Mechanism of flux motion in epitaxially grown thin films of YBa 2Cu 3O 7− x

Abstract

Resistive measurements of the critical properties of patterned thin films of epitaxially grown and c-axis oriented YBCO are carried out. The current-voltage characteristics obtained for the field direction B parallel to the crystallographic c-axis indicate that, for currents just above the critical current density, the dissipation is caused by thermally assisted motion of flux bundles. The volume of these bundles can be much smaller than the volume representing a single flux line. It is concluded, that the flux-line lattice is segmented in c direction. The flux-line segments might be decoupled vortex discs defined by the 2D superconducting layers, i.e. the CuO 2 planes. The width dependence indicates, that the flux bundles are defined by rows of FL segments oriented across the sample. The field and temperature dependence of the volume of the volume of the flux bundles is discussed in terms of the ratio of the elastic moduli, c 44/ c 66, and a possible dimension crossover from 2D to 3D superconducting behavior, respectively.