Normal-state resistance fluctuations in high-Tccuprate films

We have measured 1/f resistance fluctuations at room temperature in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{x}}$ films as a function of oxygen content, x. The films were single phase, c-axis oriented and grown by pulsed organometallic-beam epitaxy on ${\mathrm{LaAlO}}_3$ substrates. In contrast to the monotonic increase of the film resistance with decreasing x, the normalized noise power was found to exhibit a sharp minimum at x=6.5. We attribute this behavior to vacancy creation in the Cu-O chains and discuss a simple model based on parallel conduction paths through both chains and planes.