Resistive dissipation in imperfect crystals of YBa2Cu3O7−δ

We have measured ac magnetoresistance in fields up to 8 T in a variety of YBa2Cu3O7−δ single crystals containing (a) twin boundaries only in one direction, (b) multi-twin domain structure, and (c) growth steps. We find two components of the resistance: an angular dependent Lorentz force induced ‘‘excess resistivity’’ superimposed on an angular independent resistivity. The temperature and magnetic field dependence of the angular-dependent resistivity exhibit a strong correlation with crystal defects, whereas the angular-independent resistivity remains virtually unchanged. In addition, we find crystals exhibiting both ohmic and non-ohmic behavior in their I-V characteristics depending on crystal imperfections.