609 research outputs found
Directional tunnelling spectroscopy of a normal metal--wave superconductor junction
We calculate the normal metal--wave superconductor tunnelling spectrum
for various junction orientations and for two forms of the superconducting gap,
one which allows for point nodes and the other which allows for line nodes. For
a junction oriented with its normal parallel to the ab plane of the tetragonal
superconductor, we find that the tunnelling spectrum is strongly dependent on
orientation in the plane. The spectrum contains two peaks at energies
equivalent to the magnitudes of the gap function in the direction parallel to
the interface normal and in the direction making a angle with the
normal. These two peaks appear in both superconductors with point nodes and
line nodes, but are more prominent in the latter. For the tunnelling along the
c axis, we find a sharp peak at the gap maximum in the conductance spectrum of
the superconductor with line nodes, whereas with point nodes we find a peak
occurring at the value of the gap function along the c axis. We discuss the
relevance of our result to borocarbide systems.Comment: 16 pages, 10 figure
Theoretical study of electronic Raman scattering of Borocarbide superconductors
The electronic Raman scattering of Borocarbide superconductors is studied
based on the weak coupling theory with -wave gap symmetry. The low energy
behaviors and the relative peak positions can be naturally understood, while
the explanation of the detailed shape of the peak seems to require a
strong inelastic interaction not present in the weak coupling theory.Comment: Revtex 4 file, 9 pages and 5 figure
Dispersive Gap Mode of Phonons in Anisotropic Superconductors
We estimate the effect of the superconducting gap anisotropy in the
dispersive gap mode of phonons, which is observed by the neutron scattering on
borocarbide superconductors. We numerically analyze the phonon spectrum
considering the electron-phonon coupling, and examine contributions coming from
the gap suppression and the sign change of the pairing function on the Fermi
surface. When the sign of the pairing function is changed by the nesting
translation, the gap mode does not appear. We also discuss the suppression of
the phonon softening of the Kohn anomaly due to the onset of superconductivity.
We demonstrate that observation of the gap dispersive mode is useful for
sorting out the underlying superconducting pairing function.Comment: 7 pages, 12 figures, to be published in J. Phys. Soc. Jp
Impurity effects on s+g-wave superconductivity in borocarbides Y(Lu)Ni_2B_2C
Recently a hybrid s+g-wave pairing is proposed to describe the experimental
observation for a nodal structure of the superconducting gap in borocarbide
YNiBC and possibly LuNiBC. In this paper the impurity effects
on the s+g-wave superconductivity are studied in both Born and unitarity limit.
The quasiparticle density of states and thermodynamics are calculated. It is
found that the nodal excitations in the clean system are immediately prohibited
by impurity scattering and a finite energy gap increases quickly with the
impurity scattering rate. This leads to an activated behavior in the
temperature dependence of the specific heat. Qualitative agreement with the
experimental results is shown. Comparison with d-wave and some anisotropic
s-wave studied previously is also made.Comment: 6 pages, 6 eps figure
The Nernst effect and the boundaries of the Fermi liquid picture
Following the observation of an anomalous Nernst signal in cuprates, the
Nernst effect was explored in a variety of metals and superconductors during
the past few years. This paper reviews the results obtained during this
exploration, focusing on the Nernst response of normal quasi-particles as
opposed to the one generated by superconducting vortices or by short-lived
Cooper pairs. Contrary to what has been often assumed, the so-called Sondheimer
cancelation does not imply a negligible Nernst response in a Fermi liquid. In
fact, the amplitude of the Nernst response measured in various metals in the
low-temperature limit is scattered over six orders of magnitude. According to
the data, this amplitude is roughly set by the ratio of electron mobility to
Fermi energy in agreement with the implications of the semi-classical transport
theory.Comment: Final version, Topical review for JPC
Nonlocal Effects and Shrinkage of the Vortex Core Radius in YNi2B2C Probed by muSR
The magnetic field distribution in the vortex state of YNi2B2C has been
probed by muon spin rotation (muSR). The analysis based on the London model
with nonlocal corrections shows that the vortex lattice has changed from
hexagonal to square with increasing magnetic field H. At low fields the vortex
core radius, rho_v(H), decreases with increasing H much steeper than what is
expected from the sqrt(H) behavior of the Sommerfeld constant gamma(H),
strongly suggesting that the anomaly in gamma(H) primarily arises from the
quasiparticle excitations outside the vortex cores.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Effect of Pt substitution on the electronic structure of AuTe2
We report a photoemission and x-ray absorption study on Au1-xPtxTe2 (x = 0
and 0.35) triangular lattice in which superconductivity is induced by Pt
substitution for Au. Au 4f and Te 3d core-level spectra of AuTe2 suggests a
valence state of Au2+(Te2)2-, which is consistent with its distorted crystal
structure with Te-Te dimers and compressed AuTe6 otahedra. On the other hand,
valence-band photoemission spectra and pre-edge peaks of Te 3d absorption edge
indicate that Au 5d bands are almost fully occupied and that Te 5p holes govern
the transport properties and the lattice distortion. The two apparently
conflicting pictures can be reconciled by strong Au 5d/Au 6s-Te 5p
hybridization. Absence of a core-level energy shift with Pt substitution is
inconsistent with the simple rigid band picture for hole doping. The Au 4f
core-level spectrum gets slightly narrow with Pt substitution, indicating that
the small Au 5d charge modulation in distorted AuTe2 is partially suppressed.Comment: 13 pages, 4 figures, accepted by Physical Review
How Women Are Depicted In Ads? A Content Analysis Study With Brazilian Advertisements
The main purpose of this paper was to examine female roles portrayed by advertising. More specifically, the question that motivated this research project was: What messages about women have been given to society through advertisement? Have these portrayals been changed during the past decades? The study consisted of a systematic content analysis of Brazilian commercials from 1973 to 2000. The population from which this sample was drawn consisted of Brazilian commercials which got an award in international and national festivals. A probabilistic sample procedure was employed. Ninety five pieces were selected. The categories and operational rules used in the study were developed based on previous research. This study has proposed that female images in advertising are depicted in three different ways: stereotyped, idealized and plural portrayals. Our results have revealed that some specific images have changed; however, they continued to be stereotyped and idealized
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