564 research outputs found
Possible Pairing Symmetry of Three-dimensional Superconductor UPt -- Analysis Based on a Microscopic Calculation --
Stimulated by the anomalous superconducting properties of UPt, we
investigate the pairing symmetry and the transition temperature in the
two-dimensional(2D) and three-dimensional(3D) hexagonal Hubbard model. We solve
the Eliashberg equation using the third order perturbation theory with respect
to the on-site repulsion . As results of the 2D calculation, we obtain
distinct two types of stable spin-triplet pairing states. One is the
-wave(B) pairing around and in a small region, which is
caused by the ferromagnetic fluctuation. Then, the other is the (or
)-wave(E) pairing in large region far from the half-filling () which is caused by the vertex corrections only. However, we find that the
former -wave pairing is destroyed by introduced 3D dispersion. This is
because the 3D dispersion breaks the favorable structures for the -wave
pairing such as the van Hove singularities and the small pocket structures.
Thus, we conclude that the ferromagnetic fluctuation mediated spin-triplet
state can not explain the superconductivity of UPt. We also study the case
of the pairing symmetry with a polar gap. This -wave(A) is stabilized
by the large hopping integral along c-axis . It is nearly degenerate with
the suppressed (or )-wave(E) in the best fitting parameter region
to UPt (). These two p-wave pairing states exist in
the region far from the half-filling, in which the vertex correction terms play
crucial roles like the case in SrRuO.Comment: 15 pages, 12 figure
Managerial competencies of hospital managers in South Africa: a survey of managers in the public and private sectors
<p>Abstract</p> <p>Background</p> <p>South Africa has large public and private sectors and there is a common perception that public sector hospitals are inefficient and ineffective while the privately owned and managed hospitals provide superior care and are more sustainable. The underlying assumption is that there is a potential gap in management capacity between the two sectors. This study aims to ascertain the skills and competency levels of hospital managers in South Africa and to determine whether there are any significant differences in competency levels between managers in the different sectors.</p> <p>Methods</p> <p>A survey using a self administered questionnaire was conducted among hospital managers in South Africa. Respondents were asked to rate their proficiency with seven key functions that they perform. These included delivery of health care, planning, organizing, leading, controlling, legal and ethical, and self-management. Ratings were based on a five point Likert scale ranging from very low skill level to very high skill level.</p> <p>Results</p> <p>The results show that managers in the private sector perceived themselves to be significantly more competent than their public sector colleagues in most of the management facets. Public sector managers were also more likely than their private sector colleagues to report that they required further development and training.</p> <p>Conclusion</p> <p>The findings confirm our supposition that there is a lack of management capacity within the public sector in South Africa and that there is a significant gap between private and public sectors. It provides evidence that there is a great need for further development of managers, especially those in the public sector. The onus is therefore on administrators and those responsible for management education and training to identify managers in need of development and to make available training that is contextually relevant in terms of design and delivery.</p
Identification of Non-unitary triplet pairing in a heavy Fermion superconductor UPt_3
A NMR experiment recently done by Tou et al. on a heavy Fermion
superconductor UPt is interpreted in terms of a non-unitary spin-triplet
pairing state which we have been advocating. The proposed state successfully
explains various aspects of the seemingly complicated Knight shift behaviors
probed for major orientations, including a remarkable d-vector rotation under
weak fields. This entitles UPt as the first example that a charged many
body system forms a spin-triplet odd-par ity pairing at low temperatures and
demonstrates unambiguously that the putative spin-orbit coupling in UPt is
weak.Comment: 4 pages, 2 eps figures, to be published in J. Phys. Soc. Jpn. 67
(1998) No.
Quasiparticle localization in superconductors with spin-orbit scattering
We develop a theory of quasiparticle localization in superconductors in
situations without spin rotation invariance. We discuss the existence, and
properties of superconducting phases with localized/delocalized quasiparticle
excitations in such systems in various dimensionalities. Implications for a
variety of experimental systems, and to the properties of random Ising models
in two dimensions, are briefly discussed.Comment: 10 page
Evidence for a two component magnetic response in UPt3
The magnetic response of the heavy fermion superconductor UPt_3 has been
investigated on a microscopic scale by muon Knight shift studies. Two distinct
and isotropic Knight shifts have been found for the field in the basal plane.
While the volume fractions associated with the two Knight shifts are
approximately equal at low and high temperatures, they show a dramatic and
opposite temperature dependence around T_N. Our results are independent on the
precise muon localization site. We conclude that UPt_3 is characterized by a
two component magnetic response.Comment: 5 pages, 4 figure
Universal Heat Conduction in YBa_2Cu_3O_6.9
The thermal conductivity of YBa_2Cu_3O_6.9 was measured at low temperatures
in untwinned single crystals with concentrations of Zn impurities from 0 to 3%
of Cu. A linear term kappa_0/T = 0.19 mW/K^2.cm is clearly resolved as T -> 0,
and found to be virtually independent of Zn concentration. The existence of
this residual normal fluid strongly validates the basic theory of transport in
unconventional superconductors. Moreover, the observed universal behavior is in
quantitative agreement with calculations for a gap function of d-wave symmetry.Comment: Latex file, 4 pages, 3 EPS figures, to appear in Physical Review
Letter
Electron-spin-resonance in the doped spin-Peierls compound Cu(1-x)Ni(x)GeO3
ESR-study of the Ni-doped spin-Peierls compound CuGeO3 has been performed in
the frequency range 9-75 GHz. At low temperatures the g-factor is smaller than
the value expected for Cu- and Ni-ions. This anomaly is explained by the
formation of magnetic clusters around the Ni-ions within a nonmagnetic
spin-Peierls matrix. The transition into the AFM-state detected earlier by
neutron scattering for doped samples was studied by means of ESR. For x=0.032 a
gap in the magnetic resonance spectrum is found below the Neel temperature and
the spectrum is well described by the theory of antiferromagnetic resonance
based on the molecular field approximation. For x=0.017 the spectrum below the
Neel point remained gapless. The gapless spectrum of the antiferromagnetic
state in weekly doped samples is attributed to the small value of the Neel
order parameter and to the magnetically disordered spin-Peierls background.Comment: 16 pages, LATEX, 12 figures, submitted to Journal of Physics :
Condensed Matte
Nonmonotonous Magnetic Field Dependence and Scaling of the Thermal Conductivity for Superconductors with Nodes of the Order Parameter
We show that there is a new mechanism for nonmonotonous behavior of magnetic
field dependence of the electronic thermal conductivity of clean
superconductors with nodes of the order parameter on the Fermi surface. In
particular, for unitary scatterers the nonmonotony of relaxation time takes
place. Contribution from the intervortex space turns out to be essential for
this effect even at low temperatures. Our results are in a qualitative
agreement with recent experimental data for superconducting UPt_3. For
E_{2u}-type of pairing we find approximately the scaling of the thermal
conductivity in clean limit with a single parameter x=T/T_c\sqrt{B_{c2}/B} at
low fields and low temperatures, as well as weak low-temperature dependence of
the anisotropy ratio K_{zz}/K_{yy} in zero field. For E_{1g}-type of pairing
deviations from the scaling are more noticeable and the anisotropy ratio is
essentially temperature dependent.Comment: 37 pages, 8 Postscript figures, REVTE
Magnetic Resonance of the Intrinsic Defects of the Spin-Peierls Magnet CuGeO3
ESR of the pure monocrystals of CuGeO3 is studied in the frequency range 9-75
GHz and in the temperature interval 1.2-25 K. The splitting of the ESR line
into several spectral components is observed below 5 K, in the temperature
range where the magnetic susceptibility is suppressed by the spin-Peierls
dimerization. The analysis of the magnetic resonance signals allows one to
separate the signals of the S=1/2- and S=1 defects of the spin-Peierls phase.
The value of g-factor of these signals is close to that of the Cu-ion. The
additional line of the magnetic resonance is characterized by an anomalous
value of the g-factor and by the threshold-like increase of the microwave
susceptibility when the microwave power is increasing. The ESR signals are
supposingly attributed to two types of the planar magnetic defects, arising at
the boundaries of the domains of the spin-Peierls state with the different
values of the phase of the dimerization.Comment: LATEX-text, 12 PS-figures, typos corrected, LATEX-style change
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