102 research outputs found
What can we learn from comparison between cuprates and He films ? : phase separation and fluctuating superfluidity
In the underdoped, overdoped, Zn-doped or stripe-forming regions of
high- cuprate superconductors (HTSC), the superfluid density
at shows universal correlations with . Similar
strong correlations exist between 2-dimensional superfluid density and
superfluid transition temperature in thin films of He in non-porous or
porous media, and He/He film adsorbed on porous media. Based on
analogy between HTSC and He film systems, we propose a model for cuprates
where: (1) the overdoped region is characterized by a phase separation similar
to He/He; and (2) pair (boson) formation and fluctuating
superconductivity occur at separate temperatures above in the
underdoped region.Comment: 8 pages, 5 figures. Invited paper presented at the third
international conference on stripes and high-Tc superconductivity
(STRIPE-2000), Sept. 25-30th, 2000, Rome, Italy. To be published in the
International Journal of Modern Physics
Neutron scattering study of spin ordering and stripe pinning in superconducting LaSrCuO
The relationships among charge order, spin fluctuations, and
superconductivity in underdoped cuprates remain controversial. We use neutron
scattering techniques to study these phenomena in
LaSrCuO, a superconductor with a transition temperature
of ~K. At , we find incommensurate spin fluctuations with a
quasielastic energy spectrum and no sign of a gap within the energy range from
0.2 to 15 meV. A weak elastic magnetic component grows below ~K,
consistent with results from local probes. Regarding the atomic lattice, we
have discovered unexpectedly strong fluctuations of the CuO octahedra about
Cu-O bonds, which are associated with inequivalent O sites within the CuO
planes. Furthermore, we observed a weak elastic superlattice peak
that implies a reduced lattice symmetry. The presence of inequivalent O sites
rationalizes various pieces of evidence for charge stripe order in underdoped
\lsco. The coexistence of superconductivity with quasi-static spin-stripe order
suggests the presence of intertwined orders; however, the rotation of the
stripe orientation away from the Cu-O bonds might be connected with evidence
for a finite gap at the nodal points of the superconducting gap function.Comment: 13 pages, 11 figures; accepted versio
Antiferromagnetic ordering and dipolar interactions of YbAlO
In this paper we report low-temperature magnetic properties of the rare-earth
perovskite material YbAlO. Results of elastic and inelastic neutron
scattering experiment, magnetization measurements along with the crystalline
electrical field (CEF) calculations suggest that the ground state of Yb moments
is a strongly anisotropic Kramers doublet, and the moments are confined in the
-plane, pointing at an angle of to the
-axis. With temperature decreasing below K, Yb moments
order into the coplanar, but non-collinear antiferromagnetic (AFM) structure
, where the moments are pointed along their easy-axes. In addition, we
highlight the importance of the dipole-dipole interaction, which selects the
type of magnetic ordering and may be crucial for understanding magnetic
properties of other rare-earth orthorhombic perovskites. Further analysis of
the broad diffuse neutron scattering shows that one-dimensional interaction
along the -axis is dominant, and suggests YbAlO as a new member of one
dimensional quantum magnets.Comment: 8 pages, 6 figure
Spin pseudogap in Ni-doped SrCuO2
The S=1/2 spin chain material SrCuO2 doped with 1% S=1 Ni-impurities is
studied by inelastic neutron scattering. At low temperatures, the spectrum
shows a pseudogap \Delta ~ 8 meV, absent in the parent compound, and not
related to any structural phase transition. The pseudogap is shown to be a
generic feature of quantum spin chains with dilute defects. A simple model
based on this idea quantitatively accounts for the exprimental data measured in
the temperature range 2-300 K, and allows to represent the momentum-integrated
dynamic structure factor in a universal scaling form.Comment: 5 pages, 3 figure
Study of the ground state properties of using SR
is an insulating system where the magnetic Ho ions
have an Ising character, and interact mainly through magnetic dipolar fields.
We used the muon spin relaxation technique to study the nature of the ground
state for samples with x=0.25, 0.12, 0.08, 0.045 and 0.018. In contrast with
some previous works, we have not found any signature of canonical spin glass
behavior down to 15mK. Instead, below 300mK we observed
dynamic magnetism characterized by a single correlation time with a temperature
independent fluctuation rate. We observed that this low temperature fluctuation
rate increases with x up to 0.08, above which it levels off. The 300mK energy
scale corresponds to the Ho3+ hyperfine interaction strength, suggesting that
the hyperfine interaction may be intimately involved with the spin dynamics in
this system
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