Twin-boundary effect on the Hall conductivity in high-T_c superconducting thin films

The pinning influence on the Hall conductivity in the mixed state of high-temperature superconductors is still experimentally and theoretically controversial. In this work, the effect of twin-boundary pinning on the Hall conductivity is studied, with particular emphasis on the high-field results. The longitudinal and Hall resistivities were measured in YBa₂Cu₃O_7-δand YbBa₂Cu₃O_7-δ thin films, up to 18 T: a signature due to the pinning of the vortices in the twin boundaries is clearly visible in the longitudinal resistivity p_xx and in the Hall resistivity p_xy, but disappears when the Hall conductivity σ_xy≅p_xy / p²_xx is computed. However, at lower temperatures, a minimum of dσ_xy ldT is proved to be a weak signature of the twin-boundary pinning. These results are confirmed by similar measurements done on one sample rotated 16° away from the magnetic field direction.