scheurer, F.; Joly, L.; Bowen, M.; Beaurepaire, E.; Ohresser, P.; Otero, E.; Choueikani, F.; Gaspar, A. B.; Real, J. A.; Wulfhekel, W.

    2013-08-21

    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.

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

    E-print Network

    Bornholdt, Stefan

    2014-01-01

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

  14. Spin dynamics of Li Doped La[sub 2]CuO[sub 4]with a disordered ground state

    SciTech Connect

    Chen, Y.; Bao, W.; Sarrao, John L.,; Park, S.-H. L.; Lorenzo, J. E.

    2002-01-01

    Only 3% hole doping by Li is sufficient to suppress the long-range antiferromagnetic order in LazCu04. Spin dynamics in the disordered state was investigated by measuring the dynamic magnetic structure factor, S(q,w), as a function of temperature, using cold neutron spectroscopy, on La2Cuo.96Lio.0404a nd La{approx}Cuo.gLio.104s ingle crystals. The details of observed spin dynamics of the quantum disordered spin liquid were compared to the theoretical results of the nonlinear u model for a two dimensional Heisenberg antiferromagnet, which predicts a phase crossover upon cooling from a quantum critical regime of a quantum spin liquid to its quantum paramagnetic regime.

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

    SciTech Connect

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

    2011-12-15

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2003-08-01

    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.

  17. Nanocluster building blocks of artificial square spin ice: Stray-field studies of thermal dynamics

    SciTech Connect

    Pohlit, Merlin Porrati, Fabrizio; Huth, Michael; Müller, Jens

    2015-05-07

    We present measurements of the thermal dynamics of a Co-based single building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition. We employ micro-Hall magnetometry, an ultra-sensitive tool to study the stray field emanating from magnetic nanostructures, as a new technique to access the dynamical properties during the magnetization reversal of the spin-ice nanocluster. The obtained hysteresis loop exhibits distinct steps, displaying a reduction of their “coercive field” with increasing temperature. Therefore, thermally unstable states could be repetitively prepared by relatively simple temperature and field protocols allowing one to investigate the statistics of their switching behavior within experimentally accessible timescales. For a selected switching event, we find a strong reduction of the so-prepared states' “survival time” with increasing temperature and magnetic field. Besides the possibility to control the lifetime of selected switching events at will, we find evidence for a more complex behavior caused by the special spin ice arrangement of the macrospins, i.e., that the magnetic reversal statistically follows distinct “paths” most likely driven by thermal perturbation.

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

    PubMed

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

    2014-09-01

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

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

    SciTech Connect

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

    2014-12-15

    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.

  20. Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3(NIT(C6H4OPh))]: A ?{sup +} spin relaxation study

    SciTech Connect

    Arosio, Paolo Orsini, Francesco; Corti, Maurizio; Mariani, Manuel; Bogani, Lapo; Caneschi, Andrea; Lago, Jorge; Lascialfari, Alessandro

    2015-05-07

    The spin dynamics of the molecular magnetic chain [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] were investigated by means of the Muon Spin Relaxation (?{sup +}SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac){sub 3}(NIT(C{sub 6}H{sub 4}OPh))] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H?=?5, 3500, and 16500?Oe) and by performing ?{sup +}SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H?=?3500?Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate ?{sub interm}(T), associated with the intermediate relaxing component. The experimental ?{sub interm}(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to ??=??{sub 0} exp(?/k{sub B}T), corresponding to a distribution of energy barriers ?. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state.

  1. Local spin dynamics at low temperature in the slowly relaxing molecular chain [Dy(hfac)3{NIT(C6H4OPh)}]: A ?+ spin relaxation study

    NASA Astrophysics Data System (ADS)

    Arosio, Paolo; Corti, Maurizio; Mariani, Manuel; Orsini, Francesco; Bogani, Lapo; Caneschi, Andrea; Lago, Jorge; Lascialfari, Alessandro

    2015-05-01

    The spin dynamics of the molecular magnetic chain [Dy(hfac)3{NIT(C6H4OPh)}] were investigated by means of the Muon Spin Relaxation (?+SR) technique. This system consists of a magnetic lattice of alternating Dy(III) ions and radical spins, and exhibits single-chain-magnet behavior. The magnetic properties of [Dy(hfac)3{NIT(C6H4OPh)}] have been studied by measuring the magnetization vs. temperature at different applied magnetic fields (H = 5, 3500, and 16500 Oe) and by performing ?+SR experiments vs. temperature in zero field and in a longitudinal applied magnetic field H = 3500 Oe. The muon asymmetry P(t) was fitted by the sum of three components, two stretched-exponential decays with fast and intermediate relaxation times, and a third slow exponential decay. The temperature dependence of the spin dynamics has been determined by analyzing the muon longitudinal relaxation rate ?interm(T), associated with the intermediate relaxing component. The experimental ?interm(T) data were fitted with a corrected phenomenological Bloembergen-Purcell-Pound law by using a distribution of thermally activated correlation times, which average to ? = ?0 exp(?/kBT), corresponding to a distribution of energy barriers ?. The correlation times can be associated with the spin freezing that occurs when the system condenses in the ground state.

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

    ERIC Educational Resources Information Center

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

    2013-01-01

    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…

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

    PubMed

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

    2014-11-21

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

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

    PubMed

    Rózsa, L; Udvardi, L; Szunyogh, L

    2014-05-28

    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

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

    NASA Astrophysics Data System (ADS)

    Pouyandeh, Sima; Shahbazi, Farhad; Bayat, Abolfazl

    2014-07-01

    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.

  6. Poisson bracket approach to the dynamics of nematic liquid crystals: The role of spin angular momentum

    NASA Astrophysics Data System (ADS)

    Stark, H.; Lubensky, T. C.

    2005-11-01

    Nematic liquid crystals are well modeled as a fluid of rigid rods. Starting from this model, we use a Poisson-bracket formalism to derive the equations governing the dynamics of nematic liquid crystals. We treat the spin angular momentum density arising from the rotation of constituent molecules about their centers of mass as an independent field and derive equations for it, the mass density, the momentum density, and the nematic director. Our equations reduce to the original Leslie-Ericksen equations, including the inertial director term that is neglected in the hydrodynamic limit, only when the moment of inertia for angular momentum parallel to the director vanishes and when a dissipative coefficient favoring locking of the angular frequencies of director rotation and spin angular momentum diverges. Our equations reduce to the equations of nematohydrodynamics in the hydrodynamic limit but with dissipative coefficients that depend on the coefficient that must diverge to produce the Leslie-Ericksen equations.

  7. Vortex-antivortex dynamics driven by spin-torque in a nanocontact

    NASA Astrophysics Data System (ADS)

    Zaspel, C. E.; Kireev, V. E.

    2015-10-01

    A spin-polarized current in a nanocontact has been shown to induce the formation of a magnetic vortex at the nanocontact by the Oersted field, and spin-torque drives the vortex core in an elliptical orbit about the nanocontact. For the case of an external in-plane magnetic field in an extended free layer, the magnetization will be uniform far from the nanocontact, implying that vortex formation must be accompanied by the formation of an antivortex. Using the Thiele approach to describe the vortex-antivortex dynamics it is shown that the frequency of gyrotropic motion of the vortex is a function of the nanocontact current which is linear for large vortex-antivortex separations and it becomes nonlinear as the separation is decreased. The equilibrium vortex -antivortex separation can be controlled by the nanocontact current as well as the external magnetic field.

  8. Spin-Polarized Localized Exciton Photoluminescence Dynamics in GaInNAs Quantum Wells

    NASA Astrophysics Data System (ADS)

    Lu, Shulong; Nosho, Hidetaka; Tackeuchi, Atsushi; Bian, Lifeng; Dong, Jianrong; Niu, Zhichuan

    2009-10-01

    We have investigated spin polarization-related localized exciton photoluminescence (PL) dynamics in GaInNAs quantum wells by time-resolved PL spectroscopy. The emission energy dependence of PL polarization decay time as well as polarization-independent PL decay time suggests that the acoustic phonon scattering in the process of localized exciton transfer from the high-energy localized states to the low-energy ones dominates the PL polarization relaxation. By increasing the excitation power from 1 to 10 mW, the PL polarization decay time is changed from 0.17 to more than 1 ns, which indicates the significant effect of the trapping of localized electrons by nonradiative recombination centers. These experimental findings indicate that the spin-related PL polarization in diluted nitride semiconductors can be manipulated through carrier scattering and recombination process.

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

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  10. DYNAMICAL SPIN SUSCEPTIBILITY IN THE TD-LDA AND QSGW APPROXIMATIONS

    SciTech Connect

    SCHILFGAARDE, MARK VAN; KOTANI, TAKAO

    2012-10-15

    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.

  11. Low-Energy Charge and Spin Dynamics in Quantum Confined Systems

    NASA Astrophysics Data System (ADS)

    Rice, William D.

    Condensed matter systems exhibit a variety of dynamical phenomena at low energy scales, from gigahertz (GHz) to terahertz (THz) frequencies in particular, arising from complex interplay between charge, spin, and lattice. A large number of collective and elementary excitations in solids occur in this frequency range, which are further modified and enriched by scattering, interactions, and disorder. Recent advancements in spectroscopic methods for probing low-energy dynamics allow us to investigate novel aspects of charge and spin dynamics in solids. In this dissertation work, we used direct current (DC) conductivity, GHz, THz, and mid-infrared (MIR) techniques to provide significant new insights into interaction and disorder effects in low-dimensional systems. Specifically, we have studied temperature-dependent magnetoresistance (MR) and electron spin resonance (ESR) in single-wall carbon nanotubes (SWCNTs), intra-exciton scattering in InGaAs quantum wells, and high-field MIR-induced band gaps in graphene. Temperature-dependent resistance and MR were measured in an ensemble of SWCNTs from 0.3 to 350 K. The resistance temperature behavior followed a 3D variable range hopping (VRH) behavior from 0.3 to ˜100 K. A positive MR was observed at temperatures above 25 K and could be fit with a spin-dependent VRH model; negative MR was seen at low temperatures. In the GHz regime, the ESR linewidth for SWCNTs was observed to narrow by as much as 50% as the temperature was increased from 3 to 300 K, a phenomenon known as motional narrowing, suggesting that we are detecting the ESR of hopping spins. From the linewidth change versus temperature, we find the hopping frequency to be 285 GHz. For excitons in InGaAs quantum wells, we demonstrate the manipulation of intra-excitonic populations using intense, narrow-band THz pulses. The THz radiation temporarily quenches the 1s emission, which is then followed by an enhancement and subsequent decay of 2s emission. After the quenching, the 1s emission recovers and then eventually becomes enhanced, a demonstration of energy storage in intra-exciton states known as excitonic shelving. We show that the diffusive Coulomb scattering between the 2 p and 2s states produces a symmetry breaking, leading to a THz-field-induced 1s-to-2s exciton population transfer.

  12. Influence of temperature on coherent dynamics of a two-level system immersed in a dissipative spin bath

    NASA Astrophysics Data System (ADS)

    Lü, Zhiguo; Zheng, Hang

    2009-10-01

    The quantum dynamics of a two-level system coupled to an Ohmic spin bath is studied by means of the perturbation approach based on a unitary transformation. A scattering function ?k is introduced in the transformation to take into account quantum fluctuations. By the master equation within the Born approximation, nonequilibrium dynamics quantities are calculated. The method works well for the coupling constant 0spin-spin-bath model display identical behavior as the well-known spin-boson-bath model; (ii) in comparison with the known results of spin-boson-bath model, the coherence-incoherence transition point, which occurs at ?c=1/2[1+??/?c], is temperature independent; and (iii) the nonequilibrium correlation function P(t )=??z(t)?, evolves without temperature dependence, while ??x(t)? depends on temperature. Both P(t ) and ??x(t)? not only satisfy their initial conditions, respectively, and also have correct long time limits. Besides, the Shiba relation and sum rule are exactly satisfied in the coherent regime for this method. Our results show that increasing temperature does not help the system suppress decoherence in the coherent regime, i.e., finite temperature does not favor the coherent dynamics in this regime. Thus, the finite-temperature dynamics induced by two kinds of baths (spin-bath and boson-bath) exhibit distinctly different physics.

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

    SciTech Connect

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

    2008-12-05

    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.

  14. New tools for far-from-equilibrium quantum spin dynamics inspired by ultracold molecule experiments

    NASA Astrophysics Data System (ADS)

    Hazzard, Kaden; Foss-Feig, Michael; Gadway, Bryce; Yan, Bo; Moses, Steven; Covey, Jacob; Jin, Deborah; Ye, Jun; Rey, Ana Maria

    2014-03-01

    We describe new numerical techniques based on a type of cluster expansion and analytic solutions for treating far-from-equilibrium dynamics in quantum many-body spin models. Specifically, we apply them to dynamics following a quantum quench that is routinely implemented in experiments with Ramsey spectroscopy. For many observables, these new approaches converge extremely rapidly compared to existing techniques, which are unable to converge using any feasible computational resources. We describe the theoretical methods and our understanding of their superior convergence. These calculations are motivated by recent experiments with ultracold molecules in optical lattices [ Yan et al., Nature 501, 521 (2013) ] and trapped ions [ Britton et al., Nature 484, 489 (2012) ], which are described by spin models with long-range interactions in appropriate limits. We will compare theoretical predictions with experimental observations in these systems. We expect the novel methods developed to describe ultracold matter to also have applications to solid state systems, for example in the dynamics of nitrogen-vacancy centers in diamond or energy transfer in complicated molecules.

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

    SciTech Connect

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

    2011-03-15

    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.

  16. Nonadiabatic dynamics of superfluid spin-orbit-coupled degenerate Fermi gas

    NASA Astrophysics Data System (ADS)

    Dzero, Maxim; Kirmani, Ammar A.; Yuzbashyan, Emil A.

    2015-11-01

    We study a problem of nonadiabatic superfluid dynamics of spin-orbit-coupled neutral fermions in two spatial dimensions. We focus on the two cases when the out-of-equilibrium conditions are initiated by either a sudden change of the pairing strength or the population imbalance. For the case of a zero-population imbalance and within the mean-field approximation, the nonadiabatic evolution of the pairing amplitude in a collisionless regime can be found exactly by employing the method of Lax vector construction. Our main finding is that the presence of the spin-orbit coupling significantly reduces the region in the parameter space where a steady state with periodically oscillating pairing amplitude is realized. For the collisionless dynamics initiated by a sudden disappearance of the population imbalance, we obtain an exact expression for the steady-state pairing amplitude. In the general case of quenches to a state with finite population imbalance, we show that there is a region in the steady-state phase diagram where at long times the pairing amplitude dynamics is governed by the reduced number of the equations of motion in full analogy with the exactly integrable case.

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

    SciTech Connect

    Boulle, O. Buda-Prejbeanu, L. D.; Jué, E.; Miron, I. M.; Gaudin, G.

    2014-05-07

    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.

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

    PubMed

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

    2006-05-12

    We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counterpropagating coherent states is ejected from the center of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the quantum kicked rotor. From this we can analyze the entanglement production and interpret the ejected coherent states as a manifestation of the so-called "accelerator modes" of a classically chaotic system. PMID:16712391

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

    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.

  20. Absence of Magnetic Order and Persistent Spin Dynamics in Tb2Ge2O7

    NASA Astrophysics Data System (ADS)

    Hallas, Alannah; Arevalo-Lopez, Angel; Wilson, Murray; Liu, Lian; Attfield, J. Paul; Uemura, Yasutomo; Wiebe, Chris; Luke, Graeme

    2015-03-01

    The terbium pyrochlores exhibit many unique magnetic properties, which has generated significant interest in this family of frustrated materials. A candidate spin liquid, Tb2Ti2O7 fails to magnetically order, despite strong antiferromagnetic correlations. The application of external pressure has been found to produce partial antiferromagnetic order in Tb2Ti2O7. Recently, we synthesized a new member of this family, Tb2Ge2O7. Due to the large ionic radii decrease from titanium to germanium, Tb2Ge2O7 can be considered a chemical pressure analog of Tb2Ti2O7. However, neutron scattering measurements revealed an absence of magnetic order in Tb2Ge2O7 down to 20 mK and dominant ferromagnetic correlations. Now, we have investigated the low temperature magnetism of Tb2Ge2O7 with muon spin rotation. Our zero field ?SR measurements confirm an absence of static order in Tb2Ge2O7. We find a sharp increase in magnetic correlations below 10 K and persistent spin dynamics down to 25 mK. Our longitudinal field ?SR measurements on Tb2Ge2O7 at 25 mK are consistent with a system of fluctuating moments, with a fluctuation rate of 11 MHz. This fluctuation rate is nearly temperature independent below 2.5 K.

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

    NASA Astrophysics Data System (ADS)

    Laraoui, Abdelghani; Meriles, Carlos

    2012-02-01

    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).

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

    SciTech Connect

    Seung-Ho-Baek

    2004-12-19

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

  3. Statistical Mechanics of a Spin-Boson System ---The Dynamic Compensation Theorem and the Exact Partition Function---

    NASA Astrophysics Data System (ADS)

    Tsuzuki, T.

    1990-07-01

    We first extend the dynamic compensation theorem of infrared divergence for the case of finite temperatures and then obtain the exact partition function of the spin-boson system, which is different from the previous ones. We find that there exists no thermodynamic equivalence between the spin-boson system and the Kondo system in general and that such equivalence is restricted to the case of high temperature limit.

  4. Vortex Dynamics in a Spin-Orbit-Coupled Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Fetter, Alexander L.

    2015-07-01

    Vortices in a one-component dilute atomic ultracold Bose-Einstein condensate (BEC) usually arise as a response to externally driven rotation. Apart from a few special situations, these vortices are singly quantized with unit circulation (Fetter, Rev Mod Phys 81, 647-691, 2009). Recently, the NIST group has constructed a two-component BEC with a spin-orbit-coupled Hamiltonian involving Pauli matrices (Spielman, Phys Rev A 79, 063613, 2009; Y.-J. Lin et al., Nature 462, 628-632, 2009; Y.-J. Lin et al., Nature 471, 83-87, 2011), and I here study the dynamics of a two-component vortex in such a spin-orbit-coupled condensate. These spin-orbit-coupled BECs use an applied magnetic field to split the hyperfine levels. Hence, they rely on a focused laser beam to trap the atoms. In addition, two Raman laser beams create an effective (or synthetic) gauge potential. The resulting spin-orbit Hamiltonian is discussed in some detail. The various laser beams are fixed in the laboratory, so that it is not feasible to nucleate a vortex by an applied rotation that would need to rotate all the laser beams and the magnetic field. In a one-component BEC, a vortex can also be created by a thermal quench, starting from the normal state and suddenly cooling deep into the condensed state (Freilich et al., Science 329, 1182-1185, 2010). I propose that a similar method would work for a vortex in a spin-orbit-coupled BEC. Such a vortex has two components, and each has its own circulation quantum number (typically ). If both components have the same circulation, I find that the composite vortex should execute uniform precession, like that observed in a single-component BEC (Freilich et al., Science 329, 1182-1185, 2010). In contrast, if one component has unit circulation and the other has zero circulation, then some fraction of the dynamical vortex trajectories should eventually leave the condensate, providing clear experimental evidence for this unusual vortex structure. In the context of exciton-polariton condensates, such a vortex is known as a "half-quantum vortex" (Rubo, Phys Rev Lett 99, 106401, 2007; Lagoudakis et al., Science 326, 974-976, 2009).

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

    E-print Network

    Nicolas Rambaux; Eric Bois

    2003-07-17

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

  6. Nuclear depolarization and absolute sensitivity in magic-angle spinning cross effect dynamic nuclear polarization.

    PubMed

    Mentink-Vigier, Frédéric; Paul, Subhradip; Lee, Daniel; Feintuch, Akiva; Hediger, Sabine; Vega, Shimon; De Paëpe, Gaël

    2015-09-14

    Over the last two decades solid state Nuclear Magnetic Resonance has witnessed a breakthrough in increasing the nuclear polarization, and thus experimental sensitivity, with the advent of Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). To enhance the nuclear polarization of protons, exogenous nitroxide biradicals such as TOTAPOL or AMUPOL are routinely used. Their efficiency is usually assessed as the ratio between the NMR signal intensity in the presence and the absence of microwave irradiation ?on/off. While TOTAPOL delivers an enhancement ?on/off of about 60 on a model sample, the more recent AMUPOL is more efficient: >200 at 100 K. Such a comparison is valid as long as the signal measured in the absence of microwaves is merely the Boltzmann polarization and is not affected by the spinning of the sample. However, recent MAS-DNP studies at 25 K by Thurber and Tycko (2014) have demonstrated that the presence of nitroxide biradicals combined with sample spinning can lead to a depolarized nuclear state, below the Boltzmann polarization. In this work we demonstrate that TOTAPOL and AMUPOL both lead to observable depolarization at ?110 K, and that the magnitude of this depolarization is radical dependent. Compared to the static sample, TOTAPOL and AMUPOL lead, respectively, to nuclear polarization losses of up to 20% and 60% at a 10 kHz MAS frequency, while Trityl OX63 does not depolarize at all. This experimental work is analyzed using a theoretical model that explains how the depolarization process works under MAS and gives new insights into the DNP mechanism and into the spin parameters, which are relevant for the efficiency of a biradical. In light of these results, the outstanding performance of AMUPOL must be revised and we propose a new method to assess the polarization gain for future radicals. PMID:26235749

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

    SciTech Connect

    Wu Ning; Duan Liwei; Zhao Yang; Li Xin

    2013-02-28

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

  8. Sensing Polymer Chain Dynamics through Ring Topology: A Neutron Spin Echo Study

    NASA Astrophysics Data System (ADS)

    Gooßen, Sebastian; Krutyeva, Margarita; Sharp, Melissa; Feoktystov, Artem; Allgaier, Jürgen; Pyckhout-Hintzen, Wim; Wischnewski, Andreas; Richter, Dieter

    2015-10-01

    Using neutron spin echo spectroscopy, we show that the segmental dynamics of polymer rings immersed in linear chains is completely controlled by the host. This transforms rings into ideal probes for studying the entanglement dynamics of the embedding matrix. As a consequence of the unique ring topology, in long chain matrices the entanglement spacing is directly revealed, unaffected by local reptation of the host molecules beyond this distance. In shorter entangled matrices, where in the time frame of the experiment secondary effects such as contour length fluctuations or constraint release could play a role, the ring motion reveals that the contour length fluctuation is weaker than assumed in state-of-the-art rheology and that the constraint release is negligible. We expect that rings, as topological probes, will also grant direct access to molecular aspects of polymer motion which have been inaccessible until now within chains adhering to more complex architectures.

  9. Complex Langevin dynamics in the SU(3) spin model at nonzero chemical potential revisited

    E-print Network

    Gert Aarts; Frank A. James

    2012-01-25

    The three-dimensional SU(3) spin model is an effective Polyakov loop model for QCD at nonzero temperature and density. It suffers from a sign problem at nonzero chemical potential. We revisit this model using complex Langevin dynamics and assess in particular the justification of this approach, using analyticity at small mu^2 and the criteria for correctness developed recently. Finite-stepsize effects are discussed in some detail and a higher-order algorithm is employed to eliminate leading stepsize corrections. Our results strongly indicate that complex Langevin dynamics is reliable in this theory in both phases, including the critical region. This is in sharp contrast to the case of the XY model, where correct results were obtained in only part of the phase diagram.

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

    PubMed

    Wu, Jianda; Kormos, Márton; Si, Qimiao

    2014-12-12

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

    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).

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

    NASA Technical Reports Server (NTRS)

    Spain, C. V.

    1987-01-01

    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.

  13. Longitudinal and transverse spin dynamics of donor-bound electrons in fluorine-doped ZnSe: Spin inertia versus Hanle effect

    NASA Astrophysics Data System (ADS)

    Heisterkamp, F.; Zhukov, E. A.; Greilich, A.; Yakovlev, D. R.; Korenev, V. L.; Pawlis, A.; Bayer, M.

    2015-06-01

    The spin dynamics of strongly localized donor-bound electrons in fluorine-doped ZnSe epilayers is studied using pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time T1 in a wide range of magnetic fields, temperatures, and pump densities. The T1 time of the donor-bound electron spin of about 1.6 ? s remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range 1.8-45 K. These findings impose severe restrictions on possible spin relaxation mechanisms. In our opinion they allow us to rule out scattering between free and donor-bound electrons, jumping of electrons between different donor centers, scattering between phonons and donor-bound electrons, and with less certainty charge fluctuations in the environment of the donors caused by the 1.5 ps pulsed laser excitation.

  14. First-Principles Approach to Noncollinear Magnetism: Towards Spin Dynamics S. Sharma,1,2,5,* J. K. Dewhurst,2,3

    E-print Network

    Gross, E.K.U.

    of noncollinear magnetism in the framework of spin-density functional theory is presented for the exact exchange description of spin dynamics. We also show that the magnetic moments of solids Fe, Co, and Ni are well frustrated solids ( -Fe, spin glasses), and all magnets at finite temperatures. Crucial for practical

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

    E-print Network

    Yevgeny Binder; Gordon P. Ramsey; Dennis Sivers

    2011-07-26

    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.

  16. Quantum dynamics of a particle with a spin-dependent velocity

    NASA Astrophysics Data System (ADS)

    Aslangul, Claude

    2005-01-01

    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 linearization 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 Jz 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 scattering rate is small, to a unimodal standing but flattening distribution in the opposite case.

  17. Singularities of the dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field.

    PubMed

    Carmelo, J M P; Sacramento, P D; Machado, J D P; Campbell, D K

    2015-10-14

    We study the longitudinal and transverse spin dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. While the static properties of the model can be studied within a Fermi-liquid like description in terms of pseudoparticles, our derivation of the dynamical properties relies on the introduction of a form of the 'pseudofermion dynamical theory' (PDT) of the 1D Hubbard model suitably modified for the spin-only XXX chain and other models with two pseudoparticle Fermi points. Specifically, we derive the exact momentum and spin-density dependences of the exponents ?(?)(k) controlling the singularities for both the longitudinal (? = l) and transverse (? = t) dynamical structure factors for the whole momentum range k ? ]0,?[, in the thermodynamic limit. This requires the numerical solution of the integral equations that define the phase shifts in these exponents expressions. We discuss the relation to neutron scattering and suggest new experiments on spin-chain compounds using a carefully oriented crystal to test our predictions. PMID:26403307

  18. Singularities of the dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field

    NASA Astrophysics Data System (ADS)

    Carmelo, J. M. P.; Sacramento, P. D.; Machado, J. D. P.; Campbell, D. K.

    2015-10-01

    We study the longitudinal and transverse spin dynamical structure factors of the spin-1/2 XXX chain at finite magnetic field h, focusing in particular on the singularities at excitation energies in the vicinity of the lower thresholds. While the static properties of the model can be studied within a Fermi-liquid like description in terms of pseudoparticles, our derivation of the dynamical properties relies on the introduction of a form of the ‘pseudofermion dynamical theory’ (PDT) of the 1D Hubbard model suitably modified for the spin-only XXX chain and other models with two pseudoparticle Fermi points. Specifically, we derive the exact momentum and spin-density dependences of the exponents {{\\zeta}?}(k) controlling the singularities for both the longitudinal ?ft(? =l\\right) and transverse ?ft(? =t\\right) dynamical structure factors for the whole momentum range k\\in ]0,?[ , in the thermodynamic limit. This requires the numerical solution of the integral equations that define the phase shifts in these exponents expressions. We discuss the relation to neutron scattering and suggest new experiments on spin-chain compounds using a carefully oriented crystal to test our predictions.

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

    NASA Technical Reports Server (NTRS)

    Murch, Austin M.; Foster, John V.

    2007-01-01

    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.

  20. Spin-orbit relaxation and recombination dynamics in I2 ,,CO2...n and I2 ,,OCS...n cluster ions: A new type of photofragment caging reaction

    E-print Network

    Sanov, Andrei

    Spin-orbit relaxation and recombination dynamics in I2 ,,CO2...n and I2 ,,OCS...n cluster ions is observed to result in extremely fast spin-orbit relaxation. In general, we detect three reaction pathways by spin-orbit quenching leading to I I(2 P3/2) products; and 3 the I2 I I* dissociation, followed by spin-orbit

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

    NASA Astrophysics Data System (ADS)

    Xuan, Yashu

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

  2. Ground state and low-energy magnetic dynamics in the frustrated magnet CoAl2O4 as revealed by local spin probes

    NASA Astrophysics Data System (ADS)

    Iakovleva, M.; Vavilova, E.; Grafe, H.-J.; Zimmermann, S.; Alfonsov, A.; Luetkens, H.; Klauss, H.-H.; Maljuk, A.; Wurmehl, S.; Büchner, B.; Kataev, V.

    2015-04-01

    We report a combined experimental study of magnetic properties of a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4 with Co2+ electron spin resonance, 27Al nuclear magnetic resonance, and muon spin rotation/relaxation techniques. With our local probes, we show that the frustration of spin interactions and the Co/Al site disorder strongly affect the spin dynamics. The experimental results evidence inhomogeneous and slow magnetic fluctuations and the occurrence of short-range electron spin correlations far above a characteristic temperature T*=8 K at which the spin system turns into in a quasistatic state. Our data indicate that this spin order is likely short range and unconventional with spin fluctuations persistent even at T ?T* . The results of three spectroscopy techniques highlight a nontrivial role of structural disorder for the magnetism of a frustrated diamond spin lattice at the proximity to the critical point.

  3. Dynamics and ordering of lipid spin-labels along the coexistence curve of two membrane phases: an ESR study.

    PubMed

    Smith, Andrew K; Freed, Jack H

    2012-04-01

    An analysis of electron spin resonance (ESR) spectra from compositions along the liquid-ordered (L(o)) and liquid-disordered (L(d)) coexistence curve from the brain-sphingomyelin/dioleoylphosphatidylcholine/cholesterol (SPM/DOPC/Chol) model lipid system was performed to characterize the dynamic structure on a molecular level of these coexisting phases. We obtained 200 continuous-wave ESR spectra from glycerophospholipid spin-labels labeled at the 5, 7, 10, 12, 14, and 16 carbon positions of the 2nd acyl chain, a sphingomyelin spin-label labeled at the 14 carbon position of the amide-linked acyl chain, a headgroup-labeled glycerophospholipid, a headgroup-labeled sphingomyelin, and the cholesterol analogue spin-label cholestane all within multi-lamellar vesicle suspensions at room temperature. The spectra were analyzed using the MOMD (microscopic-order macroscopic-disorder) model to provide the rotational diffusion rates and order parameters which characterize the local molecular dynamics in these phases. The analysis also incorporated the known critical point and invariant points of the neighboring three-phase triangle along the coexistence curve. The variation in the molecular dynamic structures of coexisting L(o) and L(d) compositions as one moves toward the critical point is discussed. Based on these results, a molecular model of the L(o) phase is proposed incorporating the "condensing effect" of cholesterol on the phospholipid acyl chain dynamics and ordering and the “umbrella model” of the phospholipid headgroup dynamics and ordering. PMID:22586732

  4. Momentum-resolved spin dynamics of bulk and surface excited States in the topological insulator Bi(2)Se(3).

    PubMed

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

    2015-03-01

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

  5. Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions

    E-print Network

    Xu, Jun; Shen, Wen-Qing; Xia, Yin

    2015-01-01

    It is well known that non-central nuclear forces, such as the spin-orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known since only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may carry useful information about the in-medium properties of non-central nuclear interactions, besides earlier studies using the time-dependent Hartree-Fock approach to understand effects of spin-orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore dynamical effects of non-central nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focuses of these studies have been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent sing...

  6. Theoretical model of dynamic spin polarization of nuclei coupled to paramagnetic point defects in diamond and silicon carbide

    NASA Astrophysics Data System (ADS)

    Ivády, Viktor; Szász, Krisztián; Falk, Abram L.; Klimov, Paul V.; Christle, David J.; Janzén, Erik; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam

    2015-09-01

    Dynamic nuclear spin polarization (DNP) mediated by paramagnetic point defects in semiconductors is a key resource for both initializing nuclear quantum memories and producing nuclear hyperpolarization. DNP is therefore an important process in the field of quantum-information processing, sensitivity-enhanced nuclear magnetic resonance, and nuclear-spin-based spintronics. DNP based on optical pumping of point defects has been demonstrated by using the electron spin of nitrogen-vacancy (NV) center in diamond, and more recently, by using divacancy and related defect spins in hexagonal silicon carbide (SiC). Here, we describe a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization and the physics of diamond and SiC defects. Our results are in good agreement with experimental observations and provide a detailed and unified understanding. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process.

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

    PubMed

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

    2015-03-17

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

  8. Evidence for unidimensional low-energy excitations as the origin of persistent spin dynamics in geometrically frustrated magnets

    NASA Astrophysics Data System (ADS)

    Yaouanc, A.; Dalmas de Réotier, P.; Bertin, A.; Marin, C.; Lhotel, E.; Amato, A.; Baines, C.

    2015-03-01

    We report specific heat, magnetic, and muon spin relaxation measurements performed on a polycrystalline sample of the normal spinel CdHo2S4 . The rare-earth ions sit on a lattice of corner-sharing regular tetrahedra as in pyrochlore compounds. Magnetic ordering is detected at Tc?0.87 K. From spin-lattice relaxation rate measurements on both sides of Tc we uncover similar magnetic excitation modes driving the so-called persistent spin dynamics at T spin loop structures are suggested to support these excitations. The possibility of a generic mechanism for their existence is discussed.

  9. Using bio-functionalized magnetic nanoparticles and dynamic nuclear magnetic resonance to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection.

    PubMed

    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

    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

  10. 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

    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

    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

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

    SciTech Connect

    Salasnich, L.; Mazzarella, G.; Toigo, F.; Salerno, M.

    2010-02-15

    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.

  12. Interface boundary conditions for dynamic magnetization and spin wave dynamics in a ferromagnetic layer with the interface Dzyaloshinskii-Moriya interaction

    SciTech Connect

    Kostylev, M.

    2014-06-21

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

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

  14. Dynamic nuclear polarization of carbonyl and methyl 13C spins in acetate using trityl OX063

    NASA Astrophysics Data System (ADS)

    Niedbalski, Peter; Parish, Christopher; Lumata, Lloyd

    2015-03-01

    Hyperpolarization via dissolution dynamic nuclear polarization (DNP) is a physics technique that amplifies the magnetic resonance signals by several thousand-fold for biomedical NMR spectroscopy and imaging (MRI). Herein we have investigated the effect of carbon-13 isotopic location on the DNP of acetate (one of the biomolecules commonly used for hyperpolarization) at 3.35 T and 1.4 K using a narrow ESR linewidth free radical trityl OX063. We have found that the carbonyl 13C spins yielded about twice the polarization produced in methyl 13C spins. Deuteration of the methyl group, beneficial in the liquid-state, did not produce an improvement in the polarization level at cryogenic conditions. Concurrently, the solid-state nuclear relaxation of these samples correlate with the polarization levels achieved. These results suggest that the location of the 13C isotopic labeling in acetate has a direct impact on the solid-state polarization achieved and is mainly governed by the nuclear relaxation leakage factor.

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

    NASA Astrophysics Data System (ADS)

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

    2006-11-01

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

  16. Complex ordering in spin networks: Critical role of adaptation rate for dynamically evolving interactions

    NASA Astrophysics Data System (ADS)

    Pathak, Anand; Sinha, Sitabhra

    2015-09-01

    Many complex systems can be represented as networks of dynamical elements whose states evolve in response to interactions with neighboring elements, noise and external stimuli. The collective behavior of such systems can exhibit remarkable ordering phenomena such as chimera order corresponding to coexistence of ordered and disordered regions. Often, the interactions in such systems can also evolve over time responding to changes in the dynamical states of the elements. Link adaptation inspired by Hebbian learning, the dominant paradigm for neuronal plasticity, has been earlier shown to result in structural balance by removing any initial frustration in a system that arises through conflicting interactions. Here we show that the rate of the adaptive dynamics for the interactions is crucial in deciding the emergence of different ordering behavior (including chimera) and frustration in networks of Ising spins. In particular, we observe that small changes in the link adaptation rate about a critical value result in the system exhibiting radically different energy landscapes, viz., smooth landscape corresponding to balanced systems seen for fast learning, and rugged landscapes corresponding to frustrated systems seen for slow learning.

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

    PubMed

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

    2013-08-01

    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

  18. Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics

    NASA Astrophysics Data System (ADS)

    Turner, Robert M.; Jack, Robert L.; Garrahan, Juan P.

    2015-08-01

    We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ?*(T ) , which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T ) ?0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states.

  19. Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics.

    PubMed

    Turner, Robert M; Jack, Robert L; Garrahan, Juan P

    2015-08-01

    We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ?*(T), which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T)?0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states. PMID:26382352

  20. A Concept-Map Integrated Dynamic Assessment System for Improving Ecology Observation Competences in Mobile Learning Activities

    ERIC Educational Resources Information Center

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

    2012-01-01

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

  1. Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth

    PubMed Central

    Craco, Luis; Leoni, Stefano

    2015-01-01

    Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA?+?DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals. PMID:26358556

  2. Theme: Coping with Competencies.

    ERIC Educational Resources Information Center

    Brown, Daniel; And Others

    1989-01-01

    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)

  3. Vortex-induced dynamic loads on a non-spinning volleyball

    NASA Astrophysics Data System (ADS)

    Qing-ding, Wei; Rong-sheng, Lin; Zhi-jie, Liu

    1988-09-01

    An experiment on vortex-induced dynamic loads on a non-spinning Volleyball was conducted in a wind tunnel. The flow past the Volleyball was visualized, and the aerodynamic load was measured by use of a strain gauge balance. The separation on the Volleyball was measured with hot-film. The experimental results suggest that under the action of an unstable tail vortex system the separation region is changeable, and that the fluctuation of drag and lateral forces is the same order of magnitude as the mean drag, no matter whether the seam of the Volleyball is symmetric or asymmetric, with regard to the flow. Based on the experimental data a numerical simulation of Volleyball swerve motion was made.

  4. Characterization of heteronuclear decoupling through proton spin dynamics in solid-state nuclear magnetic resonance spectroscopy

    NASA Astrophysics Data System (ADS)

    De Paëpe, Gaël; Eléna, Bénédicte; Emsley, Lyndon

    2004-08-01

    The work presented here aims at understanding the performance of phase modulated heteronuclear decoupling sequences such as Cosine Modulation or Two Pulse Phase Modulation. To that end we provide an analytical description of the intrinsic behavior of Cosine Modulation decoupling with respect to radio-frequency-inhomogeneity and the proton-proton dipolar coupling network. We discover through a Modulation Frame average Hamiltonian analysis that best decoupling is obtained under conditions where the heteronuclear interactions are removed but notably where homonuclear couplings are recoupled at a homonuclear Rotary Resonance (HORROR) condition in the Modulation Frame. These conclusions are supported by extensive experimental investigations, and notably through the introduction of proton nutation experiments to characterize spin dynamics in solids under decoupling conditions. The theoretical framework presented in this paper allows the prediction of the optimum parameters for a given set of experimental conditions.

  5. Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

    SciTech Connect

    Fernández-Pacheco, A. Mansell, R.; Petit, D.; Lee, J. H.; Cowburn, R. P.; Ummelen, F. C.; Swagten, H. J. M.

    2014-09-01

    We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.

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

    SciTech Connect

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

    2014-09-21

    The magnetization dynamics of disordered Fe?.?(Pd{sub 1–x}Pt{sub x})?.? alloy films was studied by time-resolved magneto-optical Kerr effect and ferromagnetic resonance. The intrinsic Gilbert damping parameter ?? and the resonance linewidth change linearly with the Pt atomic concentration. In particular, the induced in-plane uniaxial anisotropy constant K{sub U} 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.

  7. Site-directed spin labeling studies on nucleic acid structure and dynamics

    PubMed Central

    Sowa, Glenna Z.; Qin, Peter Z.

    2009-01-01

    Site-directed spin labeling (SDSL) uses electron paramagnetic resonance (EPR) spectroscopy to monitor the behavior of a stable nitroxide radical attached at specific locations within a macromolecule such as protein, DNA, or RNA. Parameters obtained from EPR measurements, such as internitroxide distances and descriptions of the rotational motion of a nitroxide, provide unique information on features near the labeling site. With recent advances in solid-phase synthesis of nucleic acids and developments in EPR methodologies, particularly pulsed EPR technologies, SDSL has been increasingly used to study the structure and dynamics of DNA and RNA at the level of the individual nucleotides. This chapter summarizes the current SDSL studies on nucleic acids, with discussions focusing on literature from the last decade. PMID:18929141

  8. Microsecond Rotational Dynamics of Spin-Labeled Myosin Regulatory Light Chain Induced by Relaxation and Contraction of Scallop Muscle

    E-print Network

    Thomas, David D.

    primarily on their functional roles in molluscan muscle. Crystal structures of chicken skeletal S1 (11 and Contraction of Scallop Muscle Osha Roopnarine, Andrew G. Szent-Gyo¨rgyi,§ and David D. Thomas*, Department the rotational dynamics of spin-labeled regulatory light chain (RLC) in scallop (Placopecten magellanicus) muscle

  9. Novel phase-space Monte-Carlo method for quench dynamics in 1D and 2D spin models

    NASA Astrophysics Data System (ADS)

    Pikovski, Alexander; Schachenmayer, Johannes; Rey, Ana Maria

    2015-05-01

    An important outstanding problem is the effcient numerical computation of quench dynamics in large spin systems. We propose a semiclassical method to study many-body spin dynamics in generic spin lattice models. The method, named DTWA, is based on a novel type of discrete Monte-Carlo sampling in phase-space. We demonstare the power of the technique by comparisons with analytical and numerically exact calculations. It is shown that DTWA captures the dynamics of one- and two-point correlations 1D systems. We also use DTWA to study the dynamics of correlations in 2D systems with many spins and different types of long-range couplings, in regimes where other numerical methods are generally unreliable. Computing spatial and time-dependent correlations, we find a sharp change in the speed of propagation of correlations at a critical range of interactions determined by the system dimension. The investigations are relevant for a broad range of systems including solids, atom-photon systems and ultracold gases of polar molecules, trapped ions, Rydberg, and magnetic atoms. This work has been financially supported by JILA-NSF-PFC-1125844, NSF-PIF-1211914, ARO, AFOSR, AFOSR-MURI.

  10. Nonlinear Spin Dynamics and Magnetic Field Distortion of the Superfluid HELIUM-3-B Order Parameter.

    NASA Astrophysics Data System (ADS)

    Rand, Mark Randall

    Measurements of superfluid ^3He nuclear magnetic resonance provide a probe of the microscopic structure of the order parameter. In the B-phase of superfluid ^3He, the order parameter is significantly distorted by large magnetic fields. The use of NMR frequency shifts to measure this structure requires large excitations where the spin-dynamics become nonlinear and exhibit complex behavior. Using NMR to determine quantitative aspects of the order parameter structure presents a formidable challenge both theoretically and experimentally. We have performed high resolution transverse NMR in ^3He superfluid. We also derived modifications to the Leggett equations that include gap distortion and numerically solved them. These equations describe the coupled nonlinear spin and order parameter dynamics in superfluid ^3He-B. The experiments were guided by these numerical solutions. Our experimental measurements and numerical simulations have uncovered a regime of quasi-stable response permitting us to determine experimentally, for the first time, the distortion of the energy gap over a wide range of temperature and to measure the temperature dependence of the longitudinal resonance frequency. The gap distortion measurements are consistent with previous acoustic pair-breaking results obtained for the low temperature limit and agree with predictions from the quasiclassical theory of Fishman and Sauls. At high temperatures our results approach the form expected in the Ginzburg-Landau limit. Our results for the temperature dependence of the longitudinal resonance frequency is consistent with previous experimental work. In addition, a comparison of A and B-phase experimental data below the polycritical pressure in the Ginzburg-Landau temperature regime is made through the NMR relations of Leggett, which serves as an indicator of the order-parameter structure of the A-phase. Deviation of experimental data from these relations may indicate a continuous distortion of the traditional Anderson-Brinkman-Morel model toward the so-called axi-planar state. Our results are consistent with identification of the A-phase as the axial state.

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

    NASA Astrophysics Data System (ADS)

    Cheng, Cheng

    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.

  12. Solvent effects on the dynamics of amyloidogenic insulin revealed by neutron spin echo spectroscopy.

    PubMed

    Erlkamp, Mirko; Grobelny, Sebastian; Faraone, Antonio; Czeslik, Claus; Winter, Roland

    2014-03-27

    Insulin is well known to self-associate under specific solvent conditions. At low pH values, in the presence of sodium chloride (NaCl) and at elevated temperatures, insulin readily aggregates and forms amyloid fibrils. Without NaCl, but in the presence of ethanol, the lag time of this temperature-induced aggregation is increased drastically. In this study, we have analyzed the dynamical properties of bovine insulin under these two solvent conditions by using neutron spin echo (NSE) spectroscopy. In addition, small-angle X-ray scattering (SAXS) and thioflavin T (ThT) fluorescence experiments were carried out to track the concomitant structural changes of insulin. Measurements have mainly been performed at 318 K, where amyloid fibrils are formed over 25 h, when the insulin solution contains 100 mmol L(-1) of NaCl at pD = 2.4. In contrast, no amyloid fibrils are formed during 25 h at 318 K, when the insulin solution contains ethanol with a volume fraction of 20% at pD = 2.4. Remarkably, the NSE data reveal distinct dynamic signatures of insulin depending on the chosen solvent conditions. Collective diffusion of insulin molecules can be inferred from an increased diffusion coefficient at low wave vector transfers in the nonfibrillating sample, whereas self-diffusion is observed in the other case. The SAXS data confirm these dynamic behaviors because a pronounced correlation peak is only observed under conditions of collective diffusion. The dynamic responses of insulin, as revealed here by NSE spectroscopy, are in agreement with intermolecular interaction potentials derived recently from measurements of the static structure factors of insulin and lysozyme. PMID:24611749

  13. Spins Dynamics in a Dissipative Environment: Hierarchal Equations of Motion Approach Using a Graphics Processing Unit (GPU).

    PubMed

    Tsuchimoto, Masashi; Tanimura, Yoshitaka

    2015-08-11

    A system with many energy states coupled to a harmonic oscillator bath is considered. To study quantum non-Markovian system-bath dynamics numerically rigorously and nonperturbatively, we developed a computer code for the reduced hierarchy equations of motion (HEOM) for a graphics processor unit (GPU) that can treat the system as large as 4096 energy states. The code employs a Padé spectrum decomposition (PSD) for a construction of HEOM and the exponential integrators. Dynamics of a quantum spin glass system are studied by calculating the free induction decay signal for the cases of 3 × 2 to 3 × 4 triangular lattices with antiferromagnetic interactions. We found that spins relax faster at lower temperature due to transitions through a quantum coherent state, as represented by the off-diagonal elements of the reduced density matrix, while it has been known that the spins relax slower due to suppression of thermal activation in a classical case. The decay of the spins are qualitatively similar regardless of the lattice sizes. The pathway of spin relaxation is analyzed under a sudden temperature drop condition. The Compute Unified Device Architecture (CUDA) based source code used in the present calculations is provided as Supporting Information . PMID:26574467

  14. Dynamic creation of a topologically-ordered Hamiltonian using spin-pulse control in the Heisenberg model

    PubMed Central

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

    2015-01-01

    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, which plays a crucial role in the realization of both Abelian and non-Abelian anyons. Here, we show two methods to dynamically realize the Kitaev spin Hamiltonian from the conventional Heisenberg spin Hamiltonian using pulse-control techniques based on the Baker-Campbell-Hausdorff (BCH) formula. In the first method, the Heisenberg interaction is changed into Ising interactions in the first process of the pulse sequence. In the next process of the first method, we transform them to a desirable anisotropic Kitaev spin Hamiltonian. In the second more efficient method, we show that if we carefully design two-dimensional pulses that vary depending on the qubit location, we can obtain the desired Hamiltonian in only one step of applying the BCH formula. As an example, we apply our methods to spin qubits based on quantum dots, in which the effects of both the spin-orbit interaction and the hyperfine interaction are estimated. PMID:26081899

  15. Dynamically polarized hydrogen target as a broadband, wavelength-independent thermal neutron spin polarizer

    SciTech Connect

    Zhao, Jinkui; Garamus, VM; Mueller, W; Willumeit, R

    2005-01-01

    A hydrogen-rich sample with dynamically polarized hydrogen nuclei was tested as a wavelength-independent neutron transmission spin polarizer. The experiment used a modified setup of the dynamic nuclear polarization target station at the GKSS research center. The standard solvent sample at the GKSS DNP station was used. It is 2.8 mm thick and consists of 43.4 wt% water, 54.6 wt% glycerol, and 2 wt% of EHBA-Cr(v) complex. The wavelength of the incident neutrons for the transmission experiment was {lambda} = 8.1 {angstrom} with {Delta}{lambda}/{lambda} = 10%. The polarization of neutron beam after the target sample was analyzed with a supermirror analyzer. A neutron polarization of -52% was achieved at the hydrogen polarization of -69%. Further experiments will test the feasibility of other hydrogen-rich materials, such as methane, as the polarizer. A theoretical calculation shows that a polarized methane target would allow over 95% neutron polarizations with more than 30% transmission.

  16. Ultrafast high harmonics for probing the fastest spin and charge dynamics in magnetic materials

    NASA Astrophysics Data System (ADS)

    Grychtol, Patrick

    2015-03-01

    Ultrafast light based on the high-harmonic up-conversion of femtosecond laser pulses have been successfully employed to access resonantly enhanced magnetic contrast at the Mabsorption edges of the 3d ferromagnets Fe, Co and Ni in a table-top setup. Thus, it has been possible to study element-specific dynamics in magnetic materials at femtosecond time scales in a laboratory environment, providing a wealth of opportunities for a greater fundamental understanding of correlated phenomena in solid-state matter. However, these investigations have so far been limited to linear polarized harmonics, since most techniques by which circular soft x-rays can be generated are highly inefficient reducing the photon flux to a level unfit for scientific applications. Besides presenting key findings of our ultrafast studies on charge and spin dynamics, we introduce a simple setup which allows for the efficient generation of circular harmonics bright enough for XMCD experiments. Our work thus represents a critical advance that enables element-specific imaging and spectroscopy of multiple elements simultaneously in magnetic and other chiral media with very high spatial and temporal resolution on the tabletop. In collboration with Ronny Knut, Emrah Turgut, Dmitriy Zusin, Christian Gentry, Henry Kapteyn, Margaret Murnane, JILA, University of Colorado, Boulder; Justin Shaw, Hans Nembach, Tom Silva, Electromagnetics Division, NIST, Boulder, CO; and Ofer Kfir, Avner Fleischer, Oren Cohen, Extreme Nonlinear Optics Group, Solid State Institute, Technion, Israel.

  17. Probing the spin polarization of current by soft x-ray imaging of current-induced magnetic vortex dynamics

    SciTech Connect

    Kasai, Shinya; Fischer, Peter; Im, Mi-Young; Yamada, Keisuke; Nakatani, Yoshinobu; Kobayashi, Kensuke; Kohno, Hiroshi; Ono, Teruo

    2008-12-09

    Time-resolved soft X-ray transmission microscopy is applied to image the current-induced resonant dynamics of the magnetic vortex core realized in a micron-sized Permalloy disk. The high spatial resolution better than 25 nm enables us to observe the resonant motion of the vortex core. The result also provides the spin polarization of the current to be 0.67 {+-} 0.16 for Permalloy by fitting the experimental results with an analytical model in the framework of the spin-transfer torque.

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

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

    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.

  19. Nonlinear dynamics induced in liquid crystals in the presence of the orbital and spin angular momentum of light.

    PubMed

    Piccirillo, B; Vella, A; Setaro, A; Santamato, E

    2006-06-01

    We studied the dynamical effects induced in a homeotropic nematic film when a normally incident circularly polarized light beam with an elliptical intensity profile is used. A three-dimensional dynamical model shows that, besides the spin, the orbital angular momentum of photons also plays a role in the reorientation process. Our measurements fairly reproduce the main dynamical features predicted by the model in the near threshold region. The model, however, does not work, as it is, at higher incident laser power where chaotic director rotation was reported [A. Vella, A. Setaro, B. Piccirillo, E. Santamato, Phys. Rev. E 67, 051704 (2003)]. PMID:16906886

  20. Global topology & stability and local structure & dynamics in a synthetic spin-labeled four-helix bundle protein.

    PubMed

    Gibney, B R; Johansson, J S; Rabanal, F; Skalicky, J J; Wand, A J; Dutton, P L

    1997-03-11

    A maleimide nitroxide spin-label (MAL-6) linked to a cysteine in the hydrophobic core and a coproporphyrin I (CP) appended on the N-terminus of a synthetic helix-loop-helix peptide ([alpha2]) have been used to examine the designed self-association of a four-helix bundle ([alpha2]2), focusing on the bundle topology and stability and the rotational dynamics of the spin-label. Gel-permeation chromatography demonstrated that the [alpha2] peptide and the peptide modified with a spin-label ([MAL-6-alpha2]), a coproporphyrin ([CP-alpha2]) and a coproporphyrin plus a spin-label ([CP-MAL-6-alpha2]) self-associate into four helix bundles in solution as designed. Circular dichroism (CD) spectra prove that all these peptides are highly alpha-helical, confirmed for [alpha2]2 by Fourier transform infrared (FTIR) spectroscopic analysis. Electron spin resonance (ESR) spectra of the two attached maleimide spin-labels in [MAL-6-alpha2]2 shows their effective rotational correlation time (tau(c)) is 7.3 +/- 0.5 ns, consistent with that expected for the tumbling of the four helix bundle itself, indicating the labels are immobilized. The ESR spectra were also unaltered by aqueous-phase paramagnetic ions, Ni(II), demonstrating all of the spin-labels are buried within the hydrophobic core. The lack of spin-spin interaction between the buried, immobilized spin-labels indicates they are remote (> 15 A) from each other, indicating an antiparallel topology of the monomers in [MAL-6-alpha2]2. The parent [alpha2]2 and the modified [MAL-6-alpha2]2 and [CP-alpha2]2 peptides are highly stable (deltaG(H2O) approximately 25 kcal/mol) as investigated by guanidine hydrochloride denaturation curves monitored by ESR and CD spectroscopies. Guanidine hydrochloride denaturation leads to a shorter correlation time of the spin-label, tau(c) < 1 ns, approaching that of an unrestricted spin-label in solution. In contrast, trifluoroethanol caused dissociation of [MAL-6-alpha2]2 to yield two [MAL-6-alpha2] monomers with retention of secondary structure and changed the tau(c) to 2.5 +/- 0.5 ns, indicating that a significant degree of motional restriction is imposed on the spin-label by the secondary structure. The coproporphyrin probes covalently attached to the N-termini of [CP-alpha2]2 and [CP-MAL-6-alpha2]2 provided evidence that the helical monomers of both were in a parallel orientation, in contrast to the antiparallel orientation determined for [MAL-6-alpha2]2. Consequently, the ESR spectra of [MAL-6-alpha2]2 and [CP-MAL-6-alpha2]2 reveal major structural differences in the local vicinity of the spin-labels due to the topological difference between these two bundles. The ESR spectra of [CP-MAL-6-alpha2]2 contains two distinct nitroxide populations, indicating that one spin-label remains buried in the hydrophobic core and the other is excluded to solvent in this parallel topology. Alleviation of the steric interactions causing one spin-label in [CP-MAL-6-alpha2]2 to be solvent-exposed by addition of [CP-alpha2]2 results in formation of the heterodimeric [CP-alpha2]/[CP-MAL-6-alpha2], as evidenced by insertion of all the spin-labels into hydrophobic cores. The changes in global topology and local structure as evidenced by this pair of spectral probes have relatively minor effects on the course of guanidine denaturation of these bundles. PMID:9062107

  1. Numerical investigation of competing spin-spin interactions in a two-dimensional Ising model for La/sub 2/. sqrt. /sub z/CuO/sub 4/. sqrt. /sub y/

    SciTech Connect

    Fay, D.; Klemm, R.A.; Monien, H.

    1988-06-01

    We have investigated numerically the model of Klemm, Thomann, and Johnston for La/sub 2/..sqrt../sub z/CuO/sub 4/..sqrt../sub y/. We assume for computational simplicity that the orthorhombic symmetry-breaking energy is large, implying Ising-like spin interactions predominate. Monte Carlo calculations suggest that the ground states exhibit quasi-long-range order in the orthorhombic c-axis direction, but are frustrated (or incommensurate) in the a-axis direction. The excited states often exhibit triplet pairs of spins that are flipped relative to the ground state.

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

    PubMed Central

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

    2011-01-01

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

  3. Calculating the Tidal, Spin, and Dynamical Evolution of Extrasolar Planetary Systems

    NASA Astrophysics Data System (ADS)

    Mardling, Rosemary A.; Lin, D. N. C.

    2002-07-01

    Based on formulations by Heggie and by Eggleton, we present an efficient method for calculating self-consistently the tidal, spin, and dynamical evolution of a many-body system, here with particular emphasis on planetary systems. The star and innermost planet (or in general the closest pair of bodies in the system) are endowed with structure while the other bodies are treated as point masses. The evolution of the spin rates and obliquities of the extended bodies are calculated (for arbitrary initial obliquities), as is the tidal evolution of the innermost orbit. In addition, the radius of the innermost planet is evolved according to its ability to efficiently dissipate tidal energy. Relativistic effects are included to post-Newtonian order. For resonant systems such as GJ 876, the evolution equations must be integrated directly to allow for variation of the semimajor axes (other than from tidal damping) and for the possibility of instability. For systems such as Upsilon Andromedae in which the period ratio of the two inner planets is small, the innermost orbit may be averaged producing (in this case) a 50-fold reduction in the calculation time. In order to illustrate the versatility of the formulation, we consider three hypothetical primitive Earth-Moon-Sun-Jupiter systems. The parameters and initial conditions are identical in the first two models except for the Love number of the Earth, which results in dramatically different evolutionary paths. The third system is one studied by Touma & Wisdom and serves as a test of the numerical formulations presented here by reproducing two secular mean motion resonances (the evection and eviction resonances). The methods may be used for any system of bodies.

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

    PubMed

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

    2011-05-01

    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

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

    SciTech Connect

    Bordonali, L.; Furukawa, Y.; Mariani, M.; Sabareesh, K. P. V.; Garlatti, E.; Borsa, F.

    2014-05-07

    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)

  6. Spin Hall effect-controlled magnetization dynamics in NiMnSb

    SciTech Connect

    Dürrenfeld, P. Ranjbar, M.; Gerhard, F.; Gould, C.; Molenkamp, L. W.; Åkerman, J.

    2015-05-07

    We investigate the influence of a spin current generated from a platinum layer on the ferromagnetic resonance (FMR) properties of an adjacent ferromagnetic layer composed of the halfmetallic half-Heusler material NiMnSb. Spin Hall nano-oscillator devices are fabricated, and the technique of spin torque FMR is used to locally study the magnetic properties as in-plane anisotropies and resonance fields. A change in the FMR linewidth, in accordance with the additional spin torque produced by the spin Hall effect, is present for an applied dc current. For sufficiently large currents, this should yield auto-oscillations, which however are not achievable in the present device geometry.

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

    SciTech Connect

    Stewart, John Ross; Ehlers, Georg; Fouquet, Peter; Mutka, Hannu; Payen, Christophe; Lortz, Rolf

    2011-01-01

    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.

  8. Magnetic Materials at finite Temperatures: thermodynamics and combined spin and molecular dynamics derived from first principles calculations

    SciTech Connect

    Eisenbach, Markus; Perera, Meewanage Dilina N; Landau, David P; Nicholson, Don M; Yin, Junqi; Brown, Greg

    2015-01-01

    We present a unified approach to describe the combined behavior of the atomic and magnetic degrees of freedom in magnetic materials. Using Monte Carlo simulations directly combined with first principles the Curie temperature can be obtained ab initio in good agreement with experimental values. The large scale constrained first principles calculations have been used to construct effective potentials for both the atomic and magnetic degrees of freedom that allow the unified study of influence of phonon-magnon coupling on the thermodynamics and dynamics of magnetic systems. The MC calculations predict the specific heat of iron in near perfect agreement with experimental results from 300K to above Tc and allow the identification of the importance of the magnon-phonon interaction at the phase-transition. Further Molecular Dynamics and Spin Dynamics calculations elucidate the dynamics of this coupling and open the potential for quantitative and predictive descriptions of dynamic structure factors in magnetic materials using first principles derived simulations.

  9. Magnetic Materials at finite Temperatures: thermodynamics and combined spin and molecular dynamics derived from first principles calculations

    NASA Astrophysics Data System (ADS)

    Eisenbach, Markus; Perera, Dilina; Landau, David P.; Nicholson, Don M.; Yin, Jungqi; Brown, Gregory

    2015-09-01

    We present a unified approach to describe the combined behavior of the atomic and magnetic degrees of freedom in magnetic materials. Using Monte Carlo simulations directly combined with first principles the Curie temperature can be obtained ab initio in good agreement with experimental values. The large scale constrained first principles calculations have been used to construct effective potentials for both the atomic and magnetic degrees of freedom that allow the unified study of influence of phonon-magnon coupling on the thermodynamics and dynamics of magnetic systems. The MC calculations predict the specific heat of iron in near perfect agreement with experimental results from 300K to above Tc and allow the identification of the importance of the magnon-phonon interaction at the phase-transition. Further Molecular Dynamics and Spin Dynamics calculations elucidate the dynamics of this coupling and open the potential for quantitative and predictive descriptions of dynamic structure factors in magnetic materials using first principles derived simulations.

  10. Spin and phase relaxation dynamics in GaN and GaN/AlGaN quantum wells (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Gallart, Mathieu; Ziegler, Marc; Hönerlage, Bernd H.; Gilliot, Pierre; Feltin, Eric; Carlin, Jean-François; Butté, Raphaël.; Grandjean, Nicolas

    2015-09-01

    By performing time-resolved optical non-degenerate pump-probe experiments, we study the relaxation dynamics of spin-polarized excitons in wurtzite epitaxial GaN and in nitride nanostructures. Those materials are indeed promising candidates for spintronic applications because of their weak spin-orbit coupling and large exciton binding energy (~ 17 meV and ~ 26meV in bulk GaN, respectively). In epilayers, we show that the high density of dislocations increases dramatically the spin relaxation of electrons and holes through the defect assisted Elliott-Yafet mechanism. That makes the exciton dephasing time very short. In high quality GaN/AlGaN quantum wells, both the exciton-spin lifetime ?S and the exciton dephasing-time T2 were determined via pump-probe spectroscopy using polarized laser pulses and time-resolved four wave-mixing experiments. The evolution of both quantities with temperature shows that spin relaxation occurs in the motional narrowing regime up to 80 K. Above this threshold, the thermal energy becomes large enough for excitons to escape from the QW. Such measurements demonstrate that GaN-based heterostructures can reach a very high degree of control that was previously mostly restricted to conventional III-V semiconductors and more specifically to the arsenide family.

  11. Dynamic spin susceptibility of hole-doped high-temperature superconductors in a singlet-correlated conduction band model

    SciTech Connect

    Eremin, M. V. Aleev, A. A.; Eremin, I. M.

    2008-04-15

    We have derived an expression for the dynamical spin susceptibility of a hole-doped high-temperature superconductor taking into account a strong correlation between the magnetization of spins of the localized and itinerant electrons. This formula has been used to calculate the imaginary part of the susceptibility as a function of the frequency and wave vector. The results are compared to experimental data on the inelastic neutron scattering in compounds of the YBa{sub 2}Cu{sub 3}O{sub 6+y} type. A peak in the scattering intensity observed at an energy of about 40 meV in the region of wave vectors Q = ({pi}, {pi}) and an arc-shaped dispersion relief are interpreted as manifestations of the collective spin excitations in the system, the energy of which falls within a superconducting gap (spin exciton). The U-shaped divergent relief observed in the neutron scattering intensity is assigned to collective short-rage-order spin oscillations.

  12. Effective equations for the precession dynamics of electron spins and electron-impurity correlations in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Cygorek, M.; Axt, V. M.

    2015-08-01

    Starting from a quantum kinetic theory for the spin dynamics in diluted magnetic semiconductors, we derive simplified equations that effectively describe the spin transfer between carriers and magnetic impurities for an arbitrary initial impurity magnetization. Taking the Markov limit of these effective equations, we obtain good quantitative agreement with the full quantum kinetic theory for the spin dynamics in bulk systems at high magnetic doping. In contrast, the standard rate description where the carrier-dopant interaction is treated according to Fermi’s golden rule, which involves the assumption of a short memory as well as a perturbative argument, has been shown previously to fail if the impurity magnetization is non-zero. The Markov limit of the effective equations is derived, assuming only a short memory, while higher order terms are still accounted for. These higher order terms represent the precession of the carrier-dopant correlations in the effective magnetic field due to the impurity spins. Numerical calculations show that the Markov limit of our effective equations reproduces the results of the full quantum kinetic theory very well. Furthermore, this limit allows for analytical solutions and for a physically transparent interpretation.

  13. O NMR Study of the Intrinsic Magnetic Susceptibility and Spin Dynamics of the Quantum Kagome Antiferromagnet ZnCu3OH6Cl2

    E-print Network

    Paris-Sud 11, Université de

    17 O NMR Study of the Intrinsic Magnetic Susceptibility and Spin Dynamics of the Quantum Kagome report, through 17 O NMR, an unambiguous local determination of the intrinsic kagome lattice spin antiferromagnets. Finally, we discuss our relaxation measurements in the light of Cu and Cl NMR data and suggest

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    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.

  15. Coherent ultrafast spin-dynamics probed in three dimensional topological insulators.

    PubMed

    Boschini, F; Mansurova, M; Mussler, G; Kampmeier, J; Grützmacher, D; Braun, L; Katmis, F; Moodera, J S; Dallera, C; Carpene, E; Franz, C; Czerner, M; Heiliger, C; Kampfrath, T; Münzenberg, M

    2015-01-01

    Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses' light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone. PMID:26510509

  16. Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

    PubMed Central

    Boschini, F.; Mansurova, M.; Mussler, G.; Kampmeier, J.; Grützmacher, D.; Braun, L.; Katmis, F.; Moodera, J. S.; Dallera, C.; Carpene, E.; Franz, C.; Czerner, M.; Heiliger, C.; Kampfrath, T.; Münzenberg, M.

    2015-01-01

    Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses’ light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone. PMID:26510509

  17. Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

    NASA Astrophysics Data System (ADS)

    Boschini, F.; Mansurova, M.; Mussler, G.; Kampmeier, J.; Grützmacher, D.; Braun, L.; Katmis, F.; Moodera, J. S.; Dallera, C.; Carpene, E.; Franz, C.; Czerner, M.; Heiliger, C.; Kampfrath, T.; Münzenberg, M.

    2015-10-01

    Topological insulators are candidates to open up a novel route in spin based electronics. Different to traditional ferromagnetic materials, where the carrier spin-polarization and magnetization are based on the exchange interaction, the spin properties in topological insulators are based on the coupling of spin- and orbit interaction connected to its momentum. Specific ways to control the spin-polarization with light have been demonstrated: the energy momentum landscape of the Dirac cone provides spin-momentum locking of the charge current and its spin. We investigate a spin-related signal present only during the laser excitation studying real and imaginary part of the complex Kerr angle by disentangling spin and lattice contributions. This coherent signal is only present at the time of the pump-pulses’ light field and can be described in terms of a Raman coherence time. The Raman transition involves states at the bottom edge of the conduction band. We demonstrate a coherent femtosecond control of spin-polarization for electronic states at around the Dirac cone.

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    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.)

  19. Relativistic quantum dynamics of a neutral particle in external electric fields: An approach on effects of spin

    NASA Astrophysics Data System (ADS)

    Azevedo, F. S.; Silva, Edilberto O.; Castro, Luis B.; Filgueiras, Cleverson; Cogollo, D.

    2015-11-01

    The planar quantum dynamics of a spin-1/2 neutral particle interacting with electrical fields is considered. A set of first order differential equations is obtained directly from the planar Dirac equation with nonminimum coupling. New solutions of this system, in particular, for the Aharonov-Casher effect, are found and discussed in detail. Pauli equation is also obtained by studying the motion of the particle when it describes a circular path of constant radius. We also analyze the planar dynamics in the full space, including the r = 0 region. The self-adjoint extension method is used to obtain the energy levels and wave functions of the particle for two particular values for the self-adjoint extension parameter. The energy levels obtained are analogous to the Landau levels and explicitly depend on the spin projection parameter.

  20. Ultrafast laser-induced dynamics of noncollinear spin structures in amorphous NdFeCo and PrFeCo

    NASA Astrophysics Data System (ADS)

    Becker, J.; Tsukamoto, A.; Kirilyuk, A.; Maan, J. C.; Rasing, Th.; Christianen, P. C. M.; Kimel, A. V.

    2015-11-01

    The fanned out, noncollinear spin structure of the Fe(Co) sublattice in amorphous NdFeCo and PrFeCo alloys is shown to strongly affect its ultrafast laser-induced magnetization dynamics. An overshooting effect is discovered at low applied magnetic fields, where the magnetization temporarily increases above its equilibrium value. We explain this phenomenon by considering the dynamics of the noncollinear spin structure. After femtosecond laser excitation the system first reconstructs magnetic order on a time scale of 50-150 ps arriving at a state with a smaller opening angle of the fan. Subsequently, the original opening angle is restored on a time scale of nanoseconds. Increasing the field up to 0.6 T we can fully close the fan and therewith suppress the overshooting behavior.

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

    SciTech Connect

    Chenel, Aurélie; Mangaud, Etienne; Laboratoire Collisions, Agrégats, Réactivité, UMR 5589, IRSAMC, Université Paul Sabatier, F-31062 Toulouse ; Burghardt, Irene E-mail: chris@irsamc.ups-tlse.fr; Meier, Christoph E-mail: chris@irsamc.ups-tlse.fr; Desouter-Lecomte, Michèle E-mail: chris@irsamc.ups-tlse.fr; Département de Chimie, Université de Liège, Sart Tilman, B6, B-4000 Liège

    2014-01-28

    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.

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

    SciTech Connect

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

    2009-07-28

    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.

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

    PubMed Central

    Barnes, Alexander B.; Mak-Jurkauskas, Melody L.; Matsuki, Yoh; Bajaj, Vikram S.; van der Wel, Patrick C. A.; DeRocher, Ronald; Bryant, Jeffrey; Sirigiri, Jagadishwar R.; Temkin, Richard J.; Lugtenburg, Johan; Herzfeld, Judith; Griffin, Robert G.

    2009-01-01

    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 improving long-term instrument stability. Changing samples in conventional cryogenic MAS DNP/NMR experiments involves warming the probe to room temperature, detaching all cryogenic, RF, and microwave connections, removing the probe from the magnet, replacing the sample, and reversing all the previous steps, with the entire cycle requiring a few hours. The sample exchange system described here — which relies on an eject pipe attached to the front of the MAS stator and a vacuum jacketed dewar with a bellowed hole — circumvents these procedures. To demonstrate the excellent sensitivity, resolution, and stability achieved with this quadruple resonance sample exchange probe, we have performed high precision distance measurements on the active site of the membrane protein bacteriorhodopsin. We also include a spectrum of the tripeptide N-f-MLF-OH at 100 K which shows 30 Hz linewidths. PMID:19356957

  4. Religious competence as cultural competence

    PubMed Central

    2012-01-01

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

  5. Exciton spin relaxation dynamics in InGaAs /InP quantum wells

    NASA Astrophysics Data System (ADS)

    Akasaka, Shunsuke; Miyata, Shogo; Kuroda, Takamasa; Tackeuchi, Atsushi

    2004-09-01

    We have investigated the exciton spin relaxation mechanism between 13 and 300K in InGaAs /InP quantum wells using time-resolved spin-dependent pump and probe absorption measurements. The exciton spin relaxation time, ?s above 40K was found to depend on temperature, T, according to ?s?T-1.1, although the spin relaxation time is constant below 40K. The clear carrier density dependence of the exciton spin relaxation time was observed below 40K, although the carrier density dependence is weak above 40K. These results imply that the main spin relaxation mechanism above and below 40K are the D'yakonov-Perel' process and the Bir-Aronov-Pikus process, respectively.

  6. The origin of persistent spin dynamics and residual entropy in the stuffed spin ice Ho2.3Ti1.7O7-?

    SciTech Connect

    Ehlers, Georg

    2007-01-01

    The so-called 'spin ices' form when exchange interactions, crystal fields, and dipolar interactions are in a delicate balance. This gives rise to a ground state which has a considerable amount of residual spin entropy, much like the proton entropy in water ice through the freezing transition. Recently, 'stuffed' spin ices have provided a means to probe how delicate a balance is needed to stabilize the disordered ground state. Surprisingly, it is found that an increase of the density of spins results in very little change in the residual entropy, which leads to the interesting idea that residual entropy states might be more common than once believed for magnetism. In this communication, we detail the crystal growth of stuffed spin ice Ho{sub 2.3}Ti{sub 1.7}O{sub 7-{delta}}, and we complete neutron scattering experiments to observe how the spins order at low temperatures. It is found that even with this large perturbation, the system still has some key signatures of the spin ice state, but the spin dynamics is significantly altered. With this new data, an explanation emerges for the zero-point entropy in the stuffed spin ices.

  7. Criticality and spin squeezing in the rotational dynamics of a Bose-Einstein condensate on a ring lattice

    NASA Astrophysics Data System (ADS)

    Kolá?, M.; Opatrný, T.; Das, Kunal K.

    2015-10-01

    We examine the dynamics of circulating modes of a Bose-Einstein condensate confined in a toroidal lattice. Nonlinearity due to interactions leads to criticality that separates oscillatory and self-trapped phases among counterpropagating modes which however share the same physical space. In the mean-field limit, the criticality is found to substantially enhance sensitivity to rotation of the system. Analysis of the quantum dynamics reveals the fluctuations near criticality are significant, which we explain using spin-squeezing formalism visualized on a Bloch sphere. We utilize the squeezing to propose a Ramsey interferometric scheme that suppresses fluctuation in the relevant quadrature sensitive to rotation.

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

    E-print Network

    Fabiano M. Andrade; Edilberto O. Silva

    2014-12-10

    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.

  9. Electron Spin Relaxation Dynamics in InGaAs/InP Multiple-Quantum Wells

    NASA Astrophysics Data System (ADS)

    Tackeuchi, Atsushi; Wada, Osamu

    1998-01-01

    The electron spin relaxation of InGaAs/InP multiple-quantum wells is investigated at room temperature using time-resolved polarization-dependent absorption measurements. The spin relaxation time is dependent on the quantum confined energy, E1e, according to ?s?E1e-1. The dependence differs from that of the D'yakonov-Perel' interaction, which governs the spin relaxation of GaAs quantum wells at room temperature, and suggests the possibility of the existence of an additional spin relaxation mechanism.

  10. Room-temperature electron spin dynamics in GaAs/AlGaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Tackeuchi, Atsushi; Nishikawa, Yuji; Wada, Osamu

    1996-02-01

    We have investigated the spin relaxation process of electron at room temperature in nominally undoped GaAs/AlGaAs multiple-quantum wells. The spin relaxation times are measured for different well thicknesses using time-resolved polarization absorption measurement. The spin relaxation time ?s, is found to depend on the electron confined energy E1e, according to ?s?E1e-2.2, showing that the main spin relaxation mechanism at room temperature is the D'yakonov-Perel' interaction.

  11. Dynamic phase transition properties for the mixed spin-(1/2, 1) Ising model in an oscillating magnetic field

    NASA Astrophysics Data System (ADS)

    Erta?, Mehmet; Keskin, Mustafa

    2015-08-01

    Herein we study the dynamic phase transition properties for the mixed spin-(1/2, 1) Ising model on a square lattice under a time-dependent magnetic field by means of the effective-field theory (EFT) with correlations based on Glauber dynamics. We present the dynamic phase diagrams in the reduced magnetic field amplitude and reduced temperature plane and find that the phase diagrams exhibit dynamic tricitical behavior, multicritical and zero-temperature critical points as well as reentrant behavior. We also investigate the influence of frequency (?) and observe that for small values of ? the mixed phase disappears, but for high values it appears and the system displays reentrant behavior as well as a critical end point.

  12. A MEAN-FIELD MODEL FOR SPIN DYNAMICS IN MULTILAYERED FERROMAGNETIC MEDIA

    E-print Network

    . Introduction. Spintronics, i.e., the active control and manipulation of spin degrees of freedom, plays a key-wall motion ([32]), a mechanism that is important in operating spintronic memories and logic devices ([15 as a result of this spin- transfer torque (see Figure 4.1). The magnetization reversal process in a spintronic

  13. Dynamic phase diagrams of a ferrimagnetic mixed spin (1/2, 1) Ising system within the path probability method

    NASA Astrophysics Data System (ADS)

    Erta?, Mehmet; Keskin, Mustafa

    2015-11-01

    In this study we used the path probability method (PPM) to calculate the dynamic phase diagrams of a ferrimagnetic mixed spin-(1/2, 1) Ising system under an oscillating magnetic field. One of the main advantages of the PPM over the mean-field approximation and the effective-field theory based on Glauber-type stochastic dynamics is that it contains two rate constants which are very important for studying dynamic behaviors. We present the dynamic phase diagrams in the reduced magnetic field amplitude and reduced temperature plane and the twelve main different topological types of the phase diagrams are obtained. The phase diagrams contain paramagnetic (p), ferrimagnetic (i) and i + p mixed phases. They also exhibit a dynamic tricritical and reentrant behavior as well as the dynamic double critical end point (B), critical end point (E), quadruple point (QP) and triple point (TP). The dynamic phase diagrams are compared and discussed with the phase diagrams obtained in previous works within the mean-field approximation and the effective-field theory based on Glauber-type stochastic dynamics.

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

    SciTech Connect

    Singh, Pushpendra P.; Singh, B. P.; Sharma, Manoj Kumar; Unnati,; Singh, D.; Ansari, M. A.; Prasad, R.; Kumar, R.; Golda, K. S.; Singh, R. P.; Muralithar, S.; Bhowmik, R. K.

    2008-07-15

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

  15. Using coherent dynamics to quantify spin coupling within triplet-exciton/polaron complexes in organic diodes

    NASA Astrophysics Data System (ADS)

    Baker, W. J.; Keevers, T. L.; Boehme, C.; McCamey, D. R.

    2015-07-01

    Quantifying the spin-spin interactions which influence electronic transitions in organic semiconductors is crucial for understanding their magneto-optoelectronic properties. By combining a theoretical model for three spin interactions in the coherent regime with pulsed electrically detected magnetic resonance experiments on ? -conjugated polymer diodes (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]), we quantify the spin coupling within complexes comprising three spin-1/2 particles. We determine that these particles form triplet-exciton/polaron pairs, where the polaron-exciton exchange is over five orders of magnitude weaker (<170 MHz) than that within the exciton. This approach provides a direct spectroscopic approach for distinguishing between coupling regimes, and to test hypotheses relating microscopic properties to bulk characteristics of organic electronic devices.

  16. Structural, electronic and dynamical stability of heavy metal iron pernitride: a spin polarized first-principles study

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

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

    SciTech Connect

    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.

    2008-10-31

    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.

  18. Side effects of fast-acting dynamic range compression that affect intelligibility in a competing speech task

    NASA Astrophysics Data System (ADS)

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

    2004-10-01

    Using a cochlear implant simulator, Stone and Moore [J. Acoust. Soc. Am. 114, 1023-1034 (2003)] reported that wideband fast-acting compression led to poorer intelligibility than slow-acting compression in a competing speech task. Compression speed was varied by using different pairs of attack and release times. In the first experiment reported here, it is shown that attack times less than about 2 ms in a wideband compressor are deleterious to intelligibility. In experiment 2, fast wideband compression was applied to the target and background either before or after mixing. The former reduced the modulation depth of each signal but maintained the independence between the two signals, while the latter introduced ``comodulation.'' Using simulations with 6 and 11 channels, intelligibility was higher when compression was applied before mixing. In experiment 3, wideband compression was compared with multichannel compression; the latter led to reduced comodulation effects. For 6 channels, the position of the compressor, either wideband or within each channel, had no effect on intelligibility. For 11 channels, channel compression severely degraded intelligibility compared to wideband compression, presumably because of the greater reduction of across-channel contrasts. Overall, caution appears necessary in the use of fast-acting compression in cochlear implants, so as to preserve intelligibility. .

  19. Spin dynamics in the metallic state of the high- Tc superconducting system YBa 2Cu 3O 6 + x

    NASA Astrophysics Data System (ADS)

    Bourges, P.; Regnault, L. P.; Henry, J. Y.; Vettier, C.; Sidis, Y.; Burlet, P.

    1995-02-01

    The spin dynamics in single crystals of YBa 2Cu 3O 6 + x has been successfully investigated, by inelastic neutron scattering (INS) experiments, as a function of temperature in the metallic state over the whole doping range from the weakly doped ( x = 0.45, 0.51) to the heavily doped ( x = 0.69, 0.83, 0.92) and the overdoped ( x = 0.97, 1) regimes. Dynamical AF-correlations persist in all the metallic state. Actually, the imaginary part of the magnetic susceptibility ?? consists of two contributions which have different doping and temperature dependences. At low temperature, ?? exhibits an energy gap in any superconducting samples which becomes much weaker close to the insulating-metallic transition. To emphasize the characteristic features of the spin dynamics in YBCO, INS results obtained by other groups are compared with our experiments. Several theoretical approaches, which intend to describe the energy line shape of the dynamical magnetic susceptibility, are also discussed.

  20. Simulation of micro-magnet stray-field dynamics for spin qubit manipulation

    SciTech Connect

    Neumann, R.; Schreiber, L. R.

    2015-05-21

    High-fidelity control and unprecedented long dephasing times in silicon-based single spin qubits have recently confirmed the prospects of solid-state quantum computation. We investigate the feasibility of using a micro-magnet stray field for all-electrical, addressable spin qubit control in a Si/SiGe double quantum dot. For a micro-magnet geometry optimized for high Rabi-frequency, addressability, and robustness to fabrication misalignment as previously demonstrated by Yoneda et al. [Phys. Rev. Lett. 113, 267601 (2014)], we simulate the qubit decoherence due to magnetic stray-field fluctuations, which may dominate in nuclear spin-free systems, e.g., quantum dots in Si/SiGe, Si-MOS structures and (bilayer) graphene. With calculated Rabi-frequencies of 15 MHz, a qubit addressability error below 10{sup ?3} is achievable. Magnetic fluctuations from a micro-magnet limits the spin relaxation time to T{sub 1} ? 3?s, while pure spin dephasing is negligible. Our results show that micro-magnets are a promising tool for spin qubit computation in nuclear spin-free systems.

  1. Dynamical Body Frames, Orientation-Shape Variables and Canonical Spin Bases for the Non-Relativistic N-Body Problem

    E-print Network

    David Alba; Luca Lusanna; Massimo Pauri

    2000-11-02

    After the separation of the center-of-mass motion, a new privileged class of canonical Darboux bases is proposed for the non-relativistic N-body problem by exploiting a geometrical and group theoretical approach to the definition of {\\it body frame} for deformable bodies. This basis is adapted to the rotation group SO(3), whose canonical realization is associated with a symmetry Hamiltonian {\\it left action}. The analysis of the SO(3) coadjoint orbits contained in the N-body phase space implies the existence of a {\\it spin frame} for the N-body system. Then, the existence of appropriate non-symmetry Hamiltonian {\\it right actions} for non-rigid systems leads to the construction of a N-dependent discrete number of {\\it dynamical body frames} for the N-body system, hence to the associated notions of {\\it dynamical} and {\\it measurable} orientation and shape variables, angular velocity, rotational and vibrational configurations. For N=3 the dynamical body frame turns out to be unique and our approach reproduces the {\\it xxzz gauge} of the gauge theory associated with the {\\it orientation-shape} SO(3) principal bundle approach of Littlejohn and Reinsch. For $N \\geq 4$ our description is different, since the dynamical body frames turn out to be {\\it momentum dependent}. The resulting Darboux bases for $N\\geq 4$ are connected to the coupling of the {\\it spins} of particle clusters rather than the coupling of the {\\it centers of mass} (based on Jacobi relative normal coordinates). One of the advantages of the spin coupling is that, unlike the center-of-mass coupling, it admits a relativistic generalization.

  2. Dynamics of extended bodies in a Kerr spacetime with spin-induced quadrupole tensor

    E-print Network

    Bini, Donato; Geralico, Andrea

    2015-01-01

    The features of equatorial motion of an extended body in Kerr spacetime are investigated in the framework of the Mathisson-Papapetrou-Dixon model. The body is assumed to stay at quasi-equilibrium and respond instantly to external perturbations. Besides the mass, it is completely determined by its spin, the multipolar expansion being truncated at the quadrupole order, with a spin-induced quadrupole tensor. The study of the radial effective potential allows to analytically determine the ISCO shift due to spin and the associated frequency of the last circular orbit.

  3. Dynamics of extended bodies in a Kerr spacetime with spin-induced quadrupole tensor

    E-print Network

    Donato Bini; Guillaume Faye; Andrea Geralico

    2015-07-27

    The features of equatorial motion of an extended body in Kerr spacetime are investigated in the framework of the Mathisson-Papapetrou-Dixon model. The body is assumed to stay at quasi-equilibrium and respond instantly to external perturbations. Besides the mass, it is completely determined by its spin, the multipolar expansion being truncated at the quadrupole order, with a spin-induced quadrupole tensor. The study of the radial effective potential allows to analytically determine the ISCO shift due to spin and the associated frequency of the last circular orbit.

  4. Dynamics of extended bodies in a Kerr spacetime with spin-induced quadrupole tensor

    NASA Astrophysics Data System (ADS)

    Bini, Donato; Faye, Guillaume; Geralico, Andrea

    2015-11-01

    The features of equatorial motion of an extended body in Kerr spacetime are investigated in the framework of the Mathisson-Papapetrou-Dixon model. The body is assumed to stay at quasiequilibrium and respond instantly to external perturbations. Besides the mass, it is completely determined by its spin, the multipolar expansion being truncated at the quadrupole order, with a spin-induced quadrupole tensor. The study of the radial effective potential allows us to analytically determine the innermost stable circular orbit shift due to spin and the associated frequency of the last circular orbit.

  5. Out-of-equilibrium dynamics of photoexcited spin-state concentration waves.

    PubMed

    Marino, A; Buron-Le Cointe, M; Lorenc, M; Toupet, L; Henning, R; DiChiara, A D; Moffat, K; Bréfuel, N; Collet, E

    2015-01-01

    The spin crossover compound [FeIIH2L2-Me][PF6]2 presents a two-step phase transition. In the intermediate phase, a spin state concentration wave (SSCW) appears resulting from a symmetry breaking (cell doubling) associated with a long-range order of alternating high and low spin molecular states. By combining time-resolved optical and X-ray diffraction measurements on a single crystal, we study how such a system responds to femtosecond laser excitation and we follow in real time the erasing and rewriting of the SSCW. PMID:25627455

  6. The dynamics and optimal control of spinning spacecraft with movable telescoping appendages. Part C: Effect of flexibility during boom deployment

    NASA Technical Reports Server (NTRS)

    Bainum, P. M.; James, P. K.

    1977-01-01

    The dynamics of a spinning symmetrical spacecraft system during the deployment (or retraction) of flexible boom-type appendages were investigated. The effect of flexibility during boom deployment is treated by modelling the deployable members as compound spherical pendula of varying length (according to a control law). The orientation of the flexible booms with respect to the hub, is described by a sequence of two Euler angles. The boom members contain a flexural stiffness which can be related to an assumed effective restoring linear spring constant, and structural damping which effects the entire system. Linearized equations of motion for this system, when the boom length is constant, involve periodic coefficients with the frequency of the hub spin. A bounded transformation is found which converts this system into a kinematically equivalent one involving only constant coefficients.

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

    SciTech Connect

    Chui, C. P.; Zhou, Yan

    2014-08-15

    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.

  8. Neutron spin-echo studies on dynamic and static fluctuations in two types of poly(vinyl alcohol) gels

    NASA Astrophysics Data System (ADS)

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

    2005-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    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.

  10. Using Time-Varying Evidence to Test Models of Decision Dynamics: Bounded Diffusion vs. the Leaky Competing Accumulator Model

    PubMed Central

    Tsetsos, Konstantinos; Gao, Juan; McClelland, James L.; Usher, Marius

    2012-01-01

    When people make decisions, do they give equal weight to evidence arriving at different times? A recent study (Kiani et al., 2008) using brief motion pulses (superimposed on a random moving dot display) reported a primacy effect: pulses presented early in a motion observation period had a stronger impact than pulses presented later. This observation was interpreted as supporting the bounded diffusion (BD) model and ruling out models in which evidence accumulation is subject to leakage or decay of early-arriving information. We use motion pulses and other manipulations of the timing of the perceptual evidence in new experiments and simulations that support the leaky competing accumulator (LCA) model as an alternative to the BD model. While the LCA does include leakage, we show that it can exhibit primacy as a result of competition between alternatives (implemented via mutual inhibition), when the inhibition is strong relative to the leak. Our experiments replicate the primacy effect when participants must be prepared to respond quickly at the end of a motion observation period. With less time pressure, however, the primacy effect is much weaker. For 2 (out of 10) participants, a primacy bias observed in trials where the motion observation period is short becomes weaker or reverses (becoming a recency effect) as the observation period lengthens. Our simulation studies show that primacy is equally consistent with the LCA or with BD. The transition from primacy-to-recency can also be captured by the LCA but not by BD. Individual differences and relations between the LCA and other models are discussed. PMID:22701399

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

    SciTech Connect

    Evangelisti, Marco; Sorop, Tibi G; Bakharev, Oleg N; Visser, Dirk; Hillier, Adrian D.; Alonso, Juan; Haase, Markus; Boatner, Lynn A; De Jongh, L. Jos

    2011-01-01

    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.

  12. Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 667C

    SciTech Connect

    Makarov, Valeri V.; Berghea, Ciprian

    2014-01-10

    We investigate the spin-orbital evolution of the potentially habitable super-Earth GJ 667Cc in the multiple system of at least two exoplanets orbiting a nearby M dwarf. The published radial velocities for this star are re-analyzed and evidence is found for additional periodic signals, which could be taken for two additional planets on eccentric orbits making the system dynamically inviable. Limiting the scope to the two originally detected planets, we assess the dynamical stability of the system and find no evidence for bounded chaos in the orbital motion. The orbital eccentricity of the planets b and c is found to change cyclically in the range 0.06-0.28 and 0.05-0.25, respectively, with a period of approximately 0.46 yr. Taking the eccentricity variation into account, numerical integrations are performed of the spin-orbit interactions of the planet GJ 667Cc with its host star, assuming a terrestrial composition of its mantle. Depending on the interior temperature of the planet, it is likely to be entrapped in the 3:2 (probability 0.51) or even higher spin-orbit resonance. It is less likely to reach the 1:1 resonance (probability 0.24). The estimated characteristic spin-down times are quite short for the two planets, i.e., within 1 Myr for planet c and even shorter for planet b. The rate of tidal dissipation of energy in the planets of GJ 667 is estimated at 10{sup 23.7} and 10{sup 26.7} J yr{sup –1} for c and b, respectively. This raises a question of how such relatively massive, close super-Earths could survive overheating and destruction.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  14. Separation and conversion dynamics of nuclear-spin isomers of gaseous methanol.

    PubMed

    Sun, Zhen-Dong; Ge, Meihua; Zheng, Yujun

    2015-01-01

    All symmetrical molecules with non-zero nuclear spin exist in nature as nuclear-spin isomers (NSIs). However, owing to the lack of experimental information, knowledge is rare about interconversions of NSIs of gaseous molecules with torsional symmetry. Here we report our separation and conversion observations on NSI-torsion-specific transition systems of gaseous methanol from a light-induced drift experiment involving partially spatial separation of the ortho and para isomers. We find that vibrationally excited molecules of the methanol spin isomer have a smaller collision cross-section than their ground-state counterparts. Interconversion of the enriched ortho isomer with the para isomer, which is generally considered improbable, has been quantitatively studied by sensitive detections of the spectral intensities. Rather counterintuitively, this reveals that the interconversion is inhibited with increasing pressure. Our results suggest that the spin conversion mechanism in methanol is via a quantum relaxation process with the quantum Zeno effect induced by molecular collisions. PMID:25880882

  15. Separation and conversion dynamics of nuclear-spin isomers of gaseous methanol

    NASA Astrophysics Data System (ADS)

    Sun, Zhen-Dong; Ge, Meihua; Zheng, Yujun

    2015-04-01

    All symmetrical molecules with non-zero nuclear spin exist in nature as nuclear-spin isomers (NSIs). However, owing to the lack of experimental information, knowledge is rare about interconversions of NSIs of gaseous molecules with torsional symmetry. Here we report our separation and conversion observations on NSI-torsion-specific transition systems of gaseous methanol from a light-induced drift experiment involving partially spatial separation of the ortho and para isomers. We find that vibrationally excited molecules of the methanol spin isomer have a smaller collision cross-section than their ground-state counterparts. Interconversion of the enriched ortho isomer with the para isomer, which is generally considered improbable, has been quantitatively studied by sensitive detections of the spectral intensities. Rather counterintuitively, this reveals that the interconversion is inhibited with increasing pressure. Our results suggest that the spin conversion mechanism in methanol is via a quantum relaxation process with the quantum Zeno effect induced by molecular collisions.

  16. Separation and conversion dynamics of nuclear-spin isomers of gaseous methanol

    PubMed Central

    Sun, Zhen-Dong; Ge, Meihua; Zheng, Yujun

    2015-01-01

    All symmetrical molecules with non-zero nuclear spin exist in nature as nuclear-spin isomers (NSIs). However, owing to the lack of experimental information, knowledge is rare about interconversions of NSIs of gaseous molecules with torsional symmetry. Here we report our separation and conversion observations on NSI-torsion-specific transition systems of gaseous methanol from a light-induced drift experiment involving partially spatial separation of the ortho and para isomers. We find that vibrationally excited molecules of the methanol spin isomer have a smaller collision cross-section than their ground-state counterparts. Interconversion of the enriched ortho isomer with the para isomer, which is generally considered improbable, has been quantitatively studied by sensitive detections of the spectral intensities. Rather counterintuitively, this reveals that the interconversion is inhibited with increasing pressure. Our results suggest that the spin conversion mechanism in methanol is via a quantum relaxation process with the quantum Zeno effect induced by molecular collisions. PMID:25880882

  17. Spin dynamics in CuO and Cu[sub 1[minus][ital x

    SciTech Connect

    Carretta, P.; Corti, M.; Rigamonti, A. )

    1993-08-01

    [sup 63]Cu nuclear quadrupole resonance (NQR), nuclear antiferromagnetic resonance (AFNMR), and spin-lattice relaxation, as well as [sup 7]Li NMR and relaxation measurements in CuO and in Cu[sub 1[minus][ital x

  18. Generation of propagating spin waves from regions of increased dynamic demagnetising field near magnetic antidots

    NASA Astrophysics Data System (ADS)

    Davies, C. S.; Sadovnikov, A. V.; Grishin, S. V.; Sharaevskii, Yu. P.; Nikitov, S. A.; Kruglyak, V. V.

    2015-10-01

    We have used Brillouin Light Scattering and micromagnetic simulations to demonstrate a point-like source of spin waves created by the inherently nonuniform internal magnetic field in the vicinity of an isolated antidot formed in a continuous film of yttrium-iron-garnet. The field nonuniformity ensures that only well-defined regions near the antidot respond in resonance to a continuous excitation of the entire sample with a harmonic microwave field. The resonantly excited parts of the sample then served as reconfigurable sources of spin waves propagating (across the considered sample) in the form of caustic beams. Our findings are relevant to further development of magnonic circuits, in which point-like spin wave stimuli could be required, and as a building block for interpretation of spin wave behavior in magnonic crystals formed by antidot arrays.

  19. THETA SUMS, EISENSTEIN SERIES, AND THE SEMICLASSICAL DYNAMICS OF A PRECESSING SPIN \\Lambda

    E-print Network

    ] and appears in nature, say, in the nuclear quadrupole interaction with an external axial­symmetric electric as a semiclassical expansion of the value distribution of the auto­correlation function for the precessing spin

  20. Different High-Temperature Spin Dynamics of Ising Pyrochlore Dy2Sn2O7 and Heisenberg Pyrochlore Gd2Sn2O7

    NASA Astrophysics Data System (ADS)

    Kaibuchi, Tomomi; Tashiro, Hiroshi; Itou, Tetsuaki; Nishiyama, Masahide; Oyamada, Akira; Maegawa, Satoru; Matsuhira, Kazuyuki

    2012-05-01

    We measured the nuclear magnetic spin--lattice (T1-1) and spin--spin (T2-1) relaxation rates of 119Sn nuclei of the Ising pyrochlore magnet Dy2Sn2O7 and the Heisenberg pyrochlore magnet Gd2Sn2O7 at high temperatures (120--294 K for Dy2Sn2O7 and 20--284 K for Gd2Sn2O7) to investigate their high-temperature 4f-electron spin dynamics. We found the following two results, which reveal remarkable differences between the spin dynamics of Dy2Sn2O7 and Gd2Sn2O7. First, the ratio T2-1/T1-1 for powder samples is almost unity in Dy2Sn2O7, whereas it is about 6 in Gd2Sn2O7. Second, these relaxation rates increase markedly on cooling in Dy2Sn2O7, reflecting thermal activation with a gap of ˜600 K, whereas they are almost constant with temperature in Gd2Sn2O7. The former result indicates that spin fluctuations of Dy2Sn2O7 are completely restricted to the < 111 > direction, whereas Gd spins fluctuate three-dimensionally and the component of the fluctuations parallel to an externally applied field contributes to the nuclear relaxation rates in Gd2Sn2O7. The latter result indicates that the spin fluctuations of Dy2Sn2O7 are caused by an indirect spin-flip process mediated through an excited state of the crystalline electric field multiplets, whereas those of Gd2Sn2O7 are dominated by the direct mutual spin-flip process by interactions between 4f-electron spins.