Experimental evidence of twin-planes pinning in the ab plane studied in large c-axis YBa2Cu3O7 samples

The twin-planes (TP) effect on pinning is studied in large monodomain YBa2C u3O7 textured samples with the size along the c axis greater than the other s. The magnetic field angular dependence of the c-asis resistivity and c-ax is critical current density has been carried out using transport and dc-mag netization measurements. These various experimental methods show clearly th at in this configuration TP's dominate the pinning properties in the ab pla nes at high temperatures (T greater than or equal to 40 K) and when the mag netic field is close to the TP directions. Moreover, experiments demonstrat e that the TP's enhance the ab-plane irreversibility line for angles close to a critical angle Phi(c)similar to 8 degrees-10 degrees. The observed pro perties are related to the extended and correlated character of the twin pl anes. An experimental phase diagram for the angular dependence of the ab-pl ane irreversibility line is proposed with a possible existence of a Bose gl ass phase in the ab plane induced by the two directions of the TP's. The pe rsistence of the TP pinning for magnetic fields higher than 20 T is explain ed with an electromagnetic origin induced by the surface character of TP's. [S0163-1829(98)08241-1].