INFLUENCE OF PINNING BY COLUMNAR DEFECTS ON THE LONGITUDINAL AND HALLRESISTIVITIES OF YBA2CU3O7 SINGLE-CRYSTALS IN THE MIXED STATE

We have measured the longitudinal and Hall resistivities of YBa2Cu3O7 single crystals irradiated by energetic heavy ions. This type of irrad iation results in creation of continuous cylinders of amorphous matter which act as very efficient pinning centers. As a consequence we obse rve a drastic narrowing of the transition curves in magnetic field ( p arallel to the cylinders axis) and a strong increase of the pinning en ergies near T(c). In addition, the Hall voltage do present a sign chan ge below T(c) even after irradiation, which confirms that the negative Hall voltage is related to an intrinsic property of the material.