2,744 research outputs found
Probing the phase diagram of CeRu_2Ge_2 by thermopower at high pressure
The temperature dependence of the thermoelectric power, S(T), and the
electrical resistivity of the magnetically ordered CeRu_2Ge_2 (T_N=8.55 K and
T_C=7.40 K) were measured for pressures p < 16 GPa in the temperature range 1.2
K < T < 300 K. Long-range magnetic order is suppressed at a p_c of
approximately 6.4 GPa. Pressure drives S(T) through a sequence of temperature
dependences, ranging from a behaviour characteristic for magnetically ordered
heavy fermion compounds to a typical behaviour of intermediate-valent systems.
At intermediate pressures a large positive maximum develops above 10 K in S(T).
Its origin is attributed to the Kondo effect and its position is assumed to
reflect the Kondo temperature T_K. The pressure dependence of T_K is discussed
in a revised and extended (T,p) phase diagram of CeRu_2Ge_2.Comment: 7 pages, 6 figure
Anisotropy, disorder, and superconductivity in CeCu2Si2 under high pressure
Resistivity measurements were carried out up to 8 GPa on single crystal and
polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity
range. The anisotropic response to current direction and small uniaxial
stresses was explored, taking advantage of the quasi-hydrostatic environment of
the Bridgman anvil cell. It was found that both the superconducting transition
temperature Tc and the normal state properties are very sensitive to uniaxial
stress, which leads to a shift of the valence instability pressure Pv and a
small but significant change in Tc for different orientations with respect to
the tetragonal c-axis. Coexistence of superconductivity and residual
resistivity close to the Ioffe-Regel limit around 5 GPa provides a compelling
argument for the existence of a valence-fluctuation mediated pairing
interaction at high pressure in CeCu2Si2.Comment: 12 pages, 7 figure
Strain enhancement of superconductivity in CePd2Si2 under pressure
We report resistivity and calorimetric measurements on two single crystals of
CePd2Si2 pressurized up to 7.4 GPa. A weak uniaxial stress induced in the
pressure cell demonstrates the sensitivity of the physics to anisotropy. Stress
applied along the c-axis extends the whole phase diagram to higher pressures
and enhances the superconducting phase emerging around the magnetic
instability, with a 40% increase of the maximum superconducting temperature,
Tc, and a doubled pressure range. Calorimetric measurements demonstrate the
bulk nature of the superconductivity.Comment: 4 pages, 4 figure
Epitaxial growth and transport properties of Nb-doped SrTiO thin films
Nb-doped SrTiO epitaxial thin films have been prepared on (001)
SrTiO substrates using pulsed laser deposition. A high substrate
temperature () was found to be necessary to achieve
2-dimensional growth. Atomic force microscopy reveals atomically flat surfaces
with 3.9 \AA steps. The films show a metallic behavior, residual
resistivity ratios between 10 and 100, and low residual resistivity of the
order of 10cm. At 0.3 K, a sharp superconducting transition,
reaching zero resistance, is observed.Comment: 4 pages, 4 figure
From spin-Peierls to superconductivity: (TMTTF)_2PF_6 under high pressure
The nature of the attractive electron-electron interaction, leading to the
formation of Cooper-pairs in unconventional superconductors has still to be
fully understood and is subject to intensive research. Here we show that the
sequence spin-Peierls, antiferromagnetism, superconductivity observed in
(TMTTF)_2PF_6 under pressure makes the (TM)_2X phase diagram universal. We
argue that the suppression of the spin-Peierls transition under pressure, the
close vicinity of antiferromagnetic and superconducting phases at high pressure
as well as the existence of critical antiferromagnetic fluctuations above T_c
strongly support the intriguing possibility that the interchain exchange of
antiferromagnetic fluctuations provides the pairing mechanism required for
bound charge carriers.Comment: 4 pages, revtex, 4 figures (jpeg,eps,png
Growth and rheological changes of collenchyma cells: The fusicoccin effect
Fusicoccin enhanced the growth of collocytes from Apium Gravtolens petioles and modified the rheological parameters tested. But these changes do not sufficiently explain the variations of the cell wall extension. Such effects are discusse
Statistical analysis of the owl:sameAs network for aligning concepts in the linking open data cloud
The massively distributed publication of linked data has brought to the attention of scientific community the limitations of classic methods for achieving data integration and the opportunities of pushing the boundaries of the field by experimenting this collective enterprise that is the linking open data cloud. While reusing existing ontologies is the choice of preference, the exploitation of ontology alignments still is a required step for easing the burden of integrating heterogeneous data sets. Alignments, even between the most used vocabularies, is still poorly supported in systems nowadays whereas links between instances are the most widely used means for bridging the gap between different data sets. We provide in this paper an account of our statistical and qualitative analysis of the network of instance level equivalences in the Linking Open Data Cloud (i.e. the sameAs network) in order to automatically compute alignments at the conceptual level. Moreover, we explore the effect of ontological information when adopting classical Jaccard methods to the ontology alignment task. Automating such task will allow in fact to achieve a clearer conceptual description of the data at the cloud level, while improving the level of integration between datasets. <br/
High-pressure transport properties of CeRu_2Ge_2
The pressure-induced changes in the temperature-dependent thermopower S(T)
and electrical resistivity \rho(T) of CeRu_2Ge_2 are described within the
single-site Anderson model. The Ce-ions are treated as impurities and the
coherent scattering on different Ce-sites is neglected. Changing the
hybridisation \Gamma between the 4f-states and the conduction band accounts for
the pressure effect. The transport coefficients are calculated in the
non-crossing approximation above the phase boundary line. The theoretical S(T)
and \rho(T) curves show many features of the experimental data. The seemingly
complicated temperature dependence of S(T) and \rho(T), and their evolution as
a function of pressure, is related to the crossovers between various fixed
points of the model.Comment: 9 pages, 10 figure
High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7
Superconducting and structural phase transitions in a pyrochlore oxide
Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical
resistivity measurements. A rich P-T phase diagram is obtained, which contains
at least two phases with the ideal and slightly distorted pyrochlore
structures. It is found that the transition between them is suppressed with
increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa.
Remarkable enhancements in the residual resistivity as well as the coefficient
A of the AT 2 term in the resistivity are found around the critical pressure.
Superconductivity is detected only for the phase with the structural
distortion. It is suggested that the charge fluctuations of Re ions play a
crucial role in determining the electronic properties of Cd2Re2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp
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