123 research outputs found
Domain walls at the spin density wave endpoint of the organic superconductor (TMTSF)2PF6 under pressure
We report the first comprehensive investigation of the organic superconductor
(TMTSF)2PF6 in the vicinity of the endpoint of the spin density wave - metal
phase transition where phase coexistence occurs. At low temperature, the
transition of metallic domains towards superconductivity is used to reveal the
various textures. In particular, we demonstrate experimentally the existence of
1D and 2D metallic domains with a cross-over from a filamentary
superconductivity mostly along the c?-axis to a 2D superconductivity in the
b?c-plane perpendicular to the most conducting direction. The formation of
these domain walls may be related to the proposal of a soliton phase in the
vicinity of the critical pressure of the (TMTSF)2PF6 phase diagram.Comment: 5 page
Soliton phase near antiferromagnetic quantum critical point in Q1D conductors
In the frameworks of a nesting model for Q1D organic conductor at the
antiferromagnetic (SDW) quantum critical point the first-order transition
separates metallic state from the soliton phase having the periodic domain
structure. The low temperature phase diagram also displays the 2nd-order
transition line between the soliton and the uniformly gapped SDW phases. The
results agree with the phase diagram of (TMTSF)PF near critical
pressure [T. Vuletic et al., Eur. Phys. J. B 25, 319 (2002)]. Detection of the
2nd-order transition line is discussed. We comment on superconductivity at
lowest temperature.Comment: 4 pages, 1 figur
Study of the bacterial community affiliated to Hyalesthes obsoletus, the insect vector of “bois noir” phytoplasma of grape
Grape yellows caused by phytoplasmas afflict several important wine-producing areas of Europe. A grape yellows with increasingincidence in European vineyards is “bois noir” (BN), caused by ‘Candidatus Phytoplasma solani’. Its vector is the planthopperHyalesthes obsoletus Signoret (Hemiptera Cixiidae), occasionally feeding on grapevine. An innovative strategy for reducing thediffusion of the disease could be symbiotic control, exploiting the action of symbiotic microorganisms of the insect host. To investigatethe occurrence of possible microbial candidates for symbiotic control we performed a molecular characterization of thebacteria associated to H. obsoletus. Length heterogeneity PCR was applied for a preliminary population screening. Taxonomicaffiliations of the bacterial species were analyzed by denaturing gradient gel electrophoresis, showing, within the microbial diversity,the intracellular reproductive parasite Wolbachia pipientis and a Bacteroidetes symbiont with 92% nt identity with ‘CandidatusSulcia muelleri’. PCR essays specific for these bacteria showed they co-localize in several organs of H. obsoletus. Fluorescentin situ hybridization was performed to assess the distribution of these microorganisms within the insect body, showing interestinglocalization patterns, particularly in insect gonads and salivary glands. These results could be a starting point for a deeper investigationof functions and relationships between microbial species
Magnetic Determination of under Accurate Alignment in (TMTSF)ClO
Cantilever magnetometry has been used to measure the upper critical magnetic
field of the quasi-one dimensional molecular organic superconductor
(TMTSF)ClO. From simultaneous resistivity and torque magnetization
experiments conducted under precise field alignment, at low
temperature is shown to reach 5T, nearly twice the Pauli paramagnetic limit
imposed on spin singlet superconductors. These results constitute the first
thermodynamic evidence for a large in this system and provide support
for spin triplet pairing in this unconventional superconductorComment: Submitted July 1, 2003, Accepted December 9, 2003, Physical Review
Letter
SO(4) Theory of Competition between Triplet Superconductivity and Antiferromagnetism in Bechgaard Salts
Motivated by recent experiments with Bechgaard salts, we investigate the
competition between antiferromagnetism and triplet superconductivity in quasi
one-dimensional electron systems. We unify the two orders in an SO(4) symmetric
framework, and demonstrate the existence of such symmetry in one-dimensional
Luttinger liquids. SO(4) symmetry, which strongly constrains the phase diagram,
can explain coexistence regions between antiferromagnetic, superconducting, and
normal phases, as observed in (TMTSF)PF. We predict a sharp neutron
scattering resonance in superconducting samples.Comment: 5 pages, 3 figures; Added discussion of applicability of SO(4)
symmetry for strongly anisotropic Fermi liquids; Added reference
Direct Transition from Bose Glass to Normal State in the (K,Ba)BiO3 Superconductor
International audienceThe introduction of columnar defects in K; Ba BiO3 single crystals shifts both the irreversibility and thermodynamic transition lines, respectively, deduced from ac susceptibility (and/or transport) and specific heat measurements, upwards. This shift can be attributed to the defect-induced decrease of the difference ( F) between the free energies in the superconducting and the normal states, assuming that the position of the superconducting transition is given by the condition j Fj kBT= 3. This criterion also perfectly reproduces the influence of the angle between the tracks and the external field. This result suggests that no vortex liquid phase exists in this system
Concentration Dependence of Superconductivity and Order-Disorder Transition in the Hexagonal Rubidium Tungsten Bronze RbxWO3. Interfacial and bulk properties
We revisited the problem of the stability of the superconducting state in
RbxWO3 and identified the main causes of the contradictory data previously
published. We have shown that the ordering of the Rb vacancies in the
nonstoichiometric compounds have a major detrimental effect on the
superconducting temperature Tc.The order-disorder transition is first order
only near x = 0.25, where it cannot be quenched effectively and Tc is reduced
below 1K. We found that the high Tc's which were sometimes deduced from
resistivity measurements, and attributed to compounds with .25 < x < .30, are
to be ascribed to interfacial superconductivity which generates spectacular
non-linear effects. We also clarified the effect of acid etching and set more
precisely the low-rubidium-content boundary of the hexagonal phase.This work
makes clear that Tc would increase continuously (from 2 K to 5.5 K) as we
approach this boundary (x = 0.20), if no ordering would take place - as its is
approximately the case in CsxWO3. This behaviour is reminiscent of the
tetragonal tungsten bronze NaxWO3 and asks the same question : what mechanism
is responsible for this large increase of Tc despite the considerable
associated reduction of the electron density of state ? By reviewing the other
available data on these bronzes we conclude that the theoretical models which
are able to answer this question are probably those where the instability of
the lattice plays a major role and, particularly, the model which call upon
local structural excitations (LSE), associated with the missing alkali atoms.Comment: To be published in Physical Review
Geometrical barriers and lower critical field in MgB2 single crystals
International audienceThe first penetration field sHpd has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For Ha ic, the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of Hc1 deduced from Hp through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (0.11±0.01 T)
Superconductivity and Antiferromagnetism in Quasi-one-dimensional Organic Conductors
We review the current understanding of superconductivity in the
quasi-one-dimensional organic conductors of the Bechgaard and Fabre salt
families. We discuss the interplay between superconductivity,
antiferromagnetism, and charge-density-wave fluctuations. The connection to
recent experimental observations supporting unconventional pairing and the
possibility of a triplet-spin order parameter for the superconducting phase is
also presented.Comment: (v1) 30 pages, 13 figures; Review article for the 20th anniversary of
high-Tc superconductivity, to appear in J. Low Temp. Phys. (v2) 1 Ref. adde
Thermal Conductivity of superconducting (TMTSF)_2ClO_4: evidence for a nodeless gap
We report on the first measurements of thermal conductivity in the
superconducting state of (TMTSF)_2ClO_4. The electronic contribution to heat
transport is found to decrease rapidly below T_c, indicating the absence of
low-energy electronic excitations. We argue that this result provides strong
evidence for a nodeless superconducting gap function but does not exclude a
possible unconventional order parameter.Comment: 4 pages including 4 figures, submitted to Phys. Rev. Let
- …