39 research outputs found
Vortex fluctuations in underdoped Bi2Sr2CaCu2O8+d crystals
Vortex thermal fluctuations in heavily underdoped Bi2Sr2CaCu2O8+d (Tc=69.4 K)
are studied using Josephson plasma resonance (JPR). From the data in zero
magnetic field, we obtain the penetration depth along the c-axis,
lambda_{L,c}(0) = 229 micrometers and the anisotropy ratio gamma(0) = 600. The
low plasma frequency allows us to study phase correlations over the whole
vortex solid (Bragg-glass) state. The JPR results yield a wandering length
r_{w} of vortex pancakes. The temperature dependence of r_{w} as well as its
increase with applied dc magnetic field can only be explained by the
renormalization of the tilt modulus by thermal fluctuations, and suggest the
latter is responsible for the dissociation of the vortices at the first order
transition.Comment: 4 pages, 5 figures. Submitted to Phys. Rev. Let
Charge order and suppression of superconductivity in HgBa2CuO4 at high pressures
New insight into the superconducting properties of HgBa2CuO4 (Hg-1201)
cuprates is provided by combined measurements of the electrical resistivity and
single crystal X-ray diffraction under pressure. The changes induced by
increasing pressure up to 20GPa in optimally doped single crystals were
investigated. The resistivity measurements as a function of temperature show a
metallic behavior up to ~10GPa that gradually passes to an insulating state,
typical of charge ordering, that totally suppresses superconductivity above
13GPa. The changes in resistivity are accompanied by the apparition of sharp
Bragg peaks in the X-ray diffraction patterns indicating that the charge
ordering is accompanied by a 3D oxygen ordering appearing at 10GPa of
wavevector [0.25, 0, L]. As pressure induces a charge transfer of about 0.02 at
10GPa, our results are the first observation of charge order competing with
superconductivity that develops in the over-doped region of the phase diagram
of a cuprate.Comment: 9 pages, 3 figure
Nature of c-axis coupling in underdoped Bi2Sr2CaCu2O8 with varying degrees of disorder
The dependence of the Josephson Plasma Resonance (JPR) frequency in heavily
underdoped Bi2Sr2CaCu2O8+\delta on temperature and controlled pointlike
disorder, introduced by high-energy electron irradiation, is cross-correlated
and compared to the behavior of the ab-plane penetration depth. It is found
that the zero temperature plasma frequency, representative of the superfluid
component of the c-axis spectral weight, decreases proportionally with T_c when
the disorder is increased. The temperature dependence of the JPR frequency is
the same for all disorder levels, including pristine crystals. The reduction of
the c-axis superfluid density as function of disorder is accounted for by
pair-breaking induced by impurity scattering in the CuO2 planes, rather than by
quantum fluctuations of the superconducting phase. The reduction of the c-axis
superfluid density as function of temperature follows a T^{2}--law and is
accounted for by quasi-particle hopping through impurity induced interlayer
states.Comment: 10 pages, 9 Figure
c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorder
c-axis coupling in underdoped Bi(2)Sr(2)CaCu(2)O(8+δ) with varying degrees of disorde
Disorder and -axis quasiparticle dynamics in underdoped Bi2Sr2CaCu2O8
Contribution à LT25International audienceWe present measurements of the Josephson plasma frequency and the in-plane penetration depth of underdoped single crystalline Bi2Sr2CaCu2O8 with varying degrees of disorder introduced by irradiation with 2.3 MeV electrons. Increasing disorder drives T_c down, in agreement with in all model descriptions of high T_c superconductivity. However, the manner in which the JPR frequency, the square of which represents the zero-frequency spectral weight of the c-axis conductivity in the superconducting state, is driven down by disorder depends more strongly on the model description. We show that only the model of impurity assisted quasiparticle hopping in a d-wave superconductor, together with strongly scattering point defects in the superconducting layers, can explain the disorder dependence of the c-axis plasma frequency, the in-plane penetration depth, and T_c consistently. From the data, we extract the energy scale governing nodal quasiparticle excitations, Delta_0 ~ 2.5 k_BT_c
Release of mineral-bound water prior to subduction tied to shallow seismogenic slip off Sumatra
Plate-boundary fault rupture during the 2004 Sumatra-Andaman subduction earthquake extended closer to the trench than expected, increasing earthquake and tsunami size. International Ocean Discovery Program Expedition 362 sampled incoming sediments offshore northern Sumatra, revealing recent release of fresh water within the deep sediments. Thermal modeling links this freshening to amorphous silica dehydration driven by rapid burial-induced temperature increases in the past 9 million years. Complete dehydration of silicates is expected before plate subduction, contrasting with prevailing models for subduction seismogenesis calling for fluid production during subduction. Shallow slip offshore Sumatra appears driven by diagenetic strengthening of deeply buried fault-forming sediments, contrasting with weakening proposed for the shallow Tohoku-Oki 2011 rupture, but our results are applicable to other thickly sedimented subduction zones including those with limited earthquake records
Etude de la matière de vortex dans Bi2Sr2CaCU208 à l'aide de la résonnance de plasma Josephson.
The Josephson plasma resonance (JPR) enables us to evaluate the average wandering length rw of the relative thermal excursions of two consecutive pancake vortices belonging to the same flux line, in the layered superconductor Bi2Sr2CaCu2O8+d (BSCCO). Here, we have measured rw in the vortex solid in underdoped BSCCO single crystals, using the resonant cavity perturbation technique and the bolometric method to probe the JPR experimentally. In the pristine samples, at low magnetic fields, the temperature T and field B dependence of rw can only be accounted for by the dominant role of the line tension and its renormalization due to thermal fluctuations. The latter are responsible for the softening of the line tension, which eventually leads to the first order phase transition between the vortex solid and the vortex liquid. A similar rw(T,B) dependence is observed in the heavy-ion irradiated crystals, for B << Bf , validating a description in term of 'discrete superconductor' of the material.La résonance de plasma Josephson (JPR) nous permet d'évaluer la distance moyenne rw des excursions thermiques relatives de deux vortex bidimensionnels consécutifs sur la même ligne de flux, dans le supraconducteur lamellaire Bi2Sr2CaCu2O8+d (BSCCO). Ici, on a déterminé rw dans le solide de vortex dans des monocristaux de BSCCO sous-dopés, à l'aide de mesures expérimentales de la JPR en utilisant la perturbation de cavité résonante et la méthode bolométrique. Dans les échantillons vierges, sous faible champ magnétique, la dépendance en température T et en champ B de rw s'explique par le rôle dominant de la tension de ligne et sa renormalisation par les fluctuations thermiques. Celles-ci provoquent son amollissement, conduisant à la transition de phase du premier ordre entre le solide et le liquide de vortex. On observe une dépendance rw(T,B) identique dans les cristaux irradiés aux ions lourds, pour B << Bf , validant une description en terme de 'supraconducteur discret' du matériau
Dérivés organométalliques d aminoacides g-phosphorés (vers la détection électrochimique des autoanticorps de la sclérose en plaques)
DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF
Puesta en evidencia de un cÃrculo virtuoso creado por las Inversiones Socialmente Responsable entre Mercados Financieros y Empresas
El mercado emergente de las inversiones socialmente responsable esta cambiando
el panorama de los mercados financieros. Los inversores se ven muy interesados
en esta forma de invertir y los profesionales siguen esta perspectiva proponiendo
productos adaptados. Aunque haya una demanda creciente hacia los productos
de inversión responsable, el público en general tiene pocos
conocimientos acerca de este tema. En nuestro trabajo tratamos de mostrar
el funcionamiento de estas inversiones, los actores que involucran y las
relaciones entre ellos. El desarrollo de las inversiones socialmente responsables
depende de las relaciones entre los diferentes actores y de como evolucionan
por separado. Para que un sistema funcione de manera eficaz, las partes
componentes deben mejorar al mismo tiempo ya que dependen uno del otro. En
nuestro trabajo mostramos el sistema circular que se forma, esta compuesto
de las empresas, los mercados financieros asà como los inversores
potenciales