324 research outputs found
New Magnetic Excitations in the Spin-Density-Wave of Chromium
Low-energy magnetic excitations of chromium have been reinvestigated with a
single-Q crystal using neutron scattering technique. In the transverse
spin-density-wave phase a new type of well-defined magnetic excitation is found
around (0,0,1) with a weak dispersion perpendicular to the wavevector of the
incommensurate structure. The magnetic excitation has an energy gap of E ~ 4
meV and at (0,0,1) exactly corresponds to the Fincher mode previously studied
only along the incommensurate wavevector.Comment: 4 pages, 4 figure
ORTHOTOPIC LIVER TRANSPLANTATION FOR WILSON'S DISEASE
An 11-year-old boy with terminal hepatic failure due to Wilson's disease was treated 18 months ago with orthotopic liver transplantation. Postoperatively, there has been evidence of clearance of body copper stores but without accumulation of copper in biopsy specimens of the transplanted liver after 6 and 17 months. Further follow-up will be necessary before deciding whether the disorder has been cured by liver replacement and in turn whether this constitutes proof that Wilson's disease is an inborn error of hepatic metabolism. The observations so far are consistent with these conclusions. © 1971
Antiferromagnetic Excitations and Van Hove Singularities in YBaCuO
We show that in quasi-two-dimensional -wave superconductors Van Hove
singularities close to the Fermi surface lead to novel magnetic quasi-particle
excitations. We calculate the temperature and doping dependence of dynamical
magnetic susceptibility for YBCO and show that the proposed excitations are in
agreement with inelastic neutron scattering experiments. In addition, the
values of the gap parameter and in-plane antiferromagnetic coupling are much
smaller than usually believed.Comment: REVTeX, 4 pages + 3 PostScript (compressed) figures; to appear in
Phys. Rev. B (Rap. Comm.
Stripe order, depinning, and fluctuations in LaBaCuO and LaBaSrCuO
We present a neutron scattering study of stripe correlations measured on a
single crystal of LaBaCuO. Within the
low-temperature-tetragonal (LTT) phase, superlattice peaks indicative of spin
and charge stripe order are observed below 50 K. For excitation energies
meV, we have characterized the magnetic excitations that
emerge from the incommensurate magnetic superlattice peaks. In the ordered
state, these excitations are similar to spin waves. Following these excitations
as a function of temperature, we find that there is relatively little change in
the {\bf Q}-integrated dynamical spin susceptibility for
meV as stripe order disappears and then as the structure transforms from LTT to
the low-temperature-orthorhombic (LTO) phase. The {\bf Q}-integrated signal at
lower energies changes more dramatically through these transitions, as it must
in a transformation from an ordered to a disordered state. We argue that the
continuous evolution through the transitions provides direct evidence that the
incommensurate spin excitations in the disordered state are an indicator of
dynamical charge stripes. An interesting feature of the thermal evolution is a
variation in the incommensurability of the magnetic scattering. Similar
behavior is observed in measurements on a single crystal of
LaBaSrCuO; maps of the scattered intensity
in a region centered on the antiferromagnetic wave vector and measured at
meV are well reproduced by a model of disordered stripes with a
temperature-dependent mixture of stripe spacings. We discuss the relevance of
our results to understanding the magnetic excitations in cuprate
superconductors.Comment: 12 pages, 11 figures, 1 tabl
Anomalous Spin Dynamics in Doped Quantum Antiferromagnets
Finite-temperature spin dynamics in planar t-J model is studied using the
method based on the Lanczos diagonalization of small systems. Dynamical spin
structure factor at moderate dopings shows the coexistence of free-fermion-like
and spin-fluctuation timescales. At T<J, the low-frequency and static
susceptibility show pronounced T dependence, supporting a scenario, related to
the marginal Fermi-liquid one, for the explanation of neutron-scattering and
NMR-relaxation experiments in cuprates. Calculated NMR relaxation rates
reasonably reproduce experimental ones.Comment: 10 pages + 4 figures, Postscript in uuencoded compressed tar file,
IJS-TP-94/2
Small and large polarons in nickelates, manganites, and cuprates
By comparing the optical conductivities of La_{1.67}Sr_{0.33}NiO_{4} (LSNO),
Sr_{1.5}La_{0.5}MnO_4 (SLMO), Nd_2CuO_{4-y} (NCO), and
Nd_{1.96}Ce_{0.04}CuO_{4} (NCCO), we have identified a peculiar behavior of
polarons in this cuprate family. While in LSNO and SLMO small polarons localize
into ordered structures below a transition temperature, in those cuprates the
polarons appear to be large, and at low T their binding energy decreases. This
reflects into an increase of the polaron radius, which may trigger coherent
transport.Comment: File latex, 15 p. incl. 4 Figs. epsf, to appear on the Journal of
Superconductivity - Proc. "Stripes 1996" - Roma Dec 199
Recommended from our members
Polarization Dependence of the Spin-Density-Wave Excitations in Single-Domain Chromium
A polarised neutron scattering experiment has been performed on a single-Q, single domain sample of Cr in a magnetic field of 4 T in the transverse spin-density-wave phase. It is confirmed that the longitudinal fluctuations are enhanced for energy transfers E {lt} 8 meV similarly as in the longitudinal spin-density-wave phase. The spin wave modes with deltaS parallel and perpendicular to Q are isotropic within the E-range investigated
Infrared response of ordered polarons in layered perovskites
We report on the infrared absorption spectra of three oxides where charged
superlattices have been recently observed in diffraction experiments. In
LaSrNiO, polaron localization is found to suppress the
low-energy conductivity through the opening of a gap and to split the
- vibrational manifold of the oxygen octahedra. Similar effects
are detected in SrLaMnO and in LaNiO, with
peculiar differences related to the type of charge ordering.Comment: File latex, 11 p. + 3 Figures, to appear on Phys. Rev. B (Rapid
Commun.), 1 Oct. 1996. The figures will be faxed upon request.
E-mail:[email protected] Fax: +39-6-446315
Charge and orbital order in half-doped manganites
An explanation is given for the charge order, orbital order and insulating
state observed in half-doped manganese oxides, such as
NdSrMnO. The competition between the kinetic energy of
the electrons and the magnetic exchange energy drives the formation of
effectively one-dimensional ferromagnetic zig-zag chains. Due to a topological
phase factor in the hopping, the chains are intrinsically insulating and
orbital-ordered. Most surprisingly, the strong Coulomb interaction between
electrons on the same Mn-ion leads to the experimentally observed charge
ordering. For doping less than 1/2 the system is unstable towards phase
separation into a ferromagnetic metallic and charge-ordered insulating phase.Comment: To appear in Phys. Rev. Lett., 4 pages, 4 figure
Observation of New Incommensurate Magnetic Correlations at the Lower Critical Concentration for Superconductivity (x=0.05) in La(2-x)Sr(x)CuO4
Neutron-scattering experiments have been performed on lightly-doped
La(2-x)Sr(x)CuO4 single crystals in both the insulating (x=0.03,0.04,0.05) and
superconducting (x=0.06) regions. Elastic magnetic peaks are observed at low
temperatures in all samples with the maximum peak linewidth occuring at the
critical concentration x_c=0.05. New incommensurate peaks are observed only at
x=0.05, the positions of which are rotated by 45 degrees in reciprocal space
about (pi,pi) from those observed for x>=0.06 in the superconducting phase.Comment: 5 pages, LaTeX, 4 figures include
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