Electron Transport in Coupled Chains of Interacting Fermions with Impurities

We study low-temperature transport properties of a doped two-chain ladder system of interacting fermions in the presence of a barrier or of a low concentration of impurities. The conductance is suppressed above a certain value of the interaction as in a single chain, despite the presence of dominant superconducting correlations. There is, however, a region of repulsive interaction where perfect transmission across the barrier occurs unlike that in the single-chain case. We provide a possible explanation for the temperature maximum of the resistivity in the normal state of ${\mathrm{Sr}}_{0.4}{\mathrm{Ca}}_{13.6}{\mathrm{Cu}}_{24}{\mathrm{O}}_{42-\delta }$.