232 research outputs found
Collective Spin Fluctuation Mode and Raman Scattering in Superconducting Cuprates
Although the low frequency electronic Raman response in the superconducting
state of the cuprates can be largely understood in terms of a d-wave energy
gap, a long standing problem has been an explanation for the spectra observed
in the polarization orientations. We present calculations which
suggest that the peak position of the observed spectra is due to a
collective spin fluctuation mode.Comment: 4 pages, 5 eps figure
Human amniotic fluid glycoproteins expressing sialyl Lewis carbohydrate antigens stimulate progesterone production in human trophoblasts in vitro
Background: Progesterone is thought to mediate immune modulator effects by regulating uterine responsiveness. The aim of the study was to clarify the effect of transferrin and glycodelin A (former name PP14) as sialyl Lewis X-expressing glycoproteins on the release of progesterone by trophoblast cells in vitro. Methods: Cytotrophoblast cells were prepared from human term placentas by standard dispersion of villous tissue followed by a Percoll gradient centrifugation step. Trophoblasts were incubated with varying concentrations (50-300 mug/ml) of human amniotic fluid- and serum-transferrin as well as with glycodelin A. Culture supernatants were assayed for progesterone, human chorionic gonadotropin (hCG) and cortisol by enzyme immunometric methods. Results: The release of progesterone is increased in amniotic fluid transferrin- and glycodelin A-treated trophoblast cell cultures compared to untreated trophoblast cells. There is no relation between transferrin and the hCG or cortisol production of trophoblast cells. Conclusion: The results suggest that sialyl Lewis carbohydrate antigen-expressing amniotic fluid glycoproteins modulate the endocrine function of trophoblasts in culture by upregulating progesterone production. Copyright (C) 2004 S. Karger AG, Basel
Kinetic Inductance and Penetration Depth of Thin Superconducting Films Measured by THz Pulse Spectroscopy
We measure the transmission of THz pulses through thin films of YBCO at
temperatures between 10K and 300K. The pulses possess a useable bandwidth
extending from 0.1 -- 1.5 THz (3.3 cm^-1 -- 50 cm^-1). Below T_c we observe
pulse reshaping caused by the kinetic inductance of the superconducting charge
carriers. From transmission data, we extract values of the London penetration
depth as a function of temperature, and find that it agrees well with a
functional form (\lambda(0)/\lambda(T))^2 = 1 - (T/T_c)^{\alpha}, where
\lambda(0) = 148 nm, and \alpha = 2. *****Figures available upon request*****Comment: 7 Pages, LaTe
Phase-sensitive Evidence for d-wave Pairing Symmetry in Electron-doped Cuprate Superconductors
We present phase-sensitive evidence that the electron-doped cuprates
Nd1.85Ce0.15CuO4-y (NCCO) and Pr1.85Ce0.15CuO4-y (PCCO) have d-wave pairing
symmetry. This evidence was obtained by observing the half-flux quantum effect,
using a scanning SQUID microscope, in c-axis oriented films of NCCO or PCCO
epitaxially grown on tricrystal [100] SrTiO3 substrates designed to be
frustrated for a d(x2-y2) order parameter. Samples with two other
configurations, designed to b unfrustrated for a d-wave superconductor, do not
show the half-flux quantum effect.Comment: 4 pages, Latex, 4 figure
Corrosion studies on Fe-30Mn-1C alloy in chloride-containing solutions with view to biomedical application
Austenitic Fe-30Mn-1C (FeMnC) is a prospective biodegradable implant material combining high mechanical integrity with adequate corrosion rates. The fast solidified TWIP alloy, its constituents and 316L stainless steel were electrochemically analysed in various electrolytes at 37 °C under laminar flow. Potentiodynamic polarization tests were conducted in Tris-buffered simulated body fluid (SBF), in Tris-buffered saline (TBS) and in 150-0.15 mM NaCl solutions (pH 7.6, 10, 5, 2) to study initial corrosion stages. Active dissolution of FeMnC is revealed in all electrolytes and is discussed on basis of the Fe and Mn behaviour plus is compared to that of 316L. The role of Tris (Tris(hydroxymethyl)aminomethane) as organic buffer for SBFs is critically assessed, particularly with view to the sensitivity of Fe. SEM studies of FeMnC corroded in NaCl revealed preferential dissolution along Mn-rich grain boundary regions. Static immersion tests of FeMnC in SBF with surface and solution analyses (SEM/EDX, XPS, ICP-OES) indicated that dissolution processes interfere with the formation of permeable surface coatings comprising hydroxides and salt
Anomalous Low Temperature Behavior of Superconducting Nd(1.85)Ce(0.15)CuO(4-y)
We have measured the temperature dependence of the in-plane London
penetration depth lambda(T) and the maximum Josephson current Ic(T) using
bicrystal grain boundary Josephson junctions of the electron-doped cuprate
superconductor Nd(1.85)Ce(0.15)CuO(4-y). Both quantities reveal an anomalous
temperature dependence below about 4 K. In contrast to the usual monotonous
decrease (increase) of lambda(T) (Ic(T)) with decreasing temperature, lambda(T)
and Ic(T) are found to increase and decrease, respectively, with decreasing
temperature below 4 K resulting in a non-monotonous overall temperature
dependence. This anomalous behavior was found to be absent in analogous
measurements performed on Pr(1.85)Ce(0.15)CuO(4-y). From this we conclude that
the anomalous behavior of Nd(1.85)Ce(0.15)CuO(4-y) is caused by the presence of
the Nd3+ paramagnetic moments. Correcting the measured lambda(T) dependence of
Nd(1.85)Ce(0.15)CuO(4-y) for the temperature dependent susceptibility due to
the Nd moments, an exponential dependence is obtained indicating isotropic
s-wave pairing. This result is fully consistent with the lambda(T) dependence
measured for Pr(1.85)Ce(0.15)CuO(4-y).Comment: 4 pages including 4 figures, to appear in Phys. Rev. Let
Shape resonance for the anisotropic superconducting gaps near a Lifshitz transition: the effect of electron hopping between layers
The multigap superconductivity modulated by quantum confinement effects in a
superlattice of quantum wells is presented. Our theoretical BCS approach
captures the low-energy physics of a shape resonance in the superconducting
gaps when the chemical potential is tuned near a Lifshitz transition. We focus
on the case of weak Cooper-pairing coupling channels and strong pair exchange
interaction driven by repulsive Coulomb interaction that allows to use the BCS
theory in the weak-coupling regime neglecting retardation effects like in
quantum condensates of ultracold gases. The calculated matrix element effects
in the pairing interaction are shown to yield a complex physics near the
particular quantum critical points due to Lifshitz transitions in multigap
superconductivity. Strong deviations of the ratio from the
standard BCS value as a function of the position of the chemical potential
relative to the Lifshitz transition point measured by the Lifshitz parameter
are found. The response of the condensate phase to the tuning of the Lifshitz
parameter is compared with the response of ultracold gases in the BCS-BEC
crossover tuned by an external magnetic field. The results provide the
description of the condensates in this regime where matrix element effects play
a key role.Comment: 12 pages, 6 figure
Spontaneous Spin Polarized Currents in Superconductor-Ferromagnetic Metal Heterostructures
We study a simple microscopic model for thin, ferromagnetic, metallic layers
on semi-infinite bulk superconductor. We find that for certain values of the
exchange spliting, on the ferromagnetic side, the ground states of such
structures feature spontaneously induced spin polarized currents. Using a
mean-field theory, which is selfconsistent with respect to the pairing
amplitude , spin polarization and the spontaneous current
, we show that not only there are Andreev bound states in the
ferromagnet but when their energies are near zero they support
spontaneous currents parallel to the ferromagnetic-superconducting interface.
Moreover, we demonstrate that the spin-polarization of these currents depends
sensitively on the band filling.Comment: 4 pages, 5 Postscript figures (included
Electronic resonance states in metallic nanowires during the breaking process simulated with the ultimate jellium model
We investigate the elongation and breaking process of metallic nanowires
using the ultimate jellium model in self-consistent density-functional
calculations of the electron structure. In this model the positive background
charge deforms to follow the electron density and the energy minimization
determines the shape of the system. However, we restrict the shape of the wires
by assuming rotational invariance about the wire axis. First we study the
stability of infinite wires and show that the quantum mechanical
shell-structure stabilizes the uniform cylindrical geometry at given magic
radii. Next, we focus on finite nanowires supported by leads modeled by
freezing the shape of a uniform wire outside the constriction volume. We
calculate the conductance during the elongation process using the adiabatic
approximation and the WKB transmission formula. We also observe the correlated
oscillations of the elongation force. In different stages of the elongation
process two kinds of electronic structures appear: one with extended states
throughout the wire and one with an atom-cluster like unit in the constriction
and with well localized states. We discuss the origin of these structures.Comment: 11 pages, 8 figure
- …