Two-impurity Scattering in Quasi-one-dimensional Systems

In a quasi-one-dimensional system (a tube) with low concentration of defects n the resistivity rho has peaks (van-Hove singularities) as a function of Fermi-energy. We show that due to non-Born scattering effects a deep narrow gap should appear just in the center of each peak. The resistivity at the bottom of a gap (rho(min) proportional to n(2)) is dominated by scattering at rare "twin" pairs of close defects, while scattering at solitary defects is suppressed. The predicted effect is characteristic for multi-channel systems, it can not be observed in strictly one-dimensional one.