634 research outputs found
Pattern Formation in a 2D Elastic Solid
We present a dynamical theory of a two-dimensional martensitic transition in
an elastic solid, connecting a high-temperature phase which is nondegenerate
and has triangular symmetry, and a low-temperature phase which is triply
degenerate and has oblique symmetry. A global mode-based Galerkin method is
employed to integrate the deterministic equation of motion, the latter of which
is derived by the variational principle from a nonlinear, nonlocal
Ginzburg-Landau theory which includes the sound-wave viscosity. Our results
display (i) the phenomenon of surface nucleation, and (ii) the dynamical
selection of a length scale of the resultant patterns.Comment: LaTeX, 14 pages with four post-script figures included by psfig.
Three of these are colour, but viewable in black-and-white. Presented at the
conference "Collective Phenomena in Physics: Pattern Formation in Fluids and
Materials", University of Western Ontario, London, June 199
Temperature dependence of the superconducting gap anisotropy in BiSrCaCuO
We present the first detailed data of the momentum-resolved, temperature
dependence of the superconducting gap of ,
complemented by similar data on the intensity of the photoemission
superconducting condensate spectral area. The gap anisotropy between the
and directions increases markedly with increasing
temperature, contrary to what happens for conventional anisotropic-gap
superconductors such as lead. Specifically, the size of the superconducting gap
along the direction decreases to values indistinguishable from zero
at temperatures for which the gap retains virtually full value along the
direction.Comment: APS_REVTEX. 19 pages, including 8 figures, available upon request.
UW-Madison preprin
Localized electronic states and photoemission superconducting condensate in BiSrCaCuO
We present the first detailed angle-resolved photoemission evidence that
there are two types of carriers that contribute to the photoemission
superconducting condensate in . Our data
indicate that both itinerant and somewhat localized normal state carriers can
contribute to the formation of Cooper pairs.Comment: APS_Revtex, 11 pages, including 3 figures, available upon request.
UW-Madison preprint#
Superconductivity and Stoichiometry in the BSCCO-family Materials
We report on magnetization, c-axis and ab-plane resistivity, critical
current, electronic band structure and superconducting gap properties. Bulk
measurements and photoemission data were taken on similar samples.Comment: 4 pages, latex, to be published in Journal of Superconductivity. two
figures available from Jian Ma at [email protected]
Internal avalanches in a pile of superconducting vortices
Using an array of miniature Hall probes, we monitored the spatiotemporal
variation of the internal magnetic induction in a superconducting niobium
sample during a slow sweep of external magnetic field. We found that a sizable
fraction of the increase in the local vortex population occurs in abrupt jumps.
The size distribution of these avalanches presents a power-law collapse on a
limited range. In contrast, at low temperatures and low fields, huge avalanches
with a typical size occur and the system does not display a well-defined
macroscopic critical current.Comment: 5 pages including 5 figure
Effect of Iodine Doping on BiSrCaCuO: Charge Transfer or Interlayer Coupling?
A comparative study has been made of iodine-intercalated
BiSrCaCuO single crystal and 1 atm O
annealed BiSrCaCuO single crystal using AC
susceptibility measurement, X-ray photoemission (XPS) and angle-resolved
ultraviolet photoemission spectroscopy (ARUPS). AC susceptibility measurement
indicates that O-doped samples studied have T of 84 K,
whereas T of Iodine-doped samples studied are 80 K. XPS Cu 2p core
level data establish that the hole concentration in the CuO planes are
essentially the same for these two kinds of samples. ARUPS measurements show
that electronic structure of the normal states near the Fermi level has been
strongly affected by iodine intercalation. We conclude that the dominant effect
of iodine doping is to alter the interlayer coupling.Comment: LBL 9 pages, APS_Revtex. 5 Figures, available upon request.
UW-Madison preprin
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
Effect of FET geometry on charge ordering of transition metal oxides
We examine the effect of an FET geometry on the charge ordering phase diagram
of transition metal oxides using numerical simulations of a semiclassical model
including long-range Coulomb fields, resulting in nanoscale pattern formation.
We find that the phase diagram is unchanged for insulating layers thicker than
approximately twice the magnetic correlation length. For very thin insulating
layers, the onset of a charge clump phase is shifted to lower values of the
strength of the magnetic dipolar interaction, and intermediate diagonal stripe
and geometric phases can be suppressed. Our results indicate that, for
sufficiently thick insulating layers, charge injection in an FET geometry can
be used to experimentally probe the intrinsic charge ordering phases in these
materials.Comment: 4 pages, 4 postscript figure
Dynamic Vortex Phases and Pinning in Superconductors with Twin Boundaries
We investigate the pinning and driven dynamics of vortices interacting with
twin boundaries using large scale molecular dynamics simulations on samples
with near one million pinning sites. For low applied driving forces, the vortex
lattice orients itself parallel to the twin boundary and we observe the
creation of a flux gradient and vortex free region near the edges of the twin
boundary. For increasing drive, we find evidence for several distinct dynamical
flow phases which we characterize by the density of defects in the vortex
lattice, the microscopic vortex flow patterns, and orientation of the vortex
lattice. We show that these different dynamical phases can be directly related
to microscopically measurable voltage - current V(I) curves and voltage noise.
By conducting a series of simulations for various twin boundary parameters we
derive several vortex dynamic phase diagrams.Comment: 5 figures, to appear in Phys. Rev.
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