Excess conductivity and fractal analysis of experimental data of YBa2Cu3– <i>y</i> Al <i>y</i> O7– <i>x</i> single crystals

The in-plane conductivity of YBa2Cu3–yAlyO7–x single crystals with a defined topology of planar defects has been investigated. It is shown that Al impurities act as effective scattering centers for normal-state carriers. The excess conductivity of the studied samples over a wide temperature range follows an exponential temperature dependence, while near Tc it is satisfactorily described by the Aslamazov–Larkin theoretical model. Partial substitution of Cu with Al leads to a significant expansion of the temperature interval in which the pseudogap anomaly exists in the ab plane. The fractal analysis of the “tweed” structures has been performed.