131 research outputs found
Transport Properties of "Extended-s" State Superconductors
Superconducting states with "extended s-wave" symmetry have been suggested in
connection with recent ARPES experiments on BSCCO. In the presence of
impurities, thermodynamic properties of such states reflect a residual density
of states for a range of concentrations. While properties reflecting
alone will be similar to those of d-wave states, transport
measurements may be shown to qualitatively distinguish between the two. In
contrast to the d-wave case with unitarity limit scattering, limiting
low-temperature residual conductivities in the s-wave state are large and scale
inversely with impurity concentration.Comment: 4 pages, 5 figures, uuencoded compressed postscript fil
Effect of Interband Transitions on the c axis Penetration Depth of Layered Superconductors
The electromagnetic response of a system with two planes per unit cell
involves, in addition to the usual intraband contribution, an added interband
term. These transitions affect the temperature dependence and the magnitude of
the zero temperature c-axis penetration depth. When the interplane hopping is
sufficiently small, the interband transitions dominate the low temperature
behaviour of the penetration depth which then does not reflect the linear
temperature dependence of the intraband term and in comparison becomes quite
flat even for a d-wave gap. It is in this regime that the pseudogap was found
in our previous normal state calculations of the c-axis conductivity, and the
effects are connected.Comment: 8 pages, 5 figure
Dynamical probes of chemical interactions at interfaces
We report on the application of two experimental techniques developed in the field of atomic and molecular physics to investigate the dynamics of catalytic processes on a molecular scale in (model) cata!ysts. With these techniques, time-resolved pump-probe laser spectroscopy and molecular beam scattering, better insights into the fundamental processes relevant to catalysis can be obtained. With the first technique, time-resolved (picosecond) non-linear infared spectroscopy, zeolite catalysts and zeolite-adsorbate interactions are investigated. Microscopic structural information on the bare catalyst, as well as insights into the dynamics of interaction processes between catalyst and reactant (viz. zeolite and adsorbate) on a molecular scale are obtained. With the second technique, a molecular beam experiment, we obtain dynamical information on the interaction between catalytic metal surfaces and molecules; transient surface species and steric effects are observed
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
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
Quasi-particle Lifetimes in a d_{x^2-y^2} Superconductor
We consider the lifetime of quasi-particles in a d-wave superconductor due to
scattering from antiferromagnetic spin-fluctuations, and explicitly separate
the contribution from Umklapp processes which determines the electrical
conductivity. Results for the temperature dependence of the total scattering
rate and the Umklapp scattering rate are compared with relaxation rates
obtained from thermal and microwave conductivity measurements, respectively.Comment: 14 pages, 4 figure
Effect of controlled disorder on quasiparticle thermal transport in BiSrCaCuO
Low temperature thermal conductivity, , of optimally-doped Bi2212 was
studied before and after the introduction of point defects by electron
irradiation. The amplitude of the linear component of remains
unchanged, confirming the universal nature of heat transport by zero-energy
quasiparticles. The induced decrease in the absolute value of at
finite temperatures allows us to resolve a nonuniversal term in due to
conduction by finite-energy quasiparticles. The magnitude of this term provides
an estimate of the quasiparticle lifetime at subkelvin temperatures.Comment: 5 pages including 2 .eps figuer
Quasiparticle contribution to heat carriers relaxation time in DyBaCuO from heat diffusivity measurements
It is shown that the controversy on phonons or electrons being the most
influenced heat carriers below the critical temperature of high-T
superconductors can be resolved. Electrical and thermal properties of the same
DyBaCuO monodomain have been measured for two highly different
oxygenation levels. While the oxygenated sample DyBaCuO has very
good superconducting properties ( K), the DyBaCuO
sample exhibits an insulator behavior. A careful comparison between
measurements of the {\bf thermal diffusivity} of both samples allows us to
extract the electronic contribution. This contribution to the relaxation time
of heat carriers is shown to be large below and more sensitive to the
superconducting state than the phonon contribution.Comment: 13 pages, 6 figure
Scattering by impurity-induced order parameter ``holes'' in d-wave superconductors
Nonmagnetic impurities in d-wave superconductors cause strong local
suppressions of the order parameter. We investigate the observable effects of
the scatterigng off such suppressions in bulk samples by treating the order
parameter "hole" as a pointlike off-diagonal scatterer treated within a
self-consistent t-matrix approximation. Strong scattering potentials lead to a
finite-energy spectral feature in the d-wave "impurity band", the observable
effects of which include enhanced low-temperature microwave power absorption
and a stronger sensitivity of the London penetration depth to disorder than
found previously in simpler ``dirty'' d-wave models.Comment: 5 pp. Revtex including 4 postscript figures, submitted to Phys. Rev.
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
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