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Sample records for af spin fluctuations

  1. Longitudinal spin fluctuations in nickel

    SciTech Connect

    Boeni, P. , Villigen ); Martinez, J.L. ); Tranquada, J.M. )

    1989-10-10

    The longitudinal and transverse spin fluctuations in Ni have been measured below {Tc} by means of polarized neutron scattering in the momentum range 0.06 < q < 0.18 {angstrom}{sup -1}. In transverse scans spin wave peaks at E{sub q} = Dq{sup 2} appear as expected from early measurements performed with unpolarized neutrons. The longitudinal magnetic scattering {sub {chi}L}(q, E), on the other hand, is quasielastic without any signature of inelastic peaks near E{sub q}. The q and T dependences of {sub {chi}L}(q, E) resemble the paramagnetic scattering above {Tc}, i.e., the linewidth is roughly proportional to q{sup 2.5} and the integrated intensity I(q) is proportional to (q{sup 2} + {kappa}{sub z}{sup 2}){sup -1}. 8 refs., 3 figs.

  2. Spin-current noise from fluctuation relations

    SciTech Connect

    Lim, Jong Soo; Sánchez, David; López, Rosa

    2013-12-04

    We present fluctuation relations that connect spin-polarized current and noise in mesoscopic conductors. In linear response, these relations are equivalent to the fluctuation-dissipation theorem that relates equilibrium current-current correlations to the linear conductance. More interestingly, in the weakly nonlinear regime of transport, these relations establish a connection between the leading-order rectification spin conductance, the spin noise susceptibility and the third cumulant of spin current fluctuations at equilibrium. Our results are valid even for systems in the presence of magnetic fields and coupled to ferromagnetic electrodes.

  3. Electric probe for spin transition and fluctuation

    NASA Astrophysics Data System (ADS)

    Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'diaye, Alpha T.; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Tserkovnyak, Yaroslov; Qiu, Z. Q.; Saitoh, Eiji

    Spin fluctuation and transition have always been one of central topics of magnetism and condense matter science. To probe them, neutron scatterings have been used as powerful tools. A part of neutrons injected into a sample is scattered by spin fluctuation inside the sample. This process transcribes the spin fluctuation onto scattering intensity, which is commonly represented by dynamical magnetic susceptibility of the sample and is maximized at magnetic phase transitions. Importantly, a neutron carries spin without electric charge, and it thus can bring spin into a sample without being disturbed by electric energy: an advantage of neutrons, although large facilities such as a nuclear reactor is necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop micro probe for spin fluctuation and transition; not only a neutron beam, spin current is also a flux of spin without an electric charge and its transport reflects spin fluctuation in a sample. We demonstrate detection of anti-ferromagnetic transition in ultra-thin CoO films via frequency dependent spin-current transmission measurements.

  4. Coherent spin control by electromagnetic vacuum fluctuations

    SciTech Connect

    Wang Jing; Liu Renbao; Zhu Bangfen; Sham, L. J.; Steel, D. G.

    2011-05-15

    In coherent control, electromagnetic vacuum fluctuations usually cause coherence loss through irreversible spontaneous emission. However, since the dissipation via emission is essentially due to correlation of the fluctuations, when emission ends in a superposition of multiple final states, correlation between different pathways may build up if the 'which way' information is not fully resolved (i.e., the emission spectrum is broader than the transition energy range). Such correlation can be exploited for spin-flip control in a {Lambda}-type three-level system, which manifests itself as an all-optical spin echo in nonlinear optics with two orders of optical fields saved as compared with stimulated Raman processes. This finding represents a class of optical nonlinearity induced by electromagnetic vacuum fluctuations.

  5. Thermal fluctuations in artificial spin ice.

    PubMed

    Kapaklis, Vassilios; Arnalds, Unnar B; Farhan, Alan; Chopdekar, Rajesh V; Balan, Ana; Scholl, Andreas; Heyderman, Laura J; Hjörvarsson, Björgvin

    2014-07-01

    Artificial spin ice systems have been proposed as a playground for the study of monopole-like magnetic excitations, similar to those observed in pyrochlore spin ice materials. Currents of magnetic monopole excitations have been observed, demonstrating the possibility for the realization of magnetic-charge-based circuitry. Artificial spin ice systems that support thermal fluctuations can serve as an ideal setting for observing dynamical effects such as monopole propagation and as a potential medium for magnetricity investigations. Here, we report on the transition from a frozen to a dynamic state in artificial spin ice with a square lattice. Magnetic imaging is used to determine the magnetic state of the islands in thermal equilibrium. The temperature-induced onset of magnetic fluctuations and excitation populations are shown to depend on the lattice spacing and related interaction strength between islands. The excitations are described by Boltzmann distributions with their factors in the frozen state relating to the blocking temperatures of the array. Our results provide insight into the design of thermal artificial spin ice arrays where the magnetic charge density and response to external fields can be studied in thermal equilibrium. PMID:24908258

  6. Love triangles, quantum fluctuations and spin jam

    NASA Astrophysics Data System (ADS)

    Lee, Seung-Hun

    When magnetic moments are interacting with each other in a situation resembling that of complex love triangles, called frustration, a large set of states that are energetically equivalent emerge. This leads to exotic spin states such as spin liquid and spin ice. Recently, we presented evidence for the existence of a topological glassy state, that we call spin jam, induced by quantum fluctuations. The case in point is SrCr9pGa12-9pO19 (SCGO(p)), a highly frustrated magnet, in which the magnetic Cr ions form a quasi-two-dimensional triangular system of bi-pyramids. This system has been an archetype in search for exotic spin states. Understanding the nature of the state has been a great intellectual challenge. Our new experimental data and theoretical spin jam model provide for the first time a coherent understanding of the phenomenon. Furthermore, the findings strongly support the possible existence of purely topological glassy states. Reference:

  7. Spin fluctuations in 3d paramagnetic metals

    NASA Astrophysics Data System (ADS)

    Wysocki, Aleksander; Kutepov, Andrey; Antropov, Vladimir

    Spin fluctuations (SFs) in 3d paramagnetic metals were investigated using the linear response formalism within the time dependent density functional theory. An efficient scheme of frequency integration using the Matsubara technique has been implemented and tested. The SFs spectrum in 3d paramagnets is analyzed in real and reciprocal spaces as a function of frequency and temperature. For all materials the SFs are characterized by the coexistence of low and high energy branches which originate from different regions of the Brillouin zone. The low-energy ones can be measured by neutron scattering experiments while the high-energy SFs appear to be more localized. Further, we studied the nature of square of fluctuating magnetic moment in these materials. This work was supported, in part, by the Critical Materials Institute, an Energy Innovation Hub funded by the U.S. Department of Energy (DOE), and by the Office of Basic Energy Science, Division of Materials Science and Engineering. The research was performed at Ames Laboratory, which is operated for the U.S. DOE by Iowa State University under contract # DE-AC02-07CH11358.

  8. Mixed Valence and Spin Fluctuations in Cerium

    NASA Astrophysics Data System (ADS)

    Andraka, Bohdan

    The pseudobinary alloys Ce(Ni(,x)Co(,1-x))(,2), (Ce(,x)La(,1-x))Ni(,2) and (Ce(,x)Y(,1-x))Ni(,2), where 0 < x < 1, have been studied. The room temperature lattice constant, the magnetic susceptibility in the 6 to 300 K temperature range, the low temperature specific heat in the 0.4 to 25 K range and the electrical resistivity in the 0.4 to 300 K range were measured. Additionally, X -ray absorption around L(,3) edge has been studied using the synchroton radiation. Both, thermodynamic and L(,3) probes yield similar results for the changes of valence of Ce across these systems. We have established that Ce is in the saturated valence state in the Ce(Ni(,x)Co(,1 -x))(,2) for x < 0.25. The valence decreases with x in the 0.25 to 1 concentration range. Similarly, the valence of Ce decreases in the (Ce, Y)Ni(,2) systems upon substitution of Y for Ce. The results obtained for the (Ce(,x)La(,1 -x))Ni(,2) system are interpreted in terms of changes of the Ce('3+) impurity levels. Spin fluctuations due to the 3d electrons play an important role in these systems.

  9. Spin fluctuations of nonequilibrium electrons and excitons in semiconductors

    NASA Astrophysics Data System (ADS)

    Glazov, M. M.

    2016-03-01

    Effects that are related to deviations from thermodynamic equilibrium have a special place in modern physics. Among these, nonequilibrium phenomena in quantum systems attract the highest interest. The experimental technique of spin-noise spectroscopy has became quite widespread, which makes it possible to observe spin fluctuations of charge carriers in semiconductors under both equilibrium and nonequilibrium conditions. This calls for the development of a theory of spin fluctuations of electrons and electron-hole complexes for nonequilibrium conditions. In this paper, we consider a range of physical situations where a deviation from equilibrium becomes pronounced in the spin noise. A general method for the calculation of electron and exciton spin fluctuations in a nonequilibrium state is proposed. A short review of the theoretical and experimental results in this area is given.

  10. Effect of spin fluctuations on quasiparticles in simple metals

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan; Cohen, Marvin; Louie, Steven

    2014-03-01

    We present a first-principles theory for quasiparticle excitations in condensed matter systems that includes their interaction with spin fluctuations. We apply this theory to sodium and lithium. Despite several previous studies, the importance of spin fluctuations in these materials and, in particular, their effect on the occupied band width remains unclear. We show that the coupling to spin fluctuations does not significantly change the occupied band width, but gives an important contribution to the quasiparticle lifetime. To obtain quantitative agreement with experiment for the occupied band width, we find that it is necessary to include vertex corrections beyond the random-phase approximation in the screening by charge fluctuations. S. G. L. acknowledges support by a Simons Foundation Fellowship in Theoretical Physics. This work was supported by NSF Grant No. DMR10-1006184 and by DOE Grant No. DE-AC02-05CH11231.

  11. Thermal spin fluctuations in spinor Bose-Einstein condensates

    NASA Astrophysics Data System (ADS)

    Melé-Messeguer, M.; Juliá-Díaz, B.; Polls, A.; Santos, L.

    2013-03-01

    We study the thermal activation of spin fluctuations in dynamically stable spinor Bose-Einstein condensates. We analyze the specific cases of a nondipolar spin-1 condensate in the state m=0, where thermal activation results from spin-changing collisions, and of a chromium condensate in the maximally stretched state m=-3, where thermal spin fluctuations are due to dipole-induced spin relaxation. In both cases, we show that the low energy associated to the spinor physics may be employed for thermometry purposes down to extremely low temperatures, typically impossible to measure in Bose-Einstein condensates with the usual thermometric techniques. Moreover, the peculiar dependence of the system's entropy with the applied Zeeman energy opens a possible route for adiabatic cooling.

  12. Generalized theory of spin fluctuations in itinerant electron magnets: Crucial role of spin anharmonicity

    NASA Astrophysics Data System (ADS)

    Solontsov, A.

    2015-06-01

    The paper critically overviews the recent developments of the theory of spatially dispersive spin fluctuations (SF) in itinerant electron magnetism with particular emphasis on spin-fluctuation coupling or spin anharmonicity. It is argued that the conventional self-consistent renormalized (SCR) theory of spin fluctuations is usually used aside of the range of its applicability actually defined by the constraint of weak spin anharmonicity based on the random phase approximation (RPA) arguments. An essential step in understanding SF in itinerant magnets beyond RPA-like arguments was made recently within the soft-mode theory of SF accounting for strong spin anharmonicity caused by zero-point SF. In the present paper we generalize it to apply for a wider range of temperatures and regimes of SF and show it to lead to qualitatively new results caused by zero-point effects.

  13. Unconventional superconductivity from local spin fluctuations in the Kondo lattice.

    PubMed

    Bodensiek, Oliver; Žitko, Rok; Vojta, Matthias; Jarrell, Mark; Pruschke, Thomas

    2013-04-01

    The explanation of heavy-fermion superconductivity is a long-standing challenge to theory. It is commonly thought to be connected to nonlocal fluctuations of either spin or charge degrees of freedom and therefore of unconventional type. Here we present results for the Kondo-lattice model, a paradigmatic model to describe heavy-fermion compounds, obtained from dynamical mean-field theory which captures local correlation effects only. Unexpectedly, we find robust s-wave superconductivity in the heavy-fermion state. We argue that this novel type of pairing is tightly connected to the formation of heavy quasiparticle bands and the presence of strong local spin fluctuations. PMID:25167017

  14. Spin fluctuation and Fermi surface instability in ferromagnetic superconductors

    NASA Astrophysics Data System (ADS)

    Aoki, Dai; Gourgout, Adrien; Pourret, Alexandre; Bastien, Gaël; Knebel, Georg; Flouquet, Jacques

    2014-08-01

    We review the ferromagnetic superconductivity observed in the uranium based compounds, namely UGe2, URhGe and UCoGe, where the spin-triplet state is most likely realized. An unusual upper critical field Hc2, which is enhanced under a magnetic field in a certain field direction, is discussed in terms of spin fluctuations and of Fermi surface instabilities. xml:lang="fr"

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

    SciTech Connect

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

    2007-08-24

    We investigate the quantum dynamics of number fluctuations inside an atomic condensate during coherent spin mixing among internal states of the ground state hyperfine manifold, by quantizing the semiclassical nonrigid pendulum model in terms of the conjugate variable pair: the relative phase and the atom number. Our result provides a theoretical basis that resolves the resolution limit, or the effective ''shot-noise'' level, for counting atoms that is needed to clearly detect quantum correlation effects in spin mixing.

  16. Charge and spin fluctuations in the density functional theory

    SciTech Connect

    Gyoerffy, B.L.; Barbieri, A. . H.H. Wills Physics Lab.); Staunton, J.B. . Dept. of Physics); Shelton, W.A.; Stocks, G.M. )

    1990-01-01

    We introduce a conceptual framework which allow us to treat charge and spin fluctuations about the Local density Approximation (LDA) to the Density Functional Theory (DFT). We illustrate the approach by explicit study of the Disordered Local Moment (DLM) state in Fe above the Curie Temperature {Tc} and the Mott insulating state in MnO. 27 refs., 6 figs.

  17. Noncollinear spin-fluctuation theory of transition-metal magnetism: Role of transverse spin fluctuations in Fe

    NASA Astrophysics Data System (ADS)

    Garibay-Alonso, R.; Dorantes-Dávila, J.; Pastor, G. M.

    2015-05-01

    A local electronic theory of transition-metal magnetism at finite temperatures is presented, which takes into account longitudinal and transverse spin fluctuations on the same footing. The magnetic properties are determined in the framework of a rotational-invariant d -band model Hamiltonian by applying a four-field Hubbard-Stratonovich functional-integral method in the static approximation. The role of transverse spin excitations on the temperature-dependent magnetic properties is investigated by performing alloy averages in the single-site virtual crystal approximation. Bulk Fe is considered as the representative example for the applications. Results are given for the average magnetization M , for the spin-excitation energies, and for the transverse and longitudinal contributions to the local magnetic moments μl at atom l . The importance of noncollinear spin excitations is quantified by comparison with the corresponding collinear calculations. An important reduction of about 33% of the calculated Curie temperature TC is obtained, which now amounts to 1250 K and is thus relatively close to the experimental value. The longitudinal (transverse) components of μl are found to decrease (increase) as a function of temperature until the full rotational symmetry is reached at TC. This reflects the increasing importance of the transverse spin fluctuations. The origin of the temperature dependence of M and μl is analyzed in terms of the local spin-fluctuation energies.

  18. Spin Fluctuations from Hertz to Terahertz on a Triangular Lattice.

    PubMed

    Nambu, Yusuke; Gardner, Jason S; MacLaughlin, Douglas E; Stock, Chris; Endo, Hitoshi; Jonas, Seth; Sato, Taku J; Nakatsuji, Satoru; Broholm, Collin

    2015-09-18

    The temporal magnetic correlations of the triangular-lattice antiferromagnet NiGa_{2}S_{4} are examined through 13 decades (10^{-13}-1 sec) using ultrahigh-resolution inelastic neutron scattering, muon spin relaxation, and ac and nonlinear susceptibility measurements. Unlike the short-ranged spatial correlations, the temperature dependence of the temporal correlations show distinct anomalies. The spin fluctuation rate decreases precipitously upon cooling towards T^{*}=8.5 K, but fluctuations on the microsecond time scale then persist in an anomalous dynamical regime for 4 Kfluctuations bear evidence of emergent degrees of freedom within the short-range correlated incommensurate state of NiGa_{2}S_{4}. PMID:26431013

  19. Phase transition in spin systems with various types of fluctuations.

    PubMed

    Miyashita, Seiji

    2010-01-01

    Various types ordering processes in systems with large fluctuation are overviewed. Generally, the so-called order-disorder phase transition takes place in competition between the interaction causing the system be ordered and the entropy causing a random disturbance. Nature of the phase transition strongly depends on the type of fluctuation which is determined by the structure of the order parameter of the system. As to the critical property of phase transitions, the concept "universality of the critical phenomena" is well established. However, we still find variety of features of ordering processes. In this article, we study effects of various mechanisms which bring large fluctuation in the system, e.g., continuous symmetry of the spin in low dimensions, contradictions among interactions (frustration), randomness of the lattice, quantum fluctuations, and a long range interaction in off-lattice systems. PMID:20689226

  20. Zero-Point Spin-Fluctuations of Single Adatoms.

    PubMed

    Ibañez-Azpiroz, Julen; Dos Santos Dias, Manuel; Blügel, Stefan; Lounis, Samir

    2016-07-13

    Stabilizing the magnetic signal of single adatoms is a crucial step toward their successful usage in widespread technological applications such as high-density magnetic data storage devices. The quantum mechanical nature of these tiny objects, however, introduces intrinsic zero-point spin-fluctuations that tend to destabilize the local magnetic moment of interest by dwindling the magnetic anisotropy potential barrier even at absolute zero temperature. Here, we elucidate the origins and quantify the effect of the fundamental ingredients determining the magnitude of the fluctuations, namely, the (i) local magnetic moment, (ii) spin-orbit coupling, and (iii) electron-hole Stoner excitations. Based on a systematic first-principles study of 3d and 4d adatoms, we demonstrate that the transverse contribution of the fluctuations is comparable in size to the magnetic moment itself, leading to a remarkable ≳50% reduction of the magnetic anisotropy energy. Our analysis gives rise to a comprehensible diagram relating the fluctuation magnitude to characteristic features of adatoms, providing practical guidelines for designing magnetically stable nanomagnets with minimal quantum fluctuations. PMID:27248465

  1. Theory of spin and charge fluctuations in the Hubbard model

    SciTech Connect

    Vilk, Y.M.; Chen, L.; Tremblay, A.S. )

    1994-05-01

    A self-consistent theory of both spin and charge fluctuations in the Hubbard model is presented. It is in quantitative agreement with Monte Carlo data at least up to intermediate coupling ([ital U][similar to]8[ital t]). It includes both short-wavelength quantum renormalization effects, and long-wavelength thermal fluctuations, which can destroy long-range order in two dimensions. The last effect leads to a small energy scale, as often observed in high-temperature superconductors. The theory is conserving, satisfies the Pauli principle, and includes three-particle correlations necessary to account for the incipient Mott transition.

  2. Stoichiometry, spin fluctuations, and superconductivity in LaNiPO

    SciTech Connect

    Klimczuk, Tomasz; Mcqueen, Tyrel M; Williams, Anthony J; Huang, Qiang; Cava, Robert J

    2009-01-01

    Superconductivity in LaNiPO is disrupted by small ({approx}5%) amounts of non-stoichiometry on the lanthanum site, even though the electronic contribution to the heat capacity increases with increasing non-stoichiometry. All samples also exhibit specific heat anomalies consistent with the presence of ferromagnetic spin fluctuations (T{sub sf}{approx} 14K). Comparison of layered nickel phosphide and nickel borocarbide superconductors reveals different structure-property correlations in the two families.

  3. Spin jam induced by quantum fluctuations in a frustrated magnet.

    PubMed

    Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P; Huang, Q; Copley, John R D; Lee, Seung-Hun

    2015-09-15

    Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr(3+) (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga(3+) impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p > 0.8) and a cluster spin glass for lower magnetic concentration (p < 0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood. PMID:26324917

  4. Spin jam induced by quantum fluctuations in a frustrated magnet

    PubMed Central

    Yang, Junjie; Samarakoon, Anjana; Dissanayake, Sachith; Ueda, Hiroaki; Klich, Israel; Iida, Kazuki; Pajerowski, Daniel; Butch, Nicholas P.; Huang, Q.; Copley, John R. D.; Lee, Seung-Hun

    2015-01-01

    Since the discovery of spin glasses in dilute magnetic systems, their study has been largely focused on understanding randomness and defects as the driving mechanism. The same paradigm has also been applied to explain glassy states found in dense frustrated systems. Recently, however, it has been theoretically suggested that different mechanisms, such as quantum fluctuations and topological features, may induce glassy states in defect-free spin systems, far from the conventional dilute limit. Here we report experimental evidence for existence of a glassy state, which we call a spin jam, in the vicinity of the clean limit of a frustrated magnet, which is insensitive to a low concentration of defects. We have studied the effect of impurities on SrCr9pGa12-9pO19 [SCGO(p)], a highly frustrated magnet, in which the magnetic Cr3+ (s = 3/2) ions form a quasi-2D triangular system of bipyramids. Our experimental data show that as the nonmagnetic Ga3+ impurity concentration is changed, there are two distinct phases of glassiness: an exotic glassy state, which we call a spin jam, for the high magnetic concentration region (p>0.8) and a cluster spin glass for lower magnetic concentration (p<0.8). This observation indicates that a spin jam is a unique vantage point from which the class of glassy states of dense frustrated magnets can be understood. PMID:26324917

  5. Problem of Phase Transition in Spin-fluctuation Theory

    NASA Astrophysics Data System (ADS)

    Melnikov, N. B.; Paradezhenko, G. V.

    A first-order phase transition is a characteristic feature of the Gaussian approximation in spin-fluctuation theory. We describe a method for taking into account the fourth-order terms of the free energy expansion using partial averaging. In the example of the Ising model, we show that renormalization of the magnetic susceptibility leads to the second-order phase transition, which is experimentally observed in metals. Near the phase transition, we use the parameter substitution method to compute temperature dependencies. We perform a qualitative analysis and explain the mechanism of the renormalization.

  6. Mott physics and spin fluctuations: A functional viewpoint

    NASA Astrophysics Data System (ADS)

    Ayral, Thomas; Parcollet, Olivier

    2016-06-01

    We present a formalism for strongly correlated systems with fermions coupled to bosonic modes. We construct the three-particle irreducible functional K by successive Legendre transformations of the free energy of the system. We derive a closed set of equations for the fermionic and bosonic self-energies for a given K . We then introduce a local approximation for K , which extends the idea of dynamical mean-field theory (DMFT) approaches from two- to three-particle irreducibility. This approximation entails the locality of the three-leg electron-boson vertex Λ (i ω ,i Ω ) , which is self-consistently computed using a quantum impurity model with dynamical charge and spin interactions. This local vertex is used to construct frequency- and momentum-dependent electronic self-energies and polarizations. By construction, the method interpolates between the spin-fluctuation or G W approximations at weak coupling and the atomic limit at strong coupling. We apply it to the Hubbard model on two-dimensional square and triangular lattices. We complement the results of [T. Ayral and O. Parcollet, Phys. Rev. B 92, 115109 (2015), 10.1103/PhysRevB.92.115109] by (i) showing that, at half-filling, as DMFT, the method describes the Fermi-liquid metallic state and the Mott insulator, separated by a first-order interaction-driven Mott transition at low temperatures, (ii) investigating the influence of frustration, and (iii) discussing the influence of the bosonic decoupling channel.

  7. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    Werner, S.A.; Fawcett, E.; Elmiger, M.W.; Shirane, G.

    1992-11-01

    Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.

  8. High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V

    SciTech Connect

    Werner, S.A. . Dept. of Physics); Fawcett, E. . Dept. of Physics); Elmiger, M.W.; Shirane, G. )

    1992-01-01

    Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.

  9. First-principles theory of electron-spin fluctuation coupling and superconducting instabilities in iron selenide

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan H.; Cohen, Marvin L.; Louie, Steven G.

    2015-01-01

    We present first-principles calculations of the coupling of quasiparticles to spin fluctuations in iron selenide and discuss which types of superconducting instabilities this coupling gives rise to. We find that strong antiferromagnetic stripe-phase spin fluctuations lead to large coupling constants for superconducting gaps with s± symmetry, but these coupling constants are significantly reduced by other spin fluctuations with small wave vectors. An accurate description of this competition and an inclusion of band-structure and Stoner parameter renormalization effects lead to a value of the coupling constant for an s±-symmetric gap which can produce a superconducting transition temperature consistent with experimental measurements.

  10. Spin-density correlations in the dynamic spin-fluctuation theory: Comparison with polarized neutron scattering experiments

    NASA Astrophysics Data System (ADS)

    Melnikov, N. B.; Reser, B. I.; Paradezhenko, G. V.

    2016-08-01

    To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.

  11. Hanle effect in (In,Ga)As quantum dots: Role of nuclear spin fluctuations

    NASA Astrophysics Data System (ADS)

    Kuznetsova, M. S.; Flisinski, K.; Gerlovin, I. Ya.; Ignatiev, I. V.; Kavokin, K. V.; Verbin, S. Yu.; Yakovlev, D. R.; Reuter, D.; Wieck, A. D.; Bayer, M.

    2013-06-01

    The role of nuclear spin fluctuations in the dynamic polarization of nuclear spins by electrons is investigated in (In,Ga)As/GaAs quantum dots. The photoluminescence polarization under circularly polarized optical pumping in transverse magnetic fields (Hanle effect) is studied. A weak additional magnetic field parallel to the optical axis is used to control the efficiency of nuclear spin cooling and the sign of nuclear spin temperature. The shape of the Hanle curve is drastically modified when changing this control field, as observed earlier in bulk semiconductors and quantum wells. However, the standard nuclear spin cooling theory, operating with the mean nuclear magnetic field (Overhauser field), fails to describe the experimental Hanle curves in a certain range of control fields. This controversy is resolved by taking into account the nuclear spin fluctuations owed to the finite number of nuclei in the quantum dot. We propose a model considering cooling of the nuclear spin system by electron spins experiencing fast vector precession in the random Overhauser fields of nuclear spin fluctuations. The model allows us to accurately describe the measured Hanle curves and to evaluate the parameters of the electron-nuclear spin system of the studied quantum dots.

  12. Quantized massive collective modes and massive spin fluctuations in high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Kanazawa, I.; Sasaki, T.

    2015-10-01

    We have analyzed angle-resolved photoemission spectra of the single- and double-layered Bi-family high-Tc superconductors by using quantized massive gauge fields, which might contain effects of spin fluctuations, charge fluctuations, and phonons. It is suggested strongly that the quantized massive gauge fields might be mediating Cooper pairing in high-Tc cuprates.

  13. Generalized correlation functions for conductance fluctuations and the mesoscopic spin Hall effect

    NASA Astrophysics Data System (ADS)

    Ramos, J. G. G. S.; Barbosa, A. L. R.; Bazeia, D.; Hussein, M. S.; Lewenkopf, C. H.

    2012-12-01

    We study the spin Hall conductance fluctuations in ballistic mesoscopic systems. We obtain universal expressions for the spin and charge current fluctuations, cast in terms of current-current autocorrelation functions. We show that the latter are conveniently parametrized as deformed Lorentzian shape lines, functions of an external applied magnetic field and the Fermi energy. We find that the charge current fluctuations show quite unique statistical features at the symplectic-unitary crossover regime. Our findings are based on an evaluation of the generalized transmission coefficients correlation functions within the stub model and are amenable to experimental test.

  14. Fluctuation-induced heat release from temperature-quenched nuclear spins near a quantum critical point.

    PubMed

    Kim, Y H; Kaur, N; Atkins, B M; Dalal, N S; Takano, Y

    2009-12-11

    At a quantum critical point (QCP)--a zero-temperature singularity in which a line of continuous phase transition terminates--quantum fluctuations diverge in space and time, leading to exotic phenomena that can be observed at nonzero temperatures. Using a quantum antiferromagnet, we present calorimetric evidence that nuclear spins frozen in a high-temperature nonequilibrium state by temperature quenching are annealed by quantum fluctuations near the QCP. This phenomenon, with readily detectable heat release from the nuclear spins as they are annealed, serves as an excellent marker of a quantum critical region around the QCP and provides a probe of the dynamics of the divergent quantum fluctuations. PMID:20366226

  15. Stripe Antiferromagnetic Spin Fluctuations in SrCo2As2

    SciTech Connect

    Jayasekara, W.; Lee, Y; Pandey, Abishek; Tucker, G. S.; Sapkota, A; Lamsal, Jagat; Calder, Stuart A; Abernathy, Douglas L; Niedziela, Jennifer L; Harmon, B N; Kreyssig, A.; Vaknin, D; Johnston, D C; Goldman, A. I.; McQueeney, R. J.

    2013-01-01

    Inelastic neutron scattering measurements of paramagnetic SrCo2As2 at T = 5 K reveal antifer- romagnetic (AFM) spin fluctuations that are peaked at a wavevector of QAFM = (1/2, 1/2, 1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe2As2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by QAFM. SrCo2As2 has a more complex Fermi surface and band structure calculations indicate a potential instability towards either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt- based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.

  16. Stripe antiferromagnetic spin fluctuations in SrCo2As2.

    PubMed

    Jayasekara, W; Lee, Y; Pandey, Abhishek; Tucker, G S; Sapkota, A; Lamsal, J; Calder, S; Abernathy, D L; Niedziela, J L; Harmon, B N; Kreyssig, A; Vaknin, D; Johnston, D C; Goldman, A I; McQueeney, R J

    2013-10-11

    Inelastic neutron scattering measurements of paramagnetic SrCo2As2 at T=5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wave vector of Q(AFM)=(1/2,1/2,1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe2As2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by Q(AFM). SrCo2As2 has a more complex Fermi surface and band-structure calculations indicate a potential instability toward either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds. PMID:24160618

  17. Contrasting spin dynamics

    SciTech Connect

    Ning, F. L.; Ahilan, K.; Imai, T.; Sefat, A. S.; McGuire, Michael A; Sales, Brian C; Mandrus, David; Cheng, P.; Shen, B.; Wen, H.-H.

    2010-01-01

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

  18. Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals.

    PubMed

    Rice, William D; Liu, Wenyong; Baker, Thomas A; Sinitsyn, Nikolai A; Klimov, Victor I; Crooker, Scott A

    2016-02-01

    Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn(2+), Co(2+) and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large Beff that exist in Mn(2+)-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ∼ 15 -30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn(2+) moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials. PMID:26595331

  19. Zero-Temperature Fluctuations in Short-Range Spin Glasses

    NASA Astrophysics Data System (ADS)

    Arguin, L.-P.; Newman, C. M.; Stein, D. L.; Wehr, J.

    2016-06-01

    We consider the energy difference restricted to a finite volume for certain pairs of incongruent ground states (if they exist) in the d-dimensional Edwards-Anderson Ising spin glass at zero temperature. We prove that the variance of this quantity with respect to the couplings grows proportionally to the volume in any d ≥ 2. An essential aspect of our result is the use of the excitation metastate. As an illustration of potential applications, we use this result to restrict the possible structure of spin glass ground states in two dimensions.

  20. First-principles theory of electron-spin fluctuation coupling and superconducting instabilities in iron selenide

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan H.; Cohen, Marvin L.; Louie, Steven G.

    2015-03-01

    We present first-principles calculations of the coupling of quasiparticles to spin fluctuations in iron selenide and discuss which types of superconducting instabilities this coupling gives rise to. We find that strong antiferromagnetic stripe-phase spin fluctuations lead to large coupling constants for superconducting gaps with s +/- -symmetry, but these coupling constants are significantly reduced by other spin fluctuations with small wave vectors. An accurate description of this competition and an inclusion of band structure and Stoner parameter renormalization effects lead to a value of the coupling constant for an s +/- symmetric gap which can produce a superconducting transition temperature consistent with experimental measurements. This work was supported by NSF Grant No. DMR10-1006184 and by DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by the DOE at NERSC.

  1. Quantum spin fluctuations in quasi-one-dimensional chlorine-bridged platinum complexes

    NASA Astrophysics Data System (ADS)

    Wei, Xing; Donohoe, Robert J.; Wang, Wen Z.; Bishop, Alan R.; Gammel, Jan T.

    1997-12-01

    We report experimental and theoretical studies of spin dynamic process in the quasi-one-dimensional chlorine- bridged platinum complex, [PtII(en)2][PtIV(en)2Cl2](ClO4)4, where en equals ethylenediamine, C2N2H8. The process manifests itself in collapsing of the hyperfine and superhyperfine structures in the electron spin resonance spectrum and non-statistical distribution of spectral weight of the Pt isotopes. More surprisingly, it is activated only at temperatures below 6 K. We interpret the phenomenon in terms of quantum tunneling of the electronic spin in a strong electron-electron and electron-phonon coupling regime. This is modeled using a non-adiabatic many-body approach, in which polarons and solitons represent local spin-Peierls regions in a strongly disproportional charge- density-wave background and display intriguing spin-charge separation in the form of pinned charge and tunneling spin fluctuations.

  2. Superconducting mechanism due to the orbital and spin fluctuations in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Kontani, Hiroshi; Yamakawa, Youichi; Onari, Seiichiro

    The rich variety of the phase diagrams in Fe-based superconductors, such as the nonmagnetic/magnetic nematic phase in FeSe/LaFeAsO, is not able to be explained by the mean-field level approximations. Recently, we explained the phase diagrams of FeSe and LaFeAsO in term of the orbital +spin fluctuation theory, by including the Aslamazov-Larkin vertex correction (AL-VC). The nematic orbital order without magnetization in FeSe is well explained. In the present study, we analyze the superconducting states in FeSe and LaFeAsO, by applying the orbital +spin fluctuation theory. Rich variety of the superconducting gap structures are induced by the strong orbital and spin fluctuations driven by the AL-VC (=orbital-spin interplay). We find that the pairing interaction due to the orbital fluctuations is strongly enlarged by the AL-VC for the anomalous self-energy, so the Migdal theory is seriously violated in the orbital-fluctuation pairing mechanism.

  3. Comparison of the ferromagnetic Blume-Emery-Griffiths model and the AF spin-1 longitudinal Ising model at low temperature

    NASA Astrophysics Data System (ADS)

    Thomaz, M. T.; Corrêa Silva, E. V.

    2016-03-01

    We derive the exact Helmholtz free energy (HFE) of the standard and staggered one-dimensional Blume-Emery-Griffiths (BEG) model in the presence of an external longitudinal magnetic field. We discuss in detail the thermodynamic behavior of the ferromagnetic version of the model, which exhibits magnetic field-dependent plateaux in the z-component of its magnetization at low temperatures. We also study the behavior of its specific heat and entropy, both per site, at finite temperature. The degeneracy of the ground state, at T=0, along the lines that separate distinct phases in the phase diagram of the ferromagnetic BEG model is calculated, extending the study of the phase diagram of the spin-1 antiferromagnetic (AF) Ising model in S.M. de Souza and M.T. Thomaz, J. Magn. and Magn. Mater. 354 (2014) 205 [5]. We explore the implications of the equality of phase diagrams, at T=0, of the ferromagnetic BEG model with K/|J| = - 2 and of the spin-1 AF Ising model for D/|J| > 1/2.

  4. The slave-fermion approach of spin fluctuations in ferromagnet metals

    NASA Astrophysics Data System (ADS)

    Hu, C. D.

    2015-11-01

    In this work we propose a method to treat the spin fluctuations in itinerant ferromagnets. It is able to do calculation with a convergent series. The slave fermion method is applied to separate the charge (denoted by fermions) and spin (denoted by bosons) degrees of freedom. The spin operators are then replaced by the Schwinger boson fields. This way, the interaction term in the model can be reduced to a very simple form and can be teated without difficulty. Finally the equations of motion are derived in order to obtain the forms of Green's functions of fermions and bosons. The result is applied to the calculation of resistivity as a function temperature.

  5. Fluctuations of the heat exchanged between two quantum spin chains

    NASA Astrophysics Data System (ADS)

    Landi, Gabriel T.; Karevski, Dragi

    2016-03-01

    The statistics of the heat exchanged between two quantum XX spin chains prepared at different temperatures is studied within the assumption of weak coupling. This provides simple formulas for the average heat and its corresponding characteristic function, from which the probability distribution may be computed numerically. These formulas are valid for arbitrary sizes and therefore allow us to analyze the role of the thermodynamic limit in this nonequilibrium setting. It is found that all thermodynamic quantities are extremely sensitive to the quantum phase transition of the XX chain.

  6. Influence of spinons fluctuations near the spin liquid Mott transition

    NASA Astrophysics Data System (ADS)

    Lee, Tsung-Han; Florens, Serge; Dobrosavljevic, Vladimir

    We investigate the metal to Mott-insulator transition (MIT) in the Hubbard-Heisenberg model using the slave-rotor technique, which allows to combine for the first time the dynamical mean field theory (DMFT) with the Resonating Valence Bond (RVB) approach. In the spin-liquid phase at large Coulomb repulsion, the system shows a RVB transition from a trivial paramagnetic Mott insulator towards a low temperature insulating state with long lived spinons, as seen by the emergence of a linear specific heat. This quenching of the entropy in the spin liquid phase provides strong modifications in the shape of the standard DMFT phase diagram for the MIT occurring at intermediate values of the Coulomb repulsion. We find that the RVB transition happens concomitantly with the first order MIT lines at low temperature. This implies that the Mott insulator always accommodates a spinon Fermi surface, even in the coexistence regime of the MIT, and that the metallic state always stays a Fermi-liquid as it rejects the presence of free spinons, due to their strong scattering onto the holons.

  7. In-plane resistivity anisotropy in underdoped cuprates due to scattering by charge and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Schütt, Michael; Fernandes, Rafael M.

    2015-03-01

    The existence of strong in-plane electronic anisotropies in underdoped cuprates has been reported by a variety of experimental probes, such as transport measurements, scanning tunneling microscopy, and x-ray and neutron scattering. Understanding the origin of these anisotropies and their interplay is fundamental to elucidate the role played by electronic nematicity in the phase diagram of the cuprates. Here we employ a Boltzmann equation approach to investigate the resistivity anisotropy due to scattering by anisotropic spin and charge fluctuations. We show that while spin fluctuations give rise to larger resistivity along the a direction, charge fluctuations promote larger resistivity along the b direction. Because anisotropic charge and spin fluctuations compete, these behaviors give rise to a particular dependence of the resistivity anisotropy with doping, which is consistent with transport experiments performed in YBa2Cu3O7. We discuss the important role played by the CuO chains in YBCO to select the observed type of nematic domains, and propose transport measurements in strained HgBa2CuO4 and Bi2Sr2CaCu2O8 to shed light on the interplay between anisotropic fluctuations and anisotropic resistivity. MS acknowledges the support from the Humboldt Foundation. RMF is supported by the Department of Energy under Award Number DE-SC0012336.

  8. Quantifying fluctuations of resting state networks using arterial spin labeling perfusion MRI.

    PubMed

    Dai, Weiying; Varma, Gopal; Scheidegger, Rachel; Alsop, David C

    2016-03-01

    Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) has been widely used to investigate spontaneous low-frequency signal fluctuations across brain resting state networks. However, BOLD only provides relative measures of signal fluctuations. Arterial Spin Labeling (ASL) MRI holds great potential for quantitative measurements of resting state network fluctuations. This study systematically quantified signal fluctuations of the large-scale resting state networks using ASL data from 20 healthy volunteers by separating them from global signal fluctuations and fluctuations caused by residual noise. Global ASL signal fluctuation was 7.59% ± 1.47% relative to the ASL baseline perfusion. Fluctuations of seven detected resting state networks vary from 2.96% ± 0.93% to 6.71% ± 2.35%. Fluctuations of networks and residual noise were 6.05% ± 1.18% and 6.78% ± 1.16% using 4-mm resolution ASL data applied with Gaussian smoothing kernel of 6mm. However, network fluctuations were reduced by 7.77% ± 1.56% while residual noise fluctuation was markedly reduced by 39.75% ± 2.90% when smoothing kernel of 12 mm was applied to the ASL data. Therefore, global and network fluctuations are the dominant structured noise sources in ASL data. Quantitative measurements of resting state networks may enable improved noise reduction and provide insights into the function of healthy and diseased brain. PMID:26661226

  9. The role of spin fluctuations in the conductivity of CrO2

    NASA Astrophysics Data System (ADS)

    Heffernan, Kate; Talbayev, D.; Zhang, Xueyu; Gupta, A.

    2015-03-01

    Chromium dioxide is a half-metallic ferromagnet with TC = 390K. Below TC, the conductivity of CrO2 grows by two orders of magnitude and is temperature independent below about 30 K. It is believed that electron scattering by spin fluctuations is responsible for the strong temperature dependence of the conductivity. We performed time-resolved THz spectroscopy (TRTS) and time-resolved magneto-optical Kerr effect (TRMOKE) to study the role of spin fluctuations in electron conduction. A thin film CrO2 sample was excited by an optical pump pulse. The induced conductivity changes were measured by TRTS and the induced spin response by TRMOKE. A fast and a slow component were observed in both responses. The fast component dominates the TRTS response, while the slow dominates the TRMOKE which we attribute to the spin demagnetization in CrO2. Since the slow component contributes only a small fraction of the total conductivity change in TRTS, we conclude that spin fluctuations may not play the dominant role in the pump-induced conductivity change. We also observed that the film transmits less THz light after the pump excitation, which corresponds to it becoming more conductive. We will discuss the relationship of our observations to the electronic and optical properties of CrO2. The work at Tulane was supported by the Louisiana Board of Regents through the Board of Regents Support Fund Contract Number LEQSF(2012-15)-RD-A-23.

  10. Effect of spin fluctuations on quasiparticle excitations: First-principles theory and application to sodium and lithium

    NASA Astrophysics Data System (ADS)

    Lischner, Johannes; Bazhirov, Timur; MacDonald, Allan H.; Cohen, Marvin L.; Louie, Steven G.

    2014-02-01

    We present first-principles calculations for quasiparticle excitations in sodium and lithium, including the effects of charge and spin fluctuations. We employ the Overhauser-Kukkonen form for the electron self-energy arising from spin fluctuations and demonstrate that the coupling of electrons to spin fluctuations gives an important contribution to the quasiparticle lifetime but does not significantly reduce the occupied bandwidth. Including correlation effects beyond the random-phase approximation in the screening from charge fluctuations yields good agreement with experiment.

  11. Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

    NASA Astrophysics Data System (ADS)

    Chekhovich, E. A.; Hopkinson, M.; Skolnick, M. S.; Tartakovskii, A. I.

    2015-02-01

    Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2-4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging.

  12. Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain.

    PubMed

    Chekhovich, E A; Hopkinson, M; Skolnick, M S; Tartakovskii, A I

    2015-01-01

    Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear-nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2-4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

  13. Suppression of nuclear spin bath fluctuations in self-assembled quantum dots induced by inhomogeneous strain

    PubMed Central

    Chekhovich, E.A.; Hopkinson, M.; Skolnick, M.S.; Tartakovskii, A.I.

    2015-01-01

    Interaction with nuclear spins leads to decoherence and information loss in solid-state electron-spin qubits. One particular, ineradicable source of electron decoherence arises from decoherence of the nuclear spin bath, driven by nuclear–nuclear dipolar interactions. Owing to its many-body nature nuclear decoherence is difficult to predict, especially for an important class of strained nanostructures where nuclear quadrupolar effects have a significant but largely unknown impact. Here, we report direct measurement of nuclear spin bath coherence in individual self-assembled InGaAs/GaAs quantum dots: spin-echo coherence times in the range 1.2–4.5 ms are found. Based on these values, we demonstrate that strain-induced quadrupolar interactions make nuclear spin fluctuations much slower compared with lattice-matched GaAs/AlGaAs structures. Our findings demonstrate that quadrupolar effects can potentially be used to engineer optically active III-V semiconductor spin-qubits with a nearly noise-free nuclear spin bath, previously achievable only in nuclear spin-0 semiconductors, where qubit network interconnection and scaling are challenging. PMID:25704639

  14. Theoretical study of correlation between spin fluctuations and Tc in isovalent-doped 1111 iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Arai, Hayato; Usui, Hidetomo; Suzuki, Katsuhiro; Fuseya, Yuki; Kuroki, Kazuhiko

    2015-04-01

    Motivated by recent experiments on isovalent-doped 1111 iron-based superconductors LaFeAs1-xPxO1-yFy and the theoretical study that followed, we investigate, within the five-orbital model, the correlation between spin fluctuations and the superconducting transition temperature, which exhibits a double-dome feature upon varying the Fe-As-Fe bond angle. Around the first dome with higher Tc, the low-energy spin fluctuation and Tc are not tightly correlated because the finite-energy spin fluctuation also contributes to superconductivity. On the other hand, the strength of the low-energy spin fluctuation originating from the dx z /y z orbital is correlated with Tc in the second dome with lower Tc. These calculation results are consistent with a recent NMR study, and hence strongly suggest that the pairing in iron-based superconductors is predominantly caused by multiorbital spin fluctuations.

  15. Role of spin fluctuations in the conductivity of CrO2

    NASA Astrophysics Data System (ADS)

    Heffernan, Kate H.; Yu, Shukai; Deckoff-Jones, Skylar; Zhang, Xueyu; Gupta, Arunava; Talbayev, D.

    2016-04-01

    We present a time-resolved terahertz spectroscopic study of the half-metallic ferromagnet CrO2. The ultrafast conductivity dynamics excited by an optical pump displays very short (several picoseconds) and a very long (several hundred picoseconds) characteristic time scales. We attribute the former to the electron-phonon relaxation and the latter to the spin-lattice relaxation. We use this distinction to quantify the relative contribution of the scattering by spin fluctuations to the resistivity of CrO2: We find that they contribute less than one half of all scattering events below room temperature. This contribution rises to ˜70 % as the temperature approaches TC=390 K. The small effect of spin fluctuations on the resistivity is unexpected in light of the proposed double-exchange nature of the electronic and magnetic properties of CrO2.

  16. Spin Fluctuation in YBaFe4O7+δ with Geometrically Frustrated Pyrochlore Lattice of Fe Spins

    NASA Astrophysics Data System (ADS)

    Kamazawa, Kazuya; Ishikado, Motoyuki; Ohira-Kawamura, Seiko; Kakurai, Kazuhisa; Nakajima, Kenji; Kawakita, Yukinobu; Yamada, Kazuyoshi; Arai, Masatoshi; Sato, Masatoshi

    2015-10-01

    Magnetic excitation spectra were measured by inelastic neutron scattering on a powder sample of YBaFe4O7+δ having a geometrically frustrated pyrochlore lattice of Fe spins. The observed scattering intensity map constructed in the energy ω-wave vector Q space has a streaklike magnetic contribution extending to a rather high-ω region at the Q position of Qp ˜ 1.25 Å-1, where the width κ and position Qp of the streak are found to be insensitive to both the temperature T and ω. These results indicate the existence of the short-time spin correlation of Fe hexagons in the pyrochlore lattice, and can be understood by considering the spin fluctuation arising from the purely frustrating nature of three-dimensional classical insulating systems.

  17. Thermal and quantal isospin and spin fluctuations in heavy ion reactions

    SciTech Connect

    Moretto, L.G.

    1980-01-01

    The isobaric charge distributions are discussed in terms of quantal and classical isospin fluctuations. The roles of mass asymmetry and of the higher giant isovector modes are treated within the framework of a cylinder model that is worked out exactly. Spin fluctuations are considered first in terms of quantal fluctuations in a cylinder model and second in terms of thermal fluctuations in a two-sphere model. The results are applied to the calculation of in- and out-of-plane angular distributions for sequential fission, alpha and gamma decay. Analytical expressions are obtained for the angular distributions. The theoretical predictions are compared with experimental results for sequential fission, alpha, and gamma angular distributions. 23 figures.

  18. Dynamic field-frequency lock for tracking magnetic field fluctuations in electron spin resonance experiments

    NASA Astrophysics Data System (ADS)

    Asfaw, Abraham; Tyryshkin, Alexei; Lyon, Stephen

    Global magnetic field fluctuations present significant challenges to pulsed electron spin resonance experiments on systems with long spin coherence times. We will discuss results from experiments in which we follow instantaneous changes in magnetic field by locking to the free induction decay of a proton NMR signal using a phase-locked loop. We extend conventional field-frequency locking techniques used in NMR to follow slow magnetic field drifts by using a modified Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence in which the phase of the pi-pulses follows the phase of the proton spins at all times. Hence, we retain the ability of the CPMG pulse sequence to refocus local magnetic field inhomogeneities without refocusing global magnetic field fluctuations. In contrast with conventional field-frequency locking techniques, our experiments demonstrate the potential of this method to dynamically track global magnetic field fluctuations on timescales of about 2 seconds and with rates faster than a kHz. This frequency range covers the dominant noise frequencies in our electron spin resonance experiments as previously reported.

  19. Stripe Antiferromagnetic Spin Fluctuations in SrCo2As2

    SciTech Connect

    Jayasekara, Wageesha; Lee, Young-Jin; Pandey, Abhishek; Tucker, Gregory; Sapkota, Aashish; Lamsal, J.; Calder, S.; Abernathy, D. L.; Niedziela, J. L.; Harmon, Bruce; Kreyssig, Andreas; Vaknin, David; Johnston, David; Goldman, A. I.; McQueeney, R. J.

    2013-10-01

    Inelastic neutron scattering measurements of paramagnetic SrCo2As2 at T = 5 K reveal antiferromagnetic (AFM) spin fluctuations that are peaked at a wave vector of QAFM = (1/2, 1/2, 1) and possess a large energy scale. These stripe spin fluctuations are similar to those found in AFe2As2 compounds, where spin-density wave AFM is driven by Fermi surface nesting between electron and hole pockets separated by QAFM. SrCo2As2 has a more complex Fermi surface and band-structure calculations indicate a potential instability toward either a ferromagnetic or stripe AFM ground state. The results suggest that stripe AFM magnetism is a general feature of both iron and cobalt-based arsenides and the search for spin fluctuation-induced unconventional superconductivity should be expanded to include cobalt-based compounds.

  20. Possible enhancements of AFM spin-fluctuations in high-TC cuprates

    NASA Astrophysics Data System (ADS)

    Jarlborg, Thomas

    2009-03-01

    Ab-initio band calculations for high-TC cuprates, together with modelling based of a free electron like band, show a strong interaction between anti-ferromagnetic (AFM) spin waves and periodic lattice distortions as for phonons, even though this type of spin-phonon coupling (SPC) is underestimated in calculations using the local density approximation. The SPC has a direct influence on the properties of the HTC cuprates and it can explain many observations. The strongest effects are seen for modulated waves in the CuO bond direction, and a band gap is formed near the X,Y points, but unusal band dispersion (like ``waterfalls'') might also be induced below the Fermi energy (EF) in the diagonal direction. The band results are used to propose different ways of increasing AFM spin-fluctuations locally, and to have a higher density-of-states (DOS) at EF. Static potential modulations, via periodic distribution of dopants or lattice distortions, can be tuned to increase the DOS. This opens for possibilities to enhance coupling for spin fluctuations (λsf) and superconductivity. The exchange enhancement is in general increased near a surface, which suggests a tendency towards static spin configurations. The sensivity of the band results to corrections of the local density potential are discussed.

  1. Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

    DOE PAGESBeta

    Zhuravlev, I. A.; Antropov, V. P.; Belashchenko, K. D.

    2015-11-16

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1–xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit “hot spots” by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization. These peculiar electronic mechanisms are in stark contrast to the assumptions of the existing models.

  2. Spin-fluctuation mechanism of anomalous temperature dependence of magnetocrystalline anisotropy in itinerant magnets

    SciTech Connect

    Zhuravlev, I. A.; Antropov, V. P.; Belashchenko, K. D.

    2015-11-16

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1–xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit “hot spots” by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization. These peculiar electronic mechanisms are in stark contrast to the assumptions of the existing models.

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

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

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

  4. Spin-orbit fluctuations in frustrated heavy-fermion metal LiV(2)O(4).

    PubMed

    Tomiyasu, K; Iwasa, K; Ueda, H; Niitaka, S; Takagi, H; Ohira-Kawamura, S; Kikuchi, T; Inamura, Y; Nakajima, K; Yamada, K

    2014-12-01

    Spin fluctuations were studied over a wide momentum (ℏQ) and energy (E) space in the frustrated d-electron heavy-fermion metal LiV_{2}O_{4} by time-of-flight inelastic neutron scattering. We observed the overall Q-E evolutions near the characteristic Q=0.6  Å^{-1}  peak and found another weak broad magnetic peak around 2.4  Å^{-1}. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization. PMID:25526141

  5. Structural and magnetic field effects on spin fluctuations in Sr3Ru2O7

    NASA Astrophysics Data System (ADS)

    Mukherjee, Shantanu; Lee, Wei-Cheng

    2016-08-01

    We investigate the evolution of magnetic excitations in Sr3Ru2O7 in the paramagnetic metallic phase using a three-band tight-binding model. The effect of Mn or Ti dopant ions on the Sr3Ru2O7 band structure has been included by taking into account the dopant-induced suppression of the oxygen octahedral rotation in the tight-binding band structure. We find that the low-energy spin fluctuations are dominated by three wave vectors around q ⃗=( (0 ,0 ) ,(π /2 ,π /2 ) ) and (π ,0 ) , which compete with each other. As the octahedral rotation is suppressed with increasing doping, the three wave vectors evolve differently. In particular, the undoped compound has dominant wave vectors at q ⃗=( (0 ,0 ) ,(π /2 ,π /2 ) ) , but doping Sr3Ru2O7 leads to a significant enhancement in the spin susceptibility at the q ⃗=(π ,0 ) wave vector, bringing the system closer to a magnetic instability. All the features calculated from our model are in agreement with neutron scattering experiments. We have also studied the effect of a c -axis Zeeman field on the low-energy spin fluctuations. We find that an increasing magnetic field suppresses the antiferromagnetic (AFM) fluctuations and leads to stronger competition between the AFM and ferromagnetic spin fluctuations. The magnetic field dependence observed in our calculations therefore supports the scenario that the observed nematic phase in the metamagnetic region in Sr3Ru2O7 is intimately related to the presence of a competing ferromagnetic instability.

  6. Effect of spin fluctuations on the resistivity of LaCrGe3

    NASA Astrophysics Data System (ADS)

    Singh, Durgesh; Gangrade, Mohan; Ganesan, V.

    2016-05-01

    Resistivity of LaCrGe3 at low temperatures and high magnetic fields is reported for fields upto 12T. Spin fluctuations play an important role in this compound whose TC is 90K. The normal state above TC is anomalous in the sense that a T1/2 term is to be added to the normal phonon contribution [ρ=ρ0+aT+bT1/2] to get a good fit, whose origin is debatable. Magneto resistance (MR) vs. applied field H in PM region confirms the presence of strong spin fluctuations in this material. Effect of magnetic field on resistivity shows marked deviation below 170K. Suppression of resistivity in field up to 12T near TC is observed. A negative magnetoresistance (MR) is seen and is consistent with the ferromagnetic behavior. The resistivity data fitted below 80K could be fitted with an equation ρ(H,T) = ρ0(H) + B(H)*Tn where n varies between 2.3 - 2.4, closed to n=2, signifying the presence of possible spin fluctuation.

  7. Low-energy paramagnetic spin fluctuations in the weak itinerant ferromagnet MnSi

    NASA Astrophysics Data System (ADS)

    Ishikawa, Y.; Noda, Y.; Fincher, C.; Shirane, G.

    1982-01-01

    Low-energy paramagnetic excitations in the weak itinerant ferromagnet (WIF) MnSi have been studied by neutron scattering. The observed spectrum has a Lorentzian form (ΓΓ2+ω2) and is clearly separated from excitations in the Stoner continuum. The generalized susceptibility, χ(q), has been obtained by integrating the scattering intensity over energy. It is found that χ(q) depends upon the wave vector q as χ(q)-1=κ2(T)+q2 for q<=0.125(2πa) with κ2(T)=κ20(T-Tc). After extrapolating these results to q=0, it is found that χ(q=0) follows the Curie-Weiss law, suggesting that the observed spin fluctuations correspond to the Moriya-Kawabata (MK) spin fluctuations responsible for the Curie-Weiss dependence of the static susceptibility of a WIF. The linewidth Γ is found to be proportional to qχ(q) as predicted by the MK theory, in contrast with the q2χ(q) relation expected in a Heisenberg system. These results provide the first direct experimental evidence for the existence of MK spin fluctuations in a WIF above Tc.

  8. Thermal magnetization fluctuations in CoFe spin-valve devices (invited)

    NASA Astrophysics Data System (ADS)

    Smith, Neil; Synogatch, Valeri; Mauri, Danielle; Katine, J. A.; Cyrille, Marie-Claire

    2002-05-01

    Thermally induced magnetization fluctuations in the Co86Fe14 free (sense) layer of micron-sized, photolithographically defined giant magetoresistive spin-valve devices are measured electrically, by passing a dc current through the devices and measuring the current-dependent part of the voltage noise power spectrum. Using fluctuation-dissipation relations, the effective Gilbert damping parameter α for 1.2, 1.8, and 2.4 nm thick free layers is estimated from either the low-frequency white-noise tail, or independently from the observed thermally excited ferromagnetic resonance peaks in the noise power spectrum, as a function of applied field. The geometry, field, and frequency dependence of the measured noise are found to be reasonably consistent with fluctuation-dissipation predictions based on a quasianalytical eigenmode model to describe the spatial dependence for the magnetization fluctuations. The extracted effective damping constant α≈0.06 found for the 1.2 nm free layer was close to 3× larger than that measured in either the 1.8 or 2.4 films, which has potentially serious implications for the future scaling down of spin-valve read heads.

  9. Quantum Spin Fluctuations in Quasi-One-Dimensional Chlorine-Bridged Platinum Complexes

    SciTech Connect

    Wei, X.; Donohoe, R. J.; Wang, W. Z.; Bishop, A. R.; Gammel, J. T.

    1997-01-01

    We report experimental and theoretical studies of spin dynamic process in the quasi-one-dimensional chlorine-bridged platinum complex, [Pt{sup II}(en){sub 2}][Pt{sup IV}(en){sub 2}Cl{sub 2}](ClO{sub 4}){sub 4}, where en = ethylenediamine, C{sub 2}N{sub 2}H{sub 8}. The process manifests itself in collapsing of the hyperfine and superhyperfine structures in the electron spin resonance (ESR) spectrum and non-statistical distribution of spectral weight of the Pt isotopes. More surprisingly, it is activated only at temperatures below 6 K. We interpret the phenomenon in terms of quantum tunneling of the electronic spin in a strong electron-electron and electron-phonon coupling regime. This is modeled using a non-adiabatic many-body approach, in which polarons and solitons represent local spin-Peierls regions in a strongly disproportional charge-density-wave background and display intriguing spin-charge separation in the form of pinned charge and tunneling spin fluctuations. 24 refs., 5 figs., 1 tab.

  10. Strong interplay between stripe spin fluctuations, nematicity and superconductivity in FeSe.

    PubMed

    Wang, Qisi; Shen, Yao; Pan, Bingying; Hao, Yiqing; Ma, Mingwei; Zhou, Fang; Steffens, P; Schmalzl, K; Forrest, T R; Abdel-Hafiez, M; Chen, Xiaojia; Chareev, D A; Vasiliev, A N; Bourges, P; Sidis, Y; Cao, Huibo; Zhao, Jun

    2016-02-01

    In iron-based superconductors the interactions driving the nematic order (that breaks four-fold rotational symmetry in the iron plane) may also mediate the Cooper pairing. The experimental determination of these interactions, which are believed to depend on the orbital or the spin degrees of freedom, is challenging because nematic order occurs at, or slightly above, the ordering temperature of a stripe magnetic phase. Here, we study FeSe (ref. )-which exhibits a nematic (orthorhombic) phase transition at Ts = 90 K without antiferromagnetic ordering-by neutron scattering, finding substantial stripe spin fluctuations coupled with the nematicity that are enhanced abruptly on cooling through Ts. A sharp spin resonance develops in the superconducting state, whose energy (∼4 meV) is consistent with an electron-boson coupling mode revealed by scanning tunnelling spectroscopy. The magnetic spectral weight in FeSe is found to be comparable to that of the iron arsenides. Our results support recent theoretical proposals that both nematicity and superconductivity are driven by spin fluctuations. PMID:26641018

  11. Transformation between spin-Peierls and incommensurate fluctuating phases of Sc-doped TiOCl

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Wölfel, Alexander; Bykov, Maxim; Schönleber, Andreas; van Smaalen, Sander; Kremer, Reinhard K.; Williamson, Hailey L.

    2014-07-01

    Single crystals of ScxTi1-xOCl(x=0.005) have been grown by the vapor phase transport technique. Specific heat measurements prove the absence of phase transitions for 4-200 K. Instead, an excess entropy is observed over a range of temperatures that encompasses the incommensurate phase transition at 90 K and the spin-Peierls transition at 67 K of pure TiOCl. Temperature-dependent x-ray diffraction on ScxTi1-xOCl gives broadened diffraction maxima at incommensurate positions between Tc1=61.5(3) and ˜90 K, and at commensurate positions below 61.5 K. These results are interpreted as due to the presence of an incommensurate phase without long-range order at intermediate temperatures, and of a highly disturbed commensurate phase without long-range order at low temperatures. The commensurate phase is attributed to a fluctuating spin-Peierls state on an orthorhombic lattice. The monoclinic symmetry and local structure of the fluctuations are equal to the symmetry and structure of the ordered spin-Peierls state of TiOCl. A novel feature of ScxTi1-xOCl(x =0.005) is a transformation from one fluctuating phase (the incommensurate phase at intermediate temperatures) to another fluctuating phase (the spin-Peierls-like phase). This transformation is not a phase transition occurring at a critical temperature, but it proceeds gradually over a temperature range of ˜10 K wide. The destruction of long-range order requires much lower levels of doping in TiOCl than in other low-dimensional electronic crystals, like the canonical spin-Peierls compound CuGeO3. An explanation for the higher sensitivity to doping has not been found, but it is noticed that it may be the result of an increased two-dimensional character of the doped magnetic system. The observed fluctuating states with long correlation lengths are reminiscent of Kosterlitz-Thouless-type phases in two-dimensional systems.

  12. Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by muon spin rotation

    NASA Astrophysics Data System (ADS)

    Martin, N.; Deutsch, M.; Bert, F.; Andreica, D.; Amato, A.; Bonfà, P.; De Renzi, R.; Rößler, U. K.; Bonville, P.; Fomicheva, L. N.; Tsvyashchenko, A. V.; Mirebeau, I.

    2016-05-01

    We have studied by muon spin resonance (μ SR ) the helical ground state and fluctuating chiral phase recently observed in the MnGe chiral magnet. At low temperature, the muon polarization shows double-period oscillations at short-time scales. Their analysis, akin to that recently developed for MnSi [A. Amato et al., Phys. Rev. B 89, 184425 (2014), 10.1103/PhysRevB.89.184425], provides an estimation of the field distribution induced by the Mn helical order at the muon site. The refined muon position agrees nicely with ab initio calculations. With increasing temperature, an inhomogeneous fluctuating chiral phase sets in, characterized by two well-separated frequency ranges which coexist in the sample. Rapid and slow fluctuations, respectively, associated with short-range and long-range ordered helices, coexist in a large temperature range below TN=170 K. We discuss the results with respect to MnSi, taking the short helical period, metastable quenched state, and peculiar band structure of MnGe into account.

  13. Non-equilibrium spin-boson model: counting statistics and the heat exchange fluctuation theorem.

    PubMed

    Nicolin, Lena; Segal, Dvira

    2011-10-28

    We focus on the non-equilibrium two-bath spin-boson model, a toy model for examining quantum thermal transport in many-body open systems. Describing the dynamics within the noninteracting-blip approximation equations, applicable, e.g., in the strong system-bath coupling limit and/or at high temperatures, we derive expressions for the cumulant generating function in both the Markovian and non-Markovian limits by energy-resolving the quantum master equation of the subsystem. For a Markovian bath, we readily demonstrate the validity of a steady-state heat exchange fluctuation theorem. In the non-Markovian limit a "weaker" symmetry relation generally holds, a general outcome of microreversibility. We discuss the reduction of this symmetry relation to the universal steady-state fluctuation theorem. Using the cumulant generating function, an analytic expression for the heat current is obtained. Our results establish the validity of the steady-state heat exchange fluctuation theorem in quantum systems with strong system-bath interactions. From the practical point of view, this study provides tools for exploring transport characteristics of the two-bath spin-boson model, a prototype for a nonlinear thermal conductor. PMID:22047227

  14. Effect of pairing fluctuations on the spin resonance in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Hinojosa, Alberto; Chubukov, Andrey V.; Wölfle, Peter

    2014-09-01

    The spin resonance observed in the inelastic neutron scattering data on Fe-based superconductors has played a prominent role in the quest for determining the symmetry of the order parameter in these compounds. Most theoretical studies of the resonance employ an RPA-type approach in the particle-hole channel and associate the resonance in the spin susceptibility χS(q,ω) at momentum Q =(π,π) with the spin-exciton of an s+- superconductor, pulled below 2Δ by residual attraction associated with the sign change of the gap between Fermi points connected by Q. Here we explore the effect of fluctuations in the particle-particle channel on the spin resonance. Particle-particle and particle-hole channels are coupled in a superconductor and to what extent the spin resonance can be viewed as a particle-hole exciton needs to be addressed. In the case of purely repulsive interactions, we find that the particle-particle channel at total momentum Q (the π channel) contributes little to the resonance. However, if the interband density-density interaction is attractive and the π resonance is possible on its own, along with spin-exciton, we find a much stronger shift of the resonance frequency from the position of the would-be spin-exciton resonance. We also show that the expected double-peak structure in this situation does not appear because of the strong coupling between particle-hole and particle-particle channels, and ImχS(Q ,ω) displays only a single peak.

  15. Spin fluctuations and frustrated magnetism in multiferroic FeVO4

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Ma, L.; Dai, J.; Zhang, Y. P.; He, Zhangzhen; Normand, B.; Yu, Weiqiang

    2014-05-01

    We report 51V nuclear magnetic resonance (NMR) studies on single crystals of the multiferroic material FeVO4. The high-temperature Knight shift shows Curie-Weiss behavior 51K=a/(T+θ), with a large Weiss constant θ ≈ 116 K. However, the 51V spectrum shows no ordering near these temperatures, splitting instead into two peaks below 65 K, which suggests only short-ranged magnetic order on the NMR time scale. Two magnetic transitions are identified from peaks in the spin-lattice relaxation rate 1/51T1 at temperatures TN1≈ 19 K and TN2≈ 13 K, which are lower than the estimates obtained from polycrystalline samples. In the low-temperature incommensurate spiral state, the maximum ordered moment is estimated as 1.95μB/Fe, or 1/3 of the local moment. Strong low-energy spin fluctuations are also indicated by the unconventional power-law temperature dependence 1/51T1∝T2. The large Weiss constant, short-range magnetic correlations far above TN1, small ordered moment, significant low-energy spin fluctuations, and incommensurate ordered phases all provide explicit evidence for strong magnetic frustration in FeVO4.

  16. Spin fluctuations of BaFe2(As,P)2 studied by neutron scattering

    NASA Astrophysics Data System (ADS)

    Lee, Chul-Ho; Steffens, P.; Qureshi, N.; Kihou, K.; Nakajima, M.; Iyo, A.; Eisaki, H.; Braden, M.

    2013-03-01

    Superconductivity can be induced in parent compounds of iron-based superconductors by several methods: carrier doping, external pressure and chemical pressure. To understand their superconducting mechanism, clarifying what is a common property for achieving high-Tc superconductivity is crucial. To date, studies on spin fluctuations have been mainly performed on carrier doped samples. On the other hand, there are only a few studies on chemical pressurized samples examined by powder samples. In this work, thus, we studied spin fluctuations of P doped BaFe2(As,P)2>(Tc = 29.5K) using single crystal samples. Inelastic neutron scattering measurements were conducted using triple axis spectrometer IN8 of ILL. As results, well-defined commensurate peaks have been observed at (0.5,0.5, L), which is consistent with the nesting vector of the Fermi surface. Energy spectrums at T = Tc show L dependence, suggesting a three dimensional character remains even in superconducting BaFe2(As,P)2. Clear spin gap has been observed below Tc, whose gap structure depends on L. Details will be discussed at the conference.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  18. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    SciTech Connect

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

    2015-09-22

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

  19. Competing magnetic fluctuations in iron pnictide superconductors: Role of ferromagnetic spin correlations revealed by NMR

    DOE PAGESBeta

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

    2015-09-22

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

  20. Magnetic ordering in tetragonal FeS: Evidence for strong itinerant spin fluctuations

    SciTech Connect

    Kwon, K.D.; Refson, K.; Bone, S.; Qiao, R.; Yang, W.; Liu, Z.; Sposito, G.

    2010-11-01

    Mackinawite is a naturally occurring layer-type FeS mineral important in biogeochemical cycles and, more recently, in the development of microbial fuel cells. Conflicting results have been published as to the magnetic properties of this mineral, with Moessbauer spectroscopy indicating no magnetic ordering down to 4.2 K but density functional theory (DFT) predicting an antiferromagnetic ground state, similar to the Fe-based high-temperature superconductors with which it is isostructural and for which it is known that magnetism is suppressed by strong itinerant spin fluctuations. We investigated this latter possibility for mackinawite using photoemission spectroscopy, near-edge x-ray absorption fine structure spectroscopy, and DFT computations. Our Fe 3{sub s} core-level photoemission spectrum of mackinawite showed a clear exchange-energy splitting (2.9 eV) consistent with a 1 {micro}{sub B} magnetic moment on the Fe ions, while the Fe L-edge x-ray absorption spectrum indicated rather delocalized Fe 3{sub d} electrons in mackinawite similar to those in Fe metal. Our DFT computations demonstrated that the ground state of mackinawite is single-stripe antiferromagnetic, with an Fe magnetic moment (2.7 {micro}{sub B}) that is significantly larger than the experimental estimate and has a strong dependence on the S height and lattice parameters. All of these trends signal the existence of strong itinerant spin fluctuations. If spin fluctuations prove to be mediators of electron pairing, we conjecture that mackinawite may be one of the simplest Fe-based superconductors.

  1. Free-Spinning-Tunnel Investigation of a 1/24-Scale Model of the Grumman AF-2S, -2W Airplane

    NASA Technical Reports Server (NTRS)

    Klinar, Walter J.; Wilson, Jack H.

    1950-01-01

    An investigation of the spin and recovery characteristics of a 1/24-scale model of the Grumman AF-2S, -2W airplane was conducted in the Langley 20-foot free-spinning tunnel. The effects of controls on the erect and inverted spin and recovery characteristics for a range of possible loadings of the.airplane were determined. The effect of a revised-tail installation (small dual fins added to the stabilizer of the original tail and the vertical-tail height of the original tail increased) and the effect of various ventral-fin and antispin-fillet installations were determined. The investigation also included spin-recovery parachute tests.

  2. 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.

  3. Simulation of Statistical Fluctuations in the Spin Precession Measurements at RHIC

    SciTech Connect

    Poblaguev, A. A.

    2014-02-25

    Measurements of the driven spin coherent precession Sx(t)=Sx(0) - Sx(1) sin(ωt+φ0) were initiated in RHIC Run13. The expected value of the precession amplitude Sx(1) ~ 2 x 10-4 is about the statistical error in a single measurement and data fit gives a biased estimate of the Sx(1). For a proper statistical interpretation of the results of the several measurements, statistical fluctuations were studied using Monte-Carlo simulation. Preliminary results of the spin precession measurements in RHIC Run13 are presented.

  4. Spin fluctuations in La2-xSrxCuO4: NMR versus inelastic neutron scattering

    NASA Astrophysics Data System (ADS)

    Barzykin, V.; Pines, D.; Thelen, D.

    1994-12-01

    We use a one-component description to analyze the current experimental situation for the low-frequency magnetic properties of La1.85Sr0.15CuO4 as determined by NMR and neutron-scattering experiments. We show that the measured 17O spin-lattice relaxation rate is in sharp conflict with the incommensurate-magnetic-structure interpretation of neutron-scattering experiments, but is quantitatively explained if the local-spin-fluctuation spectrum (measured by NMR) possesses a commensurate peak. We conclude that the formation of domains, as suggested by Slichter and Phillips, represents the best (and, quite possibly, only) way of reconciling NMR and neutron-scattering experiments on La1.85Sr0.15CuO4.

  5. Spin Susceptibility and Effects of Inhomogeneous Strong Pairing Fluctuations in a Trapped Ultracold Fermi Gas

    NASA Astrophysics Data System (ADS)

    Tajima, H.; Hanai, R.; Ohashi, Y.

    2016-05-01

    We theoretically investigate magnetic properties of a unitary Fermi gas in a harmonic trap. Including strong pairing fluctuations within the framework of an extended T-matrix approximation, as well as effects of a trap potential within the local density approximation, we calculate the local spin susceptibility χ (T,r) above the superfluid phase transition temperature T_c. We show that the formation of preformed singlet Cooper pairs anomalously suppresses χ (T,r) in the trap center near T_c. We also point out that, in the unitarity limit, the spin-gap temperature in a uniform Fermi gas can be evaluated from the observation of the spatial variation of χ (T,r). Since a real ultracold Fermi gas is always in a trap potential, our results would be useful for the study of how this spatial inhomogeneity affects thermodynamic properties of an ultracold Fermi gas in the BCS-BEC crossover region.

  6. Link between spin fluctuations and Cooper pairing in copper oxide superconductors

    NASA Astrophysics Data System (ADS)

    Jin, Kui

    2012-02-01

    Although it is generally accepted that superconductivity is unconventional in the high-Tc cuprates, the relative importance of phenomena such as spin and charge (strip) order, superconductivity fluctuations, proximity to Mott insulator, a pseudogap phase and quantum criticality are still a matter of debate. In electron-doped cuprates, the absence of ``anomalousphase in the underdoped region of the phase diagram and weaker electron correlations suggest that Mott physics and other unidentified competing orders are less relevant and that antiferromagnetic (AFM) spin fluctuations are the dominant feature. In this talk, I will report results of low temperature magnetotransport experiments in optimal to overdoped (non-superconducting) thin films of the electron-doped cuprate La2-xCexCuO4 (LCCO). We find that a linear-in-T scattering rate is correlated with the superconductivity (Tc). Our results show that an envelope of such scattering surrounds the superconducting phase, surviving to 20 mK (the limit of our experiments) when superconductivity is suppressed by magnetic fields [1]. Comparison with similar behavior found in organic superconductors [2] strongly suggests that the linear-in-T resistivity in the electron-doped cuprates is caused by spin-fluctuation scattering. Because linear-in-T scattering has also been linked to T% c in some hole-doped cuprates [2], our results suggest a fundamental connection between AFM spin fluctuations and the pairing mechanism of high temperature superconductivity in all cuprates. In addition, I will discuss how quantum criticality plays a significant role in shaping the anomalous properties of the electron-doped cuprate phase diagram. We identify quantum critical scaling in LCCO with a line of quantum critical points that surrounds the superconducting phase as a function of magnetic field and charge doping [3]. [4pt] [1] K. Jin, N.P. Butch, K. Kirshenbaum, J. Paglione, and R.L. Greene, Nature 476, 73 (2011).[0pt] [2] L. Taillefer, Annu

  7. Spin-Fluctuation-Driven Nematic Charge-Density Wave in Cuprate Superconductors: Impact of Aslamazov-Larkin Vertex Corrections.

    PubMed

    Yamakawa, Youichi; Kontani, Hiroshi

    2015-06-26

    We present a microscopic derivation of the nematic charge-density wave (CDW) formation in cuprate superconductors based on the three-orbital d-p Hubbard model by introducing the vertex correction (VC) into the charge susceptibility. The CDW instability at q=(Δ(FS),0), (0,Δ(FS)) appears when the spin fluctuations are strong, due to the strong charge-spin interference represented by the VC. Here, Δ(FS) is the wave number between the neighboring hot spots. The obtained spin-fluctuation-driven CDW is expressed as the "intra-unit-cell orbital order" accompanied by the charge transfer between the neighboring atomic orbitals, which is actually observed by the scanning tunneling microscope measurements. We predict that the cuprate CDW and the nematic orbital order in Fe-based superconductors are closely related spin-fluctuation-driven phenomena. PMID:26197139

  8. Ti3CrCu4: A possible 2-D ferromagnetic spin fluctuating system

    NASA Astrophysics Data System (ADS)

    Dhar, S. K.; Provino, A.; Manfrinetti, P.; Kulkarni, R.; Goyal, Neeraj; Paudyal, D.

    2016-05-01

    Ti3CrCu4 is a new ternary compound which crystallizes in the tetragonal Ti3Pd5 structure type. The Cr atoms form square nets in the a-b plane (a = 3.124 Å) which are separated by an unusually large distance c = 11.228 Å along the tetragonal axis, thus forming a -2-D Cr-sublattice. The paramagnetic susceptibility is characterized by a low effective moment, μeff = 1.1 μB, a low paramagnetic Curie temperature θP (below 7 K) and a temperature independent χ0 = 6.7 x 10-4 emu/mol. The magnetization at 1.8 K increases rapidly with field nearly saturating to 0.2 μB/f.u. The zero field heat capacity C/T shows an upturn below 7 K (˜190 mJ/mol K2 at ˜0.1K) which is suppressed in applied magnetic fields and interpreted as suggesting the presence of spin fluctuations. The resistivity at low temperatures shows non-Fermi liquid behavior. Overall, the experimental data thus reveal an unusual magnetic state in Ti3CrCu4, which likely has its origin in the layered nature of the Cr sub-lattice and ferromagnetic spin fluctuations. Density functional theoretical calculations reveal a sharp Cr density of states peak just above the Fermi level, indicating the propensity of Ti3CrCu4 to become magnetic.

  9. Low-energy spin fluctuations in the metallic spinel compound LiV2O4

    NASA Astrophysics Data System (ADS)

    Yushankhai, V. Yu.; Thalmeier, P.; Takimoto, T.

    2009-08-01

    In the family of transition metal oxides the spinel compound LiV2O4 is a rare metallic system showing heavy fermion behavior. In particular, an anomalously large specific heat coefficient γ = C/T and strongly enhanced magnetic susceptibility χs were detected in the low temperature limit, T<30 K. Recently we have proposed a model which allowed us to relate such an anomalous behavior of LiV2O4 to the proximity of the underlying 3d-electron system to a magnetic instability at T→0. The emergence of a rather peculiar paramagnetic ground state with largely degenerate lowenergy "critical" antiferromagnetic fluctuations in LiV2O4 is the combined effect of strong electron correlations and the geometrical frustration of V-ion pyrochlore lattice forming the metallic system in this compound. A self-consistent renormalization theory was developed to describe effects of strong coupling between spin fluctuation modes and their evolution with varying temperature and external pressure. The theory was shown to provide a firm basis for understanding many peculiar properties of spin dynamics obtained in the inelastic neutron scattering and NMR measurements on LiV2O4.

  10. NMR Study of Superconductivity and Spin Fluctuations in Intercalated Iron Selenides AyFe2-xSe2

    NASA Astrophysics Data System (ADS)

    Yu, Weiqiang

    2012-02-01

    The role of spin fluctuations in superconductivity is an essential topic in both cuprate and Fe-based superconductors. NMR works in several Fe-based superconductors proposed that the low-energy antiferromagnetic spin fluctuations (AFSF) is a possible pairing glue for superconductivity. However, studies on other systems such as KFe2As2 and Li1-xFeAs does not support a strong correlation between low-energy spin fluctuations and superconductivity. In the newly discovered AyFe2-xSe2 superconductors with Tc˜ 32 K, our NMR study identifies unambiguously a paramagnetic superconducting phase, which is phase separated from the block antiferromagnetic state. The low-energy AFSF is not seen at all, even though the Tc is high. The AyFe2-xSe2 are singlet superconductors evidenced from the NMR Knight shift K; However, the absence of the coherence peak in the spin-lattice relaxation rate 1/T1 suggests an unconventional behavior of superconductivity. In fact, we found that both the K and the 1/T1T increase dramatically with temperature and follow a a+bT^2 form from Tc up to 300 K. Such behavior is strong evidence for spin fluctuations with a high-energy, local nature in 3D systems, and inconsistent with a band-gap effect. Furthermore, K and 1/T1T saturate above 400 K, indicating an energy scale of 35 meV, which is distinct from the low-energy spin fluctuations. The above temperature enhanced spin fluctuations seem to be universal in Fe-based superconductors. [4pt] References: W. Yu et al., Phys. Rev. Lett. 106, 197001 (2011); Long Ma et al., Phys. Rev. B 83, 174510 (2011); L. Ma et al., arXiv:1103.4960.

  11. Theory of spin-fluctuation induced superconductivity in iron-based superconductors

    SciTech Connect

    Zhang, Junhua

    2011-01-01

    In this dissertation we focus on the investigation of the pairing mechanism in the recently discovered high-temperature superconductor, iron pnictides. Due to the proximity to magnetic instability of the system, we considered short-range spin fluctuations as the major mediating source to induce superconductivity. Our calculation supports the magnetic fluctuations as a strong candidate that drives Cooper-pair formation in this material. We find the corresponding order parameter to be of the so-called ss-wave type and show its evolution with temperature as well as the capability of supporting high transition temperature up to several tens of Kelvin. On the other hand, our itinerant model calculation shows pronounced spin correlation at the observed antiferromagnetic ordering wave vector, indicating the underlying electronic structure in favor of antiferromagnetic state. Therefore, the electronic degrees of freedom could participate both in the magnetic and in the superconducting properties. Our work shows that the interplay between magnetism and superconductivity plays an important role to the understanding of the rich physics in this material. The magnetic-excitation spectrum carries important information on the nature of magnetism and the characteristics of superconductivity. We analyze the spin excitation spectrum in the normal and superconducting states of iron pnictides in the magnetic scenario. As a consequence of the sign-reversed gap structure obtained in the above, a spin resonance mode appears below the superconducting transition temperature. The calculated resonance energy, scaled with the gap magnitude and the magnetic correlation length, agrees well with the inelastic neutron scattering (INS) measurements. More interestingly, we find a common feature of those short-range spin fluctuations that are capable of inducing a fully gapped ss state is the momentum anisotropy with elongated span along the direction transverse to the antiferromagnetic momentum

  12. 21 cm signal from cosmic dawn: imprints of spin temperature fluctuations and peculiar velocities

    NASA Astrophysics Data System (ADS)

    Ghara, Raghunath; Choudhury, T. Roy; Datta, Kanan K.

    2015-02-01

    The 21 cm brightness temperature δTb fluctuations from reionization promise to provide information on the physical processes during that epoch. We present a formalism for generating the δTb distribution using dark matter simulations and a 1D radiative transfer code. Our analysis is able to account for the spin temperature TS fluctuations arising from inhomogeneous X-ray heating and Lyα coupling during cosmic dawn. The δTb power spectrum amplitude at large scales (k ˜ 0.1 Mpc-1) is maximum when ˜10 per cent of the gas (by volume) is heated above the cosmic microwave background temperature. The power spectrum shows a `bump'-like feature during cosmic dawn and its location measures the typical sizes of heated regions. We find that the effect of peculiar velocities on the power spectrum is negligible at large scales for most part of the reionization history. During early stages (when the volume averaged ionization fraction ≲ 0.2) this is because the signal is dominated by fluctuations in TS. For reionization models that are solely driven by stars within high-mass (≳ 109 M⊙) haloes, the peculiar velocity effects are prominent only at smaller scales (k ≳ 0.4 Mpc-1) where patchiness in the neutral hydrogen density dominates the signal. The conclusions are unaffected by changes in the amplitude or steepness in the X-ray spectra of the sources.

  13. Performance comparison of dynamical decoupling sequences for a qubit in a rapidly fluctuating spin bath

    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 μs. 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.

  14. Quantum critical point and spin fluctuations in lower-mantle ferropericlase

    PubMed Central

    Lyubutin, Igor S.; Struzhkin, Viktor V.; Mironovich, A. A.; Gavriliuk, Alexander G.; Naumov, Pavel G.; Lin, Jung-Fu; Ovchinnikov, Sergey G.; Sinogeikin, Stanislav; Chow, Paul; Xiao, Yuming; Hemley, Russell J.

    2013-01-01

    Ferropericlase [(Mg,Fe)O] is one of the most abundant minerals of the earth’s lower mantle. The high-spin (HS) to low-spin (LS) transition in the Fe2+ ions may dramatically alter the physical and chemical properties of (Mg,Fe)O in the deep mantle. To understand the effects of compression on the ground electronic state of iron, electronic and magnetic states of Fe2+ in (Mg0.75Fe0.25)O have been investigated using transmission and synchrotron Mössbauer spectroscopy at high pressures and low temperatures (down to 5 K). Our results show that the ground electronic state of Fe2+ at the critical pressure Pc of the spin transition close to T = 0 is governed by a quantum critical point (T = 0, P = Pc) at which the energy required for the fluctuation between HS and LS states is zero. Analysis of the data gives Pc = 55 GPa. Thermal excitation within the HS or LS states (T > 0 K) is expected to strongly influence the magnetic as well as physical properties of ferropericlase. Multielectron theoretical calculations show that the existence of the quantum critical point at temperatures approaching zero affects not only physical properties of ferropericlase at low temperatures but also its properties at P-T of the earth’s lower mantle. PMID:23589892

  15. Modeling Spin Fluctuations and Magnetic Excitations from Time-Dependent Density Functional Theory

    NASA Astrophysics Data System (ADS)

    Gorni, Tommaso; Timrov, Iurii; Dal Corso, Andrea; Baroni, Stefano

    Harnessing spin fluctuations and magnetic excitations in materials is key in many fields of technology, spanning from memory devices to information transfer and processing, to name but a few. A proper understanding of the interplay between collective and single-particle spin excitations is still lacking, and it is expected that first-principle simulations based on TDDFT may shed light on this interplay, as well as on the role of important effects such as relativistic ones and related magnetic anisotropies. All the numerical approaches proposed so far to tackle this problem are based on the computationally demanding solution of the Sternheimer equations for the response orbitals or the even more demanding solution of coupled Dyson equations for the spin and charge susceptibilities. The Liouville-Lanczos approach to TDDFT has already proven to be a valuable alternative, the most striking of its features being the avoidance of sums over unoccupied single-particle states and the frequency-independence of the main numerical bottleneck. In this work we present an extension of this methodology to magnetic systems and its implementation in the Quantum ESPRESSO distribution, together with a few preliminary results on the magnon dispersions in bulk Fe.

  16. Strong coupling critique of spin fluctuation driven charge order in underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Mishra, Vivek; Norman, M. R.

    2015-08-01

    Charge order has emerged as a generic feature of doped cuprates, leading to important questions about its origin and its relation to superconductivity. Recent experiments on two classes of hole doped cuprates indicate a novel d -wave symmetry for the order. These were motivated by earlier spin fluctuation theoretical studies based on an expansion about hot spots in the Brillouin zone that indicated such an order would be competitive with d -wave superconductivity. Here, we reexamine this problem by solving strong coupling equations in the full Brillouin zone for experimentally relevant parameters. We find that bond-oriented order, as seen experimentally, is strongly suppressed. We also include coupling to B1 g phonons and do not see any qualitative change. Our results argue against an itinerant model for the charge order, implying instead that such order is likely due to Coulombic phase separation of the doped holes.

  17. Spectroscopic Evidence for Strong Quantum Spin Fluctuations with Itinerant Character in YFe2Ge2

    DOE PAGESBeta

    Sirica, N.; Bondino, F.; Nappini, S.; Piz, I.; Poudel, L.; Christianson, Andrew D.; Mandrus, D.; Singh, David J; Mannella, Norman

    2015-03-04

    We report x-ray absorption and photoemission spectroscopy of the electronic structure in the normal state of metallic YFe2Ge2. The data reveal evidence for large fluctuating spin moments on the Fe sites, as indicated by exchange multiplets appearing in the Fe 3s core-level photoemission spectra, even though the compound does not show magnetic order. The magnitude of the multiplet splitting is comparable to that observed in the normal state of the Fe-pnictide superconductors. This shows a connection between YFe2Ge2 and the Fe-based superconductors even though it contains neither pnictogens nor chalcogens. Finally, the implication is that the chemical range of compoundsmore » showing at least one of the characteristic magnetic signatures of the Fe-based superconductors is broader than previously thought.« less

  18. Pressure dependence of critical temperature of bulk FeSe from spin fluctuation theory

    NASA Astrophysics Data System (ADS)

    Hirschfeld, Peter; Kreisel, Andreas; Wang, Yan; Tomic, Milan; Jeschke, Harald; Jacko, Anthony; Valenti, Roser; Maier, Thomas; Scalapino, Douglas

    2013-03-01

    The critical temperature of the 8K superconductor FeSe is extremely sensitive to pressure, rising to a maximum of 40K at about 10GPa. We test the ability of the current generation of fluctuation exchange pairing theories to account for this effect, by downfolding the density functional theory electronic structure for each pressure to a tight binding model. The Fermi surface found in such a procedure is then used with fixed Hubbard parameters to determine the pairing strength using the random phase approximation for the spin singlet pairing vertex. We find that the evolution of the Fermi surface captured by such an approach is alone not sufficient to explain the observed pressure dependence, and discuss alternative approaches. PJH, YW, AK were supported by DOE DE-FG02-05ER46236, the financial support of MT, HJ, and RV from the DFG Schwerpunktprogramm 1458 is kindly acknowledged.

  19. Spin fluctuations above 100 K in stoichiometric LiCoO2

    NASA Astrophysics Data System (ADS)

    Mukai, K.; Aoki, Y.; Andreica, D.; Amato, A.; Watanabe, I.; Giblin, S. R.; Sugiyama, J.

    2014-12-01

    Although stoichiometric lithium cobalt dioxide LiCoO2 (ST-LCO) is the most common positive electrode material for Li-ion batteries, the magnetic nature of ST-LCO is still not fully understood. Therefore, we measured susceptibility (χ), electron paramagnetic resonance (EPR), and μSR for ST-LCO, particularly above 100 K. The temperature dependence of χ shows a Pauli paramagnetic behavior, supporting the previous conclusion that Co3+ ions are in a low-spin state with S = 0 (t62g). However, the EPR and μSR measurements reveal a "dynamical" magnetic phase in ST-LCO above 100 K. Because the volume fraction of this magnetic phase reaches about 50% at 300 K, the appearance of the magnetic phase is not caused by impurities and/or muonium formation but is an intrinsic characteristic of ST-LCO. By considering the time windows of the three measurement techniques used in this study, we conclude that the origin of the dynamical magnetism is most likely spin fluctuations of the Co ions.

  20. Enhanced spin fluctuations and s +/- pairing by diagonal electron hopping in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Kuroki, Kazuhiko

    2015-03-01

    In the itinerant spin picture of the iron-based superconductors, the nesting between electron and hole Fermi surfaces is usually considered to be the origin of the spin fluctuation and thus the pairing glue. However, there have appeared some experimental observations suggesting absence of Fermi surface nesting. For instance, in the 1111 materials Ln FeAsO1-xHx (Ln =La,Sm, etc.), electron doping rate x reaches up to 50%, which in a rigid band picture would wipe out the hole Fermi surfaces. Still, superconductivity not only survives, but is even enhanced in the largely doped regime, in contradiction to the expectation from the bad nesting. Another example is KxFe2-ySe2, where the ARPES experiments show the absence of hole Fermi surfaces. In the present talk, we first focus on Ln FeAsO1-xHx, where the band structure is actually not rigid against doping, and the hole Fermi surface originating from the dxy orbital remains nearly unchanged. The origin of this can be traced back to real space, where the nearest neighbor hopping t1 within the dxy orbital is found to be strongly suppressed with doping. Although the nesting itself is degraded, the spin fluctuation in the largely electron doped regime is enhanced due to t2 >t1 , where t2 is the 2nd neighbor diagonal hopping. This re-enhances s +/- pairing superconductivity, and explains the double dome x-Tc phase diagram of LaFeAsO1-xHx. From this viewpoint, it is also interesting to look into the relation between t1 and t2 in other materials. For instance, our first principles estimation for KFe2Se2givest1 = - 0 . 008 eV and t2 = 0 . 056 eV, and from this strong reduction of t1, both electron and hole Fermi surfaces are expected to be present around the Γ point, in contradiction to previous experimental observations. Results of a recent ARPES experiment will be discussed from this viewpoint.

  1. Identical spin fluctuations in Cu- and Co-doped BaFe2As2 independent of electron doping

    NASA Astrophysics Data System (ADS)

    Grafe, H.-J.; Gräfe, U.; Dioguardi, A. P.; Curro, N. J.; Aswartham, S.; Wurmehl, S.; Büchner, B.

    2014-09-01

    We present As75 nuclear magnetic resonance measurements on single crystals of BaFe2As2, BaFe1.8Co0.2As2, and BaFe1.82Cu0.18As2. While only Co doping induces bulk superconductivity on a broad doping range, the spin fluctuations probed by the nuclear spin-lattice relaxation rate (T1T )-1 are identical for both dopings down to Tc. Below this temperature, (T1T)-1 of the Cu-doped sample continues to rise, proving that (a) there is a quantum critical point below the superconducting dome, and (b) adding electrons does not affect the spin fluctuations. Consequently, we analyze the Knight shift data in terms of a two-component scenario, with one hyperfine coupling to an itinerant degree of freedom and the other to Fe moments.

  2. Neutron spin-echo studies on dynamic and static fluctuations in two types of poly(vinyl alcohol) gels

    NASA Astrophysics Data System (ADS)

    Kanaya, T.; Takahashi, N.; Nishida, K.; Seto, H.; Nagao, M.; Takeda, T.

    2005-01-01

    We report neutron spin-echo measurements on two types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40 , and the second is PVA gel in an aqueous borax solution. The observed normalized intermediate scattering functions I(Q,t)/I(Q,0) are very different between them. The former I(Q,t)/I(Q,0) shows a nondecaying component in addition to a fast decay, but the latter does not have the nondecaying one. This clearly indicates that the fluctuations in the former PVA gel consist of static and dynamic fluctuations whereas the latter PVA gel does include only the dynamic fluctuations. The dynamic fluctuations of the former and latter gels have been analyzed in terms of a restricted motion in the network and Zimm motion, respectively, and the origins of these motions will be discussed.

  3. Neutron spin-echo studies on dynamic and static fluctuations in two types of poly(vinyl alcohol) gels

    SciTech Connect

    Kanaya, T.; Takahashi, N.; Nishida, K.; Seto, H.; Nagao, M.; Takeda, T.

    2005-01-01

    We report neutron spin-echo measurements on two types of poly(vinyl alcohol) (PVA) gels. The first is PVA gel in a mixture of dimethyl sulfoxide (DMSO) and water with volume ratio 60/40, and the second is PVA gel in an aqueous borax solution. The observed normalized intermediate scattering functions I(Q,t)/I(Q,0) are very different between them. The former I(Q,t)/I(Q,0) shows a nondecaying component in addition to a fast decay, but the latter does not have the nondecaying one. This clearly indicates that the fluctuations in the former PVA gel consist of static and dynamic fluctuations whereas the latter PVA gel does include only the dynamic fluctuations. The dynamic fluctuations of the former and latter gels have been analyzed in terms of a restricted motion in the network and Zimm motion, respectively, and the origins of these motions will be discussed.

  4. Spin susceptibility and effects of fluctuating Cooper pairs in the BCS-BEC crossover regime of a superfluid Fermi gas

    NASA Astrophysics Data System (ADS)

    Tajima, Hiroyuki; Hanai, Ryo; Ohashi, Yoji

    2015-03-01

    We theoretically discuss the spin susceptibility χ and effects of strong-coupling corrections in the BCS-BEC crossover regime of an ultracold Fermi gas. Using an extended T-matrix approximation, we calculate χ over the entire BCS-BEC crossover region, showing that this magnetic quantity is very sensitive to pairing fluctuations in both the normal and the superfluid phase. In the normal state, it is suppressed by preformed singlet Cooper pairs near Tc, being similar to the spin-gap phenomenon in high-Tc cuprates. Below Tc, on the other hand, pairing fluctuations enhance χ, in the sense that the suppression of this quantity by the superfluid order is weakened due to partial dissociation of Cooper pairs. From these, we determine the region where pairing fluctuations strongly affect spin excitations in the phase diagram of a Fermi gas with respect to the temperature and the strength of a pairing interaction. We also compare our results with the recent experiments on a 6Li Fermi gas. Our results indicate that the spin susceptibility is a useful observable in understanding strong-coupling properties of an ultracold Fermi gas in the BCS-BEC crossover region. H. T. was supported by Graduate School Doctoral Student Aid Program from Keio University.

  5. Hydration-induced anisotropic spin fluctuations in NaxCoO2 · 1.3H2O superconductor

    NASA Astrophysics Data System (ADS)

    Matano, K.; Lin, C. T.; Zheng, Guo-qing

    2008-12-01

    We report 59Co NMR studies in single crystals of the cobalt oxide superconductor Na0.42CoO2·1.3H2O (Tc=4.25 K) and its parent compound Na0.42CoO2. We find that both the magnitude and the temperature (T) dependence of the Knight shifts are identical in the two compounds above Tc. The spin-lattice relaxation rate (1/T1) is also identical above T0~60 K for both compounds. Below T0, the unhydrated sample is found to be a non-correlated metal that well conforms to the Fermi liquid theory, while spin fluctuations develop in the superconductor. These results indicate that water intercalation does not change the density of states at the Fermi level or the carrier density but its primary role is to bring about spin fluctuations. Our result shows that, in the hydrated superconducting compound, the electron correlation is anisotropic. Namely, the spin fluctuation around the finite wave vector is much stronger along the a-axis direction than that along the c-axis direction.

  6. Competition between spin fluctuations in Ca2-xSrxRuO4 around x=0.5

    NASA Astrophysics Data System (ADS)

    Arakawa, Naoya; Ogata, Masao

    2013-05-01

    We study the static susceptibilities for charge and spin sectors in paramagnetic states for Ca2-xSrxRuO4 in 0.5≤x≤2 within random phase approximation on the basis of an effective Ru t2g orbital Hubbard model. We find that several modes of spin fluctuation around q=(0,0) and q˜(0.797π,0) are strongly enhanced for the model of x=0.5. This enhancement arises from the increase of the corresponding susceptibilities for the dxy orbital due to the rotation-induced modifications of the electronic structure for this orbital (i.e., the flattening of the bandwidth and the increase of the density of states near the Fermi level). We also find that the ferromagnetic spin fluctuation becomes stronger for a special model than for the model of x=0.5, while the competition between the modes of spin fluctuation at q=(0,0) and around q˜(π,0) is weaker for the special model; in this special model, the van Hove singularity (vHs) for the dxy orbital is located on the Fermi level. These results indicate that the location of the vHs for the dxy orbital, which is controlled by substitution of Ca for Sr, is a parameter to control this competition. We propose that the spin fluctuations for the dxy orbital around q=(0,0) and q˜(π,0) play an important role in the electronic states around x=0.5 other than the criticality approaching the usual Mott transition where all electrons are localized.

  7. Linearized Jastrow-style fluctuations on spin-projected Hartree-Fock

    SciTech Connect

    Henderson, Thomas M.; Scuseria, Gustavo E.

    2013-12-21

    The accurate and efficient description of strong electronic correlations remains an important objective in electronic structure theory. Projected Hartree-Fock theory, where symmetries of the Hamiltonian are deliberately broken and projectively restored, all with a mean-field computational scaling, shows considerable promise in this regard. However, the method is neither size extensive nor size consistent; in other words, the correlation energy per particle beyond broken-symmetry mean field vanishes in the thermodynamic limit, and the dissociation limit of a molecule is not the sum of the fragment energies. These two problems are closely related. Recently, Neuscamman [Phys. Rev. Lett. 109, 203001 (2012)] has proposed a method to cure the lack of size consistency in the context of the antisymmetrized geminal power wave function (equivalent to number-projected Hartree-Fock-Bogoliubov) by using a Jastrow-type correlator in Hilbert space. Here, we apply the basic idea in the context of projected Hartree-Fock theory, linearizing the correlator for computational simplicity but extending it to include spin fluctuations. Results are presented for the Hubbard Hamiltonian and for some simple molecular systems.

  8. The influence of electron-phonon coupling and spin fluctuations on the superconductivity of the Ti-V alloys

    NASA Astrophysics Data System (ADS)

    Matin, Md.; Sharath Chandra, L. S.; Pandey, Sudhir K.; Chattopadhyay, Maulindu Kumar; Roy, Sindhunil Barman

    2014-06-01

    We report a study of the normal and superconducting state properties of the Ti x V1- x alloys for x = 0.4, 0.6, 0.7 and 0.8 with the help of dc magnetization, electrical resistivity and heat capacity measurements along with the electronic structure calculation. The superconducting transition temperature T c of these alloys is higher than that of elemental Ti and is also higher than elemental V for x ≤ 0.7. The roles of electron density of states, electron-phonon coupling and spin fluctuations in the normal and superconducting state properties of these alloys have been investigated in detail. The experimentally observed value of T c is found to be considerably lower than that estimated on the basis of electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys. There is some evidence as well for the preformed Cooper pair in all these Ti-V alloys in the temperature regime well above T c . Similar to x = 0.6 [Md. Matin, L.S. Sharath Chandra, R.K. Meena, M.K. Chattopadhyay, A.K. Sinha, M.N. Singh, S.B. Roy, Physica B 436, 20 (2014)], the normal state properties of the x = 0.4 alloy showed the signature of the presence of spin fluctuations. The difference between the experimentally observed T c and that estimated by considering electron density of states and electron-phonon coupling in the x = 0.4, 0.6 and 0.7 alloys is attributed to the possible influence of these spin fluctuations. We show that the non-monotonous variation of T c as a function of x in the Ti x V1- x alloys is due to the combined effects of the electron-phonon coupling and the spin fluctuations.

  9. Critical spin fluctuations and the origin of nematic order in Ba(Fe1-xCox)2As2

    NASA Astrophysics Data System (ADS)

    Kretzschmar, F.; Böhm, T.; Karahasanović, U.; Muschler, B.; Baum, A.; Jost, D.; Schmalian, J.; Caprara, S.; Grilli, M.; di Castro, C.; Analytis, J. G.; Chu, J.-H.; Fisher, I. R.; Hackl, R.

    2016-06-01

    Nematic fluctuations and order play a prominent role in material classes such as the cuprates, some ruthenates or the iron-based compounds and may be interrelated with superconductivity. In iron-based compounds signatures of nematicity have been observed in a variety of experiments. However, the fundamental question as to the relevance of the related spin, charge or orbital fluctuations remains open. Here, we use inelastic light (Raman) scattering and study Ba(Fe1-xCox)2As2 (0 <= x <= 0.085) for getting direct access to nematicity and the underlying critical fluctuations with finite characteristic wavelengths. We show that the response from fluctuations appears only in B1g (x2 - y2) symmetry (1 Fe unit cell). The scattering amplitude increases towards the structural transition at Ts but vanishes only below the magnetic ordering transition at TSDW < Ts, suggesting a magnetic origin of the fluctuations. The theoretical analysis explains the selection rules and the temperature dependence of the fluctuation response. These results make magnetism the favourite candidate for driving the series of transitions.

  10. Spin Fluctuations in (cerium, YTTRIUM)COBALT-2 and Related Systems.

    NASA Astrophysics Data System (ADS)

    Timlin, John

    The pseudobinary alloy systems (Y_ {rm x}Zr_{1 -rm x})Co_2, (Y _{rm x}Ce _{1-rm x})Co_2 , and (Ce_{rm x} Zr_{1-rm x})Co _2, for 0 < x < 1, have been studied. The temperature dependence of the electrical resistivity, magnetic susceptibility and specific heat have been measured for these systems. The temperature ranges were: for the electrical resistivity 1.5 to 300 K, for the magnetic susceptibility 6 to 300 K and for the specific heat 1.5 to 25 K. All three measurements show a rapid falloff of enhancements due to d-electron spin fluctuations as yttrium is replaced by zirconium in the (Y,Zr)Co_2 system. The variation of both the magnetic susceptibility and the specific heat as one substitutes cerium for yttrium in the (Y,Ce)Co _2 system is strikingly similar to that observed for (Y,Zr)Co_2. However, the resistivity of the (Y,Ce)Co_2 system is markedly different from that observed in (Y,Zr)Co_2 . Measurements done on the (Ce,Zr)Co_2 system confirm both the similarities between CeCo _2 and ZrCo_2 seen in the magnetic susceptibility and specific heat and the difference seen in the resistivity. Of greatest interest to this study is the evolution of the curvature of the temperature dependent magnetic susceptibility, which evolves from an upward bending form in YCo_2 to a downward bending form in both CeCo_2 and ZrCo_2 as predicted by theory for strongly enhanced paramagnets with a suitable density of states. This is the first controlled alloy study which shows such an evolution.

  11. Neutron spin echo investigation of the concentration fluctuation dynamics in melts of diblock copolymers

    NASA Astrophysics Data System (ADS)

    Montes, H.; Monkenbusch, M.; Willner, L.; Rathgeber, S.; Fetters, L.; Richter, D.

    1999-05-01

    Diblock copolymers in the melt exhibit order-disorder phase transitions (ODT), which are accompanied by strong concentration fluctuations. These transitions are generally described in terms of the random phase approximation (RPA) of Leibler and Fredrickson, which is able to explain small angle scattering results in the neighborhood of the ODT, in particular around the correlation peak at q*. The RPA theory has been extended to include dynamical phenomena, predicting the short time relaxation of the dynamic structure factor in polymeric multicomponent systems. We report small angle neutron scattering and neutron spin echo experiments on polyethylene-block-polyethylethylene (PE-PEE) and poly(ethylene-propylene)-block-polyethylethylene (PEP-PEE) copolymers with molecular weights of 16.500 and 68.000 g/mol, which explore the structure and dynamics of these block copolymers. Studying melts with different hydrogen/deuterium labeling it was possible to observe experimentally the different relaxation modes of such systems separately. In particular the collective relaxation behavior as well as the single chain motion were accessed. The experimental results were quantitatively compared with the RPA predictions, which were based solely on the dynamical properties of the corresponding homopolymers and the static structure factors. The collective dynamics exhibits an unanticipated fast relaxation mode. This mode is most visible at low wave numbers (q⩾q*) but extends to length scales considerably shorter than the radius of gyration. Furthermore, the dynamical RPA yields expressions for the mobilities of chain segments in the block copolymer melt. These combination rules are at variance with the experimental findings for the single chain dynamics, while they hold for the collective response.

  12. Superconductivity and spin fluctuations in the actinoid-platinum metal borides {Th ,U } Pt3B

    NASA Astrophysics Data System (ADS)

    Bauer, E.; Royanian, E.; Michor, H.; Sologub, O.; Scheidt, E.-W.; Gonçalves, A. P.; Bursik, J.; Wolf, W.; Reith, D.; Blaas-Schenner, C.; Moser, R.; Podloucky, R.; Rogl, P.

    2015-07-01

    Investigating the phase relations of the system {Th ,U } -Pt-B at 900 °C the formation of two compounds has been observed: cubic ThPt3B with P m 3 ¯m structure as a representative of the perovskites, and tetragonal UPt3B with P 4 m m structure being isotypic to the noncentrosymmetric structure of CePt3B . The crystal structures of the two compounds are defined by combined x-ray diffraction and transmission electron microscopy. Characterization of physical properties for ThPt3B reveals a superconducting transition at 0.75 K and an upper critical field at T =0 exceeding 0.4 T. For nonsuperconducting UPt3B a metallic resistivity behavior was found in the entire temperature range; at very low temperatures spin fluctuations become evident and the resistivity ρ (T ) follows non-Fermi liquid characteristics, ρ =ρ0+A T n with n =1.6 . Density functional theory (DFT) calculations were performed for both compounds for both types of structures. They predict that the experimentally claimed cubic structure of ThPt3B is thermodynamically not stable in comparison to a tetragonal phase, with a very large enthalpy difference of 25 kJ/mol, which cannot be explained by the formation energy of B vacancies. However, the presence of random boron vacancies possibly stabilizes the cubic structure via a local strain compensation mechanism during the growth of the crystal. For UPt3B the DFT results agree well with the experimental findings.

  13. Progressive slowing down of spin fluctuations in underdoped LaFeAsO1-xFx

    NASA Astrophysics Data System (ADS)

    Hammerath, F.; Gräfe, U.; Kühne, T.; Kühne, H.; Kuhns, P. L.; Reyes, A. P.; Lang, G.; Wurmehl, S.; Büchner, B.; Carretta, P.; Grafe, H.-J.

    2013-09-01

    The evolution of low-energy spin dynamics in the iron-based superconductor LaFeAsO1-xFx was studied over a broad doping, temperature, and magnetic field range (x= 0-0.15, T≤ 480 K, μ0H≤ 30 T) by means of 75As nuclear magnetic resonance. An enhanced spin-lattice relaxation rate divided by temperature (T1T)-1 in underdoped superconducting samples (x= 0.045, 0.05, and 0.075) suggests the presence of antiferromagnetic spin fluctuations, which are strongly reduced in optimally doped (x=0.10) and completely absent in overdoped (x=0.15) samples. In contrast to previous analysis, Curie-Weiss fits are shown to be insufficient to describe the data over the whole temperature range. Instead, a Bloembergen-Purcell-Pound (BPP) model is used to describe the occurrence of a peak in (T1T)-1 clearly above the superconducting transition, reflecting a progressive slowing down of the spin fluctuations down to the superconducting phase transition.

  14. Spin fluctuations in the exotic metallic state of Sr2RuO4 studied with β -NMR

    NASA Astrophysics Data System (ADS)

    Cortie, D. L.; Buck, T.; Dehn, M. H.; Kiefl, R. F.; Levy, C. D. P.; McFadden, R. M. L.; Morris, G. D.; Pearson, M. R.; Salman, Z.; Maeno, Y.; MacFarlane, W. A.

    2015-06-01

    A β -NMR study was performed on a Sr2RuO4 crystal in the metallic state using a beam of spin-polarized +8Li implanted at a mean depth of 90 nm. The +8Li spin-lattice relaxation rate is strongly influenced by the onset of incommensurate spin fluctuations. The nuclear relaxation rate can be explained using previously published bulk 17O NMR and inelastic neutron spectroscopy measurements of the dynamic magnetic susceptibility to model the hyperfine coupling. A well-resolved quadrupolar-split NMR for +8Li implies a static stopping position in an interstitial site. The +8Li Knight shift is highly sensitive to the anisotropic static susceptibility.

  15. Spin fluctuations and excitations in a 2D xy-ferromagnet: CoCl/sub 2/ in graphite

    SciTech Connect

    Wiesler, D.G.; Zabel, H.

    1989-01-01

    We have investigated by neutron scattering the spin fluctuations and excitations in the stage 2 CoCl/sub 2/ -- graphite intercalation compound. This compound has easy-plane anisotropy and sufficiently weak interplanar interaction to qualify as a test material for Kosterlitz-Thouless-Berezinsky type phase transitions. We have carried out quasi-elastic scattering measurements to determine the temperature variation of the spin correlation length /xi/ above the two dimensional ordering transition. We have also probed the dependence on wave vector and temperature of the inelastic scattering cross section, consisting of both a central peak, associated with vortex diffusion, and spin wave, which become strongly damped above the transition temperature. 15 refs., 5 figs.

  16. Low-frequency spin fluctuations in the superconducting La{sub 2-x}Sr{sub x}CuO{sub 4}

    SciTech Connect

    Yamada, K.; Lee, C.H.; Endoh, Y.; Shirane, G.; Birgeneau, R.J.; Kastner, M.A.

    1997-02-01

    Recent progress in low-energy neutron scattering study on the spatially modulated or so-called incommensurate spin fluctuations is reviewed. Well-defined incommensurate spin fluctuations are observed beyond x approx 0.05 and up to the highest Sr-concentration x approx. 0.25 in the present study. The incommensurability delta(x) is saturated at around 1/8 in the overdoped region and linearly scaled with the upper limit of Tc(x) between the underdoped and optimally doped region. A characteristic energy E* below which the dynamical magnetic susceptibility dramatically diminishes in the superconducting state can be determined to be around 7 meV in the energy spectrum of the spin fluctuations for x=0.15 and x=0.18 crystals. The disorder effect induces a low-frequency component of the incommensurate spin fluctuations below E*.

  17. Static and dynamic spin fluctuations in the spin glass doping regime in La sub 2-x Sr sub x CuO sub 4+y

    SciTech Connect

    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.

  18. Quantum lattice fluctuations in a frustrated Heisenberg spin-Peierls chain

    NASA Astrophysics Data System (ADS)

    Weiße, A.; Wellein, G.; Fehske, H.

    1999-09-01

    As a simple model for spin-Peierls systems we study a frustrated Heisenberg chain coupled to optical phonons. In view of the anorganic spin-Peierls compound CuGeO3 we consider two different mechanisms of spin-phonon coupling. Combining variational concepts in the adiabatic regime and perturbation theory in the antiadiabatic regime we derive effective spin Hamiltonians which cover the dynamical effect of phonons in an approximate way. Ground-state phase diagrams of these models are determined, and the effect of frustration is discussed. Comparing the properties of the ground state and low-lying excitations with exact diagonalization data for the full quantum spin-phonon models, good agreement is found especially in the antiadiabatic regime.

  19. Ferromagnetic Spin Fluctuation and Unconventional Superconductivity in Rb2Cr3As3 Revealed by 75As NMR and NQR

    NASA Astrophysics Data System (ADS)

    Yang, J.; Tang, Z. T.; Cao, G. H.; Zheng, Guo-qing

    2015-10-01

    We report 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) studies on the superconductor Rb2Cr3As3 with a quasi-one-dimensional crystal structure. Below T ˜100 K , the spin-lattice relaxation rate (1 /T1 ) divided by temperature, 1 /T1T , increases upon cooling down to Tc=4.8 K , showing a Curie-Weiss-like temperature dependence. The Knight shift also increases with decreasing temperature. These results suggest ferromagnetic spin fluctuation. In the superconducting state, 1 /T1 decreases rapidly below Tc without a Hebel-Slichter peak, and follows a T5 variation below T ˜3 K , which points to unconventional superconductivity with point nodes in the gap function.

  20. Sample-to-sample fluctuations of the overlap distributions in the three-dimensional Edwards-Anderson spin glass

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

    We study the sample-to-sample fluctuations of the overlap probability densities from large-scale equilibrium simulations of the three-dimensional Edwards-Anderson spin glass below the critical temperature. Ultrametricity, stochastic stability, and overlap equivalence impose constraints on the moments of the overlap probability densities that can be tested against numerical data. We found small deviations from the Ghirlanda-Guerra predictions, which get smaller as system size increases. We also focus on the shape of the overlap distribution, comparing the numerical data to a mean-field-like prediction in which finite-size effects are taken into account by substituting delta functions with broad peaks.

  1. Dynamic nuclear polarization and Hanle effect in (In,Ga)As/GaAs quantum dots. Role of nuclear spin fluctuations

    SciTech Connect

    Gerlovin, I. Ya.; Cherbunin, R. V.; Ignatiev, I. V.; Kuznetsova, M. S.; Verbin, S. Yu.; Flisinski, K.; Bayer, M.; Reuter, D.; Wieck, A. D.; Yakovlev, D. R.

    2013-12-04

    The degree of circular polarization of photoluminescence of (In,Ga)As quantum dots as a function of magnetic field applied perpendicular to the optical axis (Hanle effect) is experimentally studied. The measurements have been performed at various regimes of the optical excitation modulation. The analysis of experimental data has been performed in the framework of a vector model of regular nuclear spin polarization and its fluctuations. The analysis allowed us to evaluate the magnitude of nuclear polarization and its dynamics at the experimental conditions used.

  2. Spin-orbital fluctuations in the paramagnetic Mott insulator (V1-xCrx)2O3

    NASA Astrophysics Data System (ADS)

    Leiner, Jonathan; Stone, Matthew; Lumsden, Mark; Bao, Wei; Broholm, Collin

    2015-03-01

    The phase diagram of rhombohedral V2O3 features several distinct strongly correlated phases as a function of doping, pressure and temperature. When doped with chromium for 180 K spin waves indicates alternating FM and AFM interactions for nearest neighbor spin pairs that are equivalent in the PI. We argue that the corresponding spin-orbital fluctuations are responsible for the extremely short-range dynamic spin correlations that we document in the PI phase. Research at the Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Research was also supported by ORNL LDRD funding.

  3. Anomalous effect of disorder on spin fluctuations in non-centrosymmetric superconductors

    NASA Astrophysics Data System (ADS)

    Edelstein, Victor M.

    2008-09-01

    The spin susceptibility tensor χsij(T) of an impure superconductor (SC) with broken mirror symmetry has been evaluated and a great effect of impurity scattering has been shown. As opposed to conventional singlet superconductors, where the ordinary impurity scattering is known to have no effect on χs(T) , the spin susceptibility of a polar symmetry superconductor with s -wave pairing can be isotropic and equal to its value in the normal state in the “dirty” limit Tcτ≪1 , while the superconductor stays in a full-gap state. The effect is bound up with spin-flip transitions which accompany the electron scattering in conductors with the band spin-orbit coupling.

  4. Effects of thermal and quantum fluctuations on the phase diagram of a spin-1 {sup 87}Rb Bose-Einstein condensate

    SciTech Connect

    Phuc, Nguyen Thanh; Kawaguchi, Yuki; Ueda, Masahito

    2011-10-15

    We investigate the effects of thermal and quantum fluctuations on the phase diagram of a spin-1 {sup 87}Rb Bose-Einstein condensate (BEC) under the quadratic Zeeman effect. Due to the large ratio of spin-independent to spin-dependent interactions of {sup 87}Rb atoms, the effect of noncondensed atoms on the condensate is much more significant than that in scalar BECs. We find that the condensate and spontaneous magnetization emerge at different temperatures when the ground state is in the broken-axisymmetry phase. In this phase, a magnetized condensate induces spin coherence of noncondensed atoms in different magnetic sublevels, resulting in temperature-dependent magnetization of the noncondensate. We also examine the effect of quantum fluctuations on the order parameter at absolute zero and find that the ground-state phase diagram is significantly altered by quantum depletion.

  5. Short-range correlations and persistent spin fluctuations in the undistorted kagome lattice Ising antiferromagnet Co3Mg(OH)6Cl2

    NASA Astrophysics Data System (ADS)

    Fujihala, M.; Zheng, X. G.; Oohara, Y.; Morodomi, H.; Kawae, T.; Matsuo, Akira; Kindo, Koichi

    2012-01-01

    Spin fluctuations and spin-liquid behaviors of frustrated kagome antiferromagnets have received intense recent attention. Although most severe frustration was predicted for an Ising kagome antiferromagnet, a real material system of undistorted kagome lattice has not been found so far. Here we report the frustrated magnetism of a new Ising kagome antiferromagnet, MgCo3(OH)6Cl2, which can be viewed as a Co version of the intensively researched quantum kagome antiferromagnet of Herbertsmithite ZnCu3(OH)6Cl2. Experiments of magnetization, heat capacity, μSR, and neutron scattering demonstrated a partially frozen state with persistent spin fluctuations below around T = 2.7 K. The present study has provided a real material system to study the Ising spin behaviors on undistorted kagome lattice.

  6. High T_{c} via Spin Fluctuations from Incipient Bands: Application to Monolayers and Intercalates of FeSe.

    PubMed

    Linscheid, A; Maiti, S; Wang, Y; Johnston, S; Hirschfeld, P J

    2016-08-12

    We investigate superconductivity in a two-band system with an electronlike and a holelike band, where one of the bands is away from the Fermi level (or "incipient"). We argue that the incipient band contributes significantly to spin-fluctuation pairing in the strong coupling limit where the system is close to a magnetic instability and can lead to a large T_{c}. In this case, T_{c} is limited by a competition between the frequency range of the coupling (set by an isolated paramagnon) and the coupling strength itself, such that a domelike T_{c} dependence on the incipient band position is obtained. The coupling of electrons to phonons is found to further enhance T_{c}. The results are discussed in the context of experiments on monolayers and intercalates of FeSe. PMID:27563992

  7. High Tc via Spin Fluctuations from Incipient Bands: Application to Monolayers and Intercalates of FeSe

    NASA Astrophysics Data System (ADS)

    Linscheid, A.; Maiti, S.; Wang, Y.; Johnston, S.; Hirschfeld, P. J.

    2016-08-01

    We investigate superconductivity in a two-band system with an electronlike and a holelike band, where one of the bands is away from the Fermi level (or "incipient"). We argue that the incipient band contributes significantly to spin-fluctuation pairing in the strong coupling limit where the system is close to a magnetic instability and can lead to a large Tc. In this case, Tc is limited by a competition between the frequency range of the coupling (set by an isolated paramagnon) and the coupling strength itself, such that a domelike Tc dependence on the incipient band position is obtained. The coupling of electrons to phonons is found to further enhance Tc. The results are discussed in the context of experiments on monolayers and intercalates of FeSe.

  8. NMR study of spin fluctuations and superconductivity in LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Yoichi; Kontani, Hiroshi

    2013-03-01

    We have performed NMR measurements in LaFeAsO1-xHx, an isomorphic compound of LaFeAsO1-xFx. LaFeAsO1-xHx is most recently known for having double superconducting (SC) domes on H doping. LaFeAsO1-xHx is an electron- doped system, and protons act as H-1 as well as F-1. The first SC dome is very similar between F and H doping, suggesting that H doping supplies the same amount of electrons as F doping. Interestingly, an excess amount of H up to x=0.5 can be replaced with O2-. In the H-overdoped regime (x > 0 . 2), LaFeAsO1-xHx undergoes the second superconducting state. We measured the relaxation rate of LaFeAsO1-xHx for x=0.2 and 0.4, and fond an anomalous electronic state; spin fluctuations measured from 1 /T1 T is enhanced with increasing the doping level from x = 0 . 2 to 0.4. The enhancement of spin fluctuations with increasing carrier doping is a new phenomenon that has not observed in LaFeAsO1-xFx in which the upper limit of the doping level is at most x = 0 . 2 . We will discuss the phenomenon in relation to superconductivity. Grant (KAKENHI 23340101) from the Ministry of Education, Sports and Science, Japan

  9. Unusual strong spin-fluctuation effects around the critical pressure of the itinerant Ising-type ferromagnet URhAl

    NASA Astrophysics Data System (ADS)

    Shimizu, Yusei; Braithwaite, Daniel; Salce, Bernard; Combier, Tristan; Aoki, Dai; Hering, Eduardo N.; Ramos, Scheilla M.; Flouquet, Jacques

    2015-03-01

    Resistivity measurements were performed for the itinerant Ising-type ferromagnet URhAl at temperatures down to 40 mK under high pressure up to 7.5 GPa, using single crystals. We found that the critical pressure of the Curie temperature exists at around Pc˜ 5.2 GPa. Near Pc, the A coefficient of the A T2 Fermi-liquid resistivity term below T* is largely enhanced with a maximum around 5.2-5.5 GPa. Above Pc, the exponent of the resistivity ρ (T ) deviates from 2. At Pc, it is close to n =5 /3 , which is expected by the theory of three-dimensional ferromagnetic spin fluctuations for a second-order quantum-critical point (QCP). However, TC(P ) disappears as a first-order phase transition, and the critical behavior of resistivity in URhAl cannot be explained by the theory of a second-order QCP. The first-order nature of the phase transition is weak, and the electron system in URhAl is still dominated by the spin fluctuation at low temperature. With increasing pressure, the non-Fermi-liquid behavior is observed in higher fields. Magnetic field studies point out a ferromagnetic wing structure with a tricritical point (TCP) at ˜4.8 -4.9 GPa in URhAl. One open possibility is that the switch from the ferromagnetic to the paramagnetic states does not occur simply but an intermediate state arises below the TCP as suggested theoretically recently. Quite generally, if a drastic Fermi-surface change occurs through Pc, the nature of the interaction itself may change and lead to the observed unconventional behavior.

  10. Co-existence of spin fluctuation and superconductivity in electron doped cuprate Pr1-xLaCexCuO4

    NASA Astrophysics Data System (ADS)

    Song, Dongjoon; Park, S. R.; Kim, Chul; Choi, S. K.; Jung, W. S.; Koh, Y. Y.; Kim, Y. K.; Eisaki, H.; Yoshida, Y.; Kim, C.

    2012-02-01

    Even though spin fluctuation has been proposed to be as the pairing glue in the cuprate high temperature superconductivity, there is lack of a clear evidence for its coupling to electron. One of the reasons is that, for hole doped cuprates, both anti-ferromagnetism (AFM) and recently proposed charge ordering effects due to Fermi surface nesting occur in the same region of the momentum space (anti-nodal region). On the other hand, electron doped cuprates are known to have the pseudo gap effect at hot spots from AFM band renormalization. This fact makes it advantageous to investigate electron doped cuprates for the spin fluctuation issue. We performed ARPES studies on superconducting electron doped cuprates PLCCO (x=0.1, 0.15, 0.18) to investigate the relation between the spin fluctuation and superconductivity. We observe pseudo gap for all the dopings, which indicates that the short range AFM ordering survives far away from the AFM phase boundary. This coincidence of the short range AFM and superconductivity even in the over doped state may support the spin fluctuation scenarios at least in the electron doped side.

  11. Pressure dependence of spin fluctuations in metallic glasses Ni sub 25 Zr sub 75 and Fe sub 100 minus x Zr sub x ( x =75,80)

    SciTech Connect

    Hamed, F.; Razavi, F.S.; Zaleski, H.; Bose, S.K. )

    1991-02-01

    The superconducting transition temperature {ital T}{sub {ital c}} of metallic glasses Fe{sub 20}Zr{sub 80}, Fe{sub 25}Zr{sub 75}, and Cu{sub 25}Zr{sub 75} were measured under quasihydrostatic pressure up to 10 GPa. The volume (pressure) dependence of the electron-phonon coupling parameter, {lambda}{sub {ital e}-ph}, for Cu{sub 25}Zr{sub 75} was calculated using the McMillan equation. Using this volume dependence of {lambda}{sub {ital e}-ph} and the modified McMillan equation, which incorporates spin fluctuations, we determined the volume dependence of the spin-fluctuation parameter, {lambda}{sub SF}, in Ni{sub 25}Zr{sub 75} and Fe{sub 100{minus}{ital x}}Zr{sub {ital x}} ({ital x}=80, 75). It was found that with increasing pressure spin fluctuations are suppressed at a faster rate in Fe{sub 100{minus}{ital x}}Zr{sub {ital x}} as the Fe concentration is increased. The rate of suppression of spin fluctuations with pressure was also found to be higher in the Fe-Zr glasses than in Ni-Zr glasses of similar composition.

  12. Numerical study of spin relaxation by thermal fluctuation: Effect of shape anisotropy

    SciTech Connect

    Lee, K. J.; Park, N. Y.; Lee, T. D.

    2001-06-01

    Effects of the shape anisotropy on the thermally activated spin relaxation have been investigated using the stochastic Landau{endash}Lifshitz{endash}Gilbert equation. The relaxation times of a noninteracting particle and a thin film were compared with each other. In a noninteracting particle, the relaxation time largely increased with the shape anisotropy when the damping constant was smaller than a certain critical value. In this study, the critical damping constant was 0.02. However, the effect of the shape anisotropy on the energy barrier was negligible in a thin film. All of these results can be explained from the effect of magnetostatic interaction that is enhanced by precession motion at low damping constant. {copyright} 2001 American Institute of Physics.

  13. Influence of thermal fluctuations on the emission linewidth in MgO-based spin transfer oscillators

    NASA Astrophysics Data System (ADS)

    Sierra, J. F.; Quinsat, M.; Garcia-Sanchez, F.; Ebels, U.; Joumard, I.; Jenkins, A. S.; Dieny, B.; Cyrille, M.-C.; Zeltser, A.; Katine, J. A.

    2012-08-01

    The temperature dependence of the microwave emission linewidth Δf, the amplitude-phase coupling parameter ν, and the amplitude relaxation rate Γp were investigated experimentally for tunnel junction spin-transfer-oscillators. A linear increase of Δf and unexpectedly of Γp with temperature is observed, giving a ratio 2πΔf/Γp close to one. Analytical evaluation of the phase variance confirms that for this ratio the temperature dependence of Δf is linear and that in this temperature range Δf is enhanced by the amplitude-phase coupling. This is not changed when taking the temperature dependence of Γp into account, the origin of which remains to be elucidated.

  14. Inelastic neutron scattering in valence fluctuation compounds

    SciTech Connect

    Jon M Lawrence

    2011-02-15

    The valence fluctuation compounds are rare earth intermetallics where hybridization of the nearly-localized 4f electrons with the conduction electrons leads to incorporation of the 4f's into the itinerant states. This hybridization slows down the conduction electrons and hence gives them a heavy effective mass, justifying application of the term 'heavy Fermion' (HF) to these materials. During the project period, we grew large single crystals of several such compounds and measured their properties using both standard thermodynamic probes and state-of-the-art inelastic neutron scattering. We obtained three main results. For the intermediate valence compounds CePd{sub 3} and YbAl{sub 3}, we showed that the scattering of neutrons by the fluctuations of the 4f magnetic moment does not have the momentum dependence expected for the itinerant heavy mass state; rather, the scattering is more typical of a localized spin fluctuation. We believe that incoherent scattering localizes the excitation. For the heavy Fermion compound Ce(Ni{sub 0.935}Pd{sub 0.065}){sub 2}Ge{sub 2}, which sits at a T = 0 critical point for transformation into an antiferromagnetic (AF) phase, we showed that the scattering from the AF fluctuations does not exhibit any of the divergences that are expected at a phase transition. We speculate that alloy disorder profoundly suppresses the growth of the fluctuating AF regions, leading to short range clusters rather than regions of infinite size. Finally, we explored the applicability of key concepts used to describe the behavior of rare earth heavy Fermions to uranium based HF compounds where the 5f electrons are itinerant as opposed to localized. We found that scaling laws relating the spin fluctuation energy measured in neutron scattering to the low temperature specific heat and susceptibility are valid for the uranium compounds, once corrections are made for AF fluctuations; however, the degeneracy of the high temperature moment is smaller than expected

  15. Critical Casimir force and its fluctuations in lattice spin models: exact and Monte Carlo results.

    PubMed

    Dantchev, Daniel; Krech, Michael

    2004-04-01

    We present general arguments and construct a stress tensor operator for finite lattice spin models. The average value of this operator gives the Casimir force of the system close to the bulk critical temperature T(c). We verify our arguments via exact results for the force in the two-dimensional Ising model, d -dimensional Gaussian, and mean spherical model with 2 = k(b) T(c) (d-1)Delta/ (L/a)(d), where L is the distance between the plates and Delta is the (universal) Casimir amplitude. PMID:15169081

  16. Spin fluctuations and superconductivity in a 3D tight-binding model for BaFe2As2

    SciTech Connect

    Graser, Siegfried; Kemper, Alexander F; Maier, Thomas A; Cheng, Hai-Ping; Hirschfeld, Peter; Scalapino, Douglas

    2010-01-01

    Despite the wealth of experimental data on the Fe-pnictide compounds of the KFe2As2 type, K=Ba, Ca, or Sr, the main theoretical work based on multiorbital tight-binding models has been restricted so far to the study of the related 1111 compounds. This can be ascribed to the more three-dimensional electronic structure found by ab initio calculations for the 122 materials, making this system less amenable to model development. In addition, the more complicated Brillouin zone BZ of the body-centered tetragonal symmetry does not allow a straightforward unfolding of the electronic band structure into an effective 1Fe/unit cell BZ. Here we present an effective five-orbital tight-binding fit of the full density functional theory band structure for BaFe2As2 including the kz dispersions. We compare the five-orbital spin fluctuation model to one previously studied for LaOFeAs and calculate the random-phase approximation enhanced susceptibility. Using the fluctuation ex- change approximation to determine the leading pairing instability, we then examine the differences between a strictly two-dimensional model calculation over a single kz cut of the BZ and a completely three-dimensional approach. We find pairing states quite similar to the 1111 materials, with generic quasi-isotropic pairing on the hole sheets and nodal states on the electron sheets at kz=0, which however are gapped as the system is hole doped. On the other hand, a substantial kz dependence of the order parameter remains, with most of the pairing strength deriving from processes near kz=?. These states exhibit a tendency for an enhanced anisotropy on the hole sheets and a reduced anisotropy on the electron sheets near the top of the BZ.

  17. Evidence for phonon-like charge and spin fluctuations from an analysis of angle-resolved photoemission spectra of La2-xSrxCuO4 superconductors

    NASA Astrophysics Data System (ADS)

    Mazza, G.; Grilli, M.; Di Castro, C.; Caprara, S.

    2013-01-01

    In high temperature superconductors we provide evidence of spin and mixed phonon-charge collective modes as mediators of the effective electron-electron interaction and suggestive of a charge and spin density wave instability competing with superconductivity. Indeed, we show that the so-called kinks and waterfalls observed in angle-resolved photoemission spectra of La2-xSrxCuO4, a prototypical high-Tc superconducting cuprate, are due to the coupling of quasiparticles with two distinct nearly critical collective modes with finite characteristic wave vectors, typical of charge and spin fluctuations. The simultaneous presence of these two modes reconciles the long standing dichotomy whether kinks are due to phonons or spin waves.

  18. Tuning the metal-insulator transition in NdNiO3 heterostructures via Fermi surface instability and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Dhaka, R. S.; Das, Tanmoy; Plumb, N. C.; Ristic, Z.; Kong, W.; Matt, C. E.; Xu, N.; Dolui, Kapildeb; Razzoli, E.; Medarde, M.; Patthey, L.; Shi, M.; Radović, M.; Mesot, Joël

    2015-07-01

    We employed in situ pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of the metal-insulator transition (MIT) in NdNiO3 (NNO) thin films, grown on NdGaO3(110) and LaAlO3(100) substrates. In the metallic phase, we observe three-dimensional hole and electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across the MIT in NNO/NGO sample, the quasiparticles lose coherence via a spectral weight transfer from near the Fermi level to localized states forming at higher binding energies. In the case of NNO/LAO, the bands are apparently shifted upward with an additional holelike pocket forming at the corner of the Brillouin zone. We find that the renormalization effects are strongly anisotropic and are stronger in NNO/NGO than NNO/LAO. Our study reveals that substrate-induced strain tunes the crystal field splitting, which changes the FS properties, nesting conditions, and spin-fluctuation strength, and thereby controls the MIT via the formation of an electronic order parameter with QAF˜(1 /4 ,1 /4 ,1 /4 ±δ ) .

  19. Concluding Report of Free-Spinning, Tumbling, and Recovery Characteristics of a 1/18-Scale Model of the Ryan X-13 Airplane, Coord. No. AF-199

    NASA Technical Reports Server (NTRS)

    Bowman, James S., Jr.

    1957-01-01

    An investigation has been completed in the Langley 20-foot free-spinning tunnel on a l/18-scale model of the Ryan X-13 airplane to determine its spin, recovery, and tumbling characteristics, and to determine the minimum altitude from which a belly landing could be made in case of power failure in hovering flight. Model spin tests were conducted with and without simulated engine rotation. Tests without simulated engine rotation indicated two types of spins: one, a slightly oscillatory flat spin; and the other, a violently oscillatory spin. Tests with simulated engine rotation indicated that spins to the left were fast rotating and steep and those to the right were slow rotating and flat. The optimum technique for recovery is reversal of the rudder to against the spin and simultaneous movement of the ailerons to full with the spin followed by movement of the elevators to neutral after the spin rotation ceases. Tumbling tests made on the model indicated that although the Ryan X-13 airplane will not tumble in the ordinary sense (end-over-end pitching motion), it may instead tend to enter a wild gyrating'motion. Tests made to simulate power failure in hovering flight by dropping the model indicated that the model entered what appeared to be a right spin. An attempt should be made to stop this motion immediately by moving the rudder to oppose the rotation (left pedal), moving the ailerons to with the spin (stick right), and moving the stick forward after the spin rotation ceases to obtain flying speed for pullout. The minimum altitude required for a belly landing in case of power failure in hovering flight was indicated to be about 4,200 feet.

  20. Charge-spin-orbital fluctuations in mixed valence spinels: Comparative study of AlV2O4 and LiV2O4

    NASA Astrophysics Data System (ADS)

    Uehara, Amane; Shinaoka, Hiroshi; Motome, Yukitoshi

    2015-11-01

    Mixed valence spinels provide a fertile playground for the interplay between charge, spin, and orbital degrees of freedom in strongly correlated electrons on a geometrically frustrated lattice. Among them, AlV2O4 and LiV2O4 exhibit contrasting and puzzling behavior: self-organization of seven-site clusters and heavy fermion behavior. We theoretically perform a comparative study of charge-spin-orbital fluctuations in these two compounds, on the basis of the multiband Hubbard models constructed by using the maximally localized Wannier functions obtained from the ab initio band calculations. Performing the eigenmode analysis of the generalized susceptibility, we find that, in AlV2O4 , the relevant fluctuation appears in the charge sector in σ -bonding type orbitals. In contrast, in LiV2O4 , optical-type spin fluctuations in the a1 g orbital are enhanced at an incommensurate wave number at low temperature. Implications from the comparative study are discussed for the contrasting behavior, including the metal-insulator transition under pressure in LiV2O4 .

  1. 2012 IUPAP C10 Young Scientist Prize on the Structure and Dynamics of Condensed Matter Lecture: Spin Fluctuations and Pairing in Fe-based Superconductors

    NASA Astrophysics Data System (ADS)

    Christianson, A. D.

    2012-02-01

    The origin of superconductivity in the Fe-based superconductors, like that in other unconventional superconductors, remains shrouded in mystery. How the pairing bosons emerge either due to or in spite of the strong magnetic interactions found in the Fe-based superconductors is one of the most thoroughly investigated questions in the field. A prominent example of the interplay of superconductivity and magnetism is the dramatic shift of spectral weight from the low energy spin excitations to an energy which is related to the superconducting gap resulting in a peak in the spin excitation spectrum localized in both momentum and energy which occurs at the onset of superconductivity. The appearance of the new peak in the spin excitation spectrum below the superconducting transition temperature is referred to as s spin resonance and is most commonly interpreted as indicating a sign change of the superconducting order parameter on different portions of the Fermi surface and thus is consistent with an extended s-wave or s± pairing symmetry in many Fe-based superconductors. We will review the observations and implications of the spin resonance across the Fe-based superconductors. In particular we will examine the relationship between the resonance energy and the superconducting transition temperature as a function of chemical doping and pressure. While the spin resonance provides important information about pairing symmetry, there does not appear to be sufficient spectral to explain the pairing strength. Thus the remainder of the spin excitation spectrum must be examined to determine if spin fluctuations are ultimately responsible for pairing in the Fe-based materials. Consequently, we will discuss in detail the way in which the spin excitations evolve from the nonsuperconducting compounds to their superconducting relatives as a function of chemical doping.

  2. Enhanced superconducting transition temperature in hyper-interlayer-expanded FeSe despite the suppressed electronic nematic order and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Hrovat, Matevž Majcen; Jeglič, Peter; Klanjšek, Martin; Hatakeda, Takehiro; Noji, Takashi; Tanabe, Yoichi; Urata, Takahiro; Huynh, Khuong K.; Koike, Yoji; Tanigaki, Katsumi; Arčon, Denis

    2015-09-01

    The superconducting critical temperature, Tc, of FeSe can be dramatically enhanced by intercalation of a molecular spacer layer. Here we report on a 77Se,7Li , and 1H nuclear magnetic resonance (NMR) study of the powdered hyper-interlayer-expanded Lix(C2H8N2) yFe2 -zSe2 with a nearly optimal Tc=45 K. The absence of any shift in the 7Li and 1H NMR spectra indicates a complete decoupling of interlayer units from the conduction electrons in FeSe layers, whereas nearly temperature-independent 7Li and 1H spin-lattice relaxation rates are consistent with the non-negligible concentration of Fe impurities present in the insulating interlayer space. On the other hand, the strong temperature dependence of 77Se NMR shift and spin-lattice relaxation rate, 1 /77T1 , is attributed to the holelike bands close to the Fermi energy. 1 /77T1 shows no additional anisotropy that would account for the onset of electronic nematic order down to Tc. Similarly, no enhancement in 1 /77T1 due to the spin fluctuations could be found in the normal state. Yet, a characteristic power-law dependence 1 /77T1∝T4.5 still complies with the Cooper pairing mediated by spin fluctuations.

  3. Spatial modulation of low-frequency spin fluctuations in hole-doped La{sub 2}CuO{sub 4}

    SciTech Connect

    Yamada, K.; Lee, C.H.; Wada, J.; Kurahashi, K.; Kimura, H.; Endoh, Y.; Hosoya, S.; Shirane, G.; Birgeneau, R.J.; Kastner, M.A.

    1996-12-01

    Systematic neutron scattering measurements have been performed on the Sr-doped La(2-x)Sr(x) CuO4 to study the doping dependence of spatially modulated dynamical spin correlations or so-called incommensurate spin fluctuations. The modulated spin correlations appears beyond x approx. 0.05 which is close to the lower boundary of the superconducting phase. First evidence was observed for the linear relation between the degree of spatial modulation or the incommensurability delta(x) and the maximum Tc at x. We present a universal curve for delta(x) by adding data from other La2CuO4 systems such as oxygen-doped superconductors, oxygen-reduced or Zn-substituted non-superconductors and La(1.6-x)Nd(0.4)Sr(x)CuO4.

  4. Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe0.953Co0.047)2As2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

    DOE PAGESBeta

    Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; Yan, Jiaqiang; Chi, Songxue; Tucker, Gregory S.; Pratt, Daniel K.; Lynn, Jeffrey W.; McCallum, R. W.; Canfield, Paul C.; et al

    2015-02-04

    Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can be consistently described by a model that attributesmore » the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.« less

  5. Investigation of Incipient Spin Characteristics of a 1/35-Scale Model of the Convair F-102A Airplane, Coord. No. AF-AM-79

    NASA Technical Reports Server (NTRS)

    Healy, Frederick M.

    1958-01-01

    Incipient spin characteristics have been investigated on a l/35-scale dynamic model of the Convair F-10% airplane. The model was launched by a catapult apparatus into free flight with various control settings, and the motions obtained were photographed. The model was ballasted for the combat loading. All tests were made with the speed brakes and landing gear retracted, and engine effects were not simulated. The results of the investigation indicated that the model would enter motions apparently simulating entry phases of spins when the elevators were deflected full up. Deflecting the rudder had little effect on the direction of the motion obtained, but when ailerons were deflected the model always rotated in a direction opposite to the aileron setting (that is, the model entered a right spin with the stick to the left). The ailerons were very influential in initiating spin entry, and the pilot should avoid, as far as possible, the use of ailerons in low-speed flight.

  6. PAC (perturbed angular correlation) perturbation factor for spin 5/2 nuclei subject to a rapidly fluctuation EFC (electric field gradient)

    SciTech Connect

    Evenson, W.E. . Dept. of Physics and Astronomy); McKale, A.G.; Su, H.T.; Gardner, J.A. . Dept. of Physics)

    1990-01-01

    We report numerical computations of the PAC perturbation factor G{sub 2}(t) for spin 5/2 nuclei subject to a static EFG symmetric about the z-axis and an additional axially-symmetric EFG hose symmetry axis fluctuates randomly among the x,y,z directions. For sufficiently large fluctuation rates, the numerical results are described by the expression for the static interaction alone with the addition of relaxation terms. Results of applying this model to {sup 111}Cd TDPAC measurements on tetragonal ZrO{sub 2} are described briefly. The model allows one to evaluate the probability that oxygen vacancies are trapped, the energy of association of vacancy-metal pairs, and the vacancy activation energy of motion. 4 refs., 3 figs.

  7. Eliashberg analysis of optical spectra reveals a strong coupling of charge carriers to spin fluctuations in doped iron-pnictide BaFe2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Wu, D.; Barišić, N.; Dressel, M.; Cao, G. H.; Xu, Z.-A.; Schachinger, E.; Carbotte, J. P.

    2010-10-01

    The temperature and frequency dependences of the optical conductivity of Co-doped BaFe2As2 are analyzed and the electron-boson spectral density α2F(ω) are extracted using Eliashberg’s formalism. For the normal state at T=30K there is a relatively sharp and large peak around 10 meV and a secondary smaller and broader peak centered around 50 meV with the spectrum extending to high energies beyond the maximum phonon energy. The electron-boson mass enhancement parameter is 4.4, a value more consistent with spin-fluctuation scattering rather than with phonons. In addition the spectrum is found to evolve with temperature toward a less structured background at higher energies as in the spin susceptibility.

  8. Antiferromagnetic Spin Fluctuations and Pseudogap Behavior in Ca(Fe1-xCox)2 As2 Studied by 5As NMR

    NASA Astrophysics Data System (ADS)

    Cui, Jinfang; Ran, Sheng; Bud'Ko, Sergey; Canfield, Paul; Furukawa, Yuji

    2015-03-01

    75 As NMR measurements of single-crystalline Ca(Fe1-xCox)2 As2 have been carried out for four different doping concentration crystals (x = 0.023, 0.028, 0.033, 0.059) annealed at 350°C. Co-doped CaFe2As2 is a compound in 122 family of iron-pnictide superconductors with three principle phases exhibited: paramagnetic (PM), antiferromagnetic (AFM) and superconducting (SC) states. The magnetic phase transition to AFM state occurs at TN = 180K at x =0 and is suppressed to TN = 53K for x =0.028, which is accompanied by a structural phase transition from tetragonal to orthorhombic phases. 75As NMR was used to study the low energy spin dynamics via Knight shift (K) and spin-lattice relaxation rate (1/T1) measurements. From our analysis of the temperature dependence of both K and (T1T)-1 in x =0.028 (TN = 53K), 0.033 (Tc = 9K) and 0.059 (Tc = 10K), we found a gradual decrease of AFM spin fluctuations below T* = 88K for x =0.028, 72K for x =0.033 and 41K for x =0.059, respectively, indicating the possible pseudogap behavior in spin excitation spectrum in the system. Supported by USDOE under the Contract No. DE-AC02-07CH11358.

  9. Effects of antiferro-ferromagnetic phase coexistence and spin fluctuations on the magnetic and related properties of NdCuSi

    SciTech Connect

    Gupta, Sachin E-mail: suresh@phy.iitb.ac.in; Suresh, K. G. E-mail: suresh@phy.iitb.ac.in; Das, A.; Nigam, A. K.; Hoser, A.

    2015-06-01

    Polycrystalline NdCuSi is found to show co-existence of antiferromagnetic (AFM) and ferromagnetic (FM) phases at low temperatures, as revealed by neutron diffraction data. The coexistence is attributed to the competing exchange interactions and crystal field effect. The compound shows a large, low-field magnetoresistance (MR) of ∼ − 32% at 20 kOe below T{sub N} (3.1 K), which becomes ∼ − 36% at 50 kOe. The MR value at 50 kOe is found to be the highest among the RTX compounds. Magnetocaloric effect (MCE) is also found to show a large value of ∼11 J/kg K close to T{sub N}. Resistivity data show the presence of spin fluctuations, which get suppressed by the applied field. Large MR and MCE in this compound arise due to the coexistence of the two phases. The field dependencies of MR and MCE show quadratic behavior, confirming the presence of spin fluctuations.

  10. First-principles modeling of longitudinal spin fluctuations in itinerant electron antiferromagnets: High Néel temperature in the V3Al alloy

    NASA Astrophysics Data System (ADS)

    Khmelevskyi, Sergii

    2016-07-01

    The V3Al alloy with D O3 crystal structure belongs to the family of the very few metallic materials that exhibit a magnetically ordered state with a high ordering temperature (˜600 K) and consist only of nonmagnetic elements. We show that, similarly to the ferromagnetism in the fcc Ni (with ordering temperature at about 630 K), the antiferromagnetism in V3Al has itinerant character, and the high value of the Néel temperature is the result of the strong longitudinal spin fluctuations in the paramagnetic state. In order to develop an ab initio-based theory of the magnetic ordering at finite temperatures, we employ an effective magnetic Heisenberg-like Hamiltonian with varying values of the on-site magnetic moments. Using a set of approximations we map this model onto the results of the first-principle-based disordered local moment formalism and the magnetoforce theorem applied in the framework of the Korringa-Kohn-Rostoker method. Our high-temperature approach is shown to describe the experimental Néel temperature of V3Al very well and thus underlines the importance of the longitudinal spin-fluctuation mechanism of formation of the vanadium magnetic moment at high temperatures.

  11. Spin Fluctuation Effect on Electrical Resistivity of La0.8Ca0.2MnO3 Manganite Nanoparticles

    NASA Astrophysics Data System (ADS)

    Choudhary, K. K.

    2015-04-01

    The electrical resistivity ρ(T) of La0.8C0.2MnO3 manganite nanoparticles (particle size 18 nm and 70 nm) significantly depends on temperature and size of nanoparticles. ρ(T) of 70 nm La0.8C0.2MnO3 manganite exhibits metallic phase in low temperature regime (T < 250 K), develops a maxima near 250 K and decrease with T at high temperatures (250 K < T < 300 K). However, the ρ(T) of 18 nm La0.8C0.2MnO3 manganite shows insulating phase in overall temperature regime, where resistivity decrease with temperature. The resistivity in metallic phase is theoretically analyzed by considering the strong spin fluctuations effect which is modelled using Drude-Lorentz type function. In addition to the spin fluctuation-induced contribution the electron-phonon and electron-electron ρe-e(T) = BT2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons (ρac) as well as high frequency optical phonons (ρop) were estimated using Bloch-Gruneisen [BG] model of resistivity. It is observed that the resistivity contribution due to electron-electron interaction shows typical quadratic temperature dependence. Resistivity in Semiconducting/insulating phase is discussed with small polaron conduction (SPC) model. Finally the theoretically calculated resistivity compared with experimental data which found consistent in wide range of temperature.

  12. Neutron-scattering measurements of spin excitations in LaFeAsO and Ba(Fe0.953Co0.047)2As2: Evidence for a sharp enhancement of spin fluctuations by nematic order [Sharp enhancement of spin fluctuations by nematic order in iron pnictides

    SciTech Connect

    Zhang, Qiang; Fernandes, Rafael M.; Lamsal, Jagat; Yan, Jiaqiang; Chi, Songxue; Tucker, Gregory S.; Pratt, Daniel K.; Lynn, Jeffrey W.; McCallum, R. W.; Canfield, Paul C.; Lograsso, Thomas A.; Goldman, Alan I.; Vaknin, David; McQueeney, Robert J.

    2015-02-04

    Inelastic neutron scattering is employed to investigate the impact of electronic nematic order on the magnetic spectra of LaFeAsO and Ba(Fe0.953Co0.047)2As2. These materials are ideal to study the paramagnetic-nematic state, since the nematic order, signaled by the tetragonal-to-orthorhombic transition at TS, sets in well above the stripe antiferromagnetic ordering at TN. We find that the temperature-dependent dynamic susceptibility displays an anomaly at TS followed by a sharp enhancement in the spin-spin correlation length, revealing a strong feedback effect of nematic order on the low-energy magnetic spectrum. As a result, our findings can be consistently described by a model that attributes the structural or nematic transition to magnetic fluctuations, and unveils the key role played by nematic order in promoting the long-range stripe antiferromagnetic order in iron pnictides.

  13. Spin and isospin fluctuations in heavy ion collisions and their dependence upon the shape of the dinuclear complex

    SciTech Connect

    Moretto, L.G.

    1980-08-01

    The relevance of higher multipoles of giant isovector modes in the charge distribution of deep inelastic fragments is discussed and found to depend strongly on mass asymmetry. The sources of angular momentum fluctuations are investigated. Quantal effects are considered as well as effects arising from non-equilibrium and equilibrium statistical fluctuations. A model based upon equilibrium statistical mechanics is considered in detail, and used to predict both 2nd moments of the angular momentum distributions and the angular momentum misalignment. Analytical expressions are derived to calculate the angular distributions of sequentially emitted particles, fission fragments, as well as gamma rays in terms of the angular momentum misalignment. Recent data on the angular distributions of sequential alphas, fission and gamma rays are analyzed in terms of the model. 29 figures, 1 table.

  14. Absence of low energy magnetic spin-fluctuations in isovalently and aliovalently doped LaCo2B2 superconducting compounds.

    PubMed

    Majumder, M; Ghoshray, A; Khuntia, P; Mazumdar, C; Poddar, A; Baenitz, M; Ghoshray, K

    2016-09-01

    Magnetization, resistivity and (11)B, (59)Co NMR measurements have been performed on the Pauli paramagnet [Formula: see text], and the superconductors [Formula: see text] ([Formula: see text] K) and [Formula: see text] ([Formula: see text] K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides. The density of states (DOS) of Co 3d electrons has been enhanced in superconducting [Formula: see text] and [Formula: see text] with respect to the non superconducting reference compound [Formula: see text]. The occurrence of superconductivity is related to the DOS enhancement. PMID:27355521

  15. Spectroscopic Evidence for Strong Quantum Spin Fluctuations with Itinerant Character in YFe2Ge2

    SciTech Connect

    Sirica, N.; Bondino, F.; Nappini, S.; Piz, I.; Poudel, L.; Christianson, Andrew D.; Mandrus, D.; Singh, David J; Mannella, Norman

    2015-03-04

    We report x-ray absorption and photoemission spectroscopy of the electronic structure in the normal state of metallic YFe2Ge2. The data reveal evidence for large fluctuating spin moments on the Fe sites, as indicated by exchange multiplets appearing in the Fe 3s core-level photoemission spectra, even though the compound does not show magnetic order. The magnitude of the multiplet splitting is comparable to that observed in the normal state of the Fe-pnictide superconductors. This shows a connection between YFe2Ge2 and the Fe-based superconductors even though it contains neither pnictogens nor chalcogens. Finally, the implication is that the chemical range of compounds showing at least one of the characteristic magnetic signatures of the Fe-based superconductors is broader than previously thought.

  16. Studies of a Large Odd-Numbered Odd-Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8 Mn.

    PubMed

    Baker, Michael L; Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J; Barker, Claire; Blundell, Stephen J; Carretta, Stefano; Collison, David; Güdel, Hans U; Guidi, Tatiana; McInnes, Eric J L; Möller, Johannes S; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L; Santini, Paolo; Tuna, Floriana; Tregenna-Piggott, Philip L W; Vitorica-Yrezabal, Iñigo J; Timco, Grigore A; Winpenny, Richard E P

    2016-01-26

    The spin dynamics of Cr8 Mn, a nine-membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8 Mn is a rare example of a large odd-membered AF ring, and has an odd-number of 3d-electrons present. Odd-membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated-spin ground states. The chemical synthesis and structures of two Cr8 Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground-spin-state crossing from S=1/2 to S=3/2 in Cr8 Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin-pair correlations and scalar-spin chirality, shows a non-collinear spin structure that fluctuates between non-planar states of opposite chiralities. PMID:26748964

  17. Disappearance of static magnetic order and evolution of spin fluctuations in Fe1+δSexTe1-x

    SciTech Connect

    Xu, Zhijun; Wen, Jinsheng; Xu, Guangyong; Jie, Qing; Lin, Zhiwei; Li, Qiang; Chi, Songxue; Singh, D. K.; Gu, Genda; Tranquada, John M.

    2010-09-29

    We report neutron-scattering studies on static magnetic orders and spin excitations in the Fe-based chalcogenide system Fev Se1+δ Te1-x with different Fe and Se compositions. Short-range static magnetic order with an in-plane wave vector near the (0.5,0) (using the two-Fe unit cell), together with strong low-energy magnetic excitations is found in all nonsuperconducting samples for Se doping up to 45%. When the static order disappears and bulk superconductivity emerges, the spectral weight of the magnetic excitations shifts to the region of reciprocal space near the in-plane wave vector (0.5, 0.5), corresponding to “collinear” spin correlations. Our results suggest that there is a strong correlation between superconductivity and the character of the magnetic order/fluctuations in this system. Excess Fe appears to be important for stabilizing the magnetic order that competes with superconductivity.

  18. Inelastic Neutron Scattering Study of a Nonmagnetic Collapsed Tetragonal Phase in Nonsuperconducting CaFe2As2: Evidence of the Impact of Spin Fluctuations on Superconductivity in the Iron-Arsenide Compounds

    NASA Astrophysics Data System (ADS)

    Soh, J. H.; Tucker, G. S.; Pratt, D. K.; Abernathy, D. L.; Stone, M. B.; Ran, S.; Bud'ko, S. L.; Canfield, P. C.; Kreyssig, A.; McQueeney, R. J.; Goldman, A. I.

    2013-11-01

    The relationship between antiferromagnetic spin fluctuations and superconductivity has become a central topic of research in studies of superconductivity in the iron pnictides. We present unambiguous evidence of the absence of magnetic fluctuations in the nonsuperconducting collapsed tetragonal phase of CaFe2As2 via inelastic neutron scattering time-of-flight data, which is consistent with the view that spin fluctuations are a necessary ingredient for unconventional superconductivity in the iron pnictides. We demonstrate that the collapsed tetragonal phase of CaFe2As2 is nonmagnetic, and discuss this result in light of recent reports of high-temperature superconductivity in the collapsed tetragonal phase of closely related compounds.

  19. Magnetic fluctuations and possible formation of a spin-singlet cluster under pressure in the heavy-fermion spinel LiV2O4 probed by 7Li and 51V NMR

    NASA Astrophysics Data System (ADS)

    Takeda, Hikaru; Kato, Yusuke; Yoshimura, Masahiro; Shimizu, Yasuhiro; Itoh, Masayuki; Niitaka, Seiji; Takagi, Hidenori

    2015-07-01

    7Li and 51V NMR measurements up to 9.8 GPa have been made to elucidate local magnetic properties of a heavy-fermion spinel oxide LiV2O4 which undergoes a metal-insulator transition above ˜7 GPa. The temperature T and pressure P dependences of the 7Li and 51V Knight shifts and the nuclear spin-lattice relaxation rates 1 /T1 show that in the metallic phase, there is a crossover from a high-T region with weak ferromagnetic fluctuations to a low-T one with antiferromagnetic (AFM) fluctuations. The AFM fluctuations are enhanced below 20 K and 1.5 GPa, where a heavy Fermi-liquid state with the modified Korringa relation is formed. The evolution of the magnetic fluctuations is discussed from the aspect of the competition among several magnetic interactions. Above PMI˜6.7 GPa, we find the coexistence of metallic and insulating phases due to the first-order metal-insulator transition. The 7Li and 51V NMR spectra coming from the insulating phase have T -independent small Knight shifts and 7(1 /T1 ) with the thermally activated T dependence, indicating the formation of a spin-singlet cluster. We propose a model of a spin-singlet tetramer as discussed in geometrically frustrated materials.

  20. Absence of low energy magnetic spin-fluctuations in isovalently and aliovalently doped LaCo2B2 superconducting compounds

    NASA Astrophysics Data System (ADS)

    Majumder, M.; Ghoshray, A.; Khuntia, P.; Mazumdar, C.; Poddar, A.; Baenitz, M.; Ghoshray, K.

    2016-09-01

    Magnetization, resistivity and 11B, 59Co NMR measurements have been performed on the Pauli paramagnet \\text{LaC}{{\\text{o}}2}{{\\text{B}}2} , and the superconductors \\text{L}{{\\text{a}}0.9}{{\\text{Y}}0.1}\\text{C}{{\\text{o}}2}{{\\text{B}}2} ({{T}\\text{c}}≈ 4.2 K) and \\text{La}{{≤ft(\\text{C}{{\\text{o}}0.7}\\text{F}{{\\text{e}}0.3}\\right)}2}{{\\text{B}}2} ({{T}\\text{c}}≈ 5.8 K). The site selective NMR experiment reveals the multiband nature of the Fermi surface in these systems. The temperature independent Knight shift and 1/T 1 T clearly indicate the absence of correlated low energy magnetic spin-fluctuations in the normal state, which is in contrast to other Fe-based pnictides. The density of states (DOS) of Co 3d electrons has been enhanced in superconducting \\text{L}{{\\text{a}}0.9}{{\\text{Y}}0.1}\\text{C}{{\\text{o}}2}{{\\text{B}}2} and \\text{La}{{≤ft(\\text{C}{{\\text{o}}0.7}\\text{F}{{\\text{e}}0.3}\\right)}2}{{\\text{B}}2} with respect to the non superconducting reference compound \\text{LaC}{{\\text{o}}2}{{\\text{B}}2} . The occurrence of superconductivity is related to the DOS enhancement.

  1. Study on the correlation between s +/- pairing and intra-orbital spin fluctuations in 1111 iron based superconductors with isovalent doping

    NASA Astrophysics Data System (ADS)

    Usui, Hidetomo; Suzuki, Katsuhiro; Kuroki, Kazuhiko

    2015-03-01

    Recently, 1111 iron based superconductors with isovalent doping have been experimentally investigated in LnFeAsxP1-xO1-yFy (Ln =La, Nd, Pr). Interestingly, it was found that Tc takes its local maximum in the intermediate regime of arsenic/phosphorous ratio, which indicates that the superconductivity is locally optimized at a certain Fe-Pn-Fe (Pn =Pnictogen) bond angle larger than 109 deg. Given this background, we study the correlation between the local lattice structure, the orbital character of the Fermi surface, and Tc in 1111 system with isovalent doping. We calculate the band structure of LnFeAsxP1-xO1-yFy and construct effective five orbital models. To our surprise, it is found that superconductivity is indeed locally optimized in the intermediate arsenic doping regime. The origin of this local optimization is traced back to the gradual variation of the orbital character and the density of states of the hole Fermi surfaces around the Γ point, which is controlled by the bond angle. The consistency with the experiment strongly indicates the importance of the spin fluctuation played in this series of superconductors.

  2. Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn

    PubMed Central

    Lancaster, Tom; Chiesa, Alessandro; Amoretti, Giuseppe; Baker, Peter J.; Barker, Claire; Carretta, Stefano; Collison, David; Güdel, Hans U.; Guidi, Tatiana; McInnes, Eric J. L.; Möller, Johannes S.; Mutka, Hannu; Ollivier, Jacques; Pratt, Francis L.; Santini, Paolo; Tuna, Floriana; Tregenna‐Piggott, Philip L. W.; Vitorica‐Yrezabal, Iñigo J.; Timco, Grigore A.

    2016-01-01

    Abstract The spin dynamics of Cr8Mn, a nine‐membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8Mn is a rare example of a large odd‐membered AF ring, and has an odd‐number of 3d‐electrons present. Odd‐membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated‐spin ground states. The chemical synthesis and structures of two Cr8Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground‐spin‐state crossing from S=1/2 to S=3/2 in Cr8Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin‐pair correlations and scalar‐spin chirality, shows a non‐collinear spin structure that fluctuates between non‐planar states of opposite chiralities. PMID:26748964

  3. AFS controlling algorithm

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Jiang, Lanfang; Wang, Gengjie; Wang, Li

    2008-12-01

    Adaptive front lighting system (i.e., AFS) is the development trend of lighting system of motor vehicles. AFS means that headlamp can adjust beam direction to get best illumination according to road condition and its bodywork. The paper discusses the AFS key techniques: establishing calculation formulae of vehicle body state concerned road condition and steering state. Because of sensor technology limitations, it only can deal with inclination and turn of vehicle body state by means of sensor's signals. This paper studies the relationship between inclination and turn of the body and lamp lighting on the base of relative standards, and gives out the calculation formulae for the body and lamp lighting adjustment, also discusses its dynamical properties. The study is basic work for lighting adjustment automatically.

  4. Magnetic fluctuations and dynamics in the vicinity of quantum spin liquids: Cluster dynamical mean-field study of the Kitaev model

    NASA Astrophysics Data System (ADS)

    Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi

    The quantum spin liquid, which does not show any long-range ordering down to the lowest temperature, has attracted broad interest as a new quantum state of matter. Since the ground state of the Kitaev model was shown to be a quantum spin liquid in two dimensions, there has been an explosion in both theoretical and experimental studies. Nevertheless, dynamical properties at finite temperatures remain a challenge, despite the relevance to analysis of recent experiments for Ir and Ru compounds. In this contribution, we address this problem by using the cluster dynamical mean-field approximation, which we newly develop on the basis of the Majorana fermion representation. Using the continuous-time quantum Monte Carlo method for the impurity solver, we calculate the magnetic susceptibility, dynamical spin structure factor, and relaxation time in the nuclear magnetic resonance. We find that these quantities show peculiar temperature dependences in the paramagnetic state when approaching the quantum spin liquid by decreasing temperature, which reflects the fractionalization of quantum spins. We will discuss the results while changing the anisotropy and sign (ferro/antiferro) of the exchange interactions, in comparison with experiments.

  5. Multi-orbital quantum antiferromagnetism in iron pnictides-effective spin couplings and quantum corrections to sublattice magnetization.

    PubMed

    Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash

    2016-09-14

    Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the [Formula: see text] AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant [Formula: see text] average reduction from the Hartree-Fock value. PMID:27406889

  6. Multi-orbital quantum antiferromagnetism in iron pnictides—effective spin couplings and quantum corrections to sublattice magnetization

    NASA Astrophysics Data System (ADS)

    Ghosh, Sayandip; Raghuvanshi, Nimisha; Mohapatra, Shubhajyoti; Kumar, Ashish; Singh, Avinash

    2016-09-01

    Effective spin couplings and spin fluctuation induced quantum corrections to sublattice magnetization are obtained in the (π,0) AF state of a realistic three-orbital interacting electron model involving xz, yz and xy Fe 3d orbitals, providing insight into the multi-orbital quantum antiferromagnetism in iron pnictides. The xy orbital is found to be mainly responsible for the generation of strong ferromagnetic spin coupling in the b direction, which is critically important to fully account for the spin wave dispersion as measured in inelastic neutron scattering experiments. The ferromagnetic spin coupling is strongly suppressed as the xy band approaches half filling, and is ascribed to particle-hole exchange in the partially filled xy band. The strongest AF spin coupling in the a direction is found to be in the orbital off-diagonal sector involving the xz and xy orbitals. First order quantum corrections to sublattice magnetization are evaluated for the three orbitals, and yield a significant 37% average reduction from the Hartree–Fock value.

  7. Coupled Quantum Fluctuations and Quantum Annealing

    NASA Astrophysics Data System (ADS)

    Hormozi, Layla; Kerman, Jamie

    We study the relative effectiveness of coupled quantum fluctuations, compared to single spin fluctuations, in the performance of quantum annealing. We focus on problem Hamiltonians resembling the the Sherrington-Kirkpatrick model of Ising spin glass and compare the effectiveness of different types of fluctuations by numerically calculating the relative success probabilities and residual energies in fully-connected spin systems. We find that for a small class of instances coupled fluctuations can provide improvement over single spin fluctuations and analyze the properties of the corresponding class. Disclaimer: This research was funded by ODNI, IARPA via MIT Lincoln Laboratory under Air Force Contract No. FA8721-05-C-0002. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of ODNI, IARPA, or the US Government.

  8. Unusual spin fluctuations and magnetic frustration in olivine and non-olivine LiCoPO4 detected by P31 and Li7 nuclear magnetic resonance

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Klingeler, R.; Neef, C.; Koo, C.; Büchner, B.; Grafe, H.-J.

    2014-04-01

    We report P31 and Li7 nuclear magnetic resonance (NMR) studies in new non-olivine LiZnPO4-type LiCoPO4tetra microcrystals, where the Co2+ ions are tetrahedrally coordinated. Olivine LiCoPO4, which was directly transformed from LiCoPO4tetra by an annealing process, was also studied and compared. The uniform bulk magnetic susceptibility and the P31 Knight shift obey the Curie-Weiss law for both materials with a high spin Co2+ (3d7, S =3/2), but the Weiss temperature Θ and the effective magnetic moment μeff are considerably smaller in LiCoPO4tetra. The spin-lattice relaxation rate T1-1 reveals a quite different nature of the spin dynamics in the paramagnetic state of both materials. Our NMR results imply that strong geometrical spin frustration occurs in tetrahedrally coordinated LiCoPO4, which may lead to the incommensurate magnetic ordering.

  9. Critical behavior of a triangular lattice Ising AF/FM bilayer

    NASA Astrophysics Data System (ADS)

    Žukovič, M.; Bobák, A.

    2016-03-01

    We study a bilayer Ising spin system consisting of antiferromagnetic (AF) and ferromagnetic (FM) triangular planes, coupled by ferromagnetic exchange interaction, by standard Monte Carlo and parallel tempering methods. The AF/FM bilayer is found to display the critical behavior completely different from both the single FM and AF constituents as well as the FM/FM and AF/AF bilayers. Namely, by finite-size scaling (FSS) analysis we identify at the same temperature a standard Ising transition from the paramagnetic to FM state in the FM plane that induces a ferrimagnetic state with a finite net magnetic moment in the AF plane. At lower temperatures there is another phase transition, that takes place only in the AF plane, to different ferrimagnetic state with spins on two sublattices pointing parallel and on one sublattice antiparallel to the spins on the FM plane. FSS indicates that the corresponding critical exponents are close to the two-dimensional three-state ferromagnetic Potts model values.

  10. Efficient density matrix renormalization group algorithm to study Y junctions with integer and half-integer spin

    NASA Astrophysics Data System (ADS)

    Kumar, Manoranjan; Parvej, Aslam; Thomas, Simil; Ramasesha, S.; Soos, Z. G.

    2016-02-01

    An efficient density matrix renormalization group (DMRG) algorithm is presented and applied to Y junctions, systems with three arms of n sites that meet at a central site. The accuracy is comparable to DMRG of chains. As in chains, new sites are always bonded to the most recently added sites and the superblock Hamiltonian contains only new or once renormalized operators. Junctions of up to N =3 n +1 ≈500 sites are studied with antiferromagnetic (AF) Heisenberg exchange J between nearest-neighbor spins S or electron transfer t between nearest neighbors in half-filled Hubbard models. Exchange or electron transfer is exclusively between sites in two sublattices with NA≠NB . The ground state (GS) and spin densities ρr= at site r are quite different for junctions with S =1 /2 , 1, 3/2, and 2. The GS has finite total spin SG=2 S (S ) for even (odd) N and for MG=SG in the SG spin manifold, ρr>0 (<0 ) at sites of the larger (smaller) sublattice. S =1 /2 junctions have delocalized states and decreasing spin densities with increasing N . S =1 junctions have four localized Sz=1 /2 states at the end of each arm and centered on the junction, consistent with localized states in S =1 chains with finite Haldane gap. The GS of S =3 /2 or 2 junctions of up to 500 spins is a spin density wave with increased amplitude at the ends of arms or near the junction. Quantum fluctuations completely suppress AF order in S =1 /2 or 1 junctions, as well as in half-filled Hubbard junctions, but reduce rather than suppress AF order in S =3 /2 or 2 junctions.

  11. EVIDENCE FOR SPIN FLUCTUATIONS IN THE DEEP INELASTIC REACTION {sup 165}Ho + {sup 165}Ho AT 8.5 MeV/amu

    SciTech Connect

    McDonald, R. J.; Pacheco, A. J.; Wozniak, G. J.; Bolotin, H. H.; Moretto, L. G.; Schuk, C.; Shih, S.; Diamond, R. M.; Stephens, F. S.

    1981-05-01

    Both the magnitude and alignment of the transferred angular momentum in the reaction {sup 165}Ho + {sup 165}Ho have been measured as a function of Q-value via continuum {gamma}-ray multiplicity and anisotropy techniques. The spin transfer and the continuum {gamma}-ray anisotropy increase throughout the quasielastic region. The spin transfer as a function of Q-value saturates at ~35{bar h}/fragment, the anisotropy peaks at a value of ~2 and then decreases to near unity for the largest Q-values. The observed anisotropies are in good agreement with predictions from an equilibrium statistical model in which thermal excitation of angular-momentum-bearing collective modes and neutron evaporation give rise to in-plane components of the angular momentum.

  12. Magnetism in the iron-based superconductors: The determination of spin-nematic fluctuations as the primary order parameter and its implications for unconventional superconductivity

    NASA Astrophysics Data System (ADS)

    Taddei, Keith M.

    With nearly innumerable applications, superconductivity stands as a holy grail in the research of quantum phenomena. Understanding the mechanism that begets the fabled pairing of electrons which leads to zero resistance is the most significant undertaking in order to bring to fruition all of superconductivity's splendor. Yet the interaction which couples electrons in the most promising family of superconductors known as unconventional superconductors, which show the highest Tc's and largest upper critical fields remains a mystery. Intense study over the past several decades on the cuprate superconductors has allowed for the identification of several candidate mechanisms --- cardinal of which is magnetic fluctuations --- however as of yet the question still remains. Recently, the discovery of the iron-based superconductors has provided another fruitful avenue through which this mechanism can be probed. Excitingly in these materials superconductivity not only arises near a magnetic instability - a situation which is expected to be particularly suited for engendering superconductivity should magnetic fluctuations be the pairing mechanism - but also exhibit the microscopic co-existence of the two presumably adversarial phenomena. In the work presented here the powerful techniques of neutron and x-ray diffraction will be used to study two particularly interesting members of this family: the intercalated iron-selenide CsxFe 2--xSe2 and two members of the iron-arsenide 122 family (BaFe2(As1--xPx)2 and Sr1--xNaxFe2As 2). Though isostructural at high temperatures, these two materials behave remarkably differently and the idiosyncratic manifestations of superconductivity and ordered magnetism in either give clues as to how the latter might stabilize the former. The iron-selenides will be shown to exhibit a complex phase space with phase separation leading to stabilization of magnetism and superconductivity in separate phases. The structure, behavior and complex vacancy

  13. Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator.

    PubMed

    Lin, Weiwei; Chen, Kai; Zhang, Shufeng; Chien, C L

    2016-05-01

    We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM/AF/YIG, with a pronounced maximum near the Néel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM/YIG interface for NM=3d, 4d, and 5d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results. PMID:27203336

  14. Enhancement of Thermally Injected Spin Current through an Antiferromagnetic Insulator

    NASA Astrophysics Data System (ADS)

    Lin, Weiwei; Chen, Kai; Zhang, Shufeng; Chien, C. L.

    2016-05-01

    We report a large enhancement of thermally injected spin current in normal metal (NM)/antiferromagnet (AF)/yttrium iron garnet (YIG), where a thin AF insulating layer of NiO or CoO can enhance the spin current from YIG to a NM by up to a factor of 10. The spin current enhancement in NM /AF /YIG , with a pronounced maximum near the Néel temperature of the thin AF layer, has been found to scale linearly with the spin-mixing conductance at the NM /YIG interface for NM =3 d , 4 d , and 5 d metals. Calculations of spin current enhancement and spin mixing conductance are qualitatively consistent with the experimental results.

  15. Active fluctuation symmetries

    NASA Astrophysics Data System (ADS)

    Maes, Christian; Salazar, Alberto

    2014-01-01

    In contrast with the understanding of fluctuation symmetries for entropy production, similar ideas applied to the time-symmetric fluctuation sector have been less explored. Here we give detailed derivations of time-symmetric fluctuation symmetries in boundary-driven particle systems such as the open Kawasaki lattice gas and the zero-range model. As a measure of time-symmetric dynamical activity over time T we count the difference (Nℓ - Nr)/T between the number of particle jumps in or out at the left edge and those at the right edge of the system. We show that this quantity satisfies a fluctuation symmetry from which we derive a new Green-Kubo-type relation. It will follow then that the system is more active at the edge connected to the particle reservoir with the largest chemical potential. We also apply these exact relations derived for stochastic particle models to a deterministic case, the spinning Lorentz gas, where the symmetry relation for the activity is checked numerically.

  16. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    DOE PAGESBeta

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; et al

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the factmore » that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.« less

  17. Atrial Fibrillation (AF or AFib)

    MedlinePlus

    ... Pressure High Blood Pressure Tools & Resources Stroke More Atrial Fibrillation (AF or AFib) Updated:Feb 10,2016 What ... to the Terms and Conditions and Privacy Policy Atrial Fibrillation • Introduction • What is Atrial Fibrillation? • Why AFib Matters • ...

  18. Exchange anisotropy and spin-wave damping in CoFe/IrMn bilayers

    NASA Astrophysics Data System (ADS)

    Rezende, S. M.; Lucena, M. A.; Azevedo, A.; de Aguiar, F. M.; Fermin, J. R.; Parkin, S. S. P.

    2003-05-01

    The magnetic properties and the spin-wave damping in FM/AF bilayers of CoFe/IrMn have been investigated with magneto-optic Kerr effect magnetometry, ferromagnetic resonance (FMR), and Brillouin light scattering (BLS). As observed in other systems, the values of the interlayer exchange field obtained with different techniques are discrepant, but they all exhibit the expected t-1 dependence with the FM film thickness t. On the other hand the spin-wave relaxation rates measured by BLS and FMR are fit with a t-2 dependence plus a constant term. This is interpreted as the sum of two independent contributions, an intrinsic mechanism dominated by Gilbert damping and an extrinsic mechanism dominated by two-magnon scattering due to fluctuations of the interlayer exchange coupling caused by interface roughness.

  19. Pathogenesis of AF: Impact on intracardiac signals

    PubMed Central

    Shah, Ashok J; Dubois, Rémi; Miyazaki, Shinsuke; Jadidi, Amir S; Scherr, Daniel; Wilton, Stephen B; Roten, Laurent; Pascale, Patrizio; Pedersen, Michala; Derval, Nicolas; Knecht, Sebastien; Sacher, Frederic; Jais, Pierre; Narayan, Sanjiv; Hocini, Mélèze; Haïssaguerre, Michel

    2014-01-01

    Atrial fibrillation (AF) is the most common cardiac arrhythmia, and is responsible for the highest number of rhythm-related disorders and cardioembolic strokes worldwide. Intracardiac signal analysis during the onset of paroxysmal AF led to the discovery of pulmonary vein as a triggering source of AF, which has led to the development of pulmonary vein ablation—an established curative therapy for drug-resistant AF. Complex, multicomponent and rapid electrical activity widely involving the atrial substrate characterizes persistent/permanent AF. Widespread nature of the problem and complexity of signals in persistent AF reduce the success rate of ablation therapy. Although signal processing applied to extraction of relevant features from these complex electrograms has helped to improve the efficacy of ablation therapy in persistent/permanent AF, improved understanding of complex signals should help to identify sources of AF and further increase the success rate of ablation therapy. PMID:22255589

  20. Faraday rotation echo spectroscopy and detection of quantum fluctuations

    PubMed Central

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-01-01

    Central spin decoherence is useful for detecting many-body physics in environments and moreover, the spin echo control can remove the effects of static thermal fluctuations so that the quantum fluctuations are revealed. The central spin decoherence approach, however, is feasible only in some special configurations and often requires uniform coupling between the central spin and individual spins in the baths, which are very challenging in experiments. Here, by making analogue between central spin decoherence and depolarization of photons, we propose a scheme of Faraday rotation echo spectroscopy (FRES) for studying quantum fluctuations in interacting spin systems. The echo control of the photon polarization is realized by flipping the polarization with a birefringence crystal. The FRES, similar to spin echo in magnetic resonance spectroscopy, can suppress the effects of the static magnetic fluctuations and therefore reveal dynamical magnetic fluctuations. We apply the scheme to a rare-earth compound LiHoF4 and calculate the echo signal, which is related to the quantum fluctuations of the system. We observe enhanced signals at the phase boundary. The FRES should be useful for studying quantum fluctuations in a broad range of spin systems, including cold atoms, quantum dots, solid-state impurities, and transparent magnetic materials. PMID:24733086

  1. Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1-xPx)(O1-yFy): 31P-NMR studies

    NASA Astrophysics Data System (ADS)

    Mukuda, H.; Engetsu, F.; Yamamoto, K.; Lai, K. T.; Yashima, M.; Kitaoka, Y.; Takemori, A.; Miyasaka, S.; Tajima, S.

    2014-02-01

    Systematic 31P-NMR studies on LaFe(As1-xPx)(O1-yFy) with y =0.05 and 0.1 have revealed that the antiferromagnetic spin fluctuations (AFMSFs) at low energies are markedly enhanced around x =0.6 and 0.4, respectively, and as a result, Tc exhibits respective peaks at 24 and 27 K against the P substitution for As. This result demonstrates that the AFMSFs are responsible for the increase in Tc for LaFe(As1-xPx)(O1-yFy) as a primary mediator of the Cooper pairing. From a systematic comparison of AFMSFs with a series of (La1-zYz)FeAsOδ compounds in which Tc reaches 50 K for z =0.95, we remark that a moderate development of AFMSFs causes Tc to increase up to 50 K under the condition that the local lattice parameters of the FeAs tetrahedron approach those of the regular tetrahedron. We propose that Tc of Fe-pnictides exceeding 50 K is maximized under an intimate collaboration of the AFMSFs and other factors originating from the optimization of the local structure.

  2. Multiple Antiferromagnetic Spin Fluctuations and Novel Evolution of Tc in Iron-Based Superconductors LaFe(As1‑xPx)(O1‑yFy) Revealed by 31P-NMR Studies

    NASA Astrophysics Data System (ADS)

    Shiota, Takayoshi; Mukuda, Hidekazu; Uekubo, Masahiro; Engetsu, Fuko; Yashima, Mitsuharu; Kitaoka, Yoshio; Lai, Kwing To; Usui, Hidetomo; Kuroki, Kazuhiko; Miyasaka, Shigeki; Tajima, Setsuko

    2016-05-01

    We report on 31P-NMR studies of LaFe(As1‑xPx)(O1‑yFy) over wide compositions for 0 ≤ x ≤ 1 and 0 ≤ y ≤ 0.14, which provide clear evidence that antiferromagnetic spin fluctuations (AFMSFs) are one of the indispensable elements for enhancing Tc. Systematic 31P-NMR measurements revealed two types of AFMSFs in the temperature evolution, that is, one is the AFMSFs that develop rapidly down to Tc with low-energy characteristics, and the other, with relatively higher energy than the former, develops gradually upon cooling from high temperature. The low-energy AFMSFs in low y (electron doping) over a wide x (pnictogen height suppression) range are associated with the two orbitals of dxz/yz, whereas the higher-energy ones for a wide y region around low x originate from the three orbitals of dxy and dxz/yz. We remark that the nonmonotonic variation of Tc as a function of x and y in LaFe(As1‑xPx)(O1‑yFy) is attributed to these multiple AFMSFs originating from degenerated multiple 3d orbitals inherent to Fe-pnictide superconductors.

  3. Magnons, Spin Current and Spin Seebeck Effect

    NASA Astrophysics Data System (ADS)

    Maekawa, Sadamichi

    2012-02-01

    When metals and semiconductors are placed in a temperature gradient, the electric voltage is generated. This mechanism to convert heat into electricity, the so-called Seebeck effect, has attracted much attention recently as the mechanism for utilizing wasted heat energy. [1]. Ferromagnetic insulators are good conductors of spin current, i.e., the flow of electron spins [2]. When they are placed in a temperature gradient, generated are magnons, spin current and the spin voltage [3], i.e., spin accumulation. Once the spin voltage is converted into the electric voltage by inverse spin Hall effect in attached metal films such as Pt, the electric voltage is obtained from heat energy [4-5]. This is called the spin Seebeck effect. Here, we present the linear-response theory of spin Seebeck effect based on the fluctuation-dissipation theorem [6-8] and discuss a variety of the devices. [4pt] [1] S. Maekawa et al, Physics of Transition Metal Oxides (Springer, 2004). [0pt] [2] S. Maekawa: Nature Materials 8, 777 (2009). [0pt] [3] Concept in Spin Electronics, eds. S. Maekawa (Oxford University Press, 2006). [0pt] [4] K. Uchida et al., Nature 455, 778 (2008). [0pt] [5] K. Uchida et al., Nature Materials 9, 894 (2010) [0pt] [6] H. Adachi et al., APL 97, 252506 (2010) and Phys. Rev. B 83, 094410 (2011). [0pt] [7] J. Ohe et al., Phys. Rev. B (2011) [0pt] [8] K. Uchida et al., Appl. Phys. Lett. 97, 104419 (2010).

  4. Embossed Teflon AF Laminate Membrane Microfluidic Diaphragm Valves

    NASA Technical Reports Server (NTRS)

    Willis, Peter; Hunt, Brian; White,Victor; Grunthaner, Frank

    2008-01-01

    A microfluidic system has been designed to survive spaceflight and to function autonomously on the Martian surface. It manipulates microscopic quantities of liquid water and performs chemical analyses on these samples to assay for the presence of molecules associated with past or present living processes. This technology lies at the core of the Urey Instrument, which is scheduled for inclusion on the Pasteur Payload of the ESA ExoMars rover mission in 2013. Fabrication processes have been developed to make the microfabricated Teflon-AF microfluidic diaphragm pumps capable of surviving extreme temperature excursions before and after exposure to liquid water. Two glass wafers are etched with features and a continuous Teflon membrane is sandwiched between them (see figure). Single valves are constructed using this geometry. The microfabricated devices are then post processed by heating the assembled device while applying pneumatic pressure to force the Teflon diaphragm against the valve seat while it is softened. After cooling the device, the embossed membrane retains this new shape. This solves previous problems with bubble introduction into the fluid flow where deformations of the membrane at the valve seat occurred during device bonding at elevated temperatures (100-150 C). The use of laminated membranes containing commercial Teflon AF 2400 sheet sandwiched between spun Teflon AF 1600 layers performed best, and were less gas permeable than Teflon AF 1600 membranes on their own. Spinning Teflon AF 1600 solution (6 percent in FLOURINERT(Registered TradeMark) FC40 solvent, 3M Company) at 500 rpm for 1.5 seconds, followed by 1,000 rpm for 3 seconds onto Borofloat glass wafers, results in a 10-micron-thick film of extremely smooth Teflon AF. This spinning process is repeated several times on flat, blank, glass wafers in order to gradually build a thick, smooth membrane. After running this process at least five times, the wafer and Teflon coating are heated under vacuum

  5. Quantum fluctuations stabilize skyrmion textures

    NASA Astrophysics Data System (ADS)

    Roldán-Molina, A.; Santander, M. J.; Nunez, A. S.; Fernández-Rossier, J.

    2015-12-01

    We study the quantum spin waves associated to skyrmion textures. We show that the zero-point energy associated to the quantum spin fluctuations of a noncollinear spin texture produce Casimir-like magnetic fields. We study the effect of these Casimir fields on the topologically protected noncollinear spin textures known as skyrmions. In a Heisenberg model with Dzyalonshinkii-Moriya interactions, chosen so the classical ground state displays skyrmion textures, we calculate the spin-wave spectrum, using the Holstein-Primakoff approximation, and the associated zero-point energy, to the lowest order in the spin-wave expansion. Our calculations are done both for the single-skyrmion case, for which we obtain a discrete set of skyrmion bound states, as well as for the skyrmion crystal, for which the resulting spectrum gives the spin-wave bands. In both cases, our calculations show that the Casimir magnetic field contributes up to 10% of the total Zeeman energy necessary to delete the skyrmion texture with an applied field.

  6. Drift transport of helical spin coherence with tailored spin-orbit interactions

    NASA Astrophysics Data System (ADS)

    Kunihashi, Y.; Sanada, H.; Gotoh, H.; Onomitsu, K.; Kohda, M.; Nitta, J.; Sogawa, T.

    2016-03-01

    Most future information processing techniques using electron spins in non-magnetic semiconductors will require both the manipulation and transfer of spins without their coherence being lost. The spin-orbit effective magnetic field induced by drifting electrons enables us to rotate the electron spins in the absence of an external magnetic field. However, the fluctuations in the effective magnetic field originating from the random scattering of electrons also cause undesirable spin decoherence, which limits the length scale of the spin transport. Here we demonstrate the drift transport of electron spins adjusted to a robust spin structure, namely a persistent spin helix. We find that the persistent spin helix enhances the spatial coherence of drifting spins, resulting in maximized spin decay length near the persistent spin helix condition. Within the enhanced distance of the spin transport, the transport path of electron spins can be modulated by employing time-varying in-plane voltages.

  7. Spin Transport in Insulators Mediated by Magnetic Correlations Probed by Y3Fe5O12-based Spin Pumping

    NASA Astrophysics Data System (ADS)

    Du, Chunhui; Wang, Hailong; Hammel, P. Chris; Yang, Fengyuan

    2015-03-01

    Spin currents carried by mobile charges in ferromagnetic (FM) and nonmagnetic (NM) materials have been the central focus of spintronics, while spin transport in insulators is largely unexplored. FMR spin pumping has awakened intense interest in magnon-mediated spin currents in both conducting and insulating FMs and in antiferromagnets (AF). Building on the large spin pumping signals enabled by our Y3Fe5O12 (YIG) films, we report a systematic study of spin transport in six series of Pt/insulator/YIG trilayers where the insulators include one diamagnet, one paramagnet and four AFs. We observe remarkably robust spin transport in the AFs and a distinct linear relationship between the spin decay length in the insulator and the damping enhancement in the YIG, suggesting the critical role of magnetic correlations in AF insulators for spin transport. Strikingly, the insertion of a thin NiO layer between YIG and Pt significantly enhances the spin currents driven into Pt, suggesting exceptionally high spin transfer efficiency in YIG/NiO/Pt structures.

  8. Effect of X irradiation on optical properties of Teflon-AF

    NASA Astrophysics Data System (ADS)

    Jahan, M. S.; Ermer, D. R.; Cooke, D. W.

    1993-03-01

    Radiation effects in optical-grade amorphous fluoropolymer, Teflon-AF, is investigated by UV-visible absorption and electron spin resonance (ESR) measurements. When irradiated with low-energy (40 kVp) X-rays at room temperature in air, Teflon-AF is found to develop a broad, structureless UV-absorption band in the wavelength interval 200-350 nm. While the UV absorption increases as a function of X-ray dose, with relative rates of approx 2 × 10 -5 Gy -1 (1 × 10 -5 Gy -1) in Teflon-AF 1600 (Teflon-AF 2400), its optical transparency for a given dose of 67.5 kGy, however, remains unaffected. Additional measurements conducted using electron spin resonance (ESR) technique reveal that the observed UV absorption is caused by the X-ray induced peroxy radical (POO .˙). The results also suggest that the inclusion of dioxole monomer in the PTFE chain not only improves the optical clarity of Teflon-AF, as reported, but also increases its radiation tolerance. During a post-irradiation storage in air at RT for about 30 days the peroxy radical is observed to decay, with a concomitant decrease in UV absorption. A tentative model is proposed to explain the radiation damage and recovery mechanisms.

  9. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, Alice E.; Lawrence, J M.; Christianson, Andrew D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, Andrey A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, Krzysztof; Ronning, F.; Mcclellan, K. J.; Thompson, J. D.

    2014-12-03

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to research the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. In addition, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. In conclusion, we suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  10. Quantum critical fluctuations in the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2

    SciTech Connect

    Wang, C. H.; Poudel, L.; Taylor, A. E.; Lawrence, J. M.; Christianson, A. D.; Chang, S.; Rodriguez-Rivera, J. A.; Lynn, J. W.; Podlesnyak, A. A.; Ehlers, G.; Baumbach, R. E.; Bauer, E. D.; Gofryk, K.; Ronning, F.; McClellan, K. J.; Thompson, J. D.

    2015-01-14

    Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experi- ments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935 Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ≤ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ~ T3/2 and γ(T) ~ γ0 - bT1/2). However, for 2 ≤ T ≤ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

  11. Impact of magnetic fluctuations on lattice excitations in fcc nickel

    NASA Astrophysics Data System (ADS)

    Körmann, Fritz; Ma, Pui-Wai; Dudarev, Sergei L.; Neugebauer, Jörg

    2016-02-01

    The spin-space averaging formalism is applied to compute atomic forces and phonon spectra for magnetically excited states of fcc nickel. Transverse and longitudinal magnetic fluctuations are taken into account by a combination of magnetic special quasi random structures and constrained spin-density-functional theory. It turns out that for fcc Ni interatomic force constants and phonon spectra are almost unaffected by both kinds of spin fluctuations. Given the computational expense to simulate coupled magnetic and atomic fluctuations, this insight facilitates computational modeling of magnetic alloys such as Ni-based superalloys.

  12. Study about AFS swerve mode

    NASA Astrophysics Data System (ADS)

    Liu, Hong; Jiang, Lanfang; Zhao, Qin; Wang, Li

    2009-11-01

    A swerving mathematical model was established after stating the shortage of the present AFS swerving algorithm. The conception of 'expected lighting distance' was extended to 'expected lighting bound' and approximate treatment of geometry of light beam falling to ground of headlamp was processed. The expected lighting bound was ascertained and the lighting range of turning angle of headlamp was calculated. The calculation formula of turning angle of headlamp was worked out. It was indicated that the turning angle of inside and outside of headlamp calculated by revised algorithm was reasonable by comparing calculation. Finally the control strategy about the turning angle of inside and outside headlamp when turning was worked out. It is of practical significance in promoting the active safety, reducing the traffic accidents caused by insufficient angle and range of irradiation of headlamp.

  13. Fluctuations of healthy and unhealthy heartbeat intervals

    NASA Astrophysics Data System (ADS)

    Lan, Boon Leong; Toda, Mikito

    2013-04-01

    We show that the RR-interval fluctuations, defined as the difference between successive natural-logarithm of the RR interval, for healthy, congestive-heart-failure (CHF) and atrial-fibrillation (AF) subjects are well modeled by non-Gaussian stable distributions. Our results suggest that healthy or unhealthy RR-interval fluctuation can generally be modeled as a sum of a large number of independent physiological effects which are identically distributed with infinite variance. Furthermore, we show for the first time that one indicator —the scale parameter of the stable distribution— is sufficient to robustly distinguish the three groups of subjects. The scale parameters for healthy subjects are smaller than those for AF subjects but larger than those for CHF subjects —this ordering suggests that the scale parameter could be used to objectively quantify the severity of CHF and AF over time and also serve as an early warning signal for a healthy person when it approaches either boundary of the healthy range.

  14. Eaton AF5000+Genesis Communication Driver

    1995-05-25

    Communication driver allows the Genesis Control Series software to interact with Eaton AF5000+ frequency drives via RS-232 communications. All Eaton AF5000+ parameters that support communications are supported by the Genesis driver. Multidrop addressing to multiple units is available with the Genesis communication driver.

  15. Uniaxial spin-transfer torque in an exchange-biased spin valve.

    PubMed

    Xu, Jian-qing; Jin, Guojun

    2011-07-27

    We study the effects of uniaxial spin-transfer torque (USTT) on the ferromagnetic (F) as well as antiferromagnetic (AF) layers in an exchange-biased (EB) spin valve. By analytically treating the free-energy functional of the F/AF bilayer and numerically solving the Landau-Lifshitz-Gilbert equation for magnetic moments, we can reproduce and explain two existing experimental facts relevant to USTT: one is that the EB field can be reversed by both positive and negative pulsed currents, and the other is that the critical current to excite the F moments is greatly increased in the presence of an AF layer and independent of external fields. We also derive the angular dependence of the critical currents to excite AF and F moments, which suggests a possible way to quantitatively determine USTT in experiments. PMID:21727307

  16. Spin-flip noise due to nonequilibrium spin accumulation

    NASA Astrophysics Data System (ADS)

    Liu, Liang; Niu, Jiasen; Guo, Huiqiang; Wei, Jian; Li, D. L.; Feng, J. F.; Han, X. F.; Coey, J. M. D.; Zhang, X.-G.

    2016-05-01

    When current flows through a magnetic tunnel junction (MTJ), there is spin accumulation at the electrode-barrier interfaces if the magnetic moments of the two ferromagnetic electrodes are not aligned. Here we report that such nonequilibrium spin accumulation generates its own characteristic low frequency noise (LFN). Past work viewed the LFN in MTJs as an equilibrium effect arising from resistance fluctuations (SR) which a passively applied current (I ) converts to measurable voltage fluctuations (SV=I2SR ). We treat the LFN associated with spin accumulation as a nonequilibrium effect, and find that the noise power can be fitted in terms of the spin-polarized current by SIf =a I coth(I/b )-a b , resembling the form of the shot noise for a tunnel junction, but with current now taking the role of the bias voltage, and spin-flip probability taking the role of tunneling probability.

  17. State diagram of an orthogonal spin transfer spin valve device

    SciTech Connect

    Ye, Li; Wolf, Georg; Pinna, Daniele; Chaves-O'Flynn, Gabriel D.; Kent, Andrew D.

    2015-05-21

    We present the switching characteristics of a spin-transfer device that incorporates a perpendicularly magnetized spin-polarizing layer with an in-plane magnetized free and fixed magnetic layer, known as an orthogonal spin transfer spin valve device. This device shows clear switching between parallel (P) and antiparallel (AP) resistance states and the reverse transition (AP → P) for both current polarities. Further, hysteretic transitions are shown to occur into a state with a resistance intermediate between that of the P and AP states, again for both current polarities. These unusual spin-transfer switching characteristics can be explained within a simple macrospin model that incorporates thermal fluctuations and considers a spin-polarized current that is tilted with respect to the free layer's plane, due to the presence of the spin-transfer torque from the polarizing layer.

  18. Spin-polaron theory of high-{Tc} superconductivity: I, spin polarons and high-{Tc} pairing

    SciTech Connect

    Wood, R.F.

    1993-06-01

    The concept of a spin polaron is introduced and contrasted with the more familiar ionic polaron picture. A brief review of aspects of ionic bipolaronic superconductivity is given with particular emphasis on the real-space pairing and true Bose condensation characteristics. The formation energy of spin polarons is then calculated in analogy with ionic polarons. The spin-flip energy of a Cu spin in an antiferromagnetically aligned CuO{sub 2} plane is discussed. It is shown that the introduction of holes into the CuO{sub 2} planes will always lead to the destruction of long-range AF ordering due to the formation of spin polarons. The pairing of two spin polarons can be expected because of the reestablishment of local (short-range) AF ordering; the magnitude of the pairing energy is estimated using a simplified model. The paper closes with a brief discussion of the formal theory of spin polarons.

  19. An Exact SU(2) Symmetry and Persistent Spin Helix ina Spin-orbit Coupled System

    SciTech Connect

    Bernevig, B.A.; Orenstein, J.; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2007-01-22

    Spin-orbit coupled systems generally break the spin rotation symmetry. However, for a model with equal Rashba and Dresselhauss coupling constant (the ReD model), and for the [110] Dresselhauss model, a new type of SU(2) spin rotation symmetry is discovered. This symmetry is robust against spin-independent disorder and interactions, and is generated by operators whose wavevector depends on the coupling strength. It renders the spin lifetime infinite at this wavevector, giving rise to a Persistent Spin Helix (PSH). We obtain the spin fluctuation dynamics at, and away, from the symmetry point, and suggest experiments to observe the PSH.

  20. An Exact SU(2) Symmetry and Persistent Spin Helix in a Spin-Orbit Coupled System

    SciTech Connect

    Bernevig, Andrei

    2010-02-10

    Spin-orbit coupled systems generally break the spin rotation symmetry. However, for a model with equal Rashba and Dresselhauss coupling constant (the ReD model), and for the [110] Dresselhauss model, a new type of SU(2) spin rotation symmetry is discovered. This symmetry is robust against spin-independent disorder and interactions, and is generated by operators whose wavevector depends on the coupling strength. It renders the spin lifetime infinite at this wavevector, giving rise to a Persistent Spin Helix (PSH). We obtain the spin fluctuation dynamics at, and away, from the symmetry point, and suggest experiments to observe the PSH.

  1. STBC AF relay for unmanned aircraft system

    NASA Astrophysics Data System (ADS)

    Adachi, Fumiyuki; Miyazaki, Hiroyuki; Endo, Chikara

    2015-01-01

    If a large scale disaster similar to the Great East Japan Earthquake 2011 happens, some areas may be isolated from the communications network. Recently, unmanned aircraft system (UAS) based wireless relay communication has been attracting much attention since it is able to quickly re-establish the connection between isolated areas and the network. However, the channel between ground station (GS) and unmanned aircraft (UA) is unreliable due to UA's swing motion and as consequence, the relay communication quality degrades. In this paper, we introduce space-time block coded (STBC) amplify-and-forward (AF) relay for UAS based wireless relay communication to improve relay communication quality. A group of UAs forms single frequency network (SFN) to perform STBC-AF cooperative relay. In STBC-AF relay, only conjugate operation, block exchange and amplifying are required at UAs. Therefore, STBC-AF relay improves the relay communication quality while alleviating the complexity problem at UAs. It is shown by computer simulation that STBC-AF relay can achieve better throughput performance than conventional AF relay.

  2. Antiferromagnetic spin structure and lithium ion diffusion in Li2MnO3 probed by μ+SR

    NASA Astrophysics Data System (ADS)

    Sugiyama, Jun; Mukai, Kazuhiko; Nozaki, Hiroshi; Harada, Masashi; Månsson, Martin; Kamazawa, Kazuya; Andreica, Daniel; Amato, Alex; Hillier, Adrian D.

    2013-01-01

    In order to elucidate the antiferromagnetic (AF) spin structure below TN˜35 K and to clarify the diffusive behavior of Li+ ions in the layered compound Li2MnO3, we have performed a muon-spin rotation and relaxation (μ+SR) experiment using a powder sample in the temperature range between 2 and 500 K. Below TN, the zero-field (ZF-) μ+SR spectrum showed a clear oscillation that consists of two muon-spin precession signals with different frequencies. Combining with the dipole field calculations, it was found that the most probable spin structure for Li2MnO3 is the Cx-type AF order in which Mn moments align parallel or antiparallel to the a axis in the [Li1/3Mn2/3]O2 layer, and a ferromagnetic chain along the a axis aligns antiferromagnetically along both the b and c axes. The ordered Mn moment was estimated as 2.62μB at 2 K. In the paramagnetic state, ZF- and longitudinal-field μ+SR spectra exhibited a dynamic nuclear field relaxation. From the temperature dependence of the field distribution width, the Li+ ions were found to diffuse mainly along the c axis through the Li ion in the [Li1/3Mn2/3]O2 layer. Also, based on the field fluctuation rate, a self-diffusion coefficient of Li+ ions (DLi) at 300 K was estimated as 4.7(4)×10-11 cm2/s with the thermal activation energy Ea=0.156(3) eV.

  3. Universal Conductance Fluctuation in Two-Dimensional Topological Insulators.

    PubMed

    Choe, Duk-Hyun; Chang, K J

    2015-01-01

    Despite considerable interest in two-dimensional (2D) topological insulators (TIs), a fundamental question still remains open how mesoscopic conductance fluctuations in 2D TIs are affected by spin-orbit interaction (SOI). Here, we investigate the effect of SOI on the universal conductance fluctuation (UCF) in disordered 2D TIs. Although 2D TI exhibits UCF like any metallic systems, the amplitude of these fluctuations is distinguished from that of conventional spin-orbit coupled 2D materials. Especially, in 2D systems with mirror symmetry, spin-flip scattering is forbidden even in the presence of strong intrinsic SOI, hence increasing the amplitude of the UCF by a factor of √2 compared with extrinsic SOI that breaks mirror symmetry. We propose an easy way to experimentally observe the existence of such spin-flip scattering in 2D materials. Our findings provide a key to understanding the emergence of a new universal behavior in 2D TIs. PMID:26055574

  4. Korean Atrial Fibrillation (AF) Network: Genetic Variants for AF Do Not Predict Ablation Success

    PubMed Central

    Choi, Eue-Keun; Park, Jae Hyung; Lee, Ji-Young; Nam, Chung Mo; Hwang, Min Ki; Uhm, Jae-Sun; Joung, Boyoung; Ko, Young-Guk; Lee, Moon-Hyoung; Lubitz, Steven A; Ellinor, Patrick T; Pak, Hui-Nam

    2015-01-01

    Background Genomewide association studies have identified several loci associated with atrial fibrillation (AF) and have been reportedly associated with response to catheter ablation for AF in patients of European ancestry; however, associations between top susceptibility loci and AF recurrence after ablation have not been examined in Asian populations. We examined whether the top single nucleotide polymorphisms (SNPs) at chromosomes 4q25 (PITX2), 16q22 (ZFHX3), and 1q21 (KCNN3) were associated with AF in a Korean population and whether these SNPs were associated with clinical outcomes after catheter ablation for AF. Methods and Results We determined the association between 4 SNPs and AF in 1068 AF patients who underwent catheter ablation (74.6% male, aged 57.5±10.9 years, 67.9% paroxysmal AF) and 1068 age- and sex-matched controls. The SNPs at the PITX2 and ZFHX3 loci, but not the KCNN3 locus, were significantly associated with AF (PITX2/rs6843082_G: odds ratio 3.41, 95% CI 2.55 to 4.55, P=1.32×10−16; PITX2/rs2200733_T: odds ratio 2.05, 95% CI 1.66 to 2.53, P=2.20×10−11; ZFHX3/rs2106261_A: odds ratio 2.33, 95% CI 1.87 to 2.91, P=3.75×10−14; KCNN3/rs13376333_T: odds ratio 1.74, 95% CI 0.93 to 3.25, P=0.085). Among those patients who underwent catheter ablation for AF, none of the top AF-associated SNPs were associated with long-term clinical recurrence of AF after catheter ablation. Conclusions SNPs at the PITX2 and ZFHX3 loci were strongly associated with AF in Korean patients. In contrast to prior reports, none of the 4 top AF-susceptibility SNPs predicted clinical recurrence after catheter ablation. PMID:26272656

  5. Vaporization of Kitaev Spin Liquids

    NASA Astrophysics Data System (ADS)

    Nasu, Joji; Udagawa, Masafumi; Motome, Yukitoshi

    2014-11-01

    The quantum spin liquid is an exotic quantum state of matter in magnets. This state is a spin analog of liquid helium that does not solidify down to the lowest temperature due to strong quantum fluctuations. In conventional fluids, the liquid and gas possess the same symmetry and adiabatically connect to each other by bypassing the critical end point. We find that the situation is qualitatively different in quantum spin liquids realized in a three-dimensional Kitaev model; both gapless and gapped quantum spin liquid phases at low temperatures are always distinguished from the high-temperature paramagnet (spin gas) by a phase transition. The results challenge the common belief that the absence of thermodynamic singularity down to the lowest temperature is a symptom of a quantum spin liquid.

  6. Spin liquid phases of large spin Mott insulating ultracold atoms

    NASA Astrophysics Data System (ADS)

    Rutkowski, Todd C.; Lawler, Michael J.

    2015-03-01

    Understanding exotic forms of magnetism, primarily those driven by large spin fluctuations such as the quantum spin liquid state, is a major goal of condensed matter physics. But, the relatively small number of viable candidate materials poses a difficulty. We believe this problem can be solved by Mott insulating ultracold atoms with large spin moments that interact via whole-atom exchange. The large spin fluctuations of this exchange could stabilize exotic physics similar to condensed matter systems, all in an extremely tunable environment. We have approached the problem by performing a mean field theory for spin-f bosons in an optical lattice which is exact in the large-f limit. This setting is similar to that of SU(N) magnetism proposed for alkali-earth atoms but without the SU(N) symmetry. We find that states with long-range order, such as the spin nematic phase of f = 1 Na atoms, become highly entangled spin-liquid-like states for f = 3 Cr atoms. This is evidence that the magnetic phase diagram for Mott insulating atoms at larger spins generically contains exotic forms of magnetism.

  7. Efficient suppression of Overhauser field fluctuations with DNP

    NASA Astrophysics Data System (ADS)

    McNeil, Robert; Botzem, Tim; Tenberg, Stefanie; Rubbert, Sebastian; Bluhm, Hendrik

    2015-03-01

    In certain spin-qubit schemes the Overhauser field is a tuned control parameter and in many spin qubits this fluctuating nuclear field is a significant factor limiting coherence. Nuclear spins can be driven via dynamic nuclear polarisation (DNP) to a chosen field and selective feedback applied narrowing the distribution of nuclear Overhauser field fluctuations. The achievable narrowing of the Overhauser field is related to the maximum pump rate and previous experiments on gated GaAs quantum dots were limited by the pump rate of the pumping mechanism used. We present a method to reduce nuclear fluctuations by increasing the max achievable pump rate. Sequentially applying two ac electric fields with frequencies slightly detuned from the desired Larmor frequency results in a pump curve with a stable fixed point. In the absence of spin-orbit interaction, driving electron spin flips via electric dipole spin resonance (EDSR) will also drive nuclear spin flips and this scheme is expected to result in stronger pumping and efficient suppression of the Overhauser field fluctuations. We will present experimental evidence of this driven nuclear polarization including tracking of EDSR resonances.

  8. Spin-current probe for phase transition in an insulator.

    PubMed

    Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N'Diaye, Alpha T; Tan, Ali; Uchida, Ken-Ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; Qiu, Z Q; Saitoh, Eiji

    2016-01-01

    Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we show that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is a flux of spin without an electric charge and its transport reflects spin excitation. We demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices. PMID:27573443

  9. Spin-current probe for phase transition in an insulator

    DOE PAGESBeta

    Qiu, Zhiyong; Li, Jia; Hou, Dazhi; Arenholz, Elke; N’Diaye, Alpha T.; Tan, Ali; Uchida, Ken-ichi; Sato, Koji; Okamoto, Satoshi; Tserkovnyak, Yaroslav; et al

    2016-08-30

    Spin fluctuation and transition have always been one of the central topics of magnetism and condensed matter science. Experimentally, the spin fluctuation is found transcribed onto scattering intensity in the neutron-scattering process, which is represented by dynamical magnetic susceptibility and maximized at phase transitions. Importantly, a neutron carries spin without electric charge, and therefore it can bring spin into a sample without being disturbed by electric energy. However, large facilities such as a nuclear reactor are necessary. Here we present that spin pumping, frequently used in nanoscale spintronic devices, provides a desktop microprobe for spin transition; spin current is amore » flux of spin without an electric charge and its transport reflects spin excitation. Additionally, we demonstrate detection of antiferromagnetic transition in ultra-thin CoO films via frequency-dependent spin-current transmission measurements, which provides a versatile probe for phase transition in an electric manner in minute devices.« less

  10. Intrinsic topological superfluidity - fluctuations and response

    NASA Astrophysics Data System (ADS)

    Levin, K.; Wu, Chien-Te; Anderson, Brandon; Boyack, Rufus

    Recent interest in topological superconductivity is based primarily on exploiting proximity effects to obtain this important phase. However, in cold gases it is possible to contemplate ``intrinsic'' topological superfluidity produced with a synthetic spin-orbit coupling and Zeeman field. It is important for such future experiments to establish how low in temperature one needs to go to reach the ordered phase. Similarly, it will be helpful to have a probe of the normal (pseudogap) phase to determine if the ultimate superfluid order will be topological or trivial. In this talk, we address these issues by considering fluctuation effects in such a superfluid, and calculate the critical transition temperature and response functions. We see qualitative signatures of topological superfluidity in spin and charge response functions. We also explore the suppression of superfluidity due to fluctuations, and importantly find that the temperature scales necessary to reach topological superfluidity are reasonably accessible

  11. Persistence of singlet fluctuations in the coupled spin tetrahedra system Cu2Te2O5Br2 revealed by high-field magnetization, 79Br NQR, and 125Te NMR

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Choi, K.-Y.; Berger, H.; Büchner, B.; Grafe, H.-J.

    2012-11-01

    We present high-field magnetization and 79Br nuclear quadrupole resonance (NQR) and 125Te nuclear magnetic resonance (NMR) studies in the weakly coupled Cu2+ (S=1/2) tetrahedral system Cu2Te2O5Br2. The field-induced level crossing effects were observed by the magnetization measurements in a long-ranged magnetically ordered state which was confirmed by a strong divergence of the spin-lattice relaxation rate T1-1 at T0=13.5 K. In the paramagnetic state, T1-1 reveals an effective singlet-triplet spin gap much larger than that observed by static bulk measurements. Our results imply that the inter- and the intratetrahedral interactions compete, but at the same time they cooperate strengthening effectively the local intratetrahedral exchange couplings. We discuss that the unusual feature originates from the frustrated intertetrahedral interactions.

  12. Degradation of AF1Q by chaperone-mediated autophagy

    SciTech Connect

    Li, Peng; Ji, Min; Lu, Fei; Zhang, Jingru; Li, Huanjie; Cui, Taixing; Li Wang, Xing; Tang, Dongqi; Ji, Chunyan

    2014-09-10

    AF1Q, a mixed lineage leukemia gene fusion partner, is identified as a poor prognostic biomarker for pediatric acute myeloid leukemia (AML), adult AML with normal cytogenetic and adult myelodysplastic syndrome. AF1Q is highly regulated during hematopoietic progenitor differentiation and development but its regulatory mechanism has not been defined clearly. In the present study, we used pharmacological and genetic approaches to influence chaperone-mediated autophagy (CMA) and explored the degradation mechanism of AF1Q. Pharmacological inhibitors of lysosomal degradation, such as chloroquine, increased AF1Q levels, whereas activators of CMA, including 6-aminonicotinamide and nutrient starvation, decreased AF1Q levels. AF1Q interacts with HSPA8 and LAMP-2A, which are core components of the CMA machinery. Knockdown of HSPA8 or LAMP-2A increased AF1Q protein levels, whereas overexpression showed the opposite effect. Using an amino acid deletion AF1Q mutation plasmid, we identified that AF1Q had a KFERQ-like motif which was recognized by HSPA8 for CMA-dependent proteolysis. In conclusion, we demonstrate for the first time that AF1Q can be degraded in lysosomes by CMA. - Highlights: • Chaperone-mediated autophagy (CMA) is involved in the degradation of AF1Q. • Macroautophagy does not contribute to the AF1Q degradation. • AF1Q has a KFERQ-like motif that is recognized by CMA core components.

  13. AFS Estuaries Section - A Successful Partnership

    EPA Science Inventory

    The Estuaries Section of the American Fisheries Society offers travel awards to students in support of their attendance and presentations at the AFS meeting. Since 2007, the Southern Association of Marine Laboratories has partnered with the Estuaries Section to sponsor two stude...

  14. Charge dynamics and spin order in doped Hubbard models

    SciTech Connect

    Kampf, A.P.; Brenig, W.

    1994-04-01

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

  15. Steady-state spin squeezing generation in diamond nanostructures

    NASA Astrophysics Data System (ADS)

    Ma, Yong-Hong; Zhang, Xue-Feng

    2014-04-01

    As one kind of many body entangled states, spin squeezed states can be used to implement the high precise measurement beyond the standard quantum limit. Inspired by the novel spin squeezing scheme based on phonon-induced spin-spin interactions [S. D. Bennett et al., Phys. Rev. Lett. 110, 156402 (2013), 10.1103/PhysRevLett.110.156402], we reexamine the steady-state behaviors for the spin ensemble in diamond nanostructures by exerting a controllable microwave field. By using the phase-space approach we calculate analytically fluctuations of collective spin operators. We find that there is bistability and spin squeezing for the steady-state spin ensemble, despite the mechanical damping considered. Moreover, our work shows that bistability and spin squeezing can be controlled by microwave field and Zeeman splitting. The present scheme can be used to increase the stability of spin clocks, magnetometers, and other measurements based on spin-spin interaction in diamond nanostructures.

  16. Spin slush in an extended spin ice model

    PubMed Central

    Rau, Jeffrey G.; Gingras, Michel J. P.

    2016-01-01

    We present a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. We find that this disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins, while others fluctuate quickly down to zero temperature. We thus call this state spin slush, in analogy to the heterogeneous mixture of solid and liquid water. This behaviour is driven by the structure of the ground-state manifold which extends the celebrated two-in/two-out ice states to include branching structures built from three-in/one-out, three-out/one-in and all-in/all-out tetrahedra defects. Distinctive liquid-like patterns in the magnetic correlations serve as a signature of this intermediate range order. Possible applications to materials as well the effects of quantum tunnelling are discussed. PMID:27470199

  17. Spin slush in an extended spin ice model

    NASA Astrophysics Data System (ADS)

    Rau, Jeffrey G.; Gingras, Michel J. P.

    2016-07-01

    We present a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. We find that this disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins, while others fluctuate quickly down to zero temperature. We thus call this state spin slush, in analogy to the heterogeneous mixture of solid and liquid water. This behaviour is driven by the structure of the ground-state manifold which extends the celebrated two-in/two-out ice states to include branching structures built from three-in/one-out, three-out/one-in and all-in/all-out tetrahedra defects. Distinctive liquid-like patterns in the magnetic correlations serve as a signature of this intermediate range order. Possible applications to materials as well the effects of quantum tunnelling are discussed.

  18. Spin slush in an extended spin ice model.

    PubMed

    Rau, Jeffrey G; Gingras, Michel J P

    2016-01-01

    We present a new classical spin liquid on the pyrochlore lattice by extending spin ice with further neighbour interactions. We find that this disorder-free spin model exhibits a form of dynamical heterogeneity with extremely slow relaxation for some spins, while others fluctuate quickly down to zero temperature. We thus call this state spin slush, in analogy to the heterogeneous mixture of solid and liquid water. This behaviour is driven by the structure of the ground-state manifold which extends the celebrated two-in/two-out ice states to include branching structures built from three-in/one-out, three-out/one-in and all-in/all-out tetrahedra defects. Distinctive liquid-like patterns in the magnetic correlations serve as a signature of this intermediate range order. Possible applications to materials as well the effects of quantum tunnelling are discussed. PMID:27470199

  19. Nernst coefficient and magnetoresistance in high-T(c) superconductors: the role of superconducting fluctuations.

    PubMed

    Kontani, Hiroshi

    2002-12-01

    In high-T(c) cuprates, the Nernst coefficient (nu) as well as the magnetoresistance (Deltarho/rho) increases drastically below the pseudogap temperature, T(*), which attracts much attention as a key phenomenon in the pseudogap region. We study these transport phenomena in terms of the fluctuation-exchange+T-matrix approximation. In this present theory, the d-wave superconducting (SC) fluctuations, which are mediated by antiferromagnetic (AF) correlations, become dominant below T(*). We especially investigate the vertex corrections both for the charge current and the heat one to keep the conservation laws. As a result, the mysterious behaviors of nu and Deltarho/rho are naturally explained as the reflection of the enhancement of the SC fluctuation, without assuming thermally excited vortices. The present result suggests that the pseudogap phenomena are well described in terms of the Fermi liquid with AF and SC fluctuations. PMID:12485031

  20. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    SciTech Connect

    Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.

    2015-04-30

    Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.

  1. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    NASA Astrophysics Data System (ADS)

    Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.

    2015-04-01

    Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spin ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using ``two-color'' optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.

  2. Health Information in Somali (af Soomaali): MedlinePlus

    MedlinePlus

    ... af Soomaali (Somali) Bilingual PDF Health Information Translations Animal Bites Animal Bites and Scratches Qaniinyada iyo Xagashada Xayawaanka - af ... Soomaali (Somali) Bilingual PDF Health Information Translations Radiation Therapy Preventing Infections When Your White Blood Cell Count ...

  3. Health Information in Somali (af Soomaali): MedlinePlus

    MedlinePlus

    ... Bilingual PDF Health Information Translations Appendectomy for a Child Qabsin-saarid ilmo - af Soomaali (Somali) Bilingual PDF ... Somali) Bilingual PDF Health Information Translations Asthma in Children Nebulizer Treatments Daawenta wal in Xaqiiqsanaan - af Soomaali ( ...

  4. Geometrical spin symmetry and spin

    SciTech Connect

    Pestov, I. B.

    2011-07-15

    Unification of General Theory of Relativity and Quantum Mechanics leads to General Quantum Mechanics which includes into itself spindynamics as a theory of spin phenomena. The key concepts of spindynamics are geometrical spin symmetry and the spin field (space of defining representation of spin symmetry). The essence of spin is the bipolar structure of geometrical spin symmetry induced by the gravitational potential. The bipolar structure provides a natural derivation of the equations of spindynamics. Spindynamics involves all phenomena connected with spin and provides new understanding of the strong interaction.

  5. Magnetic monopoles in quantum spin ice

    NASA Astrophysics Data System (ADS)

    Petrova, Olga; Moessner, Roderich; Sondhi, Shivaji

    Typical spin ice materials can be modeled using classical Ising spins. The geometric frustration of the pyrochlore lattice causes the spins to satisfy ice rules, whereas a violation of the ice constraint constitutes an excitation. Flipping adjacent spins fractionalizes the excitation into two monopoles. Long range dipolar spin couplings result in Coulombic interactions between charges, while the leading effect of quantum fluctuations is to provide the monopoles with kinetic energy. We study the effect of adding quantum dynamics to spin ice, a well-known classical spin liquid, with a particular view of how to best detect its presence in experiment. For the weakly diluted quantum spin ice, we find a particularly crisp phenomenon, namely, the emergence of hydrogenic excited states in which a magnetic monopole is bound to a vacancy at various distances.

  6. Proteins, fluctuations and complexity

    SciTech Connect

    Frauenfelder, Hans; Chen, Guo; Fenimore, Paul W

    2008-01-01

    Glasses, supercooled liquids, and proteins share common properties, in particular the existence of two different types of fluctuations, {alpha} and {beta}. While the effect of the {alpha} fluctuations on proteins has been known for a few years, the effect of {beta} fluctuations has not been understood. By comparing neutron scattering data on the protein myoglobin with the {beta} fluctuations in the hydration shell measured by dielectric spectroscopy we show that the internal protein motions are slaved to these fluctuations. We also show that there is no 'dynamic transition' in proteins near 200 K. The rapid increase in the mean square displacement with temperature in many neutron scattering experiments is quantitatively predicted by the {beta} fluctuations in the hydration shell.

  7. Thermal field fluctuations in a magnetic tip / implications for magnetic resonance force microscopy

    NASA Astrophysics Data System (ADS)

    Hannay, J. D.; Chantrell, R. W.; Rugar, D.

    2000-05-01

    Thermally excited magnetic fluctuations are fundamental to the behavior of small ferromagnetic particles and have practical consequences for the proposed detection of individual spins by magnetic resonance force microscopy (MRFM). In particular, fluctuating fields from a nearby magnetic tip can increase the relaxation rate of spins in a sample if there is significant spectral density of field fluctuation at the Larmor frequency of the target spin. As an initial step toward understanding this issue, magnetic field fluctuations have been simulated which emanate from a magnetic tip with dimensions 60 nm×60 nm×2 μm. It was found that the fluctuations in a cobalt magnetic tip were too strong for MRFM experiments aimed at detecting individual electron spins. However, the results obtained for a PrFeB tip fell within the tolerance required.

  8. Protecting a Solid-State Spin from Decoherence Using Dressed Spin States

    NASA Astrophysics Data System (ADS)

    Golter, D. Andrew; Baldwin, Thomas K.; Wang, Hailin

    2014-12-01

    We report experimental studies of dressing an electron spin in diamond with resonant and continuous microwave fields to protect the electron spin from magnetic fluctuations induced by the nuclear spin bath. We use optical coherent population trapping (CPT) to probe the energy level structure, optically induced spin transitions, and spin decoherence rates of the dressed spin states. Dressing an electron spin with resonant microwaves at a coupling rate near 1 MHz leads to a 50 times reduction in the linewidth of the spin transition underlying the CPT process, limited by transit-time broadening. Compared with dynamical decoupling, where effects of the bath are averaged out at specific times, the dressed spin state provides a continuous protection from decoherence.

  9. Feedback control of nuclear spin bath for a single hole spin in a quantum dot

    NASA Astrophysics Data System (ADS)

    Pang, Hongliang; Gong, Zhirui; Yao, Wang

    2014-03-01

    In a semiconductor quantum dot, the nuclear spin bath plays an important role as the ultimate environment of an electron or hole spin at low temperature. Through dynamic nuclear spin polarization driven by an oscillating electric field, we show that feedback controls can be implemented on the nuclear spin bath of a single hole spin. The feedback controls utilize the anisotropic hyperfine interaction between the hole spin and the nuclear spins. The negative feedback can suppress the statistical fluctuations of the nuclear hyperfine field and lead to longer coherence time of the hole spin. Positive feedback can possibly lead to cat like state of nuclear spin bath. The efficiency of the controls schemes is investigated under different parameters and control strategies. The work is supported by the Croucher Foundation under the Croucher Innovation Award, and the Research Grant Council of Hong Kong (HKU706309P, HKU8/CRF/11G).

  10. Electrical control of single spin dynamics

    NASA Astrophysics Data System (ADS)

    Petta, Jason

    2012-02-01

    Over ten years ago, Daniel Loss and David DiVincenzo proposed using the spin of a single electron as a quantum bit. At the time of the proposal, it was not possible to trap a single electron in a device and measure its spin, let alone demonstrate control of quantum coherence. In this talk I will describe recent progress in the field, focusing on two new methods for single spin control that have been developed by my group at Princeton. The first method is based on quantum interference and implements spin-interferometry on a chip. The second method utilizes the strong spin-orbit coupling of InAs. By shifting the orbital position of the electronic wavefunction at gigahertz frequencies, we can control the orientation of a single electron spin and measure the full g-tensor, which exhibits a large anisotropy due to spin-orbit interactions. Both methods for single spin control are orders of magnitude faster than conventional electron spin resonance and allow investigations of single spin coherence in the presence of fluctuating nuclear and spin-orbit fields. I will also describe recent efforts to transfer these methods to silicon quantum dots, where the effects of fluctuating nuclear fields are much smaller.

  11. Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba1-xKxFe2As2 Studied by 75As Nuclear Magnetic Resonance Measurement0.1143/JPSJ.81.054704

    SciTech Connect

    Hirano, Masanori; Yamada, Yuji; Saito, Taku; Nagashima, Ryo; Konishi, Takehisa; Toriyama, Tatsuya; Ohta, Yukinori; Fukazawa, Hideto; Kohori, Yoh; Furukawa, Yuji; Kihou, Kunihiro; Lee, Chul-Ho; Eisaki, Hiroshi

    2012-04-12

    We have performed 75As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on single-crystalline Ba1-xKxFe2As2 for x = 0.27–1. 75As nuclear quadruple resonance frequency (νQ) increases linearly with increasing x. The Knight shift K in the normal state shows Pauli paramagnetic behavior with a weak temperature T dependence. K increases gradually with increasing x. By contrast, the nuclear spin–lattice relaxation rate 1/T1 in the normal state has a strong T dependence, which indicates the existence of large antiferomagnetic (AF) spin fluctuations for all x's. The T dependence of 1/T1 shows a gaplike behavior below approximately 100 K for 0.6 < x < 0.9. This behaviors is well explained by the change in the band structure with the expansion of hole Fermi surfaces and the shrinkage and disappearance of electron Fermi surfaces at the Brillouin zone (BZ) with increasing x. The anisotropy of 1/T1, represented by the ratio of 1/T1ab to 1/T1c, is always larger than 1 for all x's, which indicates that stripe-type AF fluctuations are dominant in this system. The K in the superconducting (SC) state decreases, which corresponds to the appearance of spin-singlet superconductivity. The T dependence of 1/T1 in the SC state indicates a multiple-SC-gap feature. A simple two-gap model analysis shows that the larger superconducting gap gradually decreases with increasing x from 0.27 to 1 and a smaller gap decreases rapidly and nearly vanishes for x > 0.6 where electron pockets in BZ disappear.

  12. Frustration and Fluctuations in Systems with Quenched Disorder

    NASA Astrophysics Data System (ADS)

    Stein, D. L.

    As Phil Anderson noted long ago, frustration can be generally defined by measuring the fluctuations in the coupling energy across a plane boundary between two large blocks of material. Since that time, a number of groups have studied the free energy fluctuations between (putative) distinct spin glass thermodynamic states. While upper bounds on such fluctuations have been obtained, useful lower bounds have been more difficult to derive. I present a history of these efforts, and briefly discuss recent work showing that free energy fluctuations between certain classes of distinct thermodynamic states (if they exist) scale as the square root of the volume. The perspective offered here is that the power and generality of the Anderson conception of frustration suggests a potential approach toward resolving some longstanding and central issues in spin glass physics.

  13. Microfluidic Pumps Containing Teflon [Trademark] AF Diaphragms

    NASA Technical Reports Server (NTRS)

    Willis, Peter; White, Victor; Grunthaner, Frank; Ikeda, Mike; Mathies, Richard A.

    2009-01-01

    Microfluidic pumps and valves based on pneumatically actuated diaphragms made of Teflon AF polymers are being developed for incorporation into laboratory-on-a-chip devices that must perform well over temperature ranges wider than those of prior diaphragm-based microfluidic pumps and valves. Other potential applications include implanted biomedical microfluidic devices, wherein the biocompatability of Teflon AF polymers would be highly advantageous. These pumps and valves have been demonstrated to function stably after cycling through temperatures from -125 to 120 C. These pumps and valves are intended to be successors to similar prior pumps and valves containing diaphragms made of polydimethylsiloxane (PDMS) [commonly known as silicone rubber]. The PDMS-containing valves ae designed to function stably only within the temperature range from 5 to 80 C. Undesirably, PDMS membranes are somwehat porous and retain water. PDMS is especially unsuitable for use at temperatures below 0 C because the formation of ice crystals increases porosity and introduces microshear.

  14. Cross-correlation spin noise spectroscopy of heterogeneous interacting spin systems

    DOE PAGESBeta

    Roy, Dibyendu; Yang, Luyi; Crooker, Scott A.; Sinitsyn, Nikolai A.

    2015-04-30

    Interacting multi-component spin systems are ubiquitous in nature and in the laboratory. As such, investigations of inter-species spin interactions are of vital importance. Traditionally, they are studied by experimental methods that are necessarily perturbative: e.g., by intentionally polarizing or depolarizing one spin species while detecting the response of the other(s). Here, we describe and demonstrate an alternative approach based on multi-probe spin noise spectroscopy, which can reveal inter-species spin interactions - under conditions of strict thermal equilibrium - by detecting and cross-correlating the stochastic fluctuation signals exhibited by each of the constituent spin species. Specifically, we consider a two-component spinmore » ensemble that interacts via exchange coupling, and we determine cross-correlations between their intrinsic spin fluctuations. The model is experimentally confirmed using “two-color” optical spin noise spectroscopy on a mixture of interacting Rb and Cs vapors. Noise correlations directly reveal the presence of inter-species spin exchange, without ever perturbing the system away from thermal equilibrium. These non-invasive and noise-based techniques should be generally applicable to any heterogeneous spin system in which the fluctuations of the constituent components are detectable.« less

  15. The Spin-flop Transition in Antiferromagnetic Superlattices

    NASA Astrophysics Data System (ADS)

    Te Velthuis, S. G. E.; Jiang, J. S.; Bader, S. D.; Felcher, G. P.

    2002-03-01

    An antiferromagnetically (AF) coupled Fe/Cr(211) superlattice with uniaxial magnetic anisotropy has been used to study the spin-flop transition in an AF with a finite number of layers. It has been predicted that, at a field a lower than the bulk spin-flop field, a domain wall is created at the surface and rapidly propagates toward the center of the sublattice^1. We present extensive polarized neutron reflectivity measurements that give the evolution of the magnetic configuration during the spin-flop transition and prove directly the existence of such a state, in which the superlattice splits in two anti-phase, AF domains. Magneto-optic Kerr measurements with the field tilted from the easy axis show that the spin-flop is stable over a finite angular region. In contrast to the situation for a bulk AF, the first-order nature of the spin-flop transition is preserved off-axis, but we report that the detailed character of the transition is altered. ^1R.W. Wang, D.L. Mills, Eric E. Fullerton, J.E. Mattson, and S.D. Bader, Phys. Rev. Lett. 72 (1994) 920.

  16. Lower preoperative fluctuation of heart rate variability is an independent risk factor for postoperative atrial fibrillation in patients undergoing major pulmonary resection

    PubMed Central

    Ciszewski, Pawel; Tyczka, Joanna; Nadolski, Jacek; Roszak, Magdalena; Dyszkiewicz, Wojciech

    2013-01-01

    OBJECTIVES The following study presents a special independent atrial fibrillation (AF) risk factor—preoperative fluctuation of heart rate variability (HRV), as well as other perioperative AF risk factors in patients qualified for pneumonectomy and undergoing pneumonectomy or lobectomy for lung cancer. METHODS The prospective study was performed in patients who had undergone anatomical resection for non-small-cell lung cancer. A total of 117 patients (92 men and 25 women) qualified for statistical research. In order to determine the risk factors, all patients were divided into two groups: Group A—98 patients without AF and Group B—19 patients with AF during the perioperative time. A number of different risk factors of AF have been analysed and further divided into preoperative, operative and postoperative. RESULTS Postoperative AF occurred in 19 patients (16%), all of them were male. The patients with higher short-term HRV parameters (SD1, RMSSD), slower mean heart rate and those with a lower fluctuation of HRV-related parameters (HRV Afternoon, Night, Day (A/N/D)) before the operation, were more prone to AF. Postoperative risk of AF was higher in patients with a higher number of ventricular ectopic beats before the operation, a higher number of supraventricular and ventricular ectopic beats and a higher maximal heart rate after the operation. Statistical analysis revealed that male gender and the extent of pulmonary resection, particularly left pneumonectomy, constituted significant risk factors. AF was more often observed in patients who had ASA physical status score of III, in comparison with ASAI and ASAII patients. CONCLUSIONS Along with other concomitant AF risk factors presented in this work, the evaluation of the fluctuation tendencies of HRV parameters should be taken into consideration before any major lung resection. The balance disturbance between the sympathetic and parasympathetic nervous systems is responsible for AF. PMID:23832838

  17. Why Cr needs a spin-density wave to become antiferromagnetic.

    NASA Astrophysics Data System (ADS)

    Marcus, P. M.; Moruzzi, V. L.; Qiu, S. L.

    1998-03-01

    First-principles, total-energy calculations on bcc Cr show that at the volume of the energy minimum Cr is nonmagnetic, i.e., the type-I antiferromagnetic (AF) phase does not exist for bcc Cr. However 0.3% expansion of the lattice constant gives a 2nd-order phase transition to the AF phase with a rapidly growing magnetic moment at the cost of a small amount of strain energy.( Marcus, Qiu, Moruzzi, submitted to Phys. Rev. B.) The AF spin-density wave (AF-SDW) modulates the moment of the AF phase over 20 lattice constants to reduce the energy, hence compensate the strain energy. (K. Hirai, J. Phys. Soc. Jpn. 66), 560 (1997). Further arguments to support this lattice-expansion theory of the AF-SDW come from a bulk modulus in agreement with experiment and from the effects of increasing the electron density, which agree with alloy behavior.

  18. Fluctuations in nuclear fragmentation

    SciTech Connect

    Aranda, A.; Dorso, C.O.; Furci, V.; Lopez, J.A.

    1995-12-01

    Heavy ion collisions can be used to study the thermodynamics of hot and dense nuclear matter only if the initial mass and energy fluctuations that lead to fragmentation are of thermal origin and survive the disassembly process. If this is the case, the observed fragment multiplicity should be directly related to those initial fluctuations and to the conditions of temperature and density causing them. The feasibility of this scenario is demonstrated with a molecular dynamics study of the evolution of mass and energy fluctuations, and fluctuations of the phase-space density. First, it is verified that the fluctuations leading to fragmentation are indeed early ones. Second, it is determined that different initial conditions of density and temperature can indeed produce varying final fragment multiplicities. The {rho}-{ital T} plane is mapped to the fragment multiplicity with good precision. This mapping should be easily reproducible with existing experimental data.

  19. Hadronic Correlations and Fluctuations

    SciTech Connect

    Koch, Volker

    2008-10-09

    We will provide a review of some of the physics which can be addressed by studying fluctuations and correlations in heavy ion collisions. We will discuss Lattice QCD results on fluctuations and correlations and will put them into context with observables which have been measured in heavy-ion collisions. Special attention will be given to the QCD critical point and the first order co-existence region, and we will discuss how the measurement of fluctuations and correlations can help in an experimental search for non-trivial structures in the QCD phase diagram.

  20. Spatial fluctuation theorem

    NASA Astrophysics Data System (ADS)

    Pérez-Espigares, Carlos; Redig, Frank; Giardinà, Cristian

    2015-08-01

    For non-equilibrium systems of interacting particles and for interacting diffusions in d-dimensions, a novel fluctuation relation is derived. The theorem establishes a quantitative relation between the probabilities of observing two current values in different spatial directions. The result is a consequence of spatial symmetries of the microscopic dynamics, generalizing in this way the Gallavotti-Cohen fluctuation theorem related to the time-reversal symmetry. This new perspective opens up the possibility of direct experimental measurements of fluctuation relations of vectorial observables.

  1. Precrystallisation fluctuation phenomena in homopolymer melts.

    NASA Astrophysics Data System (ADS)

    Ryan, A. J.; Fairclough, J. P. A.; Terrill, N. J.; Young, R. J.; Towns-Andrews, E.; Komanschek, B. U.

    1997-03-01

    In order to separate nucleation from growth, two types of experiments have been performed on polypropylene, polyethylene, polyethylene oxide and polyethylene terepthalate. Rapid crystallisations were studied by melt extrusion of a tape. The extrusion of tape is a steady-state process where the distance down the spin-line is directly proportional to the crystallisation time. This allowed long data collection times (minutes) for very short crystallisation times. Prior to the development of crystallinity, well resolved, oriented small-angle patterns could be collected with length scales (50-200Åand intensities that grew down the spin-line. The orientation of the patterns was caused by the coupling of the density fluctuations with the elongational flow-field. Slow crystallisations with long induction times have been studied by simultaneous SAXS and WAXS. Clear development of small angle scattering, due to the density fluctuations, with a characteristic length scale of ≈ 100Åwas observed prior to the presence of crystals identified by wide-angle scattering. The growth of these fluctuations is analysed in terms of Cahn Hilliard kinetics. We could estimate the both the dominant length scale and the effective diffusion coefficient and by conducting experiments at a series of temperature we could find the stability limit.

  2. Fluctuations In Electrohydrodynamic Instability

    NASA Astrophysics Data System (ADS)

    Bianco, Francesco; Lucchesi, Mauro; Capaccioli, Simone; Fronzoni, Leone; Allegrini, Paolo

    2005-11-01

    Electrohydrodynamic Convection in Liquid Crystals (EHC) is a good system for the experimental study of spatio-temporal chaos. Particularly interesting is the behavior of the Nematic in presence of weak turbulence where ordered and disordered states are mixed. In this case, the fluctuations of velocity and electric current, for instance, are typical fluctuations of a system far from equilibrium. Recently some authors have analyzed the amplitude of the fluctuations as function of the applied electric field and they present interesting interpretations provided by some theories. Although important results have been obtained by these authors, many aspects of the dynamical behavior have to be further analyzed as the role of some localized coherences inside the turbulence regions. The direct optical observation allows us to make a correspondence between fluctuations and patterns, providing important information for a theoretical interpretation.

  3. Fluctuations in Photosynthesis

    NASA Astrophysics Data System (ADS)

    Khajeh, Ramin; Nishikida, Dean; Haberstroh, John; Geissler, Phillip L.

    2015-03-01

    The dynamics of the energy gap fluctuations of chromophores in Fenna-Matthews-Olson (FMO) complex can lead to an understanding of the underlying mechanism which is responsible for an efficient exciton energy transfer in such photosynthetic structures. Using Molecular Dynamics simulation results, we investigate trajectory statistics of energy gap fluctuations in chromophores using methods of propagators and Fourier coefficient distributions and examine possible anharmonic signatures in their behavior. Berkeley Lab - Material Science Division.

  4. Direct measurement of antiferromagnetic domain fluctuations.

    PubMed

    Shpyrko, O G; Isaacs, E D; Logan, J M; Feng, Yejun; Aeppli, G; Jaramillo, R; Kim, H C; Rosenbaum, T F; Zschack, P; Sprung, M; Narayanan, S; Sandy, A R

    2007-05-01

    Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago, and have underpinned much science and technology. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometre-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometre distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value-consistent with quantum fluctuations-on cooling below 40 K. PMID:17476263

  5. Scaling metabolic rate fluctuations.

    PubMed

    Labra, Fabio A; Marquet, Pablo A; Bozinovic, Francisco

    2007-06-26

    Complex ecological and economic systems show fluctuations in macroscopic quantities such as exchange rates, size of companies or populations that follow non-Gaussian tent-shaped probability distributions of growth rates with power-law decay, which suggests that fluctuations in complex systems may be governed by universal mechanisms, independent of particular details and idiosyncrasies. We propose here that metabolic rate within individual organisms may be considered as an example of an emergent property of a complex system and test the hypothesis that the probability distribution of fluctuations in the metabolic rate of individuals has a "universal" form regardless of body size or taxonomic affiliation. We examined data from 71 individuals belonging to 25 vertebrate species (birds, mammals, and lizards). We report three main results. First, for all these individuals and species, the distribution of metabolic rate fluctuations follows a tent-shaped distribution with power-law decay. Second, the standard deviation of metabolic rate fluctuations decays as a power-law function of both average metabolic rate and body mass, with exponents -0.352 and -1/4 respectively. Finally, we find that the distributions of metabolic rate fluctuations for different organisms can all be rescaled to a single parent distribution, supporting the existence of general principles underlying the structure and functioning of individual organisms. PMID:17578913

  6. Helical Spin Order from Topological Dirac and Weyl Semimetals

    NASA Astrophysics Data System (ADS)

    Sun, Xiao-Qi; Zhang, Shou-Cheng; Wang, Zhong

    2015-08-01

    We study dynamical mass generation and the resultant helical spin orders in topological Dirac and Weyl semimetals, including the edge states of quantum spin Hall insulators, the surface states of weak topological insulators, and the bulk materials of Weyl semimetals. In particular, the helical spin textures of Weyl semimetals manifest the spin-momentum locking of Weyl fermions in a visible manner. The spin-wave fluctuations of the helical order carry electric charge density; therefore, the spin textures can be electrically controlled in a simple and predictable manner.

  7. Drift transport of helical spin coherence with tailored spin–orbit interactions

    PubMed Central

    Kunihashi, Y.; Sanada, H.; Gotoh, H.; Onomitsu, K.; Kohda, M.; Nitta, J.; Sogawa, T.

    2016-01-01

    Most future information processing techniques using electron spins in non-magnetic semiconductors will require both the manipulation and transfer of spins without their coherence being lost. The spin–orbit effective magnetic field induced by drifting electrons enables us to rotate the electron spins in the absence of an external magnetic field. However, the fluctuations in the effective magnetic field originating from the random scattering of electrons also cause undesirable spin decoherence, which limits the length scale of the spin transport. Here we demonstrate the drift transport of electron spins adjusted to a robust spin structure, namely a persistent spin helix. We find that the persistent spin helix enhances the spatial coherence of drifting spins, resulting in maximized spin decay length near the persistent spin helix condition. Within the enhanced distance of the spin transport, the transport path of electron spins can be modulated by employing time-varying in-plane voltages. PMID:26952129

  8. Penetration depth and absorption mechanisms of spin currents in Ir{sub 20}Mn{sub 80} and Fe{sub 50}Mn{sub 50} polycrystalline films by ferromagnetic resonance and spin pumping

    SciTech Connect

    Merodio, P.; Ghosh, A.; Lemonias, C.; Gautier, E.; Ebels, U.; Chshiev, M.; Béa, H. E-mail: helene.bea@cea.fr; Baltz, V. E-mail: helene.bea@cea.fr

    2014-01-20

    Spintronics relies on the spin dependent transport properties of ferromagnets (Fs). Although antiferromagnets (AFs) are used for their magnetic properties only, some fundamental F-spintronics phenomena like spin transfer torque, domain wall motion, and tunnel anisotropic magnetoresistance also occur with AFs, thus making AF-spintronics attractive. Here, room temperature critical depths and absorption mechanisms of spin currents in Ir{sub 20}Mn{sub 80} and Fe{sub 50}Mn{sub 50} are determined by F-resonance and spin pumping. In particular, we find room temperature critical depths originating from different absorption mechanisms: dephasing for Ir{sub 20}Mn{sub 80} and spin flipping for Fe{sub 50}Mn{sub 50}.

  9. Quadrupolar Spin Orders in FeSe

    NASA Astrophysics Data System (ADS)

    Wang, Zhentao; Nevidomskyy, Andriy

    Motivated by the absence of long-range magnetic order and the strong spin fluctuations observed in the Fe-based superconductor FeSe, we study spin-1 model on a square lattice up to next-nearest neighbor Heisenberg and biquadratic spin exchanges. The zero-temperature variational phase diagram gives the conventional antiferromagnetic order and also more exotic quadrupolar spin phases. These quadrupolar phases do not host long-range magnetic order and preserve time-reversal symmetry, but break the spin SU(2) symmetry. In particular, we observe a robust ferroquadrupolar order (FQ) in immediate proximity to the columnar AFM phase. We envision that FeSe may be positioned within the FQ phase close to the phase boundary. Using the flavor-wave technique, we calculate the structure factor inside the FQ phase and find a Goldstone mode emerging from Q = (0 , 0) , which however bears zero spectral weight at ω = 0 due to time reversal symmetry. At the same time, we observe strong spin fluctuations near (π , 0) / (0 , π) , which agrees with the recent neutron scattering experiments. Further, we calculate the higher order interactions between the (π , 0) and (0 , π) spin fluctuations inside the FQ phase, which may shed light on the C4 symmetry breaking in the nematic phase of FeSe.

  10. Fluctuations in the shape transitions of hot nuclei

    NASA Astrophysics Data System (ADS)

    Pacheco, J. M.; Yannouleas, C.; Broglia, R. A.

    1988-07-01

    The effect of quantal and thermal quadrupole shape fluctuations in the giant dipole response function of hot nuclei at high spin is studied within the Landau theory of phase transitions. The effects are found to be important in the relation of the nuclear shape to the experimental findings and in the identification of shape phase transitions.

  11. Nonlocal Nuclear Spin Quieting in Quantum Dot Molecules: Optically Induced Extended Two-Electron Spin Coherence Time

    NASA Astrophysics Data System (ADS)

    Chow, Colin M.; Ross, Aaron M.; Kim, Danny; Gammon, Daniel; Bracker, Allan S.; Sham, L. J.; Steel, Duncan G.

    2016-08-01

    We demonstrate the extension of coherence between all four two-electron spin ground states of an InAs quantum dot molecule (QDM) via nonlocal suppression of nuclear spin fluctuations in two vertically stacked quantum dots (QDs), while optically addressing only the top QD transitions. Long coherence times are revealed through dark-state spectroscopy as resulting from nuclear spin locking mediated by the exchange interaction between the QDs. Line shape analysis provides the first measurement of the quieting of the Overhauser field distribution correlating with reduced nuclear spin fluctuations.

  12. Nonlocal Nuclear Spin Quieting in Quantum Dot Molecules: Optically Induced Extended Two-Electron Spin Coherence Time.

    PubMed

    Chow, Colin M; Ross, Aaron M; Kim, Danny; Gammon, Daniel; Bracker, Allan S; Sham, L J; Steel, Duncan G

    2016-08-12

    We demonstrate the extension of coherence between all four two-electron spin ground states of an InAs quantum dot molecule (QDM) via nonlocal suppression of nuclear spin fluctuations in two vertically stacked quantum dots (QDs), while optically addressing only the top QD transitions. Long coherence times are revealed through dark-state spectroscopy as resulting from nuclear spin locking mediated by the exchange interaction between the QDs. Line shape analysis provides the first measurement of the quieting of the Overhauser field distribution correlating with reduced nuclear spin fluctuations. PMID:27563998

  13. 4:2:1 conduction of an AF initiating trigger

    PubMed Central

    Kojodjojo, Pipin; Chong, Eric; Lim, Toon Wei; Seow, Swee Chong

    2015-01-01

    A 44 year old male with idiopathic dilated cardiomyopathy was undergoing persistent atrial fibrillation (AF) ablation. Following antral ablation, AF terminated into a regular narrow complex rhythm. Earliest activation was mapped to a focus in the superior vena cava (SVC) which was conducted in a 2:1 ratio to the atria which in turn was conducted with 2:1 ratio to the ventricles, resulting in an unusual 4:2:1 conduction of the SVC tachycardia. 1:1 conduction of the SVC tachycardia to the atrium preceded initiation of AF. During AF, SVC tachycardia continued unperturbed. Sinus rhythm was restored following catheter ablation of the focus. PMID:27134438

  14. Detecting quantum critical points using bipartite fluctuations.

    PubMed

    Rachel, Stephan; Laflorencie, Nicolas; Song, H Francis; Le Hur, Karyn

    2012-03-16

    We show that the concept of bipartite fluctuations F provides a very efficient tool to detect quantum phase transitions in strongly correlated systems. Using state-of-the-art numerical techniques complemented with analytical arguments, we investigate paradigmatic examples for both quantum spins and bosons. As compared to the von Neumann entanglement entropy, we observe that F allows us to find quantum critical points with much better accuracy in one dimension. We further demonstrate that F can be successfully applied to the detection of quantum criticality in higher dimensions with no prior knowledge of the universality class of the transition. Promising approaches to experimentally access fluctuations are discussed for quantum antiferromagnets and cold gases. PMID:22540493

  15. Magnetoconductance fluctuations in open bismuth quantum dots

    NASA Astrophysics Data System (ADS)

    Hackens, B.; Minet, J. P.; Farhi, G.; Crahay, A.; Faniel, S.; Gustin, C.; Bayot, V.

    2002-03-01

    We investigate the low temperature (300 mK - 10 K) magnetoconductance of open circular bismuth quantum dots (diameter: 500 nm). The structures are fabricated using a combination of electron beam lithography, lift off and plasma etching techniques on bismuth thin films evaporated on heated SiO2 substrates. We observe reproducible magnetoconductance fluctuations (UCFs) up to 5T, qualitatively similar to conductance fluctuations evidenced in open quantum dots patterned in high mobility semiconductor heterostructures. In our samples, UCFs are superposed on a slowly varying negative magnetoconductance background. We also observe a sharp conductance maximum centered in B=0, which is reminescent of the spin-orbit induced anti-localisation phenomenon. The behavior of UCFs and of the conductance maximum is discussed as a function of the temperature, thickness and degree of cristallinity of the cavity.

  16. Fluctuating shells under pressure

    PubMed Central

    Paulose, Jayson; Vliegenthart, Gerard A.; Gompper, Gerhard; Nelson, David R.

    2012-01-01

    Thermal fluctuations strongly modify the large length-scale elastic behavior of cross-linked membranes, giving rise to scale-dependent elastic moduli. Whereas thermal effects in flat membranes are well understood, many natural and artificial microstructures are modeled as thin elastic shells. Shells are distinguished from flat membranes by their nonzero curvature, which provides a size-dependent coupling between the in-plane stretching modes and the out-of-plane undulations. In addition, a shell can support a pressure difference between its interior and its exterior. Little is known about the effect of thermal fluctuations on the elastic properties of shells. Here, we study the statistical mechanics of shape fluctuations in a pressurized spherical shell, using perturbation theory and Monte Carlo computer simulations, explicitly including the effects of curvature and an inward pressure. We predict novel properties of fluctuating thin shells under point indentations and pressure-induced deformations. The contribution due to thermal fluctuations increases with increasing ratio of shell radius to thickness and dominates the response when the product of this ratio and the thermal energy becomes large compared with the bending rigidity of the shell. Thermal effects are enhanced when a large uniform inward pressure acts on the shell and diverge as this pressure approaches the classical buckling transition of the shell. Our results are relevant for the elasticity and osmotic collapse of microcapsules. PMID:23150558

  17. Fluctuation-driven topological Hund insulators

    NASA Astrophysics Data System (ADS)

    Budich, Jan Carl; Trauzettel, Björn; Sangiovanni, Giorgio

    2013-06-01

    We investigate the role of electron-electron interaction in a two-band Hubbard model based on the Bernevig-Hughes-Zhang Hamiltonian exhibiting the quantum spin Hall (QSH) effect. By means of dynamical mean-field theory, we find that a system with topologically trivial noninteracting parameters can be driven into a QSH phase at finite interaction strength by virtue of local dynamical fluctuations. For very strong interaction, the system reenters a trivial insulating phase by going through a Mott transition. We obtain the phase diagram of our model by direct calculation of the bulk topological invariant of the interacting system in terms of its single-particle Green's function.

  18. Josephson-like spin current in junctions composed of antiferromagnets and ferromagnets

    NASA Astrophysics Data System (ADS)

    Moor, A.; Volkov, A. F.; Efetov, K. B.

    2012-01-01

    We study Josephson-like junctions formed by materials with antiferromagnetic (AF) order parameters. As an antiferromagnet, we consider a two-band material in which a spin density wave (SDW) arises. This could be Fe-based pnictides in the temperature interval Tc≤T≤TN, where Tc and TN are the critical temperatures for the superconducting and antiferromagnetic transitions, respectively. The spin current jSp in AF/F/AF junctions with a ballistic ferromagnetic layer and in tunnel AF/I/AF junctions is calculated. It depends on the angle between the magnetization vectors in the AF leads in the same way as the Josephson current depends on the phase difference of the superconducting order parameters in S/I/S tunnel junctions. It turns out that in AF/F/AF junctions, two components of the SDW order parameter are induced in the F layer. One of them oscillates in space with a short period ξF,b˜ℏv/H, while the other decays monotonously from the interfaces over a long distance of the order ξN,b=ℏv/2πT (where v, H, and T are the Fermi velocity, the exchange energy, and the temperature, respectively; the subindex “b” denotes the ballistic case). This is a clear analogy with the case of Josephson S/F/S junctions with a nonhomogeneous magnetization where short- and long-range condensate components are induced in the F layer. However, in contrast to the charge Josephson current in S/F/S junctions, the spin current in AF/F/AF junctions is not constant in space, but oscillates in the ballistic F layer. We also calculate the dependence of jSp on the deviation from the ideal nesting in the AF/I/AF junctions. The spin current is maximal in the insulating phase of the AF and decreases in the metallic phase. It turns to zero at the Neel point when the amplitude of the SDW is zero and changes sign for certain values of the detuning parameter.

  19. Spin dynamics in paramagnetic diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Phan, Van-Nham; Tran, Minh-Tien

    2015-10-01

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

  20. AF4 and AF4N protein complexes: recruitment of P-TEFb kinase, their interactome and potential functions

    PubMed Central

    Scholz, Bastian; Kowarz, Eric; Rössler, Tanja; Ahmad, Khalil; Steinhilber, Dieter; Marschalek, Rolf

    2015-01-01

    AF4/AFF1 and AF5/AFF4 are the molecular backbone to assemble “super-elongation complexes” (SECs) that have two main functions: (1) control of transcriptional elongation by recruiting the positive transcription elongation factor b (P-TEFb = CyclinT1/CDK9) that is usually stored in inhibitory 7SK RNPs; (2) binding of different histone methyltransferases, like DOT1L, NSD1 and CARM1. This way, transcribed genes obtain specific histone signatures (e.g. H3K79me2/3, H3K36me2) to generate a transcriptional memory system. Here we addressed several questions: how is P-TEFb recruited into SEC, how is the AF4 interactome composed, and what is the function of the naturally occuring AF4N protein variant which exhibits only the first 360 amino acids of the AF4 full-length protein. Noteworthy, shorter protein variants are a specific feature of all AFF protein family members. Here, we demonstrate that full-length AF4 and AF4N are both catalyzing the transition of P-TEFb from 7SK RNP to their N-terminal domain. We have also mapped the protein-protein interaction network within both complexes. In addition, we have first evidence that the AF4N protein also recruits TFIIH and the tumor suppressor MEN1. This indicate that AF4N may have additional functions in transcriptional initiation and in MEN1-dependend transcriptional processes. PMID:26171280

  1. Fluctuations and friction

    NASA Astrophysics Data System (ADS)

    Raine, Derek

    2005-11-01

    Einstein's 1905 (Einstein 1905 Ann. Phys. 17 549) paper on Brownian motion is his most cited work, yet in terms of the scope of its application, apparently the least understood. In this brief note, I look at some examples of problems involving frictional forces that have puzzled school teachers, university lecturers and students, all of which can be understood from a proper appreciation of the relation between fluctuations and dissipation. For completeness I shall first give a simple derivation of a fluctuation-dissipation theorem, followed by three examples.

  2. 7 CFR Exhibits A-F to Subpart A... - [Reserved

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 14 2013-01-01 2013-01-01 false A Exhibits A-F to Subpart A of Part 1955 Agriculture Regulations of the Department of Agriculture (Continued) RURAL HOUSING SERVICE, RURAL BUSINESS-COOPERATIVE... Real and Chattel Property Exhibits A-F to Subpart A of Part 1955...

  3. 7 CFR Exhibits A-F to Subpart A... - [Reserved

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 14 2012-01-01 2012-01-01 false A Exhibits A-F to Subpart A of Part 1955 Agriculture Regulations of the Department of Agriculture (Continued) RURAL HOUSING SERVICE, RURAL BUSINESS-COOPERATIVE... Real and Chattel Property Exhibits A-F to Subpart A of Part 1955...

  4. 7 CFR Exhibits A-F to Subpart A... - [Reserved

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 14 2010-01-01 2009-01-01 true A Exhibits A-F to Subpart A of Part 1955 Agriculture Regulations of the Department of Agriculture (Continued) RURAL HOUSING SERVICE, RURAL BUSINESS-COOPERATIVE... Real and Chattel Property Exhibits A-F to Subpart A of Part 1955...

  5. 7 CFR Exhibits A-F to Subpart A... - [Reserved

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 7 Agriculture 14 2011-01-01 2011-01-01 false A Exhibits A-F to Subpart A of Part 1955 Agriculture Regulations of the Department of Agriculture (Continued) RURAL HOUSING SERVICE, RURAL BUSINESS-COOPERATIVE... Real and Chattel Property Exhibits A-F to Subpart A of Part 1955...

  6. 7 CFR Exhibits A-F to Subpart A... - [Reserved

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 14 2014-01-01 2014-01-01 false A Exhibits A-F to Subpart A of Part 1955 Agriculture Regulations of the Department of Agriculture (Continued) RURAL HOUSING SERVICE, RURAL BUSINESS-COOPERATIVE... Real and Chattel Property Exhibits A-F to Subpart A of Part 1955...

  7. Part III: AFS - A Secure Distributed File System

    SciTech Connect

    Wachsmann, A.; /SLAC

    2005-06-29

    AFS is a secure distributed global file system providing location independence, scalability and transparent migration capabilities for data. AFS works across a multitude of Unix and non-Unix operating systems and is used at many large sites in production for many years. AFS still provides unique features that are not available with other distributed file systems even though AFS is almost 20 years old. This age might make it less appealing to some but with IBM making AFS available as open-source in 2000, new interest in use and development was sparked. When talking about AFS, people often mention other file systems as potential alternatives. Coda (http://www.coda.cs.cmu.edu/) with its disconnected mode will always be a research project and never have production quality. Intermezzo (http://www.inter-mezzo.org/) is now in the Linux kernel but not available for any other operating systems. NFSv4 (http://www.nfsv4.org/) which picked up many ideas from AFS and Coda is not mature enough yet to be used in serious production mode. This article presents the rich features of AFS and invites readers to play with it.

  8. Two-step spin flop transition in quantum spin ladders

    NASA Astrophysics Data System (ADS)

    Sakai, Toru; Okamoto, Kiyomi

    2008-03-01

    It is well known that the antiferromagnet with easy-axis anisotropies exhibits a field-induced first-order phase transition, the so- called spin flop. In one-dimensional quantum spin systems, instead of it, a second-order phase transition occurs because of large quantum fluctuations[1]. Particularly the S=1 antiferromagnetic chain with the easy-axis single-ion anisotropy was revealed to exhibit two successive field-induced second-order transitions by our previous numerical analysis[2]. However, such transitions have not been obseved yet. Recently a two-step spin flop transition was observed in the spin ladder system IPA-CuCl3[3], which has ferromagnetic rung coupling. In order to clarify the mechanism of the two-step field-induced transition, we investigate the anisotropic spin ladder using the numerical diagonalization and the finite-size scaling analysis. As a result, we revealed that two different field-induced second-order quantum phase transitions possibly occur. Several phase diagrams are also presented. In addition we discuss on a possible two-step spin flop in other materials[4] and some frustrated systems. [1] C. N. Yang and C. P. Yang, Phys. Rev. 151 (1966) 258. [2] T. Sakai, Phys. Rev. B 58 (1998) 6268. [3] T. Masuda et al, Phys. Rev. Lett. 96 (2006) 047210. [4] H. Miyasaka et al, Inorg. Chem. 42 (2003) 8203.

  9. Fluctuating Asymmetry and Intelligence

    ERIC Educational Resources Information Center

    Bates, Timothy C.

    2007-01-01

    The general factor of mental ability ("g") may reflect general biological fitness. If so, "g"-loaded measures such as Raven's progressive matrices should be related to morphological measures of fitness such as fluctuating asymmetry (FA: left-right asymmetry of a set of typically left-right symmetrical body traits such as finger lengths). This…

  10. GRADFLEX: Fluctuations in Microgravity

    NASA Technical Reports Server (NTRS)

    Vailati, A.; Cerbino, R.; Mazzoni, S.; Giglio, M.; Nikolaenko, G.; Cannell, D. S.; Meyer, W. V.; Smart, A. E.

    2004-01-01

    We present the results of experimental investigations of gradient driven fluctuations induced in a liquid mixture with a concentration gradient and in a single-component fluid with a temperature gradient. We also describe the experimental apparatus being developed to carry out similar measurement under microgravity conditions.

  11. Toward a petabyte-scale AFS service at CERN

    NASA Astrophysics Data System (ADS)

    van der Ster, Daniel; Moscicki, Jakub T.; Wiebalck, Arne

    2014-06-01

    AFS is a mature and reliable storage service at CERN, having worked for more than 20 years as the provider of Unix home directories and project areas. Recently, the AFS service has grown at unprecedented rates (200% in the past year); this growth was unlocked thanks to innovations in both the hardware and software components of our file servers. This work presents how AFS is used at CERN and how the service offering is evolving with the increasing storage needs of its local and remote user communities. In particular, we demonstrate the usage patterns for home directories, workspaces and project spaces, as well as show the daily work which is required to rebalance data and maintaining stability and performance. Finally, we highlight some recent changes and optimisations made to the AFS Service, thereby revealing how AFS can possibly operate at all while being subjected to frequent-almost DDOS-like-attacks from its users.

  12. Terrestrial Gravity Fluctuations

    NASA Astrophysics Data System (ADS)

    Harms, Jan

    2015-12-01

    Different forms of fluctuations of the terrestrial gravity field are observed by gravity experiments. For example, atmospheric pressure fluctuations generate a gravity-noise foreground in measurements with super-conducting gravimeters. Gravity changes caused by high-magnitude earthquakes have been detected with the satellite gravity experiment GRACE, and we expect high-frequency terrestrial gravity fluctuations produced by ambient seismic fields to limit the sensitivity of ground-based gravitational-wave (GW) detectors. Accordingly, terrestrial gravity fluctuations are considered noise and signal depending on the experiment. Here, we will focus on ground-based gravimetry. This field is rapidly progressing through the development of GW detectors. The technology is pushed to its current limits in the advanced generation of the LIGO and Virgo detectors, targeting gravity strain sensitivities better than 10^-23 Hz^-1/2 above a few tens of a Hz. Alternative designs for GW detectors evolving from traditional gravity gradiometers such as torsion bars, atom interferometers, and superconducting gradiometers are currently being developed to extend the detection band to frequencies below 1 Hz. The goal of this article is to provide the analytical framework to describe terrestrial gravity perturbations in these experiments. Models of terrestrial gravity perturbations related to seismic fields, atmospheric disturbances, and vibrating, rotating or moving objects, are derived and analyzed. The models are then used to evaluate passive and active gravity noise mitigation strategies in GW detectors, or alternatively, to describe their potential use in geophysics. The article reviews the current state of the field, and also presents new analyses especially with respect to the impact of seismic scattering on gravity perturbations, active gravity noise cancellation, and time-domain models of gravity perturbations from atmospheric and seismic point sources. Our understanding of

  13. Squeezed light spin noise spectroscopy

    NASA Astrophysics Data System (ADS)

    Lucivero, Vito Giovanni; Jiménez-Martínez, Ricardo; Kong, Jia; Mitchell, Morgan

    2016-05-01

    Spin noise spectroscopy (SNS) has recently emerged as a powerful technique for determining physical properties of an unperturbed spin system from its power noise spectrum both in atomic and solid state physics. In the presence of a transverse magnetic field, we detect spontaneous spin fluctuations of a dense Rb vapor via Faraday rotation of an off-resonance probe beam, resulting in the excess of spectral noise at the Larmor frequency over a white photon shot-noise background. We report quantum enhancement of the signal-to-noise ratio via polarization squeezing of the probe beam up to 3dB over the full density range up to n = 1013 atoms cm-3, covering practical conditions used in optimized SNS experiments. Furthermore, we show that squeezing improves the trade-off between statistical sensitivity and systematic errors due to line broadening, a previously unobserved quantum advantage.

  14. Spinon walk in quantum spin ice

    NASA Astrophysics Data System (ADS)

    Wan, Yuan; Carrasquilla, Juan; Melko, Roger

    Quantum spin ice is a novel family of spin ice magnets that possess substantial quantum fluctuations. The fractional excitations are spinons, which are quantum analog of the monopoles in classical spin ice. The spinon propagates in quantum spin ice via quantum tunnelling. As opposed to a conventional quantum particle, the spinon moves in a background of disordered spins. The orientation of background spins controls the spinon motion, whereas the spinon motion in turn alters the spin background. One may naturally ask what a suitable framework for understanding the dynamics of spinon is in quantum spin ice, and furthermore, whether the spinon propagation is coherent. In this talk, we address these issues by investigating a minimal model that captures the essential features of single spinon dynamics in quantum spin ice. We demonstrate that the spinon motion can be thought of as a quantum walk with entropy-induced memory. Our numerical simulation shows that the simple quasi-particle behaviour emerges out of the intricate interplay between the spinon and the background spins .

  15. Conductance fluctuations in nanostructures

    NASA Astrophysics Data System (ADS)

    Zhu, Ningjia

    1997-12-01

    In this Ph.D thesis the conductance fluctuations of different physical origins in semi-conductor nanostructures were studied using both diagrammatic analytical methods and large scale numerical techniques. In the "mixed" transport regime where both mesoscopic and ballistic features play a role, for the first time I have analytically calculated the non-universal conductance fluctuations. This mixed regime is reached when impurities are distributed near the walls of a quantum wire, leaving the center region ballistic. I have discovered that the existence of a ballistic region destroys the universal conductance fluctuations. The crossover behavior of the fluctuation amplitude from the usual quasi-1D situation to that of the mixed regime is clearly revealed, and the role of various length scales are identified. My analytical predictions were confirmed by a direct numerical simulation by evaluating the Landauer formula. In another direction, I have made several studies of conductance or resistance oscillations and fluctuations in systems with artificial impurities in the ballistic regime. My calculation gave explanations of all the experimental results concerning the classical focusing peaks of the resistance versus magnetic field, the weak localization peak in a Sinai billiard system, the formation of a chaotic billiard, and predicted certain transport features which were indeed found experimentally. I have further extended the calculation to study the Hall resistance in a four-terminal quantum dot in which there is an antidot array. From my numerical data I analyzed the classical paths of electron motion and its quantum oscillations. The results compare well with recent experimental studies on similar systems. Since these billiard systems could provide quantum chaotic dynamics, I have made a detailed study of the consequence of such dynamics. In particular I have investigated the resonant transmission of electrons in these chaotic systems, and found that the level

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

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

  17. Dynamic stabilization of a quantum many-body spin system.

    PubMed

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

    2013-08-30

    We demonstrate dynamic stabilization of a strongly interacting quantum spin system realized in a spin-1 atomic Bose-Einstein condensate. The spinor Bose-Einstein condensate is initialized to an unstable fixed point of the spin-nematic phase space, where subsequent free evolution gives rise to squeezing and quantum spin mixing. To stabilize the system, periodic microwave pulses are applied that rotate the spin-nematic many-body fluctuations and limit their growth. The stability diagram for the range of pulse periods and phase shifts that stabilize the dynamics is measured and compares well with a stability analysis. PMID:24033006

  18. Spin transport in helical biological systems

    SciTech Connect

    Díaz, Elena; Gutierrez, Rafael

    2014-08-20

    Motivated by the recent experimental demonstration of spin selective effects in monolayers of double-stranded DNA oligomers, our work presents a minimal model to describe electron transmission through helical fields. Our model highlight that the lack of inversion symmetry due to the chirality of the potential is a key factor which will lead to a high spin-polarization (SP). We also study the stability of the SP against fluctuations of the electronic structure induced by static disorder affecting the on-site energies. In the energy regions where the spin-filtering occurs, our results remain stable against moderate disorders although the SP is slightly reduced.

  19. Vibration-induced field fluctuations in a superconducting magnet

    NASA Astrophysics Data System (ADS)

    Britton, J. W.; Bohnet, J. G.; Sawyer, B. C.; Uys, H.; Biercuk, M. J.; Bollinger, J. J.

    2016-06-01

    Superconducting magnets enable precise control of nuclear and electron spins, and are used in experiments that explore biological and condensed-matter systems, and fundamental atomic particles. In high-precision applications, a common view is that slow (<1 Hz ) drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10-200 Hz) that limits the coherence time of Be+9 electron-spin qubits in the 4.46 -T field of a superconducting magnet. We measure a spin-echo T2 coherence time of ˜6 ms for the Be+9 electron-spin resonance at 124 GHz , limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved T2 to ˜50 ms.

  20. Extracting primordial density fluctuations

    PubMed

    Gawiser; Silk

    1998-05-29

    The combination of detections of anisotropy in cosmic microwave background radiation and observations of the large-scale distribution of galaxies probes the primordial density fluctuations of the universe on spatial scales varying by three orders of magnitude. These data are found to be inconsistent with the predictions of several popular cosmological models. Agreement between the data and the cold + hot dark matter model, however, suggests that a significant fraction of the matter in the universe may consist of massive neutrinos. PMID:9603724

  1. Continuum physics: Correlation and fluctuation analysis

    SciTech Connect

    Herskind, B.

    1993-10-01

    It is well known that the main flow of the {gamma}-decay from high spin states passes through the regions of high level density several MeV above the yrast line. Nevertheless, only very limited information about the nuclear structure in this region is available, due to the extremely high complexity of the decay patterns. The new highly efficient {gamma}-spectrometer arrays, GASP, EUROGAM and GAMMASPHERE coming into operation these years, with several orders of magnitude higher selectivity for studying weakly populated states, offers new exiting possibilities also for a much more detailed study of the high spin quasi-continuum. It is of special interest to study the phase transition from the region of discrete regular rotational band structures found close to the yrast line, into the region of damped rotational motion at higher excitation energies and investigate the interactions responsible for the damping phenomena. Some of the first large data-sets to be analyzed are made on residues around e.g. {sup 152}Dy and {sup 168}Yb produced with EUROGAM in Daresbury, UK, in addition to {sup 143}Eu and {sup 182}Pt produced with GASP in Legnaro, Italy. These data-sets will for the first time contain enough counts to allow for a fluctuation analysis of 3-fold coincidence matrixes. The high spatial resolution in a cube of triples make it possible to select transitions from specific configurations using 2 of the detectors and measure the fluctuations caused by the simplicity of feeding the selected configuration by the 3. detector. Thus, weakly mixed structures in the damped region as e.g. superdeformed- or high-K bands are expected to show large fluctuations. Results from these experiments will be discussed.

  2. Multiscale Fluctuation Analysis Revisited

    NASA Astrophysics Data System (ADS)

    Struzik, Zbigniew R.; Kiyono, Ken; Yamamoto, Yoshiharu

    2007-07-01

    Ubiquitous non-Gaussianity of the probability density of (time-series) fluctuations in many real world phenomena has been known and modelled extensively in recent years. Similarly, the analysis of (multi)scaling properties of (fluctuations in) complex systems has become a standard way of addressing unknown complexity. Yet the combined analysis and modelling of multiscale behaviour of probability density — multiscale PDF analysis — has only recently been proposed for the analysis of time series arising in complex systems, such as the cardiac neuro-regulatory system, financial markets or hydrodynamic turbulence. This relatively new technique has helped significantly to expand the previously obtained insights into the phenomena addressed. In particular, it has helped to identify a novel class of scale invariant behaviour of the multiscale PDF in healthy heart rate regulation during daily activity and in a market system undergoing crash dynamics. This kind of invariance reflects invariance of the system under renormalisation and resembles behaviour at criticality of a system undergoing continuous phase transition — indeed in both phenomena, such phase transition behaviour has been revealed. While the precise mechanism underlying invariance of the PDF under system renormalisation of both systems discussed is not to date understood, there is an intimate link between the non-Gaussian PDF characteristics and the persistent invariant correlation structure emerging between fluctuations across scale and time.

  3. Real-Time Estimation Of Aiming Error Of Spinning Antenna

    NASA Technical Reports Server (NTRS)

    Dolinsky, Shlomo

    1992-01-01

    Spinning-spacecraft dynamics and amplitude variations in communications links studied from received-signal fluctuations. Mathematical model and associated analysis procedure provide real-time estimates of aiming error of remote rotating transmitting antenna radiating constant power in narrow, pencillike beam from spinning platform, and current amplitude of received signal. Estimates useful in analyzing and enhancing calibration of communication system, and in analyzing complicated dynamic effects in spinning platform and antenna-aiming mechanism.

  4. Coherent electron-spin-resonance manipulation of three individual spins in a triple quantum dot

    NASA Astrophysics Data System (ADS)

    Noiri, A.; Yoneda, J.; Nakajima, T.; Otsuka, T.; Delbecq, M. R.; Takeda, K.; Amaha, S.; Allison, G.; Ludwig, A.; Wieck, A. D.; Tarucha, S.

    2016-04-01

    Quantum dot arrays provide a promising platform for quantum information processing. For universal quantum simulation and computation, one central issue is to demonstrate the exhaustive controllability of quantum states. Here, we report the addressable manipulation of three single electron spins in a triple quantum dot using a technique combining electron-spin-resonance and a micro-magnet. The micro-magnet makes the local Zeeman field difference between neighboring spins much larger than the nuclear field fluctuation, which ensures the addressable driving of electron-spin-resonance by shifting the resonance condition for each spin. We observe distinct coherent Rabi oscillations for three spins in a semiconductor triple quantum dot with up to 25 MHz spin rotation frequencies. This individual manipulation over three spins enables us to arbitrarily change the magnetic spin quantum number of the three spin system, and thus to operate a triple-dot device as a three-qubit system in combination with the existing technique of exchange operations among three spins.

  5. An Implicit LU/AF FDTD Method

    NASA Technical Reports Server (NTRS)

    Beggs, John H.; Briley, W. Roger

    2001-01-01

    There has been some recent work to develop two and three-dimensional alternating direction implicit (ADI) FDTD schemes. These ADI schemes are based upon the original ADI concept developed by Peaceman and Rachford and Douglas and Gunn, which is a popular solution method in Computational Fluid Dynamics (CFD). These ADI schemes work well and they require solution of a tridiagonal system of equations. A new approach proposed in this paper applies a LU/AF approximate factorization technique from CFD to Maxwell s equations in flux conservative form for one space dimension. The result is a scheme that will retain its unconditional stability in three space dimensions, but does not require the solution of tridiagonal systems. The theory for this new algorithm is outlined in a one-dimensional context for clarity. An extension to two and threedimensional cases is discussed. Results of Fourier analysis are discussed for both stability and dispersion/damping properties of the algorithm. Results are presented for a one-dimensional model problem, and the explicit FDTD algorithm is chosen as a convenient reference for comparison.

  6. Electron spin relaxation in carbon nanotubes: Dyakonov-Perel mechanism

    NASA Astrophysics Data System (ADS)

    Semenov, Yuriy; Zavada, John; Kim, Ki Wook

    2010-03-01

    The long standing problem of unaccountable short spin relaxation in carbon nanotubes (CNT) meets a disclosure in terms of curvature-mediated spin-orbital interaction that leads to spin fluctuating precession analogous to Dyakonov-Perel mechanism. Strong anisotropy imposed by arbitrary directed magnetic field has been taken into account in terms of extended Bloch equations. Especially, stationary spin current through CNT can be controlled by spin-flip processes with relaxation time as less as 150 ps, the rate of transversal polarization (i.e. decoherence) runs up to 1/(70 ps) at room temperature while spin interference of the electrons related to different valleys can be responsible for shorter spin dephasing. Dependencies of spin-relaxation parameters on magnetic field strength and orientation, CNT curvature and chirality have been analyzed.

  7. Dephasing due to Nuclear Spins in Large-Amplitude Electric Dipole Spin Resonance

    NASA Astrophysics Data System (ADS)

    Chesi, Stefano; Yang, Li-Ping; Loss, Daniel

    2016-02-01

    We analyze effects of the hyperfine interaction on electric dipole spin resonance when the amplitude of the quantum-dot motion becomes comparable or larger than the quantum dot's size. Away from the well-known small-drive regime, the important role played by transverse nuclear fluctuations leads to a Gaussian decay with characteristic dependence on drive strength and detuning. A characterization of spin-flip gate fidelity, in the presence of such additional drive-dependent dephasing, shows that vanishingly small errors can still be achieved at sufficiently large amplitudes. Based on our theory, we analyze recent electric dipole spin resonance experiments relying on spin-orbit interactions or the slanting field of a micromagnet. We find that such experiments are already in a regime with significant effects of transverse nuclear fluctuations and the form of decay of the Rabi oscillations can be reproduced well by our theory.

  8. Observation of transverse spin freezing by TDPAC

    NASA Astrophysics Data System (ADS)

    Webb, T. A.; Ryan, D. H.

    2013-05-01

    We use 181Hf time-differential perturbed angular correlation (TDPAC) spectroscopy to investigate magnetic ordering in the bond-frustrated metallic glass: a - Fe91Hf9. We show that TDPAC can be used to observe the magnetic fluctuations that are associated with the freezing of transverse spin components at T xy .

  9. Model for lightcone fluctuations due to stress tensor fluctuations

    NASA Astrophysics Data System (ADS)

    Bessa, C. H. G.; De Lorenci, V. A.; Ford, L. H.; Ribeiro, C. C. H.

    2016-03-01

    We study a model for quantum lightcone fluctuations in which vacuum fluctuations of the electric field and of the squared electric field in a nonlinear dielectric material produce variations in the flight times of probe pulses. When this material has a nonzero third order polarizability, the flight time variations arise from squared electric field fluctuations, and are analogous to effects expected when the stress tensor of a quantized field drives passive spacetime geometry fluctuations. We also discuss the dependence of the squared electric field fluctuations upon the geometry of the material, which in turn determines a sampling function for averaging the squared electric field along the path of the pulse. This allows us to estimate the probability of especially large fluctuations, which is a measure of the probability distribution for quantum stress tensor fluctuations.

  10. Anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets

    NASA Astrophysics Data System (ADS)

    Li, Yao-Dong; Wang, Xiaoqun; Chen, Gang

    2016-07-01

    Motivated by the recent experimental progress on the strong spin-orbit-coupled rare-earth triangular antiferromagnet, we analyze the highly anisotropic spin model that describes the interaction between the spin-orbit-entangled Kramers' doublet local moments on the triangular lattice. We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and the self-consistent spin wave theory to analyze the anisotropic spin Hamiltonian. The classical phase diagram includes the 120∘ state and two distinct stripe-ordered phases. The frustration is very strong and significantly suppresses the ordering temperature in the regimes close to the phase boundary between two ordered phases. Going beyond the semiclassical analysis, we include the quantum fluctuations of the spin moments within a self-consistent Dyson-Maleev spin-wave treatment. We find that the strong quantum fluctuations melt the magnetic order in the frustrated regions. We explore the magnetic excitations in the three different ordered phases as well as in strong magnetic fields. Our results provide a guidance for the future theoretical study of the generic model and are broadly relevant for strong spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3 , RZn3P3 , RCd3As3 , RZn3As3 , and R2O2CO3 .

  11. Prevention of Obesity and Insulin Resistance by Estrogens Requires ERα Activation Function-2 (ERαAF-2), Whereas ERαAF-1 Is Dispensable

    PubMed Central

    Handgraaf, Sandra; Riant, Elodie; Fabre, Aurélie; Waget, Aurélie; Burcelin, Rémy; Lière, Philippe; Krust, Andrée; Chambon, Pierre; Arnal, Jean-François; Gourdy, Pierre

    2013-01-01

    The beneficial metabolic actions of estrogen-based therapies are mainly mediated by estrogen receptor α (ERα), a nuclear receptor that regulates gene transcription through two activation functions (AFs): AF-1 and AF-2. Using mouse models deleted electively for ERαAF-1 (ERαAF-1°) or ERαAF-2 (ERαAF-2°), we determined their respective roles in the actions of estrogens on body composition and glucose homeostasis in response to either a normal diet or a high-fat diet (HFD). ERαAF-2° males and females developed accelerated weight gain, massive adiposity, severe insulin resistance, and glucose intolerance—quite reminiscent of the phenotype observed in mice deleted for the entire ERα protein (ERα−/−). In striking contrast, ERαAF-1° and wild-type (wt) mice shared a similar metabolic phenotype. Accordingly, 17β-estradiol administration regulated key metabolic genes in insulin-sensitive tissues and conferred a strong protection against HFD-induced metabolic disturbances in wt and ERαAF-1° ovariectomized mice, whereas these actions were totally abrogated in ERαAF-2° and ERα−/− mice. Thus, whereas both AFs have been previously shown to contribute to endometrial and breast cancer cell proliferation, the protective effect of estrogens against obesity and insulin resistance depends on ERαAF-2 but not ERαAF-1, thereby delineating new options for selective modulation of ERα. PMID:23903353

  12. Electrical control of quantum dot spin qubits

    NASA Astrophysics Data System (ADS)

    Laird, Edward Alexander

    This thesis presents experiments exploring the interactions of electron spins with electric fields in devices of up to four quantum dots. These experiments are particularly motivated by the prospect of using electric fields to control spin qubits. A novel hyperfine effect on a single spin in a quantum dot is presented in Chapter 2. Fluctuations of the nuclear polarization allow single-spin resonance to be driven by an oscillating electric field. Spin resonance spectroscopy revealed a nuclear polarization built up inside the quantum dot device by driving the resonance. The evolution of two coupled spins is controlled by the combination of hyperfine interaction, which tends to cause spin dephasing, and exchange, which tends to prevent it. In Chapter 3, dephasing is studied in a device with tunable exchange, probing the crossover between exchange-dominated and hyperfine-dominated regimes. In agreement with theoretical predictions, oscillations of the spin conversion probability and saturation of dephasing are observed. Chapter 4 deals with a three-dot device, suggested as a potential qubit controlled entirely by exchange. Preparation and readout of the qubit state are demonstrated, together with one out of two coherent exchange operations needed for arbitrary manipulations. A new readout technique allowing rapid device measurement is described. In Chapter 5, an attempt to make a two-qubit gate using a four-dot device is presented. Although spin qubit operation has not yet been possible, the electrostatic interaction between pairs of dots was measured to be sufficient in principle for coherent qubit coupling.

  13. Tuning the Music: Acoustic Force Spectroscopy (AFS) 2.0.

    PubMed

    Kamsma, Douwe; Creyghton, Ramon; Sitters, Gerrit; Wuite, Gijs J L; Peterman, Erwin J G

    2016-08-01

    AFS is a recently introduced high-throughput single-molecule technique that allows studying structural and mechanochemical properties of many biomolecules in parallel. To further improve the method, we developed a modelling tool to optimize the layer thicknesses, and a calibration method to experimentally validate the modelled force profiles. After optimization, we are able to apply 350pN on 4.5μm polystyrene beads, without the use of an amplifier, at the coverslip side of the AFS chip. Furthermore, we present the use of a transparent piezo to generate the acoustic force and we show that AFS can be combined with high-NA oil or water-immersion objectives. With this set of developments AFS will be applicable to a broad range of single-molecule experiments. PMID:27163865

  14. Fluctuations, Intermittency and Predictivity

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter considers the various mechanisms capable of producing amplitude and duration variations in the various dynamo models introduced in Chap. 3 (10.1007/978-3-642-32093-4_3). After a survey of observed and inferred fluctuation patterns of the solar cycle, the effects on the basic cycle of stochastic forcing, dynamical nonlinearities and time delay are considered in turn. The occurrence of intermittency in a subset of these models is then investigated, with an eye on explaining Grand Minima observed in the solar activity record. The chapter closes with a brief discussion of solar cycle prediction schemes based on dynamo models.

  15. Gambling with Superconducting Fluctuations

    NASA Astrophysics Data System (ADS)

    Foltyn, Marek; Zgirski, Maciej

    2015-08-01

    Josephson junctions and superconducting nanowires, when biased close to superconducting critical current, can switch to a nonzero voltage state by thermal or quantum fluctuations. The process is understood as an escape of a Brownian particle from a metastable state. Since this effect is fully stochastic, we propose to use it for generating random numbers. We present protocol for obtaining random numbers and test the experimentally harvested data for their fidelity. Our work is prerequisite for using the Josephson junction as a tool for stochastic (probabilistic) determination of physical parameters such as magnetic flux, temperature, and current.

  16. Spin ejector

    DOEpatents

    Andersen, John A.; Flanigan, John J.; Kindley, Robert J.

    1978-01-01

    The disclosure relates to an apparatus for spin ejecting a body having a flat plate base containing bosses. The apparatus has a base plate and a main ejection shaft extending perpendicularly from the base plate. A compressible cylindrical spring is disposed about the shaft. Bearings are located between the shaft and the spring. A housing containing a helical aperture releasably engages the base plate and surrounds the shaft bearings and the spring. A piston having an aperture follower disposed in the housing aperture is seated on the spring and is guided by the shaft and the aperture. The spring is compressed and when released causes the piston to spin eject the body.

  17. Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations.

    PubMed

    Marcuzzi, Matteo; Buchhold, Michael; Diehl, Sebastian; Lesanovsky, Igor

    2016-06-17

    Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states. PMID:27367395

  18. Absorbing State Phase Transition with Competing Quantum and Classical Fluctuations

    NASA Astrophysics Data System (ADS)

    Marcuzzi, Matteo; Buchhold, Michael; Diehl, Sebastian; Lesanovsky, Igor

    2016-06-01

    Stochastic processes with absorbing states feature examples of nonequilibrium universal phenomena. While the classical regime has been thoroughly investigated in the past, relatively little is known about the behavior of these nonequilibrium systems in the presence of quantum fluctuations. Here, we theoretically address such a scenario in an open quantum spin model which, in its classical limit, undergoes a directed percolation phase transition. By mapping the problem to a nonequilibrium field theory, we show that the introduction of quantum fluctuations stemming from coherent, rather than statistical, spin flips alters the nature of the transition such that it becomes first order. In the intermediate regime, where classical and quantum dynamics compete on equal terms, we highlight the presence of a bicritical point with universal features different from the directed percolation class in a low dimension. We finally propose how this physics could be explored within gases of interacting atoms excited to Rydberg states.

  19. Magnetism in Parent Iron Chalcogenides: Quantum Fluctuations Select Plaquette Order

    NASA Astrophysics Data System (ADS)

    Ducatman, Samuel; Perkins, Natalia B.; Chubukov, Andrey

    2012-10-01

    We analyze magnetic order in Fe chalcogenide Fe1+yTe, the parent compound of the high-temperature superconductor Fe1+yTe1-xSex. Experiments show that magnetic order in this material contains components with momentum Q1=(π/2,π/2) and Q2=(π/2,-π/2) in the Fe only Brillouin zone. The actual spin order depends on the interplay between these two components. Previous works assumed that the ordered state has a single Q (either Q1 or Q2). In such a state, spins form double stripes along one of the diagonals breaking the rotational C4 symmetry. We show that quantum fluctuations actually select another order—a double Q plaquette state with equal weight of Q1 and Q2 components, which preserves C4 symmetry. We argue that the order in Fe1+yTe is determined by the competition between quantum fluctuations and magnetoelastic coupling.

  20. Gradient Driven Fluctuations

    NASA Technical Reports Server (NTRS)

    Cannell, David

    2005-01-01

    We have worked with our collaborators at the University of Milan (Professor Marzio Giglio and his group-supported by ASI) to define the science required to measure gradient driven fluctuations in the microgravity environment. Such a study would provide an accurate test of the extent to which the theory of fluctuating hydrodynamics can be used to predict the properties of fluids maintained in a stressed, non-equilibrium state. As mentioned above, the results should also provide direct visual insight into the behavior of a variety of fluid systems containing gradients or interfaces, when placed in the microgravity environment. With support from the current grant, we have identified three key systems for detailed investigation. These three systems are: 1) A single-component fluid to be studied in the presence of a temperature gradient; 2) A mixture of two organic liquids to be studied both in the presence of a temperature gradient, which induces a steady-state concentration gradient, and with the temperature gradient removed, but while the concentration gradient is dying by means of diffusion; 3) Various pairs of liquids undergoing free diffusion, including a proteidbuffer solution and pairs of mixtures having different concentrations, to allow us to vary the differences in fluid properties in a controlled manner.

  1. A Fluctuating Torque

    NASA Astrophysics Data System (ADS)

    Zamorano, Nelson; Gómez, Alfredo

    2013-04-01

    The existence of a fluctuating torque generates a wide variety of possible orbits. This situation contrasts with those examples where the torque vanishes and the angular momentum remains constant. Here we study a two dimensional example with a logarithmic effective potential V(x,y)= 12,,^2o,[ x^2 + (y/b)^2], with a small deviation from the axis symmetry given by the constant b with b < 1. Briefly, the effective potential models the gravitational force exerted by the N point particles on a test object. This potential is used to learn about the dynamics of galaxies and among other features, generates a fluctuating torque which is our main interest here. There is not an analytical solution for these two equations of motion. A simple numerical approach (provided) is required. Also, a change on the initial conditions may generate a different shape for the orbit. This apparently simple potential, represents a challenge for the students. We propose it as a good pedagogical tool for reviewing the main concepts of newtonian dynamics.

  2. Fitness in fluctuating environments

    NASA Astrophysics Data System (ADS)

    Tanase Nicola, Sorin; Nemenman, Ilya

    2011-03-01

    Often environments change faster than the time needed to evolve optimal phenotypes through cycles of mutation and selection. We focus on this case, but assume that environmental oscillations are slower than an individual's lifetime. This is relevant, for example, for bacterial populations confronted with daily environmental changes. We analyze a resource-limited competition between a mutant phenotype and the ancestor. Environmental dynamics is represented by periodically varying, off-phase parameters of the corresponding Lotka-Volterra model. For the very slow dynamics (but still faster than the fixation time scale) the strength and the sign of selection are functions of the birth/death rates averaged over all of the environmental states and independent of the period of the fluctuations. For faster fluctuations, selection depends on the particular sequence of the successive environmental states. In particular, a time reversal of the environmental dynamics can change the sign of the selection. We conclude that the fittest phenotype in a changing environment can be very different from both the optimal phenotype in the average environment, and the phenotype with the largest average fitness.

  3. Fission mode fluctuations in the resonances of 235U(n,f)

    NASA Astrophysics Data System (ADS)

    Hambsch, F. J.; Knitter, H. H.; Budtz-Jørgensen, C.; Theobald, J. P.

    1989-01-01

    Fission fragment mass- and total kinetic energy distributions were measured for single, isolated resonances and neutron energy bins covering the incident neutron energy range from 0.006 eV to 130 eV. The measurements were performed at the Geel Electron Linear Accelerator (GELINA) of the European Communities using a Frisch-gridded ionization chamber. Fluctuations of the fission fragment mass distributions as function of resonance energy were observed, which are correlated with fluctuations of the reaction Q-value and with the measured total kinetic energy averaged over all fragments. In the resonance region the fluctuations in from resonance to resonance are observed with amplitudes up to about 450 keV. The correlations between the mass-distribution fluctuations and other parameters like spin J, spin orientation quantum number K, angular distribution fluctuations and the fluctuations of the average number of neutrons emitted in fission, overlinev, are evaluated and discussed. An interpretation of the overlinev- fluctuations observed in other experiments is given in terms of the mass distribution fluctuations. The fluctuations of the mass-distribution parameters and of the total kinetic energy distributions as function of mass are viewed in the frame of the fission channel model of Bohr and Wheeler and of the recent multi-fission mode random neck-rupture model of Brosa, Grossmann and Müller.

  4. Smeared spin-flop transition in random antiferromagnetic Ising chain

    SciTech Connect

    Timonin, P. N.

    2012-12-15

    At T = 0 and in a sufficiently large field, the nearest-neighbor antiferromagnetic Ising chain undergoes a first-order spin-flop transition into the ferromagnetic phase. We consider its smearing under the random-bond disorder such that all independent random bonds are antiferromagnetic (AF). It is shown that the ground-state thermodynamics of this random AF chain can be described exactly for an arbitrary distribution P(J) of AF bonds. Moreover, the site magnetizations of finite chains can be found analytically in this model. We consider a continuous P(J) that is zero above some -J{sub 1} and behaves near it as (-J{sub 1}-J){sup {lambda}}, {lambda} > -1. In this case, the ferromagnetic phase emerges continuously in a field H > H{sub c} = 2J{sub 1}. At 0 > {lambda} > -1, it has the usual second-order anomalies near H{sub c} with the critical indices obeying the scaling relation and depending on {lambda}. At {lambda} > 0, higher-order transitions occur (third, fourth, etc.), marked by a divergence of the corresponding nonlinear susceptibilities. In the chains with an even number of spins, the intermediate 'bow-tie' phase with linearly modulated AF order exists between the AF and ferromagnetic phases at J{sub 1} < H < H{sub c}. Its origin can be traced to the infinite correlation length of the degenerate AF phase from which it emerges. This implies the existence of similar inhomogeneous phases with size- and form-dependent order in a number of other systems with infinite correlation length. The possibility to observe the signs of the 'bow-tie' phase in low-T neutron diffraction experiments is discussed.

  5. Fluctuation effects in grain growth

    NASA Astrophysics Data System (ADS)

    Kim, Seong Gyoon; Park, Yong Bum

    2016-08-01

    In this study, we attempted to clarify the roles of fluctuation effects in grain growth. To capture the persistent nature in both space and time of fluctuations due to variations in the local surroundings of individual grains, we developed a local mean-field model. The fluctuation strength in this model is arbitrarily controlled by employing an artificial number, n , of nearest neighbor grains. Large-scale numerical computations of the model for various n values and initial GSDs were carried out to follow transient behaviors and determine the steady states. This study reveals that, in the classical mean-field model with no fluctuation effects, the steady state is not unique but is strongly dependent upon the initial GSD. However, a small fluctuation drives the mean-field model to reach the Hillert solution, independent of the fluctuation strength and initial GSD, as long as the fluctuation strength is sufficiently small. On the other hand, when the fluctuation is sufficiently strong, the fluctuation pushes the steady state of the mean-field model out of the Hillert solution, and its strength determines a unique steady state independent of the initial GSD. The strong fluctuation makes the GSD more symmetric than the Hillert distribution. Computations designed to mimic actual 2 and 3D grain growth were carried out by taking the number of nearest neighbors of each grain as a function of the scaled grain size. The resultant GSDs in two and three dimensions were compared with the direct simulations of ideal grain growth.

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

    PubMed

    Field, Timothy R

    2014-11-01

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

  7. Spin pumping and spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Saitoh, Eiji

    2012-02-01

    Utilization of a spin current, a flow of electrons' spins in a solid, is the key technology in spintronics that will allow the achievement of efficient magnetic memories and computing devices. In this technology, generation and detection of spin currents are necessary. Here, we review inverse spin-Hall effect and spin-current-generation phenomena recently discovered both in metals and insulators: inverse spin-Hall effect, spin pumping, and spin Seebeck effect. (1)Spin pumping and spin torque in a Mott insulator system We found that spin pumping and spin torque effects appear also at an interface between Pt and an insulator YIG.. This means that we can connect a spin current carried by conduction electrons and a spin-wave spin current flowing in insulators. We demonstrate electric signal transmission by using these effects and interconversion of the spin currents [1]. (2) Spin Seebeck effect We have observed, by using the inverse spin-Hall effect [2], spin voltage generation from a heat current in a NiFe, named the spin-Seebeck effect [3]. Surprisingly, spin-Seebeck effect was found to appear even in insulators [4], a situation completely different from conventional charge Seebeck effect. The result implies an important role of elementary excitation in solids beside charge in the spin Seebeck effect. In the talk, we review the recent progress of the research on this effect. This research is collaboration with K. Ando, K. Uchida, Y. Kajiwara, S. Maekawa, G. E. W. Bauer, S. Takahashi, and J. Ieda. [4pt] [1] Y. Kajiwara and E. Saitoh et al. Nature 464 (2010) 262. [0pt] [2] E. Saitoh et al., Appl. Phys. Lett. 88 (2006) 182509. [0pt] [3] K. Uchida and E. Saitoh et al., Nature 455 (2008)778. [0pt] [4] K. Uchida and E. Saitoh et al.,Nature materials 9 (2010) 894 - 897.

  8. Fluctuating Thermodynamics for Biological Processes

    NASA Astrophysics Data System (ADS)

    Ham, Sihyun

    Because biomolecular processes are largely under thermodynamic control, dynamic extension of thermodynamics is necessary to uncover the mechanisms and driving factors of fluctuating processes. The fluctuating thermodynamics technology presented in this talk offers a practical means for the thermodynamic characterization of conformational dynamics in biomolecules. The use of fluctuating thermodynamics has the potential to provide a comprehensive picture of fluctuating phenomena in diverse biological processes. Through the application of fluctuating thermodynamics, we provide a thermodynamic perspective on the misfolding and aggregation of the various proteins associated with human diseases. In this talk, I will present the detailed concepts and applications of the fluctuating thermodynamics technology for elucidating biological processes. This work was supported by Samsung Science and Technology Foundation under Project Number SSTF-BA1401-13.

  9. Test of ballistic spin-polarized electron transport across ferromagnet/semiconductor Schottky interfaces

    NASA Astrophysics Data System (ADS)

    Hirohata, A.; Guertler, C. M.; Lew, W. S.; Xu, Y. B.; Bland, J. A. C.; Holmes, S. N.

    2002-05-01

    We previously reported highly efficient spin detection associated with spin filtering at single layer ferromagnet (FM)/GaAs interfaces (NiFe, Co, and Fe as the FM) using photoexcitation at room temperature, confirming that the Schottky barrier acts as a tunnel barrier. In order to consider explicitly possible background effects, e.g., magnetic circular dichroism, we therefore prepared antiferromagnetic (AF) Cr/GaAs structures as reference, using the same growth techniques as used for the FM structures. The Cr/GaAs samples showed very good Schottky characteristics and the difference in the helicity-dependent photocurrent was found to be negligible, indicating that no spin filtering occurs at the AF Cr/GaAs interfaces. These combined results conclusively show that high efficient spin detection can be achieved at room temperature.

  10. Antiferromagnetic order in a semiconductor quantum well with spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Marinescu, D. C.

    2015-05-01

    An argument is made on the existence of a low-temperature itinerant antiferromagnetic (AF) spin alignment, rather than persistent helical (PH), in the ground state of a two dimensional electron gas in a semiconductor quantum well with linear spin-orbit Rashba-Dresselhaus interaction at equal coupling strengths, α. This result is obtained on account of the opposite-spin single-particle state degeneracy at k = 0 that makes the spin instability possible. A theory of the resulting magnetic phase is formulated within the Hartree-Fock approximation of the Coulomb interaction. In the AF state the direction of the fractional polarization is obtained to be aligned along the displacement vector of the single-particle states.

  11. Fluctuation theory of starlight polarization

    SciTech Connect

    Nee, S.F.

    1980-04-15

    The average and the variance of absolute polarization of starlight are calculated as a function of distance based on the fluctuation theory of Langevin's scheme. The computed curves from the theory agree with the sample observational data. It estimates a correlation length of 225 pc and a fluctuating angle of 22./sup 0/5 for the fluctuation of interstellar magnetic field for the observation direction within 60/sup 0/

  12. Search for the Heisenberg spin glass on rewired square lattices with antiferromagnetic interaction

    NASA Astrophysics Data System (ADS)

    Surungan, Tasrief; Bansawang B., J.; Tahir, Dahlang

    2016-03-01

    Spin glass (SG) is a typical magnetic system with frozen random spin orientation at low temperatures. The system exhibits rich physical properties, such as infinite number of ground states, memory effect, and aging phenomena. There are two main ingredients considered to be pivotal for the existence of SG behavior, namely, frustration and randomness. For the canonical SG system, frustration is led by the presence of competing interaction between ferromagnetic (FM) and antiferromagnetic (AF) couplings. Previously, Bartolozzi et al. [Phys. Rev. B73, 224419 (2006)], reported the SG properties of the AF Ising spins on scale free network (SFN). It is a new type of SG, different from the canonical one which requires the presence of both FM and AF couplings. In this new system, frustration is purely caused by the topological factor and its randomness is related to the irregular connectvity. Recently, Surungan et. al. [Journal of Physics: Conference Series, 640, 012001 (2015)] reported SG bahavior of AF Heisenberg model on SFN. We further investigate this type of system by studying an AF Heisenberg model on rewired square lattices. We used Replica Exchange algorithm of Monte Carlo Method and calculated the SG order parameter to search for the existence of SG phase.

  13. Feedback control of nuclear spin bath of a single hole spin in a quantum dot

    NASA Astrophysics Data System (ADS)

    Pang, Hongliang; Gong, Zhirui; Yao, Wang

    2015-01-01

    For a III-V semiconductor quantum dot charged with a single hole, we investigate the feedback control of the nuclear spin bath through dynamical nuclear spin polarization. The scheme utilizes the hole-nuclear flip-flop by their anisotropic hyperfine interaction, where the flip direction of the nuclear spin can be conditioned on the sign of the overall hyperfine field through initialization processes that do not involve explicit measurement. We show that a negative feedback can be implemented to suppress the statistical fluctuations of the nuclear hyperfine field for enhancing the coherence time of the hole spin qubit. Positive feedback can prepare the nuclear spin ensemble into states where the nuclear hyperfine field distribution has two well separated peaks, realizing a quantum heat bath that cannot be described by a single effective temperature.

  14. Charge noise, spin-orbit coupling, and dephasing of single-spin qubits

    SciTech Connect

    Bermeister, Adam; Keith, Daniel; Culcer, Dimitrie

    2014-11-10

    Quantum dot quantum computing architectures rely on systems in which inversion symmetry is broken, and spin-orbit coupling is present, causing even single-spin qubits to be susceptible to charge noise. We derive an effective Hamiltonian for the combined action of noise and spin-orbit coupling on a single-spin qubit, identify the mechanisms behind dephasing, and estimate the free induction decay dephasing times T{sub 2}{sup *} for common materials such as Si and GaAs. Dephasing is driven by noise matrix elements that cause relative fluctuations between orbital levels, which are dominated by screened whole charge defects and unscreened dipole defects in the substrate. Dephasing times T{sub 2}{sup *} differ markedly between materials and can be enhanced by increasing gate fields, choosing materials with weak spin-orbit, making dots narrower, or using accumulation dots.

  15. Emergent spin

    SciTech Connect

    Creutz, Michael

    2014-03-15

    Quantum mechanics and relativity in the continuum imply the well known spin–statistics connection. However for particles hopping on a lattice, there is no such constraint. If a lattice model yields a relativistic field theory in a continuum limit, this constraint must “emerge” for physical excitations. We discuss a few models where a spin-less fermion hopping on a lattice gives excitations which satisfy the continuum Dirac equation. This includes such well known systems such as graphene and staggered fermions. -- Highlights: •The spin–statistics theorem is not required for particles on a lattice. •Spin emerges dynamically when spinless fermions have a relativistic continuum limit. •Graphene and staggered fermions are examples of this phenomenon. •The phenomenon is intimately tied to chiral symmetry and fermion doubling. •Anomaly cancellation is a crucial feature of any valid lattice fermion action.

  16. Observation of magnetic fragmentation in spin ice

    NASA Astrophysics Data System (ADS)

    Petit, S.; Lhotel, E.; Canals, B.; Ciomaga Hatnean, M.; Ollivier, J.; Mutka, H.; Ressouche, E.; Wildes, A. R.; Lees, M. R.; Balakrishnan, G.

    2016-08-01

    Fractionalized excitations that emerge from a many-body system have revealed rich physics and concepts, from composite fermions in two-dimensional electron systems, revealed through the fractional quantum Hall effect, to spinons in antiferromagnetic chains and, more recently, fractionalization of Dirac electrons in graphene and magnetic monopoles in spin ice. Even more surprising is the fragmentation of the degrees of freedom themselves, leading to coexisting and a priori independent ground states. This puzzling phenomenon was recently put forward in the context of spin ice, in which the magnetic moment field can fragment, resulting in a dual ground state consisting of a fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic monopole crystal. Here we show, by means of neutron scattering measurements, that such fragmentation occurs in the spin ice candidate Nd2Zr2O7. We observe the spectacular coexistence of an antiferromagnetic order induced by the monopole crystallization and a fluctuating state with ferromagnetic correlations. Experimentally, this fragmentation manifests itself through the superposition of magnetic Bragg peaks, characteristic of the ordered phase, and a pinch point pattern, characteristic of the Coulomb phase. These results highlight the relevance of the fragmentation concept to describe the physics of systems that are simultaneously ordered and fluctuating.

  17. Effects of Iron Depletion on CALM-AF10 Leukemias

    PubMed Central

    Heath, Jessica L.; Weiss, Joshua M.

    2014-01-01

    Iron, an essential nutrient for cellular growth and proliferation, enters cells via clathrin-mediated endocytosis (CME). The clathrin assembly lymphoid myeloid (CALM) protein plays an essential role in the cellular import of iron by CME. CALM-AF10 leukemias harbor a single copy of the normal CALM gene, and may therefore be more sensitive to the growth inhibitory effect of iron restriction compared with normal hematopoietic cells. We found that Calm heterozygous (CalmHET) murine fibroblasts exhibit signs of iron deficiency, with increased surface transferrin receptor (sTfR) levels and reduced growth rates. CalmHET hematopoietic cells are more sensitive in vitro to iron chelators than their wild type counterparts. Iron chelation also displayed toxicity towards cultured CalmHET CALM-AF10 leukemia cells and this effect was additive to that of chemotherapy. In mice transplanted with CalmHET CALM-AF10 leukemia, we found that dietary iron restriction reduces tumor burden in the spleen. However, dietary iron restriction, used alone or in conjunction with chemotherapy, did not increase survival of mice with CalmHET CALM-AF10 leukemia. In summary, while Calm heterozygosity results in iron deficiency and increased sensitivity to iron chelation in vitro, our data in mice do not suggest that iron depletion strategies would be beneficial for the therapy of CALM-AF10 leukemia patients. PMID:25193880

  18. Decoupling a hole spin qubit from the nuclear spins.

    PubMed

    Prechtel, Jonathan H; Kuhlmann, Andreas V; Houel, Julien; Ludwig, Arne; Valentin, Sascha R; Wieck, Andreas D; Warburton, Richard J

    2016-09-01

    A huge effort is underway to develop semiconductor nanostructures as low-noise hosts for qubits. The main source of dephasing of an electron spin qubit in a GaAs-based system is the nuclear spin bath. A hole spin may circumvent the nuclear spin noise. In principle, the nuclear spins can be switched off for a pure heavy-hole spin. In practice, it is unknown to what extent this ideal limit can be achieved. A major hindrance is that p-type devices are often far too noisy. We investigate here a single hole spin in an InGaAs quantum dot embedded in a new generation of low-noise p-type device. We measure the hole Zeeman energy in a transverse magnetic field with 10 neV resolution by dark-state spectroscopy as we create a large transverse nuclear spin polarization. The hole hyperfine interaction is highly anisotropic: the transverse coupling is <1% of the longitudinal coupling. For unpolarized, randomly fluctuating nuclei, the ideal heavy-hole limit is achieved down to nanoelectronvolt energies; equivalently dephasing times up to a microsecond. The combination of large and strong optical dipole makes the single hole spin in a GaAs-based device an attractive quantum platform. PMID:27454044

  19. Nanometer-scale probing of spin waves using single electron spins

    NASA Astrophysics Data System (ADS)

    van der Sar, Toeno; Casola, Francesco; Walsworth, Ronald; Yacoby, Amir

    2015-05-01

    We have developed a new approach to exploring magnetic excitations in correlated-electron systems, based on single electronic spins in atom-like defects diamond known as nitrogen-vacancy (NV) color centers. We demonstrate the power of this approach by detecting spin-wave excitations in a ferromagnetic microdisc with nanoscale spatial sensitivity over a broad range of frequencies and magnetic fields. We show how spin-wave resonances can be exploited for on-chip amplification of microwave magnetic fields, allowing strongly increased spin manipulation rates and single-spin magnetometry with enhanced sensitivity. Finally, we show the possibility to detect the magnetic spin noise produced by a thin (~ 30 nm) layer of a patterned ferromagnet. For the interpretation of our results, we develop a general framework describing single-spin stray field detection in terms of a filter function sensitive mostly to spin fluctuations with wavevector ~ 1 / d , where d is the NV-ferromagnet distance. Our results pave the way towards quantitative and non-perturbative detection of spectral properties in nanomagnets, establishing NV center magnetometry as an emergent probe of collective spin dynamics in condensed matter.

  20. Quantum spin ice: a search for gapless quantum spin liquids in pyrochlore magnets.

    PubMed

    Gingras, M J P; McClarty, P A

    2014-05-01

    The spin ice materials, including Ho2Ti2O7 and Dy2Ti2O7, are rare-earth pyrochlore magnets which, at low temperatures, enter a constrained paramagnetic state with an emergent gauge freedom. Spin ices provide one of very few experimentally realized examples of fractionalization because their elementary excitations can be regarded as magnetic monopoles and, over some temperature range, spin ice materials are best described as liquids of these emergent charges. In the presence of quantum fluctuations, one can obtain, in principle, a quantum spin liquid descended from the classical spin ice state characterized by emergent photon-like excitations. Whereas in classical spin ices the excitations are akin to electrostatic charges with a mutual Coulomb interaction, in the quantum spin liquid these charges interact through a dynamic and emergent electromagnetic field. In this review, we describe the latest developments in the study of such a quantum spin ice, focusing on the spin liquid phenomenology and the kinds of materials where such a phase might be found. PMID:24787264

  1. Modeling of low- and high-frequency noise by slow and fast fluctuators

    NASA Astrophysics Data System (ADS)

    Nesterov, Alexander I.; Berman, Gennady P.

    2012-05-01

    We study the dynamics of dephasing in a quantum two-level system by modeling both 1/f and high-frequency noise by random telegraph processes. Our approach is based on a so-called spin-fluctuator model in which a noisy environment is modeled by a large number of fluctuators. In the continuous limit we obtain an effective random process (ERP) that is described by a distribution function of the fluctuators. In a simplified model, we reduce the ERP to the two (slow and fast) ensembles of fluctuators. Using this model, we study decoherence in a superconducting flux qubit and we compare our theoretical results with the available experimental data. We demonstrate good agreement of our theoretical predictions with the experiments. Our approach can be applied to many quantum systems, such as biological complexes, semiconductors, superconducting, and spin qubits, where the effects of interaction with the environment are essential.

  2. Decoherence imaging of spin ensembles using a scanning single-electron spin in diamond

    PubMed Central

    Luan, Lan; Grinolds, Michael S.; Hong, Sungkun; Maletinsky, Patrick; Walsworth, Ronald L.; Yacoby, Amir

    2015-01-01

    The nitrogen-vacancy (NV) defect center in diamond has demonstrated great capability for nanoscale magnetic sensing and imaging for both static and periodically modulated target fields. However, it remains a challenge to detect and image randomly fluctuating magnetic fields. Recent theoretical and numerical works have outlined detection schemes that exploit changes in decoherence of the detector spin as a sensitive measure for fluctuating fields. Here we experimentally monitor the decoherence of a scanning NV center in order to image the fluctuating magnetic fields from paramagnetic impurities on an underlying diamond surface. We detect a signal corresponding to roughly 800 μB in 2 s of integration time, without any control on the target spins, and obtain magnetic-field spectral information using dynamical decoupling techniques. The extracted spatial and temporal properties of the surface paramagnetic impurities provide insight to prolonging the coherence of near-surface qubits for quantum information and metrology applications. PMID:25631646

  3. Sunward-propagating Alfvénic Fluctuations Observed in the Heliosphere

    NASA Astrophysics Data System (ADS)

    Li, Hui; Wang, Chi; Belcher, John W.; He, Jiansen; Richardson, John D.

    2016-06-01

    The mixture/interaction of anti-sunward-propagating Alfvénic fluctuations (AFs) and sunward-propagating Alfvénic fluctuations (SAFs) is believed to result in the decrease of the Alfvénicity of solar wind fluctuations with increasing heliocentric distance. However, SAFs are rarely observed at 1 au and solar wind AFs are found to be generally outward. Using the measurements from Voyager 2 and Wind, we perform a statistical survey of SAFs in the heliosphere inside 6 au. We first report two SAF events observed by Voyager 2. One is in the anti-sunward magnetic sector with a strong positive correlation between the fluctuations of magnetic field and solar wind velocity. The other one is in the sunward magnetic sector with a strong negative magnetic field—velocity correlation. Statistically, the percentage of SAFs increases gradually with heliocentric distance, from about 2.7% at 1.0 au to about 8.7% at 5.5 au. These results provide new clues for understanding the generation mechanism of SAFs.

  4. Quantum size effects in competing charge and spin orderings of dangling bond wires on Si(001)

    SciTech Connect

    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.

  5. Glassiness and exotic entropy scaling induced by quantum fluctuations in a disorder-free frustrated magnet

    PubMed Central

    Klich, I.; Lee, S.-H.; Iida, K.

    2014-01-01

    When spins are arranged in a lattice of triangular motif, the phenomenon of frustration leads to numerous energetically equivalent ground states, and results in exotic states such as spin liquid and spin ice. Here we report an alternative situation: a system, classically a liquid, freezes in the clean limit into a glassy state induced by quantum fluctuations. We call such glassy state a spin jam. The case in point is a frustrated magnet, where spins are arranged in a triangular network of bipyramids. Quantum corrections break the classical degeneracy into a set of aperiodic spin configurations forming local minima in a rugged energy landscape. This is established by mapping the problem into tiling with hexagonal tiles. The number of tessellations scales with the boundary length rather than its volume, showing the absence of local zero-energy modes. Low-temperature thermodynamics is discussed to compare it with other glassy materials. PMID:24686398

  6. NMR evidence for inhomogeneous nematic fluctuations in BaFe2(As1-xPx)2

    NASA Astrophysics Data System (ADS)

    Dioguardi, Adam P.; Kissikov, Tanat; Lin, Ching-Han; Shirer, Kent R.; Lawson, Matthew M.; Grafe, Hans-Joachim; Chu, Jiun-Haw; Fisher, Ian R.; Fernandes, Rafael M.; Curro, Nicholas J.

    We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe2As2 single crystals. Both the 75As and 31P sites exhibit stretched-exponential relaxation similar to the electron-doped systems. By comparing the hyperfine fields and the relaxation rates at these sites we find that the As relaxation cannot be explained solely in terms of magnetic spin fluctuations. We demonstrate that nematic fluctuations couple to the As nuclear quadrupolar moment and can explain the excess relaxation. These results suggest that glassy nematic dynamics are a universal phenomenon in the iron-based superconductors.

  7. NMR Evidence for Inhomogeneous Nematic Fluctuations in BaFe2 (As1 -xPx )2

    NASA Astrophysics Data System (ADS)

    Dioguardi, A. P.; Kissikov, T.; Lin, C. H.; Shirer, K. R.; Lawson, M. M.; Grafe, H.-J.; Chu, J.-H.; Fisher, I. R.; Fernandes, R. M.; Curro, N. J.

    2016-03-01

    We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe2As2 single crystals. Both the 75As and 31 sites exhibit a stretched-exponential relaxation similar to the electron-doped systems. By comparing the hyperfine fields and the relaxation rates at these sites we find that the As relaxation cannot be explained solely in terms of magnetic spin fluctuations. We demonstrate that nematic fluctuations couple to the As nuclear quadrupolar moment and can explain the excess relaxation. These results suggest that glassy nematic dynamics are a common phenomenon in the iron-based superconductors.

  8. NMR evidence for inhomogeneous nematic fluctuations in BaFe2(As1-xPx)2

    DOE PAGESBeta

    Dioguardi, A. P.; Kissikov, T.; Lin, C. H.; Shirer, K. R.; Lawson, M. M.; Grafe, H. -J.; Chu, J. -H.; Fisher, I. R.; Fernandes, R. M.; Curro, N. J.

    2016-03-10

    We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe2As2 single crystals. Both the 75As and 31P sites exhibit a stretched-exponential relaxation similar to the electron-doped systems. By comparing the hyperfine fields and the relaxation rates at these sites we find that the As relaxation cannot be explained solely in terms of magnetic spin fluctuations. We demonstrate that nematic fluctuations couple to the As nuclear quadrupolar moment and can explain the excess relaxation. Lastly, these results suggest that glassy nematic dynamics are a common phenomenon in the iron-based superconductors.

  9. Chemical Applications of Fluctuation Spectroscopy.

    ERIC Educational Resources Information Center

    Green, Michael E.

    1984-01-01

    Examines some of the possibilities for applying the noise spectroscopic technique as well as the origin of noise (or fluctuations) which accompanies transport in physical systems. Indicates that fluctuation techniques are useful in studying liposome and micelle suspensions, liquid-liquid surfaces, semiconductors, and semiconductor devices. (JN)

  10. Fluctuations as stochastic deformation.

    PubMed

    Kazinski, P O

    2008-04-01

    A notion of stochastic deformation is introduced and the corresponding algebraic deformation procedure is developed. This procedure is analogous to the deformation of an algebra of observables like deformation quantization, but for an imaginary deformation parameter (the Planck constant). This method is demonstrated on diverse relativistic and nonrelativistic models with finite and infinite degrees of freedom. It is shown that under stochastic deformation the model of a nonrelativistic particle interacting with the electromagnetic field on a curved background passes into the stochastic model described by the Fokker-Planck equation with the diffusion tensor being the inverse metric tensor. The first stochastic correction to the Newton equations for this system is found. The Klein-Kramers equation is also derived as the stochastic deformation of a certain classical model. Relativistic generalizations of the Fokker-Planck and Klein-Kramers equations are obtained by applying the procedure of stochastic deformation to appropriate relativistic classical models. The analog of the Fokker-Planck equation associated with the stochastic Lorentz-Dirac equation is derived too. The stochastic deformation of the models of a free scalar field and an electromagnetic field is investigated. It turns out that in the latter case the obtained stochastic model describes a fluctuating electromagnetic field in a transparent medium. PMID:18517590

  11. Fluctuations as stochastic deformation

    NASA Astrophysics Data System (ADS)

    Kazinski, P. O.

    2008-04-01

    A notion of stochastic deformation is introduced and the corresponding algebraic deformation procedure is developed. This procedure is analogous to the deformation of an algebra of observables like deformation quantization, but for an imaginary deformation parameter (the Planck constant). This method is demonstrated on diverse relativistic and nonrelativistic models with finite and infinite degrees of freedom. It is shown that under stochastic deformation the model of a nonrelativistic particle interacting with the electromagnetic field on a curved background passes into the stochastic model described by the Fokker-Planck equation with the diffusion tensor being the inverse metric tensor. The first stochastic correction to the Newton equations for this system is found. The Klein-Kramers equation is also derived as the stochastic deformation of a certain classical model. Relativistic generalizations of the Fokker-Planck and Klein-Kramers equations are obtained by applying the procedure of stochastic deformation to appropriate relativistic classical models. The analog of the Fokker-Planck equation associated with the stochastic Lorentz-Dirac equation is derived too. The stochastic deformation of the models of a free scalar field and an electromagnetic field is investigated. It turns out that in the latter case the obtained stochastic model describes a fluctuating electromagnetic field in a transparent medium.

  12. AF-GEOSpace Version 2.5: Space Environment Software

    NASA Astrophysics Data System (ADS)

    Hilmer, R. V.; Hall, T.; Roth, C.; Ling, A.; Ginet, G. P.; Madden, D.

    2010-12-01

    AF-GEOSpace is a graphics-intensive software program with space environment models and applications developed by the Space Weather Center of Excellence at AFRL. The software addresses a wide range of physical domains, e.g., solar disturbance propagation, geomagnetic field and radiation belt configurations, auroral particle precipitation, and ionospheric scintillation. AF-GEOSpace has become a platform for developing and prototyping space weather visualization products. The new AF-GEOSpace Version 2.5 (release scheduled for 2010) expands on the content of Version 2.1 by including modules addressing the following new topics: (1) energetic proton maps for the South Atlantic Anomaly (from Ginet et al. [2007]), (2) GPS scintillation outage simulation tools, (3) magnetopause location determination (Shue et al. [1998]), (4) a plasmasphere model (Global Core Plasma Model, 2009 version based on Gallagher et al. [2000]), (5) a standard ionospheric model (International Reference Ionosphere 2007), (6) the CAMMICE/MICS model of inner magnetosphere plasma population (based on Roeder et al. [2005]), (7) magnetic field models (e.g., Tsyganenko and Sitnov [2005]), and (8) loading and displaying externally-produced 3D gridded data sets within AF-GEOSpace. Improvements to existing Version 2.1 capabilities include: (1) a 2005 update to the geomagnetic cutoff rigidity model of Smart and Shea [2003], (2) a 2005 update to the ionospheric scintillation Wide-Band Model (WBMOD) of Secan and Bussey [1994], and (3) improved magnetic field flux mapping options for the existing set of AF-GEOSpace radiation belt models. A basic review of these new AF-GEOSpace capabilities will be provided. To obtain a copy of the software, please contact the first author.

  13. AF-GEOSpace Version 2.1 Release

    NASA Astrophysics Data System (ADS)

    Hilmer, R. V.; Ginet, G. P.; Hall, T.; Holeman, E.; Madden, D.; Perry, K. L.; Tautz, M.; Roth, C.

    2006-05-01

    AF-GEOSpace Version 2.1 is a graphics-intensive software program with space environment models and applications developed recently by the Space Weather Center of Excellence at AFRL. A review of new and planned AF-GEOSpace capabilities will be given. The software addresses a wide range of physical domains and addresses such topics as solar disturbance propagation, geomagnetic field and radiation belt configurations, auroral particle precipitation, and ionospheric scintillation. Building on the success of previous releases, AF-GEOSpace has become a platform for the rapid prototyping of automated operational and simulation space weather visualization products and helps with a variety of tasks, including: orbit specification for radiation hazard avoidance; satellite design assessment and post-event anomaly analysis; solar disturbance effects forecasting; determination of link outage regions for active ionospheric conditions; satellite magnetic conjugate studies, scientific model validation and comparison, physics research, and education. Previously, Version 2.0 provided a simplified graphical user interface, improved science and application modules, significantly enhanced graphical performance, common input data archive sets, and 1-D, 2-D, and 3- D visualization tools for all models. Dynamic capabilities permit multiple environments to be generated at user- specified time intervals while animation tools enable the display of satellite orbits and environment data together as a function of time. Building on the Version 2.0 software architecture, AF-GEOSpace Version 2.1 includes a host of new modules providing, for example, plasma sheet charged particle fluxes, neutral atmosphere densities, 3-D cosmic ray cutoff maps, low-altitude trapped proton belt flux specification, DMSP particle data displays, satellite magnetic field footprint mapping determination, and meteor sky maps and shower/storm fluxes with spacecraft impact probabilities. AF-GEOSpace Version 2.1 was

  14. Frequency fluctuations in silicon nanoresonators

    NASA Astrophysics Data System (ADS)

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C.; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K.; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L.; Jourdan, Guillaume; Hentz, Sébastien

    2016-06-01

    Frequency stability is key to the performance of nanoresonators. This stability is thought to reach a limit with the resonator's ability to resolve thermally induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature and found a similar discrepancy. We propose a new method to show that this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices.

  15. Fluctuation phenomena in layered superconductors

    SciTech Connect

    Klemm, R.A.

    1996-10-01

    Gaussian fluctuations in layered superconductors have been the subject of study for many years. Although the FD was studied in detail long ago, the FC (fluctuation conductivity) was studied only recently, since the MT and DOS diagrams were previously neglected. Recent comparisons with experiment on YBCO have shown that the DOS diagrams are important and can lead to qualitatively different behaviors for the FC parallel and perpendicular to the layers. In both cases, Gaussian fluctuations fit the data above {Tc} very well, even for YBCO. To date, nearly all calculations of fluctuation quantities were for B{parallel}{cflx c}. Nevertheless, it should be possible to treat an arbitrary B, but the evaluation of the required matrix elements for the fluctuation quantities will be more complicated.

  16. Nonequilibrium fluctuations in a resistor

    NASA Astrophysics Data System (ADS)

    Garnier, N.; Ciliberto, S.

    2005-06-01

    In small systems where relevant energies are comparable to thermal agitation, fluctuations are of the order of average values. In systems in thermodynamical equilibrium, the variance of these fluctuations can be related to the dissipation constant in the system, exploiting the fluctuation-dissipation theorem. In nonequilibrium steady systems, fluctuations theorems (FT) additionally describe symmetry properties of the probability density functions (PDFs) of the fluctuations of injected and dissipated energies. We experimentally probe a model system: an electrical dipole driven out of equilibrium by a small constant current I , and show that FT are experimentally accessible and valid. Furthermore, we stress that FT can be used to measure the dissipated power P¯ =R I2 in the system by just studying the PDFs’ symmetries.

  17. Frequency fluctuations in silicon nanoresonators.

    PubMed

    Sansa, Marc; Sage, Eric; Bullard, Elizabeth C; Gély, Marc; Alava, Thomas; Colinet, Eric; Naik, Akshay K; Villanueva, Luis Guillermo; Duraffourg, Laurent; Roukes, Michael L; Jourdan, Guillaume; Hentz, Sébastien

    2016-06-01

    Frequency stability is key to the performance of nanoresonators. This stability is thought to reach a limit with the resonator's ability to resolve thermally induced vibrations. Although measurements and predictions of resonator stability usually disregard fluctuations in the mechanical frequency response, these fluctuations have recently attracted considerable theoretical interest. However, their existence is very difficult to demonstrate experimentally. Here, through a literature review, we show that all studies of frequency stability report values several orders of magnitude larger than the limit imposed by thermomechanical noise. We studied a monocrystalline silicon nanoresonator at room temperature and found a similar discrepancy. We propose a new method to show that this was due to the presence of frequency fluctuations, of unexpected level. The fluctuations were not due to the instrumentation system, or to any other of the known sources investigated. These results challenge our current understanding of frequency fluctuations and call for a change in practices. PMID:26925826

  18. GPIM AF-M315E Propulsion System

    NASA Technical Reports Server (NTRS)

    Spores, Ronald A.; Masse, Robert; Kimbrel, Scott; McLean, Chris

    2014-01-01

    The NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) Technology Demonstration Mission (TDM) will demonstrate an operational AF-M315E green propellant propulsion system. Aerojet-Rocketdyne is responsible for the development of the propulsion system payload. This paper statuses the propulsion system module development, including thruster design and system design; Initial test results for the 1N engineering model thruster are presented. The culmination of this program will be high-performance, green AF-M315E propulsion system technology at TRL 7+, with components demonstrated to TRL 9, ready for direct infusion to a wide range of applications for the space user community.

  19. Spin injection into semiconductors

    NASA Astrophysics Data System (ADS)

    Oestreich, M.; Hübner, J.; Hägele, D.; Klar, P. J.; Heimbrodt, W.; Rühle, W. W.; Ashenford, D. E.; Lunn, B.

    1999-03-01

    The injection of spin-polarized electrons is presently one of the major challenges in semiconductor spin electronics. We propose and demonstrate a most efficient spin injection using diluted magnetic semiconductors as spin aligners. Time-resolved photoluminescence with a Cd0.98Mn0.02Te/CdTe structure proves the feasibility of the spin-alignment mechanism.

  20. Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets

    NASA Astrophysics Data System (ADS)

    Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.

    2016-05-01

    Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.

  1. Controlling spin relaxation with a cavity

    NASA Astrophysics Data System (ADS)

    Bienfait, Audrey; Pla, Jarryd; Kubo, Yuimaru; Zhou, Xin; Stern, Michael; Lo, Cheuk; Weis, Christopher; Schenkel, Thomas; Vion, Denis; Esteve, Daniel; Morton, John; Bertet, Patrice

    Spontaneous emission of radiation is one of the fundamental relaxation mechanisms for a quantum system. For spins, however, it is negligible compared to non-radiative relaxation processes due to their weak coupling to the electromagnetic field. In 1946, Purcell realized that spontaneous emission is strongly enhanced when the quantum system is placed in a resonant cavity - an effect now used to control the lifetime of systems with an electrical dipole. Here, by coupling donor spins in silicon to a high quality factor superconducting microwave cavity of small mode volume, we reach the regime where spontaneous emission constitutes the dominant spin relaxation channel. The relaxation rate is increased by three orders of magnitude when the spins are tuned to the cavity resonance, showing it can be engineered and controlled on-demand. Our results provide a novel way to initialize any spin into its ground state, with applications in magnetic resonance and quantum information processing. They also show for the first time an alteration of spin dynamics by quantum fluctuations, a step towards the coherent magnetic coupling of a spin to microwave photons.

  2. Quantum dynamics in strong fluctuating fields

    NASA Astrophysics Data System (ADS)

    Goychuk, Igor; Hänggi, Peter

    A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems, such as e.g. nonadiabatic electron transfer in proteins, can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. This may occur, for example, for the tunnelling coupling between the donor and acceptor states of the transferring electron, or for the corresponding energy difference between electronic states which assume via the coupling to the fluctuating environment an explicit stochastic or deterministic time-dependence. Here, we review the general theoretical framework which is based on the method of projector operators, yielding the quantum master equations for systems that are exposed to strong external fields. This allows one to investigate on a common basis, the influence of nonequilibrium fluctuations and periodic electrical fields on those already mentioned dynamics and related quantum transport processes. Most importantly, such strong fluctuating fields induce a whole variety of nonlinear and nonequilibrium phenomena. A characteristic feature of such dynamics is the absence of thermal (quantum) detailed balance.ContentsPAGE1. Introduction5262. Quantum dynamics in stochastic fields531 2.1. Stochastic Liouville equation531 2.2. Non-Markovian vs. Markovian discrete

  3. Spin noise of electrons and holes in (In,Ga)As quantum dots: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Glasenapp, Ph.; Smirnov, D. S.; Greilich, A.; Hackmann, J.; Glazov, M. M.; Anders, F. B.; Bayer, M.

    2016-05-01

    The spin fluctuations of electron and hole doped self-assembled quantum dot ensembles are measured optically in the low-intensity limit of a probe laser for absence and presence of longitudinal or transverse magnetic fields. The experimental results are modeled by two complementary approaches based either on a semiclassical or quantum mechanical description. This allows us to characterize the hyperfine interaction of electron and hole spins with the surrounding bath of nuclei on time scales covering several orders of magnitude. Our results demonstrate (i) the intrinsic precession of the electron spin fluctuations around the effective Overhauser field caused by the host lattice nuclear spins, (ii) the comparably long time scales for electron and hole spin decoherence, as well as (iii) the dramatic enhancement of the spin lifetimes induced by a longitudinal magnetic field due to the decoupling of nuclear and charge carrier spins.

  4. What can we learn about the dynamics of transported spins by measuring shot noise in spin-orbit-coupled nanostructures?

    NASA Astrophysics Data System (ADS)

    Nikolić, Branislav K.; Dragomirova, Ralitsa L.

    2009-06-01

    We review recent studies of the shot noise of spin-polarized charge currents and pure spin currents in multiterminal semiconductor nanostructures, while focusing on the effects brought by the intrinsic Rashba spin-orbit (SO) coupling and/or extrinsic SO scattering off impurities in two-dimensional electron gas (2DEG) based devices. By generalizing the scattering theory of quantum shot noise to include the full spin-density matrix of electrons injected from a spin-filtering electrode, we show how decoherence and dephasing in the course of spin precession can lead to the substantial enhancement of the Fano factor (noise-to-current ratio) of spin-polarized charge currents. These processes are suppressed by decreasing the width of the diffusive Rashba wire, so that purely electrical measurement of the shot noise in a ferromagnet|SO-coupled-diffusive-wire|paramagnet setup can quantify the degree of quantum coherence of transported spin through a remarkable one-to-one correspondence between the purity of the spin state and the Fano factor. In four-terminal SO-coupled nanostructures, injection of unpolarized charge current through the longitudinal leads is responsible not only for the pure spin Hall current in the transverse leads, but also for nonequilibrium random time-dependent current fluctuations. The analysis of the shot noise of transverse pure spin Hall current and zero charge current, or transverse spin current and non-zero charge Hall current, driven by unpolarized or spin-polarized injected longitudinal charge current, respectively, reveals a unique experimental tool to differentiate between the intrinsic Rashba and extrinsic SO mechanisms underlying the spin Hall effect in 2DEG devices. When the intrinsic mechanisms responsible for spin precession start to dominate the spin Hall effect, they also enhance the shot noise of transverse spin and charge transport in multiterminal geometries. Finally, we discuss the shot noise of transverse spin and zero charge

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  6. Molecular and functional identification of three interleukin-17A/F (IL-17A/F) homologues in large yellow croaker (Larimichthys crocea).

    PubMed

    Ding, Yang; Ao, Jingqun; Ai, Chunxiang; Chen, Xinhua

    2016-02-01

    The interleukin-17 (IL-17) cytokine family plays a central role in the coordination of inflammatory responses. In fish species, three genes that have a similar homology to both IL-17A and IL-17F were designated IL-17A/F1, 2, and 3. In this study, we identified three IL-17A/F homologues (LycIL-17A/F1, 2, and 3) from large yellow croaker (Larimichthys crocea). The deduced LycIL-17A/F1 and 3 had four cysteine residues conserved in teleost IL-17A/F1 and 3 homologues and shared a domain similar to the B chain of human IL-17F. The deduced LycIL-17A/F2 possessed the unique arrangement of six cysteine residues as teleost IL-17A/F2 (except Fugu IL-17A/F2) and higher vertebrate IL-17A and F, and shared a domain similar to the D/E chain of human IL-17A. Phylogenetic analysis showed that teleost IL-17A/F1 and 3 fall into a major clade, whereas IL-17A/F2 forms a separated clade and is clustered with IL-17N. Based on structural and phylogenetic analyses, we suggest that teleost IL-17A/Fs may be classified into two subgroups: one consisting of IL-17A/F1 and 3, and the other composed of IL-17A/F2. The three LycIL-17A/Fs were constitutively expressed in all tissues examined although at a different level. Following challenge with Aeromonas hydrophila, expression of these three LycIL-17A/Fs was rapidly increased in head kidney and gills. The in vivo assays showed that recombinant LycIL-17A/F1, 2, and 3 all were able to enhance the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α2), chemokines (CXCL8 and CXCL13), and antimicrobial peptide hepcidin in head kidney. Furthermore, LycIL-17A/Fs appeared to mediate pro-inflammatory responses via NF-κB signalling. These results therefore reveal similar functions between the two subgroup members,LycIL-17A/F1 and 3 and LycIL-17A/F2, in promoting inflammation and host defences. PMID:26429410

  7. Spin noise in mixed Spin Systems

    NASA Astrophysics Data System (ADS)

    Bauch, Erik; Junghyun, Paul; Singh, Swati; Devakul, Trithep; Feguin, Adrian; Hart, Connor; Walsworth, Ronald

    2016-05-01

    The spin noise due to interaction of multiple spin species in mixed spin systems provides a fundamental limit to ultra-sensitive ensemble sensing and quantum information applications. In our work, we investigate the interaction of dense nuclear 13C spins with electronic nitrogen spins using Nitrogen-Vacancy centers in diamond. Our work shows experimentally and theoretically, that under certain conditions, spin noise is greatly suppressed and the coherence time of NV centers improved by order of magnitudes, providing a pathway to engineering high density ensemble samples with long coherence times at room temperature.

  8. An Empirical Test of Oklahoma's A-F School Grades

    ERIC Educational Resources Information Center

    Adams, Curt M.; Forsyth, Patrick B.; Ware, Jordan; Mwavita, Mwarumba; Barnes, Laura L.; Khojasteb, Jam

    2016-01-01

    Oklahoma is one of 16 states electing to use an A-F letter grade as an indicator of school quality. On the surface, letter grades are an attractive policy instrument for school improvement; they are seemingly clear, simple, and easy to interpret. Evidence, however, on the use of letter grades as an instrument to rank and improve schools is scant…

  9. R2 AIRS/AFS FACILITY GIS LAYER

    EPA Science Inventory

    The AFS subsystem contains emissions, compliance, and permit data for stationary sources regulated by the U.S. EPA and state and local air pollution agencies. This information is used by states in preparation of State Implementation Plans (SIPs), to track the compliance status ...

  10. R2 AIRS/AFS PERMITS GIS LAYER

    EPA Science Inventory

    The Region 2 AIRS/AFS Permits Regulated Facility GIS layer contains identification (name, address, ID), and location (latitude, longitude, and locational metadata), attributes of stationary source(s) of air pollution associated with facilities that are regulated by the U. S. EPA....

  11. Treatment Guidelines of Atrial Fibrillation (AFib or AF)

    MedlinePlus

    ... Pressure Tools & Resources Stroke More Treatment Guidelines of Atrial Fibrillation (AFib or AF) Updated:Jun 23,2016 What ... content was last reviewed on 04/16/14. Atrial Fibrillation • Introduction • What is Atrial Fibrillation? • Why AFib Matters • ...

  12. Spin-lattice relaxation of heavy spin-1/2 nuclei in diamagnetic solids: A Raman process mediated by spin-rotation interaction

    NASA Astrophysics Data System (ADS)

    Vega, Alexander J.; Beckmann, Peter A.; Bai, Shi; Dybowski, Cecil

    2006-12-01

    We present a theory for the nuclear spin-lattice relaxation of heavy spin-1/2 nuclei in solids, which explains within an order of magnitude the unexpectedly effective lead and thallium nuclear spin-lattice relaxation rates observed in the ionic solids lead molybdate, lead chloride, lead nitrate, thallium nitrate, thallium nitrite, and thallium perchlorate. The observed rates are proportional to the square of the temperature and are independent of magnetic field. This rules out all known mechanisms usually employed to model nuclear spin relaxation in lighter spin-1/2 nuclei. The relaxation is caused by a Raman process involving the interactions between nuclear spins and lattice vibrations via a fluctuating spin-rotation magnetic field. The model places an emphasis on the time dependence of the angular velocity of pairs of adjacent atoms rather than on their angular momentum. Thus the spin-rotation interaction is characterized not in the traditional manner by a spin-rotation constant but by a related physical parameter, the magnetorotation constant, which relates the local magnetic field generated by spin rotation to an angular velocity. Our semiclassical relaxation model involves a frequency-mode description of the spectral density that can directly be related to the mean-square amplitudes and mode densities of lattice vibrations in the Debye model.

  13. Extracting uranium from seawater: Promising AF series adsorbents

    SciTech Connect

    Das, Sadananda; Oyola, Y.; Mayes, Richard T.; Janke, Christopher James; Kuo, Li-Jung; Gill, Gary; Wood, Jordana; Dai, Sheng

    2015-11-02

    Here, a new family of high surface area polyethylene fiber adsorbents (AF series) was recently developed at the Oak Ridge National Laboratory (ORNL). The AF series of were synthesized by radiation-induced graft polymerization of acrylonitrile and itaconic acid (at different monomer/co-monomer mol ratios) onto high surface area polyethylene fibers. The degree of grafting (%DOG) of AF series adsorbents was found to be 154 354%. The grafted nitrile groups were converted to amidoxime groups by treating with hydroxylamine. The amidoximated adsorbents were then conditioned with 0.44M KOH at 80 C followed by screening at ORNL with simulated seawater spiked with 8 ppm uranium. Uranium adsorption capacity in simulated seawater screening ranged from 170-200 g-U/kg-ads irrespective of %DOG. A monomer/co-monomer mol ratio in the range of 7.57-10.14 seemed to be optimum for highest uranium loading capacity. Subsequently, the adsorbents were also tested with natural seawater at Pacific Northwest National Laboratory (PNNL) using flow-through exposure uptake experiments to determine uranium loading capacity with varying KOH conditioning time at 80 C. The highest adsorption capacity of AF1 measured after 56 days of marine testing was demonstrated as 3.9 g-U/kg-adsorbent and 3.2 g-U/kg-adsorbent for 1hr and 3hrs of KOH conditioning at 80 C, respectively. Based on capacity values of several AF1 samples, it was observed that changing KOH conditioning from 3hrs to 1hr at 80 C resulted in 22-27% increase in uranium loading capacity in seawater.

  14. Extracting uranium from seawater: Promising AF series adsorbents

    DOE PAGESBeta

    Das, Sadananda; Oyola, Y.; Mayes, Richard T.; Janke, Christopher James; Kuo, Li-Jung; Gill, Gary; Wood, Jordana; Dai, Sheng

    2015-11-02

    Here, a new family of high surface area polyethylene fiber adsorbents (AF series) was recently developed at the Oak Ridge National Laboratory (ORNL). The AF series of were synthesized by radiation-induced graft polymerization of acrylonitrile and itaconic acid (at different monomer/co-monomer mol ratios) onto high surface area polyethylene fibers. The degree of grafting (%DOG) of AF series adsorbents was found to be 154 354%. The grafted nitrile groups were converted to amidoxime groups by treating with hydroxylamine. The amidoximated adsorbents were then conditioned with 0.44M KOH at 80 C followed by screening at ORNL with simulated seawater spiked with 8more » ppm uranium. Uranium adsorption capacity in simulated seawater screening ranged from 170-200 g-U/kg-ads irrespective of %DOG. A monomer/co-monomer mol ratio in the range of 7.57-10.14 seemed to be optimum for highest uranium loading capacity. Subsequently, the adsorbents were also tested with natural seawater at Pacific Northwest National Laboratory (PNNL) using flow-through exposure uptake experiments to determine uranium loading capacity with varying KOH conditioning time at 80 C. The highest adsorption capacity of AF1 measured after 56 days of marine testing was demonstrated as 3.9 g-U/kg-adsorbent and 3.2 g-U/kg-adsorbent for 1hr and 3hrs of KOH conditioning at 80 C, respectively. Based on capacity values of several AF1 samples, it was observed that changing KOH conditioning from 3hrs to 1hr at 80 C resulted in 22-27% increase in uranium loading capacity in seawater.« less

  15. Long-lived nanosecond spin relaxation and spin coherence of electrons in monolayer MoS2 and WS2

    NASA Astrophysics Data System (ADS)

    Yang, Luyi; Sinitsyn, Nikolai A.; Chen, Weibing; Yuan, Jiangtan; Zhang, Jing; Lou, Jun; Crooker, Scott A.

    2015-10-01

    The recently discovered monolayer transition metal dichalcogenides (TMDCs) provide a fertile playground to explore new coupled spin-valley physics. Although robust spin and valley degrees of freedom are inferred from polarized photoluminescence (PL) experiments, PL timescales are necessarily constrained by short-lived (3-100 ps) electron-hole recombination. Direct probes of spin/valley polarization dynamics of resident carriers in electron (or hole)-doped TMDCs, which may persist long after recombination ceases, are at an early stage. Here we directly measure the coupled spin-valley dynamics in electron-doped MoS2 and WS2 monolayers using optical Kerr spectroscopy, and reveal very long electron spin lifetimes, exceeding 3 ns at 5 K (two to three orders of magnitude longer than typical exciton recombination times). In contrast with conventional III-V or II-VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. Supported by a model of coupled spin-valley dynamics, these results indicate a novel mechanism of itinerant electron spin dephasing in the rapidly fluctuating internal spin-orbit field in TMDCs, driven by fast inter-valley scattering. Additionally, a long-lived spin coherence is observed at lower energies, commensurate with localized states. These studies provide insight into the physics underpinning spin and valley dynamics of resident electrons in atomically thin TMDCs.

  16. Effect of antiferromagnetic spin correlations on lattice distortion and charge ordering in Pr0.5Ca1.5MnO4

    PubMed Central

    Chi, Songxue; Ye, F.; Dai, Pengcheng; Fernandez-Baca, J. A.; Huang, Q.; Lynn, J. W.; Plummer, E. W.; Mathieu, R.; Kaneko, Y.; Tokura, Y.

    2007-01-01

    We use neutron scattering to study the lattice and magnetic structure of the layered half-doped manganite Pr0.5Ca1.5MnO4. On cooling from high temperature, the system first becomes charge-and orbital-ordered (CO/OO) near TCO = 300 K and then develops checkerboard-like antiferromagnetic (AF) order below TN = 130 K. At temperatures above TN but below TCO (TNAF spin correlations suppresses the CO/OO-induced orthorhombic strain, contrasting with other half-doped manganites, where AF order has no observable effect on the lattice distortion. These results suggest that a strong spin-lattice coupling and the competition between AF exchange and CO/OO ordering ultimately determines the low-temperature properties of the system. PMID:17578911

  17. Effect of antiferromagnetic spin correlations on lattice distortion and charge ordering in Pr0.5Ca1.5MnO4

    SciTech Connect

    Chi, Songxue; Ye, Feng; Dai, Pengcheng; Fernandez-Baca, Jaime A; Huang, Q.; Lynn, J. W.; Plummer, E Ward; Mathieu, R.; Kaneko, Y.; Tokura, Y.

    2007-01-01

    We use neutron scattering to study the lattice and magnetic structure of the layered half-doped manganite Pr0.5Ca1.5MnO4. On cooling from high temperature, the system first becomes chargeand orbital-ordered (CO/OO) near TCO = 300 K and then develops checkerboard-like antiferromagnetic (AF) order below TN = 130 K. At temperatures above TN but below TCO (TNAF spin correlations suppresses the CO/OOinduced orthorhombic strain, contrasting with other half-doped manganites, where AF order has no observable effect on the lattice distortion. These results suggest that a strong spin-lattice coupling and the competition between AF exchange and CO/OO ordering ultimately determines the low-temperature properties of the system.

  18. 32 CFR 989.12 - AF Form 813, Request for Environmental Impact Analysis.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... record the focusing of environmental issues. ... 32 National Defense 6 2010-07-01 2010-07-01 false AF Form 813, Request for Environmental Impact... FORCE ENVIRONMENTAL PROTECTION ENVIRONMENTAL IMPACT ANALYSIS PROCESS (EIAP) § 989.12 AF Form...

  19. 32 CFR 989.12 - AF Form 813, Request for Environmental Impact Analysis.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... record the focusing of environmental issues. ... 32 National Defense 6 2011-07-01 2011-07-01 false AF Form 813, Request for Environmental Impact... FORCE ENVIRONMENTAL PROTECTION ENVIRONMENTAL IMPACT ANALYSIS PROCESS (EIAP) § 989.12 AF Form...

  20. 32 CFR 989.12 - AF Form 813, Request for Environmental Impact Analysis.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... record the focusing of environmental issues. ... 32 National Defense 6 2013-07-01 2013-07-01 false AF Form 813, Request for Environmental Impact... FORCE ENVIRONMENTAL PROTECTION ENVIRONMENTAL IMPACT ANALYSIS PROCESS (EIAP) § 989.12 AF Form...

  1. Fluctuation Probes of Quark Deconfinement

    SciTech Connect

    Asakawa, Masayuki; Heinz, Ulrich; Mueller, Berndt

    2000-09-04

    The size of the average fluctuations of net baryon number and electric charge in a finite volume of hadronic matter differs widely between the confined and deconfined phases. These differences may be exploited as indicators of the formation of a quark-gluon plasma in relativistic heavy-ion collisions, because fluctuations created in the initial state survive until freeze-out due to the rapid expansion of the hot fireball. (c) 2000 The American Physical Society.

  2. Principle of minimal work fluctuations.

    PubMed

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality 〈e-βW〉=e-βΔF, a change in the fluctuations of e-βW may impact how rapidly the statistical average of e-βW converges towards the theoretical value e-βΔF, where W is the work, β is the inverse temperature, and ΔF is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-βW. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-βW, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-βW. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014)]. PMID:26382367

  3. Principle of minimal work fluctuations

    NASA Astrophysics Data System (ADS)

    Xiao, Gaoyang; Gong, Jiangbin

    2015-08-01

    Understanding and manipulating work fluctuations in microscale and nanoscale systems are of both fundamental and practical interest. For example, in considering the Jarzynski equality =e-β Δ F , a change in the fluctuations of e-β W may impact how rapidly the statistical average of e-β W converges towards the theoretical value e-β Δ F, where W is the work, β is the inverse temperature, and Δ F is the free energy difference between two equilibrium states. Motivated by our previous study aiming at the suppression of work fluctuations, here we obtain a principle of minimal work fluctuations. In brief, adiabatic processes as treated in quantum and classical adiabatic theorems yield the minimal fluctuations in e-β W. In the quantum domain, if a system initially prepared at thermal equilibrium is subjected to a work protocol but isolated from a bath during the time evolution, then a quantum adiabatic process without energy level crossing (or an assisted adiabatic process reaching the same final states as in a conventional adiabatic process) yields the minimal fluctuations in e-β W, where W is the quantum work defined by two energy measurements at the beginning and at the end of the process. In the classical domain where the classical work protocol is realizable by an adiabatic process, then the classical adiabatic process also yields the minimal fluctuations in e-β W. Numerical experiments based on a Landau-Zener process confirm our theory in the quantum domain, and our theory in the classical domain explains our previous numerical findings regarding the suppression of classical work fluctuations [G. Y. Xiao and J. B. Gong, Phys. Rev. E 90, 052132 (2014), 10.1103/PhysRevE.90.052132].

  4. Simulation Of Fluctuating Geomagnetic Index

    NASA Technical Reports Server (NTRS)

    Vedder, John; Tabor, Jill

    1993-01-01

    Mathematical model produces synthetic geomagnetic-index (ap) data including short-term fluctuations like those of real ap data. Measures geomagnetic activity computed from measurements of fluctuations in geomagnetic field taken at 12 high-latitude stations every 3 hours. Used in studies of interactions between solar wind and Earth, especially in studies of effect of geomagnetic field upon heating of thermosphere by impacts of energetic charged solar-wind particles.

  5. Thermally excited proton spin-flip laser emission in tokamaks

    SciTech Connect

    Arunasalam, V.; Greene, G.J.

    1993-07-01

    Based on statistical thermodynamic fluctuation arguments, it is shown here for the first time that thermally excited spin-flip laser emission from the fusion product protons can occur in large tokamak devices that are entering the reactor regime of operation. Existing experimental data from TFTR supports this conjecture, in the sense that these measurements are in complete agreement with the predictions of the quasilinear theory of the spin-flip laser.

  6. Long-lived Spin Relaxation and Spin Coherence of Electrons in Monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Yang, Luyi

    Monolayer MoS2 and related transition metal dichalcogenides (TMDs) are direct-gap semiconductors in which strong spin-orbit coupling and a lack of structural inversion symmetry give rise to new coupled spin-valley physics. Although robust spin and valley degrees of freedom have been inferred from polarized photoluminescence (PL) studies of excitons, PL timescales are necessarily constrained by short (3-100 ps) electron-hole recombination. Direct probes of spin/valley dynamics of resident carriers in electron (or hole)-doped TMDs, which may persist long after recombination ceases, are still at an early stage. Here we directly measure the coupled spin-valley dynamics of resident electrons in n-type monolayer MoS2 using optical Kerr-rotation spectroscopy, and reveal very long spin lifetimes exceeding 3ns at 5K (orders of magnitude longer than typical exciton lifetimes). In contrast with conventional III-V or II-VI semiconductors, spin relaxation accelerates rapidly in small transverse magnetic fields. This suggests a novel mechanism of electron spin dephasing in monolayer TMDs, driven by rapidly-fluctuating internal spin-orbit fields due to fast intervalley scattering. Additionally, a small but very long-lived oscillatory signal is observed, indicating spin coherence of localized states. These studies provide direct insight into the physics underpinning the spin and valley dynamics of electrons in monolayer TMDs. In collaboration with S.A. Crooker & N.A. Sinitsyn (Los Alamos), W. Chen, J. Yuan, J. Zhang & J. Lou (Rice University), K.M. McCreary & B.T. Jonker (Naval Research Lab), and supported by the Los Alamos LDRD program.

  7. Quantum fluctuations of radiation pressure

    SciTech Connect

    Wu, Chun-Hsien; Ford, L. H.

    2001-08-15

    Quantum fluctuations of electromagnetic radiation pressure are discussed. We use an approach based on the quantum stress tensor to calculate the fluctuations in velocity and position of a mirror subjected to electromagnetic radiation. Our approach reveals that radiation pressure fluctuations in the case of a coherent state are due to a cross term between vacuum and state dependent terms in a stress tensor operator product. Thus observation of these fluctuations would entail experimental confirmation of this cross term. We first analyze the pressure fluctuations on a single, perfectly reflecting mirror, and then study the case of an interferometer. This involves a study of the effects of multiple bounces in one arm, as well as the correlations of the pressure fluctuations between arms of the interferometer. In all cases, our results are consistent with those previously obtained by Caves using different methods. We argue that the agreement between the different methods supports the reality of the cross term and justifies the methods used in its evaluation.

  8. Generalised tensor fluctuations and inflation

    SciTech Connect

    Cannone, Dario; Tasinato, Gianmassimo; Wands, David E-mail: g.tasinato@swansea.ac.uk

    2015-01-01

    Using an effective field theory approach to inflation, we examine novel properties of the spectrum of inflationary tensor fluctuations, that arise when breaking some of the symmetries or requirements usually imposed on the dynamics of perturbations. During single-clock inflation, time-reparameterization invariance is broken by a time-dependent cosmological background. In order to explore more general scenarios, we consider the possibility that spatial diffeomorphism invariance is also broken by effective mass terms or by derivative operators for the metric fluctuations in the Lagrangian. We investigate the cosmological consequences of the breaking of spatial diffeomorphisms, focussing on operators that affect the power spectrum of fluctuations. We identify the operators for tensor fluctuations that can provide a blue spectrum without violating the null energy condition, and operators for scalar fluctuations that lead to non-conservation of the comoving curvature perturbation on superhorizon scales even in single-clock inflation. In the last part of our work, we also examine the consequences of operators containing more than two spatial derivatives, discussing how they affect the sound speed of tensor fluctuations, and showing that they can mimic some of the interesting effects of symmetry breaking operators, even in scenarios that preserve spatial diffeomorphism invariance.

  9. Controlling spin relaxation with a cavity

    NASA Astrophysics Data System (ADS)

    Bienfait, A.; Pla, J. J.; Kubo, Y.; Zhou, X.; Stern, M.; Lo, C. C.; Weis, C. D.; Schenkel, T.; Vion, D.; Esteve, D.; Morton, J. J. L.; Bertet, P.

    2016-03-01

    Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the rate of spontaneous emission can be greatly enhanced by placing the quantum system in a resonant cavity. This effect has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, and is essential for the realization of high-efficiency single-photon sources. Here we report the application of this idea to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity with a high quality factor and a small mode volume, we reach the regime in which spontaneous emission constitutes the dominant mechanism of spin relaxation. The relaxation rate is increased by three orders of magnitude as the spins are tuned to the cavity resonance, demonstrating that energy relaxation can be controlled on demand. Our results provide a general way to initialize spin systems into their ground state and therefore have applications in magnetic resonance and quantum information processing. They also demonstrate that the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point at which quantum fluctuations have a marked effect on the spin dynamics; as such, they represent an important step towards the coherent magnetic coupling of individual spins to microwave photons.

  10. Controlling spin relaxation with a cavity.

    PubMed

    Bienfait, A; Pla, J J; Kubo, Y; Zhou, X; Stern, M; Lo, C C; Weis, C D; Schenkel, T; Vion, D; Esteve, D; Morton, J J L; Bertet, P

    2016-03-01

    Spontaneous emission of radiation is one of the fundamental mechanisms by which an excited quantum system returns to equilibrium. For spins, however, spontaneous emission is generally negligible compared to other non-radiative relaxation processes because of the weak coupling between the magnetic dipole and the electromagnetic field. In 1946, Purcell realized that the rate of spontaneous emission can be greatly enhanced by placing the quantum system in a resonant cavity. This effect has since been used extensively to control the lifetime of atoms and semiconducting heterostructures coupled to microwave or optical cavities, and is essential for the realization of high-efficiency single-photon sources. Here we report the application of this idea to spins in solids. By coupling donor spins in silicon to a superconducting microwave cavity with a high quality factor and a small mode volume, we reach the regime in which spontaneous emission constitutes the dominant mechanism of spin relaxation. The relaxation rate is increased by three orders of magnitude as the spins are tuned to the cavity resonance, demonstrating that energy relaxation can be controlled on demand. Our results provide a general way to initialize spin systems into their ground state and therefore have applications in magnetic resonance and quantum information processing. They also demonstrate that the coupling between the magnetic dipole of a spin and the electromagnetic field can be enhanced up to the point at which quantum fluctuations have a marked effect on the spin dynamics; as such, they represent an important step towards the coherent magnetic coupling of individual spins to microwave photons. PMID:26878235

  11. Spin-orbital exchange of strongly interacting fermions in the p band of a two-dimensional optical lattice.

    PubMed

    Zhou, Zhenyu; Zhao, Erhai; Liu, W Vincent

    2015-03-13

    Mott insulators with both spin and orbital degeneracy are pertinent to a large number of transition metal oxides. The intertwined spin and orbital fluctuations can lead to rather exotic phases such as quantum spin-orbital liquids. Here, we consider two-component (spin 1/2) fermionic atoms with strong repulsive interactions on the p band of the optical square lattice. We derive the spin-orbital exchange for quarter filling of the p band when the density fluctuations are suppressed, and show that it frustrates the development of long-range spin order. Exact diagonalization indicates a spin-disordered ground state with ferro-orbital order. The system dynamically decouples into individual Heisenberg spin chains, each realizing a Luttinger liquid accessible at higher temperatures compared to atoms confined to the s band. PMID:25815913

  12. Composite bosons in the two-dimensional BCS-BEC crossover from Gaussian fluctuations

    NASA Astrophysics Data System (ADS)

    Salasnich, L.; Toigo, F.

    2015-01-01

    We study Gaussian fluctuations of the zero-temperature attractive Fermi gas in the two-dimensional (2D) BCS-BEC crossover showing that they are crucial to get a reliable equation of state in the Bose-Einstein condensation (BEC) regime of composite bosons, bound states of fermionic pairs. A low-momentum expansion up to the fourth order of the quadratic action of the fluctuating pairing field gives an ultraviolent divergent contribution of the Gaussian fluctuations to the grand potential. Performing dimensional regularization we evaluate the effective coupling constant in the beyond-mean-field grand potential. Remarkably, in the BEC regime our grand potential gives exactly the Popov's equation of state of 2D interacting bosons, and allows us to identify the scattering length aB of the interaction between composite bosons as aB=aF/(21 /2e1 /4) =0.551 ...aF , with aF is the scattering length of fermions. Remarkably, the value from our analytical relationship between the two scattering lengths is in full agreement with that obtained by recent Monte Carlo calculations.

  13. Neutron scattering studies of spin excitations in superconducting Rb0.82Fe1.68Se2

    SciTech Connect

    Wang, Miaoyin; Li, Chunhong; Abernathy, Douglas L; Song, Yu; Carr, Scott V.; Lu, Xiangye; Li, Shiliang; Yamari, Zahra; Hu, Jiangping; Xiang, Tao; Dai, Pengcheng

    2012-01-01

    We use inelastic neutron scattering to show that superconducting (SC) rubidium iron selenide Rb0.82Fe1.68Se2 exhibits antiferromagnetic (AF) spin excitations near the in-plane wave vector Q = ( ,0) identical to that for iron arsenide superconductors. Moreover, we find that these excitations change from incommensurate to commensurate with increasing energy and occur at the expense of spin waves associated with the coexisting 5 5 block AF phase. Since these spin excitations cannot come from Fermi surface nesting based on angle resolved photoemission experiments, our results indicate the presence of local moments in SC Rb0.82Fe1.68Se2 that may have a similar origin as the hourglass-like spin excitations in copper oxide superconductors.

  14. Order From disorder in Frustrated Spin Systems

    NASA Astrophysics Data System (ADS)

    Coleman, Piers

    This talk will review the phemomenon of ''Order from disorder'': the mechanism by which fluctuations remove a degeneracy within a frustrated spin system. An important consequence of order-from-disorder, is the ability of frustrated Heisenberg spin systems to overcome the Mermin-Wagner theorem, developing new forms of discrete order, even when the spins themselves remain disordered with a finite correlation length. The most well-known example, is the two-dimensional frustrated J1 -J2 Heisenberg model, which undergoes a finite temperature Ising phase transition into a stripy or ''nematic'' state, even though the spins do not order until absolute zero. Nematic ordering of this kind is believed to occur in the iron-based superconductors, such as BaFe2 As2 . More recently, it has been possible to theoretically study the triangular-honeycomb versions of the J1 -J2 model, called a windmill model, in which order-from disorder drives the development of six-state clock order. Remarkably, in this case, order-from-disorder leads to an intermediate power-law spin phase, despite the underlying Heisenerg spins. This research was supported by DOE Basic Energy Sciences Grant DE-FG02-99ER45790.

  15. Spin-Spin Coupling in Asteroidal Binaries

    NASA Astrophysics Data System (ADS)

    Batygin, Konstantin; Morbidelli, Alessandro

    2015-11-01

    Gravitationally bound binaries constitute a substantial fraction of the small body population of the solar system, and characterization of their rotational states is instrumental to understanding their formation and dynamical evolution. Unlike planets, numerous small bodies can maintain a perpetual aspheroidal shape, giving rise to a richer array of non-trivial gravitational dynamics. In this work, we explore the rotational evolution of triaxial satellites that orbit permanently deformed central objects, with specific emphasis on quadrupole-quadrupole interactions. Our analysis shows that in addition to conventional spin-orbit resonances, both prograde and retrograde spin-spin resonances naturally arise for closely orbiting, highly deformed bodies. Application of our results to the illustrative examples of (87) Sylvia and (216) Kleopatra multi-asteroid systems implies capture probabilities slightly below ~10% for leading-order spin-spin resonances. Cumulatively, our results suggest that spin-spin coupling may be consequential for highly elongated, tightly orbiting binary objects.

  16. Spin-liquid condensate of spinful bosons.

    PubMed

    Lian, Biao; Zhang, Shoucheng

    2014-08-22

    We introduce the concept of a bosonic spin liquid condensate (SLC), where spinful bosons in a lattice form a zero-temperature spin disordered charge condensate that preserves the spin rotation symmetry, but breaks the U(1) symmetry due to a spinless order parameter with charge one. It has an energy gap to all the spin excitations. We show that such SLC states can be realized in a system of spin S ≥ 2 bosons. In particular, we analyze the SLC phase diagram in the spin 2 case using a mean-field variational wave function method. We show there is a direct analogy between the SLC and the resonating-valence-bond state. PMID:25192078

  17. Spin Effects in Bose-Glass Phases

    NASA Astrophysics Data System (ADS)

    Paganelli, S.; ŁaÇki, M.; Ahufinger, V.; Zakrzewski, J.; Sanpera, A.

    2011-12-01

    We study the mechanism of formation of Bose glass (BG) phases in the spin-1 Bose Hubbard model when diagonal disorder is introduced. To this aim, we analyze first the phase diagram in the zero-hopping limit, there disorder induces superposition between Mott insulator (MI) phases with different filling numbers. Then BG appears as a compressible but still insulating phase. The phase diagram for finite hopping is also calculated with the Gutzwiller approximation. The bosons' spin degree of freedom introduces another scattering channel in the two-body interaction modifying the stability of MI regions with respect to the action of disorder. This leads to some peculiar phenomena such as the creation of BG of singlets, for very strong spin correlation, or the disappearance of BG phase in some particular cases where fluctuations are not able to mix different MI regions.

  18. Spin liquid phases of large-spin Mott insulating ultracold bosons

    NASA Astrophysics Data System (ADS)

    Rutkowski, Todd C.; Lawler, Michael J.

    2016-03-01

    Mott insulating ultracold gases possess a unique whole-atom exchange interaction which enables large quantum fluctuations between the Zeeman sublevels of each atom. By strengthening this interaction—either through the use of large-spin atoms or by tuning the particle-particle interactions via optical Feshbach resonance—one may enhance fluctuations and facilitate the appearance of the long-sought-after quantum spin liquid phase—all in the highly tunable environment of cold atoms. To illustrate the relationship between the spin magnitude, interaction strength, and resulting magnetic phases, we present and solve a mean-field theory for bosons optically confined to the one-particle-per-site Mott state, using both analytic and numerical methods. We find on square and triangular lattices for bosons of hyperfine spin f >2 that making the repulsive s -wave scattering length through the singlet channel small—relative to the higher-order scattering channels—accesses a short-range resonating valence bond (s-RVB) spin liquid phase.

  19. Fluctuations quantiques atomiques et électromagnétiques

    NASA Astrophysics Data System (ADS)

    Josse, V.; Vernac, L.; Pinard, M.; Giacobino, E.

    2002-06-01

    Nous étudions les fluctuations quantiques de champs électromagnétiques et d'atomes interagissant dans une cavité de grande finesse. Les calculs théoriques prévoient une réduction du bruit atomique. Il est également possible de réduire les fluctuations du spin associé à la cohérence entre états excités. Nous nous proposons de démontrer ces réductions de bruit a l'aide du bruit de polarisation d'une sonde résonante. Nous avons tout d'abord observé la compression du bruit de polarisation de la pompe sous la limite quantique standard de l'ordre de 13%. Un modèle théorique est développé pour rendre compte des phénomènes.

  20. RHIC SPIN FLIPPER

    SciTech Connect

    BAI,M.; ROSER, T.

    2007-06-25

    This paper proposes a new design of spin flipper for RHIC to obtain full spin flip with the spin tune staying at half integer. The traditional technique of using an rf dipole or solenoid as spin flipper to achieve full spin flip in the presence of full Siberian snake requires one to change the snake configuration to move the spin tune away from half integer. This is not practical for an operational high energy polarized proton collider like RHIC where beam lifetime is sensitive to small betatron tune change. The design of the new spin flipper as well as numerical simulations are presented.

  1. Fluctuating charge-density waves in a cuprate superconductor.

    PubMed

    Torchinsky, Darius H; Mahmood, Fahad; Bollinger, Anthony T; Božović, Ivan; Gedik, Nuh

    2013-05-01

    Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and spin ordering whose significance is not fully understood. So far, static charge-density waves (CDWs) have been detected by diffraction probes only at particular doping levels or in an applied external field . However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here we present a method based on ultrafast spectroscopy to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La(1.9)Sr(0.1)CuO4 film (T(c) = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K that decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La(1.84)Sr(0.16)CuO4 film (T(c) = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favouring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials. PMID:23435216

  2. Quantifying stock-price response to demand fluctuations

    NASA Astrophysics Data System (ADS)

    Plerou, Vasiliki; Gopikrishnan, Parameswaran; Gabaix, Xavier; Stanley, H. Eugene

    2002-08-01

    We empirically address the question of how stock prices respond to changes in demand. We quantify the relations between price change G over a time interval Δt and two different measures of demand fluctuations: (a) Φ, defined as the difference between the number of buyer-initiated and seller-initiated trades, and (b) Ω, defined as the difference in number of shares traded in buyer- and seller-initiated trades. We find that the conditional expectation functions of price change for a given Φ or Ω, Φ and Ω (``market impact function''), display concave functional forms that seem universal for all stocks. For small Ω, we find a power-law behavior Ω~Ω1/8 with δ depending on Δt (δ~3 for Δt=5 min, δ~3/2 for Δt=15 min and δ~1 for large Δt). We find that large price fluctuations occur when demand is very small-a fact that is reminiscent of large fluctuations that occur at critical points in spin systems, where the divergent nature of the response function leads to large fluctuations.

  3. Quantifying stock-price response to demand fluctuations.

    PubMed

    Plerou, Vasiliki; Gopikrishnan, Parameswaran; Gabaix, Xavier; Stanley, H Eugene

    2002-08-01

    We empirically address the question of how stock prices respond to changes in demand. We quantify the relations between price change G over a time interval Deltat and two different measures of demand fluctuations: (a) Phi, defined as the difference between the number of buyer-initiated and seller-initiated trades, and (b) Omega, defined as the difference in number of shares traded in buyer- and seller-initiated trades. We find that the conditional expectation functions of price change for a given Phi or Omega, (Phi) and (Omega) ("market impact function"), display concave functional forms that seem universal for all stocks. For small Omega, we find a power-law behavior (Omega) approximately Omega(1/8) with delta depending on Deltat (delta approximately 3 for Deltat=5 min, delta approximately 3/2 for Deltat=15 min and delta approximately 1 for large Deltat). We find that large price fluctuations occur when demand is very small-a fact that is reminiscent of large fluctuations that occur at critical points in spin systems, where the divergent nature of the response function leads to large fluctuations. PMID:12241320

  4. Statistical mechanical studies on the information processing with quantum fluctuation

    NASA Astrophysics Data System (ADS)

    Otsubo, Yosuke; Inoue, Jun-Ichi; Nagata, Kenji; Okada, Masato

    2014-03-01

    Quantum fluctuation induces the tunneling between states in a system and then can be used in combinatorial optimization problems. Such an algorithm is called quantum adiabatic computing. In this work, we investigate the quality of an information processing based on Bayes inference with the quantum fluctuation through the statistical mechanical approach. We then focus on the error correcting codes and CDMA multiuser demodulation which are described by conventional solvable spin glass models and can be analyzed by replica method in the thermodynamic limit. Introducing the quantum fluctuation into the decoding process of each problem, which is called quantum maximizer of the posteriori probability (QMPM) estimate, we analyze the decoding quality and then compare the results with those by the conventional MPM estimate which corresponds to finite temperature decoding From our limited results, the MPM based on the quantum fluctuation seems to achieve the same decoding quality as the thermal MPM does. We clarify the relationship between the optimal amplitude of transverse field and temperature for the mixture of quantum and classical MPMs. This work is supported by JSPS KAKENHI Grant Numbers 12J06501, 25330283, 25120009.

  5. Spin-dependent shot noise in semiconductor and graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Dragomirova, Ralitsa L.

    Shot noise is the name given to the time-dependent non-equilibrium current (or voltage) fluctuations which persist down to zero temperature and are fundamentally related to the discrete nature of the electron charge. Over the past two decades it has become a major tool for gathering information about microscopic mechanisms of transport and correlations between charges which cannot be extracted from traditional conductance measurements. Recently a handful of theoretical and experimental studies have suggested that shot noise in systems with spin-dependent interactions provides a sensitive probe to differentiate between scattering from magnetic impurities, spin-flip scattering, and continuous spin precession effects on semiclassical or quantum transport of injected spin-polarized currents. This is due to the fact that any spin flip converts spin-↑ subsystem particle into a spin-↓ subsystem particle, where the two subsystems differ when spin degeneracy is lifted. Thus, the nonconservation of the number of particles in each subsystem generates additional source of current fluctuations. Here we generalize the scattering theory of quantum shot noise to include the full spin-density matrix of electrons. This formalism yields the spin-resolved shot noise power applicable for a generic spintronic device where partially polarized charge current or even pure spin current is injected from a spin-filtering or ferromagnetic electrode into a quantum-coherent nanostructure governed by arbitrary spin-dependent interactions. The developed formalism [2, 5] is applied in Chapter 5 to diffusive multichannel quantum wires with the Rashba spin-orbit (SO) coupling sandwiched between ferromagnetic source and ferromagnetic or normal drain electrodes. The crucial role played by the SO interactions in all-electrical control of spin in semiconductor nanostructures has ignited recent studies of their signatures on the shot noise. We investigate what is the effect of the Rahsba SO coupling

  6. High-field ESR studies of the quantum spin magnet CaCu2O3

    NASA Astrophysics Data System (ADS)

    Goiran, M.; Costes, M.; Broto, J. M.; Chou, F. C.; Klingeler, R.; Arushanov, E.; Drechsler, S.-L.; Büchner, B.; Kataev, V.

    2006-05-01

    We report an electron spin resonance (ESR) study of the s = 1/2 Heisenberg pseudo-ladder magnet CaCu2O3 in pulsed magnetic fields up to 40 T. At sub-terahertz frequencies we observe an ESR signal originating from a small amount of uncompensated spins residing presumably at the imperfections of the strongly antiferromagnetically correlated host spin lattice. The data give evidence that these few per cent of 'extra' spin states are coupled strongly to the bulk spins and are involved in the antiferromagnetic (AF) ordering at TN = 25 K. By mapping the frequency/resonance field diagram we have determined a small gap for magnetic excitations below TN of the order of ~0.3 0.8 meV. Such a small value of the gap explains the occurrence of the spin-flop transition in CaCu2O3 at weak magnetic fields μ0Hsf ~ 3 T. Qualitative changes of the ESR response with the increasing field strength give indications that strong magnetic fields reduce the AF correlations and may even suppress the long-range magnetic order in CaCu2O3. ESR data support scenarios with a significant role of the 'extra' spin states for the properties of low-dimensional quantum magnets.

  7. Characterization of physically vapor deposited AF2400 thin films

    SciTech Connect

    Chow, R.; Spragge, M.K.; Loomis, G.E.; Rainer, F.; Ward, R.; Thomas, I.M.; Kozlowski, M.R.

    1993-11-01

    Anti-reflective coatings made with Teflon AF2400 had the highest damage thresholds recorded for physical vapor deposited coatings at the Lawrence Livermore National Laboratory damage facility. Physical vapor deposited layers of Teflon AF2400, a perfluorinated amorphous polymer, maintained the bulk optical properties of a high transmittance from 200 nm to 1600 nm, and a low refractive index. In addition, the refractive index can be intentionally reduced by control of two common deposition parameters, deposition rate and substrate temperature. Scanning electron microscopy and nuclear magnetic resonance observations indicated that morphological changes caused the variations in the refractive index rather than compositional changes. The coatings adhered to fused silica and silicon wafers under normal laboratory handling conditions.

  8. Critical fluctuations in DOPC/DPPC-d62/cholesterol mixtures: 2H magnetic resonance and relaxation.

    PubMed

    Davis, James H; Ziani, Latifa; Schmidt, Miranda L

    2013-07-28

    Static and magic angle spinning (MAS) (2)H nuclear magnetic resonance experiments have been performed on a series of multilamellar dispersions of di-oleoyl-sn-glycero-3-phosphocholine/di-palmitoyl-sn-glycero-3-phosphocholine-d62/cholesterol in water to investigate the compositional fluctuations which occur in the region of the line of critical points for this ternary system. The strong dependence of the MAS line widths on temperature, sample composition, and spinning rate provides a direct measure of the magnitude of the fluctuations in the (2)H quadrupolar Hamiltonian. These data are analyzed in terms of models for critical fluctuations in composition leading to a value for the critical index for the correlation length, ν(c) = 0.628, consistent with a three dimensional Ising model. PMID:23902029

  9. Fluctuation theory of Rashba Fermi gases: Gaussian and beyond

    NASA Astrophysics Data System (ADS)

    Shenoy, Vijay B.; Vyasanakere, Jayantha P.

    Fermi gases with generalized Rashba spin orbit coupling induced by a synthetic gauge field have the potential of realizing many interesting states such as rashbon condensates and topological phases. Here we address the key open problem of the fluctuation theory of such systems and demonstrate that beyond-Gaussian effects are essential to capture finite temperature physics of such systems. We obtain their phase diagram by constructing an approximate non-Gaussian theory. We conclusively establish that spin-orbit coupling can enhance the exponentially small transition temperature (Tc) of a weakly attracting superfluid to the order of Fermi temperature, paving a pathway towards high Tc superfluids. Work supported by CSIR, DST, DAE and IUSSTF.

  10. Spin projection chromatography

    NASA Astrophysics Data System (ADS)

    Danieli, E. P.; Pastawski, H. M.; Levstein, P. R.

    2004-01-01

    We formulate the many-body spin dynamics at high temperature within the non-equilibrium Keldysh formalism. For the simplest XY interaction, analytical expressions in terms of the one particle solutions are obtained for linear and ring configurations. For small rings of even spin number, the group velocities of excitations depend on the parity of the total spin projection. This should enable a dynamical filtering of spin projections with a given parity i.e., a spin projection chromatography.

  11. Rashba spin-orbit-coupled atomic Fermi gases

    SciTech Connect

    Jiang Lei; Pu Han; Liu Xiaji; Hu Hui

    2011-12-15

    We investigate theoretically BEC-BCS crossover physics in the presence of Rashba spin-orbit coupling in a system of a two-component Fermi gas with and without a Zeeman field that breaks the population balance between the two components. A bound state (Rashba pair) emerges because of the spin-orbit interaction. We study the properties of Rashba pairs using standard pair fluctuation theory. At zero temperature, the Rashba pairs condense into a macroscopic mixed-spin state. We discuss in detail the experimental signatures for observing the condensation of Rashba pairs by calculating various physical observables which characterize the properties of the system and can be measured in experiment.

  12. Sinuladiterpenes A-F, new cembrane diterpenes from Sinularia flexibilis.

    PubMed

    Lo, Kuang-Liang; Khalil, Ashraf Taha; Kuo, Yao-Haur; Shen, Ya-Ching

    2009-12-01

    Chromatographic investigation of the octocoral Sinularia flexibilis afforded six new cembrane diterpenes, sinuladiterpenes A-F (1-6, resp.), in addition to four known cembranolides, 11-episinulariolide acetate, 11-dehydrosinulariolide, 11-episinulariolide, and sinulariolide. Their structures were elucidated by spectroscopic analysis, especially 2D-NMR and HR-ESI-MS. Compound 2 exhibited significant in vitro cytotoxic activity against human colon adenocarcinoma (WiDr) cell line. PMID:20020460

  13. Screening Nuclear Field Fluctuations in Quantum Dots for Indistinguishable Photon Generation.

    PubMed

    Malein, R N E; Santana, T S; Zajac, J M; Dada, A C; Gauger, E M; Petroff, P M; Lim, J Y; Song, J D; Gerardot, B D

    2016-06-24

    A semiconductor quantum dot can generate highly coherent and indistinguishable single photons. However, intrinsic semiconductor dephasing mechanisms can reduce the visibility of two-photon interference. For an electron in a quantum dot, a fundamental dephasing process is the hyperfine interaction with the nuclear spin bath. Here, we directly probe the consequence of the fluctuating nuclear spins on the elastic and inelastic scattered photon spectra from a resident electron in a single dot. We find the in-plane component of the nuclear Overhauser field leads to detuned Raman scattered photons, broadened over experimental time scales by field fluctuations, which are distinguishable from both the elastic and incoherent components of the resonance fluorescence. This significantly reduces two-photon interference visibility. However, we demonstrate successful screening of the nuclear spin noise, which enables the generation of coherent single photons that exhibit high visibility two-photon interference. PMID:27391751

  14. Screening Nuclear Field Fluctuations in Quantum Dots for Indistinguishable Photon Generation

    NASA Astrophysics Data System (ADS)

    Malein, R. N. E.; Santana, T. S.; Zajac, J. M.; Dada, A. C.; Gauger, E. M.; Petroff, P. M.; Lim, J. Y.; Song, J. D.; Gerardot, B. D.

    2016-06-01

    A semiconductor quantum dot can generate highly coherent and indistinguishable single photons. However, intrinsic semiconductor dephasing mechanisms can reduce the visibility of two-photon interference. For an electron in a quantum dot, a fundamental dephasing process is the hyperfine interaction with the nuclear spin bath. Here, we directly probe the consequence of the fluctuating nuclear spins on the elastic and inelastic scattered photon spectra from a resident electron in a single dot. We find the in-plane component of the nuclear Overhauser field leads to detuned Raman scattered photons, broadened over experimental time scales by field fluctuations, which are distinguishable from both the elastic and incoherent components of the resonance fluorescence. This significantly reduces two-photon interference visibility. However, we demonstrate successful screening of the nuclear spin noise, which enables the generation of coherent single photons that exhibit high visibility two-photon interference.

  15. Fluctuations in relativistic causal hydrodynamics

    NASA Astrophysics Data System (ADS)

    Kumar, Avdhesh; Bhatt, Jitesh R.; Mishra, Ananta P.

    2014-05-01

    Formalism to calculate the hydrodynamic fluctuations by applying the Onsager theory to the relativistic Navier-Stokes equation is already known. In this work, we calculate hydrodynamic fluctuations within the framework of the second order hydrodynamics of Müller, Israel and Stewart and its generalization to the third order. We have also calculated the fluctuations for several other causal hydrodynamical equations. We show that the form for the Onsager-coefficients and form of the correlation functions remain the same as those obtained by the relativistic Navier-Stokes equation and do not depend on any specific model of hydrodynamics. Further we numerically investigate evolution of the correlation function using the one dimensional boost-invariant (Bjorken) flow. We compare the correlation functions obtained using the causal hydrodynamics with the correlation function for the relativistic Navier-Stokes equation. We find that the qualitative behavior of the correlation functions remains the same for all the models of the causal hydrodynamics.

  16. Fluctuational electrodynamics of hyperbolic metamaterials

    SciTech Connect

    Guo, Yu; Jacob, Zubin

    2014-06-21

    We give a detailed account of equilibrium and non-equilibrium fluctuational electrodynamics of hyperbolic metamaterials. We show the unifying aspects of two different approaches; one utilizes the second kind of fluctuation dissipation theorem and the other makes use of the scattering method. We analyze the near-field of hyperbolic media at finite temperatures and show that the lack of spatial coherence can be attributed to the multi-modal nature of super-Planckian thermal emission. We also adopt the analysis to phonon-polaritonic super-lattice metamaterials and describe the regimes suitable for experimental verification of our predicted effects. The results reveal that far-field thermal emission spectra are dominated by epsilon-near-zero and epsilon-near-pole responses as expected from Kirchoff's laws. Our work should aid both theorists and experimentalists to study complex media and engineer equilibrium and non-equilibrium fluctuations for applications in thermal photonics.

  17. Durable Superhydrophobic Surfaces via Spontaneous Wrinkling of Teflon AF.

    PubMed

    Scarratt, Liam R J; Hoatson, Ben S; Wood, Elliot S; Hawkett, Brian S; Neto, Chiara

    2016-03-16

    We report the fabrication of both single-scale and hierarchical superhydrophobic surfaces, created by exploiting the spontaneous wrinkling of a rigid Teflon AF film on two types of shrinkable plastic substrates. Sub-100 nm to micrometric wrinkles were reproducibly generated by this simple process, with remarkable control over the size and hierarchy. Hierarchical Teflon AF wrinkled surfaces showed extremely high water repellence (contact angle 172°) and very low contact angle hysteresis (2°), resulting in droplets rolling off the surface at tilt angles lower than 5°. The wrinkling process intimately binds the Teflon AF layer with its substrate, making these surfaces mechanically robust, as revealed by macroscale and nanoscale wear tests: hardness values were close to that of commercial optical lenses and aluminum films, resistance to scratch was comparable to commercial hydrophobic coatings, and damage by extensive sonication did not significantly affect water repellence. By this fabrication method the size of the wrinkles can be reproducibly tuned from the nanoscale to the microscale, across the whole surface in one step; the fabrication procedure is extremely rapid, requiring only 2 min of thermal annealing to produce the desired topography, and uses inexpensive materials. The very low roll-off angles achieved in the hierarchical surfaces offer a potentially up-scalable alternative as self-cleaning and drag-reducing coatings. PMID:26910574

  18. Genomic functions of U2AF in constitutive and regulated splicing

    PubMed Central

    Wu, Tongbin; Fu, Xiang-Dong

    2015-01-01

    The U2AF heterodimer is generally accepted to play a vital role in defining functional 3′ splice sites in pre-mRNA splicing. Given prevalent mutations in U2AF, particularly in the U2AF1 gene (which encodes for the U2AF35 subunit) in blood disorders and other human cancers, there are renewed interests in these classic splicing factors to further understand their regulatory functions in RNA metabolism in both physiological and disease settings. We recently reported that U2AF has a maximal capacity to directly bind ˜88% of functional 3′ splice sites in the human genome and that numerous U2AF binding events also occur in various exonic and intronic locations, thus providing additional mechanisms for the regulation of alternative splicing besides their traditional role in titrating weak splice sites in the cell. These findings, coupled with the existence of multiple related proteins to both U2AF65 and U2AF35, beg a series of questions on the universal role of U2AF in functional 3′ splice site definition, their binding specificities in vivo, potential mechanisms to bypass their requirement for certain intron removal events, contribution of splicing-independent functions of U2AF to important cellular functions, and the mechanism for U2AF mutations to invoke specific diseases in humans. PMID:25901584

  19. Charge and Spin Noise in Magnetic Tunnel Junctions

    NASA Astrophysics Data System (ADS)

    Chudnovskiy, Alexander; Swiebodzinski, Jacek; Kamenev, Alex; Dunn, Thomas; Pfannkuche, Daniela

    Manipulation of magnetization by electric current lies in the mainstream of the rapidly developing field of spintronics. The electric current influences the magnetization through the spin-torque effect. Entering a magnet, spin-polarized current exerts a torque on the magnetization, which aligns the magnetization parallel or antiparallel to the spin polarization of the current. The spin-torque effect can be used for fast magnetization switching in magnetic tunnel junctions (MTJ) that consist of two magnetic layers separated by a tunnel barrier. Moreover, applying external magnetic field and passing electric current simultaneously, one can induce a wide variety of nonequilibrium dynamical regimes, ranging from hysteretic switching between two static orientations of magnetization to steady nonequilibrium magnetization precession. Theoretical description of nonlinear nonequilibrium magnetization dynamics is given by the Landau-Lifshitz-Gilbert (LLG) equation. In this approach, the magnetization is treated on a classical level, resulting in a deterministic dynamics, which can exhibit crossover from periodic to chaotic orbits. In presence of spin-polarized current, there are nonequilibrium fluctuations of magnetization - the spin shot noise - that distort the classical dynamics of magnetization. Those fluctuations originate from the discrete nature of spin and, in this respect, they are similar to the well-known shot noise in the charge transport that stems from the discreteness of charge.

  20. Spin fluctations and heavy fermions in the Kondo lattice

    SciTech Connect

    Khaliullin, G.G.

    1994-09-01

    This paper studies the spectrum of the spin and electronic excitations of the Kondo lattice at low temperatures. To avoid unphysical states, the Mattis {open_quotes}drone{close_quotes}-fermion representation for localized spins is employed. First, the known Fermi liquid properties of a single impurity are examined. The behavior of the correlator between a localized spin and the electron spin density at large distances shows that the effective interaction between electrons on the Fermi level and low-energy localized spin fluctuations scales as {rho}{sup {minus}1}, where {rho} is the band-state density. This fact is developed into a renormalization of the band spectrum in a periodic lattice. If the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins is much smaller than the Kondo fluctuation frequency {omega}{sub k}, the temperature of the crossover to the single-parameter Fermi liquid mode is determined by {omega}{sub k}. When the RKKY interaction becomes of order {omega}{sub k}, there is a new scale {omega}{sub sf}, the energy of the (antiferromagnetic) paramagnon mode, with {omega}{sub sf}{much_lt}{omega}{sub k}. Here the coherent Fermi liquid regime is realized only below a temperature T{sub coh} of order {omega}{sub sf}, while above T{sub coh} quasiparticle damping exhibits a linear temperature dependence. Finally, the nuclear-spin relaxation rate is calculated. 42 refs.

  1. Fluctuation driven electroweak phase transition

    NASA Technical Reports Server (NTRS)

    Gleiser, Marcelo; Kolb, Edward W.

    1991-01-01

    We examine the dynamics of the electroweak phase transition in the early Universe. For Higgs masses in the range 46 less than or = M sub H less than or = 150 GeV and top quark masses less than 200 GeV, regions of symmetric and asymmetric vacuum coexist to below the critical temperature, with thermal equilibrium between the two phases maintained by fluctuations of both phases. We propose that the transition to the asymmetric vacuum is completed by percolation of these subcritical fluctuations. Our results are relevant to scenarios of baryogenesis that invoke a weakly first-order phase transition at the electroweak scale.

  2. Ground state and low-energy magnetic dynamics in the frustrated magnet CoAl2O4 as revealed by local spin probes

    NASA Astrophysics Data System (ADS)

    Iakovleva, M.; Vavilova, E.; Grafe, H.-J.; Zimmermann, S.; Alfonsov, A.; Luetkens, H.; Klauss, H.-H.; Maljuk, A.; Wurmehl, S.; Büchner, B.; Kataev, V.

    2015-04-01

    We report a combined experimental study of magnetic properties of a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4 with Co2+ electron spin resonance, 27Al nuclear magnetic resonance, and muon spin rotation/relaxation techniques. With our local probes, we show that the frustration of spin interactions and the Co/Al site disorder strongly affect the spin dynamics. The experimental results evidence inhomogeneous and slow magnetic fluctuations and the occurrence of short-range electron spin correlations far above a characteristic temperature T*=8 K at which the spin system turns into in a quasistatic state. Our data indicate that this spin order is likely short range and unconventional with spin fluctuations persistent even at T ≪T* . The results of three spectroscopy techniques highlight a nontrivial role of structural disorder for the magnetism of a frustrated diamond spin lattice at the proximity to the critical point.

  3. Identification and functional characterization of grass carp IL-17A/F1: An evaluation of the immunoregulatory role of teleost IL-17A/F1.

    PubMed

    Du, Linyong; Feng, Shiyu; Yin, Licheng; Wang, Xinyan; Zhang, Anying; Yang, Kun; Zhou, Hong

    2015-07-01

    In mammals, IL-17A and IL-17F are hallmark cytokines of Th17 cells which act significant roles in eradicating extracellular pathogens. IL-17A and IL-17F homologs nominated as IL-17A/F1-3 have been revealed in fish and their functions remain largely undefined. Here we identified and characterized grass carp IL-17A/F1 (gcIL-17A/F1) in fish immune system. In this regard, both tissue distribution and inductive expression of gcIL-17A/F1 indicated its possible involvement in immune response. Moreover, recombinant gcIL-17A/F1 (rgcIL-17A/F1) was prepared and displayed an ability to enhance pro-inflammatory cytokines (IL-1β, TNF-α and IL-6) mRNA expression in head kidney leukocytes. It is suggestive of that gcIL-17A/F1 may act as a proinflammatory cytokine in fish immunity. Besides, rgcIL-17A/F1 induced gene expression and protein release of grass carp chemokine CXCL-8 (gcCXCL-8) in head kidney cells (HKCs), probably via NF-κB, p38 and Erk1/2 pathways. In particular, culture medium from the HKCs treated by rgcIL-17A/F1 could stimulate peripheral blood leukocytes migration and immunoneutralization of endogenous gcCXCL-8 could partially attenuate this stimulation, suggesting that rgcIL-17A/F1 could recruit immune cells through producing gcCXCL-8 as mammalian IL-17 A and F. Taken together, we not only identified the pro-inflammatory role of gcIL-17A/F1 in host defense, but also provided the basis for clarifying Th17 cells in teleost. PMID:25847875

  4. Spontaneous Breaking of Spatial and Spin Symmetry in Spinor Condensates

    SciTech Connect

    Scherer, M.; Luecke, B.; Topic, O.; Ertmer, W.; Klempt, C.; Gebreyesus, G.; Deuretzbacher, F.; Santos, L.; Arlt, J. J.

    2010-09-24

    Parametric amplification of quantum fluctuations constitutes a fundamental mechanism for spontaneous symmetry breaking. In our experiments, a spinor condensate acts as a parametric amplifier of spin modes, resulting in a twofold spontaneous breaking of spatial and spin symmetry in the amplified clouds. Our experiments permit a precise analysis of the amplification in specific spatial Bessel-like modes, allowing for the detailed understanding of the double symmetry breaking. On resonances that create vortex-antivortex superpositions, we show that the cylindrical spatial symmetry is spontaneously broken, but phase squeezing prevents spin-symmetry breaking. If, however, nondegenerate spin modes contribute to the amplification, quantum interferences lead to spin-dependent density profiles and hence spontaneously formed patterns in the longitudinal magnetization.

  5. Coherent control of a single ²⁹Si nuclear spin qubit.

    PubMed

    Pla, Jarryd J; Mohiyaddin, Fahd A; Tan, Kuan Y; Dehollain, Juan P; Rahman, Rajib; Klimeck, Gerhard; Jamieson, David N; Dzurak, Andrew S; Morello, Andrea

    2014-12-12

    Magnetic fluctuations caused by the nuclear spins of a host crystal are often the leading source of decoherence for many types of solid-state spin qubit. In group-IV semiconductor materials, the spin-bearing nuclei are sufficiently rare that it is possible to identify and control individual host nuclear spins. This Letter presents the first experimental detection and manipulation of a single ²⁹Si nuclear spin. The quantum nondemolition single-shot readout of the spin is demonstrated, and a Hahn echo measurement reveals a coherence time of T₂=6.3(7)  ms—in excellent agreement with bulk experiments. Atomistic modeling combined with extracted experimental parameters provides possible lattice sites for the ²⁹Si atom under investigation. These results demonstrate that single ²⁹Si nuclear spins could serve as a valuable resource in a silicon spin-based quantum computer. PMID:25541792

  6. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    DOE PAGESBeta

    S. -H. Baek; Gu, G. D.; Utz, Y.; Hucker, M.; Buchner, B.; Grafe, H. -J.

    2015-10-26

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal → low-temperature orthorhombic → low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T–11 sharply upturns at the charge-ordering temperature TCO = 54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T–11 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥ [001], which are completely suppressed for largemore » fields along the CuO2 planes. Lastly, our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.« less

  7. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    NASA Astrophysics Data System (ADS)

    Baek, S.-H.; Utz, Y.; Hücker, M.; Gu, G. D.; Büchner, B.; Grafe, H.-J.

    2015-10-01

    We report 139La nuclear magnetic resonance studies performed on a La1.875Ba0.125CuO4 single crystal. The data show that the structural phase transitions (high-temperature tetragonal→low-temperature orthorhombic→low-temperature tetragonal phase) are of the displacive type in this material. The 139La spin-lattice relaxation rate T1-1 sharply upturns at the charge-ordering temperature TCO=54 K, indicating that charge order triggers the slowing down of spin fluctuations. Detailed temperature and field dependencies of the T1-1 below the spin-ordering temperature TSO=40 K reveal the development of enhanced spin fluctuations in the spin-ordered state for H ∥[001 ] , which are completely suppressed for large fields along the CuO2 planes. Our results shed light on the unusual spin fluctuations in the charge and spin stripe ordered lanthanum cuprates.

  8. Persistence of slow fluctuations in the overdoped regime of Ba (Fe1 -xRhx) 2As2 superconductors

    NASA Astrophysics Data System (ADS)

    Bossoni, L.; Moroni, M.; Julien, M. H.; Mayaffre, H.; Canfield, P. C.; Reyes, A.; Halperin, W. P.; Carretta, P.

    2016-06-01

    We present nuclear magnetic resonance evidence that very slow (≤1 MHz) spin fluctuations persist into the overdoped regime of Ba (Fe1 -xRhx) 2As2 superconductors. Measurements of the 75As spin echo decay rate, obtained both with Hahn Echo and Carr Purcell Meiboom Gill pulse sequences, show that the slowing down of spin fluctuations can be described by short-range diffusive dynamics, likely involving domain walls motions separating (π /a ,0 ) from (0 ,π /a ) correlated regions. This slowing down of the fluctuations is weakly sensitive to the external magnetic field and, although fading away with doping, it extends deeply into the overdoped regime.

  9. Noncommutativity due to spin

    NASA Astrophysics Data System (ADS)

    Gomes, M.; Kupriyanov, V. G.; da Silva, A. J.

    2010-04-01

    Using the Berezin-Marinov pseudoclassical formulation of the spin particle we propose a classical model of spin noncommutativity. In the nonrelativistic case, the Poisson brackets between the coordinates are proportional to the spin angular momentum. The quantization of the model leads to the noncommutativity with mixed spatial and spin degrees of freedom. A modified Pauli equation, describing a spin half particle in an external electromagnetic field is obtained. We show that nonlocality caused by the spin noncommutativity depends on the spin of the particle; for spin zero, nonlocality does not appear, for spin half, ΔxΔy≥θ2/2, etc. In the relativistic case the noncommutative Dirac equation was derived. For that we introduce a new star product. The advantage of our model is that in spite of the presence of noncommutativity and nonlocality, it is Lorentz invariant. Also, in the quasiclassical approximation it gives noncommutativity with a nilpotent parameter.

  10. Spin Rotation of Formalism for Spin Tracking

    SciTech Connect

    Luccio,A.

    2008-02-01

    The problem of which coefficients are adequate to correctly represent the spin rotation in vector spin tracking for polarized proton and deuteron beams in synchrotrons is here re-examined in the light of recent discussions. The main aim of this note is to show where some previous erroneous results originated and how to code spin rotation in a tracking code. Some analysis of a recent experiment is presented that confirm the correctness of the assumptions.

  11. Spin Circuit Representation for Spin Pumping Phenomena

    NASA Astrophysics Data System (ADS)

    Roy, Kuntal; Datta, Supriyo

    2015-03-01

    There has been enormous progress in the field of spintronics and nanomagnetics in recent years with the discovery of many new materials and phenomena and it remains a formidable challenge to integrate these phenomena into functional devices and evaluate their potential. To facilitate this process a modular approach has been proposed whereby different phenomena are represented by spin circuit components. Unlike ordinary circuit components, these spin circuit components are characterized by 4-component voltages and currents (one for charge and three for spin). In this talk we will (1) present a spin circuit representation for spin pumping phenomena, (2) combine it with a spin circuit representation for the spin Hall effect to show that it reproduces established results obtained earlier by other means, and finally (3) use it to propose a possible method for enhancing the spin pumping efficiency by an order of magnitude through the addition of a spin sink layer. This work was supported by FAME, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.

  12. Spin-wave thermal population as temperature probe in magnetic tunnel junctions

    NASA Astrophysics Data System (ADS)

    Le Goff, A.; Nikitin, V.; Devolder, T.

    2016-07-01

    We study whether a direct measurement of the absolute temperature of a Magnetic Tunnel Junction (MTJ) can be performed using the high frequency electrical noise that it delivers under a finite voltage bias. Our method includes quasi-static hysteresis loop measurements of the MTJ, together with the field-dependence of its spin wave noise spectra. We rely on an analytical modeling of the spectra by assuming independent fluctuations of the different sub-systems of the tunnel junction that are described as macrospin fluctuators. We illustrate our method on perpendicularly magnetized MgO-based MTJs patterned in 50 × 100 nm2 nanopillars. We apply hard axis (in-plane) fields to let the magnetic thermal fluctuations yield finite conductance fluctuations of the MTJ. Instead of the free layer fluctuations that are observed to be affected by both spin-torque and temperature, we use the magnetization fluctuations of the sole reference layers. Their much stronger anisotropy and their much heavier damping render them essentially immune to spin-torque. We illustrate our method by determining current-induced heating of the perpendicularly magnetized tunnel junction at voltages similar to those used in spin-torque memory applications. The absolute temperature can be deduced with a precision of ±60 K, and we can exclude any substantial heating at the spin-torque switching voltage.

  13. Instrument measures dynamic pressure fluctuations

    NASA Technical Reports Server (NTRS)

    Coats, J. W.; Penko, P. E.; Reshotko, M.

    1977-01-01

    Pressure probe instrument, incorporating "infinite line" principle, can be used to remotely measure dynamic pressure fluctuations in hot high-pressure environemnts too severe for sensors. System is designed and can be utilized for measurements in core of operating turbofan engine.

  14. Spin Seebeck power generators

    SciTech Connect

    Cahaya, Adam B.; Tretiakov, O. A.; Bauer, Gerrit E. W.

    2014-01-27

    We derive expressions for the efficiency and figure of merit of two spin caloritronic devices based on the spin Seebeck effect (SSE), i.e., the generation of spin currents by a temperature gradient. The inverse spin Hall effect is conventionally used to detect the SSE and offers advantages for large area applications. We also propose a device that converts spin current into electric one by means of a spin-valve detector, which scales favorably to small sizes and approaches a figure of merit of 0.5 at room temperature.

  15. Ferrimagnetic ordering and spin entropy of field-dependent intermediate spins in Na0.82CoO2

    NASA Astrophysics Data System (ADS)

    Shu, G. J.; Chou, F. C.

    2016-04-01

    The peculiar field-dependent magnetism of Na0.82CoO2 has been investigated through an analysis of its dc and ac spin susceptibilities. To account for the easily activated narrow b2 g-a1 g gap of the crystal field for Co in the cobalt oxide layer, the spin-state transition of Co3 + (3 d6 ) between the low-spin (LS) state b2g 2a1g 0 of S =0 and the intermediate-spin (IS) state b2g 1a1g 1 of S =1 is thus seen as thermally activated and exhibits a Boltzmann distribution. The IS state of Co3 + within each √{13 }a hexagonal superlattice formed by the S =1 /2 state of the Co4 + ions appears randomly within each supercell and shows significant temperature and field dependence. The magnetic field is found to assist in pinning down the thermally activated state of Co3 + and swings the Boltzmann distribution weight toward a higher fraction of the IS state. The field dependence of the in-plane magnetic moment from the added number of S =1 spins is used to explain the origin of A -type antiferromagnetic (AF) ordering, particularly that the ferromagnetic (FM)-like behavior below TN at low field is actually a ferrimagnetic IS spin ordering of Co3 +.

  16. Quantum and classical separability of spin-orbit laser modes

    NASA Astrophysics Data System (ADS)

    Pereira, L. J.; Khoury, A. Z.; Dechoum, K.

    2014-11-01

    In this paper we investigate the quantum noise properties of polarization vortices in connection with an intensity-based Clauser-Horne-Shimony-Holt (CHSH) inequality for their spin-orbit separability. We evaluate the inequality for different input quantum states and the corresponding intensity fluctuations. The roles played by coherence and photon number squeezing provide a suitable framework for characterizing pure state spin-orbit entanglement. Structural inseparability of the spin-orbit mode requires coherence, an issue concerning either classical or quantum descriptions. In both cases, it can be witnessed by violation of this intensity-based CHSH inequality. However, in the quantum domain, entanglement requires both coherence and reduced photon number fluctuations.

  17. Spin noise spectroscopy from acoustic to GHz frequencies

    NASA Astrophysics Data System (ADS)

    Hübner, Jens

    2010-03-01

    Performing perturbation free measurements on semiconductor quantum systems has long been banished to textbooks on quantum mechanics. The emergent technique of spin noise spectroscopy is challenging this restriction. Empowered only by the ever present intrinsic spin fluctuation dynamics in thermal equilibrium, spin noise spectroscopy is capable to directly deduce several physical properties of carriers spins in semiconductors from these fluctuations. Originating from spin noise measurements on alkali metal vapors in quantum optics [1] the method has become a powerful technique to unravel the intrinsic spin dynamics in semiconductors [2]. In this talk I will present the recent progress of spin noise spectroscopy and how it is used to monitor the spin dynamic in semiconductor quantum wells at thermal equilibrium and as a consequence thereof directly detect the spatial dynamics of the carriers being marked with their own spin on a microscopic scale [3]. Further I will present measurements of how the non-perturbative nature of spin noise spectroscopy gives valuable insight into the delicate dependence of the spin relaxation time of electrons on doping density and temperature in semiconductors n-doped in the vicinity of the metal-insulator transition where hyperfine and intra-band depolarization compete [4]. Also the measurement bandwidth can be extended to GHz frequencies by ultrafast optical probing [5] yielding in conjunction with depth resolved spin noise measurements insights into the origin of inhomogeneous spin dephasing effects at high magnetic fields [5]. Additionally I will present how spin noise spectroscopy can be employed to spatially depth resolve doping profiles with optical resolution [6] and give a summary on easy to implement techniques of spin noise spectroscopy at acoustic frequencies in alkali metal vapors. [4pt] [1] E. Aleksandrov and V. Zapassky, Zh. Eksp. Teor. Fiz. 81, 132 (1981); S. A. Crooker, D. G. Rickel, A. V. Balatsky, and D. L. Smith

  18. Code-division multiple-access multiuser demodulator by using quantum fluctuations

    NASA Astrophysics Data System (ADS)

    Otsubo, Yosuke; Inoue, Jun-ichi; Nagata, Kenji; Okada, Masato

    2014-07-01

    We examine the average-case performance of a code-division multiple-access (CDMA) multiuser demodulator in which quantum fluctuations are utilized to demodulate the original message within the context of Bayesian inference. The quantum fluctuations are built into the system as a transverse field in the infinite-range Ising spin glass model. We evaluate the performance measurements by using statistical mechanics. We confirm that the CDMA multiuser modulator using quantum fluctuations achieve roughly the same performance as the conventional CDMA multiuser modulator through thermal fluctuations on average. We also find that the relationship between the quality of the original information retrieval and the amplitude of the transverse field is somehow a "universal feature" in typical probabilistic information processing, viz., in image restoration, error-correcting codes, and CDMA multiuser demodulation.

  19. Code-division multiple-access multiuser demodulator by using quantum fluctuations.

    PubMed

    Otsubo, Yosuke; Inoue, Jun-Ichi; Nagata, Kenji; Okada, Masato

    2014-07-01

    We examine the average-case performance of a code-division multiple-access (CDMA) multiuser demodulator in which quantum fluctuations are utilized to demodulate the original message within the context of Bayesian inference. The quantum fluctuations are built into the system as a transverse field in the infinite-range Ising spin glass model. We evaluate the performance measurements by using statistical mechanics. We confirm that the CDMA multiuser modulator using quantum fluctuations achieve roughly the same performance as the conventional CDMA multiuser modulator through thermal fluctuations on average. We also find that the relationship between the quality of the original information retrieval and the amplitude of the transverse field is somehow a "universal feature" in typical probabilistic information processing, viz., in image restoration, error-correcting codes, and CDMA multiuser demodulation. PMID:25122270

  20. Concentration Fluctuations of a Semidilute Polymer Solution in Good Solvent Near a Repulsive Surface

    NASA Astrophysics Data System (ADS)

    Yeh, Catherine; Pincus, Philip; Zidovska, Alexandra

    2012-02-01

    The concentration profile of a semidilute polymer solution in good solvent near a repulsive surface has been previously calculated.ootnotetextJ. F. Joanny, L. Leibler, P.-G. de Gennes, J. Polym. Sci. 17, 1073 (1979) In this work we consider fluctuation corrections to the mean field concentration profile in the presence of a repulsive surface using the Cahn-Hilliard square-gradient approach extended to polymer interfaces. Our results predict that at strongly repulsive surfaces, a polymer in good solvent exhibits concentration fluctuations associated with the surface in addition to fluctuations of the bulk polymer solution. We compare our predictions with current experiments which have measured fluctuations in the concentration of interphase chromatin (DNA with its associated proteins) inside the nucleus of mammalian cells in vivo using ultrafast high space resolution spinning disc confocal microscopy.

  1. Binding sites for two novel phosphoproteins, 3AF5 and 3AF3, are required for rbcS-3A expression.

    PubMed Central

    Sarokin, L P; Chua, N H

    1992-01-01

    Previous studies of boxes II (-151 to -138) and III (-125 to -114), binding sites for the nuclear factor GT-1 within the -166 deleted promoter of the ribulose-1,5-bisphosphate carboxylase-3A (rbcS-3A) gene, suggested that GT-1 might act in concert with an additional protein to confer light-responsive rbcS-3A expression. In this work, S1 analysis of RNA isolated from transgenic tobacco plants carrying mutant rbcS-3A constructs led to the identification of two short sequences located at the 5' and 3' ends of box III that are required for expression. These two sequences serve as binding sites for two novel proteins, 3AF5 and 3AF3. Gel shift studies using tetramerized binding sites for both 3AF5 and 3AF3 showed that complexes with faster mobilities were formed using nuclear extracts prepared from dark-adapted plants compared with those from light-grown tobacco plants. Phosphatase treatment of extracts from light-grown plants resulted in the formation of complexes with faster mobility. Although the binding of 3AF3 to its target site is dependent upon phosphorylation, the binding of 3AF5 does not appear to be affected by its phosphorylation state. These results suggest that the phosphorylated forms of both 3AF5 and 3AF3 are required for -166 rbcS-3A expression but that the mechanisms differ by which phosphorylation regulates the activities of 3AF5 and 3AF3. PMID:1498605

  2. Cooperative spin decoherence in finite spin chains

    NASA Astrophysics Data System (ADS)

    Delgado, Fernando; Fernandez-Rossier, Joaquin

    2014-03-01

    Overcoming the problem of relaxation and decoherence of magnetic nanostructures is one of the mayor goals in magnetic data storage. Although spin chains with as few as 12 magnetic atoms have revealed stability in cryogenic conditions, understanding the mechanism leading to these effects is essential for the engineered of stable structures. Here we consider the problem of spin decoherence and relaxation of finite size quantum spin chains due to elastic and spin conserving interactions with an electron gas. Specifically, we consider how the decoherence (T2) and relaxation (T1) times between the two degenerate ground states of a chain of N coupled spins compares with the one of an isolated spin in the same environment. We find that the spin decoherence time of Ising chains can be either enhanced or suppressed depending on the matching between the Fermi wavelength 2 π /kF and the inter-spin distance a. In particular, we find that depending on the values of kF a , it can show, for certain values that depends on the dimensionality of the electron gas, a cooperative enhancement proportional to N2 of the decoherence, analogous to super radiance decay of atom ensembles, or a suppression.

  3. Spin structure functions

    SciTech Connect

    Jian-ping Chen, Alexandre Deur, Sebastian Kuhn, Zein-eddine Meziani

    2011-06-01

    Spin-dependent observables have been a powerful tool to probe the internal structure of the nucleon and to understand the dynamics of the strong interaction. Experiments involving spin degrees of freedom have often brought out surprises and puzzles. The so-called "spin crisis" in the 1980s revealed the limitation of naive quark-parton models and led to intensive worldwide efforts, both experimental and theoretical, to understand the nucleon spin structure. With high intensity and high polarization of both the electron beam and targets, Jefferson Lab has the world's highest polarized luminosity and the best figure-of-merit for precision spin structure measurements. It has made a strong impact in this subfield of research. This chapter will highlight Jefferson Lab's unique contributions in the measurements of valence quark spin distributions, in the moments of spin structure functions at low to intermediate Q2, and in the transverse spin structure.

  4. Nanoscale imaging of paramagnetic spin labels using a single spin in diamond

    NASA Astrophysics Data System (ADS)

    Ariyaratne, Amila; Myers, Bryan; Pelliccione, Matthew; Jayich, Ania

    Spin-labeling molecules with paramagnetic species is a powerful technique for probing molecular structure. However, current techniques are ensemble measurements, inherently lacking the sensitivity to detect a single spin or the conformational properties of a single biomolecule. In this talk, we demonstrate an imaging technique that has the promise of single-spin imaging and ultimately molecular structure imaging. We present two-dimensional nanoscale imaging of a monolayer of gadolinium (Gd) atomic spin labels at ambient conditions. The sensing element is a single nitrogen-vacancy (NV) center in diamond. A patterned monolayer of Gd atoms self-assembled on a Si atomic force microscopy tip is controllably interacted with and detected by the NV center. The fluctuating magnetic field generated by GHz-scale Gd spin flips relaxes the NV center in a manner that depends strongly on the Gd-NV separation. Using this technique, we demonstrate a Gd-induced reduction of the T1 relaxation time of the NV center with nm spatial resolution. Our results indicate that nanometer-scale imaging of individual electronic spins at ambient conditions is within reach. This will ultimately enable the study of structural and functional studies of single biomolecules in their native, folded state.

  5. Low energy spin excitations in chromium metal

    SciTech Connect

    Pynn, R.; Azuah, R.T.; Stirling, W.G.; Kulda, J.

    1997-12-31

    Neutron scattering experiments with full polarization analysis have been performed with a single crystal of chromium to study the low-energy spin fluctuations in the transverse spin density wave (TSDW) state. A number of remarkable results have been found. Inelastic scattering observed close to the TSDW satellite positions at (1 {+-} {delta},0,0) does not behave as expected for magnon scattering. In particular, the scattering corresponds to almost equally strong magnetization fluctuations both parallel and perpendicular to the ordered moments of the TSDW phase. As the Neel temperature is approached from below, scattering at the commensurate wavevector (1,0,0) increases in intensity as a result of critical scattering at silent satellites (1,0, {+-} {delta}) being included within the spectrometer resolution function. This effect, first observed by Sternlieb et al, does not account for all of the inelastic scattering around the (1,0,0) position, however, Rather, there are further collective excitations, apparently emanating from the TSDW satellites, which correspond to magnetic fluctuations parallel to the ordered TSDW moments. These branches have a group velocity that is close to that of (1,0,0) longitudinal acoustic (LA) phonons, but assigning their origin to magneto-elastic scattering raises other unanswered questions.

  6. Spinning eggs and ballerinas

    NASA Astrophysics Data System (ADS)

    Cross, Rod

    2013-01-01

    Measurements are presented on the rise of a spinning egg. It was found that the spin, the angular momentum and the kinetic energy all decrease as the egg rises, unlike the case of a ballerina who can increase her spin and kinetic energy by reducing her moment of inertia. The observed effects can be explained, in part, in terms of rolling friction between the egg and the surface on which it spins.

  7. The Advancing State of AF-M315E Technology

    NASA Technical Reports Server (NTRS)

    Masse, Robert; Spores, Ronald A.; McLean, Chris

    2014-01-01

    The culmination of twenty years of applied research in hydroxyl ammonium nitrate (HAN)-based monopropellants, the NASA Space Technology mission Directorate's (STMD) Green Propellant Infusion Mission (GPIM) will achieve the first on-orbit demonstration of an operational AF-M315E green propellant propulsion system by the end of 2015. Following an contextual overview of the completed flight design of the GPIM propellant storage and feed system, results of first operation of a flight-representative heavyweight 20-N engineering model thruster (to be conducted in mid-2014) are presented with performance comparisons to prior lab model (heavyweight) test articles.

  8. RX-26-AY/AF rifle bullet tests

    SciTech Connect

    Sharp, D.D.

    1980-11-01

    A series of rifle bullet tests was performed on two explosives, RX-26-AY and RX-26-AF, using the Pantex version of the Picatinny Arsenal Test (PA-2). With the exception of one test, both explosives displayed a relatively low sensitivity to bullet impact. However, a marked difference was noted in the average burn time duration between the two types of explosives being tested. A minor modification was made on the rifle barrel used at the test site in order to improve the sighting procedure.

  9. Polarization of nuclear spins by a cold nanoscale resonator

    SciTech Connect

    Butler, Mark C.; Weitekamp, Daniel P.

    2011-12-15

    A cold nanoscale resonator coupled to a system of nuclear spins can induce spin relaxation. In the low-temperature limit where spin-lattice interactions are ''frozen out,'' spontaneous emission by nuclear spins into a resonant mechanical mode can become the dominant mechanism for cooling the spins to thermal equilibrium with their environment. We provide a theoretical framework for the study of resonator-induced cooling of nuclear spins in this low-temperature regime. Relaxation equations are derived from first principles, in the limit where energy donated by the spins to the resonator is quickly dissipated into the cold bath that damps it. A physical interpretation of the processes contributing to spin polarization is given. For a system of spins that have identical couplings to the resonator, the interaction Hamiltonian conserves spin angular momentum, and the resonator cannot relax the spins to thermal equilibrium unless this symmetry is broken by the spin Hamiltonian. The mechanism by which such a spin system becomes ''trapped'' away from thermal equilibrium can be visualized using a semiclassical model, which shows how an indirect spin-spin interaction arises from the coupling of multiple spins to one resonator. The internal spin Hamiltonian can affect the polarization process in two ways: (1) By modifying the structure of the spin-spin correlations in the energy eigenstates, and (2) by splitting the degeneracy within a manifold of energy eigenstates, so that zero-frequency off-diagonal terms in the density matrix are converted to oscillating coherences. Shifting the frequencies of these coherences sufficiently far from zero suppresses the development of resonator-induced correlations within the manifold during polarization from a totally disordered state. Modification of the spin-spin correlations by means of either mechanism affects the strength of the fluctuating spin dipole that drives the resonator. In the case where product states can be chosen as energy

  10. Kagome antiferromagnet: a chiral topological spin liquid?

    PubMed

    Messio, Laura; Bernu, Bernard; Lhuillier, Claire

    2012-05-18

    Inspired by the recent discovery of a new instability towards a chiral phase of the classical Heisenberg model on the kagome lattice, we propose a specific chiral spin liquid that reconciles different, well-established results concerning both the classical and quantum models. This proposal is analyzed in an extended mean-field Schwinger boson framework encompassing time reversal symmetry breaking phases, which allows both a classical and a quantum phase description. At low temperatures, we find that quantum fluctuations favor this chiral phase, which is stable against small perturbations of second- and third-neighbor interactions. For spin-1/2, this phase may be, beyond the mean field, a chiral gapped spin liquid. Such a phase is consistent with the density matrix renormalization group results of Yan et al. [Science 332, 1173 (2011)]. Mysterious features of the low-lying excitations of exact diagonalization spectra also find an explanation in this framework. Moreover, thermal fluctuations compete with quantum ones and induce a transition from this flux phase to a planar zero flux phase at a nonzero value of the renormalized temperature (T/S2), reconciling these results with those obtained for the classical system. PMID:23003183

  11. Spinning Eggs and Ballerinas

    ERIC Educational Resources Information Center

    Cross, Rod

    2013-01-01

    Measurements are presented on the rise of a spinning egg. It was found that the spin, the angular momentum and the kinetic energy all decrease as the egg rises, unlike the case of a ballerina who can increase her spin and kinetic energy by reducing her moment of inertia. The observed effects can be explained, in part, in terms of rolling friction…

  12. The influence of the structural transition on magnetic fluctuations in NaFeAs

    NASA Astrophysics Data System (ADS)

    Liu, Juanjuan; Wang, Jinchen; Luo, Wei; Sheng, Jieming; Wang, Aifeng; Chen, Xianhui; Danilkin, Sergey A.; Bao, Wei

    2016-07-01

    NaFeAs belongs to a class of Fe-based superconductors which have parent compounds that show separated structural and magnetic transitions. Effects of the structural transition on spin dynamics therefore can be investigated separately from the magnetic transition. A plateau in dynamic spin response is observed in a critical region around the structural transition temperature T S. It is interpreted as being due to the stiffening of spin fluctuations along the in-plane magnetic hard axis due to the d xz and d yz orbital ordering. The appearance of anisotropic spin dynamics in the critical region above the T S at T * offers a dynamic magnetic scattering mechanism for anisotropic electronic properties in the commonly referred ‘nematic phase’.

  13. The influence of the structural transition on magnetic fluctuations in NaFeAs.

    PubMed

    Liu, Juanjuan; Wang, Jinchen; Luo, Wei; Sheng, Jieming; Wang, Aifeng; Chen, Xianhui; Danilkin, Sergey A; Bao, Wei

    2016-07-13

    NaFeAs belongs to a class of Fe-based superconductors which have parent compounds that show separated structural and magnetic transitions. Effects of the structural transition on spin dynamics therefore can be investigated separately from the magnetic transition. A plateau in dynamic spin response is observed in a critical region around the structural transition temperature T S. It is interpreted as being due to the stiffening of spin fluctuations along the in-plane magnetic hard axis due to the d xz and d yz orbital ordering. The appearance of anisotropic spin dynamics in the critical region above the T S at T (*) offers a dynamic magnetic scattering mechanism for anisotropic electronic properties in the commonly referred 'nematic phase'. PMID:27213626

  14. Antiferromagnetic molecular nanomagnets with odd-numbered coupled spins

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.; Nsofini, J.

    2015-05-01

    In recent years, studies on cyclic molecular nanomagnets have captivated the attention of researchers. These magnets are finite in size and contain very large spins. They are interesting because they possess macroscopic quantum tunneling of Néel vectors. For antiferromagnetic molecular nanomagnets with finite number of even-numbered coupled spins, tunneling involves two classical localized Néel ground states separated by a magnetic energy barrier. The question is: can such phenomena be observed in nanomagnets with odd number of magnetic ions? The answer is not directly obvious because cyclic chains with odd-numbered coupled spins are frustrated as one cannot obtain a perfect Néel order. These frustrated spins can indeed be observed experimentally, so they are of interest. In this letter, we theoretically investigate macroscopic quantum tunneling in this odd spin system with arbitrary spins s, in the presence of a magnetic field applied along the plane of the magnet. In contrast to systems with an even-numbered coupled spins, the ground state of the cyclic odd-spin system contains a topological soliton due to spin frustration. Thus, the classical ground state is 2N-fold degenerate as the soliton can be placed anywhere along the ring with total S_z=+/- s . Small quantum fluctuations delocalize the soliton with a formation of an energy band. We obtain this energy band using degenerate perturbation theory at order 2s. We show that the soliton ground state is chiral for half-odd integer spins and non-chiral for integer spins. From the structure of the energy band we infer that as the value of the spin increases the inelastic polarized neutron-scattering intensity may increase or decrease depending on the strengths of the parameters of the Hamiltonian.

  15. Density Fluctuations in Liquid Water

    NASA Astrophysics Data System (ADS)

    English, Niall J.; Tse, John S.

    2011-01-01

    The density distributions and fluctuations in grids of varying size in liquid water at ambient pressure, both above the freezing point and in the supercooled state, are analyzed from the trajectories obtained from large-scale molecular dynamics simulations. It is found that the occurrence of low- and high-density regions (LDL and HDL) is transient and their respective residence times are dependent on the size of the simulated system. The spatial extent of density-density correlation is found to be within 7 Å or less. The temporal existence of LDL and HDL arises as a result of natural density fluctuations of an equilibrium system. The density of bulk water at ambient conditions is homogenous.

  16. Algorithm refinement for fluctuating hydrodynamics

    SciTech Connect

    Williams, Sarah A.; Bell, John B.; Garcia, Alejandro L.

    2007-07-03

    This paper introduces an adaptive mesh and algorithmrefinement method for fluctuating hydrodynamics. This particle-continuumhybrid simulates the dynamics of a compressible fluid with thermalfluctuations. The particle algorithm is direct simulation Monte Carlo(DSMC), a molecular-level scheme based on the Boltzmann equation. Thecontinuum algorithm is based on the Landau-Lifshitz Navier-Stokes (LLNS)equations, which incorporate thermal fluctuations into macroscopichydrodynamics by using stochastic fluxes. It uses a recently-developedsolver for LLNS, based on third-order Runge-Kutta. We present numericaltests of systems in and out of equilibrium, including time-dependentsystems, and demonstrate dynamic adaptive refinement by the computationof a moving shock wave. Mean system behavior and second moment statisticsof our simulations match theoretical values and benchmarks well. We findthat particular attention should be paid to the spectrum of the flux atthe interface between the particle and continuum methods, specificallyfor the non-hydrodynamic (kinetic) time scales.

  17. Thermal fluctuations and bouncing cosmologies

    SciTech Connect

    Cai, Yi-Fu; Zhang, Xinmin; Xue, Wei; Brandenberger, Robert E-mail: xuewei@physics.mcgill.ca E-mail: xmzhang@ihep.ac.cn

    2009-06-01

    We study the conditions under which thermal fluctuations generated in the contracting phase of a non-singular bouncing cosmology can lead to a scale-invariant spectrum of cosmological fluctuations at late times in the expanding phase. We consider point particle gases, holographic gases and string gases. In the models thus identified, we also study the thermal non-Gaussianities of the resulting distribution of inhomogeneities. For regular point particle radiation, we find that the background must have an equation of state w = 7/3 in order to obtain a scale-invariant spectrum, and that the non-Gaussianities are suppressed on scales larger than the thermal wavelength. For Gibbons-Hawking radiation, we find that a matter-dominated background yields scale-invariance, and that the non-Gaussianities are large. String gases are also briefly considered.

  18. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, [le][approximately][ovr J] [times] [approximately][ovr B][ge], has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  19. The fluctuation induced Hall effect

    SciTech Connect

    Shen, W.; Prager, S.C.

    1993-02-01

    The fluctuation induced Hall term, {le}{approximately}{ovr J} {times} {approximately}{ovr B}{ge}, has been measured in the MST reversed field pinch. The term is of interest as a possible source of current self-generation (dynamo). It is found to be non-negligible, but small in that it can account for less than 25% of the dynamo driven current.

  20. Boltzmann equation and hydrodynamic fluctuations.

    PubMed

    Colangeli, Matteo; Kröger, Martin; Ottinger, Hans Christian

    2009-11-01

    We apply the method of invariant manifolds to derive equations of generalized hydrodynamics from the linearized Boltzmann equation and determine exact transport coefficients, obeying Green-Kubo formulas. Numerical calculations are performed in the special case of Maxwell molecules. We investigate, through the comparison with experimental data and former approaches, the spectrum of density fluctuations and address the regime of finite Knudsen numbers and finite frequencies hydrodynamics. PMID:20364972

  1. Random numbers from vacuum fluctuations

    NASA Astrophysics Data System (ADS)

    Shi, Yicheng; Chng, Brenda; Kurtsiefer, Christian

    2016-07-01

    We implement a quantum random number generator based on a balanced homodyne measurement of vacuum fluctuations of the electromagnetic field. The digitized signal is directly processed with a fast randomness extraction scheme based on a linear feedback shift register. The random bit stream is continuously read in a computer at a rate of about 480 Mbit/s and passes an extended test suite for random numbers.

  2. Incommensurate charge density fluctuations in underdoped YBCO detected by resonant x-ray scattering

    NASA Astrophysics Data System (ADS)

    Ghiringhelli, Giacomo

    2013-03-01

    A key issue in high Tc superconductivity is the short and mid range ordering of spin and charge degrees of freedom when doping disrupts the long range antiferromagnetic order of parent compounds. Cu sites are the main, although not the only, actors in the play. Inelastic and elastic scattering of x rays, when performed at the Cu L3 absorption resonance, can be used to map the spin and charge excitation spectra and, simultaneously, to unveil the presence of spatial modulations in the charge or spin densities. We have used angle-resolved resonant inelastic soft x-ray scattering (RIXS) and resonant elastic soft x-ray scattering (REXS) to identify two-dimensional charge fluctuations with an incommensurate periodicity of ~ 3 . 2 lattice units in the copper oxide planes of the superconductors (Y,Nd)Ba2Cu3O6+x with hole concentrations 0 . 09 < p < 0 . 13 per planar Cu ion [G. Ghiringhelli et al, Science 337, 821 (2012)]. The intensity and correlation length of the fluctuation signal increase strongly upon cooling down to the superconducting transition temperature, Tc; further cooling below Tc abruptly reverses the divergence of the charge correlations. In combination with prior observations of a large gap in the spin excitation spectrum, these data indicate an incipient charge-density-wave instability that competes with superconductivity. Further measurements on an Ortho III sample have confirmed that the charge fluctuations are independent of the chain ordering [A. J. Achkar et al, Phys. Rev. Lett. 109, 167001 (2012)]. Put into perspective, these results show that often elastic and inelastic x-ray scattering experiments should be ideally performed jointly, to explore with the greatest sensitivity charge and spin fluctuations [L. Braicovich et al, Phys. Rev. Lett. 104, 077002, (2010)].

  3. Facing rim cavities fluctuation modes

    NASA Astrophysics Data System (ADS)

    Casalino, Damiano; Ribeiro, André F. P.; Fares, Ehab

    2014-06-01

    Cavity modes taking place in the rims of two opposite wheels are investigated through Lattice-Boltzmann CFD simulations. Based on previous observations carried out by the authors during the BANC-II/LAGOON landing gear aeroacoustic study, a resonance mode can take place in the volume between the wheels of a two-wheel landing gear, involving a coupling between shear-layer vortical fluctuations and acoustic modes resulting from the combination of round cavity modes and wheel-to-wheel transversal acoustic modes. As a result, side force fluctuations and tonal noise side radiation take place. A parametric study of the cavity mode properties is carried out in the present work by varying the distance between the wheels. Moreover, the effects due to the presence of the axle are investigated by removing the axle from the two-wheel assembly. The azimuthal properties of the modes are scrutinized by filtering the unsteady flow in narrow bands around the tonal frequencies and investigating the azimuthal structure of the filtered fluctuation modes. Estimation of the tone frequencies with an ad hoc proposed analytical formula confirms the observed modal properties of the filtered unsteady flow solutions. The present study constitutes a primary step in the description of facing rim cavity modes as a possible source of landing gear tonal noise.

  4. Heat fluctuations and initial ensembles.

    PubMed

    Kim, Kwangmoo; Kwon, Chulan; Park, Hyunggyu

    2014-09-01

    Time-integrated quantities such as work and heat increase incessantly in time during nonequilibrium processes near steady states. In the long-time limit, the average values of work and heat become asymptotically equivalent to each other, since they only differ by a finite energy change in average. However, the fluctuation theorem (FT) for the heat is found not to hold with the equilibrium initial ensemble, while the FT for the work holds. This reveals an intriguing effect of everlasting initial memory stored in rare events. We revisit the problem of a Brownian particle in a harmonic potential dragged with a constant velocity, which is in contact with a thermal reservoir. The heat and work fluctuations are investigated with initial Boltzmann ensembles at temperatures generally different from the reservoir temperature. We find that, in the infinite-time limit, the FT for the work is fully recovered for arbitrary initial temperatures, while the heat fluctuations significantly deviate from the FT characteristics except for the infinite initial-temperature limit (a uniform initial ensemble). Furthermore, we succeed in calculating finite-time corrections to the heat and work distributions analytically, using the modified saddle point integral method recently developed by us. Interestingly, we find noncommutativity between the infinite-time limit and the infinite-initial-temperature limit for the probability distribution function (PDF) of the heat. PMID:25314405

  5. Phase structure of the anisotropic antiferromagnetic Heisenberg model on a layered triangular lattice: Spiral state and deconfined spin liquid

    SciTech Connect

    Nakane, Kazuya; Kamijo, Takeshi; Ichinose, Ikuo

    2011-02-01

    In the present paper, we study a spin-1/2 antiferromagnetic (AF) Heisenberg model on layered anisotropic triangular lattice and obtain its phase structure. We use the Schwinger bosons for representing spin operators and also a coherent-state path integral for calculating physical quantities. Finite-temperature properties of the system are investigated by means of the numerical Monte-Carlo simulations. A detailed phase diagram of the system is obtained by calculating internal energy, specific heat, spin correlation functions, etc. There are AF Neel, paramagnetic, and spiral states. Turning on the plaquette term (i.e., the Maxwell term on a lattice) of an emergent U(1) gauge field that flips a pair of parallel spin-singlet bonds, we found that there appears a phase that is regarded as a deconfined spin-liquid state, though 'transition' to this phase from the paramagnetic phase is not of second order but a crossover. In that phase, the emergent gauge boson is a physical gapless excitation coupled with spinons. These results support our previous study on an AF Heisenberg model on a triangular lattice at vanishing temperature.

  6. Critical quadrupole fluctuations and collective modes in iron pnictide superconductors

    NASA Astrophysics Data System (ADS)

    Thorsmølle, V. K.; Khodas, M.; Yin, Z. P.; Zhang, Chenglin; Carr, S. V.; Dai, Pengcheng; Blumberg, G.

    2016-02-01

    The multiband nature of iron pnictides gives rise to a rich temperature-doping phase diagram of competing orders and a plethora of collective phenomena. At low dopings, the tetragonal-to-orthorhombic structural transition is closely followed by a spin-density-wave transition both being in close proximity to the superconducting phase. A key question is the nature of high-Tc superconductivity and its relation to orbital ordering and magnetism. Here we study the NaFe1 -xCoxAs superconductor using polarization-resolved Raman spectroscopy. The Raman susceptibility displays critical enhancement of nonsymmetric charge fluctuations across the entire phase diagram, which are precursors to a d -wave Pomeranchuk instability at temperature θ (x ) . The charge fluctuations are interpreted in terms of quadrupole interorbital excitations in which the electron and hole Fermi surfaces breathe in-phase. Below Tc, the critical fluctuations acquire coherence and undergo a metamorphosis into a coherent in-gap mode of extraordinary strength.

  7. NMR study of the AF-SC-SC-AF phased transition in a pnictide superconductor LaFeAsO1-xHx

    NASA Astrophysics Data System (ADS)

    Fujiwara, Naoki; Sakurai, Ryosuke; Iimura, Soushi; Matsuishi, Satoru; Hosono, Hideo; Yamakawa, Youichi; Kontani, Hiroshi

    2014-03-01

    We have performed 75As and 1H NMR measurements in LaFeAsO1xHx, an isomorphic compound of LaFeAsO1xFx. LaFeAsO1xHx is an electron doped system, and O2- can be replaced with H- up to x = 0.5. LaFeAsO1xHx is known for having double superconducting (SC) domes on H doping. Recently, we discovered that a new antiferromagnetic (AF) phase follows the double SC domes on further H doping, forming a symmetric AF-SC-SC-AF phase alignment in the electronic phase diagram Unlike the AF ordering in the lightly H-doped regime, the AF ordering in the highly H-doped regime is attributed to the nesting between electron pockets. In the conference, we will show the data of both NMR spectra and the relaxation rate 1/T1 in the whole doping region. We will discuss the difference of electronic states between the lightly H-doped AF-SC phases and highly H-doped SC-AF phases. This work is supported by a Grant-in-Aid (Grant No. KAKENHI 23340101) from the Ministry of Education, Science, and Culture, Japan.

  8. Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor

    NASA Astrophysics Data System (ADS)

    Kattnig, Daniel R.; Sowa, Jakub K.; Solov'yov, Ilia A.; Hore, P. J.

    2016-06-01

    The radical pair model of the avian magnetoreceptor relies on long-lived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field. Here we argue that certain spin relaxation mechanisms can enhance its performance. We focus on the flavin–tryptophan radical pair in cryptochrome, currently the only candidate magnetoreceptor molecule. Correlation functions for fluctuations in the distance between the two radicals in Arabidopsis thaliana cryptochrome 1 were obtained from molecular dynamics (MD) simulations and used to calculate the spin relaxation caused by modulation of the exchange and dipolar interactions. We find that intermediate spin relaxation rates afford substantial enhancements in the sensitivity of the reaction yields to an Earth-strength magnetic field. Supported by calculations using toy radical pair models, we argue that these enhancements could be consistent with the molecular dynamics and magnetic interactions in avian cryptochromes.

  9. Transitions in skin blood flow fractal scaling: the importance of fluctuation amplitude in microcirculation.

    PubMed

    Esen, Hamza; Ata, Necmi; Esen, Ferhan

    2015-01-01

    Detrended fluctuation analysis (DFA) of laser Doppler flowmetry (LDF) time series from volar skin reveals three scaling regions: cardiac, cardio-respiratory and local. Scaling exponents, slopes (αC, αCR and αL) of the straight lines, in these regions indicate correlation properties of LDF signal. Transitions from uncorrelated to positive in cardiac (αC) and positive to negative correlations in the cardio-respiratory (αCR) exponent have been observed for vasodilatation signals in response to local heating. However, positive correlation in local region (αL) did not change with vasodilatation. We studied whether the transitions in scaling exponents are correlated with the increase in peak to peak fluctuation amplitude (AF) of LDF signal. LDF signals were normalized to unity using average values of their pulsatile parts: baseline and saturation signals. If AF of normalized LDF signal is ≥0.5, we observed transitions in αC and in αCR but not in αL, in healthy subjects. It is suggested that the transition from positive to negative correlation in αCR with increasing amplitude may be explained by intact arteriolar myogenic activity in healthy young (Y) and middle aged (MA) subjects. In contrast, we did not observe transition in αCR suggesting impaired myogenic activity in patients with essential hypertension (EHT). PMID:25241251

  10. Low frequency spin dynamics in a quantum Hall canted antiferromagnet

    NASA Astrophysics Data System (ADS)

    Muraki, Koji

    2007-03-01

    In quantum Hall (QH) systems, Coulomb interactions combined with the macroscopic degeneracy of Landau levels (LLs) drive the electron system into strongly correlated phases as illustrated by the series of fractional QH effects and may also lead to various forms of broken symmetry dictated by the LL filing factor ν. When two layers of such electron systems are closely separated by a thin tunnel barrier, the addition of interlayer interactions and the layer degree of freedom brings about even richer electronic phases, opening up possibilities for different classes of symmetry breaking. In particular, at total filling factor νT = 2, where the two of the four lowest LLs split by the Zeeman and interlayer tunnel couplings are occupied, the competing degrees of freedom due to the layer and spin are predicted to lead to rich magnetic phases. Here we present results of resistively detected nuclear spin relaxation measurements in closely separated electron systems that reveal strong low-frequency spin fluctuations in the QH regime at νT = 2 [1]. As the temperature is decreased, the spin fluctuations, manifested by a sharp enhancement of the nuclear spin-lattice relaxation rate 1/T1, continue to grow down to the lowest temperature of 66 mK. The observed divergent behavior of 1/T1 signals a gapless spin excitation mode (i.e., a Goldstone mode) and is a hallmark of the theoretically predicted canted antiferromagnetic order. Our data demonstrate the realization of a two-dimensional system with broken planar spin rotational symmetry, in which fluctuations do not freeze out when approaching the zero temperature limit. [1] N. Kumada, K. Muraki, and Y. Hirayama, Science 313, 329 (2006).

  11. Electron spin resonance of interacting spins in n-Ge: II. Change in the width and shape of lines

    SciTech Connect

    Veinger, A. I.; Zabrodskii, A. G.; Tisnek, T. V. Goloshchapov, S. I.

    2008-11-15

    The effect of spin interaction on the width and shape of the electron spin resonance line in compensated and uncompensated n-Ge:As has been studied. It is shown that, in the case of a magnetic field oriented along the [100] axis, the width of the resonance line decreases irrespective of the degree of compensation as the critical concentration of the insulator-metal transition is approached, owing to enhancement of the exchange interaction of spins and to an increase in the spin relaxation time. When the magnetic field is directed along other axes, an additional line broadening appears in compensated samples. This broadening is determined by the influence exerted on the g factor by fluctuations of the internal electrostatic field via the stresses generated by these fluctuations. For well-conducting samples, in which the thickness of the skin layer becomes smaller than that of the sample, the line takes on an asymmetric (Dysonian) shape. In this case, the ratio between the wings of the derivative, characteristic of this line shape, is determined by the ratio between the rates of spin diffusion and spin relaxation.

  12. AFS men and women differ most in their lifestyle choices

    USGS Publications Warehouse

    Connelly, N.A.; Brown, T.L.; Hardiman, J.M.

    2006-01-01

    The American Fisheries Society sponsored a survey to examine the career development choices of men and women and how they might differ by gender. A random sample of 700 men and 700 women was selected from the AFS membership database. The survey was mailed out in October 2004 and 991 questionnaires were returned for an adjusted response rate of 71%. Some differences exist between men and women in the areas of interest development, education, and employment, but the substantive differences occur in lifestyle choices. Women with a fisheries career are less likely to be married than men, even when age is controlled for, and women who are married are more likely to have dual-career considerations than their male counterparts. Among respondents without dependents in their home during their professional career, twice as many women as men think having children will adversely affect their career. For those with dependents, more than twice as many women as men said they had to put their career "on hold" because of their dependents. While AFS members do not represent all members of the fisheries profession, their experiences shed substantial light on the lifestyle choices likely faced by most members of the profession.

  13. The Steady Spin

    NASA Technical Reports Server (NTRS)

    Fuchs, Richard; Schmidt, Wilhelm

    1931-01-01

    With the object of further clarifying the problem of spinning, the equilibrium of the forces and moments acting on an airplane is discussed in light of the most recent test data. Convinced that in a spin the flight attitude by only small angles of yaw is more or less completely steady, the study is primarily devoted to an investigation of steady spin with no side slip. At small angles, wholly arbitrary and perfectly steady spins may be forced, depending on the type of control displacements. But at large angles only very steep and only "approaching steady" spins are possible, no matter what the control displacements.

  14. Identification and characterization of the afsR homologue regulatory gene from Streptomyces peucetius ATCC 27952.

    PubMed

    Parajuli, Niranjan; Viet, Hung Trinh; Ishida, Kenji; Tong, Hang Thi; Lee, Hei Chan; Liou, Kwangkyoung; Sohng, Jae Kyung

    2005-01-01

    We have isolated an afsR homologue, called afsR-p, through genome analysis of Streptomyces peucetius ATCC 27952. AfsR-p shares 60% sequence identity with AfsR from Streptomyces coelicolor A3 (2). afsR-p was expressed under the control of the ermE* promoter in its hosts S. peucetius, Streptomyces lividans TK 24, Streptomyces clavuligerus and Streptomyces griseus. We observed overproduction of doxorubicin (4-fold) in S. peucetius, gamma-actinorhodin (2.6-fold) in S. lividans, clavulanic acid (1.5-fold) in S. clavuligerus and streptomycin (slight) in S. griseus. Overproduction was due to expression of the gene in these strains as compared to the wild-type strains harboring the vector only. Comparative study of the expression of afsR-p revealed that regulatory networking in Streptomyces is not uniform. We speculate that phosphorylated AfsR-p becomes bound to the promoter region of afsS. The latter activates other regulatory genes, including pathway regulatory genes, and induces the production of secondary metabolites including antibiotics. We identified specific conserved amino acids and exploited them for the isolation of the partial sequence of the afsR homologue from S. clavuligerus and Streptomyces achromogens (rubradirin producer). Such findings provide additional evidence for the presence of a serine/threonine and tyrosine kinase-dependent global regulatory network in Streptomyces. PMID:15921897

  15. Dual Function for U2AF35 in AG-Dependent Pre-mRNA Splicing

    PubMed Central

    Guth, Sabine; Tange, Thomas O/.; Kellenberger, Esther; Valcárcel, Juan

    2001-01-01

    The splicing factor U2AF is required for the recruitment of U2 small nuclear RNP to pre-mRNAs in higher eukaryotes. The 65-kDa subunit of U2AF (U2AF65) binds to the polypyrimidine (Py) tract preceding the 3′ splice site, while the 35-kDa subunit (U2AF35) contacts the conserved AG dinucleotide at the 3′ end of the intron. It has been shown that the interaction between U2AF35 and the 3′ splice site AG can stabilize U2AF65 binding to weak Py tracts characteristic of so-called AG-dependent pre-mRNAs. U2AF35 has also been implicated in arginine-serine (RS) domain-mediated bridging interactions with splicing factors of the SR protein family bound to exonic splicing enhancers (ESE), and these interactions can also stabilize U2AF65 binding. Complementation of the splicing activity of nuclear extracts depleted of U2AF by chromatography in oligo(dT)-cellulose requires, for some pre-mRNAs, only the presence of U2AF65. In contrast, splicing of a mouse immunoglobulin M (IgM) M1-M2 pre-mRNA requires both U2AF subunits. In this report we have investigated the sequence elements (e.g., Py tract strength, 3′ splice site AG, ESE) responsible for the U2AF35 dependence of IgM. The results indicate that (i) the IgM substrate is an AG-dependent pre-mRNA, (ii) U2AF35 dependence correlates with AG dependence, and (iii) the identity of the first nucleotide of exon 2 is important for U2AF35 function. In contrast, RS domain-mediated interactions with SR proteins bound to the ESE appear to be dispensable, because the purine-rich ESE present in exon M2 is not essential for U2AF35 activity and because a truncation mutant of U2AF35 consisting only of the pseudo-RNA recognition motif domain and lacking the RS domain is active in our complementation assays. While some of the effects of U2AF35 can be explained in terms of enhanced U2AF65 binding, other activities of U2AF35 do not correlate with increased cross-linking of U2AF65 to the Py tract. Collectively, the results argue that

  16. Spin dynamics of an individual Cr atom in a semiconductor quantum dot under optical excitation

    NASA Astrophysics Data System (ADS)

    Lafuente-Sampietro, A.; Utsumi, H.; Boukari, H.; Kuroda, S.; Besombes, L.

    2016-08-01

    We studied the spin dynamics of a Cr atom incorporated in a II-VI semiconductor quantum dot using photon correlation techniques. We used recently developed singly Cr-doped CdTe/ZnTe quantum dots to access the spin of an individual magnetic atom. Auto-correlation of the photons emitted by the quantum dot under continuous wave optical excitation reveals fluctuations of the localized spin with a timescale in the 10 ns range. Cross-correlation gives quantitative transfer time between Cr spin states. A calculation of the time dependence of the spin levels population in Cr-doped quantum dots shows that the observed spin dynamics is dominated by the exciton-Cr interaction. These measurements also provide a lower bound in the 20 ns range for the intrinsic Cr spin relaxation time.

  17. Hyperfine interaction mediated electric-dipole spin resonance: the role of frequency modulation

    NASA Astrophysics Data System (ADS)

    Li, Rui

    2016-05-01

    The electron spin in a semiconductor quantum dot can be coherently controlled by an external electric field, an effect called electric-dipole spin resonance (EDSR). Several mechanisms can give rise to the EDSR effect, among which there is a hyperfine mechanism, where the spin-electric coupling is mediated by the electron–nucleus hyperfine interaction. Here, we investigate the influence of frequency modulation (FM) on the spin-flip efficiency. Our results reveal that FM plays an important role in the hyperfine mechanism. Without FM, the electric field almost cannot flip the electron spin the spin-flip probability is only about 20%. While under FM, the spin-flip probability can be improved to approximately 70%. In particular, we find that the modulation amplitude has a lower bound, which is related to the width of the fluctuated hyperfine field.

  18. Spin transport measurements in gallium arsenide quantum dots

    NASA Astrophysics Data System (ADS)

    Folk, Joshua Alexander

    This thesis presents a series of measurements investigating the spin physics of lateral quantum dots, defined electrostatically in the 2-D electron gas at the interface of a GaAs/AlGaAs heterostructure. The experiments span a range from open dots, where the leads of the dot carry at least one fully transmitting mode, to closed dots, where the leads are set to be tunnel barriers. For open dots, spin physics is inferred from measurements of conductance fluctuations; the effects of spin degeneracy in the orbital levels as well as a spin-orbit interaction are observed. In the closed dot measurements, ground state spin transitions as electrons are added to the dot may be determined from the motion of Coulomb blockade peaks in an in-plane magnetic field. In addition, this thesis demonstrates for the first time a direct measurement of the spin polarization of current emitted from a quantum dot, or a quantum point contact, during transport. These experiments make use of a spin-sensitive focusing geometry in which a quantum point contact serves as a spin analyzer for the mesoscopic device under test. Measurements are presented both in the open dot regime, where good agreement with theory is found, as well as the closed dot regime, where the data defies a simple theoretical explanation.

  19. Inverse spin Hall effect by spin injection

    NASA Astrophysics Data System (ADS)

    Liu, S. Y.; Horing, Norman J. M.; Lei, X. L.

    2007-09-01

    Motivated by a recent experiment [S. O. Valenzuela and M. Tinkham, Nature (London) 442, 176 (2006)], the authors present a quantitative microscopic theory to investigate the inverse spin-Hall effect with spin injection into aluminum considering both intrinsic and extrinsic spin-orbit couplings using the orthogonalized-plane-wave method. Their theoretical results are in good agreement with the experimental data. It is also clear that the magnitude of the anomalous Hall resistivity is mainly due to contributions from extrinsic skew scattering.

  20. Spin-wave and electromagnon dispersions in multiferroic MnWO4 as observed by neutron spectroscopy: Isotropic Heisenberg exchange versus anisotropic Dzyaloshinskii-Moriya interaction

    NASA Astrophysics Data System (ADS)

    Xiao, Y.; Kumar, C. M. N.; Nandi, S.; Su, Y.; Jin, W. T.; Fu, Z.; Faulhaber, E.; Schneidewind, A.; Brückel, Th.

    2016-06-01

    High-resolution inelastic neutron scattering reveals that the elementary magnetic excitations in multiferroic MnWO4 consist of low-energy dispersive electromagnons in addition to the well-known spin-wave excitations. The latter can well be modeled by a Heisenberg Hamiltonian with magnetic exchange coupling extending to the 12th nearest neighbor. They exhibit a spin-wave gap of 0.61(1) meV. Two electromagnon branches appear at lower energies of 0.07(1) and 0.45(1) meV at the zone center. They reflect the dynamic magnetoelectric coupling and persist in both the collinear magnetic and paraelectric AF1 phase and the spin spiral ferroelectric AF2 phase. These excitations are associated with the Dzyaloshinskii-Moriya exchange interaction, which is significant due to the rather large spin-orbit coupling.

  1. Spin Transport in Silicon

    NASA Astrophysics Data System (ADS)

    Appelbaum, Ian

    2008-03-01

    Silicon has been broadly viewed as the ideal material for spintronics due to its low atomic weight, lattice inversion symmetry, and near lack of nuclear spin, resulting in exceptionally long spin lifetime. Despite this appeal, however, the experimental difficulties of achieving coherent spin transport in silicon were overcome for the first time only recently, by using unique spin-polarized hot-electron injection and detection techniques. [1] Our subsequent observations of very long spin lifetimes and transit lengths [2] have impact on prospects for Silicon spintronics as the basis for a new paradigm of information processing. [1] Ian Appelbaum, Biqin Huang, and Douwe J. Monsma, ``Electronic measurement and control of spin transport in silicon,'' Nature 447, 295 (2007). [2] Biqin Huang, Douwe J. Monsma, and Ian Appelbaum, ``Coherent spin transport through a 350-micron-thick silicon wafer,'' Phys. Rev. Lett. 99, 177209 (2007).

  2. Form fluctuations of polymer loaded spherical microemulsions studied by neutron scattering and dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Kuttich, B.; Falus, P.; Grillo, I.; Stühn, B.

    2014-08-01

    We investigate the structure and shell dynamics of the droplet phase in water/AOT/octane microemulsions with polyethyleneglycol (MW = 1500) molecules loaded in the droplets. Size and polydispersity of the droplets is determined with small angle X-ray scattering and small angle neutron scattering experiments. Shell fluctuations are measured with neutron spin echo spectroscopy and related to the dynamic percolation seen in dielectric spectroscopy. Shell fluctuations are found to be well described by the bending modulus of the shell and the viscosities inside and outside the droplets. Addition of the polymer decreases the modulus for small droplets. For large droplets the opposite is found as percolation temperature shifts to higher values.

  3. Effects of hydrogen sulfide on the heme coordination structure and catalytic activity of the globin-coupled oxygen sensor AfGcHK.

    PubMed

    Fojtikova, Veronika; Bartosova, Martina; Man, Petr; Stranava, Martin; Shimizu, Toru; Martinkova, Marketa

    2016-08-01

    AfGcHK is a globin-coupled histidine kinase that is one component of a two-component signal transduction system. The catalytic activity of this heme-based oxygen sensor is due to its C-terminal kinase domain and is strongly stimulated by the binding of O2 or CO to the heme Fe(II) complex in the N-terminal oxygen sensing domain. Hydrogen sulfide (H2S) is an important gaseous signaling molecule and can serve as a heme axial ligand, but its interactions with heme-based oxygen sensors have not been studied as extensively as those of O2, CO, and NO. To address this knowledge gap, we investigated the effects of H2S binding on the heme coordination structure and catalytic activity of wild-type AfGcHK and mutants in which residues at the putative O2-binding site (Tyr45) or the heme distal side (Leu68) were substituted. Adding Na2S to the initial OH-bound 6-coordinate Fe(III) low-spin complexes transformed them into SH-bound 6-coordinate Fe(III) low-spin complexes. The Leu68 mutants also formed a small proportion of verdoheme under these conditions. Conversely, when the heme-based oxygen sensor EcDOS was treated with Na2S, the initially formed Fe(III)-SH heme complex was quickly converted into Fe(II) and Fe(II)-O2 complexes. Interestingly, the autophosphorylation activity of the heme Fe(III)-SH complex was not significantly different from the maximal enzyme activity of AfGcHK (containing the heme Fe(III)-OH complex), whereas in the case of EcDOS the changes in coordination caused by Na2S treatment led to remarkable increases in catalytic activity. PMID:27395436

  4. Lindblad dynamics of a quantum spherical spin

    NASA Astrophysics Data System (ADS)

    Wald, Sascha; Henkel, Malte

    2016-03-01

    The coherent quantum dynamics of a single bosonic spin variable, subject to a constraint derived from the quantum spherical model of a ferromagnet, and coupled to an external heat bath, is studied through the Lindblad equation for the reduced density matrix. Closed systems of equations of motion for several quantum observables are derived and solved exactly. The relationship to the single-mode Dicke model from quantum optics is discussed. The analysis of the interplay of the quantum fluctuation and the dissipation and their influence on the relaxation of the time-dependent magnetisation leads to the distinction of qualitatively different regimes of weak and strong quantum couplings. Considering the model’s behaviour in an external field as a simple mean-field approximation of the dynamics of a quantum spherical ferromagnet, the magnetic phase diagram appears to be re-entrant and presents a quantum analogue of well-established classical examples of fluctuation-induced order.

  5. Self-Polarization and Dynamical Cooling of Nuclear Spins in Double Quantum Dots

    NASA Astrophysics Data System (ADS)

    Rudner, M. S.; Levitov, L. S.

    2007-07-01

    The spin-blockade regime of double quantum dots features coupled dynamics of electron and nuclear spins resulting from the hyperfine interaction. We explain observed nuclear self-polarization via a mechanism based on feedback of the Overhauser shift on electron energy levels, and propose to use the instability toward self-polarization as a vehicle for controlling the nuclear spin distribution. In the dynamics induced by a properly chosen time-dependent magnetic field, nuclear spin fluctuations can be suppressed significantly below the thermal level.

  6. Influence of orbital nematic order on spin responses in Fe-based superconductors

    NASA Astrophysics Data System (ADS)

    Su, Yuehua; Zhang, Chao; Li, Tao

    2016-05-01

    Electronic nematicity is ubiquitous in Fe-based superconductors, but what the primary nematic order is and how the various nematic phenomena correlate with each other are still elusive. In this manuscript we study the physical consequence of the orbital nematic order on the spin correlations. We find that the orbital nematic order can drive a significant spin nematicity and can enhance the integrated intensity of the spin fluctuations. Our study shows that the orbital nematic order has strong effect on the spin correlations and it can not be taken as an unimportant secondary effect of the nematic state in Fe-based superconductors.

  7. Characteristic Current Levels of a Double Quantum Dot in the Spin Blockade Regime

    NASA Astrophysics Data System (ADS)

    Sharmin, Sonia; Muraki, Koji; Fujisawa, Toshimasa

    Electron transport through a double quantum dot is suppressed by the spin blockade effect, but its leakage current depends strongly on the nuclear spin polarization of the host material. We investigate some characteristic current levels observed at zero and sufficiently high fields in the presence of small nuclear spin fluctuation. The lowest current level at the high field appears when the two dots have identical polarization. The middle and high current levels at zero field correspond respectively to off-resonant and near-resonant flip-flop transition rates. These current levels will be useful in analyzing electronic state and associated nuclear spin polarizations.

  8. Magnetoresistance in the Spin-Orbit Kondo State of Elemental Bismuth

    PubMed Central

    Craco, Luis; Leoni, Stefano

    2015-01-01

    Materials with strong spin-orbit coupling, which competes with other particle-particle interactions and external perturbations, offer a promising route to explore novel phases of quantum matter. Using LDA + DMFT we reveal the complex interplay between local, multi-orbital Coulomb and spin-orbit interaction in elemental bismuth. Our theory quantifies the role played by collective dynamical fluctuations in the spin-orbit Kondo state. The correlated electronic structure we derive is promising in the sense that it leads to results that might explain why moderate magnetic fields can generate Dirac valleys and directional-selective magnetoresistance responses within spin-orbit Kondo metals. PMID:26358556

  9. Interplay of Rashba spin orbit coupling and disorder in the conductance properties of a four terminal junction device

    NASA Astrophysics Data System (ADS)

    Ganguly, Sudin; Basu, Saurabh

    2016-04-01

    We report a thorough theoretical investigation on the quantum transport of a disordered four terminal device in the presence of Rashba spin orbit coupling (RSOC) in two dimensions. Specifically we compute the behaviour of the longitudinal (charge) conductance, spin Hall conductance and spin Hall conductance fluctuation as a function of the strength of disorder and Rashba spin orbit interaction using the Landauer Büttiker formalism via Green's function technique. Our numerical calculations reveal that both the conductances diminish with disorder. At smaller values of the RSOC parameter, the longitudinal and spin Hall conductances increase, while both vanish in the strong RSOC limit. The spin current is more drastically affected by both disorder and RSOC than its charge counterpart. The spin Hall conductance fluctuation does not show any universality in terms of its value and it depends on both disorder as well as on the RSOC strength. Thus the spin Hall conductance fluctuation has a distinct character compared to the fluctuation in the longitudinal conductance. Further one parameter scaling theory is studied to assess the transition to a metallic regime as claimed in literature and we find no confirmation about the emergence of a metallic state induced by RSOC.

  10. Cell Volume Fluctuations in MDCK Monolayers

    PubMed Central

    Zehnder, Steven M.; Suaris, Melanie; Bellaire, Madisonclaire M.; Angelini, Thomas E.

    2015-01-01

    Cells moving collectively in tissues constitute a form of active matter, in which collective motion depends strongly on driven fluctuations at the single-cell scale. Fluctuations in cell area and number density are often seen in monolayers, yet their role in collective migration is not known. Here we study density fluctuations at the single- and multicell level, finding that single-cell volumes oscillate with a timescale of 4 h and an amplitude of 20%; the timescale and amplitude are found to depend on cytoskeletal activity. At the multicellular scale, density fluctuations violate the central limit theorem, highlighting the role of nonequilibrium driving forces in multicellular density fluctuations. PMID:25606673

  11. Analysis of dynamic multiplicity fluctuations at PHOBOS

    NASA Astrophysics Data System (ADS)

    Chai, Zhengwei; PHOBOS Collaboration; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Chai, Z.; Decowski, M. P.; García, E.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Hamblen, J.; Heintzelman, G. A.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Holynski, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Katzy, J.; Khan, N.; Kucewicz, W.; Kulinich, P.; Kuo, C. M.; Lin, W. T.; Manly, S.; McLeod, D.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Pernegger, H.; Reed, C.; Remsberg, L. P.; Reuter, M.; Roland, C.; Roland, G.; Rosenberg, L.; Sagerer, J.; Sarin, P.; Sawicki, P.; Skulski, W.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tang, J. L.; Trzupek, A.; Vale, C.; van Nieuwenhuizen, G. J.; Verdier, R.; Wolfs, F. L. H.; Wosiek, B.; Wozniak, K.; Wuosmaa, A. H.; Wyslouch, B.

    2005-01-01

    This paper presents the analysis of the dynamic fluctuations in the inclusive charged particle multiplicity measured by PHOBOS for Au+Au collisions at surdsNN = 200GeV within the pseudo-rapidity range of -3 < η < 3. First the definition of the fluctuations observables used in this analysis is presented, together with the discussion of their physics meaning. Then the procedure for the extraction of dynamic fluctuations is described. Some preliminary results are included to illustrate the correlation features of the fluctuation observable. New dynamic fluctuations results will be available in a later publication.

  12. Fluctuation theorem for partially masked nonequilibrium dynamics.

    PubMed

    Shiraishi, Naoto; Sagawa, Takahiro

    2015-01-01

    We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations. PMID:25679593

  13. Fluctuation theorem for partially masked nonequilibrium dynamics

    NASA Astrophysics Data System (ADS)

    Shiraishi, Naoto; Sagawa, Takahiro

    2015-01-01

    We establish a generalization of the fluctuation theorem for partially masked nonequilibrium dynamics. We introduce a partial entropy production with a subset of all possible transitions, and show that the partial entropy production satisfies the integral fluctuation theorem. Our result reveals the fundamental properties of a broad class of autonomous as well as nonautonomous nanomachines. In particular, our result gives a unified fluctuation theorem for both autonomous and nonautonomous Maxwell's demons, where mutual information plays a crucial role. Furthermore, we derive a fluctuation-dissipation theorem that relates nonequilibrium stationary current to two kinds of equilibrium fluctuations.

  14. The first observation of Carbon-13 spin noise spectra

    PubMed Central

    Schlagnitweit, Judith; Müller, Norbert

    2012-01-01

    We demonstrate the first 13C NMR spin noise spectra obtained without any pulse excitation by direct detection of the randomly fluctuating noise from samples in a cryogenically cooled probe. Noise power spectra were obtained from 13C enriched methanol and glycerol samples at 176 MHz without and with 1H decoupling, which increases the sensitivity without introducing radio frequency interference with the weak spin noise. The multiplet amplitude ratios in 1H coupled spectra indicate that, although pure spin noise prevails in these spectra, the influence of absorbed circuit noise is still significant at the high concentrations used. In accordance with the theory heteronuclear Overhauser enhancements are absent from the 1H-decoupled 13C spin noise spectra. PMID:23041799

  15. Aging dynamics of quantum spin glasses of rotors

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  16. Nuclear magnetic resonance spectroscopy with single spin sensitivity

    PubMed Central

    Müller, C.; Kong, X.; Cai, J.-M.; Melentijević, K.; Stacey, A.; Markham, M.; Twitchen, D.; Isoya, J.; Pezzagna, S.; Meijer, J.; Du, J. F.; Plenio, M. B.; Naydenov, B.; McGuinness, L. P.; Jelezko, F.

    2014-01-01

    Nuclear magnetic resonance spectroscopy and magnetic resonance imaging at the ultimate sensitivity limit of single molecules or single nuclear spins requires fundamentally new detection strategies. The strong coupling regime, when interaction between sensor and sample spins dominates all other interactions, is one such strategy. In this regime, classically forbidden detection of completely unpolarized nuclei is allowed, going beyond statistical fluctuations in magnetization. Here we realize strong coupling between an atomic (nitrogen–vacancy) sensor and sample nuclei to perform nuclear magnetic resonance on four 29Si spins. We exploit the field gradient created by the diamond atomic sensor, in concert with compressed sensing, to realize imaging protocols, enabling individual nuclei to be located with Angstrom precision. The achieved signal-to-noise ratio under ambient conditions allows single nuclear spin sensitivity to be achieved within seconds. PMID:25146503

  17. Development of NMOR magnetometer for spin-maser EDM experiment

    NASA Astrophysics Data System (ADS)

    Yoshimi, A.; Nanao, T.; Inoue, T.; Furukawa, T.; Uchida, M.; Tsuchiya, M.; Hayashi, H.; Chikamori, M.; Asahi, K.

    We have been developing a high sensitivity atomic magnetometer for atomic EDM experiments using a lowfrequency nuclear spin maser. In the developed nuclear spin maser of 129Xe, suppression of drift and fluctuation in the magnetic field is one of the important issues. The magnetometer being developed for spin maser EDM experiments utilizes the nonlinear magneto optical rotation (NMOR) e_ect in Rb atomic vapor. The enhancement of the optical rotation in a small magnetic field relies on the long spin-coherence time of Rb atoms in a vapor cell. The NMOR spectrum was measured by using fabricated Rb cells coated with an anti-relaxation material. The NMOR spectrum dependence on laser frequency, cell coating, and laser beam diameter were investigated. The magnetic sensitivity at present is 0:2 μG/√Hz from observed NMOR and noise spectra.

  18. Robustness of topological Hall effect of nontrivial spin textures

    NASA Astrophysics Data System (ADS)

    Jalil, Mansoor B. A.; Tan, Seng Ghee

    2014-05-01

    We analyze the topological Hall conductivity (THC) of topologically nontrivial spin textures like magnetic vortices and skyrmions and investigate its possible application in the readback for magnetic memory based on those spin textures. Under adiabatic conditions, such spin textures would theoretically yield quantized THC values, which are related to topological invariants such as the winding number and polarity, and as such are insensitive to fluctuations and smooth deformations. However, in a practical setting, the finite size of spin texture elements and the influence of edges may cause them to deviate from their ideal configurations. We calculate the degree of robustness of the THC output in practical magnetic memories in the presence of edge and finite size effects.

  19. Nuclear magnetic resonance spectroscopy with single spin sensitivity.

    PubMed

    Müller, C; Kong, X; Cai, J-M; Melentijević, K; Stacey, A; Markham, M; Twitchen, D; Isoya, J; Pezzagna, S; Meijer, J; Du, J F; Plenio, M B; Naydenov, B; McGuinness, L P; Jelezko, F

    2014-01-01

    Nuclear magnetic resonance spectroscopy and magnetic resonance imaging at the ultimate sensitivity limit of single molecules or single nuclear spins requires fundamentally new detection strategies. The strong coupling regime, when interaction between sensor and sample spins dominates all other interactions, is one such strategy. In this regime, classically forbidden detection of completely unpolarized nuclei is allowed, going beyond statistical fluctuations in magnetization. Here we realize strong coupling between an atomic (nitrogen-vacancy) sensor and sample nuclei to perform nuclear magnetic resonance on four (29)Si spins. We exploit the field gradient created by the diamond atomic sensor, in concert with compressed sensing, to realize imaging protocols, enabling individual nuclei to be located with Angstrom precision. The achieved signal-to-noise ratio under ambient conditions allows single nuclear spin sensitivity to be achieved within seconds. PMID:25146503

  20. Ageostrophic fluctuations in Cozumel Channel

    NASA Astrophysics Data System (ADS)

    Ochoa, José; Candela, Julio; Badan, Antonio; Sheinbaum, Julio

    2005-02-01

    The Cayman Current flows to the west, and most of it turns north as it approaches the Yucatan coast, producing a persistent northwesterly flow on both sides of Cozumel Island. The transport between the Yucatan Peninsula and Cozumel Island (i.e., through the Cozumel Channel) is close to 5 Sverdrups in the mean, with velocities at midchannel ranging from 20 to 180 cm/s. A recent study of the subinertial flow and pressure difference across Cozumel Channel by Chávez et al. (2003) showed the existence of periods lasting over 1 month with large 3-day to 1-week ageostrophic fluctuations. The flow was measured again for a year, now at four locations around Cozumel Island, including two instruments along the axis of the channel 8.6 km apart, thus allowing estimations of the along-channel velocity gradients. The new measurements reveal that, as suggested in the previous study, the centripetal or curvature acceleration of the current is the most significant contribution in the departure from geostrophy. Indeed, the curvature is, at times, so large that the pressure difference implies a geostrophic flow in the direction opposite to that of the actual flow; that is, the curvature is anticyclonic with amplitude in Rossby number larger than unity. Measures of the intensity of suprainertial variations, in pressure differences and velocity, show that periods of ageostrophic fluctuations are consistently much richer in high-frequency fluctuations than periods of nearly geostrophic behavior. Nonetheless, the large-scale Reynolds stresses play an insignificant role throughout.

  1. Thermal Fluctuations in Nonequilibrium Systems

    NASA Astrophysics Data System (ADS)

    Garcia, Alex Luis

    A general Monte Carlo algorithm was developed for thermal systems whose transport and chemistry can be described by a Master Equation. Nicolis and Malek Mansour examined a model in which the transition rate could be derived exactly, namely a system coupled to two reservoirs by Knudsen flow. Their Fokker-Planck equation formulation of the thermal fluctuations is confirmed by the numerical simulation. In general it is very difficult to formulate the transition rate for thermal processes. Nicolis and Malek Mansour devised a parameterized transition rate using equilibrium and deterministic properties. They predicted the existence of long-range nonequilibrium temperature fluctuation correlations for a system subjected to a linear temperature gradient. Their construction, however, is not amenable to Monte Carlo simulation due to the nonkinetic nature of the resulting stochastic process. It is shown that a direct comparison can be made between their generic thermal system and the multicell Knudsen system. Quantitative confirmation of linear temperature correlations is obtained. A vectorized version of the Monte Carlo simulation which runs on an array processor is presented. The appearance of anomalous correlations when a system is not initialized at the steady state is discussed. It is found that even a deterministic system will display a fictitious long range correlation of fluctuations due to the slow decay of the lowest order mode even when the system is initially relatively close to steady state. Some guidelines for guarding against this type of data contamination are discussed. The analytic methods and numerical codes obtained in the above studies are used in the study of the stochastic temporal evolution of a complex thermal ignition system. A simple qualitative argument used for one-variable systems is found to yield important quantitative information concerning the variance of the explosion time. The results are confirmed by Monte Carlo numerical simulations.

  2. Fermionic influence on inflationary fluctuations

    NASA Astrophysics Data System (ADS)

    Boyanovsky, Daniel

    2016-04-01

    Motivated by apparent persistent large scale anomalies in the cosmic microwave background we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the nonequilibrium effective action of an inflaton-like scalar field with Yukawa interactions (YD ,M) to light fermionic degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic Gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super-Hubble fluctuations is enhanced, P (k ;η )=(H/2 π )2eγt[-k η ] with γt[-k η ]=1/6 π2 [∑i =1 NDYi,D 2+2 ∑j =1 NMYj,M 2]{ln2[-k η ]-2 ln [-k η ]ln [-k η0]} for ND Dirac and NM Majorana fermions, and η0 is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be exact in the limit of a large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom conformally coupled to gravity suggests the possibility of a finely tuned supersymmetry among these fields.

  3. Pharmacokinetics of cefaclor AF: effects of age, antacids and H2-receptor antagonists.

    PubMed

    Satterwhite, J H; Cerimele, B J; Coleman, D L; Hatcher, B L; Kisicki, J; DeSante, K A

    1992-01-01

    The pharmacokinetics and bioavailability of cefaclor advanced formulation (cefaclor AF) were investigated in two studies, one comparing healthy elderly and younger volunteers and the other assessing the effects of an antacid and H2-receptor antagonist on cefaclor AF bioavailability. The pharmacokinetics of a 750 mg dose of cefaclor AF were studied in 30 subjects ranging in age from 65 to 84 years and 10 control subjects 21-45 years of age. Compared with controls, elderly subjects exhibited higher plasma concentrations of cefaclor which were attributed to lower plasma clearance. There was a strong association between age and renal function, and the plasma clearance of cefaclor was highly dependent upon renal function. Thus, elderly patients with impaired renal function had a reduced ability to eliminate cefaclor. Due to a short elimination half-life and wide therapeutic index, dosage adjustments are not necessary in patients exhibiting moderate renal dysfunction. The 15 healthy men in the second trial were crossed over to receive five treatments, including cefaclor AF (500 mg) alone, cefaclor AF with or preceded by cimetidine, cefaclor AF followed by Maalox TC and cefaclor immediate release (500 mg) alone. Cefaclor AF and immediate release cefaclor had similar bioavailability, but plasma concentrations were maintained for a longer period of time when cefaclor AF was administered. Cimetidine did not alter the bioavailability of cefaclor AF but Maalox TC, coadministered with cefaclor AF, reduced the extent of absorption. This suggests that cefaclor AF bioavailability is influenced by the antacid Maalox TC but not by H2-receptor antagonist cimetidine. PMID:1287615

  4. Fluctuation modes of nanoconfined DNA

    PubMed Central

    Karpusenko, Alena; Carpenter, Joshua H.; Zhou, Chunda; Lim, Shuang Fang; Pan, Junhan; Riehn, Robert

    2012-01-01

    We report an experimental investigation of the magnitude of length and density fluctuations in DNA that has been stretched in nanofluidic channels. We find that the experimental data can be described using a one-dimensional overdamped oscillator chain with nonzero equilibrium spring length and that a chain of discrete oscillators yields a better description than a continuous chain. We speculate that the scale of these discrete oscillators coincides with the scale at which the finite extensibility of the polymer manifests itself. We discuss how the measurement process influences the apparent measured dynamic properties, and outline requirements for the recovery of true physical quantities. PMID:22312183

  5. Fluctuating noise drives Brownian transport

    PubMed Central

    Hasegawa, Yoshihiko; Arita, Masanori

    2012-01-01

    The transport properties of Brownian ratchet were studied in the presence of stochastic intensity noise in both overdamped and underdamped regimes. In the overdamped case, an analytical solution using the matrix-continued fraction method revealed the existence of a maximum current when the noise intensity fluctuates on intermediate timescale regions. Similar effects were observed for the underdamped case by Monte Carlo simulations. The optimal time-correlation for Brownian transport coincided with the experimentally observed time-correlation of the extrinsic noise in Escherichia coli gene expression and implied the importance of environmental noise for molecular mechanisms. PMID:22977101

  6. Emittance growth from radiation fluctuations

    SciTech Connect

    Sands, M.

    1985-12-01

    As an electron bunch travels through a transport system, fluctuations in the energy loss of individual electrons cause the size of the bunch to grow. A calculation is given of the quantum-induced growth of the emittance of a beam in one transverse coordinate, making the following approximations: (1) that the transport system is linear; (2) that there is no coupling between the two transverse motions; and (3) that the radiation effects can be described by their values on the central design trajectory. This last assumption means that systems are considered in which the quantum effects from bending magnets are much larger than from the focusing lenses.

  7. Quantum friction and fluctuation theorems

    NASA Astrophysics Data System (ADS)

    Intravaia, F.; Behunin, R. O.; Dalvit, D. A. R.

    2014-05-01

    We use general concepts of statistical mechanics to compute the quantum frictional force on an atom moving at constant velocity above a planar surface. We derive the zero-temperature frictional force using a nonequilibrium fluctuation-dissipation relation, and we show that in the large-time, steady-state regime, quantum friction scales as the cubic power of the atom's velocity. We also discuss how approaches based on Wigner-Weisskopf and quantum regression approximations fail to predict the correct steady-state zero-temperature frictional force, mainly due to the low-frequency nature of quantum friction.

  8. Velocity fluctuations of fission fragments

    NASA Astrophysics Data System (ADS)

    Llanes-Estrada, Felipe J.; Carmona, Belén Martínez; Martínez, Jose L. Muñoz

    2016-02-01

    We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

  9. Current density fluctuations and ambipolarity of transport

    SciTech Connect

    Shen, W.; Dexter, R.N.; Prager, S.C.

    1991-10-01

    The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center_dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.

  10. Current density fluctuations and ambipolarity of transport

    SciTech Connect

    Shen, W.; Dexter, R.N.; Prager, S.C.

    1991-10-01

    The fluctuation in the plasma current density is measured in the MIST reversed field pinch experiment. Such fluctuations, and the measured radial profile of the k spectrum of magnetic fluctuations, supports the view and that low frequency fluctuations (f < 30 kHz) are tearing modes and high frequency fluctuations (30 kHz < f < 250 kHz) are localized turbulence in resonance with the local equilibrium magnetic field (i.e., k {center dot} B = 0). Correlation of current density and magnetic fluctuations (< {tilde j}{parallel}{tilde B}{sub r} >) demonstrates that radial particle transport from particle motion parallel to a fluctuating magnetic field is ambipolar over the full frequency range.

  11. Constraining dark energy fluctuations with supernova correlations

    SciTech Connect

    Blomqvist, Michael; Enander, Jonas; Mörtsell, Edvard E-mail: enander@fysik.su.se

    2010-10-01

    We investigate constraints on dark energy fluctuations using type Ia supernovae. If dark energy is not in the form of a cosmological constant, that is if the equation of state w≠−1, we expect not only temporal, but also spatial variations in the energy density. Such fluctuations would cause local variations in the universal expansion rate and directional dependences in the redshift-distance relation. We present a scheme for relating a power spectrum of dark energy fluctuations to an angular covariance function of standard candle magnitude fluctuations. The predictions for a phenomenological model of dark energy fluctuations are compared to observational data in the form of the measured angular covariance of Hubble diagram magnitude residuals for type Ia supernovae in the Union2 compilation. The observational result is consistent with zero dark energy fluctuations. However, due to the limitations in statistics, current data still allow for quite general dark energy fluctuations as long as they are in the linear regime.

  12. Velocity fluctuation analysis via dynamic programming

    SciTech Connect

    Schlossberg, D. J.; Gupta, D. K.; Fonck, R. J.; McKee, G. R.; Shafer, M. W.

    2006-10-15

    A new method of calculating one-dimensional velocity fluctuations from spatially resolved density fluctuation measurements is presented. The algorithm uses vector-matching methods of dynamic programming that match structures, such as turbulent fluctuations, in two data sets. The associated time delay between data sets is estimated by determining an optimal path to transform one vector to another. This time-delay-estimation (TDE) method establishes a new benchmark for velocity analysis by achieving higher sensitivity and frequency response than previously developed methods, such as time-resolved cross correlations and wavelets. TDE has been successfully applied to beam emission spectroscopy measurements of density fluctuations to obtain poloidal flow fluctuations associated with such phenomena as the geodesic acoustic mode. The dynamic programming algorithm should allow extension to high frequency velocity fluctuations associated with underlying electrostatic potential and resulting ExB fluctuations.

  13. A Kagome Map of Spin Liquidsx

    NASA Astrophysics Data System (ADS)

    Essafi, Karim; Benton, Owen; Jaubert, Ludovic D. C.

    Competing interactions in frustrated magnets prevent ordering down to very low temperatures and stabilize exotic highly degenerate phases where strong correlations coexist with fluctuations. We study a very general nearest-neighbour Heisenberg spin model Hamiltonian on the kagome lattice which consist of Dzyaloshinskii-Moriya, ferro- and antiferromagnetic interactions. We present a three-fold mapping which transforms the well-known Heisenberg antiferromagnet (HAF) and XXZ model onto two lines of time-reversal Hamiltonians. The mapping is exact for both classical and quantum spins, i.e. preserves the energy spectrums of the HAF and XXZ model. As a consequence, our three-fold mapping gives rise to a connected network of quantum spin liquids centered around the Ising antiferromagnet. We show that this quantum disorder spreads over an extended region of the phase diagram at linear order in spin wave theory, which overlaps with the parameter region of Herbertsmithite ZnCu3(OH)6Cl2. At the classical level, all the phases have an extensively degenerate ground-state which present a variety of properties such as ferromagnetically induced pinch points in the structure factor and spontaneous scalar chirality which was absent in the original HAF and XXZ models. This work was supported by the Okinawa Institute of Science and Technology Graduate University.

  14. Kinetic equation for spin-polarized plasmas

    SciTech Connect

    Cowley, S.C.; Kulsrud, R.M.; Valeo, E.

    1984-07-01

    The usual kinetic description of a plasma is extended to include variables to describe the spin. The distribution function, over phase-space and the new spin variables, provides a sufficient description of a spin-polarized plasma. The evolution equation for the distribution function is given. The equations derived are used to calculate depolarization due to four processes, inhomogeneous fields, collisions, collisions in inhomogeneous fields, and waves. It is found that depolarization by field inhomogeneity on scales large compared with the gyroradius is totally negligible. The same is true for collisional depolarization. Collisions in inhomogeneous fields yield a depolarization rate of order 10/sup -4/S/sup -1/ for deuterons and a negligible rate for tritons in a typical fusion reactor design. This is still sufficiently small on reactor time scales. However, small amplitude magnetic fluctuations (of order one gauss) resonant with the spin precession frequency can lead to significant depolarization (depolarises triton in ten seconds and deuteron in a hundred seconds.)

  15. Optical pumping of a single hole spin in a quantum dot

    NASA Astrophysics Data System (ADS)

    Gerardot, Brian D.; Brunner, Daniel; Dalgarno, Paul A.; Öhberg, Patrik; Seidl, Stefan; Kroner, Martin; Karrai, Khaled; Stoltz, Nick G.; Petroff, Pierre M.; Warburton, Richard J.

    2008-01-01

    The spin of an electron is a natural two-level system for realizing a quantum bit in the solid state. For an electron trapped in a semiconductor quantum dot, strong quantum confinement highly suppresses the detrimental effect of phonon-related spin relaxation. However, this advantage is offset by the hyperfine interaction between the electron spin and the 104 to 106 spins of the host nuclei in the quantum dot. Random fluctuations in the nuclear spin ensemble lead to fast spin decoherence in about ten nanoseconds. Spin-echo techniques have been used to mitigate the hyperfine interaction, but completely cancelling the effect is more attractive. In principle, polarizing all the nuclear spins can achieve this but is very difficult to realize in practice. Exploring materials with zero-spin nuclei is another option, and carbon nanotubes, graphene quantum dots and silicon have been proposed. An alternative is to use a semiconductor hole. Unlike an electron, a valence hole in a quantum dot has an atomic p orbital which conveniently goes to zero at the location of all the nuclei, massively suppressing the interaction with the nuclear spins. Furthermore, in a quantum dot with strong strain and strong quantization, the heavy hole with spin-3/2 behaves as a spin-1/2 system and spin decoherence mechanisms are weak. We demonstrate here high fidelity (about 99 per cent) initialization of a single hole spin confined to a self-assembled quantum dot by optical pumping. Our scheme works even at zero magnetic field, demonstrating a negligible hole spin hyperfine interaction. We determine a hole spin relaxation time at low field of about one millisecond. These results suggest a route to the realization of solid-state quantum networks that can intra-convert the spin state with the polarization of a photon.

  16. Chain-based order and quantum spin liquids in dipolar spin ice

    NASA Astrophysics Data System (ADS)

    McClarty, P. A.; Sikora, O.; Moessner, R.; Penc, K.; Pollmann, F.; Shannon, N.

    2015-09-01

    Recent experiments on the spin-ice material Dy2Ti2O7 suggest that the Pauling "ice entropy," characteristic of its classical Coulombic spin-liquid state, may be lost at low temperatures [Pomaranski et al., Nat. Phys. 9, 353 (2013), 10.1038/nphys2591]. However, despite nearly two decades of intensive study, the nature of the equilibrium ground state of spin ice remains uncertain. Here we explore how long-range dipolar interactions D , short-range exchange interactions, and quantum fluctuations combine to determine the ground state of dipolar spin ice. We identify the organizational principle that ordered ground states are selected from a set of "chain states" in which dipolar interactions are exponentially screened. Using both quantum and classical Monte Carlo simulation, we establish phase diagrams as a function of quantum tunneling g and temperature T , and find that only a very small gc≪D is needed to stabilize a quantum spin liquid ground state. We discuss the implications of these results for Dy2Ti2O7 .

  17. Spin correlation and Majorana spectrum in chiral spin liquids in a decorated-honeycomb Kitaev model

    NASA Astrophysics Data System (ADS)

    Nasu, Joji; Motome, Yukitoshi

    2016-02-01

    Temperature evolution of the spin correlation and excitation spectrum is investigated for the Kitaev model defined on a decorated honeycomb lattice by using the quantum Monte Carlo simulation in the Majorana fermion representation. The ground state of this quantum spin model is given by two kinds of chiral spin liquids: one is topologically trivial with Abelian anyon excitations, and the other is topologically nontrivial with non-Abelian anyon excitations. While lowering temperature, the model exhibits several crossovers in the paramagnetic state, which originate from the fractionalization of quantum spins into Majorana fermions, in addition to a phase transition associated with time reversal symmetry breaking. We show that the spin correlation develops around the crossover temperatures, whereas it shows a slight change at the critical temperature, as in other Kitaev-type models. We also calculate the excitation spectrum in terms of Majorana fermions, and find that the excitation gap in the non-Abelian phase is fragile against thermal fluctuations of the Z2 fluxes, while that in the Abelian phase remains open.

  18. Spin Hall effects

    NASA Astrophysics Data System (ADS)

    Sinova, Jairo; Valenzuela, Sergio O.; Wunderlich, J.; Back, C. H.; Jungwirth, T.

    2015-10-01

    Spin Hall effects are a collection of relativistic spin-orbit coupling phenomena in which electrical currents can generate transverse spin currents and vice versa. Despite being observed only a decade ago, these effects are already ubiquitous within spintronics, as standard spin-current generators and detectors. Here the theoretical and experimental results that have established this subfield of spintronics are reviewed. The focus is on the results that have converged to give us the current understanding of the phenomena, which has evolved from a qualitative to a more quantitative measurement of spin currents and their associated spin accumulation. Within the experimental framework, optical-, transport-, and magnetization-dynamics-based measurements are reviewed and linked to both phenomenological and microscopic theories of the effect. Within the theoretical framework, the basic mechanisms in both the extrinsic and intrinsic regimes are reviewed, which are linked to the mechanisms present in their closely related phenomenon in ferromagnets, the anomalous Hall effect. Also reviewed is the connection to the phenomenological treatment based on spin-diffusion equations applicable to certain regimes, as well as the spin-pumping theory of spin generation used in many measurements of the spin Hall angle. A further connection to the spin-current-generating spin Hall effect to the inverse spin galvanic effect is given, in which an electrical current induces a nonequilibrium spin polarization. This effect often accompanies the spin Hall effect since they share common microscopic origins. Both can exhibit the same symmetries when present in structures comprising ferromagnetic and nonmagnetic layers through their induced current-driven spin torques or induced voltages. Although a short chronological overview of the evolution of the spin Hall effect field and the resolution of some early controversies is given, the main body of this review is structured from a pedagogical

  19. Fluctuation Diagnostics of the Electron Self-Energy: Origin of the Pseudogap Physics

    NASA Astrophysics Data System (ADS)

    Gunnarsson, O.; Schäfer, T.; LeBlanc, J. P. F.; Gull, E.; Merino, J.; Sangiovanni, G.; Rohringer, G.; Toschi, A.

    2015-06-01

    We demonstrate how to identify which physical processes dominate the low-energy spectral functions of correlated electron systems. We obtain an unambiguous classification through an analysis of the equation of motion for the electron self-energy in its charge, spin, and particle-particle representations. Our procedure is then employed to clarify the controversial physics responsible for the appearance of the pseudogap in correlated systems. We illustrate our method by examining the attractive and repulsive Hubbard model in two dimensions. In the latter, spin fluctuations are identified as the origin of the pseudogap, and we also explain why d -wave pairing fluctuations play a marginal role in suppressing the low-energy spectral weight, independent of their actual strength.

  20. Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors

    DOE PAGESBeta

    Tam, Yu -T.; Ku, W.; Yao, D. -X.

    2015-09-10

    We investigate the influence of itinerant carriers on dynamics and fluctuation of local moments in Fe-based superconductors, via linear spin-wave analysis of a spin-fermion model containing both itinerant and local degrees of freedom. Surprisingly against the common lore, instead of enhancing the (π,0) order, itinerant carriers with well nested Fermi surfaces is found to induce significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be intra-pocket nesting-associated long-range coupling, rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor couplingmore » reported from short-range fitting to the experimental dispersion, which turns out to result instead from the ferro-orbital order that is also found instrumental in stabilizing the magnetic order.« less