442 research outputs found
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
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
Incommensurate lattice distortion in the high temperature tetragonal phase of La(Sr,Ba)CuO
We report incommensurate diffuse (ICD) scattering appearing in the
high-temperature-tetragonal (HTT) phase of La(Sr,Ba)CuO
with observed by the neutron diffraction technique. For
all compositions, a sharp superlattice peak of the low-temperature-orthorhombic
(LTO) structure is replaced by a pair of ICD peaks with the modulation vector
parallel to the CuO octahedral tilting direction, that is, the diagonal
Cu-Cu direction of the CuO plane, above the LTO-HTT transition temperature
. The temperature dependences of the incommensurability for all
samples scale approximately as , while those of the integrated intensity
of the ICD peaks scale as . These observations together with
absence of ICD peaks in the non-superconducting sample evince a
universal incommensurate lattice instability of hole-doped 214 cuprates in the
superconducting regime.Comment: 6 pages, 6 figure
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
Free-Field Realization of D-dimensional Cylindrical Gravitational Waves
We find two-dimensional free-field variables for D-dimensional general
relativity on spacetimes with D-2 commuting spacelike Killing vector fields and
non-compact spatial sections for D>4. We show that there is a canonical
transformation which maps the corresponding two-dimensional dilaton gravity
theory into a two-dimensional diffeomorphism invariant theory of the free-field
variables. We also show that the spacetime metric components can be expressed
as asymptotic series in negative powers of the dilaton, with coefficients which
can be determined in terms of the free fields.Comment: 15 pages, Late
Strong Influence of the diffuse component on the lattice dynamics in Pb(MgNb)O
The temperature and zone dependence of the lattice dynamics in
Pb(MgNb)O is characterized using neutron inelastic
scattering. A strong correlation between the diffuse and phonon scattering is
measured. The lattice dynamics in Brillouin zones where the diffuse scattering
is strong is observed to display qualitatively different behavior than those
zones where the diffuse scattering is weak. In the (220) and (200) zones, where
there is a weak diffuse component, the dynamics are well described by coupled
harmonic oscillators. Compared with SrTiO, the coupling is weak and
isotropic, resulting in only a small transfer of spectral weight from one mode
to another. A comparison of the scattering in these zones to the (110) zone,
where a strong diffuse component is present, reveals a strong coupling of the
diffuse (or central) component to the acoustic mode. We speculate that the
coupling to the central peak is the reason for several recent conflicting
interpretations of the lattice dynamics based on data from zones with a strong
diffuse component.Comment: 7 pages, 7 figure
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