Critical current density of a YBa2Cu3O7 film: Comparison between experiment and collective pinning theory

Abstract

With the vibrating reed technique we have measured the critical current densityJc of a Y 1∶2∶3 200 nm thin film as a function of magnetic field perpendicular to the CuO2 planes (O T<B≦8 T) and temperature (20K≦T≦60 K). At fieldsB<0.1 TJc is magnetic field independent and decreases at higher fields. A comparison with theory indicates that a crossover from a single pinning to a small bundle collective pinning regime may explain the observed behaviour. According to our estimate the main pinning centers are weak point pins due to oxygen vacancies. From the temperature dependence ofJc atB→0 we obtain a temperature dependence of the thermodynamical critical fieldBc∝(1−T/Tc)2 forT≧20 K which agrees with the anomalous temperature dependence ofBc2 observed recently in highly anisotropic high temperature superconductors.