Resonant tunneling in a quasi-one-dimensional wire: Influence of evanescent modes

We calculate the transmission coefficients through two point scatterers in a quasi-one-dimensional wire as the Fermi energy and distance between scatterers are varied. At a subband minimum the standard wave-interference pattern between propagating modes, characteristic of a Fabry-Perot interferometer, is completely suppressed. Instead, we find that the shape of the lowest evanescent waveguide mode determines the electron transmission so that a different pattern of conductance oscillations emerges. If either of the scatterers is attractive, the transmission is suppressed abruptly near the ``quasidonor'' levels formed in the scatterer below each subband minimum.