Reexamination of the Branly effect

in Physical Review E (2003), 67(4, Pt 1), 40302

The electrical resistance of a metallic granular packing has been recorded at room temperature. A nearby burster between which sparks are produced, induces a decrease in the resistance of the granular ... [more ▼]

The electrical resistance of a metallic granular packing has been recorded at room temperature. A nearby burster between which sparks are produced, induces a decrease in the resistance of the granular packing as described in the works of Branly. Our measurements emphasize that the decrease is continuous and the resistance variations behave like a stretched exponential law due to the creation of new electrical paths as in nucleation-growth soldering processes. This behavior has been identified to be a diffusionlike process. [less ▲]

Synthesis of CMR manganate compounds: the consequences of the choice of a precursor method

in Materials Letters (2002), 57(3), 598-603

We have studied the electrical transport properties of manganate samples synthesized by different precursor methods. Differences in the synthesis process of the materials can result in samples with ... [more ▼]

We have studied the electrical transport properties of manganate samples synthesized by different precursor methods. Differences in the synthesis process of the materials can result in samples with similar grain size but very different physical properties, contrary to what happens in samples prepared by the same method. (C) 2002 Elsevier Science B.V. All rights reserved. [less ▲]

Magnon-polaron and spin-polaron signatures in the specific heat and electrical resistivity of La0.6Y0.1Ca0.3MnO3 in zero magnetic field and the effect of Mn - O - Mn bond environment

in Physical Review B (2002), 66(17),

La0.6Y0.1Ca0.3MnO3, an ABO(3) perovskite manganite oxide, exhibits a nontrivial behavior in the vicinity of the sharp peak found in the resistivity rho as a function of temperature T in zero magnetic ... [more ▼]

La0.6Y0.1Ca0.3MnO3, an ABO(3) perovskite manganite oxide, exhibits a nontrivial behavior in the vicinity of the sharp peak found in the resistivity rho as a function of temperature T in zero magnetic field. The various features seen on drho/dT are discussed in terms of competing phase transitions. They are related to the Mn-O-Mn bond environment depending on the content of the A crystallographic site. A Ginzburg-Landau type theory is presented for incorporating concurrent phase transitions. The specific heat C of such a compound is also examined from 50 to 200 K. A log-log analysis indicates different regimes. In the low temperature conducting ferromagnetic phase, a collective magnon signature (Csimilar or equal toT(3/2)) is found as for what are called magnon-polaron excitations. A Csimilar or equal toT(2/3) law is found at high temperature and discussed in terms of the fractal dimension of the conducting network of the weakly conducting (so-called insulating) phase and an Orbach estimate of the excitation spectral behaviors. The need of considering both independent spin scattering and collective spin scattering is thus emphasized. The report indicates a remarkable agreement for the Fisher-Langer formula, i.e., Csimilar todrho/dT at second order phase transitions. Within the Attfield model, we find an inverse square root relationship between the critical temperature(s) and the total local Mn-O-Mn strain. [less ▲]

Hysteretic behavior in metallic granular matter

in Applied Physics Letters (2002), 81(5), 936-938

Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I-V curves. A well defined critical point separates the insulating and the conducting ... [more ▼]

Various packings made of metallic grains have been electrically characterized. Electrical breakdown is observed in I-V curves. A well defined critical point separates the insulating and the conducting regime of the packing. The breakdown is reversible by submitting the packing to a small tap. This unusual property leads to hysteretic loops in I-V diagrams. The study of the behavior of I-V curves allows us to describe the system as a network of weak lossy contacts. The key parameter is the inner electrical field controlling the diode-like or diffusion-like state of the packing. (C) 2002 American Institute of Physics. [less ▲]

Cu doping as a tool for understanding CMR

in Key Engineering Materials [=KEM] (2002), 206-2

Doping at the Mn-site in CMR manganate-based perovskites has been shown to affect strongly the physical properties of those compounds. We study here the effect of copper substitution in the low doping ... [more ▼]

Doping at the Mn-site in CMR manganate-based perovskites has been shown to affect strongly the physical properties of those compounds. We study here the effect of copper substitution in the low doping range on the electrical transport properties of La0.7Ca0.3MnO3. It turns out that the transition temperature decrease observed in doped samples can be drastically reduced by addition of silicon dioxide SiO2. It is shown that copper is trapped in a secondary phase composed of La,Ca,Si,Cu and O. The resultant Mn-site vacancies appear to be less detrimental to the electronic conduction than the likely antiferromagnetic clusters induced by the copper ions in the Mn-O network. [less ▲]

Avalanches of Popping Bubbles in Collapsing Foams

in Physical Review Letters (2001), 86(1), 179-82

We report acoustic measurements of popping bubbles during the collapsing of aqueous foams. The sound pattern is analyzed using classical methods of statistical physics. It is found that membrane rupture ... [more ▼]

We report acoustic measurements of popping bubbles during the collapsing of aqueous foams. The sound pattern is analyzed using classical methods of statistical physics. It is found that membrane rupture concerns a wide variety of situations: small and large membranes at the air/foam interface. Avalanches of popping bubbles are put into evidence. Time durations in between successive pops seem to be distributed on a universal power law. [less ▲]

Quasiparticle contribution to heat carriers relaxation time in DyBa2Cu3O7-x from heat diffusivity measurements

in Physical Review. B : Condensed Matter (2001), 64

Simultaneous measurements of thermal diffusivity, thermal conductivity and thermopower with application to copper and ceramic superconductors

in European Physical Journal B -- Condensed Matter (2000), 13(3), 437-443

A home made experimental set-up allows us to measure the thermal conductivity, the thermopower and the thermal diffusivity simultaneously in the temperature range (20-300 K). Therefore the specific heat ... [more ▼]

A home made experimental set-up allows us to measure the thermal conductivity, the thermopower and the thermal diffusivity simultaneously in the temperature range (20-300 K). Therefore the specific heat can be deduced. The role of a radiation shield is shown to be relevant. Tests of the system are made on a 99.9% pure Cu sample and two polycrystalline cuprate ceramics for illustration. Without any complicated optimisation, the technique indicates much promise already due to its efficiency and rapidity. [less ▲]

Electronic specific heat of superconductors with Van Hove singularities : Effect of a magnetic field and thermal fluctuations

in Physical Review. B : Condensed Matter (1998), 57

Cooper pair-like systems at high temperature and their role on fluctuations near the critical temperature

in International Journal of Modern Physics B : Condensed Matter Physics, Statistical Physics, Applied Physics (1998), 12