Ferroelectric polarization flop in a frustrated magnet MnWO4_4 induced by magnetic fields

The relationship between magnetic order and ferroelectric properties has been investigated for MnWO$_4$ with long-wavelength magnetic structure. Spontaneous electric polarization is observed in an elliptical spiral spin phase. The magnetic-field dependence of electric polarization indicates that the noncollinear spin configuration plays a key role for the appearance of ferroelectric phase. An electric polarization flop from the b direction to the a direction has been observed when a magnetic field above 10T is applied along the b axis. This result demonstrates that an electric polarization flop can be induced by a magnetic field in a simple system without rare-earth f-moments.Comment: 9 pages, 4 figure

Solution of reduced equations derived with singular perturbation methods

For singular perturbation problems in dynamical systems, various appropriate singular perturbation methods have been proposed to eliminate secular terms appearing in the naive expansion. For example, the method of multiple time scales, the normal form method, center manifold theory, the renormalization group method are well known. In this paper, it is shown that all of the solutions of the reduced equations constructed with those methods are exactly equal to sum of the most divergent secular terms appearing in the naive expansion. For the proof, a method to construct a perturbation solution which differs from the conventional one is presented, where we make use of the theory of Lie symmetry group.Comment: To be published in Phys. Rev.

On the origin of multiple ordered phases in PrFe4P12

The nature of multiple electronic orders in skutterudite PrFe_4P_{12} is discussed on the basis of a model with antiferro-quadrupole (AFQ) interaction of \Gamma_3 symmetry. The high-field phase can be reproduced qualitatively provided (i) ferro-type interactions are introduced between the dipoles as well as between the octupoles of localized f-electrons, and (ii) separation is vanishingly small between the \Gamma_1-\Gamma_4^{(1)} crystalline electric field (CEF) levels. The high-field phase can have either the same ordering vector q=(1,0,0) as in the low-field phase, or a different one q=0 depending on the parameters. In the latter case, distortion of the crystal perpendicular to the (111) axis is predicted. The corresponding anomaly in elastic constants should also appear. The electrical resistivity is calculated with account of scattering within the CEF quasi-quartet. It is found that the resistivity as a function of the direction of magnetic field shows a sharp maximum around the (111) axis at low temperatures because of the level crossing.Comment: 16 pages, 5 figure

Electronic Orders Induced by Kondo Effect in Non-Kramers f-Electron Systems

This paper clarifies the microscopic nature of the staggered scalar order, which is specific to even number of f electrons per site. In such systems, crystalline electric field (CEF) can make a singlet ground state. As exchange interaction with conduction electrons increases, the CEF singlet at each site gives way to Kondo singlets. The collective Kondo singlets are identified with itinerant states that form energy bands. Near the boundary of itinerant and localized states, a new type of electronic order appears with staggered Kondo and CEF singlets. We present a phenomenological three-state model that qualitatively reproduces the characteristic phase diagram, which have been obtained numerically with use of the continuous-time quantum Monte Carlo combined with the dynamical mean-field theory. The scalar order observed in PrFe_4P_{12} is ascribed to this staggered order accompanying charge density wave (CDW) of conduction electrons. Accurate photoemission and tunneling spectroscopy should be able to probe sharp peaks below and above the Fermi level in the ordered phase.Comment: 7 pages, 8 figure

Normal zone in YBa2Cu3O6+xYBa_2Cu_3O_{6+x}-coated conductors

We consider the distribution of an electric field in YBCO-coated conductors for a situation in which the DC transport current is forced into the copper stabilizer due to a weak link -- a section of the superconducting film with a critical current less than the transport current. The electric field in the metal substrate is also discussed. The results are compared with recent experiments on normal zone propagation in coated conductors for which the substrate and stabilizer are insulated from each other. The potential difference between the substrate and stabilizer, and the electric field in the substrate outside the normal zone can be accounted for by a large screening length in the substrate, comparable to the length of the sample. During a quench, the electric field inside the interface between YBCO and stabilizer, as well as in the buffer layer, can be several orders of magnitude greater than the longitudinal macroscopic electric field inside the normal zone. We speculate on the possibility of using possible microscopic electric discharges caused by this large ($\sim$kV/cm) electric field as a means to detect a quench.Comment: 8 pages, 4 figure

Microscopic Mechanism for Staggered Scalar Order in PrFe4P12

A microscopic model is proposed for the scalar order in PrFe4P12 where f2 crystalline electric field (CEF) singlet and triplet states interact with two conduction bands. By combining the dynamical mean-field theory and the continuous-time quantum Monte Carlo, we obtain an electronic order with staggered Kondo and CEF singlets with the total conduction number being unity per site. The ground state becomes semimetallic provided that the two conduction bands have different occupation numbers. This model naturally explains experimentally observed properties in the ordered phase of PrFe4P12 such as the scalar order parameter, temperature dependence of the resistivity, field-induced staggered moment, and inelastic features in neutron scattering. The Kondo effect plays an essential role for ordering, in strong contrast with ordinary magnetic orders by the RKKY interaction.Comment: 4 pages, 4figure

Global Production Increased by Spatial Heterogeneity in a Population Dynamics Model

Spatial and temporal heterogeneity are often described as important factors having a strong impact on biodiversity. The effect of heterogeneity is in most cases analyzed by the response of biotic interactions such as competition of predation. It may also modify intrinsic population properties such as growth rate. Most of the studies are theoretic since it is often difficult to manipulate spatial heterogeneity in practice. Despite the large number of studies dealing with this topics, it is still difficult to understand how the heterogeneity affects populations dynamics. On the basis of a very simple model, this paper aims to explicitly provide a simple mechanism which can explain why spatial heterogeneity may be a favorable factor for production.We consider a two patch model and a logistic growth is assumed on each patch. A general condition on the migration rates and the local subpopulation growth rates is provided under which the total carrying capacity is higher than the sum of the local carrying capacities, which is not intuitive. As we illustrate, this result is robust under stochastic perturbations

Status of the Standard Solar Model Prediction of Solar Neutrino Fluxes

The Standard Solar Model (BP04) predicts a total 8B neutrino flux that is 17.2% larger than measured in the salt phase of the SNO detector (and if it were significant it will indicate oscillation to sterile neutrinos). Hence it is important to examine in details uncertainties (and values) of inputs to the SSM. Currently, the largest fractional uncertainty is due to the new evaluation of the surface composition of the sun. We examine the nuclear input on the formation of solar 8B [S17(0)] and demonstrate that it is still quite uncertain due to ill known slope of the measured astrophysical cross section factor and thus ill defined extrapolation to zero energy. This yields an additional reasonably estimated uncertainty due to extrapolation of +0.0 -3.0 eV-b (+0% -14%). Since a large discrepancy exists among measured as well as among predicted slopes, the value of S17(0) is dependent on the choice of data and theory used to extrapolate S17(0). This situation must be alleviated by new measurement(s). The "world average" is driven by the Seattle result due to the very small quoted uncertainty, which we however demonstrate it to be an over-estimated accuracy. We propose more realistic error bars for the Seattle results based on the published Seattle data.Comment: Fifth International Conferenceon Non-Accelerator New Physics, Dubna, June 20-25, 2005. Work Supported by USDOE Grant No. DE-FG02-94ER4087