403 research outputs found
Superconducting Order Parameter in Bi-Layer Cuprates: Occurrence of Phase Shifts in Corner Junctions
We study the order parameter symmetry in bi-layer cuprates such as YBaCuO,
where interesting phase shifts have been observed in Josephson junctions.
Taking models which represent the measured spin fluctuation spectra of this
cuprate, as well as more general models of Coulomb correlation effects, we
classify the allowed symmetries and determine their associated physical
properties. phase shifts are shown to be a general consequence of
repulsive interactions, independent of whether a magnetic mechanism is
operative. While it is known to occur in d-states, this behavior can also be
associated with (orthorhombic) s-symmetry when the two sub-band gaps have
opposite phase. Implications for the magnitude of are discussed.Comment: 5 pages, RevTeX 3.0, 9 figures (available upon request
Possible Microscopic Doping Mechanism in Tl-2201
X-ray absorption spectroscopy on oxygen-annealed, self-flux-grown single
crystals of Tl-2201 suggests a microscopic doping mechanism whereby
interstitial oxygens are attracted to copper substituted on the thallium site,
contributing holes to both the planes and to these coppers, and typically
promoting only one hole to the plane rather than two. These copper substituents
would provide an intrinsic hole doping. The evidence for this is discussed,
along with an alternative interpretation.Comment: 2 pages, 1 figure, submitted as conference proceedings for M2S-IX,
Toky
Plasma wave instabilities induced by neutrinos
Quantum field theory is applied to study the interaction of an electron
plasma with an intense neutrino flux. A connection is established between the
field theory results and classical kinetic theory. The dispersion relation and
damping rate of the plasma longitudinal waves are derived in the presence of
neutrinos. It is shown that Supernova neutrinos are never collimated enough to
cause non-linear effects associated with a neutrino resonance. They only induce
neutrino Landau damping, linearly proportional to the neutrino flux and
.Comment: 18 pages, 3 figures, title and references correcte
Patterns of primes in arithmetic progressions
After the proof of Zhang about the existence of infinitely many bounded gaps between consecutive primes the author showed the existence of a bounded d such that there are arbitrarily long arithmetic progressions of primes with the property that p′ = p + d is the prime following p for each element of the progression. This was a common generalization of the results of Zhang and Green-Tao. In the present work it is shown that for every m we have a bounded m-tuple of primes such that this configuration (i.e. the integer translates of this m-tuple) appear as arbitrarily long arithmetic progressions in the sequence of all primes. In fact we show that this is true for a positive proportion of all m-tuples. This is a common generalization of the celebrated works of Green-Tao and Maynard/Tao.
Dedicated to the 60th birthday of Robert F. Tich
Two-dimensional vortex behavior in highly underdoped YBa_2Cu_3O_{6+x} observed by scanning Hall probe microscopy
We report scanning Hall probe microscopy of highly underdoped superconducting
YBa_2Cu_3O_{6+x} with T_c ranging from 5 to 15 K which showed distinct flux
bundles with less than one superconducting flux quantum (Phi_0) through the
sample surface. The sub-Phi_0 features occurred more frequently for lower T_c,
were more mobile than conventional vortices, and occurred more readily when the
sample was cooled with an in-plane field component. We show that these features
are consistent with kinked stacks of pancake vortices.Comment: 11 pages, 8 figures, accepted for publication in Physical Review
S and D Wave Mixing in High Superconductors
For a tight binding model with nearest neighbour attraction and a small
orthorhombic distortion, we find a phase diagram for the gap at zero
temperature which includes three distinct regions as a function of filling. In
the first, the gap is a mixture of mainly -wave with a smaller extended
-wave part. This is followed by a region in which there is a rapid increase
in the -wave part accompanied by a rapid increase in relative phase between
and from 0 to . Finally, there is a region of dominant with a
mixture of and zero phase. In the mixed region with a finite phase, the
-wave part of the gap can show a sudden increase with decreasing temperature
accompanied with a rapid increase in phase which shows many of the
characteristics measured in the angular resolved photoemission experiments of
Ma {\em et al.} in Comment: 12 pages, RevTeX 3.0, 3 PostScript figures uuencoded and compresse
Microwave properties of : Influence of magnetic scattering
We report measurements of the surface impedance of
, . Increasing
concentration leads to some striking results not observed in samples doped
by non-magnetic constituents. The three principal features of the data
- multiple structure in the transition, a high residual resistance and, at high
concentrations, an upturn of the low data, are all characteristic of
the influence of magnetic scattering on superconductivity, and appear to be
common to materials where magnetism and superconductivity coexist. The low
behavior of appears to change from to at large
doping, and provides evidence of the influence of magnetic pairbreaking of the
.Comment: 5 pages, 3 eps figures, Revtex, 2-column format, uses graphicx. To
appear in Physica C. Postscript version also available at
http://sagar.physics.neu.edu/preprints.htm
Resonant Impurity Scattering in a Strongly Correlated Electron Model
Scattering by a single impurity introduced in a strongly correlated
electronic system is studied by exact diagonalization of small clusters. It is
shown that an inert site which is spinless and unable to accomodate holes can
give rise to strong resonant scattering. A calculation of the local density of
state reveals that, for increasing antiferromagnetic exchange coupling, d, s
and p-wave symmetry bound states in which a mobile hole is trapped by the
impurity potential induced by a local distortion of the antiferromagnetic
background successively pull out from the continuum.Comment: 10 pages, 4 figures available on request, report LPQTH-93-2
Doping dependence of superconducting gap in YBa_2Cu_3O_y from universal heat transport
Thermal transport in the T -> 0 limit was measured as a function of doping in
high-quality single crystals of the cuprate superconductor YBa_2Cu_3O_y. The
residual linear term kappa_0/T is found to decrease as one moves from the
overdoped regime towards the Mott insulator region of the phase diagram. The
doping dependence of the low-energy quasiparticle gap extracted from kappa_0/T
is seen to scale closely with that of the pseudogap, arguing against a
non-superconducting origin for the pseudogap. The presence of a linear term for
all dopings is evidence against the existence of a quantum phase transition to
an order parameter with a complex (ix) component.Comment: 2 pages, 2 figures, submitted to M2S-Rio 2003 Proceeding
Encapsulated Single Crystal Growth and Annealing of the High-Temperature Superconductor Tl-2201
Highly-perfect platelet single crystals of Tl_2Ba_2CuO_{6+d} (Tl-2201) were
grown by a self-flux technique. A novel encapsulation scheme allowed the
precursors to react prior to the sealing required to contain volatile thallium
oxides, and permitted the removal of melt at the conclusion of growth,
reproducibly producing high yields of clean crystals. The crystals were
annealed under well-controlled oxygen partial pressures, then characterised.
They have sharp superconducting transitions, narrow X-ray rocking curves and a
low 4% substitution of thallium by copper, all evidence of their high
perfection and homogeneity. The crystals are orthorhombic at most dopings, and
a previously unreported commensurate superlattice distortion is observed.Comment: 8 pages, 5 figures, submitted to Journal of Crystal Growt
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