1/f noise and morphology of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals

1/f noise measurements have been performed on ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ single crystals with distinct resistivity characteristics. The noise spectral density is found to be several orders of magnitude larger than that of metals, with a temperature dependence that is independent of the resistivity. In the superconducting-transition region, we do not observe anomalously enhanced 1/f noise. We discuss the important role played by the crystal morphology and we present a tunneling model which explains the experimental data quantitatively.