OBSERVATION OF AN ODD LONGITUDINAL MAGNETORESISTANCE IN YBA2CU3O7-DELTA SINGLE-CRYSTALS WITH UNIDIRECTED TWINS

Unidirected twin planes are the cause of anisotropic pinning of vortic es in YBa2Cu3O7-delta (below YBaCuO) single crystals. In contrast to t he case of only isotropic pinning, two new effects may appear due to t he pinning anisotropy: guiding of vortices along twin planes and aniso tropy of the Hall resistivity. The former leads to the appearance of t he even (with respect to the reversal of a magnetic field direction) t ransverse resistivity and influences the Hall angle, while the last ca uses new additional odd contribution to the longitudinal resistivity. The paper presents magnetoresistivity measurements in the vortex liqui d phase of YBaCuO single crystals with different angles between unidir ected twins and current direction in the magnetic fields up to 12 T. F ield inversion was used for separation of the even and odd components of the measured transverse and longitudinal voltages in order to selec t new contributions to the resistivity in the case of anisotropic pinn ing. The results are consistent with the model of anisotropic pinning where the anisotropy of the Hall drag coefficient is caused by twins. (C) 1998 Elsevier Science B.V. All rights reserved.