405 research outputs found
Linear dependence of peak width in \chi(\bq, \omega) vs T_c for YBCO superconductors
It is shown that the momentum space width of the peak in the spin
susceptibility, Im, is linearly proportional to the
superconducting : with \AA. This relation is similar to the linear relation between incommensurate
peak splitting and in LaSrCuO superconductors, as first proposed by
Yamada et al. (Phys. Rev. B 57, 6165, (1998)). The velocity is
smaller than Fermi velocity or the spin-wave velocity of the parent compound
and remains the same for a wide doping range. This result points towards strong
similarities in magnetic state of YBCO and LaSrCuO.Comment: 5 pages, 3 figures, latex fil
High-Energy Spin Dynamics in LaSrNiO
We have mapped out the spin dynamics in a stripe-ordered nickelate,
LaSrNiO with , using inelastic neutron
scattering. We observe spin-wave excitations up to 80 meV emerging from the
incommensurate magnetic peaks with an almost isotropic spin-velocity: eV \AA, very similar to the velocity in the undoped, insulating
parent compound, LaNiO. We also discuss the similarities and
differences of the inferred spin-excitation spectrum with those reported in
superconducting high- cuprates.Comment: 4 figure
Testing of a novel web browser interface for the Chinese market
This paper compares the perspicacity, appropriateness and preference of web browser icons from leading software providers with those of a culture-specific design. This online study was conducted in Taiwan and involved 103 participants, who were given three sets of web browser icons to review, namely Microsoft Internet Explorer, Macintosh Safari, and culturally specific icons created using the Culture-Centred Design methodology. The findings of the study show that all three sets have generally high recognition rates, but that some icon functions (e.g. Go/Visit and Favourite) in all three sets have poor recognition rates and are considered inappropriate
Double dispersion of the magnetic resonant mode in cuprates
The magnetic excitation spectra in the vicinity of the resonant peak, as
observed by inelastic neutron scattering in cuprates, are studied within the
memory-function approach. It is shown that at intermediate doping the
superconducting gap induces a double dispersion of the peak, with an anisotropy
rotated between the downward and upward branch. Similar behavior, but with a
spin-wave dispersion at higher energies, is obtained for the low-doping case
assuming a large pairing pseudogap.Comment: 4 LaTeX pages, 4 figure
Magnetic excitations in multiferroic LuMnO3 studied by inelastic neutron scattering
We present data on the magnetic and magneto-elastic coupling in the hexagonal
multiferroic manganite LuMnO3 from inelastic neutron scattering, magnetization
and thermal expansion measurements. We measured the magnon dispersion along the
main symmetry directions and used this data to determine the principal exchange
parameters from a spin-wave model. An analysis of the magnetic anisotropy in
terms of the crystal field acting on the Mn is presented. We compare the
results for LuMnO3 with data on other hexagonal RMnO3 compounds.Comment: 7 pages, 8 figures, typo correcte
High energy spin excitations in YBa_2 Cu_3 O_{6.5}
Inelastic neutron scattering has been used to obtain a comprehensive
description of the absolute dynamical spin susceptibility
of the underdoped superconducting cuprate YBa_2 Cu_3 O_{6.5} ()
over a wide range of energies and temperatures ( and ). Spin excitations of two different
symmetries (even and odd under exchange of two adjacent CuO_2 layers) are
observed which, surprisingly, are characterized by different temperature
dependences. The excitations show dispersive behavior at high energies.Comment: 15 pages, 5 figure
Observation of Magnetic Order in a Superconductor
Polarized beam neutron scattering measurements on a highly perfect crystal of
show a distinct magnetic transition with an onset at
about 235K, the temperature expected for the pseudogap transition. The moment
is found to be about 0.1 for each sublattice and have a correlation
length of at least 75 \AA. We found the critical exponent for the magnetic
neutron intensity to be 2 =0.37 0.12. This is the proper range for
the class of transition that has no specific heat divergence possibly
explaining why none is found at the pseudogap transition.Comment: 3 figure
Quantum Impurities and the Neutron Resonance Peak in : Ni versus Zn
The influence of magnetic (S=1) and nonmagnetic (S=0) impurities on the spin
dynamics of an optimally doped high temperature superconductor is compared in
two samples with almost identical superconducting transition temperatures:
YBa(CuNi)O (T=80 K) and
YBa(CuZn)O (T=78 K). In the Ni-substituted
system, the magnetic resonance peak (which is observed at E40 meV in
the pure system) shifts to lower energy with a preserved E/T ratio
while the shift is much smaller upon Zn substitution. By contrast Zn, but not
Ni, restores significant spin fluctuations around 40 meV in the normal state.
These observations are discussed in the light of models proposed for the
magnetic resonance peak.Comment: 3 figures, submitted to PR
Collective Modes in the Loop Current Ordered Phase of Cuprates
Recently two branches of weakly dispersive collective modes have been
discovered in under-doped cuprates by inelastic neutron scattering.
Polarization analysis reveals that the modes are magnetic excitations. They are
only visible for temperatures below the transition temperature to a broken
symmetry phase which was discovered earlier and their intensity increases as
temperature is further decreased. The broken symmetry phase itself has
symmetries consistent with ordering of orbital current loops within a unit-cell
without breaking translational symmetry. In order to calculate the collective
modes of such a state we add quantum terms to the Ashkin-Teller (AT) model with
which the classical loop current order has been described. We derive that the
mean field ground state of the quantum model is a product over all unit-cells
of linear combination of the four possible classical configurations of the loop
current order in each unit-cell. The collective modes are calculated by using a
generalized Holstein-Primakoff boson representation of orbital moment operators
and lead to three branches of gapped weakly dispersive collective modes. The
experimental results are consistent with the two lower energy branches; the
third mode is at a higher energy than looked for by present neutron scattering
experiments and might also be over-damped. Implications of the discovery of the
collective modes are discussed.Comment: 16 pages, 6 figure
Quantum statistics of interacting dimer spin systems
The compound TlCuCl3 represents a model system of dimerized quantum spins with strong interdimer interactions. We investigate the triplet dispersion as a function of temperature by inelastic neutron scattering experiments on single crystals. By comparison with a number of theoretical approaches we demonstrate that the description of Troyer, Tsunetsugu, and Wurtz [Phys. Rev. B 50, 13 515 (1994)] provides an appropriate quantum statistical model for dimer spin systems at finite temperatures, where many-body correlations become particularly important
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