80 research outputs found
Single-Particle Pseudogap in Two-Dimensional Electron Systems
We investigate pseudogap phenomena in the 2D electron system.
Based on the mode-mode coupling theory of antiferromagnetic (AFM) and
-wave superconducting (SC) fluctuations, single-particle
dynamics is analyzed. For the parameter values of underdoped cuprates,
pseudogap structure grows in the single-particle spectral weight
around the wave vector and below the pseudo-spin-gap
temperature \TPG signaled by the reduction of dynamical spin correlations in
qualitative agreement with the experimental data. The calculated results for
the overdoped cuprates also reproduce the absence of the pseudogap in the
experiments. We also discuss limitations of our weak-coupling approach.Comment: 6 pages with 4 figures, submitted to J. Phys. Soc. Jp
Electronic Specific Heat of La_{2-x}Sr_{x}CuO_{4}: Pseudogap Formation and Reduction of the Superconducting Condensation Energy
To examine the so-called small pseudogap and the superconducting (SC)
condensation energy U(0), the electronic specific heat Cel was measured on
La_{2-x}Sr_{x}CuO_{4} up to ~120K. In samples with doping level p (=x) less
than ~0.2, small pseudogap behavior appears in the \gamma (=Cel/T) vs. T curve
around the mean-field critical temperature for a d-wave superconductor Tco
(=2*\Delta_{0}/(4~5)k_B), where \Delta_{0} is the maximum gap at T<<Tc. The
condensation energy U(0) is largely reduced in the pseudogap regime (p< ~0.2).
The reduction of U(0) can be well reproduced by introducing an effective SC
energy scale \Delta_{eff}=\beta*p*\Delta_{0} (\beta=4.5) instead of \Delta_{0}.
The effective SC energy scale is discussed in relation to the coherent pairing
gap formed over the nodal Fermi arc.Comment: 8page
Effect of anisotropic impurity scattering in superconductors
We discuss the weak-coupling BCS theory of a superconductor with the
impurities, accounting for their anisotropic momentum-dependent potential. The
impurity scattering process is considered in the t-matrix approximation and its
influence on the superconducting critical temperature is studied in the Born
and unitary limit for a d- and (d+s)-wave superconductors. We observe a
significant dependence of the pair-breaking strength on the symmetry of the
scattering potential and classify the impurity potentials according to their
ability to alter T_c. A good agreement with the experimental data for Zn doping
and oxygen irradiation in the overdoped cuprates is found.Comment: 31 pages, RevTex, 15 PostScript figure
Exchange interactions and magnetic properties of the layered vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9
We have performed ab-initio calculations of exchange couplings in the layered
vanadates CaV2O5, MgV2O5, CaV3O7 and CaV4O9. The uniform susceptibility of the
Heisenberg model with these exchange couplings is then calculated by quantum
Monte Carlo method; it agrees well with the experimental measurements. Based on
our results we naturally explain the unusual magnetic properties of these
materials, especially the huge difference in spin gap between CaV2O5 and
MgV2O5, the unusual long range order in CaV3O7 and the "plaquette resonating
valence bond (RVB)" spin gap in CaV4O9
Impurity Effects on the Superconducting Transition Temperature of NazCoO2.yH2O
Superconducting transition temperature Tc of NazCo1-xMxO2.yH2O has been
studied for M=Ir and Ga, which can substitute for Co. It has been found that Tc
is suppressed by the M-atom doping. The decreasing rates |dTc/dx| are of the
order of 1 K/% and too small to be explained by the pair breaking mechanism for
the anisotropic order parameters by non-magnetic impurities. Brief arguments
are given on possible origins of the Tc suppression.Comment: 10 pages, 14 figures,submitted to J. Phys. Soc. Jp
suppression in co-doped striped cuprates
We propose a model that explains the reduction of due to the pinning of
stripes by planar impurity co-doping in cuprates. A geometrical argument about
the planar fraction of carriers affected by stripe pinning leads to a a linear
suppression as a function of impurity concentration . The critical
value for the vanishing of superconductivity is shown to scale like
in the under-doped regime and becomes universal in the optimally- and
over-doped regimes. Our theory agrees very well with the experimental data in
single- and bi-layer cuprates co-doped with Zn, Li, Co, etc...Comment: 4 pages, 4 figure
The study of expanded tri-lobed flap in a rabbit model: possible flap model in ear reconstruction?
BACKGROUND: Local flaps are widely used in reconstructive surgery. Tri-lobed skin flap is a relatively new flap and there has been no experimental model of this flap. This flap can be used for repair of full thickness defects in the face, ears and alar region. Based on the size of ears in a rabbit, we designed a model of ear reconstruction using expanded tri-lobed flap. Local flaps are more advantageous in that they provide excellent color and texture matching up with those of the face, adequately restore ear contour, place scars in a favorable location and ideally accomplish these goals in a single stage with minimal donor site morbidity. METHODS: Eight adult New Zealand rabbits were divided into two groups. 50 ml round tissue expander were implanted to four rabbits. After completion of the expansion, a superiorly based tri-lobed flap was elevated and a new ear was created from the superior dorsal skin of each rabbit. Scintigraphy with Technetium-99m pertecnetate was performed to evaluate flap viability. RESULTS: Subtotal flap necrosis was seen in all animals in non-expanded group. New ear in dimensions of the original ear was created in expanded group without complication. Perfusion and viability of the flaps were proved by Technetium-99m pertecnetate scintigraphy. CONCLUSION: According to our knowledge this study is the first to demonstrate animal model in tri-lobed flap. Also, our technique is the first application of the trilobed flap to the possible ear reconstruction. We speculated that this flap may be used mastoid based without hair, in human. Also, tri-lobed flap may be an alternative in reconstruction of cylindrical organs such as penis or finger
Ateriovenous subclavia-shunt for head and neck reconstruction
Reconstruction of the facial hard- and soft tissues is of special concern for the rehabilitation of patients especially after ablative tumor surgery has been performed. Impaired soft and hard tissue conditions as a sequelae of extensive surgical resection and/or radiotherapy may impede common reconstruction methodes. Even free flaps may not be used without interposition of a vein graft as recipient vessels are not available as a consequence of radical neck dissection
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