65 research outputs found
Direct Observation of a One Dimensional Static Spin Modulation in Insulating La1.95Sr0.05CuO4
We report the results of an extensive elastic neutron scattering study of the
incommensurate (IC) static spin correlations in La1.95Sr0.05CuO4 which is an
insulating spin glass at low temperatures. The present neutron scattering
experiments on the same x=0.05 crystal employ a narrower instrumental
Q-resolution and thereby have revealed that the crystal has only two
orthorhombic twins at low temperatures with relative populations of 2:1. We
find that, in a single twin, only two satellites are observed at (1, +/-0.064,
L)(ortho) and (0, 1+/-0.064, L)(ortho), that is, the modulation vector is only
along the orthorhombic b*-axis. This demonstrates unambiguously that
La1.95Sr0.05CuO4 has a one-dimensional static diagonal spin modulation at low
temperatures, consistent with certain stripe models. We have also reexamined
the x=0.04 crystal that previously was reported to show a single commensurate
peak. By mounting the sample in the (H, K, 0) zone, we have discovered that the
x=0.04 sample in fact has the same IC structure as the sample. The
incommensurability parameter d for x=0.04 and 0.05, where d is the distance
from (1/2, 1/2) in tetragonal reciprocal lattice units, follows the linear
relation d=x. These results demonstrate that the insulator to superconductor
transition in the under doped regime (0.05 </= x </= 0.06) in La2-xSrxCuO4 is
coincident with a transition from diagonal to collinear static stripes at low
temperatures thereby evincing the intimate coupling between the one dimensional
spin density modulation and the superconductivity.Comment: 9 pages 8 figure
Microbial flora of commercially produced vacuum packaged, cooked beef roast
Commercially produced vacuum
packaged, fully cooked, microwaveable beef
roasts from four producers were purchased
from local retail markets. Salt concentration,
pH, water activity (aw), and percent moisture,
fat and protein were determined. Samples of
both package juice and homogenized beef
plus juice were analyzed for the presence of
aerobic, anaerobic and lactic acid bacteria
and clostridia-type organisms. The cooked
beef products had pH values from 5.82 to
6.19, water activity of 0.992 to 0.997, and
contained 0.34 to 1.07% salt, 61.89 to
72.39% moisture, 4.29 to 18.21% fat and
15.92 to 20.62% protein. No growth was
detected in juice for aerobic, anaerobic or
lactic acid bacteria or clostridia-type
organisms. Combined beef and juice had
less than 2 CFU/g for aerobic, anaerobic or
lactic acid bacteria or clostridia-type
organisms. Cooking and chilling schedules
used in the manufacture of the four products
we evaluated in this study limited survival
and outgrowth of microorganisms
Bi-quadratic magnetoelectric coupling in underdoped La_2CuO_{4+x}
The recent discovery of relaxor ferroelectricity and magnetoelectric effect
in lightly doped cuprate material La_2CuO_{4+x} has provided a number of
questions concerning its theoretical description. It has been argued using a
Ginzburg-Landau free energy approach that the magnetoelectric effect can be
explained by the presence of bi-quadratic interaction terms in the free energy.
Here, by using the same free energy functional, we study the variety of
behavior which can emerge in the electric polarization under an external
magnetic field. Subsequently, we discuss the role of Dzyaloshinskii-Moriya
interaction in generating this magnetoelectric response. This work is
particularly relevant for such relaxor systems where the material-dependent
parameters would be affected by changes in e.g. chemical doping or cooling
rate.Comment: 8 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1112.152
Incommensurate Geometry of the Elastic Magnetic Peaks in Superconducting La1.88Sr0.12CuO4
We report magnetic neutron scattering measurements of incommensurate magnetic
order in a superconducting single crystal of La1.88Sr0.12CuO4. We find that the
incommensurate wavevectors which describe the static magnetism do not lie along
high-symmetry directions of the underlying CuO2 lattice. The positions of the
elastic magnetic peaks are consistent with those found in excess-oxygen doped
La2CuO4+y. This behavior differs from the precise magnetic order found in the
low temperature tetragonal La1.6-xNd0.4SrxCuO4 material for which stripes of
spin and charge have been observed. These observations have clear implications
for any stripe model proposed to describe the static magnetism in orthorhombic
La2CuO4-based superconductors.Comment: 4 pages, 3 eps figure
Doping and temperature dependence of incommensurate antiferromagnetism in underdoped lanthanum cuprates
The doping, temperature and energy dependence of the dynamical spin structure
factors of the underdoped lanthanum cuprates in the normal state is studied
within the t-J model using the fermion-spin transformation technique.
Incommensurate peaks are found at ,
at relatively low temperatures with linearly
increasing with doping at the beginning and then saturating at higher dopings.
These peaks broaden and weaken in amplitude with temperature and energy, in
good agreement with experiments. The theory also predicts a rotation of these
peaks by at even higher temperatures, being shifted to .Comment: 11 pages, PDF file, six figures are included, accepted for
publication in Physical Review
Stringent constraints on the scalar K pi form factor from analyticity, unitarity and low-energy theorems
We investigate the scalar K pi form factor at low energies by the method of
unitarity bounds adapted so as to include information on the phase and modulus
along the elastic region of the unitarity cut. Using at input the values of the
form factor at t=0 and the Callan-Treiman point, we obtain stringent
constraints on the slope and curvature parameters of the Taylor expansion at
the origin. Also, we predict a quite narrow range for the higher order ChPT
corrections at the second Callan-Treiman point.Comment: 5 pages latex, uses EPJ style files, 3 figures, replaced with version
accepted by EPJ
Effect of a magnetic field on the spin- and charge-density wave order in La1.45Nd0.4Sr0.15CuO4
The spin-density wave (SDW) and charge-density wave (CDW) order in
superconducting La1.45Nd0.4Sr0.15CuO4 were studied under an applied magnetic
field using neutron and X-ray diffraction techniques. In zero field,
incommensurate (IC) SDW order appears below ~ 40 K, which is characterized by
neutron diffraction peaks at (1/2 +/- 0.134, 1/2 +/- 0.134, 0). The intensity
of these IC peaks increases rapidly below T_Nd ~ 8 K due to an ordering of the
Nd^3+ spins. The application of a 1 T magnetic field parallel to the c-axis
markedly diminishes the intensity below T_Nd, while only a slight decrease in
intensity is observed at higher temperatures for fields up to 7 T. Our
interpretation is that the c-axis field suppresses the parasitic Nd^3+ spin
order at the incommensurate wave vector without disturbing the stripe order of
Cu^2+ spins. Consistent with this picture, the CDW order, which appears below
60 K, shows no change for magnetic fields up to 4 T. These results stand in
contrast to the significant field-induced enhancement of the SDW order observed
in superconducting La2-xSrxCuO4 with x ~ 0.12 and stage-4 La2CuO4+y. The
differences can be understood in terms of the relative volume fraction
exhibiting stripe order in zero field, and the collective results are
consistent with the idea that suppression of superconductivity by vortices
nucleates local patches of stripe order.Comment: 7 pages, 5 figure
Convergence of energy-dependent incommensurate antiferromagnetic neutron scattering peaks to commensurate resonance in underdoped bilayer cuprates
The recently discovered coexistence of incommensurate antiferromagnetic
neutron scattering peaks and commensurate resonance in underdoped
YBaCuO is calling for an explanation. Within the t-J model, the
doping and energy dependence of the spin dynamics of the underdoped bilayer
cuprates in the normal state is studied based on the fermion-spin theory by
considering the bilayer interactions. Incommensurate peaks are found at
and at low energies with
initially increasing with doping at low dopings and then saturating at
higher dopings. These incommensurate peaks are suppressed, and the parameter
is reduced with increasing energy. Eventually it converges to the
resonance peak. Thus the recently observed coexistence is
interpreted in terms of bilayer interactions.Comment: 15 pages, Revtex, five figures are included, accepted for publication
in Phys. Rev.
Electrode Polarization Effects in Broadband Dielectric Spectroscopy
In the present work, we provide broadband dielectric spectra showing strong
electrode polarization effects for various materials, belonging to very
different material classes. This includes both ionic and electronic conductors
as, e.g., salt solutions, ionic liquids, human blood, and
colossal-dielectric-constant materials. These data are intended to provide a
broad data base enabling a critical test of the validity of phenomenological
and microscopic models for electrode polarization. In the present work, the
results are analyzed using a simple phenomenological equivalent-circuit
description, involving a distributed parallel RC circuit element for the
modeling of the weakly conducting regions close to the electrodes. Excellent
fits of the experimental data are achieved in this way, demonstrating the
universal applicability of this approach. In the investigated ionically
conducting materials, we find the universal appearance of a second dispersion
region due to electrode polarization, which is only revealed if measuring down
to sufficiently low frequencies. This indicates the presence of a second
charge-transport process in ionic conductors with blocking electrodes.Comment: 9 pages, 6 figures, experimental data are provided in electronic form
(see "Data Conservancy"
Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4 LaCuO and LaSrCuO
This paper reports muon spin relaxation (MuSR) measurements of two single
crystals of the title high-Tc cuprate systems where static incommensurate
magnetism and superconductivity coexist. By zero-field MuSR measurements and
subsequent analyses with simulations, we show that (1) the maximum ordered Cu
moment size (0.36 Bohr magneton) and local spin structure are identical to
those in prototypical stripe spin systems with the 1/8 hole concentration; (2)
the static magnetism is confined to less than a half of the volume of the
sample, and (3) regions with static magnetism form nano-scale islands with the
size comparable to the in-plane superconducting coherence length. By
transverse-field MuSR measurements, we show that Tc of these systems is related
to the superfluid density, in the same way as observed in cuprate systems
without static magnetism. We discuss a heuristic model involving percolation of
these nanoscale islands with static magnetism as a possible picture to
reconcile heterogeneity found by the present MuSR study and long-range spin
correlations found by neutron scattering.Comment: 19 pages, 15 figures, submitted to Phys. Rev. B. E-mail:
[email protected]
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