Negative deviations from Matthiessen's rule for SrRuO3 and CaRuO3

We have measured the change in the resistivity of thin lms of SrRuO3 and Ca RuO3 upon introducing point defects by electron irradiation at low temperat ures, and we nd significant negative deviations from Matthiessens rule. For a fixed irradiation dose, the induced change in resistivity decreases with increasing temperature. Moreover, for a fixed temperature, the increase in resistivity with irradiation is found to be sublinear. We suggest that the observed behavior is due to the marked anisotropic scattering of the elect rons together with their relatively short mean free path (both characterist ic of many metallic oxides including cuprates) which amplify effects relate d to the Pippard ineffectiveness condition.