256 research outputs found
Magnetic Resonant excitations in High-{} superconductors
The observation of an unusual spin resonant excitation in the superconducting
state of various High-Tc ~copper oxides by inelastic neutron scattering
measurements is reviewed. This magnetic mode % (that does not exist in
conventional superconductors) is discussed in light of a few theoretical models
and likely corresponds to a spin-1 collective mode.Comment: 4 figures, Proceedings conference MSM'03 (september 2003) in Monastir
(Tunisia) to be published in Phys. Stat. Solid
Spin reorientation in Na-doped BaFeAs studied by neutron diffraction
We have studied the magnetic ordering in Na doped BaFeAs by
unpolarized and polarized neutron diffraction using single crystals. Unlike
previously studied FeAs-based compounds that magnetically order,
BaNaFeAs exhibits two successive magnetic transitions: For
x=0.35 upon cooling magnetic order occurs at 70\ K with in-plane magnetic
moments being arranged as in pure or Ni, Co and K-doped BaFeAs samples.
At a temperature of 46\ K a second phase transition occurs, which the
single-crystal neutron diffraction experiments can unambiguously identify as a
spin reorientation. At low temperatures, the ordered magnetic moments in
BaNaFeAs point along the direction. Magnetic
correlations in these materials cannot be considered as Ising like, and
spin-orbit coupling must be included in a quantitative theory.Comment: 5 pages, 4 figure
Magnetic order in the pseudogap phase of high- superconductors
One of the leading issues in high- superconductors is the origin of the
pseudogap phase in underdoped cuprates. Using polarized elastic neutron
diffraction, we identify a novel magnetic order in the YBaCuO
system. The observed magnetic order preserves translational symmetry as
proposed for orbital moments in the circulating current theory of the pseudogap
state. To date, it is the first direct evidence of an hidden order parameter
characterizing the pseudogap phase in high- cuprates.Comment: 3 figure
2D orbital-like magnetic order in
In high temperature copper oxides superconductors, a novel magnetic order
associated with the pseudogap phase has been identified in two different
cuprate families over a wide region of temperature and doping. We here report
the observation below 120 K of a similar magnetic ordering in the archetypal
cuprate (LSCO) system for x=0.085. In contrast to the
previous reports, the magnetic ordering in LSCO is {\it\bf only} short range
with an in-plane correlation length of 10 \AA\ and is bidimensional
(2D). Such a less pronounced order suggests an interaction with other
electronic instabilities. In particular, LSCO also exhibits a strong tendency
towards stripes ordering at the expense of the superconducting state.Comment: 4 figures, submitted to Phys. Rev. Let
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
Resonant magnetic excitations at high energy in superconducting
A detailed inelastic neutron scattering study of the high temperature
superconductor provides evidence of new resonant
magnetic features, in addition to the well known resonant mode at 41 meV: (i) a
commensurate magnetic resonance peak at 53 meV with an even symmetry under
exchange of two adjacent layers; and (ii) high energy
incommensurate resonant spin excitations whose spectral weight is around 54
meV. The locus and the spectral weight of these modes can be understood by
considering the momentum shape of the electron-hole spin-flip continuum of
d-wave superconductors. This provides new insight into the interplay between
collective spin excitations and the continuum of electron-hole excitations.Comment: 5 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
Two resonant magnetic modes in an overdoped high- superconductor
A detailed inelastic neutron scattering study of the overdoped high
temperature copper oxide superconductor
reveals two distinct magnetic resonant modes in the superconducting state. The
modes differ in their symmetry with respect to exchange between adjacent copper
oxide layers. Counterparts of the mode with odd symmetry, but not the one with
even symmetry, had been observed before at lower doping levels. The observation
of the even mode resolves a long-standing puzzle, and the spectral weight ratio
of both modes yields an estimate of the onset of particle-hole spin-flip
excitations.Comment: Submitted to PR
Doping Dependence of Bilayer Resonant Spin Excitations in
Resonant magnetic modes with odd and even symmetries were studied by
inelastic neutron scattering experiments in the bilayer high-
superconductor over a wide doping range. The
threshold of the spin excitation continuum in the superconducting state,
deduced from the energies and spectral weights of both modes, is compared with
the superconducting d-wave gap, measured on the same samples by electronic
Raman scattering in the symmetry. Above a critical doping level of
, both mode energies and the continuum threshold coincide.
We find a simple scaling relationship between the characteristic energies and
spectral weights of both modes, which indicates that the resonant modes are
bound states in the superconducting energy gap, as predicted by the
spin-exciton model of the resonant mode.Comment: 4 figure
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