Sample records for competing spin dynamics

  1. Mixed-spin ising model with one- and two-spin competing dynamics

    PubMed

    Godoy; Figueiredo

    2000-01-01

    In this work we found the stationary states of a kinetic Ising model, with two different types of spins: sigma=1/2 and S=1. We divided the spins into two interpenetrating sublattices, and found the time evolution for the probability of the states of the system. We employed two transition rates which compete between themselves: one, associated with the Glauber process, which describes the relaxation of the system through one-spin flips; the other, related to the simultaneous flipping of pairs of neighboring spins, simulates an input of energy into the system. Using the dynamical pair approximation, we determined the equations of motion for the sublattice magnetizations, and also for the correlation function between first neighbors. We found the phase diagram for the stationary states of the model, and we showed that it exhibits two continuous transition lines: one line between the ferrimagnetic and paramagnetic phases, and the other between the paramagnetic and antiferrimagnetic phases. PMID:11046258

  2. Contrasting spin dynamics

    SciTech Connect

    Ning, F. L. [McMaster University; Ahilan, K. [McMaster University; Imai, T. [McMaster University; Sefat, A. S. [Oak Ridge National Laboratory (ORNL); McGuire, Michael A [ORNL; Sales, Brian C [ORNL; Mandrus, David [ORNL; Cheng, P. [Institute of Physics, Chinese Academy of Science; Shen, B. [Institute of Physics, Chinese Academy of Science; Wen, H.-H. [Institute of Physics, Chinese Academy of Science

    2010-01-01

    We report the first NMR investigation of spin dynamics in the overdoped nonsuperconducting regime of Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} up to x=0.26. We demonstrate that the absence of interband transitions with large momentum transfer Q{sub AF}-({pi}/a,0) between the hole and electron Fermi surfaces results in complete suppression of antiferromagnetic spin fluctuations for x {ge} 0.15. Our experimental results provide direct evidence for a correlation between T{sub c} and the strength of Q{sub AF} antiferromagnetic spin fluctuations.

  3. Spin dynamics in the multiferroic materials (invited)

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  4. 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.

  5. 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.

  6. 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.

  7. Dynamical Blume–Capel Model: Competing Metastable States at Infinite Volume

    Microsoft Academic Search

    F. Manzo; E. Olivieri

    2001-01-01

    This paper concerns the microscopic dynamical description of competing metastable states. We study, at infinite volume and very low temperature, metastability and nucleation for kinetic Blume–Capel model: a ferromagnetic lattice model with spins taking three possible values: -1, 0, 1. In a previous paper ([MO]) we considered a simplified, irreversible, nucleation-growth model; in the present paper we analyze the full Blume–Capel model.

  8. Spin current driven by magnetization dynamics

    NASA Astrophysics Data System (ADS)

    Hosono, Kazuhiro; Takeuchi, Akihito; Tatara, Gen

    2009-02-01

    The spin current induced by the magnetization dynamics in metallic systems is studied theoretically. The s-d exchange interaction between the conduction electron and the local spin is treated perturbatively.

  9. 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.

  10. DYNAMICAL BLUME{CAPEL MODEL: COMPETING METASTABLE STATES AT

    E-print Network

    DYNAMICAL BLUME{CAPEL MODEL: COMPETING METASTABLE STATES AT INFINITE VOLUME F. Manzo (1) , E@mat.uniroma2.it Abstract. This paper concerns the microscopic dynamical description of com- peting metastable states. We study, at in#12;nite volume and very low temperature, metastability and nucleation for kinetic

  11. Dynamics of Skyrmionic Spin Structures

    NASA Astrophysics Data System (ADS)

    Moutafis, Christoforos

    2015-03-01

    Magnetic skyrmions are topologically protected particle-like spin structures, with a topology characterised by their Skyrmion number. They can arise due to various interactions, including exchange, dipolar and anisotropy energy in the case of bubbles (skyrmion bubbles) and an additional Dzyaloshinskii-Moriya interaction (DMi) in the case of chiral skyrmions. Numerical predictions suggest that they exhibit rich dynamical behaviour governed by their topology, such as the basic gyrotropic and breathing eigenmodes. The dynamical experiments are performed on skyrmion bubbles in nanostructures from symmetric CoB/Pt multilayers, tailored for high-frequency dynamics. Asymmetric layers were also fabricated (Co layers in-between 5d-metals) in order to tune the DMi, as expected from recent experiments. Stabilizing chiral skyrmions confined in such nanostructures is highly desirable due to their enhanced stability and smaller size that makes them ideal candidates for integration in recently proposed novel spintronics devices. By investigating the size of magnetic domains in magnetic field cycles, and comparing to micromagnetic simulations, asymmetric multilayers were explored. By performing pump-probe dynamical X-ray imaging on confined skyrmion bubbles the first observation of their basic eigenmode dynamics was demonstrated. In particular, we present picosecond nanoscale imaging data i) of the gyrotropic mode of a single skyrmion bubble in the GHz regime and ii) the breathing-like behaviour of a pair of skyrmionic configurations. The observed dynamics is used to confirm the skyrmion topology and show the existence of an unexpectedly large inertia that is key for describing skyrmion dynamics. These results demonstrate new ways for observing skyrmion dynamics and provide a framework for describing their behaviour. The next step is to achieve chiral skyrmion dynamics on a DMi system.

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

    SciTech Connect

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

    2005-07-15

    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.

  13. Ultrafast spin dynamics in II-VI diluted magnetic semiconductors with spin-orbit interaction

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    We study theoretically the ultrafast spin dynamics of II-VI diluted magnetic semiconductors in the presence of spin-orbit interaction. Our goal is to explore the interplay or competition between the exchange sd coupling and the spin-orbit interaction in both bulk and quantum-well systems. For bulk materials we concentrate on Zn1 -xMnxSe and take into account the Dresselhaus interaction, while for quantum wells we examine Hg1 -x -yMnxCdyTe systems with a strong Rashba coupling. Our calculations were performed with a recently developed formalism which incorporates electronic correlations beyond mean-field theory originating from the exchange sd coupling. For both bulk and quasi-two-dimensional systems we find that, by varying the system parameters within realistic ranges, either of the two interactions can be chosen to play a dominant role or they can compete on an equal footing with each other. The most notable effect of the spin-orbit interaction in both types of system is the appearance of strong oscillations where the exchange sd coupling by itself causes only an exponential decay of the mean electronic spin components. The mean-field approximation is also studied and an analytical interpretation is given as to why it shows a strong suppression of the spin-orbit-induced dephasing of the spin component parallel to the Mn magnetic field.

  14. Amplitude modes and dynamic coexistence of competing orders in multicomponent superconductors

    NASA Astrophysics Data System (ADS)

    Dzero, Maxim; Khodas, Maxim; Levchenko, Alex

    2015-06-01

    We study the nonequilibrium dynamics of an electronic model with competing spin-density-wave and unconventional superconductivity in the context of iron pnictides. Focusing on the collisionless regime, we find that magnetic and superconducting order parameters may coexist dynamically after a sudden quench, even though the equilibrium thermodynamic state supports only one order parameter. We consider various initial conditions concomitant with the phase diagram and in a certain regime identify different oscillatory amplitude modes with incommensurate frequencies for magnetic and superconducting responses. At the technical level we solve the equations of motion for the electronic Green's functions and self-consistency conditions by reducing the problem to a closed set of Bloch equations in a pseudospin representation. For certain quench scenarios the nonadiabatic dynamics of the pairing amplitude is completely integrable and in principle can be found exactly.

  15. Large deviations for Langevin spin glass dynamics

    Microsoft Academic Search

    G. Ben Arous; A. Guionnet

    1995-01-01

    Summary We study the asymptotic behaviour of asymmetrical spin glass dynamics in a Sherrington-Kirkpatrick model as proposed by Sompolinsky-Zippelius. We prove that the annealed law of the empirical measure on path space of these dynamics satisfy a large deviation principle in the high temperature regime. We study the rate function of this large deviation principle and prove that it achieves

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

    E-print Network

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

    2011-01-01

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

  17. Atomistic spin dynamics and surface magnons

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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.

  18. 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

  19. 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.

  20. 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.

  1. Ferromagnet dynamics in a driven spin valve

    NASA Astrophysics Data System (ADS)

    Kupferschmidt, Joern N.; Adam, Shaffique; Brouwer, Piet W.

    2006-03-01

    The magnetoresistance of a ferromagnet/normal-metal/ferromagnet trilayer depends on the relative orientation of the two magnetic moments. We analyze out-of-plane precession of the magnetization for a soft ferromagnetic layer in such a geometry, where the system is driven by an alternating charge current. We consider the effect of both spin-torque and spin-pumping on the magnetization dynamics and find that these have signatures in the magnetoresistance.

  2. Competing effective interactions of Dirac electrons in the Spin-Fermion system

    NASA Astrophysics Data System (ADS)

    Marino, E. C.; Nunes, Lizardo H. C. M.

    2014-01-01

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

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

    E-print Network

    Otani, Yoshichika

    Spin-current-induced dynamics in ferromagnetic nanopillars of lateral spin-valve structures J 4 February 2009 Under electrical injection, spin accumulation occurs in lateral spin valves in a lateral spin valve while simultaneously sweeping an external magnetic field. We observe changes

  4. 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

  5. Low-temperature Glauber dynamics under weak competing interactions.

    PubMed

    Grynberg, M D

    2015-03-01

    We consider the low but nonzero-temperature regimes of the Glauber dynamics in a chain of Ising spins with first- and second-neighbor interactions J1,J2. For 0<-J2/|J1|<1 it is known that at T=0 the dynamics is both metastable and noncoarsening, while being always ergodic and coarsening in the limit of T?0+. Based on finite-size scaling analyses of relaxation times, here we argue that in that latter situation the asymptotic kinetics of small or weakly frustrated -J2/|J1| ratios is characterized by an almost ballistic dynamic exponent z?1.03(2) and arbitrarily slow velocities of growth. By contrast, for noncompeting interactions the coarsening length scales are estimated to be almost diffusive. PMID:25871076

  6. Low-temperature Glauber dynamics under weak competing interactions

    NASA Astrophysics Data System (ADS)

    Grynberg, M. D.

    2015-03-01

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

  7. The dynamics of spinning detonation waves

    Microsoft Academic Search

    H. Jones

    1976-01-01

    The fluid motion of chemically reacting gases in a weak detonation wave is examined with a view to finding a dynamical theory of the spin phenomenon. It is shown that a reacting gas in which the rate of reaction increases with temperature is unstable with respect to wave motion. The amplitude of any wave tends to increase exponentially with time

  8. Structurally Dynamic Spin Market Networks

    NASA Astrophysics Data System (ADS)

    Horváth, Denis; Kuscsik, Zoltán

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

  9. 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.

  10. Dynamical stability of entanglement between spin ensembles

    E-print Network

    H. T. Ng; S. Bose

    2009-03-03

    We study the dynamical stability of the entanglement between the two spin ensembles in the presence of an environment. For a comparative study, we consider the two cases: a single spin ensemble, and two ensembles linearly coupled to a bath, respectively. In both circumstances, we assume the validity of the Markovian approximation for the bath. We examine the robustness of the state by means of the growth of the linear entropy which gives a measure of the purity of the system. We find out macroscopic entangled states of two spin ensembles can stably exist in a common bath. This result may be very useful to generate and detect macroscopic entanglement in a common noisy environment and even a stable macroscopic memory.

  11. Effects of magnetic anisotropy on spin dynamics of ferromagnetic frustrated chain

    NASA Astrophysics Data System (ADS)

    Onishi, Hiroaki

    2015-03-01

    By exploiting density-matrix renormalization group techniques, we investigate the spin dynamics of a spin-1/2 one-dimensional J1-J2 XXZ model with competing ferromagnetic J1 and antiferromagnetic J2 exchange couplings under applied magnetic fields. Numerical results of spin excitation spectra show that in the field-induced spin quadrupole regime, the longitudinal component has a gapless mode and the transverse component has a gapped mode irrespective of the exchange anisotropy. The excitation gap of the transverse spin excitation increases as the exchange anisotropy increases over the XY-like and Ising-like regions, demonstrating that two-magnon bound states are stabilized due to the easy-axis anisotropy.

  12. 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.

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

    SciTech Connect

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

    2014-01-01

    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.

  14. 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.

  15. Spin torque dynamics with noise in magnetic nanosystems

    Microsoft Academic Search

    J. Swiebodzinski; A. Chudnovskiy; T. Dunn; A. Kamenev

    2010-01-01

    We investigate the role of equilibrium and nonequilibrium noise in the magnetization dynamics on monodomain ferromagnets. Starting from a microscopic model, we present a detailed derivation of the spin shot-noise correlator. We investigate the ramifications of the nonequilibrium noise on the spin torque dynamics, both in the steady-state precessional regime and the spin switching regime. In the latter case, we

  16. Nonlinear damping effects in spin torque dynamics of magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Barsukov, Igor; Chen, Yu-Jin; Lee, Han Kyu; Goncalves, Alexandre; Katine, Jordan; Arias, Rodrigo; Ivanov, Boris; Krivorotov, Ilya

    2015-03-01

    Performance of nanoscale spin torque devices such as memory (STT-MRAM) and auto-oscillators critically depends on magnetic relaxation. It is commonly assumed that magnetization dynamics in the presence of spin torque can be understood as simple competition between antidamping arising from spin torque and Gilbert damping of the free layer. However our experiments reveal that the situation is more complex and that nonlinear damping processes in the free layer of magnetic tunnel junction (MTJ) nanopillars can strongly alter spin torque driven dynamics. We study elliptical MTJ nanopillars with in-plane magnetizations of the free layer and SAF layers by spin torque ferromagnetic resonance. We find an excitation spectrum associated with standing spin waves of the free layer. By varying the external field, the energy of a higher-order spin wave mode becomes twice the energy of the main mode. This opens up a nonlinear, resonant relaxation channel, giving rise to a damping increase of approximately 20 percent. With increasing spin torque provided by a DC bias current, we find that this relaxation channel competes with antidamping in a nonlinear manner, increasingly contributing to and even dominating the relaxation at subcritical currents.

  17. Spin dynamics in a two-dimensional electron system with generic spin-orbit coupling

    Microsoft Academic Search

    Tudor Stanescu; Victor Galitski

    2007-01-01

    We study the dynamics of a spin density injected into a two-dimensional electron system with generic spin-orbit interactions. We derive the general spin-charge coupled diffusion equation for a model that includes Rashba as well as linear and cubic Dresselhaus spin-orbit interaction terms. We analyze in detail two regimes: The first regime corresponds to negligible spin-charge coupling and is characterized by

  18. Coherent Heteronuclear Spin Dynamics in an Ultracold Spinor Mixture

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    We report the observation of coherent heteronuclear spin dynamics driven by interspecies 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 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.

  19. Quantum heat bath for spin-lattice dynamics

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  20. 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,…

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

    PubMed

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

    2008-04-28

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

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

    PubMed Central

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

    2008-01-01

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

  3. Spin dynamics and spin noise in the presence of randomly varying spin-orbit interaction in a semiconductor quantum wire.

    PubMed

    Agnihotri, Pratik; Bandyopadhyay, Supriyo

    2012-05-30

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

  4. Secular spin dynamics of inner main-belt asteroids

    Microsoft Academic Search

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

    2006-01-01

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

  5. Application of Molecular Dynamics Simulations to Spin-labeled Oligonucleotides

    Microsoft Academic Search

    Eva Darian; Peter M. Gannett

    2005-01-01

    The EPR study of spin labeled macromolecules has provided insight into structural and dynamical properties of DNA, proteins, and related systems. While spin labeling has been useful, it is experimentally difficult to determine if the spin label significantly alters the conformation of the macromolecule to which it is attached. Molecular modeling has proven to be a powerful tool for studying

  6. Dynamic spin injection into chemical vapor deposited graphene

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  7. Dynamic Stabilization of a Quantum Many-Body Spin System

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  9. 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 ...

  10. Enhanced spin-current tensor contribution in collision dynamics

    SciTech Connect

    Iwata, Yoritaka [GSI Helmholtzzentrum fuer Schwerionenforschung, D-64291 Darmstadt (Germany); Maruhn, Joachim A. [Institut fuer Theoretische Physik, Universitaet Frankfurt, D-60325 Frankfurt (Germany)

    2011-07-15

    The tensor and spin-orbit forces contribute essentially to the formation of the spin mean field, and give rise to the same dynamical effect, namely spin polarization. In this paper, based on time-dependent density functional calculations, we show that the tensor force, which usually acts like a small correction to the spin-orbit force, becomes more important in heavy-ion reactions and the effect increases with the mass of the system.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Yue, Han

    2013-06-01

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

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

    E-print Network

    Zhang, Wenxian

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

  14. 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.

  15. Anisotropic spin-echo dynamics: Maximizing purity for hole spins in quantum dots

    NASA Astrophysics Data System (ADS)

    Coish, William; Wang, Xiaoya Judy; Chesi, Stefano

    2014-03-01

    We theoretically study spin-echo dynamics for a central spin qubit coupled anisotropically to a spin bath. Our main focus is on hole spins in quantum dots, with an anisotropic hyperfine coupling to nuclear spins. Through direct application of a systematic Magnus expansion, we analyze the purity of the spin qubit. The purity can characterize non-classical correlations between the spin qubit and bath and provides a figure-of-merit for preserving an ancilla qubit in some initial state. Interestingly, we show that the purity can be preserved to a greater degree by `parking' the spin qubit in a superposition of Zeeman eigenstates, rather than allowing it to align along an applied magnetic field. The procedure reported here provides a general strategy for preserving ancilla qubits in the presence of anisotropic interactions.

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

    ERIC Educational Resources Information Center

    Bierschenk, Inger

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

  17. Depth-Dependent Spin Dynamics of Canonical Spin-Glass Films: A Low-Energy Muon-Spin-Rotation Study

    Microsoft Academic Search

    E. Morenzoni; H. Luetkens; T. Prokscha; A. Suter; S. Vongtragool; F. Galli; M. B. S. Hesselberth; N. Garifianov; R. Khasanov

    2008-01-01

    We have performed depth dependent muon-spin-rotation and -relaxation studies of the dynamics of single layer films of AuFe and CuMn spin glasses as a function of thickness and of its behavior as a function of distance from the vacuum interface (5 70 nm). A significant reduction in the muon-spin relaxation rate as a function of temperature with respect to the

  18. Controlling Spin-Spin Network Dynamics by Repeated Projective Measurements

    NASA Astrophysics Data System (ADS)

    Bretschneider, Christian O.; Álvarez, Gonzalo A.; Kurizki, Gershon; Frydman, Lucio

    2012-04-01

    We show that coupled-spin network manipulations can be made highly effective by repeated projections of the evolving quantum states onto diagonal density-matrix states (populations). As opposed to the intricately crafted pulse trains that are often used to fine-tune a complex network’s evolution, the strategy hereby presented derives from the “quantum Zeno effect” and provides a highly robust route to guide the evolution by destroying all unwanted correlations (coherences). We exploit these effects by showing that a relaxationlike behavior is endowed to polarization transfers occurring within a N-spin coupled network. Experimental implementations yield coupling constant determinations for complex spin-coupling topologies, as demonstrated within the field of liquid-state nuclear magnetic resonance.

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

    E-print Network

    Liu, Xin

    2012-10-19

    We study the spin dynamics in a high-mobility two dimensional electron gas (2DEG) system with generic spin-orbit interactions (SOIs). We derive a set of spin dynamic equations which capture the purely exponential to the damped oscillatory spin...

  20. Dynamic spin label study of the barstar-barnase complex

    Microsoft Academic Search

    V. P. Timofeev; T. G. Balandin; Ya. V. Tkachev; V. V. Novikov; V. A. Lapuk; S. M. Deev

    2007-01-01

    The dynamic spin label method was used to study protein-protein interactions in the model complex of the enzyme barnase (Bn)\\u000a with its inhibitor barstar. The C40A mutant of barstar (Bs) containing a single cysteine residue was modified with two different\\u000a spin labels varying in length and structure of a flexible linker. Each spin label was selectively bound to the Cys82

  1. Competing charge, spin, and superconducting orders in underdoped YBa2Cu3Oy

    NASA Astrophysics Data System (ADS)

    Hücker, M.; Christensen, N. B.; Holmes, A. T.; Blackburn, E.; Forgan, E. M.; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Gutowski, O.; Zimmermann, M. v.; Hayden, S. M.; Chang, J.

    2014-08-01

    To explore the doping dependence of the recently discovered charge-density-wave (CDW) order in YBa2Cu3Oy, we present a bulk-sensitive high-energy x-ray study for several oxygen concentrations, including strongly underdoped YBa2Cu3O6.44. Combined with previous data around the so-called 1/8 doping, we show that bulk CDW order exists at least for hole concentrations (p) in the CuO2 planes of 0.078?p?0.132. This implies that CDW order exists in close vicinity to the quantum critical point for spin-density-wave (SDW) order. In contrast to the pseudogap temperature T*, the onset temperature of CDW order decreases with underdoping to TCDW˜90 K in YBa2Cu3O6.44. Together with a weakened order parameter this suggests a competition between CDW and SDW orders. In addition, the CDW order in YBa2Cu3O6.44 shows the same type of competition with superconductivity as a function of temperature and magnetic field as samples closer to p =1/8. At low p the CDW incommensurability continues the previously reported linear increasing trend with underdoping. In the entire doping range the in-plane correlation length of the CDW order in b axis direction depends only very weakly on the hole concentration, and appears independent of the type and correlation length of the oxygen-chain order. The onset temperature of the CDW order is remarkably close to a temperature T† that marks the maximum of 1/(T1T) in planar Cu63 NQR/NMR experiments, potentially indicating a response of the spin dynamics to the formation of the CDW. Our discussion of these findings includes a detailed comparison to the charge stripe order in La2-xBaxCuO4.

  2. Dynamics of a light aircraft in spin

    Microsoft Academic Search

    Zdobys?aw Goraj; Alfred Baron; Jan Kacprzyk

    2002-01-01

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

  3. Dynamic nuclear polarization with single electron spins.

    PubMed

    Petta, J R; Taylor, J M; Johnson, A C; Yacoby, A; Lukin, M D; Marcus, C M; Hanson, M P; Gossard, A C

    2008-02-15

    We polarize nuclear spins in a GaAs double quantum dot by controlling two-electron spin states near the anticrossing of the singlet (S) and m(S)= +1 triplet (T+) using pulsed gates. An initialized S state is cyclically brought into resonance with the T+ state, where hyperfine fields drive rapid rotations between S and T+, "flipping" an electron spin and "flopping" a nuclear spin. The resulting Overhauser field approaches 80 mT, in agreement with a simple rate-equation model. A self-limiting pulse sequence is developed that allows the steady-state nuclear polarization to be set using a gate voltage. PMID:18352516

  4. Dynamical phase transition in a simple model of competing shops

    E-print Network

    Lambert, Gaultier; Bertin, Eric

    2011-01-01

    We consider a simple model in which a set of agents randomly visit one of two competing shops selling the same perishable products (typically food). The satisfaction of agents with respect to a given store is related to the freshness of the previously bought products. Agents then choose with a higher probability the store they are most satisfied with. Studying the model both through numerical simulations and mean-field analytical methods, we find a rich behaviour with continuous and discontinuous phase transitions between a symmetric phase where both stores maintain the same level of activity, and a phase with broken symmetry where one of the two shops attracts more customers than the other.

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

    SciTech Connect

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

    2014-09-15

    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.

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

    SciTech Connect

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

    2010-10-01

    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.

  7. Spin motive force driven by skyrmion dynamics in magnetic nanodisks

    NASA Astrophysics Data System (ADS)

    Shimada, Yuhki; Ohe, Jun-ichiro

    2015-05-01

    The spin motive force driven by the dynamics of the skyrmion structure formed in a nanomagnetic disk is numerically investigated. Due to the existence of the magnetic structure along the disk edge, the collective mode of the magnetization is modified from that of the bulk skyrmion lattice obtained by using the periodic boundary condition. For a single-skyrmion disk, the dynamics of the skyrmion core and the edge magnetization induce the spin motive force, and a measurable AC voltage is obtained by two probes on the disk. For a multi-skyrmions disk, the phase-locked collective mode of skyrmions is found in the lowest resonant frequency where the amplitude of the AC voltage is enhanced by the cascade effect of the spin motive force. We also investigate the effect of the Rashba spin-orbit coupling on the spin motive force.

  8. Cosmological dynamics with propagating Lorentz connection modes of spin zero

    SciTech Connect

    Chen, Hsin; Ho, Fei-Hung; Nester, James M.; Wang, Chih-Hung [Department of Physics, National Central University, No. 300, Jhongda Rd., Jhongli 320, Taiwan (China); Yo, Hwei-Jang, E-mail: hchen@ntnu.edu.tw, E-mail: 93242010@cc.ncu.edu.tw, E-mail: nester@phy.ncu.edu.tw, E-mail: chwang@phy.ncu.edu.tw, E-mail: hjyo@phys.ncku.edu.tw [Department of Physics, National Cheng-Kung University, No. 1, University Rd., Tainan 701, Taiwan (China)

    2009-10-01

    The Poincaré gauge theory of gravity has a Lorentz connection with both torsion and curvature. For this theory two good propagating connection modes, carrying spin-0{sup +} and spin-0{sup ?}, have been found. The possible effects of the spin-0{sup +} mode in cosmology were investigated in a previous work by our group; there it was found that the 0{sup +} mode could account for the presently accelerating universe. Here, we extend the analysis to also include the spin-0{sup ?} mode. The resulting cosmological model has three degrees of freedom. We present both the Lagrangian and Hamiltonian form of the dynamic equations for this model, find the late-time normal modes, and present some numerical evolution cases. In the late time asymptotic regime the two dynamic modes decouple, and the acceleration of the Universe oscillates due to the spin-0{sup +} mode.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    We experimentally investigate the protection of electron spin coherence of a nitrogen-vacancy (NV) centre in diamond by dynamic nuclear spin polarization (DNP). The electron spin decoherence of an NV centre is caused by the magnetic field fluctuation of the 13C nuclear spin bath, which contributes large thermal fluctuation to the centre electron spin when it is in an equilibrium state at room temperature. To address this issue, we continuously transfer the angular momentum from electron spin to nuclear spins, and pump the nuclear spin bath to a polarized state under the Hartmann-Hahn condition. The bath polarization effect is verified by the observation of prolongation of the electron spin coherence time (T*2). Optimal conditions for the DNP process, including the pumping pulse duration and repeat numbers, are proposed by numerical simulation and confirmed by experiment. We also studied the depolarization effect of laser pulses. Our results provide a new route for quantum information processing and quantum simulation using the polarized nuclear spin bath.

  10. 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.

  11. 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

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

  12. Depth-dependent spin dynamics of canonical spin-glass films: a low-energy muon-spin-rotation study.

    PubMed

    Morenzoni, E; Luetkens, H; Prokscha, T; Suter, A; Vongtragool, S; Galli, F; Hesselberth, M B S; Garifianov, N; Khasanov, R

    2008-04-11

    We have performed depth dependent muon-spin-rotation and -relaxation studies of the dynamics of single layer films of AuFe and CuMn spin glasses as a function of thickness and of its behavior as a function of distance from the vacuum interface (5-70 nm). A significant reduction in the muon-spin relaxation rate as a function of temperature with respect to the bulk material is observed when the muons are stopped near (5-10 nm) the surface of the sample. A similar reduction is observed for the whole sample if the thickness is reduced to, e.g., 20 nm and less. This reflects an increased impurity spin dynamics (incomplete freezing) close to the surface although the freezing temperature is only modestly affected by the dimensional reduction. PMID:18518070

  13. Gigahertz dynamics of a strongly driven single quantum spin.

    PubMed

    Fuchs, G D; Dobrovitski, V V; Toyli, D M; Heremans, F J; Awschalom, D D

    2009-12-11

    Two-level systems are at the core of numerous real-world technologies such as magnetic resonance imaging and atomic clocks. Coherent control of the state is achieved with an oscillating field that drives dynamics at a rate determined by its amplitude. As the strength of the field is increased, a different regime emerges where linear scaling of the manipulation rate breaks down and complex dynamics are expected. By calibrating the spin rotation with an adiabatic passage, we have measured the room-temperature "strong-driving" dynamics of a single nitrogen vacancy center in diamond. With an adiabatic passage to calibrate the spin rotation, we observed dynamics on sub-nanosecond time scales. Contrary to conventional thinking, this breakdown of the rotating wave approximation provides opportunities for time-optimal quantum control of a single spin. PMID:19965386

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

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  15. Spin Polarized Electron Scattering from and Spin Dynamics of Ultrathin Magnetic Films

    NASA Astrophysics Data System (ADS)

    Plihal, Martin

    1995-01-01

    Polarized electron beams interacting with the surface via exchange and spin orbit coupling established themselves as a unique tool for studying magnetic and electronic surface properties. We use the multiple scattering theory of the spin polarized low energy electron diffraction (SPLEED) to study the structural and magnetic properties of Fe bilayer on W(001) substrate. We find the spin orbit asymmetry--a measure of the spin orbit coupling--to be very sensitive to the position of the surface ions. On the other hand, the exchange asymmetry--a measure of the exchange coupling between the beam and substrate electrons--proves to be far less sensitive to changes in magnetic properties of the film. Inelastic electron scattering accompanied by the flip of the incoming beam spin is a potentially powerful probe of magnetic excitations in ultrathin films. We have investigated the spin flip component of the diffuse scattering near the bulk critical temperature of an antiferromagnetically ordered surface. Within the Landau-Ginzburg theory we explore the static correlation function. For Cr(110), we then calculate the intensity of both the diffuse peak near T_{c} and the half -order beams. We find the intensities are within the reach of the state of the art experimental techniques. While the total rate of inelastic scattering integrated over the energy loss is controlled by the static correlation function, the energy resolved loss spectrum requires the knowledge of the spin dynamics. There is currently very little understanding of the spin dynamics of itinerant electron magnetic films. We use the one band Hubbard model to study the transverse dynamic susceptibility of films consisting of magnetic layers with ferromagnetic order within the layers parallel to the surface. The coupling between the layers is arbitrary. The nature of the spin waves and Stoner spectrum is investigated and discussed. It is shown that the SPEELS spectrum contains information about the local magnetic properties of the surface layer.

  16. Quantum Communication through Spin Chain Dynamics: an Introductory Overview

    E-print Network

    Bose, Sougato

    2008-01-01

    We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.

  17. Quantum Communication through Spin Chain Dynamics: an Introductory Overview

    E-print Network

    Sougato Bose

    2008-02-08

    We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

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

    SciTech Connect

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

    2007-08-24

    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.

  20. Robust Dynamical Decoupling Sequences for Individual Nuclear Spin Addressing

    E-print Network

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

    2015-06-11

    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. 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

  2. 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

  3. Dynamic spin label study of the barstar-barnase complex.

    PubMed

    Timofeev, V P; Balandin, T G; Tkachev, Ya V; Novikov, V V; Lapuk, V A; Deev, S M

    2007-09-01

    The dynamic spin label method was used to study protein-protein interactions in the model complex of the enzyme barnase (Bn) with its inhibitor barstar. The C40A mutant of barstar (Bs) containing a single cysteine residue was modified with two different spin labels varying in length and structure of a flexible linker. Each spin label was selectively bound to the Cys82 residue, located near the Bn-Bs contact site. The formation of the stable protein complex between Bn and spin labeled Bs was accompanied by a substantial restriction of spin label mobility, indicated by remarkable changes in the registered EPR spectra. Order parameter, S, as an estimate of rapid reorientation of spin label relative to protein molecule, was sharply increasing approaching 1. However, the rotational correlation time tau for spin-labeled Bs and its complex with Bn in solution corresponded precisely to their molecular weights. These data indicate that both Bs and its complex with Bn are rigid protein entities. Spin labels attached to Bs in close proximity to an interface of interaction with Bn, regardless of its structure, undergo significant restriction of mobility by the environment of the contact site of the two proteins. The results show that this approach can be used to investigate fusion proteins containing Bn or Bs. PMID:17922659

  4. 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. 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).

  5. Spin dynamics of Gd at high temperatures

    SciTech Connect

    Cable, J. W.; Nicklow, R. M.

    1989-06-01

    The magnetic excitation spectra of Gd were measured by neutron inelastic scattering over the entire Brillouin zone in the <110> direction at temperatures from 250 to 850 K (/ital T//sub /ital c//=293 K). The data were fitted to a damped-harmonic-oscillator form for the spectral weight function and were placed on an absolute cross-section basis. Wave-vector-dependent susceptibilities were obtained by integration over energy. They clearly show the presence of static spin correlations even at /ital T/=850 K. At /ital T/greater than or equal to/ital T//sub /ital c// we observe a crossover from spin-diffusive motion at small /ital q/ to spin-wave behavior at large /ital q/. The wave vector /ital q//sub /ital c// at which this crossover occurs is determined by the ratio of the damping parameter to the second moment, <..omega../sup 2/>, of the frequency distribution. Surprisingly, <..omega../sup 2/> remains independent of temperature above /ital T//sub /ital c//, and the temperature dependence of /ital q//sub /ital c// is therefore determined by a gradual change in the damping. This results in a very weak /ital q//sub /ital c//-versus-/ital T/ dependence, which is not consistent with a magnetic short-range-order interpretation for the existence of spin waves above /ital T//sub /ital c//.

  6. Quantum Spin Dynamics and Quantum Computation

    E-print Network

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

    2000-01-14

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

  7. Dynamics of magnetization in ferromagnet with spin-transfer torque

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  8. Controlling Spin Dynamics of Magnetic Spin Chains at the Atomic Scale

    NASA Astrophysics Data System (ADS)

    Yan, Shichao; Choi, Deung-Jang; Burgess, Jacob; Rolf-Pissarczyk, Steffen; Loth, Sebastian

    2014-03-01

    By combining radio-frequency circuitry with sub-Kelvin Scanning Tunneling Microscopy (STM), fast electric pump-probe pulses of nanosecond duration can be introduced into the tunneling junction with high fidelity. We apply this technique to study dynamics of Fe trimers which can be assembled with the tip of the STM by placing Fe atoms in a regular pattern on copper nitride surface on Cu(100). The spin relaxation time of Fe trimers is found to be extremely sensitive to variations in their environment. This sensitivity can be used to sense the presence of another spin. By attaching a transition metal atom to the STM tip and approaching it to the nanostructure on the surface we deduce the coupling strength between the magnetic atoms. Furthermore, the magnetic state of long-lived spin chains can be sensed even at several nanometers distance by minute changes of the Fe trimer's spin relaxation time. This work paves the way to study and control spin dynamics of nanostructures with precisely tunable spin environments.

  9. Dynamics of spin torque switching in all-perpendicular spin valve nanopillars

    NASA Astrophysics Data System (ADS)

    Liu, H.; Bedau, D.; Sun, J. Z.; Mangin, S.; Fullerton, E. E.; Katine, J. A.; Kent, A. D.

    2014-05-01

    We present a systematic experimental study of the spin-torque-induced magnetic switching statistics at room temperature, using all-perpendicularly magnetized spin-valves as a model system. Three physical regimes are distinguished: a short-time ballistic limit below a few nanoseconds, where spin-torque dominates the reversal dynamics from a thermal distribution of initial conditions; a long time limit, where the magnetization reversal probability is determined by spin-torque-amplified thermal activation; and a cross-over regime, where the spin-torque and thermal agitation both contribute. For a basic quantitative understanding of the physical processes involved, an analytical macrospin model is presented which contains both spin-torque dynamics and finite temperature effects. The latter was treated rigorously using a Fokker-Plank formalism, and solved numerically for specific sets of parameters relevant to the experiments to determine the switching probability behavior in the short-time and cross-over regimes. This analysis shows that thermal fluctuations during magnetization reversal greatly affect the switching probability over all the time scales studied, even in the short-time limit.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  11. Static and dynamic properties of magnetic systems with competing dipolar and tensorial order parameters

    NASA Astrophysics Data System (ADS)

    Onufrieva, F. P.

    1993-05-01

    A general approach to the study of magnetic systems with competing dipolar and tensorial interactions is developed. The approach extensively uses the relevant properties of the Lie algebra SU( n) ( n=2 S+1). It allows us to find all types of possible ordered phases, to analyze the spectrum of collective excitations and to determine the thermodynamic and dynamic properties. Some applications for magnetic systems with quadrupolar intersite interactions are given.

  12. 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.

  13. Dynamics of Algebraic Spin Liquid in Kitaev-Hubbard Model

    NASA Astrophysics Data System (ADS)

    Prasad, Yogeshwar

    2015-03-01

    The Kitaev-Hubbard model is basically a Hubbard model with spin-dependent hopping, which breaks time-reversal symmetry. The zero-temperature phase diagram of the Kitaev-Hubbard model at half-filling and the stability of algebraic spin liquid (ASL) phase within this model has previously been studied in and. We study the model at half-filling, with determinant quantum monte carlo (DQMC) technique on honeycomb lattice, and mapped out the phase diagram in U- T-t' plane. We investigate the dynamics of the algebraic spin liquid phase in Kitaev-Hubbard model and foresee the experimental realization of algebraic spin liquid phase in cold atom systems. I will like to acknowledge valuable discussions with Prof. S. R. Hassan and P. V. Sriluckshmy.

  14. Controlling the quantum dynamics of a mesoscopic spin bath in diamond

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  15. Longitudinal Spin Diffusion and Nonlinear Spin Dynamics in HELIUM3HELIUM Solutions

    Microsoft Academic Search

    Geoffrey Nunes Jr.

    1991-01-01

    Dilute solutions of ^3He in ^4He offer a unique opportunity to study both the transition of a Fermi system from classical to degenerate behavior, and the spin dynamics of a highly polarized Fermi system in equilibrium with a static field. In this thesis we report the results of NMR experiments on 350 ppm and 1940 ppm solutions of ^3He in

  16. Dynamics of spinning test particles in Kerr spacetime

    E-print Network

    Michael D. Hartl

    2003-02-12

    We investigate the dynamics of relativistic spinning test particles in the spacetime of a rotating black hole using the Papapetrou equations. We use the method of Lyapunov exponents to determine whether the orbits exhibit sensitive dependence on initial conditions, a signature of chaos. In the case of maximally spinning equal-mass binaries (a limiting case that violates the test-particle approximation) we find unambiguous positive Lyapunov exponents that come in pairs +/- lambda, a characteristic of Hamiltonian dynamical systems. We find no evidence for nonvanishing Lyapunov exponents for physically realistic spin parameters, which suggests that chaos may not manifest itself in the gravitational radiation of extreme mass-ratio binary black-hole inspirals (as detectable, for example, by LISA, the Laser Interferometer Space Antenna).

  17. Glassy spin dynamics in stripe ordered cuprate system

    SciTech Connect

    Curro, N. J. (Nicholas J.)

    2004-01-01

    The unusual glassy dynamics exhibited by the spin fluctuations in the stripe-ordered cuprates can be quantitatively measured by La nuclear magnetic resonance. We analyze the spin lattice relaxation data in the low temperature tetragonal structural phase of La{sub 1.8-x}Eu{sub 0.2}Sr{sub x}CuO{sub 4} and find that there is a distribution of local fluctuations times, with a Vogel-Fulcher temperature dependence. Furthermore, the data are consistent with a stretched exponential form for the dynamical spin correlation function, typical of glassy systems. Several doped transition metal oxides exhibit unusual properties associated with heterogeneous charge order. Of particular interest are the cuprates, which become high temperature superconductors within a certain doping range. Charge stripe correlations may play a crucial role in the mechanism for the superconductivity, yet detailed information about the microscopic structure of the charge order as well as the dynamics of this stripes have remained elusive. Nuclear magnetic resonance (NMR) probes the local, low energy spin and charge fluctuations at the nuclear sites, and provides important clues to charge-stripe dynamics.

  18. Dephasing dynamics of Rydberg atom spin waves

    NASA Astrophysics Data System (ADS)

    Bariani, F.; Goldbart, Paul M.; Kennedy, T. A. B.

    2012-10-01

    A theory of Rydberg atom interactions is used to derive analytical forms for the spin-wave pair correlation function in laser-excited cold-atom vapors. This function controls the quantum statistics of light emission from dense, inhomogeneous clouds of cold atoms of various spatial dimensionalities. The results yield distinctive scaling behaviors on the microsecond time scale, including generalized exponential decay. A detailed comparison is presented with a recent experiment on a cigar-shaped atomic ensemble [Y. Dudin and A. Kuzmich, ScienceSCIEAS0036-807510.1126/science.1217901 336, 887 (2012)], in which Rb atoms are excited to a set of Rydberg levels.

  19. Spin dynamics of triangular lattice antiferromagnet CuFeO2 : Crossover from spin-liquid to paramagnetic phase

    NASA Astrophysics Data System (ADS)

    Hayashi, K.; Nozaki, T.; Fukatsu, R.; Miyazaki, Y.; Kajitani, T.

    2009-10-01

    We have investigated the spin dynamics of triangular lattice antiferromagnet CuFeO2 by measuring powder neutron inelastic-scattering spectra. A quasielastic component whose half-width oscillates with the magnitude of the scattering vector appears in the spectra above Néel temperature. A dynamics model representing the shape of quasielastic components and oscillatory behaviors changes from spin jump diffusion to Heisenberg paramagnetic (PM) scattering with increasing temperature. These findings demonstrate that CuFeO2 shows a gradual transition from a spin-liquid phase to the Heisenberg PM phase. The origin of the spin-liquid phase is discussed in terms of incommensurate short-range spin correlation.

  20. Spin noise spectroscopy in GaAs (110) quantum wells: access to intrinsic spin lifetimes and equilibrium electron dynamics.

    PubMed

    Müller, Georg M; Römer, Michael; Schuh, Dieter; Wegscheider, Werner; Hübner, Jens; Oestreich, Michael

    2008-11-14

    In this Letter, the first spin noise spectroscopy measurements in semiconductor systems of reduced effective dimensionality are reported. The nondemolition measurement technique gives access to the otherwise concealed intrinsic, low temperature electron spin relaxation time of n-doped GaAs (110) quantum wells and to the corresponding low temperature anisotropic spin relaxation. The Brownian motion of the electrons within the spin noise probe laser spot becomes manifest in a modification of the spin noise line width. Thereby, the spatially resolved observation of the stochastic spin polarization uniquely allows to study electron dynamics at equilibrium conditions with a vanishing total momentum of the electron system. PMID:19113364

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

    PubMed Central

    Maryasov, Alexander G.

    2012-01-01

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

  2. Edge dynamics in a quantum spin Hall state: effects from Rashba spin-orbit interaction.

    PubMed

    Ström, Anders; Johannesson, Henrik; Japaridze, G I

    2010-06-25

    We analyze the dynamics of the helical edge modes of a quantum spin Hall state in the presence of a spatially nonuniform Rashba spin-orbit (SO) interaction. A randomly fluctuating Rashba SO coupling is found to open a scattering channel which causes localization of the edge modes for a weakly screened electron-electron (e-e) interaction. A periodic modulation of the SO coupling, with a wave number commensurate with the Fermi momentum, makes the edge insulating already at intermediate strengths of the e-e interaction. We discuss implications for experiments on edge state transport in a HgTe quantum well. PMID:20867409

  3. Conservative effects in spin-transfer-driven magnetization dynamics

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  4. Spin torque phenomena originating from the spin Hall effect: resonance, magnetic switching, and magnetic dynamics

    NASA Astrophysics Data System (ADS)

    Liu, Luqiao

    2012-02-01

    The spin Hall effect (SHE) generates a transverse spin current with the passage of a current through a non-ferromagnetic metal (NM) film. Quite different results have been obtained for the magnitude of this effect. Here I will discuss a new technique where, by applying an RF current to a NM/FM thin film bilayer, the spin current onto the FM layer can induce a spin torque ferromagnetic resonance (ST-FMR). This enables the determination of the SHE strength with precision and without the need to assume the values of unmeasured parameters. The large magnitude of the SHE that we have established in several types of NM is sufficient to reversibly switch the magnetic orientation of a FM layer and I will discuss two different implementations of this. In the first the FM layer has a perpendicular-to-plane magnetic moment at equilibrium and the SHE injected spins are orthogonal to the moment. The spin torque can overcome the anisotropy (coercive) field restoring torque, with the polarity of the current-induced switching being determined by the sign of a small external field applied along the current direction. In the second approach, the FM moment lies in plane and the spins injected by the SHE exert a negative damping just as in conventional ST switching of a spin valve or magnetic tunnel junction (MTJ). We have fabricated three-terminal devices that incorporate a MTJ and a SHE layer to induce in-plane reversal switching. The simple architecture of this three terminal device and the high efficiency of the SHE induced switching made it a promising technique for future memory and non-volatile logic applications. We have also used this three terminal device to demonstrate DC induced dynamics in the magnetic layer due to the SHE.

  5. 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.

  6. 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.

  7. Spin and Beam Dynamics at the Fermilab Main Injector

    NASA Astrophysics Data System (ADS)

    Aidala, Christine

    2014-09-01

    Initial studies performed by the Spin@Fermi collaboration for producing and maintaining a polarized proton beam at 120 GeV using a single Siberian snake in the Fermilab Main Injector have been promising. More detailed studies incorporating a single Siberian snake into the Main Injector lattice and a partial snake as well as pulsed quadrupoles into the Booster lattice are presently underway. The resulting beam and spin dynamics given specific new equipment configurations are being examined. The current status of these simulation studies will be presented.

  8. Spin dynamics in the two-dimensional spin system SrCu 2(BO 3) 2

    NASA Astrophysics Data System (ADS)

    Fukaya, A.; Fudamoto, Y.; Gat, I. M.; Ito, T.; Larkin, M. I.; Savici, A. T.; Uemura, Y. J.; Kyriakou, P. P.; Luke, G. M.; Rovers, M. T.; Kageyama, H.; Ueda, Y.

    2003-02-01

    Muon spin relaxation measurements have been performed in the two dimensional spin system SrCu 2(BO 3) 2. As the temperature decreases, the relaxation rate increases below T=10 K, and shows a saturation below T=3 K. The line shape at low temperatures is nearly Gaussian, yet it cannot be easily decoupled by an application of longitudinal field. These results indicate the existence of magnetically active spins that show slowing down of fluctuations with decreasing temperatures, yet remain dynamic even at 0.1 K. We have also examined a sample doped with small amount of non-magnetic Zn 2+ impurity, Sr(Cu 0.99Zn 0.01) 2(BO 3) 2. The result was quite similar to the pure sample. Thus, anomalous behavior of the pure sample observed in low temperatures is not due to magnetic moments induced by impurities or a lattice defect.

  9. Matrix Formalism for Spin Dynamics Near a Single Depolarization Resonance

    SciTech Connect

    Chao, Alexander W.; /SLAC

    2005-10-26

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

  10. Structural and dynamical features of multiple metastable glassy states in a colloidal system with competing interactions

    E-print Network

    Christian L. Klix; C. Patrick Royall; Hajime Tanaka

    2010-02-08

    Systems in which a short-ranged attraction and long-ranged repulsion compete are intrinsically frustrated, leading their structure and dynamics to be dominated either by mesoscopic order or by metastable disorder. Here we report the latter case in a colloidal system with long-ranged electrostatic repulsions and short-ranged depletion attractions. We find a variety of states exhibiting slow non-diffusive dynamics: a gel, a glassy state of clusters, and a state reminiscent of a Wigner glass. Varying the interactions, we find a continuous crossover between the Wigner and cluster glassy states, and a sharp discontinuous transition between the Wigner glassy state and gel. This difference reflects the fact that dynamic arrest is driven by repulsion for the two glassy states and attraction in the case of the gel.

  11. Dynamical competition between quantum Hall and quantum spin Hall effects

    NASA Astrophysics Data System (ADS)

    Quelle, A.; Morais Smith, C.

    2014-11-01

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

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

    SciTech Connect

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

  13. Coherent spin–rotational dynamics of oxygen superrotors

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  14. 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.

  15. 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.

  16. Spin Dynamics in Exchange Biased Co\\/FeMn Bilayers

    Microsoft Academic Search

    Jeffrey Parker; Mun Chan; Melissa Haugen; Bruce Bolon; Chris Leighton; Paul Crowell

    2006-01-01

    We report a study of the spin dynamics in exchange biased Co\\/FeMn bilayers using time resolved Kerr microscopy (TKRM) with sub-nanosecond resolution. Samples were prepared via UHV dc magnetron sputter deposition onto a Si\\/SiOx substrate at room temperature in an applied field of 300 Oe. Deposition of a 30nm Cu buffer layer allowed for (111) textured growth of the subsequent

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

    SciTech Connect

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

    2009-10-15

    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.

  18. 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).

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

    SciTech Connect

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

    2010-08-15

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

  20. Dynamic switching of the spin circulation in tapered magnetic nanodisks.

    PubMed

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

    2013-05-01

    Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. With each having two possible states, there are four possible stable magnetization configurations that can be utilized for a multibit memory cell. Dynamic control of vortex core polarity has been demonstrated using both alternating and pulsed magnetic fields and currents. Here, we show controlled dynamic switching of spin circulation in vortices using nanosecond field pulses by imaging the process with full-field soft X-ray transmission microscopy. The dynamic reversal process is controlled by far-from-equilibrium gyrotropic precession of the vortex core, and the reversal is achieved at significantly reduced field amplitudes when compared with static switching. We further show that both the field pulse amplitude and duration required for efficient circulation reversal can be controlled by appropriate selection of the disk geometry. PMID:23603985

  1. Thermal stability in spin-torque-driven magnetization dynamics

    NASA Astrophysics Data System (ADS)

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

    2006-04-01

    In this article, thermal fluctuations in spin-torque-driven magnetization dynamics are described phenomenologically by introducing a Gaussian white noise term in the Landau-Lifshitz-Slonczewski equation. The ensuing stochastic magnetization dynamics is studied by considering the Fokker-Planck equation for the probability distribution of magnetization. The corresponding Fokker-Planck for the energy probability distribution is then derived in the limit of small fluctuations by averaging with respect to fast-time-scale precessional dynamics. By using this equation the stationary probability distribution of energy is analytically determined. This distribution has peaks around stable stationary states as well as around self-oscillatory regimes. On this basis, we define an effective potential barrier controlling switching between stable equilibrium states and self-oscillatory regimes.

  2. 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.

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

    E-print Network

    Thomas, David D.

    . This study uses molecular dynamics simulations of an experimental system to explore and enhance the siteMolecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle ABSTRACT We have developed a computational molecular dynamics technique to simulate the motions of spin

  4. On the Spin-axis Dynamics of the Earth

    NASA Astrophysics Data System (ADS)

    Li, Gongjie; Batygin, Konstantin

    2015-05-01

    The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, the Earth's obliquity is stabilized by the Moon, and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically-forced climate change is the rate of chaotic diffusion. Accordingly, here we reexamine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in the Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structure in a simple and intuitive manner. In addition, we examine if at any point in the Earth's evolutionary history, the obliquity varied significantly. We find that even though the orbital perturbations were different in the past, the system nevertheless avoided resonant encounters throughout its evolution. This indicates that the Earth obtained its current obliquity during the formation of the Moon.

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

    NASA Astrophysics Data System (ADS)

    Rahnavard, Yousef; Brenig, Wolfram

    2015-02-01

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

  6. 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.

  7. Spin effects and the Pauli principle in semiclassical electron dynamics

    NASA Astrophysics Data System (ADS)

    Grossmann, F.; Buchholz, M.; Pollak, E.; Nest, M.

    2014-03-01

    Several approaches to the semiclassical dynamics of fermions have been proposed in the past. The main subject under discussion was the inclusion of the Pauli principle, i.e., the fact that two electrons with parallel spins must be in orthogonal states. In the past, this was sometimes achieved by adding repulsive Pauli potentials or by using antisymmetric trial states. In this article we show that (a) the use of semiclassical propagators based on classical trajectories is sufficient to account for the Pauli principle, but (b) a semiclassical wave-function approach is not satisfactory.

  8. Spin fluctuation dynamics and multiband superconductivity in iron pnictides

    NASA Astrophysics Data System (ADS)

    Stanev, Valentin; Kang, Jian; Tesanovic, Zlatko

    2008-11-01

    Multiband superconductivity, involving resonant pair scattering between different bands, has emerged as a possible explanation of some of the main characteristics of the recently discovered iron pnictides. A key feature of such interband pairing mechanism is that it can generate or enhance superconductivity irrespective of whether it is attractive or repulsive. The latter case typically leads to the superconducting gap switching its sign among different sections of the Fermi surface. In iron pnictides, the natural scenario is that the gap changes sign between the hole and the electron Fermi surfaces. However, the macroscopic symmetry of such an extended s' -wave state still belongs to the general s -wave category, raising the question of how to distinguish it from an ordinary s wave. In such a quest, it is essential to use experimental techniques that have a momentum space resolution and can probe momenta of order (?,?) : the wave vector that separates the hole and the electron Fermi surfaces in the Brillouin zone. Here we study experimental signatures in the spin fluctuation dynamics of the fully gapped s - and s' -wave superconducting states, as well as those of the nodal d and p wave states. The coupling between spin fluctuations of the incipient nearly nested spin-density wave (SDW) and the Bogoliubov-de Gennes quasiparticles of the superconducting state leads to the Landau-type damping of the former. The intrinsic structure of the superconducting gap leaves a distinctive signature in the form of this damping, allowing it to be used to diagnose the nature of iron-based superconductivity in neutron scattering and other experiments sensitive to spin fluctuations in momentum space. We also discuss the coexistence between superconductivity and SDW order.

  9. Aircraft Spin Recovery, with and without Thrust Vectoring, Using Nonlinear Dynamic Inversion

    Microsoft Academic Search

    P. K. Raghavendra; Tuhin Sahai; P. Ashwani Kumar; Manan Chauhan; N. Ananthkrishnan

    2005-01-01

    The present paper addresses the problem of spin recovery of an aircraft as a nonlinear inverse dynamics problem of determining the control inputs that need to be applied to transfer the aircraft from a spin state to a level trim flight condition. A stable, oscillatory, flat, left spin state is first identified from a standard bifurcation analysis of the aircraft

  10. Chaotic Dynamics of Spin-Valve Oscillators Z. Yang and S. Zhang

    E-print Network

    Li, Charles

    Chaotic Dynamics of Spin-Valve Oscillators Z. Yang and S. Zhang Department of Physics and Astronomy oscillators with tunable mi- crowave frequencies in spin valves are very desirable for magnetic storage it is not an intrinsic property of the current-driven oscillator. Here we consider a single-domain current-driven spin-valve

  11. 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…

  12. Muonium chemistry and spin dynamics in sulphur, modelling interstitial hydrogen.

    PubMed

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

    2011-08-10

    The nature of the elusive muonium centre in sulphur is re-examined in the light of new data on its level-crossing resonance and spin-lattice relaxation. The aim is to provide a model for the solid-state chemistry of interstitial hydrogen in this element, which is as yet unknown, as well as to solve one of the longest standing puzzles in ?SR spectroscopy, namely the surprisingly strong depolarization of muons mimicking ion-implanted protons in this innocuous non-magnetic material. The paramagnetic muonium (and by inference hydrogen) centre is confirmed to have the character of a molecular radical, but with huge anisotropy at cryogenic temperatures and a striking shift of the resonance at ordinary temperatures, the hyperfine parameters appearing to collapse and vanish towards the melting point. New density-functional supercell calculations identify a number of possible structures for the defect centre, including a novel form of bond-centred muonium in a closed-ring S(8)Mu complex. Simulations of the spin dynamics and fits to the spectra suggest a dynamical equilibrium or chemical exchange between several configurations, with occupancy of the bond-centre site falling from unity at low cryogenic temperatures to zero near the melting point. PMID:21778564

  13. Phonon-magnon interactions in BCC iron: A combined molecular and spin dynamics study

    SciTech Connect

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

    2014-01-01

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

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

    SciTech Connect

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

    2014-05-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2006-06-01

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

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

    PubMed

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

    2012-10-14

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

  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. 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

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

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

  1. A New and Unifying Approach to Spin Dynamics and Beam Polarization in Storage Rings

    E-print Network

    Klaus Heinemann; James A. Ellison; Desmond P. Barber; Mathias Vogt

    2014-12-12

    With this paper we extend our studies [1] on polarized beams by distilling tools from the theory of principal bundles. Four major theorems are presented, one which ties invariant fields with the notion of normal form, one which allows one to compare different invariant fields, and two that relate the existence of invariant fields to the existence of certain invariant sets and relations between them. We then apply the theory to the dynamics of spin-1/2 and spin-1 particles and their density matrices describing statistically the particle-spin content of bunches. Our approach thus unifies the spin-vector dynamics from the T-BMT equation with the spin-tensor dynamics and other dynamics. This unifying aspect of our approach relates the examples elegantly and uncovers relations between the various underlying dynamical systems in a transparent way.

  2. Spin Dynamics in Exchange Biased Co/FeMn Bilayers

    NASA Astrophysics Data System (ADS)

    Parker, Jeffrey; Chan, Mun; Haugen, Melissa; Bolon, Bruce; Leighton, Chris; Crowell, Paul

    2006-03-01

    We report a study of the spin dynamics in exchange biased Co/FeMn bilayers using time resolved Kerr microscopy (TKRM) with sub-nanosecond resolution. Samples were prepared via UHV dc magnetron sputter deposition onto a Si/SiOx substrate at room temperature in an applied field of 300 Oe. Deposition of a 30nm Cu buffer layer allowed for (111) textured growth of the subsequent Co/FeMn layers. In all samples the Co thickness was held constant at 6nm, while the FeMn thickness, t, was varied between 0 and 20nm. In accordance with previous work we found a room temperature critical thickness of the FeMn layer of approximately 3.5nm and a broad peak in the coercivity at this thickness. For low FeMn thickness a noticable asymmetry occurs in the magnetization hysteresis loops only for temperatures below the blocking temperature. TRKM is used to probe the dynamic response of the magnetization to fast magnetic field pulses. The different reversal mechanisms on either side of the hysteresis loop were probed by both the static and dynamic magnetization of the films as a function of temperature (between 40 and 450 K), and applied field.

  3. Spin dynamics and entanglement growth with trapped ions, atoms & molecules

    NASA Astrophysics Data System (ADS)

    Schachenmayer, Johannes; Lanyon, Ben; Roos, Christian; Daley, Andrew; Zhu, Bihui; Rey, Ana Maria

    2014-03-01

    Trapped ions and systems of cold atoms or molecules in optical lattices offer controlled environments to experimentally study non-equilibrium dynamics of many-body quantum spin-models with interactions of varying range. Theoretically calculating dynamics of observables for these experiments is a major challenge both analytically and numerically. In 1D, the growth behavior of the entanglement entropy between different blocks of a many-body state determines whether the evolution of the system can be efficiently simulated on a classical computer or not. In return, the study of entanglement growth can guide experiments to regimes where a quantum simulator can outperform a numerical simulation. Here we present results on the entanglement growth behavior in 1D strings of ions after a quench, and show how the growth depends on the range of the interactions. Furthermore we report on progress on methods for higher dimensional systems. These can be used to model Ramsey-dynamics for current experiments with alkaline earth atoms or polar molecules in optical lattices, or for systems with Rydberg atoms.

  4. 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

  5. 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).

  6. Spin Dynamics in Oligomeric ?-Conjugated (Porphinato)metal Arrays

    NASA Astrophysics Data System (ADS)

    Angiolillo, Paul J.; Susumu, Kimihiro; Therien, Michael J.

    2002-03-01

    The electronic performance of organic conducting and semi-conducting structures is related directly to the nature of the charge (or spin) carriers, the extent to which these carriers can be spatially delocalized, and the factors that control charge (spin) migration dynamics. The radical cation states of a series of highly soluble oligomeric ethyne-bridged (porphinato)zinc(II) structures were studied in solution as a function of molecular size and temperature by electron paramagnetic resonance (EPR) spectroscopy. Line shape analyses of the temperature-dependent radical cation spectra reveal that rapid hole mobility persists remarkably in these systems down to 4 K; impressively, hole migration kinetics are thus sufficient to maintain a N-1/2 scaling (N = number of porphyrin units in oligomer) of the line width. Given the timescale of the EPR measurement, these data indicate that either: (i) Frank-Condon effects are incapable of driving charge localization in these systems, resulting in cation radical wavefunctions which are globally delocalized over distances long with respect to molecular dimensions, or (ii) polaron hopping rates in these conjugated materials exceed 10^7 s-1, even at 4 K.

  7. Probing ultrafast spin dynamics with optical pump-probe scanning tunnelling microscopy

    NASA Astrophysics Data System (ADS)

    Yoshida, Shoji; Aizawa, Yuta; Wang, Zi-Han; Oshima, Ryuji; Mera, Yutaka; Matsuyama, Eiji; Oigawa, Haruhiro; Takeuchi, Osamu; Shigekawa, Hidemi

    2014-08-01

    Studies of spin dynamics in low-dimensional systems are important from both fundamental and practical points of view. Spin-polarized scanning tunnelling microscopy allows localized spin dynamics to be characterized and plays important roles in nanoscale science and technology. However, nanoscale analysis of the ultrafast dynamics of itinerant magnetism, as well as its localized characteristics, should be pursued to advance further the investigation of quantum dynamics in functional structures of small systems. Here, we demonstrate the optical pump-probe scanning tunnelling microscopy technique, which enables the nanoscale probing of spin dynamics with the temporal resolution corresponding, in principle, to the optical pulse width. Spins are optically oriented using circularly polarized light, and their dynamics are probed by scanning tunnelling microscopy based on the optical pump-probe method. Spin relaxation in a single quantum well with a width of 6 nm was observed with a spatial resolution of ~1 nm. In addition to spin relaxation dynamics, spin precession, which provides an estimation of the Landé g factor, was observed successfully.

  8. Dynamically Corrected Quantum Gates for Two-Electron Spin Qubits

    NASA Astrophysics Data System (ADS)

    Cerfontaine, Pascal; Loebl, Matthias; Bluhm, Hendrik

    2014-03-01

    Two-electron spin qubits in double quantum dots offer the possibility of fast and fully electrical manipulation via the exchange interaction. Arbitrary single-qubit gates have been demonstrated while maintaining a magnetic field gradient. However, simple gate constructions are extremely sensitive to noise in the Hamiltonian and thus incur considerable decoherence. Dynamically corrected gates are first-order insensitive to disturbances and present an appealing solution if slow noise sources are dominant. Using a numerical model that reflects the experimentally important imperfections and hardware constraints, we find control pulses for singlet-triplet qubits in GaAs double quantum dots which decouple in both the electrical control and the hyperfine magnetic field gradient. Additionally, dephasing effects from fast noise sources are minimized by favoring operating points close to a sweet spot. For experimentally determined noise levels the resulting gates feature fidelities as high as 99.9% and are mainly limited by high-frequency noise and nonlinearities.

  9. Dynamical symmetry approach to path integrals of quantum spin systems

    NASA Astrophysics Data System (ADS)

    Ringel, Matouš; Gritsev, Vladimir

    2013-12-01

    We develop a dynamical symmetry approach to path integrals for general interacting quantum spin systems. The time-ordered exponential obtained after the Hubbard-Stratonovich transformation can be disentangled into the product of a finite number of the usual exponentials. This procedure leads to a set of stochastic differential equations on the group manifold, which can be further formulated in terms of the supersymmetric effective action. This action has the form of the Witten topological field theory in the continuum limit. As a consequence, we show how it can be used to obtain the exact results for a specific quantum many-body system which can be otherwise solved only by the Bethe ansatz. This represents an example of a many-body system treated exactly using the path-integral formulation. Moreover, our method can deal with time-dependent parameters, which we demonstrate explicitly.

  10. Laser-induced ultrafast spin dynamics and ERASE functionality on quasilinear molecular ions

    NASA Astrophysics Data System (ADS)

    Lefkidis, Georgios; Li, Chun; Zhang, Shaobin; Hübner, Wolfgang

    2015-03-01

    We present an ab initio investigation of the ?-process-based ultrafast spin manipulation on positively charged two-magnetic-center molecular ions bridged by non-magnetic oxygen. Multiple derived spin-switching and spin-transfer scenarios on the quasilinear structure [Fe-O-Co]+ are used to build two closed, irreversible spin-dynamics cycles with respect to the spin localization and orientation. A mechanism addressing the ``ERASE'' functionality is proposed by properly exploiting the irreversibility of some laser-induced spin-manipulation scenarios, and the resulting Shannon entropy change is analyzed. We compare with a presiously suggested mechanism based on chirped laser pulses. Such controllable spin-dynamics cycles and logic functionality demonstrate promising applications in the design of spintronic devices on isolated magnetic molecules.

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

    E-print Network

    Jonathan Lux; Achim Rosch

    2014-08-28

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

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

    SciTech Connect

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

    2011-06-15

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

  13. 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

  14. Temporal dynamics and genetic diversity of chemotactic-competent microbial populations in the rhizosphere.

    PubMed

    Buchan, Alison; Crombie, Burnette; Alexandre, Gladys M

    2010-12-01

    The contribution of chemotaxis to the competitive colonization of the rhizosphere for the vast majority of the soil community is unknown. We have developed and applied a molecular diagnostic tool, based on a gene encoding the central regulator of bacterial chemotaxis (cheA), to characterize and temporally track specific populations of native microbes with chemotaxis potential that are present in soil exposed to two rhizospheres: wheat and cowpea. The data show that the chemotactic-competent communities present in the rhizospheres of the two plants are distinct and less diverse than the bulk soil, indicating the development of unique microbial communities. Consistent with the supposition that selection and recruitment of specific soil microbes takes place in the rhizosphere, the dynamics of specific cheA phylotypes provides support for the hypothesis that chemotaxis provides a competitive advantage to some soil microbes. This is the first study to examine and profile the genetic diversity of chemotaxis genes in natural populations. As such, it illustrates our limited understanding of microbial chemotaxis for the majority of soil microbes. It also highlights the value of a culture-independent approach for examining chemotaxis populations in order to build empirical lines of evidence for its role in structuring of microbial assemblages. PMID:20629701

  15. 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

  16. 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.

  17. Chiral spin liquid emerging between competing magnetic order states in the spin-1/2 J1-J2-J3 kagome Heisenberg model

    NASA Astrophysics Data System (ADS)

    Gong, Shoushu; Zhu, Wei; Balents, Leon; Sheng, Dongning

    2015-03-01

    We studied the extended spin- 1 / 2 kagome model with the first neighbor (J1), the second (J2) and third neighbor (J3) couplings using density matrix renormalization group. We established a quantum phase diagram for 0 <= J 2 <= 0 . 25J1 and 0 <=J3 <=J1 , where we find a q = (0 , 0) Neel phase, a chiral spin liquid (CSL), a cuboc1 phase that breaks both time-reversal and spin rotational symmetries, and a valence-bond solid at the neighbor of the Heisenberg model, where a possible Z2 spin liquid has been previously identified. Interestingly, the classical cuboc1 phase could survive in the spin- 1 / 2 system with strong quantum fluctuations, and the CSL emerges between the q = (0 , 0) and the cuboc1 phases. We discover that the CSL has the short spin correlation pattern consistent with the cuboc1 phase, but the chiral order structure is totally different. The CSL might be understood as a result of the competitions between the q = (0 , 0) and the cuboc1 phases in the presence of strong quantum fluctuations. We further studied the quantum phase transitions from the CSL to the magnetically ordered phases, and to the possible Z2 spin liquid of the Heisenberg kagome model. Interestingly, the exotic continuous topological phase transition might be realized in the system.

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

    SciTech Connect

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

    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.

  19. Dynamics of Circular Contact Lines: Spin Coating under Marangoni forces.

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Shomeek; Behringer, Robert

    2007-11-01

    Spin Coating remains one of the most important industrial applications of fluid dynamics, where understanding and controlling the instabilities is very important. The basic configuration consists of a fluid drop that is initially centrally located on a flat horizontal rotating surface. In this work we report on experiments on thin liquid films and fingering instabilities of a liquid drop, over a large range of angular speeds (from 10 mHz to 10Hz) of completely wetting PDMS oils on oxidized silicon wafers. Using a novel experimental setup, we will look at the effect of applying a radial temperature gradient (as opposed to a vertical gradient) on the dynamics of both the drop and the thin liquid film. In this case, the Marangoni forces oppose the centrifugal body forces. Depending on the relative strength of the driving force (angular speeds of 1 to 10 Hz and temparature gradients of 10 K/cm) and the drop size (volume of the drop varies from 1 microlitre to 100 microlitre) nontrivial wave structures and patterns arise. These results will be analyzed in the framework of the lubrication approximation.

  20. Critical spin liquid at 3 magnetization in a spin-

    E-print Network

    with an emergent SU 6 symmetry. A number of nontrivial predictions follow for the dynamical spin structure factor in this "algebraic vortex liquid" phase, which can be tested via inelastic neutron scattering. We also discuss how of numer- ous competing phases arising from the geometric frustration may lead rather to an enhanced role

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  2. Real-Space Application of the Mean-Field Description of Spin-Glass Dynamics

    SciTech Connect

    Barrat, Alain; Berthier, Ludovic

    2001-08-20

    The out of equilibrium dynamics of finite dimensional spin glasses is considered from a point of view going beyond the standard 'mean-field theory' versus 'droplet picture' debate of the past decades. The main predictions of both theories concerning the spin-glass dynamics are discussed. It is shown, in particular, that predictions originating from mean-field ideas concerning the violations of the fluctuation-dissipation theorem apply quantitatively, provided one properly takes into account the role of a spin-glass coherence length, which plays a central role in the droplet picture. Dynamics in a uniform magnetic field is also briefly discussed.

  3. Force field impact and spin-probe modeling in molecular dynamics simulations of spin-labeled T4 lysozyme

    Microsoft Academic Search

    Ileana Stoica

    2005-01-01

    Several attempts have been made to compute electron paramagnetic resonance (EPR) spectra of biomolecules, using motional models or simulated trajectories to describe dynamics. Ideally, the simulated trajectories should capture “fast” (picosecond) snapshots of spin-probe rotations accurately, while being lengthy enough to ensure a proper Fourier integration of the time-domain signal. It is the interplay of the two criteria that poses

  4. Dynamical aspects of photoinduced magnetism and spin-crossover phenomena in Prussian blue analogs

    NASA Astrophysics Data System (ADS)

    Nishino, Masamichi; Boukheddaden, Kamel; Miyashita, Seiji; Varret, François

    2005-08-01

    We present dynamical properties of spin crossover compounds with photomagnetization, proposing a model in which the spin-crossover phenomena and magnetic ordering are incorporated in a unified way. By using this model, the characteristics observed in Prussian blue analogs are qualitatively well reproduced. We investigate the time evolution of the magnetization and high spin fraction taking into account multiple time scales in a master equation approach for the magnetic relaxation, the lattice (electronic) relaxation, and the photoexcitation process. In particular, processes under different temperature cycling which start from the photoinduced saturated magnetic state are studied including the effect of photoirradiation. In the temperature cycling in the low-temperature region, the photoinduced magnetization shows “quasi-static behavior,” because the photoinduced metastable high spin state has a long lifetime. On the other hand, when the temperature is raised above this region, the dynamics of the spin state and the magnetization couple and exhibit various types of dynamical cooperative phenomena under temperature cycling.

  5. EPR Investigations of Spin-Probe Dynamics in Aqueous Dispersions of a Nonionic Amphiphilic Compound

    Microsoft Academic Search

    Kouichi Nakagawa

    2009-01-01

    Dynamics of various spin probes in aqueous dispersions of nonionic amphiphilic compound, [poly(oxyethylene) hydrogenated castor\\u000a oil, HCO], were investigated by EPR (electron paramagnetic resonance) and saturation recovery (SR) spectroscopies. Partitioning,\\u000a rotational correlation time (?R), rotational diffusion coefficient, and electron spin-lattice relaxation time (T\\u000a 1e) in dispersions of the HCO membrane were obtained. The partitioning of water soluble spin probes, DTBN

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

    SciTech Connect

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

    2013-12-02

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  8. 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

  9. Spin Dynamics in Bilayer Graphene and Mono- and Bilayer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Wu, Ming-Wei

    2015-03-01

    In this talk, I am going to present our many-body investigation on spin dynamics in bilayer graphene as well as mono- and bilayer transition metal dichalcogenides. The influence of the inter-valley scattering to the spin relaxation is addressed. The valley/spin depolarization due to the inter- and intravalley electron-hole Coulomb exchange interaction is revealed. A possible primary excitation, excimer, is proposed in bilayer WS2.

  10. Strong Dynamical Heterogeneities in the Violation of the Fluctuation-Dissipation Theorem in Spin Glasses

    Microsoft Academic Search

    F. Romá; S. Bustingorry; P. M. Gleiser; D. Domínguez

    2007-01-01

    We analyze numerically the violation of the fluctuation-dissipation theorem (FDT) in the ±J Edwards-Anderson (EA) spin-glass model. Using single spin probability densities we reveal the presence of strong dynamical heterogeneities, which correlate with ground-state information. The physical interpretation of the results shows that the spins can be divided into two sets. In 3D, one set forms a compact structure which

  11. Strong Dynamical Heterogeneities in the Violation of the Fluctuation-Dissipation Theorem in Spin Glasses

    Microsoft Academic Search

    F. Roma; S. Bustingorry; P. M. Gleiser; D. Dom ´ inguez

    2006-01-01

    We analyze numerically the violation of the fluctuation-dissipation theorem\\u000a(FDT) in the $\\\\pm J$ Edwards-Anderson (EA) spin glass model. Using single spin\\u000aprobability densities we reveal the presence of strong dynamical\\u000aheterogeneities, which correlate with ground state information. The physical\\u000ainterpretation of the results shows that the spins in the EA model can be\\u000adivided in two sets. In 3D,

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

    Microsoft Academic Search

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

    2002-01-01

    We have developed a computational molecular dynamics technique to simulate the motions of spin labels bound to the regulatory domain of scallop myosin. These calculations were then directly compared with site-directed spin labeling experimental results obtained by preparing seven single-cysteine mutants of the smooth muscle (chicken gizzard) myosin regulatory light chain and performing electron paramagnetic resonance experiments on these spin-labeled

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

    SciTech Connect

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

    2009-07-15

    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.

  14. 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.

  15. John von Neumann Institute for Computing A Study on the Structure and Dynamics of Spin

    E-print Network

    Steinhoff, Heinz-Jürgen

    John von Neumann Institute for Computing A Study on the Structure and Dynamics of Spin Labeled mentioned above. http://www.fz-juelich.de/nic-series/volume34 #12;A Study on the Structure and Dynamics sphaeroides, a photosynthetic protein, is chosen as a model system to study the structure and dynamics

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

    Microsoft Academic Search

    Youshan Tao; Qian Guo

    2005-01-01

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

  17. High Field Dynamic Nuclear Polarization with High-Spin Transition Metal Ions

    E-print Network

    Barnes, Alexander

    We report the dynamic nuclear polarization of 1H spins in magic-angle-spinning spectra recorded at 5 T and 84 K via the solid effect using Mn2+ and Gd[superscript 3+] complexes as polarizing agents. We show that the magnitude ...

  18. Anatomy of field effects on magnetization dynamics and spin transfer noise

    Microsoft Academic Search

    L. Wang; G. C. Han; Y. K. Zheng

    2006-01-01

    Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields

  19. 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.

  20. EPR spin labelling studies of molecular dynamics in elastomer-silica composites

    Microsoft Academic Search

    A. Buttafava; G. M. Ghisoni; A. Faucitano; G. Negroni; A. Priola; F. Peditto; A. Turturro; M. Castellano

    2002-01-01

    Novel methods of nitroxyl spin labelling suitable for molecular dynamics studies within the interface regions of SBR elastomer\\/silica composites have been developed and used together with the nitroxyl spin probe technique. Fast and slow motional components have been identified within the interface regions and the corresponding rotational diffusion tensors have been measured as a function of the temperature and the

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

    NASA Astrophysics Data System (ADS)

    Temizer, Ümüt; Tülek, Mesimi; Yarar, Semih

    2014-12-01

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

  2. 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 ...

  3. Spin dynamics in the pseudogap state of a high-temperature superconductor

    E-print Network

    Loss, Daniel

    LETTERS Spin dynamics in the pseudogap state of a high-temperature superconductor V. HINKOV1 , P The pseudogap is one of the most pervasive phenomena of high-temperature superconductors1 . It is attributed

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

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

  5. 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

  6. 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.

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

    SciTech Connect

    Obukhov, Yuri N.; Silenko, Alexander J.; Teryaev, Oleg V. [Department of Mathematics, University College London, Gower Street, London, WC1E 6BT (United Kingdom); Research Institute of Nuclear Problems, Belarusian State University, Minsk 220080 (Belarus); Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna 141980 (Russian Federation)

    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.

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

    E-print Network

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

    2009-09-12

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

    NASA Astrophysics Data System (ADS)

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

    2009-09-01

    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.

  10. Ultrafast Spin and Carrier Dynamics in Semiconductor Heterostructures Monitored by Pump-Probe Second Harmonic Generation

    NASA Astrophysics Data System (ADS)

    Glinka, Yu. D.; Shahbazyan, T. V.; Perakis, I. E.; Tolk, N. H.; Liu, X.; Sasaki, Y.; Furdyna, J. K.

    2002-03-01

    We report the first application of pump-probe second harmonic generation (SHG) measurements to characterize optically-induced magnetization in non-magnetic multilayer semiconductors. In the experiment, spin-polarized electrons are selectively excited by a pump beam in the GaAs layer of GaAs/GaSb/InAs structures. However, the resulting net magnetization manifests itself through the induced SHG probe signal from the GaSb/InAs interface, thus indicating a spin-polarized electron transport across the heterostructure. We find that the magnetization dynamics is governed by an interplay between the spin density evolution at the interfaces and the spin dephasing.

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

    E-print Network

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

    2014-09-06

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

  12. Theory of spin dynamics in high-Tc copper oxide superconductors. Application to neutron scattering

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Rossat-Mignod, J.

    1995-09-01

    A theory of spin dynamics in copper oxide superconductors is developed. The theory is based on the t-t'-J model and the diagrammatic technique for Hubbard operators. The dynamic spin susceptibility calculated for metallic hole concentrations includes two different contributions. The ``localized'' contribution arises from the subsystem of localized Cu spins with quantum short-range correlations. The ``itinerant'' contribution arises from the subsystem of propagating carrier quasiparticles. As a result of their competition, the spin dynamics evolves continuously within the metallic state from normal-metal behavior at high doping (overdoped regime) to quantum spin-liquid-type dynamics with magnonlike excitations at low doping through non-Fermi-liquid behavior in all intermediate regimes. Based on the theory, a detailed analysis of momentum and energy dependences of the dynamic spin susceptibility for different doping regimes is performed in order to compare the theoretical predictions with the experimental results discovered by inelastic neutron scattering. We are able to understand the strange shape of Im ? versus ? and its exotic evolution with doping, the existence of the resonance peak, the gap and pseudogap effects, and many other unusual features observed for YBa2Cu3O6+x as well as the incommensurate and ``gapless'' behavior for La2-xSrxCuO4.

  13. Competing microstructure and crystalline phase formation and their roles in glass formability: a molecular dynamics study

    Microsoft Academic Search

    Payman Jalali; Mo Li

    2004-01-01

    Glass formation is often considered as the transition from a liquid to a surviving non-crystalline phase when all crystallizations fail. What the competing microstructures and crystalline phases are and precisely how they affect the glass formation are important issues that need to be resolved. In this work, we report on a systematic investigation that addresses several aspects of the issues

  14. Adsorption and molecular dynamics of spin probes on hydrophobizated silica gel microparticles: EPR spin-label study

    Microsoft Academic Search

    I. V. Ionova; M. V. Alfimov; V. A. Livshits

    2011-01-01

    The molecular dynamics parameters and hydrophobicity of the surface of Silasorb silica gel particles covalently modified with\\u000a alkyl C\\u000a n\\u000a H2n + 1 groups differing in length (n = 2, 8, 18) were studied by electron paramagnetic resonance using spin probes of different structures, sizes, and electrical\\u000a charges. It has been shown that the hydrocarbon shells of the silica gel

  15. Spontaneous synchronization and quantum correlation dynamics of open spin systems

    E-print Network

    G. L. Giorgi; F. Plastina; G. Francica; R. Zambrini

    2013-10-30

    We discuss the emergence of spontaneous synchronization for an open spin-pair system interacting only via a common environment. Under suitable conditions, and even in the presence of detuning between the natural precession frequencies of the two spins, they are shown to reach a long-lasting transient behavior where they oscillate in phase. We explore the connection between the emergence of such a behavior and the establishment of robust quantum correlations between the two spins, analyzing differences between dissipative and dephasing effects.

  16. Dynamics of extended spinning masses in a gravitational field

    SciTech Connect

    Mashhoon, Bahram; Singh, Dinesh [Department of Physics and Astronomy, University of Missouri-Columbia, Columbia, Missouri, 65211 (United States); Department of Physics, University of Regina, Regina, Saskatchewan, S4S 0A2 (Canada)

    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.

  17. Dynamics of Extended Spinning Masses in a Gravitational Field

    E-print Network

    Bahram Mashhoon; Dinesh Singh

    2006-11-30

    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.

  18. Defining Competence

    ERIC Educational Resources Information Center

    McCowan, Richard J.

    1998-01-01

    A major problem in competency-based education is the lack of clarity in defining competence. This monograph describes the levels of competence used in developing competency-based educational programs and provides a taxonomy that can be used in developing competency-based instruction. The taxonomy includes four levels. Level 1 includes specific…

  19. Dynamic Bayesian networks for the classification of spinning discs

    E-print Network

    Schmidt, Aurora Clare, 1981-

    2004-01-01

    This thesis considers issues for the application of particle filters to a class of nonlinear filtering and classification problems. Specifically, we study a prototype system of spinning discs. The system combines linear ...

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

    SciTech Connect

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

    2009-10-07

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  2. H1 -NMR spin-echo measurements of the spin dynamic properties in ?-(BETS)2FeCl4

    NASA Astrophysics Data System (ADS)

    Wu, Guoqing; Ranin, P.; Gaidos, G.; Clark, W. G.; Brown, S. E.; Balicas, L.; Montgomery, L. K.

    2007-05-01

    H1 -NMR spin-echo measurements of the spin-echo decay M(2?) with a decay rate 1/T2 under applied magnetic field B0=9T along the a axis over the temperature (T) range of 2.0-180K are reported for a single crystal of the organic conductor ?-(BETS)2FeCl4 . It provides the spin dynamic properties in the paramagnetic metal (PM) and antiferromagnetic insulator (AFI) states as well as across the PM-AFI phase transition. A large slow beat structure in the spin-echo decay is observed with a typical beat frequency of fB˜7kHz that varies across the spectrum. Its origin is attributed to the interactions between protons that are very strongly detuned by the large inhomogeneous field on a microscopic distance scale that is generated by the Fe3+ moments (spin Sd=5/2 ). A simple phenomenological model provides an excellent fit to the data. The values of 1/T2 in the PM phase are consistent with a T -independent contribution from the proton-proton dipole interaction plus the proton spin-lattice relaxation rate (1/T1) [W. G. Clark , Appl. Magn. Reson. 27, 279 (2004)], which has a significant contribution only above ˜20K . At the PM-AFI transition (3.5K) , there is a discontinuous drop in 1/T2 by ˜34% , indicating that the transition is first order, consistent with prior reports. Two possible main contributions to this drop are discussed. They are based upon the change in the local magnetic field caused by the change in the orientation of the Fe3+ moments at the transition.

  3. Magnetization dynamics driven by non-equilibrium spin-orbit coupled electron gas

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Chen, Wei-qiang; Zhang, Fu-Chun

    2015-05-01

    The dynamics of magnetization coupled with an electron gas via s-d exchange interaction is investigated by using the density matrix technique. Our theory shows that nonequilibrium spin accumulation induces a spin torque and the electron bath leads to a damping of the magnetization . For the two-dimensional magnetization thin film coupled to the electron gas with Rashba spin-orbit coupling, the result for the spin-orbit torques is consistent with previous semiclassical theory. However, our theory predicts a damping of the magnetization, which is absent in semiclassical theory. The magnitude of the damping due to the electron bath is comparable to the intrinsic Gilbert damping and may be important in describing the magnetization dynamics of the system.

  4. Mean-Field Dynamics of Spin-Orbit Coupled Bose-Einstein Condensates

    NASA Astrophysics Data System (ADS)

    Zhang, Yongping; Mao, Li; Zhang, Chuanwei

    2012-01-01

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

  5. Direct Dynamical Evidence for the Spin Glass Lower Critical Dimension 2

    NASA Astrophysics Data System (ADS)

    Guchhait, Samaresh; Orbach, Raymond

    2014-03-01

    A dynamical method is introduced to study the effect of dimensionality on phase transitions. Direct experimental measurements for the lower critical dimension for spin glasses is provided as an example. The method makes use of the spin glass correlation length ?(t,T). Once nucleated, it can become comparable to sample dimensions in convenient time and temperature ranges. Thin films of amorphous Ge:Mn alloys were prepared with thickness L ?15.5 nm. Conventional behavior is observed as long as ?(t,T)spin glass dynamics, and are consistent with a lower critical dimension for spin glasses, d ?, between 2

  6. Spin and Hole Dynamics in Carrier-Doped Quantum Haldane Chain

    NASA Astrophysics Data System (ADS)

    Yokoo, T.; Itoh, S.; Ibuka, S.; Yoshizawa, H.; Akimitsu, J.

    2014-12-01

    Quantum spins in one-dimensional (1D) chains exhibit characteristic features such as the Haldane gap (S = 1) and the spin-Peierls state (S = 1/2). Multiple degrees of freedom associated with quantum spins have recently become a focus of attention. We present here the spin dynamics in lightly hole-doped Nd2-xCaxBaNiO5 (x = 0.1), a 1D Haldane system, using pulsed neutron inelastic scattering. The entire dispersion of the 1D Haldane chain was clearly observed with a ~14 meV spin gap (Haldane gap) at the magnetic zone center. Below the gap, much spectral weight was observed, indicating an in-gap state possibly originating from the doped holes in Haldane chains.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  10. 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.

  11. Low energy spin dynamics in the spin ice, Ho2Sn2O7

    SciTech Connect

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

    2012-01-01

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

  12. Dynamics of Polymer Blend Film Formation During Spin Coating

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  13. Bopp operators and phase-space spin dynamics: Application to rotational quantum brownian motion

    E-print Network

    D. Zueco; Ivan Calvo

    2007-04-20

    As already known for nonrelativistic spinless particles, Bopp operators give an elegant and simple way to compute the dynamics of quasiprobability distributions in the phase space formulation of Quantum Mechanics. In this work, we present a generalization of Bopp operators for spins and apply our results to the case of open spin systems. This approach allows to take the classical limit in a transparent way, recovering the corresponding Fokker-Planck equation.

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

    NASA Astrophysics Data System (ADS)

    Silenko, A. J.

    2015-01-01

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

  15. Analysis of nonlinear dynamics and spin-flip parameters on elliptically polarized injection-locked VCSELs

    NASA Astrophysics Data System (ADS)

    Homayounfar, A.; Adams, Michael J.

    2008-08-01

    Using spin-flip model (SFM) of vertical-cavity surface-emitting lasers (VCSELs) subject to polarized injection, it is found that reducing the spin relaxation, or increasing the birefringence and pumping terms, can increase elliptically polarized injection locking (EPIL) stability for the slave VCSEL. The nonlinear dynamic is investigated in optically injected VCSELs with numerical simulation techniques for six fundamental VCSEL rate equations. A novel phenomenon as quasi stability which affects the EPIL is analyzed.

  16. Spin Structure and Dynamical Magnetic Response of Spin-Orbital Polarons in Lightly Doped Cobaltates

    Microsoft Academic Search

    M. Daghofer; P. Horsch; G. Khaliullin

    We present numerical results on a spin-orbital polaron for lightly doped cobaltates with x? 0.7 < 1. We compare magnetic susceptibility of the polaron with realistic parameters to experiment and find perfect agreement.\\u000a Further, we analyze magnetic excitations and argue that they are responsible for observed spin-wave scattering.\\u000a \\u000a The cobaltates Na\\u000a x\\u000a CoO2have recently enjoyed much interest for a variety

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

    SciTech Connect

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

    2010-06-15

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

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

    PubMed

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

    2014-03-21

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

  19. 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.

  20. Impurity and boundary effects on magnetic monopole dynamics in spin ice

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

    Using a SQUID magnetometer, we measure the time-dependent magnetic relaxation in Dy2Ti2O7 and find that it decays with a stretched exponential followed by a very slow long-time tail. In a Monte Carlo simulation governed by Metropolis dynamics we find that surface effects and a very low level of stuffed spins (0.30%) - magnetic Dy ions substituted for non-magnetic Ti ions - can explain these signatures in the relaxation. We find that the additional spins trap the magnetic monopole excitations and provide the first example of how defects in a spin-ice material can obstruct the flow of monopoles.

  1. Dynamic nuclear polarization studies of redox-sensitive nitroxyl spin probes in liposomal solution

    Microsoft Academic Search

    A. Milton Franklin Benial; Hideo Utsumi; Kazuhiro Ichikawa; Ramachandran Murugesan; Ken-Ichi Yamada; Yuichi Kinoshita; Tatsuya Naganuma; Masahisa Kato

    2010-01-01

    Overhauser-enhanced magnetic resonance imaging (OMRI) studies of a membrane-permeable nitroxyl spin probe, 2H-enriched 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), used in simultaneous molecular imaging is reported. Phantom imaging was performed with liposomal solutions of MC-PROXYL at varying spin probe and liposome concentrations using a field-cycle mode, custom-built OMRI scanner. Dynamic nuclear polarization (DNP) spectra of the liposomal solution of the spin probe, measured at

  2. Spin torque in the framework of random magnetization dynamics driven by a jump-noise process

    NASA Astrophysics Data System (ADS)

    Bertotti, G.; Serpico, C.; Liu, Z.; Lee, A.; Mayergoyz, I.

    2014-02-01

    It is demonstrated that the Slonczewski spin-torque term can be naturally derived from the equation for magnetization dynamics driven by a jump-noise process. The central point of the derivation is the modification of transition probability rate of the jump-noise process caused by spin-polarized current injection. This modification results in two distinct terms in the expected value of the jump-noise process: the traditional one corresponding to the Landau-Lifshitz damping and another one representing the Slonczewski spin-torque term.

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

    SciTech Connect

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

    2013-01-01

    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.

  4. 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.

  5. Electromagnon by chiral spin dynamics in the triangular lattice antiferromagnet

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  6. Optical and spin polarization dynamics in GaSe nanoslabs

    NASA Astrophysics Data System (ADS)

    Tang, Yanhao; Xie, Wei; Mandal, Krishna C.; McGuire, John A.; Lai, C. W.

    2015-05-01

    We report nearly complete preservation of "spin memory" between optical absorption and photoluminescence (PL) in nanometer slabs of GaSe pumped with up to 0.2 eV excess energy. At cryogenic temperatures, the initial degree of circular polarization (?0) of PL approaches unity, with the major fraction of the spin polarization decaying with a time constant >500 ps in sub-100-nm GaSe nanoslabs. Even at room temperature, ?0 as large as 0.7 is observed, while pumping 1 eV above the band edge yields ?0=0.15 . Angular momentum preservation for both electrons and holes is due to the separation of the nondegenerate conduction and valence bands from other bands. In contrast to valley polarization in atomically thin transition-metal dichalcogenides, here optical spin polarization is preserved in nanoslabs of 100 layers or more of GaSe.

  7. 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

  8. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

    Segal, Dvira

    2014-04-01

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

  11. 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.

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

    SciTech Connect

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

    2014-04-28

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

  13. 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.

  14. 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.

  15. Ultrafast spin dynamics in GaAs/GaSb/InAs heterostructures probed by second harmonic generation

    NASA Astrophysics Data System (ADS)

    Glinka, Yu. D.; Shahbazyan, T. V.; Perakis, I. E.; Tolk, N. H.; Liu, X.; Sasaki, Y.; Furdyna, J. K.

    2002-07-01

    We report the application of pump-probe second harmonic generation (SHG) to monitor spin dynamics in nonmagnetic semiconductor heterostructures. Spin-polarized electrons were selectively excited by a pump beam in the GaAs layer of GaAs/GaSb/InAs structures. However, the induced magnetization manifests itself through the SHG probe signal from the GaSb/InAs interface, thus indicating a spin-polarized electron transport. We find that the magnetization dynamics is governed by an interplay between the spin density evolution at the interfaces and the spin relaxation.

  16. DYNAMICS OF THE LUNAR SPIN AXIS Jack Wisdom

    E-print Network

    Wisdom, Jack

    that the obliquity of Mars evolves chaotically. Touma & Wisdom (1993) interpreted this result in terms of generalized with low obliquity, with prograde synchronous spin. The Moon evolved outward due to tidal friction Cassini state with low obliquity. As the Moon continued to evolve outward to the present configuration

  17. 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.

  18. 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.

  19. 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

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

    E-print Network

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

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

    E-print Network

    Li, Charles

    valve consists of a pinned layer whose magneti- zation is fixed at x axis and a single-domain free layerDynamic 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

  2. Time-domain study of spin-wave dynamics in two-dimensional arrays of bi-component magnetic structures

    E-print Network

    Adeyeye, Adekunle

    ; published online 19 June 2013) Spin-waves in single Ni80Fe20 (Py) and Co bi-component units embedded in twoTime-domain study of spin-wave dynamics in two-dimensional arrays of bi-component magnetic: Fri, 29 Nov 2013 06:09:52 #12;Time-domain study of spin-wave dynamics in two-dimensional arrays of bi

  3. Massive relativistic particle model with spin from free two-twistor dynamics and its quantization

    SciTech Connect

    Azcarraga, Jose A. de [Departamento de Fisica Teorica, Univ. de Valencia and IFIC (CSIC-UVEG), 46100-Burjassot (Valencia) (Spain); Frydryszak, Andrzej [Institute of Theoretical Physics, Wroclaw University, 50-204 Wroclaw (Poland); Lukierski, Jerzy; Miquel-Espanya, Cesar [Departamento de Fisica Teorica, Univ. de Valencia and IFIC (CSIC-UVEG), 46100-Burjassot (Valencia) (Spain); Institute of Theoretical Physics, Wroclaw University, 50-204 Wroclaw (Poland)

    2006-05-15

    We consider a relativistic particle model in an enlarged relativistic phase space, M{sup 18}=(X{sub {mu}},P{sub {mu}},{eta}{sub {alpha}},{eta}{sub {alpha}},{sigma}{sub {alpha}},{sigma}{sub {alpha}},e,{phi}), which is derived from the free two-twistor dynamics. The spin sector variables ({eta}{sub {alpha}},{eta}{sub {alpha}},{sigma}{sub {alpha}},{sigma}{sub {alpha}}) satisfy two second class constraints and account for the relativistic spin structure, and the pair (e,{phi}) describes the electric charge sector. After introducing the Liouville one-form on M{sup 18}, derived by a nonlinear transformation of the canonical Liouville one-form on the two-twistor space, we analyze the dynamics described by the first and second class constraints. We use a composite orthogonal basis in four-momentum space to obtain the scalars defining the invariant spin projections. The first-quantized theory provides a consistent set of wave equations, determining the mass, spin, invariant spin projection and electric charge of the relativistic particle. The wave function provides a generating functional for free, massive higher spin fields.

  4. Spin torque-induced magnetization dynamics in giant magnetoresistance devices with Heusler alloy layers

    NASA Astrophysics Data System (ADS)

    Seki, T.; Yako, H.; Yamamoto, T.; Kubota, T.; Sakuraba, Y.; Ueda, M.; Takanashi, K.

    2015-04-01

    We studied the spin torque-induced magnetization dynamics of full-Heusler Co2(Fe,Mn)Si (CFMS) layers in current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) devices, and obtained the phase diagrams of spin torque-induced phenomena such as magnetization switching and spin torque oscillation. For a device with a 3 nm-thick CFMS free layer and a 20 nm-thick CFMS fixed layer, spin torque oscillation was induced in the free layer magnetization. As the free layer thickness was increased from 3 to 7 nm, on the other hand, the magnetization dynamics were remarkably changed. A 7 nm-thick CFMS free layer showed no clear spin torque oscillation even though it showed the reversible magnetization switching. On the contrary, the magnetization in the 20 nm-thick CFMS fixed layer oscillated at a certain condition. This spin torque-induced instability in the fixed layer magnetization is attributable to the increase in the free layer thickness, the structure of the fixed layer having the extended film, and the stray field coupling between the free and the fixed layers.

  5. Dynamics and ordering in a spin-labeled oligonucleotide observed by 220 GHz electron paramagnetic resonance.

    PubMed Central

    Budil, D E; Kolaczkowski, S V; Perry, A; Varaprasad, C; Johnson, F; Strauss, P R

    2000-01-01

    The dynamics of a newly synthesized cytosine spin-label and the spin-labeled pentamer TTC*TT have been observed by high-frequency (220 GHz) electron paramagnetic resonance (EPR) in aqueous solution at ambient temperature using only nanomolar amounts of spin-label. Temperature studies were carried out for both labeled species in buffer containing glycerol. The motion of the spin-labeled monomer could be fitted using a model of fully anisotropic rotation (FAR) over the entire temperature range studied. In the single-stranded pentamer, the high-field spectra are best interpreted using a model of microscopic ordering with macroscopic disorder (MOMD) with the probe in a highly nonpolar environment. The observed local order parameters of 0.60-0.70 suggest a micelle-like structure in which the label is tightly packed with the hydrophobic bases. These preliminary studies illustrate how the excellent orientation selectivity of high-field EPR provides new dynamic information about local base motions in DNA, and also how high-field EPR of spin-labels allows one to discriminate accurately between the effects of local versus global motions in spin-labeled macromolecules. PMID:10620306

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

    NASA Astrophysics Data System (ADS)

    Barth, Ingo; Smirnova, Olga

    2014-10-01

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

  7. Influence of hole doping on spin dynamics in lightly doped copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Onufrieva, F. P.; Kushnir, V. P.; Toperverg, B. P.

    1994-11-01

    The spin dynamics in the doped antiferromagnetic (AF) state of high-Tc copper oxide superconductors has been investigated within the t-t'-J model. We have shown that a small number of doped holes affects the spin dynamics in the CuO2 planes so strongly that above a very small hole concentration, nc=0.027, the two-dimensional (2D) AF ground state becomes unstable. We have also predicted a great change in the spin excitation spectrum for the doped AF state. For doping close to nc, a hydrodynamic regime of well-defined magnons collapses, and almost the whole region of long-wavelength spin waves corresponds to the overdamped regime of softened magnons in agreement with inelastic neutron-scattering experiments in YBa2Cu3O6+x reported by Rossat-Mignod et al. Analyzing the imaginary part of the spin susceptibility ?''(q,?) we have discovered, in addition to the spin-wave part, also an incoherent band associated with electron-hole excitations. For the overdamped regime the energy ranges of coherent excitations and the incoherent band are overlapped and so it is impossible to separate them. Even for smallest q, when the magnon peak and the band are separated, the relative contribution of the band increases with increasing n and dominates near the critical point.

  8. Spin-dynamical theory of the wave-corpuscular duality

    SciTech Connect

    Gryzinski, M.

    1987-10-01

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

  9. Spin-Dynamical Theory of the Wave-Corpuscular Duality

    NASA Astrophysics Data System (ADS)

    Gryzi?ski, Micha?

    1987-10-01

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

  10. Attitude dynamic of spin-stabilized satellites with flexible appendages

    NASA Technical Reports Server (NTRS)

    Renard, M. L.

    1973-01-01

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

  11. Relaxivity and molecular dynamics of spin labeled polysaccharides

    Microsoft Academic Search

    B. Gallez; R. Debuyst; F. Dejehet; J. L. De Keyser; V. Lacour; R. Demeure; P. Dumont

    1994-01-01

    Synthetic methods are described leading to polysubstituted spin labeled polysaccharides (dextran 70, 110, 200, and arabinogalactan), which are potential contrast agents in magnetic resonance imaging. The nitroxyl moieties bound to a polysaccharide yield relaxivity enhanced by a factor of 1.6 (at 0.47 T and 37°C) compared to that of the small hydrophilic radicals. An EPR study at variable temperature and

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

    PubMed Central

    Parisi, Giorgio

    2006-01-01

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

  13. Light induced radical pair intermediates in photosynthetic reaction centres in contact with an observer spin label: spin dynamics and effects on transient EPR spectra

    NASA Astrophysics Data System (ADS)

    Salikhov, Kev M.; Zech, Stephan G.; Stehlik, Dietmar

    A novel strategy is discussed using site directed spin labelling to study the electron transfer process in photosynthetic reaction centres. An algorithm is presented for numerical simulations of the time resolved EPR spectra of radical pair states in the presence of an observer spin label. This algorithm accounts for spin dynamics, charge recombination and relaxation processes. It is shown that satisfactory agreement between experimental and simulated EPR spectra of the first stabilized radical pair state in photosystem I is achieved for various microwave frequencies. Transient EPR spectra for the radical pair state P •+Q •- in photosystem I were simulated for various distances and positions of the observer spin label with respect to the acceptor quinone molecule. It is shown that distances up to more than 20 Å give rise to observable changes in the transient EPR spectra. Both the additional spin-spin coupling between the quinone radical and the label and the polarization transfer processes contribute to the changes. Furthermore, the shape and intensity of the EPR spectrum of the spin label is altered by the coupling with the radical pair spins for distances up to 25 Å. Experiments on site directed spin labelled photosystem I are thus expected to provide valuable information on the dynamics of electron transfer in photosystem I.

  14. Dynamics of a two-level system coupled to a bath of spins

    NASA Astrophysics Data System (ADS)

    Wang, Haobin; Shao, Jiushu

    2012-12-01

    The dynamics of a two-level system coupled to a spin bath is investigated via the numerically exact multilayer multiconfiguration time-dependent Hartree (ML-MCTDH) theory. Consistent with the previous work on linear response approximation [N. Makri, J. Phys. Chem. B 103, 2823 (1999)], 10.1021/jp9847540, it is demonstrated numerically that this spin-spin-bath model can be mapped onto the well-known spin-boson model if the system-bath coupling strength obeys an appropriate scaling behavior. This linear response mapping, however, may require many bath spin degrees of freedom to represent the practical continuum limit. To clarify the discrepancies resulted from different approximate treatments of this model, the population dynamics of the central two-level system has been investigated near the transition boundary between the coherent and incoherent motions via the ML-MCTDH method. It is found that increasing temperature favors quantum coherence in the nonadiabatic limit of this model, which corroborates the prediction in the previous work [J. Shao and P. Hanggi, Phys. Rev. Lett. 81, 5710 (1998)], 10.1103/PhysRevLett.81.5710 based on the non-interacting blip approximation (NIBA). However, the coherent-incoherent boundary obtained by the exact ML-MCTDH simulation is slightly different from the approximate NIBA results. Quantum dynamics in other physical regimes are also discussed.

  15. Hyperfine and spin-orbit dynamics in GaAs double quantum dots

    NASA Astrophysics Data System (ADS)

    Shulman, Michael; Nichol, John; Harvey, Shannon; Pal, Arijeet; Halperin, Bertrand; Umansky, Vladimir; Yacoby, Amir

    2015-03-01

    Semiconductor quantum dots provide a unique platform for single-particle physics and many-body quantum mechanics. In particular, understanding the dynamics of a single electron interacting with a nuclear spin bath is key to improving spin-based quantum information processing, since the hyperfine interaction limits the performance of many spin qubits. We probe the electron-nuclear interaction by measuring the splitting at the anti-crossing between the electron singlet (S) and m =1 triplet (T +) states in a GaAs double quantum dot. Using Landau-Zener sweeps, we find that the size of this splitting varies by more than an order of magnitude depending on the magnitude and direction of the external magnetic field. These results are consistent with a competition between the spin orbit interaction and the hyperfine interaction, even though the extracted spin orbit length is much larger than the size of the double quantum dot. We confirm these results by using Landau-Zener sweeps to measure the high-frequency correlations in the S-T + splitting that arise from the Larmor precession of the nuclei. These unexpected results have implications for improving the performance of spin-based quantum information processing, as well as improving our understanding of the central spin problem.

  16. 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.

  17. Spin dynamics and horizon sensor performance for the Solar Mesosphere Explorer

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

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

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

    PubMed

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

    2015-06-21

    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. PMID:26093552

  19. Ultrafast Spin Dynamics Monitored By Pump-Probe Second Harmonic Generation

    NASA Astrophysics Data System (ADS)

    Glinka, Yuri; Shahbazyan, T.; Perakis, Ilias; Miller, Jerome; Kussainov, Arman; Tolk, Norman; Liu, X.; Sasaki, Y.; Furdyna, Jacek

    2003-03-01

    The first application of pump-probe second harmonic generation (SHG) is reported as a new technique to characterize optically induced magnetization in magnetic and non-magnetic semiconductor heterostructures. In the experiment, spin-polarized electrons are excited selectively by a pump beam in the GaAs layer of GaAs/GaSb/InAs nanostructure. However, the resulting net magnetization manifest itself through the induced SHG probe signal from GaSb/InAs interface, thus indicating a spin-polarized electron transport across the heterostructure. We find that the magnetization dynamics are governed by an interplay between the spin density evolution at the interfaces and the spin relaxation. We show that owing to the specific features of the SHG process, the pump-probe SHG technique is unique for studying local magnetic fields created at the interfaces of semiconductor multilayers and digital systems.

  20. Spin dynamics of molecular nanomagnets unraveled at atomic scale by four-dimensional inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Santini, Paolo; Baker, Michael; Guidi, Tatiana; Carretta, Stefano; Ollivier, Jacques; Mutka, Hannu; Guedel, Hans; Timco, Grigore; McInnes, Eric; Amoretti, Giuseppe; Winpenny, Richard

    2013-03-01

    Molecular nanomagnets (MNMs) have been test-beds for addressing several elusive but important phenomena in quantum dynamics, but to this point it has been impossible to determine the spin dynamics directly. We show that recently-developed inelastic-neutron-scattering instrumentation, yielding the cross-section in vast portions of reciprocal space, enables two-spin dynamical correlation functions of MNMs to be directly determined without assuming an underlying model Hamiltonian. We use the Cr8 antiferromagnetic ring as a benchmark to demonstrate the potential of this approach which allows us, for example, to examine how a quantum fluctuation propagates along the ring or to test the degree of validity of the Neel-vector-tunneling framework. This result opens remarkable perspectives in the understanding of the quantum dynamics in several classes of MNMs.

  1. Analysis of quantum Monte Carlo dynamics for quantum adiabatic evolution in infinite-range spin systems

    NASA Astrophysics Data System (ADS)

    Inoue, Jun-Ichi

    2011-03-01

    We analytically derive deterministic equations of order parameters such as spontaneous magnetization in infinite-range quantum spin systems obeying quantum Monte Carlo dynamics. By means of the Trotter decomposition, we consider the transition probability of Glauber-type dynamics of microscopic states for the corresponding classical system. Under the static approximation, differential equations with respect to macroscopic order parameters are explicitly obtained from the master equation that describes the microscopic-law. We discuss several possible applications of our approach to disordered spin systems for statistical-mechanical informatics. Especially, we argue the ground state searching for infinite-range random spin systems via quantum adiabatic evolution. We were financially supported by Grant-in-Aid for Scientific Research (C) of Japan Society for the Promotion of Science, No. 22500195.

  2. Outsourcing Competence

    E-print Network

    Bergstra, J A; van Vlijmen, S F M

    2011-01-01

    The topic of this paper, competences needed for outsourcing, is organized by first providing a generic competence scheme, which is subsequently instantiated to the area of sourcing and outsourcing. Sourcing and outsourcing are positioned as different areas of activity, neither one of which is subsumed under the other one. It is argued that competences relevant for outsourcing are mainly community based rather than evidence based. Subjective ability and objective ability are distinguished as categories, together making up ability, which are distinct but not necessarily disjoint from competence. Conjectural ability is introduced as a form of subjective ability. A person's competence profile includes competences as well as abilities, including subjective ones. Competence assessment and acquisition as well as the impact of assessed competence on practical work is described. The analysis of competence and ability thus developed is used as standpoint from which to extract a specification of an audience for a theory...

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

    SciTech Connect

    Van den Bosh, P.P.J.

    1985-12-01

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

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

    Microsoft Academic Search

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

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    E-print Network

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

    2014-10-02

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

  7. Origin of the dynamics of the spin state in undoped BaFe : Mssbauer studies

    E-print Network

    .: Condens. Matter 23 342201 (http://iopscience.iop.org/0953-8984/23/34/342201) Download details: IP Address TRACK COMMUNICATION Origin of the dynamics of the spin state in undoped BaFe2As2: M¨ossbauer studies

  8. Nuclear Quadrupole Spin-Lattice Relaxation and Critical Dynamics of Ferroelectric Crystals

    Microsoft Academic Search

    G. Bonera; F. Borsa; A. Rigamonti

    1970-01-01

    The effect on the nuclear spin-lattice relaxation of the anomalous temperature dependence of generalized unstable lattice modes near the ferroelectric transition is investigated both theoretically and experimentally. Expressions for the relaxation rate near Tc are derived for typical cases of critical dynamics of ferroelectric crystals. For the case of undamped soft-phonon modes it is shown that, on the basis of

  9. SUBMILLISECOND ROTATIONAL DYNAMICS OF SPIN-LABELED MYOSIN HEADS IN MYOFIBRILS

    E-print Network

    Thomas, David D.

    . To obtain direct information about this molecular motion, we have performed saturation transfer EPRSUBMILLISECOND ROTATIONAL DYNAMICS OF SPIN-LABELED MYOSIN HEADS IN MYOFIBRILS DAVID D. THOMAS, SHIN myosin heads bind to actin, is an essential element of most molecular models of muscle contraction

  10. Dissipative quantum dynamics with the surrogate Hamiltonian approach. A comparison between spin and harmonic baths

    E-print Network

    Koch, Christiane

    from a normal mode analysis combined with a weak system­bath coupling assumption.2 If the bath is only is closely related to a normal mode decomposi- tion. Once this is done the spectral density function iDissipative quantum dynamics with the surrogate Hamiltonian approach. A comparison between spin

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

    PubMed

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

    2014-04-11

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

  12. Dynamic MCDM, Habitual Domains and Competence Set Analysis for Effective Decision Making in Changeable Spaces

    Microsoft Academic Search

    Po-Lung Yu; Yen-Chu Chen

    \\u000a This chapter introduces the behavior mechanism that integrates the discoveries of neural science, psychology, system science,\\u000a optimization theory and multiple criteria decision making. It shows how our brain and mind works and describes our behaviors\\u000a and decision making as dynamic processes of multicriteria decision making in changeable spaces. Unless extraordinary events\\u000a occur or special effort exerted, the dynamic processes will

  13. 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.

  14. 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 ...

  15. EFFECTS OF NUCLEAR SPIN POLARIZATION ON REACTION DYNAMICS IN PHOTOSYNTHETIC

    E-print Network

    Boxer, Steven G.

    in -200 ps (Rockley et al., 1975; Kaufmann et al., 1975). To study P+I* it is useful to block this latter- cally induced dynamic nuclear polarization [CIDNP]) (Kaptein and Oosterhoff, 1969; Closs, 1969

  16. Spin dynamics of polycrystalline Ni films on Si substrate

    Microsoft Academic Search

    Fernando M. F. Rhen; Jeffrey F. Godsell; Terence O’Donnell; Saibal Roy

    2010-01-01

    We have prepared thin Ni films by direct electrodeposition onto Si substrates and investigated the magnetization dynamics up to 9GHz. Films with typical thickness of 200nm show good adhesion to the substrate. Experimental absorption spectra were fitted using a model, which combines the magnetization dynamics according to Landau–Lifshitz–Gilbert and eddy current contribution. Damping parameters ranging from 0.12 to 0.08 were

  17. Spin dynamics of polycrystalline Ni films on Si substrate

    Microsoft Academic Search

    Fernando M. F. Rhen; Jeffrey F. Godsell; Terence O'Donnell; Saibal Roy

    2010-01-01

    We have prepared thin Ni films by direct electrodeposition onto Si substrates and investigated the magnetization dynamics up to 9 GHz. Films with typical thickness of 200 nm show good adhesion to the substrate. Experimental absorption spectra were fitted using a model, which combines the magnetization dynamics according to Landau-Lifshitz-Gilbert and eddy current contribution. Damping parameters ranging from 0.12 to

  18. Dynamics of polymer film formation during spin coating

    SciTech Connect

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

    2014-09-28

    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.

  19. Dynamics of polymer film formation during spin coating

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

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

    E-print Network

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

    2015-02-01

    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.

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

    SciTech Connect

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

    1998-09-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-02-01

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

  4. Testing statics-dynamics equivalence at the spin-glass transition in three dimensions

    NASA Astrophysics Data System (ADS)

    Fernández, Luis Antonio; Martín-Mayor, Víctor

    2015-05-01

    The statics-dynamics correspondence in spin glasses relate nonequilibrium results on large samples (the experimental realm) with equilibrium quantities computed on small systems (the typical arena for theoretical computations). Here we employ statics-dynamics equivalence to study the Ising spin-glass critical behavior in three dimensions. By means of Monte Carlo simulation, we follow the growth of the coherence length (the size of the glassy domains), on lattices too large to be thermalized. Thanks to the large coherence lengths we reach, we are able to obtain accurate results in excellent agreement with the best available equilibrium computations. To do so, we need to clarify the several physical meanings of the dynamic exponent close to the critical temperature.

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

    ERIC Educational Resources Information Center

    Mandon, Nicole; Sulzer, Emmanuel

    1998-01-01

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

  6. AC susceptometer for spin-glass dynamics measurements

    NASA Astrophysics Data System (ADS)

    Lenard, Antoni; Plesiewicz, Witold; Sawicki, Maciej; Dietl, Tomasz

    This paper presents operation principle, design, and application of an ac susceptometer:a three coil, mutual inductance coaxial system. It operates within 1.5 IC - 100 K temperature range and at frequencies 5 Hz - 10 kHz. The sensitivity reaches 4-10 -8 cmu/cm 3 even at 5 Hz. Experimental set-up consists of LHc lath cryostat, variable temperature insert (top-loaded with a movable sample holder) provided with two superconducting magnets (vertical 3 kOe solenoid and Horizontal 3 kOe split-pair coil). Capabilities of the system are shown through the results of complex susceptibility measurements of the paramagnetic to spin-glass transitions. A similar device works successfully in the millikelvin temperature range.

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

    SciTech Connect

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

    2011-09-15

    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.

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

    E-print Network

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

    2014-08-28

    We develop a systematic and efficient approach for numerically solving the non-Markovian quantum state diffusion equations for open quantum systems coupled to an environment up to arbitrary orders of noises or coupling strengths. As an important application, we consider a real-time simulation of a spin-boson model in a strong coupling regime that is difficult to deal with using conventional methods. We show that the non-Markovian stochastic Schr\\"{o}dinger equation can be efficiently implemented as a real--time simulation for this model, so as to give an accurate description of spin-boson dynamics beyond the rotating-wave approximation.

  9. Current-driven chaotic magnetization dynamics in microwave assisted switching of spin-valve elements

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

    The switching process of a uniformly magnetized spin-valve is considered. The system is subject to external dc applied fields and injected radio-frequency (RF) spin-polarized currents. The possibility of using the RF power to obtain a reduced coercivity of the particle is related to the onset of chaotic magnetization dynamics for moderately low values of the RF current amplitude. Perturbation technique for the estimation of the reduced coercive field is developed and applied to the microwave assisted switching of the particle. Numerical simulations confirm the predictions of the theory.

  10. Analytical study of magnetization dynamics driven by spin-polarized currents

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

    An analytical approach is presented for the study of magnetization dynamics driven by spin-polarized currents. Two cases are considered: (i) magnetic layers with in-plane uniaxial anisotropy; (ii) magnetic layers with uniaxial anisotropy and applied field perpendicular to the layer plane. Theoretical predictions are obtained for the existence of stationary modes and self-oscillations of magnetization by solving the deterministic Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque term. Thermal fluctuations are studied by deriving the corresponding Fokker-Planck equation for the magnetization probability distribution. Analytical procedures to estimate the effective potential barrier separating self-oscillatory regimes and/or stationary modes are proposed.

  11. 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

    &, ) in any dimen- sionality. Indeed, it is generally true only for n=2 and 3 [note that when polar vectors have n components, an- tisymmetric tensors have n (n ?1)/2 components]. (1.2) The study of both static and dynamic behavior of in- teracting spins...; SJ (a=1,2, 3), Specifically, in Sec. II we show that there can be two in- dependent components of H?(e.g., H~2 and H34) in n=4, and in Sec. III we show that this yields two free- spin Larmor precession frequencies, at y(H&z+H 34). To' do this, we...

  12. Carrier and Spin Dynamics in InAsP Ternary Alloys

    NASA Astrophysics Data System (ADS)

    Meeker, Michael; McCutcheon, Kelly; Bhowmick, Mithun; Magill, Brenden; Khodaparast, Giti A.; Tischler, Joe G.; Choi, Sukgeun G.; Palmstrøm, Chris J.

    2013-03-01

    The recent rapid progress in the field of spintronics involves extensive measurements of carrier and spin relaxation dynamics in III-V semiconductors. In addition, as the switching rates in electronic and optoelectronic devices are pushed to higher frequencies, it is important to understand carrier dynamic phenomena in semiconductors on femtosecond time-scales. In this work, we employed time and polarization-resolved differential transmission measurements in near and mid-infrared, to probe carrier and spin relaxation times in several InAsP ternary alloys. Our results demonstrate the unique and complex dynamics in this material system that can be important for electronic and optoelectronic devices. We present our experimental observations and compare them with the observations in InAs and InP. The recent rapid progress in the field of spintronics involves extensive measurements of carrier and spin relaxation dynamics in III-V semiconductors. In addition, as the switching rates in electronic and optoelectronic devices are pushed to higher frequencies, it is important to understand carrier dynamic phenomena in semiconductors on femtosecond time-scales. In this work, we employed time and polarization-resolved differential transmission measurements in near and mid-infrared, to probe carrier and spin relaxation times in several InAsP ternary alloys. Our results demonstrate the unique and complex dynamics in this material system that can be important for electronic and optoelectronic devices. We present our experimental observations and compare them with the observations in InAs and InP. Supported by: NSF-Career Award DMR-0846834 and Virginia Tech ICTAS

  13. 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

  14. Static and dynamic properties of interacting spin-1 bosons in an optical lattice

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    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 nondispersive 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 superexchange-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.

  15. Spin dynamics in magnetic thin films and eletromagnetic properties of metamaterials

    NASA Astrophysics Data System (ADS)

    Cao, Rong

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

  16. Complex Reaction Environments and Competing Reaction Mechanisms in Zeolite Catalysis: Insights from Advanced Molecular Dynamics.

    PubMed

    De Wispelaere, Kristof; Ensing, Bernd; Ghysels, An; Meijer, Evert Jan; Van Speybroeck, Veronique

    2015-06-22

    The methanol-to-olefin process is a showcase example of complex zeolite-catalyzed chemistry. At real operating conditions, many factors affect the reactivity, such as framework flexibility, adsorption of various guest molecules, and competitive reaction pathways. In this study, the strength of first principle molecular dynamics techniques to capture this complexity is shown by means of two case studies. Firstly, the adsorption behavior of methanol and water in H-SAPO-34 at 350?°C is investigated. Hereby an important degree of framework flexibility and proton mobility was observed. Secondly, the methylation of benzene by methanol through a competitive direct and stepwise pathway in the AFI topology was studied. Both case studies clearly show that a first-principle molecular dynamics approach enables unprecedented insights into zeolite-catalyzed reactions at the nanometer scale to be obtained. PMID:25951509

  17. Backbone Dynamics of Alamethicin Bound to Lipid Membranes: Spin-Echo Electron Paramagnetic Resonance of TOAC-Spin Labels

    PubMed Central

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

    2008-01-01

    Alamethicin F50/5 is a hydrophobic peptide that is devoid of charged residues and that induces voltage-dependent ion channels in lipid membranes. The peptide backbone is likely to be involved in the ion conduction pathway. Electron spin-echo spectroscopy of alamethicin F50/5 analogs in which a selected Aib residue (at position n = 1, 8, or 16) is replaced by the TOAC amino-acid spin label was used to study torsional dynamics of the peptide backbone in association with phosphatidylcholine bilayer membranes. Rapid librational motions of limited angular amplitude were observed at each of the three TOAC sites by recording echo-detected spectra as a function of echo delay time, 2?. Simulation of the time-resolved spectra, combined with conventional EPR measurements of the librational amplitude, shows that torsional fluctuations of the peptide backbone take place on the subnanosecond to nanosecond timescale, with little temperature dependence. Associated fluctuations in polar fields from the peptide could facilitate ion permeation. PMID:18096632

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

    E-print Network

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

    2014-10-02

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  20. 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.

  1. General features of photoinduced spin dynamics in ferromagnetic and ferrimagnetic compounds.

    PubMed

    Ogasawara, T; Ohgushi, K; Tomioka, Y; Takahashi, K S; Okamoto, H; Kawasaki, M; Tokura, Y

    2005-03-01

    Ultrafast photoinduced spin dynamics has been investigated by time-resolved magneto-optical Kerr spectroscopy for various ferromagnetic and ferrimagnetic compounds: FeCr2S4, CoCr2S4, CuCr2Se4, CdCr2Se4, La0.6Sr0.4MnO3, and SrRuO3. The temporal demagnetization process, which is observed commonly for all the compounds, essentially consists of two components: One is an instantaneous change which originates perhaps from multiple emissions of magnetic excitations during nonradiative decay of photoexcited carriers, and the other is a delayed response due to thermalization of the spin system. The time constant of the delayed change depends strongly on materials and is scaled with the magnetocrystalline anisotropy, indicating that spin-orbit coupling is a dominant interaction for this process. PMID:15783924

  2. Nucleon spin structure I: A dynamical determination of gluon helicity distribution in the nucleon

    E-print Network

    Wei Zhu; Jianhong Ruan

    2015-03-08

    Gluon helicity distribution in the nucleon is dynamically predicted by using a nonlinear QCD evolution equation-the DGLAP equation with the parton recombination corrections - starting from a low scale, where the nucleon is almost only consisted of valence quarks. The comparisons of our predicted gluon helicity distribution with the available data are presented. We find that the contribution of the gluon helicity to the nucleon spin structure is much larger than the predictions of most other theories. This result suggests a significant orbital angular momentum of the gluons is required to balance the gluon helicity. A novel spin-orbital structure of the proton in the light-cone frame is described based on the quantitative calculations,and the nucleon spin crisis is discussed.

  3. Control and measurements of spin and carrier dynamics in InAs films

    NASA Astrophysics Data System (ADS)

    Nontapot, Kanokwan; Kini, Rajeev; Khodaparast, Giti; Guido, Louis; Welser, Roger

    2007-03-01

    In light of the growing interest in spin-related phenomena and devices, there is now renewed interest in the science and engineering of narrow gap semiconductors. We report control and measurements of spin and carrier relaxations in InAs (100) and InAs (111) films with doping densities of ˜ 3x10^12 cm-2 (mobility ˜20,000 cm^2/Vs at 77 K) and 2.0x10^12 cm-2 (mobility ˜33,00 cm^2/Vs at 77 K) at room temperature and 77K, respectively. We use standard pump-probe and magneto-optical Kerr effect (MOKE) spectroscopy at different excitation wavelengths, power densities, and temperatures. Spin relaxations in these structures demonstrate dynamics which is different from the carrier relaxations under the same experimental conditions. We explain our results using the Elliot-Yafet picture which is considered to be the dominant relaxation process in narrow gap semiconductors.

  4. Constrained spin model of phason dynamics in quasicrystals

    NASA Astrophysics Data System (ADS)

    Gronlund, Lisbeth D.; Wright, David C.; Sethna, James P.; Rokhsar, Daniel S.

    1990-11-01

    Inspired by phason dynamics in tiling models of quasicrystals, we investigate a class of constrained Ising models. Phason shifts in the Penrose tiling model of quasicrystals appear as flips of rows of tiles, known as ``worms.'' When worms cross one another, a hierarchy is established in which some of the worms cannot flip until others have. A complex set of constraints on worm flips is thereby introduced by the intricate pattern of worm crossings in quasicrystalline tilings. We introduce a simple model of interacting sets of one-dimensional Ising chains that mimics this set of constraints and study the possible consequences of these constraints for phason dynamics and the relaxation of phason strain in quasicrystals.

  5. 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.

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

    NASA Technical Reports Server (NTRS)

    1962-01-01

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

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

    E-print Network

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

    2014-10-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  9. Quantum Dynamics of Many-body Spin Chains Using Atomic Ions

    NASA Astrophysics Data System (ADS)

    Senko, Crystal

    2014-05-01

    Quantum simulation, a field in which well-controlled quantum systems are used to study many-body physics that would otherwise be challenging to model, has undergone a great deal of progress in recent years. In particular, trapped ions have proven an excellent platform for simulating quantum magnetism, with their long-lived coherence times, tunable spin-spin interactions mediated by optical dipole forces, and ease of individual readout. The manipulation of more than 10 spins is now routine and has allowed the study of dynamics that will be difficult to simulate classically in larger systems, such as spectroscopy of excitation energies (arXiv:1401.5751) and the spread of spin correlations in a system with long-range interactions (arXiv:1401.5088). In the near future, we expect to apply these techniques to the study of a variety of phenomena such as prethermalization in an isolated quantum system, and to upgrade the apparatus so as to handle many tens of spins, a system size well beyond what is classically calculable. This work is supported by grants from the U.S. Army Research Office with funding from the DARPA OLE program, IARPA, and the MURI program; and the NSF Physics Frontier Center at JQI.

  10. Dynamic nuclear polarization studies of redox-sensitive nitroxyl spin probes in liposomal solution.

    PubMed

    Benial, A Milton Franklin; Utsumi, Hideo; Ichikawa, Kazuhiro; Murugesan, Ramachandran; Yamada, Ken-ichi; Kinoshita, Yuichi; Naganuma, Tatsuya; Kato, Masahisa

    2010-05-01

    Overhauser-enhanced magnetic resonance imaging (OMRI) studies of a membrane-permeable nitroxyl spin probe, (2)H-enriched 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), used in simultaneous molecular imaging is reported. Phantom imaging was performed with liposomal solutions of MC-PROXYL at varying spin probe and liposome concentrations using a field-cycle mode, custom-built OMRI scanner. Dynamic nuclear polarization (DNP) spectra of the liposomal solution of the spin probe, measured at 14.529mT using a 5mT sweep of the electron paramagnetic resonance (EPR) irradiation field showed splitting of the low and high filed hyperfine lines. Spectral measurements using D(2)O and a spin broadening agent, K(3)Fe(CN)(6) confirmed that these peaks originated from water molecules in two different environments, compartmentalized with liposomes. The nuclear Overhauser enhancement measured at different EPR irradiation times and power levels showed reduction in water nuclear magnetic resonance (NMR) signal enhancement in liposomal membrane due to the reduction in the coupling constant, rho. This study illustrates that OMRI can be used to differentiate between the intra- and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe. PMID:20226702

  11. Dynamic nuclear polarization studies of redox-sensitive nitroxyl spin probes in liposomal solution

    NASA Astrophysics Data System (ADS)

    Benial, A. Milton Franklin; Utsumi, Hideo; Ichikawa, Kazuhiro; Murugesan, Ramachandran; Yamada, Ken-ichi; Kinoshita, Yuichi; Naganuma, Tatsuya; Kato, Masahisa

    2010-05-01

    Overhauser-enhanced magnetic resonance imaging (OMRI) studies of a membrane-permeable nitroxyl spin probe, 2H-enriched 3-methoxycarbonyl-2,2,5,5-tetramethyl-pyrrolidine-1-oxyl (MC-PROXYL), used in simultaneous molecular imaging is reported. Phantom imaging was performed with liposomal solutions of MC-PROXYL at varying spin probe and liposome concentrations using a field-cycle mode, custom-built OMRI scanner. Dynamic nuclear polarization (DNP) spectra of the liposomal solution of the spin probe, measured at 14.529 mT using a 5 mT sweep of the electron paramagnetic resonance (EPR) irradiation field showed splitting of the low and high filed hyperfine lines. Spectral measurements using D 2O and a spin broadening agent, K 3Fe(CN) 6 confirmed that these peaks originated from water molecules in two different environments, compartmentalized with liposomes. The nuclear Overhauser enhancement measured at different EPR irradiation times and power levels showed reduction in water nuclear magnetic resonance (NMR) signal enhancement in liposomal membrane due to the reduction in the coupling constant, ?. This study illustrates that OMRI can be used to differentiate between the intra- and extra- membrane water by loading the liposome vesicles with a lipid-permeable nitroxyl spin probe.

  12. Biochemistry 1991,30, 8331-8339 8331 Microsecond Rotational Dynamics of Spin-Labeled Ca-ATPase during Enzymatic

    E-print Network

    Thomas, David D.

    and detected rotational dynamics using satura- tion-transfer electron paramagnetic resonance (ST-EPR the molecular dynamics of the Ca-ATPasetransport cycle. In particular, it has been proposed that changesBiochemistry 1991,30, 8331-8339 8331 Microsecond Rotational Dynamics of Spin-Labeled Ca

  13. J. Mol. Biol. (1979) 132,257-273 Rotational Dynamics of Spin-labeled F-actin in the

    E-print Network

    Thomas, David D.

    1979-01-01

    description of the dynamics of the cont'raction process l"equires direct physical observation of the molecular&in, tropomyosin and troponin to the molecular dynamics of myosin-actin inter- actions. UJ. Mol. Biol. (1979) 132,257-273 Rotational Dynamics of Spin-labeled F-actin in the Sub

  14. Multi-Spin Interactions and Dynamics in Model Systems for Organic Molecular Materials

    NASA Astrophysics Data System (ADS)

    Gardner, Daniel M.

    This thesis presents results from the application of electron paramagnetic resonance (EPR) techniques to study the spin-spin interactions of novel organic compounds possessing one or more unpaired electron spins. The first two chapters focus on the use of steady-state techniques to probe the interaction of a single unpaired electron with its surrounding environment. The second part of this thesis expands on these studies by employing transient techniques to analyze and control the spin-spin interactions and dynamics of systems which undergo photoinduced charge separation to generate multiple unpaired electrons. In Chapter 2 a series of novel trifluoromethylated perylene and naphthalene imide and diimide compounds are chemically reduced to yield their respective radical anions. EPR spectroscopy at both X-band and W-band fields allows for characterization of the hyperfine coupling constants and g-tensors which are important for studying their role as intermediates in electron transfer reactions. In Chapter 3 continuous-wave electron-nuclear double resonance (ENDOR) spectroscopy is employed to study the sharing of an unpaired electron across oligomers of naphthalene-1,8:4,5-bis(dicarboximide) in several novel geometries. Transient EPR techniques are introduced in Chapter 4 to measure the spin-spin interactions in photogenerated radical pairs in a series of electron donor-acceptor systems designed to mimic the photosynthetic reaction center. Measurement of the dipolar interaction at X-band fields allows for the determination of the radical pair distance, while the enhanced spectral resolution at W-band fields allows for analysis of the anisotropy of the g-tensors thereby allowing for the determination of the geometry of the radical pair. In Chapter 5 a novel U-shaped electron donor-acceptor-radical system is introduced in which use of a xanthene spacer results in negligible magnetic exchange interactions between the acceptor radical anion and the appended stable radical while the short through-space distance results in a strong ferromagnetic dipolar interaction leading to unique spectral features in the transient EPR spectra. In contrast, Chapter 6 is focused on a linear electron donor-acceptor-radical system in which magnetic exchange results in polarization of the appended radical spin which is then transferred to neighboring nuclear spins through the use of pulse ENDOR sequences thereby opening possibilities for a nuclear spin memory.

  15. Detection of internal and overall dynamics of a two-atom-tethered spin-labeled DNA.

    PubMed

    Keyes, R S; Bobst, A M

    1995-07-18

    DNA motions consist of several components which couple, making their investigation difficult. This study describes an approach for obtaining dynamical information by EPR when spin-labeled nucleic acids are examined. The analysis is accomplished by implementing two motional models. The first model (i.e., dynamic cylinder model) views the spin-labeled helix as a diffusing cylinder containing internal dynamics which are characterized by an order parameter. The second model (i.e., base disk model) provides correlation times describing the diffusion of the spin-labeled base. In each model, the nitroxide motion consists of both global and internal contributions. Dynamic cylinder and base disk simulations of four duplexes containing nitroxides attached to thymidine by a two-atom tether (DUMTA)-(dT)7DUMTA-(dT)7.(dA)15, [(dT)7DUMTA(dT)7]2.(dA)30, [(dT)7DUMTA(dT)7]3.(dA)45, and [(dT)7DUMTA(dT)7]m.-(dA)n--demonstrate the useful application of this approach. From dynamic cylinder simulations, the order parameter for internal motions is found to be independent of the helix length (S = 0.32 +/- 0.01). Previous base disk simulations of a DNA 26mer and polymer labeled with a five-atom-tethered nitroxide seemed to indicate that tau perpendicular was only sensitive to internal dynamics. Results from base disk simulations of DUMTA-labeled DNA indicate that the perpendicular component of the base disk correlation time (tau perpendicular = 1.4-6.2 ns) is sensitive to global dynamics. Thus, tau perpendicular is a quantitative indicator of both internal and global dynamics. Comparison of the two models reveals that tau perpendicular infinity S2 tau rb, where tau rb represents the rigid-body diffusion of the DNA helix. This relationship between S and tau perpendicular provides a framework for studying conformational changes and size-dependent phenomena in spin-labeled nucleic acids. Application of the dynamic cylinder model to a B-Z transition generates distinct values of S for each of the conformations, indicating that Z-DNA is more rigid than B-DNA. PMID:7619828

  16. Electron Spin Echo Study of Molecular Structure and Dynamics: New Approaches Based on Spontaneous Fluctuations of Magnetic Interactions

    Microsoft Academic Search

    L. V. Kulik; S. A. Dzyuba

    2004-01-01

    Modulation phenomena that take place during electron spin echo signal decay have long been used in structural studies of free radicals and their environment. These phenomena are based on coherent dynamic effects, arising from simultaneous excitation (by microwave pulses) of two or more transitions in the EPR spectrum. Recently, a new source of stimulated electron spin echo (ESE) modulation was

  17. Growth-temperature dependence of optical spin-injection dynamics in self-assembled InGaAs quantum dots

    SciTech Connect

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

    2014-09-07

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

  18. 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.

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

    SciTech Connect

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

    2011-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Chui, C. P.; Zhou, Yan

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    PubMed

    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. PMID:12942981

  3. Multi-teraflops spin dynamics studies of the magnetic structure of FeMn\\/Co interfaces

    Microsoft Academic Search

    Andrew Canning; B. Ujfalussy; T. C. Schulthess; X.-G. Zhang; W. A. Shelton; D. M. C. Nicholson; G. M. Stocks; Yang Wang; T. Dirks

    2002-01-01

    The authors have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese\\/Cobalt (FeMn\\/Co) interfaces. These large scale quantum mechanical simulations, involving 2016-atom super-cell models, reveal details of the orientational configuration of the magnetic moments at the interface that are unobtainable by any other means. Exchange bias, which involves

  4. Multi-teraflops spin dynamics studies of the magnetic structure of FeMn\\/Co interfaces

    Microsoft Academic Search

    A. Canning; B. Ujfalussy; Thomas C. Schulthess; X.-G. Zhang; William A. Shelton; D. M. C. Nicholson; G. M. Stocks; Yang Wang; T. Dirks

    2001-01-01

    We have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese\\/Cobalt (FeMn\\/Co) interfaces. These large scale quantum mechanical simulations, involving 2016-atom super-cell models, reveal details of the orientational configuration of the magnetic moments at the interface that are unobtainable by any other means. Exchange bias, which involves the

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

    Microsoft Academic Search

    A. Canning; B. Ujfalussy; T. C. Schulthess; X.-G. Zhang; W. A. Shelton; D. M. C. Nicholson; G. M. Stocks; Y. Wang; T. Dirks

    2001-01-01

    We have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese\\/Cobalt (FeMn\\/Co) interfaces. These large scale quantum mechanical simulations, involving 2016-atom super-cell models, reveal details of the orientational con.guration of the magnetic moments at the interface that are unobtainable by any other means. Exchange bias, which involves the

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

    SciTech Connect

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

    2014-10-28

    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.

  7. Limiting Dynamics for Spherical Models of Spin Glasses at High Temperature

    Microsoft Academic Search

    Amir Dembo; Alice Guionnet; Christian Mazza

    2007-01-01

    We analyze the coupled non-linear integro-differential equations whose solution is the thermodynamical limit of the empirical\\u000a correlation and response functions in the Langevin dynamics for spherical p?spin disordered mean-field models. We provide a mathematically rigorous derivation of their FDT solution (for the high temperature\\u000a regime) and of certain key properties of this solution, which are in agreement with earlier derivations

  8. Lipid chain dynamics in stratum corneum studied by spin label electron paramagnetic resonance

    Microsoft Academic Search

    Antonio Alonso; Nilce C Meirelles; Marcel Tabak

    2000-01-01

    The lipid chain motions in stratum corneum (SC) membranes have been studied through electron paramagnetic resonance (EPR) spectroscopy of stearic acid spin-labeled at the 5th, 12th and 16th carbon atom positions of the acyl chain. Lipids have been extracted from SC with a series of chloroform\\/methanol mixtures, in order to compare the molecular dynamics and the thermotropic behavior in intact

  9. Spin dynamics of the electron-doped high-T(c) superconducting cuprates.

    PubMed

    Onufrieva, F; Pfeuty, P

    2004-06-18

    We show that a basic difference between the electron- and hole-doped cuprates is their proximity to two different quantum critical points in a 2D free fermion system on a square lattice and that the spin dynamics observed recently for the first time in the electron-doped Nd2-xCexCuO4, very different from that in the hole-doped cuprates, can be understood as a consequence of this effect. PMID:15245124

  10. Spin Dynamics of the Electron-Doped High-Tc Superconducting Cuprates

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Pfeuty, P.

    2004-06-01

    We show that a basic difference between the electron- and hole-doped cuprates is their proximity to two different quantum critical points in a 2D free fermion system on a square lattice and that the spin dynamics observed recently for the first time in the electron-doped Nd2-xCexCuO4, very different from that in the hole-doped cuprates, can be understood as a consequence of this effect.

  11. Fermi-liquid-type spin dynamics in LSCO and breakdown of itinerant magnetism picture in YBCO. How to understand?

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Rossat-Mignod, J.

    1994-12-01

    Spin dynamics in cuprates is analysed on a framework of a new theory (based on the t-t'-J model and the diagrammatic technique for Hubbard operators) which treats correctly strong electron correlations within CuO 2 layer.

  12. Prediction of EPR spectra of liquid crystals with doped spin probes from fully atomistic molecular dynamics simulations: exploring molecular order and dynamics at the phase transition.

    PubMed

    Kuprusevicius, Egidisus; Edge, Ruth; Gopee, Hemant; Cammidge, Andrew N; McInnes, Eric J L; Wilson, Mark R; Oganesyan, Vasily S

    2010-10-11

    Liquid crystals spin their secrets: Electron paramagnetic resonance (EPR) spectra are predicted directly and completely from fully atomistic molecular dynamics (MD) simulations of 4-cyano-4-n-pentylbiphenyl (5CB) nematic liquid crystals with a doped nitroxide spin probe (depicted in yellow; red curve = simulated and blue curve = measured EPR spectrum). PMID:20827705

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

    SciTech Connect

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

    1996-11-01

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

  14. Chaotic spin dynamics of a long nanomagnet driven by a current

    NASA Astrophysics Data System (ADS)

    Lan, Yueheng; Li, Y. Charles

    2008-12-01

    We study the spin dynamics of a long nanomagnet driven by an electrical current. In the case of only dc current, the spin dynamics has a sophisticated bifurcation diagram of attractors. One type of attractors is a weak chaos. On the other hand, in the case of only ac current, the spin dynamics has a rather simple bifurcation diagram of attractors. That is, for small Gilbert damping, when the ac current is below a critical value, the attractor is a limit cycle; above the critical value, the attractor is chaotic (turbulent). For normal Gilbert damping, the attractor is always a limit cycle in the physically interesting range of the ac current. We also developed a Melnikov integral theory for a theoretical prediction on the occurrence of chaos. Our Melnikov prediction seems to be performing quite well in the dc case. In the ac case, our Melnikov prediction seems to be predicting transient chaos. The sustained chaotic attractor seems to have extra support from parametric resonance leading to a turbulent state.

  15. Spin-labeled psoralen probes for the study of DNA dynamics.

    PubMed

    Spielmann, H P; Chi, D Y; Hunt, N G; Klein, M P; Hearst, J E

    1995-11-14

    Six nitroxide spin-labeled psoralen derivative have been synthesized and evaluated as probes for structural and dynamic studies. Sequence specific photoaddition of these derivatives to DNA oligonucleotides resulted in site-specifically cross-linked and spin-labeled oligomers. Comparison of the general line shape features of the observed electron paramagnetic resonance (EPR) spectra of several duplexes ranging in size from 8 to 46 base pairs with simulated EPR spectra indicate that the nitroxide spin-label probe reports the global tumbling motion of the oligomers. While there is no apparent large amplitude motion of the psoralen other than the overall tumbling of the DNA on the time scales investigated, there are some indications of bending and other residual motions. The (A)BC excinuclease DNA repair system detects structural or dynamic features of the DNA that distinguish between damaged and undamaged DNA and are independent of the intrinsic structure of the lesion. NMR studies have shown that psoralen-cross-linked DNA has altered backbone dynamics and conformational populations in the immediate vicinity of the adduct [Emsley et al. (1993) J. Am. Chem. Soc. 115, 7765-7771; Spielmann et al. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 2345-2349]. We suggested that the signal for recognition of a lesion to be repaired is in the sugar--phosphate backbone and not in the damaged base(s). PMID:7578089

  16. Non-local dynamics of weakly nonlinear spin excitations in thin ferromagnetic films

    NASA Astrophysics Data System (ADS)

    Kiseliev, V. V.; Tankeyev, A. P.

    1996-12-01

    Effective integro-differential equations of weakly nonlinear dynamics describing the interaction of quasi-one-dimensional exchange-dipole spin-waves are derived for a thin ferromagnetic slab (film). The non-local part of the magnetostatic dispersion of these waves has been taken into account. Algebraic soliton-like states have been predicted. The conditions of their existence and their dynamic properties are investigated depending on the film thickness and on the magnitude and orientation of the external magnetic field. The role of crystallographic magnetic anisotropy in the formation of these states is analysed.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  19. Spin and hole dynamics of high- Tc cuprates and their interconditional evolution with doping from antiferromagnetic to ‘strange metal’ state

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Rossat-Mignod, J.; Kushnir, V. P.

    1995-02-01

    A theory of the hole and spin dynamics in cuprates, which takes into account an intercorrelation between localized on Cu spins and itinerant quasiparticles related with doped holes within the CuO 2 layer, is developed. The calculated dynamic magnetic susceptibility and the single-hole spectral-weight function are compared with inelastic neutron scattering and photoemission experiments for YBaCuO.

  20. Spin-torque-driven magnetization dynamics in nanomagnets subject to magnetic fields perpendicular to the sample plane

    NASA Astrophysics Data System (ADS)

    Bonin, Roberto; Bertotti, Giorgio; Mayergoyz, Isaak D.; Serpico, Claudio

    2006-04-01

    We analytically solve the Landau-Lifshitz-Gilbert equation with the addition of the spin-torque term proposed by Slonczewski [J. Magn. Magn. Mater. 159, L1 (1996)] for the case of external magnetic field perpendicular to the sample plane. By using methods of nonlinear dynamical system theory we construct the complete stability diagram of the spin-torque-driven dynamics in the field-current control plane. Our predictions are compared with recent experimental results.

  1. 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.

  2. Pulsed Electrical Spin Injection into InGaAs Quantum Dots: Studies of the Electroluminescence Polarization Dynamics

    SciTech Connect

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

    2010-01-04

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

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

    2013-08-21

    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.

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

    NASA Technical Reports Server (NTRS)

    1963-01-01

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

  5. Dynamics of spin-1 bosons in an optical lattice: Spin mixing, quantum-phase-revival spectroscopy, and effective three-body interactions

    NASA Astrophysics Data System (ADS)

    Mahmud, K. W.; Tiesinga, E.

    2013-08-01

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

  6. Borehole temperature response for competing models of Laurentide ice sheet dynamics

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

  7. Density functional plus dynamical mean-field theory of the spin-crossover molecule Fe(phen)2(NCS)2

    NASA Astrophysics Data System (ADS)

    Chen, Jia; Millis, Andrew J.; Marianetti, Chris A.

    2015-06-01

    We study the spin-crossover molecule Fe(phen) 2(NCS) 2 using density functional theory (DFT) plus dynamical mean-field theory, which allows access to observables not attainable with traditional quantum chemical or electronic structure methods. The temperature dependent magnetic susceptibility, electron addition and removal spectra, and total energies are calculated and compared to experiment. We demonstrate that the proper quantitative energy difference between the high-spin and low-spin state, as well as reasonably accurate values of the magnetic susceptibility can be obtained when using reasonable interaction parameters. Comparisons to DFT and DFT+U calculations demonstrate that dynamical correlations are critical to the energetics of the low-spin state. Additionally, we elucidate the differences between DFT+U and spin density functional theory (SDFT) plus U methodologies, demonstrating that DFT+U can recover SDFT+U results for an appropriately chosen on-site exchange interaction.

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

    NASA Astrophysics Data System (ADS)

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

    2002-05-01

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

  9. Competing Risks

    Microsoft Academic Search

    Bo Henry Lindqvist

    Consider a unit which can experience any one of k competing failure types, and suppose that for each unit we observe the time to failure, T, and the type of fail- ure, C 2 f1;2; : : : ; kg. The case of observing the pair (T; C) is termed \\\\competing risks\\

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

    SciTech Connect

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

    2010-12-23

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

  11. Competing orders in the cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Zhang, Ying

    When the superconducting order in a doped cuprate system is suppressed, for example by magnetic field, impurities, finite temperature or less optimal doping condition, various competing orders are revealed. This thesis contains the theoretical analysis of these competing orders, especially the analysis of the quantum phase transitions from a d-wave superconductor to a superconductor featuring a certain other order. Such orders can be divided into two types according to whether or not they carry non-zero net momentum Q. We classify and analyze all order parameters with Q = 0 on the basis of group-theoretic and symmetry arguments. Thereafter, by a renormalization group analysis, we identify that among all these orders the fluctuations of dx2 - y2 + idxy paring order might strongly damp the nodal quasiparticles of the cuprate superconductor, while leaving antinodal quasiparticles undamped. We also study order parameters with Q ? 0, which include spin and charge density wave orders. For exact nesting case, fluctuations of these two orders also give rise to nodal quasiparticle damping. We also examine the influence of a magnetic field on the spin and charge density waves. We argue that the underdoped cuprates might undergo a second order phase transition into a region where superconducting order coexists with long-range magnetic order (and hence charge order). The transition might be driven by lowering the doping or increasing the magnetic field, all of which decrease the spin gap and affect the excitation spectrum. Our quantum field theory for the transition takes into account the quantum fluctuation of spin order, while keeping superconducting order a mean-field quantity that serves as a tuning parameter by coupling to spin order. Complete numerical solutions of a self-consistent large-N theory provide detailed information on the phase diagram and the spatial structure of the dynamic spin spectrum. We also compute the pinning of charge density order by the vortices where the spin order dynamically fluctuates. Emerging experimental evidence has strongly supported our theory and the subsequent predictions.

  12. Dynamical properties of photoinduced magnetism and spin-crossover phenomena in Prussian blue analogs

    NASA Astrophysics Data System (ADS)

    Nishino, Masamichi; Boukheddaden, Kamel; Miyashita, Seiji; Varret, François

    2005-01-01

    We investigate time evolution of the magnetization and high spin fraction of the system in which spin-crossover phenomena and magnetic transitions are involved, proposing a new model which allows us to describe both spin-crossover (SC) transition and magnetic ordering of Prussian blue analogs under photoirradiation. Both the intermolecular lattice interaction and the intermolecular magnetic interaction are considered in this model, which enables unified descriptions of the photoinduced SC transition and magnetic transitions. For the dynamics of the system, we take into account the multi-time scales in a master equation approach for the magnetic relaxation, the lattice (electronic) relaxation, and the photoexcitation process. We observe non-linear dependence of the growth of the magnetization and high spin fraction on irradiation time and that on the strength of irradiation, which are typical properties of SC and PBA compounds. We also observe irreversible magnetization process in a temperature cycle, which reproduces qualitatively well the novel behavior observed in the corresponding experiments.

  13. Polaron dynamics and decoherence in an interacting two-spin system coupled to optical phonon environment

    E-print Network

    Amit Dey; Sudhakar Yarlagadda

    2014-02-14

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

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

  15. Three-body correlation effects on the spin dynamics of double-exchange ferromagnets

    NASA Astrophysics Data System (ADS)

    Kapetanakis, M. D.; Manousaki, A.; Perakis, I. E.

    2006-05-01

    We present a variational calculation of the spin wave excitation spectrum of double-exchange ferromagnets in different dimensions. Our theory recovers the random phase approximation and 1/S expansion results as limiting cases and can be used to study the intermediate exchange coupling and electron concentration regime relevant to the manganites. In particular, we treat exactly the long range three-body correlations between a Fermi sea electron-hole pair and a magnon excitation and show that they strongly affect the spin dynamics. The manifestations of these correlations are many-fold. We demonstrate that they significantly decrease the stability of the ferromagnetic phase and the magnon stiffness. We also show that the ferromagnetic state is unstable against spin wave excitations close to the Brillouin zone boundary. As a result, we find a strong softening of the spin wave dispersion as compared to the Heisenberg ferromagnet with the same stiffness within a range of intermediate concentrations. We discuss the possible relevance of our results to experiments in colossal magnetoresistance ferromagnets.

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

    E-print Network

    Weizhu Bao; Yongyong Cai

    2014-07-22

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

  17. 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. [Department of Physics, University of California, Berkeley, California 94720 (United States); Wenz, A. N. [Department of Physics, University of California, Berkeley, California 94720 (United States); Physikalisches Institut, Ruprecht-Karls-Universitaet Heidelberg, D-69120 Heidelberg (Germany); Stamper-Kurn, D. M. [Department of Physics, University of California, Berkeley, California 94720 (United States); Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2011-12-15

    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.

  18. Theory of spin dynamics in high-{ital T}{sub {ital c}} copper oxide superconductors. Application to neutron scattering

    SciTech Connect

    Onufrieva, F.; Rossat-Mignod, J. [Laboratoire Leon Brillouin, CEA-CNRS, CE Saclay, 91191 Gif-sur-Yvette cedex (France)] [Laboratoire Leon Brillouin, CEA-CNRS, CE Saclay, 91191 Gif-sur-Yvette cedex (France)

    1995-09-01

    A theory of spin dynamics in copper oxide superconductors is developed. The theory is based on the {ital t}-{ital t}{prime}-{ital J} model and the diagrammatic technique for Hubbard operators. The dynamic spin susceptibility calculated for metallic hole concentrations includes two different contributions. The ``localized`` contribution arises from the subsystem of localized Cu spins with quantum short-range correlations. The ``itinerant`` contribution arises from the subsystem of propagating carrier quasiparticles. As a result of their competition, the spin dynamics evolves continuously within the metallic state from normal-metal behavior at high doping (overdoped regime) to quantum spin-liquid-type dynamics with magnonlike excitations at low doping through non-Fermi-liquid behavior in all intermediate regimes. Based on the theory, a detailed analysis of momentum and energy dependences of the dynamic spin susceptibility for different doping regimes is performed in order to compare the theoretical predictions with the experimental results discovered by inelastic neutron scattering. We are able to understand the strange shape of Im {chi} versus {omega} and its exotic evolution with doping, the existence of the resonance peak, the gap and pseudogap effects, and many other unusual features observed for YBa{sub 2}Cu{sub 3}O{sub 6+{ital x}} as well as the incommensurate and ``gapless`` behavior for La{sub 2{minus}{ital x}}Sr{sub {ital x}}CuO{sub 4}.

  19. 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

  20. Anatomy of field effects on magnetization dynamics and spin transfer noise

    NASA Astrophysics Data System (ADS)

    Wang, L.; Han, G. C.; Zheng, Y. K.

    2006-08-01

    Spin transfer-related phenomena in nanomagnets have attracted extensive studies. In this paper we shall focus on analysis of individual and combined effects of the external, anisotropy, and demagnetization fields on magnetization dynamics and spin transfer noise. It is found that individual roles of the external, anisotropy, and demagnetization fields, as well as the combined roles of external plus anisotropy fields and anisotropy plus demagnetization fields, do not change the behavior of current induced magnetization switching. Such magnetization reversal procedures are of low noise. Our dynamics and power spectral density calculations show that it is the demagnetization field that plays a major role in inducing spin transfer noise: the demagnetization field itself or in combination with the anisotropy field will result in wave-like switching; moreover, the demagnetization field, together with the external field (not too small), will lead to precession and hence the system would be in noisy states. Our modeling work for an elliptical Py alloy is qualitatively consistent with Cornell's experiment and simulation [Science 307 (2005) 228].

  1. Nondiffusive Spin Dynamics in a Two-Dimensional Electron Gas C. P. Weber,1

    E-print Network

    Orenstein, Joe

    , such as spin Hall currents [1­7], current-induced spin polarization [8], and spin-galvanic effects [9-orbit interaction (SOI) exhibit exotic effects that arise from the coupling of spin polarization and charge current

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

    PubMed

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

    2013-03-22

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

  3. 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.

  4. Ultrafast spin precession dynamics in exchange-biased FeNi/FeMn/FeNi films

    NASA Astrophysics Data System (ADS)

    in Lee, Joo; Hwang, Chan Yong

    2012-02-01

    We investigated the spin precession dynamics in exchange-biased FeNi/FeMn/FeNi films by means of time-resolved magneto-optical Kerr effect (TR-MOKE). We observed the spin precession of all FeNi/FeMn/FeNi films in the TR-MOKE signals. The precession oscillations of the films changed rapidly as varying a thickness of antiferromagnet (FeMn). The period of the precession oscillations was not single and in the range of 10 to 20 ps. It is supposed that this is not only related to the exchange bias between ferromagnet and antiferromagnet but also double exchange biases in FeNi/FeMn/FeNi films.

  5. Dynamical correlation effects on structure factor of spin-polarized two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Singh, Gurvinder; Kumar, Krishan; Garg, Vinayak; Moudgil, R. K.

    2015-06-01

    We report a theoretical study on static density structure factor S(q) of a spin-polarized two-dimensional electron gas over a wide range of electron number density rs. The electron correlations are treated within the dynamical version of the self-consistent mean-field theory of Singwi, Tosi, Land, and Sjolander, the so-called qSTLS approach. The calculated S(q) exhibits almost perfect agreement with the quantum Monte Carlo simulation data at rs=1. However, the extent of agreement somewhat diminishes with increasing rs, particularly for q around 2kF. Seen in conjunction with the success of qSTLS theory in dealing with correlations in the unpolarized phase, our study suggests that the otherwise celebrated qSTLS theory is not that good in treating the like-spin correlations.

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

    PubMed

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

    2013-03-13

    The low-energy (? = ?? < 1 meV), low-temperature (T = 0.05 K) spin dynamics of the s = 1/2 kagome candidate herbertsmithite are probed in the presence of magnetic fields up to 2.5 T. The zero-field spectra reveal a very weak continuum of scattering at T = 10 K and a broad inelastic peak centred at ?(max) = 0.2 meV at lower temperatures, T < 1 K. The broad peak is found to be strongly damped, with a liquid-like structure factor implying correlations at length scales up to r = 6 Å. The field dependence of the peak appears to follow the Zeeman splitting of s = 1/2 excitations, consistent with the weakly split 'doublets' observed in low-temperature specific heat. A possible explanation of these observations is a short-range correlated state involving defect spins between the kagome planes and moments in the kagome layers. PMID:23388841

  7. 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

  8. Dynamic generation of spin-squeezed states in bosonic Josephson junctions

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

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

  9. Multidimensional Instability and Dynamics of Spin Avalanches in Crystals of Nanomagnets

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  10. 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.

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

    PubMed

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

    2014-05-20

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

  12. 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.

  13. Triple-quantum dynamics in multiple-spin systems undergoing magic-angle spinning: application to 13C homonuclear correlation spectroscopy

    NASA Astrophysics Data System (ADS)

    Edén, Mattias; Brinkmann, Andreas

    2005-04-01

    We analyze the multiple-quantum dynamics governed by a new homonuclear recoupling strategy effecting an average dipolar Hamiltonian comprising three-spin triple-quantum operators (e.g., Sp+Sq+Sr+) under magic-angle spinning conditions. Analytical expressions are presented for polarization transfer processes in systems of three and four coupled spins-1/2 subject to triple-quantum filtration (3QF), and high-order multiple-quantum excitation is investigated numerically in moderately large clusters, comprising up to seven spins. This recoupling approach gives highly efficient excitation of triple-quantum coherences: ideally, up to 67% of the initial polarization may be recovered by 3QF in three-spin systems in polycrystalline powders. Two homonuclear 2D correlation strategies are demonstrated experimentally on powders of uniformly 13C-labeled alanine and tyrosine: the first correlates the single-quantum spectrum in the first dimension with the corresponding 3QF spectrum along the other. The second protocol correlates triple-quantum coherences with their corresponding single-quantum coherences within triplets of coupled spins.

  14. Spin dynamics of lightly doped La1 - xSrxMnO3 (abstract)

    NASA Astrophysics Data System (ADS)

    Moudden, A. H.; Vasiliu-Doloc, L.; de Leon-Guevara, A. M.; Pinsard, L.; Revcolevschi, A.

    1997-04-01

    Neutron scattering has been used to study the spin dynamics of the lightly doped La1-xSrxMnO3, with x between 0 and 1/8. We show that as the dopant concentration increases from 0 to 0.09, the magnetic long-range order progressively changes from a slightly to a strongly canted antiferromagnetic order, whereas the transition temperature is continuously reduced from about 140 K to about 120 K. The spin waves show a strongly anisotropic dispersion relation that can be described by a strong ferromagnetic in-plane coupling Jab and a weak antiferromagnetic out-of-plane coupling Jc. The spin wave dispersion exhibits a finite gap that continuously decreases with the dopant concentration from about 2.5 meV for x=0 to about 1.5 meV for x=0.09. Furthermore, while the ferromagnetic in-plane coupling is slightly enhanced from SJab˜1.8 meV for the undoped sample to SJab˜2.0 meV for 9% doping, the out-of-plane antiferromagnetic coupling is strongly reduced from SJc˜-1.2 meV to SJc˜-0.4 meV. In the same concentration range, the system remains orthorhombic with a continuously decreasing lattice distortion, which could indicate that part of the reduction in the out-of-plane antiferromagnetic coupling can be ascribed to steric effects, whereas the enhancement of the ferromagnetic coupling could be solely associated with electronic effects. Preliminary studies of the spin-wave linewidths in the two systems x=0 and x=0.09 show a significant increase in the damping of the in-plane ferromagnetic spin waves. These results clearly show that La1-xSrxMnO3 evolves into a two-dimensional ferromagnetic system near the concentration x=0.1.

  15. Multiple Reflection Effect on Spin-Transfer Torque Dynamics in Spin Valves with a Single or Dual Polarizer

    NASA Astrophysics Data System (ADS)

    Zhu, Weiwei; Zhang, Zongzhi; Zhang, Jianwei; Liu, Yaowen

    2015-04-01

    In this paper, spin-dependent multiple reflection effect on spin-transfer torque (STT) has been theoretically and numerically studied in a spin valve nanopillar with a single or dual spin-polarizer. By using a scattering matrix method, we formulate an analytical expression of STT that contains the multiple interfacial reflection effect. It is found that the multiple reflections could enhance the STT efficiency and reduce the critical switching current. The STT efficiency depends on the spin polarization of both the free layer and polarizer. In the nanopillars with a dual spin polarizer, the multiple reflections would cause an asymmetric frequency dependence on the applied current, albeit exactly the same parameters are used in all three ferromagnetic layers, indicating that the frequency in the negative current varies much faster than that in the positive case.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-08-01

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

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

    E-print Network

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

    2006-03-02

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

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

    NASA Astrophysics Data System (ADS)

    Boulle, O.; Buda-Prejbeanu, L. D.; Jué, E.; Miron, I. M.; Gaudin, G.

    2014-05-01

    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.

  20. Disconnected glass-glass transitions and swallowtail bifurcations in microscopic spin models with facilitated dynamics.

    PubMed

    Sellitto, Mauro

    2013-06-14

    It has been recently established that heterogeneous bootstrap percolation and related dynamic facilitation models exhibit a complex hierarchy of continuous and discontinuous transitions depending on lattice connectivity and kinetic constraints. Here the range of the previously observed phase diagram topologies and higher-order singularities is extended to disconnected glass-glass transitions and to cusp and swallowtail bifurcations (which can be generic and degenerate). The phase diagram and the order parameter for two different types of spin mixtures are analytically determined and an experimental realization of the new predictions emerging in our approach is suggested. PMID:23781805

  1. Disconnected glass-glass transitions and swallowtail bifurcations in microscopic spin models with facilitated dynamics

    NASA Astrophysics Data System (ADS)

    Sellitto, Mauro

    2013-06-01

    It has been recently established that heterogeneous bootstrap percolation and related dynamic facilitation models exhibit a complex hierarchy of continuous and discontinuous transitions depending on lattice connectivity and kinetic constraints. Here the range of the previously observed phase diagram topologies and higher-order singularities is extended to disconnected glass-glass transitions and to cusp and swallowtail bifurcations (which can be generic and degenerate). The phase diagram and the order parameter for two different types of spin mixtures are analytically determined and an experimental realization of the new predictions emerging in our approach is suggested.

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

    SciTech Connect

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

    2014-05-07

    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.

  3. Creation and dynamics of two-dimensional skyrmions in antiferromagnetic spin-1 Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

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

  4. Spin dynamics of the bilinear-biquadratic S =1 Heisenberg model on the triangular lattice: A quantum Monte Carlo study

    NASA Astrophysics Data System (ADS)

    Völl, Annika; Wessel, Stefan

    2015-04-01

    We study thermodynamic properties as well as the dynamical spin and quadrupolar structure factors of the O(3)-symmetric spin-1 Heisenberg model with bilinear-biquadratic exchange interactions on the triangular lattice. Based on a sign-problem-free quantum Monte Carlo approach, we access both the ferromagnetic and the ferroquadrupolar ordered spin nematic phase as well as the SU(3)-symmetric point that separates these phases. Signatures of Goldstone soft modes in the dynamical spin and the quadrupolar structure factors are identified, and the properties of the low-energy excitations are compared to the thermodynamic behavior observed at finite temperatures as well as to Schwinger-boson flavor-wave theory.

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  6. Simulation of electron paramagnetic resonance spectra of spin-labeled molecules from replica-exchange molecular dynamics.

    PubMed

    Tyrrell, S; Oganesyan, V S

    2013-10-01

    We report a general approach for the simulation of the electron paramagnetic resonance (EPR) spectra of spin labels attached to peptides and proteins directly from replica-exchange molecular dynamics (REMD) trajectories. Conventional MD trajectories are generally inadequate for the prediction of EPR line shapes since the label can become trapped in one or more of a set of rotameric states, thus preventing both conformational sampling and accurate estimates of the exchange rates between different rotamers. The advantage of using REMD is its ability to provide both efficient conformational sampling and kinetic information for spin-label dynamics. Our approach is illustrated with spin-labeled peptide. This approach to REMD-EPR simulation paves the way for the wider application of MD modeling to the simulation and interpretation of EPR spectra of spin-labeled molecules. PMID:24229207

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

    PubMed

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

    2011-08-01

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

  8. Magic angle spinning NMR of proteins: high-frequency dynamic nuclear polarization and (1)h detection.

    PubMed

    Su, Yongchao; Andreas, Loren; Griffin, Robert G

    2015-06-01

    Magic angle spinning (MAS) NMR studies of amyloid and membrane proteins and large macromolecular complexes are an important new approach to structural biology. However, the applicability of these experiments, which are based on (13)C- and (15)N-detected spectra, would be enhanced if the sensitivity were improved. Here we discuss two advances that address this problem: high-frequency dynamic nuclear polarization (DNP) and (1)H-detected MAS techniques. DNP is a sensitivity enhancement technique that transfers the high polarization of exogenous unpaired electrons to nuclear spins via microwave irradiation of electron-nuclear transitions. DNP boosts NMR signal intensities by factors of 10(2) to 10(3), thereby overcoming NMR's inherent low sensitivity. Alternatively, it permits structural investigations at the nanomolar scale. In addition, (1)H detection is feasible primarily because of the development of MAS rotors that spin at frequencies of 40 to 60 kHz or higher and the preparation of extensively (2)H-labeled proteins. PMID:25839340

  9. 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.

  10. Dynamic Behavior of Fatty Acid Spin Labels within a Binding Site of Soybean Lipoxygenase-1

    PubMed Central

    Wu, Fayi; Gaffney, Betty J.

    2008-01-01

    The putative substrate-binding site in lipoxygenases is long and internal. There is little direct evidence about how the unsaturated fatty acid substrates enter and move within the cavity in order to position correctly for electron transfer reactions with the catalytic non-heme iron. An EPR spectroscopy approach, with spin labeled fatty acids, is taken here to investigate dynamic behavior of fatty acids bound to soybean lipoxygenase-1. The probes are labeled on carbons 5-, 8-, 10-, 12- and 16- of stearic acid. The EPR-determined affinity for the enzyme increases as the length of the alkyl end of the probe increases, with ??G of ?190 cal/methylene. The probes in the series exhibit similar enhanced paramagnetic relaxation by the iron center. These results indicate that the members of the series have a common binding site. All of the bound probes undergo considerable local mobility. The stearate spin labeled on carbon 5 has highest affinity for the lipoxygenase and it is a competitive inhibitor, with Ki 9 ?M. Surprisingly, this stearate labeled near the carboxyl end undergoes more local motion than those labeled in the middle of the chain, when it is bound. This shows that the carboxyl end of the fatty acid spin label is not rigidly docked on the protein. During catalysis, repositioning of the substrate carboxyl on the protein surface may be coupled to motion of portions of the chain undergoing reaction. PMID:17029406

  11. A study of adsorption and molecular dynamics of spin-labeled molecules on the surface of silica nanoparticles

    Microsoft Academic Search

    V. A. Livshits; I. V. Demisheva; B. B. Meshkov; V. P. Tsybyshev; M. V. Alfimov

    2009-01-01

    Stable nitroxyl radicals of different structures, hydrophobicities, and electric charges were used as spin probes for studying\\u000a the adsorption and molecular dynamics of the adsorbed molecules on the surface of LEVASIL silica nanoparticles. Neutral hydrophobic\\u000a probes, namely, spin labeled derivatives of indole, are not adsorbed on the nanoparticles; however, the microviscosity and\\u000a hydrophobicity of their environment differ from those in

  12. Microsecond Rotational Dynamics of Spin-Labeled Myosin Regulatory Light Chain Induced by Relaxation and Contraction of Scallop Muscle †

    Microsoft Academic Search

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

    1998-01-01

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

  13. Vortex Dynamics in a Spin-Orbit-Coupled Bose-Einstein Condensate

    NASA Astrophysics Data System (ADS)

    Fetter, Alexander L.

    2015-04-01

    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 0,± 1 ). 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).

  14. 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).

  15. 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.

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

    E-print Network

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

    2015-01-01

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

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

    E-print Network

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

    2015-02-10

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

  18. 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.

  19. Spin dynamics and zero-field splitting constants of the triplet exciplex generated by photoinduced electron transfer reaction between erythrosin B and duroquinone

    Microsoft Academic Search

    Takashi Tachikawa; Yasuhiro Kobori; Kimio Akiyama; Akio Katsuki; Ulrich E. Steiner; Shozo Tero-Kubota

    2002-01-01

    The spin dynamics of the duroquinone anion radical generated by photoinduced electron transfer reactions from triplet erythrosin B to duroquinone has been studied by using transient absorption and pulsed FT-EPR spectroscopy. Triplet exciplex formation as the reaction intermediate is verified by the observation of spin–orbit coupling induced electron spin polarization. The kinetic parameters for exciplex formation and the intrinsic enhancement

  20. 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.

  1. 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.

  2. 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...

  3. 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

  4. Momentum-Resolved Spin Dynamics of Bulk and Surface Excited States in the Topological Insulator Bi2Se3

    NASA Astrophysics Data System (ADS)

    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 Bi2Se3. Our experiments reveal the existence of a surface resonance state in the second bulk band gap that is benchmarked by fully relativistic ab initio spin-resolved photoemission calculations. We propose that the newly reported state plays a major role in the ultrafast dynamics of the system, acting as a bottleneck for the interaction between the topologically protected surface state and the bulk conduction band. In fact, the spin-polarization dynamics in momentum space show that these states display macroscopically different temperatures and, more importantly, different cooling rates over several picoseconds.

  5. Spin with Inertia

    E-print Network

    Kikuchi, Toru

    2015-01-01

    We consider introducing finite moments of inertia to spin. Such inertia generally arises in spin effective dynamics, that is, when we incorporate the effect of environmental degrees of freedom (typically, conducting fermions) interacting with the spins. When the inertia is finite, new spin precession mode emerges, which is intrinsic to the system and caused by the spin Berry curvature itself. We discuss the effect of this inertia on resonance, spin waves and domain wall dynamics. We also discuss the equivalence between the dynamics of spin and those of a spinning top, which becomes explicit when we introduce the inertia.

  6. Spin with Inertia

    E-print Network

    Toru Kikuchi

    2015-02-13

    We consider introducing finite moments of inertia to spin. Such inertia generally arises in spin effective dynamics, that is, when we incorporate the effect of environmental degrees of freedom (typically, conducting fermions) interacting with the spins. When the inertia is finite, new spin precession mode emerges, which is intrinsic to the system and caused by the spin Berry curvature itself. We discuss the effect of this inertia on resonance, spin waves and domain wall dynamics. We also discuss the equivalence between the dynamics of spin and those of a spinning top, which becomes explicit when we introduce the inertia.

  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. Analysis of Cross-Polarization Dynamics between Two Abundant Nuclei, 19F and 1H, Based on Spin Thermodynamics Theory

    NASA Astrophysics Data System (ADS)

    Ando, Shinji; Harris, Robin K.; Reinsberg, Stefan A.

    1999-11-01

    The phenomenological theory of spin thermodynamics based on the spin temperature hypothesis was employed to describe the cross-polarization (CP) dynamics between two abundant nuclei, 19F and 1H, when the number of fluorine atoms is not substantially less than the number of hydrogens. The influence of T1?'s of both nuclei and the relative magnitude (heat capacity) of the two spin baths must be incorporated explicitly into the analysis in order to derive values for the parameters involved in the CP dynamics. Numerical calculations were performed to clarify the difference in the evolution of magnetization in variable contact time CP experiments between the 1H ? 13C and 1H ? 19F cases. A new type of CP-drain experiment was developed for observing the residual 1H magnetization after 1H ? 19F CP. 19F direct polarization magic-angle spinning (MAS), 1H ? 19F CP, and 1H ? 19F CP-drain MAS NMR spectra have been measured for a fluorinated polyimide, 6FDA/ODA. The CP dynamics between 1H and 19F for the polyimide were analyzed on the basis of the spin thermodynamics theory. The constant for polarization transfer (THF) was determined by the analysis using the effective CP parameters, which were directly obtained from the CP and CP-drain experiments, together with independently measured values of TH1? and TF1?.

  9. 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.

  10. Dynamical separation of spin and lattice degrees of freedom in the relaxation process from the photo-induced state

    NASA Astrophysics Data System (ADS)

    Watanabe, H.; Bréfuel, N.; Mouri, S.; Tuchagues, J.-P.; Collet, E.; Tanaka, K.

    2011-10-01

    We have studied the relaxation dynamics from the photo-induced state in the spin crossover complex [FeH2L2-Me](ClO4)2 by magnetic susceptibility and X-ray diffraction measurements. Just after turning off the laser irradiation, the photo-induced high-spin state immediately starts relaxing back to the low-spin state, while the crystal lattice shows a nucleation process. This result shows that the spin state and lattice deformation should be treated as individual parameters in the non-equilibrium phase transition from the photo-induced state. Experimental results are qualitatively explained by the two-sublattice Ising-like model.

  11. Molecular Dynamics of Spin Crossover: the (P,T) phase diagram of [Fe(PM-BIA)2(NCS)2

    E-print Network

    Marbeuf, A; Matar, S F; Kabalan, L; Létard, J F; Guionneau, P

    2013-01-01

    The spin crossover properties and the domains of existence of the different phases for the [Fe(PM-BIA)2(NCS)2] complex are obtained from combining DFT and classical molecular dynamics (MD). The potential energy surfaces expressed in the Morse form for Fe-N interactions are deduced from molecular DFT calculations and they allow producing Infra Red and Raman frequencies. These Fe-N potentials inserted in a classical force field lead from MD calculations to the relative energies of the high spin and low spin configurations of the orthorhombic structure. The MD investigations have also allowed assessing the experimental (P, T) phase diagram by showing the monoclinic polymorph in its two spin- states, and generating two triple points.

  12. Molecular Dynamics of Spin Crossover: the (P,T) phase diagram of [Fe(PM-BIA)2(NCS)2

    E-print Network

    A. Marbeuf; P. Négrier; S. F. Matar; L. Kabalan; J. F. Létard; P. Guionneau

    2013-01-19

    The spin crossover properties and the domains of existence of the different phases for the [Fe(PM-BIA)2(NCS)2] complex are obtained from combining DFT and classical molecular dynamics (MD). The potential energy surfaces expressed in the Morse form for Fe-N interactions are deduced from molecular DFT calculations and they allow producing Infra Red and Raman frequencies. These Fe-N potentials inserted in a classical force field lead from MD calculations to the relative energies of the high spin and low spin configurations of the orthorhombic structure. The MD investigations have also allowed assessing the experimental (P, T) phase diagram by showing the monoclinic polymorph in its two spin- states, and generating two triple points.

  13. Isotropic chemical shifts and quadrupolar parameters of oxygen-17 using dynamic-angle spinning NMR

    SciTech Connect

    Mueller, K.T.; Baltisberger, J.H.; Wooten, E.W.; Pines, A. [Lawrence Berkeley Laboratory, CA (United States)

    1992-08-20

    Several oxygen-17-enriched silicates were studied using dynamic-angle spinning (DAS) NMR spectroscopy at two magnetic field strengths. The DAS method averages second-order quadrupolar interactions by reorienting a sample about a time-dependent axis, thereby yielding high-resolution spectra for half-odd integer spin quadrupolar nuclei such as oxygen-17. A narrow spectral line is observed for each distinct oxygen site in a powdered sample at the sum of the isotropic chemical shift and the field-dependent isotropic second-order quadrupolar shift. Using equations for the total shift observed at two field strengths, the chemical shift is uniquely determined together with a product of the quadrupolar coupling constant (C{sub Q} = e{sup 2}qQ/h) and the quadrupolar asymmetry parameter ({eta}). For one silicate, the authors demonstrate a computer program that uses the isotropic shifts and quadrupolar products as constraints and provides simulations of overlapped magic-angle spinning line shapes. In this way the quadrupolar parameters, C{sub Q} and {eta}, are determined separately for each crystallographic site. The silicates studied include the discrete orthosilicates larnite (Ca{sub 2}SiO{sub 4}) and forsterite (Mg{sub 2}SiO{sub 4}), as well as diopside (CaMgSi{sub 2}O{sub 6}), wollastonite (CaSiO{sub 3}), and clinoenstatite (MgSiO{sub 3}), which are minerals composed of chains of silicon-oxygen tetrahedra. 49 refs., 2 figs., 2 tabs.

  14. Monitoring DNA dynamics using spin-labels with different independent mobilities.

    PubMed

    Hustedt, E J; Kirchner, J J; Spaltenstein, A; Hopkins, P B; Robinson, B H

    1995-04-01

    The electron paramagnetic resonance (EPR) spectra of spin-labeled DNA duplexes, both bound to DEAE-Sephadex and free in solution, have been analyzed. The nitroxide spin-labels are covalently linked to a deoxyuridine residue using either a monoacetylene or diacetylene tether. This difference in tether length produces a dramatic difference in the independent mobility of the nitroxide relative to the DNA. In the case of the monoacetylene tether, the motion of the nitroxide has previously been shown to be tightly coupled to that of the DNA duplex. With the diacetylene tether, there is considerable independent motion of the probe. The diacetylene tether is intended to minimize the possibility of the nitroxide producing a perturbation of the dynamics of DNA. It is demonstrated here that, when coupled via the diacetylene tether, the nitroxide undergoes a rapid uniaxial rotation about the tether. A detailed analysis of the EPR spectrum of duplex DNA in solution, spin-labeled using the diacetylene tether, demonstrates that the motion of the nitroxide can be modeled in terms of this independent uniaxial rotation together with motion of the DNA which is consistent with the global tumbling of the duplex. As was previously found using the monoacetylene tether, there is no evidence of rapid, large-amplitude motions of the base pair in the EPR spectrum of a nitroxide coupled to duplex DNA via the diacetylene tether. This result confirms the small amplitudes of internal motion, local and collective, previously observed in duplex DNA with the monoacetylene-tethered nitroxide. PMID:7703250

  15. 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

  16. Interface boundary conditions for dynamic magnetization and spin wave dynamics in a ferromagnetic layer with the interface Dzyaloshinskii-Moriya interaction

    SciTech Connect

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

    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.

  17. 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.

  18. Autonomous and forced dynamics in a spin-transfer nano-oscillator: Quantitative magnetic-resonance force microscopy

    NASA Astrophysics Data System (ADS)

    Hamadeh, A.; de Loubens, G.; Naletov, V. V.; Grollier, J.; Ulysse, C.; Cros, V.; Klein, O.

    2012-04-01

    Using a magnetic-resonance force microscope (MRFM), the power emitted by a spin-transfer nano-oscillator consisting of a normally magnetized Py|Cu|Py circular nanopillar is measured both in the autonomous and forced regimes. From the power behavior in the subcritical region of the autonomous dynamics, one obtains a quantitative measurement of the threshold current and of the noise level. Their field dependence directly yields both the spin torque efficiency acting on the thin layer and the nature of the mode which first auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. From the MRFM behavior in the forced dynamics, it is then demonstrated that in order to phase lock this auto-oscillating mode, the external source must have the same spatial symmetry as the mode profile, i.e., a uniform microwave field must be used rather than a microwave current flowing through the nanopillar.

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

    PubMed

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

    2008-02-01

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

  20. Spin label EPR studies of the effect of gramicidin S on lipid chain dynamics

    NASA Astrophysics Data System (ADS)

    Kiricsi, M.; Horváth, L. I.; Dux, L.; Páli, T.

    2001-05-01

    The effect of gramicidin S (GS) on acyl chain dynamics of 14-doxylstearic acid spin label (14-SASL) monitoring the centre of dimyristoylphosphatidylcholine (DMPC) bilayers was studied with electron paramagnetic resonance (EPR) spectroscopy. The chain-melting transition of DMPC was shifted down and broadened monotonously by several degrees with increasing peptide concentration in the range of lipid/peptide ratios of l/p=5/1-15/1. The effective rotational correlation time ?eff of 14-SASL became larger with increasing amounts of peptide bound to fluid membranes of DMPC. From the dependence of ?eff on the lipid/peptide molar ratio it was estimated that about 10 DMPC molecules per monomer GS are involved in non-covalent peptide-lipid interaction. Optimized spectral subtractions showed that, well above the chain-melting transition, 90% of the EPR spectral intensity of the spin-labeled peptide-lipid complex (l/p=5/1) originated from spectra recorded in bilayers (without peptide) at lower temperature. This was not the case 6°C above the phase transition where two components with comparable intensities were detected. The two components were identified as different motional modes of the label molecules, rather than distinct mobile/immobile lipid populations.

  1. 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.

  2. Subpicosecond time-resolved carrier, phonon, and spin dynamics in Cd(Mn)Te diluted magnetic semiconductors

    Microsoft Academic Search

    D. Wang; Roman Sobolewski; A. Mycielski

    2005-01-01

    We present here our research on time-resolved carrier, phonon, and spin dynamics in the diluted-magnetic semiconductor Cd1-xMnxTe [Cd(Mn)Te] system. Our test samples were the high-quality single crystals with the Mn doping concentrations ranging from 9% to 12%, grown by a modified Bridgeman method. Femtosecond optical pump-probe spectroscopy experiments allowed us to study time-resolved dynamics of both the excited carriers and

  3. The dynamical transition in proteins of bacterial photosynthetic reaction centers observed by echo-detected EPR of specific spin labels

    Microsoft Academic Search

    I. V. Borovykh; P. Gast; S. A. Dzuba

    2007-01-01

    An echo-detected electron paramagnetic resonance (ED EPR) approach was used to study molecular dynamics in photosynthetic\\u000a reaction centers (RCs) fromRhodobacter sphaeroides R26, employing the specific spin label methanethiosulfonate and 3-maliemido proxyl. ED EPR has recently been shown to be\\u000a sensitive to so-called dynamical transition in disordered media, which is characterized by the transition from a harmonic-like\\u000a librational motion of a

  4. Spin-labeled photosynthetic reaction centers from Rhodobacter sphaeroides studied by electron paramagnetic resonance spectroscopy and molecular dynamics simulations

    Microsoft Academic Search

    P. Gajula; I. V. Borovykh; C. Beier; T. Shkuropatova; P. Gast; H.-J. Steinhoff

    2007-01-01

    A new strategy has been applied that combines molecular dynamics (MD) simulations and electron paramagnetic resonance (EPR)\\u000a spectroscopy to study the structure and conformational dynamics of the spin-labeled photosynthetic reaction center (RC) ofRhodobacter sphaeroides. This protein serves here as a model system to demonstrate the applicability of this new methodology. The RC contains five\\u000a native cysteines and EPR experiments show

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    PubMed Central

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

    2014-01-01

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

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

    SciTech Connect

    Ma, L.; Fan, W. J., E-mail: stslts@mail.sysu.edu.cn; Chen, F. L.; Zhou, S. M. [Shanghai Key Laboratory of Special Artificial Microstructure and Pohl Institute of Solid State Physics and School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China); Li, S. F.; Lai, T. S., E-mail: eleanorfan@163.com [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275 (China); He, P. [Department of Physics, Fudan University, Shanghai 200433 (China); Xu, X. G.; Jiang, Y. [State Key Laboratory for Advanced Metals and Materials, School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    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.

  9. Dynamic spin-flip shot noise of mesoscopic transport through a toroidal carbon nanotube

    NASA Astrophysics Data System (ADS)

    Zhao, H. K.; Zhang, J.; Wang, J.

    2015-01-01

    The shot noise in a toroidal carbon nanotube (TCN) interferometer under the perturbation of a rotating magnetic field (RMF) has been investigated. A general shot noise formula has been derived by calculating the current correlation. It was found that photon absorption and emission induce novel features of dynamic shot noise. The oscillatory behavior of shot noise and Fano factor vary with the Aharonov-Bohm (AB) magnetic flux, and they are sensitively dependent on the Zeeman energy, frequency of RMF, and source-drain bias. By adjusting the Zeeman energy, the AB oscillation structures of shot noise and Fano factor show valley-to-peak transformation. The shot noise increases nonlinearly with increasing the Zeeman energy and photon energy. The enhancement and asymmetry of shot noise can be attributed to the spin-flip effect.

  10. Initial conditions and long time dynamics for a complex system: Hierarchical properties of the spin glass decay

    Microsoft Academic Search

    Gilberto Fernando Rodriguez

    2005-01-01

    This dissertation explores the influence of the initial state on spin glass dynamics. The initial state is defined as the state prepared before aging. To probe the effects of different initial states, we develop six cooling protocols. The initial state is quantified by an effective cooling time, teffc . We vary teffc from 19s to 406s. The initial state is

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  12. Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictide Superconductors

    SciTech Connect

    Nicholson, Andrew D [ORNL; Ge, Weihao [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL); Zhang, Xiaotian [Oak Ridge National Laboratory (ORNL); Riera, J. A. [Universidad Nacional de Rosario; Daghofer, M. [IFW Dresden; Olés, Andrzej M. [Max-Planck-Institut fur Feskorperforschung, Stuttgart, Germany; Martins, G. B. [Oakland University, Rochester, MI; Moreo, Adriana [ORNL; Dagotto, Elbio R [ORNL

    2011-01-01

    We introduce and study an extended t-U-J two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the %;0 - 0;% spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A1g and B2g pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B1g states, suggesting that small changes in parameters may render any of the three channels stable.

  13. 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

  14. Dynamic creation of a topologically-ordered Hamiltonian using spin-pulse control in the Heisenberg model.

    PubMed

    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. 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

  16. 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

  17. Low frequency dynamics of Magnetic Droplet Solitons in Spin Transfer Nanocontacts

    NASA Astrophysics Data System (ADS)

    Macia, Ferran; Lendínez, Sergi; Hernàndez, Joan Manel; Backes, Dirk; Kent, Andrew D.

    2015-03-01

    Localized excitations that correspond to reversed dynamically precessing magnetic moments, known as magnetic droplet solitons, were predicted to occur in uniaxial magnets in the absence of damping. However, damping is present in all magnetic materials and suppresses these excitations. It is possible now to compensate damping in ferromagnetic thin films by spin transfer torques through electrical current flow in nanometer scale contacts. Recent experiments have shown the existence of these magnetics objects and proved their stability. We explored conditions that allow formation, stabilization, and annihilation of the droplet excitations. We report spectral measurements, on the GHz range, as a function of current and applied field that challenge existing theories. Additionally, we will report low frequency (~ 300 MHz) excitations associated to the magnetic droplet dynamics. We will show that the droplet hysteretic behavior in current and field, which is related to its stability, is also present in the high and low frequencies spectra. Finally, we will present our recent simulations and compare them with the results and the existing theory.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

  19. MAGNETIC FIELD DEPENDENCE OF STATIC CORRELATIONS AND SPIN DYNAMICS OF REENTRANT SPIN GLASSES STUDIED BY NEUTRON SCATTERING

    Microsoft Academic Search

    M. Hennion; B. Hennion; I. Mirebeau; S. Lequien; F. Hippert

    1988-01-01

    We report smaH angle (SANS) and inelastic neutron scattering in zero and applied field for a-FeMn, NiMn and AuFe at composition where both ferromagnetic and frustration characters occur. We discuss the field evolution of the transverse correlations which arise below T,. A study of the field dependence of the spin wave anomalies in a-Fe-Mn is reported.

  20. Quantum Dissipative Dynamics of the Magnetic Resonance Force Microscope in the Single-Spin Detection Limit

    E-print Network

    Bruder, Christoph

    -Spin Detection Limit Hanno Gassmann Department of Physics and Astronomy, University of Basel, Klingelbergstrasse cantilever motions. They solved numerically the time-dependent Schr¨odinger equation for the spin-pl

  1. Spin dynamics in the modulation frame: application to homonuclear recoupling in magic angle spinning solid-state NMR.

    PubMed

    De Paëpe, Gaël; Lewandowski, Józef R; Griffin, Robert G

    2008-03-28

    We introduce a family of solid-state NMR pulse sequences that generalizes the concept of second averaging in the modulation frame and therefore provides a new approach to perform magic angle spinning dipolar recoupling experiments. Here, we focus on two particular recoupling mechanisms-cosine modulated rotary resonance (CMpRR) and cosine modulated recoupling with isotropic chemical shift reintroduction (COMICS). The first technique, CMpRR, is based on a cosine modulation of the rf phase and yields broadband double-quantum (DQ) (13)C recoupling using >70 kHz omega(1,C)/2pi rf field for the spinning frequency omega(r)/2=10-30 kHz and (1)H Larmor frequency omega(0,H)/2pi up to 900 MHz. Importantly, for p>or=5, CMpRR recouples efficiently in the absence of (1)H decoupling. Extension to lower p values (3.5spinning frequencies is possible using low power (1)H irradiation (<0.25 omega(r)/2pi). This phenomenon is explained through higher order cross terms including a homonuclear third spin assisted recoupling mechanism among protons. CMpRR mitigates the heating effects of simultaneous high power (13)C recoupling and (1)H decoupling. The second technique, COMICS, involves low power (13)C irradiation that induces simultaneous recoupling of the (13)C DQ dipolar and isotropic chemical shift terms. In contrast to CMpRR, where the DQ bandwidth (approximately 30 kHz at omega(0,H)/2pi=750 MHz) covers the entire (13)C spectral width, COMICS recoupling, through the reintroduction of the isotropic chemical shift, is selective with respect to the carrier frequency, having a typical bandwidth of approximately 100 Hz. This approach is intended as a general frequency selective method circumventing dipolar truncation (supplementary to R(2) experiments). These new gamma-encoded sequences with attenuated rf requirements extend the applicability of homonuclear recoupling techniques to new regimes--high spinning and Larmor frequencies--and therefore should be of major interest for high resolution biomolecular studies. PMID:18376939

  2. Competing Technologies

    Microsoft Academic Search

    Thomas Bauer

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

  3. Assessment of vessel permeability by combining dynamic contrast-enhanced and arterial spin labeling MRI.

    PubMed

    Liu, Ho-Ling; Chang, Ting-Ting; Yan, Feng-Xian; Li, Cheng-He; Lin, Yu-Shi; Wong, Alex M

    2015-06-01

    The forward volumetric transfer constant (K(trans)), a physiological parameter extracted from dynamic contrast-enhanced (DCE) MRI, is weighted by vessel permeability and tissue blood flow. The permeability?×?surface area product per unit mass of tissue (PS) in brain tumors was estimated in this study by combining the blood flow obtained through pseudo-continuous arterial spin labeling (PCASL) and K(trans) obtained through DCE MRI. An analytical analysis and a numerical simulation were conducted to understand how errors in the flow and K(trans) estimates would propagate to the resulting PS. Fourteen pediatric patients with brain tumors were scanned on a clinical 3-T MRI scanner. PCASL perfusion imaging was performed using a three-dimensional (3D) fast-spin-echo readout module to determine blood flow. DCE imaging was performed using a 3D spoiled gradient-echo sequence, and the K(trans) map was obtained with the extended Tofts model. The numerical analysis demonstrated that the uncertainty of PS was predominantly dependent on that of K(trans) and was relatively insensitive to the flow. The average PS values of the whole tumors ranged from 0.006 to 0.217?min(-1), with a mean of 0.050?min(-1) among the patients. The mean K(trans) value was 18% lower than the PS value, with a maximum discrepancy of 25%. When the parametric maps were compared on a voxel-by-voxel basis, the discrepancies between PS and K(trans) appeared to be heterogeneous within the tumors. The PS values could be more than two-fold higher than the K(trans) values for voxels with high K(trans) levels. This study proposes a method that is easy to implement in clinical practice and has the potential to improve the quantification of the microvascular properties of brain tumors. PMID:25880892

  4. Competent psychopharmacology.

    PubMed

    Gardner, David M

    2014-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  6. Electron spin dynamics of ferromagnetic Ga1-x Mnx As across the insulator-to-metal transition

    NASA Astrophysics Data System (ADS)

    Yue, Han; Zhao, Chunbo; Gao, Haixia; Wang, Hailong; Yu, Xuezhe; Zhao, Jianhua; Zhang, Xinhui

    2013-03-01

    Electron spin dephasing dynamics of ferromagnetic Ga1-xMnxAs with Mn concentration spanning from 0.5% to 15% across the insulator-to-metal transition is systematically studied using time-resolved magneto-optical Kerr effect measurements. In the insulating Ga1-xMnxAs, the impurity scattering and s-d exchange scattering induced by the magnetic impurity Mn ions are responsible for the electron spin dephasing process. While in the metallic and near metallic regime, the electron-electron Coulomb scattering becomes dominant over the impurity scattering on the spin dephasing process with D'yakonov-Perel' mechanism. Our findings are important for better engineering of Mn impurity doping in order to achieve potential Ga1-xMnxAs-based spintronics application.

  7. Spin dynamics in p-doped semiconductor nanostructures subject to a magnetic field tilted from the Voigt geometry

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

    We develop a theoretical description of the spin dynamics of resident holes in a p-doped semiconductor quantum well (QW) subject to a magnetic field slightly tilted from the Voigt geometry. We find the expressions for the signals measured in time-resolved Faraday rotation (TRFR) and resonant spin amplification (RSA) experiments and study their behavior for a range of system parameters. We find that an inversion of the RSA peaks can occur for long hole spin dephasing times and tilted magnetic fields. We verify the validity of our theoretical findings by performing a series of TRFR and RSA experiments on a p-modulation doped GaAs/Al0.3Ga0.7As single QW and showing that our model can reproduce experimentally observed signals.

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

    SciTech Connect

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

    2014-05-07

    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)

  9. Dynamics of Poly(ethyleneoxide) in the Presence of LiTFSI: Neutron Spin Echo and Dielectric Spectroscopy Study

    NASA Astrophysics Data System (ADS)

    Do, Changwoo; Sun, Xiao-Guang; Ohl, Michael; Allgaier, Jürgen; Götz, Marion; Lunkenheimer, Peter; Loidl, Alois; Richter, Dieter

    2012-02-01

    Rechargeable lithium-ion batteries based on solid polymer electrolytes (SPEs) offer many advantages over their liquid counterparts. In comparison to a liquid electrolyte, the solid polymer is less flammable and more environmentally friendly. Issues such as microscopic dynamics of lithium ions and their dependence on their polymeric matrix are known to play a key role in determining the ionic conductivity in SPEs. Therefore, understanding of the microscopic dynamic characteristics of the lithium ions in relation with the dynamics of surrounding polymeric matrix is a crucial step for the interpretation of their transportation behavior and ultimately toward the control of their properties. Here, we investigated dynamics of poly(ethylene oxide) (PEO) in the presence of LiTFSI using neutron spin echo and dielectric spectroscopy techniques. Experimental results suggest that the dynamics of PEO is dramatically slowed down and strong correlation between ion transportation and alpha-relaxation of PEO.

  10. Quantum dynamics of a spin-1/2 charged particle in the presence of magnetic field with scalar and vector couplings

    E-print Network

    Castro, Luis B

    2015-01-01

    The quantum dynamics of a spin-1/2 charged particle in the presence of magnetic field is analyzed for the general case where scalar and vector couplings are considered. The energy spectra are explicitly computed for different physical situations, as well as their dependencies on the magnetic field strength, spin projection parameter and vector and scalar coupling constants.

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

    2014-01-28

    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.

  12. 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.)

  13. Structure and spin dynamics of multiferroic BiFeO3

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  14. Combined Arterial Spin Label and Dynamic Susceptibility Contrast Measurement of Cerebral Blood Flow

    PubMed Central

    Zaharchuk, Greg; Straka, Matus; Marks, Michael P.; Albers, Gregory W.; Moseley, Michael E.; Bammer, Roland

    2010-01-01

    Dynamic susceptibility contrast (DSC) and arterial spin labeling (ASL) are both used to measure cerebral blood flow (CBF), but neither technique is ideal. Absolute DSC-CBF quantitation is challenging due to many uncertainties, including partial-volume errors and nonlinear contrast relaxivity. ASL can measure quantitative CBF in regions with rapidly arriving flow, but CBF is underestimated in regions with delayed arrival. To address both problems, we have derived a patient-specific correction factor, the ratio of ASL- and DSC-CBF, calculated only in short-arrival-time regions (as determined by the DSC-based normalized bolus arrival time [Tmax]). We have compared the combined CBF method to gold-standard xenon CT in 20 patients with cerebrovascular disease, using a range of Tmax threshold levels. Combined ASL and DSC CBF demonstrated quantitative accuracy as good as the ASL technique but with improved correlation in voxels with long Tmax. The ratio of MRI-based CBF to xenon CT CBF (coefficient of variation) was 90 ± 30% (33%) for combined ASL and DSC CBF, 43 ± 21% (47%) for DSC, and 91 ± 31% (34%) for ASL (Tmax threshold 3 sec). These findings suggest that combining ASL and DSC perfusion measurements improves quantitative CBF measurements in patients with cerebrovascular disease. PMID:20512858

  15. Multi-teraflops spin dynamics studies of the magnetic structure of FeMn/Co interfaces

    SciTech Connect

    Canning, Andrew; Ujfalussy, B.; Schulthess, T.C.; Zhang, X.-G.; Shelton, W.A.; Nicholson, D.M.C.; Stocks, G.M.; Wang, Yang; Dirks, T.

    2002-11-30

    The authors have used the power of massively parallel computers to perform first principles spin dynamics (SD) simulations of the magnetic structure of Iron-Manganese/Cobalt (FeMn/Co) interfaces. These large scale quantum mechanical simulations, involving 2016-atom super-cell models, reveal details of the orientational configuration of the magnetic moments at the interface that are unobtainable by any other means. Exchange bias, which involves the use of an antiferromagnetic (AFM) layer such as FeMn to pin the orientation of the magnetic moment of a proximate ferromagnetic (FM) layer such as Co, is of fundamental importance in magnetic multilayer storage and read head devices. Here the equation of motion of first principles SD is used to perform relaxations of model magnetic structures to the true ground (equilibrium) state. Our code is intrinsically parallel and has achieved a maximum execution rate of 2.46 Teraflops on the IBM SP at the National Energy Research Scientific Computing Center (NERSC).

  16. 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

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

    E-print Network

    Raphael Wittkowski; Hartmut Löwen

    2011-10-10

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

  18. Nonequilibrium Dynamics of Anisotropic Large Spins in the Kondo Regime: Time-Dependent Numerical Renormalization Group Analysis

    E-print Network

    ¨r Theoretische Physik, Johann Wolfgang Goethe-Universita¨t, 60438 Frankfurt/Main, Germany 2 Institut fu¨r Festko¨rper-Forschung--Theorie: 75.50.Xx, 31.70.Hq, 72.15.Qm, 75.45.+j Introduction.--Crystals of single-molecule magnets (SMMs quantum dynamics due to the anisotropic effec- tive potential induced by ligand-fields and spin-orbit cou

  19. 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.

  20. Spin dynamics in the high- Tc system YBa 2Cu 3O 6+ x: the heavily doped regime

    NASA Astrophysics Data System (ADS)

    Rossat-Mignod, J.; Bourges, P.; Onufrieva, F.; Regnault, L. P.; Henry, J. Y.; Burlet, P.; Vettier, C.

    1994-04-01

    Inelastic neutron scattering experiments have been carried out on YBa 2Cu 3O 6+ x single crystals, and we report here on the behaviour of the spin dynamics in the heavily hole-doped regime 0.6 < x < 0.94. The dynamic AF-correlations remain; the in-plane q-width increases with doping and the AF-coupling between CuO 2 layers is not affected. Below Tc, Im ? exhibits a gap and an enhancement at energies which increase with hole doping. Moreover a pseudo-gap persists above Tc.

  1. Electron spin dynamics in heavily Mn-doped (Ga,Mn)As

    NASA Astrophysics Data System (ADS)

    Zhu, Yonggang; Han, Lifen; Chen, Lin; Zhang, Xinhui; Zhao, Jianhua

    2010-12-01

    Electron spin relaxation and related mechanisms in heavily Mn-doped (Ga,Mn)As are studied by performing time-resolved magneto-optical Kerr effect measurements. At low temperature, s-d exchange scattering dominates electron spin relaxation, whereas the Bir-Aronov-Pikus mechanism and Mn impurity scattering play important roles at high temperature. The temperature-dependent spin relaxation time exhibits an anomaly around the Curie temperature (Tc) that implies that thermal fluctuation is suppressed by short-range correlated spin fluctuation above Tc.

  2. Competing together: Assessing the dynamics of team-team and player-team synchrony in professional association football.

    PubMed

    Duarte, Ricardo; Araújo, Duarte; Correia, Vanda; Davids, Keith; Marques, Pedro; Richardson, Michael J

    2013-08-01

    This study investigated movement synchronization of players within and between teams during competitive association football performance. Cluster phase analysis was introduced as a method to assess synchronies between whole teams and between individual players with their team as a function of time, ball possession and field direction. Measures of dispersion (SD) and regularity (sample entropy - SampEn - and cross sample entropy - Cross-SampEn) were used to quantify the magnitude and structure of synchrony. Large synergistic relations within each professional team sport collective were observed, particularly in the longitudinal direction of the field (0.89±0.12) compared to the lateral direction (0.73±0.16, p<.01). The coupling between the group measures of the two teams also revealed that changes in the synchrony of each team were intimately related (Cross-SampEn values of 0.02±0.01). Interestingly, ball possession did not influence team synchronization levels. In player-team synchronization, individuals tended to be coordinated under near in-phase modes with team behavior (mean ranges between -7 and 5° of relative phase). The magnitudes of variations were low, but more irregular in time, for the longitudinal (SD: 18±3°; SampEn: 0.07±0.01), compared to the lateral direction (SD: 28±5°; SampEn: 0.06±0.01, p<.05) on-field. Increases in regularity were also observed between the first (SampEn: 0.07±0.01) and second half (SampEn: 0.06±0.01, p<.05) of the observed competitive game. Findings suggest that the method of analysis introduced in the current study may offer a suitable tool for examining team's synchronization behaviors and the mutual influence of each team's cohesiveness in competing social collectives. PMID:24054894

  3. Evolution of spin dynamics with doping in copper oxide superconductors within the t-t'-J model the doped AF state

    NASA Astrophysics Data System (ADS)

    Onufrieva, F.; Kushnir, V.; Toperverg, B.

    1993-12-01

    The spin dynamics in the doped AF state of high- Tc copper oxide superconductors has been investigated within the t- t'- J model. We have shown that a small amount of doped holes affects the spin dynamics in CuO 2 planes so strongly, that above a very small hole concentration, nc=0.027, the 2D AF ground state becomes unstable. We have also predicted a great change of the spin excitation spectrum in the doped AF state, particularly, the existence of the regime of overdamped softened magnons. Analyzing the imaginary part of the spin susceptibility, ? ( q,?), we have discovered, in addition to the spin-wave part, also an incoherent band associated with electron-hole excitations. The relative contribution of the band increases with increasing n and dominates near the critical point even for the smallest q.

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

    E-print Network

    Ryan, Dominic

    transition (at T c ) where the z component of the moments order collinearly. Subsequently, at a lower tem at the transverse spin freezing transition in partially frustrated a Fe92Zr8 . The form of the selective excitation- perature (T xy ), transverse spin freezing occurs: the x and y components of the moments freeze out

  5. Dynamic Scaling in the Susceptibility of the Spin-1/2 Kagome Lattice Antiferromagnet Herbertsmithite

    E-print Network

    Helton, Joel S.

    The spin-1/2 kagome lattice antiferromagnet herbertsmithite, ZnCu[subscript 3](OH)[subscript 6]Cl[subscript 2], is a candidate material for a quantum spin liquid ground state. We show that the magnetic response of this ...

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

    2008-07-15

    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.

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

    NASA Astrophysics Data System (ADS)

    Chaudhuri, Debapriya; Xiang, Hongping; Lefkidis, Georgios; Hübner, Wolfgang

    2015-03-01

    We present a theoretical investigation of the ultrafast magneto-optical dynamics in clusters with 2, 3 and 4 Ni atoms. We study cooperative effects by increasing both the number of active centers and the multiplicities (up to quintets) in our Hilbert space. In the dinuclear cluster Ni2 a novel spin-flip scenario based on the M process is established. This process is highly operative in case the standard ? process fails. In the trinuclear cluster Ni3Na2 simultaneous spin-flip and spin-transfer is observed. Local spin-switch is also achieved via a non-linear M process which involves two off-resonant transitions. Finally, in the tetranuclear cluster (Ni2)2 the use of quintets provides an insight into an irreversible demagnetization scenario. We believe that our systematic investigation allows us to establish a relation between the magnetic centers and the multiplicities. Our research represents an important step towards the miniaturization of spintronic devices and functionalization of various logic elements based on molecular structures.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  9. Simulation of micro-magnet stray-field dynamics for spin qubit manipulation

    NASA Astrophysics Data System (ADS)

    Neumann, R.; Schreiber, L. R.

    2015-05-01

    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 10-3 is achievable. Magnetic fluctuations from a micro-magnet limits the spin relaxation time to T1 ? 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.

  10. Dynamic deuterium magic angle spinning NMR of a molecule grafted at the inner surface of a mesoporous material.

    PubMed

    Jayanthi, S; Frydman, V; Vega, S

    2012-08-30

    Deuterium magic angle spinning (MAS) NMR is used to study the dynamics of an organic molecule, N-[triethoxysilylpropyl]acetamide-d3, grafted at the inner surface of the mesoporous silica material, MCM-41. The grafted molecule has a deuterated methyl group at its free terminus to monitor its local mobility through changes in its dynamic (2)H-MAS NMR spectrum. Different spectra were recorded as a function of temperature from two different water containing samples. Observation shows that a major part of the grafted molecule remains static, irrespective of the temperature and hydration state of the sample, whereas the rest shows spectral changes indicative of a two-site jump motion of the methyl groups. Experimental observations were substantiated using molecular dynamic (MD) simulations of the grafted molecule. Subsequently, the MD results corroborate a model for the grafted molecules experiencing an exchange between two conformations consistent with the analysis of the (2)H-MAS NMR spectra. PMID:22853651

  11. Neutron spin-echo studies on dynamic and static fluctuations in two types of poly(vinyl alcohol) gels

    SciTech Connect

    Kanaya, T.; Takahashi, N.; Nishida, K. [Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011 (Japan); Seto, H. [Department of Physics, Faculty of Science, Kyoto University, Kyoto, 606-5802 (Japan); Nagao, M. [Institute for Solid State Physics, The University of Tokyo, 106-1 Shirakata, Tokai, Ibaraki-ken 319-1106 (Japan); Takeda, T. [Faculty of Integrated Arts and Sciences, Hiroshima University, Higashihiroshima, Hiroshima-ken 192-0397 (Japan)

    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.

  12. 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.

  13. Magnetic order, spin dynamics and transport properties of the pyrochlore iridate Y2Ir2O7

    NASA Astrophysics Data System (ADS)

    Liu, Hui; Tong, Wei; Ling, Langsheng; Zhang, Shile; Zhang, Ranran; Zhang, Lei; Pi, Li; Zhang, Changjin; Zhang, Yuheng

    2014-02-01

    In the present paper, we report the bulk magnetization, electron-spin-resonance spectra and transport properties of Y2Ir2O7. It is found that Y2Ir2O7 exhibits a magnetic transition at Tc=150 K and coexistence of antiferromagnetic and ferromagnetic component due to geometrical frustration. The antiferromagnetic order is due to Ir-O-Ir superexchange interactions and the ferromagnetic component is caused by canting of the moments from the antiferromagnetic state. The behavior of spin dynamics confirms that antiferromagnetic ordering with all-in/all-out structure is responsible for the existence of ferromagnetic component. The resistivity reveals that this compound is a semiconductor and the variable-range hopping process dominates the transport mechanism.

  14. Homotrinuclear Spin Cluster with Orbital Degeneracy in a Magnetic Field: Algebraic Dynamic Studies of the Geometric Phase January 25, 2008

    NASA Astrophysics Data System (ADS)

    Cheng, Ji-Wen; Zhu, Qin-Sheng; Kuang, Xiao-Yu; Zhang, Shi-Xun; Zhang, Cai-Xia

    2008-08-01

    Based on the homotrinuclear spin cluster having SU(2)?SU(2) symmetry with twofold orbital degeneracy ? = 1/2) and the SU(2) algebraic structures of both ? and ?ˆ subspaces in the external magnetic field, we calculate exactly the non-adiabatic energy levels and the cyclic and non-cyclic non-adiabatic geometric phase of the homotrinuclear spin cluster by making use of the method of algebraic dynamics. The solution will show that the Berry phase is much influenced by the parameters N =?s/?? (?s and ?? are the magnetic momentums of ? and ?? subspaces, respectively) in addition to ?/? in a rotating magnetic field. The change of the Berry phase in the basis state of the system is demonstrated from the changing diagram.

  15. Poisson-Bracket Approach to the Dynamics of Nematic Liquid Crystals. The Role of Spin Angular Momentum

    E-print Network

    H. Stark; T. C. Lubensky

    2005-11-15

    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.

  16. Time resolved measurements of spin and carrier dynamics in InAs films

    NASA Astrophysics Data System (ADS)

    Kini, R. N.; Nontapot, K.; Khodaparast, G. A.; Welser, R. E.; Guido, L. J.

    2008-03-01

    We report time resolved measurements of spin and carrier relaxation in InAs films with carrier densities of 1.3×1016 and 1.6×1016cm-3 grown on (001) and (111) GaAs, respectively. We used standard pump-probe and magneto-optical Kerr effect spectroscopy at different excitation wavelengths, power densities, and temperatures. We observed sensitivity of carrier and spin relaxation time to the photoinduced carrier density but not to the variation in temperature. We explain our results using the Elliot-Yafet picture of spin relaxation process in narrow gap semiconductors.

  17. Spin orientation driven static and dynamic magnetic process in amorphous FeCoBSi thin films

    NASA Astrophysics Data System (ADS)

    Zhou, Peiheng; Luo, Xiaojia; Zhang, Li; Lu, Haipeng; Xie, Jianliang; Deng, Longjiang

    2015-06-01

    The spin orientation dependence of magnetic hysteresis and microwave ferromagnetic resonance data are investigated in FeCoBSi amorphous thin films. Demagnetization effect allows the weak interface-rooted out-of-plane anisotropy to build up local spin orientation domains under the dominant in-plane anisotropy. As a result, two phase magnetization reversal and double-peak ferromagnetic resonance traces with varying damping behavior are observed. Due to the distribution of in-plane and out-of-plane spin orientations, the ferromagnetic resonance bandwidth has been extensively expanded with the full width at half maximum increased from 1.2 GHz to 3.5 GHz.

  18. Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 667C

    SciTech Connect

    Makarov, Valeri V.; Berghea, Ciprian, E-mail: vvm@usno.navy.mil [United States Naval Observatory, 3450 Massachusetts Ave. NW, Washington, DC 20392-5420 (United States)

    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.

  19. Structural Dynamics of the Actomyosin Complex Probed by a Bifunctional Spin Label that Cross-Links SH1 and SH2

    E-print Network

    Thomas, David D.

    Structural Dynamics of the Actomyosin Complex Probed by a Bifunctional Spin Label that Cross* *Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota showed that BSL reports the global orientation and dynamics of S1. When bound to actin in oriented muscle

  20. Dynamics of a Dirac Fermion in the presence of spin noncommutativity

    E-print Network

    A. F. Ferrari; M. Gomes; V. G. Kupriyanov; C. A. Stechhahn

    2012-07-02

    Recently, it has been proposed a spacetime noncommutativity that involves spin degrees of freedom, here called "spin noncommutativity". One of the motivations for such a construction is that it preserves Lorentz invariance, which is deformed or simply broken in other approaches to spacetime noncommutativity. In this work, we gain further insight in the physical aspects of the spin noncommutativity. The noncommutative Dirac equation is derived from an action principle, and it is found to lead to the conservation of a modified current, which involves the background electromagnetic field. Finally, we study the Landau problem in the presence of spin noncommutativity. For this scenario of a constant magnetic field, we are able to derive a simple Hermitean non-commutative correction to the Hamiltonian operator, and show that the degeneracy of the excited states is lifted by the noncommutativity at the second order or perturbation theory.

  1. Effects of axial base excitations on the dynamic stability of spinning pre-twisted cantilever beams

    NASA Astrophysics Data System (ADS)

    Lee, H. P.

    1995-08-01

    The equations of motion of a pre-twisted cantilever beam with a spinning base subject to axial base excitations are formulated by using Euler beam theory and the assumed mode method. The effects of sinusoidal perturbations in terms of the axial accelerations of the beam are then examined by using Bolotin's method. The equations of motion are transformed to the standard form of an eigenvalue problem for determining the perturbation frequencies defining the boundaries of the regions of instability of the spinning beam. The instability diagrams are found to be strongly dependent on the spinning speed, the pre-twist angle and the aspect ratio of the cross-section of the beam. Moreover, the unstable regions are complicated by the coalescence and bifurcation of the perturbation frequencies defining the boundaries of unstable regions, a phenomenon not found for the stability of a non-spinning pre-twisted beam.

  2. Spin dynamics in CuO and Cu[sub 1[minus][ital x

    SciTech Connect

    Carretta, P.; Corti, M.; Rigamonti, A. (Department of Physics Alessandro Volta,'' University of Pavia, Via Bassi 6, 27100 Pavia (Italy))

    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

  3. Competing pressures on populations: long-term dynamics of food availability, food quality, disease, stress and animal abundance.

    PubMed

    Chapman, Colin A; Schoof, Valérie A M; Bonnell, Tyler R; Gogarten, Jan F; Calmé, Sophie

    2015-05-26

    Despite strong links between sociality and fitness that ultimately affect the size of animal populations, the particular social and ecological factors that lead to endangerment are not well understood. Here, we synthesize approximately 25 years of data and present new analyses that highlight dynamics in forest composition, food availability, the nutritional quality of food, disease, physiological stress and population size of endangered folivorous red colobus monkeys (Procolobus rufomitratus). There is a decline in the quality of leaves 15 and 30 years following two previous studies in an undisturbed area of forest. The consumption of a low-quality diet in one month was associated with higher glucocorticoid levels in the subsequent month and stress levels in groups living in degraded forest fragments where diet was poor was more than twice those in forest groups. In contrast, forest composition has changed and when red colobus food availability was weighted by the protein-to-fibre ratio, which we have shown positively predicts folivore biomass, there was an increase in the availability of high-quality trees. Despite these changing social and ecological factors, the abundance of red colobus has remained stable, possibly through a combination of increasing group size and behavioural flexibility. PMID:25870398

  4. Dynamic exchange coupling and spin pumping in ferromagnetic/normal metal bilayer

    NASA Astrophysics Data System (ADS)

    Rodriguez, Roberto; Rezende, Sergio; Azevedo, Antonio

    2014-03-01

    It is known that in ultra-thin ferromagnetic (FM) layers in contact with normal metals (NM), the spin pumping is the most important magnetic relaxation channel. In this work we present a detailed calculation of the NM thickness dependence of the magnetic relaxation in FM/NM bilayers. To calculate the relaxation rate we consider that at the FM/NM interface the spins of the FM layer interact with the NM conduction electron spins through the s-d exchange interaction. The coupled motion of the FM magnetization with the NM spin accumulation transfers to the FM magnetization an additional relaxation from the overdamped motion of the conduction electron spins in the NM layer. We compare our results with the well know treatment that consider only spin currents and show that both yield the same result. Research supported in Brazil by the agencies CNPq, CAPES, FINEP and FACEPE and in Chile by the Millennium Science Nucleus ``Basic and Applied Magnetism'' No. P10-061-F and FONDECYT No. 1130705 and 1120836.

  5. Dynamics of bright and dark localized excitonic magnetic polarons in CdMnTe spin glass compound

    NASA Astrophysics Data System (ADS)

    Gnatenko, Yuriy; Bukivskij, Petro; Piryatinski, Yuriy

    2015-03-01

    The measurements of the magnetic properties of spin glass (SG) system indicate that the magnetic relaxation is characterized by a broad range of times below Tf. Here, for the first time, we have investigated time-resolved photoluminescence spectra of Cd0.70Mn0.30Te SG compound at the temperature below the freezing temperature Tf. This enables us to study the dynamics of different localized excitonic magnetic polarons (LEMPs) at T = 0.7Tfexcited in the crystal regions where various microscopic magnetic spin states (MMSSs) are formed. It was found that there is a broad distribution of the lifetimes of the LEMPs which have different lifetimes but same energies. It was shown that the presence of the long-lived LEMPs is caused by the admixture of the optically active bright exciton states to the dark exciton states as a result of the local magnetic fields formation. The lifetimes of these dark LEMPs correspond to hundreds of nanoseconds. It was also found that the decay process of the PL exciton band intensity is described by the Kohlrausch-Williams-Watts stretched exponential function which describes the recombination processes which correspond to the emission of the LEMPs formed in the crystal region of the finite clusters as well as the infinite cluster. These complex dynamical phenomena, observed for Cd1-XMnXTe at low temperatures, reflect the spatially heterogeneous dynamics in the SG system which is due to the presence of different MMSSs below Tf.

  6. Dynamic study of N’N-dimethylparanitroaniline encapsulated in silicalite-1 matrix using neutron spin-echo spectroscopy

    Microsoft Academic Search

    D. S. Bhange; C. Dejoie; F. Porcher; N. Malikova; P. Martinetto; E. Dooryhée; M. Anne

    2010-01-01

    .  \\u000a The present work focuses on the dynamic studies of N’N-dimethyl-paranitroaniline (dmpNA) encapsulated in silicalite zeolite.\\u000a Quasielastic neutron scattering (QENS) experiments are carried out using neutron spin-echo technique. Polarisation of the\\u000a scattered neutron beam is measured at carefully chosen values of Q = 0.35, 0.9, 1.1 and 1.45? Å?1 at fixed T = 298? K and at fixed Q =

  7. Cultural Competency: From Philosophy to Research and Practice

    ERIC Educational Resources Information Center

    Sue, Stanley

    2006-01-01

    Cultural competency in the delivery of mental health services has gained considerable momentum. This momentum has been accompanied by questions about the meaning, usefulness, and precision of cultural competency. The author argues that cultural competency is composed of general processes (scientific mindedness, dynamic sizing, and culture-specific…

  8. Effect of interlayer interactions and lattice distortions on the magnetic ground state and spin dynamics of a geometrically frustrated triangular-lattice antiferromagnet

    NASA Astrophysics Data System (ADS)

    Haraldsen, J. T.; Fishman, R. S.

    2010-10-01

    We investigate the effects of interlayer interactions and lattice distortions on the noncollinear ground state and spin dynamics of a geometrically frustrated triangular-lattice antiferromagnet with implications for the multiferroic phase of doped CuFeO2 , where both lattice distortions and anisotropy introduce anharmonic components into the spin ground state. In contrast to the single turn angle of a simple spiral, the turn angles of the predicted ground state are distributed about ??1 and ??2 . Using a Holstein-Primakoff expansion, we show that distinct features in the spin dynamics are associated with the anharmonic components of the spin ground state, which have recently been observed in Ga-doped CuFeO2 .

  9. Dynamics of frustrated magnetic moments in antiferromagnetically ordered TbNiAl probed by neutron time-of-flight and spin-echo spectroscopy

    SciTech Connect

    Ehlers, G.; Casalta, H.; Lechner, R. E.; Maletta, H.

    2001-06-01

    We have studied the dynamics of Tb spins in the intermetallic compound TbNiAl in the paramagnetic (pm) and ordered antiferromagnetic (afm) phases by means of neutron time-of-flight and spin-echo spectroscopy. It is a remarkable and very unusual characteristic of TbNiAl that its afm phase (below T{sub N}=47 K) contains regular long-range ordered spins as well as frustrated spins. The latter are identified by a strongly reduced moment measured by neutron diffraction. The new quasielastic measurements show that the frustrated moments relax on a time scale of 0.01 ns to 0.1 ns. Their autocorrelation function I(q,t) is q independent and exponential in time. While in the pm phase the spin relaxation is complete, i.e., I(q,t) goes to zero in the time range of the measurement, in the afm phase I(q,t) stays above zero.

  10. Variation of the lattice and spin dynamics in Bi1-xDyxFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, H. L.; Su, Y. C.; Tang, Y. H.; Lin, J. G.

    2014-04-01

    Infrared and Raman-scattering spectroscopies were employed to explore the lattice and spin dynamics of Bi1-xDyxFeO3 nanoparticles. With increasing substitution of Bi by Dy in the range of 0.00 ? x ? 0.40, we observe (1) evidence for an increase of local lattice distortion of the FeO6 octahedra, and significant changes of phonon parameters in the x = 0.15 sample, corresponding to the structural transformation from rhombohedral to orthorhombic, (2) the chemically substituted enhanced dielectric constant of 43.4 in the x = 0.20 sample, (3) the development of two-magnon excitations in Dy substituted samples, which sensitively gauges the modification of magnetic structures from a cycloidal spin to a homogeneous magnetized state, and (4) Dy substitution disrupts the lattice-spin interactions at high temperatures. These findings extend our understanding of tailoring the structural and magnetic properties of chemically substituted multiferroic nanoparticles and advance the technologically important development of these materials.

  11. Many-Body Stochastic Dynamics: Quenches in Dissipative Quantum Spin Arrays

    E-print Network

    Loïc Henriet; Karyn Le Hur

    2015-06-15

    We address dissipation effects on non-equilibrium properties of quantum spin arrays induced by quenches or Landau-Zener transitions. The dissipation is modeled by a bath of harmonic oscillators, here a ohmic bosonic bath. We develop a stochastic approach allowing to describe quantum quenches and interferometry in an exact manner beyond the "dissipative one-spin-1/2" limit. For two spins, the environment can also engender a dissipative quantum phase transition of Kosterlitz-Thouless type. In the case of a quantum Ising chain in a transverse field, we assume long-range interactions between spins and address the interplay between Landau-Zener-Stueckelberg-Majorana interferometry, many-body quenches, dissipative quantum phase transitions, and bath-engineering. We build a Kibble-Zurek type argument to account for non-equilibrium and interaction effects in the lattice. Such dissipative quantum spin arrays can be realized in ultra-cold atom, trapped ion and mesoscopic systems and are also connected to Kondo lattice systems.

  12. Spin-orbit coupling and semiclassical electron dynamics in noncentrosymmetric metals

    SciTech Connect

    Samokhin, K.V. [Department of Physics, Brock University, St. Catharines, Ont., L2S 3A1 (Canada)], E-mail: kirill.samokhin@brocku.ca

    2009-11-15

    Spin-orbit coupling of electrons with the crystal lattice plays a crucial role in materials without inversion symmetry, lifting spin degeneracy of the Bloch states and endowing the resulting nondegenerate bands with complex spin textures and topologically nontrivial wavefunctions. We present a detailed symmetry-based analysis of the spin-orbit coupling and the band degeneracies in noncentrosymmetric metals. We systematically derive the semiclassical equations of motion for fermionic quasiparticles near the Fermi surface, taking into account both the spin-orbit coupling and the Zeeman interaction with an applied magnetic field. Some of the lowest-order quantum corrections to the equations of motions can be expressed in terms of a fictitious 'magnetic field' in the momentum space, which is related to the Berry curvature of the band wavefunctions. The band degeneracy points or lines serve as sources of a topologically nontrivial Berry curvature. We discuss the observable effects of the wavefunction topology, focusing, in particular, on the modifications to the Lifshitz-Onsager semiclassical quantization condition and the de Haas-van Alphen effect in noncentrosymmetric metals.

  13. Autonomous and forced dynamics in a spin-transfer nano-oscillator: Quantitative magnetic-resonance force microscopy

    NASA Astrophysics Data System (ADS)

    Klein, Olivier

    2013-03-01

    In this talk, we will discuss how magnetic-resonance force microscopy, can provide quantitative measurement of the power emitted by a spin-transfer nano-oscillator, consisting of a normally magnetized Py|Cu|Py circular nanopillar, excited both in the autonomous and forced regimes.[2] From the power behavior in the subcritical region of the autonomous dynamics, one obtains a quantitative measurement of the threshold current and of the noise level. Their field dependence directly yields both the spin torque efficiency acting on the thin layer and the nature of the mode which first auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. We will then demonstrate that the observed spin-wave spectrum in the forced regime critically depends on the method of excitation. While the spatially uniform radio-frequency (RF) magnetic field excites only the axially symmetric modes having azimuthal index l = 0 , the RF current flowing through the nano-pillar, creating a circular RF Oersted field, excites only the modes having azimuthal index l = + 1 .[3] It is then demonstrated that in order to phase lock this auto-oscillating mode, the external source must have the same spatial symmetry as the mode profile, i.e., a uniform microwave field must be used rather than a microwave current flowing through the nanopillar. In this talk, we will discuss how magnetic-resonance force microscopy, can provide quantitative measurement of the power emitted by a spin-transfer nano-oscillator, consisting of a normally magnetized Py|Cu|Py circular nanopillar, excited both in the autonomous and forced regimes.[2] From the power behavior in the subcritical region of the autonomous dynamics, one obtains a quantitative measurement of the threshold current and of the noise level. Their field dependence directly yields both the spin torque efficiency acting on the thin layer and the nature of the mode which first auto-oscillates: the lowest energy, spatially most uniform spin-wave mode. We will then demonstrate that the observed spin-wave spectrum in the forced regime critically depends on the method of excitation. While the spatially uniform radio-frequency (RF) magnetic field excites only the axially symmetric modes having azimuthal index l = 0 , the RF current flowing through the nano-pillar, creating a circular RF Oersted field, excites only the modes having azimuthal index l = + 1 .[3] It is then demonstrated that in order to phase lock this auto-oscillating mode, the external source must have the same spatial symmetry as the mode profile, i.e., a uniform microwave field must be used rather than a microwave current flowing through the nanopillar. This research was partially supported by the French Grant Spinnova (ANR-11-NANO-0016)

  14. Molecular dynamics and spatial distribution of TOAC spin-labelled peptaibols studied in glassy liquid by echo-detected EPR spectroscopy

    Microsoft Academic Search

    Yu. V. Toropov; S. A. Dzuba; Yu. D. Tsvetkov; V. Monaco; F. Formaggio; M. Crisma; C. Toniolo; J. Raap

    1998-01-01

    2,2,6,6-tetramethylpiperidine-l-oxyl-4-carboxylic acid (TOAC) spin-labelled analogues of the Aib-rich peptide (peptaibol)\\u000a Trichogin GA IV are investigated in a glassy methanol\\/glycerol (70\\/30 v\\/v%) system, using conventional CW EPR and electron\\u000a spin echo spectroscopy. Echo-detected (ED) EPR spectra indicate that the labels undergo restricted orientational motion (libration).\\u000a Comparison with the small molecular spin probe Tempone shows that the dynamics of peptide molecules is

  15. Interface-sensitive study of ultrafast spin dynamics in multilayer semiconductors

    NASA Astrophysics Data System (ADS)

    Glinka, Y. D.; Shahbazyan, T. V.; Miller, J. K.; Liu, X.

    2005-03-01

    We report the first application of pump--probe second harmonic generation (SHG) measurements to characterize optically induced magnetization in non-magnetic multilayer semiconductors GaAs/GaSb/InAs. A circularly-polarized pump beam has been used to inject electrons into the conduction band of GaAs, where the photons impart their angular momentum to electron-hole pairs. Because of the interface-sensitive method, the spins accumulated at the GaSb/InAs interface have been monitored. Subsequent precession of these spins about the applied magnetic field has then been detected by a time-delayed probe pulse as an interfacial magnetic field induced SHG response. The electron and spin transport through the heterostructure takes place on the time frame of 15-20 ps, and it is followed by the relaxation of interfacial magnetic and electric fields on the time scale of 100 ps.

  16. Transverse dynamical magnetic susceptibilities from regular static density functional theory: Evaluation of damping and g shifts of spin excitations

    NASA Astrophysics Data System (ADS)

    Lounis, Samir; dos Santos Dias, Manuel; Schweflinghaus, Benedikt

    2015-03-01

    The dynamical transverse magnetic Kohn-Sham susceptibility calculated within time-dependent density functional theory shows a fairly linear behavior for a finite energy window. This observation is used to propose a scheme where the computation of this quantity is greatly simplified. Regular simulations based on static density functional theory can be used to extract the dynamical behavior of the magnetic response function. Besides the ability to calculate elegantly damping of magnetic excitations due to electron-hole excitations, we derive along the way useful equations giving the main characteristics of these excitations: effective g factors and the resonance frequencies that can be accessed experimentally using inelastic scanning tunneling spectroscopy or spin-polarized electron energy loss spectroscopy.

  17. Dynamic study of N'N-dimethylparanitroaniline encapsulated in silicalite-1 matrix using neutron spin-echo spectroscopy

    NASA Astrophysics Data System (ADS)

    Bhange, D. S.; Dejoie, C.; Porcher, F.; Malikova, N.; Martinetto, P.; Dooryhée, E.; Anne, M.

    2010-10-01

    The present work focuses on the dynamic studies of N'N-dimethyl-paranitroaniline (dmpNA) encapsulated in silicalite zeolite. Quasielastic neutron scattering (QENS) experiments are carried out using neutron spin-echo technique. Polarisation of the scattered neutron beam is measured at carefully chosen values of Q = 0.35, 0.9, 1.1 and 1.45 Å-1 at fixed T = 298 K and at fixed Q = 0.9 Å-1 at 150, 200, 250 and 298 K. This gives insight into the motion and the related activation energy of the guest dmpNA molecule. The quasielastic signal observed in the present system within the time range considered is due to fast local rotational motions of protons of the end methyl groups. The results are in good agreement with the dynamics of methyl group rotations reported in the literature by back-scattering QENS technique.

  18. Dynamic Nuclear Polarization by Electrical Spin Injection in Ferromagnet-Semiconductor Heterostructures

    Microsoft Academic Search

    J. Strand; B. D. Schultz; A. F. Isakovic; C. J. Palmstrøm; P. A. Crowell

    2003-01-01

    Electrical spin injection from Fe into Al$_x$Ga$_{1-x}$As quantum well\\u000aheterostructures is demonstrated in small (< 500 Oe) in-plane magnetic fields.\\u000aThe measurement is sensitive only to the component of the spin that precesses\\u000aabout the internal magnetic field in the semiconductor. This field is much\\u000alarger than the applied field and depends strongly on the injection current\\u000adensity. Details of

  19. Spin dynamics in the low-dimensional magnet TiOCl

    NASA Astrophysics Data System (ADS)

    Zakharov, D. V.; Deisenhofer, J.; Krug von Nidda, H.-A.; Lunkenheimer, P.; Hemberger, J.; Hoinkis, M.; Klemm, M.; Sing, M.; Claessen, R.; Eremin, M. V.; Horn, S.; Loidl, A.

    2006-03-01

    We present detailed electron spin resonance investigations on single crystals of the low-dimensional quantum magnet TiOCl. The anisotropy of the g factor indicates a stable orbital configuration below room temperature and allows us to estimate the energy of the first excited state as 0.3(1)eV , ruling out a possible degeneracy of the orbital ground state. Moreover, we discuss the possible spin relaxation mechanisms in TiOCl and analyze the angular and temperature dependence of the linewidth up to 250K in terms of anisotropic exchange interactions. Towards higher temperatures an exponential increase of the linewidth is observed, indicating an additional relaxation mechanism.

  20. Analytical study of synchronization in spin-transfer-driven magnetization dynamics

    NASA Astrophysics Data System (ADS)

    Bonin, Roberto; Bertotti, Giorgio; Bortolotti, Paolo; Serpico, Claudio; d'Aquino, Massimiliano; Mayergoyz, Isaak D.

    2010-01-01

    An analytical study of the synchronization effects in spin-transfer-driven nanomagnets subjected to either microwave magnetic fields or microwave electrical currents is discussed. Appropriate stability diagrams are constructed and the conditions under which the current-induced magnetization precession is synchronized by the microwave external excitation are derived and discussed. Analytical predictions are given for the existence of phase-locking effects in current-induced magnetization precessions and for the occurrence of hysteresis in phase-locking as a function of the spin-polarized current.