ANISOTROPY DEPENDENCE OF HALF-LOOP-MEDIATED VORTEX MOTION IN THALLIUM-BASED SUPERCONDUCTORS STUDIED BY MAGNETORESISTIVITY

By measuring the temperature dependence of the magnetoresistivity, we have studied the activation energy U of two Tl-based superconducting o xides having different electronic anisotropies (Tl-2212, which is very anisotropic, close to Bi-2212, and Tl-1212, the anisotropy of which i s about 10). The activation energies are described in terms of movemen ts of half loops of vortices, with a lateral size of about the intervo rtex spacing a(0). Taking into account the field dependence of the ela stic coefficients C-44 and C-66, this activation energy is estimated a nd compared to the experimental data. The precise magnetic-field depen dence of the activation energy in Tl-2212 and Tl-1212 are different. T his difference is taken into account in the frame of a single model co nsidering two different regimes according to the anisotropy value. [S0 163-1829(98)05225-4].