1,374 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
Information Technology: A Tool to Cut Health Care Costs
Old Dominion University embarked on a project to see how current computer technology could be applied to reduce the cost and or to improve the efficiency of health care services. We designed and built a prototype for an integrated medical record system (MRS). The MRS is written in Tool control language/Tool kit (Tcl/Tk). While the initial version of the prototype had patient information hard coded into the system, later versions used an INGRES database for storing patient information. Currently, we have proposed an object-oriented model for implementing MRS. These projects involve developing information systems for physicians and medical researchers to enhance their ability for improved treatment at reduced costs. The move to computerized patient records is well underway, several standards exist for laboratory records, and several groups are working on standards for other portions of the patient record
Magnetic Field Effects in the Pseudogap Phase: A Competing Energy Gap Scenario for Precursor Superconductivity
We study the sensitivity of T_c and T^* to low fields, H, within the
pseudogap state using a BCS-based approach extended to arbitrary coupling. We
find that T^* and T_c, which are of the same superconducting origin, have very
different H dependences. This is due to the pseudogap, \Delta_{pg}, which is
present at the latter, but not former temperature. Our results for the
coherence length \xi fit well with existing experiments.We predict that very
near the insulator \xi will rapidly increase.Comment: 4 pages, 4 figures, RevTe
Pseudogap effects induced by resonant pair scattering
We demonstrate how resonant pair scattering of correlated electrons above T_c
can give rise to pseudogap behavior. This resonance in the scattering T-matrix
appears for superconducting interactions of intermediate strength, within the
framework of a simple fermionic model. It is associated with a splitting of the
single peak in the spectral function into a pair of peaks separated by an
energy gap. Our physical picture is contrasted with that derived from other
T-matrix schemes, with superconducting fluctuation effects, and with preformed
pair (boson-fermion) models. Implications for photoemission and tunneling
experiments in the cuprates are discussed.Comment: REVTeX3.0; 4 pages, 4 EPS figures (included
The pseudogap state in superconductors: Extended Hartree approach to time-dependent Ginzburg-Landau Theory
It is well known that conventional pairing fluctuation theory at the Hartree
level leads to a normal state pseudogap in the fermionic spectrum. Our goal is
to extend this Hartree approximated scheme to arrive at a generalized mean
field theory of pseudogapped superconductors for all temperatures . While an
equivalent approach to the pseudogap has been derived elsewhere using a more
formal Green's function decoupling scheme, in this paper we re-interpret this
mean field theory and BCS theory as well, and demonstrate how they naturally
relate to ideal Bose gas condensation. Here we recast the Hartree approximated
Ginzburg-Landau self consistent equations in a T-matrix form. This recasting
makes it possible to consider arbitrarily strong attractive coupling, where
bosonic degrees of freedom appear at considerably above . The
implications for transport both above and below are discussed. Below
we find two types of contributions. Those associated with fermionic
excitations have the usual BCS functional form. That they depend on the
magnitude of the excitation gap, nevertheless, leads to rather atypical
transport properties in the strong coupling limit, where this gap (as distinct
from the order parameter) is virtually -independent. In addition, there are
bosonic terms arising from non-condensed pairs whose transport properties are
shown here to be reasonably well described by an effective time-dependent
Ginzburg-Landau theory.Comment: 14 pages, 5 figures, REVTeX4, submitted to PRB; clarification of the
diagrammatic technique added, one figure update
Coulomb Correlations and Pseudo-gap Effects in a Pre-formed Pair Model for the Cuprates
We extend previous work on pre-formed pair models of superconductivity to
incorporate Coulomb correlation effects. For neutral systems, these models have
provided a useful scheme which interpolates between BCS and Bose Einstein
condensation with increasing coupling and thereby describes some aspects of
pseudo-gap phenomena. However, charge fluctuations (via the plasmon,
) significantly modify the collective modes and therefore the
interpolation behavior. We discuss the resulting behavior of the pseudo-gap and
thermodynamic quantities such as , and as a function of
.Comment: 4 pages RevTeX, 3 ps figures included (Submitted to Physical Review B
August 27, 1996
Reduction of Tc due to Impurities in Cuprate Superconductors
In order to explain how impurities affect the unconventional
superconductivity, we study non-magnetic impurity effect on the transition
temperature using on-site U Hubbard model within a fluctuation exchange (FLEX)
approximation. We find that in appearance, the reduction of Tc roughly
coincides with the well-known Abrikosov-Gor'kov formula. This coincidence
results from the cancellation between two effects; one is the reduction of
attractive force due to randomness, and another is the reduction of the damping
rate of quasi-particle arising from electron interaction. As another problem,
we also study impurity effect on underdoped cuprate as the system showing
pseudogap phenomena. To the aim, we adopt the pairing scenario for the
pseudogap and discuss how pseudogap phenomena affect the reduction of Tc by
impurities. We find that 'pseudogap breaking' by impurities plays the essential
role in underdoped cuprate and suppresses the Tc reduction due to the
superconducting (SC) fluctuation.Comment: 14 pages, 28 figures To be published in JPS
Superconducting transitions from the pseudogap state: d-wave symmetry, lattice, and low-dimensional effects
We investigate the behavior of the superconducting transition temperature
within a previously developed BCS-Bose Einstein crossover picture. This
picture, based on a decoupling scheme of Kadanoff and Martin, further extended
by Patton, can be used to derive a simple form for the superconducting
transition temperature in the presence of a pseudogap. We extend previous work
which addressed the case of s-wave pairing in jellium, to explore the solutions
for T_c as a function of variable coupling in more physically relevant
situations. We thereby ascertain the effects of reduced dimensionality,
periodic lattices and a d-wave pairing interaction. Implications for the
cuprate superconductors are discussed.Comment: REVTeX, 11 pages, 6 EPS figures included, Replace with published
versio
Model driven formal development of digital libraries
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-540-68262-2_13Revised Selected Papers of the Third International Conference, WEBIST 2007, Barcelona, Spain, March 3-6, 2007This paper shows our model-driven approach for the formal construction and validation of Digital Libraries (DLs). We have defined a Domain Specific Visual Language (DSVL) called VisMODLE, which allows the description of a DL using five different viewpoints: services, behaviour, collections, structure and society. From a meta-model based description of the different viewpoints, we have generated a modelling environment for VisMODLE. We have provided the environment with a code generator that produces XUL code for the DL’s user interface and composes the application using predefined components that implement the different services. Moreover, we have also added validation and simulation capabilities to the environment. Using the behavioural models (state-machine based), we can visually animate the system. In addition, the combined behaviour of actors and services can be transformed into a Petri net for further analysis.Work sponsored by projects MODUWEB (TIN2006-09678) and MOSAIC (TIC2005-08225-C07-06) of the Spanish Ministry of Science and Educatio
Nernst Effect and Anomalous Transport in Cuprates: A Preformed-Pair Alternative to the Vortex Scenario
We address those puzzling experiments in underdoped high
superconductors which have been associated with normal state "vortices" and
show these data can be understood as deriving from preformed pairs with onset
temperature . For uncorrelated bosons in small magnetic fields, and
arbitrary , we present the exact contribution to \textit{all}
transport coefficients. In the overdoped regime our results reduce to those of
standard fluctuation theories (). Semi-quantitative agreement
with Nernst, ac conductivity and diamagnetic measurements is quite reasonable.Comment: 9 pages, 4 figures; Title, abstract and contents modified, new
references added, figures changed, one more figure added; to be published on
PR
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