INFLUENCE OF LONGITUDINAL MAGNETIC FIELD ON THE FLUCTUATION CONDUCTIVITY IN SLIGHTLY Al-DOPED YBa2Cu3-zAlzO7-δ SINGLE CRYSTALS WITH A GIVEN TOPOLOGY OF PLANE DEFECTS

In this work we study the influence of the constant magnetic field up to 14 kOe to the temperature dependence of the electrical conductivity in the ab-plane of aluminium doped YBa2Cu3O7-delta single crystals with an unidirectional twin boundaries system. The temperature dependence of the excess para-conductivity is interpreted within the Aslamazov-Larkin theoretical model of the fluctuation conductivity. It was shown that the lack of fan-shaped expansion of the resistive transitions in the magnetic field in these samples may be due to the lack of the non-pinning vortex liquid phase.