E. Osquiguil

BOSE-GLASS PHASE IN TWINNED YBA2CU3O7-DELTA

Using an extensive scaling analysis of the transport properties in twinned YBaCuO(123) crystals we have experimentally found the predicted change in the universality class of the Bose-glass to liquid transition when the magnetic field is applied at small angles away from the direction of the correlated defects. The new dynamical critical exponent is s=1.1 +/-0.2.

La1.80 Sr0.20 CuO4−δ a clean limit superconductor

Abstract The electrical resistivity of the superconductor La 1.80 Sr 0.20 Cu0 4−δ has been measured in a wide range of temperatures as a function of oxygen and vacuum heat treatments. The resistivity changes reversibly orders of magnitude with oxygen concentration. There is no sign of saturation at high temperatures, even for samples where the resistivity is increased by heat treatment in vacuum. Using the experimental data and general arguments it is concluded that the ceramic superconductors are high κ materials in the clean limit.

The granular nature of bulk superconductivity at 40K in La1.8Sr0.2CuO4

Abstract We have measured the electrical resistivity, magnetic flux expulsion and critical fields of the new high temperature superconductor La 1.8 Sr 0.2 CuO 4 after different heat treatments. Our data show that the complete flux expulsion in these samples is consistent with the presence of shielding currents induced in multiple connected structures. The magnetization measurements indicate that the lowest field where flux penetrates into the sample should not be taken to be the bulk Hcl. It is shown that the absolute value of the electrical resistivity and its temperature dependence are not correlated with the superconducting critical field and temperature. We discuss the behaviour of the superconducting parameters and their relation with the electrical resistivity.

Two dimensional collective flux pinning in melt spun superconducting amorphous Zr70Cu30

Abstract We have measured the critical currents in melt spun amorphous Zr70Cu30 and their evolution with heat treatment. We found that the pinning forces may be interpreted in terms of the Larkin-Ovchinnikov two dimensional collective pinning theory.

Non linear temperature dependence of the resistivity of LaSrCuO: Effects of Sr content

Abstract The linear temperature dependence of the electrical resistivity has been taken to be one of the characteristic features of the ceramic superconductors. Measurements of the electrical resistance of the Laue5f8Srue5f8Cuue5f8O system in a wide temperature range show that the previous statement is only an approximation valid for some values of the Sr concentration.

Angular restrictions on the glass transition and on the c-axis correlated liquid phase in twinned YBa2Cu3O7−δ

Abstract We have measured the angular dependence of the vortex velocity correlation temperature T th ( H ) in twinned YBa 2 Cu 3 O 7−δ single crystals. The data show that the c -axis correlated vortex liquid phase exists up to angles much larger than expected within a single vortex pinning picture. Despite this, the second-order solid-liquid glass transition is shown to be restricted only to external magnetic fields applied within a few degrees from the c -axis direction.

Dimensional crossovers in collective flux pinning

Abstract The pinning force density in ribbons of melt spun (a) Zr70Cu30 is found to obey the Larkin-Ovchinnikov theory of collective pinning by dislocation loops, and shows two and three dimensional behaviour, besides an intermediate regime not contemplated by the theory. The dimensional crossovers allow determination of the radius of action of the pinning forces which is shown to be proportional to the coherence length. Its magnitude is too small, which points to quantitative shortcomings of the current theory.

Comment on "Strong vortex liquid correlation from multiterminal measurements on untwinned YBa2Cu3O7-delta single crystals"

A.Rydh and O.Rapp [Phys. Rev. Lett. {bf 86}, 1873 (2001).] claim that the vortex liquid in untwinned YBa

Nonlocal transport properties and size effects in heavily twinned YBa2Cu3O7−δ single crystals

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Dynamic softening of vortex lines in YBa2Cu3O7−δ single crystals

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