L. Romanó

A comparison of I–V characteristics in YBCO and BSCCO

Abstract Current-voltage characteristics of YBCO and BSCCO at temperatures near the superconducting transition exhibit non-ohmic behaviours with power dependence ( V=AI α( T ) ) whose α( T ) trends differ strongly in the two compounds. An interpretation based on the bidimensional Kosterlitz-Thouless theory, taking into account the different anisotropy of the two compounds, is proposed.

Effects of the anisotropy on the non-Ohmic behaviour in high-Tc superconductors

Abstract Current-voltage characteristics in YBCO and BSCCO, at temperatures near the superconducting transition, exhibit non-Ohmic responses with power dependence V = Alα(T). The comparison of the α(T) trends reported for several crystals, films and ceramic samples evidences behaviour which differ in the compounds independently on the sample features. A development of the Kosteritz-Thouless model for quasi-bidimensional systems is proposed and a dependence of the non-Ohmic behaviour on the anisotropy of the material is obtained.

Zero-dimensional superconducting fluctuations and fluctuating diamagnetism in lead nanoparticles

High resolution SQUID magnetization measurements in lead nanoparticles are used to study the fluctuating diamagnetism in zero-dimensional condition, namely for particle size d lesser than the coherence length. The diamagnetic magnetization Mdia (H, T= const) as a function of the field H at constant temperature is reported in the critical region and compared with the behaviour in the temperature range where the first-order fluctuation correction is expected to hold. The magnetization curves are analysed in the framework of exact fluctuation theories based on the Ginzburg-Landau functional for the coherence length much greater than d. The role of the upturn field Hup where Mdia reverses the field dependence is discussed and its relevance for the study of the fluctuating diamagnetism, particularly in the critical region where the first-order fluctuation correction breaks down, is pointed out. The size and temperature dependence of Hup is theoretically derived and compared to the experimental data. The relevance and the magnetization curves for non-evanescent field and of the upturn field for the study of the fluctuating diamagnetism above the superconducting transition temperature is emphasized.

Ohmic-non-ohmic characteristics in YBCO single crystals

Abstract Current-voltage characteristics in YBCO single crystals are studied at temperatures near the superconducting transition. The power dependences V = Al α ( T ) , usually observed in these cases, are preceded by linear trends with an ohmic-non ohmic crossover current which increases at lower temperatures. This effect is attributed to a Josephson coupling between superconducting layers, and a quantitative description in good agreement with the experimental results is proposed.

Current and field independent dissipation in a BSCCO superconducting film

Abstract The electrical resistance of a superconducting BSCCO (2212) film is examined as a function of temperature, electric current and magnetic field. The large temperature dependence and the existence of current and magnetic field independent regions suggest a thermal origin of the fluxons. The analysis of the R ( T ) dependence, in agreement with the Kosterlitz-Thouless theory, supports this hypothesis.

The temperature dependence of the non-linear electrical response in HTSC

Abstract The dependence of the non-ohmic behaviour on the temperature in HTSC is strongly influenced by the interaction between the CuO 2 planes. The effect is studied on the basis of a Kosteritz-Thouless model developed for quasi-bidimensional superconductors and the results are used to explain the non-linear current-voltage characteristics in some YBCO and BSCCO samples. The anisotropy and the ratio n / m ∗ (supercarrier density/effective mass) are evaluated.

Non-ohmic response under low magnetic fields in BSCCO

Abstract The influence of low magnetic fields parallel to the c -axis on the vortex-antivortex (v-a) distribution in one BSCCO crystal and in one oriented film is studied by examining the changes of the non-ohmic response near the superconducting transition. The obtained results confirm the non-external magnetic origin of a v-a configuration and are interpreted by a losening and a depairing of the v-a couples in a way similar to that produced by the temperature. Phenomenological dependences of the two effects are proposed.

Superconducting phase fluctuations in SmFeAsO0.8F0.2 from diamagnetism at a low magnetic field above Tc

Superconducting fluctuations (SF) in SmFeAsO

The non-ohmic dissipation in type II planar superconductors at zero magnetic field

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Resistivity measurements in superconducting Ba1−xKxBiO3

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