CONTRIBUTIONS OF PINNING AND ANISOTROPY TO TORQUE IN YBACUO

Torque signals for Y2Ba2Cu3O7 single crystals were decomposed into a reversible and an irreversible component between 85 K and 8 K. The reversible component below 40 K cannot be modelled by the standard anisotropic Ginzburg-Landau theory. In the low temperature regime, an increase of the signal close to the ab direction is observed. We suggest that this could be the signature of a crossover between 3D and 2D behaviour of the flux lines. The irreversible component provides evidence for pinning by twin planes, 2D structure of the material and some isotropic pinning sensitive to the defects in the material. © 1990.