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Sample records for af spin fluctuations

  1. 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.

  2. 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.

  3. 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.

  4. 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:

  5. Orbital-cooperative spin fluctuation and orbital-dependent transport in ruthenates

    NASA Astrophysics Data System (ADS)

    Arakawa, Naoya

    2014-12-01

    Unusual transport properties deviating from the Fermi liquid are observed in ruthenates near a magnetic quantum-critical point (QCP). To understand the electronic properties of the ruthenates near and away from an antiferromagnetic (AF) QCP, I study the electronic structure and magnetic and transport properties for the t2 g-orbital Hubbard model on a square lattice in fluctuation-exchange approximation including Maki-Thompson (MT) current vertex correction (CVC). The results away from the AF QCP reproduce several experimental results of Sr2RuO4 qualitatively and provide new mechanisms about the enhancement of spin fluctuation at QIC -AF≈(0.66 π ,0.66 π ) , larger mass enhancement of the dx y orbital than that of the dx z /y z orbital, and nonmonotonic temperature dependence of the Hall coefficient. Also, the results near the AF QCP explain the T -linear inplane resistivity in Sr2Ru0.075Ti0.025O4 and give an experimental test on the obtained temperature dependence of the Hall coefficient. I reveal spatial correlation including the self-energy of electrons beyond mean-field approximations is essential to determine the electronic properties of the ruthenates. I also show several ubiquitous transport properties near an AF QCP and characteristic transport properties of a multiorbital system by comparison with results of a single-orbital system near an AF QCP.

  6. Thermal fluctuations in novel artificial spin ice

    NASA Astrophysics Data System (ADS)

    Stopfel, Henry; Ostman, Erik; Stein, Aaron; Arnalds, Unnar; Kapaklis, Vassilios; Hjorvarsson, Bjorgvin

    2015-03-01

    Artificial spin ice(ASI) is used as a model material to investigate frustrated systems. The square and kagome ASI has been extensively investigated since there discovery. Novel ASI structures like the Shakti lattice, have been proposed and already realized. In this structure what is not an adaption of natural magnetic materials the lattice topology leads to a high degree of degeneracy. We present here the results of Photoemission electron microscopy (using XMCD) to image the magnetization of nano-islands in a Shakti ASI. By using a three layer of Pd-Fe-Pd we can tune the Curie temperature of our magnetic material by varying the thickness of the Fe-layer. Beside a statistical analysis of the frozen-in ground state, we present also a temperature series, in which we could visualize the two energy levels of the small and large islands and due to this the different blocking temperatures for these islands. The comparison of these measurements with previous measurements on squared ASI give us a better understanding of the magnetic ordering and the thermal fluctuations in the novel Shakti ASI. Materials Physics, Department of Physics and Astronomy, Uppsala University, Sweden.

  7. Effects of thermal magnetic fluctuations on spin transport in Pt

    NASA Astrophysics Data System (ADS)

    Freeman, Ryan; Zholud, Andrei; Cao, Rongxing; Urazhdin, Sergei

    Despite extensive studies and applications of Pt as a spin Hall material in spintronic devices, its spin-dependent transport properties are still debated. We present a comprehensive experimental study of spin transport in Pt, utilizing measurements of giant magnetoresistance (GMR) in nanoscale Permalloy (Py)-based spin valves with Pt inserted in the nonmagnetic spacer. The spin diffusion length and the interfacial spin flipping coefficients are extracted from the dependence of MR on the Pt thickness. For samples with Pt separated from Py by Cu spacers, the spin diffusion length is 6 nm at 7K, and decreases to 3 nm at room temperature. The interfacial spin flipping decreases with increasing temperature, resulting in nonmonotonic temperature dependence of MR in samples with thin Pt. In contrast, in samples with Pt in direct contact with Py, we do not observe such a nonmonotonic dependence, and the spin diffusion length is significantly larger than in samples with Pt surrounded by Cu spacers. Our results indicate a large effect of the giant paramagnetic fluctuations in the nearly ferromagnetic Pt. These fluctuations are suppressed due to the proximity magnetism when Pt is in contact with Py, resulting in enhanced spin diffusion length and reduced spin flipping at the Pt interfaces. These observations indicate the need for a critical revision of spin transport and spin Hall-related properties of Pt-based structures. Supported by NSF ECCS-1305586.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. Universal spin Hall conductance fluctuations in chaotic Dirac quantum dots

    NASA Astrophysics Data System (ADS)

    Vasconcelos, T. C.; Ramos, J. G. G. S.; Barbosa, A. L. R.

    2016-03-01

    We present complete analytical and numerical results that demonstrate the anomalous universal fluctuations of the spin Hall conductance in chiral materials such as graphene and topological insulators. We investigate both the corresponding fluctuations, the universal fractionated and the universal quantized, and also the open channel orbital number crossover between the two regimes. In particular, we show that the Wigner-Dyson symmetries do not properly describe such conductances and the preponderant role of the chiral classes on the Dirac quantum dots. The results are analytical and solve outstanding issues.

  16. 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.

  17. 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

  18. 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.

  19. Coherence properties of holes subject to a fluctuating spin chirality

    SciTech Connect

    Wheatley, J.M. ); Hong, T.M. )

    1991-03-01

    The coherence properties of holes coupled to short-ranged chiral spin fluctuations with a characteristic chiral spin fluctuation time {tau}{sub ch}={omega}{sub ch}{sup {minus}1} are investigated in two dimensions. At temperatures {ital kT}{much lt}4{pi}{sup 2}{l angle}{phi}{sup 2}{r angle}{sup {minus}1}{h bar}{omega}{sub ch} hole quasiparticles exist and propagate with a renormalized mass {ital m}{sup *}/{ital m}=1+{l angle}{phi}{sup 2}{r angle}{h bar}/16{pi}{ital ma}{sub 0}{sup 2}{omega}{sub ch}. $langle phi sup 2 rangle--- is the amplitude of the local fictitious flux fluctuation and {ital a}{sub 0} is a lattice cutoff. At temperatures {ital kT}{much gt}4{pi}{sup 2}{l angle}{phi}{sup 2}{r angle}{sup {minus}1}{h bar}{omega}{sub ch} an effective-mass approximation is invalid and we find that the hole diffuses according to a {ital logarithmic} diffusion law in the quasistatic chiral field. The unusual diffusion law is a consequence of the long-ranged nature of the gauge field. The result shows that the holes do not form a coherent quantum fluid in the quasistatic regime.

  20. Antiferromagnetic exchange and spin-fluctuation pairing in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Plakida, Nikolay M.

    2006-01-01

    A microscopic theory of superconductivity is formulated within an effective p-d Hubbard model for a CuO2 plane. By applying the Mori-type projection technique, the Dyson equation is derived for the Green functions in terms of Hubbard operators. The antiferromagnetic exchange caused by interband hopping results in pairing of all carries in the conduction subband and high Tc proportional to the Fermi energy. Kinematic interaction in intraband hopping is responsible for the conventional spin-fluctuation pairing. Numerical solution of the gap equation proves the d-wave gap symmetry and defines Tc doping dependence. Oxygen isotope shift and pressure dependence of Tc are also discussed.

  1. Fluctuation theorem for a small engine and magnetization switching by spin torque.

    PubMed

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.

  2. Fluctuation Theorem for a Small Engine and Magnetization Switching by Spin Torque

    NASA Astrophysics Data System (ADS)

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem.

  3. Fluctuation theorem for a small engine and magnetization switching by spin torque.

    PubMed

    Utsumi, Yasuhiro; Taniguchi, Tomohiro

    2015-05-01

    We consider a reversal of the magnetic moment of a nanomagnet by a fluctuating spin torque induced by a nonequilibrium current of electron spins. This is an example of the problem of the escape of a particle from a metastable state subjected to a fluctuating nonconservative force. Spin torque is a nonconservative force, and its fluctuations are beyond the description of the fluctuation-dissipation theorem. We estimate the joint probability distribution of work done by the spin torque and the Joule heat generated by the current, which satisfies the fluctuation theorem for a small engine. We predict a threshold voltage above which the spin-torque shot noise induces probabilistic switching events and below which such events are blocked. We adopt the theory of full-counting statistics under the adiabatic pumping of spin angular momentum. This enables us to account for the backaction effect, which is crucial to maintain consistency with the fluctuation theorem. PMID:26001013

  4. Speckle imaging of spin fluctuations in a strongly interacting Fermi gas.

    PubMed

    Sanner, Christian; Su, Edward J; Keshet, Aviv; Huang, Wujie; Gillen, Jonathon; Gommers, Ralf; Ketterle, Wolfgang

    2011-01-01

    Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

  5. Speckle Imaging of Spin Fluctuations in a Strongly Interacting Fermi Gas

    SciTech Connect

    Sanner, Christian; Su, Edward J.; Keshet, Aviv; Huang Wujie; Gillen, Jonathon; Gommers, Ralf; Ketterle, Wolfgang

    2011-01-07

    Spin fluctuations and density fluctuations are studied for a two-component gas of strongly interacting fermions along the Bose-Einstein condensate-BCS crossover. This is done by in situ imaging of dispersive speckle patterns. Compressibility and magnetic susceptibility are determined from the measured fluctuations. This new sensitive method easily resolves a tenfold suppression of spin fluctuations below shot noise due to pairing, and can be applied to novel magnetic phases in optical lattices.

  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. Temperature Evolution of Spin Fluctuations in FeAs

    NASA Astrophysics Data System (ADS)

    Podlesnyak, A.; Ehlers, G.; Tóth, S.; Gofryk, K.; Sefat, A. S.

    2015-03-01

    The discovery of superconductivity (SC) in iron pnictides has opened a new stage in SC research. The superconducting state appears in iron pnictides with doping in metallic parent compounds. This is an important difference to the cuprates, which exhibit SC near a correlated insulating state. Therefore, the nature of the magnetism in the simplest iron pnictide - binary FeAs - is of fundamental importance for understanding the interplay between localized and itinerant magnetism and superconductivity in these materials. We use inelastic neutron scattering to map spin wave excitations in the monoarsenide FeAs at temperatures above and below the antiferromagnetic transition TN ~ 70 K. We find magnetic excitation spectrum near the Néel temperature to be strongly different from the spectrum in the ground state. Near the transition temperature, magnetic fluctuations clearly indicate two-dimensional character in an intrinsically three-dimensional (3D) system. On the other hand, at low temperature, spin waves in FeAs are anisotropic 3D, suggesting a crossover from two-dimensional to three-dimensional character. Work at ORNL was sponsored by the US DOE Scientific User Facilities Division, Office of Basic Energy Sciences (AP, GE) and Materials Science and Engineering Division (KG, AS).

  8. Fractional Spin Fluctuations as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model

    NASA Astrophysics Data System (ADS)

    Yoshitake, Junki; Nasu, Joji; Motome, Yukitoshi

    2016-10-01

    Experimental identification of quantum spin liquids remains a challenge, as the pristine nature is to be seen in asymptotically low temperatures. We here theoretically show that the precursor of quantum spin liquids appears in the spin dynamics in the paramagnetic state over a wide temperature range. Using the cluster dynamical mean-field theory and the continuous-time quantum Monte Carlo method, which are newly developed in the Majorana fermion representation, we calculate the dynamical spin structure factor, relaxation rate in nuclear magnetic resonance, and magnetic susceptibility for the honeycomb Kitaev model whose ground state is a canonical example of the quantum spin liquid. We find that dynamical spin correlations show peculiar temperature and frequency dependence even below the temperature where static correlations saturate. The results provide the experimentally accessible symptoms of the fluctuating fractionalized spins evincing the quantum spin liquids.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  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. Quantum Fluctuations of Local Magnetoresistance in Organic Spin Valves

    NASA Astrophysics Data System (ADS)

    Raikh, Mikhail; Roundy, Robert; Nemirovsky, Demitry; Kagalovsky, Victor

    2014-03-01

    Aside from interfacial effects, the performance of organic spin valves is limited by the spin memory loss in course of electron transport between the magnetized electrodes. One of the most prominent mechanisms of this loss is the spin precession in the random hyperfine fields of nuclei. We assume that the electron transport is due to incoherent multi-step tunneling. Then the precession takes place while electron ``waits'' for the subsequent tunneling step. While the spatial coherence of electron is lost after a single step, the spin evolution remains absolutely coherent all the way between the electrodes. As a result, the amplitudes of subsequent spin rotation interfere with each other. We demonstrate that this interference leads to a wide spread in the local values of tunnel magnetoresistance (TMR). Moreover, if on average the TMR is positive, the portion of the surface area where the TMR is negative is appreciable. We calculate analytically and numerically the distribution of local TMR as a function of the spin-valve thickness. Supported by the NSF through MRSEC DMR-112125 and by the US-Israel Binational Science Foundation

  15. 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.

  16. 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.

  17. Effect of spin fluctuations on charge transport in diffusive normal metal/d-wave superconductor junctions

    NASA Astrophysics Data System (ADS)

    Shigeta, Iduru; Yokoyama, Takehito; Asano, Yasuhiro; Hiroi, Masahiko; Tanaka, Yukio

    2010-12-01

    The effect of spin fluctuations on the transport properties in diffusive normal metal/d-wave superconductor (DN/DS) junctions is studied under various situations by solving the Usadel equation with Nazarov’s generalized boundary condition. Tunneling conductance of the DN/DS junctions is calculated by changing the magnitude of the resistance in DN, Thouless energy in DN, the transparency of the insulating barrier, and the angle between the lobe direction of the d-wave pair potential and the normal to the interface, together with the magnitude of spin fluctuations. A zero-bias conductance dip (ZBCD) and a zero-bias conductance peak (ZBCP) occur in line shapes by way of a coherent Andreev reflection (CAR) around zero energy in the system of DN/DS junctions. We have found that both of the ZBCD and the ZBCP become narrower with the increasing magnitude of spin fluctuations.

  18. Effect of spin fluctuations on tunneling conductance in diffusive normal metal/conventional superconductor junctions

    NASA Astrophysics Data System (ADS)

    Shigeta, I.; Yokoyama, T.; Asano, Y.; Hiroi, M.; Tanaka, Y.

    2009-03-01

    Transport property in diffusive normal metal/conventional superconductor (DN/CS) junctions is studied for the effect of spin fluctuations under various situations by solving the Usadel equation with Nazarov's generalized boundary condition. Tunneling conductance of the DN/CS junctions is calculated by changing the magnitude of the resistance in DN, Thouless energy in DN, and the transparency of the insulating barrier, together with the magnitude of spin fluctuations. A zero-bias conductance dip (ZBCD) and a zero-bias conductance peak (ZBCP) with the width given by Thouless energy occur in line shapes by way of a coherent Andreev reflection (CAR) around zero energy in the system of DN/CS junctions. We have found that both of the ZBCD and the ZBCP sharpen with increasing the magnitude of spin fluctuations in the region of the relatively large resistance in DN.

  19. Effects of power fluctuation on fast magnetic field detection using a spin-torque oscillator

    NASA Astrophysics Data System (ADS)

    Kanao, Taro; Nagasawa, Tazumi; Kudo, Kiwamu; Suto, Hirofumi; Yamagishi, Michinaga; Mizushima, Koichi; Sato, Rie

    2016-11-01

    We study the effects of power fluctuation on a high-data-transfer-rate read head with a spin-torque oscillator using a nonlinear oscillator model. By numerically solving the model under random sequences of applied pulsed magnetic fields (corresponding to stray fields from data bits), the bit-error rate is estimated. For a large damping rate of power, the bit errors are caused primarily by phase fluctuation that is enhanced by amplitude-phase coupling. In contrast, for a small damping rate of power, the bit errors are caused primarily by power fluctuation and are independent of amplitude-phase coupling.

  20. Non-Fermi-liquid behavior and spin fluctuations in doped UAl{sub 2}

    SciTech Connect

    Mayr, F.; Blanckenhagen, G.v.; Stewart, G.R.

    1997-01-01

    Using the canonical spin-fluctuation system UAl{sub 2} as a starting point, via negative chemical pressure (doping with Y) we have expanded d{sub U-U} in a system known to be near the Hill limit of f-electron localization, and characterized the samples via resistivity, magnetic susceptibility, and specific-heat measurements. All system parameters, including magnetic susceptibility, specific heat {gamma} ({equivalent_to}C/Tlim{sub T{r_arrow}0}), and spin-fluctuation temperature, behave monotonically. For U{sub 1{minus}x}Y{sub x}Al{sub 2}, 0.30{le}x{le}0.70, spin-glass behavior is found with T{sub f}{approx_equal};5.1{plus_minus}0.5 K. This spin-glass behavior weakens (T{sub f} sinks, smaller magnetic signature, no specific-heat anomaly) for x{ge}0.75 while, at the same time, the spin-fluctuation T{sup 3}lnT term also gradually disappears from the specific heat. For x{ge}0.875, a non-Fermi-liquid (nFl) lnT term is found in the low temperature C/T. This new, perhaps equilibrium, ground state persists upon further dilution of the U ions with Y. Thus, we report on the evolution of nFl behavior in the neighborhood of a spin-glass ground state but, indeed, directly out of a yet weaker form of magnetism than heretofore reported, that of spin fluctuations. {copyright} {ital 1997} {ital The American Physical Society}

  1. 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.

  2. 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.

  3. 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

    2015-02-23

    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.

  4. 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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Spin-Fluctuation Mechanism of Anomalous Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Magnets.

    PubMed

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

    2015-11-20

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe_{1-x}Co_{x})_{2}B 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 due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models. PMID:26636868

  14. 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.

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

    DOE PAGES

    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.

  16. Spin-Fluctuation Mechanism of Anomalous Temperature Dependence of Magnetocrystalline Anisotropy in Itinerant Magnets.

    PubMed

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

    2015-11-20

    The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe_{1-x}Co_{x})_{2}B 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 due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.

  17. 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.

  18. Comparison of the exact thermodynamics of the AF Blume-Emery-Grifiths and of the spin-1 ferromagnetic Ising models

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    We study in detail the thermodynamics of the anti-ferromagnetic Blume-Emery-Griffiths (AF BEG) model in the presence of a longitudinal magnetic field. Its thermodynamics is derived from the exact Helmholtz free energy (HFE) of the model, valid for T > 0. Numerical simulations of this model on a periodic space chain with 10 sites (N=10) yield the energy spectra of the model at K/J = 2 for D/J = 1 and D/J = 2, thus helping us compare, for a broad range of temperature, how some (per site) thermodynamic functions with the same value of K/J but distinct values of D/J behave, namely: the z-component of the magnetization, the specific heat and the entropy. These thermodynamic functions of the AF BEG model at K/|J| = 2 are compared to those of the spin-1 ferromagnetic Ising model with D/|J| > 1.5, for which the T=0 phase diagrams of both models are identical. This comparison is done in a large interval of temperature.

  19. Functional-integral study of spin fluctuations in small Fe clusters

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

    Finite temperature magnetic properties of small FeN clusters (N ≤6) are determined in the framework of a spin-fluctuation itinerant-electron theory based on a functional integral formulation of the canonical partition function and derived statistical averages. The free energy associated to each configuration of the exchange fields throughout the cluster are calculated by using Haydock-Heine-Kellys recursion method. The statistical averages of physical interest are obtained by performing parallel-tempering Monte Carlo simulations. Representative results are discussed for the average magnetization per atom as a function of temperature. The interplay between local environment and magnetization curves is analyzed by considering the low-temperature limit of the local spin-fluctuations energies ΔFl(ξ) at different atoms l. The electronic calculations are contrasted with the predictions of simple of phenomenological Heisenberg-like models.

  20. Suppression of polarization fluctuations in chromium alloys with commensurate spin-density waves

    NASA Astrophysics Data System (ADS)

    Michel, R. P.; Weissman, M. B.; Ritley, K.; Huang, J. C.; Flynn, C. P.

    1993-02-01

    We compare electrical resistance noise in commensurate and incommensurate phases of the spin-density wave (SDW) in Cr and dilute CrMn alloys. The commensurate phase gives much less polarization fluctuation noise than the incommensurate phase. The incommensurability of the SDW and the lattice in Cr may affect the SDW dynamics through the existence of weak planes in which the induced orbital moment contribution to the SDW is close to zero.

  1. 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.

  2. 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.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. Electronic structure and spin fluctuations in the helical ferromagnet MnSi

    NASA Astrophysics Data System (ADS)

    Povzner, A. A.; Volkov, A. G.; Yasyulevich, I. A.

    2016-07-01

    The influence of spin fluctuations on the magnetic properties of the ferromagnetic helimagnet MnSi has been studied in the Hubbard model taking into account the antisymmetric relativistic Dzyaloshinskii-Moriya interaction for band electrons. The obtained equations of the magnetic state indicate the correlation between the fine structure of the density of electronic states and the magnetization and coefficient of mode-mode coupling. It has been shown that the position of the Fermi energy in the immediate proximity on the point of the local minimum of the density of electronic states leads to large zero spin fluctuations at low magnetization of the helimagnet. When approaching from down the Néel point (approximately, at 0.9 T N), the zero fluctuation disappear, and the temperature rise of thermal spin fluctuation is accompanied by the change in the sign of the coefficient of mode-mode coupling. A magnetic field perpendicular to the helicoids plane brings about the formation and subsequent "collapse" of the helimagnetic cone. However, the condition of the change in the sign of the coefficient of mode-mode coupling divides the MnSi phase diagram into two parts, one of which corresponds to the ferromagnetic state induced by the field, and the other corresponding to the paramagnetic state. In this case, the h-T diagram has a specific region, inside which the paramagnetic and the ferromagnetic state are instable. The boundaries of the region agree with the experimental data on the boundaries of the anomalous phase ( a phase). It has been found that the results of calculations of the temperature dependence of the magnetic susceptibility agree with the experimental data.

  6. Conduction-electron spin resonance and spin-density fluctuations of CoS2-xSex (x≤0.1)

    NASA Astrophysics Data System (ADS)

    Rivadulla, F.

    2011-10-01

    I report the observation of conduction electron spin resonance (CESR) in the paramagnetic phase of weak itinerant ferromagnet (WIFM) CoS2. The observation of a narrow Lorentzian line above TC is interpreted as a signature of long-wavelength exchange-enhanced spin-density fluctuations, whose amplitude increases up to T* ≈ 2 TC. I propose that this temperature marks a characteristic energy scale below which strong exchange interactions between spin fluctuations determine the spin lifetime. This study shows that the characteristic parameters of CESR are very sensitive to electronic correlations and can be very useful in the study of the spin interactions and relaxation in itinerant electron systems in the intermediate coupling regime.

  7. 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.

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

    PubMed

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

    2015-09-25

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

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

    DOE PAGES

    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

  10. 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.

  11. Orbital-spin-coupled fluctuations in spinel vanadate MnV2O4

    NASA Astrophysics Data System (ADS)

    Nii, Yoichi; Abe, Nobuyuki; Arima, Taka-hisa

    2013-02-01

    The elastic properties of a spinel vanadate MnV2O4 that has an orbital degree of freedom in the triply degenerate t2g orbital at V3+(d2) sites are investigated by ultrasonic pulse-echo measurement. Considerable softening of the shear elastic constant (C11-C12)/2 is observed as the temperature approaches the first-order transition from the high-temperature orbital-disordered cubic phase to the low-temperature orbital-ordered tetragonal phase. The softening is attributed to fluctuations between dyz and dzx. Moreover, the elastic anomaly is found to be sensitive to the external magnetic field, revealing a coupling between spin and orbital fluctuations. The elastic anomaly is well reproduced theoretically based on Landau theory and elucidates a characteristic precursor phenomenon in MnV2O4.

  12. 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.

  13. Zitterbewegung with spin-orbit coupled ultracold atoms in a fluctuating optical lattice

    NASA Astrophysics Data System (ADS)

    Argonov, V. Yu; Makarov, D. V.

    2016-09-01

    The dynamics of non-interacting ultracold atoms with artificial spin-orbit coupling is considered. Spin-orbit coupling is created using two moving optical lattices with orthogonal polarizations. Our main goal is to study influence of lattice noise on Rabi oscillations. Special attention is paid to the phenomenon of the Zitterbewegung being trembling motion caused by Rabi transitions between states with different velocities. Phase and amplitude fluctuations of lattices are modelled by means of the two-dimensional stochastic Ornstein-Uhlenbeck process, also known as harmonic noise. In the the noiseless case the problem is solved analytically in terms of the momentum representation. It is shown that lattice noise significantly extends duration of the Zitterbewegung as compared to the noiseless case. This effect originates from noise-induced decoherence of Rabi oscillations.

  14. 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.

  15. 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

  16. 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.

  17. Spin wave collapse and incommensurate fluctuations in URU 2Si 2

    NASA Astrophysics Data System (ADS)

    Buyers, W. J. L.; Tun, Z.; Petersen, T.; Mason, T. E.; Lussier, J.-G.; Gaulin, B. D.; Menovsky, A. A.

    1994-04-01

    To test if the TN = 17.7 K transition in URu 2Si 2 is driven by a divergence of a magnetic order parameter we performed high-resolution neutron scattering. At the ordering wave vector the spin-wave energy collapsed and the susceptibility diverged as TN was approached. This confirms that the order parameter is the magnetic dipole, as shown by recent symmetry arguments and polarized neutron experiments [1]. We also observe incommensurate fluctuations, suggesting that competing temperature-dependent interactions may influence this weak-moment transition.

  18. Spin coupling between cold atoms and the thermal fluctuations of a metal surface.

    PubMed

    Jones, M P A; Vale, C J; Sahagun, D; Hall, B V; Hinds, E A

    2003-08-22

    We describe an experiment in which Bose-Einstein condensates and cold atom clouds are held by a microscopic magnetic trap near a room-temperature metal wire 500 microm in diameter. The lifetime for atoms to remain in the microtrap is measured over a range of distances down to 27 microm from the surface of the metal. We observe the loss of atoms from the microtrap due to spin flips. These are induced by radio-frequency thermal fluctuations of the magnetic field near the surface, as predicted but not previously observed.

  19. 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.

  20. 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

  1. Optical observation of spin-density-wave fluctuations in Ba122 iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Xu, B.; Dai, Y. M.; Xiao, H.; Shen, B.; Ye, Z. R.; Forget, A.; Colson, D.; Feng, D. L.; Wen, H. H.; Qiu, X. G.; Lobo, R. P. S. M.

    2016-08-01

    In iron-based superconductors, a spin-density-wave (SDW) magnetic order is suppressed with doping, and unconventional superconductivity appears in close proximity to the SDW instability. The optical response of the SDW order shows clear gap features: substantial suppression in the low-frequency optical conductivity, alongside a spectral weight transfer from low to high frequencies. Here, we study the detailed temperature dependence of the optical response in three different series of the Ba122 system [Ba1 -xKxFe2As2 , Ba (Fe1-xCox) 2As2 , and BaFe2(As1-xPx) 2 ]. Intriguingly, we find that the suppression of the low-frequency optical conductivity and spectral weight transfer appear at a temperature T* much higher than the SDW transition temperature TSDW. Since this behavior has the same optical feature and energy scale as the SDW order, we attribute it to SDW fluctuations. Furthermore, T* is suppressed with doping, closely following the doping dependence of the nematic fluctuations detected by other techniques. These results suggest that the magnetic and nematic orders have an intimate relationship, in favor of the magnetic-fluctuation-driven nematicity scenario in iron-based superconductors.

  2. 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.

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

    DOE PAGES

    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

  4. Effects of spin fluctuation on the magnetic anisotropy constant of itinerant electron magnets

    NASA Astrophysics Data System (ADS)

    Kobayashi, Naofumi; Hyodo, Kazushige; Sakuma, Akimasa

    2016-10-01

    In the disordered local moment picture, we calculated the magnetization (M) and magnetic anisotropy energy (MAE) of FePt, CoPt, and MnAl ordered alloys and a body-centered tetragonal FeCo (bct-FeCo) disordered alloy, assuming spatially fluctuated spin configurations at finite temperatures. All alloys exhibit the relation K 1(T)/K 1(0) = (M(T)/M(0)) n with the exponent n ≈ 2. This is consistent with the two-ion anisotropy model, in contrast to the usual single-ion anisotropy model exhibiting n = 3. Because these systems have different mechanisms of MAE, we suggest that this relation is a general rule for itinerant electron systems.

  5. Strong charge and spin fluctuations in La2O3Fe2Se2

    NASA Astrophysics Data System (ADS)

    Jin, Guangxi; Wang, Yilin; Dai, Xi; Ren, Xinguo; He, Lixin

    2016-08-01

    The electronic structure and magnetic properties of the strongly correlated material La2O3Fe2Se2 are studied by using both the density-functional theory plus U (DFT +U ) method and the DFT plus Gutzwiller (DFT + G) variational method. The ground-state magnetic structure of this material obtained with DFT +U is consistent with recent experiments with an appropriate U parameter, but its band gap is significantly overestimated by DFT +U , even with a small Hubbard U value. In contrast, the DFT + G method yields a band gap of 0.1-0.2 eV, in excellent agreement with experiment. Detailed analysis shows that the electronic and magnetic properties of La2O3Fe2Se2 are strongly affected by charge and spin fluctuations which are missing in the DFT +U method.

  6. 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.

  7. Characterization of the structural and magnetic fluctuations near the spin-Peierls transition in CuGeO{sub 3}

    SciTech Connect

    Hirota, K.; Shirane, G.; Harris, Q.J.; Feng, Q.; Birgeneau, R.J.; Hase, M.; Uchinokura, K.

    1995-12-01

    Extensive neutron-scattering experiments have been performed on CuGeO{sub 3} single crystals to study the structural fluctuations in the neighborhood of the spin-Peierls transition at temperature {ital T}{sub SP}. We have succeeded in measuring the critical fluctuations up to a few K above {ital T}{sub SP}. The inverse correlation lengths {kappa} associated with the structural fluctuations obtained are consistent with those reported in the low-resolution diffuse x-ray-scattering measurements of Pouge. This agreement implies that the energy-integrated scattering function {ital S}(Q)={integral}{sub {minus}{infinity}}{sup {infinity}}{ital S}(Q,{omega}){ital d}{omega} measured by diffuse x-ray scattering is dominated by structural fluctuations around {omega}=0, not by the softening of a zone-boundary phonon as expected in ordinary spin-Peierls systems. In order to examine the relationship between magnetic and structural fluctuations, further information on the magnetic excitations was collected. There remains considerable intensity above {ital T}{sub SP} in the spin-excitation spectrum at (1/2 1 1/2), slowly decaying over a wide energy range and persisting up to about 50 K. We measured the magnetic dynamical structure factor {ital S}(Q,{omega}) over a wide range of energy and momentum space at temperatures of 4 K ({much_lt}{ital T}{sub SP}) and 16 K ({gt}{ital T}{sub SP}). The wave-vector dependent susceptibility {chi}(Q) deduced from the {ital S}(Q,{omega}) contour map at 16 K yields inverse correlation lengths consistent with those which we determined for the structural fluctuations. This indicates a strong symbiotic coupling between the magnetic and structural fluctuations near {ital T}{sub SP} as expected. We speculate that the Cu ions are surrounded by strongly correlated spins and that the motions are heavily overdamped. The structural fluctuations towards dimerization are accompanied by magnetic correlations leading to a spin-singlet state.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. NMR study of nematic spin fluctuations in a detwinned single crystal of underdoped Ba (Fe1-xCox) 2As2

    NASA Astrophysics Data System (ADS)

    Kissikov, T.; Dioguardi, A. P.; Timmons, E. I.; Tanatar, M. A.; Prozorov, R.; Bud'ko, S. L.; Canfield, P. C.; Fernandes, R. M.; Curro, N. J.

    2016-10-01

    We report the experimental details of how mechanical detwinning can be implemented in tandem with high-sensitivity nuclear magnetic resonance measurements and use this setup to measure the in-plane anisotropy of the spin-lattice relaxation rate in underdoped Ba (Fe1-xCox) 2As2 with x =0.048 . The anisotropy reaches a maximum of 30% at TN, and the recovery data reveal that the glassy behavior of the spin fluctuations present in the twinned state persist in the fully detwinned crystal. A theoretical model is presented to describe the spin-lattice relaxation rate in terms of anisotropic nematic spin fluctuations.

  13. 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.

  14. 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.

  15. Spin fluctuation and local magnetism of isolated Fe impurities in Pd1-xVx alloys studied by time differential perturbed angular distribution spectroscopy

    NASA Astrophysics Data System (ADS)

    Mohanta, S. K.; Srivastava, S. K.; Mishra, S. N.

    2016-12-01

    The magnetic moment and spin fluctuation temperature of isolated Fe impurity atoms in Pd1-xVx (0 ≤ x ≤ 0.15) alloys have been studied by time differential perturbed angular distribution (TDPAD) technique. With increasing V content in Pd matrix, a large non-linear reduction of the local magnetic moment accompanied with an exponential increase of the spin fluctuation temperature TSF has been observed. At and beyond x = 0.12, the Fe atoms are found to be nonmagnetic. As an important new feature, TSF is observed to vary quadratically with composition dependent changes in host spin polarization.

  16. Ordered Spin Ice State and Magnetic Fluctuations in Tb{sub 2}Sn{sub 2}O{sub 7}

    SciTech Connect

    Mirebeau, I.; Apetrei, A.; Rodriguez-Carvajal, J.; Bonville, P.; Forget, A.; Colson, D.; Glazkov, V.; Sanchez, J.P.; Isnard, O.; Suard, E.

    2005-06-24

    We have studied the spin liquid Tb{sub 2}Sn{sub 2}O{sub 7} by neutron diffraction and specific heat measurements. Below about 2 K, the antiferromagnetic liquidlike correlations mostly change to ferromagnetic. Magnetic order settles in two steps, with a smeared transition at 1.3(1) K, then an abrupt transition at 0.87(2) K. A new magnetic structure is observed, akin to an ordered spin ice, with both ferromagnetic and antiferromagnetic character. It suggests that the ordered ground state results from the influence of dipolar interactions combined with a finite anisotropy along <111> axes. The moment value of 3.3(3){mu}{sub B} deduced from the specific heat is well below that derived from the neutron diffraction of 5.9(1){mu}{sub B}, which is interpreted by the persistence of slow collective magnetic fluctuations down to the lowest temperatures.

  17. NMR Study of the SDW ordering and the Spin Fluctuations on NaFeAs single crytals

    NASA Astrophysics Data System (ADS)

    Yu, Weiqiang; Ma, L.; Zhang, S.; Zhang, J.; Xia, T.-L.; Chen, G. F.; Yao, Dao-Xin

    2011-03-01

    In iron pnictides, the nature of the spin density wave (SDW) ordering is still not clear. Recently, increasing attention has been drawn to the correlation between the SDW transition and the high-temperature tetragonal to the low-temperature orthorhombic structure transition. In NaFeAs, the magnetic moment is small and both transitions are well separated, and therefore NaFeAs could be a good candidate to study the interplay of different degrees of freedom microscopically. In this talk, we report our 23 Na and 75 As NMR observations on NaFeAs single crystals. We found that 1) the spin fluctuations are largely enhanced below the structure transition; 2) the SDW transition temperature and the magnetic moment increase significantly with pressure; and 3) the NMR linewidth and the temperature/field dependence of the spin- lattice relaxation rate show signatures of an incommensurate SDW ordering in a limited temperature range just below the SDW transition. Based on these results, we discuss the coupling between the magnetism and the lattice/band structure in NaFeAs. Supported by NSFC and National Basic Research Program of China.

  18. 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.

  19. Quantum correlations in quenched disordered spin models: Enhanced order from disorder by thermal fluctuations

    NASA Astrophysics Data System (ADS)

    Sadhukhan, Debasis; Prabhu, R.; SenDe, Aditi; Sen, Ujjwal

    2016-03-01

    We investigate the behavior of quantum correlations of paradigmatic quenched disordered quantum spin models, viz., the X Y spin glass and random-field X Y models. We show that quenched averaged quantum correlations can exhibit the order-from-disorder phenomenon for finite-size systems as well as in the thermodynamic limit. Moreover, we find that the order-from-disorder can become more pronounced in the presence of temperature by suitable tuning of the system parameters. The effects are found for entanglement measures as well as for information-theoretic quantum correlation ones, although the former show them more prominently. We also observe that the equivalence between the quenched averages and their self-averaged cousins—for classical and quantum correlations—is related to the quantum critical point in the corresponding ordered system.

  20. Quantum correlations in quenched disordered spin models: Enhanced order from disorder by thermal fluctuations.

    PubMed

    Sadhukhan, Debasis; Prabhu, R; Sen De, Aditi; Sen, Ujjwal

    2016-03-01

    We investigate the behavior of quantum correlations of paradigmatic quenched disordered quantum spin models, viz., the XY spin glass and random-field XY models. We show that quenched averaged quantum correlations can exhibit the order-from-disorder phenomenon for finite-size systems as well as in the thermodynamic limit. Moreover, we find that the order-from-disorder can become more pronounced in the presence of temperature by suitable tuning of the system parameters. The effects are found for entanglement measures as well as for information-theoretic quantum correlation ones, although the former show them more prominently. We also observe that the equivalence between the quenched averages and their self-averaged cousins--for classical and quantum correlations--is related to the quantum critical point in the corresponding ordered system. PMID:27078300

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. Disappearance of Static Magnetic Order and Evolution of Spin Fluctuations in Fe1+ SexTe1−x

    SciTech Connect

    Xu, G.; Xu, Z.; Wen, J.; Jie, Q.; Lin, Z.; Li, Q.; Chi, S.; Singh, D.K.; Gu, G.; Tranquada, J.M.

    2010-09-29

    We report neutron-scattering studies on static magnetic orders and spin excitations in the Fe-based chalcogenide system Fe{sub 1+{delta}}Se{sub x}Te{sub 1-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.

  6. Spin fluctuations and hidden-order phases in Ce-based Kondo systems

    NASA Astrophysics Data System (ADS)

    Inosov, D. S.; Portnichenko, P. Y.; Cameron, A. S.; Paschen, S.; Prokofiev, A.; Friemel, G.; Jang, H.; Keimer, B.; Filipov, V. B.; Shitsevalova, N. Y.; Schneidewind, A.; Ivanov, A.; Ollivier, J.; Deen, P. P.; Strydom, A. M.

    Among heavy-fermion metals, both CeB6 and Ce3Pd20Si6 compounds exhibit a magnetically hidden ordered phase in their low-temperature phase diagram, which is attributed to the ordering of magnetic quadrupolar moments, known as the antiferroquadrupolar (AFQ) ordering. Using inelastic neutron scattering, we have investigated the spectrum of spin excitations in both systems. In the structurally simplest CeB6, it consists of several contributions including conventional spin waves that coexist with both ferro- and antiferromagnetic excitonic resonance-like modes. However, the structurally more complex Ce3Pd20Si6 possesses a much simpler magnetic excitation spectrum with only a single contribution peaked around the AFQ wave vector. It remains quasielastic in the absence of an external magnetic field, but then develops into dispersive magnon modes whose band width scales linearly with the applied field. Furthermore, neutron diffraction measurements on the same sample at sub-Kelvin temperatures revealed diffuse magnetic scattering that can be associated with the hidden order parameter. Supported by DFG Grant No. IN 209/3-1.

  7. Spin-wave fluctuations in ferrimagnetic MgxFe3-xO4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Franco, A.; Zapf, V. S.; Barbeta, V. B.; Jardim, R. F.

    2010-04-01

    We have performed a systematic study of the magnetic properties of a series of ferrimagnetic nanoparticles of MgxFe3-xO4 (0.8≤x≤1.5) prepared by the combustion reaction method. The magnetization data can be well fitted by Bloch's law with T3/2. Bloch's constant B determined from the fitting procedure was found to increase with Mg content x from ˜3.09×10-5 K-3/2 for x=0.8 to 6.27×10-5 K-3/2 for x=1.5. The exchange integral JAB and the spin-wave stiffness constant D of MgxFe3-xO4 nanoparticles were also determined as ˜0.842 and 0.574 meV and 296 and 202 meV Å2 for specimens with x=0.8 and 1.5, respectively. These results are discussed in terms of cation redistribution among A and B sites on these nanostructured spinel ferrites.

  8. 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.

  9. Quantum Spin Fluctuations and magnons in antiferromagnetically coupled bilayers with tuneable intra-bilayer exchange - the case of Cr2W(Te)O6

    NASA Astrophysics Data System (ADS)

    Majumdar, Kingshuk; Mahanti, S. D.

    Recent neutron diffraction studies have shown that in Cr2(W,Te)O6 systems, which consist of bilayers with strong antiferromagnetic inter-bilayer coupling between Cr moments, the intra-bilayer coupling between the Cr moments can be tuned from ferro (for W) to antiferro (for Te). Ab initio density functional calculations provide a microscopic understanding of the magnetic structure but cannot explain the magnitude of the ordered Cr3+ moments. In order to understand the reduction of the ordered moment (ROM) caused by quantum spin fluctuations we have studied the magnon dispersion and ROM using a two parameter quantum Heisenberg spin Hamiltonian with tunable intra-(j) and antiferromagnetic inter- (J) bilayer couplings. The magnon dispersion and sublattice magnetization have been calculated using non-linear spin wave theory up to second-order corrections in spin S. We acknowledge the use of HPC cluster at GVSU, supported by the National Science Foundation Grant No. CNS-1228291.

  10. 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.

  11. Analysis of Charge-spin-orbital Fluctuations by Ab Initio Calculation and Random Phase Approximation: Application to Non-coplanar Antiferromagnet Cd2Os2O7

    NASA Astrophysics Data System (ADS)

    Uehara, Amane; Shinaoka, Hiroshi; Motome, Yukitoshi

    We present a systematic analysis on the basis of ab initio calculations and many-body perturbation theory for clarifying the dominant fluctuation in complex charge-spin-orbital coupled systems. For a tight-binding multiband model obtained from the maximally-localized Wannier function analysis of the band structure by the local density approximation, we take into account electron correlations at the level of random phase approximation. To identify the dominant fluctuation, we carry out the eigenmode analysis of the generalized susceptibility that includes all the multiple degrees of freedom: charge, spin, and orbital. We apply this method to the paramagnetic metallic phase of a pyrochlore oxide Cd2Os2O7, which shows a metalinsulator transition accompanied by a peculiar noncoplanar antiferromagnetic order of all-in all-out type. We find that the corresponding spin fluctuation is dominantly enhanced by the on-site Coulomb repulsions in the presence of strong spin-orbit coupling and trigonal crystal field splitting. Our results indicate that the combined method offers an effective tool for the systematic analysis of potential instabilities in strongly correlated electron materials.

  12. 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

  13. Spin-fluctuation induced non-Fermi-liquid behaviour with suppressed superconductivity in LiFe1-xCoxAs

    NASA Astrophysics Data System (ADS)

    Miao, Hu; Dai, Yaomin; Xing, Lingyi; Wang, Xiancheng; Wang, Pengshuai; Xiao, Hong; Qian, Tian; Richard, Pierre; Qiu, Xianggang; Yu, Weiqiang; Jin, Changqing; Wang, Ziqiang; Johnson, P. D.; Homes, C. C.; Ding, Hong

    We study a series of LiFe1-xCoxAs compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behaviour in LiFe1-xCoxAs is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1-xCoxAs where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

  14. Spin-Fluctuation-Induced Non-Fermi-Liquid Behavior with Suppressed Superconductivity in LiFe1 -xCoxAs

    NASA Astrophysics Data System (ADS)

    Dai, Y. M.; Miao, H.; Xing, L. Y.; Wang, X. C.; Wang, P. S.; Xiao, H.; Qian, T.; Richard, P.; Qiu, X. G.; Yu, W.; Jin, C. Q.; Wang, Z.; Johnson, P. D.; Homes, C. C.; Ding, H.

    2015-07-01

    We study a series of LiFe1 -xCox As compounds with different Co concentrations by transport, optical spectroscopy, angle-resolved photoemission spectroscopy, and nuclear magnetic resonance. We observe a Fermi-liquid to non-Fermi-liquid to Fermi-liquid (FL-NFL-FL) crossover alongside a monotonic suppression of the superconductivity with increasing Co content. In parallel to the FL-NFL-FL crossover, we find that both the low-energy spin fluctuations and Fermi surface nesting are enhanced and then diminished, strongly suggesting that the NFL behavior in LiFe1 -xCox As is induced by low-energy spin fluctuations that are very likely tuned by Fermi surface nesting. Our study reveals a unique phase diagram of LiFe1 -xCox As where the region of NFL is moved to the boundary of the superconducting phase, implying that they are probably governed by different mechanisms.

  15. Effect of spin fluctuations on the c-axis thermoelectric power in underdoped La2- xSrxCuO4+δ

    NASA Astrophysics Data System (ADS)

    Ping, Lou

    2001-04-01

    A theory of the thermoelectric power due to the competition between interlayer direct hopping and the hopping assisted by the spin fluctuations has been developed. The prediction of the theory captures the main feature of experiment. Thus we argue that the c-axis thermoelectric power exhibits metallic behavior while the c-axis electronic conductivity appears to be nonmetallic in the underdoped LaSrCuO and may be properly understood within the theory.

  16. 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.

  17. Dynamic density and spin responses of a superfluid Fermi gas in the BCS-BEC crossover: Path integral formulation and pair fluctuation theory

    NASA Astrophysics Data System (ADS)

    He, Lianyi

    2016-10-01

    We present a standard field theoretical derivation of the dynamic density and spin linear response functions of a dilute superfluid Fermi gas in the BCS-BEC crossover in both three and two dimensions. The derivation of the response functions is based on the elegant functional path integral approach which allows us to calculate the density-density and spin-spin correlation functions by introducing the external sources for the density and the spin density. Since the generating functional cannot be evaluated exactly, we consider two gapless approximations which ensure a gapless collective mode (Goldstone mode) in the superfluid state: the BCS-Leggett mean-field theory and the Gaussian-pair-fluctuation (GPF) theory. In the mean-field theory, our results of the response functions agree with the known results from the random phase approximation. We further consider the pair fluctuation effects and establish a theoretical framework for the dynamic responses within the GPF theory. We show that the GPF response theory naturally recovers three kinds of famous diagrammatic contributions: the Self-Energy contribution, the Aslamazov-Lakin contribution, and the Maki-Thompson contribution. We also show that unlike the equilibrium state, in evaluating the response functions, the linear (first-order) terms in the external sources as well as the induced order parameter perturbations should be treated carefully. In the superfluid state, there is an additional order parameter contribution which ensures that in the static and long wavelength limit, the density response function recovers the result of the compressibility (compressibility sum rule). We expect that the f-sum rule is manifested by the full number equation which includes the contribution from the Gaussian pair fluctuations. The dynamic density and spin response functions in the normal phase (above the superfluid critical temperature) are also derived within the Nozières-Schmitt-Rink (NSR) theory.

  18. 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 .

  19. 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 PAGES

    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

  20. 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.

  1. Revisiting orbital-fluctuation-mediated superconductivity in LiFeAs: Nontrivial spin-orbit interaction effects on the band structure and superconducting gap function

    NASA Astrophysics Data System (ADS)

    Saito, Tetsuro; Yamakawa, Youichi; Onari, Seiichiro; Kontani, Hiroshi

    2015-10-01

    The precise gap structure in LiFeAs (Tc=18 K) given by ARPES studies offers significant information that helps us understand the pairing mechanism in iron-based superconductors. The most remarkable characteristic in the LiFeAs gap structure would be that "the largest gap emerges on the tiny hole-pockets around the Z point." This result has been naturally explained in terms of the orbital-fluctuation scenario [T. Saito et al., Phys. Rev. B 90, 035104 (2014)], 10.1103/PhysRevB.90.035104, whereas the opposite result is obtained by the spin-fluctuation scenario. In this paper, we study the gap structure in LiFeAs by taking the spin-orbit interaction (SOI) into account, motivated by the recent ARPES studies that revealed a significant SOI-induced modification of the Fermi surface topology. For this purpose, we construct two possible tight-binding models with finite SOI by referring the band structures given by different ARPES groups. In addition, we extend the gap equation for multiorbital systems with finite SOI, and calculate the gap functions by applying the orbital-spin fluctuation theory. On the basis of both SOI-induced band structures, the main characteristics of the gap structure in LiFeAs are naturally reproduced only in the presence of strong interorbital interactions between (dx z /y z-dx y) orbitals. Thus the experimental gap structure in LiFeAs is a strong evidence for the orbital-fluctuation pairing mechanism.

  2. Manifestation of magnetic quantum fluctuations in the dielectric properties of a multiferroic

    NASA Astrophysics Data System (ADS)

    Kim, Jae Wook; Khim, Seunghyun; Chun, Sae Hwan; Jo, Y.; Balicas, L.; Yi, H. T.; Cheong, S.-W.; Harrison, N.; Batista, C. D.; Hoon Han, Jung; Hoon Kim, Kee

    2014-07-01

    Insulating magnets can display novel signatures of quantum fluctuations as similar to the case of metallic magnets. However, their weak spin-lattice coupling has made such observations challenging. Here we find that antiferromagnetic (AF) quantum fluctuations manifest in the dielectric properties of multiferroic Ba2CoGe2O7, where a ferroelectric polarization develops concomitant to an AF ordering. Upon application of a magnetic field (H), dielectric constant shows a characteristic power-law dependence near absolute zero temperature and close to the critical field Hc=37.1 T due to enhanced AF quantum fluctuations. When H>Hc, the dielectric constant shows the temperature-dependent anomalies that reflect a crossover from a field-tuned quantum critical to a gapped spin-polarized state. We uncover theoretically that a linear relation between AF susceptibility and dielectric constant stems from the generic magnetoelectric coupling and directly explains the experimental findings, opening a new pathway for studying quantum criticality in condensed matter.

  3. Magnetism, spin fluctuations, and non-Fermi-liquid behavior in (U{sub x}La{sub 1-x}){sub 2}Zn{sub 17}

    SciTech Connect

    von Blanckenhagen, G.-F.; Scheidt, E.-W.; Schreiner, T.; Stewart, G. R.

    2001-08-01

    We present results of the low-temperature specific heat C of samples of the series (U{sub x}La{sub 1-x}){sub 2}Zn{sub 17}, combined with measurements of the low-temperature magnetic susceptibility ({chi}) and resistivity ({rho}). For x>0.8 we find antiferromagnetic order in coexistence with heavy-fermion behavior. An extrapolation of T{sub N} as a function of the uranium concentration implies that T{sub N} vanishes for x=0.8; at x=0.8, no magnetic order is detected experimentally at temperatures above 0.06 K. The non-Fermi-liquid (NFL) behavior predicted at such a point in the magnetic phase diagram may be observed, but not as clearly as in other systems; some of the behavior is more consistent with spin fluctuations. As the uranium concentration is lowered below x=0.8, C continues to rise in the low-temperature limit, while {chi}{proportional_to}{chi}{sub 0}-aT{sup 0.5}, but C seems to tend towards the behavior of a Fermi liquid with spin fluctuations at the lowest temperatures (T<0.25 K). First at x=0.3 the temperature dependence of C/T is found to be contrary to Fermi-liquid behavior, while {chi}{proportional_to}{chi}{sub 0}-a log T. Thus non-Fermi-liquid behavior is not found so unambiguously at the concentration where T{sub N} vanishes as expected by a quantum critical point theory, but rather at lower uranium concentrations. This presents the possibility that NFL behavior in (U{sub x}La{sub 1-x}){sub 2}Zn{sub 17} is not due to nearness to a quantum critical point, but rather to disorder or the presence of spin fluctuations.

  4. Model of the electronic structure of electron-doped iron-based superconductors: evidence for enhanced spin fluctuations by diagonal electron hopping.

    PubMed

    Suzuki, Katsuhiro; Usui, Hidetomo; Iimura, Soshi; Sato, Yoshiyasu; Matsuishi, Satoru; Hosono, Hideo; Kuroki, Kazuhiko

    2014-07-11

    We present a theoretical understanding of the superconducting phase diagram of the electron-doped iron pnictides. We show that, besides the Fermi surface nesting, a peculiar motion of electrons, where the next nearest neighbor (diagonal) hoppings between iron sites dominate over the nearest neighbor ones, plays an important role in the enhancement of the spin fluctuation and thus superconductivity. In the highest T(c) materials, the crossover between the Fermi surface nesting and this "prioritized diagonal motion" regime occurs smoothly with doping, while in relatively low T(c) materials, the two regimes are separated and therefore results in a double dome T(c) phase diagram. PMID:25062222

  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. Glassy low-energy spin fluctuations and anisotropy gap in La1.88Sr0.12CuO4

    NASA Astrophysics Data System (ADS)

    Rømer, A. T.; Chang, J.; Christensen, N. B.; Andersen, B. M.; Lefmann, K.; Mähler, L.; Gavilano, J.; Gilardi, R.; Niedermayer, Ch.; Rønnow, H. M.; Schneidewind, A.; Link, P.; Oda, M.; Ido, M.; Momono, N.; Mesot, J.

    2013-04-01

    We present high-resolution triple-axis neutron scattering studies of the high-temperature superconductor La1.88Sr0.12CuO4 (Tc=27 K). The temperature dependence of the low-energy incommensurate magnetic fluctuations reveals distinctly glassy features. The glassiness is confirmed by the difference between the ordering temperature TN≃Tc inferred from elastic neutron scattering and the freezing temperature Tf≃11 K obtained from muon spin rotation studies. The magnetic field independence of the observed excitation spectrum as well as the observation of a partial suppression of magnetic spectral weight below 0.75 meV for temperatures smaller than Tf, indicate that the stripe frozen state is capable of supporting a spin anisotropy gap, of a magnitude similar to that observed in the spin and charge stripe-ordered ground state of La1.875Ba0.125CuO4. The difference between TN and Tf implies that the significant enhancement in a magnetic field of nominally elastic incommensurate scattering is caused by strictly inelastic scattering—at least in the temperature range between Tf and Tc—which is not resolved in the present experiment. Combining the results obtained from our study of La1.88Sr0.12CuO4 with a critical reappraisal of published neutron scattering work on samples with chemical composition close to p=0.12, where local probes indicate a sharp maximum in Tf(p), we arrive at the view that the low-energy fluctuations are strongly dependent on composition in this regime, with anisotropy gaps dominating only sufficiently close to p=0.12 and superconducting spin gaps dominating elsewhere.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Experimental evidence of Tc enhancement without the influence of spin fluctuations: NMR study on LaFeAsO1 -xHx under a pressure of 3.0 GPa

    NASA Astrophysics Data System (ADS)

    Kawaguchi, N.; Fujiwara, N.; Iimura, S.; Matsuishi, S.; Hosono, H.

    2016-10-01

    The electron-doped high-transition-temperature (Tc) iron-based pnictide superconductor LaFeAsO1 -xHx has a unique phase diagram: Superconducting double domes are sandwiched by antiferromagnetic phases at ambient pressure and they turn into a single dome with a maximum Tc that exceeds 45 K at a pressure of 3.0 GPa. We studied whether spin fluctuations are involved in increasing Tc under a pressure of 3.0 GPa by using the 75As nuclear magnetic resonance (NMR) technique. The 75As-NMR results for the powder samples show that Tc increases up to 48 K without the influence of spin fluctuations. This fact indicates that spin fluctuations are not involved in raising Tc, which implies that other factors, such as orbital degrees of freedom, may be important for achieving a high Tc of almost 50 K.

  12. Fluctuation relations for spintronics.

    PubMed

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

    2012-06-15

    Fluctuation relations are derived in systems where the spin degree of freedom and magnetic interactions play a crucial role. The form of the nonequilibrium fluctuation theorems relies on the assumption of a local balance condition. We demonstrate that in some cases the presence of magnetic interactions violates this condition. Nevertheless, fluctuation relations can be obtained from the microreversibility principle sustained only at equilibrium as a symmetry of the cumulant generating function for spin currents. We illustrate the spintronic fluctuation relations for a quantum dot coupled to partially polarized helical edge states.

  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. Giant Fluctuations of Local Magnetoresistance of Organic Spin Valves and the Non-Hermitian 1D Anderson Model

    NASA Astrophysics Data System (ADS)

    Roundy, R. C.; Nemirovsky, D.; Kagalovsky, V.; Raikh, M. E.

    2014-06-01

    Motivated by recent experiments, where the tunnel magnetoresitance (TMR) of a spin valve was measured locally, we theoretically study the distribution of TMR along the surface of magnetized electrodes. We show that, even in the absence of interfacial effects (like hybridization due to donor and acceptor molecules), this distribution is very broad, and the portion of area with negative TMR is appreciable even if on average the TMR is positive. The origin of the local sign reversal is quantum interference of subsequent spin-rotation amplitudes in the course of incoherent transport of carriers between the source and the drain. We find the distribution of local TMR exactly by drawing upon formal similarity between evolution of spinors in time and of the reflection coefficient along a 1D chain in the Anderson model. The results obtained are confirmed by the numerical simulations.

  15. Giant fluctuations of local magnetoresistance of organic spin valves and the non-Hermitian 1D Anderson model.

    PubMed

    Roundy, R C; Nemirovsky, D; Kagalovsky, V; Raikh, M E

    2014-06-01

    Motivated by recent experiments, where the tunnel magnetoresitance (TMR) of a spin valve was measured locally, we theoretically study the distribution of TMR along the surface of magnetized electrodes. We show that, even in the absence of interfacial effects (like hybridization due to donor and acceptor molecules), this distribution is very broad, and the portion of area with negative TMR is appreciable even if on average the TMR is positive. The origin of the local sign reversal is quantum interference of subsequent spin-rotation amplitudes in the course of incoherent transport of carriers between the source and the drain. We find the distribution of local TMR exactly by drawing upon formal similarity between evolution of spinors in time and of the reflection coefficient along a 1D chain in the Anderson model. The results obtained are confirmed by the numerical simulations. PMID:24949781

  16. 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.

  17. 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

  18. 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

  19. 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.

  20. Bond-length fluctuations and the spin-state transition in LCoO3 (L=La, Pr, and Nd)

    NASA Astrophysics Data System (ADS)

    Yan, J.-Q.; Zhou, J.-S.; Goodenough, J. B.

    2004-04-01

    The temperature dependence of thermal conductivity, κ(T), and magnetic susceptibility, χ(T), have been measured on single crystals of LCoO3 (L=La, Pr, Nd) grown by the floating-zone method. The susceptibility measurement shows a progressive stabilization of the low-spin (LS) state of Co(III) with decreasing size of the L3+ ion, and the population of excited intermediate-spin (IS) or high-spin (HS) state Co(III) ions begins to increase at 200 K and 300 K for PrCoO3 and NdCoO3 compared with 35 K in LaCoO3. The low-temperature Curie-Weiss paramagnetic susceptibility of LCoO3 is an intrinsic property arising from surface cobalt and, possibly, a LS ground state bearing some IS character caused by the virtual excitation to the IS state. The transition from a LS to a IS/HS state introduces bond-length fluctuations that suppress the phonon contribution to κ(T) below 300 K. The suppressed κ(T) could be further reduced by dynamic Jahn-Teller distortions associated with the IS/HS species. A smooth transition in ρ(T) and α(T) and a nearly temperature independent α(T)≈20 μV/K above 600 K do not support a thermally induced, homogeneous Mott-Hubbard transition model for the high-temperature transition of LaCoO3 from an insulating to a conductive state. A two-phase process is proposed for the interval 300 K

  1. Influence of face-centered-cubic texturing of Co2Fe6B2 pinned layer on tunneling magnetoresistance ratio decrease in Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer

    NASA Astrophysics Data System (ADS)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Chae, Kyo-Suk; Shim, Tae-Hun; Lian, Guoda; Kim, moon; Park, Jea-Gun

    2015-05-01

    The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer.

  2. 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.

    PubMed

    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

    2013-11-27

    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.

  3. 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.

  4. 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

    SciTech Connect

    Soh, Jing-Han; Tucker, Ggregory S.; Pratt, Daniel K.; Abernathy, D. L.; Stone, M. B.; Ran, Sheng; Budko, Sergey L.; Canfield, Paul C.; Kreyssig, Andreas; McQueeney, Robert J.; Goldman, Alan I.

    2013-11-27

    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.

  5. 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.

  6. 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

  7. Reentrant phase transitions of a coupled spin-electron model on doubly decorated planar lattices with two or three consecutive critical points

    NASA Astrophysics Data System (ADS)

    Čenčariková, Hana; Strečka, Jozef; Lyra, Marcelo L.

    2016-03-01

    The generalized decoration-iteration transformation is adapted for the exact study of a coupled spin-electron model on 2D lattices in which localized Ising spins reside on nodal lattice sites and mobile electrons are delocalized over pairs of decorating sites. The model takes into account a hopping term for mobile electrons, the Ising coupling between mobile electrons and localized spins as well as the Ising coupling between localized spins (J ‧). The ground state, spontaneous magnetization and specific heat are examined for both ferromagnetic (J ‧ > 0) as well as antiferromagnetic (J ‧ < 0) interaction between the localized spins. Several kinds of reentrant transitions between the paramagnetic (P), antiferromagnetic (AF) and ferromagnetic (F) phases have been found either with a single critical point, or with two consecutive critical points (P - AF / F - P) and three successive critical points AF / F - P - F / AF - P. Striking thermal variations of the spontaneous magnetization depict a strong reduction due to the interplay between annealed disorder and quantum fluctuations in addition to the aforementioned reentrance. It is shown that the specific heat displays diverse thermal dependencies including finite cusps at the critical temperatures.

  8. Topological ferrimagnetic behaviours of coordination polymers containing manganese(II) chains with mixed azide and carboxylate bridges and alternating F/AF/AF'/AF'/AF interactions.

    PubMed

    Wang, Yan-Qin; Liu, Hou-Ting; Qi, Yan; Gao, En-Qing

    2014-08-21

    Two Mn(ii) complexes with azide and a new zwitterionic tetracarboxylate ligand 1,2,4,5-tetrakis(4-carboxylatopyridinium-1-methylene)benzene (L(1)), {[Mn5(L(1))2(N3)8(OH)2]·12H2O}n () and {[Mn5(L(1))2(N3)8(H2O)2](ClO4)2·6H2O}n (), have been synthesized and characterized crystallographically and magnetically. and contain similar alternating chains constructed by azide and carboxylate bridges. The independent sets of bridges alternate in an ABCCB sequence between adjacent Mn(ii) ions: (EO-N3)2 double bridges (EO = end-on) (denoted as A), [(EO-N3)(OCO)2] triple bridges (denoted as B) and [(EO-N3)(OCO)] double bridges (denoted as C). The alternating chains are interlinked into 2D coordination networks by the tetrapyridinium spacers. Magnetic studies demonstrate that the magnetic coupling through the double EO azide bridges is ferromagnetic and that through mixed azide/carboxylate bridges is antiferromagnetic. The unprecedented F/AF/AF'/AF'/AF coupling sequence along the chain dictates an uncompensated ground spin state (S = 5/2 per Mn5 unit) and leads to one-dimensional topological ferrimagnetism, which features a minimum in the χT versus T plot.

  9. 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.

  10. 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.

  11. 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.

  12. Y{sub 3}Fe{sub 5}O{sub 12} spin pumping for quantitative understanding of pure spin transport and spin Hall effect in a broad range of materials (invited)

    SciTech Connect

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

    2015-05-07

    Using Y{sub 3}Fe{sub 5}O{sub 12} (YIG) thin films grown by our sputtering technique, we study dynamic spin transport in nonmagnetic, ferromagnetic, and antiferromagnetic (AF) materials by ferromagnetic resonance spin pumping. From both inverse spin Hall effect and damping enhancement, we determine the spin mixing conductance and spin Hall angle in many metals. Surprisingly, we observe robust spin conduction in AF insulators excited by an adjacent YIG at resonance. This demonstrates that YIG spin pumping is a powerful and versatile tool for understanding spin Hall physics, spin-orbit coupling, and magnetization dynamics in a broad range of materials.

  13. 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.

  14. 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.

  15. 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.

  16. Duality, quantum skyrmions, and the stability of a SO(3) two-dimensional quantum spin glass

    NASA Astrophysics Data System (ADS)

    da Conceição, C. M. S.; Marino, E. C.

    2009-08-01

    Quantum topological excitations (skyrmions) are analyzed from the point of view of their duality to spin excitations in the different phases of a disordered two-dimensional, short-range interacting, SO(3) quantum magnetic system of Heisenberg type. The phase diagram displays all the phases, which are allowed by the duality relation. We study the large-distance behavior of the two-point correlation function of quantum skyrmions in each of these phases and, out of this, extract information about the energy spectrum and nontriviality of these excitations. The skyrmion correlators present a power-law decay in the spin-glass (SG) phase, indicating that these quantum topological excitations are gapless but nontrivial in this phase. The SG phase is dual to the AF phase, in the sense that topological and spin excitations are, respectively, gapless in each of them. The Berezinskii-Kosterlitz-Thouless mechanism guarantees the survival of the SG phase at T≠0 , whereas the AF phase is washed out to T=0 by the quantum fluctuations. Our results suggest a more symmetric way of characterizing a SG phase: one for which both the order and disorder parameters vanish, namely, ⟨σ⟩=0 and ⟨μ⟩=0 , where σ is the spin and μ is the topological excitation operators.

  17. 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

  18. 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.

  19. 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).

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

    DOE PAGES

    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

  1. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    PubMed

    Chen, Shao-Wen; Liu, Ren-Bao

    2014-04-15

    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.

  2. Faraday rotation echo spectroscopy and detection of quantum fluctuations.

    PubMed

    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

  3. 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.

  4. Spinor dynamics in an antiferromagnetic spin-1 condensate.

    PubMed

    Black, A T; Gomez, E; Turner, L D; Jung, S; Lett, P D

    2007-08-17

    We observe coherent spin oscillations in an antiferromagnetic spin-1 Bose-Einstein condensate of sodium. The variation of the spin oscillations with magnetic field shows a clear signature of nonlinearity, in agreement with theory, which also predicts anharmonic oscillations near a critical magnetic field. Measurements of the magnetic phase diagram agree with predictions made in the approximation of a single spatial mode. The oscillation period yields the best measurement to date of the sodium spin-dependent interaction coefficient, determining that the difference between the sodium spin-dependent s-wave scattering lengths a(f=2) - a(f=0) is 2.47+/-0.27 Bohr radii.

  5. The AFS Impact Study: Final Report. AFS Research Report 33.

    ERIC Educational Resources Information Center

    Hansel, Bettina

    The AFS Impact Study, initiated in 1977, is an attempt to document changes in learning and personal development associated with an intercultural "homestay" program. Completed in 1985, the study identifies several areas in which students show greater learning and educational growth than that shown by a group of students who had expressed interest…

  6. 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

  7. Spin Transport by Collective Spin Excitations

    NASA Astrophysics Data System (ADS)

    Hammel, P. Chris

    We report studies of angular momentum transport in insulating materials. Our measurements reveal efficient spin pumping from high wavevector k spin waves in thin film Y3Fe5O12 (YIG): spin pumping is independent of wavevector up to k ~ 20 μm-1. Optical detection of YIG FMR by NV centers in diamond reveals a role for spin waves in this insulator-to-insulator spin transfer process. Spin transport is typically suppressed by insulating barriers, but we find that fluctuating antiferromagnetic correlations enable efficient spin transport at nm-scale thicknesses in insulating antiferromagnets, even in the absence of long-range order, and that the spin decay length increases with the strength of the antiferromagnetic correlations. This research is supported by the U.S. DOE through Grants DE-FG02-03ER46054 and DE-SC0001304, by the NSF MRSEC program through Grant No. 1420451 and by the Army Research Office through Grant W911NF0910147.

  8. Topological Effects on Quantum Phase Slips in Superfluid Spin Transport

    NASA Astrophysics Data System (ADS)

    Kim, Se Kwon; Tserkovnyak, Yaroslav

    2016-03-01

    We theoretically investigate effects of quantum fluctuations on superfluid spin transport through easy-plane quantum antiferromagnetic spin chains in the large-spin limit. Quantum fluctuations result in the decaying spin supercurrent by unwinding the magnetic order parameter within the easy plane, which is referred to as phase slips. We show that the topological term in the nonlinear sigma model for the spin chains qualitatively differentiates the decaying rate of the spin supercurrent between the integer versus half-odd-integer spin chains. An experimental setup for a magnetoelectric circuit is proposed, in which the dependence of the decaying rate on constituent spins can be verified by measuring the nonlocal magnetoresistance.

  9. Kagome spin ice

    NASA Astrophysics Data System (ADS)

    Mellado, Paula

    Spin ice in magnetic pyrochlore oxides is a peculiar magnetic state. Like ordinary water ice, these materials are in apparent violation with the third law of thermodynamics, which dictates that the entropy of a system in thermal equilibrium vanishes as its temperature approaches absolute zero. In ice, a "zero-point" entropy is retained down to low temperatures thanks to a high number of low-energy positions of hydrogen ions associated with the Bernal-Fowler ice-rules. Spins in pyrochlore oxides Ho2Ti 2O7 and Dy2Ti2O7 exhibit a similar degeneracy of ground states and thus also have a sizable zero-point entropy. A recent discovery of excitations carrying magnetic charges in pyrochlore spin ice adds another interesting dimension to these magnets. This thesis is devoted to a theoretical study of a two-dimensional version of spin ice whose spins reside on kagome, a lattice of corner-sharing triangles. It covers two aspects of this frustrated classical spin system: the dynamics of artificial spin ice in a network of magnetic nanowires and the thermodynamics of crystalline spin ice. Magnetization dynamics in artificial spin ice is mediated by the emission, propagation and absorption of domain walls in magnetic nanowires. The dynamics shows signs of self-organized behavior such as avalanches. The theoretical model compares favorably to recent experiments. The thermodynamics of the microscopic version of spin ice on kagome is examined through analytical calculations and numerical simulations. The results show that, in addition to the high-temperature paramagnetic phase and the low-temperature phase with magnetic order, spin ice on kagome may have an intermediate phase with fluctuating spins and ordered magnetic charges. This work is concluded with a calculation of the entropy of kagome spin ice at zero temperature when one of the sublattices is pinned by an applied magnetic field and the system breaks up into independent spin chains, a case of dimensional reduction.

  10. Fluctuations in granular media

    NASA Astrophysics Data System (ADS)

    Howell, Daniel W.; Behringer, R. P.; Veje, C. T.

    1999-09-01

    Dense slowly evolving or static granular materials exhibit strong force fluctuations even though the spatial disorder of the grains is relatively weak. Typically, forces are carried preferentially along a network of "force chains." These consist of linearly aligned grains with larger-than-average force. A growing body of work has explored the nature of these fluctuations. We first briefly review recent work concerning stress fluctuations. We then focus on a series of experiments in both two- and three-dimension [(2D) and (3D)] to characterize force fluctuations in slowly sheared systems. Both sets of experiments show strong temporal fluctuations in the local stress/force; the length scales of these fluctuations extend up to 102 grains. In 2D, we use photoelastic disks that permit visualization of the internal force structure. From this we can make comparisons to recent models and calculations that predict the distributions of forces. Typically, these models indicate that the distributions should fall off exponentially at large force. We find in the experiments that the force distributions change systematically as we change the mean packing fraction, γ. For γ's typical of dense packings of nondeformable grains, we see distributions that are consistent with an exponential decrease at large forces. For both lower and higher γ, the observed force distributions appear to differ from this prediction, with a more Gaussian distribution at larger γ and perhaps a power law at lower γ. For high γ, the distributions differ from this prediction because the grains begin to deform, allowing more grains to carry the applied force, and causing the distributions to have a local maximum at nonzero force. It is less clear why the distributions differ from the models at lower γ. An exploration in γ has led to the discovery of an interesting continuous or "critical" transition (the strengthening/softening transition) in which the mean stress is the order parameter, and the mean

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

    PubMed

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

    2016-02-24

    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. 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.

  13. 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.

  14. Exact SU(2) symmetry and persistent spin helix in a spin-orbit coupled system.

    PubMed

    Bernevig, B Andrei; Orenstein, J; Zhang, Shou-Cheng

    2006-12-01

    Spin-orbit coupled systems generally break the spin rotation symmetry. However, for a model with equal Rashba and Dresselhauss coupling constants, 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 wave vector depends on the coupling strength. It renders the spin lifetime infinite at this wave vector, giving rise to a persistent spin helix. We obtain the spin fluctuation dynamics at, and away from, the symmetry point and suggest experiments to observe the persistent spin helix.

  15. Spin foams without spins

    NASA Astrophysics Data System (ADS)

    Hnybida, Jeff

    2016-10-01

    We formulate the spin foam representation of discrete SU(2) gauge theory as a product of vertex amplitudes each of which is the spin network generating function of the boundary graph dual to the vertex. In doing so the sums over spins have been carried out. The boundary data of each n-valent node is explicitly reduced with respect to the local gauge invariance and has a manifest geometrical interpretation as a framed polyhedron of fixed total area. Ultimately, sums over spins are traded for contour integrals over simple poles and recoupling theory is avoided using generating functions.

  16. 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.

  17. 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.

  18. Modeling two-spin dynamics in a noisy environment

    SciTech Connect

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

    2009-10-15

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

  19. 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.

  20. 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.

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

    MedlinePlus

    ... af Soomaali (Somali) Bilingual PDF Health Information Translations Tornadoes Sirens and Telephone Alerts - English Firimbiyada iyo Digniinaha telefonka - af Soomaali (Somali) PDF Healthy Roads Media Tornadoes - English Dabayl xoog badan (Ufo) - af Soomaali (Somali) ...

  2. 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

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

    PubMed Central

    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

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

    DOE PAGES

    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

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    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

    2016-08-01

    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.

  7. 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.

  8. Universal Conductance Fluctuation in Two-Dimensional Topological Insulators

    PubMed Central

    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 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

  9. Giant fluctuations of superconducting order parameter in ferromagnet-superconductor single-electron transistors.

    PubMed

    Johansson, J; Korenivski, V; Haviland, D B; Brataas, Arne

    2004-11-19

    Spin dependent transport in a ferromagnet-superconductor single-electron transistor is studied theoretically taking into account spin accumulation, spin relaxation, gap suppression, and charging effects. A strong dependence of the gap on the magnetic state of the electrodes is found, which gives rise to a magnetoresistance of up to 100%. We predict that fluctuations of the spin accumulation can play such an important role as to cause the island to fluctuate between the superconducting and normal states. Furthermore, the device exhibits a nearly complete gate-controlled spin-valve effect. PMID:15601050

  10. 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

  11. 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

  12. 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.

  13. Entanglement-fluctuation relation for bipartite pure states

    NASA Astrophysics Data System (ADS)

    Villaruel, Aura Mae B.; Paraan, Francis N. C.

    2016-08-01

    We identify subsystem fluctuations (variances) that measure entanglement in an arbitrary bipartite pure state. These fluctuations are of observables that generalize the notion of polarization to an arbitrary N -level subsystem. We express this polarization fluctuation in terms of subsystem purity and other entanglement measures. The derived entanglement-fluctuation relation is evaluated for the ground states of a one-dimensional free-fermion gas and the Affleck-Kennedy-Lieb-Tasaki spin chain. Our results provide a framework for experimentally measuring entanglement using Stern-Gerlach-type state selectors.

  14. 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.

  15. 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.

  16. 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.

  17. Decoupling a hole spin qubit from the nuclear spins

    NASA Astrophysics Data System (ADS)

    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.

  18. Plasma Heating Inside Interplanetary Coronal Mass Ejections by Alfvénic Fluctuations Dissipation

    NASA Astrophysics Data System (ADS)

    Li, Hui; Wang, Chi; He, Jiansen; Zhang, Lingqian; Richardson, John D.; Belcher, John W.; Tu, Cui

    2016-11-01

    Nonlinear cascade of low-frequency Alfvénic fluctuations (AFs) is regarded as one of the candidate energy sources that heat plasma during the non-adiabatic expansion of interplanetary coronal mass ejections (ICMEs). However, AFs inside ICMEs were seldom reported in the literature. In this study, we investigate AFs inside ICMEs using observations from Voyager 2 between 1 and 6 au. It has been found that AFs with a high degree of Alfvénicity frequently occurred inside ICMEs for almost all of the identified ICMEs (30 out of 33 ICMEs) and for 12.6% of the ICME time interval. As ICMEs expand and move outward, the percentage of AF duration decays linearly in general. The occurrence rate of AFs inside ICMEs is much less than that in ambient solar wind, especially within 4.75 au. AFs inside ICMEs are more frequently presented in the center and at the boundaries of ICMEs. In addition, the proton temperature inside ICME has a similar “W”-shaped distribution. These findings suggest significant contribution of AFs on local plasma heating inside ICMEs.

  19. 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.

  20. 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).

  1. 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

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

    DOE PAGES

    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

  3. 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.

  4. Strange fluctuations at RHIC

    NASA Astrophysics Data System (ADS)

    Abdel Aziz, Mohamed; Gavin, Sean

    2004-01-01

    Net charge fluctuations measured by the STAR experiment at RHIC agree with hadronic event generators, suggesting that more sensitive fluctuation observables are needed to extract information on collision dynamics. Important information on isospin fluctuations can be extracted from K0SK± measurements. Gavin and Kapusta proposed that disoriented chiral condensate can produce extraordinary isospin fluctuations in both strange and non-strange mesons. However, even in the absence of such a contribution, we argue that this observable is very sensitive to the collision dynamics.

  5. 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.

  6. Geometric phase of a central spin coupled to an antiferromagnetic environment

    SciTech Connect

    Yuan Xiaozhong; Zhu Kadi; Goan, H.-S.

    2010-03-15

    Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated.

  7. Nuclear spin physics in quantum dots: An optical investigation

    NASA Astrophysics Data System (ADS)

    Urbaszek, Bernhard; Marie, Xavier; Amand, Thierry; Krebs, Olivier; Voisin, Paul; Maletinsky, Patrick; Högele, Alexander; Imamoglu, Atac

    2013-01-01

    The mesoscopic spin system formed by the 104-106 nuclear spins in a semiconductor quantum dot offers a unique setting for the study of many-body spin physics in the condensed matter. The dynamics of this system and its coupling to electron spins is fundamentally different from its bulk counterpart or the case of individual atoms due to increased fluctuations that result from reduced dimensions. In recent years, the interest in studying quantum-dot nuclear spin systems and their coupling to confined electron spins has been further fueled by its importance for possible quantum information processing applications. The fascinating nonlinear (quantum) dynamics of the coupled electron-nuclear spin system is universal in quantum dot optics and transport. In this article, experimental work performed over the last decade in studying this mesoscopic, coupled electron-nuclear spin system is reviewed. Here a special focus is on how optical addressing of electron spins can be exploited to manipulate and read out the quantum-dot nuclei. Particularly exciting recent developments in applying optical techniques to efficiently establish nonzero mean nuclear spin polarizations and using them to reduce intrinsic nuclear spin fluctuations are discussed. Both results critically influence the preservation of electron-spin coherence in quantum dots. This overall recently gained understanding of the quantum-dot nuclear spin system could enable exciting new research avenues such as experimental observations of spontaneous spin ordering or nonclassical behavior of the nuclear spin bath.

  8. 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.

  9. 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...

  10. Locking electron spins into resonance by electron-nuclear feedback

    NASA Astrophysics Data System (ADS)

    Nowack, Katja

    2009-03-01

    All basic building blocks for spin-based quantum information processing using electron spins in GaAs quantum dots have recently been realized. Recent experiments have shown single-shot read-out of an individual spin [1], the implementation of the SWAP gate [2] and (magnetically induced) coherent single electron spin rotations [3]. However, the main drawback of using electron spins in a GaAs environment is the short spin coherence time, which is measured to be in the nanosecond range [2,4]. The source of this fast decoherence is the hyperfine interaction of the localized electron spin with the randomly fluctuating nuclear spins of the host lattice. The fluctuations of the nuclear spins have to be reduced to extend the electron spin coherence time. We therefore study the electron-nuclear spin interaction and use magnetically driven spin resonance to control the electron spin and indirectly manipulate the nuclear spins. We apply continuous microwave excitation to the electron spin and observe strong electron-nuclear feedback. One experimental signature of this feedback is the locking of the electron spin system into resonance with the microwaves. Once the electron spin is locked into resonance, this resonance condition remains fullfilled even when the external magnetic field or the microwave frequency is changed. This is due to dynamically build up nuclear polarizations (up to 500 mT) which generally counteract the external magnetic field. Locking of the electron spin system into resonance might indicate that the nuclear polarization exhibits stable configurations where fluctuations of the nuclear distribution are reduced [5]. [4pt] References [0pt] [1] J. M. Elzerman et al. , Nature 430, 431 (2004) [0pt] [2]. J. R. Petta et al., Science 309, 2180 (2005). [0pt] [3] F. H. L. Koppens et al., Nature 442, 766 (2006). [0pt] [4] F. H. L. Koppens et al., Phys. Rev. Lett. 100, 236802 (2008). [0pt] [5] J. Danon and Yu. V. Nazarov, private communication.

  11. 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

  12. Equalization characteristics of an upflow sludge blanket-aerated biofilter (USB-AF) system.

    PubMed

    Jun, H B; Park, S M; Park, J K; Lee, S H

    2005-01-01

    Equalization characteristics of the upflow sludge blanket-aerated bio-filter (USB-AF) were investigated with the fluctuated raw domestic sewage. Recycle of nitrified effluent from AF to USB triggered the equalization characteristics of the sludge blanket on both soluble and particulate organic matter. Increment of EPS in sludge blanket by nitrate recycle was detected and removal of turbidity and particulates increased at higher recycle ratios by bio-flocculation. Increased TCOD removal in the USB was due to both denitrification of recycled nitrate and entrapment of the particulate organic matter in sludge blanket. Capture of both soluble and particulate organic matter increased sludge blanket layer in the USB, which improved the reactor performances and reduced the organic load on the subsequent AF. Overall TCOD and SS removal efficiencies were about 98% and 96%, respectively in the USB-AF system. Turbidity in the USB effluent was about 44, 20 and 5.5 NTU, at recycle ratios of 0, 100 and 200%, respectively. Particle counts in the range 2-4 microm in the USB effluent were higher than those in influent without nitrate recycle, while particle counts in the range of 0.5-15 microm in the USB effluent decreased 70% at recycle ratio of 200%. The major constituent of EPS extracted from anaerobic sludge was protein and total EPS increased from 109.1 to 165.7 mg/g-VSS with nitrate recycle of 100%. Removal efficiency and concentration of T-N in the UBS-AF effluent was over 70% and below 16 mg/L, respectively.

  13. Helical Spin Order from Topological Dirac and Weyl Semimetals

    SciTech Connect

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

    2015-08-14

    In this paper, 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. Finally, 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.

  14. Spectroscopy of spontaneous spin noise as a probe of spin dynamics and magnetic resonance.

    PubMed

    Crooker, S A; Rickel, D G; Balatsky, A V; Smith, D L

    2004-09-01

    Not all noise in experimental measurements is unwelcome. Certain fundamental noise sources contain valuable information about the system itself-a notable example being the inherent voltage fluctuations (Johnson noise) that exist across any resistor, which allow the temperature to be determined. In magnetic systems, fundamental noise can exist in the form of random spin fluctuations. For example, statistical fluctuations of N paramagnetic spins should generate measurable noise of order N spins, even in zero magnetic field. Here we exploit this effect to perform perturbation-free magnetic resonance. We use off-resonant Faraday rotation to passively detect the magnetization noise in an equilibrium ensemble of paramagnetic alkali atoms; the random fluctuations generate spontaneous spin coherences that precess and decay with the same characteristic energy and timescales as the macroscopic magnetization of an intentionally polarized or driven ensemble. Correlation spectra of the measured spin noise reveal g-factors, nuclear spin, isotope abundance ratios, hyperfine splittings, nuclear moments and spin coherence lifetimes-without having to excite, optically pump or otherwise drive the system away from thermal equilibrium. These noise signatures scale inversely with interaction volume, suggesting a possible route towards non-perturbative, sourceless magnetic resonance of small systems. PMID:15343328

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. 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}.

  2. Liquid-state nuclear spin comagnetometers

    NASA Astrophysics Data System (ADS)

    Ledbetter, Micah; Pustelny, Szymon; Budker, Dmitry; Romalis, Michael; Blanchard, John; Pines, Alexander

    2012-06-01

    We discuss liquid-state nuclear spin comagnetometers based on mixtures of mutually miscible solvents, each rich in a different nuclear spin. In one version thereof, thermally polarized ^1H and ^19F nuclear spins in a mixture of pentane and hexafluorobenzene are monitored in 1 mG fields using alkali-vapor magnetometers. In a second version, ^1H and ^129Xe spins in a mixture of pentane and hyperpolarized liquid xenon are monitored with a superconducting quantum interference device. In the former case, we show that magnetic field fluctuations can be suppressed by a factor of about 3400 and that frequency resolution of about 5x10-11 Hz may be realized in roughly one day of integration. We discuss the application of liquid-state nuclear spin comagnetometers to precision measurements such as a search for spin-gravity coupling or a permanent electric dipole moment, as well as to sensitive gyroscopes.

  3. Detection of atomic spin labels in a lipid bilayer using a single-spin nanodiamond probe

    PubMed Central

    Kaufmann, Stefan; Simpson, David A.; Hall, Liam T.; Perunicic, Viktor; Senn, Philipp; Steinert, Steffen; McGuinness, Liam P.; Johnson, Brett C.; Ohshima, Takeshi; Caruso, Frank; Wrachtrup, Jörg; Scholten, Robert E.; Mulvaney, Paul; Hollenberg, Lloyd

    2013-01-01

    Magnetic field fluctuations arising from fundamental spins are ubiquitous in nanoscale biology, and are a rich source of information about the processes that generate them. However, the ability to detect the few spins involved without averaging over large ensembles has remained elusive. Here, we demonstrate the detection of gadolinium spin labels in an artificial cell membrane under ambient conditions using a single-spin nanodiamond sensor. Changes in the spin relaxation time of the sensor located in the lipid bilayer were optically detected and found to be sensitive to near-individual (4 ± 2) proximal gadolinium atomic labels. The detection of such small numbers of spins in a model biological setting, with projected detection times of 1 s [corresponding to a sensitivity of ∼5 Gd spins per Hz1/2], opens a pathway for in situ nanoscale detection of dynamical processes in biology. PMID:23776230

  4. Dynamics of fluctuations in smectic membranes

    SciTech Connect

    Sikharulidze, Irakli; Jeu, Wim H. de

    2005-07-01

    We present a comprehensive account of the dynamics of layer-displacement fluctuations in smectic liquid-crystal membranes as studied by x-ray photon correlation spectroscopy (XPCS) and neutron-spin echo (NSE). Combining these two techniques at fast relaxation times, three distinct relaxation regimes can be distinguished. For thin membranes, at the specular Bragg position oscillatory relaxation occurs, which transforms for thicker samples into exponential decay. Above a critical off-specular angle, in XPCS exponential relaxation is observed that does not depend on the scattering angle. This indicates relaxation times that are independent of the wavelength of the fluctuations. In this regime the relaxation of the fluctuations is dominated by the surface tension. Using NSE larger off-specular angles can be reached than by XPCS, for which the relaxation time decreases with the scattering angle. This regime is dominated by the bulk elasticity of the smectic membrane. The results are compared with theoretical models for the fluctuation behavior of smectic membranes, in which effects of the mosaic distribution and of the center of mass movement of the smectic membranes must be incorporated.

  5. MLL-AF6 fusion oncogene sequesters AF6 into the nucleus to trigger RAS activation in myeloid leukemia.

    PubMed

    Manara, Elena; Baron, Emma; Tregnago, Claudia; Aveic, Sanja; Bisio, Valeria; Bresolin, Silvia; Masetti, Riccardo; Locatelli, Franco; Basso, Giuseppe; Pigazzi, Martina

    2014-07-10

    A rare location, t(6;11)(q27;q23) (MLL-AF6), is associated with poor outcome in childhood acute myeloid leukemia (AML). The described mechanism by which MLL-AF6, through constitutive self-association and in cooperation with DOT-1L, activates aberrant gene expression does not explain the biological differences existing between t(6;11)-rearranged and other MLL-positive patients nor their different clinical outcome. Here, we show that AF6 is expressed in the cytoplasm of healthy bone marrow cells and controls rat sarcoma viral oncogene (RAS)-guanosine triphosphate (GTP) levels. By contrast, in MLL-AF6-rearranged cells, AF6 is found localized in the nucleus, leading to aberrant activation of RAS and of its downstream targets. Silencing MLL-AF6, we restored AF6 localization in the cytoplasm, thus mediating significant reduction of RAS-GTP levels and of cell clonogenic potential. The rescue of RAS-GTP levels after MLL-AF6 and AF6 co-silencing confirmed that MLL-AF6 oncoprotein potentiates the activity of the RAS pathway through retention of AF6 within the nucleus. Exposure of MLL-AF6-rearranged AML blasts to tipifarnib, a RAS inhibitor, leads to cell autophagy and apoptosis, thus supporting RAS targeting as a novel potential therapeutic strategy in patients carrying t(6;11). Altogether, these data point to a novel role of the MLL-AF6 chimera and show that its gene partner, AF6, is crucial in AML development.

  6. AfsR recruits RNA polymerase to the afsS promoter: a model for transcriptional activation by SARPs.

    PubMed

    Tanaka, Akiko; Takano, Yuji; Ohnishi, Yasuo; Horinouchi, Sueharu

    2007-06-01

    AfsR, a protein belonging to the Streptomyces antibiotic regulatory protein (SARP) family, is a global regulator of secondary metabolism in Streptomyces coelicolor A3(2). AfsR consists of three major functional domains: an N-terminal SARP domain, a central ATPase domain, and a C-terminal tetratrico peptide repeat (TPR) domain. Two truncated AfsR proteins, AfsRDeltaTPR containing the SARP and ATPase domains and AfsRDeltaC containing only the SARP domain, exhibited the same DNA-binding specificity as that of full-length AfsR. Two monomers bound cooperatively to a direct repeat located eight nucleotides 5' to the -10 element of the afsS promoter. Both truncated AfsR proteins, as well as full-length AfsR, were able to form ternary complexes with the afsS promoter and RNA polymerase (RNAP), although RNAP alone could not bind to the DNA. The DNA-(AfsRDeltaC)(2)-RNAP complex was capable of initiating afsS transcription in vitro, indicating that the ATPase and TPR domains are dispensable for the basic function of AfsR as a transcriptional activator. However, the ATPase domain was required to fully compensate for the defect in actinorhodin production in an afsR-disrupted mutant, suggesting that the ATPase domain exerts a regulatory function on the basic SARP domain. Deletion or addition of even a single nucleotide between the AfsR-binding site and the -10 element of the afsS promoter abolished afsS transcription both in vitro and in vivo, indicating that the recruitment of RNAP by AfsR to the correct location relative to the -10 element is critical for transcriptional activation. Since SARP-binding sites with similar direct repeats are located at the same position relative to the -10 element of their target promoters as is the afsS binding site, the SARP family members presumably activate transcription of their targets by recruiting RNAP to the promoter, where a ternary DNA-SARP-RNAP complex competent for transcriptional initiation is formed.

  7. 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

  8. Stabilization of Long-Range Order by Additional Anisotropic Spins in Two-Dimensional Isotropic Heisenberg Antiferromagnets —A Possible Model of an Organic Compound with Magnetic Anions—

    NASA Astrophysics Data System (ADS)

    Shimahara, Hiroshi; Ito, Kazuhiro

    2014-11-01

    We examine a two-dimensional (2D) coupled antiferromagnetic (AF) Heisenberg model that consists of two subsystems: an isotropic S = 1/2 spin subsystem with strong AF exchange interactions (main system), and a uniaxial S = 5/2 spin subsystem with weak exchange interactions. This model is an example in which additional semiclassical degrees of freedom affect a quantum system; it also describes a possible stabilization mechanism of AF long-range order (LRO) in the 2D organic compound λ-(BETS)2FeCl4, where BETS stands for bis(ethylenedithio)tetraselenafulvalene. Previous experimental studies have revealed that 3d spins on FeCl4 anions passively follow the AF LRO of the π-electron system in the BETS layers, although the AF LRO is stabilized by the 3d spins themselves. To explain this paradoxical behavior, we examine a scenario in which the uniaxial anisotropy of the 3d spins stabilizes the AF LRO on an isotropic 2D π-spin system. We extend Green's function theory, called the Tyablikov approximation, to the present system, which describes spin-wave excitations and is consistent with the Mermin-Wagner theorem. It is shown that even extremely weak interactions with the uniaxial subsystem efficiently stabilize the AF LRO in the main system, even in the absence of AF exchange interactions in the uniaxial subsystem. The AF LRO is triggered by the uniaxial subsystem, but the sublattice magnetization remains smaller than that of the main system in the high-temperature region. These results are consistent with experimental data for λ-(BETS)2FeCl4 and λ-(BETS)2GaCl4; the latter does not have the 3d spins and does not exhibit the AF LRO.

  9. Muon Spin Rotation/Relaxation Study of Ba2CoO4

    SciTech Connect

    Russo, P. L.; Sugiyama, J.; Brewer, J.; Ansaldo, E. J.; Stubbs, S. L.; Chow, K. H.; Jin, Rongying; Sha, Hao; Zhang, Jiandi

    2009-01-01

    A positive muon spin rotation and relaxation ({mu}{sup +}SR) experiment on a single crystal of Ba{sub 2}CoO{sub 4} indicates the existence of an antiferromagnetic (AF) transition occurring at T{sub N} {approx} 24 K. Weak transverse field measurements show that the paramagnetic volume fraction of the sample decreases rapidly at the magnetic transition, indicating a bulk effect which cannot be due to the presence of impurities. Zero-field measurements reveal the presence of a magnetically ordered state below T{sub N} with at least three crystallographically inequivalent muon sites. The results are compared to recent magnetic susceptibility and neutron measurements. Of the two AF spin structures proposed to explain recent neutron experiments, the {mu}{sup +}SR results clearly exclude the one involving AF order along the c axis while supporting that with AF order in the ab plane.

  10. Fluctuations of the Free Energy of the Spherical Sherrington-Kirkpatrick Model

    NASA Astrophysics Data System (ADS)

    Baik, Jinho; Lee, Ji Oon

    2016-09-01

    We consider the fluctuations of the free energy for the 2-spin spherical Sherrington-Kirkpatrick model with no magnetic field. We show that the law of the fluctuations converges to the Gaussian distribution when the temperature is above the critical temperature, and to the GOE Tracy-Widom distribution when the temperature is below the critical temperature. The orders of the fluctuations are markedly different in these two regimes. A universality of the limit law is also proved.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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…

  16. 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.

  17. Spin dynamics in a Curie-switch.

    PubMed

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

    2015-11-11

    Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2-magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affect the resonance fields of both F1 and F2 layers. Our theoretical calculations as well as measurements show that the key magnetic parameters of the spacer, which govern the ferromagnetic resonance in F1/f/F2/AF, are the magnetic exchange length (Λ), effective saturation magnetization at T  =  0 (m0) and effective Curie temperature (T(C)(eff)). The values of these key parameters are deduced from the experimental data for multilayers with f  =  Ni(x)Cu(100-x), for the key ranges in the Ni-concentration (x = 54 ÷ 70 at. %) and spacer thickness (d = 3 ÷ 6 nm). The results obtained provide a deeper insight into thermally-controlled spin precession and switching in magnetic nanostructures, with potential applications in spin-based oscillators and memory devices.

  18. [Progress in Teflon AF LWCC/LCW applications].

    PubMed

    Sun, Zhao-Hua; Zhou, Wen; Xu, Zhan-Tang; Ye, Hai-Bin; Yang, Chao-Yu; Lin, Jun-Fang; Hu, Shui-Bo; Yang, Yue-Zhong; Li, Cai; Cao, Wen-Xi

    2011-11-01

    Teflon AF is chemically very inert, quite physically and optically stable, a highly vapor-permeable polymer with optical transparency through much of the UV-Vis region and with an RI lower than that of water, so Teflon AF LWCC/LCW (Long path-length liquid waveguide capillary cell/liquid core waveguides) has been used with a range of different detection techniques, including absorbance spectroscopy, fluorescence spectroscopy, Raman spectroscopy, and gas sensor. The present article describes the properties and the aspects of Teflon AF LWCC/LCW instrumentation and applications. And finally,the future prospect and outlook of Teflon AF LWCC/LCW is also discussed.

  19. 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

  20. 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.

  1. Antiferromagnetic spin excitations in single crystals of nonsuperconducting Li$_{1-x}$FeAs

    SciTech Connect

    Wang, Meng; Wang, X.C.; Harriger, Leland W; Luo, H.Q.; Zhao, Yang; Lynn, J. W.; Liu, Q.Q.; Jin, C.Q.; Fang, Chen; Hu, Jiangping; Dai, Pengcheng

    2011-01-01

    We use neutron scattering to determine spin excitations in single crystals of nonsuperconducting Li1 xFeAs throughout the Brillouin zone. Although angle resolved photoemission experiments and local density approximation calculations suggest poor Fermi surface nesting conditions for antiferromagnetic (AF) order, spin excitations in Li1 xFeAs occur at the AF wave vectors Q = (1,0) at low energies, but move to wave vectors Q = ( 0.5, 0.5) near the zone boundary with a total magnetic bandwidth comparable to that of BaFe2As2. These results reveal that AF spin excitations still dominate the low-energy physics of these materials and suggest both itinerancy and strong electron-electron correlations are essential to understand the measured magnetic excitations.

  2. Stable mean-field solution of a short-range interacting SO(3) quantum Heisenberg spin glass.

    PubMed

    da Conceição, C M S; Marino, E C

    2008-07-18

    We present a mean-field solution for a quantum, short-range interacting, disordered, SO(3) Heisenberg spin model, in which the Gaussian distribution of couplings is centered in an antiferromagnetic (AF) coupling J[over ]>0, and which, for weak disorder, can be treated as a perturbation of the pure AF Heisenberg system. The phase diagram contains, apart from a Néel phase at T=0, spin-glass and paramagnetic phases whose thermodynamic stability is demonstrated by an analysis of the Hessian matrix of the free-energy. The magnetic susceptibilities exhibit the typical cusp of a spin-glass transition.

  3. Quantum tricritical fluctuations driving mass enhancement and reentrant superconductivity in URhGe

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Hattori, T.; Araki, S.

    2016-02-01

    The field-induced reentrant superconductivity (RSC) discovered near a quantum critical point (QCP) in a ferromagnetic superconductor URhGe highlights the close interplay between superconductivity and magnetism. While the origin of the RSC is broadly thought to be associated with quantum critical fluctuations, their exact nature had not been well identified. Here we review our recent 59Co NMR study in a single crystal of URh0.9Co0.1Ge. Our measurements of the NMR spin-spin relaxation reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced QCP at HR ≈ 13 T. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum wing-critical points. We show that these tricritical fluctuations enhance the effective mass of the conduction electrons and, further, drive the RSC near the HR.

  4. 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.

  5. Hole pairing from attraction of opposite-chirality spin vortices: Non-BCS superconductivity in underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Marchetti, P. A.; Ye, F.; Su, Z. B.; Yu, L.

    2011-12-01

    Within a gauge approach to the t-J model, we propose a non-BCS mechanism of superconductivity (SC) for underdoped cuprates. We implement the no-double-occupancy constraint with a (semionic) slave-particle formalism. The dopant in the t-J model description generates a vortexlike quantum distortion of the antiferromagnetic (AF) background centered on the empty sites, with opposite chirality for cores on the two Néel sublattices. Empty sites are described in terms of spinless fermionic holons and the long-range attraction between spin vortices on two opposite Néel sublattices serves as the holon pairing force, leading eventually to SC. The spin fluctuations are described by bosonic spinons with a gap generated by scattering on spin vortices. Due to the no-double occupation constraint, there is a gauge attraction between holon and spinon, binding them into a physical hole. Through gauge interaction the spin-vortex attraction induces the formation of spin-singlet [resonance valence bond (RVB)] spin pairs by lowering the spinon gap, due to the appearance of spin-vortex dipoles. Lowering the temperature, the proposed approach anticipates two crossover temperatures as precursors of the SC transition: at the higher crossover a finite density of incoherent holon pairs are formed, leading to reduction of the hole spectral weight, while at the lower crossover a finite density of incoherent spinon RVB pairs is also formed, giving rise to a gas of incoherent preformed hole pairs with magnetic vortices appearing in the plasma phase, supporting a Nernst signal. Finally, at an even lower temperature the hole pairs become coherent, the magnetic vortices become dilute, and SC appears beyond a critical doping. The proposed SC mechanism is not of the BCS type, because it involves a gain in kinetic energy, due to the lowering of the spinon gap, and it is “almost” of the classical three-dimensional XY type. Since both the spinon gap describing short-range antiferromagnetism order

  6. 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

  7. Extrinsic spin Hall effect induced by resonant skew scattering in graphene.

    PubMed

    Ferreira, Aires; Rappoport, Tatiana G; Cazalilla, Miguel A; Castro Neto, A H

    2014-02-14

    We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging.

  8. Extrinsic Spin Hall Effect Induced by Resonant Skew Scattering in Graphene

    NASA Astrophysics Data System (ADS)

    Ferreira, Aires; Rappoport, Tatiana G.; Cazalilla, Miguel A.; Castro Neto, A. H.

    2014-02-01

    We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging.

  9. AF-MSCs fate can be regulated by culture conditions

    PubMed Central

    Zagoura, D S; Trohatou, O; Bitsika, V; Makridakis, M; Pappa, K I; Vlahou, A; Roubelakis, M G; Anagnou, N P

    2013-01-01

    Human mesenchymal stem cells (hMSCs) represent a population of multipotent adherent cells able to differentiate into many lineages. In our previous studies, we isolated and expanded fetal MSCs from second-trimester amniotic fluid (AF) and characterized them based on their phenotype, pluripotency and proteomic profile. In the present study, we investigated the plasticity of these cells based on their differentiation, dedifferentiation and transdifferentiation potential in vitro. To this end, adipocyte-like cells (AL cells) derived from AF-MSCs can regain, under certain culture conditions, a more primitive phenotype through the process of dedifferentiation. Dedifferentiated AL cells derived from AF-MSCs (DAF-MSCs), gradually lost the expression of adipogenic markers and obtained similar morphology and differentiation potential to AF-MSCs, together with regaining the pluripotency marker expression. Moreover, a comparative proteomic analysis of AF-MSCs, AL cells and DAF-MSCs revealed 31 differentially expressed proteins among the three cell populations. Proteins, such as vimentin, galectin-1 and prohibitin that have a significant role in stem cell regulatory mechanisms, were expressed in higher levels in AF-MSCs and DAF-MSCs compared with AL cells. We next investigated whether AL cells could transdifferentiate into hepatocyte-like cells (HL cells) directly or through a dedifferentiation step. AL cells were cultured in hepatogenic medium and 4 days later they obtained a phenotype similar to AF-MSCs, and were termed as transdifferentiated AF-MSCs (TRAF-MSCs). This finding, together with the increase in pluripotency marker expression, indicated the adaption of a more primitive phenotype before transdifferentiation. Additionally, we observed that AF-, DAF- and TRAF-MSCs displayed similar clonogenic potential, secretome and proteome profile. Considering the easy access to this fetal cell source, the plasticity of AF-MSCs and their potential to dedifferentiate and

  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. 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.

  12. 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.

  13. 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.

  14. Physics of fashion fluctuations

    NASA Astrophysics Data System (ADS)

    Donangelo, R.; Hansen, A.; Sneppen, K.; Souza, S. R.

    2000-12-01

    We consider a market where many agents trade different types of products with each other. We model development of collective modes in this market, and quantify these by fluctuations that scale with time with a Hurst exponent of about 0.7. We demonstrate that individual products in the model occasionally become globally accepted means of exchange, and simultaneously become very actively traded. Thus collective features similar to money spontaneously emerge, without any a priori reason.

  15. 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.

  16. 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...

  17. 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...

  18. 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...

  19. 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...

  20. 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...

  1. 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.

  2. Embedding Assessment for Learning (AfL) into Science

    ERIC Educational Resources Information Center

    Crossland, John

    2012-01-01

    Although the National Strategies for improving English schools no longer exist, the "Pedagogy and Practice" pack provides a valuable resource for producing an Assessment for Learning (AfL) framework that describes a hierarchy of skills for AfL. Based on the hierarchy, training took place in three North Yorkshire schools. To focus attention on the…

  3. DDX6 transfers P-TEFb kinase to the AF4/AF4N (AFF1) super elongation complex

    PubMed Central

    Mück, Fabian; Bracharz, Silvia; Marschalek, Rolf

    2016-01-01

    AF4/AFF1 and AF5/AFF4 are both backbones for the assembly of “super elongation complexes” (SECs) that exert 2 distinct functions after the recruitment of P-TEFb from the 7SK snRNP: (1) initiation and elongation of RNA polymerase II gene transcription, and (2) modification of transcribed gene regions by distinct histone methylation patterns. In this study we aimed to investigate one of the initial steps, namely how P-TEFb is transferred from 7SK snRNPs to the SECs. In particular, we were interested in the role of DDX6 that we have recently identified as part of the AF4 complex. DDX6 is an evolutionarily conserved member of the DEAD-box RNA helicase family that is known to control miRNA and mRNA biology (translation, storage and degradation). Overexpressed DDX6 is associated with different cancer types and with c-Myc protein overexpression. We could demonstrate that DDX6 binds to 7SK snRNA and causes the release and transfer of P-TEFb to the AF4/AF4N SEC. DDX6 also binds stably to AF4 and AF4N as demonstrated by GST pull-down and co-immunoprecipitation experiments. As a consequence, overexpression of either AF4/AF4N or DDX6 resulted in a strong increase of mRNA production (5-6 fold), while their simultaneous expression increased the cellular mRNA production by 11-fold. Conversely, the corresponding knockdown of DDX6 decreased mRNA production by 70%. In conclusion, AF4/AF4N and DDX6 represent key molecules for the elongation process of gene transcription and a model will be proposed for the hand-over process of P-TEFb to SECs. PMID:27679741

  4. DDX6 transfers P-TEFb kinase to the AF4/AF4N (AFF1) super elongation complex.

    PubMed

    Mück, Fabian; Bracharz, Silvia; Marschalek, Rolf

    2016-01-01

    AF4/AFF1 and AF5/AFF4 are both backbones for the assembly of "super elongation complexes" (SECs) that exert 2 distinct functions after the recruitment of P-TEFb from the 7SK snRNP: (1) initiation and elongation of RNA polymerase II gene transcription, and (2) modification of transcribed gene regions by distinct histone methylation patterns. In this study we aimed to investigate one of the initial steps, namely how P-TEFb is transferred from 7SK snRNPs to the SECs. In particular, we were interested in the role of DDX6 that we have recently identified as part of the AF4 complex. DDX6 is an evolutionarily conserved member of the DEAD-box RNA helicase family that is known to control miRNA and mRNA biology (translation, storage and degradation). Overexpressed DDX6 is associated with different cancer types and with c-Myc protein overexpression. We could demonstrate that DDX6 binds to 7SK snRNA and causes the release and transfer of P-TEFb to the AF4/AF4N SEC. DDX6 also binds stably to AF4 and AF4N as demonstrated by GST pull-down and co-immunoprecipitation experiments. As a consequence, overexpression of either AF4/AF4N or DDX6 resulted in a strong increase of mRNA production (5-6 fold), while their simultaneous expression increased the cellular mRNA production by 11-fold. Conversely, the corresponding knockdown of DDX6 decreased mRNA production by 70%. In conclusion, AF4/AF4N and DDX6 represent key molecules for the elongation process of gene transcription and a model will be proposed for the hand-over process of P-TEFb to SECs. PMID:27679741

  5. DDX6 transfers P-TEFb kinase to the AF4/AF4N (AFF1) super elongation complex

    PubMed Central

    Mück, Fabian; Bracharz, Silvia; Marschalek, Rolf

    2016-01-01

    AF4/AFF1 and AF5/AFF4 are both backbones for the assembly of “super elongation complexes” (SECs) that exert 2 distinct functions after the recruitment of P-TEFb from the 7SK snRNP: (1) initiation and elongation of RNA polymerase II gene transcription, and (2) modification of transcribed gene regions by distinct histone methylation patterns. In this study we aimed to investigate one of the initial steps, namely how P-TEFb is transferred from 7SK snRNPs to the SECs. In particular, we were interested in the role of DDX6 that we have recently identified as part of the AF4 complex. DDX6 is an evolutionarily conserved member of the DEAD-box RNA helicase family that is known to control miRNA and mRNA biology (translation, storage and degradation). Overexpressed DDX6 is associated with different cancer types and with c-Myc protein overexpression. We could demonstrate that DDX6 binds to 7SK snRNA and causes the release and transfer of P-TEFb to the AF4/AF4N SEC. DDX6 also binds stably to AF4 and AF4N as demonstrated by GST pull-down and co-immunoprecipitation experiments. As a consequence, overexpression of either AF4/AF4N or DDX6 resulted in a strong increase of mRNA production (5-6 fold), while their simultaneous expression increased the cellular mRNA production by 11-fold. Conversely, the corresponding knockdown of DDX6 decreased mRNA production by 70%. In conclusion, AF4/AF4N and DDX6 represent key molecules for the elongation process of gene transcription and a model will be proposed for the hand-over process of P-TEFb to SECs.

  6. 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.

  7. Tensor Renormalization Group Study of the General Spin-S Blume-Capel Model

    NASA Astrophysics Data System (ADS)

    Yang, Li-Ping; Xie, Zhi-Yuan

    2016-10-01

    We focus on the special situation of D = 2J in the general spin-S Blume-Capel model on a square lattice. Under an infinitesimal external magnetic field, the phase transition behaviors due to the thermal fluctuations are investigated by the newly developed tensor renormalization group method. We clearly demonstrate the phase transition process: in the case of an integer spin-S, there are S first-order phase transitions with the stepwise magnetizations M = S,S - 1, ldots ,0; in the case of a half-odd integer spin-S, there are S - 1/2 first-order phase transitions with corresponding M = S,S - 1, ldots ,1/2 in addition to one continuous phase transition due to spin-flip Z2 symmetry breaking. At low temperatures, all first-order phase transitions are accompanied by the successive disappearance of the spin-component pairs (±s); furthermore, the transition temperature for the nth first-order phase transition is the same, independent of the value of the spin-S. In the absence of a magnetic field, a visualization parameter characterizing the intrinsic degeneracy of the different phases provides a different reference for the phase transition process.

  8. Fluctuations in Schottky barrier heights

    NASA Astrophysics Data System (ADS)

    Mahan, G. D.

    1984-02-01

    A double Schottky barrier is often formed at the grain boundary in polycrystalline semiconductors. The barrier height is shown to fluctuate in value due to the random nature of the impurity positions. The magnitude of the fluctuations is 0.1 eV, and the fluctuations cause the barrier height measured by capacitance to differ from the one measured by electrical conductivity.

  9. 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.

  10. 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.

  11. 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.

  12. 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

  13. Optical nuclear spin polarization in quantum dots

    NASA Astrophysics Data System (ADS)

    Li, Ai-Xian; Duan, Su-Qing; Zhang, Wei

    2016-10-01

    Hyperfine interaction between electron spin and randomly oriented nuclear spins is a key issue of electron coherence for quantum information/computation. We propose an efficient way to establish high polarization of nuclear spins and reduce the intrinsic nuclear spin fluctuations. Here, we polarize the nuclear spins in semiconductor quantum dot (QD) by the coherent population trapping (CPT) and the electric dipole spin resonance (EDSR) induced by optical fields and ac electric fields. By tuning the optical fields, we can obtain a powerful cooling background based on CPT for nuclear spin polarization. The EDSR can enhance the spin flip-flop rate which may increase the cooling efficiency. With the help of CPT and EDSR, an enhancement of 1300 times of the electron coherence time can be obtained after a 10-ns preparation time. Project partially supported by the National Natural Science Foundations of China (Grant Nos. 11374039 and 11174042) and the National Basic Research Program of China (Grant Nos. 2011CB922204 and 2013CB632805).

  14. 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.

  15. 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.

  16. Fluctuating nematic elastomer membranes.

    PubMed

    Xing, Xiangjun; Mukhopadhyay, Ranjan; Lubensky, T C; Radzihovsky, Leo

    2003-08-01

    We study the flat phase of nematic elastomer membranes with rotational symmetry spontaneously broken by an in-plane nematic order. Such a state is characterized by a vanishing elastic modulus for simple shear and soft transverse phonons. At harmonic level, the in-plane orientational (nematic) order is stable to thermal fluctuations that lead to short-range in-plane translational (phonon) correlations. To treat thermal fluctuations and relevant elastic nonlinearities, we introduce two generalizations of two-dimensional membranes in a three-dimensional space to arbitrary D-dimensional membranes embedded in a d-dimensional space and analyze their anomalous elasticities in an expansion about D=4. We find a stable fixed point that controls long-scale properties of nematic elastomer membranes. It is characterized by singular in-plane elastic moduli that vanish as a power law eta(lambda)=4-D of a relevant inverse length scale (e.g., wave vector) and a finite bending rigidity. Our predictions are asymptotically exact near four dimensions. PMID:14524954

  17. Fluctuating nematic elastomer membranes

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun; Mukhopadhyay, Ranjan; Lubensky, T. C.; Radzihovsky, Leo

    2003-08-01

    We study the flat phase of nematic elastomer membranes with rotational symmetry spontaneously broken by an in-plane nematic order. Such a state is characterized by a vanishing elastic modulus for simple shear and soft transverse phonons. At harmonic level, the in-plane orientational (nematic) order is stable to thermal fluctuations that lead to short-range in-plane translational (phonon) correlations. To treat thermal fluctuations and relevant elastic nonlinearities, we introduce two generalizations of two-dimensional membranes in a three-dimensional space to arbitrary D-dimensional membranes embedded in a d-dimensional space and analyze their anomalous elasticities in an expansion about D=4. We find a stable fixed point that controls long-scale properties of nematic elastomer membranes. It is characterized by singular in-plane elastic moduli that vanish as a power law ηλ=4-D of a relevant inverse length scale (e.g., wave vector) and a finite bending rigidity. Our predictions are asymptotically exact near four dimensions.

  18. 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.

  19. Spin frustration and fermionic entanglement in an exactly solved hybrid diamond chain with localized Ising spins and mobile electrons

    NASA Astrophysics Data System (ADS)

    Torrico, J.; Rojas, M.; Pereira, M. S. S.; Strečka, J.; Lyra, M. L.

    2016-01-01

    The strongly correlated spin-electron system on a diamond chain containing localized Ising spins on its nodal lattice sites and mobile electrons on its interstitial sites is exactly solved in a magnetic field using the transfer-matrix method. We have investigated in detail all available ground states, the magnetization processes, the spin-spin correlation functions around an elementary plaquette, fermionic quantum concurrence, and spin frustration. It is shown that the fermionic entanglement between mobile electrons hopping on interstitial sites and the kinetically induced spin frustration are closely related yet independent phenomena. In the ground state, quantum entanglement only appears within a frustrated unsaturated paramagnetic phase, while thermal fluctuations can promote some degree of quantum entanglement above the nonfrustrated ground states with saturated paramagnetic or classical ferrimagnetic spin arrangements.

  20. 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.

  1. 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.

  2. Liquid-State Nuclear Spin Comagnetometers

    NASA Astrophysics Data System (ADS)

    Ledbetter, M. P.; Pustelny, S.; Budker, D.; Romalis, M. V.; Blanchard, J. W.; Pines, A.

    2012-06-01

    We discuss nuclear spin comagnetometers based on ultralow-field nuclear magnetic resonance in mixtures of miscible solvents, each rich in a different nuclear spin. In one version thereof, Larmor precession of protons and F19 nuclei in a mixture of thermally polarized pentane and hexafluorobenzene is monitored via a sensitive alkali-vapor magnetometer. We realize transverse relaxation times in excess of 20 s and suppression of magnetic field fluctuations by a factor of 3400. We estimate it should be possible to achieve single-shot sensitivity of about 5×10-9Hz, or about 5×10-11Hz in ≈1 day of integration. In a second version, spin precession of protons and Xe129 nuclei in a mixture of pentane and hyperpolarized liquid xenon is monitored using superconducting quantum interference devices. Application to spin-gravity experiments, electric dipole moment experiments, and sensitive gyroscopes is discussed.

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

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

    PubMed

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

    2014-09-26

    Using fast electron spin resonance spectroscopy of a single nitrogen-vacancy defect in diamond, we demonstrate real-time readout of the Overhauser field produced by its nuclear spin environment under ambient conditions. These measurements enable narrowing the Overhauser field distribution by postselection, corresponding to a conditional preparation of the nuclear spin bath. Correlations of the Overhauser field fluctuations are quantitatively inferred by analyzing the Allan deviation over consecutive measurements. This method allows us to extract the dynamics of weakly coupled nuclear spins of the reservoir.

  9. Probing the Dynamics of a Nuclear Spin Bath in Diamond through Time-Resolved Central Spin Magnetometry

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    Using fast electron spin resonance spectroscopy of a single nitrogen-vacancy defect in diamond, we demonstrate real-time readout of the Overhauser field produced by its nuclear spin environment under ambient conditions. These measurements enable narrowing the Overhauser field distribution by postselection, corresponding to a conditional preparation of the nuclear spin bath. Correlations of the Overhauser field fluctuations are quantitatively inferred by analyzing the Allan deviation over consecutive measurements. This method allows us to extract the dynamics of weakly coupled nuclear spins of the reservoir.

  10. spin pumping occurred under nonlinear spin precession

    NASA Astrophysics Data System (ADS)

    Zhou, Hengan; Fan, Xiaolong; Ma, Li; Zhou, Shiming; Xue, Desheng

    Spin pumping occurs when a pure-spin current is injected into a normal metal thin layer by an adjacent ferromagnetic metal layer undergoing ferromagnetic resonance, which can be understood as the inverse effect of spin torque, and gives access to the physics of magnetization dynamics and damping. An interesting question is that whether spin pumping occurring under nonlinear spin dynamics would differ from linear case. It is known that nonlinear spin dynamics differ distinctly from linear response, a variety of amplitude dependent nonlinear effect would present. It has been found that for spin precession angle above a few degrees, nonlinear damping term would present and dominated the dynamic energy/spin-moment dissipation. Since spin pumping are closely related to the damping process, it is interesting to ask whether the nonlinear damping term could be involved in spin pumping process. We studied the spin pumping effect occurring under nonlinear spin precession. A device which is a Pt/YIG microstrip coupled with coplanar waveguide was used. High power excitation resulted in spin precession entering in a nonlinear regime. Foldover resonance lineshape and nonlinear damping have been observed. Based on those nonlinear effects, we determined the values of the precession cone angles, and the maximum cone angle can reach a values as high as 21.5 degrees. We found that even in nonlinear regime, spin pumping is still linear, which means the nonlinear damping and foldover would not affect spin pumping process.

  11. 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.

  12. 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

  13. Effect of superconducting fluctuations on the NMR relaxation rate of high-Tc superconductors

    SciTech Connect

    Appel, J. ); Fay, D.; Kautz, C. )

    1994-06-01

    The effect of superconducting order parameter fluctuations on the nuclear-spin relaxation rate, 1/T[sub 1], is studied for clean two-dimensional systems by calculating the three Maki-Thomson-type diagrams which represent the lowest-order fluctuation contributions to the transverse susceptibility. For Gaussian fluctuations and for temperatures near the mean field transition temperature, T[sub c0], we employ a weak-coupling theory in which the pair-fluctuation propagator can also include pair-breaking effects. We also go beyond the Gaussian theory and take into account the interactions between Cooper-pair fluctuations corresponding to the fourth-order Ginzburg Landau fluctuation terms. We compare our results with previous results in the dirty limit and in 3D. We obtain a pronounced peak in 1/T[sub 1] at Tc and briefly discuss possible reasons why this peak is not observed. 6 refs., 4 figs., 1 tab.

  14. Fluctuating multicomponent lattice Boltzmann model

    NASA Astrophysics Data System (ADS)

    Belardinelli, D.; Sbragaglia, M.; Biferale, L.; Gross, M.; Varnik, F.

    2015-02-01

    Current implementations of fluctuating lattice Boltzmann equations (FLBEs) describe single component fluids. In this paper, a model based on the continuum kinetic Boltzmann equation for describing multicomponent fluids is extended to incorporate the effects of thermal fluctuations. The thus obtained fluctuating Boltzmann equation is first linearized to apply the theory of linear fluctuations, and expressions for the noise covariances are determined by invoking the fluctuation-dissipation theorem directly at the kinetic level. Crucial for our analysis is the projection of the Boltzmann equation onto the orthonormal Hermite basis. By integrating in space and time the fluctuating Boltzmann equation with a discrete number of velocities, the FLBE is obtained for both ideal and nonideal multicomponent fluids. Numerical simulations are specialized to the case where mean-field interactions are introduced on the lattice, indicating a proper thermalization of the system.

  15. 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.

  16. 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

  17. 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

  18. 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.

  19. 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

  20. Collective effects in spin polarized plasmas

    SciTech Connect

    Coppi, B.; Cowley, S.; Detragiache, P.; Kulsrud, R.; Pegoraro, F.

    1984-10-01

    A fusing plasma with coherently polarized spin nuclei can be subject to instabilities due to the anisotropy of the reaction product distributions in velocity space, which is a result of their polarization. The characteristics of these instabilities depend strongly on the plasma spatial inhomogeneities and a significant rate of spin depolarization can be produced by them if adequate fluctuation amplitudes are reached. The results of the relevant analysis are, in addition, of interest for plasma heating processes with frequencies in the range of the cyclotron frequencies of the considered nuclei.

  1. Fluctuating hyperfine interactions: an updated computational implementation

    NASA Astrophysics Data System (ADS)

    Zacate, M. O.; Evenson, W. E.

    2015-04-01

    The stochastic hyperfine interactions modeling library (SHIML) is a set of routines written in the C programming language designed to assist in the analysis of stochastic models of hyperfine interactions. The routines read a text-file description of the model, set up the Blume matrix, upon which the evolution operator of the quantum mechanical system depends, and calculate the eigenvalues and eigenvectors of the Blume matrix, from which theoretical spectra of experimental techniques can be calculated. The original version of SHIML constructs Blume matrices applicable for methods that measure hyperfine interactions with only a single nuclear spin state. In this paper, we report an extension of the library to provide support for methods such as Mössbauer spectroscopy and nuclear resonant scattering of synchrotron radiation, which are sensitive to interactions with two nuclear spin states. Examples will be presented that illustrate the use of this extension of SHIML to generate Mössbauer spectra for polycrystalline samples under a number of fluctuating hyperfine field models.

  2. NMR Evidence for Inhomogeneous Nematic Fluctuations in BaFe_{2}(As_{1-x}P_{x})_{2}.

    PubMed

    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

    2016-03-11

    We present evidence for nuclear spin-lattice relaxation driven by glassy nematic fluctuations in isovalent P-doped BaFe_{2}As_{2} single crystals. Both the ^{75}As and ^{31}P 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. PMID:27015507

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

    DOE PAGES

    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.

  4. Probing variations of the Rashba spin-orbit coupling at the nanometre scale

    NASA Astrophysics Data System (ADS)

    Bindel, Jan Raphael; Pezzotta, Mike; Ulrich, Jascha; Liebmann, Marcus; Sherman, Eugene Ya.; Morgenstern, Markus

    2016-10-01

    As the Rashba effect is an electrically tunable spin-orbit interaction, it could form the basis for a multitude of applications, such as spin filters, spin transistors and quantum computing using Majorana states in nanowires. Moreover, this interaction can determine the spin dephasing and antilocalization phenomena in two dimensions. However, the real space pattern of the Rashba parameter, which critically influences spin transistors using the spin-helix state and the otherwise forbidden electron backscattering in topologically protected channels, is difficult to probe. Here, we map this pattern down to nanometre length scales by measuring the spin splitting of the lowest Landau level using scanning tunnelling spectroscopy. We reveal strong fluctuations correlated with the local electrostatic potential for an InSb inversion layer with a large Rashba coefficient (~1 eV Å). This type of Rashba field mapping enables a more comprehensive understanding of its fluctuations, which might be decisive towards robust semiconductor-based spintronic devices.

  5. 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.

  6. Complex Transcriptional Control of the Antibiotic Regulator afsS in Streptomyces: PhoP and AfsR Are Overlapping, Competitive Activators▿

    PubMed Central

    Santos-Beneit, Fernando; Rodríguez-García, Antonio; Martín, Juan F.

    2011-01-01

    The afsS gene of several Streptomyces species encodes a small sigma factor-like protein that acts as an activator of several pathway-specific regulatory genes (e.g., actII-ORF4 and redD in Streptomyces coelicolor). The two pleiotropic regulators AfsR and PhoP bind to overlapping sequences in the −35 region of the afsS promoter and control its expression. Using mutated afsS promoters containing specific point mutations in the AfsR and PhoP binding sequences, we proved that the overlapping recognition sequences for AfsR and PhoP are displaced by 1 nucleotide. Different nucleotide positions are important for binding of AfsR or PhoP, as shown by electrophoretic mobility shift assays and by reporter studies using the luxAB gene coupled to the different promoters. Mutant promoter M5 (with a nucleotide change at position 5 of the consensus box) binds AfsR but not PhoP with high affinity (named “superAfsR”). Expression of the afsS gene from this promoter led to overproduction of actinorhodin. Mutant promoter M16 binds PhoP with extremely high affinity (“superPhoP”). Studies with ΔafsR and ΔphoP mutants (lacking AfsR and PhoP, respectively) showed that both global regulators are competitive transcriptional activators of afsS. AfsR has greater influence on expression of afsS than PhoP, as shown by reverse transcriptase PCR (RT-PCR) and promoter reporter (luciferase) studies. These two high-level regulators appear to integrate different nutritional signals (particularly phosphate limitation sensed by PhoR), S-adenosylmethionine, and other still unknown environmental signals (leading to AfsR phosphorylation) for the AfsS-mediated control of biosynthesis of secondary metabolites. PMID:21378195

  7. Complex transcriptional control of the antibiotic regulator afsS in Streptomyces: PhoP and AfsR are overlapping, competitive activators.

    PubMed

    Santos-Beneit, Fernando; Rodríguez-García, Antonio; Martín, Juan F

    2011-05-01

    The afsS gene of several Streptomyces species encodes a small sigma factor-like protein that acts as an activator of several pathway-specific regulatory genes (e.g., actII-ORF4 and redD in Streptomyces coelicolor). The two pleiotropic regulators AfsR and PhoP bind to overlapping sequences in the -35 region of the afsS promoter and control its expression. Using mutated afsS promoters containing specific point mutations in the AfsR and PhoP binding sequences, we proved that the overlapping recognition sequences for AfsR and PhoP are displaced by 1 nucleotide. Different nucleotide positions are important for binding of AfsR or PhoP, as shown by electrophoretic mobility shift assays and by reporter studies using the luxAB gene coupled to the different promoters. Mutant promoter M5 (with a nucleotide change at position 5 of the consensus box) binds AfsR but not PhoP with high affinity (named "superAfsR"). Expression of the afsS gene from this promoter led to overproduction of actinorhodin. Mutant promoter M16 binds PhoP with extremely high affinity ("superPhoP"). Studies with ΔafsR and ΔphoP mutants (lacking AfsR and PhoP, respectively) showed that both global regulators are competitive transcriptional activators of afsS. AfsR has greater influence on expression of afsS than PhoP, as shown by reverse transcriptase PCR (RT-PCR) and promoter reporter (luciferase) studies. These two high-level regulators appear to integrate different nutritional signals (particularly phosphate limitation sensed by PhoR), S-adenosylmethionine, and other still unknown environmental signals (leading to AfsR phosphorylation) for the AfsS-mediated control of biosynthesis of secondary metabolites.

  8. Observation of the spin Peltier effect for magnetic insulators.

    PubMed

    Flipse, J; Dejene, F K; Wagenaar, D; Bauer, G E W; Ben Youssef, J; van Wees, B J

    2014-07-11

    We report the observation of the spin Peltier effect (SPE) in the ferrimagnetic insulator yttrium iron garnet (YIG), i.e., a heat current generated by a spin current flowing through a platinum (Pt)|YIG interface. The effect can be explained by the spin transfer torque that transforms the spin current in the Pt into a magnon current in the YIG. Via magnon-phonon interactions the magnetic fluctuations modulate the phonon temperature that is detected by a thermopile close to the interface. By finite-element modeling we verify the reciprocity between the spin Peltier and spin Seebeck effect. The observed strong coupling between thermal magnons and phonons in YIG is attractive for nanoscale cooling techniques. PMID:25062233

  9. Resonant and Time-Resolved Spin Noise Spectroscopy

    NASA Astrophysics Data System (ADS)

    Song, Xinlin; Pursley, Brennan; Sih, Vanessa

    Spin noise spectroscopy is a technique which can probe the system while it remains in equilibrium. It was first demonstrated in atomic gases and then in solid state systems. Most existing spin noise measurement setups digitize the spin fluctuation signal and then analyze the power spectrum. Recently, pulsed lasers have been used to expand the bandwidth of accessible dynamics and allow direct time-domain correlation measurements. Here we develop and test a model for ultrafast pulsed laser spin noise measurements as well as a scheme to measure spin lifetimes longer than the laser repetition period. For the resonant spin noise technique, analog electronics are used to capture correlations from the extended pulse train, and the signal at a fixed time delay is measured as a function of applied magnetic field.

  10. Force Fluctuations and Correlations

    NASA Astrophysics Data System (ADS)

    Behringer, Robert

    1998-03-01

    Granular materials exhibit a rich array of dynamic and static phenomena which are only partly understood. Here, I focus on fluctuations in kinetic properties and in forces for slowly sheared granular materials. We have carried out a series of experiments in both 2D and in 3D. For 2D, we use a novel apparatus which allows us to quantify the forces, positions and orientations associated with individual grains. For slow to moderate shear rates, we find rate independence except for small random deviations which are associated with very long time changes in the system. The system evolves to a nearly steady average flow profile in which the velocity falls off approximately exponentially with distance from the shearing surface. The particle rotation shows systematic oscillations near the shearing surface. Velocity profiles show a complicated non-gaussian structure. Force measurements in both the 2D and 3D system are approximately exponentially distributed, but there are also some systematic deviations. Companion calculations by S. Schoellmann, S. Luding and H. Herrmann capture a number of these features. The experimental work has been carried out partially at Duke and partially at the E.S.P.C.I. Paris in collaboration with D. Howell, B. Miller, S. Tennakoon, and C. Veje.

  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. 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.

  13. 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)

  14. 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.

  15. Waiting for rare entropic fluctuations

    NASA Astrophysics Data System (ADS)

    Saito, Keiji; Dhar, Abhishek

    2016-06-01

    Nonequilibrium fluctuations of various stochastic variables, such as work and entropy production, have been widely discussed recently in the context of large deviations, cumulants and fluctuation relations. Typically one looks at the probability distributions for entropic fluctuations of various sizes to occur in a fixed time interval. An important and natural question is to ask for the time one has to wait to see fluctuations of a desired size. We address this question by studying the first-passage time distribution (FPTD). We derive the general basic equation to get the FPTD for entropic variables. Based on this, the FPTD on entropy production in a driven colloidal particle in the ring geometry is illustrated. A general asymptotic form of the FPTD and integral fluctuation relation symmetry in terms of the first passages are found.

  16. Frequency fluctuations in silicon nanoresonators

    PubMed Central

    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

    2016-01-01

    Frequency stability is key to 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 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

  17. 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.

  18. 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.

  19. Core fluctuations test. Revision 1

    SciTech Connect

    Betts, W.S.

    1987-06-01

    Fluctuations were first encountered in the Fort St. Vrain reactor early in cycle 1 operation, during the initial rise from 40% to 70% power. Subsequent in-core tests and operation throughout cycles 1 and 2 demonstrated that fluctuations were repeatable, occurring at core pressure drops of between 2.5 psi and 4.0 psi, and that in each instance their characteristics were very similar. Subsequently, tests and analysis were done to understand the core fluctuation phenomenon. These efforts also lead to a design fix which stopped these fluctuations in the FSV reactor core. This fix required that keys be used in addition to the keys in the core support floor which already existed. This report outlines a test plan to validate that core fluctuations will not occur in the MHTGR core. 2 refs., 12 figs., 3 tabs.

  20. Spin relaxation in geometrically frustrated pyrochlores

    NASA Astrophysics Data System (ADS)

    Dunsiger, Sarah Ruth

    This thesis describes muSR experiments which focus on systems where the magnetic ions occupy the vertices of edge or corner sharing triangular units, in particular the pyrochlores A2B2O7. The scientific interest in pyrochlores is based on the fact that they display novel magnetic behaviour at low temperatures due to geometrical frustration. The ground state of these systems is sensitively dependent on such factors as the range of the spin-spin interactions, disorder, anisotropy, thermal and quantum fluctuations. For example, Y2Mo2O7 shows many features reminiscent of a conventional spin glass, even though this material has nominally zero chemical disorder. It is found that the muon spin polarisation obeys a time-field scaling relation which indicates that the spin-spin autocorrelation function has a power law form in time, in stark contrast with the exponential form often assumed for conventional magnets above their transition temperature. Gd2Ti2O7 shows long range order, but only at a temperature much lower than its Curie-Weiss temperature, a signature of a frustrated system. In the paramagnetic regime, it is well described by an isotropic Heisenberg Hamiltonian with nearest neighbour couplings in the presence of a Zeeman interaction, from which the spin-spin autocorrelation function may be calculated as a power series in time. The muon spin relaxation rate decreases with magnetic field as the Zeeman energy becomes comparable with the exchange coupling between Gd spins. Thus, an independent measure of the exchange coupling or equivalently the Gd spin fluctuation rate is extracted. By contrast, Tb2Ti2O7 has been identified as a type of cooperative paramagnet. Short range correlations develop below 50 K. However, there is no long range ordering down to very low temperatures (0.075 K). The Tb3+ ion is subject to strong crystal electric field effects: point charge calculations indicate that this system is Ising like at low temperatures. Thus this system may be

  1. 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.

  2. 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.

  3. The theory of spin noise spectroscopy: a review

    NASA Astrophysics Data System (ADS)

    Sinitsyn, Nikolai A.; Pershin, Yuriy V.

    2016-10-01

    Direct measurements of spin fluctuations are becoming the mainstream approach for studies of complex condensed matter, molecular, nuclear, and atomic systems. This review covers recent progress in the field of optical spin noise spectroscopy (SNS) with an additional goal to establish an introduction into its theoretical foundations. Various theoretical techniques that have been recently used to interpret results of SNS measurements are explained alongside examples of their applications.

  4. Spin Squeezing and Light Entanglement in Coherent Population Trapping

    SciTech Connect

    Dantan, A.; Cviklinski, J.; Giacobino, E.; Pinard, M.

    2006-07-14

    We show that strong squeezing and entanglement can be generated at the output of a cavity containing atoms interacting with two fields in a coherent population trapping situation, on account of a nonlinear Faraday effect experienced by the fields close to a dark-state resonance in a cavity. Moreover, the cavity provides a feedback mechanism allowing to reduce the quantum fluctuations of the ground state spin, resulting in strong steady state spin squeezing.

  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. 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

  7. Power spectrum of the fluctuation of the spectral staircase function

    NASA Astrophysics Data System (ADS)

    Lan, Boon Leong; Aun Ng, Jin; Santhanam, M. S.

    2006-12-01

    The one-sided power spectrum P(f) of the fluctuation Nfluc (E) and Nfluc(\\varepsilon) of the spectral staircase function, for respectively the original and unfolded spectrum, from its smooth average part is numerically estimated for Poisson spectrum and spectra of three Gaussian-random matrices: real symmetric, complex Hermitian, and quaternion-real Hermitian. We found that the power spectrum of Nfluc (E) and Nfluc (\\varepsilon) is a/f2 (brown) for Poisson spectrum but c/(1+ df^2) (Lorentzian) for all three random matrix spectra. This result and the Berry-Tabor and Bohigas-Giannoni-Schmit conjectures imply the following conjecture: the power spectrum of Nfluc (E) and Nfluc (\\varepsilon) is brown for classically integrable systems but Lorentzian for classically chaotic systems. Numerical evidence in support of this conjecture is presented.

  8. 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.

  9. 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

  10. Effects of iron depletion on CALM-AF10 leukemias.

    PubMed

    Heath, Jessica L; Weiss, Joshua M; Lavau, Catherine P; Wechsler, Daniel S

    2014-12-01

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

  11. Spin Relaxation and Spin Transport in Graphene

    NASA Astrophysics Data System (ADS)

    Wu, M. W.

    2012-02-01

    In this talk we are going to present our theoretical investigations on spin dynamics of graphene under various conditions based on a fully microscopic kinetic-spin-Bloch-equation approach [1]. We manage to nail down the solo spin relaxation mechanism of graphene in measurements from two leading groups, one in US and one in the Netherland. Many novel effects of the electron-electron Coulomb interaction on spin relaxation in graphene are addressed. Our theory can have nice agreement with experimental data.[4pt] [1] M. W. Wu, J. H. Jiang, and M. Q. Weng, ``Spin dynamics in semiconductors,'' Phys. Rep. 493, 61 (2010).

  12. Non-Gaussian eccentricity fluctuations

    NASA Astrophysics Data System (ADS)

    Grönqvist, Hanna; Blaizot, Jean-Paul; Ollitrault, Jean-Yves

    2016-09-01

    We study the fluctuations of the anisotropy of the energy density profile created in a high-energy collision at the LHC. We show that the anisotropy in harmonic n has generic non-Gaussian fluctuations. We argue that these non-Gaussianities have a universal character for small systems such as p+Pb collisions, but not for large systems such as Pb+Pb collisions where they depend on the underlying non-Gaussian statistics of the initial density profile. We generalize expressions for the eccentricity cumulants ɛ2{4 } and ɛ3{4 } previously obtained within the independent-source model to a general fluctuating initial density profile.

  13. Spin Liquid Condensate of Spinful Bosons

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shoucheng

    2015-03-01

    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 (RVB) state. The existence of SLC reveals the possible existence of a more general new class of superfluid phases in a lattice.

  14. Spin-Liquid Condensate of Spinful Bosons

    NASA Astrophysics Data System (ADS)

    Lian, Biao; Zhang, Shoucheng

    2014-08-01

    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.

  15. 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.

  16. Ballistic spin resonance.

    PubMed

    Frolov, S M; Lüscher, S; Yu, W; Ren, Y; Folk, J A; Wegscheider, W

    2009-04-16

    The phenomenon of spin resonance has had far-reaching influence since its discovery 70 years ago. Electron spin resonance driven by high-frequency magnetic fields has enhanced our understanding of quantum mechanics, and finds application in fields as diverse as medicine and quantum information. Spin resonance can also be induced by high-frequency electric fields in materials with a spin-orbit interaction; the oscillation of the electrons creates a momentum-dependent effective magnetic field acting on the electron spin. Here we report electron spin resonance due to a spin-orbit interaction that does not require external driving fields. The effect, which we term ballistic spin resonance, is driven by the free motion of electrons that bounce at frequencies of tens of gigahertz in micrometre-scale channels of a two-dimensional electron gas. This is a frequency range that is experimentally challenging to access in spin resonance, and especially difficult on a chip. The resonance is manifest in electrical measurements of pure spin currents-we see a strong suppression of spin relaxation length when the oscillating spin-orbit field is in resonance with spin precession in a static magnetic field. These findings illustrate how the spin-orbit interaction can be harnessed for spin manipulation in a spintronic circuit, and point the way to gate-tunable coherent spin rotations in ballistic nanostructures without external alternating current fields. PMID:19370029

  17. Effects of strong magnetic fields on pairing fluctuations in high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Eschrig, M.; Rainer, D.; Sauls, J. A.

    1999-05-01

    We present the theory for the effects of superconducting pairing fluctuations on the nuclear spin-lattice relaxation rate 1/T1 and the NMR Knight shift for layered superconductors in high magnetic fields. These results can be used to clarify the origin of the pseudogap in high-Tc cuprates, which has been attributed to spin fluctuations as well as pairing fluctuations. We present theoretical results for s-wave and d-wave pairing fluctuations and show that recent experiments in optimally doped YBa2Cu3O7-δ are described by d-wave pairing fluctuations [V. F. Mitrović et al., Phys. Rev. Lett. 82, 2784 (1999); H. N. Bachman et al. (unpublished)]. In addition, we show that the orthorhombic distortion in YBa2Cu3O7-δ accounts for an experimentally observed discrepancy between 1/T1 obtained by nuclear quadrupole resonance and nuclear magnetic resonance at low field. We propose an NMR experiment to distinguish a fluctuating s-wave order parameter from a fluctuating strongly anisotropic order parameter, which may be applied to the system Nd2-xCexCuO4-δ and possibly other layered superconductors.

  18. 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.

  19. Spin Transport in Multiply Connected Fractal Conductors

    NASA Astrophysics Data System (ADS)

    Lee, Bo-Ray; Chang, Ching-Ray; Klik, Ivo

    2014-12-01

    We consider spin and charge transport in a Sierpinski planar carpet; the interest here is its unique geometry. We analyze the fractal conductor as a combination of multiply connected quantum wires, and we observe the evolution of the transmission envelope in different fractal generations. For a fractal conductor dominated by resonant modes the transmission is characterized by strong fluctuations and conduction gaps. We show that charge and spin transport have different responses both to the presence of defects and to applied bias. At a high bias, or in a high-order fractal generation, spin accumulation is separated from charge accumulation because the larger drift velocity needs a longer polarization length, and the sample may turn into an insulator by the action of the defects. Our results are calculated numerically using the Keldysh Green function within the tight-binding framework.

  20. Transverse Momentum Fluctuations at RHIC

    NASA Astrophysics Data System (ADS)

    Gavin, Sean; Abdel-Aziz, Mohamed

    2004-10-01

    PHENIX and STAR data in Au+Au collisions at RHIC show that transverse momentum fluctuations increase as centrality increases. The approach to local thermal equilibrium can explain the similar centrality dependence of the average transverse momentum and its fluctuations [1]. Alternatively, this dependence can be attributed to jet effects, although the mechanism has not been spelled out in the literature [2]. Certainly both mechanisms play a role at some level. We review the nonequilibrium description of parton thermalization in [1]. We then extend the formulation to account for contributions to fluctuations from the energy loss of the high transverse momentum particles. Calculations are then compared to the measured average transverse momentum and its fluctuations. We then discuss how correlation function measurements may distinguish these effects. [1] Sean Gavin, Phys.Rev.Lett. 92 (2004) 162301. [2] S. S. Adler et al. [PHENIX Collaboration], arXiv:nucl-ex/0310005.

  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

    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].

  3. 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)].

  4. 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.

  5. 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.

  6. Fluctuations in classical sum rules.

    PubMed

    Elton, John R; Lakshminarayan, Arul; Tomsovic, Steven

    2010-10-01

    Classical sum rules arise in a wide variety of physical contexts. Asymptotic expressions have been derived for many of these sum rules in the limit of long orbital period (or large action). Although sum-rule convergence may well be exponentially rapid for chaotic systems in a global phase-space sense with time, individual contributions to the sums may fluctuate with a width which diverges in time. Our interest is in the global convergence of sum rules as well as their local fluctuations. It turns out that a simple version of a lazy baker map gives an ideal system in which classical sum rules, their corrections, and their fluctuations can be worked out analytically. This is worked out in detail for the Hannay-Ozorio sum rule. In this particular case the rate of convergence of the sum rule is found to be governed by the Pollicott-Ruelle resonances, and both local and global boundaries for which the sum rule may converge are given. In addition, the width of the fluctuations is considered and worked out analytically, and it is shown to have an interesting dependence on the location of the region over which the sum rule is applied. It is also found that as the region of application is decreased in size the fluctuations grow. This suggests a way of controlling the length scale of the fluctuations by considering a time dependent phase-space volume, which for the lazy baker map decreases exponentially rapidly with time.

  7. 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.

  8. 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.

  9. Nuclear spin warm up in bulk n -GaAs

    NASA Astrophysics Data System (ADS)

    Kotur, M.; Dzhioev, R. I.; Vladimirova, M.; Jouault, B.; Korenev, V. L.; Kavokin, K. V.

    2016-08-01

    We show that the spin-lattice relaxation in n -type insulating GaAs is dramatically accelerated at low magnetic fields. The origin of this effect, which cannot be explained in terms of well-known diffusion-limited hyperfine relaxation, is found in the quadrupole relaxation, induced by fluctuating donor charges. Therefore, quadrupole relaxation, which governs low field nuclear spin relaxation in semiconductor quantum dots, but was so far supposed to be harmless to bulk nuclei spins in the absence of optical pumping, can be studied and harnessed in the much simpler model environment of n -GaAs bulk crystal.

  10. 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.

  11. afsS is a target of AfsR, a transcriptional factor with ATPase activity that globally controls secondary metabolism in Streptomyces coelicolor A3(2).

    PubMed

    Lee, Ping-Chin; Umeyama, Takashi; Horinouchi, Sueharu

    2002-03-01

    AfsR is a pleiotropic, global regulator that controls the production of actinorhodin, undecylprodigiosin and calcium-dependent antibiotic in Streptomyces coelicolor A3(2). AfsR, with 993 amino acids, is phosphorylated on serine and threonine residues by a protein serine/threonine kinase AfsK and contains an OmpR-like DNA-binding fold at its N-terminal portion and A- and B-type nucleotide-binding motifs in the middle of the protein. The DNA-binding domain, in-dependently of the nucleotide-binding domain, contributed the binding of AfsR to the upstream region of afsS that locates immediately 3' to afsR and encodes a 63-amino-acid protein. No transcription of afsS in the DeltaafsR background and restoration of afsS transcription by afsR on a plasmid in the same genetic background indicated that afsR served as a transcriptional activator for afsS. Interestingly, the AfsR binding site overlapped the promoter of afsS, as determined by DNase I protection assay and high-resolution S1 nuclease mapping. The nucleotide-binding domain contributed distinct ATPase and GTPase activity. The phosphorylation of AfsR by AfsK greatly enhanced the DNA-binding activity and modulated the ATPase activity. The DNA-binding ability of AfsR was independent of the ATPase activity. However, the ATPase activity was essential for transcriptional activation of afsS, probably because the energy available from ATP hydrolysis is required for the isomerization of the closed complex between AfsR and RNA polymerase to a transcriptionally competent open complex. Thus, AfsR turns out to be a unique transcriptional factor, in that it is modular, in which DNA-binding and ATPase activities are physically separable, and the two functions are modulated by phosphorylation on serine and threonine residues.

  12. 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.

  13. Free-Energy Bounds for Hierarchical Spin Models

    NASA Astrophysics Data System (ADS)

    Castellana, Michele; Barra, Adriano; Guerra, Francesco

    2014-04-01

    In this paper we study two non-mean-field (NMF) spin models built on a hierarchical lattice: the hierarchical Edward-Anderson model (HEA) of a spin glass, and Dyson's hierarchical model (DHM) of a ferromagnet. For the HEA, we prove the existence of the thermodynamic limit of the free energy and the replica-symmetry-breaking (RSB) free-energy bounds previously derived for the Sherrington-Kirkpatrick model of a spin glass. These RSB mean-field bounds are exact only if the order-parameter fluctuations (OPF) vanish: given that such fluctuations are not negligible in NMF models, we develop a novel strategy to tackle part of OPF in hierarchical models. The method is based on absorbing part of OPF of a block of spins into an effective Hamiltonian of the underlying spin blocks. We illustrate this method for DHM and show that, compared to the mean-field bound for the free energy, it provides a tighter NMF bound, with a critical temperature closer to the exact one. To extend this method to the HEA model, a suitable generalization of Griffith's correlation inequalities for Ising ferromagnets is needed: since correlation inequalities for spin glasses are still an open topic, we leave the extension of this method to hierarchical spin glasses as a future perspective.

  14. Storage of Spin Squeezing in a Two-Component Bose-Einstein Condensate

    SciTech Connect

    Jin, Guang-Ri; Kim, Sang Wook

    2007-10-26

    A simple scheme for storage of spin squeezing in a two-component Bose-Einstein condensate is investigated by considering rapidly turning-off the external field at a time that maximal spin squeezing occurs. We show that strong reduction of spin fluctuation can be maintained in a nearly fixed direction. We explain the underlying physics using the phase model and present analytical expressions of the maximal-squeezing time and the corresponding squeezing parameter.

  15. Storage of spin squeezing in a two-component Bose-Einstein condensate.

    PubMed

    Jin, Guang-Ri; Kim, Sang Wook

    2007-10-26

    A simple scheme for storage of spin squeezing in a two-component Bose-Einstein condensate is investigated by considering rapidly turning-off the external field at a time that maximal spin squeezing occurs. We show that strong reduction of spin fluctuation can be maintained in a nearly fixed direction. We explain the underlying physics using the phase model and present analytical expressions of the maximal-squeezing time and the corresponding squeezing parameter.

  16. Polarization Dependence of the Spin-Density-Wave Excitations in Single-Domain Chromium

    SciTech Connect

    Boeni, P.; Sternlieb, B.J.; Shirane, G.; Roessli, B.; Werner, S.A.; Lorenzo, J.E.

    1997-12-31

    A polarised neutron scattering experiment has been performed on a single-Q, single domain sample of Cr in a magnetic field of 4 T in the transverse spin-density-wave phase. It is confirmed that the longitudinal fluctuations are enhanced for energy transfers E {lt} 8 meV similarly as in the longitudinal spin-density-wave phase. The spin wave modes with deltaS parallel and perpendicular to Q are isotropic within the E-range investigated.

  17. Entanglement in a two-spin system with long-range interactions

    NASA Astrophysics Data System (ADS)

    Soltani, M. R.; Mahdavifar, S.; Mahmoudi, M.

    2016-08-01

    The quantum entanglement between two spins in the Ising model with an added Dzyaloshinsky–Moriya (DM) interaction and in the presence of the transverse magnetic field is studied. The exchange interaction is considered as a function of the distance between spins. The negativity as a function of magnetic field, exchange and DM interaction is calculated. The effect of the distance between spins is studied based on the negativity. In addition, the effect of the thermal fluctuation on the negativity is also investigated.

  18. Spin Hall effect devices.

    PubMed

    Jungwirth, Tomas; Wunderlich, Jörg; Olejník, Kamil

    2012-05-01

    The spin Hall effect is a relativistic spin-orbit coupling phenomenon that can be used to electrically generate or detect spin currents in non-magnetic systems. Here we review the experimental results that, since the first experimental observation of the spin Hall effect less than 10 years ago, have established the basic physical understanding of the phenomenon, and the role that several of the spin Hall devices have had in the demonstration of spintronic functionalities and physical phenomena. We have attempted to organize the experiments in a chronological order, while simultaneously dividing the Review into sections on semiconductor or metal spin Hall devices, and on optical or electrical spin Hall experiments. The spin Hall device studies are placed in a broader context of the field of spin injection, manipulation, and detection in non-magnetic conductors.

  19. On the concentration dependence of wings of spectra of spin correlation functions of diluted Heisenberg paramagnets

    NASA Astrophysics Data System (ADS)

    Zobov, V. E.; Kucherov, M. M.

    2016-06-01

    Singular points of the autocorrelation function on the imaginary time axis that is averaged over the location of spins in the magnetically dilute spin lattice with isotropic spin-spin interaction at a high temperature have been studied. For the autocorrelation function in the approximation of the self-consistent fluctuating local field, nonlinear integral equations have been proposed which reflect the separation of the inhomogeneous spin systems into close spins and other spins. The coordinates of the nearest singular points have been determined in terms of the radius of convergence of the expansion in powers of time, the coefficients of which have been calculated from recurrence equations. It has been shown that the coordinates of singular points and, consequently, the wings of the autocorrelation function spectrum at strong magnetic dilution are determined by the modulation of the local field by the nearest pairs of spins leading to its logarithmic concentration dependence.

  20. 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.

  1. 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.

  2. Spontaneous breaking of spatial and spin symmetry in spinor condensates.

    PubMed

    Scherer, M; Lücke, B; Gebreyesus, G; Topic, O; Deuretzbacher, F; Ertmer, W; Santos, L; Arlt, J J; Klempt, C

    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.

  3. 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.

  4. 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.

  5. Quantum fluctuations and dynamic clustering of fluctuating Cooper pairs.

    SciTech Connect

    Glatz, A.; Varlamov, A. A.; Vinokur, V. M.

    2011-05-01

    We derive the complete expression for the fluctuation conductivity in two-dimensional superconductors as a function of the temperature and the magnetic field in the whole fluctuation region above the upper critical field H{sub c2}(T). Focusing on the vicinity of the quantum phase transition near zero temperature, we propose that as the magnetic field approaches the line near H{sub c2}(0) from above, a peculiar dynamic state consisting of clusters of coherently rotating fluctuation Cooper pairs forms and estimate the characteristic size and lifetime of such clusters. We find the zero-temperature magnetic-field dependence of the transverse magnetoconductivity above H{sub c2}(0) in layered superconductors.

  6. 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.

  7. 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

  8. 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

  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. 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…

  11. Ornicorrugatin, a new siderophore from Pseudomonas fluorescens AF76.

    PubMed

    Matthijs, Sandra; Budzikiewicz, Herbert; Schäfer, Mathias; Wathelet, Bernard; Cornelis, Pierre

    2008-01-01

    From a pyoverdin-negative mutant of Pseudomonas fluorescens AF76 a new lipopeptidic siderophore (ornicorrugatin) could be isolated. It is structurally related to the siderophore of Pseudomonas corrugata differing in the replacement of one Dab unit by Orn. PMID:18386480

  12. Magnetic field induced anisotropy of 139La spin-lattice relaxation rates in stripe ordered La1.875Ba0.125CuO4

    DOE PAGES

    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

  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. Estimation of fluctuating magnetic fields by an atomic magnetometer

    SciTech Connect

    Petersen, Vivi; Moelmer, Klaus

    2006-10-15

    We present a theoretical procedure to estimate with an atomic magnetometer the time dependence of a magnetic field that fluctuates according to an Ornstein-Uhlenbeck process. The magnetometer applies the detected polarization rotation of an optical probe to measure a collective atomic spin, which precesses due to the magnetic field. Based on the noisy optical detection record, our consistent Gaussian update formalism provides an estimator for the magnetic fields, and we identify analytically the steady-state performance of this estimator. We show that the estimate of the current value of the magnetic field is further improved if noisy measurement data obtained also at later times are taken into account.

  15. The commensurate spin excitation in chromium: A polarised neutron investigation

    SciTech Connect

    Pynn, R. ); Stirling, W.G. . Dept. of Physics); Severing, A. )

    1991-01-01

    A polarised neutron experiment with neutron energy analysis has been performed with a single-Q sample of chromium in a large magnetic field. The 4-meV commensurate'' mode is found to involve spin fluctuations parallel to the ordered chromium moments. 8 refs., 3 figs.

  16. Topics in fluctuating nonlinear hydrodynamics

    SciTech Connect

    Milner, S.T.

    1986-01-01

    Models of fluctuating nonlinear hydrodynamics have enjoyed much success in explaining the effect of long-wavelength fluctuations in diverse hydrodynamic systems. This thesis explores two such problems; in both, the body of hydrodynamic assumptions powerfully constrains the predictions of a well-posed theory. The effects of layer fluctuations in smectic-A liquid crystals are first examined. The static theory (introduced by Grinstein and Pelcovits) is reviewed. Ward identities, resulting from the arbitrariness of the layering direction, are derived and exploited. The static results motivate an examination of dynamic fluctuation effects. A new sound-damping experiment is proposed that would probe singular dependence of viscosities on applied stress. A theory of Procaccia and Gitterman that reaction rates of chemically reacting binary mixtures are drastically reduced near their thermodynamic critical points is analyzed. Hydrodynamic arguments and Van Hove theory are applied, concluding that the PG idea is drastically slowed, and spatially varying composition fluctuations are at best slowed down over a narrow range of wavenumbers.

  17. Reentrant Superconductivity Driven by Quantum Tricritical Fluctuations in URhGe: Evidence from Co 59 NMR in URh0.9Co0.1Ge

    NASA Astrophysics Data System (ADS)

    Tokunaga, Y.; Aoki, D.; Mayaffre, H.; Krämer, S.; Julien, M.-H.; Berthier, C.; Horvatić, M.; Sakai, H.; Kambe, S.; Araki, S.

    2015-05-01

    Our measurements of the Co 59 NMR spin-spin relaxation in URh0.9Co0.1Ge reveal a divergence of electronic spin fluctuations in the vicinity of the field-induced quantum critical point at HR≈13 T , around which reentrant superconductivity (RSC) occurs in the ferromagnetic heavy fermion compound URhGe. We map out the strength of spin fluctuations in the (Hb,Hc ) plane of magnetic field components and show that critical fluctuations develop in the same limited region near the field HR as that where RSC is observed. This strongly suggests these quantum fluctuations as the pairing glue responsible for the RSC. The fluctuations observed are characteristic of a tricritical point, followed by a phase bifurcation toward quantum critical end points.

  18. 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.

  19. Extracting uranium from seawater: Promising AF series adsorbents

    DOE PAGES

    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

  20. 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.

  1. Thermodynamic constraints on fluctuation phenomena

    NASA Astrophysics Data System (ADS)

    Maroney, O. J. E.

    2009-12-01

    The relationships among reversible Carnot cycles, the absence of perpetual motion machines, and the existence of a nondecreasing globally unique entropy function form the starting point of many textbook presentations of the foundations of thermodynamics. However, the thermal fluctuation phenomena associated with statistical mechanics has been argued to restrict the domain of validity of this basis of the second law of thermodynamics. Here we demonstrate that fluctuation phenomena can be incorporated into the traditional presentation, extending rather than restricting the domain of validity of the phenomenologically motivated second law. Consistency conditions lead to constraints upon the possible spectrum of thermal fluctuations. In a special case this uniquely selects the Gibbs canonical distribution and more generally incorporates the Tsallis distributions. No particular model of microscopic dynamics need be assumed.

  2. 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.

  3. 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.

  4. Thermodynamic constraints on fluctuation phenomena.

    PubMed

    Maroney, O J E

    2009-12-01

    The relationships among reversible Carnot cycles, the absence of perpetual motion machines, and the existence of a nondecreasing globally unique entropy function form the starting point of many textbook presentations of the foundations of thermodynamics. However, the thermal fluctuation phenomena associated with statistical mechanics has been argued to restrict the domain of validity of this basis of the second law of thermodynamics. Here we demonstrate that fluctuation phenomena can be incorporated into the traditional presentation, extending rather than restricting the domain of validity of the phenomenologically motivated second law. Consistency conditions lead to constraints upon the possible spectrum of thermal fluctuations. In a special case this uniquely selects the Gibbs canonical distribution and more generally incorporates the Tsallis distributions. No particular model of microscopic dynamics need be assumed.

  5. Spin versus charge noise from Kondo traps

    NASA Astrophysics Data System (ADS)

    da Silva, Luis G. G. V. Dias; de Sousa, Rogério

    2015-08-01

    Magnetic and charge noise have a common microscopic origin in solid-state devices, as described by a universal electron trap model. In spite of this common origin, magnetic (spin) and charge noise spectral densities display remarkably different behaviors when many-particle correlations are taken into account, leading to the emergence of the Kondo effect. We derive exact frequency sum rules for trap noise and perform numerical renormalization-group calculations to show that while spin noise is a universal function of the Kondo temperature, charge noise remains well described by single-particle theory even when the trap is deep in the Kondo regime. We obtain simple analytical expressions for charge and spin noise that account for Kondo screening in all frequency and temperature regimes, enabling the study of the impact of disorder and the emergence of magnetic 1 /f noise from Kondo traps. We conclude that the difference between charge and spin noise survives even in the presence of disorder, showing that noise can be more manageable in devices that are sensitive to magnetic (rather than charge) fluctuations and that the signature of the Kondo effect can be observed in spin noise spectroscopy experiments.

  6. 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

  7. 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.

  8. Thermal fluctuations and rubber elasticity.

    PubMed

    Xing, Xiangjun; Goldbart, Paul M; Radzihovsky, Leo

    2007-02-16

    The effects of thermal elastic fluctuations in rubbery materials are examined. It is shown that, due to their interplay with the incompressibility constraint, these fluctuations qualitatively modify the large-deformation stress-strain relation, compared to that of classical rubber elasticity. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the external deformation. PMID:17359034

  9. Thermal Fluctuations and Rubber Elasticity

    NASA Astrophysics Data System (ADS)

    Xing, Xiangjun; Goldbart, Paul M.; Radzihovsky, Leo

    2007-02-01

    The effects of thermal elastic fluctuations in rubbery materials are examined. It is shown that, due to their interplay with the incompressibility constraint, these fluctuations qualitatively modify the large-deformation stress-strain relation, compared to that of classical rubber elasticity. To leading order, this mechanism provides a simple and generic explanation for the peak structure of Mooney-Rivlin stress-strain relation and shows good agreement with experiments. It also leads to the prediction of a phonon correlation function that depends on the external deformation.

  10. 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.

  11. 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.

  12. 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 +.

  13. Magnetic Field-Independent Onset of Vortex Pinning up to 28 T by ^17O Spin-spin Relaxation in YBa_2Cu_3O_7

    NASA Astrophysics Data System (ADS)

    Bachman, H. N.; Mitrovic, V. F.; Reyes, A. P.; Halperin, W. P.; Kleinhammes, A.; Kuhns, P.; Moulton, W. G.

    1998-03-01

    We report spin-spin relaxation measurements (T_2) up to 28 T. The data confirm a field-independent pinning temperature from ≈10 T up to 28 T for aligned YBa_2Cu_3O7 powder. Below ≈10 T the pinning temperature is field-dependent, and is consistent with the melting temperature of clean, untwinned YBCO crystals (Reyes, et al.), Phys. Rev. B, 55, R14737, (1997).. Spectrum analysis shows that above ≈10 T the pinning temperature is field-independent, occurring at 80 K (H. N. Bachman, et al.), Bull. Am. Phys. Soc., 42, 661, (1997).. Spin-spin relaxation probes the z-axis fluctuations in magnetic field which arise from copper and oxygen spin fluctuations (T1 processes) and field fluctuations from vortices. The vortex contribution is observable only for vortices locally fluctuating in the pinned or frozen state. The vortex field fluctuations have a lorentzian spectral density, in contrast to the normal state relaxation which is well described by a gaussian. Work at Northwestern University is supported by the NSF (DMR 91-20000) through the Science and Technology Center for Superconductivity. The NHMFL is supported through the NSF and the state of Florida.

  14. Antiferromagnetic spin structure and negative thermal expansion of Li2Ni (WO4)2

    NASA Astrophysics Data System (ADS)

    Karna, Sunil K.; Wang, C. W.; Sankar, R.; Avdeev, M.; Singh, A.; Panneer Muthuselvam, I.; Singh, V. N.; Guo, G. Y.; Chou, F. C.

    2015-07-01

    We report the results of a study on the crystal and magnetic structure of Li2Ni (WO4)2 with a neutron diffraction technique. The Ni2 + spins of S = 1 for NiO6 octahedra are coupled via corner-sharing, nonmagnetic double tungstate groups in a super-superexchange route. Two magnetic anomalies at TN 1˜ 18 K and TN 2˜ 13 K are revealed from the measured magnetic susceptibility χ (T), and TN 2 is confirmed to be the onset of a commensurate long-range antiferromagnetic (AF) ordering through neutron diffraction. A negative thermal expansion phenomenon is observed below TN 2, which has been interpreted as a result of competing normal thermal contraction and long-range AF spin ordering through counterbalanced WO4 and NiO6 polyhedral local distortion. The AF spin structure has been modeled and used to show that Ni spins with a saturated magnetic moment of ˜1.90 (27 )μB that lies in the a -c plane approximately 46∘(±10∘) off the a axis. The experimental results are compared and found to be consistent with theoretical calculations using density-functional theory with a generalized gradient approximation plus on-site Coulomb interaction.

  15. 40 CFR 180.1206 - Aspergillus flavus AF36; exemption from the requirement of a tolerance.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 23 2010-07-01 2010-07-01 false Aspergillus flavus AF36; exemption... FOOD Exemptions From Tolerances § 180.1206 Aspergillus flavus AF36; exemption from the requirement of a... pesticide Aspergillus flavus AF36 in or on cotton, gin byproducts; cotton, hulls; cotton, meal;...

  16. Particle number fluctuations in a canonical ensemble

    SciTech Connect

    Begun, V.V.; Gazdzicki, M.; Gorenstein, M.I.; Zozulya, O.S.

    2004-09-01

    Fluctuations of charged particle number are studied in the canonical ensemble. In the infinite volume limit the fluctuations in the canonical ensemble are different from the fluctuations in the grand canonical one. Thus, the well-known equivalence of both ensembles for the average quantities does not extend for the fluctuations. In view of the possible relevance of the results for the analysis of fluctuations in nuclear collisions at high energies, a role of the limited kinematical acceptance is studied.

  17. 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.

  18. 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

  19. 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…

  20. Stage fluctuations of Wisconsin lakes

    USGS Publications Warehouse

    House, Leo B.

    1985-01-01

    This report describes lake-stage fluctuations of 83 gaged lakes in Wisconsin and presents techniques for estimating stage fluctuation at ungaged lakes. Included are stage information at 83 lakes and stage-frequency data for 32 of these lakes that had sufficient record for analysis. Lakes are classified by a hydrologic-topographic lake classification scheme as ground-water flowthrough (GWF) lakes, surface-water drainage (SWD) lakes, and surface-water flow-through (SWF) lakes. Lakes within the same class were found to have similar water-level fluctuations. The lake-stage records indicate that most annual maximums occur during the months of May and June for all three classes. Annual minimum lake levels generally occur in September for surface-water drainage lakes, in March for surface-water flowthrough lakes, and in November for ground-water flow-through lakes. Data for each lake include location, period of water-level record, hydrologic classification, drainage area, surface area, lake volume, maximum depth, long-term mean stage and its standard deviation, maximum and minimum observed lake stage, and the average annual lake-stage fluctuation.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Extrinsic Spin Hall Effect Induced by Resonant Skew Scattering in Graphene

    NASA Astrophysics Data System (ADS)

    Ferreira, Aires; Rappoport, Tatiana G.; Cazalilla, Miguel A.; Castro Neto, A. H.

    2015-03-01

    We show that the extrinsic spin Hall effect can be engineered in monolayer graphene by decoration with small doses of adatoms, molecules, or nanoparticles originating local spin-orbit perturbations. The analysis of the single impurity scattering problem shows that intrinsic and Rashba spin-orbit local couplings enhance the spin Hall effect via skew scattering of charge carriers in the resonant regime. The solution of the transport equations for a random ensemble of spin-orbit impurities reveals that giant spin Hall currents are within the reach of the current state of the art in device fabrication. The spin Hall effect is robust with respect to thermal fluctuations and disorder averaging. The author acknowledges support from the National Research Foundation-Competitive Research Programme through Grant No. R-144-000-295-281.

  9. 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

    2016-03-01

    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.

  10. Fluctuating Hydrodynamics Confronts the Rapidity Dependence of Transverse Momentum Fluctuations

    NASA Astrophysics Data System (ADS)

    Pokharel, Rajendra; Gavin, Sean; Moschelli, George

    2012-10-01

    Interest in the development of the theory of fluctuating hydrodynamics is growing [1]. Early efforts suggested that viscous diffusion broadens the rapidity dependence of transverse momentum correlations [2]. That work stimulated an experimental analysis by STAR [3]. We attack this new data along two fronts. First, we compute STAR's fluctuation observable using the NeXSPheRIO code, which combines fluctuating initial conditions from a string fragmentation model with deterministic viscosity-free hydrodynamic evolution. We find that NeXSPheRIO produces a longitudinal narrowing, in contrast to the data. Second, we study the hydrodynamic evolution using second order causal viscous hydrodynamics including Langevin noise. We obtain a deterministic evolution equation for the transverse momentum density correlation function. We use the latest theoretical equations of state and transport coefficients to compute STAR's observable. The results are in excellent accord with the measured broadening. In addition, we predict features of the distribution that can distinguish 2nd and 1st order diffusion. [4pt] [1] J. Kapusta, B. Mueller, M. Stephanov, arXiv:1112.6405 [nucl-th].[0pt] [2] S. Gavin and M. Abdel-Aziz, Phys. Rev. Lett. 97, 162302 (2006)[0pt] [3] H. Agakishiev et al., STAR, STAR, Phys. Lett. B704

  11. Chromodynamic fluctuations in quark-gluon plasma

    SciTech Connect

    Mrowczynski, Stanislaw

    2008-05-15

    Fluctuations of chromodynamic fields in the collisionless quark-gluon plasma are found as a solution of the initial value linearized problem. The plasma initial state is on average colorless, stationary, and homogeneous. When the state is stable, the initial fluctuations decay exponentially and in the long-time limit a stationary spectrum of fluctuations is established. For the equilibrium plasma it reproduces the spectrum which is provided by the fluctuation-dissipation relation. Fluctuations in the unstable plasma, where the memory of initial fluctuations is not lost, are also discussed.

  12. 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.

  13. Wild-Type U2AF1 Antagonizes the Splicing Program Characteristic of U2AF1-Mutant Tumors and Is Required for Cell Survival

    PubMed Central

    Fei, Dennis Liang; Motowski, Hayley; Chatrikhi, Rakesh; Gao, Shaojian; Kielkopf, Clara L.; Varmus, Harold

    2016-01-01

    We have asked how the common S34F mutation in the splicing factor U2AF1 regulates alternative splicing in lung cancer, and why wild-type U2AF1 is retained in cancers with this mutation. A human lung epithelial cell line was genetically modified so that U2AF1S34F is expressed from one of the two endogenous U2AF1 loci. By altering levels of mutant or wild-type U2AF1 in this cell line and by analyzing published data on human lung adenocarcinomas, we show that S34F-associated changes in alternative splicing are proportional to the ratio of S34F:wild-type gene products and not to absolute levels of either the mutant or wild-type factor. Preferential recognition of specific 3′ splice sites in S34F-expressing cells is largely explained by differential in vitro RNA-binding affinities of mutant versus wild-type U2AF1 for those same 3′ splice sites. Finally, we show that lung adenocarcinoma cell lines bearing U2AF1 mutations do not require the mutant protein for growth in vitro or in vivo. In contrast, wild-type U2AF1 is required for survival, regardless of whether cells carry the U2AF1S34F allele. Our results provide mechanistic explanations of the magnitude of splicing changes observed in U2AF1-mutant cells and why tumors harboring U2AF1 mutations always retain an expressed copy of the wild-type allele. PMID:27776121

  14. 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

  15. Control and Detection of the Larmor Precession of F = 2 87Rb Bose-Einstein Condensates by Ramsey Interferometry and Spin-Echo

    NASA Astrophysics Data System (ADS)

    Eto, Yujiro; Sekine, Sawako; Hasegawa, Sho; Sadgrove, Mark; Saito, Hiroki; Hirano, Takuya

    2013-05-01

    Radio-frequency pulses are applied to probe and control the Larmor precession of a spin-2 Bose-Einstein condensate subject to a magnetic field gradient. Using the techniques of Ramsey interferometry and Stern-Gerlach absorption imaging, a helical spin pattern was clearly observed as spatial variations in the atomic density distribution. We experimentally show that the spin echo technique reduces the effects of spatially inhomogeneous and temporally fluctuating spin evolution, and improves the repeatability of the interferometry.

  16. Spin dynamics of polarons and polaron pairs in a random hyperfine field

    NASA Astrophysics Data System (ADS)

    Roundy, Robert C.

    Spin-dependent recombination of polaron pairs and spin relaxation of a single polaron are the most fundamental processes are responsible for the performance of organic spintronics-based devices such as light-emitting diodes and organic spin valves. In organic materials, with no spin-orbit coupling, both processes are due to random hyperfine fields created by protons neighboring the polaron sites. The essence of spin-dependent recombination is that in order to recombine the pair must be in the singlet state. Hyperfine fields acting on the electron and hole govern the spin-dynamics of localized pairs during the waiting time for recombination. We demonstrate that for certain domain of trapping configurations of hyperfine fields, crossover to the singlet state is quenched. This leads to the blocking of current. The phenomenon of organic magnetoresistance (OMAR) is described by counting the weights of trapping configurations as a function of magnetic field. This explains the universality of the lineshapes of the OMAR curves. In finite samples incomplete averaging over the hyperfine fields gives rise to mesoscopic fluctuations of the current response. We also demonstrate that under the condition of magnetic resonance, new trapping configurations emerge. This leads to nontrivial evolution of current through the sample with microwave power. When discussing spin-relaxation two questions can be asked: (a) How does the local spin polarization decay as a function of distance from the spin-polarized injector? (b) How does the injected spin decay as a function of time after spatial averaging? With regard to (a), we demonstrate that, while decaying exponentially on average, local spin-polarization exhibits giant fluctuations from point to point. Concerning (b), we find that for a spin-carrier which moves diffusively in low dimensions the decay is faster than a simple exponent. The underlying physics for both findings is that in describing spin evolution it is necessary to add up

  17. 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.

  18. 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

  19. 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.

  20. 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.

  1. Strong hyperfine-induced modulation of an optically driven hole spin in an InAs quantum dot

    NASA Astrophysics Data System (ADS)

    Carter, S. G.; Economou, Sophia E.; Greilich, A.; Barnes, Edwin; Sweeney, T.; Bracker, A. S.; Gammon, D.

    2014-02-01

    Compared to electrons, holes in InAs quantum dots have a significantly weaker hyperfine interaction that leads to less dephasing from nuclear spins. Thus many recent studies have suggested that nuclear spins are unimportant for hole-spin dynamics compared to electric-field fluctuations. We show that the hole hyperfine interaction can have a strong effect on hole-spin coherence measurements through a nuclear feedback effect. The nuclear polarization is generated through a unique process that is dependent on the anisotropy of the hole hyperfine interaction and the coherent precession of nuclear spins, giving rise to strong modulation at the nuclear precession frequency.

  2. 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.

  3. 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.

  4. 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

    2014-08-22

    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.

  5. 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.

  6. 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.

  7. 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.

  8. Spin accumulation in the extrinsic spin Hall effect

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Fabian, J.; Žutić, I.; Das Sarma, S.

    2005-12-01

    The drift-diffusion formalism for spin-polarized carrier transport in semiconductors is generalized to include spin-orbit coupling. The theory is applied to treat the extrinsic spin Hall effect using realistic boundary conditions. It is shown that carrier and spin-diffusion lengths are modified by the presence of spin-orbit coupling and that spin accumulation due to the extrinsic spin Hall effect is strongly and qualitatively influenced by boundary conditions. Analytical formulas for the spin-dependent carrier recombination rates and inhomogeneous spin densities and currents are presented.

  9. 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.

  10. Effect of phase fluctuations on the Fulde-Ferrell-Larkin-Ovchinnikov state in a three-dimensional Fermi gas

    NASA Astrophysics Data System (ADS)

    Devreese, Jeroen P. A.; Tempere, Jacques

    2014-01-01

    In ultracold Fermi gases, the effect of spin imbalance on superfluidity has been the subject of intense study. One of the reasons for this is that spin imbalance frustrates the Bardeen-Cooper-Schrieffer (BCS) superfluid pairing mechanism, in which fermions in different spin states combine into Cooper pairs with zero momentum. In 1964, it was proposed that an exotic superfluid state called the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, in which the Cooper pairs have nonzero momentum, could exist in a spin-imbalanced Fermi gas. At the saddle-point (mean-field) level, it has been shown that the FFLO state only occupies a very small sliver in the ground-state phase diagram of a three-dimensional (3D) Fermi gas. However, a question that remains to be investigated is as follows: What is the influence of phase fluctuations on the FFLO state? In this work, we show that phase fluctuations only lead to relatively small quantitative corrections to the presence of the FFLO state in the saddle-point phase diagram of a 3D spin-imbalanced Fermi gas. Starting from the partition function of the system, we calculate the effective action within the path-integral adiabatic approximation. The action is then expanded up to second order in the fluctuation field around the saddle point, leading to the fluctuation free energy. Using this free energy, we calculate corrections due to phase fluctuations to the BCS-FFLO transition in the saddle-point phase diagram. At temperatures at which the FFLO state exists, we find only small corrections to the size of the FFLO area. Our results suggest that fluctuations of the phase of the FFLO order parameter, which can be interpreted as an oscillation of its momentum vector, do not cause an instability of the FFLO state with respect to the BCS state.

  11. 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

  12. 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.

  13. Current fluctuations in stochastic lattice gases.

    PubMed

    Bertini, L; De Sole, A; Gabrielli, D; Jona-Lasinio, G; Landim, C

    2005-01-28

    We study current fluctuations in lattice gases in the macroscopic limit extending the dynamic approach for density fluctuations developed in previous articles. More precisely, we establish a large deviation theory for the space-time fluctuations of the empirical current which include the previous results. We then estimate the probability of a fluctuation of the average current over a large time interval. It turns out that recent results by Bodineau and Derrida [Phys. Rev. Lett. 92, 180601 (2004)

  14. Improvement and biological applications of fluorescent probes for zinc, ZnAFs.

    PubMed

    Hirano, Tomoya; Kikuchi, Kazuya; Urano, Yasuteru; Nagano, Tetsuo

    2002-06-12

    The development and cellular applications of novel fluorescent probes for Zn2+, ZnAF-1F, and ZnAF-2F are described. Fluorescein is used as a fluorophore of ZnAFs, because its excitation and emission wavelengths are in the visible range, which minimizes cell damage and autofluorescence by excitation light. N,N-Bis(2-pyridylmethyl)ethylenediamine, used as an acceptor for Zn2+, is attached directly to the benzoic acid moiety of fluorescein, resulting in very low quantum yields of 0.004 for ZnAF-1F and 0.006 for ZnAF-2F under physiological conditions (pH 7.4) due to the photoinduced electron-transfer mechanism. Upon the addition of Zn2+, the fluorescence intensity is quickly increased up to 69-fold for ZnAF-1F and 60-fold for ZnAF-2F. Apparent dissociation constants (K(d)) are in the nanomolar range, which affords sufficient sensitivity for biological applications. ZnAFs do not fluoresce in the presence of other biologically important cations such as Ca2+ and Mg2+, and are insensitive to change of pH. The complexes with Zn2+ of previously developed ZnAFs, ZnAF-1, and ZnAF-2 decrease in fluorescence intensity below pH 7.0 owing to protonation of the phenolic hydroxyl group of fluorescein, whose pKa value is 6.2. On the other hand, the Zn2+ complexes of ZnAF-1F and ZnAF-2F emit stable fluorescence around neutral and slightly acidic conditions because the pKa values are shifted to 4.9 by substitution of electron-withdrawing fluorine at the ortho position of the phenolic hydroxyl group. For application to living cells, the diacetyl derivative of ZnAF-2F, ZnAF-2F DA, was synthesized. ZnAF-2F DA can permeate through the cell membrane, and is hydrolyzed by esterase in the cytosol to yield ZnAF-2F, which is retained in the cells. Using ZnAF-2F DA, we could measure the changes of intracellular Zn2+ in cultured cells and hippocampal slices.

  15. Crossover from spin waves to diffusive spin excitations in underdoped Ba(Fe1-xCox)2 As2

    SciTech Connect

    Tucker, G S; Fernandes, R M; Pratt, D K; Thaler, A; Ni, N; Marty, K; Christianson, A D; Lumsden, M D; Sales, B C; Sefat, A S; Bud'ko, S L; Canfield, P C; Kreyssig, A; Goldman, A I; McQueeney, R J

    2014-05-01

    Using inelastic neutron scattering, we show that the onset of superconductivity in underdoped Ba(Fe1-xCox)2As2 coincides with a crossover from well-defined spin waves to overdamped and diffusive spin excitations. This crossover occurs despite the presence of long-range stripe antiferromagnetic order for samples in a compositional range from x=0.04 to 0.055, and is a consequence of the shrinking spin-density wave gap and a corresponding increase in the particle-hole (Landau) damping. The latter effect is captured by a simple itinerant model relating Co doping to changes in the hot spots of the Fermi surface. We argue that the overdamped spin fluctuations provide a pairing mechanism for superconductivity in these materials.

  16. 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.

  17. Dielectric permittivity and temperature effects on spin-spin couplings studied on acetonitrile.

    PubMed

    Sahakyan, Aleksandr B; Shahkhatuni, Astghik A; Shahkhatuni, Aleksan G; Panosyan, Henry A

    2008-01-01

    Dielectric permittivity (epsilon) and temperature effects on indirect spin-spin coupling constants were studied using acetonitrile as a probe molecule. Experiments were accompanied by hybrid DFT (density functional theory) studies, where the solvent was modeled using the polarization continuum model. Owing to its numerous types of J-couplings, acetonitrile is a very convenient molecule against which various basis sets can be tested or the best basis set can be selected for a given study. The results show reasonable agreement between calculated and experimental values. According to our data, scalar spin-spin coupling constants undergo substantial shifts at lower values of the dielectric constant. Thus J-coupling values are not transferable between measurements made at differing epsilon-conditions, and the assumption of the epsilon-independence of the J-coupling can lead to crucial mistakes in experiments using low-epsilon media. Dielectric permittivity also causes small geometric fluctuations within the molecule, which themselves can affect J-coupling values. Examinations of the results computed with frozen and relaxed geometries show that geometry mediation mostly affects the spin-dipole term of the J-coupling; hence, for accurate evaluation of the latter, frozen geometries are not acceptable. Another interesting fact revealed is the connection between the solvent dielectric properties and the temperature-dependence slopes of J-couplings in corresponding media. PMID:18098231

  18. Electron spin resonance and muon spin relaxation studies of single molecule magnets

    NASA Astrophysics Data System (ADS)

    Blundell, Stephen

    2005-03-01

    We use a combination of electron spin resonance, muon-spin relaxation and SQUID magnetometry to study polycrystalline and single crystal samples of various novel single molecule magnets (SMMs). We also describe a theoretical framework which can be used to analyse the results from each technique. Electron spin resonance measurements are performed using a millimetre vector network analyser and data are presented on several SMM systems using microwave frequencies from 40-300 GHz. Muon-spin relaxation measurements have been performed on several SMM systems in applied longitudinal magnetic field and in temperatures down to 20 mK. The results suggest that dynamic local magnetic field fluctuations are responsible for the relaxation of the muon spin ensemble. We discuss what can be learned from these experiments concerning SMMs and suggest experiments which can probe the quantum nature of SMMs. (Work in collaboration with S Sharmin, T Lancaster, A Ardavan, F L Pratt, E J L McInnes and R E P Winpenny) References: S. J. Blundell and F. L. Pratt, J. Phys.: Condens. Matter 16, R771 (2004); T. Lancaster et al., J. Phys.: Condens. Matter 16, S4563 (2004); S. Sharmin et al., Appl. Phys. Lett. in press.

  19. Spin caloritronics in graphene

    SciTech Connect

    Ghosh, Angsula; Frota, H. O.

    2015-06-14

    Spin caloritronics, the combination of spintronics with thermoelectrics, exploiting both the intrinsic spin of the electron and its associated magnetic moment in addition to its fundamental electronic charge and temperature, is an emerging technology mainly in the development of low-power-consumption technology. In this work, we study the thermoelectric properties of a Rashba dot attached to two single layer/bilayer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current, which depends on the temperature and chemical potential. We demonstrate that the Rashba dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature, and also the Rashba term have been observed.

  20. Spin caloritronics in graphene

    NASA Astrophysics Data System (ADS)

    Frota, H. O.; Ghosh, Angsula

    2014-08-01

    Spin caloritronics, the combination of spintronics with thermoelectrics, based on spin and heat transport has attracted a great attention mainly in the development of low-power-consumption technology. In this work we study the thermoelectric properties of a quantum dot attached to two single layer graphene sheets as leads. The temperature difference on the two graphene leads induces a spin current which depends on the temperature and chemical potential. We demonstrate that the quantum dot behaves as a spin filter for selected values of the chemical potential and is able to filter electrons by their spin orientation. The spin thermopower has also been studied where the effects of the chemical potential, temperature and also the Coulomb repulsion due to the double occupancy of an energy level have been observed.

  1. Suppression of ferroelectricity and quantum fluctuations in Ru-doped TbMnO3

    NASA Astrophysics Data System (ADS)

    Guo, Y. Y.; Guo, Y. J.; Zhang, N.; Lin, L.; Liu, J.-M.

    2012-01-01

    We investigate the effects of Ru-doping in polycrystalline TbMn1- x Ru x O3 ( x≤0.10) on the multiferroicity. It is observed that the Ru substitution gradually melts away the dielectric anomaly at the ferroelectric transition point and the ferroelectricity by suppressing the polarization, accompanied with a surprising low-temperature dielectric plateau. While it is reasonable to observe the significant suppression of ferroelectricity, owing to the fact that the Ru-doping disrupts the Mn spiral spin ordering and reduces the Mn-Mn spin angle, quantum fluctuations associated with the Ru substitution, responsible for the low-temperature dielectric plateau, seems to be significant.

  2. 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

  3. Picosecond Spin Caloritronics

    NASA Astrophysics Data System (ADS)

    Cahill, David G.

    The coupling of spin and heat, i.e., spin caloritronics, gives rise to new physical phenomena in nanoscale spin devices and new ways to manipulate local magnetization. Our work in this field takes advantage of recent advances in the measurement and understanding of heat transport at the nanoscale using ultrafast lasers. We use a picosecond duration pump laser pulses as a source of heat and picosecond duration probe laser pulses to detect changes in temperature, spin accumulation, and spin transfer torque using a combination of time-domain thermoreflectance and time-resolved magneto-optic Kerr effect Our pump-probe optical methods enable us to change the temperature of ferromagnetic layers on a picosecond time-scale and generate enormous heat fluxes on the order of 100 GW m-2 that persist for ~ 30 ps. Thermally-driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The spin-dependent Seebeck effect of a perpendicular ferromagnetic layer converts a heat current into spin current, which in turn can be used to exert a spin transfer torque (STT) on a second ferromagnetic layer with in-plane magnetization. Using a [Co,Ni] multilayer as the source of spin, an energy fluence of ~ 4 J m-2 creates thermal STT sufficient to induce ~ 1 % tilting of the magnetization of a 2 nm-thick CoFeB layer.

  4. Spin coating apparatus

    DOEpatents

    Torczynski, John R.

    2000-01-01

    A spin coating apparatus requires less cleanroom air flow than prior spin coating apparatus to minimize cleanroom contamination. A shaped exhaust duct from the spin coater maintains process quality while requiring reduced cleanroom air flow. The exhaust duct can decrease in cross section as it extends from the wafer, minimizing eddy formation. The exhaust duct can conform to entrainment streamlines to minimize eddy formation and reduce interprocess contamination at minimal cleanroom air flow rates.

  5. 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

  6. Replica symmetry breaking in a quantum spin glass-antiferromagnetic Kondo lattice

    NASA Astrophysics Data System (ADS)

    Magalhaes, S. G.; Zimmer, F. M.; Coqblin, B.

    2008-04-01

    The competition between the Kondo effect and the glassy magnetic order has been studied in a theoretical model of a Kondo lattice with an intrasite Kondo interaction. The spin glass (SG) and the antiferromagnetic (AF) orderings are described by two Kondo sublattices with infinite-range Ising SG interactions among localized spins and the disordered interactions can occur with spins of same sublattices and between spins of distinct sublattices. A transverse field Γ is introduced in the effective model as a quantum mechanism to produce spin flipping. The problem is formulated in a Grassmann path integral formalism. The disorder is treated within the replica trick in one-step replica symmetry breaking (1S-RSB). The static ansatz is adopted to get a mean-field expression for the free energy and order parameters. Results show a transition from the AF order to an RSB region with a finite staggered magnetization (mixed phase) when temperature T decreases for low values of the Kondo interaction. The SG phase is not observed below the mixed phase for 1S-RSB solution, in contrast with previous replica symmetry (RS) results. The Γ field suppresses the Neel temperature leading it to a quantum critical point.

  7. Rockets for spin recovery

    NASA Technical Reports Server (NTRS)

    Whipple, R. D.

    1980-01-01

    The potential effectiveness of rockets as an auxiliary means for an aircraft to effect recovery from spins was investigated. The advances in rocket technology produced by the space effort suggested that currently available systems might obviate many of the problems encountered in earlier rocket systems. A modern fighter configuration known to exhibit a flat spin mode was selected. An analytical study was made of the thrust requirements for a rocket spin recovery system for the subject configuration. These results were then applied to a preliminary systems study of rocket components appropriate to the problem. Subsequent spin tunnel tests were run to evaluate the analytical results.

  8. Spin-dependent electron transport in nanoscale samples

    NASA Astrophysics Data System (ADS)

    Wei, Yaguang

    In this thesis, we describe the research in which we use metallic nanoparticles to explore spin-dependent electron transport at nanometer scale. Nanoscale samples were fabricated by using a state of the art electron beam lithography and shadow evaporation technique. We have investigated spin relaxation and decoherence in metallic grains as a function of bias voltage and magnetic field at low temperatures (down to ˜30mK). At low temperatures, the discrete energy levels within a metallic nanoparticle provides a new means to study the physics of the spin-polarized electron tunneling. We describe measurements of spin-polarized tunneling via discrete energy levels of single Aluminum grain. Spin polarized current saturates quickly as a function of bias voltage, which demonstrates that the ground state and the lowest excited states carry spin polarized current. The ratio of electron-spin relaxation time (T1) to the electron-phonon relaxation rate is in quantitative agreement with the Elliot-Yafet scaling, an evidence that spin-relaxation in Al grains is driven by the spin-orbit interaction. The spin-relaxation time of the low-lying excited states is T1 ≈ 0.7 mus and 0.1 mus in two samples, showing that electron spin in a metallic grain could be a potential candidate for quantum information research. We also present measurements of mesoscopic resistance fluctuations in cobalt nanoparticles at low temperature and study how the fluctuations with bias voltage, bias fingerprints, respond to magnetization-reversal processes. Bias fingerprints rearrange when domains are nucleated or annihilated. The domain wall causes an electron wave function-phase shift of ˜5 pi. The phase shift is not caused by the Aharonov-Bohm effect; we explain how it arises from the mistracking effect, where electron spins lag in orientation with respect to the moments inside the domain wall. The dephasing length at low temperatures is only 30 nm, which is attributed to the large magnetocrystalline

  9. Muon-spin relaxation study of the double perovskite insulators Sr2 BOsO6 (B  =  Fe, Y, ln).

    PubMed

    Williams, R C; Xiao, F; Thomas, I O; Clark, S J; Lancaster, T; Cornish, G A; Blundell, S J; Hayes, W; Paul, A K; Felser, C; Jansen, M

    2016-02-24

    We present the results of zero-field muon-spin relaxation measurements made on the double perovskite insulators Sr2 BOsO6 (B = Fe,Y, In). Spontaneous muon-spin precession indicative of quasistatic long range magnetic ordering is observed in Sr2FeOsO6 within the AF1 antiferromagnetic phase for temperatures below [Formula: see text] K. Upon cooling below T2≈67 K the oscillations cease to be resolvable owing to the coexistence of the AF1 and AF2 phases, which leads to a broader range of internal magnetic fields. Using density functional calculations we identify a candidate muon stopping site within the unit cell, which dipole field simulations show to be consistent with the proposed magnetic structure. The possibility of incommensurate magnetic ordering is discussed for temperatures below TN = 53 K and 25 K for Sr2YOsO6 and Sr2InOsO6, respectively.

  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. 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

  12. 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.

  13. Feedback-tuned, noise resilient gates for encoded spin qubits

    NASA Astrophysics Data System (ADS)

    Bluhm, Hendrik

    Spin 1/2 particles form native two level systems and thus lend themselves as a natural qubit implementation. However, encoding a single qubit in several spins entails benefits, such as reducing the resources necessary for qubit control and protection from certain decoherence channels. While several varieties of such encoded spin qubits have been implemented, accurate control remains challenging, and leakage out of the subspace of valid qubit states is a potential issue. Optimal performance typically requires large pulse amplitudes for fast control, which is prone to systematic errors and prohibits standard control approaches based on Rabi flopping. Furthermore, the exchange interaction typically used to electrically manipulate encoded spin qubits is inherently sensitive to charge noise. I will discuss all-electrical, high-fidelity single qubit operations for a spin qubit encoded in two electrons in a GaAs double quantum dot. Starting from a set of numerically optimized control pulses, we employ an iterative tuning procedure based on measured error syndromes to remove systematic errors.Randomized benchmarking yields an average gate fidelity exceeding 98 % and a leakage rate into invalid states of 0.2 %. These gates exhibit a certain degree of resilience to both slow charge and nuclear spin fluctuations due to dynamical correction analogous to a spin echo. Furthermore, the numerical optimization minimizes the impact of fast charge noise. Both types of noise make relevant contributions to gate errors. The general approach is also adaptable to other qubit encodings and exchange based two-qubit gates.

  14. Reduction of phase noise in nanowire spin orbit torque oscillators

    PubMed Central

    Yang, Liu; Verba, Roman; Tiberkevich, Vasil; Schneider, Tobias; Smith, Andrew; Duan, Zheng; Youngblood, Brian; Lenz, Kilian; Lindner, Jürgen; Slavin, Andrei N.; Krivorotov, Ilya N.

    2015-01-01

    Spin torque oscillators (STOs) are compact, tunable sources of microwave radiation that serve as a test bed for studies of nonlinear magnetization dynamics at the nanometer length scale. The spin torque in an STO can be created by spin-orbit interaction, but low spectral purity of the microwave signals generated by spin orbit torque oscillators hinders practical applications of these magnetic nanodevices. Here we demonstrate a method for decreasing the phase noise of spin orbit torque oscillators based on Pt/Ni80Fe20 nanowires. We experimentally demonstrate that tapering of the nanowire, which serves as the STO active region, significantly decreases the spectral linewidth of the generated signal. We explain the observed linewidth narrowing in the framework of the Ginzburg-Landau auto-oscillator model. The model reveals that spatial non-uniformity of the spin current density in the tapered nanowire geometry hinders the excitation of higher order spin-wave modes, thus stabilizing the single-mode generation regime. This non-uniformity also generates a restoring force acting on the excited self-oscillatory mode, which reduces thermal fluctuations of the mode spatial position along the wire. Both these effects improve the STO spectral purity. PMID:26592432

  15. Spin dynamics of the ordered dipolar-octupolar pseudospin-1/2 pyrochlore Nd2Zr2O7 probed by muon spin relaxation

    NASA Astrophysics Data System (ADS)

    Xu, J.; Balz, C.; Baines, C.; Luetkens, H.; Lake, B.

    2016-08-01

    We present a muon spin relaxation study on the Ising pyrochlore Nd2Zr2O7 which develops an "all-in-all-out" magnetic order below 0.4 K. At 20 mK, far below the ordering transition temperature, the zero-field muon spin relaxation spectra show no static features and can be well described by a dynamical Gaussian-broadened Gaussian Kubo-Toyabe function indicating strong fluctuations of the ordered state. The spectra of the paramagnetic state (below 4.2 K) reveal anomalously slow paramagnetic spin dynamics and show only a small difference with the spectra of the ordered state. We find that the fluctuation rate decreases with decreasing temperature and becomes nearly temperature independent below the transition temperature, indicating persistent slow spin dynamics in the ground state. The field distribution width shows a small but sudden increase at the transition temperature and then becomes almost constant. The spectra in applied longitudinal fields are well fitted by the conventional dynamical Gaussian Kubo-Toyabe function, which further supports the dynamical nature of the ground state. The fluctuation rate shows a peak as a function of external field which is associated with a field-induced spin-flip transition. The strong dynamics in the ordered state is attributed to the transverse coupling of the Ising spins introduced by the multipole interactions.

  16. 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.

  17. 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.

  18. Simulation of nanoscale density fluctuations

    NASA Astrophysics Data System (ADS)

    Reiss, Howard; Bowles, Richard K.

    2000-11-01

    Problems associated with the simulation of density fluctuations of limited breadth in a small cell are exposed and studied. The fluctuations are viewed as "physical clusters" of the type that might appear in nucleation processes and related phenomena. One of the most important features of the study stems from the fact that the simulation of a small heterogeneity in a macroscopic system presents problems that do not occur in the simulation of a bulk homogeneous property of the system. For example, once having simulated the probability of appearance of the fluctuation in a small cell, how is that result to be "mapped" onto the macrosystem in order to specify the equilibrium number of such fluctuations in that system? This problem is closely associated with the proper separation of the translational and internal degrees of freedom of the system, and has arisen in a number of fields, including the theory of nucleation. There are other problems associated with exponential dependence of cluster probability on the work of formation of the cluster, and also with rareness of some important clusters. In the latter case, simulative "umbrella sampling" does not always solve the entire problem. The present study is confined to clusters that appear in rarefied gases. Such systems are important in a number of scenarios, including nucleation processes. Several cluster models are considered including those consisting of molecules confined to a "container" of fixed volume and those constructed on the center of mass of the cluster. Connections between them are derived and rigorous solutions to the mapping problem are derived. Quantitative measures for the accuracy of approximate solutions, applied to cases in which the cluster is compact, are provided and exact solutions are provided even for the noncompact case. Some surprising results emerge from the study, among which is the fact that a cluster whose location is determined by one of its molecules, does not always have a

  19. Technological advances in site-directed spin labeling of proteins.

    PubMed

    Hubbell, Wayne L; López, Carlos J; Altenbach, Christian; Yang, Zhongyu

    2013-10-01

    Molecular flexibility over a wide time range is of central importance to the function of many proteins, both soluble and membrane. Revealing the modes of flexibility, their amplitudes, and time scales under physiological conditions is the challenge for spectroscopic methods, one of which is site-directed spin labeling EPR (SDSL-EPR). Here we provide an overview of some recent technological advances in SDSL-EPR related to investigation of structure, structural heterogeneity, and dynamics of proteins. These include new classes of spin labels, advances in measurement of long range distances and distance distributions, methods for identifying backbone and conformational fluctuations, and new strategies for determining the kinetics of protein motion.

  20. Nuclear moment of inertia and spin distribution of nuclear levels

    SciTech Connect

    Alhassid, Y.; Fang, L.; Liu, S.; Bertsch, G.F.

    2005-12-15

    We introduce a simple model to calculate the nuclear moment of inertia at finite temperature. This moment of inertia describes the spin distribution of nuclear levels in the framework of the spin-cutoff model. Our model is based on a deformed single-particle Hamiltonian with pairing interaction and takes into account fluctuations in the pairing gap. We derive a formula for the moment of inertia at finite temperature that generalizes the Belyaev formula for zero temperature. We show that a number-parity projection explains the strong odd-even effects observed in shell model Monte Carlo studies of the nuclear moment of inertia in the iron region.

  1. Itinerancy-enhanced quantum fluctuation of magnetic moments in iron-based superconductors.

    PubMed

    Tam, Yu-Ting; Yao, Dao-Xin; Ku, Wei

    2015-09-11

    We investigate the influence of itinerant carriers on the 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 are found to induce a significant amount of spatial and temporal quantum fluctuation that leads to the observed small ordered moment. Interestingly, the underlying mechanism is shown to be an intrapocket nesting-associated long-range coupling rather than the previously believed ferromagnetic double-exchange effect. This challenges the validity of ferromagnetically compensated first-neighbor coupling 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. PMID:26406850

  2. Nuclear magnetic resonance studies of pseudospin fluctuations in URu2Si2

    DOE PAGES

    Shirer, K. R.; Haraldsen, J. T.; Dioguardi, A. P.; Crocker, J.; apRoberts-Warren, N.; Shockley, A. C.; Lin, C. -H.; Nisson, D. M.; Cooley, J. C.; Janoschek, M.; et al

    2013-09-26

    Here, we report 29Si nuclear magnetic resonance measurements in single crystals and aligned powders of URu2Si2 in the hidden order and paramagnetic phases. The spin-lattice relaxation data reveal evidence of pseudospin fluctuations of U moments in the paramagnetic phase. We find evidence for partial suppression of the density of states below 30 K and analyze the data in terms of a two-component spin-fermion model. We propose that this behavior is a realization of a pseudogap between the hidden-order transition THO and 30 K. This behavior is then compared to other materials that demonstrate precursor fluctuations in a pseudogap regime abovemore » a ground state with long-range order.« less

  3. Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors

    SciTech Connect

    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 coupling 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.

  4. Itinerancy enhanced quantum fluctuation of magnetic moments in iron-based superconductors

    DOE PAGES

    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

  5. The Global Anticoagulant Registry in the FIELD-Atrial Fibrillation (GARFIELD-AF) : Exploring the changes in anticoagulant practice in patients with non-valvular atrial fibrillation in the Netherlands.

    PubMed

    Ten Cate, V; Ten Cate, H; Verheugt, F W A

    2016-10-01

    There are over 385,000 cases of atrial fibrillation (AF) in the Netherlands, with over 45,000 new cases each year. Among other things, AF patients are at high risk of stroke. Patients are often prescribed oral anticoagulation, such as vitamin K antagonists (VKA), to mitigate these risks. A recently introduced class of oral anticoagulants, non-vitamin K antagonists (NOAC), is quickly gaining currency in global clinical practice. This study provides insight into the changes these new drugs will bring about in Dutch clinical practice.GARFIELD-AF is a large-scale observational AF patient registry initiated in 2009 to track the evolution of global anticoagulation practice, and to study the impact of NOAC therapy in AF in particular. The registry includes a wide array of baseline characteristics and has a particular focus on: (1) bleeding and thromboembolic events; (2) international normalised ratio fluctuations; and (3) therapy compliance and persistence patterns. The results in this paper provide the baseline characteristics of the first cohorts of Dutch participants in this registry and discuss some of the consequences of the changes in anticoagulation practice.Although VKA therapy remains overwhelmingly favoured by Dutch practitioners, NOACs are clearly gaining in popularity. Between 2011 and 2014, NOACs constituted an increasingly large proportion of prescriptions for oral anticoagulants.The insights provided by the GARFIELD-AF registry can be used by healthcare systems to inform better budgetary strategies, by practitioners to better tailor treatment pathways to patients, and finally to promote awareness of the various available treatment options and their associated risks and benefits for patients. PMID:27561277

  6. AF64A-induced brain damage and its relation to dementia.

    PubMed

    Hörtnagl, H

    1994-01-01

    Several data obtained in the AF64A-model are of particular relevance for our understanding of the pathogenesis and progression of Alzheimer's disease. The AF64A-induced withdrawal of cholinergic function in the rat hippocampus was associated with reversible functional changes in other neurotransmitters, including noradrenaline, serotonin, somatostatin and glutamate, thereby mimicking changes in Alzheimer's disease. Identical changes in markers for synaptic vesicles were found in Alzheimer's disease and AF64A-model. A study on the role of gender revealed a higher susceptibility to the neurotoxic action of AF64A in female rats. The cholinergic deficit was also responsible for a disinhibition of the negative feedback regulation of glucocorticoids. Increased exposure to glucocorticoids, however, enhanced the vulnerability of hippocampal cholinergic neurons to AF64A. These data indicate that the AF64A-induced cholinergic deficit in the rat brain represents a reliable tool to study several mechanisms possibly involved in Alzheimer's disease.

  7. Neutron spin-echo study of the critical dynamics of spin-5/2 antiferromagnets in two and three dimensions

    NASA Astrophysics Data System (ADS)

    Tseng, K. F.; Keller, T.; Walters, A. C.; Birgeneau, R. J.; Keimer, B.

    2016-07-01

    We report a neutron spin-echo study of the critical dynamics in the S =5/2 antiferromagnets MnF2 and Rb2MnF4 with three-dimensional (3D) and two-dimensional (2D) spin systems, respectively, in zero external field. Both compounds are Heisenberg antiferromagnets with a small uniaxial anisotropy resulting from dipolar spin-spin interactions, which leads to a crossover in the critical dynamics close to the Néel temperature, TN. By taking advantage of the μ eV energy resolution of the spin-echo spectrometer, we have determined the dynamical critical exponents z for both longitudinal and transverse fluctuations. In MnF2, both the characteristic temperature for crossover from 3D Heisenberg to 3D Ising behavior and the exponents z in both regimes are consistent with predictions from the dynamical scaling theory. The amplitude ratio of longitudinal and transverse fluctuations also agrees with predictions. In Rb2MnF4 , the critical dynamics crosses over from the expected 2D Heisenberg behavior for T ≫TN to a scaling regime with exponent z =1.387 (4 ) , which has not been predicted by theory and may indicate the influence of long-range dipolar interactions.

  8. Effect of spin rotation coupling on spin transport

    SciTech Connect

    Chowdhury, Debashree Basu, B.

    2013-12-15

    We have studied the spin rotation coupling (SRC) as an ingredient to explain different spin-related issues. This special kind of coupling can play the role of a Dresselhaus like coupling in certain conditions. Consequently, one can control the spin splitting, induced by the Dresselhaus like term, which is unusual in a semiconductor heterostructure. Within this framework, we also study the renormalization of the spin-dependent electric field and spin current due to the k{sup →}⋅p{sup →} perturbation, by taking into account the interband mixing in the rotating system. In this paper we predict the enhancement of the spin-dependent electric field resulting from the renormalized spin rotation coupling. The renormalization factor of the spin electric field is different from that of the SRC or Zeeman coupling. The effect of renormalized SRC on spin current and Berry curvature is also studied. Interestingly, in the presence of this SRC-induced SOC it is possible to describe spin splitting as well as spin galvanic effect in semiconductors. -- Highlights: •Studied effect of spin rotation coupling on the spin electric field, spin current and Berry curvature. •In the k{sup →}⋅p{sup →} framework we study the renormalization of spin electric field and spin current. •For an inertial system we have discussed the spin splitting. •Expression for the Berry phase in the inertial system is discussed. •The inertial spin galvanic effect is studied.

  9. Electron spin susceptibility of superconductors

    SciTech Connect

    Levitov, L.S.; Nazarov, Y.V.; Eliashberg, G.M.

    1985-03-10

    The effect of spin polarization due to the Meissner currents on the electron spin susceptibility of a superconductor is studied. This effect accounts for a susceptibility considerably stronger than that of a normal metal. The spin distribution is discussed.

  10. Functional renormalization group study of orbital fluctuation mediated superconductivity: Impact of the electron-boson coupling vertex corrections

    NASA Astrophysics Data System (ADS)

    Tazai, Rina; Yamakawa, Youichi; Tsuchiizu, Masahisa; Kontani, Hiroshi

    2016-09-01

    In various multiorbital systems, the emergence of the orbital fluctuations and their role on the pairing mechanism attract increasing attention. To achieve deep understanding on these issues, we perform a functional renormalization group (fRG) study for the two-orbital Hubbard model. The vertex corrections for the electron-boson coupling (U -VC), which are dropped in the Migdal-Eliashberg gap equation, are obtained by solving the RG equation. We reveal that the dressed electron-boson coupling for the charge channel Ûeffc becomes much larger than the bare Coulomb interaction Û 0 due to the U -VC in the presence of moderate spin fluctuations. For this reason, the attractive pairing interaction due to the charge or orbital fluctuations is enlarged by the factor (Ûeffc/Û0) 2≫1 . In contrast, the spin fluctuation pairing interaction is suppressed by the spin-channel U -VC, because of the relation Ûeffs≪Û 0 . The present study demonstrates that the orbital or charge fluctuation pairing mechanism can be realized in various multiorbital systems thanks to the U -VC, such as in Fe-based superconductors.

  11. Characterization of Soil Organic Matter from African Dark Earth (AfDE) Soils

    NASA Astrophysics Data System (ADS)

    Plante, A. F.; Fujiu, M.; Ohno, T.; Solomon, D.; Lehmann, J.; Fraser, J. A.; Leach, M.; Fairhead, J.

    2014-12-01

    Anthropogenic Dark Earths are soils generated through long-term human inputs of organic and pyrogenic materials. These soils were originally discovered in the Amazon, and have since been found in Australia and in this case in Africa. While tropical soils are typically characterized by low soil organic matter (SOM) concentrations, African Dark Earths (AfDE) are black, highly fertile and carbon-rich soils formed through an extant but ancient soil management system. The objective of this study was to characterize the organic matter accumulated in AfDE and contrast it with non-AfDE soils. Characterization of bulk soil organic matter of several (n=11) AfDE and non-AfDE pairs of surface (0-15 cm) soils using thermal analysis techniques (TG-DSC-EGA) resulted in substantial differences in SOM composition and the presence of pyrogenic C. Such pyrogenic organic matter is generally considered recalcitrant, but the fertility gains in AfDE are generated by labile, more rapidly cycling pools of SOM. As a result, we characterized hot water- and pyrophosphate-extractable pools of SOM using fluorescence (EEM/PARAFAC) and high resolution mass spectrometry (FT-ICR-MS). EEM/PARAFAC data suggests that AfDE samples had a greater fraction of their DOM that was more humic-like than the paired non-AfDE samples. Similarly, FT-ICR-MS analyses of extracts suggest that differences among the sites analyzed were larger than between the paired AfDE and non-AfDE extracts. Overall, in spite of substantial differences in the composition of bulk SOM, the extractable fractions appear to be relatively similar between the AfDE and non-AfDE soils.

  12. MicroRNA-205 downregulates mixed-lineage-AF4 oncogene expression in acute lymphoblastic leukemia

    PubMed Central

    Dou, Liping; Li, Jingxin; Zheng, Dehua; Li, Yonghui; Gao, Xiaoning; Xu, Chengwang; Gao, Li; Wang, Lili; Yu, Li

    2013-01-01

    Myeloid/lymphoid or mixed-lineage AF4 acute lymphoblastic leukemia (MLL-AF4 ALL) is a pediatric leukemia that occurs rarely in adults. MLL-AF4 ALL is typically characterized by the presence of chromosomal translocation (t(4;1l)(q21;q23)), leading to expression of MLL-AF4 fusion protein. Although MLL-AF4 fusion protein triggers a molecular pathogenesis and hematological presentations that are unique to leukemias, the precise role of this oncogene in leukemogenesis remains unclear. Previous studies have indicated that microRNAs (miRs) might modulate the expression of MLL-AF4 ALL fusion protein, thereby suggesting the involvement of miR in progression or suppression of MLL-AF4 ALL. We have previously demonstrated that miR-205 negatively regulates transcription of an MLL-AF4 luciferase reporter. Here, we report that exogenous expression of miR-205 in MLL-AF4 human cell lines (RS4;11 and MV4-11) inversely regulates the expression of MLL-AF4 at both messenger RNA (mRNA) and protein level. Furthermore, miR-205 significantly induced apoptosis in MLL-AF4 cells as evidenced by Annex in V staining using fluorescence-activated cell sorting (FACS) analysis. The proliferative capacity of leukemic cells was suppressed by miR-205. The addition of an miR-205 inhibitor was able to restore the observed effects. In conclusion, these findings demonstrate that miR-205 may have potential value as a novel therapeutic agent in the treatment of MLL-AF4 ALL. PMID:24009426

  13. Structure and biological activities of eumenine mastoparan-AF (EMP-AF), a new mast cell degranulating peptide in the venom of the solitary wasp (Anterhynchium flavomarginatum micado).

    PubMed

    Konno, K; Hisada, M; Naoki, H; Itagaki, Y; Kawai, N; Miwa, A; Yasuhara, T; Morimoto, Y; Nakata, Y

    2000-11-01

    A new mast cell degranulating peptide, eumenine mastoparan-AF (EMP-AF), was isolated from the venom of the solitary wasp Anterhynchium flavomarginatum micado, the most common eumenine wasp found in Japan. The structure was analyzed by FAB-MS/MS together with Edman degradation, which was corroborated by solid-phase synthesis. The sequence of EMP-AF, Ile-Asn-Leu-Leu-Lys-Ile-Ala-Lys-Gly-Ile-Ile-Lys-Ser-Leu-NH(2), was similar to that of mastoparan, a mast cell degranulating peptide from a hornet venom; tetradecapeptide with C-terminus amidated and rich in hydrophobic and basic amino acids. In fact, EMP-AF exhibited similar activity to mastoparan in stimulating degranulation from rat peritoneal mast cells and RBL-2H3 cells. It also showed significant hemolytic activity in human erythrocytes. Therefore, this is the first example that a mast cell degranulating peptide is found in the solitary wasp venom. Besides the degranulation and hemolytic activity, EMP-AF also affects on neuromuscular transmission in the lobster walking leg preparation. Three analogs EMP-AF-1 approximately 3 were snythesized and biologically tested together with EMP-AF, resulting in the importance of the C-terminal amide structure for biological activities.

  14. 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.

  15. Spin Waves in Quasiequilibrium Spin Systems

    SciTech Connect

    Bedell, Kevin S.; Dahal, Hari P.

    2006-07-28

    Using the Landau Fermi liquid theory we discovered a new propagating transverse spin wave in a paramagnetic system which is driven slightly out of equilibrium without applying an external magnetic field. We find a gapless mode which describes the uniform precession of the magnetization in the absence of a magnetic field. We also find a gapped mode associated with the precession of the spin current around the internal field. The gapless mode has a quadratic dispersion leading to a T{sup 3/2} contribution to the specific heat. These modes significantly contribute to the dynamic structure function.

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

    SciTech Connect

    Zhang Keye; Zhou Lu; Zhang Weiping; Ling, Hong Y.; Pu Han

    2011-06-15

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

  17. Single spin magnetic resonance

    NASA Astrophysics Data System (ADS)

    Wrachtrup, Jörg; Finkler, Amit

    2016-08-01

    Different approaches have improved the sensitivity of either electron or nuclear magnetic resonance to the single spin level. For optical detection it has essentially become routine to observe a single electron spin or nuclear spin. Typically, the systems in use are carefully designed to allow for single spin detection and manipulation, and of those systems, diamond spin defects rank very high, being so robust that they can be addressed, read out and coherently controlled even under ambient conditions and in a versatile set of nanostructures. This renders them as a new type of sensor, which has been shown to detect single electron and nuclear spins among other quantities like force, pressure and temperature. Adapting pulse sequences from classic NMR and EPR, and combined with high resolution optical microscopy, proximity to the target sample and nanoscale size, the diamond sensors have the potential to constitute a new class of magnetic resonance detectors with single spin sensitivity. As diamond sensors can be operated under ambient conditions, they offer potential application across a multitude of disciplines. Here we review the different existing techniques for magnetic resonance, with a focus on diamond defect spin sensors, showing their potential as versatile sensors for ultra-sensitive magnetic resonance with nanoscale spatial resolution.

  18. Spin coating of electrolytes

    DOEpatents

    Stetter, Joseph R.; Maclay, G. Jordan

    1989-01-01

    Methods for spin coating electrolytic materials onto substrates are disclosed. More particularly, methods for depositing solid coatings of ion-conducting material onto planar substrates and onto electrodes are disclosed. These spin coating methods are employed to fabricate electrochemical sensors for use in measuring, detecting and quantifying gases and liquids.

  19. Coherent spin-networks

    SciTech Connect

    Bianchi, Eugenio; Magliaro, Elena; Perini, Claudio

    2010-07-15

    In this paper we discuss a proposal of coherent states for loop quantum gravity. These states are labeled by a point in the phase space of general relativity as captured by a spin-network graph. They are defined as the gauge-invariant projection of a product over links of Hall's heat kernels for the cotangent bundle of SU(2). The labels of the state are written in terms of two unit vectors, a spin and an angle for each link of the graph. The heat-kernel time is chosen to be a function of the spin. These labels are the ones used in the spin-foam setting and admit a clear geometric interpretation. Moreover, the set of labels per link can be written as an element of SL(2,C). These states coincide with Thiemann's coherent states with the area operator as complexifier. We study the properties of semiclassicality of these states and show that, for large spins, they reproduce a superposition over spins of spin-networks with nodes labeled by Livine-Speziale coherent intertwiners. Moreover, the weight associated to spins on links turns out to be given by a Gaussian times a phase as originally proposed by Rovelli.

  20. Sparkling and Spinning Words.

    ERIC Educational Resources Information Center

    Carlson, Ruth Kearney

    1964-01-01

    Teachers should foster in children's writing the use of words with "sparkle" and "spin"--"sparkle" implying brightness and vitality, "spin" connoting industry, patience, and painstaking work. By providing creative listening experiences with good children's or adult literature, the teacher can encourage students to broaden their imaginations and…

  1. Single spin magnetic resonance.

    PubMed

    Wrachtrup, Jörg; Finkler, Amit

    2016-08-01

    Different approaches have improved the sensitivity of either electron or nuclear magnetic resonance to the single spin level. For optical detection it has essentially become routine to observe a single electron spin or nuclear spin. Typically, the systems in use are carefully designed to allow for single spin detection and manipulation, and of those systems, diamond spin defects rank very high, being so robust that they can be addressed, read out and coherently controlled even under ambient conditions and in a versatile set of nanostructures. This renders them as a new type of sensor, which has been shown to detect single electron and nuclear spins among other quantities like force, pressure and temperature. Adapting pulse sequences from classic NMR and EPR, and combined with high resolution optical microscopy, proximity to the target sample and nanoscale size, the diamond sensors have the potential to constitute a new class of magnetic resonance detectors with single spin sensitivity. As diamond sensors can be operated under ambient conditions, they offer potential application across a multitude of disciplines. Here we review the different existing techniques for magnetic resonance, with a focus on diamond defect spin sensors, showing their potential as versatile sensors for ultra-sensitive magnetic resonance with nanoscale spatial resolution.

  2. Spin-orbit photonics

    NASA Astrophysics Data System (ADS)

    Cardano, Filippo; Marrucci, Lorenzo

    2015-12-01

    Spin-orbit optical phenomena involve the interaction of the photon spin with the light wave propagation and spatial distribution, mediated by suitable optical media. Here we present a short overview of the emerging photonic applications that rely on such effects.

  3. Single-spin CCD

    NASA Astrophysics Data System (ADS)

    Baart, T. A.; Shafiei, M.; Fujita, T.; Reichl, C.; Wegscheider, W.; Vandersypen, L. M. K.

    2016-04-01

    Spin-based electronics or spintronics relies on the ability to store, transport and manipulate electron spin polarization with great precision. In its ultimate limit, information is stored in the spin state of a single electron, at which point quantum information processing also becomes a possibility. Here, we demonstrate the manipulation, transport and readout of individual electron spins in a linear array of three semiconductor quantum dots. First, we demonstrate single-shot readout of three spins with fidelities of 97% on average, using an approach analogous to the operation of a charge-coupled device (CCD). Next, we perform site-selective control of the three spins, thereby writing the content of each pixel of this ‘single-spin charge-coupled device’. Finally, we show that shuttling an electron back and forth in the array hundreds of times, covering a cumulative distance of 80 μm, has negligible influence on its spin projection. Extrapolating these results to the case of much larger arrays points at a diverse range of potential applications, from quantum information to imaging and sensing.

  4. Magnetic fields and fluctuations in weakly Mn doped ZnGeP{sub 2}

    SciTech Connect

    Mengyan, P. W.; Lichti, R. L.; Baker, B. B.; Celebi, Y. G.; Catak, E.; Carroll, B. R.; Zawilski, K. T.; Schunemann, P. G.

    2014-02-21

    We report on our measurements of local and bulk magnetic features in weakly Mn doped ZnGeP{sub 2}. Utilizing muon spin rotation and relaxation measurements, we identify local ferromagnetic order and fluctuations in the local fields as sampled by an implanted muon (μ{sup +}). We also report on field induced ferromagnetism occurring above the claimed paramagnetic to ferromagnetic transition temperature (T{sub c} = 312 K)

  5. Fluctuations and the Hofmeister effect.

    PubMed Central

    Neagu, A; Neagu, M; Dér, A

    2001-01-01

    The Hofmeister effect consists in changes of protein solubility triggered by neutral electrolyte cosolutes. Based on the assumption that salts cause stochastic fluctuations of the free energy barrier profiles, a kinetic theory of this phenomenon is proposed. An exponentially correlated noise, of amplitude proportional to the salt concentration, is added to each energy level, and the time-dependence of the mean protein concentration is calculated. It is found that the theory yields the well-known Setschenow equation if the noise correlation time is low in comparison to the aggregation time constant. Experimental data on salting-in agents are well fitted, whereas, in the case of salting-out cosolutes, two independent dichotomic fluctuations are needed to fit the data. This may result from the fact that, in both cases, the low-concentration regime is dominated by salting-in electrostatic contributions, whereas, at high salt concentrations, electron donor/acceptor interactions become important; these have opposite effects. The theory offers a novel way to metricate Hofmeister effects and also leads to thermodynamic quantities, which account for the influence of salts. The formalism may also be applied to describe kinetic phenomena in the presence of cosolutes. PMID:11509345

  6. Universal bounds on current fluctuations

    NASA Astrophysics Data System (ADS)

    Pietzonka, Patrick; Barato, Andre C.; Seifert, Udo

    2016-05-01

    For current fluctuations in nonequilibrium steady states of Markovian processes, we derive four different universal bounds valid beyond the Gaussian regime. Different variants of these bounds apply to either the entropy change or any individual current, e.g., the rate of substrate consumption in a chemical reaction or the electron current in an electronic device. The bounds vary with respect to their degree of universality and tightness. A universal parabolic bound on the generating function of an arbitrary current depends solely on the average entropy production. A second, stronger bound requires knowledge both of the thermodynamic forces that drive the system and of the topology of the network of states. These two bounds are conjectures based on extensive numerics. An exponential bound that depends only on the average entropy production and the average number of transitions per time is rigorously proved. This bound has no obvious relation to the parabolic bound but it is typically tighter further away from equilibrium. An asymptotic bound that depends on the specific transition rates and becomes tight for large fluctuations is also derived. This bound allows for the prediction of the asymptotic growth of the generating function. Even though our results are restricted to networks with a finite number of states, we show that the parabolic bound is also valid for three paradigmatic examples of driven diffusive systems for which the generating function can be calculated using the additivity principle. Our bounds provide a general class of constraints for nonequilibrium systems.

  7. Rapid fluctuations in solar flares

    NASA Technical Reports Server (NTRS)

    Sturrock, Peter A.

    1986-01-01

    Study of rapid fluctuations in the emission of radiation from solar flares provides a promising approach for probing the magneto-plasma structure and plasma processes that are responsible for a flare. It is proposed that elementary flare bursts in X-ray and microwave emission may be attributed to fine structure of the coronal magnetic field, related to the aggregation of photospheric magnetic field into magnetic knots. Fluctuations that occur on a subsecond time-scale may be due to magnetic islands that develop in current sheets during magnetic reconnection. The impulsive phase may sometimes represent the superposition of a large number of the elementary energy-release processes responsible for elementary flare bursts. If so, the challenge of trying to explain the properties of the impulsive phase in terms of the properties of the elementary processes must be faced. Magnetic field configurations that might produce solar flares are divided into a number of categories, depending on: whether or not there is a filament; whether there is no current sheet, a closed current sheet, or an open current sheet; and whether the filament erupts into the corona, or is ejected completely from the Sun's atmosphere. Analysis of the properties of these possible configurations is compared with different types of flares, and to Bai's subdivision of gamma-ray/proton events.

  8. Protrusion Fluctuations Direct Cell Motion

    PubMed Central

    Caballero, David; Voituriez, Raphaël; Riveline, Daniel

    2014-01-01

    Many physiological phenomena involve directional cell migration. It is usually attributed to chemical gradients in vivo. Recently, other cues have been shown to guide cells in vitro, including stiffness/adhesion gradients or micropatterned adhesive motifs. However, the cellular mechanism leading to these biased migrations remains unknown, and, often, even the direction of motion is unpredictable. In this study, we show the key role of fluctuating protrusions on ratchet-like structures in driving NIH3T3 cell migration. We identified the concept of efficient protrusion and an associated direction index. Our analysis of the protrusion statistics facilitated the quantitative prediction of cell trajectories in all investigated conditions. We varied the external cues by changing the adhesive patterns. We also modified the internal cues using drug treatments, which modified the protrusion activity. Stochasticity affects the short- and long-term steps. We developed a theoretical model showing that an asymmetry in the protrusion fluctuations is sufficient for predicting all measures associated with the long-term motion, which can be described as a biased persistent random walk. PMID:24988339

  9. Aging and memory effects in the spin jam states of densely populated frustrated magnets

    NASA Astrophysics Data System (ADS)

    Samarakoon, Anjana; Lee, Seung-Hun; Sato, Taku; Zhou, Haidong; Sinclair, Ryan; Yang, Junjie; Chen, Tianran; Chern, Gia-Wei; Klich, Israel

    Defects and randomness has been largely studied as the key mechanism of glassiness find in a dilute magnetic system. Even though the same argument has also been made to explain the spin glass like properties in dense frustrated magnets, the existence of a glassy state arise intrinsically from a defect free spin system, far from the conventional dilute limit with different mechanisms such as quantum fluctuations and topological features, has been theoretically proposed recently. We have studied field effects on zero-field cooled and field cooled susceptibility bifurcation and memory effects below freezing transition, of three different densely populated frustrated magnets which glassy states we call spin jam, and a conventional dilute spin glass. Our data show common behaviors among the spin jam states, which is distinct from that of the conventional spin glass. We have also performed Monte Carlo simulations to understand the nature of their energy landscapes.

  10. Adiabatic freezing of long-range quantum correlations in spin chains

    NASA Astrophysics Data System (ADS)

    Shekhar Dhar, Himadri; Rakshit, Debraj; Sen(De, Aditi; Sen, Ujjwal

    2016-06-01

    We consider a process to create quasi-long-range quantum discord between the non-interacting end spins of a quantum spin chain, with the end spins weakly coupled to the bulk of the chain. The process is not only capable of creating long-range quantum correlation but the latter remains frozen, when certain weak end-couplings are adiabatically varied below certain thresholds. We term this phenomenon as adiabatic freezing of quantum correlation. We observe that the freezing is robust to moderate thermal fluctuations and is intrinsically related to the cooperative properties of the quantum spin chain. In particular, we find that the energy gap of the system remains frozen for these adiabatic variations, and moreover, considering the end spins as probes, we show that the interval of freezing can detect the anisotropy transition in quantum XY spin chains. Importantly, the adiabatic freezing of long-range quantum correlations can be simulated with contemporary experimental techniques.

  11. Magnetic resonance force microscopy of paramagnetic electron spins at millikelvin temperatures.

    PubMed

    Vinante, A; Wijts, G; Usenko, O; Schinkelshoek, L; Oosterkamp, T H

    2011-12-06

    Magnetic resonance force microscopy (MRFM) is a powerful technique to detect a small number of spins that relies on force detection by an ultrasoft magnetically tipped cantilever and selective magnetic resonance manipulation of the spins. MRFM would greatly benefit from ultralow temperature operation, because of lower thermomechanical noise and increased thermal spin polarization. Here we demonstrate MRFM operation at temperatures as low as 30 mK, thanks to a recently developed superconducting quantum interference device (SQUID)-based cantilever detection technique, which avoids cantilever overheating. In our experiment, we detect dangling bond paramagnetic centres on a silicon surface down to millikelvin temperatures. Fluctuations of such defects are supposedly linked to 1/f magnetic noise and decoherence in SQUIDs, as well as in several superconducting and single spin qubits. We find evidence that spin diffusion has a key role in the low-temperature spin dynamics.

  12. Voltage-driven spin-transfer torque in a magnetic particle

    SciTech Connect

    Gartland, P. Davidović, D.

    2015-10-26

    We discuss a spin-transfer torque device, where the role of the soft ferromagnetic layer is played by a magnetic particle or a magnetic molecule, in weak tunnel contact with two spin polarized leads. We investigate if the magnetization of the particle can be manipulated electronically, in the regime where the critical current for magnetization switching is negligibly weak, which could be due to the reduced particle dimensions. Using master equation simulations to evaluate the effects of spin-orbit anisotropy energy fluctuations on spin-transfer, we obtain reliable reading and writing of the magnetization state of such magnetic particle, and find that the device relies on a critical voltage rather than a critical current. The critical voltage is governed by the spin-orbit energy shifts of discrete levels in the particle. This finding opens a possibility to significantly reduce the power dissipation involved in spin-transfer torque switching, by using very small magnetic particles or molecules.

  13. Spin-labeled polyribonucleotides.

    PubMed Central

    Petrov, A I; Sukhorukov, B I

    1980-01-01

    Poly (U), poly (C) and poly (A) were spin labeled with N-(2,2,5,5-tetramethyl-3-carbonylpyrroline-1-oxyl)-imidazole. This spin label interacts selectively with 2' OH ribose groups of polynucleotides and does not modify the nucleic acid bases. The extent of spin labeling is not dependent upon the nature of the base and is entirely determined by rigidity of the secondary structure of the polynucleotide. The extent of modification for poly (U), poly (C) and poly (A) was 4.2, 1.7 and 1.5 per cent, respectively, the secondary structure of the polynucleotides being practically unchanged. Some physico-chemical properties of the spin-labeled polynucleotides were investigated by ESR spectroscopy. Rotational correlation times of the spin label and activation energy of its motion were calculated. PMID:6253911

  14. Spin-Wave Diode

    NASA Astrophysics Data System (ADS)

    Lan, Jin; Yu, Weichao; Wu, Ruqian; Xiao, Jiang

    2015-10-01

    A diode, a device allowing unidirectional signal transmission, is a fundamental element of logic structures, and it lies at the heart of modern information systems. The spin wave or magnon, representing a collective quasiparticle excitation of the magnetic order in magnetic materials, is a promising candidate for an information carrier for the next-generation energy-saving technologies. Here, we propose a scalable and reprogrammable pure spin-wave logic hardware architecture using domain walls and surface anisotropy stripes as waveguides on a single magnetic wafer. We demonstrate theoretically the design principle of the simplest logic component, a spin-wave diode, utilizing the chiral bound states in a magnetic domain wall with a Dzyaloshinskii-Moriya interaction, and confirm its performance through micromagnetic simulations. Our findings open a new vista for realizing different types of pure spin-wave logic components and finally achieving an energy-efficient and hardware-reprogrammable spin-wave computer.

  15. 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.

  16. 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

  17. 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.

  18. Fractionalized spin-wave continuum in kagome spin liquids

    NASA Astrophysics Data System (ADS)

    Mei, Jia-Wei; Wen, Xiao-Gang

    Motivated by spin-wave continuum (SWC) observed in recent neutron scattering experiments in Herbertsmithite, we use Gutzwiller-projected wave functions to study dynamic spin structure factor S (q , ω) of spin liquid states on the kagome lattice. Spin-1 excited states in spin liquids are represented by Gutzwiller-projected two-spinon excited wave functions. We investigate three different spin liquid candidates, spinon Fermi-surface spin liquid (FSL), Dirac spin liquid (DSL) and random-flux spin liquid (RSL). FSL and RSL have low energy peaks in S (q , ω) at K points in the extended magnetic Brillouin zone, in contrast to experiments where low energy peaks are found at M points. There is no obviuos contradiction between DSL and neutron scattering measurements. Besides a fractionalized spin (i.e. spin-1/2), spinons in DSL carry a fractionalized crystal momentum which is potentially detectable in SWC in the neutron scattering measurements.

  19. Synchronization of spin-transfer torque oscillators by spin pumping, inverse spin Hall, and spin Hall effects

    SciTech Connect

    Elyasi, Mehrdad; Bhatia, Charanjit S.; Yang, Hyunsoo

    2015-02-14

    We have proposed a method to synchronize multiple spin-transfer torque oscillators based on spin pumping, inverse spin Hall, and spin Hall effects. The proposed oscillator system consists of a series of nano-magnets in junction with a normal metal with high spin-orbit coupling, and an accumulative feedback loop. We conduct simulations to demonstrate the effect of modulated charge currents in the normal metal due to spin pumping from each nano-magnet. We show that the interplay between the spin Hall effect and inverse spin Hall effect results in synchronization of the nano-magnets.

  20. Influence of patterning fluctuation on read/write characteristics in discrete track and bit patterned media

    NASA Astrophysics Data System (ADS)

    Hashimoto, Mitsuhiro; Miura, Kenji; Muraoka, Hiroaki; Aoi, Hajime; Wood, Roger; Salo, Michael; Ikeda, Yoshihiro

    The read/write characteristics of non-patterned media (NPM), discrete track media (DTM), and bit patterned media (BPM) are examined by modeling the magnetization distribution of NPM and patterning fluctuation of DTM. By comparing spin-stand measurement with calculation, the magnetization distribution of NPM was well characterized with a new Voronoi cell magnetic cluster model, in which the cluster size at the track edge, < Dedge>, was larger than that at the track center, < Dcenter> by a factor of two. Based on an analysis of patterning fluctuations seen in SEM images of DTM, line-edge roughness (LER) was modeled as a long-wavelength center-line roughness (CLR) plus a short-wavelength line-width roughness (LWR). It was confirmed that the standard deviation of the patterning fluctuation was much smaller than that of the magnetic fluctuation for NPM. This allowed DTM to achieve higher off-track performance than NPM. By examining the 747 curves, it was revealed that DTM could have an advantage in track-density of up to approximately 25% assuming patterning fluctuations can be well controlled at high track density. In BPM, fabricating accurate dots is essential. The relationship between dot defect rate and patterning fluctuation was examined, and the maximum allowable standard deviation of LER was derived as 2 nm for achieving 1 Tbspi.