Role of Umklapp processes in the conductivity of doped two-leg ladders

Recent conductivity measurements performed on the hole-doped two-leg ladder material Sr14-xCaxCu24O41 reveal an approximately linear power law regime in the c-axis dc resistivity as a function of temperature for x=11. In this work, we employ a bosonic model to argue that Umklapp processes are responsible for this feature and for the high spectral weight in the optical conductivity which occurs beyond the finite frequency Drude-like peak. Including quenched disorder in our model allows us to reproduce experimental conductivity and resistivity curves over a wide range of energies.