Thermally activated motion of two-dimensional vortices in Bi2Sr2CaCu2Oy crystals

The magnetic resistance of two single crystals of Bi2Sr2CaCu2Oy was investigated. Measurements were performed in magnetic fields up to 1.6 T with applied current densities between 0.03 A/cm2 and 3.0 A/cm2. The resistivity of the crystals was analyzed in terms of the thermally activated flux flow expression, ϱ=ϱ0U/Texp(-U/T), where T is the temperature. It was found that the activation energy was given by U∝(H sin θ)-α, where α≈13, and that the prefactor had the form ϱ0∝H sin θ, whereH was the applied field and θ the angle of the field with respect to the CuO2 planes. These results demonstrated that dissipation can be accounted for by the thermally activated motion of two-dimensional vortices whose density is given by the field H sin θ, projected on the CuO2 planes.