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Sample records for magnetic field landau

  1. Resonant Landau-Zener transitions in a helical magnetic field

    NASA Astrophysics Data System (ADS)

    Wójcik, P.; Adamowski, J.; Wołoszyn, M.; Spisak, B. J.

    2015-06-01

    Spin-dependent electron transport has been studied in magnetic semiconductor waveguides (nanowires) in the helical magnetic field. We have shown that—apart from the well-known conductance dip located at the magnetic field equal to the helical-field amplitude Bh—the additional conductance dips (with zero conductance) appear at a magnetic field different from Bh. This effect occurring in the non-adiabatic regime is explained as resulting from the resonant Landau-Zener transitions between the spin-split subbands.

  2. Landau levels of scalar QED in time-dependent magnetic fields

    SciTech Connect

    Kim, Sang Pyo

    2014-05-15

    The Landau levels of scalar QED undergo continuous transitions under a homogeneous, time-dependent magnetic field. We analytically formulate the Klein–Gordon equation for a charged spinless scalar as a Cauchy initial value problem in the two-component first order formalism and then put forth a measure that classifies the quantum motions into the adiabatic change, the nonadiabatic change, and the sudden change. We find the exact quantum motion and calculate the pair-production rate when the magnetic field suddenly changes as a step function. -- Highlights: •We study the Landau levels of scalar QED in time-dependent magnetic fields. •Instantaneous Landau levels make continuous transitions but keep parity. •The Klein–Gordon equation is expressed in the two-component first order formalism. •A measure is advanced that characterizes the quantum motions into three categories. •A suddenly changing magnetic field produces pairs of charged scalars from vacuum.

  3. Landau levels of cold dense quark matter in a strong magnetic field

    NASA Astrophysics Data System (ADS)

    Wen, Xin-Jian; Liang, Jun-Jun

    2016-07-01

    The occupied Landau levels of strange quark matter are investigated in the framework of the SU(3) NJL model with a conventional coupling and a magnetic-field dependent coupling respectively. At lower density, the Landau levels are mainly dominated by u and d quarks. Threshold values of the chemical potential for the s quark onset are shown in the μ -B plane. The magnetic-field-dependent running coupling can broaden the region of three-flavor matter by decreasing the dynamical masses of s quarks. Before the onset of s quarks, the Landau level number of light quarks is directly dependent on the magnetic field strength B by a simple inverse proportional relation ki ,max≈Bi0/B with Bd0=5 ×1 019 G , which is approximately 2 times Bu0 of u quarks at a common chemical potential. When the magnetic field increases up to Bd0, almost all three flavors are lying in the lowest Landau level.

  4. Collisional excitation of electron Landau levels in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Langer, S. H.

    1981-01-01

    The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.

  5. Vacuum birefringence in strong magnetic fields: (II) Complex refractive index from the lowest Landau level

    SciTech Connect

    Hattori, Koichi; Itakura, Kazunori

    2013-07-15

    We compute the refractive indices of a photon propagating in strong magnetic fields on the basis of the analytic representation of the vacuum polarization tensor obtained in our previous paper. When the external magnetic field is strong enough for the fermion one-loop diagram of the polarization tensor to be approximated by the lowest Landau level, the propagating mode in parallel to the magnetic field is subject to modification: The refractive index deviates from unity and can be very large, and when the photon energy is large enough, the refractive index acquires an imaginary part indicating decay of a photon into a fermion–antifermion pair. We study dependences of the refractive index on the propagating angle and the magnetic-field strength. It is also emphasized that a self-consistent treatment of the equation which defines the refractive index is indispensable for accurate description of the refractive index. This self-consistent treatment physically corresponds to consistently including the effects of back reactions of the distorted Dirac sea in response to the incident photon. -- Highlights: •Vacuum birefringence and photon decay are described by the complex refractive index. •Resummed photon vacuum polarization tensor in the lowest Landau level is used. •Back reactions from the distorted Dirac sea are self-consistently taken into account. •Self-consistent treatment drastically changes structure in photon energy dependence. •Dependences on photon propagation angle and magnetic-field strength are presented.

  6. Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields

    NASA Astrophysics Data System (ADS)

    Kondo, Takahiro; Guo, Donghui; Shikano, Taishi; Suzuki, Tetsuya; Sakurai, Masataka; Okada, Susumu; Nakamura, Junji

    2015-11-01

    Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). However, it has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. Here, we report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields. The corresponding magnetic fields were estimated to be as much as approximately 100 T. The generation of the LLs at the area with negligible strain can be explained by inequivalent hopping of π electrons that takes place at the perimeter of high-potential domains surrounded by positively charged substituted graphitic-nitrogen atoms.

  7. Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields

    PubMed Central

    Kondo, Takahiro; Guo, Donghui; Shikano, Taishi; Suzuki, Tetsuya; Sakurai, Masataka; Okada, Susumu; Nakamura, Junji

    2015-01-01

    Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). However, it has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. Here, we report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields. The corresponding magnetic fields were estimated to be as much as approximately 100 T. The generation of the LLs at the area with negligible strain can be explained by inequivalent hopping of π electrons that takes place at the perimeter of high-potential domains surrounded by positively charged substituted graphitic-nitrogen atoms. PMID:26549618

  8. The Ginzburg-Landau theory for a thin superconducting loop in a large magnetic field

    NASA Astrophysics Data System (ADS)

    Shieh, Tien-Tsan

    When a temperature is lower than a certain critical value, a superconducting sample undergoes a phase transition from a normal state to a superconducting state. This onset process of superconductivity can be studied as a Rayleigh quotient under the framework of the Ginzburg-Landau theory. In particular, I study the onset problem for a thin superconducting loop in a large magnetic field. This double limit problem was first carried out by Richardson and Rubinstein by using formal asymptotic expansions. I rigorously show that a one-dimensional Rayleigh quotient in the spirit of Gamma-convergence. The full Gamma-convergence of the Ginzburg-Landau functional for a thin domain and a large field is also obtained. The rigorous analysis in this thesis shows the validity of Richardson and Rubinstein's formal results. It is also shown that the Rayleigh quotient related to this onset problem has a periodic variation with a parabolic background. The parabolic background effect can be explained by a non-ignorable effect if finite-width cross-section of a thin superconducting sample. This illustrate the observation of the Little-Parks experiment.

  9. Lifting of the Landau level degeneracy in graphene devices in a tilted magnetic field

    NASA Astrophysics Data System (ADS)

    Chiappini, F.; Wiedmann, S.; Novoselov, K.; Mishchenko, A.; Geim, A. K.; Maan, J. C.; Zeitler, U.

    2015-11-01

    We report on transport and capacitance measurements of graphene devices in magnetic fields up to 30 T. In both techniques, we observe the full splitting of Landau levels and we employ tilted field experiments to address the origin of the observed broken symmetry states. In the lowest energy level, the spin degeneracy is removed at filling factors ν =±1 and we observe an enhanced energy gap. In the higher levels, the valley degeneracy is removed at odd filling factors while spin polarized states are formed at even ν . Although the observation of odd filling factors in the higher levels points towards the spontaneous origin of the splitting, we find that the main contribution to the gap at ν =-4 ,-8 , and -12 is due to the Zeeman energy.

  10. Landau levels as a limiting case of a model with the morse-like magnetic field

    NASA Astrophysics Data System (ADS)

    Fakhri, H.; Mojaveri, B.; Nobary, M. A. Gomshi

    2010-12-01

    We consider the quantum mechanics of an electron trapped on an infinite band along the x-axis in the presence of the Morse-like perpendicular magnetic field B=-Bek with B0 > 0 as a constant strength and a0 as the width of the band. It is shown that the square integrable pure states realize representations of su(1, 1) algebra via the quantum number corresponding to the linear momentum in the y-direction. The energy of the states increases by decreasing the width a0 while it is not changed by B0. It is quadratic in terms of two quantum numbers, and the linear spectrum of the Landau levels is obtained as a limiting case of a0 → ∞. All of the lowest states of the su(1, 1) representations minimize uncertainty relation and the minimizing of their second and third states is transformed to that of the Landau levels in the limit a0 → ∞. The compact forms of the Barut-Girardello coherent states corresponding to l-representation of su(1, 1) algebra and their positive definite measures on the complex plane are also calculated.

  11. Landau level splitting in Cd3As2 under high magnetic fields

    PubMed Central

    Cao, Junzhi; Liang, Sihang; Zhang, Cheng; Liu, Yanwen; Huang, Junwei; Jin, Zhao; Chen, Zhi-Gang; Wang, Zhijun; Wang, Qisi; Zhao, Jun; Li, Shiyan; Dai, Xi; Zou, Jin; Xia, Zhengcai; Li, Liang; Xiu, Faxian

    2015-01-01

    Three-dimensional topological Dirac semimetals (TDSs) are a new kind of Dirac materials that exhibit linear energy dispersion in the bulk and can be viewed as three-dimensional graphene. It has been proposed that TDSs can be driven to other exotic phases like Weyl semimetals, topological insulators and topological superconductors by breaking certain symmetries. Here we report the first transport experiment on Landau level splitting in TDS Cd3As2 single crystals under high magnetic fields, suggesting the removal of spin degeneracy by breaking time reversal symmetry. The detected Berry phase develops an evident angular dependence and possesses a crossover from non-trivial to trivial state under high magnetic fields, a strong hint for a fierce competition between the orbit-coupled field strength and the field-generated mass term. Our results unveil the important role of symmetry breaking in TDSs and further demonstrate a feasible path to generate a Weyl semimetal phase by breaking time reversal symmetry. PMID:26165390

  12. Derivation of the Linear Landau Equation and Linear Boltzmann Equation from the Lorentz Model with Magnetic Field

    NASA Astrophysics Data System (ADS)

    Marcozzi, M.; Nota, A.

    2016-03-01

    We consider a test particle moving in a random distribution of obstacles in the plane, under the action of a uniform magnetic field, orthogonal to the plane. We show that, in a weak coupling limit, the particle distribution behaves according to the linear Landau equation with a magnetic transport term. Moreover, we show that, in a low density regime, when each obstacle generates an inverse power law potential, the particle distribution behaves according to the linear Boltzmann equation with a magnetic transport term. We provide an explicit control of the error in the kinetic limit by estimating the contributions of the configurations which prevent the Markovianity. We compare these results with those ones obtained for a system of hard disks in Bobylev et al. (Phys Rev Lett 75:2, 1995), which show instead that the memory effects are not negligible in the Boltzmann-Grad limit.

  13. Coherent dynamics of Landau-Levels in modulation doped GaAs quantum wells at high magnetic fields

    NASA Astrophysics Data System (ADS)

    Liu, Cunming; Paul, Jagannath; Reno, John; McGill, Stephen; Hilton, David; Karaiskaj, Denis

    By using two-dimensional Fourier transform spectroscopy, we investigate the dynamics of Landau-Levels formed in modulation doped GaAs/AlGaAs quantum wells of 18 nm thickness at high magnetic fields and low temperature. The measurements show interesting dephasing dynamics and linewidth dependency as a function of the magnetic field. The work at USF and UAB was supported by the National Science Foundation under grant number DMR-1409473. The work at NHMFL, FSU was supported by the National Science Foundation under grant numbers DMR-1157490 and DMR-1229217. This work was performed, in part, at the Center for Integrated Nanotechnologies, a U.S. Department of Energy, Office of Basic Energy Sciences user facility. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.

  14. Search for Quasi-Landau Resonance Behavior in the Photodetachment Spectra of the Sulfur and Selenium Negative Ions in a Magnetic Field.

    NASA Astrophysics Data System (ADS)

    Edge, Christopher James

    1988-06-01

    Since the late 1960's, quasi-Landau resonances (QLR's) have been observed in photoionization spectra of atoms in magnetic fields. Since the middle 1970's, photodetachment of negative ions in a magnetic field has also resulted in behaviour reminiscent of Landau level structure. Unlike the QLR's of photoionization which have an energy spacing of 3/2(hbaromega), these resonances appear to have energy spacings indistinguishable from Landau level spacings of hbaromega. The Blumberg-Itano-Larson (BIL) model that was developed to explain the photodetachment data assumed that the final state wave function of the departing electron could be accurately described by an exact Landau solution. Another model has characterized the final state wave function as being similar to those of the QLR's. As such, it was predicted that the experimentally observed photodetachment resonances may be shifted significantly from the Landau energy level spacings. These shifts would be revealed in the data. The primary objective of this dissertation was to assemble photodetachment data for S- and Se- at low and high magnetic fields in order to measure as accurately as possible any deviations from the expected minimum Landau energy, 1/2 times hbaromega. This was accomplished for 18 sets of data for S- and 13 sets of data for Se-. It was found that the Landau-type resonance occurred at 0.497(5) times hbaromega for S- and 0.493(5) times hbaromega for Se -. There is very little suggestion from the data, if any, that the Landau energies are shifted. A second objective was to extrapolate a value for the electron affinity at zero magnetic field based on the above analysis for S- and Se -. The values obtained were 16752.996(9) cm ^{-1} for S- and 16297.835(19) cm^{-1} for Se-. Finally, there is a strong suggestion in much of the data that the Zeeman populations formed during the process of dissociative attachment are somewhat aligned. Unless an alternative explanation can be found, it would seem that the

  15. Magnetic Flux Quantization of the Landau Problem

    NASA Astrophysics Data System (ADS)

    Wang, Jianhua; Li, Kang; Long, Shuming; Yuan, Yi

    2014-08-01

    Landau problem has a very important application in modern physics, in which two-dimensional electron gas system and quantum Hall effect are outstanding. In this paper, first we review the solution of the Pauli equation, then using the single electron wave function, we calculate moving area expectations of the ideal 2-dimensional electron gas system and the per unit area's degeneracy of the electron gas system. As a result, how to calculate the magnetic flux of the electron gas system is given. It shows that the magnetic flux of 2-dimensional electron gas system in magnetic field is quantized, and magnetic flux quantization results from the quantization of the moving area expectations of electron gas system.

  16. Landau Fluid Models for Magnetized Plasmas

    SciTech Connect

    Sulem, P. L.; Passot, T.; Marradi, L.

    2008-10-15

    A Landau fluid model for a magnetized plasma, that retains a linear description of low-frequency kinetic effects involving transverse scales significantly smaller than the ion Larmor radius, is discussed and validated in the context of nonlinear wave dynamics. Preliminary simulations of the turbulent regime are presented in one space dimension, as a first step towards more realistic three-dimensional computations, aimed to analyze the combined effect of dispersion and collisionless dissipation on the energy cascade.

  17. The wave magnetic field amplitude threshold for nonlinear trapping of energetic gyroresonant and Landau resonant electrons by nonducted VLF waves in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Bell, T. F.

    1986-01-01

    A recently developed theory is used to calculate the wave magnetic field amplitude threshold, B-tau, necessary to allow the nonlinear trapping of energetic gyroresonant and Landau resonant electrons by VLF whistler mode waves in the magnetosphere propagating at an arbitrary angle, psi, with respect to the earth's magnetic field. A detailed raytracing study is carried out to establish the variation of psi with position along each magnetic shell in the range L = 2-5 and for frequencies 5-17.8 kHz. It is found that the minimum values of B-tau along each L shell generally occur at points of second-order resonance. In general, for nonducted fixed frequency signals there is only one point of second-order resonance on each L shell, and this is located within a few degrees of the magnetic equator. However, over a narrow range of L, there are as many as three points of second-order resonance and as many as three associated minima in B-tau. At least one of these points is located more than 10 deg from the magnetic equator.

  18. Novel electric field effects on Landau levels in graphene.

    PubMed

    Lukose, Vinu; Shankar, R; Baskaran, G

    2007-03-16

    A new effect in graphene in the presence of crossed uniform electric and magnetic fields is predicted. Landau levels are shown to be modified in an unexpected fashion by the electric field, leading to a collapse of the spectrum, when the value of electric to magnetic field ratio exceeds a certain critical value. Our theoretical results, strikingly different from the standard 2D electron gas, are explained using a "Lorentz boost," and as an "instability of a relativistic quantum field vacuum." It is a remarkable case of emergent relativistic type phenomena in nonrelativistic graphene. We also discuss few possible experimental consequence. PMID:17501075

  19. Stochastic Landau-Lifshitz-Gilbert Equation with Delayed Feedback Field

    NASA Astrophysics Data System (ADS)

    Tutu, H.; Horita, T.

    2008-08-01

    A time-delayed feedback control to stabilize a swinging motion of magnetic moment in a single-domain magnetic system under AC field is studied. The system has a uniaxial anisotropy, and the AC field is parallel to this. Without control, it prefers the Ising state that is (anti)parallel to the anisotropy axis. The control stabilizes the oscillation across the equatorial plane perpendicular to the anisotropy axis (swinging motion). Employing a stochastic Landau-Lifshitz-Gilbert (LLG) equation, we study the effects of thermal fluctuation on the controlled state. Linear fluctuation, in which variance linearly depends on noise intensity, around the controlled state is analyzed in terms of correlation function and spectral density, and a criterion for the existence of such a linear relationship is obtained. Several technical improvements in the treatment of the stochastic LLG equation and the corresponding Fokker-Planck equation with stereographic coordinate system are also show n.

  20. REDUCTION OF COMPRESSIBILITY AND PARALLEL TRANSFER BY LANDAU DAMPING IN TURBULENT MAGNETIZED PLASMAS

    SciTech Connect

    Hunana, P.; Laveder, D.; Passot, T.; Sulem, P. L.; Borgogno, D.

    2011-12-20

    Three-dimensional numerical simulations of decaying turbulence in a magnetized plasma are performed using a so-called finite Larmor radius (FLR)-Landau fluid model which incorporates linear Landau damping and FLR corrections. It is shown that compared to simulations of compressible Hall-MHD, linear Landau damping is responsible for significant damping of magnetosonic waves, which is consistent with the linear kinetic theory. Compressibility of the fluid and parallel energy cascade along the ambient magnetic field are also significantly inhibited when the beta parameter is not too small. In contrast with Hall-MHD, the FLR-Landau fluid model can therefore correctly describe turbulence in collisionless plasmas such as solar wind, providing an interpretation for its nearly incompressible behavior.

  1. Generalized Landau Lifshitz Gilbert equation for uniformly magnetized bodies

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

    We consider generalized Landau-Lifshitz-Gilbert (LLG) deterministic dynamics in uniformly magnetized bodies. The dynamics take place on the unit sphere Σ, and are characterized by a vector field v tangential to Σ. By using Helmholtz decomposition on Σ, it is proven that v is uniquely defined by two potentials χ and ψ. Potential χ can be identified with the free energy of the system, while ψ describes non-conservative interactions of the system with the environment. The presence of ψ modifies the usual energy balance of LLG dynamics. Instead of purely relaxation dynamics we may have steady injection of energy through non-conservative interactions. The implications of the new form of the energy balance are discussed in detail.

  2. Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface

    SciTech Connect

    Simmons, J.A.; Harff, N.E.; Lyo, S.K.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.

    1997-12-31

    By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data.

  3. The frozen-field approximation and the Ginzburg-Landau equations of superconductivity.

    SciTech Connect

    Kaper, H. G.; Nordborg, H.; Univ. of Chicago

    2001-03-01

    The Ginzburg-Landau (GL) equations of superconductivity provide a computational model for the study of magnetic flux vortices in type-II superconductors. In this article it is shown through numerical examples and rigorous mathematical analysis that the GL model reduces to the frozen-field model when the charge of the Cooper pairs (the superconducting charge carriers) goes to zero while the applied field stays near the upper critical field.

  4. First- and second-order transitions for a superconducting cylinder in a magnetic field obtained from a self-consistent solution of the Ginzburg-Landau equations

    SciTech Connect

    Zharkov, G. F.

    2001-06-01

    Based on self-consistent solution of nonlinear GL equations, the phase boundary is found, which divides the regions of first- and second-order phase transitions to normal state of a superconducting cylinder of radius R, placed in magnetic field and remaining in the state of fixed vorticity m. This boundary is a complicated function of the parameters (m,R,{kappa}) ({kappa} is the GL parameter), which does not coincide with the simple phase boundary {kappa}=1/{radical}2, dividing the regions of first- and second-order phase transitions in infinite (open) superconducting systems.

  5. Counterpart of the Darrieus-Landau instability at a magnetic deflagration front

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    The magnetic instability at the front of the spin avalanche in a crystal of molecular magnets is considered. This phenomenon reveals similar features with the Darrieus-Landau instability, inherent to classical combustion flame fronts. The instability growth rate and the cutoff wavelength are investigated with respect to the strength of the external magnetic field, both analytically in the limit of an infinitely thin front and numerically for finite-width fronts. The presence of quantum tunneling resonances is shown to increase the growth rate significantly, which may lead to a possible transition from deflagration to detonation regimes. Different orientations of the crystal easy axis are shown to exhibit opposite stability properties. In addition, we suggest experimental conditions that could evidence the instability and its influence on the magnetic deflagration velocity.

  6. Magnetic Photon Splitting: The S-Matrix Formulation in the Landau Representation

    NASA Technical Reports Server (NTRS)

    Baring, Matthew G.

    1999-01-01

    Calculations of reaction rates for the third-order QED process of photon splitting gamma yields gamma.gamma in strong magnetic fields traditionally have employed either the effective Lagrangian method or variants of Schwinger's proper-time technique. Recently, Mentzel, Berg and Wunner [1] presented an alternative derivation via an S-matrix formulation in the Landau representation. Advantages of such a formulation include the ability to compute rates near pair resonances above pair threshold. This paper presents new developments of the Landau representation formalism as applied to photon splitting, providing significant, advances beyond the work of [1] by summing over the spin quantum numbers of the electron propagators, and analytically integrating over the component of momentum of the intermediate states that is parallel to field. The ensuing tractable expressions for the scattering amplitudes are satisfyingly compact, and of an appearance familiar to S-matrix theory applications. Such developments can facilitate numerical computations of splitting considerably both below and above pair threshold. Specializations to two regimes of interest are obtained, namely the limit of highly supercritical fields and the domain where photon energies are far inferior to that for the threshold of single-photon pair creation. In particular, for the first time the low-frequency amplitudes are simply expressed in terms of the Gamma function, its integral and its derivatives. In addition, the equivalence of the asymptotic forms in these two domains to extant results from effective Lagrangian/proper- time formulations is demonstrated.

  7. Optically Pumped Nuclear Magnetic Resonance near Landau level filling ν = 1/3

    NASA Astrophysics Data System (ADS)

    Khandelwal, P.; Kuzma, N. N.; Barrett, S. E.; Pfeiffer, L. N.; West, K. W.

    1997-03-01

    Optical pumping enables the direct detection of the nuclear magnetic resonance signal of ^71Ga nuclei located in an electron doped GaAs quantum well.footnote S. E. Barrett et al., Phys. Rev. Lett. 72, 1368 (1994) Using this technique, measurements of the Knight shift (K_S)footnote S. E. Barrett et al., Phys. Rev. Lett. 74, 5112 (1995) and spin-lattice relaxation time (T_1)footnote R. Tycko et al., Science 268, 1460 (1995) have been carried out in the Quantum Hall regimes. In this talk will present our recent measurements of KS and T1 near Landau level filling ν = 1/3, which were carried out in high magnetic fields (up to 12 Tesla) and at low temperatures (T < 1 Kelvin). We will compare these results to the data obtained near ν = 1 and ν = 2/3.

  8. Deviation from the Landau-Lifshitz-Gilbert equation in the inertial regime of the magnetization

    NASA Astrophysics Data System (ADS)

    Olive, E.; Lansac, Y.; Meyer, M.; Hayoun, M.; Wegrowe, J.-E.

    2015-06-01

    We investigate in details the inertial dynamics of a uniform magnetization in the ferromagnetic resonance context. Analytical predictions and numerical simulations of the complete equations within the Inertial Landau-Lifshitz-Gilbert (ILLG) model are presented. In addition to the usual precession resonance, the inertial model gives a second resonance peak associated to the nutation dynamics provided that the damping is not too large. The analytical resolution of the equations of motion yields both the precession and nutation angular frequencies. They are function of the inertial dynamics characteristic time τ, the dimensionless damping α, and the static magnetic field H. A scaling function with respect to ατγH is found for the nutation angular frequency, also valid for the precession angular frequency when ατγH ≫ 1. Beyond the direct measurement of the nutation resonance peak, we show that the inertial dynamics of the magnetization has measurable effects on both the width and the angular frequency of the precession resonance peak when varying the applied static field. These predictions could be used to experimentally identify the inertial dynamics of the magnetization proposed in the ILLG model.

  9. Time-asymptotic field amplitudes in nonlinear Landau damping

    SciTech Connect

    Buchanan, M.; Kirkitelos, P.; Dorning, J.J. )

    1993-01-01

    The behavior of an electrostatic plasma wave of initial amplitude Ei in a collisionless electron plasma depends crucially on the ratio [delta] = [gamma]L/[omega]B, where [gamma]L is the damping coefficient calculated from linear plasma kinetic theory and [omega]B = (ekEi/m)[sup 1/2] is the [open quotes]bounce[close quotes] frequency for trapped electrons. For sufficiently small E[sub i], i.e., [delta] [much gt] 1, the wave damps away completely; conversely, a wave of large initial amplitude, for which [delta] [much lt] 1, saturates at a finite final amplitude due to the nonlinear effects of particle trapping. In this paper, we report results concerning the transition region [delta] [approximately] 0(1), which separates these two regimes. For the case of weak damping, i.e., [vert bar][gamma]L/[omega]p[vert bar][much lt]1, where [omega]p is the plasma frequency, we calculate analytically the critical value [delta][sub i,e] below which complete damping occurs and derive the first explicit analytic relationship between E[sub i] and E[sub f], the time-asymptotic amplitude, for E[sub i] above the critical value E[sub i,c] = (m,ek)([gamma]L/[delta][sub i,c]). The results predict an interesting phenomenon - a finite jump [delta]E in the final field amplitude as E[sub i] is increased through E[sub i,c]. We have corroborated the reality of this phenomenon through large-scale numerical simulations of the Vlasov-Poisson system, carried out using the spectral splitting code of Klimas. These important new results establish a detailed picture of the fundamental transition between linear and nonlinear Landau damping and, in particular, show that the onset of essentially nonlinear behavior occurs very abruptly as the initial wave amplitude increases through its critical value.

  10. Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets with competing interactions

    DOE PAGESBeta

    Lin, Shi-Zeng; Hayami, Satoru

    2016-02-01

    Magnetic skyrmions have attracted considerable attention recently for their huge potential in spintronic applications. Generally skyrmions are big compared to the atomic lattice constant, which allows for the Ginzburg-Landau type description in the continuum limit. This description successfully captures the main experimental observations on skyrmions in B20 compound without inversion symmetry. Skyrmions can also exist in inversion-symmetric magnets with competing interactions. Here, we derive a general Ginzburg-Landau theory for skyrmions in these magnets valid in the long-wavelength limit. We study the unusual static and dynamical properties of skyrmions based on the derived Ginzburg-Landau theory. We show that an easy axismore » spin anisotropy is sufficient to stabilize a skyrmion lattice. Interestingly, the skyrmion in inversion-symmetric magnets has a new internal degree of freedom associated with the rotation of helicity, i.e., the “spin” of the skyrmion as a particle, in addition to the usual translational motion of skyrmions (orbital motion). The orbital and spin degree of freedoms of an individual skyrmion can couple to each other, and give rise to unusual behavior that is absent for the skyrmions stabilized by the Dzyaloshinskii-Moriya interaction. Finally, the derived Ginzburg-Landau theory provides a convenient and general framework to discuss skyrmion physics and will facilitate the search for skyrmions in inversion-symmetric magnets.« less

  11. Ginzburg-Landau theory for skyrmions in inversion-symmetric magnets with competing interactions

    NASA Astrophysics Data System (ADS)

    Lin, Shi-Zeng; Hayami, Satoru

    2016-02-01

    Magnetic skyrmions have attracted considerable attention recently for their huge potential in spintronic applications. Generally skyrmions are big compared to the atomic lattice constant, which allows for the Ginzburg-Landau type description in the continuum limit. Such a description successfully captures the main experimental observations on skyrmions in B20 compound without inversion symmetry. Skyrmions can also exist in inversion-symmetric magnets with competing interactions. Here, we derive a general Ginzburg-Landau theory for skyrmions in these magnets valid in the long-wavelength limit. We study the unusual static and dynamical properties of skyrmions based on the derived Ginzburg-Landau theory. We show that an easy axis spin anisotropy is sufficient to stabilize a skyrmion lattice. Interestingly, the skyrmion in inversion-symmetric magnets has a new internal degree of freedom associated with the rotation of helicity, i.e., the "spin" of the skyrmion as a particle, in addition to the usual translational motion of skyrmions (orbital motion). The orbital and spin degree of freedoms of an individual skyrmion can couple to each other, and give rise to unusual behavior that is absent for the skyrmions stabilized by the Dzyaloshinskii-Moriya interaction. The derived Ginzburg-Landau theory provides a convenient and general framework to discuss skyrmion physics and will facilitate the search for skyrmions in inversion-symmetric magnets.

  12. Modulation of bilayer quantum Hall states by tilted-field-induced subband-Landau-level coupling

    NASA Astrophysics Data System (ADS)

    Kumada, N.; Iwata, K.; Tagashira, K.; Shimoda, Y.; Muraki, K.; Hirayama, Y.; Sawada, A.

    2008-04-01

    We study effects of tilted magnetic fields on energy levels in a double-quantum-well (DQW) system, focusing on the coupling of subbands and Landau levels (LLs). The subband-LL coupling induces anticrossings between LLs directly manifested in the magnetoresistance. The anticrossing gap becomes larger than the spin splitting at the tilting angle θ˜20° and larger than the cyclotron energy at θ˜50° , demonstrating that the subband-LL coupling exerts a strong influence on quantum Hall states even at a relatively small θ and plays a dominant role for larger θ . We also find that when the DQW potential is asymmetric, LL coupling occurs even within a subband. Calculations including higher-order coupling reproduce the experimental results quantitatively well.

  13. Influence of the Nonlinearity Parameter on the Solar Wind Sub-ion Magnetic Energy Spectrum: FLR-Landau Fluid Simulations

    NASA Astrophysics Data System (ADS)

    Sulem, P. L.; Passot, T.; Laveder, D.; Borgogno, D.

    2016-02-01

    The cascade of kinetic Alfvén waves (KAWs) at sub-ion scales in the solar wind is simulated numerically using a fluid approach that retains ion and electron Landau damping, together with ion finite Larmor radius (FLR) corrections. Assuming initially equal and isotropic ion and electron temperatures, and an ion beta equal to unity, different simulations are performed by varying the propagation direction and the amplitude of KAWs that are randomly driven at a transverse wavenumber k0 such that {k}0{d}i=0.18 (where di is the proton inertial length), in order to maintain a prescribed level of turbulent fluctuations. The resulting turbulent regimes are characterized by the nonlinearity parameter, defined as the ratio of the characteristic times of Alfvén wave propagation and of the transverse nonlinear dynamics. The corresponding transverse magnetic energy spectra display power laws with exponents spanning a range of values consistent with spacecraft observations. The meandering of the magnetic field lines and the homogenization of ion temperature along these lines are shown to be related to the strength of the turbulence, measured by the nonlinearity parameter. The results are interpreted in terms of a recently proposed phenomenological model where the homogenization process along field lines induced by Landau damping plays a central role.

  14. Modified Fermi energy of electrons in a superhigh magnetic field

    NASA Astrophysics Data System (ADS)

    Zhu, Cui; Gao, Zhi Fu; Li, Xiang Dong; Wang, Na; Yuan, Jian Ping; Peng, Qiu He

    2016-04-01

    In this paper, we investigate the electron Landau level stability and its influence on the electron Fermi energy, EF(e), in the circumstance of magnetars, which are powered by magnetic field energy. In a magnetar, the Landau levels of degenerate and relativistic electrons are strongly quantized. A new quantity gn, the electron Landau level stability coefficient is introduced. According to the requirement that gn decreases with increasing the magnetic field intensity B, the magnetic field index β in the expression of EF(e) must be positive. By introducing the Dirac-δ function, we deduce a general formulae for the Fermi energy of degenerate and relativistic electrons, and obtain a particular solution to EF(e) in a superhigh magnetic field (SMF). This solution has a low magnetic field index of β = 1/6, compared with the previous one, and works when ρ ≥ 107g cm-3 and Bcr ≪ B ≤ 1017 Gauss. By modifying the phase space of relativistic electrons, a SMF can enhance the electron number density ne, and decrease the maximum of electron Landau level number, which results in a redistribution of electrons. According to Pauli exclusion principle, the degenerate electrons will fill quantum states from the lowest Landau level to the highest Landau level. As B increases, more and more electrons will occupy higher Landau levels, though gn decreases with the Landau level number n. The enhanced ne in a SMF means an increase in the electron Fermi energy and an increase in the electron degeneracy pressure. The results are expected to facilitate the study of the weak-interaction processes inside neutron stars and the magnetic-thermal evolution mechanism for magnetars.

  15. Optically Pumped Nuclear Magnetic Resonance near Landau level fillings ν = 1/2 and ν = 2/3

    NASA Astrophysics Data System (ADS)

    Kuzma, N. N.; Khandelwal, P.; Barrett, S. E.; Pfeiffer, L. N.; West, K. W.

    1997-03-01

    Optical pumping enables the direct detection of the nuclear magnetic resonance signal of ^71Ga nuclei located in an electron doped GaAs quantum well.footnote S. E. Barrett et al., Phys. Rev. Lett. 72, 1368 (1994) Using this technique, measurements of the Knight shift (K_S)footnote S. E. Barrett et al., Phys. Rev. Lett. 74, 5112 (1995) and spin-lattice relaxation time (T_1)footnote R. Tycko et al., Science 268, 1460 (1995) have been carried out in the Quantum Hall regimes. In this talk will present our recent measurements of KS and T1 near Landau level fillings ν = 1/2 and ν = 2/3, which were carried out in high magnetic fields (up to 12 Tesla) and at low temperatures (T < 1 Kelvin). We will discuss these results in light of our current understanding of the data obtained near ν = 1.

  16. New squeezed landau states

    NASA Technical Reports Server (NTRS)

    Aragone, C.

    1993-01-01

    We introduce a new set of squeezed states through the coupled two-mode squeezed operator. It is shown that their behavior is simpler than the correlated coherent states introduced by Dodonov, Kurmyshev, and Man'ko in order to quantum mechanically describe the Landau system, i.e., a planar charged particle in a uniform magnetic field. We compare results for both sets of squeezed states.

  17. Driving magnetic skyrmions with microwave fields

    NASA Astrophysics Data System (ADS)

    Wang, Weiwei; Beg, Marijan; Zhang, Bin; Kuch, Wolfgang; Fangohr, Hans

    2015-07-01

    We show theoretically by numerically solving the Landau-Lifshitz-Gilbert equation with a classical spin model on a two-dimensional system that both magnetic skyrmions and skyrmion lattices can be moved with microwave magnetic fields. The mechanism is enabled by breaking the axial symmetry of the skyrmion, for example, through application of a static in-plane external field. The net velocity of the skyrmion depends on the frequency and amplitude of the microwave fields as well as the strength of the in-plane field. The maximum velocity is found where the frequency of the microwave coincides with the resonance frequency of the breathing mode of the skyrmions.

  18. Landau pole in the Standard Model with weakly interacting scalar fields

    NASA Astrophysics Data System (ADS)

    Hamada, Yuta; Kawana, Kiyoharu; Tsumura, Koji

    2015-07-01

    We consider the Standard Model with a new scalar field X which is an nX representation of the SU (2)L with a hypercharge YX. The renormalization group running effects on the new scalar quartic coupling constants are evaluated. Even if we set the scalar quartic coupling constants to be zero at the scale of the new scalar field, the coupling constants are induced by the one-loop effect of the weak gauge bosons. Once non-vanishing couplings are generated, the couplings rapidly increase by renormalization group effect of the quartic coupling constant itself. As a result, the Landau pole appears below Planck scale if nX ≥ 4. We find that the scale of the obtained Landau pole is much lower than that evaluated by solving the one-loop beta function of the gauge coupling constants.

  19. From Landau`s hydrodynamical model to field theory model to field theory models of multiparticle production: a tribute to Peter...

    SciTech Connect

    Cooper, F.

    1996-12-31

    We review the assumptions and domain of applicability of Landau`s Hydrodynamical Model. By considering two models of particle production, pair production from strong electric fields and particle production in the linear {sigma} model, we demonstrate that many of Landau`s ideas are verified in explicit field theory calculations.

  20. SU(3) Landau gauge gluon and ghost propagators using the logarithmic lattice gluon field definition

    SciTech Connect

    Ilgenfritz, Ernst-Michael; Menz, Christoph; Mueller-Preussker, Michael; Schiller, Arwed; Sternbeck, Andre

    2011-03-01

    We study the Landau gauge gluon and ghost propagators of SU(3) gauge theory, employing the logarithmic definition for the lattice gluon fields and implementing the corresponding form of the Faddeev-Popov matrix. This is necessary in order to consistently compare lattice data for the bare propagators with that of higher-loop numerical stochastic perturbation theory. In this paper we provide such a comparison, and introduce what is needed for an efficient lattice study. When comparing our data for the logarithmic definition to that of the standard lattice Landau gauge we clearly see the propagators to be multiplicatively related. The data of the associated ghost-gluon coupling matches up almost completely. For the explored lattice spacings and sizes discretization artifacts, finite size, and Gribov-copy effects are small. At weak coupling and large momentum, the bare propagators and the ghost-gluon coupling are seen to be approached by those of higher-order numerical stochastic perturbation theory.

  1. Orbital Magnetism of Bloch Electrons: II. Application to Single-Band Models and Corrections to Landau-Peierls Susceptibility

    NASA Astrophysics Data System (ADS)

    Ogata, Masao

    2016-06-01

    Orbital susceptibility for Bloch electrons is calculated for the first time up to the first order with respect to overlap integrals between the neighboring atomic orbitals, assuming single-band models. A general and rigorous theory of orbital susceptibility developed in the preceding paper is applied to single-band models in two-dimensional square and triangular lattices. In addition to the Landau-Peierls orbital susceptibility, it is found that there are comparable contributions from the Fermi surface and from the occupied states in the partially filled band called intraband atomic diamagnetism. This result means that the Peierls phase used in tight-binding models is insufficient as the effect of magnetic field.

  2. Electronic properties of graphite in tilted magnetic fields

    SciTech Connect

    Goncharuk, Nataliya A.; Smrčka, Ludvík

    2014-05-15

    The minimal nearest-neighbor tight-binding model with the Peierls substitution is employed to describe the electronic structure of Bernal-stacked graphite subject to tilted magnetic fields. We show that while the presence of the in-plane component of the magnetic field has a negligible effect on the Landau level structure at the K point of the graphite Brillouin zone, at the H point it leads to the experimentally observable splitting of Landau levels which grows approximately linearly with the in-plane field intensity.

  3. Magnetic field sensor

    NASA Astrophysics Data System (ADS)

    Silva, Nicolas

    2012-09-01

    Earlier papers1-3 in this journal have described experiments on measuring the magnetic fields of current-carrying wires and permanent magnets using magnetic field probes of various kinds. This paper explains how to use an iPad and the free app MagnetMeter-3D Vector Magnetometer and Accelerometer4 (compass HD) to measure the magnetic fields.

  4. Aharonov-Anandan quantum phases and Landau quantization associated with a magnetic quadrupole moment

    NASA Astrophysics Data System (ADS)

    Fonseca, I. C.; Bakke, K.

    2015-12-01

    The arising of geometric quantum phases in the wave function of a moving particle possessing a magnetic quadrupole moment is investigated. It is shown that an Aharonov-Anandan quantum phase (Aharonov and Anandan, 1987) can be obtained in the quantum dynamics of a moving particle with a magnetic quadrupole moment. In particular, it is obtained as an analogue of the scalar Aharonov-Bohm effect for a neutral particle (Anandan, 1989). Besides, by confining the quantum particle to a hard-wall confining potential, the dependence of the energy levels on the geometric quantum phase is discussed and, as a consequence, persistent currents can arise from this dependence. Finally, an analogue of the Landau quantization is discussed.

  5. On the Infrared Behaviour of Landau Gauge Yang-Mills Theory with Differently Charged Scalar Fields

    SciTech Connect

    Alkofer, Reinhard; Maas, Axel; Macher, Veronika; Fister, Leonard

    2011-05-23

    Recently it has been argued that infrared singularities of the quark-gluon vertex of Landau gauge QCD can confine static quarks via a linear potential. It is demonstrated that the same mechanism also may confine fundamental scalar fields. This opens the possibility that within functional approaches static confinement is an universal property of the gauge sector even though it is formally represented in the functional equations of the matter sector. The colour structure of Dyson-Schwinger equations for fundamental and adjoint scalar fields is determined for the gauge groups SU(N) and G(2) exhibiting interesting cancellations purely due to colour algebra.

  6. Selective-field-ionization dynamics of a lithium m=2 Rydberg state: Landau-Zener model versus quantal approach

    SciTech Connect

    Foerre, M.; Hansen, J.P.

    2003-05-01

    The selective-field-ionization (SFI) dynamics of a Rydberg state of lithium with magnetic quantum number m=2 is studied in detail based on two different theoretical models: (1) a close coupling integration of the Schroedinger equation and (2) the multichannel (incoherent) Landau-Zener (MLZ) model. The m=2 states are particularly interesting, since they define a border zone between fully adiabatic (m=0,1) and fully diabatic (m>2) ionization dynamics. Both sets of calculations are performed up to, and above, the classical ionization limit. It is found that the MLZ model is excellent in the description of the fully diabatic dynamics while certain discrepancies between the time dependent quantal amplitudes appear when the dynamics become involved. Thus, in this region, the analysis of experimental SFI spectra should be performed with care.

  7. Compton scattering in strong magnetic fields

    NASA Technical Reports Server (NTRS)

    Daugherty, Joseph K.; Harding, Alice K.

    1986-01-01

    The relativistic cross section for Compton scattering by electrons in strong magnetic fields is derived. The results confirm and extend earlier work which has treated only transitions to the lowest or first excited Landau levels. For the teragauss field strengths expected in neutron star magnetospheres, the relative rates for excited state transitions are found to be significant, especially for incident photon energies several times the cyclotron frequency. Since these transitions must result in the rapid emission of one or more cyclotron photons as well as the Compton-scattered photon, the scattering process actually becomes a photon 'splitting' mechanism which acts to soften hard photon spectra, and also provides a specific mechanism for populating higher Landau levels in the electron distribution function. The results should be significant for models of gamma-ray bursters and pulsating X-ray sources.

  8. Modulation of periodic field on the atomic current in optical lattices with Landau-Zener tunneling considered

    NASA Astrophysics Data System (ADS)

    Yan, Jie-Yun; Wang, Lan-Yu

    2016-09-01

    We investigate the atomic current in optical lattices under the presence of both constant and periodic external field with Landau-Zener tunneling considered. By simplifying the system to a two-band model, the atomic current is obtained based on the Boltzmann equations. We focus on three situations to discuss the influence of the Landau-Zener tunneling and periodic field on the atomic current. Numerical calculations show the atomic transient current would finally become the stable oscillation, whose amplitude and average value can be further adjusted by the periodic external field. It is concluded that the periodic external field could provide an effective modulation on the atomic current even when the Landau-Zener tunneling probability has almostly become a constant.

  9. Neutrino oscillations and the Landau-Zener formula

    SciTech Connect

    Kim, C.W.; Sze, W.K.; Nussinov, S.

    1987-06-15

    We discuss solar-neutrino oscillations and the Landau-Zener probability using a heuristic picture in analogy with an electron spin in a time-dependent magnetic field. The extreme nonadiabatic resonant oscillation is also briefly investigated.

  10. D mesons in a magnetic field

    NASA Astrophysics Data System (ADS)

    Gubler, Philipp; Hattori, Koichi; Lee, Su Houng; Oka, Makoto; Ozaki, Sho; Suzuki, Kei

    2016-03-01

    We investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral Ansätze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral D mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged D mesons are further subject to Landau level effects, which together with the mixing effects almost completely saturate the mass shifts obtained in our sum rule analysis.

  11. D mesons in a magnetic field

    DOE PAGESBeta

    Gubler, Philipp; Hattori, Koichi; Lee, Su Houng; Oka, Makoto; Ozaki, Sho; Suzuki, Kei

    2016-03-15

    In this paper, we investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral Ansatze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral D mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged D mesons are further subject to Landau level effects, which together with the mixingmore » effects almost completely saturate the mass shifts obtained in our sum rule analysis.« less

  12. Bifurcation analysis of Landau{endash}Lifshitz{endash}Gilbert dynamics under circularly polarized field

    SciTech Connect

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

    2001-06-01

    Uniform solutions of Landau{endash}Lifshitz{endash}Gilbert equation coupled with magnetostatic Maxwell equations are discussed in the case where the problem is rotationally invariant around a certain axis and the external field is circularly polarized in the perpendicular plane. It is shown that a remarkably rich variety of phase portraits is present in the dynamics, with two or four time-harmonic modes rigidly rotating with the field (P modes) and zero, one, or two quasiperiodic modes (Q modes). Different portraits are separated by bifurcation lines of saddle node, Andronov{endash}Hopf, homoclinic-saddle connection, and semistable-limit-cycle type. The complete phase portrait and bifurcation diagram of thin films with negligible crystal anisotropy is presented and discussed. {copyright} 2001 American Institute of Physics.

  13. Zener tunneling in superlattices in a magnetic field

    SciTech Connect

    Meinhold, D.; Leo, K.; Fromer, N.A.; Chemla, D.S.; Glutsch, S.; Bechstedt, F.; Kohler, K.

    2002-04-15

    We present a study of the Zener effect in the optical absorption of strongly coupled superlattices with both a magnetic and an electric field in growth direction. The in-plane continuum of electron states is discretized due to Landau quantization, which allows to directly observe the transition from discrete to continuum states due to Zener tunneling in a true 1D system.

  14. Lifshitz effects on vector condensate induced by a magnetic field

    NASA Astrophysics Data System (ADS)

    Wu, Ya-Bo; Lu, Jun-Wang; Liu, Mo-Lin; Lu, Jian-Bo; Zhang, Cheng-Yuan; Yang, Zhuo-Qun

    2014-05-01

    By numerical and analytical methods, we study in detail the effects of the Lifshitz dynamical exponent z on the vector condensate induced by an applied magnetic field in the probe limit. Concretely, in the presence of the magnetic field, we obtain the Landau level independent of z, and we also find the critical value by coupling a Maxwell complex vector field and an SU(2) field into a (3+1)-dimensional Lifshitz black hole, respectively. The research results show that for the two models with the lowest Landau level, the increasing z improves the response of the critical temperature to the applied magnetic field even without the charge density, and the analytical results uphold the numerical results. In addition, we find that, even in the Lifshitz black hole, the Maxwell complex vector model is still a generalization of the SU(2) Yang-Mills model. Furthermore, we construct the square vortex lattice and discuss the implications of these results.

  15. Photospheric magnetic fields

    NASA Technical Reports Server (NTRS)

    Howard, R.

    1972-01-01

    Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

  16. Neutrino dispersion in external magnetic fields

    SciTech Connect

    Kuznetsov, A. V.; Mikheev, N. V.; Vassilevskaya, L. A.; Raffelt, G. G.

    2006-01-15

    We calculate the neutrino self-energy operator {sigma}(p) in the presence of a magnetic field B. In particular, we consider the weak-field limit eB<field' m{sub l}{sup 2}<field, we show that it is crucial to include the contributions from all Landau levels of the intermediate charged lepton, not just the ground state. For the conditions of the early universe where the background medium consists of a charge-symmetric plasma, the pure B-field contribution to the neutrino dispersion relation is proportional to (eB){sup 2} and thus comparable to the contribution of the magnetized plasma.

  17. The role of magnetic fields in hyperon stars

    SciTech Connect

    Gomes, R. O.; Vasconcellos, C. A. Z.; Dexheimer, V.

    2014-05-09

    We investigate the effects of strong magnetic fields (SMF) on the properties of neutron stars that have hyperons in their composition. The matter is described by a hadronic model in which a parameterized and derivative coupling between hadrons and mesons is considered. We study the magnetic effects on the equation of state (EoS) from Landau quantization, assuming a density dependent static magnetic field that reaches 10{sup 19} G in the center of the star. The Tolman- Oppenheimer-Volkoff (TOV) equations are solved in order to show the dependence of the massradius relation and population of hyperon stars on the central magnetic field and on different hyperon coupling schemes.

  18. Landau-Lifshitz-Gilbert micromagnetic simulation on spin transfer torque efficiency of sub-30 nm perpendicular magnetic tunnel junctions with etching damage

    NASA Astrophysics Data System (ADS)

    Ito, Kenchi; Ohuchida, Satoshi; Muraguchi, Masakazu; Endoh, Tetsuo

    2015-04-01

    The threshold current density Jc0, effective anisotropy field Heff, and the spin transfer torque (STT) efficiency of magnetic tunnel junctions with perpendicular anisotropy (p-MTJs) with the free layer diameter d from 10 to 30 nm was evaluated when etching degraded the saturation magnetization Ms and/or anisotropic energy Ku of the ferromagnetic layers with thickness of 1 to 3 nm around the pillar, using Landau-Lifshitz-Gilbert (LLG) micro-magnetic simulation. The STT efficiency for MTJs with only Ms reduction increased with a decrease in d, which reproduces the experimental trend. Jc0 and Heff for MTJs with only Ku reduction dramatically decreased even when the thickness of the damaged region is only 1 nm. The thickness of the damaged region had a large influence on Jc0 and Heff for MTJs with either Ms or Ku reduction.

  19. Inferring generalized time-dependent complex Ginzburg-Landau equations from modulus and gauge-field information

    SciTech Connect

    Yu, Rotha P.; Paganin, David M.; Morgan, Michael J.

    2008-04-01

    We develop a means to 'measure' the generalized 2+1-dimensional time-dependent complex Ginzburg-Landau equation, given both the wave-function modulus and gauge-field information over a series of five planes that are closely spaced in time. The methodology is tested using simulated data for a thin-film high-temperature superconductor in the Meissner state.

  20. Nonlinear magnetization dynamics of antiferromagnetic spin resonance induced by intense terahertz magnetic field

    NASA Astrophysics Data System (ADS)

    Mukai, Y.; Hirori, H.; Yamamoto, T.; Kageyama, H.; Tanaka, K.

    2016-01-01

    We report on the nonlinear magnetization dynamics of a HoFeO3 crystal induced by a strong terahertz magnetic field resonantly enhanced with a split ring resonator and measured with magneto-optical Kerr effect microscopy. The terahertz magnetic field induces a large change (˜40%) in the spontaneous magnetization. The frequency of the antiferromagnetic resonance decreases in proportion to the square of the magnetization change. A modified Landau-Lifshitz-Gilbert equation with a phenomenological nonlinear damping term quantitatively reproduced the nonlinear dynamics.

  1. Magnetic field generator

    DOEpatents

    Krienin, Frank

    1990-01-01

    A magnetic field generating device provides a useful magnetic field within a specific retgion, while keeping nearby surrounding regions virtually field free. By placing an appropriate current density along a flux line of the source, the stray field effects of the generator may be contained. One current carrying structure may support a truncated cosine distribution, and it may be surrounded by a current structure which follows a flux line that would occur in a full coaxial double cosine distribution. Strong magnetic fields may be generated and contained using superconducting cables to approximate required current surfaces.

  2. On Cosmic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Florido, E.; Battaner, E.

    2010-12-01

    Magnetic fields are present in all astrophysical media. However, many models and interpretations of observations often ignore them, because magnetic fields are difficult to handle and because they produce complicated morphological features. Here we will comment on the basic intuitive properties, which even if not completely true, provide a first guiding insight on the physics of a particular astrophysical problem. These magnetic properties are not mathematically demonstrated here. How magnetic fields evolve and how they introduce dynamical effects are considered, also including a short comment on General Relativity Magnetohydrodynamics. In a second part we consider some audacious and speculative matters. They are answers to three questions: a) How draw a cube without lifting the pencil from the paper so that when the pen passes through the same side do in the same direction? B) Are MILAGRO anisotropies miraculous? C) Do cosmic magnetic lenses exist?. The last two questions deal with issues related with the interplay between magnetic fields and cosmic ray propagation.

  3. Landau damping of auroral hiss

    NASA Technical Reports Server (NTRS)

    Morgan, D. D.; Gurnett, D. A.; Menietti, J. D.; Winningham, J. D.; Burch, J. L.

    1994-01-01

    Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit omega/k(sub parallel) to values of 3.4 x 10(exp 4) km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, omega/k(sub parallel) is limited to values greater than 6.8 x 10(exp 4) km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that omega/k(sub parallel) corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities.

  4. Landau damping of auroral hiss

    SciTech Connect

    Morgan, D.D.; Gurnett, D.A.; Menietti, J.D.; Winningham, J.D.; Burch, J.L.

    1994-02-01

    Auroral hiss is observed to propagate over distances comparable to an Earth radius from its source in the auroral oval. The role of Landau damping is investigated for upward propagating auroral hiss. By using a ray tracing code and a simplified model of the distribution function, the effect of Landau damping is calculated for auroral hiss propagation through the environment around the auroral oval. Landau damping is found to be the likely mechanism for explaining some of the one-sided auroral hiss funnels observed by Dynamics Explorer 1. It is also found that Landau damping puts a lower limit on the wavelength of auroral hiss. Poleward of the auroral oval, Landau damping is found in a typical case to limit {omega}/k{parallel} to values of 3.4 x 10{sup 4} km/s or greater, corresponding to resonance energies of 3.2 keV or greater and wavelengths of 2 km or greater. For equatorward propagation, {omega}/k{parallel} is limited to values greater than 6.8 x 10{sup 4} km/s, corresponding to resonance energies greater than 13 keV and wavelengths greater than 3 km. Independent estimates based on measured ratios of the magnetic to electric field intensity also show that {omega}/k{parallel} corresponds to resonance energies greater than 1 keV and wavelengths greater than 1 km. These results lead to the difficulty that upgoing electron beams sufficiently energetic to directly generate auroral hiss of the inferred wavelength are not usually observed. A partial transmission mechanism utilizing density discontinuities oblique to the magnetic field is proposed for converting auroral hiss to wavelengths long enough to avoid damping of the wave over long distances. Numerous reflections of the wave in an upwardly flared density cavity could convert waves to significantly increased wavelengths and resonance velocities. 36 refs., 12 figs., 4 tabs.

  5. Polarization and magnetization dynamics of a field-driven multiferroic structure.

    PubMed

    Sukhov, Alexander; Jia, Chenglong; Horley, Paul P; Berakdar, Jamal

    2010-09-01

    We consider a multiferroic chain with a linear magnetoelectric coupling induced by electrostatic screening at the ferroelectric/ferromagnet interface. We study theoretically the dynamic ferroelectric and magnetic response to external magnetic and electric fields by utilizing an approach based on coupled Landau-Khalatnikov and finite-temperature Landau-Lifshitz-Gilbert equations. Additionally, we make comparisons with Monte Carlo calculations. It is demonstrated that for material parameters corresponding to BaTiO(3)/Fe the polarization and the magnetization are controllable by external magnetic and electric fields, respectively. PMID:21403274

  6. Magnetic Fields in Galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Magnetic fields are a major agent in the interstellar medium. They contribute significantly to the total pressure which balances the gas disk against gravitation. They affect the gas flows in spiral arms (Gómez and Cox, 2002). The effective sound speed of the gas is increased by the presence of strong fields which reduce the shock strength. The interstellar fields are closely connected to gas clouds. They affect the dynamics of the gas clouds (Elmegreen, 1981; de Avillez and Breitschwerdt, 2004). The stability and evolution of gas clouds are also influenced by magnetic fields, but it is not understood how (Crutcher, 1999; see Chap. 7). Magnetic fields are essential for the onset of star formation as they enable the removal of angular momentum from the protostellar cloud during its collapse (magnetic braking, Mouschovias, 1990). Strong fields may shift the stellar mass spectrum towards the more massive stars (Mestel, 1990). MHD turbulence distributes energy from supernova explosions within the ISM (Subramanian, 1998) and regenerates the field via the dynamo process (Wielebinski, R., Krause, 1993, Beck et al., 1996; Sect. 6). Magnetic reconnection is a possible heating source for the ISM and halo gas (Birk et al., 1998). Magnetic fields also control the density and distribution of cosmic rays in the ISM. A realistic model for any process in the ISM needs basic information about the magnetic field which has to be provided by observations.

  7. Thermoelectric power of n-InSb in a transverse quantizing magnetic field

    SciTech Connect

    Gadzhialiev, M. M. Bashirov, R. R.; Pirmagomedov, Z. Sh.; Efendieva, T. N.; Mädge, H.; Filar, K.

    2015-07-15

    The thermoelectric power of electronic InSb is investigated in a transverse magnetic field up to 14 T at 80 K. It is established that the experimental results for a quantizing magnetic field agree with theoretical data obtained without accounting for spin splitting of the Landau levels.

  8. Magnetic field generated resistivity maximum in graphite

    NASA Technical Reports Server (NTRS)

    Wollam, J. A.; Kreps, L. W.; Rojeski, M.; Vold, T.; Devaty, R.

    1976-01-01

    In zero magnetic field, B, the electrical resistivity, rho(O,T) of highly oriented pyrolytic (polycrystalline) graphite drops smoothly with decreasing T, becoming constant below 4 K. However, in a fixed applied magnetic field B, the resistivity rho(B,T) goes through a maximum as a function of T, with larger maximum for larger B. The temperature of the maximum increases with B, but saturates to a constant value near 25 K (exact T depends on sample) at high B. In single crystal graphite a maximum in rho(B,T) as a function of T is also present, but has the effects of Landau level quantization superimposed. Several possible explanations for the rho(B,T) maximum are proposed, but a complete explanation awaits detailed calculations involving the energy band structure of graphite, and the particular scattering mechanisms involved.

  9. Landau damping

    SciTech Connect

    Ng, K.Y.; /Fermilab

    2010-10-01

    Section 2.5.8 of the Handbook of Accelerator Physics and Engineering on Landau damping is rewritten. An solvable example is first given to demonstrate the interplay between Landau damping and decoherence. This example is an actual one when the beam oscillatory motion is driven by a wake force. The dispersion relation is derived and its implication on Landau damping is illustrated. The rest of the article touches on the Landau damping of transverse and longitudinal beam oscillations. The stability criteria are given for a bunched beam and the changes of the criteria when the beam is lengthened and becomes unbunched.

  10. Magnetic field dosimeter development

    SciTech Connect

    Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

    1980-09-01

    In recent years there has been increased concern over potential health hazards related to exposure of personnel to magnetic fields. If exposure standards are to be established, then a means for measuring magnetic field dose must be available. To meet this need, the Department of Energy has funded development of prototype dosimeters at the Battelle Pacific Northwest Laboratory. This manual reviews the principle of operation of the dosimeter and also contains step-by-step instructions for its operation.

  11. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi

    The magnetic-field characteristics in spiral galaxies are investigated, with emphasis on the Milky Way. The dynamo theory is considered, and axisymmetric spiral (ASS) and bisymmetric spiral (BSS) magnetic fields are analyzed. Toroidal and poloidal magnetic fields are discussed.

  12. Dynamical mass generation in QED with weak magnetic fields

    SciTech Connect

    Ayala, A.; Rojas, E.; Bashir, A.; Raya, A.

    2006-09-25

    We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of magnetic fields using Schwinger-Dyson equations. We show that, contrary to the case where the magnetic field is strong, in the weak field limit eB << m(0)2, where m(0) is the value of the dynamically generated mass in the absence of the magnetic field, masses are generated above a critical value of the coupling and that this value is the same as in the case with no magnetic field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB)2.

  13. Solar Wind Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Smith, E. J.

    1995-01-01

    The magnetic fields originate as coronal fields that are converted into space by the supersonic, infinitely conducting, solar wind. On average, the sun's rotation causes the field to wind up and form an Archimedes Spiral. However, the field direction changes almost continuously on a variety of scales and the irregular nature of these changes is often interpreted as evidence that the solar wind flow is turbulent.

  14. Magnetic Field Measurement System

    SciTech Connect

    Kulesza, Joe; Johnson, Eric; Lyndaker, Aaron; Deyhim, Alex; Waterman, Dave; Blomqvist, K. Ingvar; Dunn, Jonathan Hunter

    2007-01-19

    A magnetic field measurement system was designed, built and installed at MAX Lab, Sweden for the purpose of characterizing the magnetic field produced by Insertion Devices (see Figure 1). The measurement system consists of a large granite beam roughly 2 feet square and 14 feet long that has been polished beyond laboratory grade for flatness and straightness. The granite precision coupled with the design of the carriage yielded minimum position deviations as measured at the probe tip. The Hall probe data collection and compensation technique allows exceptional resolution and range while taking data on the fly to programmable sample spacing. Additional flip coil provides field integral data.

  15. Magnetic Field Solver

    NASA Technical Reports Server (NTRS)

    Ilin, Andrew V.

    2006-01-01

    The Magnetic Field Solver computer program calculates the magnetic field generated by a group of collinear, cylindrical axisymmetric electromagnet coils. Given the current flowing in, and the number of turns, axial position, and axial and radial dimensions of each coil, the program calculates matrix coefficients for a finite-difference system of equations that approximates a two-dimensional partial differential equation for the magnetic potential contributed by the coil. The program iteratively solves these finite-difference equations by use of the modified incomplete Cholesky preconditioned-conjugate-gradient method. The total magnetic potential as a function of axial (z) and radial (r) position is then calculated as a sum of the magnetic potentials of the individual coils, using a high-accuracy interpolation scheme. Then the r and z components of the magnetic field as functions of r and z are calculated from the total magnetic potential by use of a high-accuracy finite-difference scheme. Notably, for the finite-difference calculations, the program generates nonuniform two-dimensional computational meshes from nonuniform one-dimensional meshes. Each mesh is generated in such a way as to minimize the numerical error for a benchmark one-dimensional magnetostatic problem.

  16. Magnetic fields at neptune.

    PubMed

    Ness, N F; Acuña, M H; Burlaga, L F; Connerney, J E; Lepping, R P; Neubauer, F M

    1989-12-15

    The National Aeronautics and Space Administration Goddard Space Flight Center-University of Delaware Bartol Research Institute magnetic field experiment on the Voyager 2 spacecraft discovered a strong and complex intrinsic magnetic field of Neptune and an associated magnetosphere and magnetic tail. The detached bow shock wave in the supersonic solar wind flow was detected upstream at 34.9 Neptune radii (R(N)), and the magnetopause boundary was tentatively identified at 26.5 R(N) near the planet-sun line (1 R(N) = 24,765 kilometers). A maximum magnetic field of nearly 10,000 nanoteslas (1 nanotesla = 10(-5) gauss) was observed near closest approach, at a distance of 1.18 R(N). The planetary magnetic field between 4 and 15 R(N) can be well represented by an offset tilted magnetic dipole (OTD), displaced from the center of Neptune by the surprisingly large amount of 0.55 R(N) and inclined by 47 degrees with respect to the rotation axis. The OTD dipole moment is 0.133 gauss-R(N)(3). Within 4 R(N), the magnetic field representation must include localized sources or higher order magnetic multipoles, or both, which are not yet well determined. The obliquity of Neptune and the phase of its rotation at encounter combined serendipitously so that the spacecraft entered the magnetosphere at a time when the polar cusp region was directed almost precisely sunward. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar, and no crossings of an imbedded magnetic field reversal or plasma neutral sheet were observed. The auroral zones are most likely located far from the rotation poles and may have a complicated geometry. The rings and all the known moons of Neptune are imbedded deep inside the magnetosphere, except for Nereid, which is outside when sunward of the planet. The radiation belts will have a complex structure owing to the absorption of energetic particles by the moons and rings of Neptune and losses associated with the significant changes

  17. Magnetic field control of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Ritzmann, Ulrike; Hinzke, Denise; Kehlberger, Andreas; Guo, Er-Jia; Kläui, Mathias; Nowak, Ulrich

    2015-11-01

    The origin of the suppression of the longitudinal spin Seebeck effect by applied magnetic fields is studied. We perform numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation of motion for an atomistic spin model and calculate the magnon accumulation in linear temperature gradients for different strengths of applied magnetic fields and different length scales of the temperature gradient. We observe a decrease of the magnon accumulation with increasing magnetic field and we reveal that the origin of this effect is a field dependent change of the frequency distribution of the propagating magnons. With increasing field the magnonic spin currents are reduced due to a suppression of parts of the frequency spectrum. By comparison with measurements of the magnetic field dependent longitudinal spin Seebeck effect in YIG thin films with various thicknesses, we find qualitative agreement between our model and the experimental data, demonstrating the importance of this effect for experimental systems.

  18. The knowledge-based system GRAPE and its application to Landau theory analysis for magnetic space groups

    NASA Astrophysics Data System (ADS)

    Gao, Junming; Cui, Zhan; Hao, Bailin

    1990-08-01

    A knowldge-based project, the GRAPE system(Group Representation and Application in Physics Environment), is described in this paper. The GRAPE system is designed to provide physicists with a group theoretical environment to help them solve problems in group theory and representation. The user can communicate with GRAPE in plain English. At the present stage, it contains the knowledge of crystallography point groups, space groups as well as magnetic space groups both in group structure and group representations. The GRAPE system consists of five modules besides the knowledge base and the data base: a natural language interface, a computation module, a tutprial module, a bibliography module, and a program library. Group theoretical analysis for the Landau theory of continuous phase transitions has been the first application of the GRAPE system. The calculation for determining directions of phase transition at the Γ point for 230 space groups, 230 grey space groups and 674 black and white magnetic space groups has been performed.

  19. High field superconducting magnets

    NASA Technical Reports Server (NTRS)

    Hait, Thomas P. (Inventor); Shirron, Peter J. (Inventor)

    2011-01-01

    A superconducting magnet includes an insulating layer disposed about the surface of a mandrel; a superconducting wire wound in adjacent turns about the mandrel to form the superconducting magnet, wherein the superconducting wire is in thermal communication with the mandrel, and the superconducting magnet has a field-to-current ratio equal to or greater than 1.1 Tesla per Ampere; a thermally conductive potting material configured to fill interstices between the adjacent turns, wherein the thermally conductive potting material and the superconducting wire provide a path for dissipation of heat; and a voltage limiting device disposed across each end of the superconducting wire, wherein the voltage limiting device is configured to prevent a voltage excursion across the superconducting wire during quench of the superconducting magnet.

  20. The interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Davis, L., Jr.

    1972-01-01

    Large-scale properties of the interplanetary magnetic field as determined by the solar wind velocity structure are examined. The various ways in which magnetic fields affect phenomena in the solar wind are summarized. The dominant role of high and low velocity solar wind streams that persist, with fluctuations and evolution, for weeks or months is emphasized. It is suggested that for most purposes the sector structure is better identified with the stream structure than with the magnetic polarity and that the polarity does not necessarily change from one velocity sector to the next. Several mechanisms that might produce the stream structure are considered. The interaction of the high and low velocity streams is analyzed in a model that is steady state when viewed in a frame that corotates with the sun.

  1. Crustal Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Taylor, Patrick T.; Ravat, D.; Frawley, James J.

    1999-01-01

    Cosmos 49, Polar Orbit Geophysical Observatory (POGO) (Orbiting Geophysical Observatory (OGO-2, 4 and 6)) and Magsat have been the only low-earth orbiting satellites to measure the crustal magnetic field on a global scale. These missions revealed the presence of long- wavelength (> 500 km) crustal anomalies predominantly located over continents. Ground based methods were, for the most part, unable to record these very large-scale features; no doubt due to the problems of assembling continental scale maps from numerous smaller surveys acquired over many years. Questions arose as to the source and nature of these long-wave length anomalies. As a result there was a great stimulant given to the study of the magnetic properties of the lower crust and upper mantle. Some indication as to the nature of these deep sources has been provided by the recent results from the deep crustal drilling programs. In addition, the mechanism of magnetization, induced or remanent, was largely unknown. For computational ease these anomalies were considered to result solely from induced magnetization. However, recent results from Mars Orbiter Laser Altimeter (MOLA), a magnetometer-bearing mission to Mars, have revealed crustal anomalies with dimensions similar to the largest anomalies on Earth. These Martian features could only have been produced by remanent magnetization, since Mars lacks an inducing field. The origin of long-wavelength crustal anomalies, however, has not been completely determined. Several large crustal magnetic anomalies (e.g., Bangui, Kursk, Kiruna and Central Europe) will be discussed and the role of future satellite magnetometer missions (Orsted, SUNSAT and Champ) in their interpretation evaluated.

  2. Magnetization dynamics using ultrashort magnetic field pulses

    NASA Astrophysics Data System (ADS)

    Tudosa, Ioan

    Very short and well shaped magnetic field pulses can be generated using ultra-relativistic electron bunches at Stanford Linear Accelerator. These fields of several Tesla with duration of several picoseconds are used to study the response of magnetic materials to a very short excitation. Precession of a magnetic moment by 90 degrees in a field of 1 Tesla takes about 10 picoseconds, so we explore the range of fast switching of the magnetization by precession. Our experiments are in a region of magnetic excitation that is not yet accessible by other methods. The current table top experiments can generate fields longer than 100 ps and with strength of 0.1 Tesla only. Two types of magnetic were used, magnetic recording media and model magnetic thin films. Information about the magnetization dynamics is extracted from the magnetic patterns generated by the magnetic field. The shape and size of these patterns are influenced by the dissipation of angular momentum involved in the switching process. The high-density recording media, both in-plane and perpendicular type, shows a pattern which indicates a high spin momentum dissipation. The perpendicular magnetic recording media was exposed to multiple magnetic field pulses. We observed an extended transition region between switched and non-switched areas indicating a stochastic switching behavior that cannot be explained by thermal fluctuations. The model films consist of very thin crystalline Fe films on GaAs. Even with these model films we see an enhanced dissipation compared to ferromagnetic resonance studies. The magnetic patterns show that damping increases with time and it is not a constant as usually assumed in the equation describing the magnetization dynamics. The simulation using the theory of spin-wave scattering explains only half of the observed damping. An important feature of this theory is that the spin dissipation is time dependent and depends on the large angle between the magnetization and the magnetic

  3. Gaussian, three-dimensional-XY, and lowest-Landau-level scalings in the low-field fluctuation magnetoconductivity of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

    SciTech Connect

    Costa, R.M.; Pureur, P.; Ghivelder, L.; Campa, J.A.; Rasines, I.

    1997-11-01

    Systematic measurements of low-field fluctuation magnetoconductivity in a single crystal of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} are reported. Gaussian, critical, and lowest-Landau-level scalings are observed. In the Gaussian regimes, large intervals corresponding to low-dimensional fluctuations are evidenced. Far above T{sub c}, effects of disorder produces a fluctuation spectrum characterized by a fractal topology. Decreasing the temperature, at first a homogeneous two-dimensional behavior is observed. Then, near T{sub c} a crossover occurs to a narrow three-dimensional (3D) mean-field regime. Still closer to T{sub c}, a scaling consistent with the predictions of the full dynamic 3D-XY universality class is clearly evidenced. This genuine critical regime is destroyed upon the application of magnetic fields above a few mT. For fields above a certain limit and in large temperature intervals, fluctuation magnetoconductivity scales as predicted by the lowest-Landau-level approximation of the Ginzburg-Landau theory. {copyright} {ital 1997} {ital The American Physical Society}

  4. Coronal Magnetic Field Models

    NASA Astrophysics Data System (ADS)

    Wiegelmann, Thomas; Petrie, Gordon J. D.; Riley, Pete

    2015-07-01

    Coronal magnetic field models use photospheric field measurements as boundary condition to model the solar corona. We review in this paper the most common model assumptions, starting from MHD-models, magnetohydrostatics, force-free and finally potential field models. Each model in this list is somewhat less complex than the previous one and makes more restrictive assumptions by neglecting physical effects. The magnetohydrostatic approach neglects time-dependent phenomena and plasma flows, the force-free approach neglects additionally the gradient of the plasma pressure and the gravity force. This leads to the assumption of a vanishing Lorentz force and electric currents are parallel (or anti-parallel) to the magnetic field lines. Finally, the potential field approach neglects also these currents. We outline the main assumptions, benefits and limitations of these models both from a theoretical (how realistic are the models?) and a practical viewpoint (which computer resources to we need?). Finally we address the important problem of noisy and inconsistent photospheric boundary conditions and the possibility of using chromospheric and coronal observations to improve the models.

  5. Duffing oscillation-induced reversal of magnetic vortex core by a resonant perpendicular magnetic field.

    PubMed

    Moon, Kyoung-Woong; Chun, Byong Sun; Kim, Wondong; Qiu, Z Q; Hwang, Chanyong

    2014-01-01

    Nonlinear dynamics of the magnetic vortex state in a circular nanodisk was studied under a perpendicular alternating magnetic field that excites the radial modes of the magnetic resonance. Here, we show that as the oscillating frequency is swept down from a frequency higher than the eigenfrequency, the amplitude of the radial mode is almost doubled to the amplitude at the fixed resonance frequency. This amplitude has a hysteresis vs. frequency sweeping direction. Our result showed that this phenomenon was due to a Duffing-type nonlinear resonance. Consequently, the amplitude enhancement reduced the vortex core-switching magnetic field to well below 10 mT. A theoretical model corresponding to the Duffing oscillator was developed from the Landau-Lifshitz-Gilbert equation to explore the physical origin of the simulation result. This work provides a new pathway for the switching of the magnetic vortex core polarity in future magnetic storage devices. PMID:25145837

  6. Tuning equilibration of quantum Hall edge states in graphene - Role of crossed electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Dubey, Sudipta; Deshmukh, Mandar M.

    2016-07-01

    We probe quantum Hall effect in a tunable 1-D lateral superlattice (SL) in graphene created using electrostatic gates. Lack of equilibration is observed along edge states formed by electrostatic gates inside the superlattice. We create strong local electric field at the interface of regions of different charge densities. Crossed electric and magnetic fields modify the wavefunction of the Landau Levels (LLs) - a phenomenon unique to graphene. In the region of copropagating electrons and holes at the interface, the electric field is high enough to modify the Landau levels resulting in increased scattering that tunes equilibration of edge states and this results in large longitudinal resistance.

  7. Resistance oscillations of two-dimensional electrons in crossed electric and tilted magnetic fields

    NASA Astrophysics Data System (ADS)

    Mayer, William; Vitkalov, Sergey; Bykov, A. A.

    2016-06-01

    The effect of dc electric field on transport of highly mobile two-dimensional electrons is studied in wide GaAs single quantum wells placed in titled magnetic fields. The study shows that in perpendicular magnetic field resistance oscillates due to electric-field induced Landau-Zener transitions between quantum levels that correspond to geometric resonances between cyclotron orbits and periodic modulation of electron density of states. Magnetic field tilt inverts these oscillations. Surprisingly the strongest inverted oscillations are observed at a tilt corresponding to nearly absent modulation of the electron density of states in regime of magnetic breakdown of semiclassical electron orbits. This phenomenon establishes an example of quantum resistance oscillations due to Landau quantization, which occur in electron systems with a constant density of states.

  8. Imaging the dynamics of free-electron Landau states.

    PubMed

    Schattschneider, P; Schachinger, Th; Stöger-Pollach, M; Löffler, S; Steiger-Thirsfeld, A; Bliokh, K Y; Nori, Franco

    2014-01-01

    Landau levels and states of electrons in a magnetic field are fundamental quantum entities underlying the quantum Hall and related effects in condensed matter physics. However, the real-space properties and observation of Landau wave functions remain elusive. Here we report the real-space observation of Landau states and the internal rotational dynamics of free electrons. States with different quantum numbers are produced using nanometre-sized electron vortex beams, with a radius chosen to match the waist of the Landau states, in a quasi-uniform magnetic field. Scanning the beams along the propagation direction, we reconstruct the rotational dynamics of the Landau wave functions with angular frequency ~100 GHz. We observe that Landau modes with different azimuthal quantum numbers belong to three classes, which are characterized by rotations with zero, Larmor and cyclotron frequencies, respectively. This is in sharp contrast to the uniform cyclotron rotation of classical electrons, and in perfect agreement with recent theoretical predictions. PMID:25105563

  9. Imaging the dynamics of free-electron Landau states

    PubMed Central

    Schattschneider, P.; Schachinger, Th.; Stöger-Pollach, M.; Löffler, S.; Steiger-Thirsfeld, A.; Bliokh, K. Y.; Nori, Franco

    2014-01-01

    Landau levels and states of electrons in a magnetic field are fundamental quantum entities underlying the quantum Hall and related effects in condensed matter physics. However, the real-space properties and observation of Landau wave functions remain elusive. Here we report the real-space observation of Landau states and the internal rotational dynamics of free electrons. States with different quantum numbers are produced using nanometre-sized electron vortex beams, with a radius chosen to match the waist of the Landau states, in a quasi-uniform magnetic field. Scanning the beams along the propagation direction, we reconstruct the rotational dynamics of the Landau wave functions with angular frequency ~100 GHz. We observe that Landau modes with different azimuthal quantum numbers belong to three classes, which are characterized by rotations with zero, Larmor and cyclotron frequencies, respectively. This is in sharp contrast to the uniform cyclotron rotation of classical electrons, and in perfect agreement with recent theoretical predictions. PMID:25105563

  10. Dynamics of Coulomb correlations in semiconductors in high magnetic fields

    SciTech Connect

    Fromer, Neil Alan

    2002-05-01

    Current theories have been successful in explaining many nonlinear optical experiments in undoped semiconductors. However, these theories require a ground state which is assumed to be uncorrelated. Strongly correlated systems of current interest, such as a two dimensional electron gas in a high magnetic field, cannot be explained in this manner because the correlations in the ground state and the low energy collective excitations cause a breakdown of the conventional techniques. We perform ultrafast time-resolved four-wave mixing on $n$-modulation doped quantum wells, which contain a quasi-two dimensional electron gas, in a large magnetic field, when only a single Landau level is excited and also when two levels are excited together. We find evidence for memory effects and as strong coupling between the Landau levels induced by the electron gas. We compare our results with simulations based on a new microscopic approach capable of treating the collective effects and correlations of the doped electrons, and find a good qualitative agreement. By looking at the individual contributions to the model, we determine that the unusual correlation effects seen in the experiments are caused by the scattering of photo-excited electron-hole pairs with the electron gas, leading to new excited states which are not present in undoped semiconductors, and also by exciton-exciton interactions mediated by the long-lived collective excitations of the electron gas, inter-Landau level magnetoplasmons.

  11. Superhorizon magnetic fields

    NASA Astrophysics Data System (ADS)

    Campanelli, Leonardo

    2016-03-01

    We analyze the evolution of superhorizon-scale magnetic fields from the end of inflation till today. Whatever is the mechanism responsible for their generation during inflation, we find that a given magnetic mode with wave number k evolves, after inflation, according to the values of k ηe , nk , and Ωk , where ηe is the conformal time at the end of inflation, nk is the number density spectrum of inflation-produced photons, and Ωk is the phase difference between the two Bogoliubov coefficients which characterize the state of that mode at the end of inflation. For any realistic inflationary magnetogenesis scenario, we find that nk-1≪|k ηe|≪1 , and three evolutionary scenarios are possible: (i) |Ωk∓π |=O (1 ) , in which case the evolution of the magnetic spectrum Bk(η ) is adiabatic, a2Bk(η )=const , with a being the expansion parameter; (ii) |Ωk∓π |≪|k ηe| , in which case the evolution is superadiabatic, a2Bk(η )∝η ; (iii) |k ηe|≪|Ωk∓π |≪1 or |k ηe|˜|Ωk∓π |≪1 , in which case an early phase of adiabatic evolution is followed, after a time η⋆˜|Ωk∓π |/k , by a superadiabatic evolution. Once a given mode reenters the horizon, it remains frozen into the plasma and then evolves adiabatically till today. As a corollary of our results, we find that inflation-generated magnetic fields evolve adiabatically on all scales and for all times in conformal-invariant free Maxwell theory, while they evolve superadiabatically after inflation on superhorizon scales in the nonconformal-invariant Ratra model, where the inflaton is kinematically coupled to the electromagnetic field. The latter result supports and, somehow, clarifies our recent claim that the Ratra model can account for the presence of cosmic magnetic fields without suffering from both backreaction and strong-coupling problems.

  12. Magnetic Field Topology in Jets

    NASA Technical Reports Server (NTRS)

    Gardiner, T. A.; Frank, A.

    2000-01-01

    We present results on the magnetic field topology in a pulsed radiative. jet. For initially helical magnetic fields and periodic velocity variations, we find that the magnetic field alternates along the, length of the jet from toroidally dominated in the knots to possibly poloidally dominated in the intervening regions.

  13. Low field magnetic resonance imaging

    DOEpatents

    Pines, Alexander; Sakellariou, Dimitrios; Meriles, Carlos A.; Trabesinger, Andreas H.

    2010-07-13

    A method and system of magnetic resonance imaging does not need a large homogenous field to truncate a gradient field. Spatial information is encoded into the spin magnetization by allowing the magnetization to evolve in a non-truncated gradient field and inducing a set of 180 degree rotations prior to signal acquisition.

  14. Electric and magnetic fields

    NASA Technical Reports Server (NTRS)

    Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

    1982-01-01

    A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

  15. Magnetic-field dependence of valley splitting in Si quantum wells grown on tilted SiGe substrates

    NASA Astrophysics Data System (ADS)

    Lee, Seungwon; von Allmen, Paul

    2006-12-01

    The valley splitting of the first few Landau levels is calculated as a function of the magnetic field for electrons confined in a strained silicon quantum well grown on a tilted SiGe substrate, using a parametrized tight-binding method. More specifically, the valley splitting arising from the effect of misorientation between the crystal axis and the confinement direction of the quantum well is investigated. In the absence of misorientation (zero substrate tilt angle), the valley splitting slightly decreases with increasing magnetic field. In contrast, the valley splitting for a finite substrate tilt angle exhibits a strong and nonmonotonic dependence on the magnetic-field strength. The valley splitting of the first Landau level shows an exponential increase followed by a slow saturation as the magnetic-field strength increases. The valley splitting of the second and third Landau levels shows an oscillatory behavior. The nonmonotonic dependence is explained by the phase variation of the Landau-level wave function along the washboardlike interface between the tilted quantum well and the buffer material. The phase variation is a direct consequence of the misorientation. This result suggests that when the misorientation effect is dominant, the magnitude of the valley splitting can be easily tuned by controlling the Landau-level filling factor through the magnetic field and the doping concentration.

  16. Mesoscopic Superposition States in Relativistic Landau Levels

    SciTech Connect

    Bermudez, A.; Martin-Delgado, M. A.; Solano, E.

    2007-09-21

    We show that a linear superposition of mesoscopic states in relativistic Landau levels can be built when an external magnetic field couples to a relativistic spin 1/2 charged particle. Under suitable initial conditions, the associated Dirac equation produces unitarily superpositions of coherent states involving the particle orbital quanta in a well-defined mesoscopic regime. We demonstrate that these mesoscopic superpositions have a purely relativistic origin and disappear in the nonrelativistic limit.

  17. Spin transistor action via tunable Landau-Zener transitions in magnetic semiconductor quantum wells

    NASA Astrophysics Data System (ADS)

    Weiss, Dieter

    2013-03-01

    Spin-transistors, employing spin-orbit interaction like Datta-Das prototypes, principally suffer from low signal levels due to limitations in spin injection efficiency, fast spin relaxation and dephasing processes. Here we present an alternative concept to implement spin transistor action where efficiency is improved by keeping spin transport adiabatic. To this end a helical stray field B, generated by ferromagnetic Dysprosium stripes, is superimposed upon a two-dimensional electron system in (Cd,Mn)Te, containing Mn ions with spin 5/2. Due to the giant spin splitting, occurring at low temperatures and small B in (Cd,Mn)Te quantum wells, the B-helix translates into a spin-helix and the electron spins follow adiabatically the imposed spin texture. Within this approach the transmission of spin-polarized electrons between two contacts is regulated by changing the degree of adiabaticity, i.e. an electron's ability to follow the spin helix. This is done by means of a small applied homogeneous magnetic field while the degree of adiabaticity is monitored by the channel resistance. Our scheme allows spin information to propagate efficiently over typical device distances and provides an alternative route to realize spintronics applications. We note that our concept is not restricted to a particular choice of materials, temperature, methods of spin injection, manipulation as well as detection. Work done in cooperation with Christian Betthausen, Institute of Experimental and Applied Physics, University of Regensburg, D-93040 Regensburg, Germany; Tobias Dollinger, Henri Saarikosi, Institute of Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany; Valeri Kolkovsky, Grzegorz Karczewski, Tomasz Wojtowicz, Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland; and Klaus Richter, Institute of Theoretical Physics, University of Regensburg. Financial support from the Deutsche Forschungsgemeinschaft through SFB 689, WE 247618, and FOR 1483 is

  18. Reconnection of Magnetic Fields

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Spacecraft observations of steady and nonsteady reconnection at the magnetopause are reviewed. Computer simulations of three-dimensional reconnection in the geomagnetic tail are discussed. Theoretical aspects of the energization of particles in current sheets and of the microprocesses in the diffusion region are presented. Terrella experiments in which magnetospheric reconnection is simulated at both the magnetopause and in the tail are described. The possible role of reconnection in the evolution of solar magnetic fields and solar flares is discussed. A two-dimensional magnetohydrodynamic computer simulation of turbulent reconnection is examined. Results concerning reconnection in Tokamak devices are also presented.

  19. Magnetic fields and stardust

    NASA Technical Reports Server (NTRS)

    Hildebrand, Roger H.

    1988-01-01

    The purpose of this paper is to outline the principles governing the use of far-infrared and submillimeter polarimetry to investigate magnetic fields and dust in interstellar clouds. Particular topics of discussion are the alignment of dust grains in dense clouds, the dependence on wavelength of polarization due to emission or to partial absorption by aligned grains, the nature of that dependence for mixtures of grains with different properties, and the problem of distinguishing between (1) the effects of the shapes and dielectric functions of the grains and (2) the degree and direction of their alignment.

  20. Phonon spectroscopy in high magnetic fields: The B + center in Si

    NASA Astrophysics Data System (ADS)

    Roshko, S.; Dietsche, W.

    1996-05-01

    Normal-state tunnel junctions have been used for phonon spectroscopY in high magnetic fields for the first time. The binding energy of the positively charged acceptor B + in Si has been measured as a function of magnetic field up to 12 Tesla. It is found to increase linearly with magnetic field. This linear dependence originates from the energy increase of the lowest Landau level of the free heavy holes. It indicates that the magnetic field dependence of both the neutral and the positively charged acceptors are small.

  1. Role of Grain Boundaries in the Coercivity of Magnetic Thin Films Investigated by a Two-Dimensional Ginzburg-Landau-Type Model

    NASA Astrophysics Data System (ADS)

    Iwano, Kaoru; Mitsumata, Chiharu; Ono, Kanta

    2016-07-01

    We investigate a two-dimensional Ginzburg-Landau-type model, with focus on grain boundaries that are prevalent in magnetic thin films with perpendicular magnetic anisotropy. The model covers four basic interactions, which are exchange, anisotropic, external, and dipole-dipole interactions, and describes magnetic thin films. Through numerical simulations for square grains, we find that there is a minimum grain-grain distance beyond which the interactions effectively vanish. Furthermore, we also find that magnetic reversals occur at the corners of grains and confirm that circular grains result in higher coercivity under similar packing ratio, because of the absence of corners.

  2. Ion-temperature gradient modes affected by helical magnetic field of magnetic islands

    SciTech Connect

    Ishizawa, A.; Diamond, P. H.

    2010-07-15

    Ion temperature gradient mode (ITG) affected by static magnetic field of magnetic islands is investigated numerically by means of Landau fluid model. The ITG is localized around O-points of magnetic islands, and the localization in poloidal direction is similar to the poloidal localization of toroidal ITG. This is because the helical magnetic field of magnetic islands causes geometrical coupling, and thus Fourier modes that have the same helicity as the islands are coupled together. The strength of coupling is characterized by the square of island width, and it corresponds to the fact that the strength of mode coupling of toroidal ITG is characterized by the inverse aspect ratio of torus in reduced fluid models.

  3. Symmetric and anti-symmetric Landau parameters and magnetic properties of dense quark matter

    NASA Astrophysics Data System (ADS)

    Pal, Kausik; Dutt-Mazumder, Abhee K.

    2010-05-01

    We calculate the dimensionless Fermi liquid parameters (FLPs), F0,1sym and F0,1asym, for spin asymmetric dense quark matter. In general, the FLPs are infrared divergent due to the exchange of massless gluons. To remove such divergences, the hard density loop (HDL) corrected gluon propagator is used. The FLPs so determined are then invoked to calculate magnetic properties such as magnetization and magnetic susceptibility χM of spin polarized quark matter. Finally, we investigate the possibility of magnetic instability by studying the density dependence of and χM.

  4. Photonic Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Wyntjes, Geert

    2002-02-01

    Small, in-line polarization rotators or isolators to reduce feedback in fiber optic links can be the basis for excellent magnetic field sensors. Based on the giant magneto-optical (GMO) or Faraday effect in iron garnets, they with a magnetic field of a few hundred Gauss, (20 mT) for an interaction length for an optical beam of a few millimeters achieve a polarization rotation or phase shift of 45 deg (1/8 cycle). When powered by a small laser diode, with the induced linear phase shift recovered at the shot noise limit, we have demonstrated sensitivities at the 3.3 nT/Hz1/2 level for frequencies from less than 1 Hz to frequencies into the high kHz range. Through further improvements; an increase in interaction length, better materials and by far the greatest factor, the addition of a flux concentrator, sensitivities at the pT/Hz1/2 level appear to be within reach. We will detail such a design and discuss the issues that may limit achieving these goals.

  5. Polar Magnetic Field Experiment

    NASA Technical Reports Server (NTRS)

    Russell, C. T.

    1999-01-01

    This grant covers the initial data reduction and analysis of the magnetic field measurements of the Polar spacecraft. At this writing data for the first three years of the mission have been processed and deposited in the key parameter database. These data are also available in a variety of time resolutions and coordinate systems via a webserver at UCLA that provides both plots and digital data. The flight software has twice been reprogrammed: once to remove a glitch in the data where there were rare collisions between commands in the central processing unit and once to provide burst mode data at 100 samples per second on a regular basis. The instrument continues to function as described in the instrument paper (1.1 in the bibliography attached below). The early observations were compared with observations on the same field lines at lower altitude. The polar magnetic measurements also proved to be most useful for testing the accuracy of MHD models. WE also made important contributions to study of waves and turbulence.

  6. Low-temperature magnetization dynamics of magnetic molecular solids in a swept field

    NASA Astrophysics Data System (ADS)

    Lenferink, Erik; Vijayaraghavan, Avinash; Garg, Anupam

    2015-05-01

    The swept-field experiments on magnetic molecular solids such as Fe8 are studied using Monte Carlo simulations, and a kinetic equation developed to understand collective magnetization phenomena in such solids, where the collective aspects arise from dipole-dipole interactions between different molecules. Because of these interactions, the classic Landau-Zener-Stückelberg theory proves inadequate, as does another widely used model constructed by Kayanuma. It is found that the simulations provide a quantitatively accurate account of the experiments. The kinetic equation provides a similarly accurate account except at very low sweep velocities, where it fails modestly. This failure is attributed to the neglect of short-range correlations between the dipolar magnetic fields seen by the molecular spins. The simulations and the kinetic equation both provide a good understanding of the distribution of these dipolar fields, although analytic expressions for the final magnetization remain elusive.

  7. Landau levels of Majorana fermions in a spin liquid

    NASA Astrophysics Data System (ADS)

    Rachel, Stephan; Fritz, Lars; Vojta, Matthias

    Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels - highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles - for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudo-magnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.

  8. Magnetic Fields: Visible and Permanent.

    ERIC Educational Resources Information Center

    Winkeljohn, Dorothy R.; Earl, Robert D.

    1983-01-01

    Children will be able to see the concept of a magnetic field translated into a visible reality using the simple method outlined. Standard shelf paper, magnets, iron filings, and paint in a spray can are used to prepare a permanent and well-detailed picture of the magnetic field. (Author/JN)

  9. Holographic non-Fermi liquid in a background magnetic field

    NASA Astrophysics Data System (ADS)

    Basu, Pallab; He, Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang

    2010-08-01

    We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS4 black hole background. Introducing a similar fermionic probe in a dyonic AdS4 black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion’s charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.

  10. Hydrodynamics on the lowest Landau level

    NASA Astrophysics Data System (ADS)

    Geracie, Michael; Son, Dam Thanh

    2015-06-01

    Using the recently developed approach to quantum Hall physics based on Newton-Cartan geometry, we consider the hydrodynamics of an interacting system on the lowest Landau level. We rephrase the non-relativistic fluid equations of motion in a manner that manifests the spacetime diffeomorphism invariance of the underlying theory. In the massless (or lowest Landau level) limit, the fluid obeys a force-free constraint which fixes the charge current. An entropy current analysis further constrains the energy response, determining four transverse response functions in terms of only two: an energy magnetization and a thermal Hall conductivity. Kubo formulas are presented for all transport coefficients and constraints from Weyl invariance derived. We also present a number of Středa-type formulas for the equilibrium response to external electric, magnetic and gravitational fields.

  11. A three-dimensional non-isothermal Ginzburg-Landau phase-field model for shape memory alloys

    NASA Astrophysics Data System (ADS)

    Dhote, R.; Fabrizio, M.; Melnik, R.; Zu, J.

    2014-12-01

    In this paper, a macroscopic three-dimensional non-isothermal model is proposed for describing hysteresis phenomena and phase transformations in shape memory alloys (SMAs). The model is of phase-field type and is based on the Ginzburg-Landau theory. The hysteresis and phase transformations are governed by the kinetic phase evolution equation using the scalar order parameter, laws of conservation of the momentum and energy and a nonlinear coupling of the stress, the strain and the order parameter in a differential form. One of the important features of the model is that the phase transformation is governed by the stress tensor, as opposed to the transformation strain tensor typically used in the literature. The model takes into account different properties of austenite and martensite phases based on the compliance tensor as a function of the order parameter and stress. Representative numerical simulations on an SMA specimen reproduce hysteretic behaviors observed experimentally in the literature.

  12. Direct discrete simulation of the kinetic Landau-Fokker-Planck equation with an alternating external electromagnetic field

    NASA Astrophysics Data System (ADS)

    Karpov, S. A.; Potapenko, I. F.

    2015-10-01

    A stochastic method of simulation of Coulomb interaction is considered. The main idea of the method is to approximate the nonlinear Landau kinetic collision integral by the Boltzmann integral. In its realization, the method can be attributed to a wide class of Monte Carlo-type methods. It is easily combined with the existing particle methods used to simulate collisionless plasmas. This is important for simulation of the dynamics of both laboratory and space plasmas when the mean free path of plasma particles is comparable with the plasma inhomogeneity scale length. Illustrative examples of relaxation of two-temperature plasma being subject to a high-frequency alternating electric field are given, and differences from their classical description are considered. The method satisfies the conservation laws for the number of particles, momentum, and energy and is simple and efficient in implementation.

  13. Direct discrete simulation of the kinetic Landau-Fokker-Planck equation with an alternating external electromagnetic field

    SciTech Connect

    Karpov, S. A.; Potapenko, I. F.

    2015-10-15

    A stochastic method of simulation of Coulomb interaction is considered. The main idea of the method is to approximate the nonlinear Landau kinetic collision integral by the Boltzmann integral. In its realization, the method can be attributed to a wide class of Monte Carlo-type methods. It is easily combined with the existing particle methods used to simulate collisionless plasmas. This is important for simulation of the dynamics of both laboratory and space plasmas when the mean free path of plasma particles is comparable with the plasma inhomogeneity scale length. Illustrative examples of relaxation of two-temperature plasma being subject to a high-frequency alternating electric field are given, and differences from their classical description are considered. The method satisfies the conservation laws for the number of particles, momentum, and energy and is simple and efficient in implementation.

  14. Observations of galactic magnetic fields

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Magnetic fields are enchored in gas clouds. Field lines are tangled in spiral arms, but highly regular between the arms. The similarity of pitch angles between gaseous and magnetic arms suggests a coupling between the density wave and the magnetic wave. Observations of large-scale patterns in Faraday rotation favour a dynamo origin of the regular fields. Fields in barred galaxies do not reveal the strong shearing shocks observed in the cold gas, but swing smoothly from the upstream region into the bar. Magnetic fields are important for the dynamcis of gas clouds, for the formation of spiral structures, bars and halos, and for mass and angular momentum transport in central regions.

  15. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Y.; Mahale, N.K.

    1996-08-06

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles. 6 figs.

  16. Fast superconducting magnetic field switch

    DOEpatents

    Goren, Yehuda; Mahale, Narayan K.

    1996-01-01

    The superconducting magnetic switch or fast kicker magnet is employed with electron stream or a bunch of electrons to rapidly change the direction of flow of the electron stream or bunch of electrons. The apparatus employs a beam tube which is coated with a film of superconducting material. The tube is cooled to a temperature below the superconducting transition temperature and is subjected to a constant magnetic field which is produced by an external dc magnet. The magnetic field produced by the dc magnet is less than the critical field for the superconducting material, thus, creating a Meissner Effect condition. A controllable fast electromagnet is used to provide a magnetic field which supplements that of the dc magnet so that when the fast magnet is energized the combined magnetic field is now greater that the critical field and the superconducting material returns to its normal state allowing the magnetic field to penetrate the tube. This produces an internal field which effects the direction of motion and of the electron stream or electron bunch. The switch can also operate as a switching mechanism for charged particles.

  17. Martian external magnetic field proxies

    NASA Astrophysics Data System (ADS)

    Langlais, Benoit; Civet, Francois

    2015-04-01

    Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.

  18. Spatial Landau-Zener-Stueckelberg interference in spinor Bose-Einstein condensates

    SciTech Connect

    Zhang, J.-N.; Sun, C.-P.; Yi, S.; Nori, Franco

    2011-03-15

    We investigate the Stueckelberg oscillations of a spin-1 Bose-Einstein condensate subject to a spatially inhomogeneous transverse magnetic field and a periodic longitudinal field. We show that the time-domain Stueckelberg oscillations result in modulations in the density profiles of all spin components due to the spatial inhomogeneity of the transverse field. This phenomenon represents the Landau-Zener-Stueckelberg interference in the space domain. Since the magnetic dipole-dipole interaction between spin-1 atoms induces an inhomogeneous effective magnetic field, interference fringes also appear if a dipolar spinor condensate is driven periodically. We also point out some potential applications of this spatial Landau-Zener-Stuekelberg interference.

  19. Quantum Interference, Geometric-phase Effects, and Semiclassical Transport in Quantum Hall Systems at Low Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Huang, Chun-Feng; Tsai, I.-H.

    It is well-established how the quantum interference induces strong localization leading to quantum Hall effect at high enough magnetic fields. Decreasing the magnetic fields, however, the localization strength can be reduced and the semiclassical magneto-oscillations following Shubnikov-de Haas formula appear in most quantum Hall systems. To understand the transport properties as the localization strength becomes weak, our team has investigated the magneto-resistance in some quantum Hall systems at low magnetic fields. Under the semiclassical transport, the crossing points in Hall plateaus showed Landau-band quantization and microwave-induced heating demonstrated the band-edge equivalence important to Landau-level addition transformation. We note that such equivalence is consistent with the edge universality based on the random matrices of Wigner type, and the Landau-band quantization can be explained by considering geometric phase effects. From our study, some quantum Hall features can survive as the semiclassical transport reveals the insufficient localization.

  20. Magnetic switching time of a Stoner-Wohlfarth particle in a perpendicular bias field

    NASA Astrophysics Data System (ADS)

    Xue, Dong

    This thesis studies magnetic switching of a Stoner-Wholfarth particle. The particle is characterized by a uniaxial magnetic anisotropy, and the magnetic field driving the switching is applied along the anisotropy axis. In addition, a constant small bias field is applied perpendicular to the easy axis. The dynamics of the magnetic moment are studied numerically by solving the Landau-Lifshitz-Gilbert (LLG) equation. Numeric results obtained without any approximations are then compared to the analytic theory of switching time in a perpendicular bias field. A good correspondence between the approximate analytic and exact numeric values of the switching time is observed in a wide parameter region.

  1. Cyclical magnetic field flow fractionation

    NASA Astrophysics Data System (ADS)

    Tasci, T. O.; Johnson, W. P.; Gale, B. K.

    2012-04-01

    In this study, a new magnetic field flow fractionation (FFF) system was designed and modeled by using finite element simulations. Other than current magnetic FFF systems, which use static magnetic fields, our system uses cyclical magnetic fields. Results of the simulations show that our cyclical magnetic FFF system can be used effectively for the separation of magnetic nanoparticles. Cyclical magnetic FFF system is composed of a microfluidic channel (length = 5 cm, height = 30 μm) and 2 coils. Square wave currents of 1 Hz (with 90 deg of phase difference) were applied to the coils. By using Comsol Multiphysics 3.5a, magnetic field profile and corresponding magnetic force exerted on the magnetite nanoparticles were calculated. The magnetic force data were exported from Comsol to Matlab. In Matlab, a parabolic flow profile with maximum flow speed of 0.4 mL/h was defined. Particle trajectories were obtained by the calculation of the particle speeds resulted from both magnetic and hydrodynamic forces. Particle trajectories of the particles with sizes ranging from 10 to 50 nm were simulated and elution times of the particles were calculated. Results show that there is a significant difference between the elution times of the particles so that baseline separation of the particles can be obtained. In this work, it is shown that by the application of cyclical magnetic fields, the separation of magnetic nanoparticles can be done efficiently.

  2. Magnetic field modification of optical magnetic dipoles.

    PubMed

    Armelles, Gaspar; Caballero, Blanca; Cebollada, Alfonso; Garcia-Martin, Antonio; Meneses-Rodríguez, David

    2015-03-11

    Acting on optical magnetic dipoles opens novel routes to govern light-matter interaction. We demonstrate magnetic field modification of the magnetic dipolar moment characteristic of resonant nanoholes in thin magnetoplasmonic films. This is experimentally shown through the demonstration of the magneto-optical analogue of Babinet's principle, where mirror imaged MO spectral dependencies are obtained for two complementary magnetoplasmonic systems: holes in a perforated metallic layer and a layer of disks on a substrate. PMID:25646869

  3. Exposure guidelines for magnetic fields.

    PubMed

    Miller, G

    1987-12-01

    The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields. PMID:3434538

  4. Exposure guidelines for magnetic fields

    SciTech Connect

    Miller, G.

    1987-12-01

    The powerful magnetic fields produced by a controlled fusion experiment at Lawrence Livermore National Laboratory (LLNL) necessitated the development of personnel-exposure guidelines for steady magnetic fields. A literature search and conversations with active researchers showed that it is currently possible to develop preliminary exposure guidelines for steady magnetic fields. An overview of the results of past research into the bioeffects of magnetic fields was compiled, along with a discussion of hazards that may be encountered by people with sickle-cell anemia or medical electronic and prosthetic implants. The LLNL steady magnetic-field exposure guidelines along with a review of developments concerning the safety of time-varying fields were also presented in this compilation. Guidelines developed elsewhere for time varying fields were also given. Further research is needed to develop exposure standards for both steady or time-varying fields.

  5. [Magnetic fields and fish behavior].

    PubMed

    Krylov, V V; Iziumov, Iu G; Izvekov, E I; Nepomniashchikh, V A

    2013-01-01

    In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25438567

  6. [Magnetic fields and fish behavior].

    PubMed

    2013-01-01

    In the review, contemporary data on the influence of natural and artificial magnetic fields on fish behavior are considered. In this regard, elasmobranchs and teleosts appear to be studied most exhaustively. Elasmobranchs and some teleosts are able to perceive magnetic fields via electroreceptors. A number of teleosts can sense magnetic fields via sensory cells containing crystals of biogenic magnetite. Laboratory experiments and field observations indicate the influence of magnetic fields on fish locomotor activity and spatial distribution. The geomagnetic field can be used by fish for navigation. Besides, artificial magnetic fields and natural fluctuations of the geomagnetic field can affect fish embryos leading to alterations in their development. It is suggested that, afterwards, these alterations can have an effect on fish behavior. PMID:25508098

  7. Magnetic-field-dosimetry system

    DOEpatents

    Lemon, D.K.; Skorpik, J.R.; Eick, J.L.

    1981-01-21

    A device is provided for measuring the magnetic field dose and peak field exposure. The device includes three Hall-effect sensors all perpendicular to each other, sensing the three dimensional magnetic field and associated electronics for data storage, calculating, retrieving and display.

  8. Landau-like states in neutral particles

    NASA Astrophysics Data System (ADS)

    Banerjee, Saikat; Ågren, Hans; Balatsky, A. V.

    2016-06-01

    We show the emergence of a new type of dispersion relation for neutral atoms with an interesting similarity to the spectrum of two-dimensional electrons in an applied perpendicular constant magnetic field. These neutral atoms can be confined in toroidal optical traps and give quasi-Landau spectra. In strong contrast to the equidistant infinitely degenerate Landau levels for charged particles, the spectral gap for such two-dimensional neutral particles increases in particular electric-field configurations. The idea in the paper is motivated by the development in cold atom experiments and builds on the seminal paper of Aharonov and Casher [Phys. Rev. Lett. 53, 319 (1984), 10.1103/PhysRevLett.53.319].

  9. Electric field control of magnetization dynamics in multiferroics

    NASA Astrophysics Data System (ADS)

    Risinggard, Vetle; Kulagina, Iryna; Linder, Jacob

    Multiferroics with a strong magnetoelectric coupling hold great promise in spintronics because they enable magnetic control of the electric polarization as well as electric control of the magnetization. We take an analytical approach, using the Landau-Lifshitz-Gilbert equation to describe the dynamic state of the magnetization. In particular, we show that in insulating multiferroics which exhibit the inhomogeneous magnetoelectric effect there exists an electrically controlled magnon-induced torque that acts even on a homogeneous magnetization. Unlike the magnon-induced torques that arise from Dzyaloshinskii-Moriya interactions or in the proximity of a topological insulator, the strength and direction of this torque is tunable by the externally applied electric field.

  10. Magnetic fields in nearby spirals

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohui; Lenc, Emil

    2013-10-01

    Magnetic fields play an important role in star formation process and dynamic evolution of galaxies. Previous studies of magnetic fields relied on narrow band polarisation observations and difficult to disentangle magnetised structures along line of sight. Thanks to the broad bandwidth and multi-channels of CABB we are now able to recover the 3D structures of magnetic fields using RM synthesis and QU-fitting. We propose to observe two nearby spirals M83 and NGC 4945 to build clear pictures of their magnetic fields.

  11. Fast domain wall propagation under an optimal field pulse in magnetic nanowires.

    PubMed

    Sun, Z Z; Schliemann, J

    2010-01-22

    We investigate field-driven domain wall (DW) propagation in magnetic nanowires in the framework of the Landau-Lifshitz-Gilbert equation. We propose a new strategy to speed up the DW motion in a uniaxial magnetic nanowire by using an optimal space-dependent field pulse synchronized with the DW propagation. Depending on the damping parameter, the DW velocity can be increased by about 2 orders of magnitude compared to the standard case of a static uniform field. Moreover, under the optimal field pulse, the change in total magnetic energy in the nanowire is proportional to the DW velocity, implying that rapid energy release is essential for fast DW propagation. PMID:20366681

  12. Vestibular stimulation by magnetic fields

    PubMed Central

    Ward, Bryan K.; Roberts, Dale C.; Della Santina, Charles C.; Carey, John P.; Zee, David S.

    2015-01-01

    Individuals working next to strong static magnetic fields occasionally report disorientation and vertigo. With the increasing strength of magnetic fields used for magnetic resonance imaging (MRI) studies, these reports have become more common. It was recently learned that humans, mice and zebrafish all demonstrate behaviors consistent with constant peripheral vestibular stimulation while inside a strong, static magnetic field. The proposed mechanism for this effect involves a Lorentz force resulting from the interaction of a strong static magnetic field with naturally occurring ionic currents flowing through the inner ear endolymph into vestibular hair cells. The resulting force within the endolymph is strong enough to displace the lateral semicircular canal cupula, inducing vertigo and the horizontal nystagmus seen in normal mice and in humans. This review explores the evidence for interactions of magnetic fields with the vestibular system. PMID:25735662

  13. Magnetic fields around evolved stars

    NASA Astrophysics Data System (ADS)

    Leal-Ferreira, M.; Vlemmings, W.; Kemball, A.; Amiri, N.; Maercker, M.; Ramstedt, S.; Olofsson, G.

    2014-04-01

    A number of mechanisms, such as magnetic fields, (binary) companions and circumstellar disks have been suggested to be the cause of non-spherical PNe and in particular collimated outflows. This work investigates one of these mechanisms: the magnetic fields. While MHD simulations show that the fields can indeed be important, few observations of magnetic fields have been done so far. We used the VLBA to observe five evolved stars, with the goal of detecting the magnetic field by means of water maser polarization. The sample consists in four AGB stars (IK Tau, RT Vir, IRC+60370 and AP Lyn) and one pPN (OH231.8+4.2). In four of the five sources, several strong maser features were detected allowing us to measure the linear and/or circular polarization. Based on the circular polarization detections, we infer the strength of the component of the field along the line of sight to be between ~30 mG and ~330 mG in the water maser regions of these four sources. When extrapolated to the surface of the stars, the magnetic field strength would be between a few hundred mG and a few Gauss when assuming a toroidal field geometry and higher when assuming more complex magnetic fields. We conclude that the magnetic energy we derived in the water maser regions is higher than the thermal and kinetic energy, leading to the conclusion that, indeed, magnetic fields probably play an important role in shaping Planetary Nebulae.

  14. Effects of the quark field on the ghost propagator of lattice Landau gauge QCD

    SciTech Connect

    Furui, Sadataka; Nakajima, Hideo

    2006-05-01

    Infrared features of the ghost propagator of color-diagonal and color antisymmetric ghost propagator of quenched SU(2) and quenched SU(3) are compared with those of unquenched Kogut-Susskind fermion SU(3) lattice Landau gauge. We compare (i) the fluctuation of the ghost propagator (ii) the ghost condensate parameter v of the local composite operator (LCO) approach, and (iii) the Binder cumulant of color antisymmetric ghost propagator between quenched and unquenched configurations. The color-diagonal SU(3) ghost dressing function of unquenched configurations has weaker singularity than the quenched configurations. In both cases fluctuations become large in q<0.5 GeV. The ghost condensate parameter v in the ghost propagator of the unquenched MILC{sub c} configuration samples is {approx}0.002-0.04 GeV{sup 2} while that of the SU(2) parallel tempering samples is consistent with 0. The Binder cumulant defined as U(q)=1-(1/3)(<{phi}-vector{sup 4}>/(<{phi}-vector{sup 2}>){sup 2}), where {phi}-vector(q) is the color antisymmetric ghost propagator measured by the sample average of gauge fixed configurations via parallel tempering method, becomes {approx}4/9 in all the momentum region. The Binder cumulant of the color antisymmetric ghost propagator of quenched SU(2) can be explained by the 3D Gaussian distribution, but that of the unquenched MILC{sub c} deviates slightly from that of the eight-dimensional Gaussian distribution. The stronger singularity and large fluctuation in the quenched configuration could be the cause of the deviation of the Kugo-Ojima confinement parameter c from 1, and the presence of ordering in the ghost propagator of unquenched configurations makes it closer to 1.

  15. Cyclotron resonance in InAs/AlSb quantum wells in magnetic fields up to 45 T

    SciTech Connect

    Spirin, K. E. Krishtopenko, S. S.; Sadofyev, Yu. G.; Drachenko, O.; Helm, M.; Teppe, F.; Knap, W.; Gavrilenko, V. I.

    2015-12-15

    Electron cyclotron resonance in InAs/AlSb heterostructures with quantum wells of various widths in pulsed magnetic fields up to 45 T are investigated. Our experimental cyclotron energies are in satisfactory agreement with the results of theoretical calculations performed using the eight-band kp Hamiltonian. The shift of the cyclotron resonance (CR) line, which corresponds to the transition from the lowest Landau level to the low magnetic-field region, is found upon varying the electron concentration due to the negative persistent photoconductivity effect. It is shown that the observed shift of the CR lines is associated with the finite width of the density of states at the Landau levels.

  16. Dynamical polarization in ABC-stacked multilayer graphene in a magnetic field

    NASA Astrophysics Data System (ADS)

    Sobol, O. O.; Gorbar, E. V.; Gusynin, V. P.

    2014-08-01

    In the continuum low-energy model, we calculate the one-loop dynamical polarization functions in ABC-stacked (rhombohedral) n-layer graphene in a magnetic field. Neglecting the trigonal warping effects, they are derived as functions of wave vector and frequency at finite chemical potential, temperature, band gap, and the width of Landau levels. The analytic results are given in terms of digamma functions and generalized Laguerre polynomials and have the form of double sums over Landau levels. Various particular limits for polarization functions (static, clean, etc.) are discussed. The intralayer and interlayer screened Coulomb potentials are numerically calculated as functions of momentum and frequency.

  17. Modelling of heat assisted magnetic recording with the Landau-Lifshitz-Bloch equation and Brillouin functions

    NASA Astrophysics Data System (ADS)

    Greaves, Simon John; Muraoka, Hiroaki; Kanai, Yasushi

    2015-05-01

    Brillouin functions were used to model the temperature dependence of magnetisation in media for heat assisted magnetic recording. Although dHk/dT was higher when Brillouin functions with J = 0.5 or J = 1 were used, an earlier onset of the linear reversal mode led to a drop in dHc/dT near to Tc, resulting in wider written bits. Tracks written with a higher thermal gradient were also wider when J was small and had lower SNR.

  18. Spinodal instabilities and the distillation effect in nuclear matter under strong magnetic fields

    SciTech Connect

    Rabhi, A.; Providencia, C.; Providencia, J. Da

    2009-01-15

    We study the effect of strong magnetic fields, of the order of 10{sup 18}-10{sup 19} G, on the instability region of nuclear matter at subsaturation densities. Relativistic nuclear models both with constant couplings and with density-dependent parameters are considered. It is shown that a strong magnetic field can have large effects on the instability regions giving rise to bands of instability and wider unstable regions. As a consequence, we predict larger transition densities at the inner edge of the crust of compact stars with strong magnetic fields. The direction of instability gives rise to a very strong distillation effect if the last Landau level is only partially filled. However, for almost completed Landau levels, an antidistillation effect may occur.

  19. Nonlinear electron acceleration by oblique whistler waves: Landau resonance vs. cyclotron resonance

    SciTech Connect

    Artemyev, A. V.; Agapitov, O. V.; Krasnoselskikh, V. V.; Mourenas, D.

    2013-12-15

    This paper is devoted to the study of the nonlinear interaction of relativistic electrons and high amplitude strongly oblique whistler waves in the Earth's radiation belts. We consider electron trapping into Landau and fundamental cyclotron resonances in a simplified model of dipolar magnetic field. Trapping into the Landau resonance corresponds to a decrease of electron equatorial pitch-angles, while trapping into the first cyclotron resonance increases electron equatorial pitch-angles. For 100 keV electrons, the energy gained due to trapping is similar for both resonances. For electrons with smaller energy, acceleration is more effective when considering the Landau resonance. Moreover, trapping into the Landau resonance is accessible for a wider range of initial pitch-angles and initial energies in comparison with the fundamental resonance. Thus, we can conclude that for intense and strongly oblique waves propagating in the quasi-electrostatic mode, the Landau resonance is generally more important than the fundamental one.

  20. The Capacitive Magnetic Field Sensor

    NASA Astrophysics Data System (ADS)

    Zyatkov, D. O.; Yurchenko, A. V.; Balashov, V. B.; Yurchenko, V. I.

    2016-01-01

    The results of a study of sensitive element magnetic field sensor are represented in this paper. The sensor is based on the change of the capacitance with an active dielectric (ferrofluid) due to the magnitude of magnetic field. To prepare the ferrofluid magnetic particles are used, which have a followingdispersion equal to 50 < Ø < 56, 45 < Ø < 50, 40 < Ø < 45 and Ø < 40micron of nanocrystalline alloy of brand 5BDSR. The dependence of the sensitivity of the capacitive element from the ferrofluid with different dispersion of magnetic particles is considered. The threshold of sensitivity and sensitivity of a measuring cell with ferrofluid by a magnetic field was determined. The experimental graphs of capacitance change of the magnitude of magnetic field are presented.

  1. Origin of cosmic magnetic fields.

    PubMed

    Campanelli, Leonardo

    2013-08-01

    We calculate, in the free Maxwell theory, the renormalized quantum vacuum expectation value of the two-point magnetic correlation function in de Sitter inflation. We find that quantum magnetic fluctuations remain constant during inflation instead of being washed out adiabatically, as usually assumed in the literature. The quantum-to-classical transition of super-Hubble magnetic modes during inflation allow us to treat the magnetic field classically after reheating, when it is coupled to the primeval plasma. The actual magnetic field is scale independent and has an intensity of few×10(-12)  G if the energy scale of inflation is few×10(16)  GeV. Such a field accounts for galactic and galaxy cluster magnetic fields. PMID:23971556

  2. Measurements of magnetic field alignment

    SciTech Connect

    Kuchnir, M.; Schmidt, E.E.

    1987-11-06

    The procedure for installing Superconducting Super Collider (SSC) dipoles in their respective cryostats involves aligning the average direction of their field with the vertical to an accuracy of 0.5 mrad. The equipment developed for carrying on these measurements is described and the measurements performed on the first few prototypes SSC magnets are presented. The field angle as a function of position in these 16.6 m long magnets is a characteristic of the individual magnet with possible feedback information to its manufacturing procedure. A comparison of this vertical alignment characteristic with a magnetic field intensity (by NMR) characteristic for one of the prototypes is also presented. 5 refs., 7 figs.

  3. Magnetic fields in young galaxies

    NASA Astrophysics Data System (ADS)

    Nordlund, Åke; Rögnvaldsson, Örnólfur

    We have studied the fate of initial magnetic fields in the hot halo gas out of which the visible parts of galaxies form, using three-dimensional numerical MHD-experiments. The halo gas undergoes compression by several orders of magnitude in the subsonic cooling flow that forms the cold disk. The magnetic field is carried along and is amplified considerably in the process, reaching μG levels for reasonable values of the initial ratio of magnetic to thermal energy density.

  4. The MAVEN Magnetic Field Investigation

    NASA Technical Reports Server (NTRS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2014-01-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a quantization uncertainty of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05%. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers - multiple rotations about the spacecraft x and z axes - to characterize spacecraft fields and/or instrument offsets in flight.

  5. The MAVEN Magnetic Field Investigation

    NASA Astrophysics Data System (ADS)

    Connerney, J. E. P.; Espley, J.; Lawton, P.; Murphy, S.; Odom, J.; Oliversen, R.; Sheppard, D.

    2015-12-01

    The MAVEN magnetic field investigation is part of a comprehensive particles and fields subsystem that will measure the magnetic and electric fields and plasma environment of Mars and its interaction with the solar wind. The magnetic field instrumentation consists of two independent tri-axial fluxgate magnetometer sensors, remotely mounted at the outer extremity of the two solar arrays on small extensions ("boomlets"). The sensors are controlled by independent and functionally identical electronics assemblies that are integrated within the particles and fields subsystem and draw their power from redundant power supplies within that system. Each magnetometer measures the ambient vector magnetic field over a wide dynamic range (to 65,536 nT per axis) with a resolution of 0.008 nT in the most sensitive dynamic range and an accuracy of better than 0.05 %. Both magnetometers sample the ambient magnetic field at an intrinsic sample rate of 32 vector samples per second. Telemetry is transferred from each magnetometer to the particles and fields package once per second and subsequently passed to the spacecraft after some reformatting. The magnetic field data volume may be reduced by averaging and decimation, when necessary to meet telemetry allocations, and application of data compression, utilizing a lossless 8-bit differencing scheme. The MAVEN magnetic field experiment may be reconfigured in flight to meet unanticipated needs and is fully hardware redundant. A spacecraft magnetic control program was implemented to provide a magnetically clean environment for the magnetic sensors and the MAVEN mission plan provides for occasional spacecraft maneuvers—multiple rotations about the spacecraft x and z axes—to characterize spacecraft fields and/or instrument offsets in flight.

  6. Cosmic Magnetic Fields - An Overview

    NASA Astrophysics Data System (ADS)

    Wielebinski, Richard; Beck, Rainer

    Magnetic fields have been known in antiquity. Aristotle attributes the first of what could be called a scientific discussion on magnetism to Thales, who lived from about 625 BC. In China “magnetic carts” were in use to help the Emperor in his journeys of inspection. Plinius comments that in the Asia Minor province of Magnesia shepherds' staffs get at times “glued” to a stone, a alodestone. In Europe the magnetic compass came through the Arab sailors who met the Portuguese explorers. The first scientific treatise on magnetism, “De Magnete”, was published by William Gilbert who in 1600 described his experiments and suggested that the Earth was a huge magnet. Johannes Kepler was a correspondent of Gilbert and at times suggested that planetary motion was due to magnetic forces. Alas, this concept was demolished by Isaac Newton,who seeing the falling apple decided that gravity was enough. This concept of dealing with gravitational forces only remains en vogue even today. The explanations why magnetic effects must be neglected go from “magnetic energy is only 1% of gravitation” to “magnetic fields only complicate the beautiful computer solutions”. What is disregarded is the fact that magnetic effects are very directional(not omni-directional as gravity) and also the fact that magnetic fields are seen every where in our cosmic universe.

  7. Anomalous coincidences between valley split Landau levels in a Si/SiGe heterostructure

    NASA Astrophysics Data System (ADS)

    Schumacher, H. W.; Nauen, A.; Zeitler, U.; Haug, R. J.; Weitz, P.; Jansen, A. G. M.; Schäffler, F.

    1998-12-01

    We have performed magneto-transport experiments on a high mobility 2DEG in a Si/SiGe heterojunction in tilted magnetic fields up to 26 T at temperatures down to 450 mK. When tilting the sample in the magnetic field the value of the spin splitting increases with respect to the Landau level splitting leading to an overlap of spin-split sub-levels of different Landau levels, the so-called coincidences. Coincidences between up to five neighbouring Landau levels are found. From their positions we deduce a Landé factor g ∗≈3.4 . Coincidences between the lowest Landau levels with fully resolved individual valley states show extremely high SdH peaks compared to the individual SdH maxima outside the coincidence suggesting strong exchange enhancement effects in the occurrence of the coincidence.

  8. Landau Levels of Majorana Fermions in a Spin Liquid

    NASA Astrophysics Data System (ADS)

    Rachel, Stephan; Fritz, Lars; Vojta, Matthias

    2016-04-01

    Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels—highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles—for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.

  9. Landau Levels of Majorana Fermions in a Spin Liquid.

    PubMed

    Rachel, Stephan; Fritz, Lars; Vojta, Matthias

    2016-04-22

    Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation. PMID:27152821

  10. Properties of the resonant tunneling diode in external magnetic field with inclusion of the Rashba effect

    NASA Astrophysics Data System (ADS)

    Niketić, Nemanja; Milanović, Vitomir; Radovanović, Jelena

    2014-07-01

    Influence of the Rashba effect on electronic properties of resonant tunneling diode in an external magnetic field is analyzed in this paper. Wave functions and energies, as well as expressions for currents densities, are determined for electrons of both spins. Appearances of many modes due to the external magnetic field induce irregularities in the current-voltage characteristics, which are observable in case when the thermal energy is lower than, or comparable to, the energy difference of two consecutive Landau levels. Current density through the heterostructure is investigated with emphasis on the degree of spin polarization; further, spin transfer is shown to depend on the direction of external magnetic field.

  11. Photonic Landau levels on cones

    NASA Astrophysics Data System (ADS)

    Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan

    2016-05-01

    We present the first experimental realization of a bulk magnetic field for optical photons. By using a non-planar ring resonator, we induce an image rotation on each round trip through the resonator. This results in a Coriolis/Lorentz force and a centrifugal anticonfining force, the latter of which is cancelled by mirror curvature. Using a digital micromirror device to control both amplitude and phase, we inject arbitrary optical modes into our resonator. Spatial- and energy- resolved spectroscopy tracks photonic eigenstates as residual trapping is reduced, and we observe photonic Landau levels as the eigenstates become degenerate. We show that there is a conical geometry of the resulting manifold for photon dynamics and present a measurement of the local density of states that is consistent with Landau levels on a cone. While our work already demonstrates an integer quantum Hall material composed of photons, we have ensured compatibility with strong photon-photon interactions, which will allow quantum optical studies of entanglement and correlation in manybody systems including fractional quantum Hall fluids.

  12. Magnetic field synthesis for microwave magnetics

    NASA Astrophysics Data System (ADS)

    Morgenthaler, F. R.

    1982-04-01

    The Microwave and Quantum Magnetics Group of the M.I.T. Department of Electrical Engineering and Computer Science undertook a two-year research program directed at developing synthesis procedures that allow magnetostatic and/or magnetoelastic modes to be specially tailored for microwave signal processing applications that include magnetically tunable filters and limiters as well as delay lines that are either linearly dispersive or nondispersive over prescribed bandwidths. Special emphasis was given to devices employing thin films of yttrium iron garnet (YIG) that are blessed with spatially nonuniform dc magnetic fields.

  13. Magnetic field structure evolution in rotating magnetic field plasmas

    SciTech Connect

    Petrov, Yuri; Yang Xiaokang; Huang, T.-S.

    2008-07-15

    A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80 cm long/40 cm diameter cylindrical chamber, in which a plasma current I{sub p}{approx_equal}2 kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial I{sub z} current. With a relatively small current (I{sub m} {<=} 600 A) in the middle coil, the plasma current is boosted up to 5 kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.

  14. Determining nodes for the Ginzburg-Landau equations of superconductivity.

    SciTech Connect

    Kaper, H. G.; Wang, B.; Wang, S.; Mathematics and Computer Science; Tsinghua Univ.; Indiana Univ.

    1998-04-01

    It is shown that a solution of the time-independent Ginsburg-Landau equations of superconductivity is determined completely and exactly by its values at a finite but sufficiently dense set of determining nodes in the domain. If the applied magnetic field is time dependent and asymptotically stationary, the large-time asymptotic behavior of a solution of the time-dependent Ginsburg-Landau equations of superconductivity is determined similarly by its values at a finite set of determining nodes, whose positions may vary with time.

  15. PREPROCESSING MAGNETIC FIELDS WITH CHROMOSPHERIC LONGITUDINAL FIELDS

    SciTech Connect

    Yamamoto, Tetsuya T.; Kusano, K.

    2012-06-20

    Nonlinear force-free field (NLFFF) extrapolation is a powerful tool for the modeling of the magnetic field in the solar corona. However, since the photospheric magnetic field does not in general satisfy the force-free condition, some kind of processing is required to assimilate data into the model. In this paper, we report the results of new preprocessing for the NLFFF extrapolation. Through this preprocessing, we expect to obtain magnetic field data similar to those in the chromosphere. In our preprocessing, we add a new term concerning chromospheric longitudinal fields into the optimization function proposed by Wiegelmann et al. We perform a parameter survey of six free parameters to find minimum force- and torque-freeness with the simulated-annealing method. Analyzed data are a photospheric vector magnetogram of AR 10953 observed with the Hinode spectropolarimeter and a chromospheric longitudinal magnetogram observed with SOLIS spectropolarimeter. It is found that some preprocessed fields show the smallest force- and torque-freeness and are very similar to the chromospheric longitudinal fields. On the other hand, other preprocessed fields show noisy maps, although the force- and torque-freeness are of the same order. By analyzing preprocessed noisy maps in the wave number space, we found that small and large wave number components balance out on the force-free index. We also discuss our iteration limit of the simulated-annealing method and magnetic structure broadening in the chromosphere.

  16. Rotationally symmetric solutions of the Landau-Lifshitz and diffusion equations

    SciTech Connect

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

    2000-05-01

    The problem of isotropic conducting ferromagnetic film subject to in-plane circular polarized magnetic fields is discussed. This problem requires simultaneous solution of diffusion and Landau-Lifshitz equations. It is observed that the mathematical formulation of the problem is invariant with respect to rotations in the film plane. By exploiting this invariance, the rotationally symmetric solutions of the Landau-Lifshitz equation coupled with the diffusion equation are obtained and examined. (c) 2000 American Institute of Physics.

  17. Reorientation of quantum Hall stripes within a partially filled Landau level

    NASA Astrophysics Data System (ADS)

    Shi, Q.; Zudov, M. A.; Watson, J. D.; Gardner, G. C.; Manfra, M. J.

    We investigate the effect of the filling factor on transport anisotropies, known as stripes, in high Landau levels of a two-dimensional electron gas. We find that at certain in-plane magnetic fields, the stripes orientation is sensitive to the filling factor within a given Landau level. This sensitivity gives rise to the emergence of stripes away from half-filling while orthogonally-oriented, native stripes reside at half-filling. We attribute this switching of the anisotropy axes within a single Landau level to a strong dependence of the native symmetry breaking potential on the filling factor.

  18. Reorientation of quantum Hall stripes within a partially filled Landau level

    NASA Astrophysics Data System (ADS)

    Shi, Q.; Zudov, M. A.; Watson, J. D.; Gardner, G. C.; Manfra, M. J.

    2016-03-01

    We investigate the effect of the filling factor on transport anisotropies, known as stripes, in high Landau levels of a two-dimensional electron gas. We find that at certain in-plane magnetic fields, the stripes orientation is sensitive to the filling factor within a given Landau level. This sensitivity gives rise to the emergence of stripes away from half-filling while orthogonally oriented, native stripes reside at half-filling. This switching of the anisotropy axes within a single Landau level can be attributed to a strong dependence of the native symmetry-breaking potential on the filling factor.

  19. Rotating superconductor magnet for producing rotating lobed magnetic field lines

    DOEpatents

    Hilal, Sadek K.; Sampson, William B.; Leonard, Edward F.

    1978-01-01

    This invention provides a rotating superconductor magnet for producing a rotating lobed magnetic field, comprising a cryostat; a superconducting magnet in the cryostat having a collar for producing a lobed magnetic field having oppositely directed adjacent field lines; rotatable support means for selectively rotating the superconductor magnet; and means for energizing the superconductor magnet.

  20. Synthetic Landau levels for photons

    NASA Astrophysics Data System (ADS)

    Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan

    2016-06-01

    Synthetic photonic materials are an emerging platform for exploring the interface between microscopic quantum dynamics and macroscopic material properties. Photons experiencing a Lorentz force develop handedness, providing opportunities to study quantum Hall physics and topological quantum science. Here we present an experimental realization of a magnetic field for continuum photons. We trap optical photons in a multimode ring resonator to make a two-dimensional gas of massive bosons, and then employ a non-planar geometry to induce an image rotation on each round-trip. This results in photonic Coriolis/Lorentz and centrifugal forces and so realizes the Fock–Darwin Hamiltonian for photons in a magnetic field and harmonic trap. Using spatial- and energy-resolved spectroscopy, we track the resulting photonic eigenstates as radial trapping is reduced, finally observing a photonic Landau level at degeneracy. To circumvent the challenge of trap instability at the centrifugal limit, we constrain the photons to move on a cone. Spectroscopic probes demonstrate flat space (zero curvature) away from the cone tip. At the cone tip, we observe that spatial curvature increases the local density of states, and we measure fractional state number excess consistent with the Wen–Zee theory, providing an experimental test of this theory of electrons in both a magnetic field and curved space. This work opens the door to exploration of the interplay of geometry and topology, and in conjunction with Rydberg electromagnetically induced transparency, enables studies of photonic fractional quantum Hall fluids and direct detection of anyons.

  1. Synthetic Landau levels for photons.

    PubMed

    Schine, Nathan; Ryou, Albert; Gromov, Andrey; Sommer, Ariel; Simon, Jonathan

    2016-06-30

    Synthetic photonic materials are an emerging platform for exploring the interface between microscopic quantum dynamics and macroscopic material properties. Photons experiencing a Lorentz force develop handedness, providing opportunities to study quantum Hall physics and topological quantum science. Here we present an experimental realization of a magnetic field for continuum photons. We trap optical photons in a multimode ring resonator to make a two-dimensional gas of massive bosons, and then employ a non-planar geometry to induce an image rotation on each round-trip. This results in photonic Coriolis/Lorentz and centrifugal forces and so realizes the Fock–Darwin Hamiltonian for photons in a magnetic field and harmonic trap. Using spatial- and energy-resolved spectroscopy, we track the resulting photonic eigenstates as radial trapping is reduced, finally observing a photonic Landau level at degeneracy. To circumvent the challenge of trap instability at the centrifugal limit, we constrain the photons to move on a cone. Spectroscopic probes demonstrate flat space (zero curvature) away from the cone tip. At the cone tip, we observe that spatial curvature increases the local density of states, and we measure fractional state number excess consistent with the Wen–Zee theory, providing an experimental test of this theory of electrons in both a magnetic field and curved space. This work opens the door to exploration of the interplay of geometry and topology, and in conjunction with Rydberg electromagnetically induced transparency, enables studies of photonic fractional quantum Hall fluids and direct detection of anyons. PMID:27281214

  2. Preflare magnetic and velocity fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Gaizauskas, V.; Chapman, G. A.; Deloach, A. C.; Gary, G. A.; Jones, H. P.; Karpen, J. T.; Martres, M.-J.; Porter, J. G.; Schmeider, B.

    1986-01-01

    A characterization is given of the preflare magnetic field, using theoretical models of force free fields together with observed field structure to determine the general morphology. Direct observational evidence for sheared magnetic fields is presented. The role of this magnetic shear in the flare process is considered within the context of a MHD model that describes the buildup of magnetic energy, and the concept of a critical value of shear is explored. The related subject of electric currents in the preflare state is discussed next, with emphasis on new insights provided by direct calculations of the vertical electric current density from vector magnetograph data and on the role of these currents in producing preflare brightenings. Results from investigations concerning velocity fields in flaring active regions, describing observations and analyses of preflare ejecta, sheared velocities, and vortical motions near flaring sites are given. This is followed by a critical review of prevalent concepts concerning the association of flux emergence with flares

  3. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

  4. Magnetic Field of Strange Dwarfs

    NASA Astrophysics Data System (ADS)

    Baghdasaryan, D. S.

    2016-03-01

    The generation of a magnetic field in a strange quark star owing to differential rotation of the superfluid and superconducting quark core relative to the normal electron-nuclear crust of the star is examined. The maximum possible magnetic field on the surface is estimated for various models of strange dwarfs. Depending on the configuration parameters, i.e., the mass M and radius R of the star, a range of 103-105 G is found. These values of the magnetic field may be an additional condition for identification of strange dwarfs among the extensive class of observed white dwarfs.

  5. Magnetic fields and scintillator performance

    SciTech Connect

    Green, D.; Ronzhin, A.; Hagopian, V.

    1995-06-01

    Experimental data have shown that the light output of a scintillator depends on the magnitude of the externally applied magnetic fields, and that this variation can affect the calorimeter calibration and possibly resolution. The goal of the measurements presented here is to study the light yield of scintillators in high magnetic fields in conditions that are similar to those anticipated for the LHC CMS detector. Two independent measurements were performed, the first at Fermilab and the second at the National High Magnetic Field Laboratory at Florida State University.

  6. Magnetoconvection in sheared magnetic fields

    SciTech Connect

    Bian, N. H.; Garcia, O. E.

    2008-10-15

    The development of magnetoconvection in a sheared magnetic field is investigated. The equilibrium magnetic field B{sub 0} is horizontal and its orientation varies linearly along the vertical axis. Preliminary consideration of the transition from the inertial to the viscous regime of the gravitational resistive interchange instability, reveals that the latter is characterized by the existence of viscoresistive boundary layers of vertical width which scales as Q{sup -1/6}, where Q is the Chandrasekhar number. The situation is analogous to the one encountered in magnetically confined laboratory plasmas, where convective flows are constrained by the magnetic shear to develop in boundary layers located around resonant magnetic surfaces in order to fulfill the 'interchange condition'k{center_dot}B{sub 0}=0, where k is the wave vector of the magnetic perturbation. It follows that when the effect of thermal diffusion is taken into account in the process, convection can only occur above a certain critical value of the Rayleigh number which scales as Q{sup 2/3} for large Q. At the onset, the convection pattern is a superposition of identically thin convective rolls everywhere aligned with the local magnetic field lines and which therefore adopt the magnetic field geometry, a situation also reminiscent of the penumbra of sunspots. Using this degeneracy, equations describing the weakly nonlinear state are obtained and discussed. A reduced magnetohydrodynamic description of magnetoconvection is introduced. Since it is valid for arbitrary magnetic field configurations, it allows a simple extension to the case where there exists an inclination between the direction of gravity and the plane spanned by the equilibrium magnetic field. These reduced magnetohydrodynamic equations are proposed as a powerful tool for further investigations of magnetoconvection in more complex field line geometries.

  7. Holographic ρ mesons in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Callebaut, N.; Dudal, D.; Verschelde, H.

    2013-03-01

    We study the ρ meson in a uniform magnetic field eB using a holographic QCD-model, more specifically a D4/D8/overline{D8} brane setup in the confinement phase at zero temperature with two quenched flavours. The parameters of the model are fixed by matching to corresponding dual field theory parameters at zero magnetic field. We show that the up- and down-flavour branes respond differently to the presence of the magnetic field in the dual QCD-like theory, as expected because of the different electromagnetic charge carried by up- and down-quark. We discuss how to recover the Landau levels, indicating an instability of the QCD vacuum at eB=m_{ρ}^2 towards a phase where charged ρ mesons are condensed, as predicted by Chernodub using effective QCD-models. We improve on these existing effective QCD-model analyses by also taking into account the chiral magnetic catalysis effect, which tells us that the constituent quark masses rise with eB. This turns out to increase the value of the critical magnetic field for the onset of ρ meson condensation to eB≈ 1.1m_{ρ}^2≈ 0.67Ge{{V}^2} . We briefly discuss the influence of pions, which turn out to be irrelevant for the condensation in the approximation made.

  8. Bioluminescence under static magnetic fields

    NASA Astrophysics Data System (ADS)

    Iwasaka, M.; Ueno, S.

    1998-06-01

    In the present study, the effect of magnetic fields on the emission of light by a living system was studied. The fireflies Hotaria parvula and Luciola cruciata were used as the bioluminescence systems. The firefly light organ was fixed at the edge of an optical fiber. The emitted light was introduced into a single-channel photon-counting system using an optical fiber. We measured both the spectrum of a constant light emission and, the time course of bioluminescence pulses. Two horizontal-type superconducting magnets, which produced 8 and 14 T magnetic fields at their center, were used as the magnetic-field generators. We also carried out an in vitro study of bioluminescence. The enzymatic activity of luciferase was measured under a 14 T magnetic field. We measured emission spectra of bioluminescence over the interval 500-600 nm at 25 °C in a stable emission state. It was observed that the peak wavelength around 550 nm shifted to 560 nm under a 14 T magnetic field. However, the effects of magnetic fields were not significant. Also, we measured the time course of emissions at 550 nm in a transient emission state. The rate in the light intensity under a 14 T magnetic field increased compared to the control. There is a possibility that the change in the emission intensities under a magnetic field is related to a change in the biochemical systems of the firefly, such as the enzymatic process of luciferase and the excited singlet state with subsequent light emission.

  9. Magnetic field structure of Mercury

    NASA Astrophysics Data System (ADS)

    Hiremath, K. M.

    2012-04-01

    Recently planet Mercury - an unexplored territory in our solar system - has been of much interest to the scientific community due to recent flybys of the spacecraft MESSENGER that discovered its intrinsic stationary and large-scale dipole like magnetic field structure with an intensity of ˜300nT confirming Mariner 10 observations. In the present study, with the observed constraint of Mercury's atmospheric magnetic field structure, internal magnetic field structure is modeled as a solution of magnetic diffusion equation. In this study, Mercury's internal structure mainly consists of a stable stratified fluid core and the convective mantle. For simplicity, magnetic diffusivity in both parts of the structure is considered to be uniform and constant with a value represented by a suitable averages. It is further assumed that vigorous convection in the mantle disposes of the electric currents leading to a very high diffusivity in that region. Thus, in order to satisfy observed atmospheric magnetic field structure, Mercury's most likely magnetic field structure consists of a solution of MHD diffusion equation in the core and a combined multipolar (dipole and quadrupole like magnetic field structures embedded in the uniform field) solution of a current free like magnetic field structure in the mantle and in the atmosphere. With imposition of appropriate boundary conditions at the core-mantle boundary for the first two diffusion eigen modes, in order to satisfy the observed field structure, present study puts the constraint on Mercury's core radius to be ˜2000km. From the estimated magnetic diffusivity and the core radius, it is also possible to estimate the two diffusion eigen modes with their diffusion time scales of ˜8.6 and 3.7 billion years respectively suggesting that the planet inherits its present-day magnetic field structure from the solar Nebula. It is proposed that permanency of such a large-scale magnetic field structure of the planet is attained during

  10. Magnetic Field Generation in Stars

    NASA Astrophysics Data System (ADS)

    Ferrario, Lilia; Melatos, Andrew; Zrake, Jonathan

    2015-10-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence (particularly thanks to the MiMeS, MAGORI and BOB surveys) through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence, in the generation and stability of neutron star fields.

  11. Compton scattering S matrix and cross section in strong magnetic field

    NASA Astrophysics Data System (ADS)

    Mushtukov, Alexander A.; Nagirner, Dmitrij I.; Poutanen, Juri

    2016-05-01

    Compton scattering of polarized radiation in a strong magnetic field is considered. The recipe for calculation of the scattering matrix elements, the differential and total cross sections based on quantum electrodynamic second-order perturbation theory is presented for the case of arbitrary initial and final Landau level, electron momentum along the field and photon momentum. Photon polarization and electron spin state are taken into account. The correct dependence of natural Landau level width on the electron spin state is taken into account in a general case of arbitrary initial photon momentum for the first time. A number of steps in the calculations were simplified analytically making the presented recipe easy to use. The redistribution functions over the photon energy, momentum and polarization states are presented and discussed. The paper generalizes already known results and offers a basis for the accurate calculation of radiation transfer in a strong B field, for example, in strongly magnetized neutron stars.

  12. Measuring Earth's Magnetic Field Simply.

    ERIC Educational Resources Information Center

    Stewart, Gay B.

    2000-01-01

    Describes a method for measuring the earth's magnetic field using an empty toilet paper tube, copper wire, clear tape, a battery, a linear variable resistor, a small compass, cardboard, a protractor, and an ammeter. (WRM)

  13. Barrier-bound resonances in semiconductor superlattices in strong magnetic fields

    NASA Astrophysics Data System (ADS)

    Duffield, T.; Bhat, R.; Koza, M.; Derosa, F.; Rush, K. M.; Allen, S. J., Jr.

    1987-12-01

    The effective ``miniband'' mass approximation is shown to break down in strong magnetic fields when the magnetic length is smaller than the superlattice period. Under these conditions a real-space description must be used and features in the inhomogeneously broadened cyclotron resonance can be indexed by the position of the cyclotron orbit with respect to the barriers and wells. The line shape agrees with a calculation of the quantum states in a magnetic field in a one-dimensional periodic potential and these experiments give us a rare view of Landau states in the limit where the periodic potential has a period that is larger than the cyclotron diameter.

  14. The magnetic field of Mercury

    NASA Technical Reports Server (NTRS)

    Ness, N. F.

    1977-01-01

    The Mariner 10 spacecraft encountered Mercury three times in 1974-1975. The first and third encounters provided detailed observations of a well-developed detached bow shock wave which results from the interaction of the solar wind. The planet possesses a global magnetic field and a modest magnetosphere, which deflects the solar wind. The field is approximately dipolar, with orientation in the same sense as earth, tilted 12 deg from the rotation axis. The magnetic moment corresponds to an undistorted equatorial field intensity of 350 gammas, approximately 1% of earth's. The field, while unequivocally intrinsic to the planet, may be due to remanent magnetization acquired from an extinct dynamo or a primordial magnetic field or due to a presently active dynamo. The latter possibility appears more plausible at present. In any case, the existence of the magnetic field provides very strong evidence of a mature differentiated planetary interior with a large core (core radius about 0.7 Mercury radius) and a record of the history of planetary formation in the magnetization of the crustal rocks.

  15. Optical sensor of magnetic fields

    DOEpatents

    Butler, M.A.; Martin, S.J.

    1986-03-25

    An optical magnetic field strength sensor for measuring the field strength of a magnetic field comprising a dilute magnetic semi-conductor probe having first and second ends, longitudinally positioned in the magnetic field for providing Faraday polarization rotation of light passing therethrough relative to the strength of the magnetic field. Light provided by a remote light source is propagated through an optical fiber coupler and a single optical fiber strand between the probe and the light source for providing a light path therebetween. A polarizer and an apparatus for rotating the polarization of the light is provided in the light path and a reflector is carried by the second end of the probe for reflecting the light back through the probe and thence through the polarizer to the optical coupler. A photo detector apparatus is operably connected to the optical coupler for detecting and measuring the intensity of the reflected light and comparing same to the light source intensity whereby the magnetic field strength may be calculated.

  16. Magnetic field induced dynamical chaos

    SciTech Connect

    Ray, Somrita; Baura, Alendu; Bag, Bidhan Chandra

    2013-12-15

    In this article, we have studied the dynamics of a particle having charge in the presence of a magnetic field. The motion of the particle is confined in the x–y plane under a two dimensional nonlinear potential. We have shown that constant magnetic field induced dynamical chaos is possible even for a force which is derived from a simple potential. For a given strength of the magnetic field, initial position, and velocity of the particle, the dynamics may be regular, but it may become chaotic when the field is time dependent. Chaotic dynamics is very often if the field is time dependent. Origin of chaos has been explored using the Hamiltonian function of the dynamics in terms of action and angle variables. Applicability of the present study has been discussed with a few examples.

  17. Dynamical transitions in large systems of mean field-coupled Landau-Stuart oscillators: Extensive chaos and cluster states

    SciTech Connect

    Ku, Wai Lim; Girvan, Michelle; Ott, Edward

    2015-12-15

    In this paper, we study dynamical systems in which a large number N of identical Landau-Stuart oscillators are globally coupled via a mean-field. Previously, it has been observed that this type of system can exhibit a variety of different dynamical behaviors. These behaviors include time periodic cluster states in which each oscillator is in one of a small number of groups for which all oscillators in each group have the same state which is different from group to group, as well as a behavior in which all oscillators have different states and the macroscopic dynamics of the mean field is chaotic. We argue that this second type of behavior is “extensive” in the sense that the chaotic attractor in the full phase space of the system has a fractal dimension that scales linearly with N and that the number of positive Lyapunov exponents of the attractor also scales linearly with N. An important focus of this paper is the transition between cluster states and extensive chaos as the system is subjected to slow adiabatic parameter change. We observe discontinuous transitions between the cluster states (which correspond to low dimensional dynamics) and the extensively chaotic states. Furthermore, examining the cluster state, as the system approaches the discontinuous transition to extensive chaos, we find that the oscillator population distribution between the clusters continually evolves so that the cluster state is always marginally stable. This behavior is used to reveal the mechanism of the discontinuous transition. We also apply the Kaplan-Yorke formula to study the fractal structure of the extensively chaotic attractors.

  18. Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots

    NASA Astrophysics Data System (ADS)

    Bustingorry, S.; Pomiro, F.; Aurelio, G.; Curiale, J.

    2016-06-01

    The so-called Arrott plot, which consists in plotting H /M against M2, with H the applied magnetic field and M the magnetization, is used to extract valuable information in second-order magnetic phase transitions. Besides, it is widely accepted that a negative slope in the Arrott plot is indicative of a first-order magnetic transition. This is known as the Banerjee criterion. In consequence, the zero-field transition temperature T* is reported as the characteristic first-order transition temperature. By carefully analyzing the mean-field Landau model used for studying first-order magnetic transitions, we show in this work that T* corresponds in fact to a triple point where three first-order lines meet. More importantly, this analysis reveals the existence of two symmetrical second-order critical points at finite magnetic field (Tc,±Hc) . We then show that a modified Arrott plot can be used to obtain information about these second-order critical points. To support this idea we analyze experimental data on La2 /3Ca1 /3MnO3 and discuss an estimate for the location of the triple point and the second-order critical points.

  19. Magnetic fields in quiescent prominences

    NASA Technical Reports Server (NTRS)

    Van Ballegooijen, A. A.; Martens, P. C. H.

    1990-01-01

    The origin of the axial fields in high-latitude quiescent prominences is considered. The fact that almost all quiescent prominences obey the same hemisphere-dependent rule strongly suggests that the solar differential rotation plays an important role in producing the axial fields. However, the observations are inconsistent with the hypothesis that the axial fields are produced by differential rotation acting on an existing coronal magnetic field. Several possible explanations for this discrepancy are considered. The possibility that the sign of the axial field depends on the topology of the magnetic field in which the prominence is embedded is examined, as is the possibility that the neutral line is tilted with respect to the east-west direction, so that differential rotation causes the neutral line also to rotate with time. The possibility that the axial fields of quiescent prominences have their origin below the solar surface is also considered.

  20. Magnetic fields in ring galaxies

    NASA Astrophysics Data System (ADS)

    Moss, D.; Mikhailov, E.; Silchenko, O.; Sokoloff, D.; Horellou, C.; Beck, R.

    2016-07-01

    Context. Many galaxies contain magnetic fields supported by galactic dynamo action. The investigation of these magnetic fields can be helpful for understanding galactic evolution; however, nothing definitive is known about magnetic fields in ring galaxies. Aims: Here we investigate large-scale magnetic fields in a previously unexplored context, namely ring galaxies, and concentrate our efforts on the structures that appear most promising for galactic dynamo action, i.e. outer star-forming rings in visually unbarred galaxies. Methods: We use tested methods for modelling α-Ω galactic dynamos, taking into account the available observational information concerning ionized interstellar matter in ring galaxies. Results: Our main result is that dynamo drivers in ring galaxies are strong enough to excite large-scale magnetic fields in the ring galaxies studied. The variety of dynamo driven magnetic configurations in ring galaxies obtained in our modelling is much richer than that found in classical spiral galaxies. In particular, various long-lived transients are possible. An especially interesting case is that of NGC 4513, where the ring counter-rotates with respect to the disc. Strong shear in the region between the disc and the ring is associated with unusually strong dynamo drivers in such counter-rotators. The effect of the strong drivers is found to be unexpectedly moderate. With counter-rotation in the disc, a generic model shows that a steady mixed parity magnetic configuration that is unknown for classical spiral galaxies, may be excited, although we do not specifically model NGC 4513. Conclusions: We deduce that ring galaxies constitute a morphological class of galaxies in which identification of large-scale magnetic fields from observations of polarized radio emission, as well as dynamo modelling, may be possible. Such studies have the potential to throw additional light on the physical nature of rings, their lifetimes, and evolution.

  1. Magnetoinfrared Spectroscopy of Landau Levels and Zeeman Splitting of Three-Dimensional Massless Dirac Fermions in ZrTe(5).

    PubMed

    Chen, R Y; Chen, Z G; Song, X-Y; Schneeloch, J A; Gu, G D; Wang, F; Wang, N L

    2015-10-23

    We present a magnetoinfrared spectroscopy study on a newly identified three-dimensional (3D) Dirac semimetal ZrTe(5). We observe clear transitions between Landau levels and their further splitting under a magnetic field. Both the sequence of transitions and their field dependence follow quantitatively the relation expected for 3D massless Dirac fermions. The measurement also reveals an exceptionally low magnetic field needed to drive the compound into its quantum limit, demonstrating that ZrTe(5) is an extremely clean system and ideal platform for studying 3D Dirac fermions. The splitting of the Landau levels provides direct, bulk spectroscopic evidence that a relatively weak magnetic field can produce a sizable Zeeman effect on the 3D Dirac fermions, which lifts the spin degeneracy of Landau levels. Our analysis indicates that the compound evolves from a Dirac semimetal into a topological line-node semimetal under the current magnetic field configuration. PMID:26551130

  2. Magnetic Fields in Stellar Jets

    NASA Astrophysics Data System (ADS)

    Hartigan, Patrick; Frank, Adam; Varniére, Peggy; Blackman, Eric G.

    2007-06-01

    Although several lines of evidence suggest that jets from young stars are driven magnetically from accretion disks, existing observations of field strengths in the bow shocks of these flows imply that magnetic fields play only a minor role in the dynamics at these locations. To investigate this apparent discrepancy we performed numerical simulations of expanding magnetized jets with stochastically variable input velocities with the AstroBEAR MHD code. Because the magnetic field B is proportional to the density n within compression and rarefaction regions, the magnetic signal speed drops in rarefactions and increases in the compressed areas of velocity-variable flows. In contrast, B~n0.5 for a steady state conical flow with a toroidal field, so the Alfvén speed in that case is constant along the entire jet. The simulations show that the combined effects of shocks, rarefactions, and divergent flow cause magnetic fields to scale with density as an intermediate power 1>p>0.5. Because p>0.5, the Alfvén speed in rarefactions decreases on average as the jet propagates away from the star. Hence, a typical Alfvén velocity in the jet close to the star is significantly larger than it is in the rarefactions ahead of bow shocks at larger distances. We find that the observed values of weak fields at large distances are consistent with strong fields required to drive the observed mass loss close to the star. Typical velocity perturbations, which form shocks at large distances, will produce only magnetic waves close to the star. For a typical stellar jet the crossover point inside which velocity perturbations of 30-40 km s-1 no longer produce shocks is ~300 AU from the source.

  3. Hysteresis in rotation magnetic field

    NASA Astrophysics Data System (ADS)

    Ivanyi, Amalia

    2000-01-01

    The different properties of the vector Jiles-Atherton hysteresis operator is proved under forced H- and B-field supply. Feeding the magnetic material with alternating and circular polarised rotational excitation, the different properties of the model under the input field intensity and the flux density are investigated and the results are proved in figures.

  4. Dynamical mass generation in strongly coupled quantum electrodynamics with weak magnetic fields

    SciTech Connect

    Ayala, Alejandro; Raya, Alfredo; Rojas, Eduardo; Bashir, Adnan

    2006-05-15

    We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of weak magnetic fields using Schwinger-Dyson equations. Contrary to the case where the magnetic field is strong, in the weak field limit the coupling should exceed certain critical value in order for the generation of masses to take place, just as in the case where no magnetic field is present. The weak field limit is defined as eB<field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB){sup 2}.

  5. MAGNETIC FIELD MEASUREMENTS FOR FAST-CHANGING MAGNETIC FIELDS.

    SciTech Connect

    JAIN, A.; ESCALLIER, J.; GANETIS, G.; LOUIE, W.; MARONE, A.; THOMAS. R.; WANDERER, P.

    2004-10-03

    Several recent applications for fast ramped magnets have been found that require rapid measurement of the field quality during the ramp. (In one instance, accelerator dipoles will be ramped at 1 T/sec, with measurements needed to the accuracy typically required for accelerators.) We have built and tested a new type of magnetic field measuring system to meet this need. The system consists of 16 stationary pickup windings mounted on a cylinder. The signals induced in the windings in a changing magnetic field are sampled and analyzed to obtain the field harmonics. To minimize costs, printed circuit boards were used for the pickup windings and a combination of amplifiers and ADPs used for the voltage readout system. New software was developed for the analysis. Magnetic field measurements of a model dipole developed for the SIS200 accelerator at GSI are presented. The measurements are needed to insure that eddy currents induced by the fast ramps do not impact the field quality needed for successful accelerator operation.

  6. Magnetic field fluctuations during substorms

    NASA Technical Reports Server (NTRS)

    Fairfield, D. H.

    1971-01-01

    Before a magnetospheric substorm and during its early phases the magnetic field magnitude in the geomagnetic tail increases and field lines in the nighttime hemisphere assume a more tail-like configuration. Before the substorm onset a minimum amount of magnetic flux is observed to cross the neutral sheet which means that the neutral sheet currents attain their most earthward locations and their greatest current densities. This configuration apparently results from an increased transport of magnetic flux to the tail caused by a southward interplanetary magnetic field. The field begins relaxing toward a more dipolar configuration at the time of a substorm onset with the recovery probably occurring first between 6 and 10 R sub E. This recovery must be associated with magnetospheric convection which restores magnetic flux to the dayside hemisphere. Field aligned currents appear to be required to connect magnetospheric currents to the auroral electrojets, implying that a net current flows in a limited range of longitudes. Space measurements supporting current systems are limited. More evidence exists for the occurrence of double current sheets which do not involve net current at a given longitude.

  7. Effects of periodic scattering potential on Landau quantization and ballistic transport of electrons in graphene

    SciTech Connect

    Gumbs, Godfrey; Iurov, Andrii; Huang, Danhong; Fekete, Paula; Zhemchuzhna, Liubov

    2014-03-31

    A two-dimensional periodic array of scatterers has been introduced to a single layer of graphene in the presence of an external magnetic field perpendicular to the graphene layer. The eigenvalue equation for such a system has been solved numerically to display the structure of split Landau subbands as functions of both wave number and magnetic flux. The effects of pseudo-spin coupling and Landau subbands mixing by a strong scattering potential have been demonstrated. Additionally, we investigated the square barrier tunneling problem when magnetic field is present, as well as demonstrate the crucial difference in the modulated band structure between graphene and the two-dimensional electron gas. The low-magnetic field regime is particularly interesting for Dirac fermions and has been discussed. Tunneling of Dirac electrons through a magnetic potential barrier has been investigated to complement the reported results on electrostatic potential scattering in the presence of an ambient magnetic field.

  8. Electron-photon coupling in semimetals in a high magnetic field

    SciTech Connect

    Mihaila, Bogdan; Albers, Robert C; Littlewood, Peter B

    2009-01-01

    We consider the effect of electron-phonon coupling in semimetals in high magnetic fields, with regard to elastic modes that can lead to a redistribution of carriers between pockets. We show that in a clean three dimensional system, at each Landau level crossing, this leads to a discontinuity in the magnetostriction, and a divergent contribution to the elastic modulus. We estimate the magnitude of this effect in the group V semimetal Bismuth.

  9. Electron correlations in semiconductors: Bulk cohesive properties and magnetic-field-induced Wigner crystal at heterojunctions

    SciTech Connect

    Louie, S.G.; Zhu, X.

    1992-08-01

    A correlated wavefunction variational quantum Monte Carlo approach to the studies of electron exchange and correlation effects in semiconductors is presented. Applications discussed include the cohesive and structural properties of bulk semiconductors, and the magnetic-field-induced Wigner electron crystal in two dimensions. Landau level mixing is shown to be important in determining the transition between the quantum Hall liquid and the Wigner crystal states in the regime of relevant experimental parameters.

  10. Indoor localization using magnetic fields

    NASA Astrophysics Data System (ADS)

    Pathapati Subbu, Kalyan Sasidhar

    Indoor localization consists of locating oneself inside new buildings. GPS does not work indoors due to multipath reflection and signal blockage. WiFi based systems assume ubiquitous availability and infrastructure based systems require expensive installations, hence making indoor localization an open problem. This dissertation consists of solving the problem of indoor localization by thoroughly exploiting the indoor ambient magnetic fields comprising mainly of disturbances termed as anomalies in the Earth's magnetic field caused by pillars, doors and elevators in hallways which are ferromagnetic in nature. By observing uniqueness in magnetic signatures collected from different campus buildings, the work presents the identification of landmarks and guideposts from these signatures and further develops magnetic maps of buildings - all of which can be used to locate and navigate people indoors. To understand the reason behind these anomalies, first a comparison between the measured and model generated Earth's magnetic field is made, verifying the presence of a constant field without any disturbances. Then by modeling the magnetic field behavior of different pillars such as steel reinforced concrete, solid steel, and other structures like doors and elevators, the interaction of the Earth's field with the ferromagnetic fields is described thereby explaining the causes of the uniqueness in the signatures that comprise these disturbances. Next, by employing the dynamic time warping algorithm to account for time differences in signatures obtained from users walking at different speeds, an indoor localization application capable of classifying locations using the magnetic signatures is developed solely on the smart phone. The application required users to walk short distances of 3-6 m anywhere in hallway to be located with accuracies of 80-99%. The classification framework was further validated with over 90% accuracies using model generated magnetic signatures representing

  11. Magnetic field of the Earth

    NASA Astrophysics Data System (ADS)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  12. Observations of Mercury's magnetic field

    NASA Technical Reports Server (NTRS)

    Ness, N. F.; Behannon, K. W.; Lepping, R. P.; Whang, Y. C.

    1975-01-01

    Magnetic field data obtained by Mariner 10 during the third and final encounter with the planet Mercury on 16 March 1975 were studied. A well developed bow shock and modest magnetosphere, previously observed at first encounter on 29 March 1974, were again observed. In addition, a much stronger magnetic field near closest approach, 400 gamma versus 98 gamma, was observed at an altitude of 327 km and approximately 70 deg north Mercurian latitude. Spherical harmonic analysis of the data provide an estimate of the centered planetary magnetic dipole of 4.7 x 10 to the 22nd power Gauss/cu cm with the axis tilted 12 deg to the rotation axis and in the same sense as Earth's. The interplanetary field was sufficiently different between first and third encounters that in addition to the very large field magnitude observed, it argues strongly against a complex induction process generating the observed planetary field. While a possibility exists that Mercury possesses a remanent field due to magnetization early in its formation, a present day active dynamo seems to be a more likely candidate for its origin.

  13. Galactic and Intergalactic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Klein, U.; Fletcher, A.

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible. In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later chapters address the role of magnetic fields in the evolution of the interstellar medium, galaxies and galaxy clusters. The book is intended for advanced undergraduate and postgraduate students in astronomy and physics and will serve as an entry point for those starting their first research projects in the field.

  14. Mars Crustal Magnetic Field Remnants

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The radial magnetic field measured is color coded on a global perspective view that shows measurements derived from spacecraft tracks below 200 km overlain on a monochrome shaded relief map of the topography.

    This image shows especially strong Martian magnetic fields in the southern highlands near the Terra Cimmeria and Terra Sirenum regions, centered around 180 degrees longitude from the equator to the pole. It is where magnetic stripes possibly resulting from crustal movement are most prominent. The bands are oriented approximately east - west and are about 100 miles wide and 600 miles long, although the longest band stretches more than 1200 miles.

    The false blue and red colors represent invisible magnetic fields in the Martian crust that point in opposite directions. The magnetic fields appear to be organized in bands, with adjacent bands pointing in opposite directions, giving these stripes a striking similarity to patterns seen in the Earth's crust at the mid-oceanic ridges.

    These data were compiled by the MGS Magnetometer Team led by Mario Acuna at the Goddard Space Flight Center in Greenbelt, MD.

  15. Satellite to study earth's magnetic field

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The Magnetic Field Satellite (Magsat) designed to measure the near earth magnetic field and crustal anomalies is briefly described. A scalar magnetometer to measure the magnitude of the earth's crustal magnetic field and a vector magnetometer to measure magnetic field direction as well as magnitude are included. The mission and its objectives are summarized along with the data collection and processing system.

  16. The magnetic field of the Milky Way

    NASA Astrophysics Data System (ADS)

    Reid, Mark J.

    Models of the magnetic field configuration of the Milky Way are reviewed. Current analyses of rotation measure data suggest that the Milky Way possesses a bisymmetric-like spiral magnetic field, that field reversals among spiral arms exist, and that the magnetic spiral may not closely match the mass spiral structure. Zeeman measurements of OH masers may provide alternative magnetic field information.

  17. Realization of the thermal equilibrium in inhomogeneous magnetic systems by the Landau-Lifshitz-Gilbert equation with stochastic noise, and its dynamical aspects

    NASA Astrophysics Data System (ADS)

    Nishino, Masamichi; Miyashita, Seiji

    2015-04-01

    It is crucially important to investigate the effects of temperature on magnetic properties such as critical phenomena, nucleation, pinning, domain wall motion, and coercivity. The Landau-Lifshitz-Gilbert (LLG) equation has been applied extensively to study dynamics of magnetic properties. Approaches of Langevin noises have been developed to introduce the temperature effect into the LLG equation. To have the thermal equilibrium state (canonical distribution) as the steady state, the system parameters must satisfy some condition known as the fluctuation-dissipation relation. In inhomogeneous magnetic systems in which spin magnitudes are different at sites, the condition requires that the ratio between the amplitude of the random noise and the damping parameter depend on the magnitude of the magnetic moment at each site. Focused on inhomogeneous magnetic systems, we systematically showed agreement between the stationary state of the stochastic LLG equation and the corresponding equilibrium state obtained by Monte Carlo simulations in various magnetic systems including dipole-dipole interactions. We demonstrated how violations of the condition result in deviations from the true equilibrium state. We also studied the characteristic features of the dynamics depending on the choice of the parameter set. All the parameter sets satisfying the condition realize the same stationary state (equilibrium state). In contrast, different choices of parameter set cause seriously different relaxation processes. We show two relaxation types, i.e., magnetization reversals with uniform rotation and with nucleation.

  18. Self-similar occurrence of massless Dirac particles in graphene under magnetic field

    NASA Astrophysics Data System (ADS)

    Rhim, Jun-Won; Park, Kwon

    2013-03-01

    Intricate interplay between the periodicity of the lattice structure and that of the cyclotron motion gives rise to a well-known self-similar fractal structure of the Hofstadter butterfly for an electron moving in lattice under magnetic field. Evolving from the n = 0 Landau level, the central band of the Hofstadter butterfly is especially interesting since it may hold a key to the mysteries of the fractional quantum Hall effect in graphene. In this paper, we develop an effective Hamiltonian method that can be used to provide an accurate analytic description of the central Hofstadter band in the weak-field regime. One of the most important discoveries obtained in this work is that massless Dirac particles always exist inside the central Hofstadter band no matter how small the magnetic flux may become. In other words, with its bandwidth broadened by the lattice effect, the n = 0 Landau level contains massless Dirac particles within itself. In fact, by carefully analyzing the self-similar recursive pattern of the central Hofstadter band, we conclude that massless Dirac particles should occur under arbitrary magnetic field. As a corollary, the central Hofstadter band also contains a self-similar structure of recursive Landau levels associated with such massless Dirac particles.

  19. Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field

    SciTech Connect

    Taniguchi, Tomohiro; Tsunegi, Sumito; Kubota, Hitoshi; Ito, Takahiro; Utsumi, Yasuhiro

    2015-08-07

    Theoretical conditions to excite self-oscillation in a spin torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer are investigated by analytically solving the Landau-Lifshitz-Gilbert equation. The analytical relation between the current and oscillation frequency is derived. It is found that a large amplitude oscillation can be excited by applying a small field pointing to the direction anti-parallel to the magnetization of the pinned layer. The validity of the analytical results is confirmed by comparing with numerical simulation, showing good agreement especially in a low current region.

  20. Stable oscillation in spin torque oscillator excited by a small in-plane magnetic field

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Ito, Takahiro; Utsumi, Yasuhiro; Tsunegi, Sumito; Kubota, Hitoshi

    2015-08-01

    Theoretical conditions to excite self-oscillation in a spin torque oscillator consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer are investigated by analytically solving the Landau-Lifshitz-Gilbert equation. The analytical relation between the current and oscillation frequency is derived. It is found that a large amplitude oscillation can be excited by applying a small field pointing to the direction anti-parallel to the magnetization of the pinned layer. The validity of the analytical results is confirmed by comparing with numerical simulation, showing good agreement especially in a low current region.

  1. Analysis of reliable sub-ns spin-torque switching under transverse bias magnetic fields

    SciTech Connect

    D'Aquino, M.; Perna, S.; Serpico, C.; Bertotti, G.; Mayergoyz, I. D.

    2015-05-07

    The switching process of a magnetic spin-valve nanosystem subject to spin-polarized current pulses is considered. The dependence of the switching probability on the current pulse duration is investigated. The further application of a transverse field along the intermediate anisotropy axis of the particle is used to control the quasi-random relaxation of magnetization to the reversed magnetization state. The critical current amplitudes to realize the switching are determined by studying the phase portrait of the Landau-Lifshtz-Slonczewski dynamics. Macrospin numerical simulations are in good agreement with the theoretical prediction and demonstrate reliable switching even for very short (below 100 ps) current pulses.

  2. Pion production via proton synchrotron radiation in strong magnetic fields in relativistic field theory: Scaling relations and angular distributions

    NASA Astrophysics Data System (ADS)

    Maruyama, Tomoyuki; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.

    2016-06-01

    We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are ni,f ∼104-105. We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of 1015 G, where ni,f ∼1012-1013, from the results for ni,f ∼104-105. The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed.

  3. Pion production via proton synchrotron radiation in strong magnetic fields in relativistic field theory: Scaling relations and angular distributions

    NASA Astrophysics Data System (ADS)

    Maruyama, Tomoyuki; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.

    2016-06-01

    We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are ni,f ∼104-105. We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of 1015 G, where ni,f ∼1012-1013, from the results for ni,f ∼104-105. The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed.

  4. Impurities in magnetic-field-induced Luttinger liquid

    NASA Astrophysics Data System (ADS)

    Tsai, Shan-Wen; Maslov, Dmitrii L.; Glazman, Leonid I.

    2001-03-01

    It has been shown recently(C. Biagini, D. L. Maslov, M. Yu. Reizer and L. I. Glazman, `` Magnetic-field-induced Luttinger liquid''), cond-mat/0006407. that a strong magnetic field applied to a bulk metal may induce a Luttinger liquid phase. This is a consequence of the reduced effective dimensionality of charge carriers from 3D to 1D, an effect which is most pronounced in the ultra-quantum limit, when only the lowest Landau level remains populated. We study the effect of impurities in this system. For the case of a point impurity, the calculation of the scattering cross section at a single impurity can be mapped exactly to a 1D problem of tunneling conductance through a barrier for interacting electrons, solved by Yue et al.(D. Yue, L. I. Glazman and K. A. Matveev, Phys. Rev. B 49) (1994) 1966.. Using this mapping, we find that the longitudinal (ɛ=+1) and transverse (ɛ=-1) Drude conductivities exhibit the scaling laws σ_ɛ∝ T^ɛα, where α=2e^2|lnκl_B|/π v_F, and vF and κ are the B-dependent Fermi velocity and screening wavevector, respectively; lB is the magnetic length. The physical reason for such a behavior of the conductivity is the almost 1D form of the Friedel oscillation around a single point impurity in the strong magnetic field.

  5. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  6. Cosmological magnetic fields from inflation

    NASA Astrophysics Data System (ADS)

    Motta, Leonardo

    In this thesis we review the methods for computation of cosmological correlations in the early universe known as the in-in formalism which are then applied to the problem of magnetogenesis from inflation. For this computation, a power-law single field slow- roll inflation is assumed together with a coupling of the form eφ/nuF μnuFμnu between the inflaton φ and the electrodynamical field strength Fμnu. For certain choice of parameters, the model produces a scale-invariant power spectrum that can be as high as 10-12 G at cosmological scales at present time. Finally, we compute the correlation between the magnetic field energy density and scalar metric fluctuations at tree-level from which the shape of the resulting non-gaussianity is analyzed.We show that the corresponding bispectrum is of order 10-5 times the power spectrum of magnetic fields.

  7. Direct observation of Landau levels of massless and massive Dirac fermions.

    NASA Astrophysics Data System (ADS)

    Li, Guohong; Andrei, Eva Y.

    2007-03-01

    The low energy quasiparticles in graphene resemble massless relativistic particles (Dirac fermions): they have a linear energy-momentum spectrum and possess internal degrees of freedom arising from the crystal symmetry of the honeycomb lattice, leading to particle anti-particle pairs. When two layers of graphene are coupled together, the quasiparticles acquire a band-mass and are transformed into chiral massive fermions. Both types of quasiparticles develop unusual Landau levels in a magnetic field which profoundly alter the magneto-transport properties. We will report the direct observation of the Landau levels associated with these quasiparticles using a low temperature STM in fields up to 12 Tesla. The experiments reveal two independent sequences of Landau levels that provide evidence for the coexistence of massless and massive Dirac fermions. The energy levels of the former exhibit a square-root dependence on both field and Landau-level index n, while the latter are linear in field with a Landau-level index dependence of [n(n+1)]^1/2. Both sequences exhibit a zero energy Landau level which is a unique and direct consequence of the quantum-relativistic nature of these quasiparticles.

  8. Large amplitude oscillation of magnetization in spin-torque oscillator stabilized by field-like torque

    SciTech Connect

    Taniguchi, Tomohiro Kubota, Hitoshi; Imamura, Hiroshi; Tsunegi, Sumito

    2015-05-07

    Oscillation frequency of spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer is theoretically investigated by taking into account the field-like torque. It is shown that the field-like torque plays an important role in finding the balance between the energy supplied by the spin torque and the dissipation due to the damping, which results in a steady precession. The validity of the developed theory is confirmed by performing numerical simulations based on the Landau-Lifshitz-Gilbert equation.

  9. Large amplitude oscillation of magnetization in spin-torque oscillator stabilized by field-like torque

    NASA Astrophysics Data System (ADS)

    Taniguchi, Tomohiro; Tsunegi, Sumito; Kubota, Hitoshi; Imamura, Hiroshi

    2015-05-01

    Oscillation frequency of spin torque oscillator with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer is theoretically investigated by taking into account the field-like torque. It is shown that the field-like torque plays an important role in finding the balance between the energy supplied by the spin torque and the dissipation due to the damping, which results in a steady precession. The validity of the developed theory is confirmed by performing numerical simulations based on the Landau-Lifshitz-Gilbert equation.

  10. Magnetic-Field-Induced Relativistic Properties in Type-I and Type-II Weyl Semimetals.

    PubMed

    Tchoumakov, Serguei; Civelli, Marcello; Goerbig, Mark O

    2016-08-19

    We investigate Weyl semimetals with tilted conical bands in a magnetic field. Even when the cones are overtilted (type-II Weyl semimetal), Landau-level quantization can be possible as long as the magnetic field is oriented close to the tilt direction. Most saliently, the tilt can be described within the relativistic framework of Lorentz transformations that give rise to a rich spectrum, displaying new transitions beyond the usual dipolar ones in the optical conductivity. We identify particular features in the latter that allow one to distinguish between semimetals of different types. PMID:27588870

  11. Fokker-Planck equation in the presence of a uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Dong, Chao; Zhang, Wenlu; Li, Ding

    2016-08-01

    The Fokker-Planck equation in the presence of a uniform magnetic field is derived which has the same form as the case of no magnetic field but with different Fokker-Planck coefficients. The coefficients are calculated explicitly within the binary collision model, which are free from infinite sums of Bessel functions. They can be used to investigate relaxation and transport phenomena conveniently. The kinetic equation is also manipulated into the Landau form from which it is straightforward to compare with previous results and prove the conservation laws.

  12. Crystal field and magnetic properties

    NASA Technical Reports Server (NTRS)

    Flood, D. J.

    1977-01-01

    Magnetization and magnetic susceptibility measurements have been made in the temperature range 1.3 to 4.2 K on powdered samples of ErH3. The susceptibility exhibits Curie-Weiss behavior from 4.2 to 2 K, and intercepts the negative temperature axis at theta = 1.05 + or - 0.05 K, indicating that the material is antiferromagnetic. The low field effective moment is 6.77 + or - 0.27 Bohr magnetons per ion. The magnetization exhibits a temperature independent contribution, the slope of which is (5 + or - 1.2) x 10 to the -6th Weber m/kg Tesla. The saturation moment is 3.84 + or - 1 - 0.15 Bohr magnetons per ion. The results can be qualitatively explained by the effects of crystal fields on the magnetic ions. No definitive assignment of a crystal field ground state can be given, nor can a clear choice between cubically or hexagonally symmetric crystal fields be made. For hexagonal symmetry, the first excited state is estimated to be 86 to 100 K above the ground state. For cubic symmetry, the splitting is on the order of 160 to 180 K.

  13. Transverse Magnetic Field Propellant Isolator

    NASA Technical Reports Server (NTRS)

    Foster, John E.

    2000-01-01

    An alternative high voltage isolator for electric propulsion and ground-based ion source applications has been designed and tested. This design employs a transverse magnetic field that increases the breakdown voltage. The design can greatly enhance the operating range of laboratory isolators used for high voltage applications.

  14. Combined topological and Landau order from strong correlations in Chern bands

    NASA Astrophysics Data System (ADS)

    Daghofer, Maria; Kourtis, Stefanos

    2014-03-01

    In recent years, topologically nontrivial and nearly dispersionless bands have attracted attention as hosts for states analogous to fractional quantum-Hall states, but without a magnetic field. Indeed, such fractional Chern insulators were found and connections to fractional quantum-Hall states in Landau levels were established. We discuss here aspects where fractional Chern insulators differ from Landau levels. In particular, we present a class of states where both topological order and symmetry breaking arise spontaneously: the states show both fractional Hall conductivity and charge order. This coexistence of topological and conventional Landau order relies on the geometric frustration of the underlying lattice and consequently goes qualitatively beyond physics found in continuous Landau levels with their weak lattice. Supported by the Emmy-Noether program of the Deutsche Forschungsgemeinschaft (DFG).

  15. Gauges for the Ginzburg-Landau equations of superconductivity

    SciTech Connect

    Fleckinger-Pelle, J.; Kaper, H.G.

    1995-12-31

    This note is concerned with gauge choices for the time-dependent Ginzburg-Landau equations of superconductivity. The requiations model the state of a superconducting sample in a magnetic field near the critical tempeature. Any two solutions related through a ``gauge transformation`` describe the same state and are physically indistinquishable. This ``gauge invariance`` can be exploited for analtyical and numerical purposes. A new gauge is proposed, which reduces the equations to a particularly attractive form.

  16. Bose-Einstein condensation of bound pairs of relativistic fermions in a magnetic field

    NASA Astrophysics Data System (ADS)

    Feng, Bo; Hou, De-fu; Ren, Hai-cang; Wu, Ping-ping

    2016-04-01

    The Bose-Einstein condensation of bound pairs made of equally and oppositely charged fermions in a magnetic field is investigated using a relativistic model. The Gaussian fluctuations have been taken into account in order to study the spectrum of bound pairs in the strong coupling region. We found, in the weak coupling region, that the condensation temperature increases with an increasing magnetic field displaying the magnetic catalysis effect. In the strong coupling region, the inverse magnetic catalysis appears when the magnetic field is low and is replaced by the usual magnetic catalysis effect when magnetic field is sufficiently high, in contrast to the nonrelativistic case where the inverse magnetic catalysis prevails in the strong coupling region regardless of the strength of the magnetic field. The resulting response to the magnetic field is the consequence of the competition between the dimensional reduction by Landau orbitals in pairing dynamics and the anisotropy of the kinetic spectrum of the bound pairs. We thus conclude that dimensional reduction dominates in the weak domain and strong coupling one except in the small magnetic field region, where the enhanced fluctuations dominate.

  17. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  18. Magnetic fields in the sun

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.

    1974-01-01

    The observed properties of solar magnetic fields are reviewed, with particular reference to the complexities imposed on the field by motions of the highly conducting gas. Turbulent interactions between gas and field lead to heating or cooling of the gas according to whether the field energy density is less or greater than the maximum kinetic energy density in the convection zone. The field strength above which cooling sets in is 700 gauss. A weak solar dipole field may be primeval, but dynamo action is also important in generating new flux. The dynamo is probably not confined to the convection zone, but extends throughout most of the volume of the sun. Planetary tides appear to play a role in driving the dynamo.

  19. The magnetic field of Jupiter

    NASA Technical Reports Server (NTRS)

    Acuna, M. H.; Ness, N. F.

    1976-01-01

    The paper is concerned mainly with the intrinsic planetary field which dominates the inner magnetosphere up to a distance of 10 to 12 Jovian radii where other phenomena, such as ring currents and diamagnetic effects of trapped charged particles, become significant. The main magnetic field of Jupiter as determined by in-situ observations by Pioner 10 and 11 is found to be relatively more complex than a simple offset tilted dipole. Deviations from a simple dipole geometry lead to distortions of the charged particle L shells and warping of the magnetic equator. Enhanced absorption effects associated with Io and Amalthea are predicted. The results are consistent with the conclusions derived from extensive radio observations at decimetric and decametric wavelengths for the planetary field.

  20. Magnetic field of the Earth

    NASA Astrophysics Data System (ADS)

    Popov, Aleksey

    2013-04-01

    The magnetic field of the Earth has global meaning for a life on the Earth. The world geophysical science explains: - occurrence of a magnetic field of the Earth it is transformation of kinetic energy of movements of the fused iron in the liquid core of Earth - into the magnetic energy; - the warming up of a kernel of the Earth occurs due to radioactive disintegration of elements, with excretion of thermal energy. The world science does not define the reasons: - drift of a magnetic dipole on 0,2 a year to the West; - drift of lithospheric slabs and continents. The author offers: an alternative variant existing in a world science the theories "Geodynamo" - it is the theory « the Magnetic field of the Earth », created on the basis of physical laws. Education of a magnetic field of the Earth occurs at moving the electric charge located in a liquid kernel, at rotation of the Earth. At calculation of a magnetic field is used law the Bio Savara for a ring electric current: dB = . Magnetic induction in a kernel of the Earth: B = 2,58 Gs. According to the law of electromagnetic induction the Faradey, rotation of a iron kernel of the Earth in magnetic field causes occurrence of an electric field Emf which moves electrons from the center of a kernel towards the mantle. So of arise the radial electric currents. The magnetic field amplifies the iron of mantle and a kernel of the Earth. As a result of action of a radial electric field the electrons will flow from the center of a kernel in a layer of an electric charge. The central part of a kernel represents the field with a positive electric charge, which creates inverse magnetic field Binv and Emfinv When ?mfinv = ?mf ; ?inv = B, there will be an inversion a magnetic field of the Earth. It is a fact: drift of a magnetic dipole of the Earth in the western direction approximately 0,2 longitude, into a year. Radial electric currents a actions with the basic magnetic field of a Earth - it turn a kernel. It coincides with laws

  1. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1990-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of the broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  2. Oxide superconductors under magnetic field

    NASA Technical Reports Server (NTRS)

    Kitazawa, K.

    1991-01-01

    One of the current most serious problems for the oxide superconductors from the standpoint of practical application is the various novel features derived mainly from their extremely short coherence. In particular, the coherence length so far observed in the cuprate superconductors is in the range of 0.1 nm perpendicular to the CuO2 plane. This seems to be creating most of the difficulties in the device fabrication and in the performance under the magnetic field. Some of the superconducting properties under the magnetic field will be discussed in terms of the short coherence length. A model will be presented based on the gradual strengthening of the pinning force with decrease in temperature and the weak coupling at the grain boundaries. Secondly, the broadening of the superconducting transition under the magnetic field is discussed. This is observed significantly only when the field is applied perpendicular to the basal plane and the relative orientation of the current to the field is insignificant in determining the extent of broadening. Besides, the change in the strength of the pinning force does not affect the width of the broadening. From these observations discussions will be made on a model based on the giant fluctuation. Based on this model, it is predicted that the coherence length along the c-axis will be the single most important material parameter to determine the performance of the superconductor under a strong magnetic field. It seems that BYCO is superior in this regard to Bi- or Tl-systems as far as the performance at 77 K is considered, although another material with the coherence length slightly longer along the c-axis is still highly desired.

  3. Quantal Description of Atomic Diamagnetism: the Quasi-Landau Resonances

    NASA Astrophysics Data System (ADS)

    Wang, Qiaoling

    We describe atomic hydrogen diamagnetism within the framework of nonrelativistic quantum mechanics. Our theoretical studies have used three descriptions: an adiabatic description, a multichannel quantum defect theory (MQDT) description using an ab initio R-matrix approach, and a model description. The analysis has conclusively demonstrated that the diamagnetic spectrum can be viewed as a perturbed Rydberg spectrum. The adiabatic analysis provides a crude but useful picture to see the overall channel structure and the nature of the perturbing configurations, where the quasi-Landau resonances are the lowest states in each Landau channel which will perturb high Rydberg states in lower Landau channels once the nonadiabatic coupling is turned on. The ab initio calculation of the photoionization spectrum in the field range 10^3 -10^4 Tesla shows that the quasi -Landau resonances are broad interlopers which perturb high Rydberg states converging to the Landau thresholds, forming complex resonances. Also in these calculations, a new partial cross section analysis has been performed to predict the relative electron populations in different Landau channels. The population is found to depend on the azimuthal quantum number and the parity of final states. For photoionization from the hydrogen ground state of final states with m = 1, the electron is predicted to escape predominantly in the higher Landau channels. In contrast, for the final states with m = 0, it escapes in the lower channels. This property is reflected in the shape of autoionizing resonances, which are more like peaks for m = 1, but are more like dips (window resonances) for m = 0. In studying the features of the complex resonances, formed by the quasi-Landau resonances perturbing the high Rydberg states, we developed an analytical description using a model based on three interacting Rydberg channels, identifying the key dynamical quantities which control the appearance of a complex resonance and its evolution

  4. The Landau-Lifshitz equation in atomistic models

    NASA Astrophysics Data System (ADS)

    Ellis, M. O. A.; Evans, R. F. L.; Ostler, T. A.; Barker, J.; Atxitia, U.; Chubykalo-Fesenko, O.; Chantrell, R. W.

    2015-09-01

    The Landau-Lifshitz (LL) equation, originally proposed at the macrospin level, is increasingly used in Atomistic Spin Dynamic (ASD) models. These models are based on a spin Hamiltonian featuring atomic spins of fixed length, with the exchange introduced using the Heisenberg formalism. ASD models are proving a powerful approach to the fundamental understanding of ultrafast magnetization dynamics, including the prediction of the thermally induced magnetization switching phenomenon in which the magnetization is reversed using an ultra-fast laser pulse in the absence of an externally applied field. This paper outlines the ASD model approach and considers the role and limitations of the LL equation in this context.

  5. Antiferromagnetic resonance excitation by terahertz magnetic field resonantly enhanced with split ring resonator

    SciTech Connect

    Mukai, Y.; Hirori, H.; Yamamoto, T.; Kageyama, H.; Tanaka, K.

    2014-07-14

    Excitation of antiferromagnetic resonance (AFMR) in a HoFeO{sub 3} crystal combined with a split ring resonator (SRR) is studied using terahertz (THz) electromagnetic pulses. The magnetic field in the vicinity of the SRR is induced by the incident THz electric field component and excites spin oscillations that correspond to the AFMR, which are directly probed by the Faraday rotation of the polarization of a near-infrared probe pulse. The good agreement of the temperature-dependent magnetization dynamics with the calculation using the two-lattice Landau-Lifshitz-Gilbert equation confirms that the AFMR is excited by the THz magnetic field, which is enhanced at the SRR resonance frequency by a factor of 20 compared to the incident magnetic field.

  6. Solitonic modulation and Lifshitz point in an external magnetic field within Nambu-Jona-Lasinio model

    NASA Astrophysics Data System (ADS)

    Cao, Gaoqing; Huang, Anping

    2016-04-01

    We study the inhomogeneous solitonic modulation of a chiral condensate within the effective Nambu-Jona-Lasinio model when a constant external magnetic field is present. The self-consistent Pauli-Villars regularization scheme is adopted to manipulate the ultraviolet divergence encountered in the thermodynamic quantities. In order to efficiently determine the chiral restoration lines, a new kind of Ginzburg-Landau expansion approach is proposed here. At zero temperature, we find that both the upper and lower boundaries of the solitonic modulation oscillate with the magnetic field in the μ - B phase diagram which is actually the de Hass-van Alphan (dHvA) oscillation. It is very interesting to find out how the tricritical Lifshitz point (TL,μL) evolves with the magnetic field: There are also dHvA oscillations in the TL- B and μL- B curves, though the tricritical temperature TL increases monotonically with the magnetic field.

  7. Field errors in superconducting magnets

    SciTech Connect

    Barton, M. Q.

    1982-01-01

    The mission of this workshop is a discussion of the techniques for tracking particles through arbitrary accelerator field configurations to look for dynamical effects that are suggested by various theoretical models but are not amenable to detailed analysis. A major motivation for this type of study is that many of our accelerator projects are based on the use of superconducting magnets which have field imperfections that are larger and of a more complex nature than those of conventional magnets. Questions such as resonances, uncorrectable closed orbit effects, coupling between planes, and diffusion mechanisms all assume new importance. Since, simultaneously, we are trying to do sophisticated beam manipulations such as stacking, high current accelerator, long life storage, and low loss extraction, we clearly need efficient and accurate tracking programs to proceed with confidence.

  8. Intrinsic surface magnetic anisotropy in Y3Fe5O12 as the origin of low-magnetic-field behavior of the spin Seebeck effect

    NASA Astrophysics Data System (ADS)

    Uchida, Ken-ichi; Ohe, Jun-ichiro; Kikkawa, Takashi; Daimon, Shunsuke; Hou, Dazhi; Qiu, Zhiyong; Saitoh, Eiji

    2015-07-01

    The magnetic-field dependence of the longitudinal spin Seebeck effect (LSSE) in a Pt /Y3Fe5O12 (YIG)-slab junction system was found to deviate from a bulk magnetization curve of the YIG slab in a low field range. In this paper, we show that the deviation originates from the difference between surface and bulk magnetization processes in the YIG slab and that it appears even when removing possible extrinsic magnetic anisotropy due to surface roughness and replacing the Pt layer with different materials. This result indicates that the anomalous field dependence of the LSSE is due to an intrinsic magnetic property of the YIG surface. Our numerical calculation based on the Landau-Lifshitz-Gilbert equation shows that the deviation between the LSSE and bulk magnetization curves is qualitatively explained by introducing easy-axis perpendicular magnetic anisotropy near the surface of YIG.

  9. Magnetic fields in irregular galaxies

    NASA Astrophysics Data System (ADS)

    Chyzy, Krzysztof T.

    Radio data of large irregular galaxies reveal some extended synchrotron emission with a substantial degree of polarization. In the case of NGC 4449 strong galaxy-scale regular magnetic fields were found, in spite of the lack of ordered rotation required for the conventional dynamo action. The rigidly rotating large irregular NGC 55 shows vertical polarized spurs connected with a network of ionized gas filaments. Small dwarf irregulars show only isolated polarized spots.

  10. Driven quantum tunneling and pair creation with graphene Landau levels

    NASA Astrophysics Data System (ADS)

    Gagnon, Denis; Fillion-Gourdeau, François; Dumont, Joey; Lefebvre, Catherine; MacLean, Steve

    2016-05-01

    Driven tunneling between graphene Landau levels is theoretically linked to the process of pair creation from vacuum, a prediction of quantum electrodynamics (QED). Landau levels are created by the presence of a strong, constant, quantizing magnetic field perpendicular to a graphene monolayer. Following the formal analogy between QED and the description of low-energy excitations in graphene, solutions of the fully interacting Dirac equation are used to compute electron-hole pair creation driven by a circularly or linearly polarized field. This is achieved via the coupled channel method, a numerical scheme for the solution of the time-dependent Dirac equation in the presence of bound states. The case of a monochromatic driving field is first considered, followed by the more realistic case of a pulsed excitation. We show that the pulse duration yields an experimental control parameter over the maximal pair yield. Orders of magnitude of the pair yield are given for experimentally achievable magnetic fields and laser intensities weak enough to preserve the Landau level structure.

  11. Self-similar occurrence of massless Dirac particles in graphene under a magnetic field

    NASA Astrophysics Data System (ADS)

    Rhim, Jun-Won; Park, Kwon

    2012-12-01

    Intricate interplay between the periodicity of the lattice structure and that of the cyclotron motion gives rise to a well-known self-similar fractal structure of the energy eigenvalue, known as the Hofstadter butterfly, for an electron moving in lattice under magnetic field. Connected with the n=0 Landau level, the central band of the Hofstadter butterfly is especially interesting in the honeycomb lattice. While the entire Hofstadter butterfly can be in principle obtained by solving Harper's equations numerically, the weak-field limit, most relevant for experiment, is intractable owing to the fact that the size of the Hamiltonian matrix, which needs to be diagonalized, diverges. In this paper, we develop an effective Hamiltonian method that can be used to provide an accurate analytic description of the central Hofstadter band in the weak-field regime. One of the most important discoveries obtained in this work is that massless Dirac particles always exist inside the central Hofstadter band no matter how small the magnetic flux may become. In other words, with its bandwidth broadened by the lattice effect, the n=0 Landau level contains massless Dirac particles within itself. In fact, by carefully analyzing the self-similar recursive pattern of the central Hofstadter band, we conclude that massless Dirac particles should occur under arbitrary magnetic field. As a corollary, the central Hofstadter band also contains a self-similar structure of recursive Landau levels associated with such massless Dirac particles. To assess the experimental feasibility of observing massless Dirac particles inside the central Hofstadter band, we compute the width of the central Hofstadter band as a function of magnetic field in the weak-field regime.

  12. Macroscopic manifestations of broken inversion symmetry in noncentrosymmetric superconductors with applied magnetic field

    NASA Astrophysics Data System (ADS)

    Oka, Masatosi; Ichioka, Masanori; Machida, Kazushige

    2007-03-01

    We numerically investigate paramagnetic properties in noncentrosymmetric superconductors under applied magnetic fields, based on the time-dependent Ginzburg-Landau theory including the Pauli paramagnetic effect and the Rashba interaction. When an applied field is perpendicular to the polar axis, the paramagnetic effect breaks centrosymmetry in the Meissner state and cylindrical symmetry in the vortices, as macroscopic manifestations of broken inversion symmetry in the spatial structures of the screening current and the penetrating field. The paramagnetic supercurrent exists even at the vortex center by their asymmetric properties, therefore the flux flow is spontaneously induced without applying external currents.

  13. Fast Vacuum Decay into Quark Pairs in Strong Color Electric and Magnetic Fields

    SciTech Connect

    Hidaka, Y.; Iritani, T.; Suganuma, H.

    2011-10-21

    We study quark-pair creations in strong color electomagnetic fields. We point out that, for massless quarks, the vacuum persistency probability per unit space-time volume is zero, i.e., the quark-pair creation rate w is infinite, in general homogeneous color electromagnetic fields, while it is finite when the color magnetic field is absent. We find that the contribution from the lowest Landau level (LLL) dominates this phenomenon. With an effective theory of the LLL projection, we also discuss dynamics of the vacuum decay, taking into account the back reaction of pair creations.

  14. Modeling of Ultrafast Heat- and Field-Assisted Magnetization Dynamics in FePt

    NASA Astrophysics Data System (ADS)

    Nieves, P.; Chubykalo-Fesenko, O.

    2016-01-01

    The switching of magnetization by ultrafast lasers alone in FePt could open a technological perspective for magnetic recording technology. Recent experimental results [D. Lambert et al., Science 345, 1337 (2014)] indicate a dynamical magnetization response in FePt under circularly polarized laser pulses. Using high-temperature micromagnetic modeling, based on the stochastic Landau-Lifshitz-Bloch equation, we investigate the possibility of magnetization switching in FePt under the action of an ultrafast heat pulse assisted by either a constant or optomagnetic field. We evaluate the necessary magnitude and duration of the inverse Faraday field to produce a reliable switching. Our results also reproduce experimentally observed magnetization patterns originated from the nonhomogeneous temperature distribution.

  15. Anisotropic Magnetism in Field-Structured Composites

    SciTech Connect

    Anderson, Robert A.; Martin, James E.; Odinek, Judy; Venturini, Eugene

    1999-06-24

    Magnetic field-structured-composites (FSCs) are made by structuring magnetic particle suspensions in uniaxial or biaxial (e.g. rotating) magnetic fields, while polymerizing the suspending resin. A uniaxial field produces chain-like particle structures, and a biaxial field produces sheet-like particle structures. In either case, these anisotropic structures affect the measured magnetic hysteresis loops, with the magnetic remanence and susceptibility increased significantly along the axis of the structuring field, and decreased slightly orthogonal to the structuring field, relative to the unstructured particle composite. The coercivity is essentially unaffected by structuring. We present data for FSCs of magnetically soft particles, and demonstrate that the altered magnetism can be accounted for by considering the large local fields that occur in FSCs. FSCS of magnetically hard particles show unexpectedly large anisotropies in the remanence, and this is due to the local field effects in combination with the large crystalline anisotropy of this material.

  16. Comparing Magnetic Fields on Earth and Mars

    NASA Video Gallery

    This animation compares the magnetic fields on Earth and Mars. The Earth has a large-scale planetary magnetic field that can protect it from space weather and other hazards. Mars, on the other hand...

  17. Field quality aspects of CBA superconducting magnets

    SciTech Connect

    Kahn, S.; Engelmann, R.; Fernow, R.; Greene, A.F.; Herrera, J.; Kirk, H.; Skaritka, J.; Wanderer, P.; Willen, E.

    1983-01-01

    A series of superconducting dipole magnets for the BNL Colliding Beam Accelerator which were manufactured to have the proper field quality characteristics has been tested. This report presents the analysis of the field harmonics of these magnets.

  18. Measurements of Solar Vector Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J. (Editor)

    1985-01-01

    Various aspects of the measurement of solar magnetic fields are presented. The four major subdivisions of the study are: (1) theoretical understanding of solar vector magnetic fields; (3) techniques for interpretation of observational data; and (4) techniques for data display.

  19. Magnetic holes in the solar wind. [(interplanetary magnetic fields)

    NASA Technical Reports Server (NTRS)

    Turner, J. M.; Burlaga, L. F.; Ness, N. F.; Lemaire, J. F.

    1976-01-01

    An analysis is presented of high resolution interplanetary magnetic field measurements from the magnetometer on Explorer 43 which showed that low magnetic field intensities in the solar wind at 1 AU occur as distinct depressions or 'holes'. These magnetic holes are new kinetic-scale phenomena, having a characteristic dimension on the order of 20,000 km. They occurred at a rate of 1.5/day in the 18-day time span (March 18 to April 6, 1971) that was analyzed. Most of the magnetic holes are characterized by both a depression in the absolute value of the magnetic field, and a change in the magnetic field direction; some of these are possibly the result of magnetic merging. However, in other cases the magnetic field direction does not change; such holes are not due to magnetic merging, but might be a diamagnetic effect due to localized plasma inhomogeneities.

  20. New physics in the second Landau Level

    NASA Astrophysics Data System (ADS)

    Csathy, Gabor

    2006-03-01

    Clean two-dimensional electron systems subjected to perpendicular magnetic fields have a long history of revealing exotic ground states. A large number of these states are only possible in the presence of electron-electron interactions. Two notable examples of such collective ground states are the fractional quantum Hall liquids of the first two Landau levels and the electronic solids called the stripe and bubble phases forming beyond the first Landau level. These two classes of phases are simultaneously present and hence compete in the second Landau level. This talk will highlight our latest results on the evolution of the states of the second Landau level as the magnetic field is tilted away from the direction perpendicular to the sample. The challenging task of cooling to millidegree temperatures and in-situ tilting in this low temperature environment is achieved with a hydraulically driven rotator equipped with sintered Silver heat exchangers mounted onto the nuclear demagnetization stage of a dilution refrigerator. We found that the bubble states are rapidly destroyed with tilt and argue that such a behavior is consistent with the formation of an electronic solid. Furthermore, the well developed ν = 2+1/5 and 2+4/5 liquids are found to be driven insulating while the 2+1/3 and 2+2/3 states survive to the largest tilt angles accessible. The simplest interpretation of the rapid evolution of these states is that bubble phases melt into a classical Hall gas and the ν = 2+1/5 and 2+4/5 liquids solidify with tilt. Our data suggest that spin interaction plays an important role in the formation of these phases. In particular, we surmise that the bubble phases are not fully spin-polarized but most likely have a substantial antiferromagnetic order. These bubble phases could be first examples of antiferromagnetically ordered solids in a single layer two-dimensional electron system. This work was done in collaboration with J.S. Xia, C.L. Vicente, E.D. Adams, N

  1. Inter-layer frictional drag in double quantum wells in perpendicular magnetic fields

    NASA Astrophysics Data System (ADS)

    Feng, Xiang Guang

    Friction drag between isolated two-dimensional electron gas (2DEG) layers is a relatively new experimental probe for the study of the inter-layer interactions of two-dimensional electron systems. By measuring drag as a function of various experimental parameters we can explore details of the electron-electron interactions and gain insight into the electronic states. As many new and interesting phenomena have been discovered for two-dimensional electron gas systems in magnetic fields, beginning with the discovery of the quantum Hall-effect, we were motivated to measure drag in magnetic fields perpendicular to the 2DEG. In our drag experiment in magnetic fields, we observed two unusual phenomena. First in intermediate field range, where the Landau level splitting is smaller than the thermal energy kT, we observed an unusual increase in drag in intermediate fields, which cannot be explained by current theory based on single particle scattering. We think the cause of this unusual increase is related to inter-layer correlation induced by magnetic field. Secondly, in strong magnetic fields and unmatched layer densities, we observed negative drag peaks at certain field values, which have opposite polarity to the drag of electron-electron system at zero field. We argue that the negative drag reveals unusual dispersion of the electronic states near the Landau level, in which electrons show hole-like behavior. We hope our work can inspire more studies, both theoretically and experimentally, on the two dimensional electron systems in magnetic field. The experiments discussed here were performed in Dr. Gramila's research group in the department of physics of Pennsylvania State University.

  2. Swarm: ESA's Magnetic Field Mission

    NASA Astrophysics Data System (ADS)

    Haagmans, R.; Menard, Y.; Floberghagen, R.; Plank, G.; Drinkwater, M. R.

    2010-12-01

    Swarm is the fifth Earth Explorer mission in ESA’s Living Planet Programme. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution. The Mission shall deliver data that allow access to new insights into the Earth system by improving our understanding of the Earth’s interior and near-Earth electro-magnetic environment. After release from a single launcher, a side-by-side flying slowly decaying lower pair of satellites will be released at an initial altitude of about 490 km together with a third satellite that will be lifted to 530 km to complete the Swarm constellation. High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the observations that are required to separate and model various sources of the geomagnetic field and near-Earth current systems. The mission aims to provide a unique view into Earth core dynamics, mantle conductivity, crustal magnetisation, ionospheric and magnetospheric current systems and upper atmosphere dynamics - ranging from understanding the geodynamo to contributing to space weather. The scientific objectives and results from recent scientific studies will be presented. In addition the current status of the project, which is presently in the development phase, will be addressed. The mission is scheduled for launch in 2012.

  3. Rotating copper plasmoid in external magnetic field

    SciTech Connect

    Pandey, Pramod K.; Thareja, Raj K.

    2013-02-15

    Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

  4. Magnetic field perturbartions in closed-field-line systems with zero toroidal magnetic field

    SciTech Connect

    Mauel, M; Ryutov, D; Kesner, J

    2003-12-02

    In some plasma confinement systems (e.g., field-reversed configurations and levitated dipoles) the confinement is provided by a closed-field-line poloidal magnetic field. We consider the influence of the magnetic field perturbations on the structure of the magnetic field in such systems and find that the effect of perturbations is quite different from that in the systems with a substantial toroidal field. In particular, even infinitesimal perturbations can, in principle, lead to large radial excursions of the field lines in FRCs and levitated dipoles. Under such circumstances, particle drifts and particle collisions may give rise to significant neoclassical transport. Introduction of a weak regular toroidal magnetic field reduces radial excursions of the field lines and neoclassical transport.

  5. Landau quantization for a neutral particle in the presence of topological defects

    SciTech Connect

    Bakke, K.; Ribeiro, L. R.; Furtado, C.; Nascimento, J. R.

    2009-01-15

    In this paper we study the Landau levels in the nonrelativistic dynamics of a neutral particle which possesses a permanent magnetic dipole moment interacting with an external electric field in the curved space-time background with the presence or absence of a torsion field. The eigenfunction and eigenvalues of the Hamiltonian are obtained. We show that the presence of the topological defect breaks the infinite degeneracy of the Landau levels arising in this system. We also apply a duality transformation to discuss this same quantization for a dynamics of a neutral particle with a permanent electric dipole moment.

  6. Magnetoinfrared spectroscopy of Landau levels and Zeeman splitting of three-dimensional massless Dirac Fermions in ZrTe5

    SciTech Connect

    R. Y. Chen; Gu, G. D.; Chen, Z. G.; Song, X. -Y.; Schneeloch, J. A.; Wang, F.; Wang, N. L.

    2015-10-22

    We present a magnetoinfrared spectroscopy study on a newly identified three-dimensional (3D) Dirac semimetal ZrTe5. We observe clear transitions between Landau levels and their further splitting under a magnetic field. Both the sequence of transitions and their field dependence follow quantitatively the relation expected for 3D massless Dirac fermions. The measurement also reveals an exceptionally low magnetic field needed to drive the compound into its quantum limit, demonstrating that ZrTe5 is an extremely clean system and ideal platform for studying 3D Dirac fermions. The splitting of the Landau levels provides direct, bulk spectroscopic evidence that a relatively weak magnetic field can produce a sizable Zeeman effect on the 3D Dirac fermions, which lifts the spin degeneracy of Landau levels. As a result, our analysis indicates that the compound evolves from a Dirac semimetal into a topological line-node semimetal under the current magnetic field configuration.

  7. Magneto-infrared spectroscopy of Landau levels and Zeeman splitting of three-dimensional massless Dirac Fermions in ZrTe5

    NASA Astrophysics Data System (ADS)

    Chen, R. Y.; Chen, Z. G.; Song, X.-Y.; Schneeloch, J. A.; Gu, G. D.; Wang, F.; Wang, N. L.

    We present a magneto-infrared spectroscopy study on a newly identified three-dimensional (3D) Dirac semimetal ZrTe5. We observe clear transitions between Landau levels and their further splitting under magnetic field. Both the sequence of transitions and their field dependence follow quantitatively the relation expected for 3D massless Dirac fermions. The measurement also reveals an exceptionally low magnetic field needed to drive the compound into its quantum limit, demonstrating that ZrTe5 is an extremely clean system and ideal platform for studying 3D Dirac fermions. The splitting of the Landau levels provides a direct and bulk spectroscopic evidence that a relatively weak magnetic field can produce a sizeable Zeeman effect on the 3D Dirac fermions, which lifts the spin degeneracy of Landau levels. Our analysis indicates that the compound evolves from a Dirac semimetal into a topological line-node semimetal under current magnetic field configuration.

  8. Superposition of DC magnetic fields by cascading multiple magnets in magnetic loops

    NASA Astrophysics Data System (ADS)

    Sun, Fei; He, Sailing

    2015-09-01

    A novel method that can effectively collect the DC magnetic field produced by multiple separated magnets is proposed. With the proposed idea of a magnetic loop, the DC magnetic field produced by these separated magnets can be effectively superimposed together. The separated magnets can be cascaded in series or in parallel. A novel nested magnetic loop is also proposed to achieve a higher DC magnetic field in the common air region without increasing the DC magnetic field in each magnetic loop. The magnetic loop can be made by a magnetic hose, which is designed by transformation optics and can be realized by the combination of super-conductors and ferromagnetic materials.

  9. Primordial magnetic field limits from cosmological data

    SciTech Connect

    Kahniashvili, Tina; Tevzadze, Alexander G.; Sethi, Shiv K.; Pandey, Kanhaiya; Ratra, Bharat

    2010-10-15

    We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.

  10. Interplanetary magnetic field data book

    NASA Technical Reports Server (NTRS)

    King, J. H.

    1975-01-01

    An interplanetary magnetic field (IMF) data set is presented that is uniform with respect to inclusion of cislunar IMF data only, and which has as complete time coverage as presently possible over a full solar cycle. Macroscale phenomena in the interplanetary medium (sector structure, heliolatitude variations, solar cycle variations, etc.) and other phenomena (e.g., ground level cosmic-ray events) for which knowledge of the IMF with hourly resolution is necessary, are discussed. Listings and plots of cislunar hourly averaged IMP parameters over the period November 27, 1963, to May 17, 1974, are presented along with discussion of the mutual consistency of the IMF data used herein. The magnetic tape from which the plots and listings were generated, which is available from the National Space Science Data Center (NSSDC), is also discussed.