520 research outputs found
Systematic Study of Short Range Antiferromagnetic Order and The Spin-Glass State in Lightly Doped La2-xSrxCuO4
Systematic measurements of the magnetic susceptibility were performed on
single crystals of lightly doped La2-xSrxCuO4 (x=0.03, 0.04 and 0.05). For all
samples the temperature dependence of the in-plane magnetic susceptibility
shows typical spin-glass features with spin-glass transition temperatures Tg of
6.3K, 5.5K and 5.0K for x=0.03, 0.04 and 0.05, respectively. The canonical
spin-glass order parameter extracted from the in-plane susceptibility of all
the samples follows a universal scaling curve. On the other hand, the
out-of-plane magnetic susceptibility deviates from Curie law below a
temperature Tdv, higher than Tg. Comparing with previous neutron scattering
results with an instrumental energy resolution of 0.25 meV from Wakimoto et
al., the x-dependence of Tdv is qualitatively the same as that of Tel, the
temperature below which the elastic magnetic scattering develops around (pi,
pi). Thus, a revised magnetic phase diagram in the lightly doped region of
La2-xSrxCuO4 is proposed. The Curie constants calculated from the in-plane
susceptibility are independent of the Sr concentration. On the basis of the
cluster spin-glass model, this fact might reflect an inhomogeneous distribution
of doped holes in the CuO2 plane, such as in a stripe structure.Comment: 7 pages, 6 figure
Field-induced transition between magnetically disordered and ordered phases in underdoped La(2-x)SrxCuO4
We report the observation of a magnetic-field-induced transition between
magnetically disordered and ordered phases in slightly under-doped
La(2-x)SrxCuO4 with x=0.144. Static incommensurate spin-density-wave order is
induced above a critical field of about 3 T, as measured by elastic neutron
scattering. Our results allow us to constrain the location of a quantum
critical point on the phase diagram.Comment: 10 pages, 2 figures; discussion on the location of a quantum critical
point is revise
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The Dodge City Tornadoes on 24 May 2016: Damage Survey, Photogrammetric Analysis Combined with Mobile Polarimetric Radar Data
Abstract
Polarimetric measurements recorded by a mobile X-band radar are combined with photographs of the Dodge City, Kansas, tornado to quantitatively document the evolving debris cloud. An inner annulus or tube of high radar reflectivity encircled the tornado at low levels. A column of low cross-correlation coefficient ρhv was centered on the funnel cloud during the early stage of the tornado’s life cycle. In addition, two areas of low ρhv were located near the inner annulus of high radar reflectivity and were hypothesized to be regions of high debris loading that have been reproduced in simulations of lofted debris. Another column of low ρhv was a result of strong wind speeds that were progressively lofting small debris and dust as inflow rotated around and within the weak echo notch of the hook echo. A column of negative differential reflectivity ZDR was also centered on the tornado and was hypothesized to result from common debris alignment. The polarimetric structure undergoes a dramatic transition when the debris cloud was prominent and enveloped most of the funnel cloud. The weak echo column (WEC) began to fill at lower levels as large amounts of debris were lofted into the circulation. The axis of minimum ρhv shifted to a radius just beyond the funnel cloud. A column of positive ZDR was collocated with the funnel surrounded by negative ZDR. The negative ZDR and low ρhv within the debris cloud were likely the result of some common debris alignment from wheat stems. The positive ZDR within the funnel signified the presence of a few hydrometeors
Free Boson Representation of
A representation of the quantum affine algebra of an
arbitrary level is constructed in the Fock module of eight boson fields.
This realization reduces the Wakimoto representation in the
limit. The analogues of the screening currents are also obtained. They commute
with the action of modulo total differences of some
fields.Comment: 12 pages, LaTeX, RIMS-920, YITP/K-101
Magnetic field effects and magnetic anisotropy in lightly doped La_{2-x}Sr_xCuO_4
The effects of the application of a magnetic field on the diagonal stripe
spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and
0.024). With increasing magnetic field, the magnetic elastic intensity at the
diagonal incommensurate (DIC) positions (1,\pm\epsilon,0) decreases as opposed
to the increase seen in superconducting samples. This diminution in intensity
with increasing magnetic field originates from a spin reorientation transition,
which is driven by the antisymmetric exchange term in the spin Hamiltonian. On
the other hand, the transition temperature, the incommensurability, and the
peak width of the diagonal incommensurate correlations are not changed with
magnetic field. This result suggests that the magnetic correlations are
determined primarily by the charge disproportionation and that the geometry of
the diagonal incommensurate magnetism is also determined by effects, that is,
stripe formation which are not purely magnetic in origin. The
Dzyaloshinskii-Moriya antisymmetric exchange is nevertheless important in
determining the local spin structure in the DIC stripe phase.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Disorder and relaxation mode in the lattice dynamics of PbMgNbO relaxor ferroelectric
The low-energy part of vibration spectrum in PbMgNbO
relaxor ferroelectric was studied by inelastic neutron scattering. We observed
the coexistence of a resolution-limited central peak with strong quasielastic
scattering. The line-width of the quasielastic component follows a
dependence. We find that is temperature-dependent.
The relaxation time follows the Arrhenius law well. The presence of a
relaxation mode associated with quasi-elastic scattering in PMN indicates that
order-disorder behaviour plays an important r\^ole in the dynamics of diffuse
phase transitions
Neutron scattering study of soft phonons and diffuse scattering in insulating LaSrCuO
Soft phonons and diffuse scattering in insulating LaSrCuO
() have been studied by the neutron scattering technique. The X-point
phonon softens from high temperature towards the structural transition
temperature K, and the Z-point phonon softens again below 200 K.
The Z-point phonon softening persists to low temperature, in contrast to the
behavior observed in the superconducting compound, in which the
Z-point phonon hardens below . The diffuse scattering associated with the
structural phase transition at 410 K appears at commensurate positions. These
results highlight interesting differences between superconducting and
insulating samples.Comment: 5 pages, 5 figure
Static and dynamic spin correlations in the spin-glass phase of slightly-doped La_{2-x}Sr_xCuO_4
Neutron scattering experiments reveal that a diagonal spin modulation, which
is a one-dimensional modulation rotated away by 45 from that in the
superconducting phase, occurs universally across the insulating spin-glass
phase in LaSrCuO (0.020.055). This establishes an
intimate relation between the magnetism and the transport properties in the
high-temperature copper oxide superconductors. Furthermore, it is found that
the charge density per unit length estimated using a charge stripe model is
almost constant throughout the phase diagram, even when the modulation rotates
away by 45 at the superconducting boundary. However, at the lowest
values for the density changes approaching 1 hole/Cu as in
LaSrNiO. Magnetic excitation spectra suggest that magnetic
correlations change from incommensurate to commensurate at 7 meV
and 70 K, indicating a characteristic energy for the incommensurate
structure of 6-7 meV.Comment: 7 pages, submitted to Phys. Rev.
A Neutron Elastic Diffuse Scattering Study of PMN
We have performed elastic diffuse neutron scattering studies on the relaxor
Pb(MgNb)O (PMN). The measured intensity distribution near a
(100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly
with extended intensity in the (110) and (10) directions. The
temperature dependence of the diffuse scattering shows that both the size of
the polar nanoregions (PNR) and the integrated diffuse intensity increase with
cooling even for temperatures below the Curie temperature K.Comment: Submitted to PR
Unusual magnetic susceptibility anisotropy in untwinned La_{2-x}Sr_xCuO_4 single crystals in the lightly-doped region
We present a study of the magnetic susceptibility in carefully detwinned
La_{2-x}Sr_{x}CuO_4 single crystals in the lightly-doped region (x=0-0.03),
which demonstrates a remarkable in-plane anisotropy of the spin system. This
anisotropy is found to persist after the long-range antiferromagnetic (AF)
order is destroyed by hole doping, suggesting that doped holes break the AF
order into domains in which the spin alignment is kept essentially intact. It
turns out that the freezing of the spins taking place at low temperatures is
also notably anisotropic, implying that the "spin-glass" feature is governed by
the domain structure as well.Comment: 4 pages, 3 figures, accepted for publication in Phys.Rev.Let
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