NASA Astrophysics Data System (ADS)
Robert, J.; Lhotel, E.; Remenyi, G.; Sahling, S.; Mirebeau, I.; Decorse, C.; Canals, B.; Petit, S.
2015-08-01
In this work, we show that the zero-field excitation spectra in the quantum spin ice candidate pyrochlore compound Yb2Ti2O7 is a continuum characterized by a very broad and almost flat dynamical response, which extends up to 1 -1.5 meV, coexisting or not with a quasielastic response depending on the wave vector. The spectra do not evolve between 50 mK and 2 K, indicating that the spin dynamics is only little affected by the temperature in both the short-range correlated and ordered regimes. Although classical spin dynamics simulations qualitatively capture some of the experimental observations, we show that they fail to reproduce this broad continuum. In particular, the simulations predict an energy scale twice smaller than the experimental observations. This analysis is based on a careful determination of the exchange couplings, able to reproduce both the zero-field diffuse scattering and the spin wave spectrum rising in the field polarized state. According to this analysis, Yb2Ti2O7 lies at the border between a ferro- and an antiferromagnetic phase. These results suggest that the unconventional ground state of Yb2Ti2O7 is governed by strong quantum fluctuations arising from the competition between those phases. The observed spectra may correspond to a continuum of deconfined spinons as expected in quantum spin liquids.
Stanley J. Brodsky
2002-01-17
Spin effects in exclusive and inclusive reactions provide an essential new dimension for testing QCD and unraveling hadron structure. Remarkable new experiments from SLAC, HERMES (DESY), and the Jefferson Laboratory present many challenges to theory, including measurements at HERMES and SMC of the single spin asymmetries in pion electroproduction, where the proton is polarized normal to the scattering plane. This type of single spin asymmetry may be due to the effects of rescattering of the outgoing quark on the spectators of the target proton, an effect usually neglected in conventional QCD analyses. Many aspects of spin, such as single-spin asymmetries and baryon magnetic moments are sensitive to the dynamics of hadrons at the amplitude level, rather than probability distributions. I illustrate the novel features of spin dynamics for relativistic systems by examining the explicit form of the light-front wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents and providing a transparent basis for understanding the structure of relativistic composite systems and their matrix elements in hadronic physics. I also present a survey of outstanding spin puzzles in QCD, particularly the double transverse spin asymmetry A_{NN} in elastic proton-proton scattering, the J/psi to rho-pi puzzle, and J/psi polarization at the Tevatron.
Brodsky, Stanley J.
2002-01-09
Spin effects in exclusive and inclusive reactions provide an essential new dimension for testing QCD and unraveling hadron structure. Remarkable new experiments from SLAC, HERMES (DESY), and Jefferson Lab present many challenges to theory, including measurements at HERMES and SMC of the single spin asymmetries in ep {yields} e{prime}{pi}X where the proton is polarized normal to the scattering plane. This type of single spin asymmetry may be due to the effects of rescattering of the outgoing quark on the spectators of the target proton, an effect usually neglected in conventional QCD analyses. Many aspects of spin, such as single-spin asymmetries and baryon magnetic moments are sensitive to the dynamics of hadrons at the amplitude level, rather than probability distributions. I will illustrate the novel features of spin dynamics for relativistic systems by examining the explicit form of the light-front wavefunctions for the two-particle Fock state of the electron in QED, thus connecting the Schwinger anomalous magnetic moment to the spin and orbital momentum carried by its Fock state constituents and providing a transparent basis for understanding the structure of relativistic composite systems and their matrix elements in hadronic physics. I also present a survey of outstanding spin puzzles in QCD, particularly A{sub NN} in elastic pp scattering, the J/{psi} {yields} {rho}{pi} puzzle, and J/{psi} polarization at the Tevatron.
Thermodynamics of quantum spin chains with competing interactions
NASA Astrophysics Data System (ADS)
Tavares, T. S.; Ribeiro, G. A. P.
2013-09-01
We consider integrable quantum spin chains with competing interactions. We apply the quantum transfer matrix approach to these spin chains. This allows us to derive a set of nonlinear integral equations for the thermodynamics of these spin chains. We provide numerical solutions of these integral equations for the entropy as a function of magnetic field, temperature and the coupling constant. In addition we describe, at low but finite temperature, the possible scenarios for the ground state diagram for high-spin chain and longer range interchain interactions.
Magnetically Tuned Spin Dynamics Resonance
Kronjaeger, J.; Becker, C.; Bongs, K.; Sengstock, K. [Institut fuer Laserphysik, Universitaet Hamburg, Luruper Chaussee 149, D-22761 Hamburg (Germany); Navez, P. [Labo Vaste-Stoffysica en Magnetisme, Katholieke Universiteit Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); additional address: Universitaet Duisburg-Essen, Universitaetsstrasse 5, 45117 Essen (Germany)
2006-09-15
We present the experimental observation of a magnetically tuned resonance phenomenon in the spin mixing dynamics of ultracold atomic gases. In particular, we study the magnetic field dependence of spin conversion in F=2 {sup 87}Rb spinor condensates in the crossover from interaction dominated to quadratic Zeeman dominated dynamics. We discuss the observations in the framework of spin dynamics as well as matter wave four wave mixing. Furthermore, we show that the validity range of the single mode approximation for spin dynamics is significantly extended at high magnetic field.
Spin dynamics in the strong spin-orbit coupling regime
Liu, Xin; Liu, Xiong-Jun; Sinova, Jairo.
2011-01-01
We study the spin dynamics in a high-mobility two-dimensional electron gas with generic spin-orbit interactions (SOI's). We derive a set of spin-dynamics equations that capture purely exponentially the damped oscillatory spin evolution modes...
Dynamic coexistence of competing orders in multi-component superconductors
NASA Astrophysics Data System (ADS)
Dzero, Maxim; Levchenko, Alex
2015-03-01
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 the quench even though the equilibrium state has only one order parameter. We consider different initial conditions concomitant with the phase diagram and in a certain regime identify new oscillatory amplitude modes with incommensurate frequencies for magnetic and superconducting responses. At the technical level we solve 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 the pseudospin representation.
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.
Imaging electrical spin generation and spin Hall dynamics in semiconductors
NASA Astrophysics Data System (ADS)
Stern, N. P.
2009-03-01
The capability to generate and manipulate spin polarization through the spin-orbit interaction drives interest in all-electrical techniques to exploit electron spins for semiconductor spintronics. The spin Hall effect refers to the generation of a pure spin current transverse to a charge current, resulting in a spontaneous spin accumulation near sample boundaries without the need for magnetic fields or materials. Recent experiments toward imaging this electrically generated spin polarization with both spatially and temporally resolved Kerr rotation microscopy in bulk zincblende semiconductors are discussed. Both current-induced in-plane spin polarization and out-of-plane spin accumulation from the spin Hall effect are observed in ZnSe up to room temperatureootnotetextN. P. Stern, S. Ghosh, G. Xiang, M. Zhu, N. Samarth, and D. D. Awschalom, Phys. Rev. Lett. 97, 126603 (2006). In GaAs devices, spatially resolved measurements of steady-state spin Hall accumulation and associated modeling clarify the important role of drift and diffusion in transporting spins generated at sample boundaries to the device interiorootnotetextN. P. Stern, D. W. Steuerman, S. Mack, A. C. Gossard, and D. D. Awschalom, Appl. Phys. Lett. 91, 062109 (2007). In these typical optical experiments, electrically-generated spin accumulation is measured using steady-state techniques that do not directly observe dynamics at timescales important for device operation. Here we discuss a time- and spatially-resolved measurement of the spin Hall effect using a pulsed current to drive spin accumulationootnotetextN. P. Stern, D. W. Steuerman, S. Mack, A. C. Gossard, and D. D. Awschalom, Nat. Physics 4, 843 (2008). The dynamical processes of spin accumulation and diffusion reveal spatially-dependent nanosecond timescales comparable to the electric-field dependent spin coherence time. A time-dependent diffusion analysis reconciles the observed spatial and temporal dynamics of spin accumulation from the spin Hall effect in one coherent picture.
Microscopic studies of nonlocal spin dynamics and spin transport (invited)
NASA Astrophysics Data System (ADS)
Adur, Rohan; Du, Chunhui; Cardellino, Jeremy; Scozzaro, Nicolas; Wolfe, Christopher S.; Wang, Hailong; Herman, Michael; Bhallamudi, Vidya P.; Pelekhov, Denis V.; Yang, Fengyuan; Hammel, P. Chris
2015-05-01
Understanding the behavior of spins coupling across interfaces in the study of spin current generation and transport is a fundamental challenge that is important for spintronics applications. The transfer of spin angular momentum from a ferromagnet into an adjacent normal material as a consequence of the precession of the magnetization of the ferromagnet is a process known as spin pumping. We find that, in certain circumstances, the insertion of an intervening normal metal can enhance spin pumping between an excited ferromagnetic magnetization and a normal metal layer as a consequence of improved spin conductance matching. We have studied this using inverse spin Hall effect and enhanced damping measurements. Scanned probe magnetic resonance techniques are a complementary tool in this context offering high resolution magnetic resonance imaging, localized spin excitation, and direct measurement of spin lifetimes or damping. Localized magnetic resonance studies of size-dependent spin dynamics in the absence of lithographic confinement in both ferromagnets and paramagnets reveal the close relationship between spin transport and spin lifetime at microscopic length scales. Finally, detection of ferromagnetic resonance of a ferromagnetic film using the photoluminescence of nitrogen vacancy spins in neighboring nanodiamonds demonstrates long-range spin transport between insulating materials, indicating the complexity and generality of spin transport in diverse, spatially separated, material systems.
Coherent heteronuclear spin dynamics in an ultracold spin-1 mixture
NASA Astrophysics Data System (ADS)
Zhu, Bing; Li, Xiaoke; He, Xiaodong; Wang, Fudong; Guo, Mingyang; Xu, Zhifang; Zhang, Shizhong; Wang, Dajun
2015-05-01
We report the observation of interspecies spin-spin interaction driven coherent heteronuclear spin dynamics in an ultracold spinor mixture, which manifests itself as periodical and well correlated magnetization transfer between two atomic species. In particular, we investigate the magnetic field dependence and control of the spin dynamics, and find excellent agreement with a many-body theoretical model. Furthermore, we present a unique knob for fine control of spinor mixtures with species dependent vector light shift. This work is supported by Hong Kong Research Grants Council (General Research Fund Projects CUHK 403813 and CUHK 14305214).
Spin Dynamics with Inertia in Metallic Ferromagnets
Toru Kikuchi; Gen Tatara
2015-06-29
Non-adiabatic contribution of environmental degrees of freedom yields effective inertia of spin in effective spin dynamics. In this paper, we study several aspects of the inertia of spin in metallic ferromagnets. (i) a concrete expression of the spin inertia $m_s$: $m_s=\\hbar S_c/(2g_{\\rm sd})$, where $S_c$ is the spin polarization of conduction electrons and $g_{\\rm sd}$ is the $sd$ coupling constant. (ii) dynamical behavior of spin with inertia, discussed from viewpoints of a spinning top and of a particle on a sphere. (iii) behavior of spin waves and domain walls in the presence of inertia, and behavior of spin with inertia in the case of a time-dependent magnetic field.
Spinning compact binary : Independent variables and dynamically preserved spin configurations
Gergely, Laszlo Arpad
2010-04-15
We establish the set of independent variables suitable to monitor the complicated evolution of the spinning compact binary during the inspiral. Our approach is valid up to the second post-Newtonian order, including leading order spin-orbit, spin-spin and mass quadrupole-mass monopole effects, for generic (noncircular, nonspherical) orbits. Then, we analyze the conservative spin dynamics in terms of these variables. We prove that the only binary black hole configuration allowing for spin precessions with equal angular velocities about a common instantaneous axis roughly aligned to the normal of the osculating orbit, is the equal mass and parallel (aligned or antialigned) spin configuration. This analytic result puts limitations on what particular configurations can be selected in numerical investigations of compact binary evolutions, even in those including only the last orbits of the inspiral.
Electron-spin dynamics induced by photon spins
Sven Ahrens; Heiko Bauke; Christoph H. Keitel; Rainer Grobe
2014-10-15
Strong rotating magnetic fields may cause a precession of the electron's spin around the rotation axis of the magnetic field. The superposition of two counterpropagating laser beams with circular polarization and opposite helicity features such a rotating magnetic field component but also carries spin. The laser's spin density, that can be expressed in terms of the lase's electromagnetic fields and potentials, couples to the electron's spin via a relativistic correction to the Pauli equation. We show that the quantum mechanical interaction of the electron's spin with the laser's rotating magnetic field and with the laser's spin density counteract each other in such a way that a net spin rotation remains with a precession frequency that is much smaller than the frequency one would expect from the rotating magnetic field alone. In particular, the frequency scales differently with the laser's electric field strength depending on if relativistic corrections are taken into account or not. Thus, the relativistic coupling of the electron's spin to the laser's spin density changes the dynamics not only quantitatively but also qualitatively as compared to the nonrelativistic theory. The electron's spin dynamics is a genuine quantum mechanical relativistic effect.
Competing decay modes of a high-spin isomer in the proton-unbound nucleus š??Ta*
Carroll, R. J.; Page, R. D.; Joss, D. T.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Cederwall, B.; Eeckhaudt, S.; Grahn, T.; Gray-Jones, C.; et al
2015-01-01
An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both ? and ? decay modes. The large spin change required to decay via ?-ray emission incurs a lifetime long enough for ? decay to compete. The ? decay has an energy of 8644(11) keV, which is among the highest observed in the region, a partial half-life of 440(70) ?s and changes the spin by 11?. In this study, additional evidence supporting the assignment of this ? decay to the high-spin isomer in 158Ta will bemore ťpresented.Ť less
A new type of spin ordering in a random magnet with competing anisotropies
Katsumata, K.; Shapiro, S.M.; Matsuda, M.; Shirane, G.; Tuchendler, J.
1992-12-31
The result of an elastic neutron scattering study of the phase transition in the random magnet with competing anisotropies Fe{sub 0.75}CO{sub 0.25}Br{sub 2} is reported. We found that the ordering of the spin component parallel to the crystalline c axis at the transition from the paramagnetic to antiferromagnetic phase induces an ordering of the spin component perpendicular to it. Thus, there is no boundary separating the higher temperature antiferromagnetic and lower temperature mixed ordering phase. We interpret this new type of spin ordering as arising from a coupling between the orthogonal spin components.
Seeing spin dynamics in atomic gases
Dan M. Stamper-Kurn
2014-12-31
The dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.
Seeing Spin Dynamics in Atomic Gases
NASA Astrophysics Data System (ADS)
Stamper-Kurn, Dan M.
2015-06-01
The dynamics of internal spin, electronic orbital, and nuclear motion states of atoms and molecules have preoccupied the atomic and molecular physics community for decades. Increasingly, such dynamics are being examined within many-body systems composed of atomic and molecular gases. Our findings sometimes bear close relation to phenomena observed in condensed-matter systems, while on other occasions they represent truly new areas of investigation. I discuss several examples of spin dynamics that occur within spinor Bose-Einstein gases, highlighting the advantages of spin-sensitive imaging for understanding and utilizing such dynamics.
Spin, Isospin and Strong Interaction Dynamics
E. Comay
2011-07-23
The structure of spin and isospin is analyzed. Although both spin and isospin are related to the same SU(2) group, they represent different dynamical effects. The Wigner-Racah algebra is used for providing a description of bound states of several Dirac particles in general and of the proton state in particular. Isospin states of the four $\\Delta (1232)$ baryons are discussed. The work explains the small contribution of quarks spin to the overall proton spin (the proton spin crisis). It is also proved that the addition of QCD's color is not required for a construction of an antisymmetric state of the $\\Delta ^{++} (1232)$ baryon.
Magnetocaloric effect in the spin-1/2 chain with competing interactions
NASA Astrophysics Data System (ADS)
Tavares, T. S.; Ribeiro, G. A. P.
2014-11-01
We study the magnetocaloric effect for the integrable antiferromagnetic Heisenberg spin chain with competing interactions. We computed the Grüneisen parameter, which is closely related to the magnetocaloric effect, for the quantum spin chain in the thermodynamic limit. This is obtained by means of the solution of a set of non-linear integral equations, which describes the thermodynamics of the model. We also provide results for the entropy S and the isentropes in the (H, T) plane.
Set-valued dynamic treatment regimes for competing outcomes
Laber, Eric B.; Lizotte, Daniel J.; Ferguson, Bradley
2014-01-01
Summary Dynamic treatment regimes operationalize the clinical decision process as a sequence of functions, one for each clinical decision, where each function maps up-to-date patient information to a single recommended treatment. Current methods for estimating optimal dynamic treatment regimes, for example Q-learning, require the specification of a single outcome by which the goodness of competing dynamic treatment regimes is measured. However, this is an over-simplification of the goal of clinical decision making, which aims to balance several potentially competing outcomes, e.g., symptom relief and side-effect burden. When there are competing outcomes and patients do not know or cannot communicate their preferences, formation of a single composite outcome that correctly balances the competing outcomes is not possible. This problem also occurs when patient preferences evolve over time. We propose a method for constructing dynamic treatment regimes that accommodates competing outcomes by recommending sets of treatments at each decision point. Formally, we construct a sequence of set-valued functions that take as input up-to-date patient information and give as output a recommended subset of the possible treatments. For a given patient history, the recommended set of treatments contains all treatments that produce non-inferior outcome vectors. Constructing these set-valued functions requires solving a non-trivial enumeration problem. We offer an exact enumeration algorithm by recasting the problem as a linear mixed integer program. The proposed methods are illustrated using data from the CATIE schizophrenia study. PMID:24400912
DYNAMIC CHARACTERISTICSOFLIQUID MOTION INPARTIALLYFILLEDTANKS OF SPINNING SPACECRAFT
of mass of the spacmaft and Z axis along the spin axis. The coordinate system xyz is fixed in the tank to predict dynamic characteristicsof liquid motion in partially filled tanks of a spinning spacecraft. The solution is obtained by solving three boundary value problems: inviscid, the boundary layer, and viscous
NASA Astrophysics Data System (ADS)
Tang, Yanhao; Xie, Wei; Mandal, Krishna C.; McGuire, John A.; Lai, Chih Wei
2015-09-01
We analyze exciton spin dynamics in GaSe under nonresonant circularly polarized optical pumping with an exciton spin-flip rate-equation model. The model reproduces polarized time-dependent photoluminescence measurements in which the initial circular polarization approaches unity even when pumping with 0.15 eV excess energy. At T = 10 K, the exciton spin relaxation exhibits a biexponential decay with sub-20 ps and >500 ps time constants, which are also reproduced by the rate-equation model assuming distinct spin-relaxation rates for hot (nonequilibrium) and cold band-edge excitons.
Unusual spin dynamics in topological insulators
Dóra, Balázs; Simon, Ferenc
2015-01-01
The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ?d?1 with d?=?2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d?=?2K???1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems. PMID:26439629
Unusual spin dynamics in topological insulators.
Dóra, Balázs; Simon, Ferenc
2015-01-01
The dynamic spin susceptibility (DSS) has a ubiquitous Lorentzian form around the Zeeman energy in conventional materials with weak spin orbit coupling, whose spectral width characterizes the spin relaxation rate. We show that DSS has an unusual non-Lorentzian form in topological insulators, which are characterized by strong SOC, and the anisotropy of the DSS reveals the orientation of the underlying spin texture of topological states. At zero temperature, the high frequency part of DSS is universal and increases in certain directions as ?(d-1) with d?=?2 and 3 for surface states and Weyl semimetals, respectively, while for helical edge states, the interactions renormalize the exponent as d?=?2K?-?1 with K the Luttinger-liquid parameter. As a result, spin relaxation rate cannot be deduced from the DSS in contrast to the case of usual metals, which follows from the strongly entangled spin and charge degrees of freedom in these systems. PMID:26439629
Parallel algorithm for spin and spin-lattice dynamics simulations
NASA Astrophysics Data System (ADS)
Ma, Pui-Wai; Woo, C. H.
2009-04-01
To control numerical errors accumulated over tens of millions of time steps during the integration of a set of highly coupled equations of motion is not a trivial task. In this paper, we propose a parallel algorithm for spin dynamics and the newly developed spin-lattice dynamics simulation [P. W. Ma , Phys. Rev. B 78, 024434 (2008)]. The algorithm is successfully tested in both types of dynamic calculations involving a million spins. It shows good stability and numerical accuracy over millions of time steps (1ns) . The scheme is based on the second-order Suzuki-Trotter decomposition (STD). The usage can avoid numerical energy dissipation despite the trajectory and machine errors. The mathematical base of the symplecticity, for properly decomposed evolution operators, is presented. Due to the noncommutative nature of the spin in the present STD scheme, a unique parallel algorithm is needed. The efficiency and stability are tested. It can attain six to seven times speed up when eight threads are used. The run time per time step is linearly proportional to the system size.
Competing decay modes of a high-spin isomer in the proton-unbound nucleus š??Ta*
Carroll, R. J.; Page, R. D.; Joss, D. T.; Uusitalo, J.; Darby, I. G.; Andgren, K.; Cederwall, B.; Eeckhaudt, S.; Grahn, T.; Gray-Jones, C.; Greenlees, P. T.; Hadinia, B.; Jones, P. M.; Julin, R.; Juutinen, S.; Leino, M.; Leppänen, A. -P.; Nyman, M.; O'Donnell, D.; Pakarinen, J.; Rahkila, P.; Sandzelius, M.; Sarén, J.; Scholey, C.; Seweryniak, D.; Simpson, J.
2015-01-01
An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus ^{158}Ta. This state was observed to decay by both ? and ? decay modes. The large spin change required to decay via ?-ray emission incurs a lifetime long enough for ? decay to compete. The ? decay has an energy of 8644(11) keV, which is among the highest observed in the region, a partial half-life of 440(70) ?s and changes the spin by 11?. In this study, additional evidence supporting the assignment of this ? decay to the high-spin isomer in ^{158}Ta will be presented.
Magnetic Suspension for Dynamic Spin Rig
NASA Technical Reports Server (NTRS)
Johnson, Dexter
1998-01-01
NASA Lewis Research Center's Dynamic Spin Rig, located in Building 5, Test Cell CW-18, is used to test turbomachinery blades and components by rotating them in a vacuum chamber. A team from Lewis' Machine Dynamics Branch successfully integrated a magnetic bearing and control system into the Dynamic Spin Rig. The magnetic bearing worked very well both to support and shake the shaft. It was demonstrated that the magnetic bearing can transmit more vibrational energy into the shaft and excite some blade modes to larger amplitudes than the existing electromagnetic shakers can.
Spin dynamics and spin freezing at ferromagnetic quantum phase transitions
NASA Astrophysics Data System (ADS)
Schmakat, P.; Wagner, M.; Ritz, R.; Bauer, A.; Brando, M.; Deppe, M.; Duncan, W.; Duvinage, C.; Franz, C.; Geibel, C.; Grosche, F. M.; Hirschberger, M.; Hradil, K.; Meven, M.; Neubauer, A.; Schulz, M.; Senyshyn, A.; Süllow, S.; Pedersen, B.; Böni, P.; Pfleiderer, C.
2015-07-01
We report selected experimental results on the spin dynamics and spin freezing at ferromagnetic quantum phase transitions to illustrate some of the most prominent escape routes by which ferromagnetic quantum criticality is avoided in real materials. In the transition metal Heusler compound Fe2TiSn we observe evidence for incipient ferromagnetic quantum criticality. High pressure studies in MnSi reveal empirical evidence for a topological non-Fermi liquid state without quantum criticality. Single crystals of the hexagonal Laves phase compound Nb1- y Fe2+ y provide evidence of a ferromagnetic to spin density wave transition as a function of slight compositional changes. Last but not least, neutron depolarisation imaging in CePd1- x Rh x underscore evidence taken from the bulk properties of the formation of a Kondo cluster glass.
Spinning compact binary dynamics and chameleon orbits
NASA Astrophysics Data System (ADS)
Gergely, László Árpád; Keresztes, Zoltán
2015-01-01
We analyze the conservative evolution of spinning compact binaries to second post-Newtonian (2PN) order accuracy, with leading-order spin-orbit, spin-spin and mass quadrupole-monopole contributions included. As a main result we derive a closed system of first-order differential equations in a compact form, for a set of dimensionless variables encompassing both orbital elements and spin angles. These evolutions are constrained by conservation laws holding at 2PN order. As required by the generic theory of constrained dynamical systems we perform a consistency check and prove that the constraints are preserved by the evolution. We apply the formalism to show the existence of chameleon orbits, whose local, orbital parameters evolve from elliptic (in the Newtonian sense) near pericenter, towards hyperbolic at large distances. This behavior is consistent with the picture that general relativity predicts stronger gravity at short distances than Newtonian theory does.
Spinning compact binary dynamics and chameleon orbits
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.
Competing effective interactions of Dirac electrons in the SpinFermion system
Marino, E.C., E-mail: marino@if.ufrj.br [Instituto de Física, Universidade Federal do Rio de Janeiro, Caixa Postal 68528, Rio de Janeiro, RJ, 21941-972 (Brazil); Nunes, Lizardo H.C.M., E-mail: lizardonunes@ufsj.edu.br [Departamento de Cięncias Naturais, Universidade Federal de Săo Joăo del Rei, 36301-000 Săo Joăo del Rei, MG (Brazil)
2014-01-15
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 SpinFermion 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 NambuJona-Lasinio-like, excitonic term and a spinspin magnetic term. The resulting phase diagram is investigated by evaluation of the mean-field free-energy as a function of the relevant order parameters. This shows the competition of the above interactions, depending on the temperature, chemical potential and coupling constants. -- Highlights: Antiferromagnetic HeisenbergKondo lattice model with itinerant Dirac fermions. Integrating out the spins generates competing interactions: BCS-like, excitonic and magnetic. Novel mechanism of superconductivity from magnetic interactions between the spins and electrons. Dome-shaped dependence of the temperature on the chemical potential in agreement with pnictides.
Spin chains with dynamical lattice supersymmetry
Christian Hagendorf
2013-02-22
Spin chains with exact supersymmetry on finite one-dimensional lattices are considered. The supercharges are nilpotent operators on the lattice of dynamical nature: they change the number of sites. A local criterion for the nilpotency on periodic lattices is formulated. Any of its solutions leads to a supersymmetric spin chain. It is shown that a class of special solutions at arbitrary spin gives the lattice equivalents of the N=(2,2) superconformal minimal models. The case of spin one is investigated in detail: in particular, it is shown that the Fateev-Zamolodchikov chain and its off-critical extension admits a lattice supersymmetry for all its coupling constants. Its supersymmetry singlets are thoroughly analysed, and a relation between their components and the weighted enumeration of alternating sign matrices is conjectured.
Localization of spin mixing dynamics in a spin-1 Bose-Einstein condensate
Zhang Wenxian; Sun Bo; Chapman, M. S.; You, L.
2010-03-15
We propose to localize spin mixing dynamics in a spin-1 Bose-Einstein condensate by a temporal modulation of spin exchange interaction, which is tunable with optical Feshbach resonance. Adopting techniques from coherent control, we demonstrate the localization and freezing of spin mixing dynamics, and the suppression of the intrinsic dynamic instability and spontaneous spin domain formation in a ferromagnetically interacting condensate of {sup 87}Rb atoms. This work points to a promising scheme for investigating the weak magnetic spin dipole interaction, which is usually masked by the more dominant spin exchange interaction.
Competing exotic quantum phases of spin-1/2 ultracold lattice bosons with extended spin interactions
NASA Astrophysics Data System (ADS)
Chang, Chia-Chen; Rousseau, Valéry G.; Scalettar, Richard T.; Batrouni, George G.
2015-08-01
Advances in pure optical trapping techniques now allow the creation of degenerate Bose gases with internal degrees of freedom. Systems such as 87Rb,39K, or 23Na in the F =1 hyperfine state offer an ideal platform for studying the interplay of superfluidity and quantum magnetism. Motivated by the experimental developments, we study ground-state phases of a two-component Bose gas loaded on an optical lattice. The system is described effectively by the Bose-Hubbard Hamiltonian with on-site and near-neighbor spin-spin interactions. An important feature of our investigation is the inclusion of interconversion (spin-flip) terms between the two species, which has been observed in optical lattice experiments. Using mean-field theory and quantum Monte Carlo simulations, we map out the phase diagram of the system. A rich variety of phases is identified, including antiferromagnetic (AF) Mott insulators and ferromagnetic and AF superfluids.
Webb, Geoff
, Dynamically Changing Models of Agent's Competencies. Feature Based Modelling: A methodology for producing coherent, consistent, dynamically changing models of agents' competencies. GEOFFREY I. WEBB and MARK's competency. This is achieved by creating a model describing the relationships between the features
Spin dynamics of cavity polaritons M.D. Martna
Vińa, Luis
Spin dynamics of cavity polaritons M.D. MartőÂna , L. VinÄaa,*, J.K. Sonb , E.E. Mendezb; accepted 25 September 2000 by F. YnduraÂin Abstract We have studied polariton spin dynamics in a Ga found that the stimulated emission of the lower polariton branch has a strong inŻuence on spin dynamics
Many-body singlets by dynamic spin polarization
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.
Four competing interactions for models with uncountable set of spin values on the Cayley Tree
F. H. Haydarov
2015-09-16
In this paper we consider four competing interactions (external field, nearest neighbor, second neighbors and triples of neighbors) of models with uncountable (i.e. $[0,1]$) set of spin values on the Cayley tree of order two. We reduce the problem of describing the "splitting Gibbs measures" of the model to the description of the solutions of some nonlinear integral equation and consider Gibbs measures for Ising and Potts models. Also we show that periodic Gibbs measures for given models are either translation-invariant or periodic with period two.
Epoch Lifetimes in the Dynamics of a Competing Population
NASA Astrophysics Data System (ADS)
Yeung, C. H.; Ma, Y. P.; Wong, K. Y. Michael
We propose a dynamical model of a competing population whose agents have a tendency to balance their decisions in time. The model is applicable to financial markets in which the agents trade with finite capital, or other multiagent systems such as routers in communication networks attempting to transmit multiclass traffic in a fair way. We find an oscillatory behavior due to the segregation of agents into two groups. Each group remains winning over epochs. The aggregation of smart agents is able to explain the lifetime distribution of epochs to 8 decades of probability. The existence of the super agents further refines the lifetime distribution of short epochs.
Multiple dynamical regimes in colloidal polymer suspension with competing interaction
NASA Astrophysics Data System (ADS)
Srivastava, Sunita; Kishore, Suhasini; Narayanan, Suresh; Bhatia, Surita
2014-03-01
We present combined x-ray photon correlation spectroscopy (XPCS), dynamic light scattering (DLS) and rheometry study of dynamical transitions in colloidal polymer suspension with short range attraction and long range repulsion. Our system is based on aqueous dispersions of laponiteŽnanoplatelets where the range and magnitude of competing short range depletion attraction and long range repulsion interparticle interaction, were tuned by varying the concentration and molecular weight of the adsorbing poly(ethylene oxide) chains. We observed three distinct dynamical regime: a state of slow dynamics consisting of finite clusters for which interparticle interactions are predominantly repulsive, second dynamical regime, at above saturation concentration of added polymer in which small clusters of nanoparticles are held by short range depleting attraction and third regime of percolating network in which nanoclusters diffuse freely in a network with characteristic length larger than the size of the cluster. Through our experiments we demonstrate experimental parameters to control the macroscopic mechanical and dynamical properties in colloidal suspension by manipulating the interparticle interactions at nanoscale.
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.
Dynamics of the Lunar Spin Axis
NASA Technical Reports Server (NTRS)
Wisdom, Jack
2006-01-01
The evolution of the lunar spin axis is studied. Prior work has assumed that the inclination of the lunar orbit is constant and that the node regresses uniformly. This work takes into account the nonconstant inclination and nonuniform regression of the node as determined from averaged models of the motion of the lunar orbit. The resulting dynamics is considerably more rich, exhibiting additional resonances, period doubling and tripling, and chaos.
Combined molecular dynamics-spin dynamics simulations of bcc iron
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.
Spin pumping and magnetization dynamics in metallic multilayers
Yaroslav Tserkovnyak; Arne Brataas; Gerrit E. Bauer
2002-01-01
We study the magnetization dynamics in thin ferromagnetic films and small ferromagnetic particles in contact with paramagnetic conductors. A moving magnetization vector causes ``pumping'' of spins into adjacent nonmagnetic layers. This spin transfer affects the magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology. The additional Gilbert damping is significant for small ferromagnets, when the nonmagnetic layers efficiently relax the injected spins,
Dynamic Assessment and Its Potential for the Assessment of Reading Competence
ERIC Educational Resources Information Center
Dorfler, Tobias; Golke, Stefanie; Artelt, Cordula
2009-01-01
This article describes the approach of dynamic assessment, focusing on general approaches as well as specific constraints for the assessment of reading competence. Starting with an overview of the literature on dynamic assessments within educational research, the framework of dynamic assessment in which the current level of competence and
Yeh, Nai-Chang
1 Effects of competing orders and quantum criticality on the quasiparticle tunneling spectroscopy of competing orders and quantum criticality on the macroscopic vortex dynamics and microscopic low phase (SC) from a phase consisting of coexisting SC and a competing order. The proximity of a cuprate
Phase Diagram in a Random Mixture of Two Antiferromagnets with Competing Spin Anisotropies. I
NASA Astrophysics Data System (ADS)
Someya, Yoshiko
1981-12-01
The phase diagram of a random mixture of two antiferromagnets with competing spin anisotropies (A1-xBx) has been analyzed by extending the theory of Matsubara and Inawashiro, and Oguchi and Ishikawa. In the model assumed, the anisotropy energies are expressed by the anisotropic exchange interactions. According to this formulation, it has been shown that the concentration dependence of TN becomes a function of \\includegraphics{dummy.eps}, where P, Q=A, B; SP is a magnitude of P-spin, and JPQ? is a ? component of exchange integral between P- and Q-spin). Further, the phase boundary between an AF phase and an OAF (oblique antiferromagnetic) phase at T{=}0 K has been shown to be determined by ?({\\equiv}SB/SA), if \\includegraphics{dummy.eps} are given. The obtained phase diagrams for Fe1-xCoxCl2, K2Mn1-xFexF4 and Fe1-xCoxCl2\\cdot2H2O are compared with the experimental ones.
Coherent Heteronuclear Spin Dynamics in an Ultracold Spinor Mixture.
Li, Xiaoke; Zhu, Bing; He, Xiaodong; Wang, Fudong; Guo, Mingyang; Xu, Zhi-Fang; Zhang, Shizhong; Wang, Dajun
2015-06-26
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. PMID:26197132
Frustration and Quantum Fluctuation in Spin-1 Antiferromagnetic Chains with Competing Interactions
NASA Astrophysics Data System (ADS)
Harada, Isao; Fujikawa, Mutsuko; Mannari, Isao
1993-10-01
Ground-state phase diagram and low-lying excitation spectrum of the one-dimensional S{=}1 anisotropic Heisenberg antiferromagnetic chain with nearest neighbor and next nearest neighbor interactions are studied by means of an approximate mapping of the original S{=}1 spin Hamiltonian to the effective fermion Hamiltonian, which describes the dynamics of spin zero defects in antiferromagnetic environments (domain walls in the Néel state). We find that the frustration due to the next nearest neighbor interactions works cooperatively with quantum fluctuation in the Haldane state and stabilizes it. This is naturally explained in terms of the spin zero defect. In addition, we discuss characteristic features of the excitation spectrum in connection with its ground-state properties.
Spin dynamics and spin disorder in frustrated TbCo xNi 1- xC 2
NASA Astrophysics Data System (ADS)
Kalvius, G. M.; Noakes, D. R.; Wäppling, R.; Grosse, G.; Schäfer, W.; Kockelmann, W.; Yakinthos, J. K.; Kotsanides, P. A.
2003-02-01
The orthogonal dicarbides RTC 2 ( R= rare earth , T= transition metal ) show ferromagnetic (fm) order of the R ions below T C?30 K for T=Co with a being the easy axis and antiferromagnetic (afm) order (with about the same transition temperature) for T=Ni with c as easy axis. The spin turning is caused by changes in the crystalline electric field (CEF) interaction. In the mixed TbCo xNi 1- xC 2 alloys, fm and afm exchange on the one side and different CEF interactions on the other compete as a function of x. These competing interactions are a source of magnetic frustration. They also cause the materials to undergo several magnetic transitions into fm, afm or spin modulated structures which are well documented by neutron diffraction. Zero, longitudinal and transverse field ?SR was carried out on TbCo xNi 1- xC 2 with x=0.3, 0.5 0.7 and 0.85 using the same samples as in the neutron studies. Marked local spin disorder and persistent spin dynamics were seen in all magnetically ordered states as a consequence of frustration, but distinct differences exist for different values of x. Not all reported phase transition show clearly in the ?SR data. In TbCo 0.85Ni 0.15C 2, a short-range dynamically correlated spin state having a strong fm polarizability exists above T C=30 K extending for about 50 K.
Spin decoherence from Hamiltonian dynamics in quantum dots
NASA Astrophysics Data System (ADS)
Bhaktavatsala Rao, D. D.; Ravishankar, V.; Subrahmanyam, V.
2006-08-01
The dynamics of a spin- 1/2 particle coupled to a nuclear spin bath through an isotropic Heisenberg interaction is studied as a model for the spin decoherence in quantum dots. The time-dependent polarization of the central spin is calculated as a function of the bath-spin distribution and the polarizations of the initial bath state. For short times, the polarization of the central spin shows a Gaussian decay, and at later times it is revived displaying nonmonotonic time dependence. The decoherence time scale depends on moments of the bath-spin distribuition, and also on the polarization strengths in various bath-spin channels. The bath polarizations have a tendency to increase the decoherence time scale. The effective dynamics of the central spin polarization is shown to be described by a master equation with non-Markovian features.
Entanglement Dynamics of Two Spins in Initially Correlated Wheel-Shaped Spin Baths
NASA Astrophysics Data System (ADS)
Sun, Kai-Le; Chen, Jun; Wang, Fa-Qiang; Yu, Ya-Fei; Zhang, Zhi-Ming
2015-06-01
We study the effects of the initial correlations in environment on the entanglement dynamics of spin system. The correlated environment is novelly simulated by two correlated wheel-shaped spin baths, each consisting of an intermediate spin interacting with a spin-ring. The correlations in environment are achieved by the entanglement between two intermediate spins. The spin system includes two system-spins, and the interaction between the spin system and the environment is implemented by the coupling between the system-spin and the intermediate spin. Firstly, we analyze the influences of the initial entanglement between the two intermediate spins, the coupling parameters and the temperature of the baths on the entanglement dynamics of the two system-spins in equivalent subsystems. It is demonstrated that the initial entanglement between the baths can act as a resource for the generation and the revivals of the entanglement of the system-spins. Moreover, the amount of the generation and the revivals of the entanglement of the system-spins can be enhanced by regulating the coupling constants and the temperature of the baths. In addition, we also investigate the influences of different coupling ratios in non-equivalent subsystems, it is found that changing the coupling ratios of two subsystems has a significant effect on the generation and revivals of entanglement of system-spins.
Ferrofluid dynamics: Spin-echo experiment
NASA Astrophysics Data System (ADS)
Lebedev, V. T.; Gordeev, G. P.; Panasiuk, E. A.; Kiss, L.; Cser, L.; Rosta, L.; Török, Gy.; Farago, B.
1993-04-01
Dependence of the dynamical behaviour of ferrofluid (FF) subsystems, i.e. nuclear and magnetic contributions to the scattering cross section, on the external magnetic field has been observed. In zero field, the nuclear subsystem of FF has a soft mode with the relation ? q4, which can be explained by means of a dipole-bond fractal. This fractal gets broken by applying a magnetic field and then the motion of particles approaches ordinary diffusion, i.e ? q2. The magnetic subsystem is superparamagnetic in a low field and it reveals the fast relaxation of spin components transversal to magnetization in a high field.
Dynamically generated pure spin current in single-layer graphene
NASA Astrophysics Data System (ADS)
Tang, Zhenyao; Shikoh, Eiji; Ago, Hiroki; Kawahara, Kenji; Ando, Yuichiro; Shinjo, Teruya; Shiraishi, Masashi
2013-04-01
The conductance mismatch problem limits the spin-injection efficiency significantly, and spin injection into graphene usually requires high-quality tunnel barriers to circumvent the conductance mismatch. We introduce an approach which enables the generation of pure spin current into single-layer graphene (SLG) that is free from electrical conductance mismatch by using dynamical spin injection. An experimental demonstration of spin-pumping-induced spin current generation and spin transport in SLG at room temperature was successfully achieved, and the spin coherence length was estimated to be 1.36 ?m by using a conventional theoretical model based on the Landau-Lifshitz-Gilbert equation. The spin coherence length is proportional to the quality of SLG, which indicates that spin relaxation in SLG is governed by the Elliot-Yafet mechanism, as was reported.
Frydman, Lucio
Controlling Spin-Spin Network Dynamics by Repeated Projective Measurements Christian O-bath interaction behaves coherently: when control is effected via projective measurements-- i.e., by driving-spin network manipulations can be made highly effective by repeated projections of the evolving quantum states
Lattice instability and competing spin structures in the double perovskite insulator Sr2FeOsO6.
Paul, Avijit Kumar; Reehuis, Manfred; Ksenofontov, Vadim; Yan, Binghai; Hoser, Andreas; Többens, Daniel M; Abdala, Paula M; Adler, Peter; Jansen, Martin; Felser, Claudia
2013-10-18
The semiconductor Sr2FeOsO6, depending on temperature, adopts two types of spin structures that differ in the spin sequence of ferrimagnetic iron-osmium layers along the tetragonal c axis. Neutron powder diffraction experiments, 57Fe Mössbauer spectra, and density functional theory calculations suggest that this behavior arises because a lattice instability resulting in alternating iron-osmium distances fine-tunes the balance of competing exchange interactions. Thus, Sr2FeOsO6 is an example of a double perovskite, in which the electronic phases are controlled by the interplay of spin, orbital, and lattice degrees of freedom. PMID:24182298
Dynamics of a macroscopic spin qubit in spin-orbit coupled Bose-Einstein condensates
Sh. Mardonov; M. Modugno; E. Ya. Sherman
2015-05-16
We consider a macroscopic spin qubit based on spin-orbit coupled Bose-Einstein condensates, where, in addition to the spin-orbit coupling, 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 spin-orbit coupling 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 spin-orbit coupling, in the spinor wave function.
Spin dynamics and fluctuations in the streaming regime
NASA Astrophysics Data System (ADS)
Smirnov, D. S.; Golub, L. E.
2015-07-01
Spin dynamics of two-dimensional electrons in moderate in-plane electric fields is studied theoretically. The streaming regime is considered, where each electron accelerates until reaching the optical phonon energy, then it emits an optical phonon, and a new period of acceleration starts. Spin-orbit interaction and elastic scattering result in anisotropic relaxation of electron-spin polarization. The overall spin dynamics is described by a superposition of spin modes in the system. The relaxation time of the most long-living mode depends quasiperiodically on the inverse electric field. The spin modes can be conveniently revealed by means of spin noise spectroscopy. It is demonstrated that the spectrum of spin fluctuations consists of peaks with the low-frequency peak much narrower than satellite ones, and the widths of the peaks are determined by the decay times of the modes.
Dynamic nuclear spin resonance in n-GaAs.
Chen, Y S; Reuter, D; Wieck, A D; Bacher, G
2011-10-14
The dynamics of optically detected nuclear magnetic resonance is studied in n-GaAs via time-resolved Kerr rotation using an on-chip microcoil for rf field generation. Both optically allowed and optically forbidden NMR are observed with a dynamics controlled by the interplay between dynamic nuclear polarization via hyperfine interaction with optically generated spin-polarized electrons and nuclear spin depolarization due to magnetic resonance absorption. Comparing the characteristic nuclear spin relaxation rate obtained in experiment with master equation simulations, the underlying nuclear spin depolarization mechanism for each resonance is extracted. PMID:22107431
Spin dynamics of chromium. II. Incommensurate alloys
Fishman, R.S.; Liu, S.H.
1996-09-01
Since magnetic moments of transition-metal antiferromagnets are created by electron-hole pairs, the spin dynamics of Cr alloys are associated with quasiparticle transitions. This paper uses random-phase approximation to investigate spin dynamics about two different spin-density-wave (SDW) states of incommensurate ({ital I}) alloys with wave vectors {ital Q}{sub {+-}}{sup {prime}}=(2{pi}/{ital a})(0,0,1{+-} {partial_derivative} {prime}). Because of the more complex quasiparticle energies, {ital I} alloys have a richer spectrum of collective excitations than the commensurate ({ital C}) alloys studied previously. Associated with the free energy`s rotational invariance are transverse spin-wave (SW) modes which evolve from each satellite wave vector {ital Q}{sub {+-}}{sup {prime}} with the same temperature-independent mode velocity {ital c}={ital v}{sub {ital F}}/{radical}(3) as in the {ital C} regime. The translational invariance of the ISDW state is responsible for longitudinal phason modes which evolve from the satellite wave vectors and are damped for any nonzero frequency. As {ital T}{r_arrow}{ital T}{sub {ital N}}, the phason mode velocity approaches {ital c}. Together with a related longitudinal damped excitation, the phason modes tilt the SW cones towards {bold G}/2=(2{pi}/{ital a}) (0,0,1) and produce a peak in the {bold G}/2 cross section at 60 meV, as observed experimentally. High-frequency amplitude modes, both transverse and longitudinal, lie near the pair-breaking edge for each satellite, which is about 40{percent} lower than in the {ital C} case. Undamped collective modes called wavons are associated with fluctuations of the SDW wave vectors {ital Q}{sub {plus_minus}}{sup {prime}} about their equilibrium values. Wavon modes were recently observed as peaks in the satellite cross sections between 15 and 20 meV. Our model predicts the temperature and doping dependences of the phason and wavon peaks. {copyright} {ital 1996 The American Physical Society.}
Aging dynamics of the Heisenberg spin glass L. Berthier*
Berthier, Ludovic
Aging dynamics of the Heisenberg spin glass L. Berthier* Theoretical Physics, 1 Keble Road, Oxford the nonequilibrium dynamics of the three-dimensional Heisenberg Edwards-Anderson spin glass following a sudden quench are now three-component vectors of unit length. The Heisenberg Edwards-Anderson model in Eq. 2 has been
Domain wall dynamics in a spin-reorientation transition system Au/Co/Au
Roy, Sujoy; Seu, Keoki; Turner, Joshua J.; Park, Sungkyun; Kevan, Steve; Falco, Charles M.
2009-05-14
We report measurements of domain wall dynamics in an ultrathin Au/Co/Au system that exhibits a spin reorientation phase transition as a function of temperature.The domain walls exhibit cooperative motion throughout the temperature range of 150 - 300 K. The decay times were found to exhibit a maximum at the transition temperature. The slowdown has been explained as due to formation of a double well in the energy landscape by the different competing interactions. Our results show that the complex, slow dynamics can provide a more fundamental understanding of magnetic phase transitions.
Influences of Initial States on Entanglement Dynamics of Two Central Spins in a Spin Environment
NASA Astrophysics Data System (ADS)
Yu, Wen-Jian; Xu, Bao-Ming; Li, Lin; Zou, Jian; Li, Hai; Shao, Bin
2015-09-01
We investigate the entanglement dynamics of two electronic spins coupled to a bath of nuclear spins for two special cases, one is that two central spins both interact with a common bath, and the other is that one of two spins interacts with a bath. We consider three types of initial states with different correlations between the system and the bath, i.e., quantum correlation, classical correlation, and no-correlation. We show that the initial correlations (no matter quantum correlations or classical correlations) can effectively avoid the occurrence of entanglement sudden death. Irrespective of whether both two spins or only one of the two spins interacts with the bath, the system can gain more entanglement in the process of the time evolution for initial quantum correlations. In addition, we find that the effects of the distribution of coupling constants on entanglement dynamics crucially depend on the initial state of the spin bath.
Dynamics of a macroscopic spin qubit in spinorbit coupled BoseEinstein condensates
NASA Astrophysics Data System (ADS)
Mardonov, Sh; Modugno, M.; Sherman, E. Ya
2015-06-01
We consider a macroscopic spin qubit based on spinorbit coupled BoseEinstein condensates, where, in addition to the spinorbit 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.
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 ...
Localizing spin dynamics in a spin-1 Bose-Einstein condensate via magnetic pulses
NASA Astrophysics Data System (ADS)
Li, Huanbin; Pu, Zhengguo; Chapman, M. S.; Zhang, Wenxian
2015-07-01
Spin-exchange interaction between atoms in a spin-1 Bose-Einstein condensate causes atomic spin evolving periodically under the single-spatial-mode approximation in the mean-field theory. By applying fast magnetic pulses according to a two-step or a four-step control protocol, we find analytically that the spin dynamics is significantly suppressed for an arbitrary initial state. Numerical calculations under single-mode approximation are carried out to confirm the validity and robustness of these protocols. This localization method can be readily utilized to improve the sensitivity of a magnetometer based on spin-1 Bose-Einstein condensates.
NASA Astrophysics Data System (ADS)
Dietl, Tomasz
2015-03-01
A physically transparent and mathematically simple semiclassical model is employed to examine dynamics in the central-spin problem. The results reproduce previous findings obtained by various quantum approaches and, at the same time, provide information on the electron spin dynamics and Berry's phase effects over a wider range of experimentally relevant parameters than available previously. This development is relevant to dynamics of bound magnetic polarons and spin dephasing of an electron trapped by an impurity or a quantum dot, and coupled by a contact interaction to neighboring localized magnetic impurities or nuclear spins. Furthermore, it substantiates the applicability of semiclassical models to simulate dynamic properties of spintronic nanostructures with a mesoscopic number of spins.
Naming Game Dynamics on Pairs of Connected Networks with Competing Opinions
Varela, Carlos
- fluence. Prior research has shown that the interpersonal relationships often drive large-scale changesNaming Game Dynamics on Pairs of Connected Networks with Competing Opinions Albert Trias Mansilla1 net- works with nodes in consensus on competing opinions are connected with new links. We consider two
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,
Romalis, Mike
. In this Letter, we investigate spin-exchange effects between K vapor and 3 He gas in a very low magnetic fieldDynamics of Two Overlapping Spin Ensembles Interacting by Spin Exchange T.W. Kornack and M interacting by spin exchange. The interactions are dominated by the imaginary part of the spin-exchange cross
Nonlinear dynamics of spin and charge in spin-Calogero model
Kulkarni, Manas; Franchini, Fabio; Abanov, Alexander G.
2009-10-15
The fully nonlinear dynamics of spin and charge in spin-Calogero model is studied. The latter is an integrable one-dimensional model of quantum spin-1/2 particles interacting through inverse-square interaction and exchange. Classical hydrodynamic equations of motion are written for this model in the regime where gradient corrections to the exact hydrodynamic formulation of the theory may be neglected. In this approximation variables separate in terms of dressed Fermi momenta of the model. Hydrodynamic equations reduce to a set of decoupled Riemann-Hopf (or inviscid Burgers') equations for the dressed Fermi momenta. We study the dynamics of some nonequilibrium spin-charge configurations for times smaller than the time scale of the gradient catastrophe. We find an interesting interplay between spin and charge degrees of freedom. In the limit of large coupling constant the hydrodynamics reduces to the spin hydrodynamics of the Haldane-Shastry model.
Electron Spin Dynamics in Semiconductor Quantum Dots
Marie, X.; Belhadj, T.; Urbaszek, B.; Amand, T.; Krebs, O.; Lemaitre, A.; Voisin, P.
2011-07-15
An electron spin confined to a semiconductor quantum dot is not subject to the classical spin relaxation mechanisms known for free carriers but it strongly interacts with the nuclear spin system via the hyperfine interaction. We show in time resolved photoluminescence spectroscopy experiments on ensembles of self assembled InAs quantum dots in GaAs that this interaction leads to strong electron spin dephasing.
Spin dynamics under local gauge fields in chiral spin-orbit coupling systems
Tan, S.G., E-mail: TAN_Seng_Ghee@dsi.a-star.edu.sg [Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Jalil, M.B.A. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Fujita, T. [Information Storage Materials Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Data Storage Institute, A-STAR (Agency for Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore 117608 (Singapore); Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore 117576 (Singapore); Liu, X.J. [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore)
2011-02-15
Research Highlights: > We derive a modified LLG equation in magnetic systems with spin-orbit coupling (SOC). > Our results are applied to magnetic multilayers, and DMS and magnetic Rashba systems. > SOC mediated magnetization switching is predicted in rare earth metals (large SOC). > The magnetization trajectory and frequency can be modulated by applied voltage. > This facilitates potential application as tunable microwave oscillators. - Abstract: We present a theoretical description of local spin dynamics in magnetic systems with a chiral spin texture and finite spin-orbit coupling (SOC). Spin precession about the relativistic effective magnetic field in a SOC system gives rise to a non-Abelian SU(2) gauge field reminiscent of the Yang-Mills field. In addition, the adiabatic relaxation of electron spin along the local spin yields an U(1) x U(1) topological gauge (Berry) field. We derive the corresponding equation of motion i.e. modified Landau-Lifshitz-Gilbert (LLG) equation, for the local spin under the influence of these effects. Focusing on the SU(2) gauge, we obtain the spin torque magnitude, and the amplitude and frequency of spin oscillations in this system. Our theoretical estimates indicate significant spin torque and oscillations in systems with large spin-orbit coupling, which may be utilized in technological applications such as current-induced magnetization-switching and tunable microwave oscillators.
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...
Semiclassical spin-spin dynamics and feedback control in transport through a quantum dot
NASA Astrophysics Data System (ADS)
Mosshammer, Klemens; Brandes, Tobias
2014-10-01
We present a theory of magnetotransport through an electronic orbital, where the electron spin interacts with a (sufficiently) large external spin via an exchange interaction. Using a semiclassical approximation, we derive a set of equations of motions for the electron density matrix and the mean value of the external spin that turns out to be highly nonlinear. The dissipation via the electronic leads is implemented in terms of a quantum master equation that is combined with the nonlinear terms of the spin-spin interaction. With an anisotropic exchange coupling a variety of dynamics is generated, such as self-sustained oscillations with parametric resonances or even chaotic behavior. Within our theory we can integrate a Maxwell-demon-like closed-loop feedback scheme that is capable of transporting particles against an applied bias voltage and that can be used to implement a spin filter to generate spin-dependent oscillating currents of opposite directions.
Spin pumping and magnetization dynamics in metallic multilayers
NASA Astrophysics Data System (ADS)
Tserkovnyak, Yaroslav; Brataas, Arne; Bauer, Gerrit E.
2002-12-01
We study the magnetization dynamics in thin ferromagnetic films and small ferromagnetic particles in contact with paramagnetic conductors. A moving magnetization vector causes ``pumping'' of spins into adjacent nonmagnetic layers. This spin transfer affects the magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology. The additional Gilbert damping is significant for small ferromagnets, when the nonmagnetic layers efficiently relax the injected spins, but the effect is reduced when a spin accumulation build-up in the normal metal opposes the spin pumping. The damping enhancement is governed by (and, in turn, can be used to measure) the mixing conductance or spin-torque parameter of the ferromagnet-normal-metal interface. Our theoretical findings are confirmed by agreement with recent experiments in a variety of multilayer systems.
Polariton Spin Dynamics in IIVI Microcavities M. D. Martin1
Vińa, Luis
Polariton Spin Dynamics in IIVI Microcavities M. D. Marti´n1 )*) (a), G. Aichmayr (a), L. Vin~a (a.36.ţc; 78.47.ţp; 78.66.Hf; S8.13 The spin dynamics of cavity polaritons, in the non-linear regime by the polariton final state stimulated scattering, the emission is counter-polarized with the excita- tion
Spin dynamics simulation of electron spin relaxation in Ni{sup 2+}(aq)
Rantaharju, Jyrki, E-mail: jjrantaharju@gmail.com; Mare, Ji?í, E-mail: jiri.mares@oulu.fi; Vaara, Juha, E-mail: juha.vaara@iki.fi [NMR Research Group, Department of Physics, University of Oulu, P.O. Box 3000, Oulu, FIN-90014 (Finland)
2014-07-07
The ability to quantitatively predict and analyze the rate of electron spin relaxation of open-shell systems is important for electron paramagnetic resonance and paramagnetic nuclear magnetic resonance spectroscopies. We present a combined molecular dynamics (MD), quantum chemistry (QC), and spin dynamics simulation method for calculating such spin relaxation rates. The method is based on the sampling of a MD trajectory by QC calculations, to produce instantaneous parameters of the spin Hamiltonian used, in turn, to numerically solve the Liouville-von Neumann equation for the time evolution of the spin density matrix. We demonstrate the approach by simulating the relaxation of electron spin in an aqueous solution of Ni{sup 2+} ion. The spin-lattice (T{sub 1}) and spin-spin (T{sub 2}) relaxation rates are extracted directly from the simulations of the time dependence of the longitudinal and transverse magnetization, respectively. Good agreement with the available, indirectly obtained experimental data is obtained by our method.
Spin and charge dynamics of chromium alloys
Fishman, R.S.; Viswanath, V.S.; Liu, S.H.
1996-07-01
Both the spin- and charge-density waves of Cr alloys are produced by the Coulomb attraction between electrons and holes on nearly nested Fermi surfaces. Driven by quasi-particle transitions, transverse spin- wave and longitudinal phason modes are associated with rotational and translational symmetries of pure Cr and its dilute alloys. At low frequencies, both spin and charge phasons have a nearly linear dispersion with a mode velocity which approaches the spin-wave velocity as T approaches T{sub N} or as the mismatch between the Fermi surfaces increases.
Phase diagram and quench dynamics of the Cluster-XY spin chain
Sebastian Montes; Alioscia Hamma
2012-08-04
We study the complete phase space and the quench dynamics of an exactly solvable spin chain, the cluster-XY model. In this chain, the cluster term and the XY couplings compete to give a rich phase diagram. The phase diagram is studied by means of the quantum geometric tensor. We study the time evolution of the system after a critical quantum quench using the Loschmidt echo. The structure of the revivals after critical quantum quenches presents a non trivial behavior depending on the phase of the initial state and the critical point.
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
Dynamics, synchronization, and quantum phase transitions of two dissipative spins
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.
Optimized dynamical control of state transfer through noisy spin chains
Analia Zwick; Gonzalo A. Alvarez; Guy Bensky; Gershon Kurizki
2015-01-09
We propose a method of optimally controlling the tradeoff of speed and fidelity of state transfer through a noisy quantum channel (spin-chain). This process is treated as qubit state-transfer through a fermionic bath. We show that dynamical modulation of the boundary-qubits levels can ensure state transfer with the best tradeoff of speed and fidelity. This is achievable by dynamically optimizing the transmission spectrum of the channel. The resulting optimal control is robust against both static and fluctuating noise in the channel's spin-spin couplings. It may also facilitate transfer in the presence of diagonal disorder (on site energy noise) in the channel.
Heteronuclear coherent spinor dynamics in an ultracold spin-1 mixture
NASA Astrophysics Data System (ADS)
Wang, Dajun; Li, Xiaoke; Zhu, Bing; Wang, Fudong; He, Xiaodong; Chen, Jun; Guo, Mingyang
2014-03-01
Ultracold spinor gas has been a subject of great interest in quantum gas research for many years. So far, however, all the experimental studies are carried out with a single atomic species, mostly either 23Na or 87Rb atom. Only very recently, it has been proposed theoretically that spinor dynamics can also exist in heteronuclear spin-1 mixtures. To explore this, we have prepared an optically trapped ultracold mixture of spin-1 23Na and 87Rb atoms. With well controlled initial spin populations and magnetic fields, we have observed rapid spin population and magnetization oscillations for both Na and Rb due to heteronuclear spin-spin interactions. Following this first demonstration, we believe that rich heteronuclear spinor physics can be studied in the future. We are supported by RGC Hong Kong (grant nos. CUHK 403111 and CUHK 404712).
Nonadiabatic multichannel dynamics of a spin-orbit coupled condensate
Bo Xiong; Jun-hui Zheng; Daw-wei Wang
2015-06-05
We investigate the nonadiabatic dynamics of a driven spin-orbit-coupled Bose-Einstein condensate in both weak and strong driven force. It is shown that the standard Landau-Zener (LZ) tunneling fails in the regime of weak driven force and/or strong spin-orbital coupling, where the full nonadiabatic dynamics requires a new mechanism through multichannel effects. Beyond the semiclassical approach, our numerical and analytical results show an oscillating power-law decay in the quantum limit, different from the exponential decay in the semiclassical limit of the LZ effect. Furthermore, the condensate density profile is found to be dynamically fragmented by the multichannel effects and enhanced by interaction effects. Our work therefore provides a complete picture to understand the nonadiabatic dynamics of a spin-orbit coupled condensate, including various range of driven force and interaction effects through multichannel interference. The experimental indication of these nonadiabatic dynamics is also discussed.
NMR with generalized dynamics of spin and spatial coordinates
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.
Spin supercurrent, magnetization dynamics, and ?-state in spin-textured Josephson junctions
NASA Astrophysics Data System (ADS)
Kulagina, Iryna; Linder, Jacob
2014-08-01
The prospect of combining the dissipationless nature of superconducting currents with the spin polarization of magnetic materials is interesting with respect to exploring superconducting analogs of topics in spintronics. In order to accomplish this aim, it is pivotal to understand not only how such spin supercurrents can be created, but also how they interact dynamically with magnetization textures. In this paper, we investigate the appearance of a spin supercurrent and the resulting magnetization dynamics in a textured magnetic Josephson current by using three experimentally relevant models: (i) a superconductor?ferromagnet?superconductor (S?F?S) junction with spin-active interfaces, (ii) a S?F1?F2?F3?S Josephson junction with a ferromagnetic trilayer, and (iii) a Josephson junction containing a domain wall. In all of these cases, the supercurrent is spin polarized and exerts a spin-transfer torque on the ferromagnetic interlayers which causes magnetization dynamics. Using a scattering matrix formalism in the clean limit, we compute the Andreev bound states and resulting free energy of the system which in turn is used to solve the Landau-Lifshiftz-Gilbert equation. We compute both how the inhomogeneous magnetism influences the phase dependence of the charge supercurrent and the magnetization dynamics caused by the spin polarization of the supercurrent. Using a realistic experimental parameter set, we find that the spin supercurrent can induce magnetization switching that is controlled by the superconducting phase difference. Moreover, we demonstrate that the combined effect of chiral spin symmetry breaking of the system as a whole with interface scattering causes the systems above to act as phase batteries that may supply any superconducting phase difference ? in the ground state. Such a ?-junction is accompanied by an anomalous supercurrent appearing even at zero phase difference, and we demonstrate that the flow direction of this current is controlled by the chirality of the magnetization configuration.
Competing risks analysis in mountain pine beetle dynamics
Walter E. Cole; Intermountain Forest
1973-01-01
Summary This paper presents an application and evaluation of competing risks analysis (Chiang, 1968) of mountain pine beetle life tables. Three known and one group of unknown risks are used. Interpretation of the results\\u000a imply that only the crude probability of death from a specific cause is applicable to this situation; net and partial crude\\u000a probabilities are yet incomplete. None of
Simulating spin dynamics in organic solids under heteronuclear decoupling.
Frantsuzov, Ilya; Ernst, Matthias; Brown, Steven P; Hodgkinson, Paul
2015-09-01
Although considerable progress has been made in simulating the dynamics of multiple coupled nuclear spins, predicting the evolution of nuclear magnetisation in the presence of radio-frequency decoupling remains challenging. We use exact numerical simulations of the spin dynamics under simultaneous magic-angle spinning and RF decoupling to determine the extent to which numerical simulations can be used to predict the experimental performance of heteronuclear decoupling for the CW, TPPM and XiX sequences, using the methylene group of glycine as a model system. The signal decay times are shown to be strongly dependent on the largest spin order simulated. Unexpectedly large differences are observed between the dynamics with and without spin echoes. Qualitative trends are well reproduced by modestly sized spin system simulations, and the effects of finite spin-system size can, in favourable cases, be mitigated by extrapolation. Quantitative prediction of the behaviour in complex parameter spaces is found, however, to be very challenging, suggesting that there are significant limits to the role of numerical simulations in RF decoupling problems, even when specialist techniques, such as state-space restriction, are used. PMID:26073419
Effect of cosmic string on spin dynamics
Debashree Chowdhury; B. Basu
2014-11-07
In the present paper, we have investigated the role of cosmic string on spin current and Hall electric field. Due to the background cosmic string, the modified electric field of the system generates renormalized spin orbit coupling, which induces a modified non-Abelian gauge field. The defect causes a change in the AB and AC phases appearing due to the modified electromagnetic field. In addition, for a time varying electric field we perform explicit analytic calculations to derive the exact form of spin electric field and spin current, which is defect parameter dependent and of oscillating type. Furthermore, in an asymmetric crystal within the Drude model approach we investigate the dependence of the cosmic string parameters on cosmic string induced Hall electric field.
On the dynamics of XY spin chains with impurities
NASA Astrophysics Data System (ADS)
Genovese, Giuseppe
2015-09-01
We provide a theoretical set up for studying the dynamics in quantum spin chain models with inhomogeneous two-body interaction. We frame in our formalism models that can be mapped into fermion systems with quadratic Hamiltonian, namely XY chains with transverse magnetic field. Local and global existence results of the dynamics are discussed.
Spin Dynamics in Highly Spin Polarized Co1-xFexS2
NASA Astrophysics Data System (ADS)
Hoch, Michael J. R.; Kuhns, Philip L.; Moulton, William G.; Reyes, Arneil P.; Lu, Jun; Wang, Lan; Leighton, Chris
2006-09-01
Highly spin polarized or half-metallic systems are of considerable current interest because of their potential for spin injection in spintronics applications. The ferromagnet (FM) CoS2 is close to being a half-metal. Recent theoretical and experimental work has shown that the alloys Co1-xFexS2 (0.07 < x < 0.9) are highly spin polarized at low temperatures. The Fe concentration may be used to tune the spin polarization. Using 59Co FM- NMR we have investigated the spin dynamics in this family of alloys and have obtained information on the evolution of the d-band density of states at the Fermi level with x in the range 0 to 0.3. The results are compared with available theoretical predictions.
Competing d -Wave and p -Wave Spin-Singlet Superconductivities in the Two-Dimensional Kondo Lattice
NASA Astrophysics Data System (ADS)
Otsuki, Junya
2015-07-01
The Kondo lattice model describes a quantum phase transition between the antiferromagnetic state and heavy-fermion states. Applying the dual-fermion approach, we explore possible superconductivities emerging due to the critical antiferromagnetic fluctuations. The d -wave pairing is found to be the leading instability only in the weak-coupling regime. As the coupling is increased, we observe a change of the pairing symmetry into a p -wave spin-singlet pairing. The competing superconductivities are ascribed to crossover between small and large Fermi surfaces, which occurs with the formation of heavy quasiparticles.
Voltage controlled electron spin dynamics in resonant tunnelling devices
NASA Astrophysics Data System (ADS)
Galeti, H. V. A.; Brasil, M. J. S. P.; Gobato, Y. Galv ao; Henini, M.
2014-04-01
We investigate the electron spin dynamics in a p-type GaAs/AlAs resonant tunnelling device by measuring the time- and polarized-resolved photoluminescence (PL) from the GaAs quantum well under a high magnetic field (15 T). The voltage dependence of the PL transients have revealed various tunnelling processes with different time constants that give rise to distinct spin-polarized carriers injected into the double-barrier structure.
NASA Astrophysics Data System (ADS)
Chen, Yao; Fang, Jiancheng
2015-05-01
Two spin ensembles which occupy the same volume in a spherical alkali vapor cell can coupled together by the spin exchange interaction. In a K-Rb-21Ne co-magnetometer which was used for rotation sensing, Rb atomic spins and the 21Ne nuclear spins couple together by spin exchange. Due to the large Rb density and the Fermi contact constant of Rb-21Ne pair, the magnetization field of Rb atomic spins is much larger than that of the K in a K-3He co-magnetometer. At the co-magnetometer working point, the precession frequency of Rb atomic spins are much larger than that of the 21Ne spins. The decay rate and precession frequency of 21Ne atoms is much smaller than that of the point when the precession frequencies of the Rb and 21Ne atoms are the same. In this experiment, the dynamics of the Rb- 21Ne pair at different holding magnetic field point were studied. The frequency response of the co-magnetometer to oscillating magnetic field at different holding magnetic field point was also studied.
NASA Astrophysics Data System (ADS)
Holt, Michael; Powell, Ben J.; Merino, Jaime
2014-05-01
We investigate the effect of ring exchange on the ground-state properties and magnetic excitations of the S =1/2 Heisenberg model on the anisotropic triangular lattice with ring exchange at T =0 using linear spin-wave theory. Classically, we find stable Néel, spiral and collinear magnetically ordered phases. Upon including quantum fluctuations to the model, linear spin-wave theory shows that ring exchange induces a large quantum disordered region in the phase diagram, completely wiping out the classically stable collinear phase. Analysis of the spin-wave spectra for each of these three models demonstrates that the large spin-liquid phase observed in the full model is a direct manifestation of competing classical orders. To understand the origin of these competing phases, we introduce models where either the four spin contributions from ring exchange, or the renormalization of the Heisenberg terms due to ring exchange are neglected. We find that these two terms favor rather different physics.
Dynamics of Spin and Orbital Phase Transitions in YVO3
NASA Astrophysics Data System (ADS)
Mazurenko, Dmitry A.; Nugroho, Agung A.; Palstra, Thomas T. M.; van Loosdrecht, Paul H. M.
2008-12-01
YVO3 exhibits a well separated sequence of orbital and spin order transitions at 200 and 116 K, followed by a combined spin-orbital reorientation at 77 K. It is shown that the spin order can be destroyed by a sufficiently strong optical pulse within less than 4 ps. In contrast, the orbital reordering transition from C-type to G-type orbital order is slower than 100 ps and goes via an intermediate nonthermal phase. We propose that the dynamics of phase transitions is subjected to symmetry relations between the associated phases.
Robust Dynamical Decoupling Sequences for Individual Nuclear Spin Addressing
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.
Numerical Researches on Dynamical Systems with Relativistic Spin
NASA Astrophysics Data System (ADS)
Han, W. B.
2010-04-01
It is well known that spinning compact binaries are one of the most important research objects in the universe. Especially, EMRIs (extreme mass ratio inspirals) involving stellar compact objects which orbit massive black holes, are considered to be primary sources of gravitational radiation (GW) which could be detected by the space-based interferometer LISA. GW signals from EMRIs can be used to test general relativity, measure the masses and spins of central black holes and study essential physics near horizons. Compared with the situation without spin, the complexity of extreme objects, most of which rotate very fast, is much higher. So the dynamics of EMRI systems are numerically and analytically studied. We focus on how the spin effects on the dynamics of these systems and the produced GW radiations. Firstly, an ideal model of spinning test particles around Kerr black hole is considered. For equatorial orbits, we present the correct expression of effective potential and analyze the stability of circular orbits. Especially, the gravitational binding energy and frame-dragging effect of extreme Kerr black hole are much bigger than those without spin. For general orbits, spin can monotonically enlarge orbital inclination and destroy the symmetry of orbits about equatorial plane. It is the most important that extreme spin can produce orbital chaos. By carefully investigating the relations between chaos and orbital parameters, we point out that chaos usually appears for orbits with small pericenter, big eccentricity and orbital inclination. It is emphasized that Poincaré section method is invalid to detect the chaos of spinning particles, and the way of systems toward chaos is the period-doubling bifurcation. Furthermore, we study how spins effect on GW radiations from spinning test particles orbiting Kerr black holes. It is found that spins can increase orbit eccentricity and then make h+ component be detected more easily. But for h× component, because spins change orbital inclination in a complicated way, it is more difficult to build GW signal templates. Secondly, based on the scalar gravity theory, a numerical relativistic model of EMRIs is constructed to consider the self-gravity and radiation reaction of low-mass objects. Finally, we develop a new method with multiple steps for Hamilton systems to meet the needs of numerical researches. This method can effectively maintain each conserved quantity of the separable Hamilton system. In addition, for constrained system with a few first integrals, we present a new numerical stabilization method named as adjustment-stabilization method, which can maintain all known conserved quantities in a given dynamical system and greatly improve the numerical accuracy. Our new method is the most complete stabilization method up to now.
NASA Astrophysics Data System (ADS)
Chang, Chia-Chen; Rousseau, Valery; Scalettar, Richard T.; Batrouni, George
2014-03-01
Rapid progress in pure optical trapping techniques makes it possible now to create degenerate Bose gases with spin degrees of freedom. Systems such as 87Rb or 23Na in the F = 1 hyperfine state offer a unique platform for studying the interplay of superfluidity and magnetism, phases resulting from macroscopic quantum coherence and symmetry breaking respectively. Motivated by these experimental developments, we study ground state phases of a two-component spinor Bose gas loaded on an optical lattice. The system is described effectively by the Bose-Hubbard Hamiltonian with onsite and extended spin-spin interactions. Using mean-field theory and quantum Monte Carlo simulations, we map out the phase diagram of the system. A rich variety of phases is identified, including antiferromagnetic (AF) Mott insulators, ferromagnetic or AF superfluids, and supersolids. Research supported by the CNRS-UC Davis EPOCAL LIA joint re- search grant; by NSF-PIF-1005503 and DOE SSAAP DE-NA0001842.
Storing entanglement of nuclear spins via Uhrig dynamical decoupling
Roy, Soumya Singha; Mahesh, T. S.; Agarwal, G. S.
2011-06-15
Stroboscopic spin flips have already been shown to prolong the coherence times of quantum systems under noisy environments. Uhrig's dynamical decoupling scheme provides an optimal sequence for a quantum system interacting with a dephasing bath. Several experimental demonstrations have already verified the efficiency of such dynamical decoupling schemes in preserving single-qubit coherences. In this work we describe the experimental study of Uhrig's dynamical decoupling in preserving two-qubit entangled states using an ensemble of spin-1/2 nuclear pairs in solution state. We find that the performance of odd-order Uhrig sequences in preserving entanglement is superior to both even-order Uhrig sequences and periodic spin-flip sequences. We also find that there exists an optimal order of the Uhrig sequence in which a singlet state can be stored at high correlation for about 30 seconds.
Storing entanglement of nuclear spins via Uhrig Dynamical Decoupling
Soumya Singha Roy; T. S. Mahesh; G. S. Agarwal
2011-10-07
Stroboscopic spin flips have already been shown to prolong the coherence times of quantum systems under noisy environments. Uhrig's dynamical decoupling scheme provides an optimal sequence for a quantum system interacting with a dephasing bath. Several experimental demonstrations have already verified the efficiency of such dynamical decoupling schemes in preserving single qubit coherences. In this work we describe the experimental study of Uhrig's dynamical decoupling in preserving two-qubit entangled states using an ensemble of spin-1/2 nuclear pairs in solution state. We find that the performance of odd-order Uhrig sequences in preserving entanglement is superior to both even-order Uhrig sequences and periodic spin-flip sequences. We also find that there exists an optimal length of the Uhrig sequence at which the decoherence time gets boosted from a few seconds to about 30 seconds.
Spin-orbital dynamics in a system of polar molecules
NASA Astrophysics Data System (ADS)
Syzranov, Sergey; Wall, Michael; Gurarie, Victor; Rey, Ana Maria
2015-05-01
We consider the dynamics of a two-dimensional system of ultracold polar molecules weakly perturbed from a stationary state. We demonstrate that dipole-dipole interactions in such a system generate chiral excitations with a non-trivial Berry phase 2 ? . These excitations, which we call chirons, resemble low-energy quasiparticles in bilayer graphene and emerge regardless of the quantum statistics and for arbitrary ratios of kinetic to interaction energies. Chirons manifest themselves in the dynamics of the spin density profile, spin currents, and spin coherences, even for molecules pinned in a deep optical lattice. We derive the kinetic equation that describes chiron dynamics and calculate the distributions of physical observables for experimentally realisable initial conditions. This work was supported by NIST: JILA-NSF-PFC-1125844, NSF-PIF-1211914, NSF-PHY11-25915, ARO, ARO-DARPA-OLE, AFOSR, AFOSR-MURI; NSF: DMR-1001240, PHY-1125844, and the Alexander von Humboldt Foundation.
Tunable nonequilibrium dynamics of field quenches in spin ice.
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
Theory of quantum control of spin-photon dynamics and spin decoherence in semiconductors
NASA Astrophysics Data System (ADS)
Yao, Wang
Single electron spin in a semiconductor quantum dot (QD) and single photon wavepacket propagating in an optical waveguide are investigated as carriers of quantum bit (qubit) for information processing. Cavity quantum electrodynamics of the coupled system composed of charged QD, microcavity and waveguide provides a quantum interface for the interplay of stationary spin qubits and flying photon qubits via cavity assisted optical control. This interface forms the basis for a wide range of essential functions of a quantum network, including transferring, swapping, and entangling qubits at distributed quantum nodes as well as a deterministic source and an efficient detector of a single photon wavepacket with arbitrarily specified shape. The cavity assisted optical process also made possible ultrafast initialization and QND readout of the spin qubit in QD. In addition, the strong optical nonlinearity of dot-cavity-waveguide coupled system enables phase gate and entanglement operation for flying single photon qubits in waveguides. The coherence of the electron spin is the wellspring of these quantum applications being investigated. At low temperature and strong magnetic field, the dominant cause of electron spin decoherence is the coupling with the interacting lattice nuclear spins. We present a quantum solution to the coupled dynamics of the electron with the nuclear spin bath. The decoherence is treated in terms of quantum entanglement of the electron with the nuclear pair-flip excitations driven by the various nuclear interactions. A novel nuclear interaction, mediated by virtue spin-flips of the single electron, plays an important role in single spin free-induction decay (FID). The spin echo not only refocuses the dephasing by inhomogeneous broadening in ensemble dynamics but also eliminates the decoherence by electron-mediated nuclear interaction. Thus, the decoherence times for single spin FID and ensemble spin echo are significantly different. The quantum theory of decoherence also leads to a method of coherence recovery of the electron by disentanglement, realized through maneuvering the nuclear bath evolution by control of the electron spin-flip. The studies form the basis to outline the construction of a solid-state quantum network for scalable and distributed processing of quantum information.
Quantum Spin Dynamics and Quantum Computation
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.
Theoretical aspects of Magic Angle Spinning - Dynamic Nuclear Polarization.
Mentink-Vigier, Frederic; Akbey, Ümit; Oschkinat, Hartmut; Vega, Shimon; Feintuch, Akiva
2015-09-01
Magic Angle Spinning (MAS) combined with Dynamic Nuclear Polarization (DNP) has been proven in recent years to be a very powerful method for increasing solid-state NMR signals. Since the advent of biradicals such as TOTAPOL to increase the nuclear polarization new classes of radicals, with larger molecular weight and/or different spin properties have been developed. These have led to unprecedented signal gain, with varying results for different experimental parameters, in particular the microwave irradiation strength, the static field, and the spinning frequency. Recently it has been demonstrated that sample spinning imposes DNP enhancement processes that differ from the active DNP mechanism in static samples as upon sample spinning the DNP enhancements are the results of energy level anticrossings occurring periodically during each rotor cycle. In this work we present experimental results with regards to the MAS frequency dependence of the DNP enhancement profiles of four nitroxide-based radicals at two different sets of temperature, 110 and 160K. In fact, different magnitudes of reduction in enhancement are observed with increasing spinning frequency. Our simulation code for calculating MAS-DNP powder enhancements of small model spin systems has been improved to extend our studies of the influence of the interaction and relaxation parameters on powder enhancements. To achieve a better understanding we simulated the spin dynamics of a single three-spin system {ea-eb-n} during its steady state rotor periods and used the Landau-Zener formula to characterize the influence of the different anti-crossings on the polarizations of the system and their necessary action for reaching steady state conditions together with spin relaxation processes. Based on these model calculations we demonstrate that the maximum steady state nuclear polarization cannot become larger than the maximum polarization difference between the two electrons during the steady state rotor cycle. This study also shows the complexity of the MAS-DNP process and therefore the necessity to rely on numerical simulations for understanding parametric dependencies of the enhancements. Finally an extension of the spin system up to five spins allowed us to probe the first steps of the transfer of polarization from the nuclei coupled to the electrons to further away nuclei, demonstrating a decrease in the spin-diffusion barrier under MAS conditions. PMID:26232770
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.
Dynamics of a mesoscopic nuclear spin ensemble interacting with an optically driven electron spin
Megan J. Stanley; Clemens Matthiesen; Jack Hansom; Claire Le Gall; Carsten H. H. Schulte; Edmund Clarke; Mete Atatüre
2014-11-17
The ability to discriminate between simultaneously occurring noise sources in the local environment of semiconductor InGaAs quantum dots, such as electric and magnetic field fluctuations, is key to understanding their respective dynamics and their effect on quantum dot coherence properties. We present a discriminatory approach to all-optical sensing based on two-color resonance fluorescence of a quantum dot charged with a single electron. Our measurements show that local magnetic field fluctuations due to nuclear spins in the absence of an external magnetic field are described by two correlation times, both in the microsecond regime. The nuclear spin bath dynamics show a strong dependence on the strength of resonant probing, with correlation times increasing by a factor of four as the optical transition is saturated. We interpret the behavior as motional averaging of both the Knight field of the resident electron spin and the hyperfine-mediated nuclear spin-spin interaction due to optically-induced electron spin flips.
Spin dynamics and a novel orbital-antiphase pairing symmetry in iron-based superconductors
NASA Astrophysics Data System (ADS)
Yin, Zhiping; Haule, Kristjan; Kotliar, Gabriel
2014-03-01
We use first-principles many-body method, including ab initio determined two-particle vertex function, to study the spin dynamics and superconducting pairing symmetry in a large number of Fe-based superconductors. In Fe compounds with high transition temperature, we find both the dispersive high-energy spin excitations, and very strong low energy commensurate or nearly commensurate spin response, suggesting that these low energy spin excitations play the dominate role in cooper pairing. We find three closely competing types of pairing symmetries, which take a very simple form in the space of active Fe 3 d orbitals, and differ only in the relative quantum mechanical phase of the xz , yz and xy orbital contributions. The extensively discussed s+- symmetry appears when contributions from all orbitals have equal sign, while the opposite sign in xz and yz orbitals leads to the d wave symmetry. A novel orbital antiphase s+- symmetry emerges when xy orbital has opposite sign to xz and yz orbitals. We propose that this orbital-antiphase pairing symmetry explains the puzzling variation of the experimentally observed superconducting gaps on all the Fermi surfaces of LiFeAs. This novel symmetry of the order parameter may be realized in other Fe superconductors.
Quantum dynamics of two-spin-qubit systems.
Nguyen, Van Hieu
2009-07-01
The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks. PMID:21828484
TOPICAL REVIEW: Quantum dynamics of two-spin-qubit systems
NASA Astrophysics Data System (ADS)
Nguyen, Van Hieu
2009-07-01
The aim of this topical review is a systematic and concise presentation of the results of a series of theoretical works on the quantum dynamics of two-spin-qubit systems towards the elaboration of a physical mechanism of the quantum information transfer between two spin-qubits. For this purpose the main attention is paid to exactly solvable models of two-spin-qubit systems, since the analytical expressions of the elements of their reduced density matrices explicitly exhibit the mutual dependence of the quantum information encoded into the spin-qubits. The treatment of their decoherence due to the interaction with the environment is performed in the Markovian approximation. Rate equations for axially symmetric systems of two coupled spin-qubits non-interacting, as well as interacting, with the environment are exactly solved. It is shown how the solutions of rate equations demonstrate the physical mechanism of the quantum information exchange between the spin-qubits. This mechanism holds also in all two-spin-qubit systems whose rate equations can be solved only by means of numerical calculations. Exact solutions of rate equations for two uncoupled spin-qubits interacting with two separate environments reveal an interesting physical phenomenon in the time evolution of the qubit-qubit entanglement generated by their interaction with the environments: the entanglement sudden death and revival. A two-spin-qubit system with an asymptotically decoherence free subspace was also explicitly constructed. The presented calculations and reasonings can be extended for application to the study of spin-qubit chains or networks.
Thermalization and dynamic phase transition of quantum spins
NASA Astrophysics Data System (ADS)
Babadi, Mehrtash; Demler, Eugene; Knap, Michael
2015-03-01
We develop a controlled field theoretic technique for studying far-from-equilibrium dynamics of interacting quantum spins. This is achieved by combining the Majorana fermion representation of spins and 1/N expansion of the two-particle irreducible effective action (2PI-EA). We use the technique to study the relaxation dynamics of quantum spin spirals in the Heisenberg model. The non-equilibrium magnetization and spin correlations are found by solving the Kadanoff-Baym and Bethe-Salpeter equations resulting from the 1/N expansion of the 2PI-EA to the next-to-leading order. In three dimensions, we identify a dynamic phase transition in the steady state magnetization for spiral states near the Neél order. We further find a dynamical stabilization of the initial out-of-plane ordering instability in the course of the relaxation dynamics, in contrast to the linear response analysis. M.B. was supported by IQIM, an NSF Physics Frontiers Center. MK an ED acknowledge support from Harvard-MIT CUA, ARO-MURI Quism program, ARO-MURI on Atomtronics, as well as the Austrian Science Fund (FWF) Project No. J 3361-N20.
Spacetime dynamics of spinning particles - exact gravito-electromagnetic analogies
L. Filipe O. Costa; José Natário; Miguel Zilhăo
2015-07-29
We compare the rigorous equations describing the motion of spinning test particles in gravitational and electromagnetic fields, and show that if the Mathisson-Pirani spin condition holds then exact gravito-electromagnetic analogies emerge. These analogies provide a familiar formalism to treat gravitational problems, as well as a means for comparing the two interactions. Fundamental differences are manifest in the symmetries and time projections of the electromagnetic and gravitational tidal tensors. The physical consequences of the symmetries of the tidal tensors are explored comparing the following analogous setups: magnetic dipoles in the field of non-spinning/spinning charges, and gyroscopes in the Schwarzschild, Kerr, and Kerr-de Sitter spacetimes. The implications of the time-projections of the tidal tensors are illustrated by the work done on the particle in various frames; in particular, a reciprocity is found to exist: in a frame comoving with the particle, the electromagnetic (but not the gravitational) field does work on it, causing a variation of its proper mass; conversely, for "static observers", a stationary gravitomagnetic (but not a magnetic) field does work on the particle, and the associated potential energy is seen to embody the Hawking-Wald spin-spin interaction energy. The issue of hidden momentum, and its counterintuitive dynamical implications, is also analyzed. Finally, a number of issues regarding the electromagnetic interaction are clarified, namely the differences in the dynamics of electric and magnetic dipoles, and the physical meaning of Dixon's equations.
Global attractors and extinction dynamics of cyclically competing species
NASA Astrophysics Data System (ADS)
Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin
2013-05-01
Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases.
Global attractors and extinction dynamics of cyclically competing species.
Rulands, Steffen; Zielinski, Alejandro; Frey, Erwin
2013-05-01
Transitions to absorbing states are of fundamental importance in nonequilibrium physics as well as ecology. In ecology, absorbing states correspond to the extinction of species. We here study the spatial population dynamics of three cyclically interacting species. The interaction scheme comprises both direct competition between species as in the cyclic Lotka-Volterra model, and separated selection and reproduction processes as in the May-Leonard model. We show that the dynamic processes leading to the transient maintenance of biodiversity are closely linked to attractors of the nonlinear dynamics for the overall species' concentrations. The characteristics of these global attractors change qualitatively at certain threshold values of the mobility and depend on the relative strength of the different types of competition between species. They give information about the scaling of extinction times with the system size and thereby the stability of biodiversity. We define an effective free energy as the negative logarithm of the probability to find the system in a specific global state before reaching one of the absorbing states. The global attractors then correspond to minima of this effective energy landscape and determine the most probable values for the species' global concentrations. As in equilibrium thermodynamics, qualitative changes in the effective free energy landscape indicate and characterize the underlying nonequilibrium phase transitions. We provide the complete phase diagrams for the population dynamics and give a comprehensive analysis of the spatio-temporal dynamics and routes to extinction in the respective phases. PMID:23767569
Antiferromagnetic order and spin dynamics in iron-based superconductors
NASA Astrophysics Data System (ADS)
Dai, Pengcheng
2015-07-01
High-transition temperature (high-Tc) superconductivity in the iron pnictides or chalcogenides emerges from the suppression of the static antiferromagnetic order in their parent compounds, similar to copper oxide superconductors. This raises a fundamental question concerning the role of magnetism in the superconductivity of these materials. Neutron scattering, a powerful probe to study the magnetic order and spin dynamics, plays an essential role in determining the relationship between magnetism and superconductivity in high-Tc superconductors. The rapid development of modern neutron time-of-flight spectrometers allows a direct determination of the spin dynamical properties of iron-based superconductors throughout the entire Brillouin zone. In this paper, an overview is presented of the neutron scattering results on iron-based superconductors, focusing on the evolution of spin-excitation spectra as a function of electron and hole doping and isoelectronic substitution. Spin dynamical properties of iron-based superconductors are compared with those of copper oxide and heavy fermion superconductors and the common features of spin excitations in these three families of unconventional superconductors and their relationship with superconductivity are discussed.
Dynamics of Flexible Spinning Satellites with Radial Wire Antennas
NASA Technical Reports Server (NTRS)
Longman, R. W.; Fedor, J. V.
1973-01-01
A dynamic analysis is presented for a spin stabilized spacecraft employing four radial wire antennas with tip masses, a configuration first employed in the IMP-J spacecraft. The use of wires in place of the usual booms represents the ultimate in weight reduction at the expanse of flexibility. The satellite is modelled as a 14 degree of freedom system, and the linearized equations of motion are found. The lowest order vibrational modes and natural frequencies of the gyroscopically coupled system are then determined. Because the satellite spin rate is decreased by antenna deployment, a spin-up maneuver is needed. The response of the time varying mode equations during spin-up is found, for the planar modes, in terms of Bessel functions and a Struve function of order -1/4. Because tables of the latter are not readily available, the particular solution is expressed in various forms including an infinite series of Bessel functions and a particularly useful asymptotic expansion.
Extended dynamic spin-fluctuation theory of metallic magnetism.
Melnikov, N B; Reser, B I; Grebennikov, V I
2011-07-13
A dynamic spin-fluctuation theory that directly takes into account nonlocality of thermal spin fluctuations and their mode-mode interactions is developed. The Gaussian approximation in the theory is improved by a self-consistent renormalization of the mean field and spin susceptibility due to the third-and fourth-order terms of the free energy, respectively. This eliminates the fictitious first-order phase transition, which is typical for the Gaussian approximation, and yields a proper second-order phase transition. The effect of nonlocal spin correlations is enhanced by taking into account uniform fluctuations in the single-site mean Green function. Explicit computational formulae for basic magnetic characteristics are obtained. The extended theory is applied to the calculation of magnetic properties of Fe-Ni Invar. Almost full agreement with experiment is achieved for the magnetization, Curie temperature, and local and effective magnetic moments. PMID:21685553
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.
Sipe,J. E.
Physical limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics for the seminal proposal of Datta and Das of a ballistic spin-field-effect tran- sistor DD-SFET .5 However-SFET to the ballistic re- gime. Schliemann et al.7 have recently suggested a way to de- sign a SFET in 001 -plane
Thomas, David D.
Molecular Dynamics Simulation of Site-Directed Spin Labeling: Experimental Validation in Muscle, Molecular Biology, and Biophysics Department, University of Minnesota, Minneapolis, Minnesota 55455 USA ABSTRACT We have developed a computational molecular dynamics technique to simulate the motions of spin
Magnetization dynamics of imprinted non-collinear spin textures
NASA Astrophysics Data System (ADS)
Streubel, Robert; Fischer, Peter; Kopte, Martin; Schmidt, Oliver G.; Makarov, Denys
2015-09-01
We study the magnetization dynamics of non-collinear spin textures realized via imprint of the magnetic vortex state in soft permalloy into magnetically hard out-of-plane magnetized Co/Pd nanopatterned heterostructures. Tuning the interlayer exchange coupling between soft- and hard-magnetic subsystems provides means to tailor the magnetic state in the Co/Pd stack from being vortex- to donut-like with different core sizes. While the imprinted vortex spin texture leads to the dynamics similar to the one observed for vortices in permalloy disks, the donut-like state causes the appearance of two gyrofrequencies characteristic of the early and later stages of the magnetization dynamics. The dynamics are described using the Thiele equation supported by the full scale micromagnetic simulations by taking into account an enlarged core size of the donut states compared to magnetic vortices.
PUBLISHED VERSION Quantum heat bath for spin-lattice dynamics
of the classical fluctuation-dissipation relation (FDR) used for temperature control in spin-lattice dynamics heats and magnetization over a wide temperature range, from 0 K to above the Curie temperature many properties of the atomic lattice, such as the type of crystal structure [1], thermal expansivity
Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictide Superconductors
Tennessee, University of
Competing Pairing Symmetries in a Generalized Two-Orbital Model for the Pnictide Superconductors are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility are allowed to compete, as opposed to studying a few isolated states, are difficult for multiorbital Hubbard
Terahertz electromagnons in spin-diluted cupric oxide: dynamics of twisted spin states
NASA Astrophysics Data System (ADS)
Lloyd-Hughes, James; Jones, Samuel; Wurz, Nicola; Failla, Michele; McConville, Chris; Prabhakaran, Dharmalingham
2015-03-01
Understanding the physics of magnetoelectric materials may lead to their application in actuators, sensors and solid state memories. Improper multiferroics also have novel quasiparticle excitations: electromagnons form when spin-waves become electric-dipole active. We investigated magnons, electromagnons and spin-lattice coupling in Cu(1-x)Zn(x)O (0
Dynamical Encoding by Networks of Competing Neuron Groups: Winnerless Competition
M. Rabinovich; A. Volkovskii; P. Lecanda; R. Huerta; H. D. I. Abarbanel; G. Laurent
2001-01-01
Following studies of olfactory processing in insects and fish, we investigate neural networks whose dynamics in phase space is represented by orbits near the heteroclinic connections between saddle regions (fixed points or limit cycles). These networks encode input information as trajectories along the heteroclinic connections. If there are N neurons in the network, the capacity is approximately e(N-1)!, i.e., much
Group dynamics for the acquisition of competences in Project Management
NASA Astrophysics Data System (ADS)
Taguas, E. V.; Aguilar, M. C.; Castillo, C.; Polo, M. J.; Pérez, R.
2012-04-01
The Bologna Process promotes European citizens' employability from teaching fields in the University which implies the design of activities addressed to the development of skills for the labor market and engagement of employers. This work has been conceived for improving the formation of Engineering Project Management through group dynamics focused on: 1) the use of the creativity for solving problems; 2) promoting leadership capacities and social skills in multidisciplinary/multicultural work groups; 3) the ethical, social and environmental compromise; 4) the continuous learning. Different types of activities were designed: short activities of 15-30 minutes where fragments of books or songs are presented and discussed and long activities (2 h) where groups of students take different roles for solving common problems and situations within the Engineering Projects context. An electronic book with the content of the dynamics and the material for the students has been carried out. A sample of 20 students of Electronic Engineering degree which had participated at least in two dynamics, evaluated the utility for improving their formation in Engineering Project Management with a mark of 8.2 (scale 0-10, standard deviation equal to 0.9). On the other hand, the teachers observed how this type of work, promotes the interdisciplinary training and the acquisition of social skills, usually not-included in the objectives of the subjects.
Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2
NASA Astrophysics Data System (ADS)
Maryasov, Alexander G.; Bowman, Michael K.
2012-08-01
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.
Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Li, Yan; Qu, Chunlei; Zhang, Yongsheng; Zhang, Chuanwei
2015-07-01
Synthetic spin-orbit (SO) coupling, an important ingredient for quantum simulation of many exotic condensed matter physics, has recently attracted considerable attention. The static and dynamic properties of a SO-coupled Bose-Einstein condensate (BEC) have been extensively studied in both theory and experiment. Here we numerically investigate the generation and propagation of a dynamical spin-density wave (SDW) in a SO-coupled BEC using a fast moving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to the barrier's velocity while varies slightly with the barrier's peak potential or width. We qualitatively explain the generation of SDW by considering a rectangular barrier in a one-dimensional system. Our results may motivate future experimental and theoretical investigations of rich dynamics in the SO-coupled BEC induced by a moving barrier.
On the spin-axis dynamics of a Moonless Earth
Li, Gongjie; Batygin, Konstantin, E-mail: gli@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, The Institute for Theory and Computation, 60 Garden Street, Cambridge, MA 02138 (United States)
2014-07-20
The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, Earth's obliquity is stabilized by the Moon and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically forced climate change is the rate of chaotic diffusion. Accordingly, here we re-examine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structure in a simple and intuitive manner.
Chaotic dynamics in a periodically driven spin-1 condensate
Cheng Jing
2010-02-15
We use periodically modulated magnetic fields to drive spin-1 Bose-Einstein condensates (BECs) and study the corresponding spin-mixing dynamics. Due to the time-dependent driving, this system permits chaotic dynamics depending on the drive parameters, which could not occur in previous studies. From the investigation of the Poincare sections, we find there exist complex trajectories in the phase space, leading to very complicated structures of the phase space with mixed regular and chaotic regions. By calculating the quasienergy levels of the corresponding Floquet operators, the signatures of quantum chaos are also found in this system. The level spacing distribution is very close to the Poisson distribution or Wigner distribution when the corresponding classical dynamics is regular or chaotic.
Universal dynamic scaling in three-dimensional Ising spin glasses
NASA Astrophysics Data System (ADS)
Liu, Cheng-Wei; Polkovnikov, Anatoli; Sandvik, Anders W.; Young, A. P.
2015-08-01
We use a nonequilibrium Monte Carlo simulation method and dynamical scaling to study the phase transition in three-dimensional Ising spin glasses. The transition point is repeatedly approached at finite velocity v (temperature change versus time) in Monte Carlo simulations starting at a high temperature. This approach has the advantage that the equilibrium limit does not have to be strictly reached for a scaling analysis to yield critical exponents. For the dynamic exponent we obtain z =5.85 (9 ) for bimodal couplings distribution and z =6.00 (10 ) for the Gaussian case. Assuming universal dynamic scaling, we combine the two results and obtain z =5.93 ą0.07 for generic 3D Ising spin glasses.
Computer studies of multiple-quantum spin dynamics
Murdoch, J.B.
1982-11-01
The excitation and detection of multiple-quantum (MQ) transitions in Fourier transform NMR spectroscopy is an interesting problem in the quantum mechanical dynamics of spin systems as well as an important new technique for investigation of molecular structure. In particular, multiple-quantum spectroscopy can be used to simplify overly complex spectra or to separate the various interactions between a nucleus and its environment. The emphasis of this work is on computer simulation of spin-system evolution to better relate theory and experiment.
Same-spin dynamical correlation effects on the electron localization
Pittalis, Stefano; Rozzi, Carlo Andrea
2015-01-01
The Electron Localization Function (ELF) -- as proposed originally by Becke and Edgecombe -- has been widely adopted as a descriptor of atomic shells and covalent bonds. The ELF takes into account the antisymmetry of Fermions but it neglects the multi-reference character of a truly interacting many-electron state. Electron-electron interactions induce, schematically, different kind of correlations: non-dynamical correlations mostly affect stretched molecules and strongly correlated systems; dynamical correlations dominate in weakly correlated systems. Here, within an affordable computational effort, we estimate the effects of same-spin dynamical correlations on the electron localization by means of a simple modification of the ELF.
Spin Transport and Dynamics in Antiferromagnetic Metals and Magnetic Insulators
NASA Astrophysics Data System (ADS)
Swaving, A. C.
2012-03-01
It is demonstrated that in an antiferromagnetic metal a steady-state transport current generates a current-induced out-of-plane spin density, resulting in torques on the magnetization. This spin density is parameterized by a velocity that is proportional to the current. The generalization of the non-linear sigma model equation of motion for antiferromagnetic magnetization dynamics in an antiferromagnetic metal in the presence of a transport current is presented. From this equation of motion a current-induced shift of the spin-wave dispersion is found, as well as current-induced torques that lead to current-driven antiferromagnetic domain wall motion. A key finding is that the form of the current-induced spin density, expressed in terms of the Néčl vector is similar to the current-induced spin density in ferromagnets with the Néčl vector replaced by the magnetization direction. The velocity that characterizes the efficiency of the coupling between current and magnetization is calculated, using linear-response theory in the Boltzmann transport regime. In the absence of dissipation, current-driven antiferromagnetic domain walls are found to move with this characteristic velocity. When magnetization damping is included, the domain wall moves a finite amount and then stops, similar to the intrinsic pinning of current-driven ferromagnetic domain walls. Like in the latter case, including dissipative coupling or non-adiabatic effects between current and magnetization removes this intrinsic pinning. In magnetic insulators there is no transport of electronic charge. Still, there can be transport of spin in the form of spin waves, or, in their quantized form, magnons. Spin transport, carried by quasi-equilibrium magnons, in a magnetic insulator within a Boltzmann transport framework is considered. The spin resistivity of quasi-equilibrium magnons is found to be strongly reduced in comparison with equilibrium magnons, a property that may be useful in designing magnon spintronics applications. The contribution of magnon interactions to their resistivity has been studied for the reason that these dominate in the materials that are experimentally relevant, such as yttrium-iron-garnet (YIG). Firstly, the spin resistivity of a magnon gas using the simplest model, the Heisenberg model, is used. The investigation of material-specific models, in particular for YIG, is then presented. Despite the simplified model, the main qualitative result, the reduction of spin resistivity as a result of enhancing the magnon number by pumping, remains valid. This is because it only depends on the bosonic nature of the magnon excitations that leads to enhanced scattering into states that are already occupied
Dynamics and inertia of skyrmionic spin structures
NASA Astrophysics Data System (ADS)
Büttner, Felix; Moutafis, C.; Schneider, M.; Krüger, B.; Günther, C. M.; Geilhufe, J.; Schmising, C. V. Korff; Mohanty, J.; Pfau, B.; Schaffert, S.; Bisig, A.; Foerster, M.; Schulz, T.; Vaz, C. A. F.; Franken, J. H.; Swagten, H. J. M.; Kläui, M.; Eisebitt, S.
2015-03-01
Skyrmions are topologically protected winding vector fields characterized by a spherical topology. Magnetic skyrmions can arise as the result of the interplay of various interactions, including exchange, dipolar and anisotropy energy in the case of magnetic bubbles and an additional Dzyaloshinskii-Moriya interaction in the case of chiral skyrmions. Whereas the static and low-frequency dynamics of skyrmions are already well under control, their gigahertz dynamical behaviour has not been directly observed in real space. Here, we image the gigahertz gyrotropic eigenmode dynamics of a single magnetic bubble and use its trajectory to experimentally confirm its skyrmion topology. The particular trajectory points to the presence of strong inertia, with a mass much larger than predicted by existing theories. This mass is endowed by the topological confinement of the skyrmion and the energy associated with its size change. It is thereby expected to be found in all skyrmionic structures in magnetic systems and beyond. Our experiments demonstrate that the mass term plays a key role in describing skyrmion dynamics.
The impact of competing zealots on opinion dynamics
NASA Astrophysics Data System (ADS)
Verma, Gunjan; Swami, Ananthram; Chan, Kevin
2014-02-01
An individuals opinion on an issue is greatly impacted by others in his or her social network. Most people are open-minded and ready to change their opinion when presented evidence; however, some are zealots or inflexibles, that is, individuals who refuse to change their opinion while staunchly advocating an opinion in hopes of convincing others. Zealotry is present in opinions of significant personal investment, such as political, religious or corporate affiliation; it tends to be less commonplace in opinions involving rumors or fashion trends. In this paper, we examine the effect that zealots have in a population whose opinion dynamics obey the naming game model. We present numerical and analytical results about the number and nature of steady state solutions, demonstrating the existence of a bifurcation in the space of zealot fractions. Our analysis indicates conditions under which a minority zealot opinion ultimately prevails, and conditions under which neither opinion attains a majority. We also present numerical and simulation analysis of finite populations and on networks with partial connectivity.
Long-term orbital and spin dynamics of Mars
NASA Technical Reports Server (NTRS)
Ward, William R.
1992-01-01
This review of the long-term dynamical behavior of Mars covers secular variations of the orbit, oscillations of the obliquity, and polar wandering. Calculations of the large-scale obliquity oscillations of Mars are updated using the most recent orbit theory and contrasted with the earth. The motion for Mars is characterized by about 100,000-yr oscillations driven by differential spin axis and orbit plane precession rates during which the obliquity may change by as much as about 20 deg. The possible role of spin-orbit secular resonances to the spin axis histories of the earth and Mars is also considered. Numerical integrations of the equations of motion indicate that Mars may have passed through resonance as little as 5 Myr ago and that obliquities approaching about 45 deg could have been achieved during such an event.
Quantum size effects in competing charge and spin orderings of dangling bond wires on Si(001)
Lee, Ji Young; Cho, Jun-Hyung; Zhang, Zhenyu
2009-01-01
Using spin-polarized density-functional theory calculations, we investigate the competition between charge and spin orderings in dangling-bond DB wires of increasing lengths fabricated on an H-terminated Si 001 surface. For wires containing less than ten DBs as studied in recent experiments, we find antiferromagnetic AF ordering to be energetically much more favorable than charge ordering. The energy preference of AF ordering shrinks in an oscillatory way as the wire length increases and preserves its sign even for DB wires of infinite length. The oscillatory behavior can be attributed to quantum size effects as the DB electrons fill discrete quantum levels. The predicted AF ordering is in startling contrast with the prevailing picture of charge ordering due to Jahn-Teller distortion or Peierls instability for wires of finite or infinite lengths, respectively.
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.
Spin transport and magnetization dynamics in various magnetic systems
NASA Astrophysics Data System (ADS)
Zhang, Shulei
The general theme of the thesis is the interplay between magnetization dynamics and spin transport. The main presentation is divided into three parts. The first part is devoted to deepening our understanding on magnetic damping of ferromagnetic metals, which is one of the long-standing issues in conventional spintronics that has not been completely understood. For a nonuniformly-magnetized ferromagnetic metal, we find that the damping is nonlocal and is enhanced as compared to that in the uniform case. It is therefore necessary to generalize the conventional Landau-Lifshitz-Gilbert equation to include the additional damping. In a different vein, the decay mechanism of the uniform precession mode has been investigated. We point out the important role of spin-conserving electron-magnon interaction in the relaxation process by quantitatively examining its contribution to the ferromagnetic resonance linewidth. In the second part, a transport theory is developed for magnons which, in addition to conduction electrons, can also carry and propagate spin angular momentum via the magnon current. We demonstrate that the mutual conversion of magnon current and spin current may take place at magnetic interfaces. We also predict a novel magnon-mediated electric drag effect in a metal/magnetic-insulator/metal trilayer structure. This study may pave the way to the new area of insulator-based spintronics. In the third part of thesis, particular attention is paid to the influence the spin orbit coupling on both charge and spin transport. We theoretically investigate magnetotransport anisotropy and the conversion relations of spin and charge currents in various magnetic systems, and apply our results to interpret recent experiments.
Spin/Orbital Dynamics in Titanates and Vanadates
NASA Astrophysics Data System (ADS)
Ulrich, Clemens
2004-03-01
In cubic perovskite systems like the titanates and vanadates, the d-valence electrons exhibit a multitude of competing many-body ground states where quantum fluctuations play an important role. Neutron spectroscopy in the Mott-Hubbard insulator LaTiO3 has revealed a reduced magnetic moment and a nearly isotropic spin wave dispersion [1]. These results are difficult to reconcile with predictions based on the standard Goodenough-Kanamori rules. Due to the small or even absent distortion of the TiO6 octahedra, the t_2g levels are fully degenerate. Theoretical considerations indicate that these orbitals are only weakly ordered or may even form a coherent orbital-liquid ground state [2]. Our investigations of the ferromagnetic Mott insulator YTiO3 have shown, that even in a system with Jahn-Teller distortion, orbital zero-point fluctuations have to be taken into account [3]. YVO3 undergoes a series of temperature induced phase transitions between states with different spin and orbital ordering patterns, i.e. a C-type and a G-type magnetic phase [4]. The C-type magnetic phase has a highly unusual magnetic structure and spin wave spectrum than cannot be understood within a conventional spin wave theory. A good description of the neutron scattering data is obtained by introducing quasi-1D orbital fluctuations [5]. This leads to the tentative identification of this phase with a previously theoretically proposed 'orbital Peierls state'. [1] B. Keimer et al., Phys. Rev. Lett. 85, 3946 (2000). [2] G. Khaliullin and S. Maekawa, Phys. Rev. Lett. 85, 3950 (2000). [3] C. Ulrich et al., Phys. Rev. Lett. 89, 167202 (2002). [4] Y. Ren et al., Nature 396, 441 (1998). [5] C. Ulrich et al., cond.-mat./0211589; accepted for publication in Phys. Rev. Lett.
Dynamics, crystallization and structures in colloid spin coating
Moorthi Pichumani; Payam Bagheri; Kristin M. Poduska; Wenceslao Gonzalez-Vinas; Anand Yethiraj
2013-01-10
Spin coating is an out-of-equilibrium technique for producing polymer films and colloidal crystals quickly and reproducibly. In this review, we present an overview of theoretical and experimental studies of the spin coating of colloidal suspensions. The dynamics of the spin coating process is discussed first, and we present insights from both theory and experiment. A key difference between spin coating with polymer solutions and with monodisperse colloidal suspensions is the emergence of long range (centimeter scale) orientational correlations in the latter. We discuss experiments in different physical regimes that shed light on the many unusual partially-ordered structures that have long-range orientational order, but no long-range translational order. The nature of these structures can be tailored by adding electric or magnetic fields during the spin coating procedure. These partially-ordered structures can be considered as model systems for studying the fundamentals of poorly crystalline and defect-rich solids, and they can also serve as templates for patterned and/or porous optical and magnetic materials.
Coherent spinrotational 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 spinrotation coupling in the coherent rotational dynamics of oxygen. The decay rate of spinrotational 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.
NASA Astrophysics Data System (ADS)
Kurihara, T.; Nakamura, K.; Yamaguchi, K.; Sekine, Y.; Saito, Y.; Nakajima, M.; Oto, K.; Watanabe, H.; Suemoto, T.
2014-10-01
We demonstrate enhancement of the spin precession of orthoferrite ErFeO3 using the magnetic near-field produced by a split-ring resonator (SRR), using the terahertz pump-optical Faraday probe measurement. The precession amplitude was enhanced by 8 times when the resonance frequency of spin precession was close to the magnetic resonance of SRR. The time evolution of spin precession was successfully reproduced by a coupled spin- and SRR-resonance model mediated by the magnetic near-field. It is suggested that optimization of the metamaterial structure would further increase the enhancement factor, leading to the nonlinear control of spin dynamics using terahertz radiation.
Spin-motive Force Induced by Domain Wall Dynamics in the Antiferromagnetic Spin Valve
NASA Astrophysics Data System (ADS)
Sugano, Ryoko; Ichimura, Masahiko; Takahashi, Saburo; Maekawa, Sadamichi; Crest Collaboration
2014-03-01
In spite of no net magnetization in antiferromagnetic (AF) textures, the local magnetic properties (Neel magnetization) can be manipulated in a similar fashion to ferromagnetic (F) ones. It is expected that, even in AF metals, spin transfer torques (STTs) lead to the domain wall (DW) motion and that the DW motion induces spin-motive force (SMF). In order to study the Neel magnetization dynamics and the resultant SMF, we treat the nano-structured F1/AF/F2 junction. The F1 and F2 leads behave as a spin current injector and a detector, respectively. Each F lead is fixed in the different magnetization direction. Torsions (DW in AF) are introduced reflecting the fixed magnetization of two F leads. We simulated the STT-induced Neel magnetization dynamics with the injecting current from F1 to F2 and evaluate induced SMF. Based on the adiabatic electron dynamics in the AF texture, Langevin simulations are performed at finite temperature. This research was supported by JST, CREST, Japan.
Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig
NASA Technical Reports Server (NTRS)
Morrison, Carlos R.; Provenza, Andrew; Kurkov, Anatole; Mehmed, Oral; Johnson, Dexter; Montague, Gerald; Duffy, Kirsten; Jansen, Ralph
2005-01-01
The Five-Axis, Three-Magnetic-Bearing Dynamic Spin Rig is an apparatus for vibration testing of turbomachine blades in a vacuum at rotational speeds from 0 to 40,000 rpm. This rig includes (1) a vertically oriented shaft on which is mounted an assembly comprising a rotor holding the blades to be tested, (2) two actively controlled heteropolar radial magnetic bearings at opposite ends of the shaft, and (3) an actively controlled magnetic thrust bearing at the upper end of the shaft. This rig is a more capable successor to a prior apparatus, denoted the Dynamic Spin Rig (DSR), that included a vertically oriented shaft with a mechanical thrust bearing at the upper end and a single actively controlled heteropolar radial magnetic bearing at the lower end.
NASA Astrophysics Data System (ADS)
Dickel, Christian; Foletti, Sandra; Yacoby, Amir; Mahalu, Diana; Umansky, Vladimir; Bluhm, Hendrik
2014-03-01
In GaAs-based double quantum dot spin qubits, nuclear spins have been used for qubit control, but are also an important source of decoherence. The S and T+ levels exhibit a small avoided crossing as a function of detuning. It has been used for S-T+ qubit control and for dynamic nuclear polarization (DNP). The transition matrix element contains the nuclear Overhauser fields perpendicular to the external B-field and spin-orbit coupling. We show, both theoretically and experimentally, that nuclear spin dynamics can be seen in the temporal correlation of single-shot measurements after Landau-Zener sweeps across this transition. A semi-classical model of the nuclear spins is sufficient. The dynamics consist of the relative Larmor precession of the three GaAs nuclear spin species in the external B-field and dephasing of the oscillations due to local field fluctuations. Theoretically, it is expected that the absolute Larmor precessions also become visible in the presence of spin-orbit coupling. This can be used to qualitatively and quantitatively observe spin-orbit coupling and to distinguish it from the nuclear spin contribution. Understanding these dynamics is relevant for the fidelity of S-T+ qubit operations and the effectiveness of DNP.
MEMBRANE PROTEIN STRUCTURE AND DYNAMICS STUDIED BY SITE-DIRECTED SPIN LABELING ESR
Steinhoff, Heinz-Jürgen
CHAPTER 5 MEMBRANE PROTEIN STRUCTURE AND DYNAMICS STUDIED BY SITE-DIRECTED SPIN LABELING ESR Enrica of spin-labeled variants of a given protein allows defining elements of secondary structure, including) Membrane protein structure and dynamics studied by site-directed spin labeling ESR. In: Hemminga, M
Nuclear spin dynamics in parabolic quantum wells Ionel Tifrea* and Michael E. Flatte
Flatte, Michael E.
Nuclear spin dynamics in parabolic quantum wells Ionel T¸ifrea* and Michael E. Flatte´ Department March 2004 We present a detailed analytical and numerical analysis of the nuclear spin dynamics of the electronic wave function in small electric fields. The nuclear spin relaxation via the hyperfine interaction
Mean-field dynamics of the spin-magnetization coupling in ferromagnetic materials
the Landau-Lifchitz-Gilbert equation and the spin transfer torque. The method is general and systematic coupling, the spin angular momentum is trans- ferred to magnetization dynamics by a mechanism known as spin to magne- tization dynamics given by the Landau-Lifshitz-Gilbert (LLG) equation [21], [22] to further study
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).
Dynamics and stability of spinning flexible space tether systems
NASA Astrophysics Data System (ADS)
Tyc, George
This dissertation focuses on a detailed dynamical investigation of a previously unexplored tether configuration that involves a spinning two-body tethered system with flexible appendages on each end-body where the spin axis is nominally aligned along the tether. The original motivation for this work came after the flight of the first Canadian sub-orbital tether mission OEDIPUS-A in 1989 which employed this spinning tethered configuration. To everyone's surprise, one of the end-bodies was observed to exhibit a rapid divergence of its nutation angle. It was clear after this flight that there were some fundamental mechanisms associated with the interaction between the tether and the end-body that were not fully understood at that time. Hence, a Tether Dynamics Experiment (TDE) was formed and became a formal part of the scientific agenda for the follow-on mission OEDIPUS-C which flew in 1995. This dissertation describes the work that was conducted as part of the TDE and involves: theoretical investigations into the dynamics of this spinning tethered flexible body system; ground testing to validate the models and establish the tether properties; application of the models to develop a stabilization approach for OEDIPUS-C, and comparisons between theory and flight data from both OEDIPUS-A and OEDIPUS-C. Nonlinear equations of motion are developed for a spinning tethered system where the tether could be either spinning with the end-bodies or attached to small de-spun platforms on the end-bodies. Since the tether used for the OEDIPUS missions is not a string, as is often assumed, but rather a wire that has some bending stiffness, albeit small, the tether bending was also taken into account in the formulation. Two sets of ground tests are described that were used to validate the stability conditions and gain confidence in the mathematical models. One set involved hanging a body by a tether and spinning at different speeds to investigate the end-body stability. The other set used a tethered spinning end-body suspended on a set of gimbals and had a means to measure the end-body attitude in real-time. The mathematical models were then applied to investigate suitable stabilization approaches for OEDIPUS-C. In general, very good agreement was found between the theory and both the ground experiments and flight data. One of the surprising results from this work is the significance of the tether root bending effects. It is shown that it is this subtle effect that caused the rapid divergence in one of the end-bodies in the OEDIPUS-A mission which was unstable. For OEDIPUS-C, the situation was rectified by adding the booms to ensure "short term" stability and also by not spinning as rapidly. The OEDIPUS-C was very successful as all systems worked as planned and hence a superb set of flight dynamics data was collected. (Abstract shortened by UMI.)
Dynamics of flexible spinning satellites with radial wire antennas
NASA Technical Reports Server (NTRS)
Longman, R. W.; Fedor, J. V.
1976-01-01
A dynamic analysis is presented for a spin-stabilized spacecraft employing four radial wire antennas with tip masses. The satellite is modelled as a 14-degree-of-freedom system, and the linearized equations of motion are found. The lowest-order vibrational modes and natural frequencies of the gyroscopically coupled system are then determined. Because the satellite spin rate is decreased by antenna deployment, a spin-up maneuver is needed. The response of the time-varying mode equations during spin-up is found for the planar modes in terms of Bessel functions and a Struve function of order -0.25. The particular solution is expressed in various forms, including an infinite series of Bessel functions and a particularly useful asymptotic expansion. An error formula for the latter is derived, showing that it gives good accuracy. A simple approximation to the complementary function is obtained using the Wenzel-Kramers-Brillouin method, and the phase error in the approximation is shown to be small.
Spin Dynamics in InAs Quantum Dots
NASA Astrophysics Data System (ADS)
Whitaker, Janica; Bracker, Allan; Gammon, Daniel; Kennedy, Thomas
2006-03-01
Spin coherence in InAs Self-Assemble Quantum Dots (SAQD's) could be useful for optical delay lines and quantum information technology. Very uniform dots and a very accurate measurement of dephasing processes are required to realize these possibilities. To this effect we report decoherence times in InAs SAQD. Here we describe measurements of spin dynamics from a 17 layered nominally undoped wafer of InAs SAQDs with a varying dot-size. We used Time Resolved Kerr Rotation (TRKR) for a wavelength resonant with the 3D InAs Stranski-Krastanow strain mediated quantum dots. Response is observed from 0 to 5 T that corresponds to a freely precessing spin with g = 0.45, a 1.2 ns lifetime at B=0 that decreases with B, and a sine-like phase. We attribute this spin to an electron from either the ground state of a negative trion or the excited state of a positive trion. The dots are dots unintentionally doped from background doping in the MBE chamber. Work supported in part by ONR, NSA/ARO, and DARPA/QUIST. JW is an NRC/NRL Postdoctoral Research Associate.
Time domain mapping of spin torque oscillators dynamics
NASA Astrophysics Data System (ADS)
Zhang, Jieyi; Chen, Yujin; Rowlands, Graham; Krivorotov, Ilya; Braganca, Patrick; Childress, Jeff; Gurney, Bruce; UC Irvine, HGST; Cornell Univ Collaboration
2015-03-01
Time domain measurements of spin torque oscillators (STOs) offer important insights into the magnetization dynamics under the action of spin torque. We use the time domain data to map statistical distributions of the STO free layer trajectories and analyze them in the framework of the Fokker-Planck effective energy approach. We make time-resolved measurements of the microwave voltage signal generated by an STO based on a 90 nm circular nanopillar patterned from IrMn/ Co/CoFe/ CoFeGe/ CoFe/ Cu/ CoFe/ CoFeGe/ CoFe multilayer. Based on our time domain data and the angular dependence of giant magneto-resistance of the device, we map out dynamic trajectories of the free layer. We then apply the Fokker-Planck approach to calculate spin torque dependent STO effective energy Eeff from the experimentally measured statistical distributions of the free layer trajectories. We compare the measured Eeff to that calculated in the macrospin approximation and discuss how such a comparison can be used for quantification of non-linear damping in the high-amplitude regime of STO operation.
Dynamics Of Proton Spin : Role Of $qqq$ Force
A. N. Mitra
2007-12-18
The analytic structure of the $qqq$ wave function, obtained recently in the high momentum regime of QCD, is employed for the formulation of baryonic transition amplitudes via quark loops. A new aspect of this study is the role of a direct ($Y$-shaped, Mercedes-Benz type) $qqq$ force in generating the $qqq$ wave function. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. The dynamics of this 3-body force shows up through a characteristic singularity in the hypergeometric differential equation for the 3D wave function $\\phi$, corresponding to a $negative$ eigenvalue of the spin operator $i \\sigma_1.\\sigma_2\\times \\sigma_3$ which is an integral part of the $qqq$ force. As a first application of this wave function to the problem of the proton spin anomaly, the two-gluon contribution to the anomaly yields an estimate of the right sign, although somewhat smaller in magnitude. Keywords: 3bodyforce; proton-spin; 2gluon anomaly; fractional correction $\\theta$
Coherent spin-rotational dynamics of oxygen super rotors
Milner, Alexander A; Milner, Valery
2014-01-01
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 $N \\approx 50$ 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 $N\\leqslant 109$ 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-rotation coherence due to collisions is measured as a function of the molecular angular momentum and explained in terms of the general scaling law. We find that at high values of $N$, the rotational decoherence of oxygen is much faster than t...
Orbital and spin dynamics of intraband electrons in quantum rings driven by twisted light.
Quinteiro, G F; Tamborenea, P I; Berakdar, J
2011-12-19
We theoretically investigate the effect that twisted light has on the orbital and spin dynamics of electrons in quantum rings possessing sizable Rashba spin-orbit interaction. The system Hamiltonian for such a strongly inhomogeneous light field exhibits terms which induce both spin-conserving and spin-flip processes. We analyze the dynamics in terms of the perturbation introduced by a weak light field on the Rasha electronic states, and describe the effects that the orbital angular momentum as well as the inhomogeneous character of the beam have on the orbital and the spin dynamics. PMID:22274257
Quantum transport and spin dynamics on shearless tori.
Kudo, K; Monteiro, T S
2008-05-01
We investigate quantum dynamics in phase-space regions containing "shearless tori." We show that the properties of these peculiar classical phase-space structures-important to the dynamics of tokamaks-may be exploited for quantum information applications. In particular we show that shearless tori permit the nondispersive transmission of localized wave packets. The quantum many-body Hamiltonian of a Heisenberg ferromagnetic spin chain, subjected to an oscillating magnetic field, can be reduced to a classical one-body "image" dynamical system which is the well-studied Harper map. The Harper map belongs to a class of Hamiltonian systems (nontwist maps) which contain shearless tori. We show that a variant with sinusoidal time driving "driven Harper model" produces shearless tori which are especially suitable for quantum state transfer. The behavior of the concurrence is investigated as an example. PMID:18643121
Dynamic switching of the spin circulation in tapered magnetic nanodisks.
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
Effect of electron spin dynamics on solid-state dynamic nuclear polarization performance.
Siaw, Ting Ann; Fehr, Matthias; Lund, Alicia; Latimer, Allegra; Walker, Shamon A; Edwards, Devin T; Han, Song-I
2014-09-21
For the broadest dissemination of solid-state dynamic nuclear polarization (ssDNP) enhanced NMR as a material characterization tool, the ability to employ generic mono-nitroxide radicals as spin probes is critical. A better understanding of the factors contributing to ssDNP efficiency is needed to rationally optimize the experimental condition for the practically accessible spin probes at hand. This study seeks to advance the mechanistic understanding of ssDNP by examining the effect of electron spin dynamics on ssDNP performance at liquid helium temperatures (4-40 K). The key observation is that bi-radicals and mono-radicals can generate comparable nuclear spin polarization at 4 K and 7 T, which is in contrast to the observation for ssDNP at liquid nitrogen temperatures (80-150 K) that finds bi-radicals to clearly outperform mono-radicals. To rationalize this observation, we analyze the change in the DNP-induced nuclear spin polarization (Pn) and the characteristic ssDNP signal buildup time as a function of electron spin relaxation rates that are modulated by the mono- and bi-radical spin concentration. Changes in Pn are consistent with a systematic variation in the product of the electron spin-lattice relaxation time and the electron spin flip-flop rate that constitutes an integral saturation factor of an inhomogeneously broadened EPR spectrum. We show that the comparable Pn achieved with both radical species can be reconciled with a comparable integral EPR saturation factor. Surprisingly, the largest Pn is observed at an intermediate spin concentration for both mono- and bi-radicals. At the highest radical concentration, the stronger inter-electron spin dipolar coupling favors ssDNP, while oversaturation diminishes Pn, as experimentally verified by the observation of a maximum Pn at an intermediate, not the maximum, microwave (?w) power. At the maximum ?w power, oversaturation reduces the electron spin population differential that must be upheld between electron spins that span a frequency difference matching the (1)H NMR frequency-characteristic of the cross effect DNP. This new mechanistic insight allows us to rationalize experimental conditions where generic mono-nitroxide probes can offer competitive ssDNP performance to that of custom designed bi-radicals, and thus helps to vastly expand the application scope of ssDNP for the study of functional materials and solids. PMID:24968276
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.
Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors
NASA Astrophysics Data System (ADS)
Yin, Z. P.; Haule, K.; Kotliar, G.
2014-11-01
The symmetry of the wavefunction describing the Cooper pairs is one of the most fundamental quantities in a superconductor, but for iron-based superconductors it has proved to be problematic to determine, owing to their complex multi-band nature. Here we use a first-principles many-body method, including the two-particle vertex function, to study the spin dynamics and the superconducting pairing symmetry of a large number of iron-based compounds. Our results show that these high-temperature superconductors have both dispersive high-energy and strong low-energy commensurate or nearly commensurate spin excitations, which play a dominant role in Cooper pairing. We find three closely competing types of pairing symmetries, which take a very simple form in the space of active iron 3d orbitals, and differ only in the relative quantum mechanical phase of the xz, yz and xy orbital components of the Cooper pair wavefunction. The extensively discussed s+- symmetry appears when contributions from all orbitals have equal sign, whereas a novel orbital-antiphase s+- symmetry emerges when the xy orbital has an opposite sign to the xz and yz orbitals. This orbital-antiphase pairing symmetry agrees well with the angular variation of the superconducting gaps in LiFeAs (refs , ).
S U (3 ) Semiclassical Representation of Quantum Dynamics of Interacting Spins
NASA Astrophysics Data System (ADS)
Davidson, Shainen M.; Polkovnikov, Anatoli
2015-01-01
We present a formalism for simulating quantum dynamics of lattice spin-1 systems by first introducing local hidden variables and then doing semiclassical (truncated Wigner) approximation in the extended phase space. In this way, we exactly take into account the local on-site Hamiltonian and approximately treat spin-spin interactions. In particular, we represent each spin with eight classical S U (3 ) variables. Three of them represent the usual spin components and five others are hidden variables representing local spin-spin correlations. We compare our formalism with exact quantum dynamics of fully connected spin systems and find very good agreement. As an application, we discuss quench dynamics of a Bose-Hubbard model near the superfluid-insulator transition for a 3D lattice system consisting of 1000 sites.
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.
Spin-state configuration induced faster spin dynamics in epitaxial La1-xSrxCoO3 thin films
NASA Astrophysics Data System (ADS)
Cui, W. Y.; Li, P.; Bai, H. L.
2015-05-01
Two important features: spin-state configuration and spin dynamics in phase-separated ferromagnetic/spin-glass epitaxial La1-xSrxCoO3 thin films (x=0.07, 0.17, 0.26, 0.30, 0.40, 0.60) have been investigated and elaborated, proved by both magnetic analyses and first principle calculations. The configuration with high-spin (HS) state Co3+ and low-spin (LS) state Co4+ is considered to be the most stable spin-state configuration for La1-xSrxCoO3 at ground state, which was demonstrated by calculating the magnetic moments of La1-xSrxCoO3, as well as first principle calculation. The stretched Co-O bond by Sr doping causes the decrease of crystal field splitting, resulting in the HS state Co3+ and LS state Co4+. The spin dynamics in the La1-xSrxCoO3 thin films was found to be faster than the classic spin-glass compounds, which is attributed to the higher-spin Co3+, and rather smaller ferromagnetic cluster size (~2.16 to ~21.5 nm) in the epitaxial films than that in referenced polycrystalline compounds (~35 to ~240 nm).
Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling
Yang, Luyi; Orenstein, J.; Lee, Dung-Hai
2010-09-27
We introduce and solve a semiclassical random walk (RW) model that describes the dynamics of spin polarization waves in zinc-blende semiconductor quantum wells. We derive the dispersion relations for these waves, including the Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the effects of an electric field applied parallel to the spin polarization wave vector. In agreement with calculations based on quantum kinetic theory [P. Kleinert and V. V. Bryksin, Phys. Rev. B 76, 205326 (2007)], the RW approach predicts that spin waves acquire a phase velocity in the presence of the field that crosses zero at a nonzero wave vector, q{sub 0}. In addition, we show that the spin-wave decay rate is independent of field at q{sub 0} but increases as (q-q{sub 0}){sup 2} for q {ne} q{sub 0}. These predictions can be tested experimentally by suitable transient spin grating experiments.
Random walk approach to spin dynamics in a two-dimensional electron gas with spin-orbit coupling
NASA Astrophysics Data System (ADS)
Yang, Luyi; Orenstein, J.; Lee, Dung-Hai
2010-10-01
We introduce and solve a semiclassical random walk (RW) model that describes the dynamics of spin polarization waves in zinc-blende semiconductor quantum wells. We derive the dispersion relations for these waves, including the Rashba, linear and cubic Dresselhaus spin-orbit interactions, as well as the effects of an electric field applied parallel to the spin polarization wave vector. In agreement with calculations based on quantum kinetic theory [P. Kleinert and V. V. Bryksin, Phys. Rev. B 76, 205326 (2007)10.1103/PhysRevB.76.205326], the RW approach predicts that spin waves acquire a phase velocity in the presence of the field that crosses zero at a nonzero wave vector, q0 . In addition, we show that the spin-wave decay rate is independent of field at q0 but increases as (q-q0)2 for q?q0 . These predictions can be tested experimentally by suitable transient spin grating experiments.
Local factorisation of the dynamics of quantum spin systems
Sven Bachmann; Andreas Bluhm
2015-08-24
Motivated by the study of area laws for the entanglement entropy of gapped ground states of quantum spin systems and their stability, we prove that the unitary cocycle generated by a local time-dependent Hamiltonian can be approximated, for any finite set $X$, by a tensor product of the corresponding unitaries in $X$ and its complement, multiplied by a dynamics strictly supported in the neighbourhood of the surface $\\partial X$. The error decays almost exponentially in the size of the neighbourhood and grows with the square of the area~$\\vert \\partial X\\vert^2$.
Spin-down dynamics of magnetized solar-type stars
Oglethorpe, R. L. F.; Garaud, P.
2013-12-01
It has long been known that solar-type stars undergo significant spin-down, via magnetic braking, during their main-sequence lifetimes. However, magnetic braking only operates on the surface layers; it is not yet completely understood how angular momentum is transported within the star and how rapidly the spin-down information is communicated to the deep interior. In this work, we use insight from recent progress in understanding internal solar dynamics to model the interior of other solar-type stars. We assume, following Gough and McIntyre, that the bulk of the radiation zone of these stars is held in uniform rotation by the presence of an embedded large-scale primordial field, confined below a stably stratified, magnetic-free tachocline by large-scale meridional flows downwelling from the convection zone. We derive simple equations to describe the response of this model interior to spin-down of the surface layers, which are identical to the two-zone model of MacGregor and Brenner, with a coupling timescale proportional to the local Eddington-Sweet timescale across the tachocline. This timescale depends both on the rotation rate of the star and on the thickness of the tachocline, and it can vary from a few hundred thousand years to a few Gyr, depending on stellar properties. Qualitative predictions of the model appear to be consistent with observations, although they depend sensitively on the assumed functional dependence of the tachocline thickness on the stellar rotation rate.
Spin-down Dynamics of Magnetized Solar-type Stars
NASA Astrophysics Data System (ADS)
Oglethorpe, R. L. F.; Garaud, P.
2013-12-01
It has long been known that solar-type stars undergo significant spin-down, via magnetic braking, during their main-sequence lifetimes. However, magnetic braking only operates on the surface layers; it is not yet completely understood how angular momentum is transported within the star and how rapidly the spin-down information is communicated to the deep interior. In this work, we use insight from recent progress in understanding internal solar dynamics to model the interior of other solar-type stars. We assume, following Gough & McIntyre, that the bulk of the radiation zone of these stars is held in uniform rotation by the presence of an embedded large-scale primordial field, confined below a stably stratified, magnetic-free tachocline by large-scale meridional flows downwelling from the convection zone. We derive simple equations to describe the response of this model interior to spin-down of the surface layers, which are identical to the two-zone model of MacGregor & Brenner, with a coupling timescale proportional to the local Eddington-Sweet timescale across the tachocline. This timescale depends both on the rotation rate of the star and on the thickness of the tachocline, and it can vary from a few hundred thousand years to a few Gyr, depending on stellar properties. Qualitative predictions of the model appear to be consistent with observations, although they depend sensitively on the assumed functional dependence of the tachocline thickness on the stellar rotation rate.
Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots
NASA Astrophysics Data System (ADS)
Nichol, John M.; Harvey, Shannon P.; Shulman, Michael D.; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I.; Halperin, Bertrand I.; Yacoby, Amir
2015-07-01
The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin-orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron-nuclear system, despite weak spin-orbit coupling in GaAs. Using Landau-Zener sweeps to measure static and dynamic properties of the electron spin-flip probability, we observe that the size of the spin-orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin-orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin-orbit coupling in central-spin systems.
Surface Contributions to Mn(2+) Spin Dynamics in Colloidal Doped Quantum Dots.
Schimpf, Alina M; Ochsenbein, Stefan T; Gamelin, Daniel R
2015-02-01
Colloidal impurity-doped quantum dots (QDs) are attractive model systems for testing the fundamental spin properties of semiconductor nanostructures relevant to future spin-based information processing technologies. Although static spin properties of this class of materials have been studied extensively in recent years, their spin dynamics remain largely unexplored. Here we use pulsed electron paramagnetic resonance (pEPR) spectroscopy to probe the spin relaxation dynamics of colloidal Mn(2+)-doped ZnO, ZnSe, and CdSe quantum dots in the limit of one Mn(2+) per QD. pEPR spectroscopy is particularly powerful for identifying the specific nuclei that accelerate electron spin relaxation in these QDs. We show that the spin-relaxation dynamics of these colloidal QDs are strongly influenced by dipolar coupling with proton nuclear spins outside the QDs and especially those directly at the QD surfaces. Using this information, we demonstrate that spin-relaxation times can be elongated significantly via ligand (or surface) deuteration or shell growth, providing two tools for chemical adjustment of spin dynamics in these nanomaterials. These findings advance our understanding of the spin properties of solution-grown semiconductor nanostructures relevant to spin-based information technologies. PMID:26261963
Quenching of dynamic nuclear polarization by spinorbit coupling in GaAs quantum dots
Nichol, John M.; Harvey, Shannon P.; Shulman, Michael D.; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I.; Halperin, Bertrand I.; Yacoby, Amir
2015-01-01
The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spinorbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electronnuclear system, despite weak spinorbit coupling in GaAs. Using LandauZener sweeps to measure static and dynamic properties of the electron spinflip probability, we observe that the size of the spinorbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spinorbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spinorbit coupling in central-spin systems. PMID:26184854
Quenching of dynamic nuclear polarization by spin-orbit coupling in GaAs quantum dots.
Nichol, John M; Harvey, Shannon P; Shulman, Michael D; Pal, Arijeet; Umansky, Vladimir; Rashba, Emmanuel I; Halperin, Bertrand I; Yacoby, Amir
2015-01-01
The central-spin problem is a widely studied model of quantum decoherence. Dynamic nuclear polarization occurs in central-spin systems when electronic angular momentum is transferred to nuclear spins and is exploited in quantum information processing for coherent spin manipulation. However, the mechanisms limiting this process remain only partially understood. Here we show that spin-orbit coupling can quench dynamic nuclear polarization in a GaAs quantum dot, because spin conservation is violated in the electron-nuclear system, despite weak spin-orbit coupling in GaAs. Using Landau-Zener sweeps to measure static and dynamic properties of the electron spin-flip probability, we observe that the size of the spin-orbit and hyperfine interactions depends on the magnitude and direction of applied magnetic field. We find that dynamic nuclear polarization is quenched when the spin-orbit contribution exceeds the hyperfine, in agreement with a theoretical model. Our results shed light on the surprisingly strong effect of spin-orbit coupling in central-spin systems. PMID:26184854
Information-flux approach to multiple-spin dynamics
NASA Astrophysics Data System (ADS)
di Franco, C.; Paternostro, M.; Palma, G. M.; Kim, M. S.
2007-10-01
We introduce and formalize the concept of information flux in a many-body register as the influence that the dynamics of a specific element receive from any other element of the register. By quantifying the information flux in a protocol, we can design the most appropriate initial state of the system and, noticeably, the distribution of coupling strengths among the parts of the register itself. The intuitive nature of this tool and its flexibility, which allow for easily manageable numerical approaches when analytic expressions are not straightforward, are greatly useful in interacting many-body systems such as quantum spin chains. We illustrate the use of this concept in quantum cloning and quantum state transfer and we also sketch its extension to nonunitary dynamics.
Dynamics of artificial spin ice: a continuous honeycomb network
NASA Astrophysics Data System (ADS)
Shen, Yichen; Petrova, Olga; Mellado, Paula; Daunheimer, Stephen; Cumings, John; Tchernyshyov, Oleg
2012-03-01
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 and absorption of domain walls in the sites of the lattice, and their propagation in its links. These domain walls carry two natural units of magnetic charge, whereas sites of the lattice contain a unit magnetic charge. Magnetostatic Coulomb forces between these charges play a major role in the physics of the system, as does quenched disorder caused by imperfections of the lattice. We identify and describe different regimes of magnetization reversal in an applied magnetic field determined by the orientation of the applied field with respect to the initial magnetization. One of the regimes is characterized by magnetic avalanches with a 1/n distribution of lengths.
Dynamic clustering and dispersion of lipid rafts contribute to fusion competence of myogenic cells
Mukai, Atsushi; Kurisaki, Tomohiro; Sato, Satoshi B.; Kobayashi, Toshihide; Kondoh, Gen; Hashimoto, Naohiro
2009-10-15
Recent research indicates that the leading edge of lamellipodia of myogenic cells (myoblasts and myotubes) contains presumptive fusion sites, yet the mechanisms that render the plasma membrane fusion-competent remain largely unknown. Here we show that dynamic clustering and dispersion of lipid rafts contribute to both cell adhesion and plasma membrane union during myogenic cell fusion. Adhesion-complex proteins including M-cadherin, {beta}-catenin, and p120-catenin accumulated at the leading edge of lamellipodia, which contains the presumptive fusion sites of the plasma membrane, in a lipid raft-dependent fashion prior to cell contact. In addition, disruption of lipid rafts by cholesterol depletion directly prevented the membrane union of myogenic cell fusion. Time-lapse recording showed that lipid rafts were laterally dispersed from the center of the lamellipodia prior to membrane fusion. Adhesion proteins that had accumulated at lipid rafts were also removed from the presumptive fusion sites when lipid rafts were laterally dispersed. The resultant lipid raft- and adhesion complex-free area at the leading edge fused with the opposing plasma membrane. These results demonstrate a key role for dynamic clustering/dispersion of lipid rafts in establishing fusion-competent sites of the myogenic cell membrane, providing a novel mechanistic insight into the regulation of myogenic cell fusion.
Dynamical spin structure factor of one-dimensional interacting fermions
NASA Astrophysics Data System (ADS)
Zyuzin, Vladimir A.; Maslov, Dmitrii L.
2015-02-01
We revisit the dynamic spin susceptibility ? (q ,? ) of one-dimensional interacting fermions. To second order in the interaction, backscattering results in a logarithmic correction to ? (q ,? ) at q ?kF , even if the single-particle spectrum is linearized near the Fermi points. Consequently, the dynamic spin structure factor Im ? (q ,? ) is nonzero at frequencies above the single-particle continuum. In the boson language, this effect results from the marginally irrelevant backscattering operator of the sine-Gordon model. Away from the threshold, the high-frequency tail of Im ? (q ,? ) due to backscattering is larger than that due to finite mass by a factor of kF/q . We derive the renormalization group equations for the coupling constants of the g -ology model at finite ? and q and find the corresponding expression for ? (q ,? ) , valid to all orders in the interaction but not in the immediate vicinity of the continuum boundary, where the finite-mass effects become dominant.
Phonon-magnon interactions in BCC iron: A combined molecular and spin dynamics study
Perera, Meewanage Dilina N; Landau, David P; Nicholson, Don M; Stocks, George Malcolm; Eisenbach, Markus; Yin, Junqi; Brown, Greg
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.
Phonon-magnon interactions in body centered cubic iron: A combined molecular and spin dynamics study
Perera, Dilina Landau, David P.; Nicholson, Don M.; Malcolm Stocks, G.; Eisenbach, Markus; Yin, Junqi; Brown, Gregory
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.
NASA Astrophysics Data System (ADS)
Taguchi, Katsuhisa; Shintani, Kunitaka; Tanaka, Yukio
2015-07-01
We theoretically study the spin and charge generations along with the electron transport on a disordered surface of a doped three-dimensional topological insulator/magnetic insulator junction by using Green's function techniques. We find that the spin and charge currents are induced by not only local, but also nonlocal magnetization dynamics through nonmagnetic impurity scattering on the disordered surface of the doped topological insulator. We also clarify that the spin current as well as charge density are induced by spatially inhomogeneous magnetization dynamics, and the spin current diffusively propagates on the disordered surface. Using these results, we discuss both local and nonlocal spin torques before and after the spin and spin-current generations on the surface, and provide a procedure to detect the spin current.
Interplay of spin and motional dynamics in ultracold atoms and molecules
NASA Astrophysics Data System (ADS)
Hazzard, Kaden
2015-05-01
Several recent ultracold experiments have realized many-body ``spin models'' - systems where interacting spins are frozen in space. One example I will discuss is polar molecules in an optical lattice. By comparing the JILA group's measurements of far-from-equilibrium molecule dynamics with theoretical predictions, we were able to characterize the spin Hamiltonian and benchmark a new numerical algorithm. Even richer possibilities exist beyond spin models, where both spin and motional degrees of freedom evolve dynamically. Such interplay of spin and motion underlies exotic phenomena such as high-temperature superconductivity. I will describe how the unique properties of emerging ultracold systems - nonreactive ultracold molecules, Rydberg atoms, and alkaline earth atoms - make possible the independent control of the spins, their motion, and the spin-motion coupling.
Non-diffusive spin dynamics in a two-dimensional electron gas
Weber, C.P.
2010-04-28
We describe measurements of spin dynamics in the two-dimensional electron gas in GaAs/GaAlAs quantum wells. Optical techniques, including transient spin-grating spectroscopy, are used to probe the relaxation rates of spin polarization waves in the wavevector range from zero to 6 x 10{sup 4} cm{sup -1}. We find that the spin polarization lifetime is maximal at nonzero wavevector, in contrast with expectation based on ordinary spin diffusion, but in quantitative agreement with recent theories that treat diffusion in the presence of spin-orbit coupling.
Dynamics of a localized spin excitation close to the spin-helix regime
NASA Astrophysics Data System (ADS)
Salis, G.; Walser, M. P.; Altmann, P.; Reichl, C.; Wegscheider, W.
2014-01-01
The time evolution of a local spin excitation in a (001)-confined two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit interactions of similar strength is investigated theoretically and compared with experimental data. Specifically, the consequences of the finite spatial extension of the initial spin polarization are studied for nonbalanced Rashba and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction. We show that the initial out-of-plane spin polarization evolves into a helical spin pattern with a wave number that gradually approaches the value q0 of the persistent spin helix mode. In addition to an exponential decay of the spin polarization that is proportional to both the spin-orbit imbalance and the cubic Dresselhaus term, the finite width w of the spin excitation reduces the spin polarization by a factor that approaches exp(-q02w2/2) at longer times.
Engineering nuclear spin dynamics with optically pumped nitrogen-vacancy center
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)].
Many-Body Quantum Spin Dynamics with Monte Carlo Trajectories on a Discrete Phase Space
Johannes Schachenmayer; Alexander Pikovski; Ana Maria Rey
2015-02-25
Interacting spin systems are of fundamental relevance in different areas of physics, as well as in quantum information science, and biology. These spin models represent the simplest, yet not fully understood, manifestation of quantum many-body systems. An important outstanding problem is the efficient numerical computation of dynamics in large spin systems. Here we propose a new semiclassical method to study many-body spin dynamics in generic spin lattice models. The method is based on a discrete Monte Carlo sampling in phase-space in the framework of the so-called truncated Wigner approximation. Comparisons with analytical and numerically exact calculations demonstrate the power of the technique. They show that it correctly reproduces the dynamics of one- and two-point correlations and spin squeezing at short times, thus capturing entanglement. Our results open the possibility to study the quantum dynamics accessible to recent experiments in regimes where other numerical methods are inapplicable.
Electron spin dynamics and hyperfine interactions in ferromagnet-semiconductor heterostructures
NASA Astrophysics Data System (ADS)
Strand, Jonathan J.
This thesis describes electron spin dynamics in the presence of nuclear spin polarization in Al0.1Ga0.9As/GaAs quantum well (QW) structures. The spin-polarized electrons are electrically injected from an Fe contact into the Al0.1Ga0.9As/GaAs heterostructure, where they interact with lattice nuclei via the hyperfine interaction. These interactions transfer some of the electron spin polarization to the nuclear spin system, which in turn acts back on the electron spin system as an effective magnetic field. This effective magnetic field significantly alters the electron spin precession and hence the steady-state electron spin. The steady-state electron spin polarization is detected via the circular polarization of electroluminescence as a function of applied field, device bias, injected electron spin orientation, and laboratory time. Parameters characterizing the level of nuclear spin polarization as well as the nuclear polarization and depolarization time constants are extracted from the data. Electron spin dynamics are confined to the GaAs QW and are modeled using a theory for electron and nuclear spin dynamics in GaAs. Measurements of the electron spin are made in geometries that are, respectively, sensitive and insensitive to the presence of nuclear spin polarization, allowing self-consistent modeling of the electron response to dynamic nuclear polarization. Modeling of the nuclear spin polarization is constrained by independent measurements of the magnetization of the ferromagnetic contact, the steady-state injected electron spin polarization, and the characteristic field scale for electron spin precession in the QW. The level of nuclear spin polarization is found to depend most strongly on the steady-state electron spin polarization in the QW. Although the electron spin polarization and density in the QW change dramatically as a function of device bias, the ratio of the total nuclear spin relaxation rate to the nuclear spin-lattice relaxation rate due to oriented electrons remains essentially unchanged. Evidence of strong nuclear dipole-dipole interactions appears in nuclear magnetic resonance spectra, which show forbidden features at frequencies that correspond to harmonics and sums of the principle nuclear dipole transitions. These forbidden transitions appear only when the ordinary NMR transitions are saturated.
Spin probe dynamics of n-hexadecane in confined geometry
NASA Astrophysics Data System (ADS)
Lukeová, Miroslava; vajdlenková, Helena; Sippel, Pit; Macová, Eva; Berek, Duan; Loidl, Alois; Barto, Josef
2015-02-01
A combined study of the rotational dynamics of the stable free radical 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and the phase behavior of n-hexadecane (n-HXD) in the bulk and the confined states in a series of silica gels (SG) by means of ESR and DSC is presented. A slow to fast motion transition of the spin probe TEMPO in the bulk n-HXD occurs at T50 G,bulk ? Tm,bulk, i.e., well below the melting temperature due to its trapping and localized mobility in the interlamellar gap of the crystallites [J. Barto, H. vajdlenková, M. Zaleski, M. Edelmann, M. Lukeová, Physica B 430, 99 (2013)]. On the other hand, the dynamics of the TEMPO in the confined systems is strongly slowing down with T50 G (Dpore) >Tm(Dpore) and slightly increases with the pore size Dpore = 60, 100 and 300 Ĺ of the SG's. At the same time, both the corresponding melting temperature, Tm (Dpore), and melting enthalpy, ?Hm (Dpore), decrease with Dpore together with the mutual anti-correlation between T50 G and Tm as a function of the inverse of pore diameter, 1/Dpore. Moreover, the dynamic heterogeneity of the TEMPO in the confined state below T50 G (Dpore) is closely related to the phase transformation. The strong slowing down of the spin probe motion likely results from its preferential localization at the interface layer of the matrix pore due to specific interaction of TEMPO molecules with the polar silanol groups of the SG matrix. This is supported by special study on a series of the variously filled n-HXD/SG systems, other similar experimental findings as well as by theoretical spectral argument.
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.
Wenxian Zhang; Paola Cappellaro; Natania Antler; Brian Pepper; David G. Cory; Viatcheslav V. Dobrovitski; Chandrasekhar Ramanathan; Lorenza Viola
2009-06-12
The 19F spins in a crystal of fluorapatite have often been used to experimentally approximate a one-dimensional spin system. Under suitable multi-pulse control, the nuclear spin dynamics may be modeled to first approximation by a double-quantum one-dimensional Hamiltonian, which is analytically solvable for nearest-neighbor couplings. Here, we use solid-state nuclear magnetic resonance techniques to investigate the multiple quantum coherence dynamics of fluorapatite, with an emphasis on understanding the region of validity for such a simplified picture. Using experimental, numerical, and analytical methods, we explore the effects of long-range intra-chain couplings, cross-chain couplings, as well as couplings to a spin environment, all of which tend to damp the oscillations of the multiple quantum coherence signal at sufficiently long times. Our analysis characterizes the extent to which fluorapatite can faithfully simulate a one-dimensional quantum wire.
Zhang, Wenxian; Antler, Natania; Pepper, Brian; Cory, David G; Dobrovitski, Viatcheslav V; Ramanathan, Chandrasekhar; Viola, Lorenza
2009-01-01
The 19F spins in a crystal of fluorapatite have often been used to experimentally approximate a one-dimensional spin system. Under suitable multi-pulse control, the nuclear spin dynamics may be modeled to first approximation by a double-quantum one-dimensional Hamiltonian, which is analytically solvable for nearest-neighbor couplings. Here, we use solid-state nuclear magnetic resonance techniques to investigate the multiple quantum coherence dynamics of fluorapatite, with an emphasis on understanding the region of validity for such a simplified picture. Using experimental, numerical, and analytical methods, we explore the effects of long-range intra-chain couplings, cross-chain couplings, as well as couplings to a spin environment, all of which tend to damp the oscillations of the multiple quantum coherence signal at sufficiently long times. Our analysis characterizes the extent to which fluorapatite can faithfully simulate a one-dimensional quantum wire.
Spin dynamics of polaritons in II-VI microcavities: detuning dependence
Vińa, Luis
Spin dynamics of polaritons in II-VI microcavities: detuning dependence G. Aichmayr1 , M.D. Martín1 the spin dynamics of the polaritons, shows a very rich and novel behaviour in this non-linear regime. Introduction Since the so called strong coupling between exciton and cavity photon to cavity polaritons
Ryan, Dominic
A muon spin relaxation study of spin dynamics in a polysaccharide iron complex J. van Lierop, DGill University, 3600 University Street, Montreal, Quebec H3A 2T8, Canada Polysaccharide iron complex (PIC
Sherman, EY; Sinova, Jairo.
2005-01-01
Physical limits of the ballistic and nonballistic spin-field-effect transistor: Spin dynamics in remote-doped structures E. Ya. Sherman1 and Jairo Sinova2 1Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario... for the seminal proposal of Datta and Das of a ballistic spin-field-effect tran- sistor #1;DD-SFET#2;.5 However, a decade-long quest to realize such a device has yielded disappointing results.1,2 In part, this is due to the fact that the SO coupling, which...
A New and Unifying Approach to Spin Dynamics and Beam Polarization in Storage Rings
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.
Solid effect in magic angle spinning dynamic nuclear polarization
NASA Astrophysics Data System (ADS)
Corzilius, Björn; Smith, Albert A.; Griffin, Robert G.
2012-08-01
For over five decades, the solid effect (SE) has been heavily utilized as a mechanism for performing dynamic nuclear polarization (DNP). Nevertheless, it has not found widespread application in contemporary, high magnetic field DNP experiments because SE enhancements display an ? _0 ^{ - 2} field dependence. In particular, for nominally forbidden zero and double quantum SE transitions to be partially allowed, it is necessary for mixing of adjacent nuclear spin states to occur, and this leads to the observed field dependence. However, recently we have improved our instrumentation and report here an enhancement of ? = 91 obtained with the organic radical trityl (OX063) in magic angle spinning experiments performed at 5 T and 80 K. This is a factor of 6-7 higher than previous values in the literature under similar conditions. Because the solid effect depends strongly on the microwave field strength, we attribute this large enhancement to larger microwave field strengths inside the sample volume, achieved with more efficient coupling of the gyrotron to the sample chamber. In addition, we develop a theoretical model to explain the dependence of the buildup rate of enhanced nuclear polarization and the steady-state enhancement on the microwave power. Buildup times and enhancements were measured as a function of 1H concentration for both trityl and Gd-DOTA. Comparison of the results indicates that for trityl the initial polarization step is the slower, rate-determining step. However, for Gd-DOTA the spread of nuclear polarization via homonuclear 1H spin diffusion is rate-limiting. Finally, we discuss the applicability of the solid effect at fields > 5 T and the requirements to address the unfavorable field dependence of the solid effect.
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).
Meriles, Carlos A.; Doherty, Marcus W.
2014-07-14
Key to future spintronics and spin-based information processing technologies is the generation, manipulation, and detection of spin polarization in a solid state platform. Here, we theoretically explore an alternative route to spin injection via the use of dynamically polarized nitrogen-vacancy (NV) centers in diamond. We focus on the geometry where carriers and NV centers are confined to proximate, parallel layers and use a trap-and-release model to calculate the spin cross-relaxation probabilities between the charge carriers and neighboring NV centers. We identify near-unity regimes of carrier polarization depending on the NV spin state, applied magnetic field, and carrier g-factor. In particular, we find that unlike holes, electron spins are distinctively robust against spin-lattice relaxation by other, unpolarized paramagnetic centers. Further, the polarization process is only weakly dependent on the carrier hopping dynamics, which makes this approach potentially applicable over a broad range of temperatures.
Spin-boson dynamics beyond conventional perturbation theories
NASA Astrophysics Data System (ADS)
Nesi, Francesco; Paladino, Elisabetta; Thorwart, Michael; Grifoni, Milena
2007-10-01
A generalized approximation scheme is proposed to describe the dynamics of the spin-boson problem. Being nonperturbative in the coupling strength nor in the tunneling frequency, it gives reliable results over a wide regime of temperatures and coupling strength to the thermal environment for a large class of bath spectral densities. We use a path-integral approach and start from the exact solution for the two-level system population difference in the form of a generalized master equation (GME). Then, we approximate interblip and blip-sojourn interactions up to linear order, while retaining all intrablip correlations to find the kernels entering the GME in analytical form. Our approximation scheme, which we call weakly interacting blip approximation, fully agrees with conventional perturbative approximations in the tunneling matrix element (noninteracting-blip approximation) or in the system-bath coupling strength in the proper parameter regime.
Quantum information processing in spin chains via quantum Zeno dynamics
Monras, Alex
2008-01-01
We show how the quantum Zeno effect can be exploited to control quantum information in a spin chain in a flexible way. In particular, we consider a one dimensional array of three level systems interacting via a swap operator, an interaction found in a generalized Heisenberg Hamiltonian. By encoding the qubit into two levels and using simple projective frequent measurements, the dynamics of the chain is guided to achieve basic quantum information manipulation tools, \\emph{i.e.}, quantum registers, single qubit operations and quantum state transfer on demand, while local addressability is not required. State transfer is perfect, robust against errors and delivers qubits at a constant rate, unconditional of the length of the transfer. Moreover, two dimensional lattices with tunable global interactions in different directions offer the possibility of performing two-qubit gates.
A quantum jump description for the non-Markovian dynamics of the spin-boson model
E. -M. Laine
2009-09-30
We derive a time-convolutionless master equation for the spin-boson model in the weak coupling limit. The temporarily negative decay rates in the master equation indicate short time memory effects in the dynamics which is explicitly revealed when the dynamics is studied using the non-Markovian jump description. The approach gives new insight into the memory effects influencing the spin dynamics and demonstrates, how for the spin-boson model the the co-operative action of different channels complicates the detection of memory effects in the dynamics.
Dynamics of a localized spin excitation close to the spin-helix regime
NASA Astrophysics Data System (ADS)
Salis, Gian; Walser, Matthias; Altmann, Patrick; Reichl, Christian; Wegscheider, Werner
2014-03-01
The time evolution of a local spin excitation in a (001)-confined two-dimensional electron gas subjected to Rashba and Dresselhaus spin-orbit interactions of similar strength is investigated theoretically and compared with experimental data. Specifically, the consequences of a finite spatial extension of the initial spin polarization are studied for non-balanced Rashba and Dresselhaus terms and for finite cubic Dresselhaus spin-orbit interaction. We show that the initial out-of-plane spin polarization evolves into a helical spin pattern with a wave number that gradually approaches the value q0 of the persistent spin helix mode. In addition to an exponential decay of the spin polarization that is proportional to both the spin-orbit imbalance and the cubic Dresselhaus term, the finite width w of the spin excitation reduces the spin polarization by a factor that approaches exp(-q02w2 / 2) at longer times. This result bridges the gap between the formation of a long-lived helical spin mode and a spatially homogeneous spin decay described by the Dyakonov-Perel mechanism. This work is financially supported by NCCR QSIT.
Influence of Impurity Spin Dynamics on Quantum Transport in Epitaxial Graphene
NASA Astrophysics Data System (ADS)
Lara-Avila, Samuel; Kubatkin, Sergey; Kashuba, Oleksiy; Folk, Joshua A.; Lüscher, Silvia; Yakimova, Rositza; Janssen, T. J. B. M.; Tzalenchuk, Alexander; Fal'ko, Vladimir
2015-09-01
Experimental evidence from both spin-valve and quantum transport measurements points towards unexpectedly fast spin relaxation in graphene. We report magnetotransport studies of epitaxial graphene on SiC in a vector magnetic field showing that spin relaxation, detected using weak-localization analysis, is suppressed by an in-plane magnetic field B?, and thereby proving that it is caused at least in part by spinful scatterers. A nonmonotonic dependence of the effective decoherence rate on B? reveals the intricate role of the scatterers' spin dynamics in forming the interference correction to the conductivity, an effect that has gone unnoticed in earlier weak localization studies.
Continuous Weak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble
Greg A. Smith; Souma Chaudhury; Andrew Silberfarb; Ivan H. Deutsch; Poul S. Jessen
2004-10-14
A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a non-perturbing measurement on the much longer timescale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation.
Continuous weak measurement and nonlinear dynamics in a cold spin ensemble.
Smith, Greg A; Chaudhury, Souma; Silberfarb, Andrew; Deutsch, Ivan H; Jessen, Poul S
2004-10-15
A weak continuous quantum measurement of an atomic spin ensemble can be implemented via Faraday rotation of an off-resonance probe beam, and may be used to create and probe nonclassical spin states and dynamics. We show that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement window. Removing the nonlinearity allows a nonperturbing measurement on the much longer time scale set by decoherence. The nonlinear spin Hamiltonian is of interest for studies of quantum chaos and real-time quantum state estimation. PMID:15524989
Resolving Remoter Nuclear Spins in a Noisy Bath by Dynamical Decoupling Design
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.
NASA Astrophysics Data System (ADS)
Ito, A.; Anma, T.
1987-03-01
Mössbauer measurements have been made on a two-dimensional (2D) random mixture K2Ni1- x Fe x F4 with competing spin anisotropies. The concentration versus temperature phase diagram predicted by Oguchi and Ishikawa for mixed systems with competition between orthorhombic anisotropies has been shown to exist in K2Ni1- x Fe x F4. The coexistence of two kinds of Mössbauer spectra is seen in the transition regions, and is believed to be an intrinsic property of this system.
Electric detection ofmagnetization dynamics through inverse spin Hall effects
NASA Astrophysics Data System (ADS)
Saitoh, Eiji
2010-03-01
Spin currents, flows of spin angular momentum, are essential in spintronics. To explore the physics of spin currents, effective methods for detecting and generating spin currents should be established. Here we report the observation of the inverse/direct spin-Hall effects in metallic films. These effects enable electric generation and detection of spin currents. We have applied these effects to the observation of the spin-Seebeck effect. The inverse spin-Hall effect (ISHE) is the generation of a charge current from a spin current via the spin-orbit interaction. We have observed ISHE in metallic films at room temperature. The sample used in the present study is a bilayer film comprising a 10-nm-thick ferromagnetic NiFe layer and a 7- nm-thick nonmagnetic metallic (NM=Pt, Pd, Cu, Nb, and Au) layer. In our sample system, a pure spin current is injected from the NiFe layer into the NM layer using the spin-pumping effect operated by ferromagnetic resonance (FMR). ISHE in the NM layer converts the spin current into an electric current, which causes charge accumulation at the edges of the NM layer, or a difference of electric potential between the edges. By measuring this potential difference, this method allows us to detect ISHE in the films. We also demonstrated that the reverse effect of this spin- pumping induced ISHE allows the electric manipulation of magnetization relaxation even in a large-area film. This result can be argued in terms of the combination of the spin-torque effect and the direct spin-Hall effect. A model calculation reproduces the experimental data. This effect can be applied to a quantitative measurement of spin currents without assuming microscopic parameters. We have applied ISHE to the observation of the spin-Seebeck effect. By means of ISHE, we measured spin voltage generated from a temperature gradient in NiFe. This thermally induced spin voltage persists even at distances far from the sample ends and its sign is reversed between the ends of the sample along the temperature gradient. These behaviors are consistent with a phenomenological two-band model for the spin-Seebeck effect. The spin-Seebeck effect can be applied directly to constructing thermal spin generators for driving spintronics devices, thereby opening the door to thermo-spintronics.
Free vibration and dynamic response analysis of spinning structures
NASA Technical Reports Server (NTRS)
1986-01-01
The proposed effort involved development of numerical procedures for efficient solution of free vibration problems of spinning structures. An eigenproblem solution procedure, based on a Lanczos method employing complex arithmetic, was successfully developed. This task involved formulation of the numerical procedure, FORTRAN coding of the algorithm, checking and debugging of software, and implementation of the routine in the STARS program. A graphics package for the E/S PS 300 as well as for the Tektronix terminals was successfully generated and consists of the following special capabilities: (1) a dynamic response plot for the stresses and displacements as functions of time; and (2) a menu driven command module enabling input of data on an interactive basis. Finally, the STARS analysis capability was further improved by implementing the dynamic response analysis package that provides information on nodal deformations and element stresses as a function of time. A number of test cases were run utilizing the currently developed algorithm implemented in the STARS program and such results indicate that the newly generated solution technique is significantly more efficient than other existing similar procedures.
Low energy states dynamic of entanglement for spin systems
R. Jafari
2010-11-13
We have composed the ideas of quantum renormalization group and quantum information by exploring the low energy states dynamic of entanglement resources of a system close to its quantum critical point. We demonstrate the low energy states dynamical quantities of the one dimensional magnetic systems could show the quantum phase transition point and shows the scaling behavior in the vicinity of the transition point. To present our idea, we study the evolution of two spins entanglement 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 evolvement of the generation of entanglement with increasing the magnetic field. We have obtained that the derivative of the time at which the entanglement reaches its maximums with respect to the transverse field, diverges at the critical point and its scaling behaviors versus the size of the system are as same as the static ground state entanglement of the the system.
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.
Magnetization dynamics in an artificial spin ice on kagome
NASA Astrophysics Data System (ADS)
Petrova, Olga; Mellado, Paula; Tchernyshyov, Oleg
2010-03-01
We study magnetization dynamics in an artificial spin ice on kagome realized as a honeycomb network of connected ferromagnetic nanowires studied recently by several experimental groups [1]. The sites of the honeycomb network carry magnetic charge, defined as the source of the magnetic field H, of strength ą1 in suitably chosen units. Magnetization reversal in individual wires under the action of an applied magnetic field is mediated by the emission of a domain wall carrying magnetic charge ą2 at one of the wire's ends, its propagation along the wire and its absorption at the other end. We include the effects of quenched disorder, arising from lattice imperfections, domain wall's inertia, observed recently in permalloy nanowires, and magnetostatic interactions between magnetic charges [2]. The inertia and magnetostatic repulsion between like charges are responsible for avalanches in magnetization reversal observed experimentally [1]. That and an inherently dissipative character of the magnetization dynamics suggest interesting parallels with granular materials [3]. [1] Y. Qi, T. Brintlinger, and J. Cumings, Phys. Rev. B 77, 094418 (2008). [2] E. Saitoh et al., Nature 432, 203 (2004). [3] X. Ke et al., Phys. Rev. Lett. 101, 037205 (2008).
Dynamic message-passing approach for kinetic spin models with reversible dynamics
NASA Astrophysics Data System (ADS)
Del Ferraro, Gino; Aurell, Erik
2015-07-01
A method to approximately close the dynamic cavity equations for synchronous reversible dynamics on a locally treelike topology is presented. The method builds on (a) a graph expansion to eliminate loops from the normalizations of each step in the dynamics and (b) an assumption that a set of auxilary probability distributions on histories of pairs of spins mainly have dependencies that are local in time. The closure is then effectuated by projecting these probability distributions on n -step Markov processes. The method is shown in detail on the level of ordinary Markov processes (n =1 ) and outlined for higher-order approximations (n >1 ). Numerical validations of the technique are provided for the reconstruction of the transient and equilibrium dynamics of the kinetic Ising model on a random graph with arbitrary connectivity symmetry.
Huo, Liu; Yan, Zhibo; Jia, Xingtao; Gao, Xingsen; Qin, Minghui; Liu, Junming
2012-01-01
The competing spin orders and fractional magnetization plateaus of classical Heisenberg model with long-range interactions on a Shastry-Sutherland lattice are investigated using Monte Carlo simulations, in order to understand the fascinating spin ordering sequence observed in TmB4 and other rare-earth tetraborides. The simulation reproduces the experimental 1/2 magnetization plateau at low temperature by considering multifold long range interactions. It is found that more local long range interactions can be satisfied in the 1/2 plateau state than those in the 1/3 plateau state, leading to the stabilization of the extended 1/2 plateau. A mean-field theory on the spin ground states in response to magnetic field is proposed, demonstrating the simulation results. When the energies of the Neel state and the collinear state are degenerated, the former state is more likely to be stabilized due to the competitions among the local collinear spin orders. The present work provides a comprehensive proof of the phase tra...
Competing 1??* mediated dynamics in mequinol: O-H versus O-CH3 photodissociation pathways.
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
Studies of quantum fluctuations and competing orders on vortex dynamics in cuprate superconductors
NASA Astrophysics Data System (ADS)
Beyer, A. D.; Zapf, V. S.; Park, M.-S.
2005-03-01
The existence of competing orders (CO) and the proximity to quantum criticality (QC) in cuprate superconductors create unconventional low energy excitations and significant quantum fluctuations (QF) which can alter the low temperature vortex dynamics of cuprates. We report studies on the effect of QF and CO on vortex dynamics in cuprates at low temperatures, focusing on the four-layer, hole-doped HgBa2Ca3Cu4Ox (Hg-1234). Hg-1234 has two underdoped inner layers that are anti-ferromagnetic and two optimally doped outer layers that are superconducting. Vortex phase diagrams, derived from 3^rd harmonic AC hall probe and high-field DC cantilever magnetization measurements, allow comparison of Hg-1234 with other cuprates such as YBa2Cu3O7-x and La0.1Sr0.9CuO2. Comparison plots of the ab-plane reduced fields (normalized by the paramagnetic field, Hpara), hirr.(t)=Hirr.(t)/Hpara and hC2(t)=HC2(t)/Hpara versus reduced temperature, t, demonstrate that QF and CO indeed affect Hg-1234 more than other cuprates, with Hg-1234 having the smallest extrapolated value of h*? hirr.(0) 0.12, indicating its closest proximity to QC.
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
3d spin dynamics in co-oxypnictides: NMR investigation
NASA Astrophysics Data System (ADS)
Ghoshray, Kajal
2012-06-01
31P NMR study in the paramagnetic state of SmCoPO, reveals a strong temperature dependent anisotropic internal magnetic field, wherein dominant contribution is from Sm-4f spins over that of Co-3d. The behavior of nuclear spin-lattice relaxation rate (1/T1) indicates anisotropic nature of the spin fluctuations, with 2D FM type in plane spin-correlations. In contrast, out of plane spin correlations contain a weak 2D antiferromagnetic component over the 2D ferromagnetic one.
Probing dynamics of a spin ensemble of P1 centers in diamond using a superconducting resonator
NASA Astrophysics Data System (ADS)
de Lange, Gijs; Ranjan, Vishal; Schutjens, Ron; Debelhoir, Thibault; Groen, Joost; Szombati, Daniel; Thoen, David; Klapwijk, Teun; Hanson, Ronald; Dicarlo, Leonardo
2013-03-01
Solid-state spin ensembles are promising candidates for realizing a quantum memory for superconducting circuits. Understanding the dynamics of such ensembles is a necessary step towards achieving this goal. Here, we investigate the dynamics of an ensemble of nitrogen impurities (P1 centers) in diamond using magnetic-field controlled coupling to the first two modes of a superconducting (NbTiN) coplanar waveguide resonator. Three hyperfine-split spin sub-ensembles are clearly resolved in the 0.25-1.2 K temperature range, with a collective coupling strength extrapolating to 23 MHz at full polarization. The coupling to multiple modes allows us to distinguish the contributions of dipolar broadening and magnetic field inhomogeneity to the spin linewidth. We find the spin polarization recovery rate to be temperature independent below 1 K and conclude that spin out-diffusion across the resonator mode volume provides the mechanism for spin relaxation of the ensemble. Furthermore, by pumping spins in one sub-ensemble and probing the spins in the other sub-ensembles, we observe fast steady-state cross-relaxation (compared to spin repolarization) across the hyperfine transitions. These observations have important implications for using the three sub-ensembles as independent quantum memories. Solid-state spin ensembles are promising candidates for realizing a quantum memory for superconducting circuits. Understanding the dynamics of such ensembles is a necessary step towards achieving this goal. Here, we investigate the dynamics of an ensemble of nitrogen impurities (P1 centers) in diamond using magnetic-field controlled coupling to the first two modes of a superconducting (NbTiN) coplanar waveguide resonator. Three hyperfine-split spin sub-ensembles are clearly resolved in the 0.25-1.2 K temperature range, with a collective coupling strength extrapolating to 23 MHz at full polarization. The coupling to multiple modes allows us to distinguish the contributions of dipolar broadening and magnetic field inhomogeneity to the spin linewidth. We find the spin polarization recovery rate to be temperature independent below 1 K and conclude that spin out-diffusion across the resonator mode volume provides the mechanism for spin relaxation of the ensemble. Furthermore, by pumping spins in one sub-ensemble and probing the spins in the other sub-ensembles, we observe fast steady-state cross-relaxation (compared to spin repolarization) across the hyperfine transitions. These observations have important implications for using the three sub-ensembles as independent quantum memories. Research supported by NWO, FOM, and EU Project SOLID
Electron-Nuclear Spin Dynamics in a Mesoscopic Solid-State Quantum Computer
Berman, G.P.; Campbell, D.K.; Doolen, G.D.; Nagaev, K.E.
1998-12-07
We numerically simulate the process of nuclear spin measurement in Kane's quantum computer. For this purpose, we model the quantum dynamics of two coupled nuclear spins located on {sup 31}P donors implanted in Si. We estimate the minimum time of measurement necessary for the reliable transfer of quantum information from the nuclear spin subsystem to the electronic one and the probability of error for typical values of external noise.
Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond
Lucio Robledo; Hannes Bernien; Toeno van der Sar; Ronald Hanson
2010-10-06
We investigate spin-dependent decay and intersystem crossing in the optical cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We use spin control and pulsed optical excitation to extract both the spin-resolved lifetimes of the excited states and the degree of optically-induced spin polarization. By optically exciting the centre with a series of picosecond pulses, we determine the spin-flip probabilities per optical cycle, as well as the spin-dependent probability for intersystem crossing. This information, together with the indepedently measured decay rate of singlet population provides a full description of spin dynamics in the optical cycle of NV centres. The temperature dependence of the singlet population decay rate provides information on the number of singlet states involved in the optical cycle.
Spin dynamics in the optical cycle of single nitrogen-vacancy centres in diamond
Robledo, Lucio; van der Sar, Toeno; Hanson, Ronald
2010-01-01
We investigate spin-dependent decay and intersystem crossing in the optical cycle of single negatively-charged nitrogen-vacancy (NV) centres in diamond. We use spin control and pulsed optical excitation to extract both the spin-resolved lifetimes of the excited states and the degree of optically-induced spin polarization. By optically exciting the centre with a series of picosecond pulses, we determine the spin-flip probabilities per optical cycle, as well as the spin-dependent probability for intersystem crossing. This information, together with the indepedently measured decay rate of singlet population provides a full description of spin dynamics in the optical cycle of NV centres. The temperature dependence of the singlet population decay rate provides information on the number of singlet states involved in the optical cycle.
Detection and measurement of spin-dependent dynamics in random telegraph signals.
House, M G; Xiao, Ming; Guo, Guoping; Li, Haiou; Cao, Gang; Rosenthal, M M; Jiang, Hongwen
2013-09-20
A quantum point contact was used to observe single-electron fluctuations of a quantum dot in a GaAs heterostructure. The resulting random telegraph signals (RTS) contain statistical information about the electron spin state if the tunneling dynamics are spin dependent. We develop a statistical method to extract information about spin-dependent dynamics from RTS and use it to demonstrate that these dynamics can be studied in the thermal energy regime. The tunneling rates of each spin state are independently measured in a finite external magnetic field. We confirm previous findings of a decrease in overall tunneling rates for the spin excited state compared to the ground state as an external magnetic field is increased. PMID:24093289
Gradual evolution in spin dynamics of TlCu1-xMgxCl3 probed by muon-spin-relaxation (?SR) technique
NASA Astrophysics Data System (ADS)
Suzuki, Takao; Watanabe, Isao; Yamada, Fumiko; Ishii, Yasuyuki; Ohishi, Kazuki; Goto, Takayuki; Tanaka, Hidekazu
2014-04-01
Longitudinal-field muon-spin-relaxation (LF-?SR) measurements in TlCu1-xMgxCl3 were carried out to investigate the spin dynamics in the non-magnetic impurity doped spin gap system. As reported before, in the case of x >= 0.006, LF-?SR time spectra are well fitted by the two components function, which means the phase separation to a spin frozen region and to a spin flucuating region. In this report, we focus on the spin fluctuating region, and discuss the gradual change in its magnetic properties with increasing the Mg-doping.
The excitation operator method in the spin dynamics of the one-dimensional XXZ model
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.
ContinuousWeak Measurement and Nonlinear Dynamics in a Cold Spin Ensemble Greg A. Smith,1
Deutsch, Ivan H.
that the probe light shift leads to nonlinearity in the spin dynamics and limits the useful Faraday measurement.80.t The process of quantum measurement involves a fun- damental trade-off between information gain limited polarimeter provides a weak measurement of the ensemble-averaged spin in real time. If the sample
Pinning of dynamic spin density wave fluctuations in the cuprate superconductors
insulator with no static spin moment on any site and dynamic antiferro- magnetic spin density wave (SDW by the long-range Coulomb interactions. Ref 2 studied the doping of the charge-ordered para- magnetic Mott]. Bulk charge order with this, and related, periods has been discussed in insulat- ing
Spin Dynamics in Highly Spin Polarized Co1-xFexS2
Michael J. R. Hoch; Philip L. Kuhns; William G. Moulton; Arneil P. Reyes; Jun Lu; Lan Wang; Chris Leighton
2006-01-01
Highly spin polarized or half-metallic systems are of considerable current interest because of their potential for spin injection in spintronics applications. The ferromagnet (FM) CoS2 is close to being a half-metal. Recent theoretical and experimental work has shown that the alloys Co1-xFexS2 (0.07 < x < 0.9) are highly spin polarized at low temperatures. The Fe concentration may be used
Cryogenic sample exchange NMR probe for magic angle spinning dynamic nuclear polarization
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 ...
Doronin, S. I.; Fel'dman, E. B.; Zenchuk, A. I., E-mail: zenchuk@itp.ac.ru [Russian Academy of Sciences, Institute of Problems of Chemical Physics (Russian Federation)
2011-09-15
The multiple quantum (MQ) NMR dynamics in the system of equivalent spins with the dipolar ordered initial state is considered. The high symmetry of the Hamiltonian responsible for the MQ NMR dynamics (the MQ Hamiltonian) is used to develop analytic and numerical methods for the investigation of the MQ NMR dynamics in systems consisting of hundreds of spins from the 'first principles.' We obtain the dependence of the intensities of the MQ NMR coherences on their orders (profiles of the MQ NMR coherences) for systems of 200-600 spins. It is shown that these profiles may be well approximated by exponential distribution functions. We also compare the MQ NMR dynamics in the systems of equivalent spins having two different initial states, the dipolar ordered state and the thermal equilibrium state in a strong external magnetic field.
Interaction-tuned dynamical transitions in a Rashba spin-orbit-coupled Fermi gas.
Radi?, Juraj; Natu, Stefan S; Galitski, Victor
2014-03-01
We consider the time evolution of the magnetization in a Rashba spin-orbit coupled Fermi gas, starting from a fully polarized initial state. We model the dynamics using a Boltzmann equation, which we solve in the Hartree-Fock approximation. The resulting nonlinear system of equations gives rise to three distinct dynamical regimes with qualitatively different asymptotic behaviors of the magnetization at long times. The distinct regimes and the transitions between them are controlled by the ratio of interaction and spin-orbit coupling strength ?: for small ?, the magnetization decays to zero. For intermediate ?, it displays undamped oscillations about zero, and for large ?, a partially magnetized state is dynamically stabilized. The dynamics we find is a spin analog of interaction induced self-trapping in double-well Bose Einstein condensates. The predicted phenomena can be realized in trapped Fermi gases with synthetic spin-orbit interactions. PMID:24655264
Spin and Charge Dynamics in Atomic Fermions Loaded on Optical Lattice
NASA Astrophysics Data System (ADS)
Okumura, Masahiko; Onishi, Hiroaki; Yamada, Susumu; Machida, Masahiko
2009-03-01
We study spin and charge dynamics of trapped two-component fermions loaded on an optical lattice by using the time dependent density matrix renormalization group (TDDMRG) method. The present target issue is dynamics of spin and charge in Mott state recently realized experimentally by [1]. Firstly, we simply shake a trapped potential superposed onto an optical lattice and observe the charge dynamics on the Mott state by using TDDMRG. Secondly, we do the same thing on a trapped potential which works only on a pseudo-spin species and observe the spin density dynamics. These results are compared with non-trapped case with an open boundary condition. Also, we compare one-dimensional chain like cases with those of n-legs square and triangular ladder systems. References [1] U. Schneider, L. Hackermuller, S. Will, Th. Best, I. Bloch, T. A. Costi, R. W. Helmes, D. Rasch, A. Rosch, arXiv:0809.1464.
NEWS AND VIEWS Exciting fluctuations: monitoring competence
van Oudenaarden, Alexander
NEWS AND VIEWS Exciting fluctuations: monitoring competence induction dynamics at the single coupled with noisy components in the competence induction network of Bacillus subtilis were shown to be responsible for its transient differentiation into the competent state. Natural genetic competence
Collective dynamics of solid-state spin chains and ensembles in quantum information processing
NASA Astrophysics Data System (ADS)
Ping, Yuting
This thesis is concerned with the collective dynamics in different spin chains and spin ensembles in solid-state materials. The focus is on the manipulation of electron spins, through spin-spin and spin-photon couplings controlled by voltage potentials or electromagnetic fields. A brief review of various systems is provided to describe the possible physical implementation of the ideas, and also outlines the basis of the adopted effective interaction models. The first two ideas presented explore the collective behaviour of non-interacting spin chains with external couplings. One focuses on mapping the identical state of spin-singlet pairs in two currents onto two distant, static spins downstream, creating distributed entanglement that may be accessed. The other studies a quantum memory consisting of an array of non-interacting, static spins, which may encode and decode multiple flying spins. Both chains could effectively `enhance' weak couplings in a cumulative fashion, and neither scheme requires active quantum control. Moreover, the distributed entanglement generated can offer larger separation between the qubits than more conventional protocols that only exploit the tunnelling effects between quantum dots. The quantum memory can also `smooth' the statistical fluctuations in the effects of local errors when the stored information is spread. Next, an interacting chain of static spins with nearest-neighbour interactions is introduced to connect distant end spins. Previously, it has been shown that this approach provides a cubic speed-up when compared with the direct coupling between the target spins. The practicality of this scheme is investigated by analysing realistic error effects via numerical simulations, and from that perspective relaxation of the nearest-neighbour assumption is proposed. Finally, a non-interacting electron spin ensemble is reviewed as a quantum memory to store single photons from an on-chip stripline cavity. It is then promoted to a full quantum processor, with major error effects analysed.
Nonlinear analysis of magnetization dynamics excited by spin Hall effect
NASA Astrophysics Data System (ADS)
Taniguchi, Tomohiro
2015-03-01
We investigate the possibility of exciting self-oscillation in a perpendicular ferromagnet by the spin Hall effect on the basis of a nonlinear analysis of the Landau-Lifshitz-Gilbert (LLG) equation. In the self-oscillation state, the energy supplied by the spin torque during a precession on a constant energy curve should equal the dissipation due to damping. Also, the current to balance the spin torque and the damping torque in the self-oscillation state should be larger than the critical current to destabilize the initial state. We find that these conditions in the spin Hall system are not satisfied by deriving analytical solutions of the energy supplied by the spin transfer effect and the dissipation due to the damping from the nonlinear LLG equation. This indicates that the self-oscillation of a perpendicular ferromagnet cannot be excited solely by the spin Hall torque.
Damour, Thibault; Jaranowski, Piotr; Schaefer, Gerhard [Institut des Hautes Etudes Scientifiques, 91440 Bures-sur-Yvette (France); Faculty of Physics, University of Bialystok, Lipowa 41, 15-424 Bialystok (Poland); Theoretisch-Physikalisches Institut, Friedrich-Schiller-Universitaet, Max-Wien-Pl. 1, 07743 Jena (Germany)
2008-07-15
Using a recent, novel Hamiltonian formulation of the gravitational interaction of spinning binaries, we extend the effective one body (EOB) description of the dynamics of two spinning black holes to next-to-leading order (NLO) in the spin-orbit interaction. The spin-dependent EOB Hamiltonian is constructed from four main ingredients: (i) a transformation between the 'effective' Hamiltonian and the 'real' one; (ii) a generalized effective Hamilton-Jacobi equation involving higher powers of the momenta; (iii) a Kerr-type effective metric (with Pade-resummed coefficients) which depends on the choice of some basic 'effective spin vector' S{sub eff}, and which is deformed by comparable-mass effects; and (iv) an additional effective spin-orbit interaction term involving another spin vector {sigma}. As a first application of the new, NLO spin-dependent EOB Hamiltonian, we compute the binding energy of circular orbits (for parallel spins) as a function of the orbital frequency, and of the spin parameters. We also study the characteristics of the last stable circular orbit: binding energy, orbital frequency, and the corresponding dimensionless spin parameter a{sub LSO}{identical_to}cJ{sub LSO}/(G(H{sub LSO}/c{sup 2}){sup 2}). We find that the inclusion of NLO spin-orbit terms has a significant 'moderating' effect on the dynamical characteristics of the circular orbits for large and parallel spins.
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.
Dynamic neutron scattering on incoherent systems using efficient resonance spin flip techniques
Häussler, Wolfgang; Kredler, Lukas
2014-05-15
We have performed numerical ray-tracing Monte-Carlo-simulations of incoherent dynamic neutron scattering experiments. We intend to optimize the efficiency of incoherent measurements depending on the fraction of neutrons scattered without and with spin flip at the sample. In addition to conventional spin echo, we have numerically and experimentally studied oscillating intensity techniques. The results point out the advantages of these different spin echo variants and are an important prerequisite for neutron resonance spin echo instruments like RESEDA (FRM II, Munich), to choose the most efficient technique depending on the scattering vector range and the properties of the sample system under study.
1H-NMR study of the spin dynamics of fine superparamagnetic nanoparticles
Bordonali, L.; Furukawa, Y.; Kraken, M.; Litterst, F.J.; Sangregorio, C.; Casula, M.F.; Lascialfari, A.
2012-05-25
We report a broadband 1H-NMR study of the temperature spin dynamics of nearly monodisperse dextran-coated ?-Fe2O3 magnetic nanoparticles. We observed a maximum in T1?1(T) that decreases in amplitude and shifts toward higher temperatures with increasing field. We suggest that this is related to the progressive superparamagnetic spin blocking of the ferrite core. The data can be explained by assuming a single electronic spin-spin correlation time and introducing a field-dependent distribution of anisotropy energy barriers.
Using action dynamics to assess competing stimulus control during stimulus equivalence testing.
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 (WiimoteŽ) 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
Dynamic relationships between motor skill competence and health-related fitness in youth.
Stodden, David F; Gao, Zan; Goodway, Jacqueline D; Langendorfer, Stephen J
2014-08-01
This cross-sectional study examined associations among motor skill competence (MSC) and health-related fitness (HRF) in youth. A convenient sample of 253 boys and 203 girls (aged 4-13 years) participated in the study. Associations among measures of MSC (throwing and kicking speed and standing long jump distance) and a composite measure of HRF (push-ups, curl-ups, grip strength and PACER test) across five age groups (4-5, 6-7, 8-9, 10-11 and 12-13 yrs.) were assessed using hierarchical regression modeling. When including all children, throwing and jumping were significantly associated with the composite HRF factor for both boys and girls (throw, t = 5.33; jump, t = 4.49) beyond the significant age effect (t = 4.98) with kicking approaching significance (t = 1.73, p = .08). Associations between throwing and kicking speed and HRF appeared to increase from early to middle to late childhood age ranges. Associations between jumping and HRF were variable across age groups. These results support the notion that the relationship between MSC and HRF performance are dynamic and may change across childhood. These data suggest that the development of object control skills in childhood may be important for the development and maintenance of HRF across childhood and into adolescence. PMID:25111159
Electrical control of spin dynamics in spin-orbit coupled ferromagnets
Skinner, Timothy
2015-01-06
the spins must exert a torque on the magnetisation. The generalised spin-transfer torque can be formulated (for an in-plane mag- netisation) as an in-plane and out-of-plane torque51 TS = aMf × (Mp ×Mf ) + bMp ×Mf . (2.23) Mf and Mp are the magnetisations...
NASA Astrophysics Data System (ADS)
Adelnia, Fatemeh; Mariani, Manuel; Ammannato, Luca; Caneschi, Andrea; Rovai, Donella; Winpenny, Richard; Timco, Grigore; Corti, Maurizio; Lascialfari, Alessandro; Borsa, Ferdinando
2015-05-01
We present the room temperature proton nuclear magnetic resonance (NMR) nuclear spin-lattice relaxation rate (NSLR) results in two 1D spin chains: the Heisenberg antiferromagnetic (AFM) Eu(hfac)3NITEt and the magnetically frustrated Gd(hfac)3NITEt. The NSLR as a function of external magnetic field can be interpreted very well in terms of high temperature spin dynamics dominated by a long time persistence of the decay of the two-spin correlation function due to the conservation of the total spin value for isotropic Heisenberg chains. The high temperature spin dynamics are also investigated in Heisenberg AFM molecular rings. In both Cr8 closed ring and in Cr7Cd and Cr8Zn open rings, i.e., model systems for a finite spin segment, an enhancement of the low frequency spectral density is found consistent with spin diffusion but the high cut-off frequency due to intermolecular anisotropic interactions prevents a detailed analysis of the spin diffusion regime.
Spin transport and dynamics in the F/N junction
NASA Astrophysics Data System (ADS)
Li, Hua; Bedell, Kevin
2015-03-01
We study the spin transport in the low temperature regime (often referred to as the precession-dominated regime) between a ferromagnetic Fermi liquid (FFL) and a normal metal metallic Fermi liquid (NFL), the F/N junction, which is considered one of the basic spintronic devices. In particular, we explore the propagation of spin waves and transport of magnetization through the interface of the F/N junction where non-equilibrium spin polarization is created on the normal metal side of the junction by spin injection. We calculate the probable spin wave modes in the precession-dominated regime on both sides of the junction especially on the NFL side where the system is out of equilibrium. Proper boundary conditions at the interface are introduced to establish the transport of the spin properties through the F/N junction. In the end, a possible transmission conduction electron spin resonance experiment is suggested on the F/N junction to see if the predicted spin wave modes could propagate through the junction.
Brownian motion and quantum dynamics of magnetic monopoles in spin ice
Bovo, L.; Bloxsom, J.A.; Prabhakaran, D.; Aeppli, G.; Bramwell, S.T.
2013-01-01
Spin ice illustrates many unusual magnetic properties, including zero point entropy, emergent monopoles and a quasi liquidgas transition. To reveal the quantum spin dynamics that underpin these phenomena is an experimental challenge. Here we show how crucial information is contained in the frequency dependence of the magnetic susceptibility and in its high frequency or adiabatic limit. The typical response of Dy2Ti2O7 spin ice indicates that monopole diffusion is Brownian but is underpinned by spin tunnelling and is influenced by collective monopole interactions. The adiabatic response reveals evidence of driven monopole plasma oscillations in weak applied field, and unconventional critical behaviour in strong applied field. Our results clarify the origin of the relatively high frequency response in spin ice. They disclose unexpected physics and establish adiabatic susceptibility as a revealing characteristic of exotic spin systems. PMID:23443563
Nonperturbative master equation solution of central spin dephasing dynamics.
Barnes, Edwin; Cywi?ski, ?ukasz; Das Sarma, S
2012-10-01
We solve the long-standing central spin problem for a general set of inhomogeneous bath couplings and a large class of initial bath states. We compute the time evolution of the coherence of a central spin coupled to a spin bath by resumming all orders of the time-convolutionless master equation, thus avoiding the need to assume weak coupling to the bath. The fully quantum, non-markovian solution is obtained in the large-bath limit and is valid up to a time scale set by the largest coupling constant. Our result captures the full decoherence of an electron spin qubit coupled to a nuclear spin bath in a GaAs quantum dot for experimentally relevant parameters. In addition, our solution is quite compact and can readily be used to make quantitative predictions for the decoherence process and to guide the design of nuclear state preparation protocols. PMID:23083231
Álvarez, Gonzalo A; Suter, Dieter; Kaiser, Robin
2015-08-21
Nonequilibrium dynamics of many-body systems are important in many scientific fields. Here, we report the experimental observation of a phase transition of the quantum coherent dynamics of a three-dimensional many-spin system with dipolar interactions. Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we quench the interaction Hamiltonian to drive the evolution of the system. Depending on the quench strength, we then observe either localized or extended dynamics of the system coherence. We extract the critical exponents for the localized cluster size of correlated spins and diffusion coefficient around the phase transition separating the localized from the delocalized dynamical regime. These results show that NMR techniques are well suited to studying the nonequilibrium dynamics of complex many-body systems. PMID:26293957
Localization-delocalization transition in the dynamics of dipolar-coupled nuclear spins
NASA Astrophysics Data System (ADS)
Álvarez, Gonzalo A.; Suter, Dieter; Kaiser, Robin
2015-08-01
Nonequilibrium dynamics of many-body systems are important in many scientific fields. Here, we report the experimental observation of a phase transition of the quantum coherent dynamics of a three-dimensional many-spin system with dipolar interactions. Using nuclear magnetic resonance (NMR) on a solid-state system of spins at room-temperature, we quench the interaction Hamiltonian to drive the evolution of the system. Depending on the quench strength, we then observe either localized or extended dynamics of the system coherence. We extract the critical exponents for the localized cluster size of correlated spins and diffusion coefficient around the phase transition separating the localized from the delocalized dynamical regime. These results show that NMR techniques are well suited to studying the nonequilibrium dynamics of complex many-body systems.
Theoretical studies of the spin dynamics of quadrupolar nuclei at rotational resonance conditions
NASA Astrophysics Data System (ADS)
Walls, Jamie D.; Lim, Kwang Hun; Pines, Alexander
2002-01-01
A theory of the spin dynamics of I=3/2 quadrupolar nuclei in the sudden-passage limit is discussed in relation to the recently observed rotational resonance (RR) effects on the excitation and conversion of triple-quantum coherence in the FASTER multiple-quantum magic-angle spinning (MQMAS) experiments [T. Vosegaard, P. Florian, D. Massiot, and P. J. Grandinetti, J. Chem. Phys. 114, 4618 (2001)]. A novel interaction frame, which combines the quadrupolar interaction with the central transition radio frequency irradiation, is shown to be useful in understanding the complex spin dynamics at and away from RR conditions. Analytical expressions for the Hamiltonian obtained from bimodal Floquet theory are included in order to provide insight into the spin dynamics observed in the FASTER MQMAS experiments. Numerical simulations have been performed and were found to support the theoretical formalism.
Strain-induced coherent dynamics of coupled carriers and Mn spins in a quantum dot
NASA Astrophysics Data System (ADS)
Lafuente-Sampietro, A.; Boukari, H.; Besombes, L.
2015-08-01
We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton (X+). We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical ? systems which can be addressed independently. We show that the spin dynamics of the X+-Mn complex is dominated by the electron-Mn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in the time domain. Quantum beats reflecting the coherent transfer of population between electron-Mn spin states, which are mixed by an anisotropic strain in the plane of the quantum dot, are clearly observed. We finally highlight that this strain-induced coherent coupling is tunable with an external magnetic field.
NASA Astrophysics Data System (ADS)
Pilawa, B.; Boffinger, R.; Keilhauer, I.; Leppin, R.; Odenwald, I.; Wendl, W.; Berthier, C.; Horvati?, M.
2005-05-01
The dynamic properties of the cyclic hexanuclear iron(III) complex Fe6(triethanolaminate3-)6 are studied by electron spin (ESR) and H1 nuclear magnetic resonance. We analyze the angular and temperature dependence of the ESR absorption lines at 9.4 GHz in the magnetic field range up to 1 T, the temperature dependence of the H1 longitudinal relaxation rate T1-1 at 1.2 T, and the magnetic field dependence of T1-1 between 12 and 17 T at 0.2, 1.5, and 5 K. The influence of the intermolecular dipolar interaction on the resonance properties of the Fe6(triethanolaminate3-)6 complex is numerically calculated. The discussion of the experimental results indicates the importance of spin-lattice relaxation processes for the understanding of the dynamics of the iron ring.
Finite temperature spin-dynamics and phase transitions in spin-orbital models
Chen, C.-C.
2010-04-29
We study finite temperature properties of a generic spin-orbital model relevant to transition metal compounds, having coupled quantum Heisenberg-spin and Ising-orbital degrees of freedom. The model system undergoes a phase transition, consistent with that of a 2D Ising model, to an orbitally ordered state at a temperature set by short-range magnetic order. At low temperatures the orbital degrees of freedom freeze-out and the model maps onto a quantum Heisenberg model. The onset of orbital excitations causes a rapid scrambling of the spin spectral weight away from coherent spin-waves, which leads to a sharp increase in uniform magnetic susceptibility just below the phase transition, reminiscent of the observed behavior in the Fe-pnictide materials.
Herrera-Aguilar, José L.; Larralde, Hernán; Aldana, Maximino
2012-01-01
We study the properties of the dynamical phase transition occurring in neural network models in which a competition between associative memory and sequential pattern recognition exists. This competition occurs through a weighted mixture of the symmetric and asymmetric parts of the synaptic matrix. Through a generating functional formalism, we determine the structure of the parameter space at non-zero temperature and near saturation (i.e., when the number of stored patterns scales with the size of the network), identifying the regions of high and weak pattern correlations, the spin-glass solutions, and the order-disorder transition between these regions. This analysis reveals that, when associative memory is dominant, smooth transitions appear between high correlated regions and spurious states. In contrast when sequential pattern recognition is stronger than associative memory, the transitions are always discontinuous. Additionally, when the symmetric and asymmetric parts of the synaptic matrix are defined in terms of the same set of patterns, there is a discontinuous transition between associative memory and sequential pattern recognition. In contrast, when the symmetric and asymmetric parts of the synaptic matrix are defined in terms of independent sets of patterns, the network is able to perform both associative memory and sequential pattern recognition for a wide range of parameter values. PMID:22900014
Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters. Part II
NASA Astrophysics Data System (ADS)
Anderson, Kassandra R.; Storch, Natalia I; Lai, Dong
2014-05-01
Secular Kozai oscillations, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planet's orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as $10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincar\\'{e} surfaces of section to demonstrate thechaotic behavior. As the system parameters (such as planet mass) vary, ``periodic islands'' can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.
Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters
NASA Astrophysics Data System (ADS)
Storch, Natalia I; Anderson, Kassandra R; Lai, Dong
2014-05-01
Secular Kozai oscillation, induced by a distant stellar companion and acting in concert with tidal dissipation, is one of the major channels for the production of hot Jupiters (extrasolar gas giants in 1-5 day orbits) and close stellar binaries. This mechanism is particularly attractive due to the high degree of misalignment between the stellar spin and planet/binary orbital angular momentum axes that has been observed in many systems. In the typical Kozai picture, this misalignment is thought to be the result of large variation in the planets orbital axis, while the stellar spin orientation remains mostly fixed. Here we demonstrate that gravitational interaction between the stellar spin and the planetary orbit can induce a variety of dynamical behaviors for the stellar spin evolution during the Kozai cycle. In particular, in systems hosting giant planets, the stellar spin exhibits rich, often strongly chaotic dynamics, with Lyapunov times as short as 10 Myr. This arises from secular spin-orbit resonances and resonance overlaps. We construct Poincare surfaces of section to demonstrate the chaotic behavior. As the system parameters (such as planet mass) vary, periodic islands can appear in largely chaotic domains, in a manner reminiscent of the logistic map or Lorenz chaos. We show that in the presence of tidal dissipation, the memory of chaotic spin evolution can be preserved, leaving an imprint on the final spin-orbit misalignment angles.
Dynamics of three types of annual plants competing for water and light
NASA Astrophysics Data System (ADS)
P?kalski, Andrzej; Szwabi?ski, Janusz
2013-02-01
We present and discuss a Monte Carlo model describing the dynamics of three types of annual plants which have different tolerances to shade and drought. External conditions (water and light) fluctuate around some values which are our control parameters and which decide how many resources the system receives. The plants compete with their nearest neighbours for the resources, however not in the same way. We show that for certain ranges of the control parameters a coexistence of the three species is observed. We discuss how the characteristics of the the plants - their number, germination, biomass or the number of nearest neighbours, depend on the two control parameters characterising external conditions. We show that elimination is done at the level of adult plants, not seedlings. We find also cooperative behaviour of plants in difficult conditions, as observed in field studies and we propose an explanation for this fact. Apart from plants tolerating shade but requiring more water and those tolerating drought but needing more light, which are common in nature, we introduce a third species with intermediary demands. We investigate under what conditions this new species could dominate and whether the total number of plants, regardless of their type, is larger with or without the intermediate plant. We show that in our model, like in nature, systems with two kinds of plants with opposite characteristics are, in general, as effective as a system with an additional third type of plants. We show that two contradictory hypotheses made by biologists, concerning the demands of plants in drought and shade, could be both true, however in different regimes.
Competing quantum effects in the dynamics of a flexible water model
Scott Habershon; Thomas E. Markland; David E. Manolopoulos
2010-11-04
Numerous studies have identified large quantum mechanical effects in the dynamics of liquid water. In this paper, we suggest that these effects may have been overestimated due to the use of rigid water models and flexible models in which the intramolecular interactions were described using simple harmonic functions. To demonstrate this, we introduce a new simple point charge model for liquid water, q-TIP4P/F, in which the O--H stretches are described by Morse-type functions. We have parameterized this model to give the correct liquid structure, diffusion coefficient, and infra-red absorption frequencies in quantum (path integral-based) simulations. By comparing classical and quantum simulations of the liquid, we find that quantum mechanical fluctuations increase the rates of translational diffusion and orientational relaxation in our model by a factor of around 1.15. This effect is much smaller than that observed in all previous simulations of simple empirical water models, which have found a quantum effect of at least 1.4 regardless of the quantum simulation method or the water model employed. The small quantum effect in our model is a result of two competing phenomena. Intermolecular zero point energy and tunneling effects destabilize the hydrogen bonding network, leading to a less viscous liquid with a larger diffusion coefficient. However this is offset by intramolecular zero point motion, which changes the average water monomer geometry resulting in a larger dipole moment, stronger intermolecular interactions, and slower diffusion. We end by suggesting, on the basis of simulations of other potential energy models, that the small quantum effect we find in the diffusion coefficient is associated with the ability of our model to produce a single broad O-H stretching band in the infra-red absorption spectrum.
Dynamic Bayesian networks for the classification of spinning discs
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 ...
Atom-diatom scattering dynamics of spinning molecules
NASA Astrophysics Data System (ADS)
Eyles, C. J.; Floß, J.; Averbukh, I. Sh.; Leibscher, M.
2015-01-01
We present full quantum mechanical scattering calculations using spinning molecules as target states for nuclear spin selective atom-diatom scattering of reactive D+H2 and F+H2 collisions. Molecules can be forced to rotate uni-directionally by chiral trains of short, non-resonant laser pulses, with different nuclear spin isomers rotating in opposite directions. The calculations we present are based on rotational wavepackets that can be created in this manner. As our simulations show, target molecules with opposite sense of rotation are predominantly scattered in opposite directions, opening routes for spatially and quantum state selective scattering of close chemical species. Moreover, two-dimensional state resolved differential cross sections reveal detailed information about the scattering mechanisms, which can be explained to a large degree by a classical vector model for scattering with spinning molecules.
Entanglement dynamics via geometric phases in quantum spin chains
Castro, C. S.; Sarandy, M. S. [Instituto de Fisica, Universidade Federal Fluminense, Avenida Gal. Milton Tavares de Souza s/n, Gragoata, 24210-346, Niteroi, Rio de Janeiro (Brazil)
2011-04-15
We introduce a connection between entanglement induced by interaction and geometric phases acquired by a composite quantum spin system. We begin by analyzing the evaluation of cyclic (Aharonov-Anandan) and noncyclic (Mukunda-Simon) geometric phases for general spin chains evolving in the presence of time-independent magnetic fields. Then, by considering Heisenberg chains, we show that the interaction geometric phase, namely, the total geometric phase with subtraction of free spin contributions, is directly related to the global (Meyer-Wallach) entanglement exhibited by an initially separable state during its evolution in Hilbert space. This is analytically shown for N=2 spins and numerically illustrated for larger chains. This relationship promotes the interaction geometric phase to an indicator of global entanglement in the system, which may constitute a useful tool for quantum tasks based on entanglement as a resource to their performance.
Cavity Exciton-Polaritons, Bose Einstein Condensation and Spin Dynamics
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.
Nuclear magnetometry studies of spin dynamics in quantum Hall systems
NASA Astrophysics Data System (ADS)
Fauzi, M. H.; Watanabe, S.; Hirayama, Y.
2014-12-01
We performed a nuclear magnetometry study on quantum Hall ferromagnet with a bilayer total filling factor of ?tot=2 . We found not only a rapid nuclear relaxation but also a sudden change in the nuclear-spin polarization distribution after a one-second interaction with a canted antiferromagnetic phase. We discuss the possibility of observing cooperative phenomena coming from nuclear-spin ensemble triggered by hyperfine interaction in quantum Hall system.
Spin dynamics and magnetoelectric properties of the coupled-spin tetrahedral compound Cu2Te2O5Cl2
NASA Astrophysics Data System (ADS)
Besara, T.; Choi, E. S.; Choi, K.-Y.; Kuhns, P. L.; Reyes, A. P.; Lemmens, P.; Berger, H.; Dalal, N. S.
2014-08-01
We report on the spin dynamics and discovery of magnetoelectricity in the coupled-spin tetrahedral compound Cu2Te2O5Cl2. Te125 NMR measurements show an anomalous resonance frequency shift and a signal wipe-out phenomenon around the Néel temperature TN = 18.2 K, which could be attributed to the anomalous critical slowing down of the Cu spin fluctuations on the NMR time scale (10-100 MHz). The critical exponent of (T1T)-1?(T-TN)-? is 0.40 ą 0.03, as compared to 0.5 for a three-dimensional mean-field model. This is in contrast to the Br compound [S.-H. Baek et al., Phys. Rev. B 86, 180405 (2012), 10.1103/PhysRevB.86.180405], which exhibits pronounced singlet dynamics with a large spin gap. Electric polarization (Pc) is observed along the c axis for temperatures below TN under finite magnetic field but not sensitive to the electric poling. Pc increases sharply over zero to 2 T and then reaches saturation. Below TN, Pc changes its sign depending on the applied magnetic field direction, positive for the H?c axis and negative for H ? c axis. We discuss possible explanations for the observed magnetoelectric (ME) behavior in terms of linear ME effect, spin-driven multiferroicity, and an exchange striction of intertetrahedral exchange paths involving the Te4+ lone-pair ions. Our results suggest that Cu2Te2O5Cl2 is a type of ME material whose properties are tuned by intertetrahedral exchange interactions involving polarizable Te4+ ions.
Jeffery B. Klauda; Mary F. Roberts; Alfred G. Redfield; Bernard R. Brooks; Richard W. Pastor
2008-01-01
Molecular dynamics simulations and 31P-NMR spin-lattice (R1) relaxation rates from 0.022 to 21.1 T of fluid phase dipalmitoylphosphatidylcholine bilayers are compared. Agreement between experiment and direct prediction from simulation indicates that the dominant slow relaxation (correlation) times of the dipolar and chemical shift anisotropy spin-lattice relaxation are ?10ns and 3ns, respectively. Overall reorientation of the lipid body, consisting of the
EUROPEAN CONFERENCE FOR AEROSPACE SCIENCES Study on the eddy current damping of the spin dynamics of
As the number of debris orbiting around the Earth has steadily increased since the early days of space programs dynamics of spatial debris from the Ariane launcher Nicolas Praly , Nicolas Petit , Christophe Bonnal This paper addresses the topic of damping of the spinning dynamics of a spatial debris orbiting around
Cascaded spin motive force driven by the dynamics of the skyrmion lattice
Ohe, Jun-ichiro; Shimada, Yuhki
2013-12-09
We numerically investigate the spin motive force (SMF) driven by the dynamics of a Skyrmion lattice. The rotating mode of the Skyrmion core excited by the AC magnetic field induces the large spin-dependent electric field near the core. Due to the collective dynamics of Skyrmion lattice, the measurable voltage is enhanced by the cascade effect of the SMF. The amplitude of the AC voltage is estimated to 30??V in a macroscopic sample, where 100 Skyrmions exist between two probes. We also investigate the SMF due to the dynamics of the helical magnetic state, where the enhancement of the SMF does not occur.
Dynamic Business Share Allocation in a Supply Chain with Competing Suppliers
Li, Hongmin
This paper studies a repeated game between a manufacturer and two competing suppliers with imperfect monitoring. We present a principal-agent model for managing long-term supplier relationships using a unique form of ...
L. Chotorlishvili; E. Ya. Sherman; Z. Toklikishvili; A. Komnik; J. Berakdar
2011-10-01
We study the dynamics of an electron confined in a one-dimensional double quantum dot in the presence of driving external magnetic fields. The orbital motion of the electron is coupled to the spin dynamics by spin orbit interaction of the Dresselhaus type. We derive an effective time-dependent Hamiltonian model for the orbital motion of the electron and obtain a synchronization condition between the orbital and the spin dynamics. From this model we deduce an analytical expression for the Arnold tongue and propose an experimental scheme for realizing the synchronization of the orbital and spin dynamics.
Spin-orbit coupling quenches dynamic nuclear polarization in GaAs double quantum dots
NASA Astrophysics Data System (ADS)
Nichol, John; Harvey, Shannon; Shulman, Michael; Pal, Arijeet; Rashba, Emmanuel; Halperin, Bertrand; Umansky, Vladimir; Yacoby, Amir
2015-03-01
Dynamic nuclear polarization (DNP) occurs in a wide variety of condensed matter systems and enables the transfer of angular momentum from electron to nuclear spins via the hyperfine interaction. In semiconductor devices, DNP is exploited for coherent electron spin manipulation, but the mechanisms limiting the maximum-achievable polarization in gate-defined quantum dots to only a few percent remain incompletely understood. We demonstrate here that spin-orbit coupling quenches DNP in a GaAs double quantum dot, even though the spin-orbit length is much larger than the interdot spacing. The observed suppression of DNP is consistent with theoretical models. These results demonstrate the surprising competition between the hyperfine and spin-orbit interactions in GaAs double quantum dots and highlight the importance of field orientation for efficient DNP.
Extending the electron spin coherence time of atomic hydrogen by dynamical decoupling.
Mitrikas, George; Efthimiadou, Eleni K; Kordas, George
2014-02-14
We study the electron spin decoherence of encapsulated atomic hydrogen in octasilsesquioxane cages induced by the (1)H and (29)Si nuclear spin bath. By applying the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence we significantly suppress the low-frequency noise due to nuclear spin flip-flops up to the point where a maximum T2 = 56 ?s is observed. Moreover, dynamical decoupling with the CPMG sequence reveals the existence of two other sources of decoherence: first, a classical magnetic field noise imposed by the (1)H nuclear spins of the cage organic substituents, which can be described by a virtual fluctuating magnetic field with the proton Larmor frequency, and second, decoherence due to anisotropic hyperfine coupling between the electron and the inner (29)Si spins of the cage. PMID:24352700
NASA Astrophysics Data System (ADS)
Yamaguchi, Keita; Kurihara, Takayuki; Watanabe, Hiroshi; Nakajima, Makoto; Suemoto, Tohru
2015-08-01
The effects of femtosecond laser excitation on the anisotropy parameter in orthoferrites ErFe O3 and DyFe O3 were probed through Faraday rotation induced by coherent spin precession, which was triggered by a terahertz pulse. Through the delayed frequency shift of the precession, gradual change in the anisotropic energy of the iron spins is evidenced. This is attributed to the slow energy transfer from the F e3 + 3 d electron system to the rare-earth 4 f electron system, which in turn alters the anisotropy parameter of the F e3 + spins. The result presented here reveals the time dependent spin alignment mechanism in cant-type antiferromagnetic orthoferrites and enables deeper understanding of spin orientation dynamics triggered by electronic excitation.
Anomalous magnetic structure and spin dynamics in magnetoelectric LiFePO4
NASA Astrophysics Data System (ADS)
Toft-Petersen, Rasmus; Reehuis, Manfred; Jensen, Thomas B. S.; Andersen, Niels H.; Li, Jiying; Le, Manh Duc; Laver, Mark; Niedermayer, Christof; Klemke, Bastian; Lefmann, Kim; Vaknin, David
2015-07-01
We report significant details of the magnetic structure and spin dynamics of LiFePO4 obtained by single-crystal neutron scattering. Our results confirm a previously reported collinear rotation of the spins away from the principal b axis, and they determine that the rotation is toward the a axis. In addition, we find a significant spin-canting component along c . The possible causes of these components are discussed, and their significance for the magnetoelectric effect is analyzed. Inelastic neutron scattering along the three principal directions reveals a highly anisotropic hard plane consistent with earlier susceptibility measurements. Using a spin Hamiltonian, we show that the spin dimensionality is intermediate between X Y - and Ising-like, with an easy b axis and a hard c axis. It is shown that both next-nearest neighbor exchange couplings in the b c plane are in competition with the strongest nearest neighbor coupling.
Low energy spin dynamics in the spin ice, Ho2Sn2O7
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.
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)
Charge localization and dynamical spin locking in double quantum dots driven by ac magnetic fields
NASA Astrophysics Data System (ADS)
Gómez-León, Álvaro; Platero, Gloria
2011-09-01
We investigate electron localization and dynamical spin locking induced by ac magnetic fields in double quantum dots. We demonstrate that by tuning the ac magnetic fields parameters, i.e., the field intensity, frequency, and the phase difference between the fields within each dot, coherent destruction of tunneling (and thus charge localization) can be achieved. We show that in contrast with ac electric fields, ac magnetic fields are able to induce spin locking, i.e., to freeze the electronic spin, at certain field parameters. We show how the symmetry of the Hamiltonian determines the quasienergy spectrum which presents degeneracies at certain field parameters, and how it is reflected in the charge and spin dynamics.
Ultrafast optical control of orbital and spin dynamics in a solid-state defect.
Bassett, Lee C; Heremans, F Joseph; Christle, David J; Yale, Christopher G; Burkard, Guido; Buckley, Bob B; Awschalom, David D
2014-09-12
Atom-scale defects in semiconductors are promising building blocks for quantum devices, but our understanding of their material-dependent electronic structure, optical interactions, and dissipation mechanisms is lacking. Using picosecond resonant pulses of light, we study the coherent orbital and spin dynamics of a single nitrogen-vacancy center in diamond over time scales spanning six orders of magnitude. We develop a time-domain quantum tomography technique to precisely map the defect's excited-state Hamiltonian and exploit the excited-state dynamics to control its ground-state spin with optical pulses alone. These techniques generalize to other optically addressable nanoscale spin systems and serve as powerful tools to characterize and control spin qubits for future applications in quantum technology. PMID:25123482
Mean-field dynamics of spin-orbit coupled Bose-Einstein condensates.
Zhang, Yongping; Mao, Li; Zhang, Chuanwei
2012-01-20
Spin-orbit coupling (SOC), the interaction between the spin and momentum of a quantum particle, is crucial for many important condensed matter phenomena. The recent experimental realization of SOC in neutral bosonic cold atoms provides a new and ideal platform for investigating spin-orbit coupled quantum many-body physics. In this Letter, we derive a generic Gross-Pitaevskii equation as the starting point for the study of many-body dynamics in spin-orbit coupled Bose-Einstein condensates. We show that different laser setups for realizing the same SOC may lead to different mean-field dynamics. Various ground state phases (stripe, phase separation, etc.) of the condensate are found in different parameter regions. A new oscillation period induced by the SOC, similar to the Zitterbewegung oscillation, is found in the center-of-mass motion of the condensate. PMID:22400756
F. Heisterkamp; E. A. Zhukov; A. Greilich; D. R. Yakovlev; V. L. Korenev; A. Pawlis; M. Bayer
2015-03-26
The spin dynamics of the strongly localized, donor-bound electrons in fluorine-doped ZnSe epilayers is studied by pump-probe Kerr rotation techniques. A method exploiting the spin inertia is developed and used to measure the longitudinal spin relaxation time, $T_1$, in a wide range of magnetic fields, temperatures, and pump densities. The $T_1$ time of the donor-bound electron spin of about 1.6 $\\mu$s remains nearly constant for external magnetic fields varied from zero up to 2.5 T (Faraday geometry) and in a temperature range $1.8-45$ K. The inhomogeneous spin dephasing time, $T_2^*=8-33$ ns, is measured using the resonant spin amplification and Hanle effects under pulsed and steady-state pumping, respectively. These findings impose severe restrictions on possible spin relaxation mechanisms.
Hyperfine interaction and its effects on spin dynamics in organic solids
NASA Astrophysics Data System (ADS)
Yu, Z. G.; Ding, Feizhi; Wang, Haobin
2013-05-01
Hyperfine interaction (HFI) and spin-orbit coupling are two major sources that affect electron spin dynamics. Here we present a systematic study of the HFI and its role in organic spintronic applications. For electron spin dynamics in disordered ?-conjugated organics, the HFI can be characterized by an effective magnetic field whose modular square is a weighted sum of contact and dipolar contributions. We determine the effective HFI fields of some common ?-conjugated organics studied in the literature via first-principles calculations. Most of them are found to be less than 2 mT. While the H atoms are the major source of the HFI in organics containing only the C and H atoms, many organics contain other nuclear spins, such as Al and N in tris-(8-hydroxyquinoline) aluminum, that contribute to the total HFI. Consequently, the deuteration effect on the HFI in the latter may be much weaker than in the former. The HFI gives rise to multiple resonance peaks in electron spin resonance. In disordered organic solids, these individual resonances are unresolved, leading to a broad peak whose width is proportional to the effective HFI field. As electrons hop among adjacent organic molecules, they experience a randomly varying local HFI field, inducing electron spin relaxation and diffusion. This is analyzed rigorously based on master equations. Electron spin relaxation undergoes a crossover along the ratio between the electron hopping rate ?Ż and the Larmor frequency ? of the HFI field. The spin relaxation rate increases (decreases) with ?Ż when ?Ż?? (?Ż??). A coherent beating of electron spin at ? is possible when the external field is small compared to the HFI. In this regime, the magnetic field is found to enhance the spin relaxation.
Coherent spin dynamics in nanopatterned ferromagnet-semiconductor hybrids at room-temperature
Hohage, P. E.; Nannen, J.; Bacher, G. [Werkstoffe der Elektrotechnik and CeNIDE, Universitaet Duisburg-Essen, Bismarckstrasse 81, D-47057 Duisburg (Germany); Wahle, M.; Fischer, S. F.; Kunze, U. [Lehrstuhl fuer Werkstoffe und Nanoelektronik, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44780 Bochum (Germany); Reuter, D.; Wieck, A. D. [Lehrstuhl fuer Angewandte Festkoerperphysik, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, D-44780 Bochum (Germany)
2010-01-04
We used time-resolved Kerr rotation to study the coherent spin dynamics of electrons in Py-GaAs hybrid structures up to room temperature. The geometry of the nanopatterned Py wires was varied in a wide range to modify the fringe field from the ferromagnets and thus the Larmor frequency of the precessing electron spins compared to a reference. At room temperature, the observed fringe field effect is in good agreement with theory while at low temperatures additional strain effects occur.
Low temperature spin dynamics in Cr7Ni-Cu-Cr7Ni coupled molecular rings
NASA Astrophysics Data System (ADS)
Bordonali, L.; Furukawa, Y.; Mariani, M.; Sabareesh, K. P. V.; Garlatti, E.; Carretta, S.; Lascialfari, A.; Timco, G.; Winpenny, R. E. P.; Borsa, F.
2014-05-01
Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50 mK) to determine the effect of coupling two Cr7Ni molecular rings via a Cu2+ ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5 K. At lower temperature, the 1H-NMR line broadens dramatically indicating spin freezing. From the plot of the line width vs. magnetization, it is found that the freezing temperature is higher (260 mK) in the coupled ring with respect to the single Cr7Ni ring (140 mK).
The dynamics of particle disks. II - Effects of spin degrees of freedom
NASA Technical Reports Server (NTRS)
Araki, Suguru
1988-01-01
The present treatment of the thermal equilibria of differentially-rotating, axisymmetric disks consisting of identical, spin-possessing as well as translational DOF-possessing hard sphere particles characterizes these disks' dynamics by means of two novel parameters: (1) the tangential restitution coefficient, and (2) the dimensionless moment of inertia. It is established that rings composed of spinning particles can generally be thermally balanced within more restricted ranges of the optical depth, as well as at higher values of the normal restitution coefficient, than spinless rings. Mean spin is indefinite in the present framework of neglected finite particle-size effects.
Spin dynamics and domain formation of a spinor Bose-Einstein condensate in an optical cavity
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.
Low temperature spin dynamics in Cr7Ni-Cu-Cr7Ni coupled molecular rings
Bordonali, L; Furukawa, Y; Mariani, M; Sabareesh, K P; Garlatti, E; Carretta, S; Lascialfari, A; Timco, G; Winpenny, R E; Borsa, F
2014-05-07
Proton Nuclear Magnetic Resonance (NMR) relaxation measurements have been performed down to very low temperature (50?mK) to determine the effect of coupling two Cr7 Ni molecular rings via a Cu 2+ ion. No difference in the spin dynamics was found from nuclear spin lattice relaxation down to 1.5?K. At lower temperature, the 1H-NMR line broadens dramatically indicating spin freezing. From the plot of the line width vs. magnetization, it is found that the freezing temperature is higher (260?mK) in the coupled ring with respect to the single Cr7 Ni ring (140?mK).
Neutron Scattering Study on spin dynamics in superconducting (TlRb)2Fe4Se5
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.
Direct observation of dynamics of single spinning dust grains in weakly magnetized complex plasma
Dzlieva, E. S.; Karasev, V. Yu., E-mail: plasmadust@yandex.ru [St. Petersburg State University, Institute of Physics (Russian Federation); Petrov, O. F. [Russian Academy of Sciences, Institute for High Energy Densities, Joint Institute for High Temperatures (Russian Federation)
2012-01-15
The rotational dynamics of single dust grains in a weak magnetic field is investigated on a kinetic level. Experiments reveal spin-up of spherical dust grains and alignment of their magnetic moments parallel to the magnetic induction vector. The angular velocity of spinning prolate grains varies as magnetic induction increases to 250 G. Spinning dust grains are found to flip over only when the magnetic field magnitude is changing. The results demonstrate that dusty plasma has paramagnetic properties. Qualitative interpretations are proposed to explain newly discovered phenomena.
Nonlinear magnetic vortex dynamics in a circular nanodot excited by spin-polarized current
2014-01-01
We investigate analytically and numerically nonlinear vortex spin torque oscillator dynamics in a circular magnetic nanodot induced by a spin-polarized current perpendicular to the dot plane. We use a generalized nonlinear Thiele equation including spin-torque term by Slonczewski for describing the nanosize vortex core transient and steady orbit motions and analyze nonlinear contributions to all forces in this equation. Blue shift of the nano-oscillator frequency increasing the current is explained by a combination of the exchange, magnetostatic, and Zeeman energy contributions to the frequency nonlinear coefficient. Applicability and limitations of the standard nonlinear nano-oscillator model are discussed. PMID:25147490
Spatial dynamics and spin squeezing in Bose-Einstein condensates
Thanvanthri, Sulakshana [Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250 (United States); Dutton, Zachary [Naval Research Laboratory, Washington, DC 20375 (United States)
2007-02-15
We develop a cumulant based formalism to deterministically calculate the lowest order quantum fluctuations of a two-component Bose-Einstein condensate. We use this to study spin squeezing induced by the atom-atom interaction nonlinearity. Our formalism naturally accounts for the multimode spatial description of the condensate, extending previous spin squeezing work which assumed a single spatial mode. We study spin squeezing in both the miscible and immiscible (phase separating) regimes for the scattering lengths. In the miscible regime, we find the squeezing parameter deviates very little from the single spatial mode approach, while in the phase separating regime, we find the squeezing is slightly reduced, though significant squeezing still occurs.
Dimensionality crossover and frustrated spin dynamics on a triangular lattice
NASA Astrophysics Data System (ADS)
Wikberg, J. M.; Dahbi, M.; Saadoune, I.; Gustafsson, T.; Edström, K.; Svedlindh, P.
2010-06-01
Investigations of the magnetic behavior of the layered oxide, LiNi0.65Co0.25Mn0.10O2 , through ac and time-dependent susceptibility, dc linear and nonlinear susceptibility as well as neutron-diffraction measurements are presented. A ferrimagneticlike spin ordering appears at 119 K with a spontaneous magnetization coexisting with spin frustration in two dimensions (2D). At lower temperature, a cluster-glass transition is found at 17.4 K indicating a transformation to a completely frustrated state in three dimensions (3D). A dimensionality crossover with temperature, from 2D to 3D, in a magnetically frustrated system has been demonstrated. The observed magnetic behavior is believed to originate from a percolating system of spin clusters defined by disordered and frustrated exchange interactions and the findings conform well with predictions of the percolation cluster model.
NASA Astrophysics Data System (ADS)
Ambal, K.; Payne, A.; Waters, D. P.; Williams, C. C.; Boehme, C.
2015-08-01
The suitability of the spin dynamics of paramagnetic silicon dangling bonds (E' centers) in high-E'-density amorphous silicon dioxide (SiO2 ) as probe spins for single-spin tunneling force microscopy (SSTFM) is studied. SSTFM is a spin-selection-rule-based scanning-probe single-spin readout concept. Following the synthesis of SiO2 thin films on (111)-oriented crystalline-silicon substrates with room-temperature stable densities of [E'] >5 ×1018 cm-3 throughout the 60-nm thin film, pulsed electron paramagnetic resonance spectroscopy is conducted on the E' centers at temperatures between T =5 K and T =70 K . The measurements reveal that the spin coherence (the transverse spin-relaxation time T2) of these centers is significantly shortened compared to low-E'-density SiO2 films and within error margins not dependent on temperature. In contrast, the spin-flip times (the longitudinal relaxation times T1) are dependent on the temperature but with much weaker dependence than low-density SiO2 , with the greatest deviations from low-density SiO2 seen for T =5 K . These results, discussed in the context of the spin-relaxation dynamics of dangling-bond states of other silicon-based disordered solids, indicate the suitability of E' centers in high-density SiO2 as probe spins for SSTFM.
Exact out-of-equilibrium central spin dynamics from integrability
NASA Astrophysics Data System (ADS)
Fioretto, Davide; Caux, Jean-Sébastien; Gritsev, Vladimir
2014-04-01
We consider a Gaudin magnet (central spin model) with a time-dependent exchange couplings. We explicitly show that the Schrödinger equation is analytically solvable in terms of generalized hypergeometric functions for particular choices of the time dependence of the coupling constants. Our method establishes a new link between this system and the SU\\left( 2 \\right) Wess-Zumino-Witten model, and sheds new light on the implications of integrability in out-of-equilibrium quantum physics. As an application, a driven four-spin system is studied in detail.
Spin crossover in ferropericlase from first-principles molecular dynamics.
Holmström, E; Stixrude, L
2015-03-20
Ferropericlase, (Mg,Fe)O, is the second-most abundant mineral of Earth's lower mantle. With increasing pressure, the Fe ions in the material begin to collapse from a magnetic to nonmagnetic spin state. We present a finite-temperature first-principles phase diagram of this spin crossover, finding a broad pressure range with coexisting magnetic and nonmagnetic ions due to favorable enthalpy of mixing of the two. Furthermore, we find the electrical conductivity of the mineral to reach semimetallic values inside Earth. PMID:25839305
Slow Spin Dynamics in Superconducting Ca0.9Ce0.1Fe2As2
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
Slow Spin Dynamics in Superconducting Ca0.9Ce0.1Fe2As2.
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
Dynamic strain-mediated coupling of a single diamond spin to a mechanical resonator
NASA Astrophysics Data System (ADS)
Ovartchaiyapong, Preeti; Lee, Kenneth W.; Myers, Bryan A.; Jayich, Ania C. Bleszynski
2014-07-01
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.
Two-level system in spin baths: Non-adiabatic dynamics and heat transport
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.
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.
Dynamical magnetic anisotropy in spin--1 molecular systems
NASA Astrophysics Data System (ADS)
Ruiz-Tijerina, David; Cornaglia, Pablo; Balseiro, Carlos; Ulloa, Sergio
2012-02-01
We study electronic transport through a deformable spin-1 molecular system in a break junction setup, under the influence of a local vibrational mode. Our study shows that the magnetic anisotropy, which arises due to stretching along the transport axis[Science 328 1370 (2010)], is renormalized by the interactions with vibrations. The coupling induces additional spin--asymmetric hybridizations that contribute to the net molecular anisotropy. We show that the low temperature physics of such device can be described by an anisotropic Kondo model (J> J), with a magnetic anisotropy term, ANetSz^2, negative at zero stretching. A quantum phase transition (QPT) is explored by stretching the molecule, driving ANet into positive values, and changing the character of the device from a non--Fermi--liquid (NFL) to a Fermi liquid (FL) ground state. This transition can be directly observed through the zero--bias conductance, which we find to be finite for negative anisotropy, zero for positive anisotropy, and to reach the unitary limit at ANet 0. At that point, an underscreened spin-1 Kondo ground state appears due to the restitution of the spin-1 triplet degeneracy.
Gravitational radiation and angular momentum flux from a spinning dynamical black hole
Wang, Chih-Hung
2013-01-01
A four-dimensional asymptotic expansion scheme is used to study the next order effects of the nonlinearity near a spinning dynamical black hole. The angular momentum flux and energy flux formula are then obtained by asymptotic expansion and the compatibility of the coupling Newman-Penrose equations. After constructing the reference frame in terms of the compatible constant spinors, the energy-momentum flux is derived and it is related to the black hole area growth. Directly from the flux formula of the spinning dynamical horizon, we find that the physically reasonable condition on the positivity of the gravitational energy flux yields that the shear will monotonically decrease with time.
Geometric phases and quantum correlations dynamics in spin-boson model
Wu, Wei; Xu, Jing-Bo, E-mail: xujb@zju.edu.cn [Zhejiang Institute of Modern Physics and Physics Department, Zhejiang University, Hangzhou 310027 (China)
2014-01-28
We explore the dynamics of spin-boson model for the Ohmic bath by employing the master equation approach and obtain an explicit expression of reduced density matrix. We also calculate the geometric phases of the spin-boson model by making use of the analytical results and discuss how the dissipative bosonic environment affects geometric phases. Furthermore, we investigate the dynamics of quantum discord and entanglement of two qubits each locally interacting with its own independent bosonic environments. It is found that the decay properties of quantum discord and entanglement are sensitive to the choice of initial state's parameter and coupling strength between system and bath.
Spin dynamics and relaxation in graphene nanoribbons: electron spin resonance probing.
Rao, Singamaneni S; Stesmans, Andre; van Tol, Johan; Kosynkin, Dmitry V; Higginbotham-Duque, A; Lu, Wei; Sinitskii, Alexander; Tour, James M
2012-09-25
Here we report the results of a multifrequency (~9, 20, 34, 239.2, and 336 GHz) variable-temperature continuous wave (cw) and X-band (~9 GHz) pulse electron spin resonance (ESR) measurement performed at cryogenic temperatures on potassium split graphene nanoribbons (GNRs). Important experimental findings include the following: (a) The multifrequency cw ESR data infer the presence of only carbon-related paramagnetic nonbonding states, at any measured temperature, with the g value independent of microwave frequency and temperature. (b) A linear broadening of the ESR signal as a function of microwave frequency is noticed. The observed linear frequency dependence of ESR signal width points to a distribution of g factors causing the non-Lorentzian line shape, and the g broadening contribution is found to be very small. (c) The ESR process is found to be characterized by slow and fast components, whose temperature dependences could be well described by a tunneling level state model. This work not only could help in advancing the present fundamental understanding on the edge spin (or magnetic)-based properties of GNRs but also pave the way to GNR-based spin devices. PMID:22901098
Proving Competence: Integrative Assessment and Web-Based Portfolio System in a Dynamic Curriculum.
ERIC Educational Resources Information Center
Wielenga, Douwe
Since 1997, the Amsterdam Faculty of Education (EFA) has been officially recognized as a center for experimental teacher education. This paper describes the development of an assessment system and a World Wide Web-based portfolio system to help students take responsibility for their learning and their competence at three consecutive integrative
Academic Freedom, the First Amendment and Competing Stakeholders: The Dynamics of a Changing Balance
ERIC Educational Resources Information Center
Jorgensen, James D.; Helms, Lelia B.
2008-01-01
The Supreme Court first affirmed the importance of academic freedom in 1957. Yet in subsequent cases, First Amendment precedent has displaced the concept of academic freedom to resolve disputes among competing interests on public campuses, primarily in favor of institutions. This paper draws on the concepts of path dependence and policy space to
ERIC Educational Resources Information Center
Sperry, Len
2010-01-01
Cultural sensitivity and cultural competence in the selection of culturally sensitive treatments is a requisite for effective counseling practice in working with diverse clients and their families, particularly when clients present with health issues or medical problems. Described here is a strategy for selecting culturally sensitive treatments
RosettaEPR: Rotamer Library for Spin Label Structure and Dynamics
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. Rosettas 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 Ĺ. 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 Ĺ. 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
NASA Astrophysics Data System (ADS)
Soh, Wee Tee; Peng, Bin; Ong, C. K.
2015-08-01
The spin rectification effect (SRE), a phenomenon that generates dc voltages from ac microwave fields incident onto a conducting ferromagnet, has attracted widespread attention due to its high sensitivity to ferromagnetic resonance (FMR) as well as its relevance to spintronics. Here, we report the non-local detection of yttrium iron garnet (YIG) spin dynamics by measuring SRE voltages from an adjacent conducting NiFe layer up to 200 nm thick. In particular, we detect, within the NiFe layer, SRE voltages stemming from magnetostatic surface spin waves (MSSWs) of the adjacent bulk YIG which are excited by a shorted coaxial probe. These non-local SRE voltages within the NiFe layer that originates from YIG MSSWs are present even in 200 nm-thick NiFe films with a 50 nm thick SiO2 spacer between NiFe and YIG, thus strongly ruling out the mechanism of spin-pumping induced inverse spin Hall effect in NiFe as the source of these voltages. This long-range influence of YIG dynamics is suggested to be mediated by dynamic fields generated from YIG spin precession near YIG/NiFe interface, which interacts with NiFe spins near the simultaneous resonance of both spins, to generate a non-local SRE voltage within the NiFe layer.
Distinguishing the ultrafast dynamics of orbital and spin magnetic moments in solids
NASA Astrophysics Data System (ADS)
Boeglin, Christine
2011-03-01
Ultrafast magnetization dynamics is an important issue for both fundamental science and for applications in order to optimize spin manipulation on a microscopic level. Since the first observation of laser induced spin dynamics, the mechanisms of angular momentum dissipation at picosecond timescales have been widely debated. In order to progress in the understanding of such microscopic ultrafast mechanisms, it is now possible to probe absolute values of magnetization with a high temporal resolution (100 fs). In this context, we have used ultrashort optical laser pulses (60 fs duration) to induce changes of the magnetization in a ferromagnetic CoPd alloy film with perpendicular anisotropy. The dynamics was probed with ultrashort circularly polarized femtosecond X-ray pulses, measuring the X-ray magnetic circular dichroism (XMCD) at Co L2 , 3 edges. , We observe that the two components of the magnetic moments (L and S) show different ultrafast dynamics and that the spin-orbit coupling related to the magneto-crystalline anisotropy in solids is strongly affected by fs laser pulses in the ultrashort time scales. These dynamics can be compared to the purely electronic effect at the Co L3 edge. Electronic excitations and their response to the laser pump pulse will be discussed and related to the modifications in the spin-orbit coupling. We will compare our results with time resolved MOKE experiments recently performed on CoPd alloys. Beaurepaire, E., Merle, J.C., Daunois, A., and Bigot, J.-Y. Phys. Rev. Lett. 76, 4250 (1996).
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.
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.
Dynamics and control of flexible spinning solar sails under reflectivity modulation
NASA Astrophysics Data System (ADS)
Mu, Junshan; Gong, Shengping; Ma, Pengbin; Li, Junfeng
2015-10-01
Electrochromic devices have been used for the attitude control of a spinning solar sail in a deep space mission by modulating the reflectivity of the sail membrane. As a flexible spinning solar sail has no rigid structure to support its membrane, the distributed load due to solar radiation will lead to the deformation of the sail membrane, and the control torque generated by reflectivity modulation can introduce oscillatory motion to the membrane. By contrast, the deformation and oscillatory motion of the sail membrane have an impact on the performance of the reflectivity control. This paper investigates the dynamics and control of flexible spinning solar sails under reflectivity modulation. The static deformation of a spinning sail membrane subjected to solar radiation pressure in an equilibrium state is analyzed. The von Karman theory is used to obtain the displacements and the stress distribution in the equilibrium states. A simplified analytical first-order mode is chosen to model the membrane oscillation. The coupled membrane oscillation-attitude-orbit dynamics are considered for a GeoSail formation flying mission. The relative attitude and orbit control of flexible spinning solar sails under reflectivity modulation are numerically tested. The simulations indicate that the membrane deformation and oscillation have a lower impact on the control of the reflectivity modulated sails than the increase of the spinning rate.
Gibney, Brian R.
Global Topology & Stability and Local Structure & Dynamics in a Synthetic Spin-Labeled Four and stability and the rotational dynamics of the spin-label. Gel-permeation chromatography demonstrated.3 ( 0.5 ns, consistent with that expected for the tumbling of the four helix bundle itself, indicating
Direct observation of coherent interorbital spin-exchange dynamics.
Cappellini, G; Mancini, M; Pagano, G; Lombardi, P; Livi, L; Siciliani de Cumis, M; Cancio, P; Pizzocaro, M; Calonico, D; Levi, F; Sias, C; Catani, J; Inguscio, M; Fallani, L
2014-09-19
We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold 173Yb fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of 173Yb atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism. PMID:25279608
Flight dynamics of a spinning projectile descending on a parachute
Benedetti, G.A.
1989-02-01
During the past twenty years Sandia National Laboratories and the US Army have vertically gun launched numerous 155mm and eight-inch diameter flight test projectiles. These projectiles are subsequently recovered using an on-board parachute recovery system which is attached to the forward case structure of the projectile. There have been at least five attempts to describe, through analytical and numerical simulations, the translational and rotational motions of a spinning projectile descending on a parachute. However, none of these investigations have correctly described the large nutational motion of the projectile since all of them overlooked the fundamental mechanism which causes these angular motions. Numerical simulations as well as a closed form analytical solution show conclusively that the Magnus moment is responsible for the large nutational motion of the projectile. That is, when the center of pressure for the Magnus force is aft of the center of mass for the projectile, the Magnus moment causes an unstable (or large) nutational motion which always tends to turn the spinning projectile upside down while it is descending on the parachute. Conversely, when the center of mass for the projectile is aft of the center of pressure for the Magnus force, the Magnus moment stabilizes the nutational motion tending to always point the base of the spinning projectile down. The results of this work are utilized to render projectile parachute recovery systems more reliable and to explain what initially may appear to be strange gyrodynamic behavior of a spinning projectile descending on a parachute. 14 refs., 20 figs.
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.
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.
Chaotic spin-dependent electron dynamics in a field-driven double dot potential
L. Chotorlishvili; Z. Toklikishvili; A. Komnik; J. Berakdar
2011-10-30
We study the nonlinear classical dynamics of an electron confined in a double dot potential and subjected to a spin-orbit coupling and a constant external magnetic field. It is shown that due to the spin orbit coupling, the energy can be transferred from the spin to the orbital motion. This naturally heats up the orbital motion which, due to the presence of the separatrix line in the phase space of the system, results in a motion of the electron between the dots. It is shown that depending on the strength of the spin orbit coupling and the energy of the system, the electronic orbital motion undergoes a transition from the regular to the chaotic regime.
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.
NASA Astrophysics Data System (ADS)
Mance, Deni; Gast, Peter; Huber, Martina; Baldus, Marc; Ivanov, Konstantin L.
2015-06-01
We develop a theoretical description of Dynamic Nuclear Polarization (DNP) in solids under Magic Angle Spinning (MAS) to describe the magnetic field dependence of the DNP effect. The treatment is based on an efficient scheme for numerical solution of the Liouville-von Neumann equation, which explicitly takes into account the variation of magnetic interactions during the sample spinning. The dependence of the cross-effect MAS-DNP on various parameters, such as the hyperfine interaction, electron-electron dipolar interaction, microwave field strength, and electron spin relaxation rates, is analyzed. Electron spin relaxation rates are determined by electron paramagnetic resonance measurements, and calculations are compared to experimental data. Our results suggest that the observed nuclear magnetic resonance signal enhancements provided by MAS-DNP can be explained by discriminating between "bulk" and "core" nuclei and by taking into account the slow DNP build-up rate for the bulk nuclei.
Chaotic dynamics of stellar spin in binaries and the production of misaligned hot Jupiters.
Storch, Natalia I; Anderson, Kassandra R; Lai, Dong
2014-09-12
Many exoplanetary systems containing hot Jupiters are observed to have highly misaligned orbital axes relative to the stellar spin axes. Kozai-Lidov oscillations of orbital eccentricity and inclination induced by a binary companion, in conjunction with tidal dissipation, constitute a major channel for the production of hot Jupiters. We demonstrate that gravitational interaction between the planet and its oblate host star can lead to chaotic evolution of the stellar spin axis during Kozai cycles. As parameters such as the planet mass and stellar rotation period are varied, periodic islands can appear in an ocean of chaos, in a manner reminiscent of other dynamical systems. In the presence of tidal dissipation, the complex spin evolution can leave an imprint on the final spin-orbit misalignment angles. PMID:25214623
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.
Dynamical symmetries and crossovers in a three-spin system with collective dissipation
NASA Astrophysics Data System (ADS)
Pigeon, S.; Xuereb, A.; Lesanovsky, I.; Garrahan, J. P.; De Chiara, G.; Paternostro, M.
2015-01-01
We consider the non-equilibrium dynamics of a simple system consisting of interacting spin-1/2 particles subjected to a collective damping. The model is close to situations that can be engineered in hybrid electro/opto-mechanical settings. Making use of large-deviation theory, we find a GallavottiCohen symmetry in the dynamics of the system as well as evidence for the coexistence of two dynamical phases with different activity levels. We show that additional damping processes smooth out this behavior. Our analytical results are backed up by Monte Carlo simulations that reveal the nature of the trajectories contributing to the different dynamical phases.
Time-resolved study of dynamic electrical spin transport in Fe/GaAs devices
NASA Astrophysics Data System (ADS)
Sizeland, James; Cheng, Tuyuan; Hu, Xuefeng; Lu, Cong; Will, Iain; Xu, Yongbing; Lazarov, Vlado; Wu, Jing
2013-03-01
Fe/GaAs(100) samples have been grown containing a bilayer of progressively doped layers of GaAs to regulate the Schottky barrier to coherent spin-injection. These have been fabricated into devices using photolithography techniques. Time-resolved spin transport studies have been undertaken by picosecond MOKE probing of the exposed undoped-GaAs surface between, 10nm thick, magnetically saturated Fe pads set 50 ?m apart. This has been done at systematic time intervals (from 0-1ns with 25ps steps) after electrical current pumping, at varied distance from the point of injection (in 1 ?m steps) and over a range of temperatures from 4K - 300K. In this manner the dynamic spin transport has been observed and related to these key factors. Cross-sectional STEM data has been produced to complement this investigation making comment on the interfacial ordering effects on the spin injection properties. Fe/GaAs(100) samples have been grown containing a bilayer of progressively doped layers of GaAs to regulate the Schottky barrier to coherent spin-injection. These have been fabricated into devices using photolithography techniques. Time-resolved spin transport studies have been undertaken by picosecond MOKE probing of the exposed undoped-GaAs surface between, 10nm thick, magnetically saturated Fe pads set 50 ?m apart. This has been done at systematic time intervals (from 0-1ns with 25ps steps) after electrical current pumping, at varied distance from the point of injection (in 1 ?m steps) and over a range of temperatures from 4K - 300K. In this manner the dynamic spin transport has been observed and related to these key factors. Cross-sectional STEM data has been produced to complement this investigation making comment on the interfacial ordering effects on the spin injection properties. EPSRC, York JEOL nanocentre
Muon spin relaxation study of spin dynamics in a polysaccharide iron complex
van Lierop, J.; Ryan, D. H.; Pumarol, M. E.; Roseman, M.
2001-06-01
Polysaccharide iron complex, a ferritin analog, has been examined with zero-field muon spin-relaxation at temperatures from 2 to 40 K. Spectra exhibit a clear separation of static moments and collective excitations at low temperatures. At intermediate temperatures, superparamagnetic relaxation is observed and a blocking temperature of T{sub B}=10{+-}2.5K is measured, in agreement with transmission Mossbauer spectra and frequency dependent {chi}{sub ac} data. Superparamagnetic relaxation rates of 20{endash}150 MHz are in agreement with those extrapolated from Mossbauer spectra using a multilevel magnetic relaxation model. {copyright} 2001 American Institute of Physics.
Dynamics revealed by correlations of time-distributed weak measurements of a single spin
R. -B. Liu; Shu-Hong Fung; Hok-Kin Fung; A. N. Korotkov; L. J. Sham
2009-12-20
We show that the correlations in stochastic outputs of time-distributed weak measurements can be used to study the dynamics of an individual quantum object, with a proof-of-principle setup based on small Faraday rotation caused by a single spin in a quantum dot. In particular, the third order correlation can reveal the "true" spin decoherence, which would otherwise be concealed by the inhomogeneous broadening effect in the second order correlations. The viability of such approaches lies in that (1) in weak measurement the state collapse which would disturb the system dynamics occurs at a very low probability, and (2) a shot of measurement projecting the quantum object to a known basis state serves as a starter or stopper of the evolution without pumping or coherently controlling the system as otherwise required in conventional spin echo.
NASA Astrophysics Data System (ADS)
Cygorek, M.; Tamborenea, P. I.; Axt, V. M.
2015-09-01
We study the spin dynamics of carriers due to the Rashba interaction in semiconductor quantum disks and wells after excitation with light with orbital angular momentum. We find that although twisted light transfers orbital angular momentum to the excited carriers and the Rashba interaction conserves their total angular momentum, the resulting electronic spin dynamics is essentially the same for excitation with light with orbital angular momentum l =+|l | and l =-|l | . The differences between cases with different values of |l | are due to the excitation of states with slightly different energies and not to the different angular momenta per se and vanish for samples with large radii where a k -space quasicontinuum limit can be established. These findings apply not only to the Rashba interaction but also to all other envelope-function-approximation spin-orbit Hamiltonians like the Dresselhaus coupling.
Non-Gaussian stochastic dynamics of spins and oscillators: A continuous-time random walk approach
NASA Astrophysics Data System (ADS)
Packwood, Daniel M.; Tanimura, Yoshitaka
2011-12-01
We consider separately a spin and an oscillator that are coupled to their environment. After a finite interval of random length, the state of the environment changes, and each change causes a random change in the resonance frequency of the spin or vibrational frequency of the oscillator. Mathematically, the evolution of these frequencies is described by a continuous-time random walk. Physically, the stochastic dynamics can be understood as non-Gaussian because the frequency of the system and state of the environment change on comparable time scales. These dynamics are also nonstationary, and so might apply to a nonequilibrium environment. The re-sonance and vibrational spectra of the spin and oscillator, as well as the ensemble-averaged displacement of the oscillator, are investigated in detail. We observe some distinct non-Gaussian features of the dynamics, such as the narrow, leptokurtic shape of the resonance spectrum of the spin and beating of the average oscillator displacement. The convergence to Gaussian dynamics as changes in the environment occur with increasing frequency is also considered. Among other results, we observe narrowing of the resonance and vibrational lines in the Gaussian limit due to a weakening of the system-environment interaction.
Kais, Sabre
helium atoms M. El-Batanouny, G. Murthy, and C. R. Willis Department of Physics, Boston University atoms (He*) from surfaces of magnetic insulators to study the dynamical properties of surface electron a metastable He atom and the surface electron spins are determined by a configuration interaction calculation
Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments V. V. Dobrovitski,1
Decay of Rabi Oscillations by Dipolar-Coupled Dynamical Spin Environments V. V. Dobrovitski,1 A. E, California 93106, USA (Received 1 April 2009; published 9 June 2009) We study the Rabi oscillations decay and rate of Rabi oscillations decay can be used to experimentally determine the intrabath coupling strength
van Saarloos, Wim
Charged domain-wall dynamics in doped antiferromagnets and spin fluctuations in cuprate is characterized by many- hole correlations of the charged magnetic domain-wall type. Here we focus on the strong-coupling limit where all holes are bound to domain walls. We assert that at high temperatures a classical domain
Spin-transfer induced vortex dynamics with non-standard angular dependence torque
NASA Astrophysics Data System (ADS)
Bortolotti, Paolo; Locatelli, Nicolas; Cros, Vincent; Grollier, Julie; Machedo, Rita; Ferreira, Ricardo; Cardoso, Susana; Fert, Albert
2011-03-01
Microwave emissions driven by spin-transfer were firstly observed on FeNi/Cu/FeNi pillars (standard samples) characterized by uniform magnetization. Interestingly, by tuning the spin accumulation profile, i.e., choosing Co/Cu/FeNi pillars with opportune ratio of thickness/spin diffusion length (non-standard samples), it is possible to obtain strong modification of the torque angular dependence and, more generally, of the magnetization dynamics itself. Eventually, oscillations at zero applied field were observed for these non-standard pillars, again for uniform magnetization. However, when a large current density is applied, the uniform hypothesis is broken and vortex states are favoured. In this work we want to stress that non standard-angular dependence, obtained for such Co/Cu/FeNi samples, plays an important role also for vortex dynamics. By the combined study of static and dynamic response, we can discriminate among all possible combinations of vortex chiralities and polarities. The evolution with field and current of such configurations clearly differs from samples with standard spin-torque angular dependence, resulting in a different dynamics for such non-standard samples.
Three-dimensional Computational Fluid Dynamics Investigation of a Spinning Helicopter Slung Load
NASA Technical Reports Server (NTRS)
Theorn, J. N.; Duque, E. P. N.; Cicolani, L.; Halsey, R.
2005-01-01
After performing steady-state Computational Fluid Dynamics (CFD) calculations using OVERFLOW to validate the CFD method against static wind-tunnel data of a box-shaped cargo container, the same setup was used to investigate unsteady flow with a moving body. Results were compared to flight test data previously collected in which the container is spinning.
Efficient Lie-Poisson Integrator for Secular Spin Dynamics of Rigid Bodies Slawomir Breiter
Nesvorny, David
in item 2. As far as the problems of major planets are concerned, the rotation history of Mercury-orbit coupling of close planetary satellites, Mercury or secondary components of asteroid binaries. 2. Precession), but on the other hand Earth and Mars remain the distinguished cases where secular spin dynamics (type 2) applies
Polariton and spin dynamics in semiconductor microcavities under non-resonant excitation
NASA Astrophysics Data System (ADS)
Martín, M. D.; Aichmayr, G.; Amo, A.; Ballarini, D.; Klopotowski, L.; Vińa, L.
2007-07-01
Semiconductor microcavities offer an ideal scenario to study strong radiation-matter interactions. In this paper we review the temporal dynamics of polaritons in II-VI and III-V based microcavities under non-resonant excitation conditions. We present evidence of final-state stimulated scattering and discuss the spin-dependent emission, which exhibits a remarkably rich behaviour.
Room-temperature electric-field controlled spin dynamics in ,,110... InAs quantum wells
Flatte, Michael E.
are promising for the prospect of nonmagnetic low-power, high-speed spintronics. Š 2005 American InstituteRoom-temperature electric-field controlled spin dynamics in ,,110... InAs quantum wells K. C. Halla; accepted 20 April 2005; published online 13 May 2005 We report the demonstration of room temperature gate
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.
Competing exchanges and spin-phonon coupling in Eu1-xRxMnO3 (R=Y, Lu)
NASA Astrophysics Data System (ADS)
Mota, D. A.; Romaguera Barcelay, Y.; Tavares, P. B.; Chaves, M. R.; Almeida, A.; Oliveira, J.; Ferreira, W. S.; Agostinho Moreira, J.
2013-06-01
This work is focused on the phase diagrams and physical properties of Y-doped and Lu-doped EuMnO3. The differences in the corresponding phase boundaries in the (x,T) phase diagram could be overcome by considering a scaling of the Y3+ and Lu3+ concentrations to the tolerance factor. This outcome evidences that the tolerance factor is in fact a more reliable representative of the lattice deformation induced by doping. The normalization of the phase boundaries using the tolerance factor corroborates previous theoretical outcomes regarding the key role of competitive FM and AFM exchanges in determining the phase diagrams of manganite perovskites. However, significant differences in the nature and number of phases at low temperatures and concentrations could not be explained by just considering the normalization to the tolerance factor. The vertical phase boundary observed just for Lu-doped EuMnO3, close to 10% Lu, is understood by considering a low temperature Peierls-type spin-phonon coupling, which stabilizes the AFM-4 phase in Lu-doped EuMnO3.
Dynamics of polymer film formation during spin coating
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.
Solid effect in magic angle spinning dynamic nuclear polarization
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 ...
Advances and applications of dynamic-angle spinning nuclear magnetic resonance
Baltisberger, J.H.
1993-06-01
This dissertation describes nuclear magnetic resonance experiments and theory which have been developed to study quadrupolar nuclei (those nuclei with spin greater than one-half) in the solid state. Primarily, the technique of dynamic-angle spinning (DAS) is extensively reviewed and expanded upon in this thesis. Specifically, the improvement in both the resolution (two-dimensional pure-absorptive phase methods and DAS angle choice) and sensitivity (pulse-sequence development), along with effective spinning speed enhancement (again through choice of DAS conditions or alternative multiple pulse schemes) of dynamic-angle spinning experiment was realized with both theory and experimental examples. The application of DAS to new types of nuclei (specifically the {sup 87}Rb and {sup 85}Rb nuclear spins) and materials (specifically amorphous solids) has also greatly expanded the possibilities of the use of DAS to study a larger range of materials. This dissertation is meant to demonstrate both recent advances and applications of the DAS technique, and by no means represents a comprehensive study of any particular chemical problem.
Resolving the role of femtosecond heated electrons in ultrafast spin dynamics
Mendil, J.; Nieves, P.; Chubykalo-Fesenko, O.; Walowski, J.; Santos, T.; Pisana, S.; Münzenberg, M.
2014-01-01
Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal. PMID:24496221
Optimizing a dynamical decoupling protocol for solid-state electronic spin ensembles in diamond
NASA Astrophysics Data System (ADS)
Farfurnik, D.; Jarmola, A.; Pham, L. M.; Wang, Z. H.; Dobrovitski, V. V.; Walsworth, R. L.; Budker, D.; Bar-Gill, N.
2015-08-01
We demonstrate significant improvements of the spin coherence time of a dense ensemble of nitrogen-vacancy (NV) centers in diamond through optimized dynamical decoupling (DD). Cooling the sample down to 77 K suppresses longitudinal spin relaxation T1 effects and DD microwave pulses are used to increase the transverse coherence time T2 from 0.7 ms up to 30 ms . We extend previous work of single-axis (Carr-Purcell-Meiboom-Gill) DD towards the preservation of arbitrary spin states. Following a theoretical and experimental characterization of pulse and detuning errors, we compare the performance of various DD protocols. We 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.
Optimizing a Dynamical Decoupling Protocol for Solid-State Electronic Spin Ensembles in Diamond
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.
Dynamics and performance optimization of spin-torque switching in magnetic tunnel junctions
NASA Astrophysics Data System (ADS)
Dunn, Thomas Edward
In this thesis I present a theoretical description for spin-torque switching using AC and DC spin-currents. This description builds from the standard Landau-Lifshitz-Gilbert equation with Slonczewski spin-torque. By exploiting a separation in time-scales between the fast precessional motion of the free layer magnetization about the effective field and the slow drift of the free layer towards higher or lower energies that results from ST and damping, I reduce the free layer switching dynamics to that of a one dimensional system. Using this description I characterize certain current and frequency values important to switching, such as the DC critical current and the AC upper bifurcation frequency. Finally, using this description I show how to optimize the efficiency of AC, DC, and combination AC/DC spin-current strategies to minimize the Joule heat loss associated with switching. This leads to a well-defined range of spin-current polarization and free layer anisotropy values where each spin-current strategy is optimal.
Dynamical transition in the D=3 Edwards-Anderson spin glass in an external magnetic field.
Baity-Jesi, M; Bańos, R A; Cruz, A; Fernandez, L A; Gil-Narvion, J M; Gordillo-Guerrero, A; Ińiguez, D; Maiorano, A; Mantovani, F; Marinari, E; Martin-Mayor, V; Monforte-Garcia, J; Muńoz Sudupe, A; Navarro, D; Parisi, G; Perez-Gaviro, S; Pivanti, M; Ricci-Tersenghi, F; Ruiz-Lorenzo, J J; Schifano, S F; Seoane, B; Tarancon, A; Tripiccione, R; Yllanes, D
2014-03-01
We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses. PMID:24730822
Dynamical transition in the D =3 Edwards-Anderson spin glass in an external magnetic field
NASA Astrophysics Data System (ADS)
Baity-Jesi, M.; Bańos, R. A.; Cruz, A.; Fernandez, L. A.; Gil-Narvion, J. M.; Gordillo-Guerrero, A.; Ińiguez, D.; Maiorano, A.; Mantovani, F.; Marinari, E.; Martin-Mayor, V.; Monforte-Garcia, J.; Muńoz Sudupe, A.; Navarro, D.; Parisi, G.; Perez-Gaviro, S.; Pivanti, M.; Ricci-Tersenghi, F.; Ruiz-Lorenzo, J. J.; Schifano, S. F.; Seoane, B.; Tarancon, A.; Tripiccione, R.; Yllanes, D.; Janus Collaboration
2014-03-01
We study the off-equilibrium dynamics of the three-dimensional Ising spin glass in the presence of an external magnetic field. We have performed simulations both at fixed temperature and with an annealing protocol. Thanks to the Janus special-purpose computer, based on field-programmable gate array (FPGAs), we have been able to reach times equivalent to 0.01 s in experiments. We have studied the system relaxation both for high and for low temperatures, clearly identifying a dynamical transition point. This dynamical temperature is strictly positive and depends on the external applied magnetic field. We discuss different possibilities for the underlying physics, which include a thermodynamical spin-glass transition, a mode-coupling crossover, or an interpretation reminiscent of the random first-order picture of structural glasses.
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.
Order and thermalized dynamics in Heisenberg-like square and Kagomé spin ices.
Wysin, G M; Pereira, A R; Moura-Melo, W A; de Araujo, C I L
2015-02-25
Thermodynamic properties of a spin ice model on a Kagomé lattice are obtained from dynamic simulations and compared with properties in square lattice spin ice. The model assumes three-component Heisenberg-like dipoles of an array of planar magnetic islands situated on a Kagomé lattice. Ising variables are avoided. The island dipoles interact via long-range dipolar interactions and are restricted in their motion due to local shape anisotropies. We define various order parameters and obtain them and thermodynamic properties from the dynamics of the system via a Langevin equation, solved by the Heun algorithm. Generally, a slow cooling from high to low temperature does not lead to a particular state of order, even for a set of coupling parameters that gives well thermalized states and dynamics. At very low temperature, however, square ice is more likely to reach states near the ground state than Kagomé ice, for the same island coupling parameters. PMID:25640326
Static and Dynamic Properties of Interacting Spin-1 Bosons in an Optical Lattice
Stefan S. Natu; J. H. Pixley; S. Das Sarma
2015-02-03
We study the physics of interacting spin-$1$ bosons in an optical lattice using a variational Gutzwiller technique. We compute the mean-field ground state wave-function and discuss the evolution of the condensate, spin, nematic, and singlet order parameters across the superfluid-Mott transition. We then extend the Gutzwiller method to derive the equations governing the dynamics of low energy excitations in the lattice. Linearizing these equations, we compute the excitation spectra in the superfluid and Mott phases for both ferromagnetic and antiferromagnetic spin-spin interactions. In the superfluid phase, we recover the known excitation spectrum obtained from Bogoliubov theory. In the nematic Mott phase, we obtain gapped, quadratically dispersing particle and hole-like collective modes, whereas in the singlet Mott phase, we obtain a non-dispersive gapped mode, corresponding to the breaking of a singlet pair. For the ferromagnetic Mott insulator, the Gutzwiller mean-field theory only yields particle-hole like modes but no Goldstone mode associated with long range spin order. To overcome this limitation, we supplement the Gutzwiller theory with a Schwinger boson mean-field theory which captures super-exchange driven fluctuations. In addition to the gapped particle-hole-like modes, we obtain a gapless quadratically dispersing ferromagnetic spin-wave Goldstone mode. We discuss the evolution of the singlet gap, particle-hole gap, and the effective mass of the ferromagnetic Goldstone mode as the superfluid-Mott phase boundary is approached from the insulating side. We discuss the relevance and validity of Gutzwiller mean-field theories to spinful systems, and potential extensions of this framework to include more exotic physics which appears in the presence of spin-orbit coupling or artificial gauge fields.
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.
Approach to solving spin-boson dynamics via non-Markovian quantum trajectories
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.
Homoclinic solutions and motion chaotization in attitude dynamics of a multi-spin spacecraft
NASA Astrophysics Data System (ADS)
Doroshin, Anton V.
2014-07-01
The attitude dynamics of the multi-spin spacecraft (MSSC) and the torque-free angular motion of the multi-rotor system are considered. Some types of homoclinic and general solutions are obtained in hyperbolic and elliptic functions. The local homoclinic chaos in the MSSC angular motion is investigated under the influence of polyharmonic perturbations. Some possible applications of the multi-rotor system are indicated, including gyrostat-satellites, dual-spin spacecraft, roll-walking robots, and also the inertialess method of the spacecraft attitude (angular) reorientation/control.
Wasielewski, M. R.
1998-08-27
Our current work in modeling reaction center dynamics has resulted in the observation of each major spin-dependent photochemical pathway that is observed in reaction centers. The development of new, simpler model systems has permitted us to probe deeply into the mechanistic issues that drive these dynamics. Based on these results we have returned to biomimetic chlorophyll-based electron donors to mimic these dynamics. Future studies will focus on the details of electronic structure and energetic of both the donor-acceptor molecules and their surrounding environment that dictate the mechanistic pathways and result in efficient photosynthetic charge separation.
Dynamical effects of spin-dependent interactions in low- and intermediate-energy heavy-ion reactions
Jun Xu; Bao-An Li; Wen-Qing Shen; Yin Xia
2015-08-16
It is well known that non-central nuclear forces, such as the spin-orbital coupling and the tensor force, play important roles in understanding many interesting features of nuclear structures. However, their dynamical effects in nuclear reactions are poorly known since only the spin-averaged observables are normally studied both experimentally and theoretically. Realizing that spin-sensitive observables in nuclear reactions may carry useful information about the in-medium properties of non-central nuclear interactions, besides earlier studies using the time-dependent Hartree-Fock approach to understand effects of spin-orbital coupling on the threshold energy and spin polarization in fusion reactions, some efforts have been made recently to explore dynamical effects of non-central nuclear forces in intermediate-energy heavy-ion collisions using transport models. The focuses of these studies have been on investigating signatures of the density and isospin dependence of the form factor in the spin-dependent single-nucleon potential. Interestingly, some useful probes were identified in the model studies while so far there is still no data to compare with. In this brief review, we summarize the main physics motivations as well as the recent progress in understanding the spin dynamics and identifying spin-sensitive observables in heavy-ion reactions at intermediate energies. We hope the interesting, important, and new physics potentials identified in the spin dynamics of heavy-ion collisions will stimulate more experimental work in this direction.
General features of photoinduced spin dynamics in ferromagnetic and ferrimagnetic compounds.
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
Exploiting Quench Dynamics in Spin Chains for Distant Entanglement and Quantum Communication
Hannu Wichterich; Sougato Bose
2009-07-13
We suggest a method of entangling significantly the distant ends of a spin chain using minimal control. This entanglement between distant individual spins is brought about solely by exploiting the dynamics of an initial mixed state with Neel order if the lattice features nearest-neighbor XXZ interaction. There is no need to control single spins or to have engineered couplings or to pulse globally. The method only requires an initial nonadiabatic switch (a quench) between two Hamiltonians followed by an evolution under the second Hamiltonian. The scheme is robust to randomness of the couplings as well as the finiteness of an appropriate quench and could potentially be implemented in various experimental setups, ranging from atoms in optical lattices to Josephson-junction arrays.
Generalized Number Theoretic Spin Chain-Connections to Dynamical Systems and Expectation Values
Jan Fiala; Peter Kleban
2005-03-12
We generalize the number theoretic spin chain, a one-dimensional statistical model based on the Farey fractions, by introducing a new parameter x>=0. This allows us to write recursion relations in the length of the chain. These relations are closely related to the Lewis three-term equation, which is useful in the study of the Selberg \\zeta-function. We then make use of these relations and spin orientation transformations. We find a simple connection with the transfer operator of a model of intermittency in dynamical systems. In addition, we are able to calculate certain spin expectation values explicitly in terms of the free energy or correlation length. Some of these expectation values appear to be directly connected with the mechanism of the phase transition.
Proton-driven spin diffusion in rotating solids via reversible and irreversible quantum dynamics
NASA Astrophysics Data System (ADS)
Veshtort, Mikhail; Griffin, Robert G.
2011-10-01
Proton-driven spin diffusion (PDSD) experiments in rotating solids have received a great deal of attention as a potential source of distance constraints in large biomolecules. However, the quantitative relationship between the molecular structure and observed spin diffusion has remained obscure due to the lack of an accurate theoretical description of the spin dynamics in these experiments. We start with presenting a detailed relaxation theory of PDSD in rotating solids that provides such a description. The theory applies to both conventional and radio-frequency-assisted PDSD experiments and extends to the non-Markovian regime to include such phenomena as rotational resonance (R2). The basic kinetic equation of the theory in the non-Markovian regime has the form of a memory function equation, with the role of the memory function played by the correlation function. The key assumption used in the derivation of this equation expresses the intuitive notion of the irreversible dissipation of coherences in macroscopic systems. Accurate expressions for the correlation functions and for the spin diffusion constants are given. The theory predicts that the spin diffusion constants governing the multi-site PDSD can be approximated by the constants observed in the two-site diffusion. Direct numerical simulations of PDSD dynamics via reversible Liouville-von Neumann equation are presented to support and compliment the theory. Remarkably, an exponential decay of the difference magnetization can be observed in such simulations in systems consisting of only 12 spins. This is a unique example of a real physical system whose typically macroscopic and apparently irreversible behavior can be traced via reversible microscopic dynamics. An accurate value for the spin diffusion constant can be usually obtained through direct simulations of PDSD in systems consisting of two 13C nuclei and about ten 1H nuclei from their nearest environment. Spin diffusion constants computed by this method are in excellent agreement with the spin diffusion constants obtained through equations given by the relaxation theory of PDSD. The constants resulting from these two approaches were also in excellent agreement with the results of 2D rotary resonance recoupling proton-driven spin diffusion (R3-PDSD) experiments performed in three model compounds, where magnetization exchange occurred over distances up to 4.9 Ĺ. With the methodology presented, highly accurate internuclear distances can be extracted from such data. Relayed transfer of magnetization between distant nuclei appears to be the main (and apparently resolvable) source of uncertainty in such measurements. The non-Markovian kinetic equation was applied to the analysis of the R2 spin dynamics. The conventional semi-phenomenological treatment of relxation in R2 has been shown to be equivalent to the assumption of the Lorentzian spectral density function in the relaxatoin theory of PDSD. As this assumption is a poor approximation in real physical systems, the conventional R2 treatment is likely to carry a significant model error that has not been recognized previously. The relaxation theory of PDSD appears to provide an accurate, parameter-free alternative. Predictions of this theory agreed well with the full quantum mechanical simulations of the R2 dynamics in the few simple model systems we considered.
Replica exchange Monte Carlo simulations of the ising spin glass: Static and dynamic properties
NASA Astrophysics Data System (ADS)
Yucesoy, Burcu
Spin glasses have been the subject of intense study and considerable controversy for decades, and the low-temperature phase of short-range spin glasses is still poorly understood. Our main goal is to improve our understanding in this area and find an answer to the following question: Are there only a single pair or a countable infinity of pure states in the low temperature phase of the EA spin glass? To that aim we first start by introducing spin glasses and provide a brief history of their research, then proceed to describe our method of simulation, the parallel tempering Monte Carlo algorithm. Next, we present the results of a large-scale numerical study of the equilibrium three-dimensional Edwards-Anderson Ising spin glass with Gaussian disorder. In order to understand how the parallel tempering algorithm works, we measure various static, as well as dynamical quantities, such as the autocorrelation times and round-trip times for the parallel tempering Monte Carlo method. We examine the correlation between static and dynamic observables for 5000 disorder realizations and up to 1000 spins down to temperatures at 20% of the critical temperature, and our results show that autocorrelation times are directly correlated with the roughness of the free-energy landscape. In the following chapters, the three- and four-dimensional Edwards-Anderson and mean-field Sherrington-Kirkpatrick Ising spin glasses are studied again via large scale Monte Carlo simulations at low temperatures, deep within the spin glass phase. Performing a careful statistical analysis of several thousand independent disorder realizations and using an observable that detects peaks in the overlap distribution, we show that the Sherrington-Kirkpatrick and Edwards-Anderson models have a distinctly different low-temperature behavior. We arrive to the following conclusion: The structure of the spin-glass overlap distribution for the Edwards-Anderson model suggests that its low-temperature phase has only a single pair of pure states. Finally we present results for several new observables, along with a few preliminary studies and suggestions for future research.
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
Uniqueness regime for Markov dynamics on quantum lattice spin systems
Nicholas Crawford; Wojciech De Roeck; Marius Schütz
2015-06-01
We consider a lattice of weakly interacting quantum Markov processes. Without interaction, the dynamics at each site is relaxing exponentially to a unique stationary state. With interaction, we show that there remains a unique stationary state in the thermodynamic limit, i.e. absence of phase coexistence, and the relaxation towards it is exponentially fast for local observables. We do not assume that the quantum Markov process is reversible (detailed balance) w.r.t. a local Hamiltonian.
Finite Temperature Dynamics of the Spin-1/2 Heisenberg Chain.
NASA Astrophysics Data System (ADS)
Starykh, Oleg A.
1998-03-01
We report on our recent studies of the finite temperature (T) dynamics of the isotropic antiferromagnetic S=1/2 Heisenberg chain for all values of the ratio T/J (J is the nearest-neighbor exchange). (A) Dynamics in the low-T region (T/J << 1) is studied via a simple ansatz taking into account marginally irrelevant operator which describes Umklapp scattering between right- and left-moving spinons (O. A. Starykh, R. R. P. Singh, A. W. Sandvik, Phys. Rev. Lett.) 78, 539 (1997). This operator is found to produce (i) logarithmic T-dependent corrections to the scaling dimension of the spin operator, and (ii) multiple logarithmic corrections to the spin correlation function, in agreement with previous renormalization group and thermal Bethe-ansatz studies. As a result, the staggered spin susceptibility \\chi(q,?) shows deviations from the quantum-critical scaling behavior expected for the model with critical correlations in the ground state. Our quantum Monte Carlo (QMC) and high-temperature expansions (HTE) studies provide striking quantitative confirmation of this behavior. We also demonstrate that these logarithmic corrections are essential for the quantitative comparison with the measured spin-lattice (1/T_1) and Gaussian spin-echo (1/T_2G) NMR decay rates of Sr_2CuO3 (M. Takigawa, O. A. Starykh. A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 56, 13681 (1997). (B) Spin dynamics in the intermediate and high-T regions (T/J >= 0.5) is studied by combining HTE with the recursion method, and QMC with the maximum entropy method. We find that the spectral weight of the dynamic structure factor S(k,?) gradually transfers from a diffusive long-wavelenght modes (k ~ 0) at T >> J to a propagating antiferromagnetic ones (k ~ ?) at intermediate temperatures (T ~ J). We extract the NMR 1/T1 rate from the ? arrow 0 limit of S(k,?), and also discuss temperature scaling of the structure factor and staggered spin susceptibility ( O. A. Starykh, A. W. Sandvik, R. R. P. Singh, Phys. Rev. B) 55, 14953 (1997).
New insights into electron spin dynamics in the presence of correlated noise.
Spezia, S; Adorno, D Persano; Pizzolato, N; Spagnolo, B
2012-02-01
The changes in the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which takes into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examining the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitudes lower than the Gunn field, the dephasing length shortens with increasing noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed. PMID:22193943
Charge Dynamics and Spin Blockade in a Hybrid Double Quantum Dot in Silicon
NASA Astrophysics Data System (ADS)
Urdampilleta, Matias; Chatterjee, Anasua; Lo, Cheuk Chi; Kobayashi, Takashi; Mansir, John; Barraud, Sylvain; Betz, Andreas C.; Rogge, Sven; Gonzalez-Zalba, M. Fernando; Morton, John J. L.
2015-07-01
Electron spin qubits in silicon, whether in quantum dots or in donor atoms, have long been considered attractive qubits for the implementation of a quantum computer because of silicon's "semiconductor vacuum" character and its compatibility with the microelectronics industry. While donor electron spins in silicon provide extremely long coherence times and access to the nuclear spin via the hyperfine interaction, quantum dots have the complementary advantages of fast electrical operations, tunability, and scalability. Here, we present an approach to a novel hybrid double quantum dot by coupling a donor to a lithographically patterned artificial atom. Using gate-based rf reflectometry, we probe the charge stability of this double quantum-dot system and the variation of quantum capacitance at the interdot charge transition. Using microwave spectroscopy, we find a tunnel coupling of 2.7 GHz and characterize the charge dynamics, which reveals a charge T2* of 200 ps and a relaxation time T1 of 100 ns. Additionally, we demonstrate a spin blockade at the inderdot transition, opening up the possibility to operate this coupled system as a singlet-triplet qubit or to transfer a coherent spin state between the quantum dot and the donor electron and nucleus.
A theoretical study of the dynamical switching of a single spin by exchange forces
NASA Astrophysics Data System (ADS)
Wieser, R.; Caciuc, V.; Lazo, C.; Hölscher, H.; Vedmedenko, E. Y.; Wiesendanger, R.
2013-01-01
We demonstrate the possibility of dynamically switching the spin of a single atom or molecule with the magnetic tip of an atomic force microscope making use of the acting exchange forces. We choose single V-, Nb- and Ta-benzene molecules as model systems and calculate the exchange interaction with an Fe tip using density functional theory. The exchange energy displays a Bethe-Slater-type behavior with ferromagnetic coupling at large tip-sample distance and antiferromagnetic coupling at closer proximity. The exchange energies reach maximum values of a few tens of meV, which allows one to switch single spins by overcoming the energy barrier due to the magneto-crystalline anisotropy. The spin dynamics of the system was explored by solving the time-dependent Schrödinger equation with additional Landau-Lifshitz-like spin relaxation. We find that the distance dependence of the exchange interaction as well as the appearance of quantum tunneling results in different scenarios for the switching behavior, e.g. the tip can switch the adatom or lead to a stable superposition state with zero magnetization.
Coupled intertwiner dynamics - a toy model for coupling matter to spin foam models
Steinhaus, Sebastian
2015-01-01
The universal coupling of matter and gravity is one of the most important features of general relativity. In quantum gravity, in particular spin foams, matter couplings have been defined in the past, yet the mutual dynamics, in particular if matter and gravity are strongly coupled, are hardly explored, which is related to the definition of both matter and gravitational degrees of freedom on the discretisation. However extracting this mutual dynamics is crucial in testing the viability of the spin foam approach and also establishing connections to other discrete approaches such as lattice gauge theories. Therefore, we introduce a simple 2D toy model for Yang--Mills coupled to spin foams, namely an Ising model coupled to so--called intertwiner models defined for $\\text{SU}(2)_k$. The two systems are coupled by choosing the Ising coupling constant to depend on spin labels of the background, as these are interpreted as the edge lengths of the discretisation. We coarse grain this toy model via tensor network renor...
Dissipation dynamics and spin-orbit force in time-dependent Hartree-Fock theory
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.
Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro
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.
Rapid 3D dynamic arterial spin labeling with a sparse model-based image reconstruction.
Zhao, Li; Fielden, Samuel W; Feng, Xue; Wintermark, Max; Mugler, John P; Meyer, Craig H
2015-11-01
Dynamic arterial spin labeling (ASL) MRI measures the perfusion bolus at multiple observation times and yields accurate estimates of cerebral blood flow in the presence of variations in arterial transit time. ASL has intrinsically low signal-to-noise ratio (SNR) and is sensitive to motion, so that extensive signal averaging is typically required, leading to long scan times for dynamic ASL. The goal of this study was to develop an accelerated dynamic ASL method with improved SNR and robustness to motion using a model-based image reconstruction that exploits the inherent sparsity of dynamic ASL data. The first component of this method is a single-shot 3D turbo spin echo spiral pulse sequence accelerated using a combination of parallel imaging and compressed sensing. This pulse sequence was then incorporated into a dynamic pseudo continuous ASL acquisition acquired at multiple observation times, and the resulting images were jointly reconstructed enforcing a model of potential perfusion time courses. Performance of the technique was verified using a numerical phantom and it was validated on normal volunteers on a 3-Tesla scanner. In simulation, a spatial sparsity constraint improved SNR and reduced estimation errors. Combined with a model-based sparsity constraint, the proposed method further improved SNR, reduced estimation error and suppressed motion artifacts. Experimentally, the proposed method resulted in significant improvements, with scan times as short as 20s per time point. These results suggest that the model-based image reconstruction enables rapid dynamic ASL with improved accuracy and robustness. PMID:26169322
Spin Dynamics of a Single Mn Ion in a CdTe/(Cd, Mg, Zn)Te Quantum Dot
Goryca, Mateusz; Kossacki, Piotr; Golnik, Andrzej; Kazimierczuk, Tomasz; Nawrocki, Michal; Wojnar, Piotr
2010-01-04
The spin dynamics of a single Mn ion confined in a CdTe/(Cd, Mg, Zn)Te quantum dot is determined by measurements of photon correlation of photoluminescence. The characteristic time of spin flip is a few nanoseconds and strongly depends on the excitation power.
Flatte, Michael E.
and Optical Science and Technology Center, University of Iowa, Iowa City, Iowa 52242, USA (Received 16 AugustElectric Field Tunability of Nuclear and Electronic Spin Dynamics due to the Hyperfine Interaction 2002; published 10 June 2003) We present formulas for the nuclear and electronic spin relaxation times
An efficient numerical method for computing dynamics of spin F = 2 Bose-Einstein condensates
Wang Hanquan
2011-07-01
In this paper, we extend the efficient time-splitting Fourier pseudospectral method to solve the generalized Gross-Pitaevskii (GP) equations, which model the dynamics of spin F = 2 Bose-Einstein condensates at extremely low temperature. Using the time-splitting technique, we split the generalized GP equations into one linear part and two nonlinear parts: the linear part is solved with the Fourier pseudospectral method; one of nonlinear parts is solved analytically while the other one is reformulated into a matrix formulation and solved by diagonalization. We show that the method keeps well the conservation laws related to generalized GP equations in 1D and 2D. We also show that the method is of second-order in time and spectrally accurate in space through a one-dimensional numerical test. We apply the method to investigate the dynamics of spin F = 2 Bose-Einstein condensates confined in a uniform/nonuniform magnetic field.
Non-Markovian dynamics of a qubit coupled to an Ising spin bath
NASA Astrophysics Data System (ADS)
Krovi, Hari; Oreshkov, Ognyan; Ryazanov, Mikhail; Lidar, Daniel A.
2007-11-01
We study the analytically solvable Ising model of a single qubit system coupled to a spin bath. The purpose of this study is to analyze and elucidate the performance of Markovian and non-Markovian master equations describing the dynamics of the system qubit, in comparison to the exact solution. We find that the time-convolutionless master equation performs particularly well up to fourth order in the system-bath coupling constant, in comparison to the Nakajima-Zwanzig master equation. Markovian approaches fare poorly due to the infinite bath correlation time in this model. A recently proposed post-Markovian master equation performs comparably to the time-convolutionless master equation for a properly chosen memory kernel, and outperforms all the approximation methods considered here at long times. Our findings shed light on the applicability of master equations to the description of reduced system dynamics in the presence of spin baths.
F. S. Azevedo; Edilberto O. Silva; Luis B. Castro; Cleverson Filgueiras; D. Cogollo
2015-06-11
The planar quantum dynamics of spin-1/2 neutral particle interacting with electrical fields is considered. A set of first order differential equations are obtained directly from the planar Dirac equation with nonminimum coupling. New solutions of this system, in particular, for the Aharonov-Casher effect, are found and discussed in detail. Pauli equation is also obtained by studying the motion of the particle when it describes a circular path of constant radius. We also analyze the planar dynamics in the full space, including the $r=0$ region. The self-adjoint extension method is used to obtain the energy levels and wave functions of the particle for two particular values for the self-adjoint extension parameter. The energy levels obtained are analogous to the Landau levels and explicitly depend on the spin projection parameter.
Azevedo, F S; Castro, Luis B; Filgueiras, Cleverson; Cogollo, D
2015-01-01
The planar quantum dynamics of spin-1/2 neutral particle interacting with electrical fields is considered. A set of first order differential equations are obtained directly from the planar Dirac equation with nonminimum coupling. New solutions of this system, in particular, for the Aharonov-Casher effect, are found and discussed in detail. Pauli equation is also obtained by studying the motion of the particle when it describes a circular path of constant radius. We also analyze the planar dynamics in the full space, including the $r=0$ region. The self-adjoint extension method is used to obtain the energy levels and wave functions of the particle for two particular values for the self-adjoint extension parameter. The energy levels obtained are analogous to the Landau levels and explicitly depend on the spin projection parameter.
Heteroclinic dynamics and attitude motion chaotization of coaxial bodies and dual-spin spacecraft
NASA Astrophysics Data System (ADS)
Doroshin, Anton V.
2012-03-01
Heteroclinic dynamics of a free coaxial bodies system and dual-spin spacecraft is examined. New analytical solutions for heteroclinic orbits, corresponded to the polhodes-separatrices in the space of the angular moment components, are obtained. On the base of these analytical heteroclinic solutions analysis of possibility of the system motion chaotization with the help of Melnikov method is conducted. The analysis shows the polhode-separatrix-orbit splitting at presence of small harmonical perturbation torques between the coaxial bodies. The separatrix splitting generates the chaotic layer near the unperturbed separatrix region. This fact proves possibility of realization of non-regular dynamics and chaotic tilting motion of the dual-spin spacecraft.
Alexander J. Silenko
2007-10-02
A buildup of the vertical polarization in the resonant electric dipole moment (EDM) experiment [Y. F. Orlov, W. M. Morse, and Y. K. Semertzidis, Phys. Rev. Lett. 96, 214802 (2006)] is affected by a horizontal electric field in the particle rest frame oscillating at a resonant frequency. This field is defined by the Lorentz transformation of an oscillating longitudinal electric field and a uniform vertical magnetic one. The effect of a longitudinal electric field is significant, while the contribution from a magnetic field caused by forced coherent longitudinal oscillations of particles is dominant. The effect of electric field on the spin dynamics was not taken into account in previous calculations. This effect is considerable and leads to decreasing the EDM effect for the deuteron and increasing it for the proton. The formula for resonance strengths in the EDM experiment has been derived. The spin dynamics has been calculated.
Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment
Yi-Chong, Ren
2015-01-01
We propose a new approach called Ket-Bra Entangled State (KBES) Method for converting master equation into Schr\\"{o}dinger-like equation. With this method, we investigate decoherence process and entanglement dynamics induced by a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the corresponding master equation is solved concisely by KBES method; Furthermore, the effects of anisotropy, temperature, external field and initial state on concurrence dynamics is analyzed in detail for the case that initial state is Extended Wenger-Like(EWL) state. Finally we research the coherence and concurrence of the final state (namely the density operator for time tend to infinite)
Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment
Ren Yi-Chong; Fan Hong-Yi
2015-09-03
We propose a new approach called Ket-Bra Entangled State (KBES) Method for converting master equation into Schr\\"{o}dinger-like equation. With this method, we investigate decoherence process and entanglement dynamics induced by a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the corresponding master equation is solved concisely by KBES method; Furthermore, the effects of anisotropy, temperature, external field and initial state on concurrence dynamics is analyzed in detail for the case that initial state is Extended Wenger-Like(EWL) state. Finally we research the coherence and concurrence of the final state (namely the density operator for time tend to infinite)
The dynamics of spin stabilized spacecraft with movable appendages, part 2
NASA Technical Reports Server (NTRS)
Bainum, P. M.
1976-01-01
The dynamics and stability of a spin stabilized spacecraft with a hinged appendage system are treated analytically and numerically. The hinged system consists of a central hub with masses attached to (assumed) massless booms of fixed length whose orientation relative to the main part can change. The general three dimensional deployment dynamics of such a hinged system is considered without any restriction on the location of the hinge points. The equations of motion for the hinged system, with viscous damping at both hinge points, are linearized about the nominal equilibrium position where the booms are orthogonal to the nominal spin axis for the case of two dimensional and three dimensional motion. Analytic stability criteria are obtained from the necessary condition on the sign of all the coefficients in the system characteristic equation.
1H nuclear spin relaxation of liquid water from molecular dynamics simulations.
Calero, C; Martí, J; Guŕrdia, E
2015-02-01
We have investigated the nuclear spin relaxation properties of (1)H in liquid water with the help of molecular dynamics simulations. We have computed the (1)H nuclear spin relaxation times T1 and T2 and determined the contribution of the different interactions to the relaxation at different temperatures and for different classical water models (SPC/E, TIP3P, TIP4P, and TIP4P/2005). Among the water models considered, the TIP4P/2005 model exhibits the best agreement with the experiment. The same analysis was performed with Car-Parrinello ab initio molecular dynamics simulations of bulk water at T = 330 K, which provided results close to the experimental values at room temperature. To complete the study, we have successfully accounted for the temperature-dependence of T1 and T2 in terms of a simplified model, which considers the reorientation in finite angle jumps and the diffusive translation of water molecules. PMID:25584483
Critical dynamics near the glass transition as explored with muon spin relaxation
Bermejo, F.J.; Bustinduy, I.; Gonzalez, M.A.; Chong, S.H.; Cabrillo, C.; Cox, S.F.J.
2004-12-01
The dynamics of two molecular glass formers are monitored at microsecond scales via muon spin relaxation. Measurements in transverse magnetic fields display unambiguous signatures of critical behavior at temperatures somewhat above those signaling the thermodynamic glass transition, namely at the onset of stochastic molecular motions. The temperature dependence of transverse relaxation rates and amplitudes is found to provide accurate and unbiased estimates for a critical temperature T{sub c} as predicted by kinetic theories of the glass transition.
Quantum Jumps and Spin Dynamics of Interacting Atoms in a Strongly Coupled Atom-Cavity System
M. Khudaverdyan; W. Alt; T. Kampschulte; S. Reick; A. Thobe; A. Widera; D. Meschede
2009-01-01
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 the mutual influence of two atoms simultaneously coupled to the cavity
Photochemically Induced Dynamic Nuclear Polarization (Photo-CIDNP) Magic-Angle Spinning NMR
Eugenio Daviso; Gunnar Jeschke; Jörg Matysik
Photochemically induced dynamic nuclear polarization (photo-CIDNP) is non-Boltzmann nuclear magnetization which can be observed\\u000a by NMR spectroscopy as enhanced absorptive (positive) or emissive (negative) signals. In solids, photo-CIDNP has been observed\\u000a since its discovery in 1994 in various photosynthetic reaction centers (RCs) by magic angle spinning (MAS) solid-state NMR.\\u000a The photo-CIDNP effect in solids can be explained by a combination
Domain Wall Dynamics Driven by a Localized Injection of a Spin-Polarized Current
Giovanni Finocchio; Natale Maugeri; Luis Torres; Bruno Azzerboni
2010-01-01
This paper introduces an oscillator scheme based on the oscillations of magnetic domain walls due to spin-polarized currents, where the current is injected perpendicular to the sample plane in a localized part of a nanowire. Depending on the geometrical and physical characteristic of the system, we identify two different dynamical regimes (auto-oscillations) when an out-of-plane external field is applied. The
Imaging of dynamic magnetic fields with spin-polarized neutron beams
NASA Astrophysics Data System (ADS)
Tremsin, A. S.; Kardjilov, N.; Strobl, M.; Manke, I.; Dawson, M.; McPhate, J. B.; Vallerga, J. V.; Siegmund, O. H. W.; Feller, W. B.
2015-04-01
Precession of neutron spin in a magnetic field can be used for mapping of a magnetic field distribution, as demonstrated previously for static magnetic fields at neutron beamline facilities. The fringing in the observed neutron images depends on both the magnetic field strength and the neutron energy. In this paper we demonstrate the feasibility of imaging periodic dynamic magnetic fields using a spin-polarized cold neutron beam. Our position-sensitive neutron counting detector, providing with high precision both the arrival time and position for each detected neutron, enables simultaneous imaging of multiple phases of a periodic dynamic process with microsecond timing resolution. The magnetic fields produced by 5- and 15-loop solenoid coils of 1 cm diameter, are imaged in our experiments with ?100 ?m resolution for both dc and 3 kHz ac currents. Our measurements agree well with theoretical predictions of fringe patterns formed by neutron spin precession. We also discuss the wavelength dependence and magnetic field quantification options using a pulsed neutron beamline. The ability to remotely map dynamic magnetic fields combined with the unique capability of neutrons to penetrate various materials (e.g., metals), enables studies of fast periodically changing magnetic processes, such as formation of magnetic domains within metals due to the presence of ac magnetic fields.
Spin Dynamics of Kelvin's Pebbles, Jellett's Eggs, and Shiva's Lingam Stones
NASA Astrophysics Data System (ADS)
Brecher, Kenneth
2015-04-01
Study of the problem of the rise of the center of mass (COM) of spinning objects is said to have begun in the late nineteenth century. These early mathematical treatments aimed to explain the motion of the newly invented and patented ``tippe top.'' This semi-spheroidal top will invert when spun on a smooth surface while raising its COM. Because of the importance of friction in their dynamics, such non-holonomic systems are not readily amenable to analytic treatment, or of intuitive understanding. In notes written in 1844 - before the invention of the tippe top - Lord Kelvin (William Thomson) discussed the problem of the rising COM of spinning objects. He experimented with both oblate and prolate ellipsoidal pebbles, but did not publish a complete theoretical treatment of the problem. J. H. Jellett, in his 1872 book ``Theory of Friction,'' provided a partial account of the related problem of the rise of the COM for an egg-shaped (ovoid) object, making use of a new (adiabatic) invariant of the motion that he devised. Naturally occurring prolate ellipsoidal ``Lingam stones'' from the Narmada River in India exhibit similar counter-intuitive dynamical behavior. When spun around its minor axis in a horizontal plane, a Lingam stone will stand erect and spin around its major axis in a vertical position. This presentation will explore the history and some of the experimental facts and theoretical ideas about the rotational dynamics of such physical objects.
The dynamics of diluted Ho spin ice Ho2-xYxTi2O7 studied byneutron spin echo spectroscopy
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.
Relaxation dynamics in a transient network fluid with competing gel and glass phases
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.
Relaxation dynamics in a transient network fluid with competing gel and glass phases
NASA Astrophysics Data System (ADS)
Chaudhuri, Pinaki; Hurtado, Pablo I.; Berthier, Ludovic; Kob, Walter
2015-05-01
We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics.
Relaxation dynamics in a transient network fluid with competing gel and glass phases.
Chaudhuri, Pinaki; Hurtado, Pablo I; Berthier, Ludovic; Kob, Walter
2015-05-01
We use computer simulations to study the relaxation dynamics of a model for oil-in-water microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, three-step decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the four-point dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics. PMID:25956109
Cumulative quantum work-deficit versus entanglement in the dynamics of an infinite spin chain
NASA Astrophysics Data System (ADS)
Dhar, Himadri Shekhar; Ghosh, Rupamanjari; Sen(De), Aditi; Sen, Ujjwal
2014-03-01
We find that the dynamical phase transition (DPT) in nearest-neighbor bipartite entanglement of time-evolved states of the anisotropic infinite quantum XY spin chain, in a transverse time-dependent magnetic field, can be quantitatively characterized by the dynamics of an information-theoretic quantum correlation measure, namely, quantum work-deficit (QWD). We show that only those nonequilibrium states exhibit entanglement resurrection after death, on changing the field parameter during the DPT, for which the cumulative bipartite QWD is above a threshold. The results point to an interesting inter-relation between two quantum correlation measures that are conceptualized from different perspectives.
Competing thermodynamic and dynamic factors select molecular assemblies on a gold surface.
Haxton, Thomas K; Zhou, Hui; Tamblyn, Isaac; Eom, Daejin; Hu, Zonghai; Neaton, Jeffrey B; Heinz, Tony F; Whitelam, Stephen
2013-12-27
Controlling the self-assembly of surface-adsorbed molecules into nanostructures requires understanding physical mechanisms that act across multiple length and time scales. By combining scanning tunneling microscopy with hierarchical ab initio and statistical mechanical modeling of 1,4-substituted benzenediamine (BDA) molecules adsorbed on a gold (111) surface, we demonstrate that apparently simple nanostructures are selected by a subtle competition of thermodynamics and dynamics. Of the collection of possible BDA nanostructures mechanically stabilized by hydrogen bonding, the interplay of intermolecular forces, surface modulation, and assembly dynamics select at low temperature a particular subset: low free energy oriented linear chains of monomers and high free energy branched chains. PMID:24483804
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, LOrme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France)] [Synchrotron SOLEIL, LOrme des Merisiers, Saint-Aubin, BP48, 91192 Gif-sur-Yvette (France); Gaspar, A. B.; Real, J. A. [Institut of Molecular Science, Universitat de Valčncia, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 Valčncia (Spain)] [Institut of Molecular Science, Universitat de Valčncia, Edifici de Instituts de Paterna, Apartat de Correus 22085, 46071 Valčncia (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.
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
Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.
Osborn, R.; Rosenkranz, S.; Goremychkin, E. A.; Christianson, A. D.
2009-03-20
Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.
Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics inIron Arsenide Compounds
Christianson, Andrew D; Osborn, R.; Rosenkranz, Stephen; Goremychkin, E. A.
2009-01-01
Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely to be extended-s{sub {+-}} wave in character.
José L. Herrera-Aguilar; Hernán Larralde; Maximino Aldana
2012-01-01
We study the properties of the dynamical phase transition occurring in neural network models in which a competition between associative memory and sequential pattern recognition exists. This competition occurs through a weighted mixture of the symmetric and asymmetric parts of the synaptic matrix. Through a generating functional formalism, we determine the structure of the parameter space at non-zero temperature and
The Study of Competence-Anxiety Relations within Social Interaction: A Dynamic Systems Approach.
ERIC Educational Resources Information Center
Phillips, Sian
This study presents a dynamic systems model that suggests that social behavior emerges from the self-organization of cognition-emotion relationships and becomes stable through a process of positive feedback and coupling of components over time. Five 10- to 12-year-old children identified as anxious in evaluative situations by their teacher were
Bioengineering Spin-Offs from Dynamical Systems Theory
NASA Astrophysics Data System (ADS)
Collins, J. J.
1997-03-01
Recently, there has been considerable interest in applying concepts and techniques from dynamical systems and statistical physics to physiological systems. In this talk, we present work dealing which two active topics in this area: stochastic resonance and (2) chaos control. Stochastic resonance is a phenomenon wherein the response of nonlinear system to a weak input signal is optimally enhanced by the presence of a particular level of noise. Here we demonstrate that noise-based techniques can be used to lower sensory detection thresholds in humans. We discuss how from a bioengineering and clinical standpoint, these developments may be particularly relevant for individuals with elevated sensory thresholds, such as older adults and patients with peripheral neuropathy. Chaos control techniques have been applied to a wide range of experimental systems, including biological preparations. The application of chaos control to biological systems has led to speculations that these methods may be clinically useful. Here we demonstrate that the principles of chaos control can be utilized to stabilize underlying unstable periodic orbits in non-chaotic biological systems. We discuss how from a bioengineering and clinical standpoint, these developments may be important for suppressing or eliminating certain types of cardiac arrhythmias.
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.
Esquiaqui, Jackie M; Sherman, Eileen M; Ionescu, Sandra A; Ye, Jing-Dong; Fanucci, Gail E
2014-06-10
Site-directed spin labeling with continuous wave electron paramagnetic resonance (EPR) spectroscopy was utilized to characterize dynamic features of the kink-turn motif formed through a leader-linker interaction in the Vibrio cholerae glycine riboswitch. Efficient incorporation of spin-labels into select sites within the phosphate backbone of the leader-linker region proceeded via splinted ligation of chemically synthesized spin-labeled oligonucleotides to in vitro transcribed larger RNA fragments. The resultant nitroxide EPR line shapes have spectral characteristics consistent with a kink-turn motif and reveal differential backbone dynamics that are modulated by the presence of magnesium, potassium, and glycine. PMID:24849816
NASA Astrophysics Data System (ADS)
Xu, Wenhu; Weber, Cedric; Kotliar, Gabriel
2012-02-01
We study the magnetic properties of periodic Anderson model when the system approaches to the vicinity of a spin-density-wave(SDW) instability from paramagnetic phase. Static and dynamical Q-dependent susceptibility are calculated using a two-particle approach in dynamical mean field theory. The SDW instability at a critical value of hybridyztion Vc is identified by the divergence of static susceptibility at low temperature and at a wavevector Qc which connects the ``hot zones'' of the conduction band. Away from Vc, spin fluctuations at Qc is suppressed at low energy and at low temperature in the heavy Fermi liquid regime, while near Vc, spin fluctuations at Qc are significantly enhanced as temperature decreases. This indicates that the SDW instability is due to the competition between RKKY interaction and Kondo coupling in the crossover regime.
Structural and dynamical properties of ionic liquids: Competing influences of molecular properties.
Spohr, Heidrun V; Patey, G N
2010-04-21
Room temperature ionic liquids differ from molten salts in many ways, our work concentrates on two distinguishing features. These are large cation-anion size disparities and at least one ionic species where the center of mass and the center of charge do not coincide. In earlier work, we examined the influences of these features in isolation on simple spherical models. This paper extends this work to ionic liquid models where both features are present, and where the characteristic distance sigma(+-) (') determining the strength of the Coulombic attractions is unconstrained. We consider the interplay among these molecular features and elucidate their relative importance to the behavior of ionic liquids. Particular attention is focused on the transport properties. We find that size disparity, charge location, and sigma(+-) (') can all have large (often competing) effects. In our models, size disparity and small charge displacements lead to weakly bound, directional ion pairs, and the resulting asymmetric ion-counterion distribution gives rise to increased diffusion coefficients, consequently lower viscosity, and increased conductivity. These observations are analogous to effects reported in the literature, and we see similarities between the directional ion pairs in our models and directional cation-anion pairing through weak hydrogen bonding in room temperature ionic liquids. In our models, large charge displacements lead to strongly bound, long-lived, directional ion pairs, and in this regime the trends noted above are reversed, increased viscosities, and decreased conductivities are observed. Recently, creating more strongly hydrogen bonded, directional ion pairs has been put forward as possible means of achieving larger viscosity reductions. The trend reversal that we observe suggests that this might not work in practice. PMID:20423186
Neutron spin filtering with dynamically polarized protons using photo-excited triplet states
NASA Astrophysics Data System (ADS)
Eichhorn, T. R.; Niketic, N.; van den Brandt, B.; Hautle, P.; Wenckebach, W. Th
2014-07-01
The use of polarized protons as neutron spin filter is an attractive alternative to the well established neutron polarization techniques. The spin-dependent neutron scattering cross section of protons is usefully large up to the sub-Mev region. Employing optically excited triplet states for the dynamic nuclear polarization (DNP) of the protons, low temperatures and strong magnetic fields are not required and the apparatus can be simplified. The triplet DNP method can be used to build a reliably working neutron spin filter that is operated in 0.3T and about 100 K. The high proton polarization of 0.5 obtained is presently still limited by the cooling of the sample. The corresponding analyzing power of A ~ 0.5, obtained with the 5 mm thick sample, can be further increased using a longer sample. Interesting possibilities for a triplet spin filter are opened by the use of neutron optics elements that allow to adapt the beam to the filter cross section.
Long-time-scale dynamics of spin textures in a degenerate F=1 {sup 87}Rb spinor Bose gas
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.
Tracking protein dynamics with photoconvertible Dendra2 on spinning disk confocal systems.
Woods, Elena; Courtney, Jane; Scholz, Dimitri; Hall, William W; Gautier, Virginie W
2014-12-01
Understanding the dynamic properties of cellular proteins in live cells and in real time is essential to delineate their function. In this context, we introduce the Fluorescence Recovery After Photobleaching-Photoactivation unit (Andor) combined with the Nikon Eclipse Ti E Spinning Disk (Andor) confocal microscope as an advantageous and robust platform to exploit the properties of the Dendra2 photoconvertible fluorescent protein (Evrogen) and analyse protein subcellular trafficking in living cells. A major advantage of the spinning disk confocal is the rapid acquisition speed, enabling high temporal resolution of cellular processes. Furthermore, photoconversion and imaging are less invasive on the spinning disk confocal as the cell exposition to illumination power is reduced, thereby minimizing photobleaching and increasing cell viability. We have tested this commercially available platform using experimental settings adapted to track the migration of fast trafficking proteins such as UBC9, Fibrillarin and have successfully characterized their differential motion between subnuclear structures. We describe here step-by-step procedures, with emphasis on cellular imaging parameters, to successfully perform the dynamic imaging and photoconversion of Dendra2-fused proteins at high spatial and temporal resolutions necessary to characterize the trafficking pathways of proteins. PMID:25186063
Effect of hawk-dove game on the dynamics of two competing species.
Moussaoui, Ali; Auger, Pierre; Roche, Benjamin
2014-09-01
Outcomes of interspecific competition, and especially the possibility of coexistence, have been extensively studied in theoretical ecology because of their implications in community assemblages. During the last decades, the influence of different time scales through the local/regional dynamics of animal communities has received an increasing attention. Nevertheless, different time scales involved in interspecific competition can result form other processes than spatial dynamics. Here, we envision and analyze a new theoretical framework that couples a game theory approach for competition with a demographic model. We take advantage of these two time scales to derive a reduced model governing the total densities of the two populations and we study how these two time scales interfere and influence outcomes of species competition. We find that a competition process occurring on a faster time scale than demography yields a "priority effect" where the first species introduced outcompetes the other one. We then confirm previous findings stipulating that species coexistence is favored by large difference in time scales because the extinction/recolonization process. Our results then highlight that an integration of demographic and competition time scales at both local and regional levels is mandatory to explain communities assemblages and should become a research priority. PMID:24908380
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.
Role of initial conditions in the mean-field theory of spin-glass dynamics
NASA Astrophysics Data System (ADS)
Houghton, A.; Jain, S.; Young, A. P.
1983-09-01
We discuss the dynamics of the infinite-range Sherrington-Kirkpatrick spin-glass model for which relaxation times diverge when N, the number of spins, tends to infinity. Calculations on a large but finite system are very difficult, so we mimic a large finite system in equilibrium by working with N=? and imposing, by hand, a canonical distribution at an initial time. For short times, where no barrier hopping has occurred, we find that the Edwards-Anderson order parameter, qEA, is identical to that obtained from an analysis of the mean-field equations of Thouless, Anderson, and Palmer and, with further assumptions, gives q(x=1) in Parisi's theory, in agreement with earlier work. For times longer than the longest relaxation time (of the finite system), true equilibrium is reached and our theory agrees with previous statistical-mechanics calculations using the replica trick. There is no violation of the fluctuation-dissipation theorem.
Langevin spin dynamics based on ab initio calculations: numerical schemes and applications.
Rózsa, L; Udvardi, L; Szunyogh, L
2014-05-28
A method is proposed to study the finite-temperature behaviour of small magnetic clusters based on solving the stochastic Landau-Lifshitz-Gilbert equations, where the effective magnetic field is calculated directly during the solution of the dynamical equations from first principles instead of relying on an effective spin Hamiltonian. Different numerical solvers are discussed in the case of a one-dimensional Heisenberg chain with nearest-neighbour interactions. We performed detailed investigations for a monatomic chain of ten Co atoms on top of a Au(0?0?1) surface. We found a spiral-like ground state of the spins due to Dzyaloshinsky-Moriya interactions, while the finite-temperature magnetic behaviour of the system was well described by a nearest-neighbour Heisenberg model including easy-axis anisotropy. PMID:24806308
Spin dynamics and implications for superconductivity: Some problems with the d-wave scenario
Levin, K.; Zha, Y.; Radtke, R.J. [Chicago Univ., IL (United States). Dept. of Physics; Si, Q. [Rutgers Univ., Piscataway, NJ (United States). Serin Physics Lab.; Norman, M.R. [Argonne National Lab., IL (United States); Schuttler, H.B. [Georgia Univ., Athens, GA (United States). Dept. of Physics and Astronomy
1993-09-01
We review the spin dynamics of the normal state of the cuprates with special emphasis on neutron data in both the YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} and La{sub 2-x}Sr{sub x}CuO{sub 4} systems. When realistic models of the Fermi surface shapes are incorporated, along with a moderate degree of spin fluctuations, we find good semi-quantiative agreement with experiment for both cuprates. Building on the success of this Fermi-liquid-based scheme, we explore the implications for d-wave pairing from a number of vantage points. We conclude that our present experimental and theoretical understanding is inadequate to confirm or refute the d-wave scenario.
NASA Astrophysics Data System (ADS)
Stark, H.; Lubensky, T. C.
2005-11-01
Nematic liquid crystals are well modeled as a fluid of rigid rods. Starting from this model, we use a Poisson-bracket formalism to derive the equations governing the dynamics of nematic liquid crystals. We treat the spin angular momentum density arising from the rotation of constituent molecules about their centers of mass as an independent field and derive equations for it, the mass density, the momentum density, and the nematic director. Our equations reduce to the original Leslie-Ericksen equations, including the inertial director term that is neglected in the hydrodynamic limit, only when the moment of inertia for angular momentum parallel to the director vanishes and when a dissipative coefficient favoring locking of the angular frequencies of director rotation and spin angular momentum diverges. Our equations reduce to the equations of nematohydrodynamics in the hydrodynamic limit but with dissipative coefficients that depend on the coefficient that must diverge to produce the Leslie-Ericksen equations.
Amy G. Halberstadt; Susanne A. Denham; Julie C. Dunsmore
2001-01-01
A theoretical model for affective social competence is described. Affective social com- petence (ASC) is comprised of three integrated and dynamic components: sending affective messages, receiving affective messages, and experiencing affect. Central and interconnected abilities within each component include awareness and identification of affect, working within a complex and constantly changing social context, and man- agement and regulation. The dynamic
Real-time dynamics of open quantum spin systems driven by dissipative processes
NASA Astrophysics Data System (ADS)
Hebenstreit, F.; Banerjee, D.; Hornung, M.; Jiang, F.-J.; Schranz, F.; Wiese, U.-J.
2015-07-01
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, disregarding unitary Hamiltonian dynamics. 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.
Real-time dynamics of open quantum spin systems driven by dissipative processes
Florian Hebenstreit; Debasish Banerjee; Manes Hornung; Fu-Jiun Jiang; Franziska Schranz; Uwe-Jens Wiese
2015-07-10
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, disregarding unitary Hamiltonian dynamics. 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.
DYNAMICAL SPIN SUSCEPTIBILITY IN THE TD-LDA AND QSGW APPROXIMATIONS
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 Ă˘Â?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 NĂ?Â´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.
Spin diffusion and the dynamic structure of a protein. Streptomyces subtilisin inhibitor
NASA Astrophysics Data System (ADS)
Akasaka, Kazuyuki
The method of cross saturation in the 1H NMR spectrum is examined in detail at 360 to 400 MHz in a medium-sized globular protein, Streptomyces subtilisin inhibitor (SSI) (MW 23,000) in neutral aqueous (D 2O) solution for the purpose of clarifying the relationship between the phenomenon of spin diffusion and the dynamic structure of a protein. Continuous irradiation of a portion of the spectrum with a weak radiofrequency field of ?H2/2 ? = 50- to 70-Hz order results in saturation extending over the entire spectral range, showing a similar hot spin temperature for a large group of protons which, according to X-ray and NMR results, exist in a rigid core region of SSI. However, there are a number of resonances that receive saturation at distinctively slower rates. Some of these lines are identified with side-chain protons of amino acids in the exposed segments of SSI. Transverse relaxation measurements show that in solution most of these side chains undergo rapid internal motions. Differential efficiency of cross saturation between the core and the exposed segments observed above is discussed in terms of the overall cross-relaxation rate ( TIS-1) between irradiated (S) and observed (I) protons, which represents the spin-diffusion efficiency. The time constant TIS is particularly sensitive to the interresidue geometry as well as to local motion. It is proposed that the method of cross saturation in 1H NMR may be used for studying the gross dynamic structure, in particular for the detection of exposed and/or mobile segments, in proteins of a wide range of molecular weight, i.e., above 10,000 daltons for which the conventional 1H spin-lattice relaxation measurement is no longer useful.
Tracking the charge and spin dynamics of electronic excited states in inorganic complexes
NASA Astrophysics Data System (ADS)
Gaffney, Kelly
2015-03-01
Inorganic complexes have many advantageous properties for solar energy applications, including strong visible absorption and photocatalytic activity. Whether used as a photocatalyst or a photosensitizer, the lifetime of electronic excited states and the earth abundance of the molecular components represent a key property for solar energy applications. These dual needs have undermined the usefulness of many coordination compounds. Isoelectronic iron and ruthenium based complexes represent a clear example. Ru-polypyridal based molecules have been the workhorse of solar energy related research and dye sensitized solar cells for decades, but the replacement of low abundance Ru with Fe leads to million-fold reductions in metal to ligand charge transfer (MLCT) excited state lifetimes. Understanding the origin of this million-fold reduction in lifetime and how to control excited state relaxation in 3d-metal complexes motivates the work I will discuss. We have used the spin sensitivity of hard x-ray fluorescence spectroscopy and the intense femtosecond duration pulses generated by the LCLS x-ray laser to probe the spin dynamics in a series of electronically excited [Fe(CN)6-2N(2,2'-bipyridine)N]2 N - 4 complexes, with N = 1-3. These femtosecond resolution measurements demonstrate that modification of the solvent and ligand environment can lengthen the MLCT excited state lifetime by more than two orders of magnitude. They also verify the role of triplet ligand field excited states in the spin crossover dynamics from singlet to quintet spin configurations. Work supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.
NASA Astrophysics Data System (ADS)
Schüler, M.; Pavlyukh, Y.; Berakdar, J.
2012-04-01
Inelastic scanning tunneling microscopy (STM) has recently been shown (Loth et al 2010 Science 329 1628) to be extendable to access the nanosecond, spin-resolved dynamics of magnetic adatoms and molecules. Here we analyze this novel tool theoretically by considering the time-resolved spin dynamics of a single adsorbed Fe atom excited by a tunneling current pulse from a spin-polarized STM tip. The adatom spin configuration can be controlled and probed by applying voltage pulses between the substrate and the spin-polarized STM tip. We demonstrate how, in a pump-probe manner, the relaxation dynamics of the sample spin is manifested in the spin-dependent tunneling current. Our model calculations are based on the scattering theory in a wave-packet formulation. The scheme is non-perturbative and, hence, is valid for all voltages. The numerical results for the tunneling probability and the conductance are contrasted with the predictions of simple analytical models and compared with experiments.
Competencies of the Competent Recruiter.
ERIC Educational Resources Information Center
Beebe, Bill
1996-01-01
Outlines the various skills, behaviors, attitudes, and other qualities needed for the competent hiring of employees. Emphasizes that knowledge, a model for human resource development, experience, and difference competencies are essential to the hiring process. Lists 35 human resource development competencies, grouped under the headings of
Kaul, Ribhu K.; Melko, Roger G.
2008-07-01
We present computations of certain finite-size scaling functions and universal amplitude ratios in the large-N limit of the CP{sup N-1} field theory. We pay particular attention to the uniform susceptibility, the spin stiffness, and the specific heat. Field theoretic arguments have shown that the long-wavelength description of the phase transition between the Neel and valence-bond solid states in square lattice S=1/2 antiferromagnets is expected to be the noncompact CP{sup 1} field theory. We provide a detailed comparison between our field theoretic calculations and quantum Monte Carlo data close to the Neel-VBS transition on a S=1/2 square-lattice model with competing four-spin interactions (the JQ model)
Field dependent spin dynamics in Dysprosium2Titanium2Oxygen7
NASA Astrophysics Data System (ADS)
Matthews, Maria Jane
We have studied the field dependent magnetic properties of three crystalline directions of the spin ice material Dy2Ti 2O7---the [100], [110], and [111] directions. Comprehensive magnetization and ac susceptibility data were taken in the temperature range 1.8 K < T < 7 K at fields of up to H = 4 T in the frequency range from dc to f = 10 kHz. We found that crystalline anisotropy plays an important role in determining the spin dynamics in this temperature and magnetic field regime, as well as surprising features presenting in the kHz frequency range where the ac measurement is performed faster than the characteristic relaxation time of the system. In particular, the [110] direction showed a distinct region of freezing into the "spin-chain" state and the [111] direction showed a distinct "kagome-ice" region, as well as an unexpected peak at higher frequencies---remnant of the first-order phase transition at lower temperatures. The [110] and [111] crystalline directions were determined to be of enough interest to extend to lower temperature using a much more difficult dilution refrigerator experiment. Two large crystals were provided by groups at Universidad Nacional de La Plata -CONICET, Argentina, and University of Oxford, United Kingdom, respectively, for the additional purpose of probing the spatial variation inside the crystal (as opposed to measuring the whole crystal as is traditionally done in ac susceptibility experiments). Differences between the end and the center of the crystals were observed in an applied field and approaching the higher frequency measurement limit. Additionally, two more projects are presented on the related materials Tb2Ti2O7 and Tb2Ti2-xSn xO7. The former was lead by Sean Giblin and Peter Baker from ISIS, and the latter by Maria Dahlberg from the Pennsylvania State University. A search for the magnetization plateau associated with the quantum spin ice state was the motivation behind the Tb2Ti2O7 study; however, only unusual dynamics in a regime that coincided with muon results were found. Thus, the set of materials Tb2Ti2-xSn xO7 provided an excellent way to probe the interactions that determine the nature of the low-temperature phase (soft spin ice or spin liquid, in this case), and several intermediate states of interest were found.
Magnetization and spin dynamics of the spin S=(1)/(2) hourglass nanomagnet Cu5(OH)2(NIPA)4ˇ10H2O
NASA Astrophysics Data System (ADS)
Nath, R.; Tsirlin, A. A.; Khuntia, P.; Janson, O.; Förster, T.; Padmanabhan, M.; Li, J.; Skourski, Yu.; Baenitz, M.; Rosner, H.; Rousochatzakis, I.
2013-06-01
We report a combined experimental and theoretical study of the spin S=(1)/(2) nanomagnet Cu5(OH)2(NIPA)4ˇ10H2O (Cu5-NIPA). Using thermodynamic, electron spin resonance, and 1H nuclear magnetic resonance measurements on one hand, and ab initio density-functional band-structure calculations, exact diagonalizations, and a strong-coupling theory on the other, we derive a microscopic magnetic model of Cu5-NIPA and characterize the spin dynamics of this system. The elementary fivefold Cu2+ unit features an hourglass structure of two corner-sharing scalene triangles related by inversion symmetry. Our microscopic Heisenberg model comprises one ferromagnetic and two antiferromagnetic exchange couplings in each triangle, stabilizing a single spin S=(1)/(2) doublet ground state (GS), with an exactly vanishing zero-field splitting (by Kramers' theorem), and a very large excitation gap of ??68 K. Thus, Cu5-NIPA is a good candidate for achieving long electronic spin relaxation (T1) and coherence (T2) times at low temperatures, in analogy to other nanomagnets with low-spin GS's. Of particular interest is the strongly inhomogeneous distribution of the GS magnetic moment over the five Cu2+ spins. This is a purely quantum-mechanical effect since, despite the nonfrustrated nature of the magnetic couplings, the GS is far from the classical collinear ferrimagnetic configuration. Finally, Cu5-NIPA is a rare example of a S=(1)/(2) nanomagnet showing an enhancement in the nuclear spin-lattice relaxation rate 1/T1 at intermediate temperatures.
Do Bitcoins make the world go round? On the dynamics of competing crypto-currencies
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.
Loss, Daniel
. The charge dynamics of the iron-based superconductors is controlled by the strong Hund's coupling on the iron of the electrons and Hund's interaction on an equal footing. Using non-perturbative many-body method and ab initio describe the spin dynamics and symmetry of the superconducting order parameter, and we will show that Hund
in the LandauLifshitzGilbert (LLG) model of thin, narrow strips, is a characteristic property of such systems, the spin dynamics is purely quantum mechanical and in such strongly quantum fluctuating systems it must mechan- ical motion, the existence of which has to be confirmed. 2. Dynamically Stable Domain Walls
NASA Astrophysics Data System (ADS)
Stone, Michael A.; Moore, Brian C. J.
2003-08-01
Using a ``noise-vocoder'' cochlear implant simulator [Shannon et al., Science 270, 303-304 (1995)], the effect of the speed of dynamic range compression on speech intelligibility was assessed, using normal-hearing subjects. The target speech had a level 5 dB above that of the competing speech. Initially, baseline performance was measured with no compression active, using between 4 and 16 processing channels. Then, performance was measured using a fast-acting compressor and a slow-acting compressor, each operating prior to the vocoder simulation. The fast system produced significant gain variation over syllabic timescales. The slow system produced significant gain variation only over the timescale of sentences. With no compression active, about six channels were necessary to achieve 50% correct identification of words in sentences. Sixteen channels produced near-maximum performance. Slow-acting compression produced no significant degradation relative to the baseline. However, fast-acting compression consistently reduced performance relative to that for the baseline, over a wide range of performance levels. It is suggested that fast-acting compression degrades performance for two reasons: (1) because it introduces correlated fluctuations in amplitude in different frequency bands, which tends to produce perceptual fusion of the target and background sounds and (2) because it reduces amplitude modulation depth and intensity contrasts.
Dynamical phases in quenched spin-orbit-coupled degenerate Fermi gas.
Dong, Ying; Dong, Lin; Gong, Ming; Pu, Han
2015-01-01
The spin-orbit-coupled degenerate Fermi gas provides a new platform for realizing topological superfluids and related topological excitations. However, previous studies have been mainly focused on the topological properties of the stationary ground state. Here, we investigate the quench dynamics of a spin-orbit-coupled two-dimensional Fermi gas in which the Zeeman field serves as the major quench parameter. Three post-quench dynamical phases are identified according to the asymptotic behaviour of the order parameter. In the undamped phase, a persistent oscillation of the order parameter may support a topological Floquet state with multiple edge states. In the damped phase, the magnitude of the order parameter approaches a constant via a power-law decay, which may support a dynamical topological phase with one edge state at the boundary. In the overdamped phase, the order parameter decays to zero exponentially although the condensate fraction remains finite. These predictions can be observed in the strong-coupling regime. PMID:25600665
Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath
Ajoy, Ashok [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany); Birla Institute of Technology and Science, Pilani, Zuarinagar, Goa 403726 (India); NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India); Alvarez, Gonzalo A.; Suter, Dieter [Fakultaet Physik, Technische Universitaet Dortmund, D-44221 Dortmund (Germany)
2011-03-15
Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses [the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence [the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are {sup 13}C nuclear spins and the environment consists of a {sup 1}H nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.
Spin Dynamics Simulations of Multiple Echo Spacing Pulse Sequences in Grossly Inhomogeneous Fields
Heidler, R.; Bachman, H. N.; Johansen, Y.
2008-12-05
Pulse sequences with multiple lengths of echo spacings are used in oilfield NMR logging for diffusion-based NMR applications such as rock and fluid characterization. One specific implementation is the so-called diffusion editing sequence comprising two long echo spacings followed by a standard CPMG at a shorter echo spacing. The echoes in the CPMG portion contain signal from both the direct and stimulated echoes.Modern oilfield NMR logging tools are designed for continuous depth logging of earth formations by projecting both the static (B{sub 0}) and dynamic (B{sub 1}) fields into the formation. Both B{sub 0} and B{sub 1} profiles are grossly inhomogeneous which results in non-steady-state behavior in the early echoes. The spin dynamics effects present a challenge for processing the echo amplitudes to measure porosity (amplitude extrapolated to zero time) and attenuations for fluid or pore size characterization.In this work we describe a calculation of the spin dynamics of the diffusion editing sequence with two long echo spacings. The calculation takes into account full B{sub 1} and B{sub 0} field maps, and comparisons will be made for sensors and parameters typical of oilfield logging tools and environments.
Spin dynamics in the negatively charged terbium (III) bis-phthalocyaninato complex.
Branzoli, Francesca; Carretta, Pietro; Filibian, Marta; Zoppellaro, Giorgio; Graf, Michael J; Galan-Mascaros, Jose R; Fuhr, Olaf; Brink, Susan; Ruben, Mario
2009-04-01
The experimental and theoretical study of the electron spin dynamics in the anionic form of a single-ion molecule magnet (SIMM), the bis-phthalocyaninato terbium (III) molecule [Pc(2)Tb](-)[TBA](+), has been addressed by means of solid state (1)H NMR spectroscopy. The magnetic properties of the caged Tb(3+) metal center were investigated in a series of diamagnetically diluted preparations, where the excess of tetrabutylamonium bromide ([TBA]Br)(n) salt was used as diamagnetic matrix complement. We found that a high temperature activated spin dynamics characterizes the systems, which involved phonon-assisted transitions among the crystal field levels in qualitative agreements with literature results. However, the activation barriers in these processes range from 641 cm(-1) for the diamagnetically diluted samples to 584 cm(-1) for those undiluted; thus, they exhibit barriers 2-3 times larger than witnessed in earlier (230 cm(-1)) reports (e.g., Ishikawa, N.; Sugita, M.; Ishikawa, T.; Koshihara, S.; Kaizu, Y. J. Am. Chem. Soc. 2003, 125, 8694-8695). At cryogenic temperatures, fluctuations are driven by tunneling processes between the m = +6 and -6 low-energy levels. We found that the barrier Delta and the tunneling rates change from sample to sample and especially the diamagnetically diluted [Pc(2)Tb](-) molecules appear affected by the sample's magneto/thermal history. These observations emphasize that matrix arrangements around [Pc(2)Tb](-) can appreciably alter the splitting of the crystal field levels, its symmetry, and hence, the spin dynamics. Therefore, understanding how small differences in molecular surroundings (as for instance occurring by depositing on surfaces) can trigger substantial modifications in the SIMM property is of utmost importance for the effective operation of such molecules for single-molecule data storage, for example. PMID:19275145
Current induced domain wall dynamics in the presence of spin orbit torques
Boulle, O. Buda-Prejbeanu, L. D.; Jué, E.; Miron, I. M.; Gaudin, G.
2014-05-07
Current induced domain wall (DW) motion in perpendicularly magnetized nanostripes in the presence of spin orbit torques is studied. We show using micromagnetic simulations that the direction of the current induced DW motion and the associated DW velocity depend on the relative values of the field like torque (FLT) and the Slonczewski like torques (SLT). The results are well explained by a collective coordinate model which is used to draw a phase diagram of the DW dynamics as a function of the FLT and the SLT. We show that a large increase in the DW velocity can be reached by a proper tuning of both torques.
Spin crossover in solid and liquid (Mg,Fe)O from first-principles molecular dynamics
NASA Astrophysics Data System (ADS)
Stixrude, L. P.; Holmstrom, E.
2014-12-01
Ferropericlase, (Mg,Fe)O, is a major constituent of the Earth's lowermantle. Understanding the properties of this component is importantnot only in the solid state, but also in the molten state, as theplanet almost certainly hosted an extensive magma ocean in Hadeantimes. Using first-principles molecular dynamics simulations,thermodynamic integration, and adiabatic switching, we present a phasediagram of the spin crossover, i.e., the pressure-induced collapse ofmagnetic moments, in both solid and liquid (Mg,Fe)O. Furthermore, wecompute the thermodynamic properties and the electrical conductivityof the crystal and melt over a wide range of conditions. We thenpresent the geophysical implications of our findings.
CP violation from spin-1 resonances in a left-right dynamical Higgs context
Yepes, Juan; Shu, Jing
2015-01-01
New physics field content in the nature, more specifically, from spin-1 resonances sourced by the extension of the SM local gauge symmetry to the larger local group $SU(2)_L\\otimes SU(2)_R\\otimes U(1)_{B-L}$, may induce CP-violation signalling NP effects from higher energy regimes. In this work we completely list and study all the CP-violating operators up to the $p^4$-order in the Lagrangian expansion, for a non-linear left-right electroweak chiral context and coupled to a light dynamical Higgs.
Calibration of the spin-scan ozone imager aboard the dynamics Explorer 1 satellite
NASA Technical Reports Server (NTRS)
Bressette, Walter E.; Keating, Gerald M.; Young, David F.
1987-01-01
The calibration technique, which contains the calibrated backscattered radiance values necessary for performing the calibrations, is presented. The calibration constants for September to October 1981 to determine total columnar ozone from the Spin-Scan Ozone Imager (SOI), which is a part of the auroral imaging instrumentation aboard the Dynamics Explorer 1 Satellite, are provided. The precision of the SOI-derived total columnar ozone is estimated to be better than 2.4 percent. Linear regression analysis was used to calculate correlation coefficients between total columnar ozone obtained from Dobson ground stations and SOI which indicate that the SOI total columnar ozone determination is equally accurate for clear or cloudy weather conditions.
Chaos and its avoidance in spinup dynamics of an axial dual-spin spacecraft
NASA Astrophysics Data System (ADS)
Doroshin, Anton V.
2014-02-01
Attitude dynamics of a dual-spin spacecraft (DSSC) and a torque-free angular motion of a coaxial bodies system are considered. Some regimes of the heteroclinic chaos are described. The local chaotization of the DSSC is investigated at the presence of polyharmonic perturbations and small nutation restoring/overturning torques on the base of the Melnikov method and Poincaré Maps. Reasons of the chaotic regimes initiation at the spinup maneuver realization are studied. An approach for the local heteroclinic chaos escape/avoidance at the modification of the classical spinup maneuver is suggested.
Entanglement and dynamics of spin chains in periodically pulsed magnetic fields: accelerator modes.
Boness, T; Bose, S; Monteiro, T S
2006-05-12
We study the dynamics of a single excitation in a Heisenberg spin-chain subjected to a sequence of periodic pulses from an external, parabolic, magnetic field. We show that, for experimentally reasonable parameters, a pair of counterpropagating coherent states is ejected from the center of the chain. We find an illuminating correspondence with the quantum time evolution of the well-known paradigm of quantum chaos, the quantum kicked rotor. From this we can analyze the entanglement production and interpret the ejected coherent states as a manifestation of the so-called "accelerator modes" of a classically chaotic system. PMID:16712391
Dynamics and Scaling in a Quantum Spin Chain Material with Bond Randomness
Masuda, Takatsugu; Zheludev, Andrey I; Uchinokura, K.; Chung, J.-H.; Park, S.
2004-01-01
Single crystal inelastic neutron scattering is used to study dynamic spin correlations in the quasi-one-dimensional quantum antiferromagnet BaCu{sub 2}(Si{sub 0.5}Ge{sub 0.5}){sub 2}O{sub 7}, where the exchange constant fluctuates due to a random distribution of Si and Ge atoms. The measured low-energy spectrum is dominated by localized excitations and can be understood in the framework of the random singlet model. The observed scaling relations for the frequency dependencies of the correlation length and structure factor are in excellent agreement with recent theoretical predictions for the renormalization group fixed point.
Entanglement and dynamics of spin-chains in periodically-pulsed magnetic fields: accelerator modes
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.
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. PMID:25554062
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.
NASA Astrophysics Data System (ADS)
Goslar, Janina; Lijewski, Stefan; Hoffmann, Stanis?aw K.; Jankowska, Aldona; Kowalak, Stanis?aw
2009-05-01
X-band electron spin resonance (ESR) spectra of S3- radicals in ultramarine analog (pigment) prepared from zeolite A and maintaining the original structure of parent zeolite were recorded in the temperature range of 4.2-380 K. Electron spin echo experiments (echo detected ESR, electron spin-lattice relaxation, and spin echo dephasing) were performed in the temperature range of 4.2-50 K. The rigid lattice g factors are gx=2.0016, gy=2.0505, and gz=2.0355, and they are gradually averaged with temperature to the final collapse into a single line with g =2.028 above 300 K. This is due to reorientations of S3- molecule between 12 possible orientations in the sodalite cage through the energy barrier of 2.4 kJ/mol. The low-lying orbital states of the open form of S3- molecule having C2v symmetry are considered and molecular orbital (MO) theory of the g factors is presented. The orbital mixing coefficients were calculated from experimental g factors and available theoretical orbital splitting. They indicate that the unpaired electron spin density in the ground state is localized mainly (about 50%) on the central sulfur atom of S3- anion radical, whereas in the excited electronic state the density is localized mainly on the lateral sulfur atoms (90%). A strong broadening of the ESR lines in directions around the twofold symmetry axis of the radical S3- molecule (z-axis) is discovered below 10 K. It is due to a distribution of the S-S-S bond angle value influencing mainly the energy of the B22-symmetry MO. This effect is smeared out by molecular dynamics at higher temperatures. A distribution of the g factors is confirmed by the recovery of the spin system magnetization during spin-lattice relaxation measurements, which is described by a stretched exponential function. Both the spin-lattice relaxation and electron spin echo dephasing are governed by localized phonon mode of energy of about 40 cm-1. Thus, the anion-radical S3- molecules are weakly bonded to the zeolite framework, and they do not participate in the phonon motion of the host lattice because of their own local dynamics.
NASA Astrophysics Data System (ADS)
Álvarez, Gonzalo A.; Ajoy, Ashok; Peng, Xinhua; Suter, Dieter
2010-10-01
Avoiding the loss of coherence of quantum mechanical states is an important prerequisite for quantum information processing. Dynamical decoupling (DD) is one of the most effective experimental methods for maintaining coherence, especially when one can access only the qubit system and not its environment (bath). It involves the application of pulses to the system whose net effect is a reversal of the system-environment interaction. In any real system, however, the environment is not static, and therefore the reversal of the system-environment interaction becomes imperfect if the spacing between refocusing pulses becomes comparable to or longer than the correlation time of the environment. The efficiency of the refocusing improves therefore if the spacing between the pulses is reduced. Here, we quantify the efficiency of different DD sequences in preserving different quantum states. We use C13 nuclear spins as qubits and an environment of H1 nuclear spins as the environment, which couples to the qubit via magnetic dipole-dipole couplings. Strong dipole-dipole couplings between the proton spins result in a rapidly fluctuating environment with a correlation time of the order of 100 ?s. Our experimental results show that short delays between the pulses yield better performance if they are compared with the bath correlation time. However, as the pulse spacing becomes shorter than the bath correlation time, an optimum is reached. For even shorter delays, the pulse imperfections dominate over the decoherence losses and cause the quantum state to decay.
Dynamic Behavior of Fatty Acid Spin Labels within a Binding Site of Soybean Lipoxygenase-1
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
NASA Astrophysics Data System (ADS)
Marsat, Sylvain
2015-04-01
We investigate cubic-in-spin effects for inspiralling compact object binaries, both in the dynamics and in the energy flux emitted in gravitational waves, at the leading post-Newtonian order. We use a Lagrangian formalism to implement finite-size effects, and extend it to cubic order in the spins, which corresponds to the octupolar order in a multipolar decomposition. This formalism allows us to derive the equation of motion, equations of precession for the spin, and stressenergy tensor of each body in covariant form, and admits a formal generalization to any multipolar order. For spin-induced multipoles, i.e.in the case where the rotation of the compact object is solely responsible for the additional multipole moments, we find a unique structure for the octupolar moment representing cubic-in-spin effects. We apply these results to compute the associated effects in the dynamics of compact binary systems, and deduce the corresponding terms in the energy loss rate due to gravitational waves. These effects enter at the third-and-a-half post-Newtonian order, and can be important for binaries involving rapidly spinning black holes. We provide simplified results for spin-aligned circular orbits, and discuss the quantitative importance of the new contributions.
Blanche, Paul; Proust-Lima, Cécile; Loubčre, Lucie; Berr, Claudine; Dartigues, Jean-François; Jacqmin-Gadda, Hélčne
2015-03-01
Thanks to the growing interest in personalized medicine, joint modeling of longitudinal marker and time-to-event data has recently started to be used to derive dynamic individual risk predictions. Individual predictions are called dynamic because they are updated when information on the subject's health profile grows with time. We focus in this work on statistical methods for quantifying and comparing dynamic predictive accuracy of this kind of prognostic models, accounting for right censoring and possibly competing events. Dynamic area under the ROC curve (AUC) and Brier Score (BS) are used to quantify predictive accuracy. Nonparametric inverse probability of censoring weighting is used to estimate dynamic curves of AUC and BS as functions of the time at which predictions are made. Asymptotic results are established and both pointwise confidence intervals and simultaneous confidence bands are derived. Tests are also proposed to compare the dynamic prediction accuracy curves of two prognostic models. The finite sample behavior of the inference procedures is assessed via simulations. We apply the proposed methodology to compare various prediction models using repeated measures of two psychometric tests to predict dementia in the elderly, accounting for the competing risk of death. Models are estimated on the French Paquid cohort and predictive accuracies are evaluated and compared on the French Three-City cohort. PMID:25311240
Dynamical passage to approximate equilibrium shapes for spinning, gravitating rubble asteroids
NASA Astrophysics Data System (ADS)
Sharma, Ishan; Jenkins, James T.; Burns, Joseph A.
2009-03-01
Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study for static and dynamical situations the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an ellipsoid with an interior modeled as a rigid-plastic, cohesion-less material with a Drucker-Prager yield criterion. Using an approximate volume-averaged procedure, based on the classical method of moments, we investigate the dynamical process by which such objects may achieve equilibrium. We first collapse our dynamical approach to its statical limit to derive regions in spin-shape parameter space that allow equilibrium solutions to exist. At present, only a graphical illustration of these solutions for a prolate ellipsoid following the Drucker-Prager failure law is available [Sharma, I., Jenkins, J.T., Burns, J.A., 2005a. Bull. Am. Astron. Soc. 37, 643; Sharma, I., Jenkins, J.T., Burns, J.A., 2005b. Equilibrium shapes of ellipsoidal soil asteroids. In: García-Rojo, R., Hermann, H.J., McNamara, S. (Eds.), Proceedings of the 5th International Conference on Micromechanics of Granular Media, vol. 1. A.A. Balkema, UK; Holsapple, K.A., 2007. Icarus 187, 500-509]. Here, we obtain the equilibrium landscapes for general triaxial ellipsoids, as well as provide the requisite governing formulae. In addition, we demonstrate that it may be possible to better interpret the results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361] within the context of a Drucker-Prager material. The graphical result for prolate ellipsoids in the static limit is the same as those of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] because, when worked out, his final equations will match ours. This is because, though the formalisms to reach these expressions differ, in statics, at the lowest level of approximation, volume-averaging and the approach of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] coincide. We note that the approach applied here was obtained independently [Sharma, I., Jenkins, J.T., Burns, J.A., 2003. Bull. Am. Astron. Soc. 35, 1034; Sharma, I., 2004. Rotational Dynamics of Deformable Ellipsoids with Applications to Asteroids. Ph.D. thesis, Cornell University] and it provides a general, though approximate, framework that is amenable to systematic improvements and is flexible enough to incorporate the dynamical effects of a changing shape, different rheologies and complex rotational histories. To demonstrate our technique, we investigate the non-equilibrium dynamics of rigid-plastic, spinning, prolate asteroids to examine the simultaneous histories of shape and spin rate for rubble piles. We have succeeded in recovering most results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361], who obtained equilibrium shapes by studying numerically the passage into equilibrium of aggregates containing discrete, interacting, frictionless, spherical particles. Our mainly analytical approach aids in understanding and quantifying previous numerical simulations.
Vold, Robert L; Hoatson, Gina L
2009-05-01
This paper describes EXPRESS (EXchange Program for RElaxing Spin Systems), a computer program that simulates the effects of Markovian jump dynamics for a wide variety of solid state nuclear magnetic resonance experiments. A graphical interface is described that facilitates the definition of rotational jumps around non-commuting axes that may occur at arbitrary, different rates. Solid state deuteron NMR is widely used to investigate such processes, and EXPRESS allows simulations of deuteron quadrupole echo and magic angle spinning line (MAS) shapes, as well as partially relaxed line shapes for measurements of anisotropic relaxation of Zeeman and quadrupolar order. Facilities are included for chemical shift tensors (at user-defined orientations relative to the quadrupole coupling tensors), so that EXPRESS is potentially useful for studies of paramagnetic systems where these interactions are of comparable magnitude. Many of the same techniques used for deuterons can be extended to half-integer quadrupolar nuclei. The same interface that specifies rotational "sites" for deuteron NMR studies is usable in EXPRESS to simulate static line shapes, MAS line shapes, and multiple pulse Carr-Purcell-Meiboom-Gill (CPMG) line shapes for the central transition of high spin quadrupoles with second order quadrupole coupling and chemical shift anisotropy. Representative simulations are displayed that show effects of slow libration on deuteron quadrupole echo line shapes and relaxation time anisotropies. EXPRESS is also used to investigate fundamental differences in the mechanism of echo formation in deuteron MAS and quadrupole CPMG experiments, and to illustrate significant differences between these techniques in the context of high spin quadrupolar nuclei. The program is modular and platform-independent, with facilities for users to add routines for experiments not yet envisioned. PMID:19201232
Mentink-Vigier, Frédéric; Paul, Subhradip; Lee, Daniel; Feintuch, Akiva; Hediger, Sabine; Vega, Shimon; De Paëpe, Gaël
2015-09-14
Over the last two decades solid state Nuclear Magnetic Resonance has witnessed a breakthrough in increasing the nuclear polarization, and thus experimental sensitivity, with the advent of Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). To enhance the nuclear polarization of protons, exogenous nitroxide biradicals such as TOTAPOL or AMUPOL are routinely used. Their efficiency is usually assessed as the ratio between the NMR signal intensity in the presence and the absence of microwave irradiation ?on/off. While TOTAPOL delivers an enhancement ?on/off of about 60 on a model sample, the more recent AMUPOL is more efficient: >200 at 100 K. Such a comparison is valid as long as the signal measured in the absence of microwaves is merely the Boltzmann polarization and is not affected by the spinning of the sample. However, recent MAS-DNP studies at 25 K by Thurber and Tycko (2014) have demonstrated that the presence of nitroxide biradicals combined with sample spinning can lead to a depolarized nuclear state, below the Boltzmann polarization. In this work we demonstrate that TOTAPOL and AMUPOL both lead to observable depolarization at ?110 K, and that the magnitude of this depolarization is radical dependent. Compared to the static sample, TOTAPOL and AMUPOL lead, respectively, to nuclear polarization losses of up to 20% and 60% at a 10 kHz MAS frequency, while Trityl OX63 does not depolarize at all. This experimental work is analyzed using a theoretical model that explains how the depolarization process works under MAS and gives new insights into the DNP mechanism and into the spin parameters, which are relevant for the efficiency of a biradical. In light of these results, the outstanding performance of AMUPOL must be revised and we propose a new method to assess the polarization gain for future radicals. PMID:26235749
Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E? symmetry.
Wu, Jianda; Kormos, Márton; Si, Qimiao
2014-12-12
A spectrum exhibiting E? symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E? description for CoNb?O?. PMID:25541800
Dynamics of the sub-Ohmic spin-boson model: A time-dependent variational study
NASA Astrophysics Data System (ADS)
Wu, Ning; Duan, Liwei; Li, Xin; Zhao, Yang
2013-02-01
The Dirac-Frenkel time-dependent variation is employed to probe the dynamics of the zero temperature sub-Ohmic spin-boson model with strong friction utilizing the Davydov D1 ansatz. It is shown that initial conditions of the phonon bath have considerable influence on the dynamics. Counterintuitively, even in the very strong coupling regime, quantum coherence features still manage to survive under the polarized bath initial condition, while such features are absent under the factorized bath initial condition. In addition, a coherent-incoherent transition is found at a critical coupling strength ? ? 0.1 for s = 0.25 under the factorized bath initial condition. We quantify how faithfully our ansatz follows the Schrödinger equation, finding that the time-dependent variational approach is robust for strong dissipation and deep sub-Ohmic baths (s ? 1).
Application of a system modification technique to dynamic tuning of a spinning rotor blade
NASA Technical Reports Server (NTRS)
Spain, C. V.
1987-01-01
An important consideration in the development of modern helicopters is the vibratory response of the main rotor blade. One way to minimize vibration levels is to ensure that natural frequencies of the spinning main rotor blade are well removed from integer multiples of the rotor speed. A technique for dynamically tuning a finite-element model of a rotor blade to accomplish that end is demonstrated. A brief overview is given of the general purpose finite element system known as Engineering Analysis Language (EAL) which was used in this work. A description of the EAL System Modification (SM) processor is then given along with an explanation of special algorithms developed to be used in conjunction with SM. Finally, this technique is demonstrated by dynamically tuning a model of an advanced composite rotor blade.
Reversal of spin dynamics in an antiferromagnetic F = 1 spinor Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Schwettmann, Arne; Summy, Gil; Pechkis, Hyewon; Wrubel, Jonathan; Barnett, Ryan; Wilson, Ryan; Tiesinga, Eite; Lett, Paul
2014-05-01
The antiferromagnetic F = 1 sodium spinor Bose-Einstein condensate (BEC) exhibits coherent population oscillations of the magnetic sublevels that are internally driven by spin-exchange collisions. Here, we experimentally demonstrate reversals of the collisional dynamics. The reversals are controlled with microwave pulses. We observe nearly complete reversals even after a significant amount of population oscillation has already occurred. In addition, and somewhat surprisingly, we can generate partial reversals in the cold, non-condensed normal gas. We explain our results with numerical calculations based on the truncated Wigner approximation and an analytical theory based on the Bogoliubov approximation. In the future, this type of microwave control of collisional dynamics will allow us to implement matter-wave analogs of devices known from quantum optics with photons, such as a phase-sensitive matter-wave amplifier.
Probing the physics of high-temperature superconductivity: Spin dynamics and pair-breaking effects
NASA Astrophysics Data System (ADS)
Kao, Ying-Jer
In this thesis we study two important aspects of the high critical temperature cuprate superconductors: spin dynamics in the superconducting state and pair-breaking effects in the pseudogap phase. Understanding magnetic correlations in the cuprates is essential to a full understanding of the underlying physics in these materials. And our studies of pair-breaking may provide a deeper understanding of the pseudogap origin. Indeed, these very intriguing pseudogap phenomena still remain a mystery which when solved will contribute an important piece to the jigsaw puzzle of high temperature superconductivity. In our study of spin dynamics, we employ an RPA formalism with strong Coulomb repulsion. These calculations give a natural explanation of the observed evolution with frequency of neutron peaks from incommensurate to commensurate and back to incommensurate at higher frequencies found in underdoped YB 2Cu3O6+x. We also explain related phenomena such as peak sharpening, and the spin gap observed in La2-xSr xCuO4. We find these phenomena are generic manifestations of d-wave pairing symmetry, while the underlying Fermi surface topology plays a less important role. We probe the physics of the pseudogap state by studying two different pair-breaking phenomena: magnetic fields and impurities. We generalize our theory of an extended BCS superconductivity in the clean case to include the effects of a magnetic field and impurities. In our physical picture the pseudogap state derives from the same pairing interaction which leads to superconductivity. The different responses of Tc and T* to these pair-breakers are due to a normal state gap at Tc which is absent at T*. This new physics cannot be obtained from common BCS intuition. Because of the presence of a pseudogap, there exist multiple length scales in the system, which only become equivalent in the BCS (weak coupling) regime.
High-dynamic-range magnetometry with a single nuclear spin in diamond
NASA Astrophysics Data System (ADS)
Waldherr, G.; Beck, J.; Neumann, P.; Said, R. S.; Nitsche, M.; Markham, M. L.; Twitchen, D. J.; Twamley, J.; Jelezko, F.; Wrachtrup, J.
2012-02-01
Sensors based on the nitrogen-vacancy defect in diamond are being developed to measure weak magnetic and electric fields at the nanoscale. However, such sensors rely on measurements of a shift in the Lamor frequency of the defect, so an accumulation of quantum phase causes the measurement signal to exhibit a periodic modulation. This means that the measurement time is either restricted to half of one oscillation period, which limits accuracy, or that the magnetic field range must be known in advance. Moreover, the precision increases only slowly (as T-0.5) with measurement time T (ref. 3). Here, we implement a quantum phase estimation algorithm on a single nuclear spin in diamond to combine both high sensitivity and high dynamic range. By achieving a scaling of the precision with time to T-0.85, we improve the sensitivity by a factor of 7.4 for an accessible field range of 16 mT, or, alternatively, we improve the dynamic range by a factor of 130 for a sensitivity of 2.5 ľT Hz-1/2. Quantum phase estimation algorithms have also recently been implemented using a single electron spin in a nitrogen-vacancy centre. These methods are applicable to a variety of field detection schemes, and do not require quantum entanglement.
High-dynamic-range magnetometry with a single nuclear spin in diamond.
Waldherr, G; Beck, J; Neumann, P; Said, R S; Nitsche, M; Markham, M L; Twitchen, D J; Twamley, J; Jelezko, F; Wrachtrup, J
2012-02-01
Sensors based on the nitrogen-vacancy defect in diamond are being developed to measure weak magnetic and electric fields at the nanoscale. However, such sensors rely on measurements of a shift in the Lamor frequency of the defect, so an accumulation of quantum phase causes the measurement signal to exhibit a periodic modulation. This means that the measurement time is either restricted to half of one oscillation period, which limits accuracy, or that the magnetic field range must be known in advance. Moreover, the precision increases only slowly (as T(-0.5)) with measurement time T (ref. 3). Here, we implement a quantum phase estimation algorithm on a single nuclear spin in diamond to combine both high sensitivity and high dynamic range. By achieving a scaling of the precision with time to T(-0.85), we improve the sensitivity by a factor of 7.4 for an accessible field range of 16 mT, or, alternatively, we improve the dynamic range by a factor of 130 for a sensitivity of 2.5 ľT Hz(-1/2). Quantum phase estimation algorithms have also recently been implemented using a single electron spin in a nitrogen-vacancy centre. These methods are applicable to a variety of field detection schemes, and do not require quantum entanglement. PMID:22179568
The co-evolutionary dynamics of directed network of spin market agents
NASA Astrophysics Data System (ADS)
Horváth, Denis; Kuscsik, Zoltán; Gmitra, Martin
2006-09-01
The spin market model [S. Bornholdt, Int. J. Mod. Phys. C 12 (2001) 667] is generalized by employing co-evolutionary principles, where strategies of the interacting and competitive traders are represented by local and global couplings between the nodes of dynamic directed stochastic network. The co-evolutionary principles are applied in the frame of Bak-Sneppen self-organized dynamics [P. Bak, K. Sneppen, Phys. Rev. Lett. 71 (1993) 4083] that includes the processes of selection and extinction actuated by the local (node) fitness. The local fitness is related to orientation of spin agent with respect to the instant magnetization. The stationary regime is formed due to the interplay of self-organization and adaptivity effects. The fat tailed distributions of log-price returns are identified numerically. The non-trivial model consequence is the evidence of the long time market memory indicated by the power-law range of the autocorrelation function of volatility with exponent smaller than one. The simulations yield network topology with broad-scale node degree distribution characterized by the range of exponents 1.3
2011-01-01
Background The human thymine-DNA glycosylase (TDG) plays a dual role in base excision repair of G:U/T mismatches and in transcription. Regulation of TDG activity by SUMO-1 conjugation was shown to act on both functions. Furthermore, TDG can interact with SUMO-1 in a non-covalent manner. Results Using NMR spectroscopy we have determined distinct conformational changes in TDG upon either covalent sumoylation on lysine 330 or intermolecular SUMO-1 binding through a unique SUMO-binding motif (SBM) localized in the C-terminal region of TDG. The non-covalent SUMO-1 binding induces a conformational change of the TDG amino-terminal regulatory domain (RD). Such conformational dynamics do not exist with covalent SUMO-1 attachment and could potentially play a broader role in the regulation of TDG functions for instance during transcription. Both covalent and non-covalent processes activate TDG G:U repair similarly. Surprisingly, despite a dissociation of the SBM/SUMO-1 complex in presence of a DNA substrate, SUMO-1 preserves its ability to stimulate TDG activity indicating that the non-covalent interactions are not directly involved in the regulation of TDG activity. SUMO-1 instead acts, as demonstrated here, indirectly by competing with the regulatory domain of TDG for DNA binding. Conclusions SUMO-1 increases the enzymatic turnover of TDG by overcoming the product-inhibition of TDG on apurinic sites. The mechanism involves a competitive DNA binding activity of SUMO-1 towards the regulatory domain of TDG. This mechanism might be a general feature of SUMO-1 regulation of other DNA-bound factors such as transcription regulatory proteins. PMID:21284855
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.
Gonzalo A. Alvarez
2007-05-15
The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.
Dynamics at the Protein-Water Interface from 17O Spin Relaxation in Deeply Supercooled Solutions
Mattea, Carlos; Qvist, Johan; Halle, Bertil
2008-01-01
Most of the decisive molecular events in biology take place at the protein-water interface. The dynamical properties of the hydration layer are therefore of fundamental importance. To characterize the dynamical heterogeneity and rotational activation energy in the hydration layer, we measured the 17O spin relaxation rate in dilute solutions of three proteins in a wide temperature range extending down to 238 K. We find that the rotational correlation time can be described by a power-law distribution with exponent 2.12.3. Except for a small fraction of secluded hydration sites, the dynamic perturbation in the hydration layer is the same for all proteins and does not differ in any essential way from the hydration shell of small organic solutes. In both cases, the dynamic perturbation factor is <2 at room temperature and exhibits a maximum near 262 K. This maximum implies that, at low temperatures, the rate of water molecule rotation has a weaker temperature dependence in the hydration layer than in bulk water. We attribute this difference to the temperature-independent constraints that the protein surface imposes on the water H-bond network. The free hydration layer studied here differs qualitatively from confined water in solid protein powder samples. PMID:18586840
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.
NASA Astrophysics Data System (ADS)
Triaud, A. H. M. J.; Collier Cameron, A.; Queloz, D.; Anderson, D. R.; Gillon, M.; Hebb, L.; Hellier, C.; Loeillet, B.; Maxted, P. F. L.; Mayor, M.; Pepe, F.; Pollacco, D.; Ségransan, D.; Smalley, B.; Udry, S.; West, R. G.; Wheatley, P. J.
2010-12-01
Context. Several competing scenarios for planetary-system formation and evolution seek to explain how hot Jupiters came to be so close to their parent stars. Most planetary parameters evolve with time, making it hard to distinguish between models. The obliquity of an orbit with respect to the stellar rotation axis is thought to be more stable than other parameters such as eccentricity. Most planets, to date, appear aligned with the stellar rotation axis; the few misaligned planets so far detected are massive (> 2 MJ). Aims: Our goal is to measure the degree of alignment between planetary orbits and stellar spin axes, to search for potential correlations with eccentricity or other planetary parameters and to measure long term radial velocity variability indicating the presence of other bodies in the system. Methods: For transiting planets, the Rossiter-McLaughlin effect allows the measurement of the sky-projected angle ? between the stellar rotation axis and a planet's orbital axis. Using the HARPS spectrograph, we observed the Rossiter-McLaughlin effect for six transiting hot Jupiters found by the WASP consortium. We combine these with long term radial velocity measurements obtained with CORALIE. We used a combined analysis of photometry and radial velocities, fitting model parameters with the Markov Chain Monte Carlo method. After obtaining ? we attempt to statistically determine the distribution of the real spin-orbit angle ?. Results: We found that three of our targets have ? above 90°: WASP-2b: ? = 153°+11-15, WASP-15b: ? = 139.6°+5.2-4.3 and WASP-17b: ? = 148.5°+5.1-4.2; the other three (WASP-4b, WASP-5b and WASP-18b) have angles compatible with 0°. We find no dependence between the misaligned angle and planet mass nor with any other planetary parameter. All six orbits are close to circular, with only one firm detection of eccentricity e = 0.00848+0.00085-0.00095 in WASP-18b. No long-term radial acceleration was detected for any of the targets. Combining all previous 20 measurements of ? and our six and transforming them into a distribution of ? we find that between about 45 and 85% of hot Jupiters have ? > 30°. Conclusions: Most hot Jupiters are misaligned, with a large variety of spin-orbit angles. We find observations and predictions using the Kozai mechanism match well. If these observational facts are confirmed in the future, we may then conclude that most hot Jupiters are formed from a dynamical and tidal origin without the necessity to use type I or II migration. At present, standard disc migration cannot explain the observations without invoking at least another additional process. Using observations with the high resolution échelle spectrograph HARPS mounted on the ESO 3.6 m (under proposals 072.C-0488, 082.C-0040 & 283.C-5017), and with the high resolution échelle spectrograph CORALIE on the 1.2 m Euler Swiss Telescope, both installed at the ESO La Silla Observatory in Chile.RV data is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/524/A25
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
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
NASA Astrophysics Data System (ADS)
Kawasaki, Yu; Gavilano, Jorge L.; Keller, Lukas; Schefer, Jürg; Christensen, Niels Bech; Amato, Alex; Ohno, Takashi; Kishimoto, Yutaka; He, Zhangzhen; Ueda, Yutaka; Itoh, Mitsuru
2011-02-01
We report a neutron diffraction and muon spin relaxation ?SR study of static and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional spin-chain system. A proposed model for the antiferromagnetic structure includes: a propagation vector k?AF=(0,0,1), independent of external magnetic fields for fields below a critical value Hc(T). The ordered moments of 2.18 ?B per Co ion are aligned along the crystallographic c axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged ferromagnetically (forming zigzag paths) along one of the axes and antiferromagnetically along the other. The temperature dependence of the sublattice magnetization is consistent with the expectations of the three-dimensional (3D) Ising model. A similar behavior is observed for the internal static fields at different muon stopping sites. Muon time spectra measured at weak longitudinal fields and temperatures much higher than TN can be well described using a single muon site with an exponential muon spin relaxation that gradually changes into an stretched exponential on approaching TN. The temperature-induced changes of the relaxation suggest that the Co fluctuations dramatically slow down and the system becomes less homogeneous as it approaches the antiferromagnetic state.
NASA Astrophysics Data System (ADS)
Huang, Lei
In the forefront of spintronics research, transmission electron microscopy (TEM) is not only an essential tool for examining matter with high spatial resolution, but also associated with it is a rich variety of in-situ capabilities making quantitative investigation of the intriguing microscopic magnetic phenomena possible. This dissertation covers TEM studies of nanoscale magnetization reversal and high frequency spin dynamics of patterned magnetic elements, which hold great promise for the development of next generation recording/memory technologies. We first focus on the static spin configurations and magnetization reversal processes of patterned soft magnetic thin films. Using in-situ Lorentz microscopy and off-axis electron holography, we find patterning the same magnetic material with different geometries can create sharply distinct domain structures and switching properties, which can be effectively explained by shape anisotropy and interlayer stray field coupling. We then exploit these effects by designing shape-engineered tri-layer nanomagnets, of which the magnetization reversal process can be precisely controlled to achieve specific remanent states. We also study the magnetic behavior of nanomagnets in the high frequency regime, where spin torque transfer between current and magnetization represents a radically new data-writing concept. Here, we design and construct a novel TEM stage to apply microwave excitation stimulus to the patterned nanomagets, and directly observe the current-induced resonant precession of the vortex core with unprecedented spatial resolution. We measure the precession orbits as a function of both frequency and current density, and succeed in quantifying the resonant frequency and damping coefficient. For the first time we obtain experimental proof with nanometer resolution that the vortex precession orbit is elliptical when it's off-resonance.
Bastrop, Martin; Meister, Annette; Metz, Hendrik; Drescher, Simon; Dobner, Bodo; Mäder, Karsten; Blume, Alfred
2009-01-15
The aggregation behavior of the bolaamphiphilic hydrogelators dotriacontane-1,32-diyl-bis[2-(trimethylammonio)ethylphosphate] (PC-C32-PC) and the pH-sensitive dotriacontane-1,32-diyl-bis[2-(dimethylammonio)-ethylphosphate] (Me2PE-C32-Me2PE) was characterized before using different methods. Dependent on the temperature, pH, and concentration, these bolaamphiphiles self-asssemble into long nanofibers or other aggregates, such as short rods or micelles. In order to obtain information about the motional dynamics and microscopic order inside of these aggregates, we carried out a systematic ESR spin probe study. The spectra obtained with the spin probes 5-, 12- and 16-doxyl stearic acid (n-DSA) were found to be highly sensitive to changes in the bolaamphiphilic arrangement. Rotational correlation times and order parameters were obtained from full ESR line shape simulations with the programs EasySpin and EPRSIM. The maximum hyperfine splitting, 2Amax, was used to determine the transition temperatures, which are in agreement with the DSCdata. By comparison of 5-DSA and 12-DSA, which are residing at different positions in the alkyl chain region of the aggregates, it was found that trans-gauche isomerization is predominantly occurring in the outer region of the aggregates. For Me2PE-C32-Me2PE at pH 10, our ESR data indicate that micelles are short rods rather than being spherical in shape. Therefore, increasing the concentration from 1 to 10 mg/mL leads only to a one-dimensional growth of these micelles. PMID:19072161
Quantum-tunneling dynamics of a spin-polarized Fermi gas in a double-well potential
Salasnich, L.; Mazzarella, G.; Toigo, F. [Dipartimento di Fisica 'Galileo Galilei' and CNISM, Universita di Padova, Via Marzolo 8, I-35122 Padua (Italy); Salerno, M. [Dipartimento di Fisica 'E.R. Caianiello', CNISM and INFN-Gruppo Collegato di Salerno, Universita di Salerno, Via Ponte don Melillo, I-84084 Fisciano(Italy)
2010-02-15
We study the exact dynamics of a one-dimensional spin-polarized gas of fermions in a double-well potential at zero and finite temperature. Despite the system being made of noninteracting fermions, its dynamics can be quite complex, showing strongly aperiodic spatio-temporal patterns during the tunneling. The extension of these results to the case of mixtures of spin-polarized fermions interacting with self-trapped Bose-Einstein condensates (BECs) at zero temperature is considered as well. In this case we show that the fermionic dynamics remains qualitatively similar to that observed in the absence of BEC but with the Rabi frequencies of fermionic excited states explicitly depending on the number of bosons and on the boson-fermion interaction strength. From this, the possibility of controlling quantum fermionic dynamics by means of Feshbach resonances is suggested.
Memory-keeping effects and forgetfulness in the dynamics of a qubit coupled to a spin chain
T. J. G. Apollaro; C. Di Franco; F. Plastina; M. Paternostro
2011-03-14
Using recently proposed measures for non-Markovianity [H. P. Breuer, E. M. Laine, and J. Piilo, Phys. Rev. Lett. {\\bf 103}, 210401 (2009)], we study the dynamics of a qubit coupled to a spin environment via an energy-exchange mechanism. We show the existence of a point, in the parameter space of the system, where the qubit dynamics is effectively Markovian and that such a point separates two regions with completely different dynamical behaviors. Indeed, our study demonstrates that the qubit evolution can in principle be tuned from a perfectly forgetful one to a deep non-Markovian regime where the qubit is strongly affected by the dynamical back-action of the environmental spins. By means of quantum process tomography, we provide a complete and intuitive characterization of the qubit channel.
Birgeneau, R.J.; Belk, N.; Kastner, M.A.; Keimer, B. . Dept. of Physics); Endoh, Y. . Dept. of Physics); Erwin, R.W. ); Shirane, G. )
1991-01-01
We review the results of neutron scattering studies of the static and dynamic spin fluctuations crystals of La{sub 2-x}Sr{sub x}CuO{sub 4+{delta}} in the doping regime intermediate between the Neel and superconducting regions. In this regime the in-plane resistance is linear in temperature down to {approximately}80 K with a crossover due to logarithmic conductance effects at lower temperatures. The static spin correlations are well-described by a simple model in which the inverse correlation length {kappa}(x,T) ={kappa}(x,0) + {kappa}(0,T). The most dramatic new result is the discovery by Keimer et al. that the dynamic spin fluctuations exhibit a temperature dependence which is a simple function of {omega}/T for temperatures 10 K{le}T{le}500 K for a wide range of energies. This scaling leads to a natural explanation of a variety of normal state properties of the copper oxides. 21 refs., 4 figs.
Spin Dynamics of the LAGEOS Satellite in Support of a Measurement of the Earth's Gravitomagnetism
Salman Habib; Daniel E. Holz; Arkady Kheyfets; Richard A. Matzner; Warner A. Miller; Brian W. Tolman
1994-06-20
LAGEOS is an accurately-tracked, dense spherical satellite covered with 426 retroreflectors. The tracking accuracy is such as to yield a medium term (years to decades) inertial reference frame determined via relatively inexpensive observations. This frame is used as an adjunct to the more difficult and data intensive VLBI absolute frame measurements. There is a substantial secular precession of the satellite's line of nodes consistent with the classical, Newtonian precession due to the non-sphericity of the earth. Ciufolini has suggested the launch of an identical satellite (LAGEOS-3) into an orbit supplementary to that of LAGEOS-1: LAGEOS-3 would then experience an equal and opposite classical precession to that of LAGEOS-1. Besides providing a more accurate real-time measurement of the earth's length of day and polar wobble, this paired-satellite experiment would provide the first direct measurement of the general relativistic frame-dragging effect. Of the five dominant error sources in this experiment, the largest one involves surface forces on the satellite, and their consequent impact on the orbital nodal precession. The surface forces are a function of the spin dynamics of the satellite. Consequently, we undertake here a theoretical effort to model the spin ndynamics of LAGEOS. In this paper we present our preliminary results.
Control Study for Five-axis Dynamic Spin Rig Using Magnetic Bearings
NASA Technical Reports Server (NTRS)
Choi, Benjamin; Johnson, Dexter; Provenza, Andrew; Morrison, Carlos; Montague, Gerald
2003-01-01
The NASA Glenn Research Center (GRC) has developed a magnetic bearing system for the Dynamic Spin Rig (DSR) with a fully suspended shaft that is used to perform vibration tests of turbomachinery blades and components under spinning conditions in a vacuum. Two heteropolar radial magnetic bearings and a thrust magnetic bearing and the associated control system were integrated into the DSR to provide magnetic excitation as well as non-contact mag- netic suspension of a 15.88 kg (35 lb) vertical rotor with blades to induce turbomachinery blade vibration. For rotor levitation, a proportional-integral-derivative (PID) controller with a special feature for multidirectional radial excitation worked well to both support and shake the shaft with blades. However, more advanced controllers were developed and successfully tested to determine the optimal controller in terms of sensor and processing noise reduction, smaller rotor orbits, more blade vibration amplitude, and energy savings for the system. The test results of a variety of controllers that were demonstrated up to 10.000 rpm are shown. Furthermore, rotor excitation operation and conceptual study of active blade vibration control are addressed.
NASA Astrophysics Data System (ADS)
Pathak, Anand; Sinha, Sitabhra
2015-09-01
Many complex systems can be represented as networks of dynamical elements whose states evolve in response to interactions with neighboring elements, noise and external stimuli. The collective behavior of such systems can exhibit remarkable ordering phenomena such as chimera order corresponding to coexistence of ordered and disordered regions. Often, the interactions in such systems can also evolve over time responding to changes in the dynamical states of the elements. Link adaptation inspired by Hebbian learning, the dominant paradigm for neuronal plasticity, has been earlier shown to result in structural balance by removing any initial frustration in a system that arises through conflicting interactions. Here we show that the rate of the adaptive dynamics for the interactions is crucial in deciding the emergence of different ordering behavior (including chimera) and frustration in networks of Ising spins. In particular, we observe that small changes in the link adaptation rate about a critical value result in the system exhibiting radically different energy landscapes, viz., smooth landscape corresponding to balanced systems seen for fast learning, and rugged landscapes corresponding to frustrated systems seen for slow learning.
Morphologic parameters of normal swallowing events using single-shot fast spin echo dynamic MRI.
Hartl, Dana M; Albiter, Marcella; Kolb, Frédéric; Luboinski, Bernard; Sigal, Robert
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 dry swallow, water swallow, marshmallow swallow, cake swallow, and cookie chewing for a total of five series, with 15 acquisitions per series at a rate of 700 ms per acquisition. A checklist of swallowing events and anatomic landmarks was used to determine which anatomic landmarks are always visible, which phases or swallowing movements are always visible, and which landmarks can be used to measure oral and pharyngeal motion in swallowing. The oral preparatory, oral, and oropharyngeal phases of deglutition were visible in all cases. No aspiration, reflux, or abnormal residue was observed. Spatial resolution allowed for anatomical measurements of laryngeal elevation, oropharyngeal diameter, and tongue base and velum displacement in all cases. SSFSE dynamic MRI is pertinent for evaluation of the anatomical and physiological characteristics of swallow. The temporal parameters, however, cannot be studied using this technique. Motion artifacts preclude its use in the study of mastication. It remains complementary to videofluoroscopy and other techniques in swallow evaluation. PMID:14571329
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.
Dynamics of the sub-Ohmic spin-boson model: A comparison of three numerical approaches
NASA Astrophysics Data System (ADS)
Yao, Yao; Duan, Liwei; Lü, Zhiguo; Wu, Chang-Qin; Zhao, Yang
2013-08-01
Dynamics of the sub-Ohmic spin-boson model is examined using three numerical approaches, namely the Dirac-Frenkel time-dependent variation with the Davydov D1 ansatz, the adaptive time-dependent density matrix renormalization group method within the representation of orthogonal polynomials, and a perturbative approach based on a unitary transformation. In order to probe the validity regimes of the three approaches, we study the dynamics of a qubit coupled to a bosonic bath with and without a local field. Comparison of the up-state population evolution shows that the three approaches are in agreement in the weak-coupling regime but exhibit marked differences when the coupling strength is large. The Davydov D1 ansatz and the time-dependent density matrix renormalization group can both be reliably employed in the weak-coupling regime, while the former is also valid in the strong-coupling regime as judged by how faithfully the trial state follows the Schrödinger equation. We further explore the bipartite entanglement dynamics between two qubits coupled with individual bosonic baths which reveals entanglement sudden death and revival.
Overlap and activity glass transitions in plaquette spin models with hierarchical dynamics
NASA Astrophysics Data System (ADS)
Turner, Robert M.; Jack, Robert L.; Garrahan, Juan P.
2015-08-01
We consider thermodynamic and dynamic phase transitions in plaquette spin models of glasses. The thermodynamic transitions involve coupled (annealed) replicas of the model. We map these coupled-replica systems to a single replica in a magnetic field, which allows us to analyze the resulting phase transitions in detail. For the triangular plaquette model (TPM), we find for the coupled-replica system a phase transition between high- and low-overlap phases, occurring at a coupling ?*(T ) , which vanishes in the low-temperature limit. Using computational path sampling techniques, we show that a single TPM also displays "space-time" transitions between active and inactive dynamical phases. These first-order dynamical transitions occur at a critical counting field sc(T ) ?0 that appears to vanish at zero temperature in a manner reminiscent of the thermodynamic overlap transition. In order to extend the ideas to three dimensions, we introduce the square pyramid model, which also displays both overlap and activity transitions. We discuss a possible common origin of these various phase transitions, based on long-lived (metastable) glassy states.
Synthesis of (6-(13)C)pyrimidine nucleotides as spin-labels for RNA dynamics.
Wunderlich, Christoph H; Spitzer, Romana; Santner, Tobias; Fauster, Katja; Tollinger, Martin; Kreutz, Christoph
2012-05-01
We present a (13)C-based isotope labeling protocol for RNA. Using (6-(13)C)pyrimidine phosphoramidite building blocks, site-specific labels can be incorporated into a target RNA via chemical oligonucleotide solid-phase synthesis. This labeling scheme is particularly useful for studying milli- to microsecond dynamics via NMR spectroscopy, as an isolated spin system is a crucial prerequisite to apply Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion type experiments. We demonstrate the applicability for the characterization and detection of functional dynamics on various time scales by incorporating the (6-(13)C)uridine and -cytidine labels into biologically relevant RNAs. The refolding kinetics of a bistable terminator antiterminator segment involved in the gene regulation process controlled by the preQ(1) riboswitch class I was investigated. Using (13)C CPMG relaxation dispersion NMR spectroscopy, the milli- to microsecond dynamics of the HIV-1 transactivation response element RNA and the Varkud satellite stem loop V motif was addressed. PMID:22489874
Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth
Craco, Luis; Leoni, Stefano
2015-01-01
Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA?+?DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals. PMID:26358556
Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth.
Craco, Luis; Leoni, Stefano
2015-01-01
Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA?+?DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals. PMID:26358556
Fernández-Pacheco, A. Mansell, R.; Petit, D.; Lee, J. H.; Cowburn, R. P.; Ummelen, F. C.; Swagten, H. J. M.
2014-09-01
We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.
NASA Astrophysics Data System (ADS)
De Paëpe, Gaël; Eléna, Bénédicte; Emsley, Lyndon
2004-08-01
The work presented here aims at understanding the performance of phase modulated heteronuclear decoupling sequences such as Cosine Modulation or Two Pulse Phase Modulation. To that end we provide an analytical description of the intrinsic behavior of Cosine Modulation decoupling with respect to radio-frequency-inhomogeneity and the proton-proton dipolar coupling network. We discover through a Modulation Frame average Hamiltonian analysis that best decoupling is obtained under conditions where the heteronuclear interactions are removed but notably where homonuclear couplings are recoupled at a homonuclear Rotary Resonance (HORROR) condition in the Modulation Frame. These conclusions are supported by extensive experimental investigations, and notably through the introduction of proton nutation experiments to characterize spin dynamics in solids under decoupling conditions. The theoretical framework presented in this paper allows the prediction of the optimum parameters for a given set of experimental conditions.
Micromagnetic modeling of spin-wave dynamics in exchange-biased permalloy disks.
Heinonen, O. G.; Schreiber, D. K.; Petford-Long, A. K.; Materials Science Division; Seagate Tech.; Northwestern Univ.
2007-01-01
The magnetization dynamics in exchange-biased 12 nm thick micron-sized permalloy disks have been studied using micromagnetic modeling. The magnetization in the permalloy and in the adjacent antiferromagnetic layer are set in a vortex configuration, and the disk is equilibrated in an applied field, which is then released. The behavior of the magnetization has been modeled as a function of both exchange bias strength and applied field, in both the time and frequency domains. We show that the exchange bias increases the curvature of the effective potential confining the vortex and that the gyrotropic frequency of the vortex core motion increases linearly with exchange bias. The eigenmodes of the spin waves to which the field couples are either azimuthal (for an in-plane field) or circularly symmetric (for a perpendicular field), with several orders of modes being visible. For the circularly symmetric modes, the increase in frequency with exchange bias is in good agreement with an analytical model.
NASA Astrophysics Data System (ADS)
Pal, S.; Klos, J. W.; Das, K.; Hellwig, O.; Gruszecki, P.; Krawczyk, M.; Barman, A.
2014-10-01
We present an all-optical time-resolved measurement of spin wave (SW) dynamics in a series of antidot lattices based on [Co(0.75 nm)/Pd(0.9 nm)]8 multilayer (ML) systems with perpendicular magnetic anisotropy. The spectra depend significantly on the areal density of the antidots. The observed SW modes are qualitatively reproduced by the plane wave method. The interesting results found in our measurements and calculations at small lattice constants can be attributed to the increase of areal density of the shells with modified magnetic properties probably due to distortion of the regular ML structure by the Ga ion bombardment and to increased coupling between localized modes. We propose and discuss the possible mechanisms for this coupling including exchange interaction, tunnelling, and dipolar interactions.
Vortex-induced dynamic loads on a non-spinning volleyball
NASA Astrophysics Data System (ADS)
Qing-ding, Wei; Rong-sheng, Lin; Zhi-jie, Liu
1988-09-01
An experiment on vortex-induced dynamic loads on a non-spinning Volleyball was conducted in a wind tunnel. The flow past the Volleyball was visualized, and the aerodynamic load was measured by use of a strain gauge balance. The separation on the Volleyball was measured with hot-film. The experimental results suggest that under the action of an unstable tail vortex system the separation region is changeable, and that the fluctuation of drag and lateral forces is the same order of magnitude as the mean drag, no matter whether the seam of the Volleyball is symmetric or asymmetric, with regard to the flow. Based on the experimental data a numerical simulation of Volleyball swerve motion was made.
Quantum discord dynamics of two-qubit system in a quantum spin environment
NASA Astrophysics Data System (ADS)
Guo, J. L.; Mi, Y. J.; Song, H. S.
2012-01-01
We study the dynamics of quantum discord of two-qubit system in a quantum spin environment at finite temperature in the thermodynamics limit. Special attention is paid to the difference between the entanglement and quantum discord when considering the influences of the environment temperature and the initial system states. We show that in the same range of the physical parameters, when the system states behave no entanglement or entanglement sudden death, the quantum discord keeps nonzero. So the quantum discord is more robust than entanglement under this decoherence environment. Furthermore, we also illustrate that we can tune the parameters related to the system and the environment to suppress the decay of quantum discord.
Lü, Zhiguo; Zheng, Hang
2009-10-01
The quantum dynamics of a two-level system coupled to an Ohmic spin bath is studied by means of the perturbation approach based on a unitary transformation. A scattering function xi(k) is introduced in the transformation to take into account quantum fluctuations. By the master equation within the Born approximation, nonequilibrium dynamics quantities are calculated. The method works well for the coupling constant 0
Otani, Yoshichika
2007-01-01
the dynamics of a magnetic vortex under spin-polarized electric current in ferromagnets. The equation of motion for current-induced vortex displacement and resonance motion in a ferromagnetic nanodot. Our estimate-induced motion of a vortex wall in a ferromagnetic thin wire. r 2006 Elsevier B.V. All rights reserved. PACS: 72
Novel phase-space Monte-Carlo method for quench dynamics in 1D and 2D spin models
NASA Astrophysics Data System (ADS)
Pikovski, Alexander; Schachenmayer, Johannes; Rey, Ana Maria
2015-05-01
An important outstanding problem is the effcient numerical computation of quench dynamics in large spin systems. We propose a semiclassical method to study many-body spin dynamics in generic spin lattice models. The method, named DTWA, is based on a novel type of discrete Monte-Carlo sampling in phase-space. We demonstare the power of the technique by comparisons with analytical and numerically exact calculations. It is shown that DTWA captures the dynamics of one- and two-point correlations 1D systems. We also use DTWA to study the dynamics of correlations in 2D systems with many spins and different types of long-range couplings, in regimes where other numerical methods are generally unreliable. Computing spatial and time-dependent correlations, we find a sharp change in the speed of propagation of correlations at a critical range of interactions determined by the system dimension. The investigations are relevant for a broad range of systems including solids, atom-photon systems and ultracold gases of polar molecules, trapped ions, Rydberg, and magnetic atoms. This work has been financially supported by JILA-NSF-PFC-1125844, NSF-PIF-1211914, ARO, AFOSR, AFOSR-MURI.
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.
Cobb, C E; Hustedt, E J; Beechem, J M; Beth, A H
1993-01-01
An acyl spin-label derivative of 5-aminoeosin (5-SLE) was chemically synthesized and employed in studies of rotational dynamics of the free probe and of the probe when bound noncovalently to bovine serum albumin using the spectroscopic techniques of fluorescence anisotropy decay and electron paramagnetic resonance (EPR) and their long-lifetime counterparts phosphorescence anisotropy decay and saturation transfer EPR. Previous work (Beth, A. H., Cobb, C. E., and J. M. Beechem, 1992. Synthesis and characterization of a combined fluorescence, phosphorescence, and electron paramagnetic resonance probe. Society of Photo-Optical Instrumentation Engineers. Time-Resolved Laser Spectroscopy III. 504-512) has shown that the spin-label moiety only slightly altered the fluorescence and phosphorescence lifetimes and quantum yields of 5-SLE when compared with 5-SLE whose nitroxide had been reduced with ascorbate and with the diamagnetic homolog 5-acetyleosin. In the present work, we have utilized time-resolved fluorescence anisotropy decay and linear EPR spectroscopies to observe and quantitate the psec motions of 5-SLE in solution and the nsec motions of the 5-SLE-bovine serum albumin complex. Time-resolved phosphorescence anisotropy decay and saturation transfer EPR studies have been carried out to observe and quantitate the microseconds motions of the 5-SLE-albumin complex in glycerol/buffer solutions of varying viscosity. These latter studies have enabled a rigorous comparison of rotational correlation times obtained from these complementary techniques to be made with a single probe. The studies described demonstrate that it is possible to employ a single molecular probe to carry out the full range of fluorescence, phosphorescence, EPR, and saturation transfer EPR studies. It is anticipated that "dual" molecular probes of this general type will significantly enhance capabilities for extracting dynamics and structural information from macromolecules and their functional assemblies. PMID:7682451
NASA Astrophysics Data System (ADS)
Procissi, D.; Shastri, A.; Rousochatzakis, I.; Al Rifai, M.; Kögerler, P.; Luban, M.; Suh, B. J.; Borsa, F.
2004-03-01
We report susceptibility and nuclear magnetic resonance (NMR) measurements in a polyoxovanadate compound with formula (NHEt)3[VIV8VV4As8O40(H2O)]?H2O?{V12}. The magnetic properties can be described by considering only the central square of localized V4+ ions and treated by an isotropic Heisenberg Hamiltonian of four intrinsic spins 1/2 coupled by nearest-neighbor antiferromagnetic interaction with J17.6 K. In this simplified description the ground state is nonmagnetic with ST=0. The 1H NMR linewidth (full width at half maximum) data depend on both the magnetic field and temperature, and are explained by the dipolar interaction between proton nuclei and V4+ ion spins. The behavior of the nuclear spin-lattice relaxation rate T-11 in the temperature range (4.2 300 K) is similar to that of ?T vs T and it does not show any peak at low temperatures contrary to previous observations in antiferromagnetic rings with larger intrinsic spins. The results are explained by using the general features of the Moriya formula and by introducing a single T-independent broadening parameter for the electronic spin system. From the exponential T dependence of T-11 at low T (2.5 K
NASA Astrophysics Data System (ADS)
Yildirim, Taner
2009-03-01
From all-electron fixed-spin-moment calculations [1], we showed that the ferromagnetic and checkerboard antiferromagnetic ordering in LaOFeAs were not stable and the stripe Fe-spin configuration (i.e. SDW) was the only stable ground state. The main exchange interaction between Fe ions are large, antiferromagnetic, and frustrated. The magnetic stripe SDW phase breaks the tetragonal symmetry, removes the frustration, and causes a structural distortion. We unravel surprisingly strong interactions between arsenic ions, the strength of which is controlled by the Fe-spin state in an unprecedented way [2]. Reducing the Fe-magnetic moment, weakens the Fe-As bonding, and in turn, increases As-As interactions, causing giant reduction in the c-axis. For CaFe2As2 system, this reduction of c-axis with the loss of the Fe-moment is as large as 1.4 ĺ, an unheard of giant coupling of local spin-state of an ion to its lattice. Since the calculated large c-reduction has been recently observed only under high-pressure, our results suggest that the iron magnetic moment should be present in Fe-pnictides at all times at ambient pressure. Implications of these findings on the mechanism of superconductivity in iron-pnictides will be discussed. [4pt] [1] T. Yildirim, Phys. Rev. Lett. 101, 057010 (2008) (arXiv:0804.2252). [0pt] [2] T. Yildirim, arXiv:0807.3936 (2008)
Materials optimization and ghz spin dynamics of metallic ferromagnetic thin film heterostructures
NASA Astrophysics Data System (ADS)
Cheng, Cheng
Metallic ferromagnetic (FM) thin film heterostructures play an important role in emerging magnetoelectronic devices, which introduce the spin degree of freedom of electrons into conventional charge-based electronic devices. As the majority of magnetoelectronic devices operate in the GHz frequency range, it is critical to understand the high-frequency magnetization dynamics in these structures. In this thesis, we start with the static magnetic properties of FM thin films and their optimization via the field-sputtering process incorporating a specially designed in-situ electromagnet. We focus on the origins of anisotropy and hysteresis/coercivity in soft magnetic thin films, which are most relevant to magentic susceptibility and power dissipation in applications in the sub-GHz frequency regime, such as magnetic-core integrated inductors. Next we explore GHz magnetization dynamics in thin-film heterostructures, both in semi-infinite samples and confined geometries. All investigations are rooted in the Landau-Lifshitz-Gilbert (LLG) equation, the equation of motion for magnetization. The phenomenological Gilbert damping parameter in the LLG equation has been interpreted, since the 1970's, in terms of the electrical resistivity. We present the first interpretation of the size effect in Gilbert damping in single metallic FM films based on this electron theory of damping. The LLG equation is intrinsically nonlinear, which provides possibilities for rf signal processing. We analyze the frequency doubling effect at small-angle magnetization precession from the first-order expansion of the LLG equation, and demonstrate second harmonic generation from Ni81 Fe19 (Permalloy) thin film under ferromagnetic resonance (FMR), three orders of magnitude more efficient than in ferrites traditionally used in rf devices. Though the efficiency is less than in semiconductor devices, we provide field- and frequency-selectivity in the second harmonic generation. To address further the relationship between the rf excitation and the magnetization dynamics in systems with higher complexity, such as multilayered thin films consisting of nonmagnetic (NM) and FM layers, we employ the powerful time-resolved x-ray magnetic circular dichroism (TR-XMCD) spectroscopy. Soft x-rays have element-specific absorption, leading to layer-specific magnetization detection provided the FM layers have distinctive compositions. We discovered that in contrast to what has been routinely assumed, for layer thicknesses well below the skin depth of the EM wave, a significant phase difference exists between the rf magnetic fields H rf in different FM layers separated by a Cu spacer layer. We propose an analysis based on the distribution of the EM waves in the film stack and substrate to interpret this striking observation. For confined geometries with lateral dimensions in the sub-micron regime, there has been a critical absence of experimental techniques which can image small-amplitude dynamics of these structures. We extend the TR-XMCD technique to scanning transmission x-ray microscopy (STXM), to observe directly the local magnetization dynamics in nanoscale FM thin-film elements, demonstrated at picosecond temporal, 40 nm spatial and < 6° angular resolution. The experimental data are compared with our micromagnetic simulations based on the finite element analysis of the time-dependent LLG equation. We resolve standing spin wave modes in nanoscale Ni81 Fe19 thin film ellipses (1000 nm x 500 nm x 20 nm) with clear phase information to distinguish between degenerate eigenmodes with different symmetries for the first time. With the element-specific imaging capability of soft x-rays, spatial resolution up to 15 nm with improved optics, we see great potential for this technique to investigate functional devices with multiple FM layers, and provide insight into the studies of spin injection, manipulation and detection.
Spin dynamics of qqq wave function on light front in high momentum limit of QCD: Role of qqq force
NASA Astrophysics Data System (ADS)
Mitra, A. N.
2008-04-01
The contribution of a spin-rich qqq force (in conjunction with pairwise qq forces) to the analytical structure of the qqq wave function is worked out in the high momentum regime of QCD where the confining interaction may be ignored, so that the dominant effect is Coulombic. A distinctive feature of this study is that the spin-rich qqq force is generated by a ggg vertex (a genuine part of the QCD Lagrangian) wherein the 3 radiating gluon lines end on as many quark lines, giving rise to a (Mercedes-Benz type) Y-shaped diagram. The dynamics is that of a Salpeter-like equation (3D support for the kernel) formulated covariantly on the light front, a la Markov-Yukawa Transversality Principle (MYTP) which warrants a 2-way interconnection between the 3D and 4D Bethe-Salpeter (BSE) forms for 2 as well as 3 fermion quarks. With these ingredients, the differential equation for the 3D wave function ? receives well-defined contributions from the qq and qqq forces. In particular a negative eigenvalue of the spin operator i?1 ˇ ?2 × ?3 which is an integral part of the qqq force, causes a characteristic singularity in the differential equation, signalling the dynamical effect of a spin-rich qqq force not yet considered in the literature. The potentially crucial role of this interesting effect vis-a-vis the so-called 'spin anomaly' of the proton, is a subject of considerable physical interest.