173 research outputs found
Mechanisms of Electrical Conductivity in Y(1-x)CaxBa2Cu3O6.1 System
Systematic studies of transport properties in deoxygenated
Y(1-x)CaxBa2Cu3O6.1 series allowed to propose a diagram of conductivity
mechanisms for this system. At intermediate temperature a variable range
hopping (VRH) in 2 dimensions prevails. At lower temperature VRH in the
presence of a Coulomb gap for smaller x and VRH in 2 dimensions for larger x
are found. In a vicinity of superconductivity we observe conductivity
proportional to \sqrt{T}. Thermally activated conductivity dominates at higher
temperature. This diagram may be universal for the whole family of undoped high
Tc related cuprates.Comment: 5 page
Electronic structure and transport properties of CeNi9In2
We investigated CeNi9In2 compound, which has been considered as a mixed
valence (MV) system. Electrical resistivity vs. temperature variation was
analysed in terms of the model proposed by Freimuth for systems with unstable
4f shell. At low temperature the resistivity dependence is consistent with a
Fermi liquid state with a contribution characteristic of electron-phonon
interaction. Ultraviolet photoemission spectroscopy (UPS) studies of the
valence band did not reveal a Kondo peak down to 14 K. A difference of the
spectra obtained with photon energies of low and high photoionization cross
sections for Ce 4f electrons indicated that 4f states are located mainly close
to the Fermi energy. The peaks related to f_{5/2}^1 and f_{7/2}^1 final states
cannot be resolved but form a plateau between -0.3 eV and the Fermi energy.
X-ray photoemission spectroscopy (XPS) studies were realized for the cerium 3d
level. The analysis of XPS spectra within the Gunnarsson-Sh\"onhammer theory
yielded a hybridization parameter of 104 meV and non-integer f level
occupation, being close to 3. Calculations of partial densities of states were
realized by a full potential local orbital (FPLO) method. They confirm that the
valence band is dominated by Ni 3d states and are in general agreement with the
experiment except for the behavior of f-electrons.Comment: 10 pages, 5 figure
Evidence of momentum dependent hybridization in Ce2Co0.8Si3.2
We studied the electronic structure of the Kondo lattice system Ce2Co0.8Si3.2
by angle-resolved photoemission spectroscopy (ARPES). The spectra obtained
below the coherence temperature consist of a Kondo resonance, its spin-orbit
partner and a number of dispersing bands. The quasiparticle weight related to
the Kondo peak depends strongly on Fermi vectors associated with bulk bands.
This indicates a highly anisotropic hybridization between conduction band and
4f electrons - V_{cf} in Ce2Co0.8Si3.2.Comment: 6 page
Electronic structure of TmPdIn
Electronic structure of a ternary TmPdIn compound, which crystallizes in the hexagonal ZrNiAl-type structure,
was studied by X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy. Density of states
in the valence band was calculated by means of the augmented plane wave/local orbital method based on density
functional theory. The results showed that the valence band is formed mainly of Tm 4f and Pd 4d states. In the
ultraviolet photoemission spectra one can distinguish Pd 4d maximum and Tm 4f multiplet peaks, which are
displaced with respect to those of pure Tm
Direct observation of a Fermi surface and superconducting gap in LuNi2B2C
We measured the Fermi surface (FS), band dispersion and superconducting gap
in LuNi2B2C using Angle Resolved Photoemission Spectroscopy. Experimental data
were compared with the tight-binding version of the Linear Muffin-Tin Orbital
(LMTO) method and Linearized Augmented Plane-Wave (LAPW) calculations. We found
reasonable agreement between the two calculations and experimental data. The
measured FS exhibits large parallel regions with a nesting vector that agrees
with a previous positron annihilation study and calculations of the generalized
susceptibility. The measured dispersion curves also agree reasonably well with
the TB-LMTO calculations, albeit with some differences in the strength of the
hybridization. In addition, the spectrum in the superconducting state revealed
a 2meV superconducting gap. The data also clearly shows the presence of a
coherent peak above the chemical potential, that originates from thermally
excited electrons above the energy of 2 delta. This feature was not previously
observed in the Lu-based material.Comment: 5 pages, 3 figure
Generalized Spectral Signatures of Electron Fractionalization in Quasi-One and -Two Dimensional Molybdenum Bronzes and Superconducting Cuprates
We establish the quasi-one-dimensional Li purple bronze as a photoemission
paradigm of Luttinger liquid behavior. We also show that generalized signatures
of electron fractionalization are present in the angle resolved photoemission
spectra for quasi-two-dimensional purple bronzes and certain cuprates. An
important component of our analysis for the quasi-two-dimensional systems is
the proposal of a ``melted holon'' scenario for the k-independent background
that accompanies but does not interact with the peaks that disperse to define
the Fermi surface.Comment: 7 pages, 8 figure
Fully Gapped Single-Particle Excitations in the Lightly Doped Cuprates
The low-energy excitations of the lightly doped cuprates were studied by
angle-resolved photoemission spectroscopy. A finite gap was measured over the
entire Brillouin zone, including along the d_{x^2 - y^2} nodal line. This
effect was observed to be generic to the normal states of numerous cuprates,
including hole-doped La_{2-x}Sr_{x}CuO_{4} and Ca_{2-x}Na_{x}CuO_{2}Cl_{2} and
electron-doped Nd_{2-x}Ce_{x}CuO_{4}. In all compounds, the gap appears to
close with increasing carrier doping. We consider various scenarios to explain
our results, including the possible effects of chemical disorder, electronic
inhomogeneity, and a competing phase.Comment: To appear in Phys. Rev.
Effects of articaine on [3H]noradrenaline release from cortical and spinal cord slices prepared from normal and streptozotocin-induced diabetic rats and compared to lidocaine.
Since a significant proportion of diabetic patients have clinical or subclinical neuropathy, there may be concerns about the use of local anaesthetics. The present study was designed to determine and compare the effects of articaine, a widely used anaesthetic in dental practice, and lidocaine on the resting and axonal stimulation-evoked release of [3H]noradrenaline ([3H]NA) in prefrontal cortex slices and the release of [3H]NA in spinal cord slices prepared from non-diabetic and streptozocin (STZ)-induced diabetic (glucose level=22.03+/-2.31mmol/l) rats. The peak of allodynia was achieved 9 weeks after STZ-treatment. Articaine and lidocaine inhibited the stimulation-evoked release in a concentration-dependent manner and increased the resting release by two to six times. These effects indicate an inhibitory action of these anaesthetics on Na+- and K+-channels. There was no difference in clinically important nerve conduction between non-diabetic and diabetic rats, as measured by the release of transmitter in response to axonal stimulation. The uptake and resting release of NA was significantly higher in the brain slices prepared from diabetic rats, but there were no differences in the spinal cord. For the adverse effects, the effects of articaine on K+ channels (resting release) are more pronounced compared to lidocaine. In this respect, articaine has a thiophene ring with high lipid solubility, which may present potential risks for some patients
CB1 Antagonism Exerts Specific Molecular Effects on Visceral and Subcutaneous Fat and Reverses Liver Steatosis in Diet-Induced Obese Mice
International audienceThe beneficial effects of the inactivation of endocannabinoid system (ECS) by administration of antagonists of the cannabinoid receptor (CB) 1 on several pathological features associated with obesity is well demonstrated, but the relative contribution of central versus peripheral mechanisms is unclear. We examined the impact of CB1 antagonism on liver and adipose tissue lipid metabolism in a mouse model of diet-induced obesity. Mice were fed either with a standard diet or a high-sucrose high-fat (HSHF) diet for 19 weeks and then treated with the CB1-specific antagonist SR141716 (10 mg x kg(-1) x day(-1)) for 6 weeks. Treatment with SR141716 reduced fat mass, insulin levels, and liver triglycerides primarily increased by HSHF feeding. Serum adiponectin levels were restored after being reduced in HSHF mice. Gene expression of scavenger receptor class B type I and hepatic lipase was induced by CB1 blockade and associated with an increase in HDL-cholesteryl ether uptake. Concomitantly, the expression of CB1, which was strongly increased in the liver and adipose tissue of HSHF mice, was totally normalized by the treatment. Interestingly, in visceral but not subcutaneous fat, genes involved in transport, synthesis, oxidation, and release of fatty acids were upregulated by HSHF feeding, while this effect was counteracted by CB1 antagonism. A reduction in the CB1-mediated ECS activity in visceral fat is associated with a normalization of adipocyte metabolism, which may be a determining factor in the reversion of liver steatosis induced by treatment with SR141716
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