1,643 research outputs found
Spin order in the one-dimensional Kondo and Hund lattices
We study numerically the one-dimensional Kondo and Hund lattices consisting
of localized spins interacting antiferro or ferromagnetically with the
itinerant electrons, respectively. Using the Density Matrix Renormalization
Group we find, for both models and in the small coupling regime, the existence
of new magnetic phases where the local spins order forming ferromagnetic
islands coupled antiferromagnetically. Furthermore, by increasing the
interaction parameter we find that this order evolves toward the
ferromagnetic regime through a spiral-like phase with longer characteristic
wave lengths. These results shed new light on the zero temperature magnetic
phase diagram for these models.Comment: PRL, to appea
Two-state behaviour of Kondo trimers
The electronic properties and spectroscopic features of a magnetic trimer
with a Kondo-like coupling to a non-magnetic metallic substrate are analyzed at
zero temperature. The substrate density of states is depressed in the trimer
neighbourhood, being exactly zero at the substrate chemical potential. The size
of the resonance strongly depends on the magnetic state of the trimer, and
exhibits a two-state behavior. The geometrical dependence of these results
agree qualitatively with recent experiments and could be reproduced in a
triangular quantum dot arrangement.Comment: 5 pages, including 4 figure
Estimation of Dietary Iron Bioavailability from Food Iron Intake and Iron Status
Currently there are no satisfactory methods for estimating dietary iron absorption (bioavailability) at a population level, but this is essential for deriving dietary reference values using the factorial approach. The aim of this work was to develop a novel approach for estimating dietary iron absorption using a population sample from a sub-section of the UK National Diet and Nutrition Survey (NDNS). Data were analyzed in 873 subjects from the 2000–2001 adult cohort of the NDNS, for whom both dietary intake data and hematological measures (hemoglobin and serum ferritin (SF) concentrations) were available. There were 495 men aged 19–64 y (mean age 42.7±12.1 y) and 378 pre-menopausal women (mean age 35.7±8.2 y). Individual dietary iron requirements were estimated using the Institute of Medicine calculations. A full probability approach was then applied to estimate the prevalence of dietary intakes that were insufficient to meet the needs of the men and women separately, based on their estimated daily iron intake and a series of absorption values ranging from 1–40%. The prevalence of SF concentrations below selected cut-off values (indicating that absorption was not high enough to maintain iron stores) was derived from individual SF concentrations. An estimate of dietary iron absorption required to maintain specified SF values was then calculated by matching the observed prevalence of insufficiency with the prevalence predicted for the series of absorption estimates. Mean daily dietary iron intakes were 13.5 mg for men and 9.8 mg for women. Mean calculated dietary absorption was 8% in men (50th percentile for SF 85 µg/L) and 17% in women (50th percentile for SF 38 µg/L). At a ferritin level of 45 µg/L estimated absorption was similar in men (14%) and women (13%). This new method can be used to calculate dietary iron absorption at a population level using data describing total iron intake and SF concentration
Phase diagram of the extended Hubbard chain with charge-dipole interactions
We consider a modified extended Hubbard model (EHM) which, in addition to the
on-site repulsion U and nearest-neighbor repulsion V, includes polarization
effects in second-order perturbation theory. The model is equivalent to an EHM
with renormalized U plus a next-nearest-neighbor repulsion term. Using a method
based on topological quantum numbers (charge and spin Berry phases), we
generalize to finite hopping t the quantum phase diagram in one dimension
constructed by van den Brink et al. (Phys. Rev. Lett. 75, 4658 (1995)). At
hopping t=0 there are two charge density-wave phases, one spin density-wave
phase and one intermediate phase with charge and spin ordering, depending on
the parameter values. At t \neq 0 the nature of each phase is confirmed by
studying correlation functions. However, in addition to the strong-coupling
phases, a small region with bond ordering appears. The region occupied by the
intermediate phase first increases and then decreases with increasing t, until
it finally disappears for t of the order but larger than U. For small t, the
topological transitions agree with the results of second order perturbation
theory.Comment: 6 pages, 5 figures, two columns latex version. Accepted for
publication in Physical Review B. Mistaken reference 16 has been correcte
Electron Spin Resonance of defects in the Haldane System Y(2)BaNiO(5)
We calculate the electron paramagnetic resonance (EPR) spectra of the
antiferromagnetic spin-1 chain compound Y(2)BaNi(1-x)Mg(x)O(5) for different
values of x and temperature T much lower than the Haldane gap (~100K). The
low-energy spectrum of an anisotropic Heisenberg Hamiltonian, with all
parameters determined from experiment, has been solved using DMRG. The observed
EPR spectra are quantitatively reproduced by this model. The presence of
end-chain S=1/2 states is clearly observed as the main peak in the spectrum and
the remaining structure is completely understood.Comment: 5 pages, 4 figures include
Hole dynamics in generalized spin backgrounds in infinite dimensions
We calculate the dynamical behaviour of a hole in various spin backgrounds in
infinite dimensions, where it can be determined exactly. We consider hypercubic
lattices with two different types of spin backgrounds. On one hand we study an
ensemble of spin configurations with an arbitrary spin probability on each
sublattice. This model corresponds to a thermal average over all spin
configurations in the presence of staggered or uniform magnetic fields. On the
other hand we consider a definite spin state characterized by the angle between
the spins on different sublattices, i.e a classical spin system in an external
magnetic field. When spin fluctuations are considered, this model describes the
physics of unpaired particles in strong coupling superconductors.Comment: Accepted in Phys. Rev. B. 18 pages of text (1 fig. included) in Latex
+ 2 figures in uuencoded form containing the 2 postscripts (mailed
separately
Paper Session I-C - Non-Destructive Detection of Corrosion Under Paint on Critical Surfaces
We describe our proof-of-concept demonstration of the well-known thermal diffusion imaging technique *\u3e 2\u3e3 for detection of corrosion under paint on critical surfaces. Our first application will be the detection and mapping of corrosion on arbiter vehicle wing spars and rudder speed brakes. The technique will also used for the evaluation of doubler plate bond integrity on the rudder speed brakes
Spin-orbit coupling and ESR theory for carbon nanotubes
A theoretical description of ESR in 1D interacting metals is given, with
primary emphasis on carbon nanotubes. The spin-orbit coupling is derived, and
the resulting ESR spectrum is analyzed by field theory and exact
diagonalization. Drastic differences in the ESR spectra of single-wall and
multi-wall nanotubes are found. For single-wall tubes, the predicted double
peak spectrum could reveal spin-charge separation.Comment: 4 pages, 1 figure, final version to appear in PR
Shadow band in the one-dimensional large Hubbard model
We show that the factorized wave-function of Ogata and Shiba can be used to
calculate the dependent spectral functions of the one-dimensional, infinite
Hubbard model, and of some extensions to finite . The resulting spectral
function is remarkably rich: In addition to low energy features typical of
Luttinger liquids, there is a well defined band, which we identify as the
shadow band resulting from spin fluctuations. This band should be
detectable experimentally because its intensity is comparable to that of the
main band for a large range of momenta.Comment: Latex file. 4 pages. Figures upon reques
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