Upper critical field, fluctuation conductivity, and dimensionality of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$

The upper critical field $H_{c2}$ and fluctuation conductivity were measured for highly oriented thin films of ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{x}}$. The $H_{c2}$ results demonstrate the intrinsic anisotropy in this layered superconductor. The broadening of the resistive transition under fields is interpreted in terms of critical fluctuations. The fluctuation conductivity shows dimensional crossover as expected for quasi-two-dimensional material. Using this data we determine the intra- and interlayer coherence lengths ${\xi }_c$(0) and ${\xi }_{\mathrm{ab}}$(0), and discuss the dimensionality of the superconductivity in this material.