19 research outputs found
Acoustic Attenuation in High- Superconductors
We analyze the acoustic attenuation rate in high- superconductors, and
find that this method offers an additional way to examine the anisotropy of the
superconducting order parameter in these materials. We argue that it should be
possible to distinguish the electronic contribution to the acoustic
attenuation, which has a strong temperature dependence near , from the
lattice contribution, which does not show a strong temperature dependence near
. We propose that this can be utilized to measure the anisotropy of the
order parameter by measuring the attenuation rate near in different
directions.Comment: 9 pages, latex, 2 postscript figures, in press Physica C, (uuencoded
file consisting of paper and 2 figures, please contact J.C. Swihart
([email protected]) for a printed copy
Calculation of electronic properties of amorphous alloys
We describe the application of the
locally-self-consistent-multiple-scattering (LSMS)[1] method to amorphous
alloys. The LSMS algorithm is optimized for the Intel XP/S-150, a
multiple-instruction-multiple-data parallel computer with 1024 nodes and 2
compute processors per node. The electron density at each site is determined by
solving the multiple scattering equation for atoms within a specified distance
of the atom under consideration. Because this method is carried out in real
space it is ideal for treating amorphous alloys. We have adapted the code to
the calculation of the electronic properties of amorphous alloys. In these
calculations we determine the potentials in the atomic sphere approximation
self consistently at each site, unlike previous calculations[2] where we
determined the potentials self consistently at an average site. With these
self-consistent potentials, we then calculate electronic properties of various
amorphous alloy systems. We present calculated total electronic densities of
states for amorphous NiP and NiPdP with 300
atoms in a supercell.Comment: 10 pages, plain tex, 2 figures. Paper accepted for publication in
Proceedings of LAM-9 and Journal of non-Crystalline Solids. Please request
preprints from J.C. Swihart ([email protected]
Electromagnetic waves in a Josephson junction in a thin film
We consider a one-dimensional Josephson junction in a superconducting film
with the thickness that is much less than the London penetration depth. We
treat an electromagnetic wave propagating along this tunnel contact. We show
that the electrodynamics of a Josephson junction in a thin film is nonlocal if
the wave length is less than the Pearl penetration depth. We find the
integro-differential equation determining the phase difference between the two
superconductors forming the tunnel contact. We use this equation to calculate
the dispersion relation for an electromagnetic wave propagating along the
Josephson junction. We find that the frequency of this wave is proportional to
the square root of the wave vector if the wave length is less than the Pearl
penetration depth.Comment: 12 pages, a figure is included as a uuencodeded postscript file,
ReVTe
Zurek-Kibble domain structures: The Dynamics of Spontaneous Vortex formation in Annular Josephson Tunnel Junctions
Phase transitions executed in a finite time show a domain structure with
defects, that has been argued by Zurek and Kibble to depend in a characteristic
way on the quench rate. In this letter we present an experiment to measure the
Zurek-Kibble scaling exponent sigma. Using symmetric and long Josephson Tunnel
Junctions, for which the predicted index is sigma = 0.25, we find sigma = 0.27
+/- 0.05. Further, there is agreement with the ZK prediction for the overall
normalisation.Comment: To be published in Phys. Rev. Lett
Strong Electron-Phonon Coupling in Superconducting MgB: A Specific Heat Study
We report on measurements of the specific heat of the recently discovered
superconductor MgB in the temperature range between 3 and 220 K. Based on a
modified Debye-Einstein model, we have achieved a rather accurate account of
the lattice contribution to the specific heat, which allows us to separate the
electronic contribution from the total measured specific heat. From our result
for the electronic specific heat, we estimate the electron-phonon coupling
constant to be of the order of 2, significantly enhanced compared to
common weak-coupling values . Our data also indicate that the
electronic specific heat in the superconducting state of MgB can be
accounted for by a conventional, s-wave type BCS-model.Comment: 4 pages, 4 figure
Josephson Coupling and Fiske Dynamics in Ferromagnetic Tunnel Junctions
We report on the fabrication of Nb/AlO_x/Pd_{0.82}Ni_{0.18}/Nb
superconductor/insulator/ferromagnetic metal/superconductor (SIFS) Josephson
junctions with high critical current densities, large normal resistance times
area products, high quality factors, and very good spatial uniformity. For
these junctions a transition from 0- to \pi-coupling is observed for a
thickness d_F ~ 6 nm of the ferromagnetic Pd_{0.82}Ni_{0.18} interlayer. The
magnetic field dependence of the \pi-coupled junctions demonstrates good
spatial homogeneity of the tunneling barrier and ferromagnetic interlayer.
Magnetic characterization shows that the Pd_{0.82}Ni_{0.18} has an out-of-plane
anisotropy and large saturation magnetization, indicating negligible dead
layers at the interfaces. A careful analysis of Fiske modes provides
information on the junction quality factor and the relevant damping mechanisms
up to about 400 GHz. Whereas losses due to quasiparticle tunneling dominate at
low frequencies, the damping is dominated by the finite surface resistance of
the junction electrodes at high frequencies. High quality factors of up to 30
around 200 GHz have been achieved. Our analysis shows that the fabricated
junctions are promising for applications in superconducting quantum circuits or
quantum tunneling experiments.Comment: 15 pages, 9 figure