Excitations of the spin-density wave in pure chromium
Werner, S.A.; Shirane, G.; Fincher, C.R.; Grier, B.H.
1981-01-01
This paper summarizes recent investigations of the magnetic excitations of the spin density wave (SDW) in pure Cr in both the low temperature longitudinally polarized phase (T < 122K) and in the higher temperature transversely polarized phase (122K < T < 312K). In both phases spin wave modes of very high velocity are observed originating from the incommensurate Bragg points. In the transversely polarized SDW phase new additional excitations are observed, centered in reciprocal space at the (1,0,0) commensurate point. These excitations are not affected by a magnetic field. Inelastic scattering in the paramagnetic phase above the Neel point (312K) is observed in a reasonably well localized region of reciprocal space near (1,0,0) indicating that there are spin-spin correlations extending over many bcc unit cells and persisting to temperatures at least as high as 1.7 T/sub N/.
Lifshitz transition in two-dimensional spin density wave models.
Lin, J.; Materials Science Division
2010-11-09
We argue that both pocket-disappearing and neck-disrupting types of Lifshitz transitions can be realized in two-dimensional spin-density wave models for underdoped cuprates, and study both types of transitions with impurity scattering treated in the self-consistent Born approximation. We first solve for the electron self-energy from the self-consistent equation, and then study the low-temperature electrical conductivity and thermopower. Close to the Lifshitz transition, the thermopower is strongly enhanced. For the pocket-disappearing type, it has a sharp peak while for the neck-disrupting type, it changes sign at the transition, with its absolute value peaked on both sides of the transition. We discuss possible applications to underdoped cuprates.
Quasiclassical description of a superconductor with a spin density wave
NASA Astrophysics Data System (ADS)
Moor, A.; Volkov, A. F.; Efetov, K. B.
2011-04-01
We derive equations for the quasiclassical Green’s functions ǧ within a simple model of a two-band superconductor with a spin density wave (SDW). The elements of the matrix ǧ are the retarded, advanced, and Keldysh functions, each of which is an 8×8 matrix in the Gor’kov-Nambu, the spin, and the band space. In equilibrium, these equations are a generalization of the Eilenberger equation. On the basis of the derived equations, we analyze the Knight shift, the proximity, and the dc Josephson effects in the superconductors under consideration. The Knight shift is shown to depend on the orientation of the external magnetic field with respect to the direction of the vector of the magnetization of the SDW. The proximity effect is analyzed for an interface between a superconductor with the SDW and a normal metal. The function describing both superconducting and magnetic correlations is shown to penetrate the normal metal or a metal with the SDW due to the proximity effect. The dc Josephson current in an SSDW/N/SSDW junction is also calculated as a function of the phase difference φ. It is shown that in our model, the Josephson current does not depend on the mutual orientation of the magnetic moments in the superconductors SSDW and is proportional to sinφ. The dissipationless spin current jsp depends on the angle α between the magnetization vectors in the same way (jsp~sinα) and is not zero above the superconducting transition temperature.
NASA Astrophysics Data System (ADS)
Venderbos, J. W. F.
2016-03-01
We study hexagonal spin-channel ("triplet") density waves with commensurate M -point propagation vectors. We first show that the three Q =M components of the singlet charge density and charge-current density waves can be mapped to multicomponent Q =0 nonzero angular momentum order in three dimensions (3D) with cubic crystal symmetry. This one-to-one correspondence is exploited to define a symmetry classification for triplet M -point density waves using the standard classification of spin-orbit coupled electronic liquid crystal phases of a cubic crystal. Through this classification we naturally identify a set of noncoplanar spin density and spin-current density waves: the chiral spin density wave and its time-reversal invariant analog. These can be thought of as 3 DL =2 and 4 spin-orbit coupled isotropic β -phase orders. In contrast, uniaxial spin density waves are shown to correspond to α phases. The noncoplanar triple-M spin-current density wave realizes a novel 2 D semimetal state with three flavors of four-component spin-momentum locked Dirac cones, protected by a crystal symmetry akin to nonsymmorphic symmetry, and sits at the boundary between a trivial and topological insulator. In addition, we point out that a special class of classical spin states, defined as classical spin states respecting all lattice symmetries up to global spin rotation, are naturally obtained from the symmetry classification of electronic triplet density waves. These symmetric classical spin states are the classical long-range ordered limits of chiral spin liquids.
Effect of vacancies on the spin density waves onset in Fe/Cr superlattices
NASA Astrophysics Data System (ADS)
Parlebas, J. C.; Demangeat, C.; Mokrani, A.; Yartsev, S. V.; Ustinov, V. V.; Yartseva, N. S.
2011-05-01
The spin density wave's onset in Cr based superlattices is considered within proximity of Fe interlayer boundaries and the effect of randomly located vacancies in Cr monolayers is examined. The study is performed for Fe/Cr, Fe/Cr/V superlattices with odd and even number of Cr monolayers. It is shown that the number of Cr monolayer determines the spin density wave's nodes onset in the perfect Fe/Cr super lattices. Pinning of Cr magnetic moments on vacancies destroys this determination and leads to appearance or disappearance of nodes.
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; Grenier, B.; Ressouche, E.; Samulon, Eric C.; Fisher, Ian R.
2015-07-28
Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba_{3}Mn_{2}O_{8} using single crystal neutron diffraction. We find that for magnetic fields between μ_{0}H=8.80 T and 10.56 T applied along the $1\\bar{1}0$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ_{0}H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.
Field-induced spin density wave and spiral phases in a layered antiferromagnet
Stone, Matthew B.; Lumsden, Mark D.; Garlea, Vasile O.; Grenier, B.; Ressouche, E.; Samulon, Eric C.; Fisher, Ian R.
2015-07-28
Here we determine the low-field ordered magnetic phases of the S=1 dimerized antiferromagnet Ba3Mn2O8 using single crystal neutron diffraction. We find that for magnetic fields between μ0H=8.80 T and 10.56 T applied along themore » $$1\\bar{1}0$$ direction the system exhibits spin density wave order with incommensurate wave vectors of type (η,η,ε). For μ0H > 10.56 T, the magnetic order changes to a spiral phase with incommensurate wave vectors only along the [hh0] direction. For both field induced ordered phases, the magnetic moments are lying in the plane perpendicular to the field direction. Finally, the nature of these two transitions is fundamentally different: the low-field transition is a second order transition to a spin-density wave ground state, while the one at higher field, toward the spiral phase, is of first order.« less
High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V
Werner, S.A.; Fawcett, E.; Elmiger, M.W.; Shirane, G.
1992-11-01
Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.
High-energy spin-density-wave correlated fluctuations in paramagnetic Cr + 5 at. % V
Werner, S.A. . Dept. of Physics); Fawcett, E. . Dept. of Physics); Elmiger, M.W.; Shirane, G. )
1992-01-01
Measurements of the magnetic fluctuations, termed spin-density-wave (SDW) paramagnons, in the nearly antiferromagnetic alloy Cr + 5 at.%V are extended up in energy to about 80 MeV. These fluctuating spin-spin correlations occur at incommensurate positions, corresponding to the SDW wavevector Q. Their characteristic energy is at least an order of magnitude larger than that of the magnetic fluctuations seen in the paramagnetic phase of pure Cr, but their intensity is more than two orders of magnitude smaller. We find that the dynamic susceptibility decreases by about 50% between temperature T = 10K and 300K.
The η-Pairing Superconductivity in Spin-Density Wave Background
NASA Astrophysics Data System (ADS)
X, M. Qiu; Z, J. Wang
1993-10-01
In this letter, we propose a modified attractive Hubbard model at half filling that can exhibit superconductivity through η-pairing mechanism in spin-density wave representation and derive a concise relationship between the energy disparity and the single-particle energy spectrum. This relationship, in the two limits of U, clearly shows that the system does not display superconductivity for very low doping concentration. but demonstrates superconductivity when the doping concentration exceeds a certain critical value. This conclusion is in qualitative agreement with the familiar experiments on high-Tc superconductivity.
Projector augmented-wave method: Application to relativistic spin-density functional theory
NASA Astrophysics Data System (ADS)
Dal Corso, Andrea
2010-08-01
Applying the projector augmented-wave (PAW) method to relativistic spin-density functional theory (RSDFT) we derive PAW Dirac-Kohn-Sham equations for four-component spinor pseudo-wave-functions. The PAW freedom to add a vanishing operator inside the PAW spheres allows us to transform these PAW Dirac-type equations into PAW Pauli-type equations for two-component spinor pseudo-wave-functions. With these wave functions, we get the frozen-core energy as well as the charge and magnetization densities of RSDFT, with errors comparable to the largest between 1/c2 and the transferability error of the PAW data sets. Presently, the latter limits the accuracy of the calculations, not the use of the Pauli-type equations. The theory is validated by applications to isolated atoms of Fe, Pt, and Au, and to the band structure of fcc-Pt, fcc-Au, and ferromagnetic bcc-Fe.
Lifshitz transition in two-dimensional spin-density wave models
Lin, Jie
2010-11-09
We argue that both pocket-disappearing and neck-disrupting types of Lifshitz transitions can be realized in two-dimensional spin-density wave models for underdoped cuprates, and study both types of transitions with impurity scattering treated in the self-consistent Born approximation. We first solve for the electron self-energy from the self-consistent equation, and then study the low-temperature electrical conductivity and thermopower. Close to the Lifshitz transition, the thermopower is strongly enhanced. For the pocket-disappearing type, it has a sharp peak while for the neck-disrupting type, it changes sign at the transition, with its absolute value peaked on both sides of the transition. We discuss possible applications to underdoped cuprates.
Incommensurate spin-density-wave antiferromagnetism in CeRu2Al2B
NASA Astrophysics Data System (ADS)
Bhattacharyya, A.; Khalyavin, D. D.; Krüger, F.; Adroja, D. T.; Strydom, A. M.; Kockelmann, W. A.; Hillier, A. D.
2016-02-01
The newly discovered Ising-type ferromagnet CeRu2Al2B exhibits an additional phase transition at TN=14.2 K before entering the ferromagnetic ground state at TC=12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of TC
NASA Astrophysics Data System (ADS)
Jiang, Hong-Min; Yao, Zi-Jian; Zhang, Fu-Chun
2012-11-01
The nesting of electron Fermi pocket with one of the two hole pockets around the Brillouin zone center has been attributed to the spin density wave (SDW) instability in the parent compound of superconducting iron pnictides. We propose here that the second hole Fermi pocket may be nested with the electron pocket in the doped case, which results in a new SDW instability. Our work is motivated by and may explain the recent scanning tunneling spectroscopy (STM) measurements on NaFe1-xCoxAs, which show an asymmetric gap-like feature near the Fermi level in the overdoped regime (Zhou X. et al., Phys. Rev. Lett., 109 (2012) 037002). We use a multi-band model to examine this feature within random phase approximation to include the coupling between the itinerant electron and the local spins.
Why Cr needs a spin-density wave to become antiferromagnetic.
NASA Astrophysics Data System (ADS)
Marcus, P. M.; Moruzzi, V. L.; Qiu, S. L.
1998-03-01
First-principles, total-energy calculations on bcc Cr show that at the volume of the energy minimum Cr is nonmagnetic, i.e., the type-I antiferromagnetic (AF) phase does not exist for bcc Cr. However 0.3% expansion of the lattice constant gives a 2nd-order phase transition to the AF phase with a rapidly growing magnetic moment at the cost of a small amount of strain energy.( Marcus, Qiu, Moruzzi, submitted to Phys. Rev. B.) The AF spin-density wave (AF-SDW) modulates the moment of the AF phase over 20 lattice constants to reduce the energy, hence compensate the strain energy. (K. Hirai, J. Phys. Soc. Jpn. 66), 560 (1997). Further arguments to support this lattice-expansion theory of the AF-SDW come from a bulk modulus in agreement with experiment and from the effects of increasing the electron density, which agree with alloy behavior.
Dynamical spin-density waves in a spin-orbit-coupled Bose-Einstein condensate
NASA Astrophysics Data System (ADS)
Li, Yan; Qu, Chunlei; Zhang, Yongsheng; Zhang, Chuanwei
2015-07-01
Synthetic spin-orbit (SO) coupling, an important ingredient for quantum simulation of many exotic condensed matter physics, has recently attracted considerable attention. The static and dynamic properties of a SO-coupled Bose-Einstein condensate (BEC) have been extensively studied in both theory and experiment. Here we numerically investigate the generation and propagation of a dynamical spin-density wave (SDW) in a SO-coupled BEC using a fast moving Gaussian-shaped barrier. We find that the SDW wavelength is sensitive to the barrier's velocity while varies slightly with the barrier's peak potential or width. We qualitatively explain the generation of SDW by considering a rectangular barrier in a one-dimensional system. Our results may motivate future experimental and theoretical investigations of rich dynamics in the SO-coupled BEC induced by a moving barrier.
Helical spin-density wave in Fe/Cr trilayers with perfect interfaces
Fishman, R.S.
1998-07-01
Despite the presence of only collinear, commensurate (C) and incommensurate (I) spin-density waves (SDW`s) in bulk Cr, the interfacial steps in Fe/Cr multilayers are now believed to stabilize a helical (H) SDW within the Cr spacer. Yet H SDW`s were first predicted in an Fe/Cr trilayer with perfect interfaces when the orientation of the Fe moments does not favor C ordering: if the number of Cr monolayers is even (odd) and the Fe moments are pointing in the same (opposite) direction, then a C SDW does not gain any coupling energy. Under these circumstances, a simple model verifies that H ordering is indeed favored over 1 ordering provided that the Fermi surface mismatch is sufficiently small or the temperature sufficiently high.
Spin-density-wave magnetism in dilute copper-manganese alloys
Lamelas, F.J.; Werner, S.A.; Shapiro, S.M.; Mydosh, J.A.
1995-02-01
Elastic neutron-scattering measurements on two samples of Cu alloyed with 1.3% Mn and 0.55% Mn show that the spin-density-wave (SDW) features found in more concentrated alloys persist in the limit of very dilute alloys. These features consist of temperature-dependent incommensurate peaks in magnetic neutron scattering, with positions and strengths which are fully consistent with those in the concentrated alloys. The implications of these measurements are twofold. First, it is clear from this data that SDW magnetic ordering occurs across the entire range of CuMn alloys which have typically been interpreted as spin glasses. Second, the more fundamental significance of this work is the suggestion via extrapolation that a peak in the magnetic susceptibility x(q) occurs in pure copper, at a value of q given by the Fermi-surface diameter 2k{sub F}.
Spin density waves predicted in zigzag puckered phosphorene, arsenene and antimonene nanoribbons
NASA Astrophysics Data System (ADS)
Wu, Xiaohua; Zhang, Xiaoli; Wang, Xianlong; Zeng, Zhi
2016-04-01
The pursuit of controlled magnetism in semiconductors has been a persisting goal in condensed matter physics. Recently, Vene (phosphorene, arsenene and antimonene) has been predicted as a new class of 2D-semiconductor with suitable band gap and high carrier mobility. In this work, we investigate the edge magnetism in zigzag puckered Vene nanoribbons (ZVNRs) based on the density functional theory. The band structures of ZVNRs show half-filled bands crossing the Fermi level at the midpoint of reciprocal lattice vectors, indicating a strong Peierls instability. To remove this instability, we consider two different mechanisms, namely, spin density wave (SDW) caused by electron-electron interaction and charge density wave (CDW) caused by electron-phonon coupling. We have found that an antiferromagnetic Mott-insulating state defined by SDW is the ground state of ZVNRs. In particular, SDW in ZVNRs displays several surprising characteristics:1) comparing with other nanoribbon systems, their magnetic moments are antiparallelly arranged at each zigzag edge and almost independent on the width of nanoribbons; 2) comparing with other SDW systems, its magnetic moments and band gap of SDW are unexpectedly large, indicating a higher SDW transition temperature in ZVNRs; 3) SDW can be effectively modified by strains and charge doping, which indicates that ZVNRs have bright prospects in nanoelectronic device.
Effect of spin-density waves on the lattice dynamics of lead
NASA Astrophysics Data System (ADS)
Chen, X. M.; Overhauser, A. W.
1989-05-01
The phonon spectrum of Pb, first determined by Brockhouse et al. in 1962, exhibits large depressions in both longitudinal and transverse modes at the zone-boundary points \\{100\\}. The origin of this behavior has remained unclear. We show that a possible explanation involves the existence of a cubic family of small-amplitude spin-density waves (SDW's), having wave vectors \\{Q\\} at each of the twelve \\{211\\}, or alternatively \\{210\\}, superlattice points. Each SDW causes a peak in the conduction-electron charge response function χ(q) near the points q=+/-Q. SDW's have built-in charge modulations, equal in magnitude but opposite in sign, for both spin states. Only a small shift in the spatial phase δφ=ɛσz, depending on the spin σz, creates an additional charge response for q near +/-Q. When this spin-split-phase contribution to χ(q) is incorporated into the theory for the phonon spectrum, the anomalous behavior at \\{100\\} can be understood.
Quantum Hall effect in field-induced spin density wave systems
NASA Astrophysics Data System (ADS)
Tevosyan, Kahren
The research work described in this thesis is motivated by recent theoretical and experimental studies of the Quantum Hall Effect (QHE) in the quasi-one-dimensional conductors such as organic metals of the (TMTSF)sb2X family. These materials consist of weakly coupled parallel conducting chains that lie in the same plane. They exhibit very interesting behavior in the presence of a strong magnetic field which is perpendicular to the plane. At low temperatures a series of phase transitions from the metallic state to spin density wave states occur with increasing magnetic field. The latter are called the Field-Induced Spin Density Wave (FISDW) states. Within each FISDW phase, the value of the Hall resistance is quantized, signalling the presence of the Quantum Hall Effect. In contrast with the conventional QHE in isotropic two-dimensional systems, finite-width Landau bands appear naturally in the disorder-free (TMTSF)sb2X materials. In fact, the theory of the QHE in quasi-one-dimensiona1 organic conductors has so far been developed without any consideration of the effect of the disorder required to broaden Landau bands in isotropic systems. Here we address for the first time the localization properties of the quantum states in FISDW Landau bands. We employ the Thouless approach which uses the sensitivity of the eigenvalues to the choice of boundary conditions to study localization. Our results show that the localization properties of the states are very different from those of the conventional QHE systems. We find that the Thouless numbers do not decrease exponentially with the system size, indicating that states are not localized on the scales we can study. Another aspect of the dissertation deals with the edge state picture of the QHE which states that gapless excitations localized at the system edge are present whenever the quantum Hall effect occurs. We examine these properties of edge states for the FISDW systems by performing computer simulations to model the
Spin density wave instabilities in the NbS2 monolayer
NASA Astrophysics Data System (ADS)
Güller, F.; Vildosola, V. L.; Llois, A. M.
2016-03-01
In the present work, we study the magnetic properties of the NbS2 monolayer by first-principles calculations. The transition metal dichalcogenides (TMDCs) are a family of laminar materials presenting exciting properties such as charge density waves (CDWs), superconductivity, and metal-insulating transitions. 2 H -NbS2 is a particular case within the family, because it is the only one that is a superconductor without exhibiting a CDW order. Although no long-range magnetic order was experimentally observed in the TMDCs, we show here that the single monolayer of NbS2 is on the verge of a spin density wave (SDW) phase. Our calculations indicate that a wavelike magnetic order is stabilized in the NbS2 monolayer in the presence of magnetic defects or within zigzag nanoribbons, due to the presence of unpaired electrons. We calculate the real part of the bare electronic susceptibility and the corresponding nesting function of the clean NbS2 monolayer, showing that there are strong electronic instabilities at the same wave vector associated with the calculated SDWs, also corresponding with one of the main nesting vectors of the Fermi surface. We conclude that the physical mechanism behind the spin-wave instabilities are the nesting properties, accentuated by the quasi-2D character of this system, and the rather strong Coulomb interactions of the 4 d band of the Nb atom. We also estimate the amplitude of the spin fluctuations and find that they are rather large, as expected for a system on the verge of a quantum critical transition.
NASA Astrophysics Data System (ADS)
Schoonmaker, Robert; Clark, Stewart; Lancaster, Tom; Frawley, Thomas; Hatton, Peter
Iron arsenide intersects interesting physics between novel superconductors and other helical magnetic ordering in Pnma metal arsenide materials. Recent diffraction data has found a more complex ordering than a simple helical incommensurate spin density wave. Instead iron arsenide exhibits a definite chirality to the helimagnetism, an ellipticity in the spiral not aligned with the crystal axis, and resonant diffraction peaks forbidden by the Pnma symmetry. From non-magnetic and collinear density functional theory calculations we present insight into the mechanisms for the formation of this helimagnetic state. We find that ferromagnetic superexchange is a likely mechanism for the spin ordering and that the noncollinear ordering under this regime is caused by the spins on neighbouring irons arranging to minimise direct exchange between iron atoms, and also minimize disruption of the ferromagnetic superexchange between priveleged iron-arsenic pairs. To explain the forbidden peaks in the diffraction we have performed second-order spin-orbit perturbation calculations on the nonmagnetic calculation, which finds that the orbital ordering on the iron atoms coupled to the helimagnetism will lead to the otherwise symmetry-forbidden peaks.
Itinerant Double-Q Spin-Density Wave in Iron Arsenide Superconductors
NASA Astrophysics Data System (ADS)
Osborn, Raymond; Allred, Jared; Chmaissem, Omar; Rosenkranz, Stephan; Brown, Dennis; Taddei, Keith; Krogstad, Matthew; Bugaris, Daniel; Chung, Duck-Young; Claus, Helmut; Lapidus, Saul; Kanatzidis, Mercouri; Kang, Jian; Fernandes, Rafael; Eremin, Ilya
The recent observation of a tetragonal magnetic (C4) phase in hole-doped iron arsenide superconductors has provided evidence of a magnetic origin for the electronic nematicity in the C2 phase of these compounds. Now, Mössbauer data shows that the new phase also establishes the itinerant character of the antiferromagnetism of these materials and the primary role played by magnetic over orbital degrees of freedom. Neutron diffraction had shown that the magnetic order in the C4 phase was compatible with a double-Q structure arising from a collinear spin-density wave along both the X and Y directions simultaneously. The coherent superposition of the two modulations produces a non-uniform magnetic structure, in which the spin amplitudes vanish on half of the sites and double on the others, a uniquely itinerant effect that is incompatible with local moment magnetism. Mössbauer spectra in the C4 phase confirm this double-Q structure, with 50% of the spectral weight in a zero-moment peak and 50% with double the magnetic splitting seen in the C2 phase. Supported by the US DOE Office of Science, Materials and Engineering Division.
Double-Q spin-density wave in iron arsenide superconductors
NASA Astrophysics Data System (ADS)
Allred, J. M.; Taddei, K. M.; Bugaris, D. E.; Krogstad, M. J.; Lapidus, S. H.; Chung, D. Y.; Claus, H.; Kanatzidis, M. G.; Brown, D. E.; Kang, J.; Fernandes, R. M.; Eremin, I.; Rosenkranz, S.; Chmaissem, O.; Osborn, R.
2016-05-01
Elucidating the nature of the magnetic ground state of iron-based superconductors is of paramount importance in unveiling the mechanism behind their high-temperature superconductivity. Until recently, it was thought that superconductivity emerges only from an orthorhombic antiferromagnetic stripe phase, which can in principle be described in terms of either localized or itinerant spins. However, we recently reported that tetragonal symmetry is restored inside the magnetically ordered state of certain hole-doped compounds, revealing the existence of a new magnetic phase at compositions close to the onset of superconductivity. Here, we present Mössbauer data that show that half of the iron sites in this tetragonal phase are non-magnetic, establishing conclusively the existence of a novel magnetic ground state with a non-uniform magnetization that is inconsistent with localized spins. Instead, this state is naturally explained as the interference between two commensurate spin-density waves, a rare example of collinear double-Q magnetic order. Our results demonstrate the itinerant character of the magnetism of the iron pnictides, and the primary role played by magnetic degrees of freedom in determining their phase diagram.
Superconductivity at the onset of spin-density-wave order in a metal.
Wang, Yuxuan; Chubukov, Andrey V
2013-03-22
We revisit the issue of superconductivity at the quantum-critical point (QCP) between a 2D paramagnet and a spin-density-wave metal with ordering momentum (π, π). This problem is highly nontrivial because the system at criticality displays a non-Fermi-liquid behavior and because the effective coupling constant λ for the pairing is generally of order one, even when the actual interaction is smaller than fermionic bandwidth. Previous study [M. A. Metlitski and S. Sachdev, Phys. Rev. B 82, 075128 (2010)] has found that the renormalizations of the pairing vertex are stronger than in BCS theory and hold in powers of log(2)(1/T). We analyze the full gap equation and argue that summing up of the leading logarithms does not lead to a pairing instability. Yet, we show that superconductivity has no threshold and appears even if λ is set to be small, because subleading logarithmical renormalizations diverge and give rise to a BCS-like result log1/T(c) ∝ 1/λ. We argue that the analogy with BCS is not accidental as at small λ superconductivity at a QCP predominantly comes from fermions that retain Fermi-liquid behavior at criticality. We compute T(c) for the actual λ ∼ O(1), and find that both Fermi-liquid and non-Fermi-liquid fermions contribute to the pairing. PMID:25166835
NASA Astrophysics Data System (ADS)
Kaneko, Tatsuya; Zenker, Bernd; Fehske, Holger; Ohta, Yukinori
2015-09-01
We analyze the stability of excitonic ground states in the two-band Hubbard model with additional electron-phonon and Hund's rule couplings using a combination of mean-field and variational cluster approaches. We show that both the interband Coulomb interaction and the electron-phonon interaction will cooperatively stabilize a charge density wave (CDW) state which typifies an "excitonic" CDW if predominantly triggered by the effective interorbital electron-hole attraction or a "phononic" CDW if mostly caused by the coupling to the lattice degrees of freedom. By contrast, the Hund's rule coupling promotes an excitonic spin density wave. We determine the transition between excitonic charge and spin density waves and comment on a fixation of the phase of the excitonic order parameter that would prevent the formation of a superfluid condensate of excitons. The implications for exciton condensation in several material classes with strongly correlated electrons are discussed.
Probing the coexistence of spin density wave and superconducting orders in organic superconductors
NASA Astrophysics Data System (ADS)
Narayanan, Arjun
We have conducted thermal and electrical transport measurements on the compound (TMTSF)2PF6 at temperatures down to 300 mK , magnetic fields up to 32 T and pressures up to 8 kbar. (TMTSF)2PF 6 may be tuned by pressure to exhibit a variety of low temperature ground states. From SDW at low pressures, to Superconducting metal at high pressures. In the vicinity of 6 kbar of pressure, samples show on cooling, first a SDW phase transition and then superconductivity. This coexistence of two transitions, is also seen in other material classes, for example, The Pnictides and the Heavy fermion superconductors. While in those classes the physics of simultaneous competing orders is not easy to explore, in (TMTSF)2PF 6 , owing in part to its remarkably reliable crystal growth, and its simple yet feature rich electronic structure, the situation is now clearer. Simultaneous resistivity and thermopower measurements under pressure along all three crystal axes, provide evidence for phase separation between SDW and metallic domains. The pressure evolution of the phase boundaries may also be qualitatively followed. The metallic domains in coexistence are identi ed as the high pressure metal phase by a variety of signatures in magnetoresistance( the presence of Field induced Spin density waves, Rapid oscillations, the Lebed oscillations and Danner-Chaikin-Kang oscillations.) The main result of this thesis is a characterisation of the coexistence state that allows us to eliminate various theoretical models and assert that the result of interacting SDW and Metallic orders is a phase separation into large scale domains with domain widths of the order of micrometers in these salts. Further that the domain walls follow a well defined geometry linked to the geometry of the lattice.
NASA Astrophysics Data System (ADS)
Wu, Ya-Jie; Li, Ning; He, Jing; Kou, Su-Peng
2016-03-01
In this paper, based on mean-field approach and random-phase-approximation, we study the magnetic properties of the repulsive Haldane-Hubbard model on a square lattice. We find antiferromagnetic order driven topological spin density waves beyond Landau’s symmetry-breaking paradigm, for which the effective low energy physics is determined by Chern-Simons-Hopf gauge field theories with different K matrices.
Collinear spin-density-wave ordering in Fe/Cr multilayers and wedges
Fishman, R.S.; Shi, Z.
1999-06-01
Several recent experiments have detected a spin-density wave (SDW) within the Cr spacer of Fe/Cr multilayers and wedges. We use two simple models to predict the behavior of a collinear SDW within an Fe/Cr/Fe trilayer. Both models combine assumed boundary conditions at the Fe-Cr interfaces with the free energy of the Cr spacer. Depending on the temperature and the number {ital N} of Cr monolayers, the SDW may be either commensurate ({ital C}) or incommensurate ({ital I}) with the bcc Cr lattice. Model I assumes that the Fe-Cr interface is perfect and that the Fe-Cr interaction is antiferromagnetic. Consequently, the {ital I} SDW antinodes lie near the Fe-Cr interfaces. With increasing temperature, the Cr spacer undergoes a series of transitions between {ital I} SDW phases with different numbers {ital n} of nodes. If the {ital I} SDW has n=m nodes at T=0, then {ital n} increases by one at each phase transition from {ital m} to m{minus}1 to m{minus}2 up to the {ital C} phase with n=0 above T{sub IC}(N). For a fixed temperature, the magnetic coupling across the Cr spacer undergoes a phase slip whenever {ital n} changes by one. In the limit N{r_arrow}{infinity}, T{sub IC}(N) is independent of the Fe-Cr coupling strength. We find that T{sub IC}({infinity}) is always larger than the bulk N{acute e}el transition temperature and increases with the strain on the Cr spacer. These results explain the very high IC transition temperature of about 600 K extrapolated from measurements on Fe/Cr/Fe wedges. Model II assumes that the {ital I} SDW nodes lie precisely at the Fe-Cr interfaces. This condition may be enforced by the interfacial roughness of sputtered Fe/Cr multilayers. As a result, the {ital C} phase is never stable and the transition temperature T{sub N}(N) takes on a seesaw pattern as n{ge}2 increases with thickness. In agreement with measurements on both sputtered and epitaxially grown multilayers, model II predicts the {ital I} phase to be unstable above the bulk N
Ferroelectricity Induced by Acentric Spin-Density Waves in YMn{sub 2}O{sub 5}
Chapon, L.C.; Radaelli, P.G.; Blake, G.R.; Park, S.; Cheong, S.-W.
2006-03-10
The commensurate and incommensurate magnetic structures of the magnetoelectric system YMn{sub 2}O{sub 5}, as determined from neutron diffraction, were found to be spin-density waves lacking a global center of symmetry. We propose a model, based on a simple magnetoelastic coupling to the lattice, which enables us to predict the polarization based entirely on the observed magnetic structure. Our data accurately reproduce the temperature dependence of the spontaneous polarization, particularly its sign reversal at the commensurate-incommensurate transition.
Exchange Bias as a Probe of the Incommensurate Spin-Density Wave in Epitaxial Fe/Cr(001)
NASA Astrophysics Data System (ADS)
Parker, J. S.; Wang, L.; Steiner, K. A.; Crowell, P. A.; Leighton, C.
2006-12-01
We report clear multiple period oscillations in the temperature dependence of exchange bias in an Fe thin film exchange coupled to a neighboring Cr film. The oscillations arise due to an incommensurate spin-density wave in the Cr, with wave vector perpendicular to the Fe/Cr(001) interface. The exchange bias and coercivity allow for a determination of the extent of the thermally driven wavelength expansion, the (strain-suppressed) spin-flip transition temperature, and the Cr Néel temperature, which show a crossover from bulklike to finite-size behavior at a Cr thickness of ˜1100Å. The data are consistent with a transition from a transverse to longitudinal wave on cooling.
Yi, M.
2010-06-02
Through a systematic high-resolution angle-resolved photoemission study of the iron pnictide compounds (Ba,Sr)Fe{sub 2}As{sub 2}, we show that the electronic structures of these compounds are significantly reconstructed across the spin density wave transition, which cannot be described by a simple folding scenario of conventional density wave ordering. Moreover, we find that LDA calculations with an incorporated suppressed magnetic moment of 0.5{mu}{sub B} can match well the details in the reconstructed electronic structure, suggesting that the nature of magnetism in the pnictides is more itinerant than local, while the origin of suppressed magnetic moment remains an important issue for future investigations.
Resonant X-ray magnetic scattering studies of the TmNi 2B 2C spin density wave
NASA Astrophysics Data System (ADS)
Mannix, Danny; Thompson, Paul; Brown, Simon; Bouchenoire, Laurence; Canfield, Paul
2004-11-01
We report on polarisation resolved, resonant X-ray magnetic scattering (RXMS) studies of the spin density wave (SDW) formed in the TmNi 2B 2C superconductor. From this high wave-vector resolution investigation, we find the incommensurate magnetic SDW propagation vector to be ( 0±τ0±τ0) with τ=0.096 rlu, slightly larger than the value previously deduced from magnetic neutron studies ( τ=0.093 rlu). The widths of the SDW peaks at 1 K are consistent with long-range magnetic order and we have deduced a magnetic correlation length of ∼1200 Å. When the incident photons are tuned to the Tm L 3 absorption edge, the RXMS energy response consists of a double peak feature, arising from both dipole (E1) transitions, probing the 5d conduction band polarisation, and quadrupole (E2) transitions, probing the Tm 4f magnetic moments. The RXMS wave-vector dependences of the (0± τ 0± τ L) SDW satellites are consistent with the transverse spin-density wave structure, with moments orientated along the crystallographic c-axis, originally proposed from neutron-scattering measurements. Our RXMS data are also in good agreement with the magnetic neutron-scattering response for the thermal evolution of the magnetic moments down to 1 K and in deducing a Nèel temperature of T=1.5 K. However, the RXMS probe reveals a small shift of the magnetic propagation vector of the order 3×10 -3 rlu along the (1 1 0) direction, on decreasing temperature below TN. Using very high-resolution X-ray studies with a conventional Si(1 1 1) analyser, no change in width or position is found below TN or Tc. We have also not observed any charge modulation peaks at 2τ, indicating that the SDW does not couple to the lattice.
A temperature dependent tunneling study of the spin density wave gap in EuFe2As2 single crystals.
Dutta, Anirban; Anupam; Hossain, Z; Gupta, Anjan K
2013-09-18
We report temperature dependent scanning tunneling microscopy and spectroscopy measurements on single crystals of EuFe2As2 in the 15-292 K temperature range. The in situ cleaved crystals show atomic terraces with homogeneous tunnel spectra that correlate well with the spin density wave (SDW) transition at a temperature, TSDW ≈ 186 K. Above TSDW the local tunnel spectra show a small depression in the density of states (DOS) near the Fermi energy (EF). The gap becomes more pronounced upon entering the SDW state with a gap value ∼90 meV at 15 K. However, the zero bias conductance remains finite down to 15 K indicating a finite DOS at the EF in the SDW phase. Furthermore, no noticeable change is observed in the DOS at the antiferromagnetic ordering transition of Eu(2+) moments at 19 K. PMID:23962901
NASA Astrophysics Data System (ADS)
Parker, D.; Vavilov, M. G.; Chubukov, A. V.; Mazin, I. I.
2009-09-01
We investigate the effect of a spin-density wave (SDW) on s± superconductivity in Fe-based superconductors. We show that, contrary to the common wisdom, no nodes open at the new, reconnected Fermi surfaces when the hole and electron pockets fold down in the SDW state, despite the fact that the s± gap changes sign between the two pockets. Instead, the order parameter preserves its sign along the newly formed Fermi surfaces. The familiar experimental signatures of an s± symmetry are still preserved, although they appear in a mathematically different way. For a regular s case (s++) the nodes do appear in the SDW state. This distinction suggests a specific way to experimentally separate an s± state from a regular s in the pnictides. We argue that recently published thermal-conductivity data in the coexisting state are consistent with the s± , but not the s++ state.
NASA Astrophysics Data System (ADS)
Levchenko, A.; Vavilov, M. G.; Khodas, M.; Chubukov, A. V.
2013-04-01
Recent measurements of the doping dependence of the London penetration depth λ(x) at low T in clean samples of isovalent BaFe2(As1-xPx)2 at T≪Tc [Hashimoto et al., Science 336, 1554 (2012)SCIEAS0036-8075] revealed a peak in λ(x) near optimal doping x=0.3. The observation of the peak at T≪Tc, points to the existence of a quantum critical point beneath the superconducting dome. We associate such a quantum critical point with the onset of a spin-density-wave order and show that the renormalization of λ(x) by critical magnetic fluctuations gives rise to the observed feature. We argue that the case of pnictides is conceptually different from a one-component Galilean invariant Fermi liquid, for which correlation effects do not cause the renormalization of the London penetration depth at T=0.
NASA Astrophysics Data System (ADS)
Suzuki, Kenta M.; Ichioka, Masanori; Machida, Kazushige
2011-04-01
A spin-density-wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low-temperature phase in CeCoIn5. In the vortex state strong Pauli effect and nodal gap conspire to enhance the momentum-resolved density of states over the normal state value exclusively along the nodal direction, providing a favorable nesting condition for SDW with Q=(2kF,2kF,0.5) only at high fields (H). We can consistently understand observed mysteries of the field-induced SDW confined below Hc2, such as facts that Q is directed to the nodal direction independent of H, SDW diminishes under tilting field from the ab plane, and the SDW transition line in (H,T) has a positive slope.
NASA Astrophysics Data System (ADS)
Wang, Qing-Wei; Liu, Da-Yong; Quan, Ya-Min; Zou, Liang-Jian
2016-08-01
We theoretically study the coexistence of spin density wave (SDW) and superconductivity (SC) in ironpnictide superconductors based on a three-orbital model, focusing on the momentum-space and real-space distributions of SDW and SC order parameters in the coexistence region. We show that a SDW-SC coexisting state lies in the T-n phase diagram, in qualitative agreement with those of NaFe1 - xCoxAs and Ba(Fe1 - xCox)2As2. In the SC state the pairing wavefunction has s± symmetry with sx2y2 and sx2+y2 components. In the coexisting state, the SDW and SC order parameters display strong orbital-selective competitions in momentum space, which also result in real-space modulation and spin singlet-triplet mixing in the Cooper pairing amplitude. We expect that the obtained features may be observed in future experiments.
Switching of the Spin-Density-Wave in CeCoIn5 probed by Thermal Conductivity
NASA Astrophysics Data System (ADS)
Kim, Duk Y.; Lin, Shi-Zeng; Weickert, Franziska; Bauer, Eric D.; Ronning, Filip; Thompson, Joe D.; Movshovich, Roman
Unconventional superconductor CeCoIn5 orders magnetically in a spin-density-wave (SDW) in the low-temperature and high-field corner of the superconducting phase. Recent neutron scattering experiment revealed that the single-domain SDW's ordering vector Q depends strongly on the direction of the magnetic field, switching sharply as the field is rotated through the anti-nodal direction. This switching may be manifestation of a pair-density-wave (PDW) p-wave order parameter, which develops in addition to the well-established d-wave order parameter due to the SDW formation. We have investigated the hypersensitivity of the magnetic domain with a thermal conductivity measurement. The heat current (J) was applied along the [110] direction such that the Q vector is either perpendicular or parallel to J, depending on the magnetic field direction. A discontinuous change of the thermal conductivity was observed when the magnetic field is rotated around the [100] direction within 0 . 2° . The thermal conductivity with the Q parallel to the heat current (J ∥Q) is approximately 15% lager than that with the Q perpendicular to the heat current (J ⊥Q). This result is consistent with additional gapping of the nodal quasiparticle by the p-wave PDW coupled to SDW. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.
NASA Astrophysics Data System (ADS)
Dupuis, N.; Yakovenko, V. M.
1999-02-01
We study the collective modes in the magnetic-field induced spin-density-wave (FISDW) phases experimentally observed in organic conductors of the Bechgaard salts family. In phases that exhibit a sign reversal of the quantum Hall effect (Ribault anomaly), the coexistence of two spin-density waves gives rise to additional long-wavelength collective modes besides the Goldstone modes due to spontaneous translation and rotation symmetry breaking. These modes strongly affect the charge and spin response functions. We discuss some experimental consequences for the Bechgaard salts.
Accurate ab Initio Spin Densities
2012-01-01
We present an approach for the calculation of spin density distributions for molecules that require very large active spaces for a qualitatively correct description of their electronic structure. Our approach is based on the density-matrix renormalization group (DMRG) algorithm to calculate the spin density matrix elements as a basic quantity for the spatially resolved spin density distribution. The spin density matrix elements are directly determined from the second-quantized elementary operators optimized by the DMRG algorithm. As an analytic convergence criterion for the spin density distribution, we employ our recently developed sampling-reconstruction scheme [J. Chem. Phys.2011, 134, 224101] to build an accurate complete-active-space configuration-interaction (CASCI) wave function from the optimized matrix product states. The spin density matrix elements can then also be determined as an expectation value employing the reconstructed wave function expansion. Furthermore, the explicit reconstruction of a CASCI-type wave function provides insight into chemically interesting features of the molecule under study such as the distribution of α and β electrons in terms of Slater determinants, CI coefficients, and natural orbitals. The methodology is applied to an iron nitrosyl complex which we have identified as a challenging system for standard approaches [J. Chem. Theory Comput.2011, 7, 2740]. PMID:22707921
Jiang, Kun; Zhang, Yi; Zhou, Sen; Wang, Ziqiang
2015-05-29
We study the Hubbard model on the frustrated honeycomb lattice with nearest-neighbor hopping t_{1} and second nearest-neighbor hopping t_{2}, which is isomorphic to the bilayer triangle lattice, using the SU(2)-invariant slave boson theory. We show that the Coulomb interaction U induces antiferromagnetic (AF) chiral spin density wave (χSDW) order in a wide range of κ=t_{2}/t_{1} where both the two-sublattice AF order at small κ and the decoupled three-sublattice 120° order at large κ are strongly frustrated, leading to three distinct phases with different anomalous Hall responses. We find a continuous transition from a χSDW semimetal with the anomalous Hall effect to a topological chiral Chern insulator exhibiting the quantum anomalous Hall effect, followed by a discontinuous transition to a χSDW insulator with a zero total Chern number but an anomalous ac Hall effect. The χSDW is likely a generic phase of strongly correlated and highly frustrated hexagonal lattice electrons. PMID:26066448
Field-tunable spin-density-wave phases in Sr3Ru2O7.
Lester, C; Ramos, S; Perry, R S; Croft, T P; Bewley, R I; Guidi, T; Manuel, P; Khalyavin, D D; Forgan, E M; Hayden, S M
2015-04-01
The conduction electrons in a metal experience competing interactions with each other and the atomic nuclei. This competition can lead to many types of magnetic order in metals. For example, in chromium the electrons order to form a spin-density-wave (SDW) antiferromagnetic state. A magnetic field may be used to perturb or tune materials with delicately balanced electronic interactions. Here, we show that the application of a magnetic field can induce SDW magnetic order in a quasi-2D metamagnetic metal, where none exists in the absence of the field. We use magnetic neutron scattering to show that the application of a large (B ≈ 8 T) magnetic field to the perovskite metal Sr3Ru2O7 (refs 3-7) can be used to tune the material through two magnetically ordered SDW states. The ordered states exist over relatively small ranges in field (≲0.4 T), suggesting that their origin is due to a new mechanism related to the electronic fine structure near the Fermi energy, possibly combined with the stabilizing effect of magnetic fluctuations. The magnetic field direction is shown to control the SDW domain populations, which naturally explains the strong resistivity anisotropy or 'electronic nematic' behaviour observed in this material. PMID:25581627
NASA Astrophysics Data System (ADS)
Jiang, Kun; Zhang, Yi; Zhou, Sen; Wang, Ziqiang
2015-05-01
We study the Hubbard model on the frustrated honeycomb lattice with nearest-neighbor hopping t1 and second nearest-neighbor hopping t2, which is isomorphic to the bilayer triangle lattice, using the SU(2)-invariant slave boson theory. We show that the Coulomb interaction U induces antiferromagnetic (AF) chiral spin density wave (χ SDW ) order in a wide range of κ =t2/t1 where both the two-sublattice AF order at small κ and the decoupled three-sublattice 120° order at large κ are strongly frustrated, leading to three distinct phases with different anomalous Hall responses. We find a continuous transition from a χ SDW semimetal with the anomalous Hall effect to a topological chiral Chern insulator exhibiting the quantum anomalous Hall effect, followed by a discontinuous transition to a χ SDW insulator with a zero total Chern number but an anomalous ac Hall effect. The χ SDW is likely a generic phase of strongly correlated and highly frustrated hexagonal lattice electrons.
Commensurate and incommensurate spin-density waves in heavy electron systems
NASA Astrophysics Data System (ADS)
Schlottmann, P.
2016-05-01
The nesting of the Fermi surfaces of an electron and a hole pocket separated by a nesting vector Q and the interaction between electrons gives rise to itinerant antiferromagnetism. The order can gradually be suppressed by mismatching the nesting and a quantum critical point (QCP) is obtained as the Néel temperature tends to zero. The transfer of pairs of electrons between the pockets can lead to a superconducting dome above the QCP (if Q is commensurate with the lattice, i.e. equal to G/2). If the vector Q is not commensurate with the lattice there are eight possible phases: commensurate and incommensurate spin and charge density waves and four superconductivity phases, two of them with modulated order parameter of the FFLO type. The renormalization group equations are studied and numerically integrated. A re-entrant SDW phase (either commensurate or incommensurate) is obtained as a function of the mismatch of the Fermi surfaces and the magnitude of |Q - G/2|.
Field-controlled spin-density-wave order and quantum critically in Sr3 Ru2 O7
NASA Astrophysics Data System (ADS)
Hayden, Stephen
The quasi-2D metamagnetic perovskite metal Sr3Ru2O7 has been an enigma for the last decade. The application of a large magnetic field of 8T parallel to the c-axis creates a new phase at low temperatures. This phase shows ``electronic nematic'' properties in that strong anisotropy its resistivity can be created by tilting the field away from the c-axis. In addition, measurement of transport and thermodynamic properties suggest that the phase is at the centre of a quantum critical region. Here we use neutron scattering to show that the magnetic field actually induces spin-density-wave magnetic order in the proximity of a metamagnetic critical endpoint. In fact, Sr3Ru2O7 can be tuned through two magnetically-ordered SDW states which exist over relatively small ranges in field (< 0.4 T). Their origin is probably due to the electronic fine structure near the Fermi energy. The magnetic field direction is shown to control the SDW domain populations which naturally explains the strong resistivity anisotropy or ''electronic nematic'' behaviour observed in this material. We find that Sr3Ru2O7 is also unique in that its the quantum critical region is controlled by overdamped incommensurate low-energy spin fluctuations with a diverging relaxation time. The low-energy electronic properties reflect the presence of these fluctuations and, in particular, the field-dependent low-temperature specific heat is proportional to the spin relaxation rate. [Based on C. Lester, S. Ramos, R. S. Perry at el. Natural Materials 14, 373 (2015).
Giner, Emmanuel Angeli, Celestino
2015-09-28
The aim of this paper is to unravel the physical phenomena involved in the calculation of the spin density of the CuCl{sub 2} and [CuCl{sub 4}]{sup 2−} systems using wave function methods. Various types of wave functions are used here, both variational and perturbative, to analyse the effects impacting the spin density. It is found that the spin density on the chlorine ligands strongly depends on the mixing between two types of valence bond structures. It is demonstrated that the main difficulties found in most of the previous studies based on wave function methods come from the fact that each valence bond structure requires a different set of molecular orbitals and that using a unique set of molecular orbitals in a variational procedure leads to the removal of one of them from the wave function. Starting from these results, a method to compute the spin density at a reasonable computational cost is proposed.
NASA Astrophysics Data System (ADS)
Willenberg, B.; Schäpers, M.; Wolter, A. U. B.; Drechsler, S.-L.; Reehuis, M.; Hoffmann, J.-U.; Büchner, B.; Studer, A. J.; Rule, K. C.; Ouladdiaf, B.; Süllow, S.; Nishimoto, S.
2016-01-01
Low-temperature neutron diffraction and NMR studies of field-induced phases in linarite are presented for magnetic fields H ∥b axis. A two-step spin-flop transition is observed, as well as a transition transforming a helical magnetic ground state into an unusual magnetic phase with sine-wave-modulated moments ∥H . An effective J˜ 1-J˜ 2 single-chain model with a magnetization-dependent frustration ratio αeff=-J˜2/J˜1 is proposed. The latter is governed by skew interchain couplings and shifted to the vicinity of the ferromagnetic critical point. It explains qualitatively the observation of a rich variety of exotic longitudinal collinear spin-density wave, SDWp , states (9 ≥p ≥2 ).
NASA Astrophysics Data System (ADS)
Jiang, Shenghan; Mesaros, Andrej; Ran, Ying
2014-07-01
Recently, two interesting candidate quantum phases—the chiral spin-density wave state featuring anomalous quantum Hall effect and the d+id superconductor—were proposed for the Hubbard model on the honeycomb lattice at 1/4 doping. Using a combination of exact diagonalization, density matrix renormalization group, the variational Monte Carlo method, and quantum field theories, we study the quantum phase diagrams of both the Hubbard model and the t-J model on the honeycomb lattice at 1/4 doping. The main advantage of our approach is the use of symmetry quantum numbers of ground-state wave functions on finite-size systems (up to 32 sites) to sharply distinguish different quantum phases. Our results show that for 1≲U/t<40 in the Hubbard model and for 0.1
NASA Astrophysics Data System (ADS)
Zhang, W.-L.; Yin, Z. P.; Ignatov, A.; Bukowski, Z.; Karpinski, Janusz; Sefat, Athena S.; Ding, H.; Richard, P.; Blumberg, G.
2016-05-01
We present a polarization-resolved and temperature-dependent Raman scattering study of A Fe2As2 (A =Ca , Eu). In the spin-density-wave phase, spectral weight redistribution is observed in the fully symmetric and nonsymmetric scattering channels at different energies. An anisotropic Raman response is observed in the fully symmetric channel in spontaneously detwinned CaFe2As2 samples. We calculate the orbital-resolved electronic structures using a combination of density functional theory and dynamical mean field theory. We identify the electronic transitions corresponding to these two spectral features and find that the anisotropic Raman response originates from the lifted degeneracy of the dx z /y z orbitals in the broken-symmetry phase.
NASA Astrophysics Data System (ADS)
Dupuis, N.; Yakovenko, Victor M.
2000-05-01
We study the long-wavelength collective modes in the magnetic-field-induced spin-density-wave (FISDW) phases experimentally observed in organic conductors of the Bechgaard salts family, focusing on phases that exhibit a sign reversal of the quantum Hall effect (Ribault anomaly). We have recently proposed that two SDW's coexist in the Ribault phase, as a result of umklapp processes. When the latter are strong enough, the two SDW's become circularly polarized (helicoidal SDW's). In this paper, we study the collective modes that result from the presence of two SDW's. We find two Goldstone modes, an out-of-phase sliding mode and an in-phase spin-wave mode, and two gapped modes. The sliding Goldstone mode carries only a fraction of the total optical spectral weight, which is determined by the ratio of the amplitude of the two SDW's. In the helicoidal phase, all the spectral weight is pushed up above the SDW gap. We also point out similarities with phase modes in two-band, bilayer, or d+id' superconductors. We expect our conclusions to hold for generic two-SDW systems.
Yi, Ming
2011-08-19
Nematicity, defined as broken rotational symmetry, has recently been observed in competing phases proximate to the superconducting phase in the cuprate high temperature superconductors. Similarly, the new iron-based high temperature superconductors exhibit a tetragonal to orthorhombic structural transition (i.e. a broken C{sub 4} symmetry) that either precedes or is coincident with a collinear spin density wave (SDW) transition in undoped parent compounds, and superconductivity arises when both transitions are suppressed via doping. Evidence for strong in-plane anisotropy in the SDW state in this family of compounds has been reported by neutron scattering, scanning tunneling microscopy, and transport measurements. Here we present an angle resolved photoemission spectroscopy study of detwinned single crystals of a representative family of electron-doped iron-arsenide superconductors, Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} in the underdoped region. The crystals were detwinned via application of in-plane uniaxial stress, enabling measurements of single domain electronic structure in the orthorhombic state. At low temperatures, our results clearly demonstrate an in-plane electronic anisotropy characterized by a large energy splitting of two orthogonal bands with dominant d{sub xz} and d{sub yz} character, which is consistent with anisotropy observed by other probes. For compositions x > 0, for which the structural transition (T{sub S}) precedes the magnetic transition (T{sub SDW}), an anisotropic splitting is observed to develop above T{sub SDW}, indicating that it is specifically associated with T{sub S}. For unstressed crystals, the band splitting is observed close to T{sub S}, whereas for stressed crystals the splitting is observed to considerably higher temperatures, revealing the presence of a surprisingly large in-plane nematic susceptibility in the electronic structure.
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
NASA Astrophysics Data System (ADS)
Abdel-Hafiez, Mahmoud; Zhang, Yuanyuan; He, Zheng; Zhao, Jun; Bergmann, Christoph; Krellner, Cornelius; Duan, Chun-Gang; Lu, Xingye; Luo, Huiqian; Dai, Pengcheng; Chen, Xiao-Jia
2015-01-01
The characteristics of Fe-based superconductors are manifested in their electronic, magnetic properties, and pairing symmetry of the Cooper pair, but the latter remain to be explored. Usually in these materials, superconductivity coexists and competes with magnetic order, giving unconventional pairing mechanisms. We report on the results of the bulk magnetization measurements in the superconducting state and the low-temperature specific heat down to 0.4 K for BaFe2-xNixAs2 single crystals. The electronic specific heat displays a pronounced anomaly at the superconducting transition temperature and a small residual part at low temperatures in the superconducting state. The normal-state Sommerfeld coefficient increases with Ni doping for x =0.092 , 0.096, and 0.10, which illustrates the competition between magnetism and superconductivity. Our analysis of the temperature dependence of the superconducting-state specific heat and the London penetration depth provides strong evidence for a two-band s -wave order parameter. Further, the data of the London penetration depth calculated from the lower critical field follow an exponential temperature dependence, characteristic of a fully gapped superconductor. These observations clearly show that the superconducting gap in the nearly optimally doped compounds is nodeless.
Li, Hai-Feng; Cao, Chongde; Wildes, Andrew; Schmidt, Wolfgang; Schmalzl, Karin; Hou, Binyang; Regnault, Louis-Pierre; Zhang, Cong; Meuffels, Paul; Löser, Wolfgang; Roth, Georg
2015-01-01
Identifying the nature of magnetism, itinerant or localized, remains a major challenge in condensed-matter science. Purely localized moments appear only in magnetic insulators, whereas itinerant moments more or less co-exist with localized moments in metallic compounds such as the doped-cuprate or the iron-based superconductors, hampering a thorough understanding of the role of magnetism in phenomena like superconductivity or magnetoresistance. Here we distinguish two antiferromagnetic modulations with respective propagation wave vectors at Q± = (H ± 0.557(1), 0, L ± 0.150(1)) and QC = (H ± 0.564(1), 0, L), where (H, L) are allowed Miller indices, in an ErPd2Si2 single crystal by neutron scattering and establish their respective temperature- and field-dependent phase diagrams. The modulations can co-exist but also compete depending on temperature or applied field strength. They couple differently with the underlying lattice albeit with associated moments in a common direction. The Q± modulation may be attributed to localized 4f moments while the QC correlates well with itinerant conduction bands, supported by our transport studies. Hence, ErPd2Si2 represents a new model compound that displays clearly-separated itinerant and localized moments, substantiating early theoretical predictions and providing a unique platform allowing the study of itinerant electron behavior in a localized antiferromagnetic matrix. PMID:25608949
Measuring the transverse spin density of light.
Neugebauer, Martin; Bauer, Thomas; Aiello, Andrea; Banzer, Peter
2015-02-13
We generate tightly focused optical vector beams whose electric fields spin around an axis transverse to the beams' propagation direction. We experimentally investigate these fields by exploiting the directional near-field interference of a dipolelike plasmonic field probe placed adjacent to a dielectric interface. This directionality depends on the transverse electric spin density of the excitation field. Near- to far-field conversion mediated by the dielectric interface enables us to detect the directionality of the emitted light in the far field and, therefore, to measure the transverse electric spin density with nanoscopic resolution. Finally, we determine the longitudinal electric component of Belinfante's elusive spin momentum density, a solenoidal field quantity often referred to as "virtual." PMID:25723220
Generalized local-spin-density-functional theory
NASA Astrophysics Data System (ADS)
Guo, Yufei; Whitehead, M. A.
1991-01-01
An alternative density-functional theory, the generalized local-spin-density-functional (G-LSD) theory, is proposed based on the boundary conditions and sum rule of the Fermi-correlation factor in the Hartree-Fock (HF) limit. It avoids the physical restrictions to the boundary conditions and the sum rule used in the generalized exchange local-spin-density-functional (GX-LSD) theory completely, the homogeneous electron-density approximation in the Hartree-Fock-Slater (HFS) theory and in the Gáspár-Kohn-Sham (GKS) theory partly, and the time-consuming step to search for the optimal exchange parameter for each atom or ion in the Xα and Ξa theories. The alternative G-LSD theory generates the GX-LSD, HFS, GKS, Xα, and Ξa theories, when additional approximations or certain Fermi-hole shapes or high electron-density limit in a system are used. Theoretically, the G-LSD theory is more rigorous than the GX-LSD, HFS, GKS, and Ξa theories. Numerically, the statistical total energies for atoms in the G-LSD theory are in excellent agreement with the HF results, when the Gopinathan, Whitehead, and Bogdanovic [Phys. Rev. A 14, 1 (1976)] Fermi-hole parameters are used.
The evaluation of spin-density matrices within the graphically contracted function method
NASA Astrophysics Data System (ADS)
Gidofalvi, Gergely; Shepard, Ron
An efficient algorithm is presented to compute spin-density matrices from wave functions expanded in a basis of graphically contracted functions (GCF). The GCFs are based on the graphical unitary group approach (GUGA), which is a "spin-free" formulation of the electronic wave function. The spin-density matrix elements are computed from one-particle and two-particle charge-density matrix elements. The recursive algorithm allows the spin-density matrix to be computed with O(N 2GCFωn2) total effort where NGCF is the dimension of the GCF basis and n is the dimension of the orbital basis. The scale factor ω depends on the number of electrons N and ranges from O(N0) to O(N2) depending on the complexity of the underlying Shavitt graph. Because the "spin-free" GCF formulation eliminates the need to expand the wave function in a spin-dependent Slater determinant basis, it is possible to treat wave functions with large numbers of electrons and orbitals. Timings are given for wave functions that correspond to determinantal expansions over 10200 in length. The implementation is applicable to arbitrary spin states and to both ground and excited electronic states.
The evaluation of spin-density matrices within the graphically contracted function method.
Gidofalvi, G.; Shepard, R.; Chemical Sciences and Engineering Division
2009-12-01
An efficient algorithm is presented to compute spin-density matrices from wave functions expanded in a basis of graphically contracted functions (GCF). The GCFs are based on the graphical unitary group approach (GUGA), which is a 'spin-free' formulation of the electronic wave function. The spin-density matrix elements are computed from one-particle and two-particle charge-density matrix elements. The recursive algorithm allows the spin-density matrix to be computed with O(N{sub 2}{sup GCF}{omega}n{sup 2}) total effort where N{sub GCF} is the dimension of the GCF basis and n is the dimension of the orbital basis. The scale factor {omega} depends on the number of electrons N and ranges from O(N{sup 0}) to O(N{sup 2}) depending on the complexity of the underlying Shavitt graph. Because the 'spin-free' GCF formulation eliminates the need to expand the wave function in a spin-dependent Slater determinant basis, it is possible to treat wave functions with large numbers of electrons and orbitals. Timings are given for wave functions that correspond to determinantal expansions over 10{sup 200} in length. The implementation is applicable to arbitrary spin states and to both ground and excited electronic states.
NASA Astrophysics Data System (ADS)
Ayuel, K.; de Châtel, P. F.; Amani, Salah
2002-04-01
Charge, current and spin densities are calculated for a two-electron system, maintaining the explicit form of the wave functions, in terms of Slater determinants. The two-electron Russell-Saunders spin-orbit coupled eigenstates | L, S, J, MJ> are expressed as four-component spinors, and the operators of the above densities as 4×4 matrices. The contributions of various one-electron states to these densities are identified.
Zhou, Tao; Gao, Yi; Zhu, Jian -Xin
2015-03-07
Recenmore » tly it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the d-wave nodal lines (nodal gap) contrasts the common understanding of the d-wave pairing symmetry, which challenges the present theories for the high-Tcsuperconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-Tcsuperconductors.« less
Vernarsky, Brian J.
2014-01-01
In an effort towards a ''complete'' experiment for the ω meson, we present studies from an experiment with an unpolarized target and a circularly polarized photon beam (g1c), carried out using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. The experiment was analyzed using an extended maximum likelihood fit with partial wave amplitudes. New likelihood functions were calculated to account for the polarization of the photon beam. Both circular and linear polarizations are explored. The results of these fits are then used to project out the spin density matrix for the {omega}. First measurements of the {rho}{sup 3} spin density matrix elements will be presented using this method.
NASA Astrophysics Data System (ADS)
Singh, D.; Clougherty, D. P.; MacLaren, J. M.; Albers, R. C.; Wang, C. S.
1991-10-01
The influence of local-spin-dependent correlation effects on the predicted stable ground-state phase of iron is reexamined with use of general-potential linearized augmented-plane-wave calculations. Differences in the form of the Vosko-Wilk-Nusair (VWN) local-spin-density functional used in previous studies are noted, since in previous studies significant additional approximations were made with respect to those of Vosko, Wilk, and Nusan [Can. J. Phys. 58, 1200 (1980)] and of MacLaren, Clougherty, and Albers [Phys. Rev. B 42, 3205 (1990)]. While the results of previous linear muffin-tin orbital calculations using the VWN functional predict a bcc ferromagnetic ground state, the present calculations show that the VWN spin-correlation effects fail to stabilize a bcc ground state. Considerable sensitivity to the form of the spin interpolation is found.
Transverse spin gradient functional for non-collinear Spin Density Functional Theory
NASA Astrophysics Data System (ADS)
Eich, F. G.; Vignale, G.; Gross, E. K. U.
2013-03-01
The ab-initio description of non-collinear magnetism is essential for the search of new materials suitable for the construction of spintronic devices. We present a novel functional explicitly constructed for the description of non-collinear magnetism. It is formulated in terms of a Spin Gradient Extension (SGE) to the Local Spin Density Approximation, which introduces a dependence on the transverse gradients of the spin magnetization. While collinear Generalized Gradient Approximations provide a dependence on longitudinal spin gradients the SGE takes into account that longitudinal and transverse variations of the spin magnetization affect the energy differently. The explicit dependence on the transverse gradients is obtained from a reference systems which exhibits non-collinearity, i.e., the spin-spiral-wave state of the uniform electron gas. The inclusion of transverse spin gradients yields exchange-correlation magnetic fields that are non-collinear w.r.t. the spin magnetization. This implies that the spin-current density of the Kohn-Sham system does not vanish even if no external magnetic field is applied. As an example we present the application of the SGE to the non-collinear 120°-Néel state of a Chromium mono-layer. F.G.E. is supported by DOE grant No. DE-FG02-05ER46203
Testing for parity violation in nuclei using spin density matrices for nuclear density functionals
NASA Astrophysics Data System (ADS)
Barrett, B. R.; Giraud, B. G.
2015-06-01
The spin density matrix (SDM) used in atomic and molecular physics is revisited for nuclear physics, in the context of the radial density functional theory. The vector part of the SDM defines a ‘hedgehog’ situation, which exists only if nuclear states contain some amount of parity violation. A toy model is given as an illustrative example.
NASA Astrophysics Data System (ADS)
Giner, Emmanuel; Angeli, Celestino
2016-03-01
The present work describes a new method to compute accurate spin densities for open shell systems. The proposed approach follows two steps: first, it provides molecular orbitals which correctly take into account the spin delocalization; second, a proper CI treatment allows to account for the spin polarization effect while keeping a restricted formalism and avoiding spin contamination. The main idea of the optimization procedure is based on the orbital relaxation of the various charge transfer determinants responsible for the spin delocalization. The algorithm is tested and compared to other existing methods on a series of organic and inorganic open shell systems. The results reported here show that the new approach (almost black-box) provides accurate spin densities at a reasonable computational cost making it suitable for a systematic study of open shell systems.
Effect of disorder on superconductivity in the presence of spin-density wave order
NASA Astrophysics Data System (ADS)
Mishra, Vivek
2015-03-01
The majority of unconventional superconductors has close proximity to a magnetic phase. In many cases, the magnetic phase coexists with superconductivity in some fraction of the phase diagram. The response of these two competing phases to disorder can be used as a tool to gain a better understanding of these complex systems. Here I consider the effect of disorder on a multiband superconductor appropriate for the ferro-pnictide superconductors. I consider both interband and intraband scattering for a two-band model consisting of a hole pocket and an electron pocket. The scattering from pointlike impurities is treated within the self-consistent Born approximation. I calculate the effect of disorder on the transition temperature to the superconducting state. The influence of impurity scattering on the low-energy excitation spectrum in the superconducting state is also studied for different kinds of gap structures.
Differential cross sections and spin density matrix elements for the reaction gamma p -> p omega
M. Williams, D. Applegate, M. Bellis, C.A. Meyer
2009-12-01
High-statistics differential cross sections and spin density matrix elements for the reaction gamma p -> p omega have been measured using the CLAS at Jefferson Lab for center-of-mass (CM) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide CM energy bins, each subdivided into cos(theta_CM) bins of width 0.1. These are the most precise and extensive omega photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.
Spin Density Matrix Elements from {rho}{sup 0} and {phi} Meson Electroproduction at HERMES
Borissov, A.
2009-03-23
Exclusive production of {rho}{sup 0} and {phi} mesons on hydrogen and deuterium targets is studied in the HERMES kinematic region 1Spin density matrix elements are presented. Violation of s-Channel Helicity Conservation is observed through several non-zero values of SDMEs for {rho}{sup 0}, but not for {phi}. In exclusive {rho}{sup 0} production on the proton an indication is observed of a contribution of unnatural-parity exchange amplitudes, for which the dependence on Q{sup 2} and t' is shown.
Spin Density Matrix Elements in exclusive production of ω mesons at Hermes
NASA Astrophysics Data System (ADS)
Marianski, B.; Terkulov, A.
2014-03-01
Spin density matrix elements have been determined for exclusive ω meson production on hydrogen and deuterium targets, in the kinematic region of 1.0 < Q2 < 10.0 GeV2, 3.0 < W < 6.3 GeV and -t' < 0.2 GeV2. The data, from which SDMEs are determined, were accumulated with the HERMES forward spectrometer during the running period of 1996 to 2007 using the 27.6 GeV electron or positron beam of HERA. A sizable contribution of unnatural parity exchange amplitudes is found for exclusive ω meson production.
Existence of minimizers for Kohn-Sham within the local spin density approximation
NASA Astrophysics Data System (ADS)
Gontier, David
2015-01-01
The purpose of this article is to extend the work by Anantharaman and Cancès (2009 Ann. Inst. Henri Poincaré (C) 26 2425-55) and prove the existence of minimizers for the spin-polarized Kohn-Sham model in the presence of a magnetic field within the local spin density approximation. We show that for any magnetic field that vanishes at infinity, the existence of minimizers is ensured for neutral or positively charged systems. The proof relies on classical concentration-compactness techniques.
Ionization potentials of cobalt and nickel ions in the local-spin-density approximation
Dhar, S. ); Kestner, N.R. )
1990-06-15
In this article we report on the ionization potentials of all configurations of the Co{sup {ital n}+} and Ni{sup {ital n}+} ions obtained via transition-state calculations using local-spin-density (LSD) potentials. The calculations were performed numerically with and without modifications of the local exchange potential for fractional occupation numbers. When the exchange potential is corrected for noninteger occupation numbers, a more consistent picture of the ionization process is obtained than that given by the LSD Kohn-Sham exchange. The agreement with experimental results is also significantly improved.
Electron affinities for rare gases and some actinides from local-spin-density-functional theory
Guo, Y.; Wrinn, M.C.; Whitehead, M.A. )
1989-12-01
The negative ions of the rare gases (He, Ne, Ar, Kr, Xe, and Rn) and some actinides (Pu, Am, Bk, Cf, and Es) have been calculated self-consistently by the generalized exchange local-spin-density-functional theory with self-interaction correction and correlation. The electron affinities were obtained as the differences between the statistical total energies of the negative ions and neutral atoms; the electron affinities were positive around several millirydbergs. Consequently, the negative ions are predicted stable for the rare gases and actinides.
Study of spin-density matrix in exclusive electroproduction of ω meson at HERMES
NASA Astrophysics Data System (ADS)
Manaenkov, S. I.
2016-02-01
Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied in the kinematic region of Q2 > 1.0 GeV2, 3.0 GeV < W < 6.3 GeV, and -t' < 0.2 GeV2. The data were accumulated with the HERMES forward spectrometer during the 1996-2007 running period using the 27.6 GeV longitudinally polarized electron or positron beam of HERA. Spin-density matrix elements are presented in projections of Q2 or -t'. Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is established for special combinations of spin-density matrix elements. The determination of the virtual-photon longitudinal-to- transverse cross-section ratio reveals that a dominant part of the cross section arises from transversely polarized photons. Good agreement is found between the HERMES proton data and results of a pQCD-inspired Goloskokov-Kroll model that includes pion-pole contributions.
Coarse-grained spin density-functional theory: Infinite-volume limit via the hyperfinite
NASA Astrophysics Data System (ADS)
Lammert, Paul E.
2013-06-01
Coarse-grained spin density functional theory (SDFT) is a version of SDFT which works with number/spin densities specified to a limited resolution — averages over cells of a regular spatial partition — and external potentials constant on the cells. This coarse-grained setting facilitates a rigorous investigation of the mathematical foundations which goes well beyond what is currently possible in the conventional formulation. Problems of existence, uniqueness, and regularity of representing potentials in the coarse-grained SDFT setting are here studied using techniques of (Robinsonian) nonstandard analysis. Every density which is nowhere spin-saturated is V-representable, and the set of representing potentials is the functional derivative, in an appropriate generalized sense, of the Lieb internal energy functional. Quasi-continuity and closure properties of the set-valued representing potentials map are also established. The extent of possible non-uniqueness is similar to that found in non-rigorous studies of the conventional theory, namely non-uniqueness can occur for states of collinear magnetization which are eigenstates of Sz.
NASA Astrophysics Data System (ADS)
Solovyeva, Alisa; Pavanello, Michele; Neugebauer, Johannes
2012-05-01
Subsystem density-functional theory (DFT) is a powerful and efficient alternative to Kohn-Sham DFT for large systems composed of several weakly interacting subunits. Here, we provide a systematic investigation of the spin-density distributions obtained in subsystem DFT calculations for radicals in explicit environments. This includes a small radical in a solvent shell, a π-stacked guanine-thymine radical cation, and a benchmark application to a model for the special pair radical cation, which is a dimer of bacteriochlorophyll pigments, from the photosynthetic reaction center of purple bacteria. We investigate the differences in the spin densities resulting from subsystem DFT and Kohn-Sham DFT calculations. In these comparisons, we focus on the problem of overdelocalization of spin densities due to the self-interaction error in DFT. It is demonstrated that subsystem DFT can reduce this problem, while it still allows to describe spin-polarization effects crossing the boundaries of the subsystems. In practical calculations of spin densities for radicals in a given environment, it may thus be a pragmatic alternative to Kohn-Sham DFT calculations. In our calculation on the special pair radical cation, we show that the coordinating histidine residues reduce the spin-density asymmetry between the two halves of this system, while inclusion of a larger binding pocket model increases this asymmetry. The unidirectional energy transfer in photosynthetic reaction centers is related to the asymmetry introduced by the protein environment.
Solovyeva, Alisa; Pavanello, Michele; Neugebauer, Johannes
2012-05-21
Subsystem density-functional theory (DFT) is a powerful and efficient alternative to Kohn-Sham DFT for large systems composed of several weakly interacting subunits. Here, we provide a systematic investigation of the spin-density distributions obtained in subsystem DFT calculations for radicals in explicit environments. This includes a small radical in a solvent shell, a {pi}-stacked guanine-thymine radical cation, and a benchmark application to a model for the special pair radical cation, which is a dimer of bacteriochlorophyll pigments, from the photosynthetic reaction center of purple bacteria. We investigate the differences in the spin densities resulting from subsystem DFT and Kohn-Sham DFT calculations. In these comparisons, we focus on the problem of overdelocalization of spin densities due to the self-interaction error in DFT. It is demonstrated that subsystem DFT can reduce this problem, while it still allows to describe spin-polarization effects crossing the boundaries of the subsystems. In practical calculations of spin densities for radicals in a given environment, it may thus be a pragmatic alternative to Kohn-Sham DFT calculations. In our calculation on the special pair radical cation, we show that the coordinating histidine residues reduce the spin-density asymmetry between the two halves of this system, while inclusion of a larger binding pocket model increases this asymmetry. The unidirectional energy transfer in photosynthetic reaction centers is related to the asymmetry introduced by the protein environment.
Electrically tunable spin polarization in silicene: A multi-terminal spin density matrix approach
NASA Astrophysics Data System (ADS)
Chen, Son-Hsien
2016-05-01
Recent realized silicene field-effect transistor yields promising electronic applications. Using a multi-terminal spin density matrix approach, this paper presents an analysis of the spin polarizations in a silicene structure of the spin field-effect transistor by considering the intertwined intrinsic and Rashba spin-orbit couplings, gate voltage, Zeeman splitting, as well as disorder. Coexistence of the stagger potential and intrinsic spin-orbit coupling results in spin precession, making any in-plane polarization directions reachable by the gate voltage; specifically, the intrinsic coupling allows one to electrically adjust the in-plane components of the polarizations, while the Rashba coupling to adjust the out-of-plan polarizations. Larger electrically tunable ranges of in-plan polarizations are found in oppositely gated silicene than in the uniformly gated silicene. Polarizations in different phases behave distinguishably in weak disorder regime, while independent of the phases, stronger disorder leads to a saturation value.
Self-interaction-corrected local-spin-density calculations for rare earth materials
Svane, A.; Temmerman, W.M.; Szotek, Z.; Laegsgaard, J.; Winter, H.
2000-04-20
The ab initio self-interaction-corrected (SIC) local-spin-density (LSD) approximation is discussed with emphasis on the ability to describe localized f-electron states in rare earth solids. Two methods for minimizing the SIC-LSD total energy functional are discussed, one using a unified Hamiltonian for all electron states, thus having the advantages of Bloch's theorem, the other one employing an iterative scheme in real space. Results for cerium and cerium compounds as well as other rare earths are presented. For the cerium compounds the onset of f-electron delocalization can be accurately described, including the intricate isostructural phase transitions in elemental cerium and CeP. In Pr and Sm the equilibrium lattice constant and zero temperature equation of state is greatly improved in comparison with the LSD results.
Differential cross sections and spin density matrix elements for the reaction γp→pω
NASA Astrophysics Data System (ADS)
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Adhikari, K. P.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Berman, B. L.; Biselli, A. S.; Bookwalter, C.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Careccia, S. L.; Carman, D. S.; Cole, P. L.; Collins, P.; Crede, V.; D'Angelo, A.; Daniel, A.; Vita, R. De; Sanctis, E. De; Deur, A.; Dey, B.; Dhamija, S.; Dickson, R.; Djalali, C.; Dodge, G. E.; Doughty, D.; Dugger, M.; Dupre, R.; Alaoui, A. El; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fradi, A.; Gabrielyan, M. Y.; Garçon, M.; Gevorgyan, N.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Hassall, N.; Hicks, K.; Holtrop, M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jawalkar, S. S.; Jo, H. S.; Johnstone, J. R.; Joo, K.; Keller, D.; Khandaker, M.; Khetarpal, P.; Kim, W.; Klein, A.; Klein, F. J.; Krahn, Z.; Kubarovsky, V.; Kuleshov, S. V.; Kuznetsov, V.; Livingston, K.; Lu, H. Y.; Mayer, M.; McAndrew, J.; McCracken, M. E.; McKinnon, B.; Mikhailov, K.; Mirazita, M.; Mokeev, V.; Moreno, B.; Moriya, K.; Morrison, B.; Moutarde, H.; Munevar, E.; Nadel-Turonski, P.; Nepali, C. S.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Niroula, M. R.; Niyazov, R. A.; Osipenko, M.; Ostrovidov, A. I.; Paris, M.; Park, K.; Park, S.; Pasyuk, E.; Pereira, S. Anefalos; Perrin, Y.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Raue, B. A.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salamanca, J.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seraydaryan, H.; Sharabian, Y. G.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tedeschi, D. J.; Tkachenko, S.; Ungaro, M.; Vineyard, M. F.; Voutier, E.; Watts, D. P.; Weinstein, L. B.; Weygand, D. P.; Wood, M. H.; Zhang, J.; Zhao, B.
2009-12-01
High-statistics differential cross sections and spin-density matrix elements for the reaction γp→pω have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 11210-MeV wide c.m. energy bins, each subdivided into cosθc.m.ω bins of width 0.1. These are the most precise and extensive ω photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.
Constrained spin-density dynamics of an iron-sulfur complex: Ferredoxin cofactor
NASA Astrophysics Data System (ADS)
Ali, Md. Ehesan; Nair, Nisanth N.; Staemmler, Volker; Marx, Dominik
2012-06-01
The computation of antiferromagnetic exchange coupling constants J by means of efficient density-based approaches requires in practice to take care of both spin projection to approximate the low spin ground state and proper localization of the magnetic orbitals at the transition metal centers. This is demonstrated here by a combined approach where the extended broken-symmetry (EBS) technique is employed to include the former aspect, while spin density constraints are applied to ensure the latter. This constrained EBS (CEBS) approach allows us to carry out ab initio molecular dynamics on a spin-projected low spin potential energy surface that is generated on-the-fly by propagating two coupled determinants and thereby accessing the antiferromagnetic coupling along the trajectory. When applied to the prototypical model of the oxidized [2Fe-2S] cofactor in Ferredoxins, [Fe2S2(SH)4]2-, at room temperature, CEBS leads to remarkably good results for geometrical structures and coupling constants J.
The dipole moment of the spin density as a local indicator for phase transitions
Schmitz, D.; Schmitz-Antoniak, C.; Warland, A.; Darbandi, M.; Haldar, S.; Bhandary, S.; Eriksson, O.; Sanyal, B.; Wende, H.
2014-01-01
The intra-atomic magnetic dipole moment - frequently called 〈Tz〉 term - plays an important role in the determination of spin magnetic moments by x-ray absorption spectroscopy for systems with nonspherical spin density distributions. In this work, we present the dipole moment as a sensitive monitor to changes in the electronic structure in the vicinity of a phase transiton. In particular, we studied the dipole moment at the Fe2+ and Fe3+ sites of magnetite as an indicator for the Verwey transition by a combination of x-ray magnetic circular dichroism and density functional theory. Our experimental results prove that there exists a local change in the electronic structure at temperatures above the Verwey transition correlated to the known spin reorientation. Furthermore, it is shown that measurement of the dipole moment is a powerful tool to observe this transition in small magnetite nanoparticles for which it is usually screened by blocking effects in classical magnetometry. PMID:25041757
NASA Astrophysics Data System (ADS)
Melnikov, N. B.; Reser, B. I.; Paradezhenko, G. V.
2016-08-01
To study the spin-density correlations in the ferromagnetic metals above the Curie temperature, we relate the spin correlator and neutron scattering cross-section. In the dynamic spin-fluctuation theory, we obtain explicit expressions for the effective and local magnetic moments and spatial spin-density correlator. Our theoretical results are demonstrated by the example of bcc Fe. The effective and local moments are found in good agreement with results of polarized neutron scattering experiment over a wide temperature range. The calculated short-range order is small (up to 4 Å) and slowly decreases with temperature.
LCAO-local-spin-density calculations for V 2 and Mn 2
NASA Astrophysics Data System (ADS)
Salahub, D. R.; Baykara, N. A.
1985-06-01
Binding-energy curves for V 2 and Mn 2 have been obtained through spin-polarized, broken-symmetry LCAO-local-spin-density (LSD) calculations. For V 2 the region near Re is characterized by full-symmetry ( D∞h) molecular orbitals. The LSD ground state (configuration 1π 4u 1σ 2g 1δ 2g 2σ 2g) is a triplet with R e = 1.75 Å, ω e = 594 cm -1. There is a state with αβ spin about 0.4 eV higher. These results are in good agreement with recent beam spectroscopy experiments. The large- R part of the V 2 potential curve is, however, inaccurate since the molecule dissociates into two d 4s 1 atoms (the LSD ground state for a spherical V atom) rather than two ground-state (d 3s 2) atoms. For Mn 2 the magnetic aspects are more dominant; symmetry breaking is essential. We find a long ( R e = 2.52 Å), relatively weak ( De = 0.86 eV) bond with ωe = 144 cm-1, for an "antiferro magnetic" 1σ 2 1δ 4 1π 4 2σ 2 3σ 2 configuration. These results are in good agreement with experimental data, where available.
Generalized-exchange local-spin-density-functional theory: Self-interaction correction
NASA Astrophysics Data System (ADS)
Manoli, S.; Whitehead, M. A.
1988-07-01
The local-spin-density (LSD) generalized-exchange (GX) theory is corrected for self-interaction by splitting the single-particle Fermi hole into pure-exchange and self-interaction holes. An analysis of these components shows that the non-self-interaction-corrected GX scheme overestimates the pure exchange while underestimating the self-interaction. This self-interaction-corrected scheme is called the GX-SI scheme. Using this method of correcting for self-interaction, two other approximate self-interaction-corrected (SIC) GX schemes can be derived in which (1) the GX-LSD-SI total exchange does not include the nonlocal, self-interaction potential and (2) the GX-SIX exchange is very similar to the exchange derived by Gopinathan [Phys. Rev. A 15, 2135 (1977)]. Neither of these exchanges obeys the sum rule. The GX-SI scheme contains correction terms to the LSD GX which are smaller than the corresponding ones derived in the SIC of Perdew and Zunger [Phys. Rev. B 23, 5048 (1981)]. This shows that the LSD-GX exchange is a better approximation to the true exchange of an inhomogeneous electron gas around an atom than the LSD free-electron gas exchange.
Density versus spin-density functional in DFT+U and DFT+DMFT
NASA Astrophysics Data System (ADS)
Park, Hyowon; Millis, Andrew; Marianetti, Chris
2015-03-01
The construction of multi-variable effective action theories such as DFT+U and DFT+DMFT requires the choice of a local subspace of correlated orbitals and an additional variable being either the charge density or spin density. This talk examines the differences between using charge-only and spin-dependent exchange-correlation functionals with the aim of providing guidance for constructing more sophisticated beyond-density functional theories. The widely used spin-dependent approximations to the exchange-correlation functional are found to lead to a large and in some cases unphysical effective exchange coupling within the correlated subspace. Additionally, the differences between Wannier and Projector based definitions of the correlated orbitals are examined, and only small differences are found provided that the orbitals are orthonormal and strongly localized. These results are documented in the context of the rare earth nickelates. This work is supported under the Grant DOE-ER-046169 and under the FAME grant, one of six centers of STARnet, a Semiconductor Research Corporation program sponsored by MARCO and DARPA.
Local-spin-density calculations for iron: Effect of spin interpolation on ground-state properties
NASA Astrophysics Data System (ADS)
MacLaren, J. M.; Clougherty, D. P.; Albers, R. C.
1990-08-01
Scalar-relativistic self-consistent linear muffin-tin orbital (LMTO) calculations for bcc and fcc Fe have been performed with several different local approximations to the exchange and correlation energy density and potential. Overall, in contrast to the conclusions of previous studies, we find that the local-spin-density approximation to exchange and correlation can provide an adequate description of bulk Fe provided that a proper parametrization of the correlation energy density and potential of the homogeneous electron gas over both spin and density is used. Lattice constants, found from the position of the minimum of the total energy as a function of Wigner-Seitz radius, agree to within 1% (for s,p,d LMTO's only) and within 1-2% (for s,p,d,f LMTO's) of the experimental lattice constants for all forms used for the local correlation. The best agreement, however, was obtained using a local correlation potential derived from the Vosko-Wilk-Nusair form for the spin dependence of the correlation energy density. The calculation performed with this correlation potential was also the only calculation to correctly predict a bcc ferromagnetic ground state.
Spin Density Matrix Elements in Exclusive Production of Omega Mesons at HERMES
NASA Astrophysics Data System (ADS)
Marukyan, Hrachya
2016-02-01
Exclusive electroproduction of ω mesons on unpolarized hydrogen and deuterium targets is studied at HERMES in the kinematic region of Q2 > 1.0GeV2, 3.0GeV < W < 6.3GeV, and ‑ t‧ < 0.2GeV2. The data were accumulated during the 1996-2007 running period using the 27.6GeV longitudinally polarized electron or positron beams at HERA. The determination of the virtual-photon longitudinal-to-transverse cross-section ratio shows that a considerable part of the cross section arises from transversely polarized photons. Spin density matrix elements are derived and presented in projections of Q2 or ‑ t‧. Violation of s-channel helicity conservation is observed for some of these elements. A sizable contribution from unnatural-parity-exchange amplitudes is found and the phase shift between those amplitudes that describe transverse ω production by longitudinal and transverse virtual photons is determined for the first time. Good agreement is found between the HERMES proton data and results of a pQCD-inspired phenomenological model that includes pion-pole contributions.
Calculations with the quasirelativistic local-spin-density-functional theory for high-Z atoms
Guo, Y.; Whitehead, M.A.
1988-10-01
The generalized-exchange local-spin-density-functional theory (LSD-GX) with relativistic corrections of the mass velocity and Darwin terms has been used to calculate statistical total energies for the neutral atoms, the positive ions, and the negative ions for high-Z elements. The effect of the correlation and relaxation correction on the statistical total energy is discussed. Comparing the calculated results for the ionization potentials and electron affinities for the atoms (atomic number Z from 37 to 56 and 72 to 80) with experiment, shows that for the atoms rubidium to barium both the LSD-GX and the quasirelativistic LSD-GX, with self-interaction correction, Gopinathan, Whitehead, and Bogdanovic's Fermi-hole parameters (Phys. Rev. A 14, 1 (1976)), and Vosko, Wilk, and Nusair's correlation correction (Can. J. Phys. 58, 1200 (1980)), are very good methods for calculating ionization potentials and electron affinities. For the atoms hafnium to mercury the relativistic effect has to be considered.
Matar, S.F.
2000-04-20
The electronic and magnetic structures of different uranium-based ternary intermetallic systems are self-consistently calculated within local spin density functional theory using the augmented spherical wave method. The influence of hybridization on the chemical bonding and on the magnetic behavior is discussed from the densities of states as well as from the crystal orbital overlap population. From this the author addresses the mechanisms of chemical bonding and of the onset of magnetism. The original concept of building blocks between different intermetallic systems is discussed.
NASA Astrophysics Data System (ADS)
Rajagopal, A. K.; Mochena, Mogus
2000-12-01
The group-theory framework developed by Fukutome for a systematic analysis of the various broken-symmetry types of Hartree-Fock solution exhibiting spin structures is here extended to the general many-body context using spinor Green function formalism for describing magnetic systems. Consequences of this theory are discussed for examining the magnetism of itinerant electrons in nanometric systems of current interest as well as bulk systems where a vector spin-density form is required, by specializing our work to spin-density-functional formalism. We also formulate the linear-response theory for such a system and compare and contrast our results with the recent results obtained for localized electron systems. The various phenomenological treatments of itinerant magnetic systems are here unified in this group-theoretical description. We apply this theory to the one-band Hubbard model to illustrate the usefulness of this approach.
Spin density studies on p-O2NC6F4CNSSN : A heavy p -block organic ferromagnet
NASA Astrophysics Data System (ADS)
Luzon, J.; Campo, J.; Palacio, F.; McIntyre, G. J.; Rawson, J. M.; Less, R. J.; Pask, C. M.; Alberola, A.; Farley, R. D.; Murphy, D. M.; Goeta, A. E.
2010-04-01
A complete picture of the spin density distribution in the organic radical p-O2NC6F4CNSSN has been obtained by a combination of polarized neutron diffraction, electron paramagnetic resonance (EPR), and electron-nuclear double resonance (ENDOR) spectroscopies, and ab initio density-functional theory (DFT) calculations. Polarized neutron diffraction revealed that the spin distribution is predominantly localized on the N and S atoms ( +0.25μB and +0.28μB , respectively) of the heterocyclic ring with a small negative spin density on the heterocyclic C atom (-0.06μB) . These spin populations are in excellent agreement with both ab initio DFT calculations (spin populations on the C, N, and S sites of -0.07 , 0.22 and 0.31, respectively) and cw-EPR studies which estimated the spin population on the N site as 0.24. The DFT calculated spin density revealed less than 1% spin delocalization onto the perfluoroaryl ring, several orders of magnitude lower than the density on the heterocyclic ring. cw-ENDOR studies at both X -band (9 GHz) and Q -band (34 GHz) frequencies probed the spin populations on the two chemically distinct F atoms. These spin populations on the F atoms ortho and meta to the dithiadiazolyl ring are of magnitude 10-3 and 10-4 , respectively.
Bode, Bela E; Plackmeyer, Jörn; Prisner, Thomas F; Schiemann, Olav
2008-06-12
Metal ions are functionally or structurally important centers in metalloproteins or RNAs, which makes them interesting targets for spectroscopic investigations. In combination with site-directed spin labeling, pulsed electron-electron double resonance (PELDOR or DEER) could be a well-suited method to characterize and localize them. Here, we report on the synthesis, full characterization, and PELDOR study of a copper(II) porphyrin/nitroxide model system. The X-band PELDOR time traces contain besides the distance information a convolution of orientational selectivity, conformational flexibility, exchange coupling, and spin density distribution, which can be deconvoluted by experiments with different frequency offsets and simulations. The simulations are based on the known experimental and spin Hamiltonian parameters and make use of a geometric model as employed for structurally similar bis-nitroxides and spin density parameters as obtained from density functional theory calculations. It is found that orientation selection with respect to dipolar angles is only weakly resolvable at X-band frequencies due to the large nitrogen hyperfine coupling of the copper porphyrin. On the other hand, the PELDOR time traces reveal a much faster oscillation damping than observed for structurally similar bis-nitroxides, which is mainly assigned to a small distribution in exchange couplings J. Taking the effects of orientation selectivity, distribution in J, and spin density distribution into account leads finally to a narrow distance distribution caused solely by the flexibility of the structure, which is in agreement with distributions from known bis-nitroxides of similar structure. Thus, X-band PELDOR measurements at different frequency offsets in combination with explicit time trace simulations allow for distinguishing between structural models and quantitative interpretation of copper-nitroxide PELDOR data gives access to localization of copper(II) ions. PMID:18491846
Spin density matrix elements for radiative decays of the omega meson in photoproduction at 5 GeV
NASA Astrophysics Data System (ADS)
Mokaya, Fridah
2016-03-01
The photoproduction of ω(782) meson on the nucleon at high energies is well described by a sum of t-channel exchanges. In the high energy limit of diffractive scattering, where Pomeron exchange dominates the total cross section, the helicity of the incident photon is transferred directly to the vector meson. At intermediate energies, other Regge exchanges compete with the Pomeron, leading to a complex energy dependence in the spin density matrix for vector mesons like the omega. High statistics measurements of the spin density matrix elements for the reaction γp ωp, ω π0 γ are presented based on data taken with the Radphi experiment at Jefferson Lab in the energy range 4.4 - 5.5 GeV. The results binned in Eγ and |t | are analysed in both the Gottfried Jackson and s-channel helicity frames and compared to a model with the Pomeron and other Regge exchanges contributing to the omega meson photoproduction amplitude.
Vinod, K. Sharma, Shilpam; Sundar, C. S.; Bharathi, A.
2015-06-24
Heat capacity measurements were done on sub-micron sized BaFe{sub 2−x}Ru{sub x}As{sub 2} single crystals using thin film membrane based the AC steady state calorimetry technique. Noticeable thermal hysteresis is observed in the heat capacity of the BaFe{sub 2−x}Ru{sub x}As{sub 2} during cooling and warming cycles, indicating first order nature of the SDW transition.
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Dey, B.; Dickson, R.; Krahn, Z.; McCracken, M. E.; Moriya, K.; Schumacher, R. A.; Adhikari, K. P.; Careccia, S. L.; Dodge, G. E.; Klein, A.; Mayer, M.; Nepali, C. S.; Niroula, M. R.; Seraydaryan, H.; Tkachenko, S.; Weinstein, L. B.
2009-12-15
High-statistics differential cross sections and spin-density matrix elements for the reaction {gamma}p{yields}p{omega} have been measured using the CEBAF large acceptance spectrometer (CLAS) at Jefferson Lab for center-of-mass (c.m.) energies from threshold up to 2.84 GeV. Results are reported in 112 10-MeV wide c.m. energy bins, each subdivided into cos{theta}{sub c.m.}{sup {omega}} bins of width 0.1. These are the most precise and extensive {omega} photoproduction measurements to date. A number of prominent structures are clearly present in the data. Many of these have not previously been observed due to limited statistics in earlier measurements.
Zhou, Tao; Gao, Yi; Zhu, Jian -Xin
2015-03-07
Recently it was revealed that the whole Fermi surface is fully gapped for several families of underdoped cuprates. The existence of the finite energy gap along the $d$-wave nodal lines (nodal gap) contrasts the common understanding of the $d$-wave pairing symmetry, which challenges the present theories for the high-${T}_{c}$superconductors. Here we propose that the incommensurate diagonal spin-density-wave order can account for the above experimental observation. The Fermi surface and the local density of states are also studied. Our results are in good agreement with many important experiments in high-${T}_{c}$superconductors.
NASA Astrophysics Data System (ADS)
Pederson, Mark R.; Heaton, Richard A.; Harrison, Joseph G.
1989-01-01
The uniform-density electron gas is studied within the framework of the Wannier-function (WF) formulation of the self-interaction-corrected local-spin-density approximation (SIC-LSD). While the results of the present work follow rigorously from a variational formulation, they may also be qualitatively understood in terms of the local-bonding-site concept introduced by Mott in his theory of the metal-insulator transition. SIC-LSD admits metallic-state solutions at ordinary electron densities just as in traditional LSD theory. The result of introducing SIC to the metallic state is an overall downward shift of the LSD eigenvalues. This shift is largest for states near k=0 and vanishes for states near the Fermi energy ɛF. As such, the orbital energies at ɛF are found to be in exact agreement with both the exchange-only version of LSD and Hartree-Fock (HF). Beyond metallic-state solutions, this formulation of SIC-LSD also admits insulator solutions at very low electron densities and may thus have important application to the problem of Wigner crystallization.
NASA Astrophysics Data System (ADS)
Gillon, Béatrice; Aebersold, Michael A.; Kahn, Olivier; Pardi, Luca; Delley, Bernard
1999-11-01
The compound 2-{3-[4-methyl-1,2,4-triazolyl]}-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide, abbreviated as Metrz-Nit, crystallizes in the non-centrosymmetric space group P2 12 12 1. The investigation of the magnetic properties has revealed the occurrence of intermolecular ferromagnetic interactions. The crystal structure has been refined by neutron diffraction at 11 K. The spin density distribution has been determined from polarized neutron diffraction experiments carried out at 1.5 K under a magnetic field of 5 T. As expected, the main contributions of the spin distribution have been observed in the 2p π orbitals of the nitrogen and oxygen atoms of the two NO groups, and a significant negative spin population has been detected on the sp 2 carbon atom of the nitronyl nitroxide moiety. The spin distribution is slightly dissymmetrical, so that the sp 3 carbon atoms in α-position of the nitro nitrogen atoms carry spin populations of opposite signs. Concerning the triazole ring, the main spin population, of negative sign, has been found on the nitrogen atom occupying the 3-position. The carbon atom of the methyl group attached to the 4-position has been also found to carry a significant negative spin population. The spin populations on the hydrogen atoms have been determined. These experimental data have been compared to the results of LSD calculations performed on an isolated molecule. The role of intermolecular interactions in the spin distribution has been discussed.
St Pierre, Tim G; El-Beshlawy, Amal; Elalfy, Mohsen; Al Jefri, Abdullah; Al Zir, Kusai; Daar, Shahina; Habr, Dany; Kriemler-Krahn, Ulrike; Taher, Ali
2014-01-01
Purpose Magnetic resonance imaging (MRI)-based techniques for assessing liver iron concentration (LIC) have been limited by single scanner calibration against biopsy. Here, the calibration of spin-density projection-assisted (SDPA) R2-MRI (FerriScan®) in iron-overloaded β-thalassemia patients treated with the iron chelator, deferasirox, for 12 months is validated. Methods SDPA R2-MRI measurements and percutaneous needle liver biopsy samples were obtained from a subgroup of patients (n = 233) from the ESCALATOR trial. Five different makes and models of scanner were used in the study. Results LIC, derived from mean of MRI- and biopsy-derived values, ranged from 0.7 to 50.1 mg Fe/g dry weight. Mean fractional differences between SDPA R2-MRI- and biopsy-measured LIC were not significantly different from zero. They were also not significantly different from zero when categorized for each of the Ishak stages of fibrosis and grades of necroinflammation, for subjects aged 3 to <8 versus ≥8 years, or for each scanner model. Upper and lower 95% limits of agreement between SDPA R2-MRI and biopsy LIC measurements were 74 and −71%. Conclusion The calibration curve appears independent of scanner type, patient age, stage of liver fibrosis, grade of necroinflammation, and use of deferasirox chelation therapy, confirming the clinical usefulness of SDPA R2-MRI for monitoring iron overload. Magn Reson Med 71:2215–2223, 2014. © 2013 Wiley Periodicals, Inc. PMID:23821350
Nie, Hai-Jing; Yang, Wen-Wen; Shao, Jiang-Yang; Zhong, Yu-Wu
2016-06-21
In response to the application of low electrochemical potentials, ruthenium-tris(bipyridine) complexes decorated with multiple electron-rich and redox-active amine substituents show reversible absorption and emission spectral changes in the deep-red to NIR region. The number of amine substituents strongly affects the electrochemical and spectroscopic properties and the spin density distributions of the complex in the one-electron-oxidized state. PMID:27240642
Beiden, S.V.; Gehring, G.A.; Temmerman, W.M.; Szotek, Z.
1997-11-01
In this Letter we present an {ital ab initio,} density functional theory, justification for the validity of Hund{close_quote}s type of rules in the solid state with localized electrons. We demonstrate that an orbital dependent functional, such as the self-interaction-corrected local spin density, is capable of fully describing the localized nature of the f state, so that all three Hund{close_quote}s rules are fulfilled. We argue this on the basis of linear-muffin-tin-orbital calculations in the atomic-sphere approximation for the {gamma} phase of Ce. {copyright} {ital 1997} {ital The American Physical Society}
NASA Astrophysics Data System (ADS)
Chen, Hanghui; Millis, Andrew J.
2016-01-01
Previous work on the physical content of exchange-correlation functionals that depend on both charge and spin densities is extended to elemental transition metals and a wider range of perovskite transition metal oxides. A comparison of spectra and magnetic moments calculated using charge-only and spin-dependent exchange-correlation functionals as well as their +U and +J extensions confirms previous conclusions that the spin-dependent part of the exchange-correlation functional provides an effective Hund's interaction acting on the transition metal d orbitals. For the local spin density approximation and spin-dependent generalized gradient approximation in the Perdew-Burke-Ernzerhof parametrization, the effective Hund's exchange implied by the spin dependence of the exchange correlation functional is found to be larger than 1 eV. The results indicate that at least as far as applications to transition metals and their oxides are concerned, +U , +J , and +dynamical-mean-field-theory extensions of density functional theory should be based on charge-only exchange-correlation functionals.
NASA Astrophysics Data System (ADS)
Aitala, E. M.; Amato, S.; Anjos, J. C.; Appel, J. A.; Ashery, D.; Banerjee, S.; Bediaga, I.; Blaylock, G.; Bracker, S. B.; Burchat, P. R.; Burnstein, R. A.; Carter, T.; Carvalho, H. S.; Copty, N. K.; Cremaldi, L. M.; Darling, C.; Denisenko, K.; Devmal, S.; Fernandez, A.; Fox, G. F.; Gagnon, P.; Gobel, C.; Gounder, K.; Halling, A. M.; Herrera, G.; Hurvits, G.; James, C.; Kasper, P. A.; Kwan, S.; Langs, D. C.; Leslie, J.; Lundberg, B.; Magnin, J.; Massafferri, A.; MayTal-Beck, S.; Meadows, B.; de Mello Neto, J. R. T.; Mihalcea, D.; Milburn, R. H.; de Miranda, J. M.; Napier, A.; Nguyen, A.; d'Oliveira, A. B.; O'Shaughnessy, K.; Peng, K. C.; Perera, L. P.; Purohit, M. V.; Quinn, B.; Radeztsky, S.; Rafatian, A.; Reay, N. W.; Reidy, J. J.; dos Reis, A. C.; Rubin, H. A.; Sanders, D. A.; Santha, A. K. S.; Santoro, A. F. S.; Schwartz, A. J.; Sheaff, M.; Sidwell, R. A.; Slaughter, A. J.; Sokoloff, M. D.; Solano Salinas, C. J.; Stanton, N. R.; Stefanski, R. J.; Stenson, K.; Summers, D. J.; Takach, S.; Thorne, K.; Tripathi, A. K.; Watanabe, S.; Weiss-Babai, R.; Wiener, J.; Witchey, N.; Wolin, E.; Yang, S. M.; Yi, D.; Yoshida, S.; Zaliznyak, R.; Zhang, C.; Fermilab E791 Collaboration
2002-07-01
We report differential cross sections for the production of D ∗±(2010) produced in 500 GeV/ cπ--nucleon interactions from experiment E791 at Fermilab, as functions of Feynman- x ( xF) and transverse momentum squared ( pT2). We also report the D ∗± charge asymmetry and spin-density matrix elements as functions of these variables. Investigation of the spin-density matrix elements shows no evidence of polarization. The average values of the spin alignment are < η>=0.01±0.02 and -0.01±0.02 for leading and non-leading particles, respectively.
NASA Astrophysics Data System (ADS)
Carmelo, J. M. P.; Gu, Shi-Jian; Sampaio, M. J.
2014-06-01
Finite-temperature T > 0 transport properties of integrable and nonintegrable one-dimensional (1D) many-particle quantum systems are rather different, showing ballistic and diffusive behavior, respectively. The repulsive 1D Hubbard model is a prominent example of an integrable correlated system. For electronic densities n ≠ 1 (and spin densities m ≠ 0) it is an ideal charge (and spin) conductor, with ballistic charge (and spin) transport for T ⩾ 0. In spite of the fact that it is solvable by the Bethe ansatz, at n = 1 (and m = 0) its T > 0 charge (and spin) transport properties are an issue that remains poorly understood. Here we combine this solution with symmetry and the explicit calculation of current-operator matrix elements between energy eigenstates to show that for on-site repulsion U > 0 and at n = 1 the charge stiffness Dη(T) vanishes for T > 0 in the thermodynamic limit. A similar behavior is found by such methods for the spin stiffness Ds(T) for U > 0 and T > 0, which vanishes at m = 0. This absence of finite temperature n = 1 ballistic charge transport and m = 0 ballistic spin transport are exact results that clarify long-standing open problems.
Abriata, Luciano A.; Zaballa, María-Eugenia; Berry, Robert E.; Yang, Fei; Zhang, Hongjun; Walker, F. Ann; Vila, Alejandro J.
2013-01-01
The electronic structure of heme proteins is exquisitely tuned by the interaction of the iron center with the axial ligands. NMR studies of paramagnetic heme systems have been focused on the heme signals, but signals from the axial ligands have been rather difficult to detect and assign. We report an extensive assignment of the 1H, 13C and 15N resonances of the axial His ligand in the NO-carrying protein nitrophorin 2 (NP2) in the paramagnetic high-spin and low-spin forms, as well as in the diamagnetic NO complex. We find that the high-spin protein has σ spin delocalization to all atoms in the axial His57, which decreases in size as the number of bonds between Fe(III) and the atom in question increase, except that within the His57 imidazole ring the contact shifts are a balance between positive σ and negative π contributions. In contrast, the low-spin protein has π spin delocalization to all atoms of the imidazole ring. Our strategy, adequately combined with a selective residue labeling scheme, represents a straightforward characterization of the electron spin density in heme axial ligands. PMID:23327568
Dhar, S.
1989-02-01
In electronic-structure calculations for finite systems using the local-spin-density (LSD) approximation, it is assumed that the eigenvalues of the Kohn-Sham equation should obey Fermi-Dirac (FD) statistics. In order to comply with this assumption for some of the transition-metal atoms, a nonintegral occupation number is used which also minimizes the total energy. It is shown here that for finite systems it is not necessary that the eigenvalues of the Kohn-Sham equation obey FD statistics. It is also shown that the Kohn-Sham exchange potential used in all LSD models is correct only for integer occupation number. With a noninteger occupation number the LSD exchange potential will be smaller than that given by the Kohn-Sham potential. Ab initio self-consistent spin-polarized calculations have been performed numerically for the total energy of an iron atom. It is found that the ground state belongs to the 3d/sup 6/4s/sup 2/ configuration. The ionization potentials of all the Fe/sup n//sup +/ ions are reported and are in agreement with experiment.
Dey, B.; Meyer, C. A.; Bellis, M.; Williams, M.; Adhikari, K. P.; Adikaram, D.; Aghasyan, M.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Bedlinskiy, I.; Biselli, A. S.; Bono, J.; Boiarinov, S.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Carman, D. S.; Celentano, A.; Chandavar, S.; Colaneri, L.; Cole, P. L.; Contalbrigo, M.; Cortes, O.; Crede, V.; D'Angelo, A.; Dashyan, N.; De Vita, R.; De Sanctis, E.; Deur, A.; Djalali, C.; Doughty, D.; Dugger, M.; Dupre, R.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fedotov, G.; Fegan, S.; Fleming, J. A.; Garçon, M.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Glazier, D. I.; Goetz, J. T.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Hafidi, K.; Hanretty, C.; Harrison, N.; Hattawy, M.; Hicks, K.; Ho, D.; Holtrop, M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Jenkins, D.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, A.; Klein, F. J.; Koirala, S.; Kubarovsky, V.; Kuhn, S. E.; Kuleshov, S. V.; Lenisa, P.; Livingston, K.; Lu, H.; MacGregor, I. J.D.; Markov, N.; Mayer, M.; McCracken, M. E.; McKinnon, B.; Mineeva, T.; Mirazita, M.; Mokeev, V.; Montgomery, R. A.; Moriya, K.; Moutarde, H.; Munevar, E.; Munoz Camacho, C.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Pappalardo, L. L.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Peng, P.; Phillips, J. J.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Puckett, A. J. R.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rizzo, A.; Rossi, P.; Roy, P.; Sabatié, F.; Saini, M. S.; Schott, D.; Schumacher, R. A.; Seder, E.; Senderovich, I.; Sharabian, Y. G.; Simonyan, A.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tang, W.; Tkachenko, S.; Ungaro, M.; Vernarsky, B.; Vlassov, A. V.; Voskanyan, H.; Voutier, E.; Watts, D. P.; Zachariou, N.; Zana, L.; Zhang, J.; Zhao, Z. W.; Zonta, I.
2014-05-27
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γ p → Φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the Φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the Φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (Φ → K⁺K⁻) and neutral- (Φ → K^{0}_{S}K^{0}_{L}) KK̄ decay modes of the Φ. Further, for the charged mode, we differentiate between the cases where the final K⁻ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed Φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-mode, respectively. Possible effects from K⁺Λ* channels with pKK̄ final-states are discussed. These present results constitute the most precise and extensive Φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.
García-Rubio, Inés; Mitrikas, George
2010-08-01
The wide use of the heme group by nature is a consequence of its unusual "electronic flexibility." Major changes in the electronic structure of this molecule can result from small perturbations in its environment. To understand the way the electronic distribution is dictated by the structure of the heme site, it is extremely important to have methods to reliably determine both of them. In this work we propose a way to obtain this information in ferric low-spin heme centers via the determination of g, A, and Q tensors of the coordinated nitrogens using electron spin echo envelope modulation experiments at Q-band microwave frequencies. The results for two bisimidazole heme model complexes, namely, PPIX(Im)(2) and CPIII(Im)(2), where PPIX is protoporphyrin IX, CPIII is coproporphyrin III, and Im is imidazole, selectively labeled with (15)N on the heme or imidazole nitrogens are presented. The planes of the axial ligands were found to be parallel and oriented approximately along one of the N-Fe-N directions of the slightly ruffled porphyrin ring (approximately 10 degrees ). The spin density was determined to reside in an iron d orbital perpendicular to the heme plane and oriented along the other porphyrin N-Fe-N direction, perpendicular to the axial imidazoles. The benefit of the method presented here lies in the use of Q-band microwave frequencies, which improves the orientation selection, results in no/fewer combination lines in the spectra, and allows separation of the contributions of hyperfine and quadrupole interactions due to the fulfillment of the exact cancellation condition at g ( Z ) and the possibility of performing hyperfine decoupling experiments at the g ( X ) observer position. These experimental advantages make the interpretation of the spectra straightforward, which results in precise and reliable determination of the structure and spin distribution. PMID:20407914
Dey, B.; Meyer, C. A.; Bellis, M.; Williams, M.; Adhikari, K. P.; Adikaram, D.; Aghasyan, M.; Amaryan, M. J.; Anderson, M. D.; Anefalos Pereira, S.; et al
2014-05-27
High-statistics measurements of differential cross sections and spin density matrix elements for the reaction γ p → Φp have been made using the CLAS detector at Jefferson Lab. We cover center-of-mass energies (√s) from 1.97 to 2.84 GeV, with an extensive coverage in the Φ production angle. The high statistics of the data sample made it necessary to carefully account for the interplay between the Φ natural lineshape and effects of the detector resolution, that are found to be comparable in magnitude. We study both the charged- (Φ → K⁺K⁻) and neutral- (Φ → K0SK0L) KK̄ decay modes of themore » Φ. Further, for the charged mode, we differentiate between the cases where the final K⁻ track is directly detected or its momentum reconstructed as the total missing momentum in the event. The two charged-mode topologies and the neutral-mode have different resolutions and are calibrated against each other. Extensive usage is made of kinematic fitting to improve the reconstructed Φ mass resolution. Our final results are reported in 10- and mostly 30-MeV-wide √s bins for the charged- and the neutral-mode, respectively. Possible effects from K⁺Λ* channels with pKK̄ final-states are discussed. These present results constitute the most precise and extensive Φ photoproduction measurements to date and in conjunction with the ω photoproduction results recently published by CLAS, will greatly improve our understanding of low energy vector meson photoproduction.« less
Novel itinerant transverse spin waves
NASA Astrophysics Data System (ADS)
Feldmann, John Delaney
wavelengths, or can lead to spin waves that are characterized by a square root dependence on the wave number at long wavelength. The author also presents new results for spin waves in a fermi liquid that has a spin density wave in its ground state. A spin density wave is characterized by a spiral magnetization in the ground state, and is observed to occur in materials such as MnSi.
Datta, Dipayan Gauss, Jürgen
2015-07-07
We report analytical calculations of isotropic hyperfine-coupling constants in radicals using a spin-adapted open-shell coupled-cluster theory, namely, the unitary group based combinatoric open-shell coupled-cluster (COSCC) approach within the singles and doubles approximation. A scheme for the evaluation of the one-particle spin-density matrix required in these calculations is outlined within the spin-free formulation of the COSCC approach. In this scheme, the one-particle spin-density matrix for an open-shell state with spin S and M{sub S} = + S is expressed in terms of the one- and two-particle spin-free (charge) density matrices obtained from the Lagrangian formulation that is used for calculating the analytic first derivatives of the energy. Benchmark calculations are presented for NO, NCO, CH{sub 2}CN, and two conjugated π-radicals, viz., allyl and 1-pyrrolyl in order to demonstrate the performance of the proposed scheme.
NASA Technical Reports Server (NTRS)
Bradas, James C.; Fennelly, Alphonsus J.; Smalley, Larry L.
1987-01-01
It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.
NASA Astrophysics Data System (ADS)
Bradas, James C.; Fennelly, Alphonsus J.; Smalley, Larry L.
1987-04-01
It is shown that a generalized (or 'power law') inflationary phase arises naturally and inevitably in a simple (Bianchi type-I) anisotropic cosmological model in the self-consistent Einstein-Cartan gravitation theory with the improved stress-energy-momentum tensor with the spin density of Ray and Smalley (1982, 1983). This is made explicit by an analytical solution of the field equations of motion of the fluid variables. The inflation is caused by the angular kinetic energy density due to spin. The model further elucidates the relationship between fluid vorticity, the angular velocity of the inertially dragged tetrads, and the precession of the principal axes of the shear ellipsoid. Shear is not effective in damping the inflation.
Charge-density wave and magnetic phase diagram of chromium alloys
Fishman, R.S.; Jiang, X.W.
1996-08-08
The magnetic phase diagrams of all dilute Cr alloys can be explained by a simple theoretical model with coupled spin- and charge-density waves and a finite electron reservoir. If the charge-density wave and electron reservoir are sufficiently large, the paramagnetic to commensurate spin-density wave transition becomes strongly first order, as found in Cr{sub 1- x}Fe{sub x} and Cr{sub 1-x}Si{sub x} alloys. The observed discontinuity of the slope dT{sub N}/dx at the triple point and the bending of the CI phase boundary are also natural consequences of this model.
Direct Observation of Spin- and Charge-Density Waves in a Luttinger Liquid
NASA Astrophysics Data System (ADS)
Cao, Chenglin; Marcum, Andrew; Mawardi Ismail, Arif; Fonta, Francisco; O'Hara, Kenneth
2016-05-01
At low energy, interacting fermions in one dimension (e.g. electrons in quantum wires or fermionic atoms in 1D waveguides) should behave as Luttinger liquids. In stark contrast to Fermi liquids, the low-energy elementary excitations in Luttinger liquids are collective sound-like modes that propagate independently as spin-density and/or charge-density (i.e. particle-density) waves with generally unequal, and interaction-dependent, velocities. Here we aim to unambiguously confirm this hallmark feature of the Luttinger liquid - the phenomenon of spin-charge separation - by directly observing in real space the dynamics of spin-density and ``charge''-density waves excited in an ultracold gas of spin-1/2 fermions confined in an array of 1D optical waveguides. Starting from a two-component mixture of 6 Li atoms harmonically confined along each of the 1D waveguides, we excite low lying normal modes of the trapped system - namely the spin dipole and density dipole and quadrupole modes - and measure their frequency as a function of interaction strength. Luttinger liquid theory predicts that the spin dipole frequency is strongly dependent on interaction strength whereas the density dipole and quadrupole mode frequencies are relatively insensitive. We will also discuss extending our approach to exciting localized spin density and particle density wavepackets which should propagate at different velocities. Supported by AFOSR and NSF.
NASA Astrophysics Data System (ADS)
Min, Byeong June; Jeong, Hae Kyung; Lee, ChangWoo
2015-08-01
We studied via plane wave pseudopotential total-energy calculations within the local spin density approximation (LSDA) the electronic and the structural properties of amino acids (alanine, glycine, and histidine) attached to graphene oxide (GO) by peptide bonding. The HOMO-LUMO gap, the Hirshfeld charges, and the equilibrium geometrical structures exhibit distinctive variations that depend on the species of the attached amino acid. The GO-amino acid system appears to be a good candidate for a biosensor.
Topological density-wave states in a particle-hole symmetric Weyl metal
NASA Astrophysics Data System (ADS)
Wang, Yuxuan; Ye, Peng
2016-08-01
We study the instabilities of a particle-hole symmetric Weyl metal with both electron and hole Fermi surfaces (FSs) around the Weyl points. For a repulsive interaction we find that the leading instability is towards a longitudinal spin-density-wave (SDWz) order. Besides, there exist three degenerate subleading instabilities: a charge-density-wave (CDW) instability, and two transverse spin-density-wave (SDWx ,y) instabilities. For an attractive interaction the leading instabilities are towards two pair-density-wave (PDW) orders which pair the two FSs separately. Both the PDW and SDWz order parameters fully gap out the FSs, while the CDW and SDWx ,y ones leave line nodes on both FSs. For the SDWz and the PDW states, the surface Fermi arc in the metallic state evolves to a chiral Fermi line which passes the projection of the Weyl points and traverses the full momentum space. For the CDW state, the line node projects to a "drumhead" band localized on the surface, which can lead to a topological charge polarization. We verify the surface states by computing the angular-resolved photoemission spectroscopy data.
NASA Astrophysics Data System (ADS)
Johnson, R. D.; Khalyavin, D. D.; Manuel, P.; Bombardi, A.; Martin, C.; Chapon, L. C.; Radaelli, P. G.
2016-05-01
Through a combination of neutron diffraction and Landau theory we describe the spin ordering in the ground state of the quadruple perovskite manganite CaMn7O12 —a magnetic multiferroic supporting an incommensurate orbital density wave that onsets above the magnetic ordering temperature, TN 1=90 K. The multi-k magnetic structure in the ground state was found to be a nearly-constant-moment helix with modulated spin helicity, which oscillates in phase with the orbital occupancies on the Mn3 + sites via trilinear magneto-orbital coupling. Our phenomenological model also shows that, above TN 2=48 K, the primary magnetic order parameter is locked into the orbital wave by an admixture of helical and collinear spin density wave structures. Furthermore, our model naturally explains the lack of a sharp dielectric anomaly at TN 1 and the unusual temperature dependence of the electrical polarization.
Quantum mechanisms of density wave transport
Miller, John H.; Wijesinghe, Asanga I.
2012-01-01
We report on new developments in the quantum picture of correlated electron transport in charge and spin density waves. The model treats the condensate as a quantum fluid in which charge soliton domain wall pairs nucleate above a Coulomb blockade threshold field. We employ a time-correlated soliton tunneling model, analogous to the theory of time-correlated single electron tunneling, to interpret the voltage oscillations and nonlinear current-voltage characteristics above threshold. An inverse scaling relationship between threshold field and dielectric response, originally proposed by Grüner, emerges naturally from the model. Flat dielectric and other ac responses below threshold in NbSe3 and TaS3, as well as small density wave phase displacements, indicate that the measured threshold is often much smaller than the classical depinning field. In some materials, the existence of two distinct threshold fields suggests that both soliton nucleation and classical depinning may occur. In our model, the ratio of electrostatic charging to pinning energy helps determine whether soliton nucleation or classical depinning dominates. PMID:22711979
NASA Astrophysics Data System (ADS)
Raghuvanshi, Nimisha; Singh, Avinash
2010-10-01
Spin waves in the (0, π) and (0, π, π) ordered spin-density-wave (SDW) states of the t-t' Hubbard model are investigated at finite doping. In the presence of small t', these composite ferro-antiferromagnetic (F-AF) states are found to be strongly stabilized at finite hole doping due to enhanced carrier-induced ferromagnetic spin couplings as in metallic ferromagnets. Anisotropic spin-wave velocities, a spin-wave energy scale of around 200 meV, reduced magnetic moment and rapid suppression of magnetic order with electron doping x (corresponding to F substitution of O atoms in LaO1 - xFxFeAs or Ni substitution of Fe atoms in BaFe2 - xNixAs2) obtained in this model are in agreement with observed magnetic properties of doped iron pnictides.
Tran, Thai T H; Chang, Yan-Ru; Hoang, Tuan K A; Kuo, Ming-Yu; Su, Yuhlong O
2016-07-21
In this study, the electrochemical behavior of free base and zinc meso-substituted porphyrins is examined by cyclic voltammetry (CV) and density functional theory (DFT). The results show that the half-wave oxidation potential splitting of the two oxidation states (ΔE= second E1/2 - first E1/2) of tetraphenylporphyrin (H2TPP) and its zinc complex (ZnTPP) are higher than those of porphyrins and their zinc complexes with meso-substituted five-membered heterocylic rings. The ΔE values follow the trend of TPP > T(3'-thienyl)P > T(3'-furyl)P > T(2'-thienyl)P for both meso-porphyrins and their respective zinc complexes. By employing DFT calculations, we have found that the trend of ΔE values is consistent with that of highest spin density (HSD) distribution and HOMO-LUMO energy gaps of cationic radicals as well as the π-conjugation between central porphyrin and meso-substituted rings. Also, they exhibit the better resonance between the porphyrin ring with meso-substituted rings as moving from porphyrins and their zinc complexes with phenyl rings to five-membered heterocyclic rings. A good agreement between calculated and experimental results indicates that cationic radicals, especially their spin density distribution, do play an important role in half-wave oxidation potential splitting of meso-porphyrins and their zinc complexes. PMID:27379447
NASA Astrophysics Data System (ADS)
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
Heat Waves Dangers we face during periods of very high temperatures include: Heat cramps: These are muscular pains and spasms due ... that the body is having trouble with the heat. If a heat wave is predicted or happening… - ...
Atmospheric Science Data Center
2013-04-19
article title: Gravity Waves Ripple over Marine Stratocumulus Clouds ... Imaging SpectroRadiometer (MISR), a fingerprint-like gravity wave feature occurs over a deck of marine stratocumulus clouds. Similar ... that occur when a pebble is thrown into a still pond, such "gravity waves" sometimes appear when the relatively stable and stratified air ...
Properties of Charge Density Waves in La2-xBaxCuO4
Kim,Y.; Gu, G.; Gog, T.; Casa, D.
2008-01-01
We report a comprehensive x-ray scattering study of charge density wave (stripe) ordering in La2-xBaxCuO4 (x{approx}1/8), for which the bulk superconducting Tc is greatly suppressed. Strong superlattice reflections corresponding to static ordering of charge stripes were observed in this sample. The structural modulation at the lowest temperature was deduced based on the intensity of over 70 unique superlattice positions surveyed. We found that the charge order in this sample is described with one-dimensional charge density waves, which have incommensurate wave vectors (0.23, 0, 0.5) and (0, 0.23, 0.5), respectively, on neighboring CuO2 planes. The structural modulation due to the charge density wave order is simply sinusoidal, and no higher harmonics were observed. Just below the structural transition temperature, short-range charge density wave correlation appears, which develops into a large scale charge ordering around 40 K, close to the spin density wave ordering temperature. However, this charge ordering fails to grow into a true long range order, and its correlation length saturates at {approx}230 Angstroms, and slightly decreases below about 15 K, which may be due to the onset of two-dimensional superconductivity.
Partial wave analysis of the reaction gamma p -> p omega$ and the search for nucleon resonances
M. Williams, D. Applegate, M. Bellis, C.A. Meyer
2009-12-01
An event-based partial wave analysis (PWA) of the reaction gamma p -> p omega has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> pi+ pi - pi0. The data confirm the dominance of the t-channel pi0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as well as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2(+) state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.
ERIC Educational Resources Information Center
Reed, Chris
2000-01-01
Third Wave is a Christian charity based in Derby (England) that offers training in vocational skills, preindustrial crafts, horticultural and agricultural skills, environmental education, and woodland survival skills to disadvantaged people at city and farm locations. Third Wave employs a holistic approach to personal development in a community…
Utz, Marcel; Begley, Matthew R; Haj-Hariri, Hossein
2011-11-21
The propagation of pressure waves in fluidic channels with elastic covers is discussed in view of applications to flow control in microfluidic devices. A theory is presented which describes pressure waves in the fluid that are coupled to bending waves in the elastic cover. At low frequencies, the lateral bending of the cover dominates over longitudinal bending, leading to propagating, non-dispersive longitudinal pressure waves in the channel. The theory addresses effects due to both the finite viscosity and compressibility of the fluid. The coupled waves propagate without dispersion, as long as the wave length is larger than the channel width. It is shown that in channels of typical microfluidic dimensions, wave velocities in the range of a few 10 m s(-1) result if the channels are covered by films of a compliant material such as PDMS. The application of this principle to design microfluidic band pass filters based on standing waves is discussed. Characteristic frequencies in the range of a few kHz are readily achieved with quality factors above 30. PMID:21966667
NASA Technical Reports Server (NTRS)
2007-01-01
With its Multispectral Visible Imaging Camera (MVIC), half of the Ralph instrument, New Horizons captured several pictures of mesoscale gravity waves in Jupiter's equatorial atmosphere. Buoyancy waves of this type are seen frequently on Earth - for example, they can be caused when air flows over a mountain and a regular cloud pattern forms downstream. In Jupiter's case there are no mountains, but if conditions in the atmosphere are just right, it is possible to form long trains of these small waves. The source of the wave excitation seems to lie deep in Jupiter's atmosphere, below the visible cloud layers at depths corresponding to pressures 10 times that at Earth's surface. The New Horizons measurements showed that the waves move about 100 meters per second faster than surrounding clouds; this is about 25% of the speed of sound on Earth and is much greater than current models of these waves predict. Scientists can 'read' the speed and patterns these waves to learn more about activity and stability in the atmospheric layers below.
Beklaryan, Leva A
2011-02-11
A finite difference analogue of the wave equation with potential perturbation is investigated, which simulates the behaviour of an infinite rod under the action of an external longitudinal force field. For a homogeneous rod, describing solutions of travelling wave type is equivalent to describing the full space of classical solutions to an induced one-parameter family of functional differential equations of point type, with the characteristic of the travelling wave as parameter. For an inhomogeneous rod, the space of solutions of travelling wave type is trivial, and their 'proper' extension is defined as solutions of 'quasitravelling' wave type. By contrast to the case of a homogeneous rod, describing the solutions of quasitravelling wave type is equivalent to describing the quotient of the full space of impulsive solutions to an induced one-parameter family of point-type functional differential equations by an equivalence relation connected with the definition of solutions of quasitravelling wave type. Stability of stationary solutions is analyzed. Bibliography: 9 titles.
NASA Technical Reports Server (NTRS)
Thompson, B. J.
1999-01-01
"Moreton waves," named for the observer who popularized them, are a solar phenomenon also known in scientific literature as "Moreton-Ramsey wave," "flare waves," "flare-associated waves," "MHD blast waves," "chromospheric shock fronts" and various other combinations of terms which connote violently propagating impulsive disturbances. It is unclear whether all of the observations to which these terms have been applied pertain to a single physical phenomenon: there has perhaps been some overlap between the observations and the assumed physical properties of the observed occurrence. Moreton waves are ideally observed in the wings of H alpha, and appear as semi-circular fronts propagating at speeds ranging from several hundred to over a thousand km/sec. They form an arc, or "brow shape" which can span up to 180 degrees. Extrapolating the speed and locations of the arc indicates that the phenomenon's origin intersects well with the impulsive phase of the associated H alpha flare (if the flare exhibits an impulsive phase). However, the arc may not form or may not be observable until it is tens of megameters from the flaring region, and subsequently can propagate to distances exceeding 100 megameters. The high speeds and distances of propagation, plus the associated radio and energetic particle observations, provided strong evidence of a coronal, rather than a chromospheric origin. The H alpha manifestation of the wave is assumed to be the "ground track" or "skirt" of a three-dimensional disturbance.
NASA Technical Reports Server (NTRS)
Sharman, R. D.; Wurtele, M. G.
1983-01-01
Dynamics analogous to those of surface ship waves on water of finite depth are noted for the three-dimensional trapped lee wave modes produced by an isolated obstacle in a stratified fluid. This vertical trapping of wave energy is modeled by uniform upstream flow and stratification, bounded above by a rigid lid, and by a semiinfinite fluid of uniform stability whose wind velocity increases exponentially with height, representing the atmosphere. While formal asymptotic solutions are produced, limited quantitative usefulness is obtained through them because of the limitations of the approximations and the infinity of modes in the solution. Time-dependent numerical models are accordingly developed for both surface ship waves and internal and atmospheric ship waves, yielding a variety of results.
NASA Astrophysics Data System (ADS)
Hatakeyama, Yuhki; Ikeda, Ryusuke
2016-03-01
We theoretically investigate k-space structures of dx2-y2-wave superconducting (SC) and spin-density-wave (SDW) orders in their coexistent phase induced by a paramagnetic pair-breaking (PPB) effect in relation to the high-field and low-temperature SC phase in CeCoIn5. It is shown that, in k space, the SDW order develops near the gap nodes where the SC order is suppressed by PPB, and the nesting condition for the SDW ordering is satisfied. By comparing the results in the dx2-y2-wave SC model and those in an artificial model with no sign change of the gap function in k space with each other, it is shown that the dx2-y2-wave SC and SDW orders are enhanced altogether in k space due to the sign change of the dx2-y2-wave gap function there, and that this mutual enhancement largely stabilizes the coexistence of these orders in real space. It is also discussed that the field dependence of a SDW moment can be affected by the k-space structure of these orders, which is dependent on the curvature of the Fermi surface.
Flambard, Alexandrine; Köhler, Frank H; Lescouëzec, Rodrigue; Revel, Bertrand
2011-10-01
Magic-angle spinning (MAS) NMR spectroscopy is used to study the local structure and spin delocalisation in Prussian blue analogues (PBAs). We selected two common archetypes of PBAs (A(I)M(II)[M(III)(CN)(6)]·xH(2)O and M(II)(3)[M(III)(CN)(6)](2)·xH(2)O, in which A(I) is an alkali ion, and M(II) and M(III) are transition-metal ions) that exhibit similar cubic frameworks but different microscopic structures. Whereas the first type of PBA contains interstitial alkali ions and does not exhibit any [M(III)(CN)(6)](3-) vacancies, the second type of PBA exhibits [M(III)(CN)(6)](3-) vacancies, but does not contain inserted alkali ions. In this study, we selected Cd(II) as a divalent metal in order to use the (113)Cd nuclei (I=1/2) as a probe of the local structure. Here, we present a complete MAS NMR study on two series of PBAs of the formulas Cd(II)(3)[Fe(III)(x)Co(III)(1-x)(CN)(6)](2)·15H(2)O with x=0 (1), 0.25 (2), 0.5 (3), 0.75 (4) and 1 (5), and CsCd(II)[Fe(III)(x)Co(III)(1-x)(CN)(6)]·0.5H(2)O with x=0 (6), 0.25 (7), 0.5 (8), 0.75 (9) and 1 (10). Interestingly, the presence of Fe(III) magnetic centres in the vicinity of the cadmium sites has a magnifying-glass effect on the NMR spectrum: it induces a striking signal spread such that the resolution is notably improved compared to that achieved for the diamagnetic PBAs. By doping the sample with varying amounts of diamagnetic Co(III) and comparing the NMR spectra of both types of PBAs, we have been able to give a view of the structure which is complementary to that usually obtained from X-ray diffraction studies. In particular, this study has shown that the vacancies are not randomly distributed in the mesoporous PBAs. Moreover the cadmium chemical shift, which is a measure of the hyperfine coupling, allows the estimation of the spin density on the cadmium nucleus, and consequently, the elucidation of the spin delocalisation mechanism in these compounds along with its dependency on structural parameters. PMID
Ignatovich, V. K.
2009-01-15
It is shown that neutron surface waves do not exist. The difference between the neutron wave mechanics and the wave physics of electromagnetic and acoustic processes, which allows the existence of surface waves, is analyzed.
NASA Technical Reports Server (NTRS)
Vanzandt, T. E.
1985-01-01
Atmospheric parameters fluctuate on all scales. In the mesoscale these fluctuations are occasionally sinusoidal so that they can be interpreted as gravity waves. Usually, however, the fluctuations are noise like, so that their cause is not immediately evident. Results of mesoscale observations in the 20 to 120 m altitude range that are suitable for incorporation into a model atmosphere are very limited. In the stratosphere and lower mesosphere observations are sparse and very little data has been summarized into appropriate form. There is much more data in the upper mesosphere and lower thermosphere, but again very little of it has been summarized. The available mesoscale spectra of horizontal wind u versus vertical wave number m in the 20 to 120 km altitude range are shown together with a spectrum from the lower atmosphere for comparison. Further information about these spectra is given. In spite of the large range of altitudes and latitudes, the spectra from the lower atmosphere (NASA, 1971 and DEWAN, 1984) are remarkably similar in both shape and amplitude. The mean slopes of -2.38 for the NASA spectrum and -2.7 for the Dewan spectra are supported by the mean slope of -2.75 found by ROSENBERG et al. (1974). The mesospheric spectrum is too short to establish a shape. Its amplitude is about an order of magnitude larger than the NASA spectrum in the same wave number range. The NASA and Dewan spectra suggest that the mesoscale spectra in the lower atmosphere are insensitive to meteorological conditions.
Enhancement of superconductivity at the onset of charge-density-wave order in a metal
NASA Astrophysics Data System (ADS)
Wang, Yuxuan; Chubukov, Andrey V.
2015-09-01
We analyze superconductivity in the cuprates near the onset of an incommensurate charge-density-wave (CDW) order with momentum Q =(Q ,0 )/(0 ,Q ) , as observed in experiments. We first consider a semiphenomenological charge-fermion model in which hot fermions, separated by Q , attract each other by exchanging soft CDW fluctuations. We find that in a quantum-critical region near the CDW transition, Tc=A g¯c , where g¯c is charge-fermion coupling and A is the prefactor, which we explicitly compute. We then consider the particular microscopic scenario in which the CDW order parameter emerges as a composite field made of primary spin-density-wave fields. We show that charge-fermion coupling g¯c is of the order of spin-fermion coupling g¯s. As a consequence, superconducting Tc is substantially enhanced near the onset of CDW order. Finally, we analyze the effect of an external magnetic field H . We show that, as H increases, the optimal Tc decreases and the superconducting dome becomes progressively more confined to the CDW quantum-critical point. These results are consistent with experiments.
NASA Technical Reports Server (NTRS)
2000-01-01
The pattern on the right half of this image of the Bay of Bengal is the result of two opposing wave trains colliding. This ASTER sub-scene, acquired on March 29, 2000, covers an area 18 kilometers (13 miles) wide and 15 kilometers (9 miles) long in three bands of the reflected visible and infrared wavelength region. The visible and near-infrared bands highlight surface waves due to specular reflection of sunlight off of the wave faces.
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels over the entire land surface, as well as black and white stereo images. With revisit time of between 4 and 16 days, ASTER will provide the capability for repeat coverage of changing areas on Earth's surface. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is one of five Earth-observing instruments launched December 18, 1999, on NASA's Terra satellite. The instrument was built by Japan's Ministry of International Trade and Industry. A joint U.S./Japan science team is responsible for validation and calibration of the instrument and the data products. Dr. Anne Kahle at NASA's Jet Propulsion Laboratory, Pasadena, California, is the U.S. science team leader; Moshe Pniel of JPL is the project manager. ASTER is the only high-resolution imaging sensor on Terra. The primary goal of the ASTER mission is to obtain high-resolution image data in 14 channels
MHD simple waves and the divergence wave
Webb, G. M.; Pogorelov, N. V.; Zank, G. P.
2010-03-25
In this paper we investigate magnetohydrodynamic (MHD) simple divergence waves in MHD, for models in which nablacentre dotBnot =0. These models are related to the eight wave Riemann solvers in numerical MHD, in which the eighth wave is the divergence wave associated with nablacentre dotBnot =0. For simple wave solutions, all physical variables (the gas density, pressure, fluid velocity, entropy, and magnetic field induction in the MHD case) depend on a single phase function phi. We consider the form of the MHD equations used by both Powell et al. and Janhunen. It is shown that the Janhunen version of the equations possesses fully nonlinear, exact simple wave solutions for the divergence wave, but no physically meaningful simple divergence wave solution exists for the Powell et al. system. We suggest that the 1D simple, divergence wave solution for the Janhunen system, may be useful for the testing and validation of numerical MHD codes.
ERIC Educational Resources Information Center
Frashure, K. M.; Chen, R. F.; Stephen, R. A.; Bolmer, T.; Lavin, M.; Strohschneider, D.; Maichle, R.; Micozzi, N.; Cramer, C.
2007-01-01
Demonstrating wave processes quantitatively in the classroom using standard classroom tools (such as Slinkys and wave tanks) can be difficult. For example, waves often travel too fast for students to actually measure amplitude or wavelength. Also, when teaching propagating waves, reflections from the ends set up standing waves, which can confuse…
NASA Technical Reports Server (NTRS)
Anderson, D. L.
1984-01-01
Vertically polarized shear wave velocity (VSV), determined primarily from fundamental mode Rayleigh waves, and the difference between the velocity of horizontally polarized shear waves (VSH) and VSV, therefore a measure of anisotropy, are shown.
Geometrical versus wave optics under gravitational waves
NASA Astrophysics Data System (ADS)
Angélil, Raymond; Saha, Prasenjit
2015-06-01
We present some new derivations of the effect of a plane gravitational wave on a light ray. A simple interpretation of the results is that a gravitational wave causes a phase modulation of electromagnetic waves. We arrive at this picture from two contrasting directions, namely, null geodesics and Maxwell's equations, or geometric and wave optics. Under geometric optics, we express the geodesic equations in Hamiltonian form and solve perturbatively for the effect of gravitational waves. We find that the well-known time-delay formula for light generalizes trivially to massive particles. We also recover, by way of a Hamilton-Jacobi equation, the phase modulation obtained under wave optics. Turning then to wave optics—rather than solving Maxwell's equations directly for the fields, as in most previous approaches—we derive a perturbed wave equation (perturbed by the gravitational wave) for the electromagnetic four-potential. From this wave equation it follows that the four-potential and the electric and magnetic fields all experience the same phase modulation. Applying such a phase modulation to a superposition of plane waves corresponding to a Gaussian wave packet leads to time delays.
NASA Astrophysics Data System (ADS)
Andreev, Pavel A.
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin
Andreev, Pavel A
2015-03-01
The quantum hydrodynamic (QHD) model of charged spin-1/2 particles contains physical quantities defined for all particles of a species including particles with spin-up and with spin-down. Different populations of states with different spin directions are included in the spin density (the magnetization). In this paper I derive a QHD model, which separately describes spin-up electrons and spin-down electrons. Hence electrons with different projections of spins on the preferable direction are considered as two different species of particles. It is shown that the numbers of particles with different spin directions do not conserve. Hence the continuity equations contain sources of particles. These sources are caused by the interactions of the spins with the magnetic field. Terms of similar nature arise in the Euler equation. The z projection of the spin density is no longer an independent variable. It is proportional to the difference between the concentrations of the electrons with spin-up and the electrons with spin-down. The propagation of waves in the magnetized plasmas of degenerate electrons is considered. Two regimes for the ion dynamics, the motionless ions and the motion of the degenerate ions as the single species with no account of the spin dynamics, are considered. It is shown that this form of the QHD equations gives all solutions obtained from the traditional form of QHD equations with no distinction of spin-up and spin-down states. But it also reveals a soundlike solution called the spin-electron acoustic wave. Coincidence of most solutions is expected since this derivation was started with the same basic equation: the Pauli equation. Solutions arise due to the different Fermi pressures for the spin-up electrons and the spin-down electrons in the magnetic field. The results are applied to degenerate electron gas of paramagnetic and ferromagnetic metals in the external magnetic field. The dispersion of the spin-electron acoustic waves in the partially spin
ERIC Educational Resources Information Center
Temiz, Burak Kagan; Yavuz, Ahmet
2015-01-01
This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the…
NASA Astrophysics Data System (ADS)
Yan, Zhen-Ya
2010-11-01
We analytically give the financial rogue waves in the nonlinear option pricing model due to Ivancevic, which is nonlinear wave alternative of the Black—Scholes model. These rogue wave solutions may he used to describe the possible physical mechanisms for rogue wave phenomenon in financial markets and related fields.
Gravity wave transmission diagram
NASA Astrophysics Data System (ADS)
Tomikawa, Yoshihiro
2016-07-01
A possibility of gravity wave propagation from a source region to the airglow layer around the mesopause has been discussed based on the gravity wave blocking diagram taking into account the critical level filtering alone. This paper proposes a new gravity wave transmission diagram in which both the critical level filtering and turning level reflection of gravity waves are considered. It shows a significantly different distribution of gravity wave transmissivity from the blocking diagram.
Photoelectron wave function in photoionization: plane wave or Coulomb wave?
Gozem, Samer; Gunina, Anastasia O; Ichino, Takatoshi; Osborn, David L; Stanton, John F; Krylov, Anna I
2015-11-19
The calculation of absolute total cross sections requires accurate wave functions of the photoelectron and of the initial and final states of the system. The essential information contained in the latter two can be condensed into a Dyson orbital. We employ correlated Dyson orbitals and test approximate treatments of the photoelectron wave function, that is, plane and Coulomb waves, by comparing computed and experimental photoionization and photodetachment spectra. We find that in anions, a plane wave treatment of the photoelectron provides a good description of photodetachment spectra. For photoionization of neutral atoms or molecules with one heavy atom, the photoelectron wave function must be treated as a Coulomb wave to account for the interaction of the photoelectron with the +1 charge of the ionized core. For larger molecules, the best agreement with experiment is often achieved by using a Coulomb wave with a partial (effective) charge smaller than unity. This likely derives from the fact that the effective charge at the centroid of the Dyson orbital, which serves as the origin of the spherical wave expansion, is smaller than the total charge of a polyatomic cation. The results suggest that accurate molecular photoionization cross sections can be computed with a modified central potential model that accounts for the nonspherical charge distribution of the core by adjusting the charge in the center of the expansion. PMID:26509428
Shear wave logging using guided waves
Winbow, G.A.; Chen, S.T.; Rice, J.A.
1988-09-27
This patent describes a method for acoustically logging an earth formation surrounding a borehole which contains a liquid where the approximate shear wave velocity v of the formation is known. The method consists of: vibrating a dipole source in the liquid to generate in the liquid a guided wave the frequencies of which include a critical frequency f given by zeta = ..nu..12a where a is the borehole radius, so that the fastest component of the guided wave has velocity substantially equal to ..nu..; and detecting the arrival of the fastest component of the guided wave at least one location in the liquid spaced longitudinally along the borehole from the dipole source.
NASA Astrophysics Data System (ADS)
Kim, E.-H.; Boardsen, S. A.; Johnson, J. R.; Slavin, J. A.
2016-02-01
This chapter provides a brief overview of the observed characteristics of ultra-low-frequency (ULF) waves at Mercury. It shows how field-aligned propagating ULF waves at Mercury can be generated by externally driven fast compressional waves (FWs) via mode conversion at the ion-ion hybrid resonance. Then, the chapter reviews the interpretation that the strong magnetic compressional waves near and its harmonics observed with 20 of Mercury's magnetic equator could be the ion Bernstein wave (IBW) mode. A recent statistical study of ULF waves at Mercury based on MESSENGER data reported the occurrence and polarization of the detected waves. The chapter further introduces the field line resonance and the electromagnetic ion Bernstein waves to explain such waves, and shows that both theories can partially explain the observations.
NASA Technical Reports Server (NTRS)
Thomas, J. H.
1983-01-01
A theoretical treatment of magneto-atmospheric waves is presented and applied to the modelling of waves in the solar atmosphere. The waves arise in compressible, stratified, electrically conductive atmospheres within gravitational fields when permeated by a magnetic field. Compression, buoyancy, and distortion of the magnetic field all contribute to the existence of the waves. Basic linearized equations are introduced to describe the waves and attention is given to plane-stratified atmospheres and their stability. A dispersion relation is defined for wave propagation in a plane-stratified atmosphere when there are no plane-wave solutions. Solutions are found for the full wave equation in the presence of either a vertical or a horizontal magnetic field. The theory is applied to describing waves in sunspots, in penumbrae, and flare-induced coronal disturbances.
Alternating-Sign S-Wave Superconductivity in Single-Layer FeSe from the Local Moment Limit
NASA Astrophysics Data System (ADS)
Rodriguez, Jose
We obtain the exact low-energy spectrum of two mobile electrons roaming over a 4 by 4 lattice of iron atoms governed by a t-J model for a monolayer of FeSe. Each iron atom contains the minimum dxz and dyz orbitals. The hopping parameters (t) account only for electron bands centered at wave vectors (π , 0) and (0 , π) , while the Heisenberg exchange parameters (J) imply a quantum-critical point (QCP) at half-filling that separates a commensurate spin-density wave (cSDW) at strong Hund coupling from a hidden-order antiferromagnet at weak Hund coupling. The hidden-order antiferromagnet has ordering wavevector (π , π) . After tuning the Hund coupling near the QCP, we find an S+- ground state and a D+- excited state that are separated in energy from the edge of a quasi-particle continuum. Both bound states alternate in sign between electron pairs at cSDW momenta and electron pairs at emergent electronic structure with zero 2D momentum. Exact calculations for a single electron with the same t-J model parameters find that the emergent electronic structure at zero 2D momentum moves off the Fermi level as Hund coupling weakens below the QCP. We therefore suggest that the above S+- groundstate describes Coopers pairs in a monolayer of FeSe. Research supported in part by AFOSR Grant No. FA9550-13-1-0118.
Nihei, K.T.; Yi, W.; Myer, L.R.; Cook, N.G.; Schoenberg, M.
1999-03-01
The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh-Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A{sub 0} mode) and demonstrates the ease with which a fracture channel wave can be generated and detected. {copyright} 1999 American Geophysical Union
Structure and magnetism of bulk Fe and Cr: from plane waves to LCAO methods.
Soulairol, R; Fu, Chu-Chun; Barreteau, C
2010-07-28
Magnetic, structural and energetic properties of bulk Fe and Cr were studied using first-principles calculations within density functional theory (DFT). We aimed to identify the dependence of these properties on key approximations of DFT, namely the exchange-correlation functional, the pseudopotential and the basis set. We found a smaller effect of pseudopotentials (PPs) on Fe than on Cr. For instance, the local magnetism of Cr was shown to be particularly sensitive to the potentials representing the core electrons, i.e. projector augmented wave and Vanderbilt ultrasoft PPs predict similar results, whereas standard norm-conserving PPs tend to overestimate the local magnetic moments of Cr in bcc Cr and in dilute bcc FeCr alloys. This drawback is suggested to be closely correlated to the overestimation of Cr solution energy in the latter system. On the other hand, we point out that DFT methods with very reduced localized basis sets (LCAO: linear combination of atomic orbitals) give satisfactory results compared with more robust plane-wave approaches. A minimal-basis representation of '3d' electrons comes to be sufficient to describe non-trivial magnetic phases including spin spirals in both fcc Fe and bcc Cr, as well as the experimental magnetic ground state of bcc Cr showing a spin density wave (SDW) state. In addition, a magnetic 'spd' tight binding model within the Stoner formalism was proposed and validated for Fe and Cr. The respective Stoner parameters were obtained by fitting to DFT data. This efficient semiempirical approach was shown to be accurate enough for studying various collinear and non-collinear phases of bulk Fe and Cr. It also enabled a detailed investigation of different polarization states of SDW in bcc Cr, where the longitudinal state was suggested to be the ground state, consistent with existing experimental data. PMID:21399309
Dust-Acoustic Waves: Visible Sound Waves
Merlino, Robert L.
2009-11-10
A historical overview of some of the early theoretical and experimental work on dust acoustic waves is given. The basic physics of the dust acoustic wave and some of the theoretical refinements that have been made, including the effects of collisions, plasma absorption, dust charge fluctuations, particle drifts and strong coupling effects are discussed. Some recent experimental findings and outstanding problems are also presented.
NASA Astrophysics Data System (ADS)
Freire, Hermann; de Carvalho, Vanuildo
2015-03-01
The two-loop renormalization group (RG) calculation is considerably extended here for a two-dimensional (2D) fermionic effective field theory model, which includes only the so-called ``hot spots'' that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t -t' Hubbard model at low hole doping. We compute the Callan-Symanzik RG equation up to two loops describing the flow of the single-particle Green's function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that - in addition to clearly dominant SDW correlations - an approximate (pseudospin) symmetry relating a short-range incommensurate d-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates. We acknowledge financial support from CNPq under Grant No. 245919/2012-0 and FAPEG under Grant No. 201200550050248 for this project.
NASA Technical Reports Server (NTRS)
Wiley, Scott
2008-01-01
This viewgraph document reviews some mountain wave turbulence and operational hazards while soaring. Maps, photographs, and satellite images of the meteorological phenomena are included. Additionally, photographs of aircraft that sustained mountain wave damage are provided.
... this page: //medlineplus.gov/ency/article/002693.htm Cold wave lotion poisoning To use the sharing features on this page, please enable JavaScript. Cold wave lotion is a hair care product used ...
Menikoff, Ralph
2015-12-14
The Zel’dovich-von Neumann-Doering (ZND) profile of a detonation wave is derived. Two basic assumptions are required: i. An equation of state (EOS) for a partly burned explosive; P(V, e, λ). ii. A burn rate for the reaction progress variable; d/dt λ = R(V, e, λ). For a steady planar detonation wave the reactive flow PDEs can be reduced to ODEs. The detonation wave profile can be determined from an ODE plus algebraic equations for points on the partly burned detonation loci with a specified wave speed. Furthermore, for the CJ detonation speed the end of the reaction zone is sonic. A solution to the reactive flow equations can be constructed with a rarefaction wave following the detonation wave profile. This corresponds to an underdriven detonation wave, and the rarefaction is know as a Taylor wave.
Oceanic wave measurement system
NASA Technical Reports Server (NTRS)
Holmes, J. F.; Miles, R. T. (Inventor)
1980-01-01
An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion.
NASA Astrophysics Data System (ADS)
Abramson, Guillermo
2003-03-01
A spatially extended model of the hantavirus infection in deer mice is analyzed. Traveling waves solutions of the infected and susceptible populations are studied in different regimes, controlled by an environmental parameter. The wave of infection is shown to lag behind the wave of susceptible population, and the delay between the two is analyzed numerically and through a piecewise linearization.
Wave turbulence in annular wave tank
NASA Astrophysics Data System (ADS)
Onorato, Miguel; Stramignoni, Ettore
2014-05-01
We perform experiments in an annular wind wave tank at the Dipartimento di Fisica, Universita' di Torino. The external diameter of the tank is 5 meters while the internal one is 1 meter. The tank is equipped by two air fans which can lead to a wind of maximum 5 m/s. The present set up is capable of studying the generation of waves and the development of wind wave spectra for large duration. We have performed different tests including different wind speeds. For large wind speed we observe the formation of spectra consistent with Kolmogorv-Zakharov predictions.
Detectors of gravitational waves
NASA Astrophysics Data System (ADS)
Pizzella, G.
Gravitational waves Motion of test bodies in a g.w. field Energy carried by gravitational waves Gravitational-wave sources Spinning star Double-star systems Fall into a Schwarzschild black hole Radiation from gravitational collapse Gravitational-wave detectors The nonresonant detectors The resonant detectors Electromechnical transducers Piezoelectric ceramic The capacitor The inductor Data analysis The Brownian noise The back-action The wide-band noise, data analysis and optimization The resonant transducer The Wiener-Kolmogoroff filter The cross-section and the effective temperature The antenna bandwidth The gravitational-wave experiments in the world The laser interferometers The resonant detectors
NASA Astrophysics Data System (ADS)
Okihiro, Michele; Guza, R. T.; Seymour, R. J.
1992-07-01
Model predictions of bound (i.e., nonlinearly forced by and coupled to wave groups) infragravity wave energy are compared with about 2 years of observations in 8- to 13-m depths at Imperial Beach, California, and Barbers Point, Hawaii. Frequency-directional spectra of free waves at sea and swell frequencies, estimated with a small array of four pressure sensors, are used to predict the bound wave spectra below 0.04 Hz. The predicted total bound wave energy is always less than the observed infragravity energy, and the underprediction increases with increasing water depth and especially with decreasing swell energy. At most half, and usually much less, of the observed infragravity energy is bound. Bound wave spectra are also predicted with data from a single wave gage in 183-m depth at Point Conception, California, and the assumption of unidirectional sea and swell. Even with energetic swell, less than 10% of the total observed infragravity energy in 183-m depth is bound. Free waves, either leaky or edge waves, are more energetic than bound waves at both the shallow and deep sites. The low level of infragravity energy observed in 183-m depth compared with 8- to 13-m depths, with similarly moderate sea and swell energy, suggests that leaky (and very high-mode edge) waves contribute less than 10% of the infragravity energy in 8-13 m. Most of the free infragravity energy in shallow water is refractively trapped and does not reach deep water.
NASA Technical Reports Server (NTRS)
Pirraglia, J. A.
1975-01-01
Mariner 9 television pictures of Mars extensive mountain lee wave phenomenon in the northern mid-latitudes during winter were evaluated. The characteristic wave length of the lee waves is readily observable, and in a few cases the boundaries of the wave patterns, as well as the wave length, are observed. The cloud patterns resulting from the waves generated by the flow across a mountain or crater are shown to be dependent upon the velocity profile of the air stream and the vertical stability of the atmosphere. Using the stability as inferred by the temperature structure obtained from the infrared spectrometer data, a two layer velocity model of the air stream is used in calculations based on the theory of mountain lee waves. Results yield magnitudes generally in agreement with various other circulation models.
NASA Astrophysics Data System (ADS)
Sych, Robert
2016-02-01
The study of magnetohydrodynamic (MHD) waves and oscillations in the solar atmosphere is one of the fastest developing fields in solar physics, and lies in the mainstream of using solar instrumentation data. This chapter first addresses the spatial frequency morphology of sources of sunspot oscillations and waves, including their localization, size, oscillation periods, and height localization with the mechanism of cutoff frequency that forms the observed emission variability. Then, it presents a review dynamic of sunspot wave processes, provides the information about the structure of wave fronts and their time variations, and investigates the oscillation frequency transformation depending on the wave energy. The chapter also addresses the initializing solar flares caused by trigger agents like magnetoacoustic waves, accelerated particle beams, and shocks. Special attention is paid to the relation between the flare reconnection periodic initialization and the dynamics of sunspot slow magnetoacoustic waves.
Teleseismic S wave microseisms.
Nishida, Kiwamu; Takagi, Ryota
2016-08-26
Although observations of microseisms excited by ocean swells were firmly established in the 1940s, the source locations remain difficult to track. Delineation of the source locations and energy partition of the seismic wave components are key to understanding the excitation mechanisms. Using a seismic array in Japan, we observed both P and S wave microseisms excited by a severe distant storm in the Atlantic Ocean. Although nonlinear forcing of an ocean swell with a one-dimensional Earth model can explain P waves and vertically polarized S waves (SV waves), it cannot explain horizontally polarized S waves (SH waves). The precise source locations may provide a new catalog for exploring Earth's interior. PMID:27563094
NASA Astrophysics Data System (ADS)
Coco, G.; Guza, R. T.; Garnier, R.; Lomonaco, P.; Lopez De San Roman Blanco, B.; Dalrymple, R. A.; Xu, M.
2014-12-01
Edge waves, gravity waves trapped close to the shoreline by refraction, can in some cases form a standing wave pattern with alongshore periodic sequence of high and low runup. Nonlinear mechanisms for generation of edge waves by monochromatic waves incident on a planar beach from deep water have been elaborated theoretically and in the lab. Edge waves have been long considered a potential source for alongshore periodic morphological patterns in the swash (e.g., beach cusps), and edge-wave based predictions of cusp spacing compare qualitatively well with many field observations. We will discuss the extension of lab observations and numerical modeling to include incident waves with significant frequency and directional bandwidth. Laboratory experiments were performed at the Cantabria Coastal and Ocean Basin. The large rectangular basin (25 m cross-shore by 32 m alongshore) was heavily instrumented, had reflective sidewalls, and a steep concrete beach (slope 1:5) with a constant depth (1m) section between the wavemaker and beach. With monochromatic, normally incident waves we observed the expected, previously described subharmonic observations. Edge wave vertical heights at the shoreline reached 80cm, and edge wave uprushes exceeded the sloping beach freeboard. When frequency and frequency-directional spread are increased, the excited edge wave character changes substantially. In some cases, subharmonic excitation is suppressed completely. In other cases, edge waves are excited intermittently and unpredictably. The spatially and temporally steady forcing required for strong, persistent subharmonic instability is lacking with even modestly spread (direction and frequency) incident waves. An SPH numerical model is capable of reproducing aspects of the observations. It seems unlikely to us that subhamonic edge waves alone are responsible for most cusp formation on natural beaches. The steady incident wave forcing needed to initiate subharmonic growth, and to maintain
Cycloidal Wave Energy Converter
Stefan G. Siegel, Ph.D.
2012-11-30
This program allowed further advancing the development of a novel type of wave energy converter, a Cycloidal Wave Energy Converter or CycWEC. A CycWEC consists of one or more hydrofoils rotating around a central shaft, and operates fully submerged beneath the water surface. It operates under feedback control sensing the incoming waves, and converts wave power to shaft power directly without any intermediate power take off system. Previous research consisting of numerical simulations and two dimensional small 1:300 scale wave flume experiments had indicated wave cancellation efficiencies beyond 95%. The present work was centered on construction and testing of a 1:10 scale model and conducting two testing campaigns in a three dimensional wave basin. These experiments allowed for the first time for direct measurement of electrical power generated as well as the interaction of the CycWEC in a three dimensional environment. The Atargis team successfully conducted two testing campaigns at the Texas A&M Offshore Technology Research Center and was able to demonstrate electricity generation. In addition, three dimensional wave diffraction results show the ability to achieve wave focusing, thus increasing the amount of wave power that can be extracted beyond what was expected from earlier two dimensional investigations. Numerical results showed wave cancellation efficiencies for irregular waves to be on par with results for regular waves over a wide range of wave lengths. Using the results from previous simulations and experiments a full scale prototype was designed and its performance in a North Atlantic wave climate of average 30kW/m of wave crest was estimated. A full scale WEC with a blade span of 150m will deliver a design power of 5MW at an estimated levelized cost of energy (LCOE) in the range of 10-17 US cents per kWh. Based on the new results achieved in the 1:10 scale experiments these estimates appear conservative and the likely performance at full scale will
NASA Astrophysics Data System (ADS)
Fontana, Giorgio
2005-02-01
There is only one experimental proof that gravitational waves exist. With such a limitation, it may seem premature to suggest the possibility that gravitational waves can became a preferred space propulsion technique. The present understanding of the problem indicates that this is not the case. The emission of gravitational waves from astrophysical sources has been confirmed by observation, the respective detection at large distance from the source is difficult and actually we have no confirmation of a successful detection. Therefore the required preliminary discovery has been already made. This opinion is enforced by many different proposals for building the required powerful gravitational wave generators that have recently appeared in the literature and discussed at conferences. It is no longer reasonable to wait for additional confirmation of the existence of gravitational waves to start a program for building generators and testing their possible application to space travel. A vast literature shows that gravitational waves can be employed for space propulsion. Gravitational wave rockets have been proposed, non-linearity of Einstein equations allows the conversion of gravitational waves to a static gravitational field and ``artificial gravity assist'' may become a new way of travelling in space-time. Different approaches to gravitational wave propulsion are reviewed and compared. Gravitational wave propulsion is also compared to traditional rocket propulsion and an undeniable advantage can be demonstrated in terms of efficiency and performance. Testing the predictions will require gravitational wave generators with high power and wavelength short enough for producing high energy densities. Detectors designed for the specific application must be developed, taking into account that non-linearity effects are expected. The study and development of Gravitational wave propulsion is a very challenging endeavor, involving the most complex theories, sophisticated
Wouters, L.F.
1960-08-30
Radiation waves can be detected by simultaneously measuring radiation- wave intensities at a plurality of space-distributed points and producing therefrom a plot of the wave intensity as a function of time. To this end. a detector system is provided which includes a plurality of nuclear radiation intensity detectors spaced at equal radial increments of distance from a source of nuclear radiation. Means are provided to simultaneously sensitize the detectors at the instant a wave of radiation traverses their positions. the detectors producing electrical pulses indicative of wave intensity. The system further includes means for delaying the pulses from the detectors by amounts proportional to the distance of the detectors from the source to provide an indication of radiation-wave intensity as a function of time.
Kinesthetic Transverse Wave Demonstration
NASA Astrophysics Data System (ADS)
Pantidos, Panagiotis; Patapis, Stamatis
2005-09-01
This is a variation on the String and Sticky Tape demonstration "The Wave Game," suggested by Ron Edge. A group of students stand side by side, each one holding a card chest high with both hands. The teacher cues the first student to begin raising and lowering his card. When he starts lowering his card, the next student begins to raise his. As succeeding students move their cards up and down, a wave such as that shown in the figure is produced. To facilitate the process, students' motions were synchronized with the ticks of a metronome (without such synchronization it was nearly impossible to generate a satisfactory wave). Our waves typically had a frequency of about 1 Hz and a wavelength of around 3 m. We videotaped the activity so that the students could analyze the motions. The (17-year-old) students had not received any prior instruction regarding wave motion and did not know beforehand the nature of the exercise they were about to carry out. During the activity they were asked what a transverse wave is. Most of them quickly realized, without teacher input, that while the wave propagated horizontally, the only motion of the transmitting medium (them) was vertical. They located the equilibrium points of the oscillations, the crests and troughs of the waves, and identified the wavelength. The teacher defined for them the period of the oscillations of the motion of a card to be the total time for one cycle. The students measured this time and then several asserted that it was the same as the wave period. Knowing the length of the waves and the number of waves per second, the next step can easily be to find the wave speed.
Solli, D R; Ropers, C; Koonath, P; Jalali, B
2007-12-13
Recent observations show that the probability of encountering an extremely large rogue wave in the open ocean is much larger than expected from ordinary wave-amplitude statistics. Although considerable effort has been directed towards understanding the physics behind these mysterious and potentially destructive events, the complete picture remains uncertain. Furthermore, rogue waves have not yet been observed in other physical systems. Here, we introduce the concept of optical rogue waves, a counterpart of the infamous rare water waves. Using a new real-time detection technique, we study a system that exposes extremely steep, large waves as rare outcomes from an almost identically prepared initial population of waves. Specifically, we report the observation of rogue waves in an optical system, based on a microstructured optical fibre, near the threshold of soliton-fission supercontinuum generation--a noise-sensitive nonlinear process in which extremely broadband radiation is generated from a narrowband input. We model the generation of these rogue waves using the generalized nonlinear Schrödinger equation and demonstrate that they arise infrequently from initially smooth pulses owing to power transfer seeded by a small noise perturbation. PMID:18075587
NASA Technical Reports Server (NTRS)
Jones, Robert E.; Kramarchuk, Ihor; Williams, Wallace D.; Pouch, John J.; Gilbert, Percy
1989-01-01
Computer-controlled thermal-wave microscope developed to investigate III-V compound semiconductor devices and materials. Is nondestructive technique providing information on subsurface thermal features of solid samples. Furthermore, because this is subsurface technique, three-dimensional imaging also possible. Microscope uses intensity-modulated electron beam of modified scanning electron microscope to generate thermal waves in sample. Acoustic waves generated by thermal waves received by transducer and processed in computer to form images displayed on video display of microscope or recorded on magnetic disk.
NASA Astrophysics Data System (ADS)
Boyd, Jeffrey
2010-02-01
As preposterous as it might sound, if quantum waves travel in the reverse direction from subatomic particles, then most of quantum physics can be explained without quantum weirdness or Schr"odinger's cat. Quantum mathematics is unchanged. The diffraction pattern on the screen of the double slit experiment is the same. This proposal is not refuted by the Innsbruck experiments; this is NOT a hidden local variable theory. Research evidence will be presented that is consistent with the idea waves travel in the opposite direction as neutrons. If one's thinking shifts from forwards to backwards quantum waves, the world changes so drastically it is almost unimaginable. Quantum waves move from the mathematical to the real world, multiply in number, and reverse in direction. Wave-particle duality is undone. In the double slit experiment every part of the target screen is emitting such quantum waves in all directions. Some pass through the two slits. Interference occurs on the opposite side of the barrier than is usually imagined. They impinge on ``S'' and an electron is released at random. Because of the interference it is more likely to follow some waves than others. It follows one and only one wave backward; hitting the screen where it's wave originated. )
Internal Solitary Wave Tunnelling
NASA Astrophysics Data System (ADS)
Sutherland, Bruce; Keating, Scott; Shrivistava, Ishita
2013-11-01
In a two-layer fluid, solitary waves of depression (elevation) propagate in a shallow upper (lower) layer. The transition from depressed to elevated is known to occur as a solitary wave of depression passes over a bottom slope. If impacting a coastline the shoaling waves deposit some energy and partially reflect. Here we consider what happens if a solitary wave passes over a sill or the shoulder of an island. Specifically, through lock-release laboratory experiments, we examine the evolution of a solitary wave of depression incident upon a submerged thin vertical barrier and triangular submarine topography. From the measured interface displacement, we determine the available potential energy associated with the wave. The method of Hilbert transforms is used to subdivide the displacement signal into rightward- and leftward-propagating disturbances, from which we measure the available potential energy of the transmitted and reflected waves. These are used to measure the relative transmission, reflection and deposition of energy in terms of the barrier height and slope, the relative depths of the ambient fluid and the amplitude of the incident wave. Implications for internal wave scattering around Dongsha Atoll in the South China Sea are discussed. Research performed while visiting the University of Alberta under the UARE program.
Partial wave analysis of the reaction {gamma}p{yields}p{omega} and the search for nucleon resonances
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Dey, B; Dickson, R.; Krahn, Z.; McCracken, M. E.; Moriya, K.; Schumacher, R. A.; Adhikari, K. P.; Careccia, S. L.; Dodge, G. E.; Guler, N.; Klein, A.; Mayer, M.; Nepali, C. S.; Niroula, M. R.; Seraydaryan, H.; Tkachenko, S.
2009-12-15
An event-based partial wave analysis (PWA) of the reaction {gamma}p{yields}p{omega} has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of {omega}{yields}{pi}{sup +}{pi}{sup -}{pi}{sup 0}. The data confirm the dominance of the t-channel {pi}{sup 0} exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F{sub 15}(1680) and D{sub 13}(1700) near threshold, as well as the G{sub 17}(2190) at higher energies. Suggestive evidence for the presence of a J{sup P}=5/2{sup +} state around 2 GeV, a ''missing'' state, has also been found. Evidence for other states is inconclusive.
Partial wave analysis of the reaction γp→pω and the search for nucleon resonances
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Adhikari, K. P.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; et al
2009-12-30
We performed an event-based partial wave analysis (PWA) of the reaction γ p -> p ω on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world's first high precision spin density matrix element measurements, available to the event-based PWA through the decay distribution of omega-> π+ π - π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F[15](1680) and D[13](1700) near threshold, as wellmore » as the G[17](2190) at higher energies. Suggestive evidence for the presence of a J(P)=5/2+ state around 2 GeV, a "missing" state, has also been found. Evidence for other states is inconclusive.« less
Partial wave analysis of the reaction γp→pω and the search for nucleon resonances
NASA Astrophysics Data System (ADS)
Williams, M.; Applegate, D.; Bellis, M.; Meyer, C. A.; Adhikari, K. P.; Anghinolfi, M.; Baghdasaryan, H.; Ball, J.; Battaglieri, M.; Bedlinskiy, I.; Berman, B. L.; Biselli, A. S.; Briscoe, W. J.; Brooks, W. K.; Burkert, V. D.; Careccia, S. L.; Carman, D. S.; Cole, P. L.; Collins, P.; Crede, V.; D'Angelo, A.; Daniel, A.; de Vita, R.; de Sanctis, E.; Deur, A.; Dey, B.; Dhamija, S.; Dickson, R.; Djalali, C.; Dodge, G. E.; Doughty, D.; Dugger, M.; Dupre, R.; Alaoui, A. El; Elouadrhiri, L.; Eugenio, P.; Fedotov, G.; Fegan, S.; Fradi, A.; Gabrielyan, M. Y.; Garçon, M.; Gilfoyle, G. P.; Giovanetti, K. L.; Girod, F. X.; Gohn, W.; Golovatch, E.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guler, N.; Guo, L.; Hafidi, K.; Hakobyan, H.; Hanretty, C.; Hassall, N.; Hicks, K.; Holtrop, M.; Ilieva, Y.; Ireland, D. G.; Ishkhanov, B. S.; Isupov, E. L.; Jawalkar, S. S.; Jo, H. S.; Johnstone, J. R.; Joo, K.; Keller, D.; Khandaker, M.; Khetarpal, P.; Kim, W.; Klein, A.; Klein, F. J.; Krahn, Z.; Kubarovsky, V.; Kuleshov, S. V.; Kuznetsov, V.; Livingston, K.; Lu, H. Y.; Mayer, M.; McAndrew, J.; McCracken, M. E.; McKinnon, B.; Mirazita, M.; Mokeev, V.; Moreno, B.; Moriya, K.; Morrison, B.; Munevar, E.; Nadel-Turonski, P.; Nepali, C. S.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Niroula, M. R.; Niyazov, R. A.; Osipenko, M.; Ostrovidov, A. I.; Paris, M.; Park, K.; Park, S.; Pasyuk, E.; Pereira, S. Anefalos; Perrin, Y.; Pisano, S.; Pogorelko, O.; Pozdniakov, S.; Price, J. W.; Procureur, S.; Protopopescu, D.; Ricco, G.; Ripani, M.; Ritchie, B. G.; Rosner, G.; Rossi, P.; Sabatié, F.; Saini, M. S.; Salamanca, J.; Salgado, C.; Schott, D.; Schumacher, R. A.; Seraydaryan, H.; Sharabian, Y. G.; Smith, E. S.; Sober, D. I.; Sokhan, D.; Stepanyan, S. S.; Stoler, P.; Strakovsky, I. I.; Strauch, S.; Taiuti, M.; Tedeschi, D. J.; Tkachenko, S.; Ungaro, M.; Vineyard, M. F.; Voutier, E.; Watts, D. P.; Weygand, D. P.; Wood, M. H.; Zhang, J.; Zhao, B.
2009-12-01
An event-based partial wave analysis (PWA) of the reaction γp→pω has been performed on a high-statistics dataset obtained using the CLAS at Jefferson Lab for center-of-mass energies from threshold up to 2.4 GeV. This analysis benefits from access to the world’s first high-precision spin-density matrix element measurements, available to the event-based PWA through the decay distribution of ω→π+π-π0. The data confirm the dominance of the t-channel π0 exchange amplitude in the forward direction. The dominant resonance contributions are consistent with the previously identified states F15(1680) and D13(1700) near threshold, as well as the G17(2190) at higher energies. Suggestive evidence for the presence of a JP=5/2+ state around 2 GeV, a “missing” state, has also been found. Evidence for other states is inconclusive.
Modal Waves Solved in Complex Wave Number
NASA Astrophysics Data System (ADS)
Xu, W.-J.; Jenot, F.; Ourak, M.
2005-04-01
A numerical algorithm is proposed for the resolution in complex domain of the ultrasonic modal waves from the characteristic equation of elastic structures. The method is applicable to any numerically available function given explicitly or implicitly. The complex root loci of the modal waves are constructed by varying other parameters. Different situations which can cause the roots searching and following failure are analysed and the corresponding solutions are proposed. The computation examples are given for a three layered adhesive joint and a composite plate.
Oceanic-wave-measurement system
NASA Technical Reports Server (NTRS)
Holmes, J. F.; Miles, R. T.
1980-01-01
Barometer mounted on bouy senses wave heights. As wave motion raises and lowers barometer, pressure differential is proportional to wave height. Monitoring circuit samples barometer output every half cycle of wave motion and adds magnitudes of adjacent positive and negative peaks. Resulting output signals, proportional to wave height, are transmitted to central monitoring station.
Those Elusive Gravitational Waves
ERIC Educational Resources Information Center
MOSAIC, 1976
1976-01-01
The presence of gravitational waves was predicted by Einstein in his theory of General Relativity. Since then, scientists have been attempting to develop a detector sensitive enough to measure these cosmic signals. Once the presence of gravitational waves is confirmed, scientists can directly study star interiors, galaxy cores, or quasars. (MA)
Wu, Tsung-Tsong; Hsu, Jin-Chen; Sun, Jia-Hong
2011-10-01
In the past two decades, phononic crystals (PCs) which consist of periodically arranged media have attracted considerable interest because of the existence of complete frequency band gaps and maneuverable band structures. Recently, Lamb waves in thin plates with PC structures have started to receive increasing attention for their potential applications in filters, resonators, and waveguides. This paper presents a review of recent works related to phononic plate waves which have recently been published by the authors and coworkers. Theoretical and experimental studies of Lamb waves in 2-D PC plate structures are covered. On the theoretical side, analyses of Lamb waves in 2-D PC plates using the plane wave expansion (PWE) method, finite-difference time-domain (FDTD) method, and finite-element (FE) method are addressed. These methods were applied to study the complete band gaps of Lamb waves, characteristics of the propagating and localized wave modes, and behavior of anomalous refraction, called negative refraction, in the PC plates. The theoretical analyses demonstrated the effects of PC-based negative refraction, lens, waveguides, and resonant cavities. We also discuss the influences of geometrical parameters on the guiding and resonance efficiency and on the frequencies of waveguide and cavity modes. On the experimental side, the design and fabrication of a silicon-based Lamb wave resonator which utilizes PC plates as reflective gratings to form the resonant cavity are discussed. The measured results showed significant improvement of the insertion losses and quality factors of the resonators when the PCs were applied. PMID:21989878
ERIC Educational Resources Information Center
Newman, J. N.
1979-01-01
Discussed is the utilization of surface ocean waves as a potential source of power. Simple and large-scale wave power devices and conversion systems are described. Alternative utilizations, environmental impacts, and future prospects of this alternative energy source are detailed. (BT)
Advanced Gravitational Wave Detectors
NASA Astrophysics Data System (ADS)
Blair, D. G.; Howell, E. J.; Ju, L.; Zhao, C.
2012-02-01
Part I. An Introduction to Gravitational Wave Astronomy and Detectors: 1. Gravitational waves D. G. Blair, L. Ju, C. Zhao and E. J. Howell; 2. Sources of gravitational waves D. G. Blair and E. J. Howell; 3. Gravitational wave detectors D. G. Blair, L. Ju, C. Zhao, H. Miao, E. J. Howell, and P. Barriga; 4. Gravitational wave data analysis B. S. Sathyaprakash and B. F. Schutz; 5. Network analysis L. Wen and B. F. Schutz; Part II. Current Laser Interferometer Detectors: Three Case Studies: 6. The Laser Interferometer Gravitational-Wave Observatory P. Fritschel; 7. The VIRGO detector S. Braccini; 8. GEO 600 H. Lück and H. Grote; Part III. Technology for Advanced Gravitational Wave Detectors: 9. Lasers for high optical power interferometers B. Willke and M. Frede; 10. Thermal noise, suspensions and test masses L. Ju, G. Harry and B. Lee; 11. Vibration isolation: Part 1. Seismic isolation for advanced LIGO B. Lantz; Part 2. Passive isolation J-C. Dumas; 12. Interferometer sensing and control P. Barriga; 13. Stabilizing interferometers against high optical power effects C. Zhao, L. Ju, S. Gras and D. G. Blair; Part IV. Technology for Third Generation Gravitational Wave Detectors: 14. Cryogenic interferometers J. Degallaix; 15. Quantum theory of laser-interferometer GW detectors H. Miao and Y. Chen; 16. ET. A third generation observatory M. Punturo and H. Lück; Index.
NASA Astrophysics Data System (ADS)
Viswanathan, Koushik; Sundaram, Narayan; Chandrasekar, Srinivasan
Stick-slip, manifest as intermittent tangential motion between two dry solid surfaces, is a friction instability that governs diverse phenomena from automobile brake squeals to earthquakes. We show, using high-speed in situ imaging of an adhesive polymer interface, that low velocity stick-slip is fundamentally of three kinds, corresponding to passage of three different surface waves -- separation pulses, slip pulses and the well-known Schallamach waves. These waves, traveling much slower than elastic waves, have clear distinguishing properties. Separation pulses and Schallamach waves involve local interface separation, and propagate in opposite directions while slip pulses are characterized by a sharp stress front and do not display any interface detachment. A change in the stick-slip mode from separation to slip pulse is effected simply by increasing the normal force. Together, these three waves constitute all possible stick-slip modes in adhesive friction and are shown to have direct analogues in muscular locomotory waves in soft bodied invertebrates. A theory for slow wave propagation is also presented which is capable of explaining the attendant interface displacements, velocities and stresses.
ERIC Educational Resources Information Center
Houlrik, Jens Madsen
2009-01-01
The Lorentz transformation applies directly to the kinematics of moving particles viewed as geometric points. Wave propagation, on the other hand, involves moving planes which are extended objects defined by simultaneity. By treating a plane wave as a geometric object moving at the phase velocity, novel results are obtained that illustrate the…
NASA Astrophysics Data System (ADS)
Lan, Jin; Yu, Weichao; Wu, Ruqian; Xiao, Jiang
2015-10-01
A diode, a device allowing unidirectional signal transmission, is a fundamental element of logic structures, and it lies at the heart of modern information systems. The spin wave or magnon, representing a collective quasiparticle excitation of the magnetic order in magnetic materials, is a promising candidate for an information carrier for the next-generation energy-saving technologies. Here, we propose a scalable and reprogrammable pure spin-wave logic hardware architecture using domain walls and surface anisotropy stripes as waveguides on a single magnetic wafer. We demonstrate theoretically the design principle of the simplest logic component, a spin-wave diode, utilizing the chiral bound states in a magnetic domain wall with a Dzyaloshinskii-Moriya interaction, and confirm its performance through micromagnetic simulations. Our findings open a new vista for realizing different types of pure spin-wave logic components and finally achieving an energy-efficient and hardware-reprogrammable spin-wave computer.
NASA Astrophysics Data System (ADS)
Busswell, Geoff; Ash, Ellis; Piolle, Jean-Francois; Poulter, David J. S.; Snaith, Helen; Collard, Fabrice; Sheera, Harjit; Pinnock, Simon
2010-12-01
The ESA GlobWave project is a three year initiative, funded by ESA and CNES, to service the needs of satellite wave product users across the globe. Led by Logica UK, with support from CLS, IFREMER, SatOC and NOCS, the project will provide free access to satellite wave data and products in a common format, both historical and in near real time, from various European and American SAR and altimeter missions. Building on the successes of similar projects for Sea Surface Temperature and ocean colour, the project aims to stimulate increased use and analysis of satellite wave products. In addition to common-format satellite data the project will provide comparisons with in situ measurements, interactive data analysis tools and a pilot spatial wave forecast verification scheme for operational forecast production centres. The project will begin operations in January 2010, with direction from regular structured user consultation.
Electromagnetic wave energy converter
NASA Technical Reports Server (NTRS)
Bailey, R. L. (Inventor)
1973-01-01
Electromagnetic wave energy is converted into electric power with an array of mutually insulated electromagnetic wave absorber elements each responsive to an electric field component of the wave as it impinges thereon. Each element includes a portion tapered in the direction of wave propagation to provide a relatively wideband response spectrum. Each element includes an output for deriving a voltage replica of the electric field variations intercepted by it. Adjacent elements are positioned relative to each other so that an electric field subsists between adjacent elements in response to the impinging wave. The electric field results in a voltage difference between adjacent elements that is fed to a rectifier to derive dc output power.
NASA Astrophysics Data System (ADS)
Shugan, I.; Hwung, Hwung-Hweng; Yang, Ray-Yeng
2012-04-01
The problem of wave interaction with current is still a big challenge in physical oceanography. In spite of numerous numbers of papers devoting to the analysis of the phenomenon some very strong effects are still waiting for its clear description. One of the problems here is the Benjamin-Feir instability in the presence of variable current. Modulation instability is one of the most ubiquitous types of instabilities in nature. In modern nonlinear physics, it is considered as a basic process that classifies the qualitative behavior of modulated waves (``envelope waves'') and may initialize the formation of stable entities such as envelope solitons. We theoretically describe the explosion instability of waves on the adverse blocking current and corresponding frequency downshifting. Waves can be blocked only partly and overpass the opposite current barrier at the lower side band resonance frequency. Theoretical results are compared with available experiments.
Leavitt, M.A.; Lutz, I.C.
1958-08-01
An amplifier circuit is described for amplifying sigmals having an alternating current component superimposed upon a direct current component, without loss of any segnnent of the alternating current component. The general circuit arrangement includes a vibrator, two square wave amplifiers, and recombination means. The amplifier input is connected to the vibrating element of the vibrator and is thereby alternately applied to the input of each square wave amplifier. The detailed circuitry of the recombination means constitutes the novelty of the annplifier and consists of a separate, dual triode amplifier coupled to the output of each square wave amplifier with a recombination connection from the plate of one amplifier section to a grid of one section of the other amplifier. The recombination circuit has provisions for correcting distortion caused by overlapping of the two square wave voltages from the square wave amplifiers.
NASA Astrophysics Data System (ADS)
Groenenboom, P. H. L.
The phenomenon of wave propagation is encountered frequently in a variety of engineering disciplines. It has been realized that for a growing number of problems the solution can only be obtained by discretization of the boundary. Advantages of the Boundary Element Method (BEM) over domain-type methods are related to the reduction of the number of space dimensions and of the modelling effort. It is demonstrated how the BEM can be applied to wave propagation phenomena by establishing the fundamental relationships. A numerical solution procedure is also suggested. In connection with a discussion of the retarded potential formulation, it is shown how the wave propagation problem can be cast into a Boundary Integral Formulation (BIF). The wave propagation problem in the BIF can be solved by time-successive evaluation of the boundary integrals. The example of pressure wave propagation following a sodium-water reaction in a Liquid Metal cooled Fast Breeder Reactor steam generator is discussed.
Sculpting Waves (Presentation Recording)
NASA Astrophysics Data System (ADS)
Engheta, Nader
2015-09-01
In electronics controlling and manipulating flow of charged carriers has led to design of numerous functional devices. In photonics, by analogy, this is done through controlling photons and optical waves. However, the challenges and opportunities are different in these two fields. Materials control waves, and as such they can tailor, manipulate, redirect, and scatter electromagnetic waves and photons at will. Recent development in condensed matter physics, nanoscience, and nanotechnology has made it possible to tailor materials with unusual parameters and extreme characteristics and with atomic precision and thickness. One can now construct structures much smaller than the wavelengths of visible light, thus ushering in unprecedented possibilities and novel opportunities for molding fields and waves at the nanoscale with desired functionalities. At such subwavelength scales, sculpting optical fields and waves provides a fertile ground for innovation and discovery. I will discuss some of the exciting opportunities in this area, and forecast some future directions and possibilities.
NASA Astrophysics Data System (ADS)
Yan, Zhenya
2011-11-01
The coupled nonlinear volatility and option pricing model presented recently by Ivancevic is investigated, which generates a leverage effect, i.e., stock volatility is (negatively) correlated to stock returns, and can be regarded as a coupled nonlinear wave alternative of the Black-Scholes option pricing model. In this Letter, we analytically propose vector financial rogue waves of the coupled nonlinear volatility and option pricing model without an embedded w-learning. Moreover, we exhibit their dynamical behaviors for chosen different parameters. The vector financial rogue wave (rogon) solutions may be used to describe the possible physical mechanisms for the rogue wave phenomena and to further excite the possibility of relative researches and potential applications of vector rogue waves in the financial markets and other related fields.
Carvalho, Vanuildo S de; Freire, Hermann
2014-09-15
The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called “hot spots” that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t−t{sup ′} Hubbard model at low hole doping. We compute the Callan–Symanzik RG equation up to two loops describing the flow of the single-particle Green’s function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that–in addition to clearly dominant SDW correlations–an approximate (pseudospin) symmetry relating a short-range incommensurated-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates.
Phase randomization of three-wave interactions in capillary waves.
Punzmann, H; Shats, M G; Xia, H
2009-08-01
We present new experimental results on the transition from coherent-phase to random-phase three-wave interactions in capillary waves under parametric excitation. Above the excitation threshold, coherent wave harmonics spectrally broaden. An increase in the pumping amplitude increases spectral widths of wave harmonics and eventually causes a strong decrease in the degree of the three-wave phase coupling. The results point to the modulation instability of capillary waves, which leads to breaking of continuous waves into ensembles of short-lived wavelets or envelope solitons, as the reason for the phase randomization of three-wave interactions. PMID:19792572
Standing Waves on a Shoestring.
ERIC Educational Resources Information Center
Hendrix, Laura
1992-01-01
Describes the construction of a wave generator used to review the algebraic relationships of wave motion. Students calculate and measure the weight needed to create tension to generate standing waves at the first eight harmonics. (MDH)
NASA Astrophysics Data System (ADS)
Löhner-Böttcher, Johannes
2016-03-01
Context: The dynamic atmosphere of the Sun exhibits a wealth of magnetohydrodynamic (MHD) waves. In the presence of strong magnetic fields, most spectacular and powerful waves evolve in the sunspot atmosphere. Allover the sunspot area, continuously propagating waves generate strong oscillations in spectral intensity and velocity. The most prominent and fascinating phenomena are the 'umbral flashes' and 'running penumbral waves' as seen in the sunspot chromosphere. Their nature and relation have been under intense discussion in the last decades. Aims: Waves are suggested to propagate upward along the magnetic field lines of sunspots. An observational study is performed to prove or disprove the field-guided nature and coupling of the prevalent umbral and penumbral waves. Comprehensive spectroscopic observations at high resolution shall provide new insights into the wave characteristics and distribution across the sunspot atmosphere. Methods: Two prime sunspot observations were carried out with the Dunn Solar Telescope at the National Solar Observatory in New Mexico and with the Vacuum Tower Telescope at the Teide Observatory on Tenerife. The two-dimensional spectroscopic observations were performed with the interferometric spectrometers IBIS and TESOS. Multiple spectral lines are scanned co-temporally to sample the dynamics at the photospheric and chromospheric layers. The time series (1 – 2.5 h) taken at high spatial and temporal resolution are analyzed according to their evolution in spectral intensities and Doppler velocities. A wavelet analysis was used to obtain the wave power and dominating wave periods. A reconstruction of the magnetic field inclination based on sunspot oscillations was developed. Results and conclusions: Sunspot oscillations occur continuously in spectral intensity and velocity. The obtained wave characteristics of umbral flashes and running penumbral waves strongly support the scenario of slow-mode magnetoacoustic wave propagation along
Lucia, L.V.
1982-03-16
A wave action power plant powered by the action of water waves has a drive shaft rotated by a plurality of drive units, each having a lever pivotally mounted on and extending from said shaft and carrying a weight, in the form of a float, which floats on the waves and rocks the lever up and down on the shaft. A ratchet mechanism causes said shaft to be rotated in one direction by the weight of said float after it has been raised by wave and the wave has passed, leaving said float free to move downwardly by gravity and apply its full weight to pull down on the lever and rotate the drive shaft. There being a large number of said drive units so that there are always some of the weights pulling down on their respective levers while other weights are being lifted by waves and thereby causing continuous rotation of the drive shaft in one direction. The said levers are so mounted that they may be easily raised to bring the weights into a position wherein they are readily accessible for cleaning the bottoms thereof to remove any accumulation of barnacles, mollusks and the like. There is also provided means for preventing the weights from colliding with each other as they independently move up and down on the waves.
NASA Astrophysics Data System (ADS)
Ewans, Kevin; Feld, Graham; Jonathan, Philip
2014-09-01
The SAAB REX WaveRadar sensor is widely used for platform-based wave measurement systems by the offshore oil and gas industry. It offers in situ surface elevation wave measurements at relatively low operational costs. Furthermore, there is adequate flexibility in sampling rates, allowing in principle sampling frequencies from 1 to 10 Hz, but with an angular microwave beam width of 10° and an implied ocean surface footprint in the order of metres, significant limitations on the spatial and temporal resolution might be expected. Indeed there are reports that the accuracy of the measurements from wave radars may not be as good as expected. We review the functionality of a WaveRadar using numerical simulations to better understand how WaveRadar estimates compare with known surface elevations. In addition, we review recent field measurements made with a WaveRadar set at the maximum sampling frequency, in the light of the expected functionality and the numerical simulations, and we include inter-comparisons between SAAB radars and buoy measurements for locations in the North Sea.
Undamped electrostatic plasma waves
Valentini, F.; Perrone, D.; Veltri, P.; Califano, F.; Pegoraro, F.; Morrison, P. J.; O'Neil, T. M.
2012-09-15
Electrostatic waves in a collision-free unmagnetized plasma of electrons with fixed ions are investigated for electron equilibrium velocity distribution functions that deviate slightly from Maxwellian. Of interest are undamped waves that are the small amplitude limit of nonlinear excitations, such as electron acoustic waves (EAWs). A deviation consisting of a small plateau, a region with zero velocity derivative over a width that is a very small fraction of the electron thermal speed, is shown to give rise to new undamped modes, which here are named corner modes. The presence of the plateau turns off Landau damping and allows oscillations with phase speeds within the plateau. These undamped waves are obtained in a wide region of the (k,{omega}{sub R}) plane ({omega}{sub R} being the real part of the wave frequency and k the wavenumber), away from the well-known 'thumb curve' for Langmuir waves and EAWs based on the Maxwellian. Results of nonlinear Vlasov-Poisson simulations that corroborate the existence of these modes are described. It is also shown that deviations caused by fattening the tail of the distribution shift roots off of the thumb curve toward lower k-values and chopping the tail shifts them toward higher k-values. In addition, a rule of thumb is obtained for assessing how the existence of a plateau shifts roots off of the thumb curve. Suggestions are made for interpreting experimental observations of electrostatic waves, such as recent ones in nonneutral plasmas.
Kerschensteiner, Daniel
2016-01-01
Spontaneous activity patterns propagate through many parts of the developing nervous system and shape the wiring of emerging circuits. Prior to vision, waves of activity originating in the retina propagate through the lateral geniculate nucleus (LGN) of the thalamus to primary visual cortex (V1). Retinal waves have been shown to instruct the wiring of ganglion cell axons in LGN and of thalamocortical axons in V1 via correlation-based plasticity rules. Across species, retinal waves mature in three stereotypic stages (I–III), in which distinct circuit mechanisms give rise to unique activity patterns that serve specific functions in visual system refinement. Here, I review insights into the patterns, mechanisms, and functions of stage III retinal waves, which rely on glutamatergic signaling. As glutamatergic waves spread across the retina, neighboring ganglion cells with opposite light responses (ON vs. OFF) are activated sequentially. Recent studies identified lateral excitatory networks in the inner retina that generate and propagate glutamatergic waves, and vertical inhibitory networks that desynchronize the activity of ON and OFF cells in the wavefront. Stage III wave activity patterns may help segregate axons of ON and OFF ganglion cells in the LGN, and could contribute to the emergence of orientation selectivity in V1. PMID:27242446
NASA Astrophysics Data System (ADS)
Chen, P. F.
2016-02-01
After the Solar and Heliospheric Observatory (SOHO) was launched in 1996, the aboard Extreme Ultraviolet Imaging Telescope (EIT) observed a global coronal wave phenomenon, which was initially named ``EIT wave" after the telescope. The bright fronts are immediately followed by expanding dimmings. It has been shown that the brightenings and dimmings are mainly due to plasma density increase and depletion, respectively. Such a spectacular phenomenon sparked long-lasting interest and debates. The debates were concentrated on two topics, one is about the driving source, and the other is about the nature of this wavelike phenomenon. The controversies are most probably because there may exist two types of large-scale coronal waves that were not well resolved before the Solar Dynamics Observatory (SDO) was launched: one is a piston-driven shock wave straddling over the erupting coronal mass ejection (CME), and the other is an apparently propagating front, which may correspond to the CME frontal loop. Such a two-wave paradigm was proposed more than 13 years ago, and now is being recognized by more and more colleagues. In this paper, we review how various controversies can be resolved in the two-wave framework and how important it is to have two different names for the two types of coronal waves.
Stress wave focusing transducers
Visuri, S.R., LLNL
1998-05-15
Conversion of laser radiation to mechanical energy is the fundamental process behind many medical laser procedures, particularly those involving tissue destruction and removal. Stress waves can be generated with laser radiation in several ways: creation of a plasma and subsequent launch of a shock wave, thermoelastic expansion of the target tissue, vapor bubble collapse, and ablation recoil. Thermoelastic generation of stress waves generally requires short laser pulse durations and high energy density. Thermoelastic stress waves can be formed when the laser pulse duration is shorter than the acoustic transit time of the material: {tau}{sub c} = d/c{sub s} where d = absorption depth or spot diameter, whichever is smaller, and c{sub s} = sound speed in the material. The stress wave due to thermoelastic expansion travels at the sound speed (approximately 1500 m/s in tissue) and leaves the site of irradiation well before subsequent thermal events can be initiated. These stress waves, often evolving into shock waves, can be used to disrupt tissue. Shock waves are used in ophthalmology to perform intraocular microsurgery and photodisruptive procedures as well as in lithotripsy to fragment stones. We have explored a variety of transducers that can efficiently convert optical to mechanical energy. One such class of transducers allows a shock wave to be focused within a material such that the stress magnitude can be greatly increased compared to conventional geometries. Some transducer tips could be made to operate regardless of the absorption properties of the ambient media. The size and nature of the devices enable easy delivery, potentially minimally-invasive procedures, and precise tissue- targeting while limiting thermal loading. The transducer tips may have applications in lithotripsy, ophthalmology, drug delivery, and cardiology.
NASA Astrophysics Data System (ADS)
Gurnett, Donald
2008-11-01
Although low-frequency radio waves of extra-terrestrial origin were known over a century ago, it wasn't until the beginning of the space era fifty years ago that the origin of these waves could be adequately investigated. Since then spacecraft-borne instruments have shown that space plasmas exhibit an almost bewildering variety of wave phenomena, sometimes referred to as the plasma wave zoo. In this talk I will focus on two types of waves that occur in the magnetospheres of the strongly magnetized planets. They are whistler mode emissions and cyclotron maser radiation. Whistler mode emissions are generated in the now famous plasma wave mode known as the whistler mode, and cyclotron maser radiation is emitted mainly in the right-hand polarized free space mode. Both involve a cyclotron resonant interaction and require a perpendicular anisotropy to achieve wave growth. However, the origin of the anisotropy is different in the two cases. Whistler mode emissions occur in planetary radiation belts and are driven by the loss-cone anisotropy imposed by the planet. The resulting waves play a major role in the scattering and loss of radiation belt electrons. In contrast, the cyclotron maser radiation is generated in the auroral regions where parallel electric fields accelerate down-going electrons to high energies. The wave growth is driven by the shell distribution that arises from a combination of the parallel electric field and the magnetic mirror force. The resulting radiation is extremely intense and can be detected at great distances as an escaping radio emission. Both the whistler mode emissions and the cyclotron maser radiation display an amazing amount of fine structure. This structure is thought to be due to nonlinear trapping of the resonant electrons. The exact nonlinear mechanisms involved are still a topic of current study.
Progress in gravitational wave detection
NASA Astrophysics Data System (ADS)
Cheng, Jing-Quan; Yang, De-Hua
2005-09-01
General theory of Einstein's relativity predicts the existence of gravitational wave when mass is accelerated. However, no material has direct effect when the gravitational wave passes. Therefore, gravitational wave can only be detected indirectly. The effort in gravitational wave detection was started in the 60s of last century by using a huge cylinder of aluminum. This paper introduced all the relevant projects in the gravitational wave detection. These projects include Weber's bar, Laser interferometer Gravitational wave Detector (LGD), Laser Interferometer Gravitational wave Observatory (LIGO), GEO600, VIRGO, TAMA300, Advanced LIGO, Large scale Cryogenic Gravitational wave Telescope (LCGO), and Laser Interferometer Space Antenna (LISA).
Atmospheric waves and the ionosphere.
NASA Technical Reports Server (NTRS)
Beer, T.
1972-01-01
A review of evidence supporting the existence of atmospheric waves is presented, and a simple, theoretical approach for describing them is shown. Suggestions for gravity wave sources include equatorial and auroral electrojet, auroral and polar substorm heating, atmospheric jet streams, and large oceanic tides. There are reviewed previous studies dealing with the interaction between ionization and atmospheric waves believed to exist at ionospheric heights. These waves include acoustic waves, evanescent waves, and internal atmospheric gravity waves. It is explained that mode analysis, often employed when an increased number of layers is used for a more complete profile, is inapplicable for waves very close to a source.
Wave-wave interactions in solar type III radio bursts
Thejappa, G.; MacDowall, R. J.
2014-02-11
The high time resolution observations from the STEREO/WAVES experiment show that in type III radio bursts, the Langmuir waves often occur as localized magnetic field aligned coherent wave packets with durations of a few ms and with peak intensities well exceeding the strong turbulence thresholds. Some of these wave packets show spectral signatures of beam-resonant Langmuir waves, down- and up-shifted sidebands, and ion sound waves, with frequencies, wave numbers, and tricoherences satisfying the resonance conditions of the oscillating two stream instability (four wave interaction). The spectra of a few of these wave packets also contain peaks at f{sub pe}, 2f{sub pe} and 3 f{sub pe} (f{sub pe} is the electron plasma frequency), with frequencies, wave numbers and bicoherences (computed using the wavelet based bispectral analysis techniques) satisfying the resonance conditions of three wave interactions: (1) excitation of second harmonic electromagnetic waves as a result of coalescence of two oppositely propagating Langmuir waves, and (2) excitation of third harmonic electromagnetic waves as a result of coalescence of Langmuir waves with second harmonic electromagnetic waves. The implication of these findings is that the strong turbulence processes play major roles in beam stabilization as well as conversion of Langmuir waves into escaping radiation in type III radio bursts.
NASA Astrophysics Data System (ADS)
Zetie, K. P.
2015-05-01
There are many examples on the internet of videos of ‘pendulum wave machines’ and how to make them (for example, www.instructables.com/id/Wave-Pendulum/). The machine is simply a set of pendula of different lengths which, when viewed end on, produce wave-like patterns from the positions of the bobs. These patterns change with time, with new patterns emerging as the bobs change phase. In this article, the physics of the machine is explored and explained, along with tips on how to build such a device.
Acoustic and electromagnetic waves
NASA Astrophysics Data System (ADS)
Jones, Douglas Samuel
Theoretical models of EM and acoustic wave propagation are presented in an introductory text intended for intermediate-level science and engineering students. Chapters are devoted to the mathematical representation of acoustic and EM fields, the special theory of relativity, radiation, resonators, waveguide theory, refraction, surface waves, scattering by smooth objects, diffraction by edges, and transient waves. The mathematical tools required for the analysis (Bessel, Legendre, Mathieu, parabolic-cylinder, and spheroidal functions; tensor calculus; and the asymptotic evaluation of integrals) are covered in appendices.
Lattice Waves, Spin Waves, and Neutron Scattering
DOE R&D Accomplishments Database
Brockhouse, Bertram N.
1962-03-01
Use of neutron inelastic scattering to study the forces between atoms in solids is treated. One-phonon processes and lattice vibrations are discussed, and experiments that verified the existence of the quantum of lattice vibrations, the phonon, are reviewed. Dispersion curves, phonon frequencies and absorption, and models for dispersion calculations are discussed. Experiments on the crystal dynamics of metals are examined. Dispersion curves are presented and analyzed; theory of lattice dynamics is considered; effects of Fermi surfaces on dispersion curves; electron-phonon interactions, electronic structure influence on lattice vibrations, and phonon lifetimes are explored. The dispersion relation of spin waves in crystals and experiments in which dispersion curves for spin waves in Co-Fe alloy and magnons in magnetite were obtained and the reality of the magnon was demonstrated are discussed. (D.C.W)
Resonance wave pumping with surface waves
NASA Astrophysics Data System (ADS)
Carmigniani, Remi; Gharib, Morteza; Violeau, Damien; Caltech-ENPC Collaboration
2015-11-01
The valveless impedance pump enables the production or amplification of a flow without the use of integrated mobile parts, thus delaying possible failures. It is usually composed of fluid-filled flexible tubing, closed by solid tubes. The flexible tube is pinched at an off-centered position relative to the tube ends. This generates a complex wave dynamic that results in a pumping phenomenon. It has been previously reported that pinching at intrinsic resonance frequencies of the system results in a strong pulsating flow. A case of a free surface wave pump is investigated. The resonance wave pump is composed of a rectangular tank with a submerged plate separating the water into a free surface and a recirculation rectangular section connected through two openings at each end of the tank. A paddle placed at an off-center position above the submerged plate is controlled in a heaving motion with different frequencies and amplitudes. Similar to the case of valveless impedance pump, we observed that near resonance frequencies strong pulsating flow is generated with almost no oscillations. A linear theory is developed to pseudo-analytically evaluate these frequencies. In addition, larger scale applications were simulated using Smoothed Particle Hydrodynamic codes.
Dark- and bright-rogue-wave solutions for media with long-wave-short-wave resonance.
Chen, Shihua; Grelu, Philippe; Soto-Crespo, J M
2014-01-01
Exact explicit rogue-wave solutions of intricate structures are presented for the long-wave-short-wave resonance equation. These vector parametric solutions feature coupled dark- and bright-field counterparts of the Peregrine soliton. Numerical simulations show the robustness of dark and bright rogue waves in spite of the onset of modulational instability. Dark fields originate from the complex interplay between anomalous dispersion and the nonlinearity driven by the coupled long wave. This unusual mechanism, not available in scalar nonlinear wave equation models, can provide a route to the experimental realization of dark rogue waves in, for instance, negative index media or with capillary-gravity waves. PMID:24580164
Weinstein, Alla
2011-11-01
Presentation from the 2011 Water Peer Review includes in which principal investigator Alla Weinstein discusses project progress in development of a floating offshore wind structure - the WindFloat - and incorporation therin of a Spherical Wave Energy Device.
ERIC Educational Resources Information Center
Fisher, Arthur
1983-01-01
Physicists and engineers advance the state of several arts in the design of gravitational-wave detection equipment. Provides background information and discusses the equipment (including laser interferometer), its use, and results of several experimental studies. (JN)
... heat has caused more deaths than all other weather events, including floods. A heat wave is a ... care for heat- related emergencies … ❏ Listen to local weather forecasts and stay aware of upcoming temperature changes. ❏ ...
NASA Astrophysics Data System (ADS)
seyithocuk; jjeherrera; eltodesukane; GrahamRounce; rloldershaw; Beaker, Dr; Sandhu, G. S.; Ophiuchi
2016-03-01
In reply to the news article on the LIGO collaboration's groundbreaking detection of gravitational waves, first predicted by Einstein 100 years ago, from two black holes colliding (pp5, 6-7 and http://ow.ly/Ylsyt).
Observation of Gravitational Waves
NASA Astrophysics Data System (ADS)
Gonzalez, Gabriela
2016-06-01
On September 14 2015, the two LIGO gravitational wave detectors in Hanford, Washington and Livingston, Louisiana registered a nearly simultaneous signal with time-frequency properties consistent with gravitational-wave emission by the merger of two massive compact objects. Further analysis of the signals by the LIGO Scientific Collaboration and Virgo Collaboration revealed that the gravitational waves detected by LIGO came from the merger of a binary black hole (BBH) system approximately 420 Mpc distant (z=0.09) with constituent masses of 36 and 29 M_sun. I will describe the details of the observation, the status of ground-based interferometric detectors, and prospects for future observations in the new era of gravitational wave astronomy.
Hietala, V.M.; Vawter, G.A.
1993-12-14
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size. 4 figures.
Hietala, Vincent M.; Vawter, Gregory A.
1993-01-01
The traveling-wave photodetector of the present invention combines an absorptive optical waveguide and an electrical transmission line, in which optical absorption in the waveguide results in a photocurrent at the electrodes of the electrical transmission line. The optical waveguide and electrical transmission line of the electrically distributed traveling-wave photodetector are designed to achieve matched velocities between the light in the optical waveguide and electrical signal generated on the transmission line. This velocity synchronization provides the traveling-wave photodetector with a large electrical bandwidth and a high quantum efficiency, because of the effective extended volume for optical absorption. The traveling-wave photodetector also provides large power dissipation, because of its large physical size.
Sound wave transmission (image)
When sounds waves reach the ear, they are translated into nerve impulses. These impulses then travel to the brain where they are interpreted by the brain as sound. The hearing mechanisms within the inner ear, can ...
Turbulence generation by waves
Kaftori, D.; Nan, X.S.; Banerjee, S.
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Energy Science and Technology Software Center (ESTSC)
2007-01-08
WPP is a massively parallel, 3D, C++, finite-difference elastodynamic wave propagation code. Typical applications for wave propagation with WPP include: evaluation of seismic event scenarios and damage from earthquakes, non-destructive evaluation of materials, underground facility detection, oil and gas exploration, predicting the electro-magnetic fields in accelerators, and acoustic noise generation. For more information, see Users Manual [1].
Sound Waves Levitate Substrates
NASA Technical Reports Server (NTRS)
Lee, M. C.; Wang, T. G.
1982-01-01
System recently tested uses acoustic waves to levitate liquid drops, millimeter-sized glass microballoons, and other objects for coating by vapor deposition or capillary attraction. Cylindrical contactless coating/handling facility employs a cylindrical acoustic focusing radiator and a tapered reflector to generate a specially-shaped standing wave pattern. Article to be processed is captured by the acoustic force field under the reflector and moves as reflector is moved to different work stations.
Périnet, Nicolas; Falcón, Claudio; Chergui, Jalel; Juric, Damir; Shin, Seungwon
2016-06-01
We report on the numerical and theoretical study of the subcritical bifurcation of parametrically amplified waves appearing at the interface between two immiscible incompressible fluids when the layer of the lower fluid is very shallow. As a critical control parameter is surpassed, small amplitude surface waves bifurcate subcritically toward highly nonlinear ones with twice their amplitude. We relate this hysteresis with the change of shear stress using a simple stress balance, in agreement with numerical results. PMID:27415365
NASA Astrophysics Data System (ADS)
Gemmrich, J.; Farmer, D.
2003-04-01
Breaking surface waves are believed to provide a major pathway for the energy input from the atmosphere to the ocean and are a source of enhanced turbulent kinetic energy levels in the near-surface layer. Increased turbulence levels relate to enhanced air-sea exchange processes. The ocean surface is a complex system with a wide range of relevant scales. We use direct measurement of the small-scale velocity field as a first step to evaluate near-surface turbulence. At wind speed up to 14 m/s, velocity profiles were obtained with pulse-to-pulse coherent acoustic Doppler profilers. Based on wavenumber spectra calculated with the empirical mode decomposition, dissipation of turbulent kinetic energy at ~1m beneath the free surface and 1 Hz sampling rate is estimated. In addition, bubble size distributions were obtained from acoustic resonator measurements and whitecap occurrence was monitored with video cameras. High turbulence levels with dissipation rates more than four orders larger than the background dissipation are linked to wave breaking. The decay and depth-dependence of the wave-induced turbulence are examined and implications for turbulence models are discussed. In individual breaking waves, the onset of enhanced dissipation occurs up to a quarter wave period prior to the air entrainment. Magnitude and occurrence of the pre-breaking turbulence are consistent with wave-turbulence interaction in a rotational wave field. The detailed structure of the turbulence and bubble field associated with breaking waves will be presented. Implications for air-sea exchange processes will be discussed.
NASA Astrophysics Data System (ADS)
López Ariste, A.; Centeno, R.; Khomenko, E.
2016-06-01
Context. Waves in the magnetized solar atmosphere are one of the favourite means of transferring and depositing energy into the solar corona. The study of waves brings information not just on the dynamics of the magnetized plasma, but also on the possible ways in which the corona is heated. Aims: The identification and analysis of the phase singularities or dislocations provide us with a complementary approach to the magnetoacoustic and Aflvén waves propagating in the solar atmosphere. They allow us to identify individual wave modes, shedding light on the probability of excitation or the nature of the triggering mechanism. Methods: We use a time series of Doppler shifts measured in two spectral lines, filtered around the three-minute period region. The data show a propagating magnetoacoustic slow mode with several dislocations and, in particular, a vortex line. We study under what conditions the different wave modes propagating in the umbra can generate the observed dislocations. Results: The observed dislocations can be fully interpreted as a sequence of sausage and kink modes excited sequentially on average during 15 min. Kink and sausage modes appear to be excited independently and sequentially. The transition from one to the other lasts less than three minutes. During the transition we observe and model the appearance of superoscillations inducing large phase gradients and phase mixing. Conclusions: The analysis of the observed wave dislocations leads us to the identification of the propagating wave modes in umbrae. The identification in the data of superoscillatory regions during the transition from one mode to the other may be an important indicator of the location of wave dissipation.
Zhokhov, P A; Zheltikov, A M
2013-05-01
Shock-wave formation is a generic scenario of wave dynamics known in nonlinear acoustics, fluid dynamics, astrophysics, seismology, and detonation physics. Here, we show that, in nonlinear optics, remarkably short, attosecond shock transients can be generated through a strongly coupled spatial and temporal dynamics of ultrashort light pulses, suggesting a pulse self-compression scenario whereby multigigawatt attosecond optical waveforms can be synthesized. PMID:23683197
The wave of the future - Searching for gravity waves
NASA Astrophysics Data System (ADS)
Goldsmith, Donald
1991-04-01
Research on gravity waves conducted by such scientists as Gamov, Wheeler, Weber and Zel'dovich is discussed. Particular attention is given to current trends in the theoretical analysis of gravity waves carried out by theorists Kip Thorne and Leonid Grishchuk. The problems discussed include the search for gravity waves; calculation of the types of gravity waves; the possibility of detecting gravity waves from localized sources, e.g., from the collision of two black holes in a distant galaxy or the collapse of a star, through the Laser Interferometer Gravitational Wave Observatory; and detection primordial gravity waves from the big bang.
NASA Astrophysics Data System (ADS)
Dehandschoewercker, Eline; Quere, David; Clanet, Christophe
2014-11-01
Surfing is a free surface sport in which the athlete rides a wave standing on a board. However, any object plunged into the water or put on its surface is not always captured by an approaching wave, just like the classic example of a fisching float. So, a particle can be captured or not by a wave. Two regimes are defined: surf (captured) and drift (not captured). We focus on the question of the transition between these two regimes. Here we address the question with a magnetic wave. We have developed an experimental setup which allows the control of all relevant physical parameters. Liquid oxygen, which is paramagnetic and undergoes Leidenfrost effect, can be used to ensure magnetic and frictionless particles. A permanent magnet in translatory movement allows us to create a definite magnetic wave. We discuss the motion of oxygen drops deposited on an smooth and horizontal surface above an approaching magnet. First we show the existence of a critical speed below which drops are captured and determine how it depends on the velocity and intensity of the magnetic wave. Then we experimentally investigate the parameters that would affect the movement of drops in each regime. Finally, models have been developed to interpret magnetic drops motion and guarantee an efficient control.
NASA Technical Reports Server (NTRS)
Kory, Carol L.
1998-01-01
The traveling-wave tube (TWT) is a vacuum device invented in the early 1940's used for amplification at microwave frequencies. Amplification is attained by surrendering kinetic energy from an electron beam to a radio frequency (RF) electromagnetic wave. The demand for vacuum devices has been decreased largely by the advent of solid-state devices. However, although solid state devices have replaced vacuum devices in many areas, there are still many applications such as radar, electronic countermeasures and satellite communications, that require operating characteristics such as high power (Watts to Megawatts), high frequency (below 1 GHz to over 100 GHz) and large bandwidth that only vacuum devices can provide. Vacuum devices are also deemed irreplaceable in the music industry where musicians treasure their tube-based amplifiers claiming that the solid-state and digital counterparts could never provide the same "warmth" (3). The term traveling-wave tube includes both fast-wave and slow-wave devices. This article will concentrate on slow-wave devices as the vast majority of TWTs in operation fall into this category.
NASA Astrophysics Data System (ADS)
Conklin, John
2016-03-01
With the expected direct detection of gravitational waves by Advanced LIGO and pulsar timing arrays in the near future, and with the recent launch of LISA Pathfinder this can arguably be called the decade of gravitational waves. Low frequency gravitational waves in the mHz range, which can only be observed from space, provide the richest science and complement high frequency observatories on the ground. A space-based observatory will improve our understanding of the formation and growth of massive black holes, create a census of compact binary systems in the Milky Way, test general relativity in extreme conditions, and enable searches for new physics. LISA, by far the most mature concept for detecting gravitational waves from space, has consistently ranked among the nation's top priority large science missions. In 2013, ESA selected the science theme ``The Gravitational Universe'' for its third large mission, L3, under the Cosmic Visions Program, with a planned launch date of 2034. NASA has decided to join with ESA on the L3 mission as a junior partner and has recently assembled a study team to provide advice on how NASA might contribute to the European-led mission. This talk will describe these efforts and the activities of the Gravitational Wave Science Interest Group and the L3 Study Team, which will lead to the first space-based gravitational wave observatory.
NASA Astrophysics Data System (ADS)
Kağan Temiz, Burak; Yavuz, Ahmet
2015-08-01
This study was done to develop a simple and inexpensive wave driver that can be used in experiments on string waves. The wave driver was made using a battery-operated toy car, and the apparatus can be used to produce string waves at a fixed frequency. The working principle of the apparatus is as follows: shortly after the car is turned on, the wheel starts to turn at a constant angular speed. A rod that is fixed on the wheel turns at the same constant angular speed, too. A tight string that the wave will be created on is placed at a distance where the rod can touch the string. During each rotation of the wheel, the rod vibrates the string up and down. The vibration frequency of this rod equals the wheel’s rotation frequency, and this frequency value can be measured easily with a small magnet and a bicycle speedometer. In this way, the frequency of the waves formed in the rope can also be measured.
Magnetosphere-ionosphere waves
NASA Astrophysics Data System (ADS)
Russell, A. J. B.; Wright, A. N.
2012-01-01
Self-consistent electrodynamic coupling of the ionosphere and magnetosphere produces waves with clearly defined properties, described here for the first time. Large scale (ideal) disturbances to the equilibrium, for which electron inertia is unimportant, move in the direction of the electric field at a characteristic speed. This may be as fast as several hundred meters per second or approximately half the E × B drift speed. In contrast, narrow scale (strongly inertial) waves are nearly stationary and oscillate at a specific frequency. Estimates of this frequency suggest periods from several tenths of a second to several minutes may be typical. Both the advection speed and frequency of oscillation are derived for a simple model and depend on a combination of ionospheric and magnetospheric parameters. Advection of large scale waves is nonlinear: troughs in E-region number density move faster than crests and this causes waves to break on their trailing edge. Wavebreaking is a very efficient mechanism for producing narrow (inertial) scale waves in the coupled system, readily accessing scales of a few hundred meters in just a few minutes. All magnetosphere-ionosphere waves are damped by recombination in the E-region, suggesting that they are to be best observed at night and in regions of low ionospheric plasma density. Links with observations, previous numerical studies and ionospheric feedback instability are discussed, and we propose key features of experiments that would test the new theory.
Ocean wave electric generators
Rosenberg, H.R.
1986-02-04
This patent describes an apparatus for generating electricity from ocean waves. It consists of: 1.) a hollow buoyant duck positioned in the path of waves including a core about the center axis of which the duck rotates, a lower chamber portion having liquid therein and an upper chamber portion having air therein. The air is alternately compressed and expanded by the liquid in the chamber during the rotational motion of the duck caused by waves. A turbine mounted in the upper portion of the duck is driven by the compressed and expanded air. A generator is coupled to the turbine and operated to produce electrical energy and an air bulb; 2.) a spine having a transverse axial shaft anchoring the spine to the ocean floor. The upper portion of the spine engages the duck to maintain the duck in position. The spine has a curved configuration to concentrate and direct wave energy. The spine configuration acts as a scoop to increase the height of wave peaks and as a foil to increase the depth of wave troughs.
Ultrasonic Lamb wave tomography
NASA Astrophysics Data System (ADS)
Leonard, Kevin R.; Malyarenko, Eugene V.; Hinders, Mark K.
2002-12-01
Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our recent work using ultrasonic Lamb wave tomography to address this pressing NDE technology need. Lamb waves are ultrasonic guided waves, which allow large sections of aircraft structures to be rapidly inspected for structural flaws such as disbonds, corrosion and delaminations. Because the velocity of Lamb waves depends on thickness, for example, the travel times of the fundamental Lamb modes can be converted into a thickness map of the inspection region. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. Our work focuses on tomographic reconstruction to produce quantitative maps that can be easily interpreted by technicians or fed directly into structural integrity and lifetime prediction codes. Laboratory measurements discussed here demonstrate that Lamb wave tomography using a square perimeter array of transducers with algebraic reconstruction tomography is appropriate for detecting flaws in aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this paper.
NASA Astrophysics Data System (ADS)
Cavaleri, Luigi; Bertotti, Luciana; Bidlot, Jean-Raymond
2015-05-01
We consider the effect of rain on wind wave generation and dissipation. Rain falling on a wavy surface may have a marked tendency to dampen the shorter waves in the tail of the spectrum, the related range increasing with the rain rate. Historical and sailors' reports suggest that this leads to calmer wave conditions, certainly so for the action of breakers. We have explored this situation using a fully coupled meteorological-wave model system, adding an artificial rain rate-dependent damping of the tail. Contrarily to direct marine experience, the experimental results show higher wind speeds and wave heights. A solid indication of the truth is achieved with the direct comparison between operational model (where rain effect is ignored) and measured data. These strongly support the sailors' claims of less severe wave conditions under heavy rain. This leads to a keen analysis of the overall process, in particular on the role of the tail of the spectrum in modulating the wind input and the white-capping, and how this is presently modeled in operational activity. We suggest that some revision is due and that the relationship between white-capping and generation by wind is deeper and more implicative than presently generally assumed.
Rain waves-wind waves interaction application to scatterometry
NASA Technical Reports Server (NTRS)
Kharif, C.; Giovanangeli, J. P.; Bliven, L.
1989-01-01
Modulation of a rain wave pattern by longer waves has been studied. An analytical model taking into account capillarity effects and obliquity of short waves has been developed. Modulation rates in wave number and amplitude have been computed. Experiments were carried out in a wave tank. First results agree with theoretical models, but higher values of modulation rates are measured. These results could be taken into account for understanding the radar response from the sea surface during rain.
Electron-spin dynamics in elliptically polarized light waves
NASA Astrophysics Data System (ADS)
Bauke, Heiko; Ahrens, Sven; Grobe, Rainer
2014-11-01
We investigate the coupling of the spin angular momentum of light beams with elliptical polarization to the spin degree of freedom of free electrons. It is shown that this coupling, which is of similar origin as the well-known spin-orbit coupling, can lead to spin precession. The spin-precession frequency is proportional to the product of the laser field's intensity and its spin density. The electron-spin dynamics is analyzed by employing exact numerical methods as well as time-dependent perturbation theory based on the fully relativistic Dirac equation and on the nonrelativistic Pauli equation that is amended by a relativistic correction that accounts for the light's spin density.
Various Boussinesq solitary wave solutions
Yates, G.T.
1995-12-31
The generalized Boussinesq (gB) equations have been used to model nonlinear wave evolution over variable topography and wave interactions with structures. Like the KdV equation, the gB equations support a solitary wave solution which propagates without changing shape, and this solitary wave is often used as a primary test case for numerical studies of nonlinear waves using either the gB or other model equations. Nine different approximate solutions of the generalized Boussinesq equations are presented with simple closed form expressions for the wave elevation and wave speed. Each approximates the free propagation of a single solitary wave, and eight of these solutions are newly obtained. The author compares these solutions with the well known KdV solution, Rayleigh`s solution, Laitone`s higher order solution, and ``exact`` numerical integration of the gB equations. Existing experimental data on solitary wave shape and wave speed are compared with these models.
NASA Astrophysics Data System (ADS)
Siu Tapia, A. L.; Blanco-Cano, X.; Kajdic, P.; Aguilar-Rodriguez, E.; Russell, C. T.; Jian, L. K.; Luhmann, J. G.
2013-05-01
Complex events are formed by two or more large-scale structures which interact in the solar wind. Typical cases are interactions of: (i) a magnetic cloud/interplanetary coronal mass ejection (MC/ICME) with another MC/ICME transient; (ii) a MC/ICME embedded within a stream interaction region (SIR); and (iii) a MC/ICME followed by a fast stream. Using data from the STEREO mission during the years 2007-2011 we found 17 ICMEs forming complex events with an associated shock wave. All the ICMEs included in this study showed a smooth rotation of the magnetic field and low proton beta plasma, and were classified as MCs. We use magnetic field and plasma data to study the waves observed within these MCs. To determine wave characteristics we perform Power Spectra and Minimum Variance Analysis. We also analyze 10 MCs driving shocks which were not associated with complex events. We compare wave characteristics within the Magnetic Clouds forming Complex Events (MCCE), with those waves observed within the Magnetic Clouds that were isolated (IMC), i. e., not associated with complex events. Transverse and almost parallel propagating ion cyclotron waves were observed within both, MCCE and IMC. Compressive mirror mode waves were observed only within MCCE. Both modes can grow due to temperature anisotropy. Most of the mirror mode events found within MCCE are observed in regions with enhanced plasma beta. This is in agreement with kinetic theory, which predicts that mirror mode growth is favored by high plasma beta values. It is possible that the observed enhancements in plasma beta are due to compressions inside MCCE.
NASA Astrophysics Data System (ADS)
Finn, Lee Samuel
2012-03-01
If two black holes collide in a vacuum, can they be observed? Until recently, the answer would have to be "no." After all, how would we observe them? Black holes are "naked" mass: pure mass, simple mass, mass devoid of any matter whose interactions might lead to the emission of photons or neutrinos, or any electromagnetic fields that might accelerate cosmic rays or leave some other signature that we could observe in our most sensitive astronomical instruments. Still, black holes do have mass. As such, they interact—like all mass—gravitationally. And the influence of gravity, like all influences, propagates no faster than that universal speed we first came to know as the speed of light. The effort to detect that propagating influence, which we term as gravitational radiation or gravitational waves, was initiated just over 50 years ago with the pioneering work of Joe Weber [1] and has been the object of increasingly intense experimental effort ever since. Have we, as yet, detected gravitational waves? The answer is still "no." Nevertheless, the accumulation of the experimental efforts begun fifty years ago has brought us to the point where we can confidently say that gravitational waves will soon be detected and, with that first detection, the era of gravitational wave astronomy—the observational use of gravitational waves, emitted by heavenly bodies—will begin. Data analysis for gravitational wave astronomy is, today, in its infancy and its practitioners have much to learn from allied fields, including machine learning. Machine learning tools and techniques have not yet been applied in any extensive or substantial way to the study or analysis of gravitational wave data. It is fair to say that this owes principally to the fields relative youth and not to any intrinsic unsuitability of machine learning tools to the analysis problems the field faces. Indeed, the nature of many of the analysis problems faced by the field today cry-out for the application of
NASA Astrophysics Data System (ADS)
Yuan, Tao
Sensing and imaging using Terahertz (THz) radiation has attracted more and more interest in the last two decades thanks to the abundant material 'finger prints' in the THz frequency range. The low photon energy also makes THz radiation an attractive tool for nondestructive evaluation of materials and devices, biomedical applications, security checks and explosive screening. Due to the long wavelength, the far-field THz wave optical systems have relatively low spatial resolution. This physical limitation confines THz wave sensing and imaging to mostly macro-size samples. To investigate local material properties or micro-size structures and devices, near-field technology has to be employed. In this dissertation, the Electro-Optical THz wave emission microscope is investigated. The basic principle is to focus the femtosecond laser to a tight spot on a thin THz emitter layer to produce a THz wave source with a similar size as the focus spot. The apparatus provides a method for placing a THz source with sub-wavelength dimension in the near-field range of the investigated sample. Spatial resolution to the order of one tenth of the THz wavelength is demonstrated by this method. The properties of some widely used THz wave emission materials under tight focused pump light are studied. As an important branch of THz time domain spectroscopy (THz-TDS), THz wave emission spectroscopy has been widely used as a tool to investigate the material physics, such as energy band structure, carrier dynamics, material nonlinear properties and dynamics. As the main work of this dissertation, we propose to combine the THz wave emission spectroscopy with scanning probe microscopy (SPM) to build a tip-assisted THz wave emission microscope (TATEM), which is a valuable extension to current SPM science and technology. Illuminated by a femtosecond laser, the biased SPM tip forms a THz wave source inside the sample beneath the tip. The source size is proportional to the apex size of the tip so
Wave interaction in relativistic harmonic gyro-traveling-wave devices
Ngogang, R.; Nusinovich, G. S.; Antonsen, T. M. Jr.; Granatstein, V. L.
2006-05-15
In gyro-traveling-wave devices, several waves can be excited at different cyclotron harmonics simultaneously. This paper analyzes the interaction between three waves synchronous with gyrating electrons at different cyclotron harmonics in two relativistic gyro-amplifier configurations; viz., gyro-traveling-wave tubes and gyrotwystrons. Two types of nonlinear interactions are considered: (a) excitation of two waves at cyclotron harmonics by a wave excited at the fundamental resonance, and (b) excitation of a wave at the fundamental resonance and another wave at the third harmonic by a wave excited at the second cyclotron harmonic. The effect of the overlapping of electron cyclotron resonances on the performance of relativistic gyrodevices is investigated as well.
Hurricane, O A; Hammer, J H
2005-10-11
Radiation driven heat waves (Marshak Waves) are ubiquitous in astrophysics and terrestrial laser driven high energy density plasma physics (HEDP) experiments. Generally, the equations describing Marshak waves are so nonlinear, that solutions involving more than one spatial dimension require simulation. However, in this paper we show how one may analytically solve the problem of the two-dimensional nonlinear evolution of a Marshak wave, bounded by lossy walls, using an asymptotic expansion in a parameter related to the wall albedo and a simplification of the heat front equation of motion. Three parameters determine the nonlinear evolution, a modified Markshak diffusion constant, a smallness parameter related to the wall albedo, and the spacing of the walls. The final nonlinear solution shows that the Marshak wave will be both slowed and bent by the non-ideal boundary. In the limit of a perfect boundary, the solution recovers the original diffusion-like solution of Marshak. The analytic solution will be compared to a limited set of simulation results and experimental data.
NASA Astrophysics Data System (ADS)
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-02-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.
Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan
2016-01-01
Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099