Vortex structure and resistive transitions in high-Tc superconductors

The nature of the resistive transition for a current applied parallel to the magnetic field in high-Tc materials is investigated by numerical simulation on the three dimensional Josephson junction array model. It is shown by using finite size scaling that for samples with disorder the critical temperature Tp for the c axis resistivity corresponds to a percolation phase transition of vortex lines perpendicularly to the applied field. The value of Tp is higher than the critical temperature for j perpendicular to H, but decreases with the thickness of the sample and with anisotropy. We predict that critical behavior around Tp should reflect in experimentally accessible quantities, as the I-V curves.Comment: 8 pages + 6 figure

The phase diagram of high-Tc's: Influence of anisotropy and disorder

We propose a phase diagram for the vortex structure of high temperature superconductors which incorporates the effects of anisotropy and disorder. It is based on numerical simulations using the three-dimensional Josephson junction array model. We support the results with an estimation of the internal energy and configurational entropy of the system. Our results give a unified picture of the behavior of the vortex lattice, covering from the very anysotropic BiSrCaCuO to the less anisotropic YBaCuO, and from the first order melting ocurring in clean samples to the continuous transitions observed in samples with defects.Comment: 8 pages with 7 figure

Beyond ‘BRICS’: ten theses on South–South cooperation in the twenty-first century

Grounded in a review of past and present academic South–South cooperation literatures, this article advances ten theses that problematise empirical, theoretical, conceptual and methodological issues essential to discussions of South–South cooperation in the 21st century. This endeavour is motivated by the perceived undermining, especially in the contemporary Anglophone academic South–South cooperation literature, of the emancipatory potential historically associated with South–South cooperation. By drawing on the interventionist South–South cooperation agendas of ‘left’-leaning Latin America-Caribbean governments, the article seeks to establish a dialogue between social science theories and less ‘visible’ analyses from academic (semi)peripheries. The ten theses culminate in an exploration of the potential of South–South cooperation to promote ‘alternative’ development