CRITICAL-FIELD FOR THE ONSET OF THE DISSIPATION AND 2-D BEHAVIOR IN BI-SR-CA-CU-O

We present measurements of the angular dependence of the critical field connected to the onset of the resistivity as a function of the magnetic field in Bi-Sr-Ca-Cu-O 2212. The measurements are performed by a four-probe dc resistance method. The sample is a highly c-axis oriented epitaxial film. When the measurements are carried out with the direction of the external magnetic field parallel to the Cu-O planes, the main result is the existence of a crossover temperature at which the superconductor goes from an anisotropic 3-D to a 2-D behavior with the lowering of the temperature.