Can fractional power-law conductivity explain the deviations from Matthiessen's rule in SrRuO 3?

In a recent work on the optical conductivity of the ferromagnetic metal SrRuO3 it was suggested that its electrical DC conductivity σ might not be proportional to the scattering time τ, but to some fractional power of it: σ∝τα with α≃0.4. We examine whether this empirical law can account for the unusual deviations from Matthiessen's rule found in this compound.