ANOMALOUS BEHAVIOR IN THE TORQUE DUE TO THE LORENTZ FORCE IN HIGH T-CSUPERCONDUCTORS

We have investigated the contribution of the torque caused by the Lore ntz force due to the transport currents in Tl2Ba2CaCu2O8 and TlBa2Ca2C u3O8 single crystals as the magnetic field, H-c1 < H < H-c2, rotated f rom normal to parallel to the CuO2 layers. Our main result is the disc overy of an unexpected disappearance of the Lorentz torque when the ma gnetic field is oriented parallel to the layers. This anomaly is discu ssed within the concept of intrinsic flux pinning and flux dynamics of vortices. The observation of a threshold behavior for the Lorentz tor que as a function of the applied sample currents exhibits conceptual a greement with pinning and depinning of flux lines. The results from th e measurements indicate a correlation between the transport and the ma gnetic properties. The nature of the flux structure and its motion in highly anisotropic layered superconductors is inferred from this exper iment.