Two-dimensional behavior and critical-current anisotropy in epitaxial ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{8+\mathit{x}}$ thin films

The critical-current anisotropy ${\mathit{j}}_{\mathit{c}}$(B,T,Θ) of epitaxial ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{8+\mathit{x}}$ films has been measured in detail. Below 70 K, the measured ${\mathit{j}}_{\mathit{c}}$(B,T,Θ) can be fully accounted for by the assumption that only the field component ${\mathit{B}}_{\mathrm{\parallel }}$=B cosΘ influences ${\mathit{j}}_{\mathit{c}}$, as has been proposed by Kes et al.. Above this temperature, a 2D-to-3D dimensional crossover results in additional dissipation. By comparison with results on polycrystalline samples, evidence is given for the absence of any influence of the grain boundaries on ${\mathit{j}}_{\mathit{c}}$(Θ).