Flux pinning behavior in twin boundaries of single crystal YBa2Cu3O7-δ

We present magnetoresistance measurements up to H = 6 Tesla using a crossed magnetic field technique to demonstrate pinning by twin boundaries (TB) in YBa2Cu3O7-δ. We investigate geometries for H parallel c parallel TB, H parallel ab parallel TB and for H rotated within a twin boundary plane. We find the critical angle Θ* for TB pinning to be field dependent and field independent for H parallel c parallel TB and H parallel ab parallel TB respectively in fields up to 6 Tesla and temperatures near Tc. In addition, we report on the full phase diagram for the onset of TB pinning. The TB pinning onset temperature coincides with the ''shoulder'' feature observed in the resistive transition in magnetic fields in these crystals