360 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
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
Absence of an isotope effect in the magnetic resonance in high- superconductors
An inelastic neutron scattering experiment has been performed in the
high-temperature superconductor to search for an
oxygen-isotope shift of the well-known magnetic resonance mode at 41 meV.
Contrary to a recent prediction (I. Eremin, {\it et al.}, Phys. Rev. B {\bf
69}, 094517 (2004)), a negligible shift (at best +0.2 meV) of the
resonance energy is observed upon oxygen isotope substitution
(OO). This suggests a negligible spin-phonon interaction in
the high- cuprates at optimal doping.Comment: 3 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
Dispersion of the odd magnetic resonant mode in near-optimally doped Bi2Sr2CaCu2O8+d
We report a neutron scattering study of the spin excitation spectrum in the
superconducting state of slightly overdoped Bi2Sr2CaCu2O8+d system (Tc=87 K).
We focus on the dispersion of the resonance peak in the superconducting state
that is due to a S=1 collective mode. The measured spin excitation spectrum
bears a strong similarity to the spectrum of the YBa2Cu3O6+x system for a
similar doping level i.e. x= 0.95-1), which consists of intersecting upward-
and downward-dispersing branches. A close comparison of the threshold of the
electron-hole spin flip continuum, deduced from angle resolved photo-emission
measurements in the same system, indicates that the magnetic response in the
superconducting state is confined, in both energy and momentum, below the
gapped Stoner continuum. In contrast to YBa2Cu3O6+x, the spin excitation
spectrum is broader than the experimental resolution. In the framework of an
itinerant-electron model, we quantitatively relate this intrinsic energy width
to the superconducting gap distribution observed in scanning tunnelling
microscopy experiments. Our study further suggests a significant in-plane
anisotropy of the magnetic response.Comment: 10 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
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
Phase separation in the vicinity of "quantum critical" doping concentration: implications for high temperature superconductors
A general quantitative measure of the tendency towards phase separation is
introduced for systems exhibiting phase transitions or crossovers controlled by
charge carrier concentration. This measure is devised for the situations when
the quantitative knowledge of various contributions to free energy is
incomplete, and is applied to evaluate the chances of electronic phase
separation associated with the onset of antiferromagnetic correlations in
high-temperature cuprate superconductors. The experimental phenomenology of
lanthanum- and yittrium-based cuprates was used as input to this analysis. It
is also pointed out that Coulomb repulsion between charge carriers separated by
the distances of 1-3 lattice periods strengthens the tendency towards phase
separation by accelerating the decay of antiferromagnetic correlations with
doping. Overall, the present analysis indicates that cuprates are realistically
close to the threshold of phase separation -- nanoscale limited or even
macroscopic with charge density varying between adjacent crystal planes
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
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